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Jayam college of Engineering and Technology

B.E Mechanical Engineering / III Semester

Manufacturing Technology IIABRASIVE PROCESS, SAWING, BROACHING AND GEAR CUTTING

Abrasive processes: grinding wheel – specifications and selection, types of grinding process –cylindrical grinding, surface grinding, centre less grinding – honing, lapping, super finishing, polishingand buffing, abrasive jet grinding Sawing machine: hack saw, band saw, circular saw; broachingmachines: broach construction – push, pull, surface and continuous broaching machines, gear cutting:forming, generation, shaping, hobbing.

ABRASIVE PROCESS

GRINDING MACHINES

INTRODUCTIONGrinding is metal cutting operation performed by means of a rotating abrasive wheel that acts as a

tool. This is used to finish workpieces which must show a high surface quality, accuracy of shape anddimension.

KINDS OF GRINDINGGrinding is done on surfaces of almost all conceivable shapes and materials of all kinds. Grinding may

be classified broadly into two groups• Rough or non-precision grinding.• Precision grinding.

Rough grinding:The common forms of rough grinding are snagging and off-hand grinding where the work is held in the

operator’ s hand. The work is pressed hard against the wheel, or vice -versa. The accuracy and surfacefinish obtained are of secondary importance.

Precision grinding:This is concerned with producing good surface finish and high degree of accuracy. The wheel or workboth are guided in precise paths.

Grinding, in accordance with the type of surface to be ground, is classified asv External cylindrical grinding.v Internal cylindrical grinding.v Surface grinding.v Form grinding.

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External cylindrical grinding produces a straight or tapered surface on a workpiece.o The workpiece must be rotated about its own axis between centers as it passes lengthwise across

the face of a revolving grinding wheel. It produces internal cylindrical holes and tapers.o The workpieces are chucked and precisely rotated about their own axis.o The grinding wheel or, in the case of small bore holes, the cylinder wheel rotates against the sense

of rotation of the workpiece.

Surface grinding produces flat surface.o The work may be ground by either the periphery or by the end face of the grinding wheel.o The workpiece is reciprocated at a constant speed below or on the end face of the grinding wheel.

Form grinding is done with specially shaped grinding wheels that grind the formed surfaces as ingrinding gear teeth, threads, splined shafts, holes, and spheres, etc.In Grinding machines, according to the quality of surface finish, may be classified as:

§ Rough grinders.§ Precision grinders.

ROUGH GRINDERS: Rough grinders are those grinding machines whose chief work is the removal ofstock without any reference to the accuracy of the results.

They are mainly of the following types:v Floor stand and bench grinders.vPortable and flexible shaft grinders.vSwing frame grinders.v Abrasive belt grinders.

PRECISION GRINDERS: Precision grinders are those that finish parts to a very accurate dimensions.According to the type of surface generated or work done they may be classified as follows

1. Cylindrical grinders• Centre-type (Plain)• Centre-type (Universal)• Centre less

2. Internal grinders(a)Chuckingo Plaino Universal

(b) Planetary(c) Centre less

3. Surface grinders(a)Reciprocating table

(i) Horizontal spindle(ii) Vertical spindle

(b) Rotating table(i) Horizontal spindle(ii) Vertical spindle

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4. Tool and cutter grindersoUniversalo Special

5. Special grinding machines

FLOOR-STAND AND BENCH GRINDERS

The simplest type of grinder is the floor-stand grinder. A floor-stand grinder has a horizontal spindlewith wheels usually at both ends and is mounted on a base or pedestal.v There is provision for driving the wheel spindle by belt from motor at the rear, at floor level.vThe headstock can be swiveled at an angle in a horizontal plane.v The wheel head and slide can be swivelled and traversed at any angle.v The wheelhead can also be arranged for internal grinding by the addition of an auxiliary

wheelhead to revolve small wheels at high speeds.

