Truing and dressing of CBN/seeded gel hybrid wheels with emphasis on grinding process economics and quality

In this study, an analytical and experimental investigation of truing and dressing process of CBN/SG grinding wheels is described. An analytical model of the interaction between CBN wheel grits and truing diamond grits was developed for rotary disc parallel and perpendicular arrangements of wheel-truer axes. The model takes into account the truing parameters, the geometry and features of the grinding wheel and truing disc, and grit retention capabilities of both these tools. It was found that number of collisions between CBN grits and diamond grits is predominantly dependent on truer specification. From the truing process parameters, when preparing a grinding wheel surface, lead is the most influential, followed by speed ratio and truing depth.^ Experiments confirmed the importance of the above truing parameters as predicted by the analytical model. The limiting factor governing the frequency of wheel truing has been shown to be due to loss of profile rather than volumetric wear. In addition, if the truing conditions produce a dull grinding wheel the steady-state level of grinding force will be at a higher level than for optimally trued wheels.^ A comprehensive cost model of the entire grinding operation, including auxiliary activities, was also developed. It can be used for continuous and batch-type production including reoccurring jobs. The model accounts for different types of superabrasive wheels and conventional abrasive wheels, as well as for continuous dress operation. It takes into account costs of various pieces of the equipment used, performance characteristics of each process involved in the entire grinding operation, and cost of machine time. The model allows for calculation of cost-per-part as well as target costs for all pieces of the equipment. Optimal batch sizes can be calculated for different types of wheels. Simulation results using the cost model in industrial applications are also presented. It has been shown that contrary to widespread beliefs, CBN wheels can be very cost-efficient even when used for production in small batches. In environments characterized by a high labor cost, the time efficiency of truing, dressing and other auxiliary operations is crucial in reduction of total grinding costs.