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Production technology
B.E VI SEMESTER
DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY
DEPARTMENT OF MECHANICAL ENGINEERING
B.E. - SEMESTER – VI
PRODUCTION TECHNOLOGY (2161909)
INDEX
Sr.
No. Experiment
Page
Number Dates
Sign. Grades/
Remarks Start End Start End
1. To study about single and multi-
point cutting tools.
2. To study about the different types
dies and press tool design.
3.
To study and practicing about jigs
and fixtures for various machining
operations.
4. Study About Various Thermal
Aspects In Machining.
5. To study about different types of
gears manufacturing processes.
6. To study about various non-
conventional machining process.
7. Prepare press tool design based on
given data.
8. Prepare Jig Design And Drawing
For Given Components.
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 1
Date: ___ /___ /______
EXPERIMENT NO.1
AIM: STUDY OF SINGLE POINT AND MULTI POINT CUTTING TOOL.
1.1 Types of Cutting Tools
The cutting tools may be classified in different ways. Depending upon the number of cutting
points on the tool, the cutting tools are of two types:
1. Single-point cutting tools,
2. Multi-point cutting tools.
A single-point cutting tool has only one cutting point or edge. The tools used for turning,
boring, shaping, or planning operations, that is, tools used on lathes, boring machines, shaper,
planer, etc. are single point tools. A multi-point tool has two or more than two cutting [for
example, tools used on drilling machines, milling machines, broaching machines etc.] multi-
point tool can be considered to be basically a series of single-point tools.
Depending upon the construction of the cutting tool, it is classified as :
1. Solid tools,
2. Tipped cutting tools.
The solid cutting tools are made entirely of the same material, whereas, in a tipped cutting tool,
an insert of cutting tool material is brazed or held mechanically to the shank of another material.
1.1.1 Single Point Cutting Tools
The solid single point cutting tools have been discussed here.
1.1.2 Tipped Single Point Cutting Tools.
As already discussed the carbides, ceramics, cast alloys, diamond, CBN and UCON are used
as tips or inserts which are either brazed into a prepared seat machined on a tough steel tool
shank or are clamped to the shank, The second type of tips or inserts are known as indexable
inserts or throwaway tips.
1.1.2 Brazed Tipped Tools.
Fig. 1.1 Brazed Tipped Tools
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 2
Suitable shapes of tool material tips or inserts gets worm out are brazed in a steel shank. When
the tip or insert gets worn out, it is resharpened with the help of special grinding wheels. For
resharpening purposes, the tool wheel has to be removed from the machine involving a resetting
operation. The main drawback of a brazed tip is that of difference in co-efficient of expansion
of tip material and tool shank material, the brazing has to be done very carefully.
Fig.1.2 Single point cutting tool nomenclature
1.1.3 Mechanically Clamped Tip Tools.
In these tools, the tips or inserts are clamped mechanically on to the tool shank. These tips arc
known as index able because these have more than one cutting edges which are used one by
one by indexing. The tip and these tips are known as throwaway type because once all the edges
of the tip have been used, the tip or insert is removed from the tool shank and thrown away or
is disposal off (disposable tip). The most common shapes in which these tips are available are
: Square, triangular and diamond. The edges of the inserts may be at 90° to the tip face, or the
edges may be at a small angle to the face, In the first case, the tips will provide negative rake
angle because these will have to be clamped on to shank with the seating slopping downwards
to provide a clearance angle. Here, the number of cutting points will be twice the number of
edges, because when all the edges on the lop face have been used, the insert can be turned over
to give an additional equal number of cutting edges.
In the second case, positive rake is obtained on the tip. Here, the insert cannot be turned over
to use the cutting edges on the bottom face, because the small angles provided on the sides of
the tip will prevent this.
When a cutting edge on the tip gets worn, the clamp is released and the tip is (indexed) to bring
a new cutting edge into the cutting position. When all the edges have been used the tip is
thrown away and a new tip is substituted.
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 3
The various methods for fastening the tip are:
(i) Screw fastening
(ii) Bridge type clamp
(iii) Pin type clamp.
1.2 Multipoint Cutting Tools
1.2.1 Milling Cutters
Milling cutters are multi-point cylindrical cutting tools with cutting teeth spaced around the
periphery. The most appropriate way to classifying the milling cutters is on the method of
providing relief on the tools. According to this, the milling cutters are classified into two
categories:
1. Profile relieved cutters.
2. Form relieved cutters.
Fig. 1.2 Milling Cutters
The profile-relieved cutters are obtained by sharpening a narrow land behind the cutting edge.
This narrow land is re sharpened by grinding when the cutting edge become dull, relieved
cutters have a curved relief behind the cutting edge and these cutters have a curved relief behind
the cutting edge and these cutters are sharpened by grinding the tool face. There is greater
flexibility in adjusting relief angles in profile-relieved cutters since it is fixed in the
manufacture of the cutter. However, this type is more suitable for cutters with intricate
shapes/profile since the relief is not changed during re sharpening.
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 4
Fig.1.3 Milling Cutter Nomenclature
The milling cutters can also be classified according to the method of their mounting, example,
arbor type, shank type 'or spindle mounted type'. Most milling cutters are made as solid of
H.S.S., but they are also a\ a liable with carl tipped teeth or with disposable tips of various tool
materials.
The milling process is divided into two main types:
1. Peripheral milling, and
2. Face milling.
In peripheral milling, the finished surface is parallel to the axis of the cutter and is machined
by cutter teeth located on the periphery of the cutter, In face milling, the finished surface is at
right angle to the cutter axis and it is obtained by teeth on the periphery and the flat end of the
cutter.
1.2.2 Broach Tool
A broach is a multi-point cutting tool consisting of a bar having a surface containing a series
of cutting teeth or edges which gradually increase in size from the starting or entering end to
the rear end. Broaches are used for machining either internal or external surfaces .The surfaces
produced may be flat, circular or of any intricate shape. In broaching, the broach is
Fig.1. 3 Broaches.
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 5
Fig.1.4 Broach Nomenclature
pushed or pulled over or through a surface of a workpiece. Each tooth of the tool takes a thin
slice from the surface. Broaching of inside surface is called 'Internal or hole broaching' and
outside surfaces as "Surface broaching".
1.2.3 Drills
Drilling is the process of cutting or originating a round hole from the solid material. The tool
(drill) and not the workpiece is revolved and is fed into the material along its axis. There are
many ways of classifying drills, for example, according to: material, number and type of flutes,
drill size, type of shank (straight or taper) and cutting point geometry, etc.
Fig.1. 4 Drill bits
However the most common type of drill is the fluted twist drill, It is made from a round bar of
tool material, and has three principal parts: the point, the body and the shank. The drill is held
and rotated by its shank. The point comprises the cutting elements while the body guides the
drill in operation. The body of the drill has two helical grooves called "flutes" cut into its
surface. The flutes form the cutting surface and also assist in removing chips out of the drilled
hole. The two cutting edges are straight and are separated by web thickness of the drill which
is provided to strengthen the drill structure. The body of the drill is made slightly less in
circumference leaving a narrow "margin" at Ml nominal diameter along the edge of each flute.
This reduces rubbing action between the drill and the hole wall and allows the cutting fluid to
reach the point of the drill. The metal cut away to form the margin is known as "body diameter
clearance". To help further in reducing the rubbing action, drill bodies are given a slight back
taper (About 0.0075 mm per cm of length). The shank can be either straight or tapered (for big
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 6
drills). Straight shanks are provided for small drills (upto 10 to 12 mm diameter) and are held
in chucks.
1.2.3.1 Nomenclature of Drill Bits.
1. Axis: It is the imaginary longitudinal centre line of the drill.
2. Body: It is the portion of the drill extending from the outer corners of the cutting lips up to
the commencement of neck (if present) or shank.
3. Back taper: A slight decrease in diameter of the drill from the front end to the back in the
body of the drill.
Fig.1.5 Drill Bits Nomenclature
4. Flutes: Straight or helical grooves cut or formed in the body of the drill to provide cutting
edges, to allow chip removal, and to allow cutting fluid to reach the cutting edges.
5. Land: The peripheral portion of the drill body between adjacent flutes.
6. Body clearance: It is the space provided to eliminate undesirable contact between the drill
and the workpiece.
7. Margin: It is the cylindrical portion of the land which is not cut away to provide body
clearance. It is ground to the diameter of drill. There are 2 margins. Drill guidance and friction
losses in drilling depend on the margins.
8. Drill diameter. It is the diameter of the drill over the margins measured at the point.
9. Clearance diameter. It is the diameter over the cutaway portion of the drill lands.
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 7
10. Web. It is the central portion of the drill body that connects the lands. The extreme of the
web forms the chiesel edge on the two-flute drill.
11. Point. It is the cutting end of a drill formed by the ends of the lands and the web.
12. Lips or cutting edges. These are the cutting edges of a two-flute drill extending from the
chiesel edge to the periphery.
13. Chiesel edge. It is the edge at the end of the web that connects the cutting edges.
14. Shank. The part of the drill by which it is held and rotated.
15. Tang. The flattened end of a taper shank which fits a driving slot in a socket.
16. Lip relief. It is the axial relief on the drill point.
17. Lip relief angle. It is the axial relief angle at the outer comer of the lip. It is the angle by
the flank and a plane at right angles to drill axis.
18. Face. It is the portion of the flute surface adjacent to the lip on which the cut chips impinge.
19. Flank. It is the surface on a drill point which extends behind the lip to the following Pate.
20. Heel. The edges formed by the intersection of flute surface and body clearance. It is the
trailing edge of the land.
21. Point angle. It is the included angle of the cone formed by the cutting lips.
22. Helix angle. It is the angle made by the leading edge of the land with a plane containing
the axis of the drill.
23. Chiesel edge angle. It is the angle included between the chiesel edge and the cutting lip as
viewed from the end of the drill.
24. Web thickness. Thickness of web at the point, unless another location is indicated
25. Neck. It is a section of reduced diameter between the body and shank.
1.2.4 REAMERS
A reamer is a rotary cutting tool generally of cylindrical shape, which is used to enlarge and
finish holes to accurate dimensions to a previously formed hole. It is a multiple edge cutting
tool, having the cutting edges on its periphery. A reamer consists of three main parts : fluted
section, neck and shank, The fluted part consists of chamfer l1 starting taper l2, sizing section
l3 and the back taper L4. Chamfer length or bevel lead length L1, ensures proper and easy entry
of the reamer into the hole. The main cutting action of reamer is done by starting taper l2. The
sizing section serves to guide the reamer and also smooths or sizes the hole. The back taper l4
(with a difference between the maximum and minimum diameters of from 0.01 to 0.08 mm)
reduces friction between the reamer and the hole surface.
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 8
1.2.4.1 Types of Reamers
1. Hand reamers. These reamers are operated by hand with a tap wrench fitted on the square
end of the reamer. The work is held in the vise or vice versa. The flutes may be straight or
helical. The shank is straight with a square tang for the wrench.
2. Machine reamers. These are similar to hand reamers except that the shank is tapered.
3. Chucking reamers. These are machine reamers with shorter flutes. These may be either of
the type known as Rose reamers or Fluted reamers. Rose reamers do not cut on the
circumference of the flutes but are beveled off and clearanced to cut on their ends. These are
used for heavy roughing cuts, for example, for clearing out cored holes.
4. Floating reamers. Here the holders are not rigid but are floating. This permits the reamer to
follow the previously made hole naturally and without restraint resulting in a better hole.
5. Expanding reamers. These reamers allow slight increase in their size to allow for wear or
to remove an extra amount of material. For this, the body of the reamer is bored taper and is
slitted. A taper plug runs through the hole and is operated by a screw so that it acts as the
expander. The possible variation is generally between 0.15 to 0.50 mm.
Fig. 1.6 Reamers
6. Adjustable reamers. In these reamers, separate blades are inserted into the grooves provided
in the body of the reamer. The blades can be moved up or down to increase or decrease the size
of the reamer.
7. Taper reamers. These reamers are used to finish the taper holes for cutting the taper pins
used to secure the collars, pulleys etc. to the shafts.
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 9
Fig 1.7 Reamers
8. Shell reamers. Solid reamers (up to about 20 mm diameter) are usually made of H.S.S. To
reduce the cost of larger reamers, the cutting portion is made as separate shells which are
mounted on standard shanks made of lower cost sheels. These reamers, are, however, not very
rigid and accurate. Inserted teeth or blades in shells will further reduce the cost of the reamer.
To increase their production capacity, the reamers can be tipped with cemented carbides.
1.2.4.2 Nomenclature:
1. Axis. It is the longitudinal centre line of the reamer.
2. Back Taper. It is a slight decrease in diameter from front to back, in the flute length of the
reamer. As pointed out above, it is provided to reduce friction between the reamer and the hole
surface. It is also called "longitudinal relief.
3. Blade. It is the tooth or cutting element inserted in the reamer body. It may be adjustable
and/or replaceable.