CENTRE LESSS GRINDERS

Centre less grinding is a method of grinding exterior cylindrical, tapered, and formed surfaces onworkpieces that are not held and rotated on centres.v The principal elements of an external centreless grinder are the grinding wheel, regulating or

back up wheel, and the work rest. Both wheels are rotated in the same direction.v The work rest is located between the wheels. The work is placed upon the work rest, and the

latter, together with the regulating wheel, is fed forward, forcing the work against the grindingwheel.

External centerless grinding

Internal grinders of chucking type may be classified as plain and universal grinders.In a plain internal grinder, the workhead can be swivelled to grind a straight hole tapers upto 450included angle. The wheel head is moved into and away from the bole and can be cross fed into thework.

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Internal centre less grinding

SURFACE GRINDERSSurface grinding machines are employed to finish plane or flat surfaces. They are also capable of

grinding irregular, curved, convex, and concave surfaces.• Conventional surface grinders may be divided into two classes• One class has reciprocating tables for work ground along straight lines• while the other covers the machines with rotating work tables for• The first two are most commonly used for repetitive work by hand operation or with simple

fixtures.• The third type is widely used for production operations where parallel surfaces are ground

simultaneously.

Block diagram of a plain center type grinder

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Horizontal surface grinder

Vertical surface grinder

TOOL AND CUTTER GRINDERSTool and cutter grinders are used mainly to sharpen and recondition multiple tooth cutters like

reamers, milling cutters, drills, taps, hobs and other types of tools used in the shop.

Ø Universal tool and cutter grinders.Ø Single —purpose tool and cutter grinders.

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Universal tool and cutter grinders The universal tool and cutter grinders made by differentmanufacturers vary more or less as to details, but they are similar in their general arrangement andoperate on the same general principle.

Block diagram of a tool and cutter grinder

MOUNTED WHEELSMounted wheels are small shaped wheels (50 mm dia and below) mounted securely and permanently

to steel spindle or mandrel by cementing or other means.

o Mounted wheels and points are showno Great care should be taken in using mounted wheels and points.o Pressure between wheel and work small at no time be so heavy that any considerable springing of

the spindle will result.o It is particularly important to observe this rule in connection with small wheels and points where

the end of the mandrel entering the wheel is of reduced diameter.

SELECTION OF GRINDING WHEELSIt is customary for grinding wheel manufactures to provide, through their published literature,

information on the selection and use of grinding wheels, but it may not always be possible or convenientfor users to take advantage of such consultative service.

GRINDING WHEEL SELECTION FACTORS

Constant factors Variable factorsI. Material to be ground 1. Wheel speed2. Amount of stock to be

removed2. Work speed

3. Area of contact 3. Condition of the

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1. The material to be ground This influences the selection of (a) abrasive, (b) grain size, (c) grade, (d)structure, and (e) bond.

As general guide the grit and grade ranges given in Table would be suitable for the class of work shownagainst each

v Aluminum Oxide abrasive is recommended for materials of high tensile strength and siliconcarbide for low tensile strength.

v Fine grain is used for hard and brittle materials and coarse grain for soft ductile metals.v Hard wheel is used for soft materials and soft wheel for hard materials.v Generally, close spacing is required for hard and brittle materials and wide for soft and

ductile.v The class of work usually dictates the bond to be used. Bond selection, of course, can be

safely left to the manufacturers, if the class of work for which the wheel is required is clearlystated. However, majority of wheels are manufactured with vitrified bonds.

2. Amount of stock to be removed: This involves accuracy and finish.• Coarse grain is used for fast cutting and fine grain for fine finish;• Wide spacing for rapid removal and close for fine finish; resinoid, rubber, and shellac bond

for high finish.

3. Area of contact: Area of contact influences the selection ofv Grit sizev Gradev Structure number.

Fine grain and close grain spacing are useful where the area of contact involved is small, and coarsegrain and spacing are employed where a large area of contact is concerned.

