TRAINING REPORT

BHARAT HEAVY ELECTRICALS LIMITED,BHOPAL

TRAINING REPORT ON: T.G.M

GUIDANCE :Shri B.L.Verma

BY:

RAHUL KUMAR WAHANE

ADM NO. : 9531

BRANCH:MECHANICAL ENGINEERING

COLLEGE: INDIAN SCHOOL OF MINES UNIVERSITY-DHANBAD,JHARKHAND

ACKNOWLEDGEMENT

We owe this moment of satisfaction with deep sense of gratitude to our project guide by

Mr. Shri B.L. Verma .For invaluable guidance significant &help in my respect to accomplish the project work. Their persisting encouragement, ever-lasting passions & wholehearted inspiration guidance, which help us a lot molding the present shape of the project.

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CERTIFICATE

THIS IS TO CERTIFY THAT RAHUL KUMAR WAHANE ,ROLL NO. 9531.STUDYING IN SECOND YEAR ,MECHANICAL ENGINEERING ,B.TECH OF INDIAN SCHOOLM OF MINES UNIVERSITY,DHANBAD HAS SUCCESSFULLY COMPLETED THE PROJECT ON T.G.M. DIVISION ,B.H.E.L. BHOPAL AND GIVEN THE SATISFACTORY ACCOUNT OF IT IN THIS PROJECT REPORT.IN THE GUIDANCE OF Shri B.L.Verma

DATE................... TEACHER’S SIGN

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HOBBING

A hobbing machine is a special form of milling machine that cuts gears. It is the major industrial process for cutting (as opposed to grinding) spur gears of

involute form.

The machine forms the gear via a generating process by rotating the gear blank and the cutter (called a hob) at the same time with a fixed gearing ratio between hob and blank. The hob has a profile given in cross-section by the

fundamental rack for the gear tooth profile and is in the form of a helix so that the sides of the teeth on the hob generate the curve on the gear. The helix has a number of cuts parallel to the axis to form the cutting teeth and the profile is

suitably relieved to provide cutting clearance.

For a tooth profile which is a theoretical involute, the fundamental rack is straight-sided, with sides inclined at the pressure angle of the tooth form, with

flat top and bottom. The necessary addendum correction to allow the use of small-numbered pinions can either be obtained by suitable modification of this rack to a cycloidal form at the tips, or by hobbing at other than the theoretical pitch circle diameter. Since the gear ratio between hob and blank is fixed, the

resulting gear will have the correct pitch on the pitch circle, but the tooth thickness will not be equal to the space width.

Hobbing is invariably used to produce throated worm wheels, but it is not possible to cut all useful tooth profiles in this way; if any portion of the hob

profile is perpendicular to the axis then it will have no cutting clearance generated by the usual backing off process, and it will not cut well. The NHS

Swiss tooth standards give rise to such problems. Such small gears normally must be milled instead.

ITS COMPONENTS:-

A hobbing machine comprising: a rotatable clamp fixture adapted to retain a gear blank; a rotatable cutter translatable into engagement

The hobbing machine of claim 1, wherein the sharpened peripheral edge is adjacent to the contact surface.

The hobbing machine of claim 1, wherein the contact surface may include compositions of high speed steel, carbide, or abrasive compositions.

The hobbing machine of claim 3, wherein the abrasive compositions include aluminum oxide or cubic boron nitride.

The hobbing machine of claim 1, further comprising a motor to power said powered spindle.

The hobbing machine of claim 1, including: a first motor operatively connected to the clamp fixture to rotate the clamp fixture and the gear blank at a

predetermined speed; and a second motor to power said de-burring tool spindle.

The hobbing machine of claim 6 further including a controller controlling output of said second motor, wherein the predefined speed and direction of

said de-burring tool spindle is programmable through said controller.

The hobbing machine of claim 7, wherein said de-burring tool spindle is translatable between two or more positions including a first disengaged

position with respect to said first end surface and a second engaged position with respect tosaid first end surface and wherein position translation is

programmable through the controller.

The hobbing machine of claim 8 further comprising: a second de-burring tool translatable into engagement with a second end surface of the gear blank, said

second de-burring tool configured to remove burrs from the second end surface of thegear blank; and said second de-burring tool configured to rotate

at a predefined speed and direction, the speed and direction selected to facilitate removal of burrs, wherein said predefined rotary speed of said second de-burring tool spindle isprogrammable through said controller.

