Individual Piece Lapping

Individual Piece Lapping

Individual Piece Lapping - In individual piece lapping, loose abrasives held in suspension in a vehicle are rubbed against the workpiece by means of a special tool called a lap. Laps are made of soft materials, such as non ferrous metals and alloys, plastics, mirror glass and others.

Cast iron is also used for making laps. Loose abrasives used in lapping (lapping media) are natural corundum, standard and white aluminium oxide, chromium oxide, diamond powder and boron carbide. The size of the abrasive grains effects the metal removal and surface finish in lapping.

Kerosene, petrol and machine oils are used as the vehicle (sometimes called the lubricant) which is mixed with the lapping medium.

By having the lap softer than the work, the abrasive particles become embedded in the lap and cause the greatest wear to occur on the hard surface i.e. the work.

The lapping operation consists of having the work surface in contact with lap, (with, in between abrasive) the two having moti0n with one another in such a way that fresh contacts are constantly being made. In lapping, after the lapping medium is placed between the lap and the workpiece, the two are rubbed together by moving one of these over the other which is stationary.

It is important that the lap and the work should have their relative rubbing movement along an ever changing path and not repeated along the same path.

Individual piece lapping is most effective on hard metals or materials. It is used to produce optically flat surfaces, to produce accurate planes from which other planes can be located (as for gauge blocks), and to finish parallel faces. A few examples of hand lapping are those of surface plates and engine valve and valve seat (matched piece lapping) etc.