ABSTRACT

Lapping is low pressure, low speed abrading operation for refining

surface finish within the high dimensional and geometrical accuracies.

Lapping is generally used for flat, regular surfaces, gauges, piston

rings, pins. valves, roller bearings, crank shaft, cylindrical surfaces etc.

centreless lapping machine is generally used for super finishing operations

on cylindrical surfaces and this machine gives super finish in microns.

CONTENTS

1. INTRODUCTION

2. TYPES OF SURFACE FINISH

2.1 HONING

2.2 SUPERFINISHING

2.3 ROLLER BURNISHING

2.4 LAPPING

3. TYPES OF LAPPING

3.1 HAND LAPPING

3.1.1 LAPPING FLAT SURFACES

3.1.2 LAPPING OF INTERNAL CYLINDRICAL SURFACES

3.2 MACHINE LAPPING

3.2.1 VERTICAL LAPPING M/C WITH TWO CIRCULAR PLAT

3.2.2 MACHINE WITH SINGLE ROTATING CIRCULAR PLATE LAP

3.2.3 CENTRELESS ROLL LAPPING MACHINE

3.2.4 CENTRELESS LAPPING MACHINE

3.2.5 LAPPING MACHINES FOR INTRENAL CYLINDRICAL

SURFACES

4. LAPPING OF SLIP GAUGES

5. LAPPING FINISHES AND ACCURACIES

6. LAP MATERIALS

7. LAPPING MEDIUM

7.1 SILICON CARBIDE

7.2 ALUMINIUM OXIDE

7.3 BORONCARB1DE

7.4 DIAMOND

8. VEHICLES

9. LAPPING SPEEDS AND PRESSURES

10. ALLOWANCES FOR LAPPING

11. DESIGN

11.1 MOTOR SPECIFICATION

11.2 PULLIES SELECTION

11.3 CALCULATION FOR LENGTH OF BELT

11.3.1 FOR LAPPING WHEEL

11.3.2 FOR REGULATING WHEEL

11.4 CALCULATION FOR BELT TENSION

11.4.1 FOR LAPPING WHEEL

11.4.2 FOR REGULATING WHEEL

11.5 SHAFT DESIGN

11.5.1 1NTERMIDIATE SHAFT

11.5.2 SHAFT DESIGN FOR LAPPING WHEEL

11.5.3 SHAFT DESIGN FOR REGULATING WHEEL

11.6 BEARING SELECTION

12 PROCESS CHARTS

12.1 LAPPING WHEEL SHAFT

12.2 REGULATING WHEEL SHAFT

12.3 INTERMIDIATE SHAFT

12.4 BEARING HOLDRE

12.5 LAPPING WHEEL

12.6 REGULATING WHEEL

13. COST SHEET

14. CONCLUSION

15. REFERENCES

LIST OF FIGURE

TITLE

LAP FOR EXTERNAL THREADS.

LAPPING MANDREL.

VERTICAL LAPPING M/CWITII UONDLD AIJKAC'IVI-S LAPS

CENTRELESS ROLL LAPPING M/C

SPHERICAL LAPPING

DIAGRAMS FOR DESIGNS

DIAGRAMS FOR PROCESS CHARTS

LIST OF TABLES

TAB.NO. TITLE

LAPPING ACCURACY AND FINISH

RECOMMENDED LAPPING ALLOWANCES

LIST OF PROCESS CHART

CHART NO. TITLE

01 LAPPING WHEEL SHAFT

02 REGULATING WHEEL SHAFT

03 INTERMIDIATE SHAFT

04 BEARING HOLDER

05 LAPPING WHEEL

06 REGULATING WHEEL

1. INTRODUCTION

The dimensional and geometrical accuracy obtained by normal

method of machining, like turning, milling, etc. are limited. The geometrical

error includes circularity, cylindrical, flatness and parallelism of functional

surfaces. Also, the surface finish has vital influence on most important

functional properties such as wear resistant, fatigue strength, corrosion

resistance and power losses due to friction. Poor surface finish will lead to

rupture of oils films on the picks of micro irregularities, which lead to state

approaching dry friction, and results in excessive wear of rubbing surfaces.

Therefore, fine finishing processes are employed in machining the surfaces

of many critical components to obtained very high surface finish or high

dimensional and geometrical accuracies. Such processes include honing,

super finishing, burnishing and lapping.

2. TYPES OF SURFACE FINISH

There are four types of surface finishing methods, they are as follows.

1. Honing.

2. Super finishing.

3. Roller burnishing.

4. Lapping.

2.1 HONING

Honing is low velocity abrading process in which the stock is removed from

metallic or non-metallic surfaces by bonded abrasive sticks. It is a finishing

operation employed not only to produce high surface finish, but also to

correct out-of-roundness, taper and axial distortion in work pieces.

In honing, since a simultaneous rotating and reciprocating motion is given to

stick, the surface produce will have a characteristic crosshatch lay pattern.

Honing is employed very frequently for finishing of bores, but there arc

numerous external surfaces, which are honed to obtain required properties.

Some examples are gear teeth, valves setting, race of ball and roller bearing.

