deep drawing.project
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I
DESIGN AND MANUFACTURING OF
DEEP DRAWING DIES FOR WARM FORMING
A Project Report Submitted In Partial Fulfillment of the Requirement For
The Award of the Degree of Bachelor of Technology
By
Jatin Garg (Reg. No. 09241A0367)
Arun Kapil Kumar (Reg. No. 09241A0368)
Department Of Mechanical Engineering
Gokaraju Rangaraju Institute of Engineering and Technology
Bachupally – HYDERABAD - 500 090, A.P, INDIA
April, 2013
II
Department Of Mechanical Engineering
Gokaraju Rangaraju Institute of Engineering and Technology
CERTIFICATE
This is to certify that the Project Report on Design and Manufacturing of Deep
Drawing Dies for Warm Forming that is being submitted by Mr. Jatin Garg
(Reg.No.09241A0367)Arun Kapil Kumar (Reg. No. 09241A0368)in partial
fulfillment for the award of Bachelor of Technology in Mechanical Engineering to the
Department of Mechanical Engineering, Gokaraju Rangaraju Institute of Engineering
and Technology, affiliated to Jawaharlal Nehru Technological University, Hyderabad
is a record of bonafide work carried out by him under our guidance and supervision.
The results embodied in this Project report have not been submitted to any other
university or institute for the award of any degree or diploma.
Signature of Guide
Name: Dr. Swadesh Kumar Singh
Designation: Professor
III
Acknowledgement
With great pleasure we want to take this opportunity to express our heartfelt gratitude
to all the people who helped in making this main project work a grand success.
We express our deep sense of gratitude to Dr. Swadesh Kumar Singh (Professor) for
his constant guidance throughout our main project work.
We thank Mr. K.G.K.MURTHI (HOD, Mechanical Engineering) who has been an
excellent guide and also a great source of inspiration to our work and also Dr. P.A.P
NAGENDRA VARMA under whose kind supervision we accomplished our Project
“Design and Manufacturing of Deep Drawing Dies for Warm Forming”.
The satisfaction and euphoria that accompany the successful completion of the task
would be great but incomplete without the mention of the people who made it
possible with their constant guidance and encouragement peaks all the efforts with
success. In this context we would like thank all the staff members, both teaching and
non-teaching, who have extended their timely help and eased our task. Last but not
least, we would like to thank our friends who have patiently extended all sorts of help
for accomplishing this undertaking.
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Abstract
Deep drawing is a sheet metal forming process in which a sheet metal blank is
radially drawn into a forming die by the mechanical action of a punch. The process is
considered "deep" drawing when the depth of the drawn part exceeds its
diameter. The flange region (sheet metal in the die shoulder area) experiences a radial
drawing stress and a tangential compressive stress due to the material retention
property. These compressive stresses (hoop stresses) result in flange wrinkles
(wrinkles of the first order). Wrinkles can be prevented by using a blank holder, the
function of which is to facilitate controlled material flow into the die radius.
The present investigation deals with the design and manufacturing
consideration of die. While designing the die it consider the design parameters punch
shape (hemispherical), clearance, deep drawing force, and deep drawing speed/punch
speed, die material, operating pressure and temperature. Die are used for deep
drawing the sheets of up to 1mm thickness only and the experiment can be carried out
from room temperature to 600°C. For this reason the central part of blank holder and
die is made up of nickel based super alloy to avoid thermal expansions at high
temperatures.
Deep Drawing die equipment consists of special die with D3 steel as base and
nickel super alloy at center, while hydraulically driven vertical ram deforms the metal
sheet. In sheet metal forming process sheet can be deformed only to a certain limit
that is usually imposed by the onset of localized necking and which leads to fracture.
So the sheet deformation is stopped before fracture occurs.
Keywords: Nickel super alloy, worm forming.
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Contents
1) Introduction………………………………………………….……………1
2) Die Operations and Types...................................................................3
3) Die material and lubrication...............................................................8
4) Die Failures.......................................................................................10
5) About The Material Used(D3)……………………….……………..…13
6) About the Machines/Methods Used…………………….…..….…......18
6.1 Wire Cut EDM……...………………………………..….......…18
6.2 Grinding…………………………………………...………..…..37
6.3 Lathe………………………………………….………………....49
6.4 Drilling……………………………………………….....…........57
6.5 Tapping………………………………………………...…....….72
6.6 Lapping……………………………………………..….….……75
7) Manufacturability Aspects..............................................................80
8) What Constitutes Suitability For Die Production..........................81
9) Procedure for Deep Drawing die…………………………...….…....84
10) Procedure for Punch……………………………………………….…98
11) Summary………………………………………………………..…....101
12) Conclusion………………………………………………….…...……103
13) Bibliography……………………………………………………….…104
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List of Figures
Figure 2.1 shows Press with bending die.
Figure 2.2 shows Roll Forming Stand
Figure4.1shows typical unit cost (cost per piece) in forging
Figure 6.1.2 shows Wire cut EDM
Figure 6.1.4 shows Schismatic diagram of wire cut EDM
Figure 6.1.4.2 shows Schismatic Work piece and cutting wire
Figures 6.1.5 shows Programs are input through 3.5” floppy disk unit, or keyboard.
Figure 6.1.7 shows used brass wire
Figure 6.2.4 shows verticalsurface grinding
Figure6.3.2 shows Different parts of a lathe
Figure 6.3.4(a) shows Tools for turning external diameters
Figure 6.3.4(b)shows Internal turning tools
Figure 6.3.4(c) shows carbide tools used while machining.
Figure 6.4.3 Line Diagram Drilling machine showing various parts
Figure 6.4.6 shows PCD drilling machine used
Figure 6.4.9 shows various drilling operation
Figure 6.4.17(a) shows center drill
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Figure 6.4.17(b) shows drilling specimen from one side
Figure 6.5.1.1(a) shows Taper
Figure 6.5.1.1(b) shows plug
Figure 6.5.1.1(c) shows Bottoming
Figure 6.5.1.2(a) shows Gun
Figure 6.5.1.2(b) shows Stub-flute
Figure 6.5.1.2(c) shows Spiral-flute
Figure 6.5.2 shows Fluteless tap
Figure 9.1 Shows Super alloy after grinding and taper removal
Figure 9.2 shows Ni super alloy clamped in EDM machine
Figure 9.3 shows the sparking process
Figure 9.4 shows line diagram of the super alloy after EDM
Figure 9.5shows Super alloy after wire cut EDM
Figure 9.6 shows line diagram on die
Figure 9.7 shows machining of super alloy on grinding wheel
Figure 9.8 shows single point boring D3 steel
Figure 9.9 shows the D3 steel and nickel alloy after machining and PCD drilling
Figure 9.10 shows tapping process on D3
VIII
Figure 9.11 shows die after removing from furnace
Figure 10.1 shows turning of punch on lathe
Figure 10.2 shows saucer wheel on grinding
Figure 10.2 shows punch fixed with the help of 2 holes
Figure 9.12 shows top view of die
Figure 9.13 shows top view of blank holder
Figure 11 shows the setup of die, blank holder, punch
List of tables
Table 5.1shows Chemical composition of D3
Table 5.1shows Physical Properties
Table 6.2.7 shows Various lubrication oils used
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1. Introduction
Today’s world places greater and greater demands on products and materials,
from which they are made. Years ago, many designers never figured out stress and
strain, elasticity, fatigue, or similar values. If it broke, then you just made it 2 inches
thicker, or 3 inches, or 5 inches, whatever you preferred. But that is not how current
manufacturing is governed. Resources are getting scarer, perhaps even limited in
some cases, and designers are forced to economize. After all, why should a car body
be thick and heavy, when a thinner-gauge galvanized or annealed steel will bring
about the same, if not better, results. Demands for special alloys are continuously
expanding, and they are in equal competition with all the new and increasingly better
alloys that are being produced. Ferrous and non-ferrous alloys, titanium and its alloys,
and alloys with traces of rare metals added for additional qualities are all available to
fill that specific gap where they are needed.
Manufacturing methods are next on the list of economizing designers. Avoiding
secondary operations whenever possible, designers apply cost-conscious strategies
and planning not only in small shops, but in medium and large plants as well. This
certainly is a good approach to any given problem, since every product has its price. If
manufacturing costs become greater than the value of a product, such an item
becomes unsalable. For these reasons, manufacturability of products is extremely
important. Almost anything can be manufactured somehow, if people put their minds
to it. But at what cost? And who will be willing to pay for it? Out of this ever-present
regard for price versus actual value, new methods are being devised daily, new
approaches to old problems sought for.
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Crowds of engineers, designers, tool makers, model makers, and representatives
of other professions are nit-picking new, almost new, or old problems, in an attempt
to come up with a simple, straightforward, and cost-effective answer. Sometimes,
however, shortcuts are taken, where cheaper materials, thinner coatings, less durable
tools, or less experienced labour are used. These steps are just what they present
themselves as: shortcuts. They usually produce more returns, more repairs, more
problems around their drawbacks, and even more expenses. There is a time and a
place for everything, but these remedies are not always helpful. You pay for them
later.
A good, sound design and overall manufacturability cannot be replaced by
trinkets. The old saying “if it isn’t good, fix it” should perhaps be replaced by “if it
isn’t good, Redesign it!”
"So the need to know the exact fracture and maximum deformation points on
the metal at any temp which is found with the help of Warm Stretching Dies and the
required machinery"
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2. Die operations and type
Die operations are often named after the specific type of die that performs the
operation. For example a bending operation is performed by a bending die. Operations
are not limited to one specific die as some dies may incorporate multiple operation
types:
2.1 Bending -The bending operation is the act of bending blanks at a
predetermined angle. An example would be an "L" bracket which is a straight
piece of metal bent at a 90° angle. The main difference between a forming
operation and a bending operation is the bending operation creates a straight line
bend (such as a corner in a box) as where a form operation may create a curved
bend (such as the bottom of a drink can).
Figure 2.1 shows Press with bending die.
2.2 Blanking -A blanking die produces a flat piece of material by cutting the
desired shape in one operation. The finish part is referred to as a blank. Generally
a blanking die may only cut the outside contour of a part, often used for parts with
no internal features. Three benefits to die blanking are:
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1. Accuracy -A properly sharpened die, with the correct amount of clearance
between the punch and die will produce a part that holds close dimensional
tolerances in relationship to the parts edges.
2. Appearance- Since the part is blanked in one operation, the finish edges of
the part produce a uniform appearance as opposed to varying degrees of
burnishing from multiple operations.
3. Flatness - Due to the even compression of the blanking process, the end result
is a flat part that may retain a specific level of flatness for additional
manufacturing operations.
2.3 Bulging - A bulging die expands the closed end of tube through the use of two
types of bulging dies. Similar to the way a chefs hat bulges out at the top from the
cylindrical band around the chefs head.
1. Bulging fluid dies -Uses water or oil as a vehicle to expand the part.
2. Bulging rubber dies -Uses a rubber pad or block under pressure to move the
wall of a work piece.
2.4 Coining -is similar to forming with the main difference being that a coining
die may form completely different features on either face of the blank, these
features being transferred from the face of the punch or die respectively. The
coining die and punch flow the metal by squeezing the blank within a confined
area, instead of bending the blank. For example: an Olympic medal that was
formed from a coining die may have a flat surface on the back and a raised feature
on the front. If the medal was formed (or embossed), the surface on the back
would be the reverse image of the front
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2.5 Broaching - The process of removing material through the use of multiple
cutting teeth, with each tooth cutting behind the other. A broaching die is often
used to remove material from parts that are too thick for shaving.
