Roughness Generation In Precision Grinding Of Small Optical Surfaces

Small steel moulds for injection moulding of polymer lenses are precision ground at Philips Research Laboratories. As part of a broader research program the relations between the process parameters and the generated surface roughness are investigated. A computer simulation technique used to investigate these relations is described. This technique allows us to investigate the effects of grinding wheel and workpiece geometries and of grain size, distribution and concentration. Process parameters such as depth of cut, infeed, and angular velocities can be chosen. The effects of initial workpiece roughness and of multiple passes of the grinding wheel over the surface can be investigated. Unbalance of the grinding wheel can also be taken into account. A simple geometrical model is used to calculate the shape of the scratches made by grains engaging the workpiece. The wear behaviour of grains can be taken into account assuming a simplified wear law. Some results of these simulations are presented. Predicted trends are compared with experimental results.