A hobbing machine for cutting gear teeth into a gear blank, comprising: a rotatable clamp fixture adapted to retain the gear blank; a first motor

operatively connected to the clamp fixture to rotate the clamp fixture and the gear blank ata predetermined speed; a rotatable cutter translatable into

engagement with the gear blank, said cutter configured to cut the gear blank and thereby produce plurality of gear teeth and potentially burrs; a first

rotatable de-burring tool translatableinto engagement with a first end surface of the gear blankburring tool also including a contact surface extending

generally in the direction of the first end surface and configured to grind off and thereby remove others of said burrs.

The hobbing machine for cutting gear teeth into a gear blank of claim 11, further comprising: a second de-burring tool translatable into engagement with a second end surface of the gear blank, said second de-burring tool configured

toremove burrs from the second end surface of the gear blank as the gear teeth are being cut by the rotatable cutter; and a spacer adapted to position said second de-burring tool at a predetermined distance from the first de-burring tool, said spacersecured at one end to said powered spindle, said

spacer secured at an opposing second end .

VERTICAL LATHE MACHINE TEETH MACHINE GRINDING

The Milling Machine uses a rotating milling cutter to produce machined surfaces by progressively removing material from a work piece. The vertical

milling machine also can function like a drill press because the spindle is perpendicular to the table and can be lowered into the work piece.

THE CONTROLS

START/STOP

The green button starts the spindle motor and the red button shuts the motor off.

Variable motor drive

Variable Motor Drive used on some of the Milling Machines

FORWARD/REVERSE

This switch changes the rotation direction of the spindle. When the milling machine is in high range this switch is in the forward position for cutting but in

low range the switch is in the reverse position. Putting the switch in the

opposite position while remaining in the same range reverses the rotation of the spindle.

HAND BRAKE

Also known as the spindle brake, it is used to bring the spindle rotation to a stop after the power is turned off and to aid in removing collets and chucks.

The spindle can be locked by pressing or pulling the brake and then pushing it up.

SPINDLE SPEED

This wheel is used to change the speed of the spindle for both high range and low range. The milling machine must be running when changing the speed.

POWER FEED

The power feed uses a motor to control the motion of the longitudinal feed in either direction at various speeds. Not all of the milling machines in the shop

have this option.

CROSS-FEED HANDWHEEL

This handwheel moves the table in and out.

VERTICAL FEED HANDCRANK

This is used to raise and lower the table.

Vertical Milling Machine

QUILL FEED HANDLE

You can raise and lower the quill (spindle) with this handle.

QUILL LOCK

Pushing this lever down will lock the quill, pulling it back up releases the lock. The quill must be locked when milling.

QUILL STOP

The quill stop can be adjusted by hand to set a limit on the quill travel is also used to disengage the quill feed. This is useful when multiple holes have to be

drilled to the same depth.

QUILL FEED LEVER AND SELECTOR

These are used to activate the power feed for the quill. The selector will adjust the speed of the power feed and the lever activates the drive. The quill feed can

BORE GRINDING

A bore grinding machine having a horizontal work table rotatably mounted on a base. The work table has a portion of its central area cut away to form a

passageway opening for a vertical tool spindle assembly which is mounted with its top portion in said opening. The tool spindle assembly is mounted on a vertical slide which allows the top portion of the spindle assembly to be raised

above the top surface of the work table when in grinding position and allowed to be lowered back into said passageway opening where it is out of the way

and below the top of the table during loading and unloading of the work pieces to be machined. A wheel dressing unit is mounted below the top of the

passageway opening which dresses the grinding wheel upon movement thru the opening. A retractable guard cover is mounted below the top of the

opening to cover the grinding wheel when a worker is loading or unloading the parts to be machined on the top of the table. A combination wheel guard and coolant hood is pivotally mounted on the top of the work table support and it

covers the work piece and work table during the grinding operation while coolant is being floodingly circulated therewith. A plurality of cams are used to

control the x axis movement of the work table with respect to the grinding wheel and the y axis movement of the wheel feed slide with respect to the work while a work rotation gear forming a part of the rotatable table is connected to

a drive motor that controls the concurrent rotation of the work table.

CNC

Computer Numerical Control (CNC) Drilling

Computer Numerical Control (CNC) Drilling is commonly implemented for mass production. The drilling machine, however, is often a multi-function

machining center that also mills and sometimes turns. The largest time sink for CNC drilling is with tool changes, so for speed, variation of hole diameters

should be minimized. The fastest machines for drilling varying hole sizes have multiple spindles in turrets with drills of varying diameters already mounted for drilling. The appropriate drill is brought into position through movement of the turret, so that bits do not need to be removed and replaced. A turret-type CNC

drilling machine is shown below.

A variety of semi-automated drilling machines are also used. An example is a simple drill press which, on command, drills a hole of a set depth into a part

set up beneath it.