4. Type of grinding machine:Type of grinding machine determines to an extent the grade of the wheel.

• Heavy rigidly constructed machines take softer wheels than the lighter more flexible types.• The combination of speeds and feeds on some precision machines may affect the grade of

wheel desirable for best results.

o Wheel speed: The wheel speed influences the selection of grade and bond.• The higher the wheel speed with relation to work speed, the softer the wheel should be used.• Vitrified bond is usually specified for speeds upto 2000 s.m.p.m. (or 6~00 s.f.p.m.) and

rubber, shellac or resinoid bonds for speed over 2000 s.m.p.m. (or 6500 s.f.p.m.).

machine4. Type of grinding

machine4. Personal factor

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Work speed: The work speed with relation to the wheel speed determines the hardness of the wheel.• The higher the work speed with relation to the wheel speed.• Variable work speed are often provided on grinding machines to preserve the proper relative

surface speeds between the work and wheel as the wheel diameter decreases because of wear.

MOUNTING THE GRINDING WHEELSGreat care must taken in mounting the grinding wheels on the spindle because of the high cutting

speeds of the grinding wheel. The following points are important in connection with mounting thewheel.

o All wheels should be closely inspected just before mounting to make sure that they have notbeen damaged in transit, storage, or otherwise.

o The wheel must first be subjected to the ringing test. For this purpose, the grinding wheel isput on an arbor while it is subjected to slight hammer blows.

o A clear, ringing, vibrating sound must be heard.o If a grinding wheel contains fine cracks, discordant sound that fail to vibrate will be emitted.o This test is applicable to vitrified and silicate wheels. Shellac, resinoid or Rubber loaded

wheels will not ring distinctly.o The abrasive wheels should have an easy fit on their spindles or locating spigots. They

should not be forced on.

BALANCING GRINDING WHEELSIf wheels become out of balance through wear and cannot be balanced by truing or dressing, they

should be removed from the machine and discarded.

v Wheels should be tested for balance occasionally and rebalanced if necessary.v Wheels that are out of balance not only produce poor work but may put undue strains on the

machine. Small wheels may be balanced by milling a short recess on the inside of the flanges andfilling with lead. Large wheels should be placed on a balancing stand and balanced by movingweights around a recessed flange.

v Now-a-days, grinding wheel mounts are provided with devices to enable balancing to be donewhilst the wheel is running and between grinding operations.

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SAWINGSawing is one of the basic operations carried out in a carpentry shop.A wood is required to be sawn along the grains or across the grains and in many shapes such asstraight inclined or curved.To start the cut, the thumb of the left hand is placed against the blade

Band Saw

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The band saw consists of a flexible endless bladeThis moves around two revolving wheelsThe job to be cut is placed on a flat table and is fed by hand towards the blade for cutting. Blades of different widths are used with the band saw.Blades having narrow widths are used for fine work

I. The curve to be cut is first marked on the job in pencil.2. For bevel cutting the table of the band saw is tilted to the desired angle.3. For Ripping, a fence should be employed.Construction4. For Re sawing, a wider band saw blade should be used.

Circular sawA circular saw has a table which can be tilted also in order to make angular cuts.Angular cuts can, however also be made by tilting the arbor (i.e., the circular blade).The other parts of a circular saw are the saw or blade, ripping fence, cut off fence, hand wheeletc.Sizes of circular saws are given as the diameter of the blade e.g. 200 mm, 250mm etc.

OPERATIONS PERFORMED:Cross cuttingRippingMiteringBevelingRabbeting etc.,

PRINCIPLE OF CIRCULAR SAW

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• A saw should never be forced and it is kept moving steadily for nearly its fill length.• Its own weight plus the slightest pressure is all that is needed.• The hacksaw is used for sawing all metal except hardened steel.• They are made in two types:• The solid frame in which the length cannot be changed and the adjustable frame which has aback

that can be lengthened or shortened to hold blades of different length.• All hard blades made of high speed steel are used for cutting the harder metals, such as alloy

steels, while flexible blades are good for use by. Un skilled or semiskilled operators or where thework is inconveniently placed.

• These flexible blades are less liable to break and are used for general work.