4. Body. It is the fluted portion of the reamer, inclusive of the chamfer, taper and bevel.
5. Flutes. These are the longitudinal channels formed in the body of the reamer to provide
cutting edges, permit passage of chips and allow cutting fluid to reach the cutting edges.
6. Helix angle. Reamers may have straight flutes or helical flutes. Straight flutes are easy to
cut and resharpened. A helical flute or a spiral flute is formed in a helical path around the axis
of a reamer. Helix angle is the angle which a helical cutting edge at a given point makes with
an axial plane through the same point.
7. Land. It is the section of the reamer between adjacent flutes.
8. Cutting edge. It is the leading edge of the land in the direction of rotation for cutting.
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 10
9. Face. It is the portion of the flute surface adjacent to the cutting edge on which the chips
impinge after they are cut from the work.
10. Heel. It is the trailing edge of the land in the direction of rotation for cutting.
11. Chamfer. It is the angular cutting portion at the entering end of the reamer. It is also called
"Bevel" or "Bevel lead".
12. Neck. It is the section of reduced diameter connecting the reamer body to the shank.
13. Shank. It is the portion of the reamer by which it is held and driven.
14. Squared Shank. A cylindrical shank having a driving square on the back end.
15. Tang. It is the flattened end of a shank which fits a slot in the socket.
16. Periphery. It is the outside circumference of a reamer.
Fig.1.8 Reamer Nomenclature
17. Chamfer angle. It is the angle between the axis and the cutting edges of the chamfer
measured in an axial plane at the cutting edge. It is also called "Bevel Lead Angle".
SINGLE AND MULTIPOINT CUTTING TOOL
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 11
18. Pilot. A cylindrical portion ahead of the entering end of the reamer body, which is
sometimes provided to maintain alignment.
19. Starting Taper. It is a slight relieved taper on the front end of the reamer. It facilitate.'
cutting and finishing of the hole. It is also called 'Taper Lead'.
20. Rake Angle. It is the angle between the face and a radical line from the cutting edge. It can
be zero, Negative or Positive,
21. Hook. It is the concave condition of a cutting face. The rake angle of a hooked cutting face
must be determined at a given point.
22. Clearance Angle. Practically, all the cutting action of the reamer is confined to the front
tapered portion. Suitable relief angles should be provided to ensure proper cutting action
without rubbing. Clearance angles are the angles formed by the primary or secondary
clearances and the tangent to the periphery of the reamer at the cutting edge,
23. Taper Lead Length. It is the length of the taper lead measured axially.
24. Taper Lead Angle. It is the angle formed by the cutting edges of the taper lead with the
reamer axis.
25. Bevel Lead Length. It is the length of the bevel lead measured axially.
26. Bevel Lead Angle. It is the angle formed by the cutting edges of the bevel lead
With I the reamer axis.
27. Margin or circular land. It is the cylindrically ground surface adjacent to the cutting edge
on the leading edge of the land.
__________
References: Production Engineering -by P.C. SHARMA
Manufacturing Processes I - by Prof. Pradeep Kumar (IIT ROORKEE)
PRESSES AND PRESS WORK
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 12
Date: ___ /___ /______
EXPERIMENT NO.2
AIM: TO STUDY ABOUT DIFFERENT TYPES DIES AND PRESS TOOL DESIGN.
2.1 Classification of presses
Types of presses for sheet metal working can be classified by one or a combination of
characteristics, such as source of power, number of slides, type of frame and construction, type
of drive, and intended applications.
2.1.1 Classification on the basis of source of power
Manual Presses. These are either hand or foot operated through levers, screws or gears.
A common press of this type is the arbor press used for assembly operations.
Mechanical presses. These presses utilize flywheel energy which is transferred to the
work piece by gears, cranks, eccentrics, or levers.
Hydraulic Presses. These presses provide working force through the application of fluid
pressure on a piston by means of pumps, valves, intensifiers, and accumulators. These
presses have better performance and reliability than mechanical presses.
Pneumatic Presses. These presses utilize air cylinders to exert the required force. These
are generally smaller in size and capacity than hydraulic or mechanical presses, and
therefore find use for light duty operations only.
2.1.2 Classification on the basis of number of slides
Single Action Presses. A single action press has one reciprocation slide that carries the
tool for the metal forming operation. The press has a fixed bed. It is the most widely
used press for operations like blanking, coining, embossing, and drawing.
Double Action Presses. A double action press has two slides moving in the same
direction against a fixed bed. It is more suitable for drawing operations, especially deep
drawing, than single action press. For this reason, its two slides are generally referred
to as outer blank holder slide and the inner draw slide. The blank holder slide is a hollow
rectangle, while the inner slide is a solid rectangle that reciprocates within the blank
holder. The blank holder slide has a shorter stroke and dwells at the bottom end of its
stroke, before the punch mounted on the inner slide touches the work piece. In this way,
practically the complete capacity of the press is available for drawing operation.
Another advantage of double action press is that the four corners of the blank holder
are individually adjustable. This permits the application of non-uniform forces on the
work if needed. A double action press is widely used for deep drawing operations and
irregular shaped stampings.
Triple Action Presses. A triple action press has three moving slides. Two slides (the
blank holder and the inner slide) move in the same direction as in a double – action
press and the third or lower slide moves upward through the fixed bed in a direction
opposite to that of the other two slides. This action allows reverse – drawing, forming
or bending operations against the inner slide while both upper actions are dwelling.
PRESSES AND PRESS WORK
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 13
Cycle time for a triple – action press is longer than for a double – action press because
of the time required for the third action.
2.1.3 Classification on the basis of frame and construction
Arch – Frame Presses. These presses have their frame in the shape of an arch. These
are not common.
Gap Frame Presses. These presses have a C-shaped frame. These are most versatile and
common in use, as they provide un – obstructed access to the dies from three sides and
their backs are usually open for the ejection of stampings and / or scrap.
Straight Side Presses. These presses are stronger since the heavy loads can be taken in
a vertical direction by the massive side frame and there is little tendency for the punch
and die alignment to be affected by the strain. The capacity of these presses is usually
greater than 10 MN.
Horn Presses. These presses generally have a heavy shaft projecting from the machine
frame instead of the usual bed. This press is used mainly on cylindrical parts involving
punching, riveting, embossing, and flanging edges.
Fig. 2.1 Typical frame designs used for power presses.
PRESSES AND PRESS WORK
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 14
2.2 Press Working Terminology
Base The all machine tool, base is the one of the parts of a press. It is main supporting member for work
piece holding dies and different controlling mechanisms of press. Size of the table limits the size of
work piece that can be processed on a press. In case of some special presses the base carries mechanism
for tilting the frame in any desirable inclined position too.
Frame Frame constitutes main body of the press located at one edge of its base. It houses support for ram,
driving mechanism and control mechanisms. Some of the press have column shaped frame.
Ram This is main operating part of the press which works directly during processing of a work piece. Ram
reciprocates to and fro within its guide ways with prescribed stroke length and power. The stroke length
and power transferred can be adjusted as per the requirements. Ram at its bottom end carries punch to
process the work piece.
Pitman It is the part which connects the ram and crankshaft or ram eccentric.
Driving Mechanism Different types of driving mechanisms are used in different types of presses like cylinder and piston
arrangement in hydraulic press, crankshaft and eccentric mechanisms in mechanical press, etc. these
mechanisms are used to drive ram by transferring power from motor to ram.
Controlling Mechanisms Controlling mechanisms are used to operate a press under predetermined controlled conditions.
Normally two parameters are adjusted by controlling mechanisms length of stroke of ram and power of
stroke. Transfer of power can be disengaged with the help of clutch provided with driving mechanisms
as per need. In most of the presses controlling mechanisms is in built with the driving mechanisms.
Now-a-days compute controlled presses are being used in which controlling is guided by
microprocessor. These presses provide reliable and accurate control with automation.
Flywheel In most of the presses driven gear or driven pulley is made of the shape of flywheel, which is used for
storing the energy reserve wire of energy) for maintaining constant speed of ram when punch is pressed
against the work piece. Flywheel is placed in the driving mechanism just before the clutch is sequence
of power transmission.
Brakes Brakes are very urgent in any mobile system. Generally two types of brakes are used normal brake,
which can bring the driven shaft to rest quickly after disengaging it from flywheel. Other is emergency
brakes which are provided as foot brake to any machine. These brakes include power off switch along
with normal stronger braking to bring all motions to rest quickly.
Balster Plate It is a thick plate attached to the bed or base of the press. It is used to clamp the die assembly rigidly to
support the work piece. The die used in press working may have more than one part that is why the
phrase die assembly is being used at the place of die.
PRESSES AND PRESS WORK
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 15
Die Set It is the unit assembly which incorporates a top shoe and bottom shoe, two or more guide
pillars and guide bushings.
Advantages: 1) It aligns the punch and dies members.
2) It reduces the setup time in the press to a minimum.
3) This facilitates resharpening of punch and die without removing from the
die set.
Fig. 2.2 Simple Cutting Die
Top shoe
this is the upper part of the die set which contains guide bushings and punch holding
assembly. It is directly fastened to the press ram with the help of shank.
Bottom shoe
this is the lower part of the die set which contains guide pillars. It is generally mounted on the
press bed. The die block is mounted on the bottom shoe.
Punch
punch is the male part of the die assembly, which is directly or indirectly moved by and
fastened
to the press ram. Punches are made from good grade of tool steel or high carbon high
chromium steel material and it is hardened. Punch is the master of piercing.
Die
die is the female part of the die assembly, which is mounted on the lower shoe. Dies are made
from tool steels or high carbon high chromium steel and it is hardened. Die is the master of
blanking.
Backup plate
Backup plate or pressure plate placed between the top plate and punch holder plate. It is a
hardened one. It is used to prevent the punch making any impression on the soft top plate.
The plate distributes the pressure over a wide area and the intensity of pressure on the punch
PRESSES AND PRESS WORK
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 16
holder is reduced to avoid crushing. Backup plates are made from oil hardened non-shrinkage
steel materials and carbon steels (c45) and it is hardened and ground parallel. The thickness
of the backup plate depends upon the stock thickness.
For up to 2mm stock thickness, 3mm thickness backup plate is used.
For about 3mm stock thickness, 6mm thickness backup plate is used.
Punch holder plate
it is fastened to the top plate through the backup plate. It is used to hold the punch correctly.
These plates are made from mild steel material.
Guide pillars and guide bushings guide pillars are mounted on the bottom shoe and guide bushings are mounted on the top
shoe. Both they are press fitted on their plates. Pillar and bush have a slide fit to them. They
are help in obtaining alignment of the punch and die. These are made from carbon steels and
hardened and ground.
Stripper Plate
This plate is mounted on the die plate. It is called as fixed stripper plate. A channel is
provided in this plate for feeding the metal strip. It is used to strip out the strip from the
punch during the return stroke of the press. It is also helps to correctly guide the punch into
the die opening. In some cases, it is mounted to the punch assembly. It is called as spring
loaded stripper.
2.3 Specification of press
Expressing size of a machine (press) includes expressing each of the parameters pertaining to it
quantitatively in appropriate units. Expressing size in the above mentioned way is the specifications of
press. The following parameters are expressed as specifications of a press.
(a) Maximum Force: Maximum force that its ram can exert on the work piece, this is
expressed in tones and called tonnage. It varies from 5 to 4000 tons for mechanical
press. It may be up to 50,000 tons by hydraulic press.
(b) Maximum Stroke Length: Maximum distance traveled by the ram from its top most
position to extreme down position. It is expressed in mm. the stroke length is adjustable
so different values that can be obtained between minimum and maximum of stroke
length, these are also the part of specifications.
(c) Die Space: Total (maximum) surface area, along with (b x d), of bed, base, ram base.
This the area in which dies can be maintained.
(d) Shut Height: Total opening between the ram and base when ram is at its extreme down
position. This is the minimum height of the processed work piece.
(e) Press Adjustments: Different stroke lengths (already covered in point number 2).
Different tonnage that can be set as per the requirement.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 17
(f) Ram Speed: It is expressed as number of strokes per minute. Generally it can be 5 to
5000 strokes per minute.
(g) Stroke: The stroke of press is distance of ram movement from its up position to its
down position.
2.4 Classification of Die
There is a broader classification of single operation dies and multi-operation dies.
(a) Single operation dies are designed to perform only a single operation in each stroke of ram.
(b) Multi operation dies are designed to perform more than one operation in each stroke of ram.
Single operation dies are further classified as described below.
Cutting Dies These dies are meant to cut sheet metal into blanks. The operation performed so is named as blanking
operation. These dies and concerned punches are given specific angles to their edges. These are used
for operation based on cutting of metal by shearing action.
Forming Dies These dies are used to change two shape of work piece material by deforming action. No cutting takes
place in these dies. These dies are used to change the shape and size related configuration of metal
blanks.
As there is a classification of single operation dies, multi-operation dies are can also be classified
(further) as described below.