In order to be cost-effective, the appropriate type of CNC drilling machine needs to be applied to a particular part geometry. For low-volume jobs, manual or semi-automated drilling may suffice. For hole patterns with large differences in sizes and high volume, a geared head is most appropriate. If holes are close

to each other and high throughput is desired, a gearless head can locate spindles close together so that the hole pattern can be completed in one pass.

For further reference for CNC processes, please refer to the CNC, metal forming section.

HEAT TREATMENT

CARBURISING:

Carburising can be carried out in the temperature range 850 - 1000°C using a variety of processes to produce the carbon:

Pack carburising uses a solid granular form of carbon such as charcoal with an activator to assist the its break down to give active carbon

which can diffuse into the steel surface.

Salt bath carburising uses a liquid form of a carbon containing species such as sodium cyanide, potassium cyanide or calcium cyanide.

Gas carburising uses a gaseous atmosphere in a sealed furnace usually containing propane (C3H8) or butane (C4H10).

Gas carburising is the most frequently used technique. The depth to which the carbon diffuses is controlled by the surface concentration of carbon, and the

temperature and time of carburising.

Low Pressure Carburising (LPC) is an advanced technology that offers the design engineer an alternative to atmosphere carburising for improved case

depth uniformity, dimensional control, part cleanliness, and process flexibility. LPC is a method of pure carburisation combined with pure diffusion. The steel surface is vacuum conditioned eliminating surface oxide, trapped gases and

foreign material that may deter carbon saturation of the austenite.

High Pressure Gas Quenching (HPGQ) offers a number of attractive benefits including unprecedented part cleanliness and less overall dimensional change. Fixed or variable cooling rates are applied as required to control hardness and

distortion with the ability to vary quench pressure depending on load size, material type and part section thickness. Product consistency and repeatability

are excellent using high pressure gas quenching.Low pressure vacuum carburising has been successfully applied to a number of different

components including gears, shafts, bearings, tool holders and fuel injection components to name a few. Industrial sectors such as automotive, aerospace,

off-road, autosport, agricultural, power generation and tooling have already found particular benefits.

Carburising involves the diffusion of carbon into the surface layers of a low carbon steel at high temperatures. Controlled cooling after carburising (water, oil or polymer quenching) produces hard martensitic layers at the surface (this

is due to the increased hardenability of the carbon enriched surface region).

This 3% nickel–chrome–molybdenum steel is used when a core strength of 55 to 80 tons/sq.in is required along with a case hardness of around 60 Rockwell

C.

Distortion can arise from:

Heavy machining prior carburising

Retained austenite on quenching

Poor design

Metallurgical anomalies in the steel.

This is most likely due to the presence of retained austenite on heat treatment. It is recommended that the steel is carburised and hardened in two separate

cycles.

An alternative grade depends on the size of the component. However it is likely that a steel to AISI 8620 should form a cheaper alternative and yet produce the

required properties. Similar carburising and heat treatment parameters are applicable to both steels.

This grade of steel can be successfully carburised. It is basically a 0.30%C version of carburising grade EN36 (832M13).

A greater carbon potential must be used in order to drive the carbon into the surface and a two stage treatment is recommended to overcome any potential

problems with retained austenite

This grade of steel can be successfully carburised. It is basically a 0.30%C version of carburising grade EN36 (832M13).

A greater carbon potential must be used in order to drive the carbon into the surface and a two stage treatment is recommended to overcome any potential

problems with retained austenite.

This grade of steel can be successfully carburised. It is basically a 0.30%C version of carburising grade EN36 (832M13).

A greater carbon potential must be used in order to drive the carbon into the surface and a two stage treatment is recommended to overcome any potential

problems with retained austenite.

Although EN 40B is often used in the un-nitrided condition for applications requiring high tensile strength at temperatures up to 600ºC, it is intended to be

nitrided to improve wear and corrosion resistance.

Nitriding is usually carried out at temperatures around 500ºC and prior tempering should have been done at a higher temperature.

STRESS REVEALING

A process for permitting defects or stresses in a structure to be revealed, including (a) securing by molecular bonding of a face of a first element

containing crystalline material with a face of a second element containing crystalline material, so that the faces have offset crystalline lattices, the

securing causing the formation of a lattice of crystalline defects andor stress fields in a crystalline zone next to the securing interface, and (b) reducing the

thickness of one of the elements until at least a thin film is obtained which adheres to the other element, along the securing interface to form the

structure, the thickness of the thin film being such that its free face does not reveal the crystalline defect lattice andor the stress fields, but allowing to

perform (c) treatment of the thin film resulting in that its free face reveals the crystalline defect lattice andor the stress fields.