Moreover, bores of any size can be honed whether long, short, blind,

tandem, or with keyways. It is effective on almost any ferrous or non-ferrous

material in a hardened or soft conditioned.

2.2 SUPERFINISHING

Super finishing is an abrasive process utilizing either a bonded abrasive

stone for cylindrical surfaces or a cup wheel for flat and spherical surfaces.

It is, in a way, a fine honing operation. By this process it is possible to

achieve higher surface finish on components. In addition, Super finishing

removes chatter marks, feed spirals, grindings commas and other

imperfection left by the previous grinding operation.

Stock removal in the Super finishing process is of the order of 0.005 to

0.025 mm on diameter. The surface produce will have a mirror like finish,

and surface finish obtained is of order of 0.05 to 0.2 micrometers.

In super finishing, the stones makes contact with the work piece over a large

area. The stone is given an oscillating motion in the axial direction and

simultaneously the job is given a rotary motion about the axis. As feed

movement could also be given, if necessary. The contact pressure exerted by

the stone on the work piece is very low, and it normally depends on material

being machined. Some time a light pressure is used in the beginning and

when the operation near completion, the pressure is increased to about 3

Kg/cm". The low operating pressure does not cause any appreciable

temperature rise and has a tendency to improve (he geometrical shape of the

part.

2.3 ROLLER BURNISHING

Roller burnishing is cold working process, by which improvement in surface

finish; dimensional accuracy and work hardening can be effected, without

the removing metal. It is finishing operation, and normally done on parts

which arc turned, bored, reamed, or ground. Any ductile or malleable

material with hardness less than 40 HRC can be successfully burnished.

Surfaces that could be burnished include external and internal cylindrical

surfaces, external and internal tapered surfaces, spherical surfaces and

circular flat surfaces. Machines normally used for burnishing operations can

be drill presses, lathe, boring machine, automatic bar chucking machines,

multispindles machines, or even special purpose transfer machines.

Instead of reaming, roller burnishing is some time used for finishing, but it is

most often used to supplement reaming or boring. Since roller burnishing

improves the surface hardness, metals that work hardens rapidly must be at

lower hardness before roller burnishing is done. The depth of surface

hardness obtained by roller burnishing varies from 0.1 to 0.7 mm.

2.4 LAPPING

Lapping is a low pressure abrading process, which is employed as precision

finishing operation to:

Improve geometrical accuracy

Achieve high dimensional accuracy

Refine surface finish

Ensure close fit between mating parts

Lapping is perform manually or by machine by charging a lap made of

material softer than the works piece with abrasive particles and rubbing with

over the work piece surface with slight pressure. Special lubricating and

bonding agent, known as vehicles, are used during the process

Hand lapping is done with abrasive powder as the lapping medium, where as

machine lapping is done either with abrasive powder, or with bonded

abrasive wheels. In both manual and machine lapping operations, the quality

of surface finish and the extent of dimensional accuracy that can be achieved

mainly depend on-

1] The type of lap material. 2] Type of lapping medium. 3] Speed of lapping

motion and pressure applied. 4] Material to be lapped.

Various lapping methods are divided in two main groups.

3. Types of lapping

1] Hand lapping. 2] Machine lapping.

3.1HAND LAPPING

3.1.1 LAPPING FLAT SURFACES

Hand lapping of flat pieces is perform by rubbing the parts over the

accurately finish flat surface of a master lap, accomplishing the abrading

action by a very fine abrasive powder mixed with vehicle. The work is

moved relative to master lap, along an ever changing path to ensure uniform

abrasive of both work and lap, and to eliminate, as far as possible, parallel

grain marks. A suitable abrasive should be selected for the works and it must

used sparingly as its excessive used will increase the wear op lap.

In lapping flat surfaces, fairly thick lapping blocks made of soft close-grain

cast iron, are used as a lap. For rough works, lap works better if it surface is

serrated. The lapping compounds collects in the grooves and continuously

rolls in and out as the work is moved, getting between the plate and work,

and it is crush into the cast iron, thus charging it toughly in short time. Cast

iron Laps, with plane flat surfaces, are used for work pieces, which have

been ground on a surface grinder.

Manual lapping of flat surfaces demands high operating skill since the

proper lapping speed and pressure depend upon his feel and judgment. Ring

lapping is simplest method of lapping external cylindrical surfaces. Ring

Laps are generally made of close grain cast iron.

Ring lap should always be shorter than the work piece and if the size

permits, it should have adjustable slots. The bore of ring lap should be very

close to size of work. Precision adjustments are normally made with the

used of closing and expanding screws provide on the lap. In some design, to

cover a range of diameters, a single holder with a set of interchangeable

bushes is employed. The work to be lapped is held in the chuck of lathe and

rotated, while the split ring lap held over the cylindrical surface is

reciprocated. The abrasive and vehicle are fed through the slots in the ring

lap and, when reciprocated, the lap should overrun the work by about one

third of its length.

Ring lapping recommended for plug gauges made in small quantities and for

precision machine spindle where great roundness accuracy is required.

External threads can also be lapped by this method. The laps [fig 01] are the

once which have an interchangeable threaded bush corresponding to the

external thread to lapped, with provision for precise adjustment.