Compound Dies
Fig. 4.3 Compound die
In these dies two or more cutting actions (operations) can be executed in a single stroke of the ram.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 18
Transfer Die It is also like a progressive die having more than one working points. It is different form progressive
die as it has feeding fingers in the die which transfer the work piece from one work station to other. In
some cases feeding fingers are attached to press, and then the press is called transfer press.
Combination Dies
Fig. 4.3 Combination dies
As indicated by their names these dies are meant to do combination of two or more operations
simultaneously. This may be cutting action followed by forming operation. All the operations are done
in a single action of ram.
Progressing Dies
Fig. 4.4 Progressing Dies
These dies are able to do progressive actions (operations) on the work piece like one operation followed
by another operation and so on. An operation is performed at one point and then work piece is shifted
to another working point in each stroke of ram.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 19
2.5 Principle of metal cutting:
The cutting of sheet metal in press work is a shearing process. The punch and die have same
shape of the part.
The sheet metal is held between punch and die. The punch moves down and presses the metal
into the opening of the die. There is a gap between the punch and die opening. This is called as
“Clearance”.
Fig. 4.5 Principle of Metal Cutting
The amount of clearance depends upon the type and thickness of the material. The punch
touches the metal and travels downward.
The material is subjected to both tensile and compressive stresses. By this pressure, the metal
is deformed plastically. The plastic deformation takes place in small area between punch and
die cutting edges. So the metal in this area is highly stressed. When the stress exceeds the
ultimate strength of the material, fracture takes place. The cutting edge of the punch starts the
fracture, in the metal from the bottom. The cutting edge of the die starts the fracture from the
top.
These fractures meet at center of the plate. As the punch continuous to move down, the metal
under the die is completely cutoff from the sheet metal. The cut out portion of the metal drops
down through the die opening. To make the metal to drop down freely, a die relief is given in
the die block. If the clearance is too large or too small cracks do not meet and a ragged edge
results due to the material being dragged and torn through the die.
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2.6 Clearance
Clearance is the intentional space (gap) between the punch and die cutting edges.
Proper clearances between the punch and die cutting edges enable the fracture to meet, and the
fracture portion of the sheared edge has a clean appearance.
For improper clearances, cracks do not meet and ragged edge results due to the material being
dragged and torn through the die.
Clearances are calculated by depending upon the materials thickness and their cutting
allowances.
The usual clearances preside of the die for various materials are given below, in terms of the
stock thickness “t”.
For copper, aluminum, brass and soft steel = 3 to 5% of t
for medium steel = 6% of t
for hard steel = 7% of t
Excessive cutting clearance provides larger burr on the components and gives long tool life.
Insufficient cutting clearance prevents a clear break. It also increases pressure on punch and
dies, thereby reduces the tool life.
Correct cutting clearance will allow the fractures to meet evenly resulting in a clear break and
the sheared edge as a clear appearance and minimum burr.
2.6.1 How to Apply Cutting Clearance
Piercing Operation:
Fig. 2.6 Piercing Operation
In piercing operation, clearance is given to
the die.
The component size is equal to the punch.
Here slug is a scrap.
Die opening size = Hole to be pierced +2C.
Blanking Operation
Fig.2.7 Blanking Operation
In blanking operation, clearance is given to
the punch.
The component size is equal to the die.
Here slug is desired part.
Blank punch size = Hole to be blanked – 2C
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 21
2.7 Punch and Die Clearance after Considering the Elastic Recovery of the
Material.
In blanking operation, after the release of blanking pressure, the blank expands slightly. The
blanked part is actually larger than the die opening that has produced it.
Similarly in piercing operation, after the strip is stripped off the punch, the material recovers
and the hole contracts. Thus, the hole is actually small then the size of the punch which
produced it. Thus to produce correct hole and blank sizes, the punch size should be increase
and the die opening size should be decreased by an amount for elastic recovery.
The elastic recovery will depend upon blank size, stock thickness and material. It may be taken
as between 0.0125mm to0.075mm.
For stock thickness up to 0.25mm, this difference may be taken as zero.
For stock thickness 0.25mm to 0.75mm it may be equal to 0.025mm.
For stock thickness more than 0.75mm it may be taken as 0.05mm.
2.8 Press Selection Proper selection of a press is necessary for successful and economical operation. Press is a
costly machine, and the return on investment depends upon how well it performs the job.
There is no press that can provide maximum productively and economy for all application so,
when a press is required to be used for several widely varying jobs, compromise is generally
made between economy and productivity. Important factors affecting the selection of a press
are size, force, energy and speed requirements.
Size. Bed and slide areas of the press should be of enough size so as to accommodate the dies
to be used and to make available adequate space for die changing and maintenance. Stroke
requirements are related to the height of the parts to be produced. Press with short stroke should
be preferred because it would permit faster operation, thus increasing productivity. Size and
type of press to be selected also depends upon the method and nature of part feeding, the type
of operation, and the material being formed.
Force and Energy. Press selected should have the capacity to provide the force and energy
necessary for carrying out the operation. The major source of energy in mechanical presses is
the flywheel, and the energy available is a function of mass of flywheel and square of its speed.
Press Speed. Fast speeds are generally desirable, but they are limited by the operations
performed. High speed may not, however, be most productive or efficient. Size, shape and
material of work piece, die life, maintenance costs, and other factors should be considered
while attempting to achieve the highest production rate at the lowest cost per piece.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 22
2.9 Mechanical versus Hydraulic Presses
Mechanical presses are very widely used for blanking, forming and drawing operations
required to be done on sheet metal. For certain operations which require very high force, for
example, hydraulic presses are more advantageous. Table 2.1 gives a comparison of
characteristics and preferred application of the two types of press.
Characteristic Mechanical Presses Hydraulic Presses
Force Depends upon slide
position. Dose not depends upon slide position. Relatively constant.
Stroke length Short strokes Long strokes, even as much as 3 m.
Slide speed High. Highest at mid-
stroke. Can be variable
Slow. Rapid advance and retraction. Variable speeds
uniform throughout stroke.
Capacity About 50 MN (maximum) About 500 MN, or even more.
Control Full stroke generally
required before reversel. Adjustable, slide reversal possible from any position.
Application
Operations requiring
maximum pressure near
bottom of stroke. Cutting
operations(blanking,
shearing, piercing, Forming
and drawing to depths of
about 100 mm.
Operations requiring steady pressure through-out stoke.
Deep drawing. Drawing irregular shaped parts.
Straightening. Operations requiring variable forces and /or
strokes.
2.10 Press Feeding Devices
Safety is an important consideration in press operation and every precaution must be taken to
protect the operator. Material must be tried to be fed to the press that eliminates any chance of
the operator having his or her hands near the dies. The use of feeding device allows faster and
uniform press feeding in addition to the safety features.
• Blank and Stamping Feeds.
Feeding of blanks or previously formed stampings to presses can be done in several ways.
Selection of a specific method depends upon factors like production rate needed, cost, and
safety considerations.
Manual feeding
Feeding of blanks or stampings by hand is generally limited to low production rate
requirements which do not warrant the cost of automatic or semi- automatic feeding devices.
Manual feeding, however, is accomplished with the use of a guard or, if a guard is not possible,
hand feeding tools and a point – of – operation safety device. Some commonly used hand
feeding tools are special pliers, tongs, tweezes, vacuum lifters and magnetic pick – ups.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 23
Push feeds
These feeds are used when blanks need orientation in specific relation to the die. Work piece
is manually placed in a nest in a slide, one at a time, and the slide pushed until the piece falls
into the die nest. An interlock is provided so that the press cannot be operation until the slide
has correctly located the part in the die. To increase production rate, push feeds can be
automated by actuating the feed slide through mechanical attachment to the press slide.
Lift and transfer devices.
In some automatic installations vacuum or suction cups are used for lifting of blanks one at a
time from stacks and then moved to the die by transfer units. Separation of the top blank from
a stack is achieved by devices which are operated magnetically, pneumatically or mechanically.
• Dial Feeds.
Dial feeds consist of rotary indexing tables (or turntables) having fixtures for holding work
pieces as they are taken to the press tooling. Parts are placed in the fixtures at the loading station
(which are located away from the place of press operation) manually or by other means like
chutes, hoppers, vibratory feeders, robots etc. Such feeds are being increasingly used because
of higher safety and productivity associated with them.
• Coil Stock Feed.
Two main classifications of automatic press feeds for coil stock are slide (or gripper) and roll
feeds. Both of these may be press or independently driven.
Mechanical slide feeds.
Press – driven slide feeds have a gripper arrangement which clamps and feeds the stock during
its forward movement and releases it on the return stroke. Material is prevented from backing
up during the return stroke of the gripper by a drag unit like a frictional brake. Grippers
reciprocate on rods or slides between adjustable positive stops to ensure accuracy. Slide feeds
are available in a variety of sizes and designs. These are generally best for narrow coil stock
and short feed lengths.
Hitch – type feed.
This feed differs from press – driven mechanical slide feed in that actuation is by a simple flat
cam attached to the ram or punch holder instead of by the press. On the downward stroke of
the ram, one or more springs are compressed by the cam action, then on the upstroke, the
springs provide the force to feed stock into the die.
These feeds are best suited for coil stock of small to medium thickness and for relatively short
feed progression. These are one of the oldest and least expensive feeding devices still used vary
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 24
widely. Due to their low cost, they are generally left permanently attached to the dies, thus
reducing setup time.
Pneumatic slide feeds.
These feeds are similar to mechanical slide feeds in that they have grippers or clamps that
reciprocate on guide rails or slides between adjustable positive stops to push and / or pull stock
into a die. However, these differ in that they are powered by an air cylinder, with actuation and
timing of valves by cam – operated limit switches.
These feeds are best for short progression, and find wide applications in job shops because of
their low cost and versatility.
Roll feeds.
In these feeds, coil stock is advanced by pressure exerted between intermittently driven,
opposed rolls which allow the stock to dwell during the working part of the press cycle.
Intermittent rotation (or indexing) of the feed rolls, with the rolls rotating in only one direction,
is accomplished in many ways. In one common design, the rolls are indexed through a one –
way clutch by a rack – and – pinion mechanism that is actuated by an adjustable eccentric on
the press – crankshaft.
These feeds are available in several types and sizes to suit almost any width and thickness of
stock. Though their initial cost is slightly higher, their greater durability and lower maintenance
cost account for their extensive use.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 25
2.11 Mounting Methods of Punches and Dies
Fig. 2.8 Mounting and holding of punches
PRESSES AND PRESS WORK
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 26
Fig. 2.9 mounting of dies
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 27
Punch mounting methods
Type Mounting method Remarks
a Flange
fixing
The position and perpendicularity of the
punch are maintained by the shank, and
the head prevents the punch from coming
off.
Standard type for round punches. Reliable in
preventing the punch from coming off.
B Flange
(positioning
with a key
flat)
The position and perpendicularity of the
punch are maintained by the shank, and
the head prevents the punch from coming
off.
The position is determined by a key flat
shank machined by WEDM and inserted
into a hole.
C Locating
with
dowel pin
Positional accuracy is achieved with the
dowel pin, and the head fastens the punch
in place.
The dowel hole is created by NC machining,
allowing easy positioning. This type is often
used for automobile dies.
D Fixing with
adjustment
pins
The position and perpendicularity of the
punch are maintained by the shank, and
the head is fastened with a bolt.
This type allows the punch to be replaced
easily.
E Bolt fixing
(tapping)
The position and perpendicularity of the
punch are maintained by the punch plate,
and the bolt prevents the punch from
coming off.
Highly accurate and also reliable in
preventing the punch from coming off. Not
suitable for thin punches or punching for
heavy load.
F Key fixing The groove of the punch is fixed in place
with a key.
This type allows the punch to be installed
and replaced easily. This type is often used
for precision dies based on the stripper
plates.
G Holder
fixing
The head of the punch is screwed in place
with a holder.
This type allows the punch to be replaced
easily. This type is used in cases when the
clearance between the punch plate and
stripper plate is small.
H Ball lock A steel ball inside a special retainer locks
the punch groove to fasten the punch in
place.
The punch can be mounted and removed
easily by lifting up the steel ball with a pin.
This type is often used for automobile dies.
I Taper fixing A tapered part prevents the punch from
coming off.
This type is inexpensive because the head is
produced by upsetting. This type is often
used for quill punches.
J Taper+ring A special ring supports the tapered part. The special ring allows tapered head
punches with high strength heads to be
easily installed.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 28
2.11.1 Punch holding methods
·Based on punch plate (fig.2.8)
This is the most commonly-used method, and because the punch is press-fit into the
punch plate, dies can be produced easily.
If the punch concentricity (fig.4.8) or accuracy of hole machining is poor, variation is
likely to occur in the clearance between the punch and die. As a result, this method is
not suitable for cases when clearance between the punch and die is small.
·Based on stripper plate (fig.2.9)
This method is primarily used for thin, high-precision dies (fig.4.9).