HARDENING

Precipitation Hardening

The process of precipitation hardening, also called age hardening, is widely used to add strength to metal alloy materials. The precipitation hardening

capabilities of Applied Thermal Technologies, Inc. include stainless steel, high temperature alloys and titanium.

We began our company in 1992 to service the medical and specialty components industries in Northern Indiana and have since expanded

nationally. If you are in search of a precipitation hardening type solution, call (574) 269-7116. For questions, please enter your contact information on our

web site and then click the next button. We will respond ASAP. We can also do a titanium cast design, a stainless steel solid cast and an alloy cast.

Applied Thermal Technologies can comply with the following industry standards and specifications:

AMS 2675, Nickel Alloy Brazing, AMS 2750, Pyrometry, AMS 2759, Heat Treatment of Steel Parts–General Requirements, AMS 2759/3, Heat Treatment–P.H. , C.R. , and Maraging Steel Parts, AMS 2759/4, Heat Treatment–Austenitic

Corrosion Resistant Steel Parts, AMS 2759/5, Heat Treatment–Martensitic Corrosion Resistant Steel Parts, AMS 2769, Heat Treatment of Parts in Vacuum,AMS 2773, Heat Treatment–Cast Nickel Alloy and Cobalt Alloy

Parts,AMS 2774, Heat Treatment–Wrought Nickel Alloy and Cobalt Alloy Parts,AMS 2801, Heat Treatment of Titanium Alloy Parts, MIL-B-7883, MIL-H-

6875, MIL-H-81200

TURNING

Turning is the process whereby a lathe is used to produce "solids of revolution". It can be done manually, in a traditional form of latheA wire cut

electric discharge machine having rollers is disclosed. It has a wire electrode disposed in a working zone of the electric discharge machine. This wire

electrode is rolled by a rolling device so that the cross-sectional area of this wire electrode changes from a circular area into an elongated one. After rolled,

the wire electrode has two parallel rolled flat surfaces. The working width between these flat surfaces is smaller than the original diameter of the wire

electrode before rolled. So, the cutting width is narrower than before. By using the rolled wire electrode, this invention can reduce the cutting width limit. I can improve the precision of the product, without changing the material property of

the wire electrode. And, it can reduce the cost of the wire electrode.

flushes material away

serves as a coolant to minimize the heat affected zone (thereby preventing potential damage to the workpiece)

acts as a conductor for the current to pass between the electrode and the workpiece.

In wire EDM a very thin wire serves as the electrode. Special brass wires are typically used; the wire is slowly fed through the material and the electrical

discharges actually cut the workpiece. Wire EDM is usually performed in a bath of water.

If you were to observe the wire EDM process under a microscope, you would discover that the wire itself does not actually touch the metal to be cut; the

electrical discharges actually remove small amounts of material and allow the wire to be moved through the workpiece. The path of the wire is typically controlled by a computer, which allows extremely complex shapes to be

produced.

Perhaps the best way to explain wire EDM is to use an analogy. Imagine stretching a thin metal wire between your hands and sliding it though a block

of cheese cutting any shape you want. You can alter the positions of your hands on either side of the cheese to define complex and curved shapes. Wire

EDM works in a similar fashion, except electrical discharge machining can handle some of the hardest materials used in industry. Also note, that in

dragging a wire through cheese, the wire is actually displacing the cheese as it cuts, but in EDM a thin kerf is created by removing tiny particles of metal.

Electrical discharge machining is frequently used to make dies and molds. It has recently become a standard method of producing prototypes and some production parts, particularly in low volume applications. For more details

regarding a typical application, you can read about a custom bronze branding-iron that was made with EDM.

Electrical discharge machines (EDM) remove metal from a workpiece by using a series of electric sparks to erode material. An electrical discharge machine is

considered to be the most precision oriented manufacturing process and is widely used for creating simple and complex shapes and geometries. EDM

machining is favored in situations where high accuracy of work and low count is required. An EDM machine consists of a workpiece and the wire electrode. A workpiece is sometimes dipped in a dielectric to develop a potential difference

between the workpiece and wire electrode. Electrical discharge machine supply is applied to the workpiece. Electrical discharge machines (EDM) work

by eroding the material that appears in the electrical discharge path. This material is responsible for generating an arc between the workpiece and wire electrode. The wire electrode rotates acts as wire EDM tooling and rotates a

two-three axis and cuts the internal cavities in the workpiece. There are many

types of electrical discharge machines (EDM). Examples include a CNC EDM and a wire EDM machine. A CNC EDM is a computer numerical control machine and is used for removing metal using electrical discharge spark erosion. A wire

EDM machine is designed for precision machining purposes and is used for cutting prismatic metal components. Other electrical discharge machines

(EDM) are commonly available.