SURFACE FINISHING PROCESSESINTRODUCTION

If a better finish is desired, for looks, for accuracy, for wearing qualities, or for any other reasons, oneof the micro finishes that include lapping, honing, super finishing, polishing, buffing, may be employed.In some cases other operations are done only -to get durable finishes.

LAPPINGLapping is an abrading process that is used to produce geometrically true surfaces, correct minor

surface imperfections, improve dimensional accuracy, or provide a very close fit between two contactsurfaces.

• Very thin layers of metal (0.005 to 0.01 mm) are removed in lapping and it is, therefore, evidentthat lapping is unable to correct substantial errors in the form and sizes of surfaces.

• It is, however, low efficiency process and is used only when specified accuracy and surfacefinish cannot be obtained by other methods.

Abrasive powders (flours) such as emery, corundum, iron oxide, chromium oxide, etc., mixed with oilor special pastes with some carrier are used in lapping.v Most lapping is done by Tneans of lapping shoes or quills, called laps, which are rubbed against

the work.v The face of a lap becomes “charged” with abrasive particles. Charging a lap means to embed the

abrasive grains into its surface.v Laps may be made of almost any material soft enough to receive and retain the abrasive grains.v They are made of soft cast iron, brass, copper, lead or soft steel. The method of charging a lap

depends upon the shape of lap.v When the lap is once charged, it should be used without applying more abrasive until it ceases to

cut. Laps may be operated by hand or machine, the motion being rotary or reciprocating.v Cylindrical work may be lapped by rotating the work in lathe or drill press and reciprocating the

lap over the work in an ever-changing path.

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v Small flat surfaces may be lapped by holding the work against a rotating disc, or the work maybe moved by hand in an irregular path over a stationary faceplate lap.

v In equalizing lapping the work and lap mutually improve each others surface as they slide oneach other.

There are three important types of lapping machines.o The vertical axis lapping machine laps flat or round surfaces between two opposed laps on

vertical spindles.o The centreless lapping machine is designed for continuous production of round parts such as

piston pins, bearing races and cups, valve tappets and shafts.o The centreless lapping machine operates on the same principle as centreless grinding.o The abrasive belt lapping machine laps bearings and cam surfaces by means of abrasive coated

clothes.

HONINGHoning is grinding or a abrading process mostly for finishing round holes by means of bonded

abrasive stones, called hones.

v Honing is therefore a cutting operation and has been used to remove as much as 3 mm of stockbut -is normally confined to amounts less than 0.25 mm.

v So honing is primarily used to correct some out of roundness, taper, tool marks, and axialdistortion. Honing stones are made from common abrasive and bonding materials, oftenimpregnated with sulphur, resin, or wax to improve cutting action and lengthen tool life.

v Materials honed range from plastics, silver, aluminum, brass, and cast iron to hard steel andcemented carbides. This method is mostly used for finishing automobile crankshaft journals.

v When honing is done manually the tool rotated, and the workpiece is passed back and forth overthe tool.

Honing tool head for holes1. stone 2.guide

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• For precision honing, the tool is given a slow reciprocating motion as it rotates. Honing may beloosely held in holders, cemented into metal shells which are clamped into holders, cementeddirectly in holders, or cast into plastic tabs which are held in holders.

• Some stones are spaced at regular intervals around the holder, while others are interlocking sothat they present a continuous surface to the bore.

• The honing tool may be so made that a floating action between the work and tool prevails andany pressure exerted in the tool may be transmitted equally to all sides.

• Coolants are essential to the operation of this process to flush away small chips and to keeptemperatures uniform.

o Honing is done on general purpose machines, such as the lathe, drill press, and portable drills, asan expedient.

o But more economical results can be obtained by honing machines for production work. There aretwo general types of honing machines Horizontal and vertical.

o A honing machine rotates and reciprocates the hone inside holes being finished.o The two motions produce round and straight holes that have a very fine surface finish of random

scratches.o Vertical honing machines are probably more common.o Horizontal honing machines are often used for guns and large bores.