2.6 Curling -The curling operation is used to roll the material into a curved shape.
A door hinge is an example of a part created by a curling die.
2.7 Compound operations - Compound dies perform multiple operations on the
part. The compound operation is the act of implementing more than one operation
during the press cycle.
2.8 Compound die - A type of die that has the die block (matrix) mounted on a
punch plate with perforators in the upper die with the inner punch mounted in the
lower die set. An inverted type of blanking die that punches upwards, leaving the
part sitting on the lower punch (after being shed from the upper matrix on the
press return stroke) instead of blanking the part through. A compound die allows
the cutting of internal and external part features on a single press stroke.
2.9 Cut off -Cut off dies is used to cut off excess material from a finished end of a
part or to cut off a predetermined length of material strip for additional operations.
2.10 Drawing -The drawing operation is very similar to the forming operation
except that the drawing operation undergoes severe plastic deformation and the
material of the part extends around the sides. A metal cup with a detailed feature
at the bottom is an example of the difference between formed and drawn. The
bottom of the cup was formed while the sides were drawn.
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2.11 Extruding - Extruding is the act of severely deforming blanks of metal called
slugs into finished parts such as an aluminum I-beam. Extrusion dies use
extremely high pressure from the punch to squeeze the metal out into the desired
form. The difference between cold forming and extrusion is extruded parts do not
take shape of the punch.
2.12 Forming - Forming dies bend the blank along a curved surface. An example
of a part that has been formed would be the positive end(+) of a AA battery.
2.13 Cold forming (cold heading) - Cold forming is similar to extruding in that it
squeezes the blank material but cold forming uses the punch and the die to create
the desired form, extruding does not.
2.14 Roll forming - a continuous bending operation in which sheet or strip metal is
gradually formed in tandem sets of rollers until the desired cross-sectional
configuration is obtained. Roll forming is ideal for producing parts with long
lengths or in large quantities.
Figure 2.2 shows Roll Forming Stand
2.15 Horning - A horning die provides an arbor or horn which the parts are place
for secondary operations.
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2.16 Pancake die - A Pancake die is a simple type of manufacturing die that
performs blanking and/or piercing. While many dies perform complex procedures
simultaneously, a pancake die may only perform one simple procedure with the
finished product being removed by hand.
2.17 Hydro forming -Forming of tubular part from simpler tubes with high water
pressure.
2.18 Piercing -The piercing operation is used to pierce holes in stampings.
2.19 Progressive die -Progressive dies provide different stations for operations to
be performed. A common practice is to move the material through the die so it is
progressively modified at each station until the final operation ejects a finished
part.
2.20 Shaving -The shaving operation removes a small amount of material from the
edges of the part to improve the edges finish or part accuracy. (Compare to
Trimming).
2.21 Sub press operation - Sub-press dies blank and/or form small watch, clock,
and instrument parts.
2.22 Swaging -Swaging (necking) is the process of "necking down" a feature on a
part. Swaging is the opposite of bulging as it reduces the size of the part. The end
of a shell casing that captures the bullet is an example of swaging.
2.23 Trimming - Trimming dies cut away excess or unwanted irregular features
from a part, they are usually the last operation performed.
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3. Die material and lubrication
3.1 Die material
Most forging operations, particularly for large parts, are carried out at
elevated. General requirement for die materials therefore are
1. Strength and toughness at elevated temperatures
2. Hardenability and ability to harden uniformly
3. Resistance to mechanical thermal shock, and
4. Wear resistance, particularly resistance to abrasive wear, because of presence
of scale in hot forging.
Selection of proper die materials depends on such factors as the die size, the
composition and the properties of the work piece, the complexity of shape, the forging
temperatures, and the type of forging operations, the cost of the die material, and the
number of forgings required. Heat transfer from the hot-work piece to the dies (and
subsequent distortion of the dies) is also an important factor.
Common die materials are tool and die steel containing chromium, nickel,
molybdenum, and vanadium. Dies are made for die blocks, which are forged from
casting and then machined and finished to the desired shape and surface finish.
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3.2 Lubrication
Lubricants greatly influence friction wear; consequently, they affect
the forces required and the flow of the metal die cavities. They can also act as a
thermal barrier between the hot work piece and the relatively cool dies, slowing the
rate of cooling of the work piece and improving the metal flow. Another important
role of the lubricant is to server as a parting agent, that is, one which inhibits the
forging from sticking to the dies and help in its release from the die
A wide variety of the lubricants can be used in forging .For hot forging
graphite, molybdenum disulfide, and sometimes glasses are used. For cold forging,
mineral oils and soaps are common lubricants, applied after conversion coating of the
blacks. In hot forging, the lubricants are usually applied directly to the dies: in cold
forging, it is applied to the work piece. The method of application and the uniformity
of the lubricant’s thickness on the blank are important to product quality
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4. Die Failures
Failures of die in manufacturing operation generally results one or more of the
following causes
1. Improper design
2. Defective material
3. Improper heat treatment and finishing operations
4. Overheating and heat checking ( crack caused by temperature cycling)
5. Excessive wear
6. Overloading
7. Misuse
8. Improper handling
Some of the major factors leading to die failures are described below.
Although these factors apply to dies made of tool and die steel, many are also
applicable to other die materials.
The proper design of dies is as important as the proper selection of die
material. In order to withstand forces in manufacturing process, a die must have
proper cross-sectional and clearance. Sharp corner, radii, and the fillets, as well as
abrupt changes in cross section, act as stress raiser and can have detrimental effects on
die life. Dies may be made in segments and pre-stressed during assembly for
improved strength.
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The proper handling, installation, assembly, and the aligning of dies are
essential. Over loading of tools and dies can cause premature failure. For example, a
common cause of failure of cold extrusion dies is the failure of the operator or a
programmable robot to remove a formed fart from the die before loading it with
another blank.
In spite of their hardness and resistance to abrasion, die material such as
carbides and diamond are susceptible to cracking and chipping from the impact force
or from thermal stresses caused by temperature gradients within the die. Surface
penetration and finishing are important. Even metal working fluids can adversely
affect tool and die material. Sulfur and chlorine additives in lubricants and coolants,
for example, can leach away the cobalt binder in tungsten carbide and lower its
strength and toughness.
Even if they are manufactured properly, dies are subjected to high stresses and
high temperature during their use, factors which cause wear and (hence) shape
changes. Dei wear is important because when the die shape changes, the parts, in turn
have improper dimension. In both these ways, the economics of the manufacturable
operations is adversely affected.
During use, dies may also undergo heat checking from thermal cycling,
particularly in die casting. To reduce heat checking (Which has the appearance on
parched land) and eventual dies breakage in hot working operations, dies usually
preheated to temperature of about 1500°C to 2500°C (3000°F to 5000°F). Cracked or
worn dies may be repaired by welding and metal- deposition techniques, including
laser
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Dies may be designed and constructed with inserts that can be replaced when
worn or cracked. The proper design and placement of these inserts is important,
because, if it is ignored, the inserts themselves can crack. Die failures and fracture in
manufacturing plants can be hazardous to employees.
It is not unusual for a set of dies resting on the floor or on a shelf to
disintegrate suddenly, because of the highly stressed internal condition (residual
stress) of its components. The broken pieces are propelled at high speed and can cause
serious injury or fatality. Highly stressed dies and tooling should always be
surrounded by metal shielding. This shield should be properly designed and
sufficiently strong to contain the fractured pieces in the event of die failure.
Figure4.1 shows typical unit cost (cost per piece) in forging
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5. About the Material Used(D3)
5.1 Chemical composition
ELEMENT CONTENT (%)
C 2.00-2.35
Mn 0.60
Si 0.60
Cr 11.00-13.50
Ni 0.30
W 1.00
V 1.00
P 0.03
S 0.03
Cu 0.25
Table 5.1shows Chemical composition of D3
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5.2 Physical Properties
Density 7.7*1000 kg/m3
Melting Point 1421oC
Poisson’s Ratio 0.27-0.30(at 25oC)
Table 5.1shows Physical Properties
5.3 Principal Design Features
D3 is an oil hardening, high Carbon/ Chromium type tool steel with very high
wear resistance. It hardens with a very slight change in size. The alloy possesses very
high compressive strength and is deep hardening.
5.4 Applications
D3 is used in tooling applications requiring a high degree of accuracy in
hardening, such as draw dies, forming rolls, powder metal tooling and blanking and
forming dies.
5.5 Machinability
The machinability rating of D3 is roughly 25% that of free machining carbon
steel 1018.. Due to its abrasion resistant nature, machining in the hardened condition
should be limited to finish grinding.
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5.6 Heat Treatment
Maximum properties are achieved through the process of hardening and
tempering. See the processes below. For maximum accuracy, parts should be stress
relieved after roughing operations. Stress relieves at 1200F for one hour and cool
slowly.
5.7 Annealing
Annealing should be performed in a controlled atmosphere furnace. Heat
thoroughly to 1600 F and cool slowly, at a rate of not more than 20 F per hour, until
furnace is black. Material may then be removed and air cooled.
5.8 Tempering
After cooling to room temperature, parts should be tempered immediately.
Place parts in the tempering furnace and raise slowly to desired tempering
temperature. Temper for 1 hour per inch of thickness.
5.9 Hardening
Do not overheat this material, it is very sensitive to overheating and will not
achieve maximum hardness if heated improperly. Harden by placing the work directly
into a furnace preheated to 1750F and soak for 20-25 minutes, plus 5 minutes per inch
of thickness, and quench in oil.
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5.10 Heat Treating Instruction
5.10.1 Hardening
Critical Temperature:
Ac1: 1440°F
(782°C)
Ac3: 1530°F
(832°C)
Ar1: 1410°F
(766°C)
Ar3: 1370°F
(743°C)
5.10.2 Preheating: To minimize distortion and stresses in large or complex tools use
a double preheat. Heat at a rate not exceeding 400°F per hour (222°C per hour) to
1200-1250°F (649-677°C) equalize, then heat to 1400-1450°F (760-788°C). For
normal tools, use only the first temperature range as a single preheating treatment.
5.10.3 Austenizing (High Heat): Heat slowly from the preheat to 1700-1750°F
(927-954°C)
5.10.4 Quenching: For oil, quench until black, about 900°F (482°C), then cool in
still air to 150-125°F (66-51°C).
For pressurized gas, the furnace should have a minimum quench pressure of 4
bars. A quench rate of approximately 400°F (222°C) per minute to below 1000°F
(538°C) is critical to obtain the desired properties.
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5.10.5 Tempering: Temper immediately after quenching. Hold at temperature for
1hour per inch (25.4 mm) of thickness, 2 hours minimum, then air cool to ambient
temperature.
For maximum wear resistance, temper between 300-350°F (149-177°C) for a
hardness of 62-63 HRC. For the optimal balance between wear resistance and
toughness, temper between 450-500°F (232-260°C). This will produce 58-60 HRC.
To minimize internal stresses in cross sections greater than 6 inches (152.4
mm) and to improve stability in tools that will be EDM'd after heat treatment, soaking
times of 4 to 6 hours at the tempering temperature are strongly recommended.
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6. About the Machines/Methods Used
6.1 Wire-cut EDM
6.1.1 Introduction
Wire cut EDM means Electric discharge machining by wire. Wire cut EDM
machines a single table, and has revolutionized the tool and die, mould, and
metalworking industries.EDM is a machining method primarily used for hard metals
or those that would be impossible to machine with traditional techniques. One critical
limitation, however, is that EDM only works with materials that are electrically
conductive. EDM can cut small or odd-shaped angles, intricate contours or cavities in
pre-hardened steel without the need for heat treatment to soften and re-harden them as
well as exotic metals such as titanium, hastelloy, kovar, and Inconel.