There are several ways in which electrical discharge machines (EDM) function. Electrical discharge machines (EDM) are used where fast turn around time is

required. Electrical discharge machines (EDM) works by removing the workpiece that generates an arc with the wire electrode and creating a cavity in the workpiece. The dimensional accuracy required for an electrical discharge machine is + / - 0.0005 inches per inch. Electrical discharge machines (EDM) also require a 0.0003 feature profile accuracy across the workpiece cutting

path. Electrical discharge machines (EDM) are designed and manufactured to meet most industry specifications.

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 or Electrical Discharge Machining, is especially well-suited for cutting

intricate contours or delicate cavities that would be difficult to produce with a grinder, an end mill or other cutting tools. Metals that can be machined with EDM include hastalloy, hardened tool-steel, titanium, carbide, inconel and

kovar.

EDM is sometimes called "spark machining" because it removes metal by producing a rapid series of repetitive electrical discharges. These electrical discharges are passed between an electrode and the piece of metal being

machined. The small amount of material that is removed from the workpiece is flushed away with a continuously flowing fluid. The repetitive discharges

create a set of successively deeper craters in the work piece until the final shape is produced.

There are two primary EDM methods: ram EDM and wire EDM. The primary difference between the two involves the electrode that is used to perform the machining. In a typical ram EDM application, a graphite electrode is machined

with traditional tools. The now specially-shaped electrode is connected to the power source, attached to a ram, and slowly fed into the workpiece. The entire machining operation is usually performed while submerged in a fluid bath. The

fluid serves the following three purposes:

Jig boring machines are mainly to perform machining operations like boring, drilling, reaming, counter boring holes in metal jigs and counter-sinking holes

in metal work pieces. Some jig boring machines are used for accurately enlarging the existing holes and making their diameters highly accurate.

Jig boring can also maintain high accuracy between multiple holes or holes and surfaces. Some jig boring machines are designed to machine holes with

the tightest tolerances possible with a machine tool. The constant demand for accuracy within many branches of metalworking has been fulfilled with the

help of applications possible by jig-boring machines.

For long holes such as those found in gun bores, gun drills are used. The length of the hole requires that coolant be delivered through the shaft of the gun drill to the cutting front. The coolant also serves to eject chips from the cutting

area and to move them back and out of the hole entrance. The figures below illustrate a gun drill and the cutting/cooling configuration.

Jig BoringJig boring is used to accurately enlarge existing holes and make their

diameters highly accurate. Jig boring is used for holes that need to have diameter and total runout controlled to a high degree. Typically, a part has holes machined on regular equipment and then the part is transferred to a

dedicated jig boring machine for final operations on the especially accurate holes. Jig boring can also maintain high accuracy between multiple holes or holes and surfaces. Tolerances can be held readily within ±.005 mm (±0.0002

inches). Dedicated jig boring machines are designed to machine holes with the tightest tolerances possible with a machine tool.

When designing a part with holes, it is important to determine what holes must be jig bored. The reason for this is that jig boring requires extra time and

attention, and the jig boring machine at the machine shop may have a back log of jobs. Jig boring can therefore have a big impact on the lead time of a part. A

cross section of a hole being jig bored is shown below.

Standard boring can be carried out on a mill fitted with a boring head or on a lathe. Boring is most accurate on a lathe since a lathe is dedicated to solids of

revolution (axially symmetric parts).

Carburising involves the diffusion of carbon into the surface layers of a low carbon steel at high temperatures. Controlled cooling after carburising (water, oil or polymer quenching) produces hard martensitic layers at the surface (this

is due to the increased hardenability of the carbon enriched surface region).

This 3% nickel–chrome–molybdenum steel is used when a core strength of 55 to 80 tons/sq.in is required along with a case hardness of around 60 Rockwell

C.

Distortion can arise from:

Heavy machining prior carburising

Retained austenite on quenching

Poor design

Metallurgical anomalies in the steel.

This is most likely due to the presence of retained austenite on heat treatment. It is recommended that the steel is carburised and hardened in two separate

cycles.

An alternative grade depends on the size of the component. However it is likely that a steel to AISI 8620 should form a cheaper alternative and yet produce the

required properties. Similar carburising and heat treatment parameters are applicable to both steels.

This grade of steel can be successfully carburised. It is basically a 0.30%C version of carburising grade EN36 (832M13).

A greater carbon potential must be used in order to drive the carbon into the surface and a two stage treatment is recommended to overcome any potential

problems with retained austenite

This grade of steel can be successfully carburised. It is basically a 0.30%C version of carburising grade EN36 (832M13).