SUPERFINISHINGSuperfinshing is an operation using bonded abrasive stones in a particular way to produce an

extremely high quality of surface finish in conjunction with an almost complete absence of defects in thesurface layer.

v A very thin layer of metal (0.005 to 0.02 mm) is removed in superfinishing.v This operation may be applied for external and internal surfaces of parts made of steel, cast iron

and non-ferrous alloys, which have been previously ground or precision turned.v It is most frequently used to obtain very fine surface finish.

Schematic diagram for shaft super finishing

v In superfinishing, a very fine grit (grain size 400 to 600) abrasive stick is retained in a suitableholder and applied to the surface of the workpiece with a light spring pressure.

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v The stick is given a feeding and oscillating motion, and the workpiece is rotated or reciprocatedaccording to the requirements of the shape being superfinished,

v In this process, the work rotational speed is low (2 to 20 in/mm.) the longitudinal feed rangesfrom 0.1 to 0.15mm per workpiece revolution, the abrasive stick oscillates rapidly in shortstrokes (2 to 5mm) with a frequency from 500 to 1,800 strokes per minute and the springs holdthe stick against the work with a force from 2 to 10 kg.

v A special lubricant, usually a mixture of kerosene and oil, is used to obtain a high quality ofsurface finish.

v Special general-purpose machine tools are available for superfinishing.v Other types of ordinary machines, in particular, lathes, are sometimes employed for this purpose.v Single purpose machine tools for example, for finishing crankshaft journals, camshafts, etc. are

also used.

BROACHING MACHINEBroaching is a method of removing metal by pushing or pulling a cutting tool called a broach which cutsin fixed path.

o The tool may be pulled or pushed through the surfaces to be finished. Surfaces finished bybroaching may be flat or contoured and may be either internal or external.

o Broaching is generally limited to the removal of about 6 mm of stock or less.o The term broaching may have derived from an ancient Roman word braces, which meant an

object having projecting teeth.o The operation itself dates only to the 1850’ s when broaching tools, then called “drifts” were

hammered in blacksmith shops through the work or pushed through with an arbor press.

BROACHESA broach is a multiple-edge cutting tool that has successively higher cutting edges along the length of

the tool.

TYPES OF BROACHES:Broaches may be classified in various ways, according to:

v Type of operation: internal or external.vMethod of operation: push or pull.vType of construction: solid, built-up, inserted tooth, progressive cut, rotor cut, double jump, or

overlapping tooth.’v Function: surface, keyway, round hole, splint, spiral, burnishing, etc.

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• Broaching of inside surfaces is called internal or hole broaching and of outside surfaces, externalor surface broaching.

• Internal broaching tools are designed to enlarge and cut various contours in holes already made bydrilling, punching, casting, forging, etc.

• External surface broaching competes with milling, planing, shaping, shaping, and similaroperations. It offers a combination of a high degree of accuracy and excellent surface finish,combined with high output rate and low downtime.

• A push broach is one that is designed to be pushed through the workpiece by special press or apush broaching matching.

Because of the tendency to bend under compressive loads, the push broach must be short and stocky,which means fewer teeth are in the broach and, less material can be removed for each pass of the tool.

o Holes are machined by push broaches only for sizing.o In a pullbroach the tool is entirely in tension and long slender broaches are possible, having a

large number of teeth, consequently more stock can be removed for each pass.o When a broach is made in one piece, it is called a solid broach. Internal broaches are usually of

the solid type.o Broaches are sometimes built up of several sections, and sometimes made up of a series of

teeth inserted in a block of steel.o Surface broach are usually of the built up or inserted tooth type.o Progressive cut broaches have teeth, a par of which are of the same height along the broach

have different widths.o In progressive cut broaching metal is removed in thick layers by each tooth only part of the

work-surface.o The last teeth of progressive cut broach remove a thin layer over the entire profile of the work

surface as in ordinary broaching.

BROACH MATERIAL:Most broaches are made from 18-4-1 tungsten chromium vanadium steel ground after hardening.Carbide broaches are.

