Lapping-Honing-FITTER ONLINE NOTE

1. LAPPING:-

i)- Lapping is a precision finishing operation carried out using fine abrasive materials.

ii)- There are some jobs which need more accuracy and finishing even after machining and grinding. So for that the process adopted is called lapping. 

iii)- This process lapping compound and lapping tool is used.

iv)- Lapping is used on many jobs like piston pins, piston rings and gauge blocks etc.

Advantages of Lapping:-

(a)- Job gets super quality polish and finish.

(b)- To raised the dots on the small points.

(c)- Surface becomes so smooth and fine that both sides have vacuum.

(d)- Less chances of rust.

(e)- Job can be moved on high speed.

(f)- Required fit can be obtained.

2. Lapping Process:-

The lapping Process are Two types a)- Hand lapping of flat surfaces, b)- Wet and dry lapping.

a)- Hand lapping of flat surfaces:- 

i)-  Flat surfaces are hand- lapped using lapping plate.

ii)- made out of close grained cast iron.

iii)-  The surface of the plate should be in a true plane for accurate results in lapping.

iv)- The lapping plate generally used in tool rooms will have narrow grooves cut on its surface both lengthwise and crosswise forming a series of squares.

v)- While lapping, the lapping compound collects in the sharping teeth and rolls in and out as the work is moved.

vi)- Before lapping of the component, the cast iron plate should be CHARGED with abrasive particles.

vii)- When carrying out fine lapping, the surface should be kept moist with the help of kerosene.

b)- Wet and dry lapping:-

i)- In this process Lapping can be carried out either wet or dry.

ii)- In wet lapping there is surplus oil and abrasives on the surface of the lap.  

iii)- In dry method the lap is first charged by rubbing the abrasives on the surface of the lap.

iv)- After lapping The surplus oil and abrasives are then washed of.The abrasives implanted on the surface of the lap will only be remaining.

v)- The implanted abrasives act like a fine oil-stone. when metal pins to be lapped are moved over the surface with light pressure. 

vii)- while lapping, the surface being lapped is kept soaked with kerosene or petrol.  

viii)- Surfaces finished by the dry method will have better finish and appearance. 

3- Laps:-

i)- The material used for making laps should be softer than the work piece being lapped. 

ii)- It helps to charge the abrasives on the lap. 

iii)- If the lap is harder than the work piece, the work piece will get charged with the abra- sives and cut the lap instead of the work piece being lapped. 

iv)- Laps are usually made of: a)– close grained iron, b)– copper, c) – brass or lead

a)– close grained iron:-

i)- The best material used for making lap is cast iron, 

ii)- It cannot be used for all applications.

b)– copper & brass:- 

i)- When there is excessive lapping allowance it will be used.

ii)- Copper and brass laps are preferred as they can be charged more easily and cut more rapidly than cast iron.

c)- lead:-

i)- Lead is an inexpensive form of lap commonly used for holes. 

ii)- Lead is cast to the required size on steel arbor. 

iii)- These laps can be expanded when they are worn out. 

iv)- It Charging the lap is much quicker.

4- Lapping abrasives:-

 i)- Abrasives of different types are used for lapping.

ii)- The commonly used abrasives are: a)– Silicon Carbide , b)– Aluminium Oxide , c)– Boron Carbide and d)– Diamond.

a)– Silicon Carbide:-

i)- This is an extremely hard abrasive.

ii)-   Its grit is sharp and brittle.  

iii)- While lapping, the sharp cutting edges continuously break down exposing new cutting edges.  

iv)- Due to this reason this is considered as very ideal for lapping hardened steel and cast iron, particularly where heavy stock removal is required.

b)– Aluminium Oxide:-

i)-  Aluminium oxide is sharp and tougher than silicon carbide.  

ii)- Aluminium oxide is used in un-fused and fused forms.  

iii)- Un-fused alumina (aluminium oxide) removes stock effectively and is capable of obtaining high quality finish.

iv)- Fused alumina is used for lapping soft steels and non- ferrous metals.

c)– Boron Carbide:-

i)- This is an expensive abrasive material which is next to diamond in hardness.

ii)-  It has excellent cutting properties and high cost.

iii)- It is used only in specialized application like dies and gauges.

d)– Diamond:-

i)-  This being the hardest of all materials.

ii)- It is used for lapping tungsten carbide.  

iii)- This laps are also prepared for accurately finishing very small holes which cannot be ground.

NOTE:-Abrasive of varying grain sizes from 50 to 800 are  used for lapping, depending on the surface finish required on the component.

5)- LAPPING ALLOWANCES:-

i)- Normally lapping allowance is maintained from 0.005 to 0.001mm, but coarse grits laps from 80 to 120 numbers have allowance of 0.02 mm.

ii)- fine grit laps from 150 to 200 numbers have 0.001 to 0.02 mm allowance.

6)- METHOD OF LAPPING:-

i)- The method of lapping is like this that first of all apply oil on the job and coated with thin layer of charging powder or paste.

Then moved the lap turn by turn forward -backward and left-right with hand. 

iii)- This process is continued till the accurate surface and shining is obtained. 

iv)- Lapping process can be performed with hand or machine.

v)- Heavy work lapping like drilling and boring is done by machine, now-a-days special lapping machines are used for lapping.

Refer for this post knowledge about

http://anilitistudy.blogspot.com/2020/05/grinding-1-grinding-is-finishing.html

7)- Honing:-

i)- Honing is a super finishing process carried out using abrasive sticks for the removal of stock from metallic and non-metallic surfaces.

ii)- Honing is used for finishing of bores in ferrous and non-ferrous materials.

iii)- Honing can be done in hardened or un-hardened state.

iv)- Bores of any size, length, blind or through, tandem or interrupted surfaces can also be honed.

v)- Honing stones consist of particles of aluminium oxide, silicon carbide or bonded together with vitrified clay, cork, carbon or metal.

v)- Honing process helps to: a)- produces high surface finish, b)- corrects the profiles of cylindrical surfaces, c)- removes taper.

Working principle:-

i)- The honing tool with abrasives mounted on it is held on the spindle of a machine which can be rotated in its axis.

ii)- As the spindle rotates, a reciprocating motion is also given to the tool.  

iii)- The surface produced will have a cross hatched pattern. 

iv)- This pattern of the surface texture provides better lubrication in cylindrical bores.