A greater carbon potential must be used in order to drive the carbon into the surface and a two stage treatment is recommended to overcome any potential

problems with retained austenite.

This grade of steel can be successfully carburised. It is basically a 0.30%C version of carburising grade EN36 (832M13).

Precipitation Hardening

The process of precipitation hardening, also called age hardening, is widely used to add strength to metal alloy materials. The precipitation hardening

capabilities of Applied Thermal Technologies, Inc. include stainless steel, high temperature alloys and titanium.

A process for permitting defects or stresses in a structure to be revealed, including (a) securing by molecular bonding of a face of a first element

containing crystalline material with a face of a second element containing crystalline material, so that the faces have offset crystalline lattices, the

securing causing the formation of a lattice of crystalline defects andor stress fields in a crystalline zone next to the securing interface, and (b) reducing the

thickness of one of the elements until at least a thin film is obtained which

adheres to the other element, along the securing interface to form the structure, the thickness of the thin film being such that its free face does not

reveal the crystalline defect lattice andor the stress fields, but allowing to perform (c) treatment of the thin film resulting in that its free face reveals the

crystalline defect lattice andor the stress fields.

A greater carbon potential must be used in order to drive the carbon into the surface and a two stage treatment is recommended to overcome any potential

problems with retained austenite.

Although EN 40B is often used in the un-nitrided condition for applications requiring high tensile strength at temperatures up to 600ºC, it is intended to be

nitrided to improve wear and corrosion resistance.

Nitriding is usually carried out at temperatures around 500ºC and prior tempering should have been done at a higher temperature.

machine tool is referred to as having computer numerical control, better known as CNC. and is commonly used with many other types of machine tool besides

the lathe.

When turning, a piece of material (wood, metal, plastic even stone) is rotated and a cutting tool is traversed along 2 axes of motion to produce precise

diameters and depths. Turning can be either on the outside of the cylinder or on the inside (also known as boring) to produce tubular components to various

geometries. Although now quite rare, early lathes could even be used to produce complex geometric figures, even the platonic solids; although until the advent of CNC it had become unusual to use one for this purpose for the last three quarters of the twentieth century. It is said that the lathe is the only

machine tool that can reproduce itself.

The turning processes are typically carried out on a lathe, considered to be the oldest machine tools, and can be of four different types such as straight

turning, taper turning, profiling or external grooving. Those types of turning processes can produce various shapes of materials such as straight, conical,

curved, or grooved workpiece. In general, turning uses simple single-point cutting tools. Each group of workpiece materials has an optimum set of tools

angles which have been developed through the years.

, which frequently requires continuous supervision by the operator, or by using a computer controlled and automated lathe which does not. This type of

machine tool is referred to as having computer numerical control, better known as CNC. and is commonly used with many other types of machine tool besides

the lathe.

When turning, a piece of material (wood, metal, plastic even stone) is rotated and a cutting tool is traversed along 2 axes of motion to produce precise

diameters and depths. Turning can be either on the outside of the cylinder or on the inside (also known as boring) to produce tubular components to various

geometries. Although now quite rare, early lathes could even be used to produce complex geometric figures, even the platonic solids; although until the advent of CNC it had become unusual to use one for this purpose for the last three quarters of the twentieth century. It is said that the lathe is the only

machine tool that can reproduce itself.

The turning processes are typically carried out on a lathe, considered to be the oldest machine tools, and can be of four different types such as straight

turning, taper turning, profiling or external grooving. Those types of turning processes can produce various shapes of materials such as straight, conical,

curved, or grooved workpiece. In general, turning uses simple single-point cutting tools. Each group of workpiece materials has an optimum set of tools

angles which have been developed through the years.

The bits of waste metal from turning operations are known as chips (North America), or swarf in Britain. In some locales they may be known as turnings.

TEMPERING

Tempering is a heat treatment technique for metals, alloys and glass. In steels, tempering is done to "toughen" the metal by transforming brittle martensite

into bainite or a combination of ferrite and cementite. Precipitation hardening alloys, like many grades of aluminum and superalloys, are tempered to

precipitate intermetallic particles which strengthen the metal.

The brittle martensite becomes strong and ductile after it is tempered. Carbon atoms were trapped in the austenite when it was rapidly cooled, typically by oil

or water quenching, forming the martensite. The martensite becomes strong after being tempered because when reheated, the microstructure can rearrange and the carbon atoms can diffuse out of the distorted BCT structure. After the

carbon diffuses, the result is nearly pure ferrite.

In metallurgy, there is always a tradeoff between strength and ductility. This delicate balance highlights many of the subtleties inherent to the tempering

process. Precise control of time and temperature during the tempering process are critical to achieve a metal with well balanced mechanical properties.

