The selection of a finishing process for a particular application depends on part shape and size, ease of fixturing, requirements concerning the acceptable shape errors. Lapping is the basic flattening process which allows for achieving a high degree of flatness and parallelism of machined parts. It is still one of the most common processes to flatten the sliced silicon wafers. Grinding or wire-sawing induced waviness can be effectively removed or reduced by lapping. A required high degree of the tool flatness is not maintained permanently. The active surface of the tool used for machining with lapping kinematics has some shape errors of concavity or convexity due to the wear. This in turn influences the shape accuracy of the workpiece and the tool flatness must be checked after machining of some workpiece batches. Depending on the tool shape error either the facing operations are carried out to flatten the active surface of the tool or proper kinematical parameters are applied which allow for obtaining required workpiece flatness. Computer simulations can be useful to make o proper decision about achievable accuracy for actual tool shape error. Simulation model for the shape error estimation based on the kinematics of lapping and local shape errors of the tool is presented in the paper. The movement of the workpiece is analyzed and the average distance from the workpiece surface, represented by discrete points, to the tool surface is calculated. Proposed model can be applied for lapping or grinding with single or double discs lapping kinematics. Geometrical and kinematical relations with some simulations are presented in the work.

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