Ring lapping when performed by a skill operator, offers two advantages over

machine lapping:

1} The out-of-roundness error can be corrected to higher degree than in

machine lapping.

2] The parts can be produced to extremely close tolerances.

Since ring lapping is tedious and calls for higher skills of the operator, it

should be considered only when:

1] There is too much of out of roundness in the work piece

2] The lot size is small

3] The works piece has key way or flats or similar interruptions on the

surface

4] The work piece has two or more different diameters to be lapped.

3.1.2 LAPPING; OF INTERNAL CYLINDRICAL SURFACES

Holes or bores are lapped using solid or adjustable laps. Rolling the laps on honing

machines, lathes or polishing heads, while the works piece is reciprocated over it does

the tapping operation.

Solid lap for larger sizes are generally made of cast iron, For the smaller sizes, steel or

hard brass is used. The laps are ground straight and round. Helical grooves cut on the

surface provide clearance for feeding abrasive and vehicles.

Adjustable laps are suitable for all plasters of hole lapping. Design of adjustable laps

for hole lapping include laps with partial split sleeves with screws expansion devices,

and laps with replaceable copper sleeves on taper mandrels for expansion of sleeves

(tig.02). Ring gauges arc examples of apart that are hip to extremely accurate

dimension with adjustable lap.

To obtain good results with lapping holes, the length of the lap should longer than the

work. The lap makes contact with the full length of the hole, thus preventing the

tendency to follow any already existing curvature. In internal cylindrical lapping,

virtually no material is removed, as the ease in honing. Sometimes, lapping follows

honing has touch up operation. The widest application of internal lapping is in match

lapping. In this, the male or female parts are hipped together to obtain the matched

pairs.

3.2 LAPPING MACHINES AND MACHINE LAPPING

Lapping machine has facilitated the machining of economic batch quantity. On

lapping machine, three types of lapping media arc used. Machines using metal laps

and abrasive powder mixed with suitable vehicle are employed where extreme

accuracy is required. Machines using bonded abrasive wheels are suitable for

commercial production. More recently, machines which employ abrasive paper or

cloth as lapping medium have also been developed.

Lapping machines can be mainly classified in to three types:-

Machine using cast iron or bonded abrasive circular plates as laps for lapping

cylindrical and Hat work pieces.

Machines using cast iron or bonded abrasive wheels as laps working on centre less

lapping principle for lapping cylindrical work pieces.

Machines similar to honing machine used for lapping internal cylindrical surfaces.

3.2.1 VERTICLE LAPPING MACHINE WITH TWO CIRCULER

PLATES

This type of lapping machine consists of two opposed, heavy east iron or bonded

abrasive circular plates held in vertical spindles (12.17). When cast iron laps are used,

the lower lap drive the work pieces when the former is rotated at a speed of not more

than 100m/min. the upper lap is held stationary but is free to float in the vertical

direction . It rest upon the work during the lapping operation, thus applying the

constant pressure.

The work pieces are retained between these laps in slotted plates and made to rotate

and slide. The lower lap regulates the speed of rotation. The abrasive is used with a

paste type vehicle and is applied on the lap before the cycle is started. Oil or kerosene

is added during the cycle to prevent drying of vehicle.

Very fine finish of the order of 0.02micrometcr and tolerance of 0.5 micrometer are

feasible when cast iron laps are used. When bonded abrasive laps are used, both laps

are rotated. The laps are rigidly supported on the spindles and separately driven at

speed higher than that used for cast iron laps. Kerosene or similar lubricant is used as

coolant as well as to Hush the chips. Lapping takes place al a faster rate and

consequently, the machine does not produce extreme accuracy possible with

machines using cast iron laps. Since bonded abrasive laps must be dressed with

diamond tools, it is not possible le to make them as flat as cast iron laps on which the

machine generates flatness. Both cylindrical and flat lapping operation can be done on

this type of machine with the same arrangement of lapping plates.

Machine lapping between plates is an economical finishing method for parts like plug

gauges, piston pins, small valve piston, roller bearing, diesel injection valve, plungers

etc. a work piece with a diameter greater than its length is difficult or impossible to

lap between plates.

3.2.2 MACHINE WITH SINGLE ROTATING CIRCULAR PLATE LAP

Machines using single rotating cast iron lap are used for lapping. Work pieces placed

in carrier rings are given in a cycloid motion to distribute the wear evenly on the lap.

Pressure plates with or without air cylinders arc used to apply pressure, particularly

for light work pieces. The lap for single plates machines is usually made of cast iron,

For lapping with diamond powder, copper or other non-ferrous metals are preferred

because these metals readily become charge with abrasive,

The pressure plate and lap must be lapped together if work pieces are to be held to

close tolerance of thickness, flatness or parallelism,

Machine of this type, on which feeding, discharging and gauging of work piece is

performed in an automatic cycle, have been developed for production work. Such

machines have an automatic control of facility for the flow of lapping compound, and

they can also be equipped with pneumatic cylinder lifts for raising and lowering the

carrier rings and pressure plates. This speeds up loading and unloading of work piece.