SHOT PEENING

Shot peening is a process used to produce a compressive residual stress layer and modify mechanical properties of metals. It entails impacting a surface with shot (round metallic, glass or ceramic particles) with force sufficient to create plastic deformation. It is similar to sandblasting, except that it operates by the mechanism of plasticity rather than abrasion: each particle functions as a ball-

peen hammer. In practice, this means that less material is removed by the process, and less dust created.

Peening a surface spreads it plastically, causing changes in the mechanical properties of the surface. Shot peening is often called for in aircraft repairs to relieve tensile stresses built up in the grinding process and replace them with

beneficial compressive stresses. Depending on the part geometry, part material, shot material, shot quality, shot intensity, shot coverage, shot

peening can increase fatigue life from 0%-1000%.

Plastic deformation induces a residual compressive stress in a peened surface, along with tensile stress in the interior. Surface compressive stresses confer resistance to metal fatigue and to some forms of corrosion. The tensile

stresses deep in the part are not as problematic as tensile stresses on the surface because cracks are less likely to start in the interior.

Shot peening may be used for cosmetic effect. The surface roughness resulting from the overlapping dimples causes light to scatter upon reflection.

Because peening typically produces larger surface features than sand-blasting, the resulting effect is more pronounced.

Shot peening was originally developed by John Almen when he was working for Buick Motor Division of General Motors Corporation. He noticed that shot

blasting, as it was called back when he was working, made the side of the sheet metal that was exposed begin to bend and stretch. John Almen also

created the Almen Strip to measure the comprehensive stresses in the strip created by the ball peening operation. One can obtain what is referred to as the

"Intensity of the Blast Stream" by measuring the deformation on the Almen strip that is in the shot peening operation. As the strip reaches a 10%

deformation, the Almen strip is then hit with the same intensity for twice the amount of time. If the strip deforms another 10%, then you have the, "Intensity

of the Blast Stream."

A study done through the SAE Fatigue Design and Evaluation Committee showed what shot peening can do for welds compared to welds that didn't

have this operation done. The study claimed that the regular welds would fail after 250,000 cycles when welds that had been shot peened would fail after 2.5 million cycles, and outside the weld area. This is part of the reason that shot peening is a popular operation with aerospace parts. However, the beneficial

prestresses can anneal out at higher temperatures.

ECC-EDDY CURRENT CLUTCH

Eddy Current clutches give torque as a function of RPM. The faster you turn the rotor, the more torque. This means by increasing or decreasing the RPM,

you can get infinite torque adjustment. Typically, we rate the clutch with a gain factor (k), which is gram millimeters/rpm or Newton meters/rpm and we design

the clutch to have an operating "slip rpm" between 1 and 300 rpm.

JIG BORING

Jig boring is used to accurately enlarge existing holes and make their diameters highly accurate. Jig boring is used for holes that need to have

diameter and total runout controlled to a high degree. Typically, a part has holes machined on regular equipment and then the part is transferred to a

dedicated jig boring machine for final operations on the especially accurate holes. Jig boring can also maintain high accuracy between multiple holes or holes and surfaces. Tolerances can be held readily within ±.005 mm (±0.0002

inches). Dedicated jig boring machines are designed to machine holes with the tightest tolerances possible with a machine tool.

When designing a part with holes, it is important to determine what holes must be jig bored. The reason for this is that jig boring requires extra time and

attention, and the jig boring machine at the machine shop may have a back log of jobs. Jig boring can therefore have a big impact on the lead time of a part. A

cross section of a hole being jig bored is shown below.

Standard boring can be carried out on a mill fitted with a boring head or on a lathe. Boring is most accurate on a lathe since a lathe is dedicated to solids of

revolution (axially symmetric parts).

Gun Drilling

For long holes such as those found in gun bores, gun drills are used. The length of the hole requires that coolant be delivered through the shaft of the gun drill to the cutting front. The coolant also serves to eject chips from the

cutting area and to move them back and out of the hole entrance. The figures below illustrate a gun drill and the cutting/cooling configuration.

Jig boring machines are mainly to perform machining operations like boring, drilling, reaming, counter boring holes in metal jigs and counter-sinking holes

in metal work pieces. Some jig boring machines are used for accurately enlarging the existing holes and making their diameters highly accurate.

Jig boring can also maintain high accuracy between multiple holes or holes and surfaces. Some jig boring machines are designed to machine holes with

the tightest tolerances possible with a machine tool. The constant demand for accuracy within many branches of metalworking has been fulfilled with the

help of applications possible by jig-boring machines.