It can machine anything that is electrically conductive regardless of the
hardness, from relatively common materials such as tool steel, aluminum, copper, and
graphite, to exotic space-age alloys including hastaloy, titanium, carbide,
polycrystalline diamond compacts and conductive ceramics. The wire does not touch
the work piece, so there is no physical pressure imparted on the work piece compared
to grinding wheels and milling cutters. The amount of clamping pressure required to
hold small, thin and fragile parts is minimal, preventing damage or distortion to the
work piece.
The accuracy, surface finish and time required to complete a job is extremely
predictable, making it much easier to quote; EDM leaves a totally random pattern on
the surface as compared to tooling marks left by milling cutters and grinding wheels.
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The EDM process leaves no residual burrs on the work piece, which reduces
or eliminates the need for subsequent finishing operations.
Wire EDM also gives designers more latitude in designing dies, and
management more control of manufacturing, since the machining is completed
automatically. Parts that have complex geometry and tolerances don't require you to
rely on different skill levels or multiple equipment. A substantial increase in
productivity is achieved since the machining is untended, allowing operators to do
work in other areas.
Most machines run overnight in a “lights-out" environment. Long jobs are cut
overnight, or over the weekend, while shorter jobs are scheduled during the day. Most
work pieces come off the machine as a finished part, without the need for secondary
operations. It's a one-step process.
Wire cut EDM has generally been used only for tool and die manufacture.
Typical tolerances of +/- 0.0001mm" have made the process highly attractive for
precision machining. The reduction in machining steps has also reduced production
times and costs for many operations. It is probably the most exciting and diversified
machine tool developed for the industries in the last fifty years.
The programmer provides dimensional data to a computer via keyboard. Then
the software within the computer will automatically generate either a punched paper
tape or cassette, which will drive the wire EDM machine.
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6.1.2 Major components
A Wire EDM system is comprised of four major components.
1. Computerized Numerical Control (CNC)
In this wire cut machine we use ELCAM software for giving machining information
to CNC machine or we can use CAD software to develop component and load in
CNC with DXF format.
Think of this as “The Brains.”
2. Power Supply
Provides energy to the spark.
Think of this as “The Muscle.”
3. Mechanical Section
Worktable, work stand, taper unit, and wire drive mechanism.
(This is the actual machine tool.)
Think of this as “The Body.”
4. Dielectric System
The water reservoir where filtration, condition of the water
(resistivity/conductivity)and temperature of the water is provided and maintained.
Think of this as “The Nourishment.
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Figure 6.1.2 shows Wire cut EDM
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6.1.3 Wire Cut EDM Specifications:
Make : Electronica (India).
Model : Ultra cut S1.
Software : ELCAM.
Specification : X : 400mm
: Y : 300mm
: Z : 250mm
Job load capacity : 400KG (max).
Accuracy : 0.0001mm.
Job material : Hard (or) soft can cut.
Wire diameter : 0.25mm.
Wire material : Brass.
Special cases : 0.1, 0.15, 0.25mm.
6.1.4 Principle of Wire Electrical Discharge Machining
The basic EDM system consists of an electrode and the work piece connected
to a DC power supply and placed in a dielectric fluid. In wire EDM, the conductive
materials are machined with a series of electrical discharges (sparks) that are
produced between an accurately positioned moving wire (the electrode) and the work
piece. High frequency pulses of alternating or direct current is discharged from the
wire to the work piece with a very small spark gap and hence material is removed
from the work piece. Many sparks can be observed at one time. This is because actual
discharges can occur more than one hundred thousand times per second, with
discharge sparks lasting in the range of 1/1,000,000 of a second or less.
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The volume of metal removed during this short period of spark discharge
depends on the desired cutting speed and the surface finish required. The heat of each
electrical spark, estimated at around 15,000° to 21,000° Fahrenheit, erodes away a
tiny bit of material that is vaporized and melted from the work piece.(Some of the
wire material is also eroded away) These particles (chips) are flushed away from the
cut with a stream of de-ionized water through the top and bottom flushing nozzles.
The water also prevents heat build-up in the work piece. Without this cooling,
thermal expansion of the part would affect size and positional accuracy. To stop the
sparking process from shorting out, a non conductive fluid or dielectric is also
applied. The waste material is removed by the dielectric, and the process continues.
Figure 6.1.4.1shows Schismatic diagram of wire cut EDM
24
Electrode wire is connecting to cathode of impulse power source, and work
piece is connecting to anode of impulse power source. When work piece is
approaching electrode wire in the insulating liquid and gap between them getting
small to a certain value, insulating liquid was broken through; very shortly,
discharging channel forms, and electrical discharging happens. And release huge high
temperature instantaneously, up to more than 10000 degree centigrade, the eroded
work piece is cooling down swiftly in dielectric fluid and flushed away..
The functions of the dielectric fluids are to:
1. Act as insulator until the potential is sufficiently high.
2. Provide cooling medium.
3. Act as a flushing medium and carry away the debris in the gap.
The most common dielectric fluids are:
Mineral oils,Kerosene andDistilled water andDe-ionized water.
Clear, low viscosity fluids are also available although they are more expansive.
However, these f lu id s ma ke c le a n i ng e a s ie r . T he ma c h in e s u su a l l y
a r e eq u ip p e d w i t h a p u m p a nd fi l t e r in g system for dielectric fluid. When
the potential is difference between the tool and the work piece is sufficiently high, the
dielectric breaks down and a transient spark discharge through the fluid, removing a
very small amount of metal from the work piece surface.
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The work piece is fixed within the tank containing the dielectric fluid, and its
movements are controlled by numerical controlled systems. The gap between the tool
and the work piece is critical. Thus, the downward feed of the tool is controlled by a
servomechanism, which automatically maintains a constant gap. Because of the
process doesn’t involve mechanical energy, the hardness, strength and toughness of
the work piece material do not necessarily influence the removal rate. The frequency
of discharge or the energy per discharge, the voltage and the current usually are varied
to control the removal rate.
The removal rate and surface roughness increase with:
a) Increasing current density
b) Decreasing frequency of spark.
Figure 6.1.4.2 shows Schismatic Work piece and cutting wire
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Three basic conditions that wire cut EDM work correctly:
1. The gap between electrode wire and work piece should be certainly maintained in
a required range. Within this range, not only impulse power can break through
insulating liquid to create spark discharging, but also the eroded work piece can be
flushed away after discharging process. If gap is too big, insulating liquid can’t be
break through and there will be no spark discharging; if gap is too small, short
circuit is easy to happen, no spark discharging neither.
2. The procedure should happen in the liquid with insulate capacity, for example
saponification and deionizer water, the liquid could act as medium of discharging
channel and provide cooling and flushing.
3. Electrical discharging should be short time impulse discharging, As with short
discharging time, the released heat won’t affect inside material of work piece, and
limits energy to a tiny field and keep characteristics of cool machining of wire cut
EDM machine
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6.1.5 COMPUTER NUMERICAL CONTROL (CNC)
Today’s numerical control is produced with the needs of the operator in mind.
Programs, machine coordinates, cutting speeds, graphics and relevant information is
displayed on a color monitor, with easy to use menu’s.
The control unit displays menu’s that is designed to give top priority to
operability. Characters and commands are input using the keyboard. The system is
very easy to use, allowing the operator to quickly become familiar with it, resulting in
his/her learning curve being drastically reduced.
Besides executing NC data for positioning movement of the axes, the control
amends these movements when using offsets, tapering, scaling, rotation, mirror
images, or axis exchange. The control also compensates for any pitch error
compensation or backlash error in the axes drives, to ensure high accuracy
positioning. The machine has multiple coordinate systems, and jobs can be
programmed in absolute or incremental modes saving valuable programming time.
For example, multiple jobs can be set-up on the worktable, while storing the
separate reference points or locations of these jobs in specific coordinate registers.
The numerical control offers the capabilities of scaling, mirror imaging, rotation,
axis exchange and assist programs. This enables an operator to produce an entire
family of parts from a single program without the need to edit the program. Mirror
imaging is great for left and right handed parts. Scaling is useful when working with
"shrink factors" for plastic cavities or extrusion dies. Assist programs find the edge of
parts, vertically align the wire, and perform centering routines that are very useful to
the operator when setting up jobs.
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Other features include technology to aid in the prevention of wire breaks,
background, editing and graphic display of programs while the machine is running.
Figure 6.1.5shows Programs are input through the floppy disk unit, or keyboard.
One of the most important features that the control handles is offset. Programs
are created and written for the center of the tool (wire) to follow the outline of the
part. Let’s sayyou are using a .010" diameter wire and it cuts a .012" slot with the
power settings provided for the particular material. A .006" offset would be needed to
put the part "on-size". Which side of the part (left or right) we apply the offset is
determined by two factors.
1. Is the part we are saving, the male (slug), or the female (opening)?
2. Are we cutting the part in a clockwise or counterclockwise direction?
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Using a die as an example, the same program can be used to cut the die block,
punch, pad, stripper, and even the die shoe. By changing the offset amount, the sizes
and clearances required are maintained on all the parts.
6.1.6 Power Supply
When wire EDM machines were first introduced in the United States, they
were equipped with power supplies that could achieve less than one square inch per
hour.
Today, most machines are rated to cut over twenty square inches per hour and
faster. Faster or slower speeds are obtained depending on the work piece material,
part thickness, wire diameter, type of wire, nozzle position, flushing condition and
required part accuracy.
Adaptive Control is yet another improvement where high speed circuitry has
improved the spark gap sensitivity, reaction time of the servo motors, and changes to
the power. With these improved capabilities, wire breakage is reduced to a minimum,
making today’s machines far more "forgiving" than in the past.
Another feature is the anti-electrolysis circuitry that prevents the risk of
electrolysis while cutting work pieces that are in the machine for extended periods.
This AC circuit also eliminates the blue discoloration that appears when cutting
titanium alloys with DC circuits and is a beneficial feature when cutting aluminum.
Surface finishes on steel parts today are around sixty RMS for the roughing
operations and surface finishes better than 0.5 µ Rmax can achieved with multiple
passes. In many cases, this eliminates or minimizes "benching", hand polishing, or
lapping of parts that have fine finish requirements.
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6.1.7 Mechanical section
6.1.7.1 Table movement
Machine movement is accomplished with precision lead screws with
recirculating ball bearings on all axes that are driven by AC motors. Before shipping,
the machine’s position is checked and any errors or backlash are corrected by pitch
error compensation that is permanently stored in the computer’s memory.
6.1.7.2 Wire path
When wire EDM was first introduced, copper wire was used on the machines
because it conducted electricity the best. But as speeds increased, its limitations were
soon discovered. The low tensile strength of copper wire made it subject to wire
breaks when too much tension was applied. Poor flushability was another problem,
due to coppers highthermal conductivity. A good portion of the heat from the EDM
spark was transferred to the wire and carried away from the work zone instead of
using that heat to melt and vaporize the work piece. There is a vast array of wires to
choose from with brass wire normally being used however; molybdenum, graphitized,
and thick and thin layered composite wires are available for different applications.
Needs for various wires include: optimizing for maximum cutting speeds,
(coated or layered wire) cutting large tapers, (soft brass) or cutting thick work pieces
(high tensile strength with good flush ability).
