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What is lapping?

Lapping is a type of finishing process which is carried out with the help of loose abrasives. In this finishing process, surface smoothening is achieved by the abrasive grains which are supported by the lap, which functions as a cutting tool shank. Ceramic machining, Brittle material machining, and Glass machining are some of the applications of the lapping process.

The principle of lapping is based on the cutting power of either a free abrasive grain in a carrier or a fixed abrasive particle within a composite lapping plate matrix. The lapping plate on which a slurry medium is applied moves under the workpiece/job surface while the workpiece/job rotates on the lapping plate. The uniform abrasive layer forming between the lapping plate and the workpiece gradually removes material from all the contacting areas simultaneously, putting very little stress into the workpiece. Ultimately when the whole workpiece has been lapped, the shape of the lapping plate is imparted on the workpiece. For this reason, flat lapping machines are capable of generating incredibly flat workpieces.

It seems as if the abrasive grains are working in a free movement which is not entirely true. Depending on the lapping process used, the abrasives are either freely rolling or sliding between the workpiece and lapping plate. In diamond lapping, the abrasive particles become fixed within the machined medium. The material removal takes place slowly due to the movement of the lapping plate with respect to the workpiece.

Lapping is a process that requires precision, hence it takes quite a bit of time. In order to speed up the process, the two-step operation can be used. The first step is to remove material and create flatness and the second step is to produce a specific surface roughness (Ra value). This is only necessary when our desired Ra is below 0.05µm and we need to remove a lot of material.

With conventional lapping, abrasives such as aluminum oxide or silicon carbide are applied in a carrying medium (e.g Oil) onto a hard-worked surface (e.g. cast iron). The particles can’t be pressed into the surface and remain secured there, so they roll and displace freely in all directions. They hammer small particles out of the workpiece, imparting deep deformations. This phenomenon takes place as the free-moving abrasive particles are not able to produce a real scratch on the component surface. Instead, it hammers out small pockets.

Typically the lapping process is used to:

-Produce a fine surface finish

-Produce sealing surfaces

-Produce sharp cutting edges

-Produce flat stress-free surfaces

-Produce a datum face

-Improve the wear-resistant properties of surfaces