The punch tip is guided by the stripper plate, which is located close to the punch and
die, making it possible to minimize precision error. The punch is held in the punch
plate by a clearance
2.12 Strip Layout
Since, the components are to be ultimately blanked out of a stock strip; hence, precaution is to
be taken while designing the dies for utilizing as much of stock as possible.
It is also necessary in progressive dies, to ensure continuous handling of the scrap on the die
block, which means that the scrap strip should have sufficient strength.
Fig 2.5 strip layout terms
The distance between the blank and edge of strip known as back scrap
a = t + 0.015 h
Feed or advance or length of one piece of stock
S= w + b
The number of black which can be produced from one length of stock can be found out
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 29
N = (L – b) / s
The scrap remaining at end of length of strip may be calculated
Y = L – (Ns + b)
Measure of material of utilization
Ƞm = area of black to be cut / area of material available
Ƞm = (B/A) X 100
Percentage of scrap = [(A – B)/A] x 100
Where
a = Lead End
t = strip thickness
h = stock width
L = length of strip
W = black length
On material thickness the scrap bridge may be taken as
Material Thickness (mm) Scrap Bridge (mm)
0.8 0.8
0.8 to 3.2 t
Over 3.2 3.2
__________________
References:
Production Engineering -by P.C. SHARMA
Manufacturing Processes I - by Prof. Pradeep Kumar (IIT ROORKEE)
JIGS AND FIXTURES
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 30
Date: ___ /___ /______
EXPERIMENT NO.3
AIM: TO STUDY AND PRACTICING ABOUT JIGS AND FIXTURES FOR VARIOUS
MACHINING OPERATIONS.
3.1 Fixture and Jig
3.1.1 Fixtures
Fixtures being used in machine shop are strong and rigid mechanical devices which enable
easy, quick and consistently accurate locating, supporting and clamping, blanks against cutting
tool(s) and result faster and accurate machining with consistent quality, functional ability and
interchangeability.
3.1.2 Jig
Jig is a fixture with an additional feature of tool guidance.
3.2 Purpose of Using Fixtures and Jigs
For a machining work, like drilling a through hole of given diameter eccentrically in a
premachined mild steel disk as shown in Fig. 3.1
Fig. 3.1 A through hole has to be drilled in a pre-machined mild steel disc.
In conventional drilling machine the following steps are followed with using jigs and fixtures.
cleaning and deburring the blank (disc)
marking on the blank showing the location of the hole and its axis on the blank
punch the centre at the desired location and prick punch the periphery of the hole to be
made in the disc
mount the blank in a drilling vice using parallel block, a small Vee block etc. to provide
support and clamp the blank firmly
position the vice along with the marked blank to bring the hole axis in alignment with the
drill axis by
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- either adjusting the vise position w.r.t. the fixed drill axis or moving the drilling
machine table and then locking the table position or moving the radial arm and the
drilling head, if it is a radial drilling machine
after fixing the blank, vise and the table, alignment is checked again
if error, like eccentricity, is found to occur then readjustment of location of the hole – axis
is to be done before and even after starting drilling
Drilling is accomplished.
Therefore it appears that so many operations are needed to be carried out carefully and skillfully
by the machinist or operator for such a simple job. Even after that there may be inaccuracies in
machining. Such tedious and time consuming manual work are eliminated or drastically reduced in
mass production by automatic or special purpose machine tools. But such machine tools are quite
expensive and hence are economically justified for only huge or mass production and not viable
for small lot or batch production. For batch production proper design and use of simple but effective
jigs and fixtures are appropriate and economically justified. This is schematically illustrated in Fig.
3.2.
The basic purposes of developing and using suitable jigs and fixtures for batch production in
machine shops are:
• To eliminate marking, punching, positioning, alignments etc.
• easy, quick and consistently accurate locating, supporting and clamping the blank in
alignment of the cutting tool
• Guidance to the cutting tool like drill, reamer etc.
• increase in productivity and maintain product quality consistently
• to reduce operator’s labour and skill – requirement
• to reduce measurement and its cost
• enhancing technological capacity of the machine tools
• Reduction of overall machining cost and also increases in interchangeability.
W – without using jig & fixture P – piece production
M – mass production B – batch production
F – using jig and fixture A – automatic (special purpose) machine
Fig. 3.2 Role of Jigs and Fixtures on machining cost
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 32
3.3 Design Considerations for Jigs and Fixtures
Jigs and fixtures are manually or partially power operated devices. To fulfill their basic purposes,
jigs and fixtures are comprised of several elements (as indicated in Fig. 3.3):
• Base and body or frame with clamping features
• locating elements for proper positioning and orientation of the blank
• supporting surfaces and base
• clamping elements
• Tool guiding frame and bushes (for jig)
• Indexing plates or systems, if necessary
• Auxiliary elements
• fastening parts
Fig 3.3 Major Elements of jig and fixtures.
Therefore keeping in view increase in productivity, product quality, repeatability i.e.
interchangeability and overall economy in batch production by machining, the following factors
are essentially considered during design, fabrication and assembly of jigs and fixtures:
• easy, quick and consistently accurate locating of the blank in the jig or fixture in reference
to the cutting tool
• providing strong, rigid and stable support to the blank
• quick, strong and rigid clamping of the blank in the jig or fixture without interrupting any
other operations
• tool guidance for slender cutting tools like drills and reamers
• easy and quick loading and unloading the job to and from the jig or fixture
• use of minimum number of parts for making the jig or fixture
• use of standard parts as much as possible
• Reasonable amount of flexibility or adjustability, if feasible, to accommodate slight
variation in the job - dimensions.
• prevention of jamming of chips, i.e. wide chips-space and easy chip disposal
• Easy, quick and accurate indexing system if required.
• easy and safe handling and moving the jig or fixture on the machine table, i.e., their shape,
size, weight and sharp edges and corners
• easy and quick removal and replacement of small parts
• manufacturability i.e. ease of manufacture
• durability and maintainability
• Service life and overall expenses.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 33
3.4 Principles and Methods of Locating, Supporting and Clamping Blanks
and Tool Guidance in Jigs and Fixtures
It is already emphasized that the main functions of the jigs and fixtures are:
(a) Easily, quickly, firmly and consistently accurately
• locating
• supporting and
• clamping
The blank (in the jig or fixture) in respect to the cutting tool(s)
(b) Providing guidance to the slender cutting tools using proper bushes
There are and can be several methods of locating, supporting and clamping depending upon the
size, shape and material of the job, cutting tool and the machining work required. But some basic
principles or rules are usually followed while designing for locating, supporting and clamping of
blank in fixtures.
Principles or rules of locating in jigs and fixtures
For accurate machining, the work piece is to be placed and held in correct position and orientation
in the fixture (or jig) which is again appropriately located and fixed with respect to the cutting tool
and the machine tool. It has to be assured that the blank, once fixed or clamped, does not move at
all.
Any solid body may have maximum twelve degrees of freedom as indicated in Fig. 3.4. By properly
locating, supporting and clamping the blank it’s all degrees of freedom are to be arrested as
typically shown in Fig.
Fig. 3.4 Possible degrees of freedom of a solid body.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 34
The three adjacent locating surfaces of the blank (work piece) are resting against 3, 2 and 1 pins
respectively, which prevent 9 degrees of freedom. The rest three degrees of freedom are arrested
by three external forces usually provided directly by clamping. Some of such forces may be attained
by friction.
Fig 3.5 Arresting all degree of freedom of blank in fixture
Some basic principles or rules need to be followed while planning for locating blanks in
fixtures, such as;
• One or more surfaces (preferably machined) and / or drilled / bored hole(s) are to be taken
for reference
• The reference surfaces should be significant and important feature(s) based on which most
of the dimensions are laid down
• Locating should be easy, quick and accurate
• In case of locating by pin, the pins and their mounting and contact points should be strong,
rigid and hard
• A minimum of three point must be used to locate a horizontal flat surface
• The locating pins should be as far apart as feasible
• Vee block and cones should be used for self-locating solid and hollow cylindrical jobs as
typically shown in Fig.
• Sight location is applicable to first – operation location of blank with irregular surfaces
produced by casting, forging etc. as indicated in Fig. when the bracket is first located on
two edges to machine the bottom surface which will be used for subsequent locating.
• Adjustable locating pin(s) as indicated in Fig. is to be used to accommodate limited part
size variation.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 35
Fig. 3.6 Locating by Vee block and cone.
• For locating large jobs by rough bottom surface one of the three pins may be replaced
by a pivoted arm as indicated in Fig. 3.6. The pivoted arm provides two contact
points.
Fig. 3.7 (a) Sight location and (b) location by pivoted points (equalizer)
3.4.1 General methods of locating
3.4.1.1 Locating blanks for machining in lathes
In lathes, where the job rotates, the blanks are located by
- fitting into self centering chuck
- fitting into 4 – independent jaw chuck and dead centre
- in self – centering collets
- in between live and dead centers
- by using mandrel fitted into the head stock – spindle
- Fitting in a separate fixture which is properly clamped on a driving plate which is
coaxially fitted into the lathe spindle.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 36
3.4.1.2 Locating for machining in other than lathes
In machine tools like drilling machine, boring machine, milling machine, planning machine,
broaching machine and surface grinding machine the job remains fixed on the bed or work table of
those machine tools.
Fixtures are mostly used in the aforesaid machine tools and jig specially for drilling, reaming etc.
for batch production.
For machining in those jigs and fixtures, the blank is located in several ways which include the
followings
3.4.1.3 Locating by flat surfaces
Fig. 3.8 typically shows locating jobs by their flat surfaces using various types of flat ended pins
and buttons.
Fig. 3.8 Locating by (a) flat surfaces and (b) types of pins used for that.
3.4.1.4 Locating by holes
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 37
In several cases, work pieces are located by premachined (drilled, bored or pierced) holes, such as;
• Locating by two holes as shown in Fig. 3.9 (a) where one of the pins has to be
diamond shaped to accommodate tolerance on the distance between the holes and
their diameters
• Locating by one hole and an external pin which presents rotation of the blank around
the inner pin as indicated in Fig. 3.9 (b)
• Locating by one hole and one Vee-block as shown in Fig. 3.10
Fig. 3.9 Locating by holes.
Fig. 3.10 Locating by a pin and Vee block.
3.4.1.5 Locating on mandrel or plug
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 38
Ring or disc type work pieces are conveniently located on mandrel or single plug as shown in Fig.
3.11.
However there may be several other ways of locating depending upon the machining conditions
and requirements.
Fig. 3.11 Locating by mandrel or plug.
3.4.2 Supporting – principles and methods
A work piece has to be properly placed in the jig or fixture not only for desired positioning and
orientation but also on strong and rigid support such that the blank does not elastically deflect or
deform under the actions of the clamping forces, cutting forces and even its own weight.
Basic principles or rules to be followed while designing or planning for supporting • supporting should be provided at least at three points
• supporting elements and system have to be enough strong and rigid to prevent deformation
due to clamping and cutting forces
• Unsupported span should not be large to cause sagging as indicated in fig.
• Supporting should keep the blank in stable condition under the forces as indicated in fig.
• for supporting large flat area proper recess is to be provided, as indicated in fig. for better
and stable support.
• round or cylindrical work pieces should be supported (along with locating) on strong vee
block of suitable size
• Heavy work pieces with pre-machined bottom surface should be supported on wide flat
areas, otherwise on flat ended strong pins or plugs.
• if more than three pins are required for supporting large work pieces then the additional
supporting pins are to be spring loaded or adjustable mandrel work piece job jig plate plug
• additional adjustable supporting pins need to be provided
- to compensate part size variation
- when the supporting surface is large and irregular
- when clamping and cutting forces are large
• ring or disc type jobs, specially requiring indexing should be supported (and located) in
mandrel
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Fig. 3.12 Deflection due to force(s) for wide gap in between supports.
Fig. 3.13 Stability in supporting.
Fig. 3.14 Recess in long span supporting.
Common methods of supporting job in fixtures
- supporting on vices
- supporting on flat surfaces / blocks (fig. 3.15 (a))
- supporting by fixed pins (fig. 3.15 (b))
- additional supporting by adjustable pins and plugs or jack screws as shown in fig. 3.16
- Supporting (and locating) on vee blocks and mandrels.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 40
Fig. 3.15 Supporting (a) by flat surface and (b) by pins
Fig. 3.16 Adjustable supporting pins.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 41
3.4.3 Clamping of work piece in fixtures
In jigs and fixtures the work piece or blank has to be strongly and rigidly clamped against the
supporting surfaces and also the locating features so that the blank does not get displaced at all
under the cutting forces during machining.