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Wire diameters range from .004" through .014" with .010" being the most
commonlyused. The wire originates from a supply spool, then passes through a
tension device (different diameter wires require different amounts of tension to keep it
straight). It then comes in contact with power feed contacts where the electric current
is applied. The wire then passes through a set of precision, round diamond guides, and
is then transported into a waste bin. The wire can only be used once, due to it being
eroded from the EDM process.
Figure 6.1.7shows used brass wire
(The used brass wire is sold to the scrap dealer for recycling)
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6.1.8 Automatic wire threading (AWT)
The demand for automatic wire threading (AWT) and dependent reliability has
been met with new and improved designs. This feature allows multiple openings to be
cut in die blocks, progressive dies, production, and prototype work pieces
automatically and unattended without the intervention of an operator, resulting in
higher productivity. With the addition of the programmable "Z" axis, work pieces of
different thickness, can also be machined. For example, the die openings and dowel
pin holes can be machined on a one inch thick die block, then the machine can be
programmed to move to another location and machine the punches on a two or three
inch thick work piece.
Cutting and threading of the wire are controlled by codes in the program. If
there is a wire break during machining, the machine returns to the start point of that
opening, re-threads the wire and move through the program path to the position where
it broke, powers up, and continues cutting as if the wire had never broken. Some
EDM’s can also rethread the wire through the slot. The threading process of the
automatic wire threaded takes place automatically if there is a broken wire or by a
command in the program. In a wire break situation, the end of the wire is clamped
while the supply wire is drawn back; annealing and separating the wire, while leaving
a sharp point on the end of the supply wire.
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The wire tip segment that was clamped is disposed of in a wire tip disposal
unit. The supply wire is then directed into the lower guide. The wire then proceeds to
the back of the machine where it is discarded in a scrap wire bin. AWT offers the
ability to cut multiple openings in a work piece without operator intervention. Parts
with multiple openings or even several jobs are cut overnight while many jobs can be
cut over the weekend without operator intervention.
6.1.9 Dielectric system
Wire EDM uses deionized water as the dielectric compared to Vertical EDM’s
that use oil. The dielectric system includes the water reservoir, filtration system,
deionizationsystem, and water chiller unit. During cutting, the dirty water is drained
into the unfiltered side of the dielectric reservoir where the water is then pumped and
filtered through a paper filter, and returned to the clean side of the dielectric tank.
Following filtration, the clean water is measured for conductivity, and if
required passes through a vessel that contains a mixed bed of anion and cation beads.
This mixed bed resin (the ion exchange unit) controls the resistivity of the water to set
values automatically.
The clean water fills the clean side of the dielectric reservoir and proceeds to
the cutting area. Used water is drained and returned to the unfiltered side of the
dielectric reservoir to complete the cycle. A water chiller is provided as standard
equipment to keep the dielectric, work piece, worktable, control arms, and fixtures
thermally stable.
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During the cutting process the chips from the material that is being eroded,
gradually changes the water conductivity level. Resistivity levels of the water are set
according to thecutting requirements of the work piece material being machined.
6.1.10 Submerged Machining
Submerged machining is extremely useful for applications that generally have
poor flushing conditions. Some applications and examples where submerged
machining is more practical would be cutting large taper angles, tall work pieces,
laminations, tubes, irregular shaped parts, work pieces with undercuts and cutting
very close to the edge of the work piece.
6.1.10.1 Starting a cut from the Edge of a Work Piece
When starting a cut from the edge of a work piece, cutting a form tool, slicing
a tube or bar stock, or starting a cut from a large diameter start hole, is a slower
process without submerged machining capabilities. There is a greater risk of breaking
a wire if the flush is not set properly or if too much power is used. This condition is
greatly reduced when cutting the part submerged.
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6.1.11 Some of the advantages of EDM include :
1. Complex shapes that would otherwise be difficult to produce with conventional
cutting tools
2. Extremely hard material to very close tolerances
3. Very small work pieces where conventional cutting tools may damage the part
from excess cutting tool pressure.
4. There is no direct contact between tool and work piece. Therefore delicate
sections and weak materials can be machined without any distortion.
5. A good surface finish can be obtained.
6. Very fine holes can be easily drilled.
7. The Accurate and Economic Machining of Exotic Materials. Exotic materials
including A-286 Super alloys, medical grade stainless, titanium, Hastelloy,
tungsten carbide, molybdenum, aluminum alloys and copper can all be machined.
6.1.12 Some of the dis-advantages of EDM include:
1. The slow rate of material removal.
2. The additional time and cost used for creating electrodes for ram/sinker EDM.
3. Reproducing sharp corners on the work piece is difficult due to electrode wear.
4. Specific power consumption is very high.
5. Power consumption is high.
6. "Overcut" is formed.
7. Excessive tool wear occurs during machining.
8. Electrically non-conductive materials can be machined only with specific set-up
of the process.
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6.1.13 Applications
1. Parts with complex geometry’s.
2. Parts requiring "tenths" tolerances.
3. Parts where burrs can’t be tolerated.
4. Thin or delicate parts those are susceptible to tool pressure.
5. Progressive, blanking and trim dies.
6. Extrusion dies.
7. Precious metals.
8. Narrow slots and keyways.
9. Mould components.
10. Tooling for forging, or injection molding operations.
11. Medical and dental instrumentation.
12. Cutting hardened materials such as carbide, C.B.N. etc. Cutting difficult to
machine materials like hastaloy, Inconel and titanium.
13. Aerospace, defense and electronic parts.
14. Production parts.
15. Form tools and inserts.
16. Electrodes (graphite or copper) for vertical EDM.
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6.2 Grinding
6.2.1 Introduction
Grinding is the process of removing metal by the application of abrasives
which are bonded to form a rotating wheel. When the moving abrasive particles
contact the work piece, they act as tiny cutting tools, each particle cutting a tiny chip
from the work -piece. It is a common error to believe that grinding abrasive wheels
remove material by a rubbing action; actually, the process is as much a cutting action
as drilling, milling, andlathe turning. The grinding machine supports and rotates the
grinding abrasive wheel and often supports and positions the work piece in proper
relation to the wheel.
The grinding machine is used for roughing and finishing flat, Cylindrical, and
conical surfaces; finishing internal cylinders or bores; forming and sharpening cutting
tools; snagging or removing rough projections from castings and stampings; and
Cleaning, polishing, and buffing surfaces. Once strictly a finishing machine, modern
production grinding machines are used for complete roughing and finishing of certain
classes of work.
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6.2.2 Construction
The grinding machine consists of a power driven grinding wheel spinning at
the required speed (which is determined by the wheel’s diameter and manufacturer’s
rating, usually by a formula) and a bed with a fixture to guide and hold the work-
piece. The grinding head can be controlled to travel across a fixed work piece or the
work piece can be moved while the grind head stays in a fixed position.
Very fine control of the grinding head or table’s position is possible using a
vernier calibrated hand wheel, or using the features of NC or CNC controls. Grinding
machines remove material from the work piece by abrasion, which can generate
substantial amounts of heat; they therefore incorporate a coolant to cool the work
piece so that it does not overheat and go outside its tolerance. The coolant also
benefits the machinist as the heat generated may cause burns in some cases.
In very high-precision grinding machines (most cylindrical and surface
grinders) the final grinding stages are usually set up so that they remove about
2/10000mm (less than 1/100000 in) per pass - this generates so little heat that even
with no coolant, the temperature rise is negligible.
6.2.3 Types of Grinders
These includes
1. Belt Grinder
This is usually used as a machining method to process metals and other materials,
with the aid of coated abrasives. Sanding is the machining of wood; grinding is
the common name for machining metals. Belt grinding is a versatile process
suitable for all kind of applications like finishing, deburring, and stock removal.
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2. Bench Grinder
This usually has two wheels of different grain sizes for roughing and finishing
operations and is secured to a workbench. It is used for shaping tool bits or
various tools that need to be made or repaired. Bench grinders are manually
operated.
3. Cylindrical Grinder
This includes the center-less grinder. A cylindrical grinder may have multiple
grinding wheels. The work piece is rotated and fed past the wheels to form a
cylinder. It is used to make precision rods.
4. Surface Grinder
This includes the wash grinder. A surface grinder has a "head" which is lowered,
and the work piece is moved back and forth past the grinding wheel on a table that
has a permanent magnet for use with magnetic stock. Surface grinders can be
manually operated or have CNC controls.
5. Tool and Cutter Grinder and the D-bit Grinder.
These usually can perform the minor function of the drill bit grinder, or other
specialist tool room grinding operations.
6. Jig Grinder
This as the name implies, has a variety of uses when finishing jigs, dies, and
fixtures. Its primary function is in the realm of grinding holes and pins. It can also
be used for complex surface grinding to finish work started on a mill.
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7. Internal grinding
It is used to grind the internal diameter of the work piece. Tapered holes can be
ground with the use of internal grinders that can swivel on the horizontal.
6.2.4 Surface Grinding
This is used to produce a smooth finish on flat surfaces. It is a widely used
abrasive machining process in which a spinning wheel covered in rough particles
(grinding wheel) cuts chips of metallic or non metallic substance from a work piece,
making a face of it flat or smooth.
A surface grinder has a "head" which is lowered, and the work piece is moved
back and forth past the grinding wheel on a table
That has a permanent magnet for use with magnetic stock. Surface grinders can be
manually operated or have CNC controls.
6.2.4.1 Process
Surface grinding is the most common of the grinding operations. It is a
finishing process that uses a rotating abrasive wheel to smooth the flat surface of
metallic or non-metallic materials to give them a more refined look or to attain a
desired surface for a functional purpose.
The surface grinder is composed of an abrasive wheel, a workholding device
known as a chuck, and a reciprocating table. The chuck holds the material in place
while it is being worked on. It can do this one of two ways: ferromagnetic pieces are
held in place by a magnetic chuck, while non-ferromagnetic and non-metallic pieces
are held in place by vacuum or mechanical means. A machine vice (made from ferro-
magnetic steel or cast iron) placed on the magnetic chuck can be used to hold
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Figure 6.2.4 shows veritical surface grinding
The grinding wheel is not limited to a cylindrical shape and can have a variety
of options that are useful in transferring different geometries to the object being
worked on. Straight wheels can be dressed by the operator to produce custom
geometries. When surface grinding an object, one must keep in mind that the shape of
the wheel will be transferred to the material of the object like a mirror image.
6.2.4.2 Work Speed & Feed for Surface Grinding:
Surface grinding machines usually have fixed work speeds of approximately
50 SFPM or have variable work speed ranges between 0 and 80 SFPM.
The feed of the grinding wheel is the distance the wheel moves laterally across
the work piece for each pass of the piece in surface grinding.
An abrasive that is suited to grind alloy is Silicon Carbide.
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6.2.4.3 Factors to consider in surface grinding are:
1. The material of the grinding wheel and
2. The material of the piece being worked on.
6.2.4.4 Operation
The following sequence is provided as a step-by-step example of a surface grinding
operation:
1. Adjust the surface grinding machine so that grinding headand worktable are
absolutely parallel.
2. Place a grinding wheel of the proper grain, grade, structure, and bond on the
wheel spindle.
3. Place the guard over the wheel and check security of all adjustable members of
the grinding machine for rigidityand lack of backlash.
4. True and dress the grinding wheel.
5. Mount the work piece to the worktable. Make sure thesurface to be ground is
parallel to the worktable and thegrinding wheel.
6. Adjust wheel speed, work speed, and work feed.
7. Proceed with grinding, adjusting depth of cut as necessary. Check for accuracy
between each cut and determine that the work piece is square and the wheel is not
out of alignment. If it is necessary to use more than one grinding wheel to
complete the grinding, each wheel should be trued and dressed after it is mounted.
