Abstract

Mechanical part quality and productivity depend on many parameters in CNC milling processes, such as workpiece material, cutters, tool paths, feed rate, and spindle speed, etc. To pursue high performance machining, the cutting parameter optimization is in high demand in industry, though it is quite challenge. This innovative research successfully addresses some essential problems in optimizing the cutting parameters by developing a new geometric-and-physics integrated model of milling and proposing an effective approach to the medial axis transforms of free-form pockets. In this research, an original geometric model of 21/2- and 3-axis CNC milling is developed and integrated with a well-established mechanistic model. A main research contribution is that this integrated model can predict complex milling processes in higher fidelity with instantaneous material remove rates, cutting forces and spindle powers, compared to prior machining models. In the geometric model, an in-process workpiece model is introduced by using a group of discrete Z-layers and applying the B-Rep scheme to represent the workpiece shape on each layer, in order to accurately represent instantaneous cutter-and-workpiece engagement in 2Yz- and 3-axis milling. Hence, the un-deformed chip geometry can be found even for complex part milling, which is then fed to the mechanistic model to predict instantaneous cutting forces. By using this integrated model, cutting parameters can be optimized for profiling, pocketing, and surface milling to ensure steady cut and the maximum material removal rates. This model has been verified by experiments, and will be implemented into a software tool for Bombardier Aerospace. Another important research in this work is to propose aggressive roughing of free-form pockets for ultimately high cutting efficiency. For this purpose, an accurate, efficient approach to the medial axis transforms of free-form pockets and an optimal approach to multiple cutters selection and their path generation are proposed. The main contributions of this research include (1) a new mathematical model of medial axis point, (2) an innovative global optimization solver, the hybrid global optimization method, (3) an optimization model of selecting multiple cutters for the maximum material removal rate. This research can substantially promote aggressive roughing in the machining industry to increase cutting efficiency of free-form pockets. The technique has been validated using considerable number of cutting tests and can be directly implemented into commercial CAD/CAM software