• Used extensively in the broaching of cast iron in the automotive field.• They are also used for surface broaches, for high production and for finishing broaches.

BROACHING METHODS:Broaching, according to the method of operation, may be classified as follows

• Pull broaching: The work is held stationary and the broach is pulled through the work. Broachesare usually long and are held in a special head.

• Pull broaching is used mostly for internal. Broaching but it can do some surface broaching.

• Push broaching: The work is held stationary and the broach is pushed through the work. Handand hydraulic arbor presses are popular for push broaching.

• This method is used mostly for sizing holes and cutting keyways.

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Push broach

Broaching operations

• Surface broaching: Either the work or the broaching tool moves across the other. This methodhas rapidly become as important means of surface finishing.

• Fixtures are most important in broaching operations.• They are used particularly for two reasons first, because of the high pressures used and because of

the manner in which the cutting is done; second, broaching being essential a mass-productionoperation, fixtures speed up the operation and help to keep it accurate.

Broaching fixtures perform one or more of the following functions:v Move the work into and out of cutting position.v Hold the work rigidly so that it will not deflect.v Guide the broach in relation to the work.v Locate the work in correct position.v Index or feed the work between cuts

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BROACHING OPERATIONBroaching is applied for machining various internal and external surfaces, for round or irregular

shaped holes from 6 to 100 mm in diameter, for external flat and contoured surfaces.

• Certain types of surfaces, for example, splint holes, are machined at the present time only bybroaching due to the exceptional difficulties in machining such surfaces by other methods.

• Most broaching operations are completed in one pass, but some are arranged for repeated cuts tosimplify the design of the broach.

• The teeth of a gear or splint may be broached altogether or one or a few at a time.• A comparatively simple broach can be made to cut one or a few tooth spaces, After one pass, the

gear blank is indexed, and more of its teeth are cut.• Successive passes are made until all the teeth are finished.

ADVANTAGES AND LIMITATIONS OF BROACHINGBroaching has been adopted for mass production work because of the following outstanding features

and advantages:o Rate of production is very high. With properly applied broaches, fixtures, and machines, more

pieces can be turned per hour by broaching than by any other means,o Little skill is required to perform a broaching operation. In most cases the operator merely loads

and unloads the workpiece.o High accuracy and a high class of surface finish is possible. A tolerance of ± 0.0075 mm and a

surface finish of about 0.8 microns (1 micron = 0.001mm) can be easily obtained in broaching.o Both roughing and finishing cuts are completed in one pass of the tool.o The process can be used for either internal or external surface finishing.o Any form that can be reproduced on a broaching can be machined.oCutting fluid may be readily applied where it is most effective because a broach tends to draw the

fluid into the cut.

Certain reasons, however, limit the application of the broaching process. They are:v High tool cost. A broach usually does only one job and is expensive to make and sharpen.v Very large workpieces cannot be broached.v The surfaces to be broached cannot have an obstruction.v Broaching cannot be used for the removal of a large amount of stock.v Parts to be broached must be capable of being rigidly supported and must be able to withstand

the forces that set up during V Cutting.

GEAR CUTTINGGEAR MANUFACTURINGGears are toothed wheels used for transmission of power or motion.There are different types of gears used in industry.They are,1. Spur gears2. Helical gears3. Rack and pinion gears.4. Worm arid worm wheel.5. Bevel gears. Etc.

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WORM AND WORM WHEEL:Worm and worm wheel are used to get heavy reduction in speed. Here the axes are perpendicular to each other.

BEVEL GEARS:Bevel gears are used to transmit motion from one gear to another gear with their axes inclined to oneanother.A set of mitre bevel gears have equal number of teeth and their axes are at right angles to each other.

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FORMING METHODIn form machining, a form cutter is used.The formed cutter may be single point cutting tool or a multipoint milling cutter.The cutting edges of the formed cutter has been finished to the shape of the space between thegear teeth being cut. Forming method is used forVery small number of gears.Gears produced by forming are less accurate.Forming process is simple and cheaper.This method is takes more time.Gears are produced by forming method in milling, machine, shaper, planer, and broachingmachine.