While designing for clamping the following factors essentially need to be considered.
clamping need to be strong and rigid enough to hold the blank firmly during machining
clamping should be easy, quick and consistently adequate
clamping should be such that it is not affected by vibration, chatter or heavy pressure
the way of clamping and unclamping should not hinder loading and unloading the blank in
the jig or fixture
the clamp and clamping force must not damage or deform the work piece
clamping operation should be very simple and quick acting when the jig or fixture is to be
used more frequently and for large volume of work
clamps, which move by slide or slip or tend to do so during applying clamping forces,
should be avoided
clamping system should comprise of less number of parts for ease of design, operation and
maintenance
the wearing parts should be hard or hardened and also be easily replaceable
clamping force should act on heavy part(s) and against supporting and locating surfaces
clamping force should be away from the machining thrust forces
clamping method should be fool proof and safe
Clamping must be reliable but also inexpensive.
3.4.4 Various methods of clamping Clamping method and system are basically of two categories:
3.4.4.1 General type without much consideration on speed of clamping operations
3.4.4.2 Quick acting types
3.4.4.1 General clamping methods of common use
Screw operated strap clamps as typically shown in Fig. 3.17. The clamping end of the strap is
pressed against a spring which enables quick unclamping
Fig. 3.17 Common strap type clamping
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Clamping from side for unobstructed through machining (like milling, planning and
broaching) of
the top surface. Some commonly used such clamping are shown in Fig. 3.18
Fig. 3.18 Clamping from side for free machining of the top surface.
Fig. 3.19 Clamping by swing plates.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 43
3.4.1.1 Clamping by swing plates
Such clamping, typically shown in Fig. 3.19, are simple and relatively quick in operation but is
suitable for jobs of relatively smaller size, simpler shape and requiring lesser clamping forces.
• Other conventional clamping methods include:
∗ Vices like drilling and milling vices
∗ Magnetic chucks
∗ Chucks and collets for lathe work.
3.4.1.2 Quick clamping methods and systems
Use of quick acting nut – a typical of such nut and its application is visualized schematically in
Fig. 3.20
Fig. 3.20 Quick acting nut for rapid clamping.
3.4.1.3 Cam clamping -
Quick clamping by cam is very effective and very simple in operation. Some popular methods and
systems of clamping by cam are shown in Fig. 3.21
The cam and screw type clamping system is used for clamping through some interior parts where
other simple system will not have access.
Fig. 3.21 Quick clamping by cams.
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Quick multiple clamping by pivoted clamps in series and parallel. This method shown in Fig. is
capable to simultaneously clamp number of rods even with slight diameter variation.
3.5 Locating Devices:
Pins of various designs and made of hardened steel are the most common locating devices used
to locate a work piece in z jig or fixture. The shank of the pin is press fitted or driven into the
body of the jig or fixture. The locating diameter Of the pin is made larger than the shank to
prevent it from being forced into the jig or fixture body due to the weight of the work piece or
the cutting forces. Depending upon the mutual relation between the work piece and pin, the
pins may be classified as:
1. Locating pins 2. Support pins 3. Jack pins
3.5.1 Locating pins: When reamed or finely finished holes are available in the workpiece,
these can be used for locating purposes. Depending upon their form, the locating pins are
classified as:
Fig.3.5.1 Locating Pins
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3.5.1.1 Conical locating pins
These pins are used to locate a work piece which is cylindrical and with or without a hole. Any
variation in the hole size will be easily accommodated due to the conical shape of the pin.
3.5.1.2 Cylindrical locating pins
In these pins, the locating diameter of the pin is made a push fit with the hole in the work piece,
with which it has to engage. The top portion of these pins is given a sufficient lead either by
chamfering or by means of radius to facilitate the loading of the work piece.
3.5.2 Support pins
With these pins (also known as rest pins, buttons or pads), work pieces with flat surfaces can
be supported at convenient points. In the fixed type of support pins, the locating surface is
either ground flat or is curved. Support pins with flat head are usually employed to provide
location and support to machined surfaces, because more contact area is available during
location. It would ensure accurate and stable location and would not indent the work. The
spherical head or rounded-head rest buttons are conventionally used for supporting rough
surfaces (unmachined and cast surfaces), because they provide a point support which may be
stable under these circumstances. Adjustable type support pins are used for work pieces whose
dimensions can vary, e.g., sand castings, forging or unmachined faces.
Fig. 3.5.2 support pin
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If the component is to be located in the jig/fixture body, without the aid of these support pins,
then the surface of the jig/ fixture body where the component will be supported will have to be
machined. This will involve unnecessary machining time. The use of support pins saves
machining time as only seats for the pins can be machined instead of the entire body of a large
fixture. For small work pieces, however, no support pins are necessary. The fixture body itself
can be machined suitably to provide the locating surfaces. An ample recess should be provided
in corners so that burr on the work piece corners or dirt and swarf do not obstruct proper
location through positive contact of the work piece with the locating surface. Support pins in
large fixtures automatically provide similar recesses.
3.5.3 Jack pins.
Fig. 3.5.3 jack pin
Jack pins or spring pins are also used to locate the work pieces whose dimensions are subject
to variation. The pin is allowed to come up under spring pressure or conversely is pressed down
by the work piece. When the location of the work piece is secured, the pin is locked in this
position by means of the locking screw.
3.5.4 Radial or Angular Location.
Work pieces such as connecting rod or lever, which have two previously machined and finished
holes at the two ends, may be located with the help of two pins projecting from the base surface
of a jig or fixture, which will fit into the two holes in the work piece. Assuming that the work
piece is effectively located on pin A, the only movement the work piece can have is that of
rotation about the pin A. Now, neither the work piece nor the jig or fixture can be made to the
exact dimensions. It means the centre distances between pins A and B and between holes A
and B is subject to variation. Let the tolerance for the centre distance between the holes A and
B be 'x' and that for the centre distance between the pins, A and B by 'y'. Then if the work piece
is effectively located on pin A and if the pin B is a complete cylinder, the allowance between
pin B and hole B will be x plus y. When the centre distance dimensions for the pins and holes
are at maximum and minimum conditions, a large allowance will result between the hole and
pin at B in the Y direction. Due to this, the work piece will have undesirable rotation about the
pin A and the pin B becomes useless. Therefore, to locate the component completely, location
faces opposed to this rotational movement should be provided at the hole B. This is achieved
by relieving the pin B on two sides perpendicular to the X-axis. This will allow for variations
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in the X-direction but will provide cylindrical locating surfaces in the Y-direction. This will
result in a flattened or diamond pin locator as shown in respectively.
The- important and accurate hole of the two holes should be used for principal cylindrical-
location with a full cylindrical pin. The diamond pin is used to constrain the pivoting of the
work piece around the principal location. The principal locator should be longer than the
diamond pin so that the work piece can be located and pivoted around it before engaging with
the diamond pin. This simplifies and speeds up locating of the work piece.
Fig. 3.5.4 flattened pin locator
A work piece with only one hole can also be fully located as shown in Fig. The principal
location is secured from pin A. The radial movement in both the directions of y-axis is restricted
by providing two pins B confining the periphery of the work piece. The basic principle for
radial locations so as to minimize deviations from true locations is to position the radial locators
as far from the axis of rotation as possible.
3.6 Types of Clamps
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While the types of clamps are numerous, they can be classified in seven basic groups: strap,
cam, screw, latch, wedge or key, toggle, and rack and pinion. Most clamping devices contain
one or more of these elements. In a combination, the name of the most prominent element is
given to the complete clamping device.
3.6.1 Lever of strap clamps
Fig. 3.22 Lever of strap clamps
This is the most popular clamping device used in workshops, and tool rooms of jigs and
fixtures.
Figs. B, C and D show lever type clamps in which the layout is based on fig A. In these, as the
nut is unscrewed the spring pushes the clamp upward. The clamp has a longitudinal slot so that
it can be speed up by using a threaded handle or a quick action locking cam in place of
hexagonal nut .Fig shows the hinge clamp, the sliding clamp, and the latch clamp. The fulcrum
is positioned so that clamp bar is parallel to the base of the tool at all times. Strap clamp can be
operated by either manual or power driven devices. Manual devices include hexagonal nuts,
hand knobs, and cams as shows in fig.3.22. The holding power of a strap clamp is determined
by the size of the threaded member binding the clamp.
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Fig. 3.22 Types of clamps
3.6.2 Screw clamps
These are widely used for jigs and fixtures. These have lover costs. However, their operating
speed is quite slow. The basic screw clamp uses the torque developed by a screw thread to hold
a part in place. This is done by direct pressure or by acting on another clamp.
Fig. 3.23 indirect clamping with a screw clamp.
There are variations of the screw type clamp. The efficiency of the screw clamp can be
improved by using swing clamps, hook clamps and quick acting knobs.
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3.6.3 Cam action clamps
Cam action clamps, when properly selected and used, provide a fast, efficient and simple way
to hold work, as shows in fig.
Fig 3.24 direct pressure cam clamps
Due to their construction and basic operating principles, the use of cam action clamps is limited
in some types of tools.
3.6.3 hinged clamps
These utilize hinged lids for loading and unloading the components. Generally the clamp is
made integral with the hinged lib.
Fig. 3.25 hinged clamped bolt
fig. shows an arrangement using combination of hinged clamps and hinged bolt. This type of
clamp is often required when it is necessary to move both the clamp and the bolt completely
out of the way for the loading of component. The casing is designed such that the lugs are
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provided for locating the hinge pins. In order to save the operator’s time, a coil spring is used
to hold the washer under the nut.
fig shows an arrangement in which a hook cam is fitted which permits the job to be handled
faster. it is only suitable for light clamping. The clamping lever is hinged on the clamping bar
which, in its turn, is hinged on the fixture. along the clamping bar is fitted a floating pad which
holds the work and the clamping lever is then forced against a pin or other abutment fitted to
the fixture.
3.6.4 two way clamps
Fig. shows an example of rapid clamping in two directions from one screw. Clamping force
is applied to the top and one side of the work piece.
Fig. 3.26 two way clamps
the clamp has a quick release action. in this arrangement, the length of the levers should be
approximately such that equal pressure is applied by each clamp at its clamping position. the
top clamp is slotted at the end so that the whole of its clamping mechanism could be swung
clear of the work.
3.6.5 Wedge operated clamps
Fig. shows the operation of wedge operated clamps in which the horizontal movement of the
wedge causes upward vertical clamping force on the work piece. the wedge could be operated
either manually by a screw or cam, or by pneumatic or hydraulic cylinder in which case
automatic clamping of the work piece as part of a fully automatic machine cycle is possible.
Wedges having angle of 1-4’ are self holding type and normally hold the work without
additional attachments. large angle wedges are used where large movement is required. in these
wedge clamps, another holding device is required to hold and wedge the work piece in place.
Fig. 3.28 wedge operated clamp
3.6.6 Cam operated clamps
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These provide a fast, efficient, and simple way to hold work. if cam clamps apply pressure
directly to work and work is subjected to vibration, then clamp may loosen and such clamp
should not be used. Direct pressure cam clamps must be positioned to resist the natural
tendencies of the clamp to shift or move the work when the clamp is engaged. to prevent this
movement, the clamp is always positioned such that work is pushed into the locaters when
pressure is applied.
Fig. 3.29 indirect pressure cam clamp
the advantages of cam action can be obtained in indirect clamping method by using cam action
rather than screw threads to bind strap clamps as shown in fig. in this method, the possibility
of loosening or shifting the work during clamping is decreased.
There are three basic type of cams used for clamping mechanisms: flat eccentric, flat spiral,
and cylindrical.
3.67 Toggle action clamps
These are fast acting clamps. These have the natural ability to move completely free of the
work, allowing for faster taking out of parts. The holding force to toggle clamps compared to
the application force is very high.
fig. shows the four basic clamping actions, viz. hold down, pull, squeeze, and straight line
action.
3.6.8 Power clamping:
Power activated clamps may operate under hydraulic power, pneumatic power, or with an air-
to-hydraulic booster.
The power clamps have better control of clamping pressures. Wear on moving parts of the
clamp is less, operating cycles becomes faster. Production speeds and efficiency are higher but
initial cost is high. Fig. shows a typical application of power clamp.
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Fig. 3.30 toggle clamps
Fig 3.31 power clamp
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3.7 Types of jig bushes
Depending upon nature of fitting, quick mounting and replacement, job requirement etc. jig bushes
are classified into several types.
• Bushes may be
⎯ Press fitted type
⎯ Slip type
⎯ Screwed type
Press fitted thin sleeve type bushes are generally used for shorter runs and are not renewable.
Renewable type slip bushes are used with liner. But screw bushes, though renewable may be used
without or with liner.
• Bushes may be
⎯ Without head
⎯ With head
⎯ With a flange being screwed on the bracket.
Fig. 3.32 Bushes (a) without head, (b) with head and (c) flange.
Fig. 3.32.1 Jig bushes
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Frequently replaceable bushes are provided with some locking system as shown in Fig. 3.33
Fig. 3.33 Locking of frequently replaceable bushes.
Some special jig bushings are often designed and used as and when required as indicated in Fig.
3.34
Fig. 3.34 Special jig – bushes for critical requirements.