3.2.3 CENTRELESS ROLL LAPPING MACHINE

A centre less roll lapping machine is designed for processing a single piece at time, and it

is used for lapping plug gauges, measuring wires, and similar straight or taper cylindrical

objects.

The machine [fig,04] consists of two cast iron rolls and a reciprocating device for holding

down the work piece and controlling the size. The diameter of larger roller, known as

lapping roller, is twice that of regulating roller. In opera I ion abrasive compound is

applied to the rolls and both the rolls are rotated in the same direction. Because of its

increased surface speed over that of the work, the lapping roller creates a lapping action.

The work piece feeds across the rolls at very slow rates as the 1200 V-Notched fiber stick

is uniformly reciprocated over (lie entire surface. This machine needs less time to be

setup and is suitable for lapping small quantities of jobs.

Workpiece

3.2.4 CENTRELESS LAPPING MACHINE

A center less lapping machine works on same principle as that of center less grinding

machine. But the lapping machine is constructed to produce very high roundness

accuracy and fine surface finish. The bonded abrasive lapping and regulating wheels

are much wider than those used for centerless grinding to allow the work to remain

longer in abrading contact and to receive final finish. The lapping wheels speed vary

from 175m/min to650m/min, depending upon the surface finish and production

requirement, where as the regulating wheels speed range between 70m/minto

175m/min.

The axis of regulating wheels and lapping wheel are not parallel normally, the axis of

regulating wheel is adjusted to an angle of 1 to 3° in the vertical plane depending

upon production and finish requirement and lapping wheel is generally adjusted to an

angle of 4° in the opposite direction. When the wheels are trued, they form a slight

hourglass shape, which causes a wrapper- round effect on the work pieces as it passes

between them. Also, wheels come in contact with the work piece at an angle to their

axes, which are different from axial line of contact of grinding wheel. This

arrangement eliminates lapping marks.

To obtain the fine finish of the order of 0.05 micrometer by centreless lapping,

the work piece requires three passes each with progressively finer lapping wheels.

Clean flow of coolant should be ensured through the operation.

During the first operation, a vitrified bond wheel of a 200P grad is used to

remove a maximum of 0.012mm of stock and surface finish of the order of 0.1 to 0.15

micrometer is obtained. For the second and third operations, the work piece is

supported on a rubber blade. During the second operation, to obtain a finish of 0.06 to

0.08 micrometer a maximum of 0.005 mm stock is removed, using resinoid bonded

wheel of C 320 T grade. For the third operation, resionoid bonded wheel of C 500 T

grade is used to remove less than 0.002 mm stock, which produces a finish of 0.05

micrometer.

3.2.5 LAPPING MACHINES FOR INTERNAL CYLINDRICAL

SURFACES

Lapping machine used for lapping internal cylindrical ssurfaces resemble honing

machines used for power stroking.

These machines reciprocate either the lap. Either solid or adjustable laps, in addition

to rotating the lap. Either the work piece or the lap, usually made of cast iron, is used.

Machines, which have one or two rotating spindles, such as drill presses or milling

machines, can be used for spindle against a stationary work piece. The work piece

axis. The lap itself must be heavy enough to provide the lapping pressure. When

machines with two spindles are used, the work piece is held in one spindle and

rotated, while the lap is held in the other spindle, which is free to rotate (fig. 05). The

spindle carrying the lap is including to the work spindle at a suitable angle. The axial

alignment must be accurate so as to generate a true radius. One of the spindles must

be so designed that it is free to slide to account for the wear of the lap and work piece,

and to apply the necessary pressure. The lap can be in the form of a ring with a

concave or convex rim.

4. LAPPING OF SLIP GAUGES

Lapping of slip gauges is carried out on special lapping machines after finish grinding the

gauge blocks to a reasonable accuracy in parallelism and thickness. with an allowance of

0.2 mm for lapping.

The lapping machine consists of two horizontal circular lapping plates of which the lower

one is fixed to the body of the machine whereas the upper one is supported freely from an

overhanging arm, which can be swung to one side so as to expose the gauge blocks.

When in use, the laps face each other and enclose between them a batch of 24 gauge

blocks, each resting freely en a circular hole in the steel plate, which acts as a guide. The

guide plate is toothed round its periphery and is driven by three pinions rigidly attached

to the ends of short cranks.

The lapping plates are held stationary while the gauges are carried round between them

by a rotary motion of the gauge plate. The guide plate is made to rotate about its axis,

while the gauges also move over a circular path. The ratio of the two circular motions is

such that the gauge blocks traverse different parts of the lapping plates at successive

revolutions distributing the wear uniformly.

The non magnetic cast iron plates with chequered working surfaces are machined and

scraped to a very high degree of flatness and then finished true by lapping together in sets

of three, taking them in consecutive pairs. During the truing operation they are charged

with a fine grade of emery, a small quantity of which is also added when lapping the

gauge blocks. Paraffin is used as lubricant.

In order to obtain a high degree of accuracy in parallelism and equality in thickness every

gauge block is transposed into a diametrically opposite position at integrals during the

lapping process. The lapping machine, which is driven electrically, can be set to perform

a given number of revolutions after which it stops automatically. A few gauge blocks arc

removed and measured and knowing the amount still to be removed, the machine is reset

to a further number of revolutions, after which the gauges are remeasured.

