LAPPING PROCESS

Lapping and polishing are precision finishing processes which involve different mechanical arrangements. Used for many materials such as glass, ceramic, plastic, metals and their alloys, sintered materials, stellite, ferrite, copper, iron, steel and etc. Lapping is a slow material removal operation.  Though lapping tends to decrease the original surface roughness, it main purpose is to remove material and modify the shape. Lapping is used primarily to improve form accuracy rather than to reduce surface roughness. Polishing on the other hand deals with material surface finish and plays little attention to form accuracy.

The relative speeds in lapping and polishing are much lower than in grinding. Consequently the concentration of energy in the contact area is much lower than in grinding.

POLISHING PROCESS

Polishing is a surface smoothing operating. Polishing typically involves removing or smoothing out grinding or lapping lines, scratches, and other surface defects in order to decrease the surface roughness of material. Emphasis is placed in obtaining best surface finish without much regard for shame and form accuracy. As well as removing damage (such as microcarcks, voids, and inclusions) caused by previous machining operations such as cutting and grinding.

LAPPING, GRINDING, & POLISHING MEDIA

 There is a large variety of abrasives than can be used for lapping, grinding, & polishing. Below is a description of various lapping, grinding, and polishing media/powders that is typically used for most lapping, grinding, and polishing operations.

Diamond – typically used for ultra hard materials and tungsten carbide. A disc embedded with diamond will cut fast and produce fine finish. Diamond is the hardest material known to man kind.

Cubic Boron Nitride (CBN) – typically used for lapping ferrous metals, including 52100 bearing steel, cast iron, tool steel, stellite, super alloys, and occasionally ceramic materials.

Aluminum Oxide – for general lapping, grinding, & polishing with low surface roughness. Typically used for high tensile strength materials, rough lapping operations, hardened gears, ball bearing grooves, and lapping operations where pressure can be exerted to break down the crystals.

Silicon Carbide – fast stock removal  for hard to soft materials. Typically used for rough lapping and grinding operations, forged or hardened gears, valves, tool room work and general maintenance where polish is not essential.

Boron Carbide – for use with ceramic, carbide, and other hard materials

Calcined Alumina – for use with metals, optics, silicon wafers, and other semiconductor materials

Unfused Alumina (hdrate-calcined) – Relatively soft and used for polishing. Unfused alumina abrasives are recommended for lapping and polishing of harder materials (Rockwell C 45-63). The shape, unlike the blocky crystals, is composed of flat or plated crystals with a thickness about one six the diameter. Unused aluminas allow more equal pressure to be distributed over a large surface area than the fused ones because of their plated shape. The disc shaped particles work with a shaving action rather than the rolling and gouging action of blocky abrasives and are less likely to produce deep scratches on the workpiece.

Abrasive Size & Distribution

The size and size distribution of abrasive plays an important role in surface obtained by lapping, grinding, & polishing. The size of abrasive is directly proportional to material removal rate and surface roughness. Larger grain sizes have a higher material removal rate. However smaller abrasive particles will produce a lower surface roughness.

Another factor than may affect your lapping, grinding, & polishing operation is the concentration of abrasive used. Number of abrasive grains in contact with surface of material being worked on. Change in abrasive concentration will affect distribution of load. Hence increasing the number of grins, load per grain decreases due to larger number of contact points.

UKAM Industrial Superhard Tools   Division of LEL Diamond Tools International, Inc.

28231 Avenue Crocker, Unit 80  Valencia, CA 91355  Phone: (661) 257-2288  Fax: (661) 257-3833

e-mail: lel@ukam.com