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6.2.4.5 Types of Surface Grinders:
1. Horizontal-spindle (peripheral) surface grinders:
The periphery (flat edge) of the wheel is in contact with the workpiece, producing
the flat surface. Peripheral grinding is used in high-precision work on simple flat
surfaces; tapers or angled surfaces; slots; flat surfaces next to shoulders; recessed
surfaces; and profiles.
2. Vertical-spindle (wheel-face) grinders:
The face of a wheel (cup, cylinder, disc, or segmental wheel) is used on the flat
surface. Wheel-face grinding is often used for fast material removal, but some
machines can accomplish high-precision work. The workpiece is held on a
reciprocating table, which can be varied according to the task, or a rotary-table
machine, with continuous or indexed rotation. Indexing allows loading or unloading
one station while grinding operations are being performed on another.
3. Disc grinders and double-disc grinders :
Disc grinding is similar to surface grinding, but with a larger contact area between
disc and workpiece. Disc grinders are available in both vertical and horizontal spindle
types. Double disc grinders work both sides of a workpiece simultaneously. Disc
grinders are capable of achieving especially fine tolerances.
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6.2.5 Form Grinding
Spindle that is used as a machine tool is used for grinding. But actually, there
are several types of spindles that craft-men use in performing different types of
grinding. One kind of grinding that is commonly done is most machine shops is form
grinding. It is considered as a finishing process or a finishing operation that has a lot
of different applications when it comes to the form and grinding industry as well as in
the machine tool industry. But on a much general scale, grinding covers practically a
wide range of finishing and machining tasks such as:
1. Abrading hard metals
2. Improving surface finish
3. Tightening the tolerance on a cylindrical or any flat surface by removing a
small amount of the material
4. Re-sharpening cutting tools
5. Surface grinding of mold sections
6. Surface grinding of wood fixtures
7. Grinding the internal diameter and outer diameter of valve bodies, on top of
many other useful applications.
Form grinding has the same principles with the regular grinding process (except
that it grinds the material into a certain desired shape). But for material removal, the
method used in grinding is called abrasion. That means that in grinding, an abrasive
material is rubbed against the metal part and clears of removes small pieces of that
material.
45
The whole process of grinding basically implies that instead of cutting the
material a bit, the material is gradually and steadily worn away. The material gets
worn away because when you compare the abrasive to the material being ground, the
former is definitely much harder than the latter. The grinding wheel therefore acts like
hundreds of very small teeth, cutting off some of the metal slowly, bit by bit.
In order for the grinding process to be successful, the abrasive must be strong
enough to withstand any kind of force that acts upon it while grinding. Most of the
time, there is some sort of impact shock that happens when the abrasive comes in
contact with the material.
When you come to think of it, the grinding process is somehow similar to another
machine finishing process called sanding. However, grinding is done in more types of
machines like the lathe and the mill, with certain add on accessories such as the
spindle, which makes the grinding process more efficient and much faster.
If you are looking for a very hardworking grinding machine, the internet can give
you a lot of options. So know what type of grinding machine you want first, and ask
free quotes from different sites.
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6.2.6 Grinding wheels
Grinding wheels come in many different sizes, shapes, and abrasives. Some of the
various types are listed below:
1. Straight
Straight wheels, numbers 1, 5, and 7, are commonly applied to internal, cylindrical,
horizontal spindle, surface, tool, and Off-hand grinding and snagging. The recesses in
type numbers 5 and 7 accommodate mounting flanges. Type number 1 wheels from
0.006-inch to l/8-inch thick are used for cutting off stock and slotting.
2. Cylinder
Cylinder wheels, type number 2, may be arranged for grinding on either the periphery
or side of the wheel.
3. Straight Cup
The straight cup wheel, type number 6, is used primarily for surface grinding, but can
also be used for off-hand grinding of flat surfaces. Plain or beveled faces are
available.
4. Flaring Cup
The flaring cup wheel, type number 11, is commonly used for tool grinding. With a
resinoid bond, it is useful for snagging. Its face may be plain or beveled.
5. Saucer
The saucer wheel, type number 13, is also known as a saw gummer because it is used
for sharpening saws
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6.2.7 Lubrication
The use of fluids in a grinding process is necessary to cool and lubricate the wheel
and work piece as well as remove the chips produced in the grinding process. The
most common grinding fluids are water-soluble chemical fluids, water-soluble oils,
synthetic oils, and petroleum-based oils. It is imperative that the fluid be applied
directly to the cutting area to prevent the fluid being blown away from the piece due
to rapid rotation of the wheel.
Work Material Cutting Fluid Application
Aluminum Light duty oil Flood
Brass Light duty oil Flood
Cast Iron Heavy duty emulsifiable oil, light duty chemical oil,
synthetic oil
Flood
Mild Steel Heavy duty water soluble oil Flood
Stainless Steel Heavy duty emulsifiable oil, heavy duty chemical oil,
synthetic oil
Flood
Plastics Water soluble oil, dry, heavy duty emulsifiable oil, dry,
light duty chemical oil, synthetic oil
Flood
Table 6.2.7 shows various lubrication oils used
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6.2.8 ADVANTAGES
1. It is very suitable for cutting hardened steels etc.
2. Extremely smooth finish desirable at contact and bearing surfaces can be
produced only by the grinding operation due to large no. Of cutting edges on the
grinding wheel.
3. No marks of feeding are there because the wheel has the considerable width.
4. Very accurate dimensions and smoother surface finish can be achieved in very
short time.
5. Complex profile can be produced accurately etc....
6.2.9 SAFETY PRECAUTIONS
Grinding machines are used daily in a machine shop. To avoid injuries follow the
safety precautions listed below.
1. Wear goggles for all grinding machine operations.
2. Check grinding wheels for cracks before mounting.
3. Never operate grinding wheels at speeds in excess of therecommended speed.
4. Never adjust the work piece or work mounting deviceswhen the machine is
operating
5. Do not exceed recommended depth of cut for the grinding wheel or machine.
6. Remove work piece from grinding wheel before turning machine off.
7. Use proper wheel guards on all grinding machines.
8. On bench grinders, adjust tool rest 1/16 to 1/8 inch from the wheel.
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6.3 Lathe
6.3.1 Introduction
The lathe is a machine tool used principally for shaping articles of metal (and
sometimes wood or other materials) by causing the work piece to be held and rotated
by the lathe while a tool bit is advanced into the work causing the cutting action. The
basic lathe that was designed to cut cylindrical metal stock has been developed further
to produce screw threads, Tapered work. Drilled holes, knurled surfaces, and
crankshafts. The typical lathe provides a variety of rotating speeds and a means to
manually and automatically move the cutting tool into the work piece. Machinists and
maintenance shop personnel must be thoroughly familiar with the lathe and its
operations to accomplish the repair and fabrication of needed part
6.3.2 Lathes Components
Engine lathes all have the same general functional parts, Even though the specific
location or shape of a certain part may differ from one manufacturer The bed is the
foundation of the working parts of the lathe to another.The main feature of its
construction is the ways which are formed on its upper surface and run the full length
of the bed.
Ways provide the means for holding the tailstock and carriage, which slide along
the ways, in alignment with the permanently attached headstock .The headstock is
located on the operator’s left end of the lathe bed. It contains the main spindle and oil
reservoir and the gearing mechanism for obtaining various spindle speeds and for
transmitting power to the feeding and threading mechanism.
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The headstock mechanism is driven by an electric motor connected either to a belt
or pulley system or to a geared system. The main spindle is mounted on bearings in
the headstock and is hardened and specially ground to fit different lathe holding
devices. The spindle has a hole through its entire length to accommodate long
workplaces. The hole in the nose of the spindle usually has a standard Morse taper
which varies with the size of the lathe. Centers, collets, drill chucks, tapered shank
drills and reamers may be inserted into the spindle. Chucks, drive plates, and face
plates may be screwed onto the spindle or clamped onto the spindle nose.
The tailstock is located on the opposite end of the lathe from the headstock. It
supports one end of the work when machining between centers, supports long pieces
held in the chuck, and holds various forms of cutting tools, such as drills, reamers,
and taps. The tailstock is mounted on the ways and is designed to be clamped at any
point along the ways. It has a sliding spindle that is operated by a hand wheel and
clamped in position by means of a spindle clamp. The tailstock may be adjusted
laterally (toward or away from the operator) by adjusting screws. It should be
unclamped from the ways before any lateral adjustments are made, as this will allow
the tailstock to be moved freely and prevent damage to the lateral adjustment screws.
The carriage includes the apron, saddle, compound rest, cross slide, tool post, and
the cutting tool. It sits across the lathe ways and in front of the lathe bed. The function
of the carriage is to carry and move the cutting tool. It can be moved by hand or by
power and can be clamped into position with a locking nut. The saddle carries the
cross slide and the compound rest. The cross slide is mounted on the dovetail ways on
the top of the saddle and is moved back and forth at 90° to the axis of the lathe by the
cross slide lead screw.
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The lead screw can be hand or power activated. A feed reversing lever, located on
the carriage or headstock, can be used to cause the carriage and the cross slide to
reverse the direction of travel. The compound rest is mounted on the cross slide and
can be swiveled and clamped at any angle in a horizontal plane. The compound rest is
used extensively in cutting steep tapers and angles for lathe centers. The cutting tool
and tool holder are secured in the tool post which is mounted directly to the
compound rest. The apron contains the gears and feed clutches which transmit motion
from the feed rod or lead screw to the carriage and cross slide.
Figure6.3.2shows Different parts of a lathe
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6.3.3 Care and Maintenance of Lathes
Lathes are highly accurate machine tools designed to operate around the clock if
properly operated and maintained. Lathes must be lubricated and checked for
adjustment before operation. Improper lubrication or loose nuts and bolts can cause
excessive wear and dangerous operating conditions. The lathe ways are precision
ground surfaces and must not be used as tables for other tools and should be kept
clean of grit and dirt. The lead screw and gears should be checked frequently for any
metal chips that could be lodged in the gearing mechanisms. Check each lathe prior to
operation for any missing parts or broken shear pins. Refer to the operator’s
instructions before attempting to lift any lathe.
Newly installed lathes or lathes that are transported in mobile vehicles
should be properly leveled before any operation to prevent vibration and
wobble. Any lathes that are transported out of a normal shop environment should be
protected from dust, excessive heat, and very cold conditions. Change the lubricant
frequently if working in dusty conditions. In hot working areas, use care to avoid
overheating the motor or damaging any seals. Operate the lathe at slower speeds than
normal when working in cold environments.
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6.3.4 Types of Lathe Tools
The type of lathe tool to be used in each respective case is determined by the
shape of the work piece which has to be worked. For longitudinal turning, roughing
and finishing lathe tools are required, for turning internal surfaces such as corners side
cutting turning tools, for plunging and cutting-off parting-off tools etc.
If much material has to be removed, the roughing tool has to be used first. If high
demands are made on the surface quality of the work piece, the finishing lathe tool
has to be used. Each operation requires the corresponding lathe tool. It would be a
waste of time and expensive material to permanently adapt one lathe tool - for
instance a side cutting turning tool for all sorts of turning.
Figure 6.3.4(a)shows Tools for turning external diameters
1) straight left roughing lathe tool, 2) bent right roughing lathe tool, 3) straight
finishing tool, 4) broad finishing tool, 5) straight right-end-cut turning tool, 6) offset
side cutting turning tool, 7) V thread cutting tool, 8) form turning tool
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Figure 6.3.4(b)shows Internal turning tools
o Single-point boring tool; 2) internal side cutting turning tool; 3) thread groove
plunging tool; 4) right undercutting tool; 5) internal screw-cutting tool
Figure 6.3.4(c)shows carbide tools used while machining
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The most important lathe tools are standardizes as to their shapes and dimensions.