Many other types are possible and made depending upon the working situation and critical
requirements.
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3.8 Types of jigs
3.8.1 Template jig
3.8.2 Plate type jig
3.8.3 Open type jig
3.8.4 Channel jig
3.8.5 Leaf Jig
3.8.6 Box type jig
3.8.1 Template Jig This is the simplest type of jig; It is simply a plate made to the shape and size of the work piece;
with the required number of holes made it. It is placed on the work piece and the hole will be
made by the drill; which will be guided through the holes in the template plate should be
hardened to avoid its frequent replacement this type of jig is suitable if only a few part are to
be made.
Fig.3.35 Template Jig
3.8.2 Plate Type Jig: This is an improvement of the template type of jig. In place of simple holes, drill bushes are
provided in the plate to guide the drill. The work piece can be clamped to the plate and holes
can be drilled. The plate jigs are employed to drill holes in large parts, maintaining accurate
spacing with each other.
Fig. 3.36 Plate type jig
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3.8.3 Open Type Jig: In this jig the top of the jig is open; the work piece is placed on the top.
Fig. 3.37 Open type jig
3.8.4 Channel jig; The channel jig is a simple type of jig having channel like cross section. The component is
fitted within the channel is located and clamped by locating the knob. The tool is guided
through the drill bush.
Fig. 3.38 Channel jig
3.8.5 Leaf Jig It is also a sort of open type jig , in which the top plate is arrange to swing about a fulcrum
point , so that it is completely clears the jig for easy loading and unloading of the work piece.
The drill bushes are fitted into the plates, which are also known as leaf, latch or lid.
Fig. 3.37 Leaf Jig
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3.8.6 Box Type Jig When the holes are to drill more than one plane of the work piece, the jig has to be provided
with equalant number of bush plates. For positioning jig on the machine table feet have to be
provided opposite each drilling bush plate. One side of the jig will be provided with a swinging
leaf for loading and unloading the work piece, such a jig would take the form of a box. Such a
jig should be as light as possible. Since it will have lifted again and again. Typical figure of
box type jig is shown:
Fig. 3.38 Box Type jig
3.8.7 Angular Jig
Fig. 3.39 Angular Jig
This type of jig is used when the hole is
drilled at an angle to the drilling bush axis.
These types of jigs are used to drill holes in
collars and hubs of pulleys and gears.
__________
References:
Production Engineering -by P.C. SHARMA
Manufacturing Processes I - by Prof. Pradeep Kumar (IIT ROORKEE)
THERMAL ASPECTS IN MACHINING
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING
DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 59
Date: ___ /___ /______
EXPERIMENT NO. 4
AIM: STUDY ABOUT VARIOUS THERMAL ASPECTS IN MACHINING
Introduction:
Temperature is the main limitation in the selection of process parameters such as cutting
speed and feed rate in the machinability and production of some advanced materials
such as titanium and nickel-based alloys.
In such materials due to their lower thermal conductivity, most of heat flows into tool
and which accelerates tool failure.
When a metal is deformed plastically as in cutting operations, the energy spent is
converted into heat, raising the temperature of chip, tool, and work piece.
The heat generated during machining operation depends on the rate of metal cutting,
cutting speed, specific heat and thermal conductivity of the work piece and tool
material.
Cutting speed has more influence on the temperature because as speed increases, the
time for heat dissipation decrease, thus temperature increase.
The total heat generated during operation is distributed between work piece, tool, chip
and surrounding. The amount of dissipated by surroundings is very small and can be
neglected. The heat distributed in metal cutting operation is approximately 70:15:15
between chips, tool and work piece.
4.1. Amount of heat Generation
The amount of heat generated in metal machining per unit time is equivalent to
mechanical work done given by,
Q Fc.V J/s
4.2. Effect of Cutting Temperature on tool and Workpiece
For cutting tool:
Plastic deformation of cutting edges if tool material is not enough hard.
Thermal fracturing of cutting edges.
Formation of built up edge.
Rapid tool wear.
THERMAL ASPECTS IN MACHINING
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING
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For Workpiece:
Dimensional inaccuracy
Rapid corrosion due to surface damage by oxidation.
Burning
Micro-cracks at the surface.
4.3 Source of Heat generation in machining
During machining heat is generated at the cutting point from three sources Those
sources and causes of development of cutting temperature are:
• Primary shear zone, where the major part of the energy is converted into heat
• Secondary deformation zone at the chip – tool interface where further heat is
generated due to rubbing and / or shear
• At the worn out flanks due to rubbing between the tool and the finished surfaces.
4.4 Cutting Fluid:
Cutting fluid are those liquid and gases which are applied to cutting zone to facilitate
cutting operation by removing heat.
THERMAL ASPECTS IN MACHINING
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING
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4.4.1 Characteristics of Good cutting Fluid:
High specific heat and thermal conductivity
Ability of spreading and wetting
High lubricity without gumming and foaming
Chemically stable and non corrosive
Non toxic, odorless and colorless
Easily available with low cost.
4.4.2 Method for application of cutting Fluid:
Flood cooling
Mist cooling
High pressure refrigerated cooling
Student Activity:
Prepare table for recommended cutting fluid for various engineering materials.
GEAR MANUFACTURING METHODS
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING
DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 62
Date: ___ /___ /______
EXPERIMENT NO. 5
AIM: STUDY OF GEAR MANUFACTURING METHODS.
Introduction:
The methods commonly used for gear manufacturing include the following:
4.1. Machining:
Gear cutting by machining may be done by the following methods:
• Form cutting
• Template process
• Generating processes
4.1.1. Form cutting:
In the form cutting process a tool or cutter having a profile corresponding to the tooth space is
used to cut each space.
The accuracy of the tooth space is, therefore, a function of the accuracy of the cutter.
The other factors that contribute to the accuracy are:
a) Centralized location of the cutter relative to the blank
b) Proper division of the blank while cutting successive tooth spaces.
c) Depth of tooth space.
d) Concentricity of the teeth with the axis of the gear.
The various machining processes that use form cutters include:
a) Form milling with a disc cutter
b) Cutting with a single point tool on a shaper or planer
c) Broaching
4.1.2. Template process:
In the template method of gear cutting, a single point tool guided by a template is used to cut
the form of the tooth instead of a form tool. The process is carried out on special machines
called gear planers. The template guides and reciprocates the tool while the gear blank is held
stationary. If a template many times larger than the size of the teeth to be cut is used, very high
accuracy of tooth form can be ensured. Normally three sets of templates are used to complete
the tooth, one set for producing rough form of the tooth and the other two sets for finishing one
side each. The method is suitable for cutting very large size teeth which are difficult to cut with
a form tool. It can also be used for cutting straight bevel gears but has been replaced by
generating methods which are much more accurate and faster. The method is frequently used
for finishing the gear teeth formed by other methods.
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4.1.3. Gear generation:
In the generation processes the profile to be cut is produced by a combination of movements
co-ordinated in such a way that the kinematic principle upon which the surface depends is fully
realized. The turning operation on a centre lathe is a simple example of a generated surface.
The kinematic derivation of this shape is that of sweeping a straight line about a parallel axis.
The necessary movements are provided by a combination of straight line movement of a tool
and rotation of the workpiece by the spindle. As has already been illustrated in the discussion
of the tooth profile a fundamental basis for the system which can be produced easily and
accurately is the involute rack. The rack forms the basis for some of the important methods of
gear generation the generating methods commonly used include:
(i) By the use of a pinion cutter in a gear shaping machine
(ii) By the use of a rack cutter in a gear shaping machine.
(iii) By the use of a hob in a gear hobbing machine.
(iv) By the use of bevel gear generator.
Machining of gears is the most common method of producing accurate gears for high speed
and high duty applications.
4.2. Casting:
Gears for low duty applications can be produced by casting processes. Large gears can be
produced by conventional dry sand or green sand processes but such gears are not accurate
dimensionally and have rough surfaces. They are generally used as cast and are found in
applications like concrete mixers, road rollers and gardening equipment where speeds are low
and noise and inaccuracy can be tolerated. Main advantage of casting is that the cost of
production is low. Hence the method is used mainly for production of large gears in which
inaccuracy of profile can be tolerated. More accurate gears in small size and large volume are
produced by die casting processes. They are generally made in nonferrous materials, are fairly
accurate and have good surface finish. Spur helical, bevel, worm and face gears can be
produced by this method. Die cast gears are used for light load conditions as in toys, hand tools,
gardening equipment etc. Gears required for transmitting heavier loads may be made by
investment casting.
Such gears are more accurate and have better surface characteristics. They also have more
strength. Gears made by die casting and investment casting processes, however, are limited to
low melting temperature metals and alloys and do not have the strength and wear characteristics
equal to those of heat treated steel gears.
4.3. Stamping:
Thin gears are sheared out of sheet stock upto 3mm thick by the use of punch and die sets. The
stock used in the gears is usually received as rolls. The stock is passed through a roll
straightener which irons out the stock and makes it flat. The stock then passes through the dies
and gears are sheared out. Because of the shearing action the cut edges tend to be rough and
the gears may be finished by passing them through shaving dies. If some other feature is to be
produced on the gear they are produced by the use of compound or progressive dies. A
compound die is preferable for better concentricity of centre hole with gear teeth as the entire
gear is produced in one stroke. Stamped gears are used in toys, clocks, watches, timer
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mechanisms, water and electric meters etc. A wide variety of materials are used for the
production of these gears. They include plain carbon steels, stainless steels, aluminium alloys
and copper alloys. Although initial tooling costs are high, unit cost of production can be very
low when production quantities are large.It should be noted that a die set will be required for
each gear and the entire range of [ gears of a given module cannot be produced with one die.
4.4. Coining:
In this process gears are produced from blocks in a hydraulic press or forging hammers
applying heavy pressure. Gears produced by this process may be used as such or sometimes
may require light K machining.
4.5. Cold drawing:
In this process the gear tooth shape is produced progressively as the stock runs through several
dies. The final die gives the desired shape. The material is squeezed into the shape of the die
under pressure and hence the surface of the teeth is quite hard and smooth. Good drawing
quality materials like plain carbon steels, stainless steel, brass, bronze and aluminium can be
drawn. Gears produced by this process are used in clocks, type writers and other small
appliances.
4.6. Rolling:
In the rolling process, the workpiece is rolled between two cylindrical rollers of equal diameter
and having equal number of teeth (same module). The rollers are driven at the same pitch line
speed. During roll forming the rolls are gradually fed inwards till the gear teeth are produced.
The centre distance between the rollers is adjustable and the rollers are mounted in strong
bearings capable of taking heavy loads that occur during the process. Rolling of gears may be
done hot or cold. For hot rolling the gear stock is heated by induction heating and then rolled
while in the I plastic state. Large deformations are therefore possible in hot rolling. Hot rolled
gears may be finished by cold rolling to give a smooth finish to the gear teeth. Cold rolling of
gears is done without any heating and involves much higher pressures compared to hot rolling.
The gears produced by this process generally need no further finishing. The material also
becomes stronger and more fatigue resistant due to cold working. The rolling process is mainly
used for production of worms and involute splines. The produced teeth have good accuracy.
Since there is no metal cutting involved considerable material saving may result. The accuracy
of the finished gears depends upon the accuracy of the blank size provided. An approximation
to the blank size can be made by subtracting one depth from the finished outside diameter of
the gear. Plain carbon steels, alloy steels and brasses are the materials commonly used for rolled
gears. Because of the heavy equipment cost, rolled gears are economical only in large
quantities.
4.7. Extrusion:
Quite accurate gears of small size can be produced by the extrusion process. In this process
heated blocks of material to be extruded are placed in the extrusion cylinder and forced from
one end by a ram. Long lengths of rods having the cross section of the desired gear come out
from the die at the other end. These rods are then cut to required gear width with hack saws
and the resulting gears are finished. The materials that can be extruded include brass, bronze
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING
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and alloys of aluminium, magnesium and zinc. The method is used for production of spur gears
only.
4.8. Powder Metallurgy:
In this process raw material in the form of metal powders is mixed with a suitable binder and
forced under high pressure into a die cavity to take the desired shape of the gear. The compact
is then taken out and sintered in furnaces to produce the necessary bond. The gears so produced
may be further finished by coining. Coining helps remove any distortion due to the heat
treatment process and involves repressing the sintered gear in another die. The process also
improves gear accuracy and surface finish. Gears of Cast iron, steel, brass and other alloys can
be produced by this process. The process of producing gears by powder metallurgy is restricted
to small size gears not more than 25 mm diameter. Larger gears are produced by the Powder
Metallurgy Forging process. In this process powder metallurgy performs are forged to produce
the final gear form. This gives strength and durability to the gears. Gears produced by this
method also do not require further finishing. Gears produced by powder metallurgy have high
dimensional accuracy and surface finish and find applications in electrical appliances, small
motor drives, instruments and toys. Accurate gear pump rotors made of stainless steel can also
be produced by this method.