5. LAPPING FINISHES AND ACCURACIES:-

The dimensional accuracy, geometrical accuracy and finish that could be achieved by

various lapping process are given in table 01.

Property Dimensional Accuracy Geometrical accuracy Surface finish (CLA)

Method of lapping

Very fine

Fine Normal Very fine

Fine Normal Veryfine

Nine Normal

External cylindrical

IT I To

IT3 To

IT5 0.05 To

0.1 To

0.6 To 0.025 To

0.05 To

O.I To

surface IT2 IT4 0.1 0.5 1.0 01 0.1 0.2

lapping.

Internal IT3 IT3 IT4 0.05 0.1 0.05 0.005 0.05 0.1

lapping. To To To To To To To

IT6 0.1 0.5 0.5 0.5 0.1 0.4

Flat IT1 IT3 IT4 0.03 0.05 0.6 0.005 0.05 0.1

Surface To To To To To To To To To

lapping. IT3 IT4 IT6 0.05 0.5 1.0 0.05 0.1 0.4

Table no. (01) Lapping accuracy and finish

6. LAP MATERIALS:-

The most efficient lap material for machine lapping is cast iron. Other materials, such

as soft steel, bronze, brass and lead are also used in manual lapping. Generally, the

material of the lap should be softer than the work piece material; so that the loose

abrasive material gets embedded in the lap until it is fractured from the pressure of the

lapping action.

7. LAPPING MEDIUM:-

Of the manufactured abrasives, silicon carbide and fused alumina are the most widely

used lapping media for the majority of lapping operations. Softer abrasives such as

emery, garnet, unfuscd alumina and chromium oxide are used for lapping soft metals

or for obtaining highly reflective surfaces without any significant material removal.

7.1 SILICON CARBIDE

Silicon carbide is extremely hard, being rated at 9.5 on the Moll's scale. Its grit is

sharp and brittle, making it idle as an abrasive for many lapping application. Because

it continuously breaks down and produces new cutting edges, silicon carbide is used

for lapping hardened steel or cast iron, particularly when an appreciable amount of

stock is to be removed.

7.2 ALUMINIUM OXIDE

Aluminum oxide rotted on the Moh's scale is sharp but it is tougher than silicon

carbide. Fused alumina is generally used to improve the finish in lapping soft still and

non-ferrous metals. Unfused alumina removes stock efficiently, but it is specially

suitable for obtaining extremely fine finishes.

7.3 BORON CARBIDE

Boron carbide is next to diamond in hardness (9.75 Moll's scale) and it an excellent

abrasive for lapping. However, it is used only in some specialized applications such

as lapping of dies, gauges, etc, owing to it's high cost.

7.4 DIAMOND

Diamond is hardest of all materials and it is used mainly for lapping tungsten carbide.

8 VEHICLES

Vehicles or binders used for loose abrasive include wide Varily of compound. The

commonly employed vehicles are water-soluble cutting oils, vegetable oils, mineral,

petroleum gully and grease. A good vehicle should have following properties:

The abrasive particles should be held in uniform suspension during the operation.

It should not evaporate easily.

Temperature changes should not seriously affect the viscosity.

It should be non-corrosive when in contact with any metal.

The lapping compound made out of abrasive and vehicle must be capable of being

easily removed by normal cleaning method.

It should be non-toxic.

Vehicles with an oils or grease based usually used for lapping ferrous metals. For

specific application, where oil or grease would be objectional, such as in copper based

alloys and other non-ferrous metals, water-soluble vehicles arc used. These vehicles,

which are readily removed with water, are low viscosity

9. LAPPING SPEEDS AND PRESSURES

The most efficient lapping speed range between 100 to 250 m/min. for fine lapping of

bores, with lapping allowances of 0,03 mm, a maximum lapping speed of 50 m/min is

recommended. With higher lapping allowances, higher lapping speed could be

employed. For lapping flat surfaces, the cutting speed can be as high as 250 m/min.

The amount of pressure applied depends upon the nature of abrasive used, the

material being lapped, and surface finish required. While lapping with loose

abrasives, the pressure ranges between 0.1 and 0.3 Kg/cm2 for soil materials including

not ferrous metals and alloys and upto 0.7 Kg/cm2 for hard materials. Excessive

pressures may cause scouring of workpiece surfaces. A uniform pressure during the

lapping operation provides the best result.

10. ALLOWANCES FOR LAPPING

Lapping allowances should not be high. The higher the allowances more will be time

for lapping. Lapping allowances are influenced by many factors, the most important

of them being the type of operation done on the part before lapping.

For example, if part has to be lapped after grinding normally 0.005 to 0.03 mm

allowance is left. Similarly, after milling, 0.1 to 0.2 mm and after broaching up to

0.03 mm allowances maintained.

Another factor to be taken into consideration is the hardness of the parts to be lapped.

Harder the material, lower should be lapping allowance.

Allowances recommended for different materials are given in table below.

