Effect of applied pneumatic pressure on the polishing spot size and the total normal force in pneumatically configurable polishing

Abstract

The present study pertains to a compliant polishing technique called Pneumatically Configurable Polishing (PCP) which uses the precise inflation of a thin elastomeric diaphragm or membrane using pneumatic pressure for generating nano level surface finish on substrate surfaces. The PC polishing tool which has a cup shape is made to contact the workpiece surface such that its flexible nature can adapt itself to the macro features on the workpiece. This inflated tool-work contact leads to the entrapment of the hard abrasives preplaced in the interface zone in the form of a slurry. The rotary motion of the tool along with the relative motion between the workpiece and tool, help to generate an improved surface finish in the interface area. The area of the finishing zone is an important outcome of the polishing regime because it defines the dimensions of the area which will be affected by the tool. It also helps to estimate the time needed for polishing a large area. Also, the force transmitted to the workpiece surface is an important measure to estimate the functional life of the tool. In the current study, the variation of the spot size and total normal force are modelled mathematically in terms of the physical and geometrical properties of the tool as well as the applied fluid pressure. The Hertz theory of contact is used to model the contact conditions in the polishing interface zone. The model studies the effect of pneumatic pressure on membrane inflation and its influence on the area of the polishing spot at varying working gaps. The effect of the applied fluid pressure is studied on the normal force experienced by the workpiece, and the results obtained from the model are validated with experimental verification under identical polishing conditions. The values obtained experimentally show a close agreement with the theoretical results obtained from the model.