4.9. Plastic Moulding:
This process is used for mass production of plastic gears. These gears generally are lighter, run
quieter, have less friction and have smooth surfaces. They also do not need lubrication.
Thermoplastic materials like nylon are generally moulded by the injection moulding process
while thermosetting materials are handled by compression moulding. More accurate gears for
heavy duty applications may even be produced by machining from laminated plastics.
4.10. Gear Finishing Processes:
In order for gears to operate efficiently and without noise at a high speed for a reasonable life
span it is important that the profile of the gear teeth be accurate, smooth, without any
irregularities, projections or nicks. Gears produced by most processes with the possible
exception of roll forming are found not up to the mark in many cases. Gears produced by
milling may not have accurate tooth profile because of the use of a limited number of cutters.
Gear tooth surfaces produced by shaping or hobbing are composed of tiny flats which may not
be acceptable. The size of these flats can be reduced by reducing the feed rate but that increases
the cutting time. In many cases gears are hardened after cutting the teeth to improve their life.
This may introduce slight distortion or surface roughness. Use of gears with inaccurate or rough
profile leads to noisy operation, unequal loading of gear teeth, faster wear and early failure of
the gears. For economic production, it is considered more desirable to cut slightly inaccurate
gears at a fast rate and finish the tooth surfaces by a subsequent finishing operations.
The finishing operation is intended to perform the following functions :
(i) Correct any errors of profile and pitch
(ii) Eliminate any after effect of heat treatment.
(iii) Ensure proper concentricity of the pitch circle and the central hole.
The processes commonly used for gear finishing include.
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1. Gear shaving
2. Gear burnishing
3. Gear grinding
4. Gear lapping
5. Honing
These processes remove very small amount of material from the tooth surface clearing any
irregularities, rectifying defects and producing a smooth, accurate surface for efficient
operation.
4.10.1. Gear Shaving:
Gear shaving is the most common method for gear finishing. In this method, the gear teeth are
finished by making the gear run at high speed in mesh and pressed against a hardened gear
shaving cutter. Sharp edges of the shaving cutter scrape small amount of metal from the surface
of the teeth removing any surface irregularities and correcting any errors. The axis of cutter
and gear are generally crossed at 5 to 15 degrees. This produces a small sliding action between
the gear and cutter teeth giving a smooth surface. Two types of gear shaving cutters are in
common use : rotary type and rack type. The rotary type of cutter is a gear with serrations or
grooves on its flanks. The edges of these grooves are sharpened to produce the cutting action.
The shaving operation with these cutters is carried out on rotary shaving machines. The cutter
is mounted on a mandrel and rotated at a surface speed of about 2 metres/second. The work
piece is loaded between live centres, raised to the level of the cutter and reciprocated at a slow
speed while being driven. The reciprocating action is to ensure that the shaving operation
extends over the entire length of the gear tooth.
During the shaving operation workpiece may be fed radialy or tangentially to the cutter. The
rack type shaving operation is carried out on rack type shaving machines using a rack type
cutter. The cutter is reciprocated at high speed in mesh with the workpiece. At the same time
the workpiece is reciprocated sideways and fed into the cutter. This type of cutter gives more
accurate gear teeth than the rotary cutter because an accurate rack is more easy to produce. It
also has a fuller contact with the workpiece compared to a rotary cutter. But rack type of
shaving cutters cannot be used for cluster type and very large size gears. Gear shaving is a fast
and rapid production process producing accurate teeth profiles on unhardened gears. If desired,
the process can also be used to crown gear teeth slightly at the centre to localize tooth contact
and provide better clearance during operation. Gear shaving corrects small errors in tooth
spacing, tooth profile, concentricity and helix angle. It also improves the surface finish.
4.10.2. Gear Burnishing:
Gear burnishing is a cold working process in which any high spots on unhardened gears are
plastically deformed to produce smooth and accurate surfaces. The gear to be finished is
mounted on a vertical floating spindle in mesh with three hardened burnishing gears. One of
these burnishing gears is power driven. During burnishing operation, the burnishing gears are
fed inwards towards workpiece and made to turn a few rotations in each direction. The surface
irregularity of the gear teeth are squeezed and a good surface finish obtained. The gear teeth
also get slightly hardened due to cold working. The process is however not recommended for
very precise gears because of hi localized residual stresses produced. Gear burnishing is used
for unhardened gears. The process can only improve the surface finish of the teeth and does
not correct t tooth profile or pitch of the teeth. As such the process is suitable only for gears
which do not require high accuracy.
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PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING
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4.10.3. Gear Grinding:
Gear grinding is the most accurate method of finishing gear teeth. It is most suitable for
finishing of hardened gears which cannot be finished by shavi: or burnishing. Heat treatment
often causes considerable distortion and oxide film formation whi needs deeper cuts for
complete removal. Grinding can accomplish this job easily because of the abrasive action and
is oft preferred to lapping because of the better accuracy obtained with grinding.
4.10.3.1. Form Wheel grinding:
Form wheel grinding shown at (a) is done with the help of a grinding wheel shaped to the exact
profile of a gear tooth space like a disc type form millii cutter. The workpiece is reciprocated
under the grinding wheel which is plunge fed in the work gear to the desired depth. The teeth
are finished one by one and after one tooth is finished to the desired si; the blank is indexed to
the next tooth space as in the form milling operation. Spur, helical, bevel and worm gears are
finished by this method.
4.10.3.2. Threaded wheel grinding :
Threaded wheel finishing operation uses a wheel on which a helical thread has been developed.
The wheel is rotated about its own axis to give a cutting speed of 20-30 m/second and also
given a feeding motion of 0.5 to 0.6 mm/rev. of the workpiece along the axis of the workpiece.
The work piece is also given a rotational movement in mesh with the wheel and a periodic in
feed towards the wheel. This method is very fast but a lot of time is required to prepare the
grinding wheel.
4.10.4. Lapping:
Lapping is often done on hardened gears (Hardness, > 45RC) to remove bun's, scales,
abrasions, nicks and irregularities from the surface and to remove small errors caused by heat
treatment. It is carried out by running the work gear in mesh with a mating gear or one or more
small cast iron toothed laps under a flow of fine abrasives in oil. The teeth on the lapping gear
are so formed that when the lap and the work gear are meshed together their centre lines are
not parallel. This creates a sliding action between the teeth all over the contact surface. The
sliding action causes the abrasive grains to remove irregularities form the tooth surface and
make it smooth. During lapping the work is turned first in one direction and then in the other
to finish both sides of the tooth. The work may be moved back and forth to cover the total face
with of the gear. Very small amount of material is removed during lapping. As such the process
can only correct minor errors but in many cases it proves faster and cheaper than form grinding.
4.10.5. Honning:
Like lapping, honing is also suitable for finishing heat treated gears. It is carried out with the
help of steel tools having abrasive or cemented carbide particles embedded in their surface.
Plastic tools, impregnated with abrasives are also used for honing. Plastic honing tools have
the advantage of being lighter and can be trued many times before being scrapped. The honing
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tool is pushed with constant force along the tooth space but unlike the shaving tools (which are
rigid) the honing tools are allowed to float. An axial vibratory motion may also be provided to
the honing tool. Honing is done on machines similar to gear shaving machines but there is no
infeed mechanism in these machines. The honing tool and the work gear are mounted in relation
to each other such that honing tool rotates the work gear at a high speed. The work gear is also
provided with a reciprocating motion while rotating. Honing is done on internal and external
spur and helical gears to correct small error to produce smooth surfaces so that the finished
gears run quieter. The honing tools are costlier than lapping tools but the process is much faster.
As such honing is often preferred to lapping for large quantity operation.
NON CONVENTIONAL MACHINING PROCESSES
PRODUCTION TECHNOLOGY (181903) DEPARTMENT OF MECHANICAL ENGINEERING
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Date: ___ /___ /______
EXPERIMENT NO. 6
AIM: PROCESS PRINCIPLE, PROCESS PARAMETER AND APPLICATION OF
NON-CONVENTIONAL MACHINING.
5.1. Introduction:
With the development of technology, more and more challenging problems are faced by the
scientists and technologists in the field of manufacturing. The difficulty in adopting the
traditional manufacturing processes can be attributed mainly to the following three basic
sources:
1. New materials with a low machinability
2. Dimensional and accuracy requirements
3. A higher production rate and economy
Many new materials and alloys that have been developed for specific uses possess a very low
machinability. Producing complicated geometries in such materials becomes extremely
difficult with the usual methods. Also, sometimes the combination of the materials properties
and the job dimensions is such that it makes the use of the traditional processes impossible.
Examples of these types of jobs are machining a complicated turbine blade made of
superalloys, and producing holes and slots (both through and blind) in materials such as glass
and semiconductors. At times, the job becomes difficult because of the dimensional
complications. So, drilling a noncircular hole or a micro hole becomes problematic (and
sometimes impossible) if the traditional processes are used. Apart from the situations cited,
higher production rate and economic requirements may demand the use of nontraditional (or
unconventional) machining processes.
To take such difficult jobs, two approaches are possible, viz, (i) a modification of the traditional
processes e.g., hot machining) and (ii) the development of new processes. Here, we will discuss
the presently available common unconventional machining processes. Such processes are
becoming increasingly unavoidable and popular; therefore, knowledge of these is essential for
a mechanical engineer. The basic objective of all machining operations is to remove the excess
material to obtain the desired shape and size. These operations use various types of energies.
Table shows the possible machining processes using the different types of energies and various
methods of material removal.
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PRODUCTION TECHNOLOGY (181903) DEPARTMENT OF MECHANICAL ENGINEERING
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5.2. Abrasive Jet Machining (AJM):
In AJM, the material removal takes places place due to the impingement of the fine abrasive
particles. These particles move with a high speed air (or gas) stream. The abrasive particles are
typically of 0.025 mm diameter and the air discharges at aj pressure of several atmospheres.
5.2.1. Mechanics of AJM:
When an abrasive particle impinges on the work surface at a high velocity, the impact causes
a tiny brittle fracture and the flowing air (or gas) carries away the dislodged small work piece
particle (wear particle). Thus, it is obvious that the process is more suitable when the work
material is brittle and fragile.
5.2.2. Process Parameters:
The process characteristics can be evaluated by judging (i) the burr, (ii) the geometry of
the cut, (iii) the roughness of the surface produced, and (iv) the rate of nozzle wear. The
major parameters which control these quantities are
(i) The abrasive (composition, strength, size, and mass flow rate),
Energy type
Mechanics of
material removal
Energy source
Process
Mechanical erosion
Mechanical/fluid motion Abrasive jet machining (AJM)
Ultrasonic machining(USM)
Electrochemical Ion displacement
Electric current
Electrochemical machining(ECM)
Mechanical and
electrochemical
Plastic shear and
ion displacement
Electric current and
mechanical motion Electrochemical grinding(ECG)
Chemical Corrosive reaction Corrosive agent
Chemical machining(CHM)
Fusion and
vaporization
Electric spark
Electric discharge
machining(EDM)
High speed electrons
Electron beam machining(EBM)
Thermal
Powerful radiation
Laser beam machining(LBM)
Ionized substance
Ion beam machining(IBM)
Plasma arc machining(PAM)
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(ii) The gas (composition, pressure, and velocity),
(iii) The nozzle (geometry, material, distance from and inclination to the work
surface).
5.2.3. Summary of AJM Characteristics:
Mechanics of material
removal
Media Abrasives
Velocity
Pressure
Nozzle
Critical parameters
Materials application
Shape (job) application
Limitations
Brittle fracture by impinging abrasive grains at high speed Air, CO2
AI203, SiC
0.025 mm diameter, 2-20 g/mm, non recirculating
150-300 m/sec
2-10 atm
WC, sapphire
Orifice area 0.05-0.2 mm2
Life 12-300 hr
Nozzle tip distance 0.25-75 mm
Abrasive flow rate and velocity, nozzle tip distance
from work surface, abrasive grain size and jet
inclination
Hard and brittle metals, alloys, and non-metallic materials
(e.g., germanium, silicon, glass, ceramics, and mica)
Specially suitable for thin sections
Drilling, cutting deburring, etching, cleaning
Low metal removal rate (40 mg/min, 15 mm3/rnin),
embedding of abrasive in work piece, tapering of
drilled holes, possibility of stray abrasive action
5.3. Ultrasonic Machining (USM):
The basic USM process involves a tool (made of a ductile and tough material) vibrating with a
very high frequency and a continuous flow of abrasive slurry in the small gap between the tool
and the work surface (figure) The tool is gradually fed with a uniform force. The impact of the
hard abrasive grains fractures the hard and brittle work surface, resulting in the removal of the
work material in the form of small wear particles which are carried away by the abrasive slurry.
The tool material, being tough and ductile, wears out at a much slower rate.