Materrial Lapping allowance, mmCast iron 0.2Aluminium alloy 0.1Soft steel 0.01-0.02Ductile steel 0.005-0.1Hardened steel 0.005-0.02Glass 0.03Cemented carbide 0.03-0.05Bronge 0.03Table no. (02)

Recommended lapping allowance

11. Design

Power selection -

Lapping is low pressure abrading process which is material is employed as a precision

finish operation; rate of material removed from work piece is very minor (in microns). So

that power required for this operation is also low,

So we have selected here 1 H.P. motor.

11.1 Motor Specification-Three phase, induction type. Power-1 H.P.-746 W. R.P.M. -

1440 RPM.

11.2 Pullies Selection: -

In lapping machine the lapping will spits very from 175 m/min. to 650 m/min., where

as regulating wheel speed range between 70m/min to 175m/min. here motor rpm is

1440 reduction have been done to achieve required speed.

First step reduction we know

N1D1= N2D2

D1=Motor pulley, mm

= 3 inch = 76.2 mm

N1 = Motor rpm = 1440

1440x76.2=N2xl27

N2=864

N2 = Intermediate shaft speed

D2 = Intermediate shaft pulley mm

=5 inch = 127mm

Second step reduction

N2 = Intermediate Shaft speed

N2D2=N3D3 D2 = Intermediate Shaft pulley

864x76.2=N3xl52.4 = 3 inch = 76.2 mm.

N3=432

N3 = Lapping wheel &

regulating wheel space

Now check for speed ranges where

For lapping wheel V = Lapping wheel speed, in m/min

D = Diameter of Lapping wheel

V= πd n = 150 mm

= 0.15m

= π x 0.15x432

=- 203.5m/min n = Lapping wheel speed in rpm

= 432rpm

(Lapping wheel speed ranges from 175m/min to 650m/min)

For regulating wheel

V=πdn Where

= π x0.75x432 d = Diameter of regulating wheel

= 101.78m/min = 75mm=0.075m

11.3 Calculation for length of belt:-

First step:-

We know,

L=2C + (π/2) (D+d) + {(D-d)2 /4C}

Where

C= Centre distance = 250mm

D = Diameter of large pulley

= 5 inch = 127 mm

d = Diameter of small pulley

= 3 inch = 76.2 mm

L = Pitch length

Second step:-

1) Lapping wheel:-

L = 2C + {π/2} {D+d} + {(D-d)2 / 4C}

= 3 x 345+(π/2) (152.4+76.2) + {(152.4-76.2)2 /4x345}

= 1053.29mm

= 1017.29 mm

= 40 inch.

So we have selected belt A40/1016

2) For regulating wheel:-

L = 2C + (π/2) (D+d) {(D-d)2 /4C}

= 3 x 345+(π/2) (152.4+76.2) + {(152.4-76.2)2 /4x345}

= 1053.29mm

= 1017.29 mm

= 40 inch.

So we have selected belt A40/1016

1.4 Calculation for belt tension:-

1) For first step:-

We know that for V belt

T1/T2= еδα/sinθ/2………………………………(A)

Where T1 = tension in tight side in N

T2 = tension in slack side N

δ = coefficient of friction = 0.3

α = Wedge angle = 400

α = 180 – 2 sin–1 {(D-d)/2C

= 180 – 2 sin-1 {(127-76.2)/2x265}

= 30

Putting this values in equation (A)

T1/T2 = е (0.3X2.938)/sin (40/2)

T1/T2 = 13.893

T1 = 13.893 T2…………………………….(1)

Also

Power = (T1- t2) x V

Where

V = Linear speed, m/sec

= πdn/60 = (πx0.0762x1440)/60

= 5.745m/sec

373 = (T1-T2) x 5.745

T1 – T2 = 64.926 ……………………………..(2)

Solving equation (1) & (2) we get

T1 = 69.95 = 70N

T2 5.35 = 6n

2) For second step

For lapping wheel

For V belt

T1/T2 = е δα/sin(θ/2)

α = 180 – 2sin-1 {(D-d)/2C}

= 180 – 2 SIN-1 {(152.4-76.2)/2x345}

= 167.3190

= 2.92 rad.

T1/T2= е (0.3x2.938)/sin(40/2)

T1=12.952…………………………….(1)

Also power = (T1-T2) x V

Where V = πd n/60 = 3.447m/sec

373 = (T1-T2) x 3.447

T1-T2 = 108.21 ……………………….(2)

Solving equations (1) & (2) we get

T1 = 117.26 =118N

T2 = 9.053 = 9n

For regulating wheel:-

For “V” belt

T1/T2 = е fα/sin(θ/2)

α = 180 – 2sin-1 {(D-d)/2C}

= 180 – 2 SIN-1 {(152.4-76.2)/2x345}

= 167.3190

= 2.92 rad.

T1/T2= е (0.3x2.92)/0.342

T1 = 12.952 T2 …………………………..(1)

Also

Power = (T1-T2) x V (V=(πdn)/60) = 3.447

373 = (T1-T2) x 3.447

T1-T2 = 108.21 ……………………………..(2)

Solving equation (1) & (2) we get

T1 = 117.26 = 118 N

T2 = 9.053 = 9 N

11.5 Shaft design :-

11.5.1Intermediate shaft :-

Here shall goes into twisting and bending.