As far as the designations of the angles and surfaces as well as of the various types of
lathe tools are concerned, there are generally valid international arrangements, to
Lathe tools for turning internal and external surfaces are generally distinguished as
shown in the pictures. What does the use of the respective types of lathe tools depend
on?
6.3.5 Safety
All lathe operators must be constantly aware of the safety hazards that are
associated with using the lathe and must know all safety precautions to avoid
accidents and injuries. Carelessness and ignorance are two great menaces to personal
safety. Other hazards can be mechanically related to working with the lathe, such as
proper machine maintenance and setup.
Some important safety precautions to follow when using lathes are:
1. Correct dress is important, remove rings and watches, and roll sleeves above
elbows.
2. Always stop the lathe before making adjustments.
3. Do not change spindle speeds until the lathe comes to a complete stop.
4. Handle sharp cutters, canters, and drills with care.
5. Remove chuck keys and wrenches before operating
6. Always wear protective eye protection.
7. Handle heavy chucks with care and protect the lathe ways with a block of wood
when installing a chuck.
8. Know where the emergency stop is before operating the lathe.
9. Use pliers or a brush to remove chips and swarf, never your hands.
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10. Never lean on the lathe.
11. Never lay tools directly on the lathe ways. If a separate table is not available, use a
wide board with a cleat on each side to lay on the ways.
12. Keep tools overhang as short as possible.
13. Never attempt to measure work while it is turning.
14. Never file lathe work unless the file has a handle.
15. Protect the lathe ways when grinding or filing.
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6.4 Drilling
Drilling is the operation of producing circular hole in the work-piece by using a
rotating cutter called DRILL. The machine used for drilling is called drilling
machine.The drilling operation can also be accomplished in lathe, in which the drill is
held in tailstock and the work is held by the chuck.The most common drill used is the
twist drill.
It is the simplest and accurate machine used in production shop.The work piece is
held stationary i.e. clamped in position and the drill rotates to make a hole.
6.4.1 Types:-
a) Based on construction:
Portable, Sensitive, Radial, up- right, Gang, Multi-spindle
b) Based on Feed:
Hand and Power driven
6.4.2 Four main parts
a) Base
b) Column
c) Table and
d) Drilling head
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6.4.3 Radial Drilling Machine
It the largest and most versatile used for drilling medium to large and heavy work
pieces.
Figure 6.4.3 shows Line Diagram Drilling machine showing various parts
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6.4.4 CHARACTERISTICS
All drilling machines have the following construction characteristics of a spindle,
Sleeve or quill, column, head, worktable, and base.
1. The spindle holds the drill or cutting tools and revolves in a fixed position in a
sleeve. In most drilling machines, the spindle is vertical and the work is supported
on a horizontal table.
2. The sleeve or quill assembly does not revolve but may slide in its bearing in a
direction parallel to its axis. When the sleeve carrying the spindle with a cutting
tool is lowered, the cutting tool is fed into the work: and when it is moved upward,
the cutting tool is withdrawn from the work. Feed pressure applied to the sleeve
by hand or power causes the revolving drill to cut its way into the work a few
thousandths of an inch per revolution.
3. The column of most drill presses is circular and built rugged and solid. The
column supports the head and the sleeve or quill assembly.
4. The head of the drill press is composed of the sleeve, spindle, electric motor, and
feed mechanism. The head is bolted to the column.
5. The worktable is supported on an arm mounted to the column. The worktable can
be adjusted vertically to accommodate different heights of work. or it may be
swung completely out of the way. It may be tilted up to 90° in either direction, to
allow for long pieces to be end or angled drilled.
6. The base of the drilling machine supports the entire machine and when bolted to
the floor, provides form vibration-free operation and best machining accuracy.
The top of the base is similar to a worktable and maybe equipped with T-slots for
mounting work too large for the table.
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6.4.5 Drilling to an Accurate Layout
1. Clean and coat surface with layout dye.
2. Locate position of hole from two machined edges of work piece and scribe
lines.
3. Lightly prick-punch where two lines intersect.
4. Check accuracy of punch mark.
5. Scribe circle to indicate diameter of hole.
6. Scribe test circle .060 in. smaller than hole.
7. Punch four witness marks on circles up to .750 in. in diameter and eight
witness marks on larger circles.
8. Deepen center of hole location with center punch to provide larger indentation
for drill to follow.
9. Center drill work to just beyond depth of drill point.
10. Mount proper size drill in machine and drill hole to depth equal to one-half to
two-thirds drill diameter.
11. Examine drill indentation; should be concentric with inner proof circle.
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12. If spotting off center, cut shallow V-grooves with cape
or diamond-point chisel on side toward which drill must be moved.
13. Start drill in spotted and grooved hole. Drill will be drawn toward direction of
grooves
14. Continue cutting grooves into spotted hole until drill point drawn to center.
15. Continue to drill hole to desired depth
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6.4.6 Polycrystalline compact diamond (PCD) Drilling Machine
6.4.6.1 Reason for developing Variable PCD Drilling Machine
Through our experiences in the market, we found people are using expensive
VMC for these operations. There are components in small and medium batch
quantities. Lot of companies are facing problem on delivering components on time.
They are using expensive VMC and very high skilled labor to meet target, finally they
spend more money and the production cost goes up very high. All this will be
replaced by this low cast machine. An unskilled labor can also start working in 2 or
3days training. Thus, you can cut down the cost by 30 - 50% approximately.
6.4.6.2 Bit Design & Attachments
PCD bits as a general rule require adequate flushing in order to gain the
optimum result from the bit. Bits ranging from 25mm to 112mm in diameter can be
supplied. A variety of configurations and attachment methods, depending on the rock
formation and the available drilling equipment, can be provided. Our sales engineers
will be happy to discuss individual applications and requirements.
6.4.6.3 Energy Requirement
The wear resistance of the PCD layer results in the bit retaining the cutting
edge more effectively thus reducing the thrust requirement.
6.4.6.4 Drilling Productivity
The retention of sharp and effective cutting edges on the drill bit facilitates
consistently high rates of penetration, protection of the gauge diameter and reduces
the interruptions caused by worn or blunted bits.
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Figure 6.4.6 shows PCD drilling machine used
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6.4.6.5 The advantages of PCD drills are:
1. Vastly improved drill life.
2. Greater tolerance control.
3. Rugged construction enables the Everlast® drill to handle difficult conditions that
damage other drills beyond use.
4. Increased drill speeds and feeds.
5. Designed for use on: very high silica aluminum, Carbon Fiber Reinforced
Plastics (C.F.R.P.), Reinforced Ceramic Composites (RCC), Carbon
Fiber/Aluminum stack material (C.F.R.P/AL), Metal Matrix Composites
(M.M.C.), green carbide.
6. New grade of PCD diamond material is tougher & more rugged, which gives a
sharper cutting edge and improves wear and chip resistance.
6.4.6.6 Applications
The PCD bits are particularly suited for the drilling of hard competent
formations. Roof bolting, cable bolting, as well as face drilling and deep hole drilling
such as probing ahead of the cutting face and methane drainage are comfortably
within the capability of PCD bits. In certain conditions the PCD bits can be used as a
successful alternative to rotary percussive bits with consequential benefits in reduced
noise levels, less demand on the drill string and lower maintenance on the rotary
actuator.
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6.4.6.7 Safety
Since the PCD bits last many times longer than the equivalent bits with
tungsten carbide inserts the operators can remain in the safe environment away from
the unsupported roof. The PCD bits tend to cut very efficiently thus reducing the fines
generated and creating a less demanding working environment in terms of both dust
and noise levels.
6.4.7 Drill Materials
The two most common types are
1. HSS drill- Low cost
2. Carbide- tipped drills - High production and in CNC machines
6.4.8 Cutting Fluids
1. Provide both cooling and lubrication
2. Properties of an effective liquid in dissipating heat
3. Able to absorb heat rapidly
4. Have high thermal conductivity
6.4.9 USES
A drilling machine, called a drill press, is used to cut holes into or through metal,
wood, or other materials. Drilling machines use a drilling tool that has cutting edges at
its point. This cutting tool is held in the drill press by a chuck or Morse taper and is
rotated and fed into the work at variable speeds. Drilling machines may be used to
perform other operations. They can perform countersinking, boring, counter boring,
spot facing, reaming, and tapping. Drill press operators must know how to set up the
work, set speed and feed, and provide for coolant to get an acceptable finished
product.
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The size or capacity of the drilling machine is usually determined by the largest
piece of stock that can be center-drilled. For instance, a 15-inch drilling machine can
center-drill a 30-inch-diameter piece of stock. Other ways to determine the size of the
drill press are by the largest hole that can be drilled, the distance between the spindle
and column, and the vertical distance between the worktable and spindle.
Figure 6.4.9 shows various drilling operation
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6.4.10 Care of drilling machines
6.4.10.1 Lubrication
Lubrication is important because of the heat and friction generated by the moving
parts. Follow the manufacturer’s manual for proper lubrication methods. Clean each
machine after use. Clean T-slots. grooves. and dirt from belts and pulleys. Remove
chips to avoid damage to moving parts. Wipe all spindles and sleeves free of grit to
avoid damaging the precision fit. Put a light coat of oil on all unpainted surfaces to
prevent rust. Operate all machines with care to avoid overworking the electric motor.
6.4.10.2 Special Care
Operations under adverse conditions require special care. If machines are operated
under extremely dusty conditions. Operate at the slowest speeds to avoid rapid
abrasive wear on the moving parts and lubricate the machines more often. Under
extreme cold conditions, start the machines at a slow speed and allow the parts and
lubricants to warm up before increasing the speeds. Metal becomes very brittle in
extreme cold. So do not strike the machines with hard tools. Extreme heat may cause
the motor to overheat.
6.4.11 Cutting Speeds
It depends upon two important factors
1. Diameter and material of cutting tool
2. Type of material being cut
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6.4.12 Feed
Distance drill advances into work for each revolution. May be expressed in decimals,
fractions of an inch, or millimeters. Three factors govern rate of feed
1. Diameter of drill.
2. Material of work piece
3. Condition of drilling machine
6.4.13 Depth of Cut (d)
The distance from the machined surface to the drill axis
d = D / 2
6.4.14 Material Removal Rate:-
It’s the volume of material removed by the drill per unit time
MRR = (Π D
2
/ 4) * f * N mm
3
/ min
6.4.15 Machining Time (T)
It depends upon the length (l) of the hole to be drilled, to the Speed (N) and feed (f) of
the drill
t = L / f N min
6.4.16 Twist Drill Parts
1. Most made of high-speed steel.Replaced carbon-steel drills for two reasons.
a. Can be operated at double the cutting speed.
b. Cutting edge lasts longer.
2. Carbide-tipped drills: - Speeds for production have increased up to 300%
over high-speed drills.
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6.4.17 Lathe center hole
• It uses a combination of drill and countersink. Commonly called as center
drill
Figure 6.4.17(a) shows center drill
• Specimen must be drilled to correct size and depth to avoid ovality.
Figure 6.4.17(b) shows drilling specimen from one side
Spotting Hole Location With a Center Drill
• Chisel end on drill wider than center-punch mark on work. Spot center-punch
mark with center drill
Small point on center drill will accurately follow center-punch mark and provide
guide for larger drill
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Spotting Hole Location With a Center Drill
1. Mount small-size center drill in drill chuck.
2. Mount work in vise. Do not clamp
3. Set drill speed to 1500 r/min.
4. Bring point of center drill into center-punch mark and allow work to center
itself with drill point.