5.3.1. Mechanics of USM:-
The physics of ultrasonic machining is neither complete nor uncontroversial. The reasons of
material removal during USM are believed to be
(i) The hammering of the abrasive particles on the work surface by the tool,
(ii) The impact of the free abrasive particles on the work surface,
(iii) The erosion due to cavitation, and
(iv) The chemical action associated with the fluid used.
A number of researchers have tried to develop the theories to predict the characteristics of
ultrasonic machining. The model proposed by M.C. Shaw is generally well-accepted and
despite its limitations, explains the material removal process reasonably well. In this model,
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the direct impact of the tool on the grains in contact with the work piece (which is responsible
for the major portion of the material removal) is taken into consideration. Also, the assumptions
made are that
(i) The rate of work material removal is proportional to the volume of work material per
impact,
(ii) The rate of work material removal is proportional to the number of particles making
impact per cycle,
(iii)The rate of work material removal is proportional to the frequency (number of cycles
per unit time),
(iv) All impacts are identical,
(v) All abrasive grains are identical and spherical in shape.
5.3.2. Process Parameters:
The important parameters which affect the process are the
(i) Frequency,
(ii) Amplitude,
(iii) Static loading (feed force).
(iv) Hardness ratio of the tool and the workpiece,
(v) Grain size,
(vi) Concentration of abrasive in the slurry.
5.3.3. Summary of USM Characteristics
Mechanics of material
removal
Medium
Absrasives
Vibration Frequency
Tool Material
Critical parameters
Materials application
Shape application
Limitations
Brittle fracture caused by impact of abrasive grains due to tool
vibrating at high frequency
Slurry
B4C,SiC, AI2O3 ,
diamond 100-800 grit size 4
15-30 kHz, 25-100
Soft steel
Frequency, amplitude, tool material, grit size, abrasive
material, feed force, slurry concentration, slurry viscosity
Metals and alloys (particularly hard and brittle), semiconductors,
nonmetals, e.g., glass and ceramics
Round and irregular holes, impressions
Very low MRR, tool wear, depth of holes and cavities small
5.4. Electro-chemical Machining (ECM):
This process may be considered as the reverse of electroplating with some
modifications. Further, it is based on the principle of electrolysis. In a metal, electricity
conducted by the free electrons, but it has been established that in an electrolyte the conduction
of electricity is achieved through the movement of ions. Thus, the flow of current
through an electrolyte is always accompanied by the movement of matter. In electrochemical
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machining the objective is to remove metal, the workpiece is connected to the positive,
and the tool to the negative, terminal. Figure shows a workpiece and a suitably-shaped tool, the
gap between the tool and the work being full of a suitable electrolyte. When the current is
passed, the dissolution of the anode occurs. However, the dissolution rate is more where the
gap is less and vice versa as the current density is inversely proportional to the gap. Now, if the
tool is given a downward motion, the work surface tends to take the same shape as that of the
tool, and at a steady state, the gap is uniform, as shown in figure. Thus, the shape of the tool is
reproduced in the job.
In an electrochemical machining process, the tool is provided with a constant feed motion. The
electrolyte is pumped at a high pressure through the tool and the small gap between the tool
and the workpiece (figure). The electrolyte is so chosen that the anode is dissolved but no
deposition takes place on the cathode (the tool). The order of the current and voltage are a few
thousand amperes and 8-20 volts. The gap is of the order of 0.1-0.2 mm.
5.4.1. Electrochemistry of ECM Process:
The electrolysis process is governed by the following two laws proposed by Faraday:
(i) The amount of chemical change produced by an electric current, that is the amount of
any material dissolved or deposited, is proportional to the quantity of electricity passed.
(ii) The amounts of different substances dissolved or deposited by the same quantity of
electricity are proportional to their chemical equivalent weights.
5.4.2. Summary of ECM Characteristics
Electrolysis
Critical parameters
Materials
application
Shape application
Limitations
Conducting electrolyte Cu, brass, steel
Voltage, current, feed rate, electrolyte, electrolyte conductivity
All conducting metals and alloys
Blind complex cavities, curved surfaces, through cutting, large
through cavities
High specific energy consumption (about 150 times that required for
conventional processes), not applicable with electrically
nonconducting materials and for jobs with very small dimension,
expensive machine
5.5. Electric Discharge Machining (EDM):
When discharge takes place between two points of the anode and the cathode, the intense heat
generated near the zone melts and evaporates the materials in the sparking zone. For improving
the effectiveness, the work-piece and the tool are submerged in a dielectric fluid
(hydrocarbon or mineral oils). It has been observed that if both the electrodes are made of the
same material, the electrode connected to the positive terminal generally erodes
at a faster rate. For this reason, the workpiece is normally made anode. A suitable gap, known
as the spark gap, is maintained between the tool and the workpiece surfaces. The sparks
are made to discharge at a high frequency with a suitable source. Since
the spark occurs at the spot where the tool and the workpiece surfaces are the closest and since
the spot changes after each spark (because of the material removal after each spark), the sparks
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travel all over the surface. This result in a uniform material removal all over the surface, and
finally the work face conforms to the tool surface. Thus, the tool produces the required
impression in the workpiece. For maintaining the predetermined spark gap, a servocontrol unit
is generally used. The gap is sensed through the average voltage across it and this volt is
compared with a preset value. Sometimes, a stepper motor is used instead of a servo-motor. Of
course, for primitive operations, a solenoid control is also possible, and with this it becomes
extremely inexpensive and simple to construct. The spark frequency normally in the range 200-
500,000 Hz, the spark gap being of the order of 0.025-0 mm. The peak voltage across the gap
is kept in the range 30-250 volts. A MRR up 300mm3/min can be obtained with this process,
the specific power being of the order 10 W/mm3/min. The efficiency and the accuracy of
performance have been found improve when a forced circulation of the dielectric fluid is
provided. The most common used dielectric fluid is kerosene. The tool is generally made of
brass or a copper alloy.
5.5.1. EDM Circuits and Operating Principles:
Several basically different electric circuits are available to provide the pulsating across the
work-tool gap. Though the operational characteristics are different, in almost all such circuits
a capacitor is used for storing the electric charge before the discharge takes place across the
gap. The suitability of a circuit depends on the machining conditions and requirements. The
commonly-used principles for supplying the pulsating dc can be classified into the following
three groups:
(i) Resistance-capacitance relaxation circuit with a constant dc source
(ii) Rotary impulse generator
(iii) Controlled pulse circuit
5.5.2. Electrode Material:
The selection of the electrode material depends on the
(i) Material removal rate,
(ii) Wear ratio,
(iii) Ease of shaping the electrode,
(iv) Cost
The most commonly-used electrode materials are brass, copper, graphite, Al alloys, copper-
tungsten alloys, and silver-tungsten alloys.
The methods use for making the electrodes are:
(i) Conventional machining (used for copper, brass, Cu-W alloys, Ag-W alloys, and
graphite),
(ii) Casting (used for Zn base die casting alloys, Zn-Sn alloys, and Al alloys).
(iii) Metal spraying
(iv) Press forming
Flow holes are normally provided for the circuit of the dielectric, and three holes should be as
large as possible for rough cuts to allow large flow rates at a low pressure.
5.5.3. Dielectric Fluids:
NON CONVENTIONAL MACHINING PROCESSES
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DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 75
The basic requirements of an ideal dielectric fluid are
(i) Low viscosity,
(ii) Absence of toxic vapours,
(iii) Chemical neutrality,
(iv) Absence of inflaming tendency
(v) Low cost
5.5.4. Summary of EDM Characteristics
Machanics of material
removal
Medium
Tool Materials
Material removal rate
Critical parameters
Materials application
Shape application
Limitations
Melting and evaporation aided by cavitation
Dielectric fluid
Cu, brass, Cu-W alloy, Ag-W alloy, graphite 0.1-10
5xl03mm3 /min
Voltage, capacitance, spark gap, dielectric circulation, melting
temperature
All conducting metals and alloys
Blind complex cavities, micro holes for nozzles, through cutting of non
circular holes, narrow slots
High specific energy consumption (about 50 times that in conventional
machining); when forced circulation of dielectric is not possible,
removal rate is quite low; surface tends to be rough for larger removal
rates; not applicable to non-conducting materials
5.6. Electro Beam Machining (EBM):
Basically, electron beam machining is also a thermal process. Here, a stream of high speed
electrons impinges on the work surface whereby the kinetic energy, transferred to the work
material, produces intense heating. Depending on the intensity of the heat thus generated, the
material can melt or vaporize. The process of heating by an electron beam can n, depending on
the intensity, be used for annealing, welding, or metal removal.
5.6.1. Summary of EBM Characteristics: Mechanics of material removal
Medium
Tool
Maximum material removal rate
Specific power consumption
(typical)
Critical parameters
Materials application
Shape application
Limitations
Melting , vaporization
Vacuum
Beam of electrons moving at very high
velocity
10mm3 /min
450W/mm3 -min
Accelerating voltage, beam current,
beam diameter, work speed, melting
temperature
All materials
Drilling fine holes, cutting contours in
sheets, cutting narrow slots
Very high specific energy consumption,
necessity of vacuum , expensive machine
NON CONVENTIONAL MACHINING PROCESSES
PRODUCTION TECHNOLOGY (181903) DEPARTMENT OF MECHANICAL ENGINEERING
DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 76
5.7. Laser Beam Machining (LBM):
Like a beam of high velocity electrons, a laser beam is also capable of producing very high
power density. Laser is a highly coherent (in space and time) beam of electromagnetic
radiation.
5.7.1. Summary of LBM Characteristics:
Mechanics of material removal
Medium
Tool
Maximum material removal rate
Specific power consumption (typical)
Critical parameters
Materials application
Shape application
Limitations
Melting, vaporization
Normal atmosphere
High power laser beam
5mm3/min
1000W/mm3/min
Beam power intensity, beam diameter,
melting temperature
All materials
Drilling fine holes
Very large power consumption, cannot cut
materials with high heat conductivity and high
reflectivity
5.8. Plasma Beam Machining (PBM):
A plasma is a high temperature ionized gas. The plasma arc machining is done with a high
speed jet of a high temperature plasma. The plasma jet heats up the workpiece (where the jet
impinges on it), causing a quick melting. PAM can be used on all materials which conduct
electricity, including those which are resistance to oxy-fuel gas cutting. This process is
extensively used for profile cutting of stainless steel, monel, and superalloy plates.
A plasma is generated by subjecting a flowing gas to the electron bombardment of an arc. For
this, the arc is set up between the electrode and the anodic nozzle; the gas is forced to flow
through this arc.
The high velocity electrons of the arc collide with the gas molecules, causing a dissociation of
the diatomic molecules or atoms into ions and electrons resulting in a substantial increase in
the conductivity of the gas which is now in plasma state. The free electrons, subsequently,
accelerate and cause more ionization and heating. Afterwards, a further increase in temperature
takes place when the ions and free electron recombine into atoms or when the atoms recombine
into molecules as thee are exothermic processes. So, a high temperature plasma is generated
which is forced through the nozzle in the form of a jet.
The mechanics of material removal is based on
(i) heating and melting
(ii) Removal of the molten metal by the blasting action of the plasma jet.
NON CONVENTIONAL MACHINING PROCESSES
PRODUCTION TECHNOLOGY (181903) DEPARTMENT OF MECHANICAL ENGINEERING
DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 77
5.8.1. Summary of PBM Characteristics:
Mechanics of material removal
Medium
Tool
Maximum temperature
Maximum velocity of plasma jet
Maximum material removal rate
Specific energy
Power range
Maximum plate thickness
Cutting speed
Voltage
Current
Critical parameters
Materials application
Shape application Limitation
Melting
Plasma
Plasma jet
16,000°C
500 m/sec
150cm3 /min
1000W/cm3 -min
2-200 kW
Up to 200 mm (depends on material)
0.1-7.5 m/min
30-250 V
Up to 600 amp
Voltage, current, electrode gap, flow rate, nozzle
dimensions, melting temperature
All conducting materials, Cutting plates
Low accuracy
PRESS TOOL DESIGN
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 78
Date: ___ /___ /______
EXPERIMENT NO.7
AIM: PREPARE PRESS TOOL DESIGN BASED ON GIVEN DATA.
A Washer with 12.7 mm internal hole and an outside diameter of 25.4 mm is to be made from 1.5 mm thick strip of 0.2% carbon steel. Considering the elastic recovery of the material Design the press tool and its various parameters.
JIG DESIGN
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 79
Date: ___ /___ /______
EXPERIMENT NO.8
AIM: PREPARE JIG DESIGN AND DRAWING FOR GIVEN COMPONENTS.
Design and Draw Drilling Jigs for drilling holes in given components by using any CAD software.
Figure No.1 For Batch No. 1
Figure No. 2 For Batch NO.2
JIG DESIGN
PRODUCTION TECHNOLOGY (2161909) DEPARTMENT OF MECHANICAL ENGINEERING DARSHAN INSTITUTE OF ENGINEERING AND TECHNOLOGY RAJKOT 80
Figure No. 3 for Batch No. 3
________________