ELECTRIC DISCHARGE MACHINE WIRE CUTTING

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 or Electrical Discharge Machining, is especially well-suited for cutting

intricate contours or delicate cavities that would be difficult to produce with a grinder, an end mill or other cutting tools. Metals that can be machined with EDM include hastalloy, hardened tool-steel, titanium, carbide, inconel and

kovar.

EDM is sometimes called "spark machining" because it removes metal by producing a rapid series of repetitive electrical discharges. These electrical discharges are passed between an electrode and the piece of metal being

machined. The small amount of material that is removed from the workpiece is flushed away with a continuously flowing fluid. The repetitive discharges

create a set of successively deeper craters in the work piece until the final shape is produced.

There are two primary EDM methods: ram EDM and wire EDM. The primary difference between the two involves the electrode that is used to perform the machining. In a typical ram EDM application, a graphite electrode is machined with traditional tools. The now specially-shaped electrode is connected to the power source, attached to a ram, and slowly fed into the workpiece. The entire machining operation is usually performed while submerged in a fluid bath. The

fluid serves the following three purposes:

flushes material away

serves as a coolant to minimize the heat affected zone (thereby preventing potential damage to the workpiece)

acts as a conductor for the current to pass between the electrode and the workpiece.

In wire EDM a very thin wire serves as the electrode. Special brass wires are typically used; the wire is slowly fed through the material and the electrical

discharges actually cut the workpiece. Wire EDM is usually performed in a bath of water.

If you were to observe the wire EDM process under a microscope, you would discover that the wire itself does not actually touch the metal to be cut; the

electrical discharges actually remove small amounts of material and allow the wire to be moved through the workpiece. The path of the wire is typically controlled by a computer, which allows extremely complex shapes to be

produced.

Perhaps the best way to explain wire EDM is to use an analogy. Imagine stretching a thin metal wire between your hands and sliding it though a block

of cheese cutting any shape you want. You can alter the positions of your hands on either side of the cheese to define complex and curved shapes. Wire

EDM works in a similar fashion, except electrical discharge machining can handle some of the hardest materials used in industry. Also note, that in

dragging a wire through cheese, the wire is actually displacing the cheese as it cuts, but in EDM a thin kerf is created by removing tiny particles of metal.

Electrical discharge machining is frequently used to make dies and molds. It has recently become a standard method of producing prototypes and some production parts, particularly in low volume applications. For more details

regarding a typical application, you can read about a custom bronze branding-iron that was made with EDM.

Electrical discharge machines (EDM) remove metal from a workpiece by using a series of electric sparks to erode material. An electrical discharge machine is

considered to be the most precision oriented manufacturing process and is widely used for creating simple and complex shapes and geometries. EDM

machining is favored in situations where high accuracy of work and low count is required. An EDM machine consists of a workpiece and the wire electrode. A workpiece is sometimes dipped in a dielectric to develop a potential difference

between the workpiece and wire electrode. Electrical discharge machine supply is applied to the workpiece. Electrical discharge machines (EDM) work

by eroding the material that appears in the electrical discharge path. This material is responsible for generating an arc between the workpiece and wire electrode. The wire electrode rotates acts as wire EDM tooling and rotates a

two-three axis and cuts the internal cavities in the workpiece. There are many types of electrical discharge machines (EDM). Examples include a CNC EDM

and a wire EDM machine. A CNC EDM is a computer numerical control machine and is used for removing metal using electrical discharge spark erosion. A wire

EDM machine is designed for precision machining purposes and is used for cutting prismatic metal components. Other electrical discharge machines

(EDM) are commonly available.

There are several ways in which electrical discharge machines (EDM) function. Electrical discharge machines (EDM) are used where fast turn around time is

required. Electrical discharge machines (EDM) works by removing the workpiece that generates an arc with the wire electrode and creating a cavity in the workpiece. The dimensional accuracy required for an electrical discharge machine is + / - 0.0005 inches per inch. Electrical discharge machines (EDM)

also require a 0.0003 feature profile accuracy across the workpiece cutting path. Electrical discharge machines (EDM) are designed and manufactured to

meet most industry specifications.

WIRE CUTTING EDM

A wire cut electric discharge machine having rollers is disclosed. It has a wire electrode disposed in a working zone of the electric discharge machine. This wire electrode is rolled by a rolling device so that the cross-sectional area of this wire electrode changes from a circular area into an elongated one. After rolled, the wire electrode has two parallel rolled flat surfaces. The working

width between these flat surfaces is smaller than the original diameter of the wire electrode before rolled. So, the cutting width is narrower than before. By

using the rolled wire electrode, this invention can reduce the cutting width limit. I can improve the precision of the product, without changing the material property of the wire electrode. And, it can reduce the cost of the wire electrode.