5. Continue drill until one-third of tapered section of center drill has entered
work
6. Spot all holes to be drilled.
6.4.18 Work-Holding Devices
1. Angle vise - Angular adjustment on base to allow operator to drill holes at an
angle without tilting table.
2. Drill vise - Used to hold round, square or odd-shaped rectangular, pieces.
3. V-blocks - Made of cast iron or hardened steel.Used in pairs to support round
work for drilling.
4. Drill jigs - Used in production for drilling holes in large number of identical
parts.Eliminate need for laying out a hole location.
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6.4.19 Precautions for Drilling machine
1. Lubrication is important to remove heat and friction.
2. Machines should be cleaned after use.
3. Chips should be removed using brush.
4. T-slots, grooves, spindles sleeves, belts, pulley should be cleaned.
5. Machines should be lightly oiled to prevent from rusting.
6.4.20 Safety Precautions
1. Do not support the work piece by hand – use work holding device.
2. Use brush to clean the chip.
3. No adjustments while the machine is operating.
4. Ensure for the cutting tools running straight before starting the operation.
5. Never place tools on the drilling table.
6. Avoid loose clothing and protect the eyes.
7. Ease the feed if drill breaks inside the work piece.
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6.5 Tapping
Tapping is cutting a thread in a drilled hole. Tapping is accomplished on the drilling
machine by selecting and drilling the tap drill size, then using the drilling machine
chuck to hold and align the tap while it is turned by hand. The drilling machine is not
a tapping machine, so it should not be used to power tap. To avoid breaking taps,
ensure the tap aligns with the center axis of the hole, keep tap flutes clean to avoid
jamming, and clean chips out of the bottom of the hole before attempting to tap.
6.5.1 Types
1. Hand taps - In sets containing taper, plug, bottoming tap.
2. Machine taps - Designed to withstand torque required to thread hole and clear
chips.
6.5.1.1 Types of Hand Taps
Figure 6.5.1.1(a) shows Taper
Figure 6.5.1.1(b) shows plug
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Figure 6.5.1.1(c) shows Bottoming
6.5.1.2 Types of Machine Taps
Figure 6.5.1.2(a) shows Gun
Figure 6.5.1.2(b) shows Stub-flute
Figure 6.5.1.2(c) shows Spiral-flute
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6.5.2 Fluteless Tap
Actually a forming tool used to produce internal threads in ductile material like
Copper, brass, Aluminum, Leaded steels.
Figure 6.5.2 shows Fluteless tap
6.5.3 Tapping speed
Ranges from 60 – 100 r/min.
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6.6 LAPPING
Lapping, like polishing, is an abrading process in which small amounts of
material are removed. Unlike polishing, however, lapping is intended to produce very
smooth, accurate surfaces, and is never used instead of polishing or buffing when
clearance is the only consideration.
Lapping is accomplished by charging metal forms called laps with abrasives
and then rubbing the work piece with the lap. The lap may be of any shape and may
be designed to fit into most power machine tools. The only requirements of the lap are
that it be of softer material than the material being lapped, and that it is sufficiently
porous to accept the imbedded abrasive grain. Common materials for laps are soft cast
iron, copper, brass, and lead. Some laps are flat and others are cylindrical to fit on
steel arbors for internal lapping of bores.
Mostly used abrasives are iron oxide, corundum, emery, chromium oxide etc.
The work piece is then held against the lap and moved in unrepeated paths. A suitable
cutting fluid called lapping vehicle such as oil is applied for lapping. Lapping vehicle
controls to some extent the cutting action and protects work piece.
6.6.1 Types of Lapping operations
1. Equalizing Lapping
Equalizing lapping is the process of running together two matting parts with an
abrasive between them. Due to this, the surface finish of the parts gets improved and
also the deviation in shape gets corrected. It is used to establish or improve the fit
between two mating parts of an assembly. In this case, the two shapes mutually
improve each other and a non-embedding form of lapping is usually desired.
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2. Form Lapping
In this operation the tool used is a form lap containing the shape to be lapped. In
form lapping concern is to establish same absolute geometric shape or dimensions.
Such as flatness, roundness, length of a diameter. For flat surfaces, this is usually
done by producing an accurate reference surface and transferring it to the work by
means of embedded lapping.
6.6.2 Type of Lapping process
1. Flat surface Lapping
Hand lapping of flat pieces is performed by rubbing the parts over the accurately
finished flat surface of a master lap, accomplishing the broaching action by a very
fine abrasive powder mixed with a vehicle.
2. Ring lapping of an external cylindrical surface
This are made up of close grained cast iron. The work to be lapped is held in the
chuck of a lathe and rotated ., while the split ring lap held over the cylindrical surface
is reciprocated . The abrasive and vehicle are fed through the slot in the ring lap and
when reciprocated. The lap should overturn the work by 1/3rd
of its length.
3. Lapping of an internal cylindrical surfaces
Holes or bores are lapped using solid or adjustable laps. This lapping operation is
done by rotating the laps on honing machines, lathes are polishing heads, while the
work piece is manually reciprocated over it.
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6.6.3 Lap material
Cast iron is mostly used for machining lapping. The lap material should be
soft (softer then the work piece so that the abrasive compounds gets embedded the
lap), close grained, free from porosity and surface defects. When cast iron is not
suitable then steel, brass, copper, aluminum type metal can be used.
For lapping by diamond, diamond is hammered into the metal where it is
embedded permanently. Soft laps are used for special purposes and for super
finishing.
6.6.4 Abrasive
Only the finest abrasives are used for lapping. These may be either natural or
artificial. Lapping compounds are generally mixed with water or oil so that they can
be readily applied to the lap.
Hard abrasive are used for harder work materials and soft abrasive for softer
work materials. Diamond is the hardest material and is used for lapping tungsten
carbide and precious stone. Next comes boron carbide, silicon carbide and aluminium
oxide. SiC is used for rapid stock removal and aluminium oxide for surface finish.
6.6.5 Vehicle
Abrasive are mixed with carrier medium called vehicle. Its purpose is to
suspend abrasive and keep grains separated as well as to lubricate the work and
prevent scoring. Vehicles vary from clean water to heavy grease. Vehicle should be
selected to suit works, method and type of finish. For machine lapping with cast iron
lap oil base is used. Commercial mixture of kerosene and machine oil is also used. In
some application spindle oil, sperm oil, lard oil, naphta or benzene may be used.
Grease base is used for softer materials.
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6.6.6 Material to be lapped
Softer and non-ferrous materials require finer grits size to obtain good finish.
6.6.7 Surface Roughness
Lapping can be used to obtain a specific surface roughness; it is also used to
obtain very accurate surfaces, usually very flat surfaces. Surface roughness and
surface flatness are two quite different concepts. Unfortunately, they are concepts that
are often confused by the novice.
A typical range of surface roughness that can be obtained without resort to
special equipment would fall in the range of 1 to 30 Ra.
6.6.8 Speed
It is performed at 18000 rpm.
6.6.9 Accuracy
Surface accuracy or flatness is usually measured in Helium Light Bands, one
HLB measuring about 0.000011 inches (11 millionths of an inch). Again, without
resort to special equipment accuracies of 1 to 3 HLB are typical. Though flatness is
the most common goal of lapping, the process is also used to obtain other
configurations such as a concave or convex surface.
6.6.10 Tool aspects of lapping
1. Increase in cutting speed results in increase in tool life.
2. In lapping operation, smooth surface finish decreases the coefficient of friction
whic increases the tool life.
3. Diamond lapping increases the tool life to about 5 times.
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6.6.11 Advantages
1. Increases the work life by removing the surface roughness and irregularities.
2. Provide superfine surface finish, greater uniformity and optical flatness.
3. Provides liquid and gas tight seals without using gaskets between plunger and
piston without rings.
4. Removes errors in gears which produce noise and wear.
6.6.12 Application
1. Brittle material such as sapphire, crystal, optic glass and crystallized glass
2. Various kinds of ceramics such as alumina, silicon carbide, zirconia, altic and
alumina nitride
3. Iron material such as cold rolled steel, bearing steel, tool steel and stainless steel
4. Magnetic materials such as ferrite
5. Semiconductor materials such as silicon and sapphire
6. Cemented carbide
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7. Manufacturability Aspects
The manufacturability of products depends on many factors. Sometimes a lack
of space may prevent a mechanic from reaching the area of concern, and long hours
may be lost before this obstacle is overcome. Or a wrong sequence of operations will
cause the final product to become distorted. Sometimes an adhesive may not hold
because the part was not degreased enough, or a screw may fall out because someone
forgot to add that second nut or a drop of Loctite.
In die work, the manufacturability of parts is dependent on much narrower
range of influences. The main areas of concern are
1. Grain direction of the material
2. Openings, their shape and location
3. Bends and other three-dimensional alterations to the flat part, their shape and
location
4. Outline of the part and its size
5. Applicable tolerance ranges
6. Surface finish, flatness, straightness, and burr allowance
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8. What Constitutes Suitability For Die Production
When evaluating a part for die production, the most restrictive aspect to be
considered is the cost of the tooling. To build a metal stamping die is a costly process,
involving many people, many machines, and several technologies. For that reason, the
demand for tooling must first be economically justified. The quantitative demands per
given time span should be evaluated first, because a scenario of 50,000 washers to be
delivered each month requires a different treatment from 50,000 washers to be
delivered each week.
A correct evaluation of the problem must be performed on the basis of:
1. Availability of the appropriate press.
2. The equipment’s running speed.
3. The length of production shifts.
4. Scheduling for the needed time interval.
For a small run with few repetitions, a single line of tooling may be chosen.
However, if the quantities are large and the time constraint exists, a multiple-part-
producing tool must be built. Such a die, generating at least two or more complete
parts with each stroke of a press, will speed up production admirably. But increasing
the size of the tool necessitates the use of a larger and more powerful press and may
even require a nonstandard width of a strip, which will certainly cost more and will
have longer lead (i.e., delivery) times. With parts other than simple washers, the shut
height of the press versus the height of the part (and subsequently the height of the
die) is another production-influencing factor. The width of the opening in the press
plus the width of the proposed die must definitely be in congruence. The possibility of
reorders should be considered at this point, as they may result in an extended
production run, greater material demands, and longer occupancy of the press.
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Such longer runs are usually beneficial from the economical standpoint, as
they save on die-mounting procedures and press adjustments, while also decreasing
the demand for quality control personnel involvement.
On the other hand, a problem of storage of these extra parts may arise along
with the existence of temporarily unrewarded financial investments into the purchase
of material, workforce compensation, taxes, utilities, and overhead.