FORMING OF GEARS IN MILLING MACHINE:v Spur gears, helical gears and straight bevel gears are cut on a milling machine.v Here a disc like form cutter is used.v A dividing head is used for holding and indexing the gear blank.v Indexing is the operation of dividing the periphery of the (gear blank) in to any number of

equal divisions.

GEAR GENERATING PROCESS

Gear shaping

Gear Shaping

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v In gear shaping, a pinion type cutter is used.v The cutter teeth are ground with a top rake and clearance.v The cutter is mounted on a vertical spindle.v The axes of the cutter and blank are parallel.v The cutter and the blank are made to rotate together as two gears which are in mesh.v The surface speeds of the cutter and the blank are the same.v The cutter reciprocates in a vertical direction along the width of the blank.

Shaping External Gear

Shaping Internal Gearo The pinion cutter is fed radially into the gear blank to give the depth of cut.o The cutter and blank slowly rotate together till all the teeth are generated on the blank.o During each return stroke of the cutter, the blank is withdrawno This is done to prevent rubbing of the cutting edges and damage to gear teeth being cut.

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The different movements are given below;

v Rotary motion of the cutter and the blank.v Vertical reciprocating motion of the cutter.v Radial feed of the cutter towards the blank.v Withdrawal motion of the blank away from the cutter during return stroke.

GEAR HOBBINGv Hobbing is a process of generating a gear by means of a rotating cutter called hob.v The hob has helical threads.v Grooves are cut in the threads parallel to the axis.v This will provide the cutting edges.v Proper rake and clearance angles are ground on these cutting edges.v The rotating hob acts like a continuously moving rack as it cuts.

Gear hobbing

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BEVEL GEAR GENERATOR

There are two types of bevel gear generator.Ø Straight bevel gear generator.Ø Spiral bevel gear generator.

STRAIGHT BEVEL GEAR GENERATOR

v The generating process is similar to rolling of a bevel gear blank of an imaginary crownwheel.

v The crown wheel is a bevel gear having pitch cone angle of 180°v The teeth of the crown wheel are straight and radial. In practice, instead of full crown

wheel only two teeth are used for generation of a bevel gear from a blank.v Two cutting tools in the form of two teeth of a crown wheel are used.v The tools have the profile of teeth being cutv The two tools together cut only one tooth space at a time.

Straight bevel gear generator

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Spiral bevel gear generator.

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UNIT IV

ABRASIVE PROCESS, SAWING, BROACHING AND GEAR CUTTING

PART A (2 marks questions)

1. What is meant by grinding?

2. What are the types of precession grinders?

3. What are the ‘ types of surface grinding?

4. What are the uses of internal and external grinders?

5. What is centre less grinding?

6. What are the advantages of centre less grinding?

7. What is the use of Magnetic chuck in surface grinding?

8. What does dressing of grinding wheels mean?

9. What is honing?

10. What is meant by polishing?

11. What are the abrasives and binders used in binding?

12. State the principle involved in gear shaping?

13. Distingush between forming and generating methods?

14. What is the main disadvantage of gear shaping?

15. What is broaching?

16. What are the advantages of broaching?

17. How broachers are classified?

18. What are the broaching operations?

19. What are the importances of sawing?

20. What are all the gear manufacturing methods?

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Part B (16 marks questions)

1. What are various abrasive marching operations? Explain their application and limitations.

2. What are the grinding process parameters that are of interest? Explain their effect and the grinding

performance and the wear rates

3. What are the advantages and limitations of using center less grinding

4. Describe the dressing and balancing requirements in grinding

5. What is the difference between form cutting and generation of gears with respect to the principle?

6. Give comparison of various gear machining methods in terms of their application, accuracy and

processes

7. Compare the gear shaping and gear hobbing; give the process and product requirement

8. Explain the principle of gear shaping

9. Explain various types of sawing machines

10. Explain the following

A) Gear forming

b) Gear hobbing

c) Gear shaping

d) Gear generation

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