According to A.S.M,E code, The permissible shear stress for shaft with out key way

is taken as 30% of the yield strength in tension or 18% of the ultimate tensile strength

of material, which ever is minimum.

ζd=0.3Syt

ζd = 0.18 (whichever is minimum)

For twisting and bending

ζd = (16/7πd3)/((Kbmb)2+(Kt.mt)2...............,...(A)

Where

Kb = combined shock and fatigue factor to bending moment =1.5

Kt = combined shock and fatigue factor to torsion moment = 1

Shaft made of plain carbon steel 55C8

(Sut = 720 N/mm2 and Syt - 460 N/mm2)

ζd = 0.3xSyt

= 0.3 x460 -138 N/mm2

ζd = 0.18xSut

= 0.18 x 720

= 129.6 N/mm2

The lower of two is 129.6 N/mm2

Therefore

ζd = 129.6 N/mm2

Calculation for bending and torsional moment: -

a) Bending moment: -

Taking moment about A

174 RB- 76 x 227- 127x 53 - 127 x 98 = 0

RB = 209.362 N

ΣMB = 0

-127 x 272 - 127 x 227 - 174 x RA - 76 x 53 = 0

RB = 387.362 N

ΣMB = 127 x 45 = 5715 N mm

ΣMB = -127x98 -127x53

= 19177 N mm.

= - 76 x 53 - 4028 N mm.

Maximum bending moment occurs at A, that is 19177 N mm.

For torsional moment

Power = (2πNT)/60

373 = (2π x 864 x T)/60

T = 4.122Nm

T = 4122.55 N mm.

Putting all the values in the equation (A).

ζd = 16/(πd3) / {(Kbmb)2 + (Ktmt)2}

129.6= 16/(πd3) / {(1.5 x 19177)2 + (1 x 4122.55)2

d= 10.45mm.

So we selected the diameter for intermediate shaft d - 16 mm.

11.5.2 Shaft design form lapping wheel:-

The procedure is same as we followed. Lapping wheel shaft is also made of plain carbon

55C8 (Sut = 760 N/mm2 & Syt = 460 N/mm2).

Permissible shear stress (ζd) = 0.75 x 129.6

= 97.2 N/mm2

Calculation for bending moment and torsional moment:-

Bending moment:-

Taking moment about “A”.

127 x 98 + 224 x RB = 0

RB = -55.562 N.

Taking ∑MB = 0

127 x 322 – 224 x RA = 0

RA = 182.562 N.

Maximum bending moment occurs at “A”.

MA = 127 x 98 = 12446 N mm.

Torsional moment:-

Power P - (2πN T)/60

373 - (2π x 432 x T)/60

T = 8.245110 Nm.

T = 8245.11N mm.

Putting all these values I the equation given below.

ζd = 16/(πd3) /{(Kbmb)2 + (Ktmt)2}

97.2 = (16/πd3) x / {(1.5xl2446)2 + (l x 8245.11)2}

d = 10.22mm.

We have selected diameter for lapping wheel shaft is 16 mm.

11.5.3 Shaft design for regulating wheel shaft:-

Here shaft is made of 55C8.

Therefore ζd = 97.2 N/mm2.

Calculation for bending moment and torsional moment:-

Bending moment: -

Taking ΣMA - 0

224 RB+ 127 x 53 = 0

RB = 30.044 N.

Taking ΣMB = 0

127x277.224 x RA -0

RA = 157.049 N.

Maximum bending moment occurs at "A" =127 x 53 = 6731 N mm.

Putting all these values in the equation given below.

ζd = 16/ (πd3) /{(Kbmb)2 + (Ktmt)2

97.2 = (16/πd3) x /{(1.5 x 6331)2 + (1 x 8245.11)2}

d = 8.8mm.

We have selected diameter for regulating wheel shaft that is "d"= 18 mm.

Lapping Machine

11.6 Bearing selection: -

We know that L = (60 x n x Lh)/106 Where

L = bearing life in million revolution.

Lh = bearing life in hours = 15000.

N = revolution per minute.

L = (60x864xl5000)/106

L = 777.6 million revolution.

AlsoC-Lpl/3 .

Where

C = dynamic load capacity

C = 777.6 x 412.5l/3

C = 5788.47 N.

So we have selected bearing 6004. Dynamic load capacity is 7350 N.

Inner diameter = 20 mm.

Outer diameter = 42 mm.

B = 20.

PROCESS CHARTS

12.1 Process chart

Part name: - Lapping wheel shaft. Material: - Plain carbon steel

Quantity: - 01 Raw material size:-φ25x325L

Sr. No. Operation Machined used Tool used Time

(Min)01 Cutting to the length

(325 mm.).

Power hacksaw. — 15

02 Setting, facing & Centre

drilling. (Both side).

Lathe machine. Single point

cutting tool &

centre drill.

30

03 Holding the job between

centre & turning for φ23

mm &φ20 mm up to

length 4 mm & 1 6 mm

respectively, as per

Drawing (both side).

Lathe machine. Single point

cutting tool.

40

04 Grooving. Lathe machine Parting tool. 20

05 Turning of φ18 & φ16

up to length 45 mm

respectively.

