Workholding Optimization for Turning of Ring Shaped Parts

Abstract

The ability to produce precision ring shaped parts using the turning process depends significantly on the workholding characteristics. Workholding parameters such as the number of jaws and chucking force are known to influence the roundness tolerance of ring shaped parts commonly used in bearing applications. Experimental trial and error methods are often used in practice to optimize the workholding parameters to achieve the desired part quality. This thesis develops a systematic mathematical approach for optimizing these parameters using a finished cut roundness prediction model and a model for determining the reaction force between the chuck jaws and the ring. The roundness prediction model is verified through experiments for different cutting conditions. The optimization approach takes as input the required roundness tolerance, geometry and mechanical properties of the ring, cutting forces, and the coefficient of friction between the jaws and the ring. The output consists of the minimum number of jaws and the range of acceptable chucking forces that satisfy the required tolerance while preventing slip of the ring. Simulation examples are used to illustrate the proposed workholding optimization approach for a hard turning application. In addition, based on the optimization model, the thesis proposes a novel concept of dynamic chucking force control that promises to yield part roundness that is superior to conventional chucking.