These all need to be taken into account since they will only increase the final
cost of the product, long before it can be sold to a customer.To properly evaluate the
situation, all applicable expenditures should be added up as follows:
1. Cost of the storage space (prorated rent or property taxes, cost of the building and
Improvements)
2. Cost of all packaging and repackaging material, storage containers, protective
barriers, and insulation
3. Cost of stacking and restacking of parts, sorting them out, and discarding rusty or
damaged pieces
4. Spoilage of possible storage-sensitive material and the scrap rate
5. Cost of raw material and other production-related necessities
6. Overhead, such as electricity, cost of heating or cooling, water, and fuel applicable
to the storage of parts
7. Cost of labor, including possible overtime
8. Cost of paperwork involved with storage and subsequent handling of products
9. Interest rate at which the monies allocated to the above activities could have
generated when invested otherwise
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The combined expenses 1 through 9, when added up, should be equal to or less than
the
1. Cost of the removal of a die from the press
2. Cost of the installation of a die in the press (for the subsequent run)
3. Cost of the machine’s downtime during the die removal and installation
4. Cost of the press operator’s standby, if applicable
5. Cost of the press adjustments and trial runs
6. Cost of the first piece inspection and the cost of further adjustments and
approvals, if applicable
7. Cost of the extra material and supplies, which must be purchased ahead of the
time even if not immediately utilized
8. Overhead, such as cost of electricity, heating, cooling, water, and fuel
9. Cost of all subsequent billing and paperwork
10. Combined interest (per going rate) the finances allocated to the above causes
would have generated when invested otherwise
The length of each run and its influence on the need for sharpening and
maintenance of tooling must be evaluated for the entire production run. Should a
maintenance-related interruption be necessary, a possible split of the previously
planned combined run should be considered. A definite advantage of the die
production is its unrivaled consistency in the products’ quality and dimensional
stability. In absence of design and construction mistakes, the die, once built, needs
minimal amount of alterations, aside from regular sharpening. Some dies, true, are
more sensitive than others, which is mostly attributable to excessive demands on close
tolerance ranges of parts and on the variation in material thickness.
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9. Procedure for Deep Drawing Die
1. First the Ni super alloy is taken and is cut in to two pieces using Wire-cut EDM
with Brass wire. (I.e. upper die of height 32mm & lower die of height of 27mm).
2. Wire-cut EDM is used as it is not possible to cut Ni super alloy by conventional
method due to its high hardness.
3. The taper on the two pieces of die is removed with the help of coolant cutter.
4. Taper is not removed with the help of wire-cut EDM or grinding machine as the
machining cost will be very high.
5. Now grinding is done to both the pieces of super alloy.
Figure 9.1 Shows Super alloy after grinding and taper removal
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6. Grinding is done on the die pieces to make them flat w.r.t surface, if grinding is
not done, then performing sparking will not produce a 90 degrees perpendicular
hole.
7. It must be noted that grinding is done by supporting the super alloy as it is not
magnetic
8. Now a small hole is made on the two pieces of the die using a Sparking technique
as EDM process required an initial hole for the process to carry out.
Figure 9.2 shows the sparking process
9. Now as the super alloy is hard and costly, required hole is made via wire EDM
with a close tolerance of 0.05mm
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Figure 9.3 shows Ni super alloy clamped in EDM machine
10. To obtain the required dimension of holes on both the die pieces in close
tolerances, the machining is done on wire-cut EDM by passing Brass wire through
that hole; with distilled water has a coolant.
11. Following is the programs of Upper & Lower dies on EDM panel:
���� Program of Blank Holder
N90G92X0.00000Y0.00000
N0001
G90
G00X0.00000Y0.00000
G01G42X11.12696Y10.79077D1G50T0.0
G02X-11.12696Y-10.79077I-11.12696J-10.79077
G02X11.53623Y10.35207I11.12696J10.79077
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M00G01X0.00000Y0.00000G40G50
M00
G01G41X11.53623Y10.35207D2G50T0.0
G03X-11.12696Y-10.79077I-11.53623J-10.35207
G03X11.12696Y10.79077I11.12696J10.79077
G01X0.00000Y0.00000G40G50
G00X0.00000Y0.00000
M02
(TOTAL CUT LENGTH = 128.4MM).
Figure 9.4 shows line diagram of the super alloy after EDM
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Figure 9.5shows Super alloy after wire cut EDM
���� Program of Die
N90G92X0.00000Y0.00000
N0001
G90
G00X0.00000Y0.00000
G01G42X10.89798Y11.98641D1G50T0.0
G02X-10.89798Y-11.98641I-10.89798J-11.98641
G02X11.33435Y11.57465I10.89798J11.98641
M00
89
G01X0.00000Y0.00000G40G50
M00
G01G41X11.33435Y11.57465D2G50T0.0
G03X-10.89798Y-11.98641I-11.33435J-11.57465
G03X10.89798Y11.98641I10.89798J11.98641
G01X0.00000Y0.00000G40G50
G00X0.00000Y0.00000
M02
(TOTAL CUT LENGTH = 134.2MM)
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Figure 9.6 shows line diagram on die
12. Now mandrel is prepared for the above machined super alloys. Mandrel is made
tapered.( varying from 33 to 32(for die) and 32 to 31 (for blank holder)
13. Now the die and the blank holder (only super alloy part) is held with the help of
tapered mandrel for grinding outer diameter to perfect round shape.
14. It must be noted that the die is not held in chuck as the outer diameter obtained in
that case may have ovality.
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15. It must be noted that this grinding of outer diameter is carried out very slowly as
the Ni super alloy is hard and the process causes many jerks on mandrel which
can break the mandrel.
16. Now a small step is provided over the die as well as blank holder. This is done to
ensure proper binding between super alloy and D3 steel after shrink fit.
Figure 9.7 shows machining of super alloy on grinding wheel
17. Now D3 steel specimen of 200 radius and 28 mm (for die) and 33mm (for blank
holder) is taken for casing of super alloy.
18. The D3 steel pieces is tightly secured in the chuck of the lathe to perform turning
operation with single point cutting tool at feed, depth of cut and speed of
0.7mm.0.7mm and 1000rpm till the outer diameter reduces to 185mm.
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19. Now the 2 pieces of D3 steel is secured in the jaws, to perform radial drilling
operation on the D3 steel, first the drill bit of diameter 15 mm is used to make the
hole on the 2 pieces and followed by other drill bit of diameter 25, 30, 35,40mm is
used to drill hole successively.
Figure 9.8 shows single point boring D3 steel
20. The D3 is again secured in the chuck of a lathe to perform boring operation with
single point cutting tool till the diameter obtain by the blank holder is 69.8mm
and that of die is 74.8mm.
21. The external and internal grinding on both the D3 steel pieces is performed for
finishing purpose at feed rate 0.02mm.
22. Now the internal diameter of the D3 is 69.85mm, 74.85mm and outer diameter of
the D3 is 185mm.
23. Now with the help of PCD drilling machine at a radius of 160 mm from center 4
holes with the help of 10.5 mm drill bit are drilled.
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Figure 9.9 shows the D3 steel and nickel alloy after machining and PCD drilling
24. The drilling is carried out at 630 rpm
25. Now tapping is done on all 4 holes with the help of M12 tap. Coconut oil is used
as a lubricant. It helps in reducing the temperature rise at the specimen.
26. Tapping is carried out at 50 rpm.
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Figure 9.10 shows tapping process on D3
27. Now the Ni super alloy and D3 is joined together.
28. Ni super alloy and D3 is not brazed as D3 and Ni super alloy is too hard so they
may break.
29. Ni super alloy and D3 is not fit by inference fit as the operating temp is 600oC so
the D3 may expand and may come out.
30. So Ni super alloy and D3 is fit by shrink fit to avoid any problem at high
temperature also.
31. The two D3 steel pieces are kept in a furnace which is at a temperature of around
400°C and is taken out of furnace after few minutes.
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32. Now the Ni super alloy is placed in between the D3 steel.
33. The two pieces are left to cool in air for some time so that the fit obtain is tight.
34. The interference provided between D3 and Ni super alloy is 0.3mm (0.15mm on
both side)
Figure 9.11 shows die after removing from furnace
35. Now the die is left to reach the room temperature
36. Now surface grinding is done on the die and blank holder steel pieces till it is
completely flat with the alloy pieces. This also helps in removal of carbon
deposits on the surface of the die
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37. Now the inner diameter of Ni super alloy must be lapped in order to deep draw the
sheet easily.
38. With the help of lapping process mirror like finishing is obtained on the internal
surface of the super alloy.
39. Rough lapping operation is performed with paste of D124 at feed of 0.01mm on
the inner diameter of both Ni super alloy pieces with help of internal cylindrical
grinder.
40. Finishing lapping operation is performed with paste of D60 at feed of 0.01mm on
the inner diameter of both Ni super alloy pieces.
41. The accuracy of the holes drilled varies from 0.5mm to 0.1mm
42. Similarly fine finishing, lapping, and fine lapping is performed with pastes of
D30, D7 and D3 at feed of 5 microns on the inner diameter of both Ni super alloy
pieces.
43. Now mirror finish is obtained at the inner surface of the Ni super alloy.
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Figure 9.12 shows top view of die
Figure 9.13 shows top view of blank holder
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10. Procedure for Punch
1. A punch is made by taking a round of D3 steel, of diameter 32mm and length
206mm and fixed in the chuck of lathe to perform turning operation till the
diameter reduces to 30.7mm at feed and speed of 0.7mm and 900rpm.
Figure 10.1 shows turning of punch on lathe
2. Between Centers of a punch, a hole is made by a Centre drill on both the side.
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3. This is done to avoid ovality while machining the punch which can create problem
while deep drawing
4. Now heat treatment is done on the round specimen to increase its hardness and it’s
hardness is found to be HRC-60(Brinell hardness).
Figure 10.2 shows punch fixed with the help of 2 holes
5. Again the round specimen is fixed between centers to perform external grinding.
6. The round specimen is fixed in the vice to perform surface grinding to remove
hole drilled at one of its face.
7. Now with the help of saucer wheel on grinding, a radius of 5mm is given on one
of its face(the side from which we removed the hole).
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Figure 10.3 shows saucer wheel on grinding
8. Tapping operation is performed in hole on the other face with the help of M12 tap.
Coconutoil is used as a lubricant. It helps in reducing the temperature rise at the
specimen.
9. Tapping is carried out at 50 rpm.
10. Finally the punch is ready.
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11. Summary
In warm and hot sheet metal forming processes Ni based materials are used to
manufacture upper die, lower die and punch. It is because by change in temperature,
their will be change in dimensions of material and hence clearance between punch
and die will change. Such dies either may lead to fracture due to excessive ironing or
fracture due to excessive wrinkiling. Previouly INCONEL 600 materials were used to
manufacture these dies but the strength of theses material also goes down by
increasing the temperature and while deforming hard material like stainless steel and
soon their used to be scractches over the die. So the present project was taken up to
manufacture these die out of Ni super alloy. This super alloy was provided by defence
material laboratory, hyderabad. Since it is Ni based super alloy, it is not only very
hard and strong but also having very low coefficient of thermal expansion. Procedure
adopted to manufacture these die’s were explained in previous section of these thesis.
Succesful forming operations were conducted by using these dies
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-
Figure 11 shows the setup of die, blank holder and punch
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12. Conclusion
Inconel super alloy dies were machined and manufactured in present project.
For machining this material wire cut EDM is used for making hole and 10 R curve,
and remaining machining is done with the help of grinding wheel, as the material is
very hard. This super alloy die was shrink fit into a die steel D3 material. This dies
was used to successfully draw high strength material like austenite stainless steel.
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13. BIBLIOGRAPHY:
1. International Journal of Engineering Trends and Technology- Volume3Issue1-
2012
2. Donaldson. “Tool Design’ Tata McGraw Hill Publication, New Delhi, 1976.
3. Manabe, K., Soeda, K., Nagashima, T., and Nishimura, H., “Adaptive control
method of deep drawing using the variable blank holding force technique”,
Journal of the Japan Society for Technology of Plasticity.
4. http://en.wikipedia.org/wiki/Grinding_machine
5. Production Technology By R.k.jain
6. http://www.hssforum.com/TappingEN.pdf
7. http://en.wikipedia.org/wiki/Lathe
8. http://www.steelexpress.co.uk/toolsteel/D3-Steel-properties.html
9. http://www.azom.com/article.aspx?ArticleID=6215