Lathe machine. Single point

cutting tool.

25

2.2 Process chart

Part name: - Regulating wheel shaft Material: - Plain carbon steel

Quantity: - 01 raw material size:-φ25 X 285 L

Sr. No. Operation Machine used Tool used Time

(Min)

01 Cutting to the length 285

mm.

Power hacksaw. — 15

02 Setting, facing & centre

drilling (both side).

Lathe machine. Single point

cutting tool.

30

03 Holding job between

centres & turning for φ23

& φ20 mm up to length 4

mm & 1 6 mm

respectively.

Lathe machine. Single point

cutting tool.

40

04 Grooving for circle. Lathe machine. Parting tool. 20

05 Turning for φ1 8 up to

length 45 mm.

Lathe machine. Single point

cutting tool

20

12.3 Process chart

Part name: -Intermediate shaft Material:- Plain carbon steel

Quantity:- 01 Raw material size:- 25x325L

Sr.No. Operation Machine used Tool Used Time

(Min)01 Cutting to the length 325

mm.

Power hacksaw 15

02 Turning for 23 mm &

20 mm upto 4 mm &

16 mm respectively.

Lathe machine Single point

cutting tool.

30

03 Grooving for circle as

per drawing.

Lathe machine. Parting tool. 20

04 Turning for 1 8 mm

upto length 45 mm.

Lathe machine. Single point

cutting tool.

15

05 Turning for 1 8 and

1 6 mm upto 45 mm

respectively.

Lathe machine. Single point

cutting tool.

20

12.4 Process chart

Part name: - Bearing holder

Quantity: - 06

Material: - Mild steel.

Raw material size; - 20x50x70

Sr. No. Operation Machine used Tool used Time

(Min)01 Cutting to the length

70mm

Power hacksaw — __

02 Marking for drilling

through out.

— Markers, scale,

punch &

hammer etc.

10

03 Drilling for 36 mm,

through out.

Lathe machine. Boring tool. 20

04 Boring of 42 mm &

36 mm upto length 1 6

mm & 4 mm

respectively.

Lathe machine. Boring tool. 40

05 Chamfering. Lathe machine. Single point

cutting tool.

10

12.5 Process chart

Part name: - lapping wheel Quantity: - 01

material; - Mild steel niw material size: - φ153 x 200 mm (pipe)

Sr. No. Operation Machine used Tool used Time

(Min)01 Cutting to the size 200

mm.

Gas cutting. 15

02 Setting, facing both

sides.

Lathe machine. Single point

cutting tool.

20

03 Boring φ147 mm up to

length 6mm as per

drawing (both side).

Lathe machine. Boring tool. 20

04 Chamfering (3x3) both

sides.

Lathe machine. Single point

cutting tool.

15

12.6 Process chart

Part name: - regulating wheel. Material: - mild steel

Quantity: - 01 raw material size: - φ88 x 180 (pipe)

Sr.No. Operation Machine used Tool used Time

(Min)

01 Cutting to the size 180

mm.

Gas cutting. 15

02 Setting, facing both sides. Lathe machine. Lathe machine. 25

03 Boring φ82 mm up to

length 5 mm both sides as

per drawing.

Lathe machine. Boring tool. 20

04 Chamfering (3x3) both

sides.

Lathe machine. Single point

cutting tool.

15

13. COST SHEET

Sr. No. Name of

component

Material Quantit

y

Dimentions

(mm)

Weight (gm) Rate of raw

material

Machining cost Rs. Total cost Rs. Machine used

Lapping wheel C.1 01 φ153x200 3500 175 150 Lathe

02

A1"*

Regulating

wheel

C.I 01 φ88x200

φ152.4

1900 95 140 Lathe

0.5 Pulley MS 06 φ127 ---- ---

φ76.2

φ30

04 Intermediate

shaft

Plain carbon 01 φ25x325L 2600 156 120 Lathe

steel

Sr.

No.

Name of

component

Material Quantity Dimentions (mm) Weight

(gm)

Rate of

raw

material

Machining

cost Rs.

Total Cost Rs. Machine used

04

05

Bearings

Bearing

holder

M.S

M.S

04

04

φ42 x 20

φ42

900

1100

56 240 ---- -----

Lathe

06

07

Frame

Belt

C.I

Rubb

er

01

03

500x400x850

40A 36A

8500 425 400 Welding m/c

08

09

Motor

Miscell

aneous

_____

14. CONCLUSION

A lathe machine alter turning a cylindrical purl finishes ihe job, hut this finish is not

super finish. So to obtain the super finish part Ihc lapping machine is introduced. This

lapping machine gives the superfmish in micro meter scale. The plug gauges, m in micro

meter scale. The plug gauges, measuring wires, various tools can also be superfmish with

the help of lapping machine.

TECHNICAL SPECIFICATIONS

ELECTRIC MOTOR:-

3-PHASE INDUCTION TYPE

POWER 1-H.P = 746 W

SPEED = 1440 R.P.M.

15. REFERENCES

Production Technology By H.M.T.

Production technology By R.K.Jain

www.google.com

www.howstuffworks.com