Modelling of Hard Broaching

Hard broaching is a finishing process to correct geometrical deviations of internal profiles on hardened workpieces, typically using a hardened steel body overlaid with a single layer of metal-bonded diamond grits. The tool essentially has the opposite contour as the workpiece. The process is characterized by an oscillating movement of the broaching tool, while the tool is pushed sequentially deeper into the workpiece. During the retraction phase the chips are removed from the chip spaces. The tool consists of a roughing part and a finishing part to increase the surface quality and reduce the tolerances. For gaining a deeper understanding of the process and for its optimization a stochastic tool model is introduced, which takes into account the differing shape, size, orientation and position of the single grains. Specifications about the tool geometry and the diamond coating as well as process parameters are used as input. The model is capable to predict the active grains, the respective cutting areas, cutting forces and surface roughness of such a virtual image of the broaching tool, which is thus capable to be used to layout and optimize the shape, layer and process strategy of hard broaching. It further allows analyzing the effects of the feed per stroke on the process in dependence of different process and tool parameters. By the modeling a strategy for process optimization is derived. The influences of the optimization strategy on the process are presented and discussed.