Part Programming to Realize Chatter Free and Efficient High Speed Milling

High speed milling (HSM) is the most known machining process due to its application in various industries. In milling, a rotating cutting tool removes a large amount of material along a predefined toolpath to manufacture the final part with a desired shape. Milling of prismatic parts1 is very important in automotive, aerospace, mold and die industries. Even complicated parts are machined from a blank first by 2.5D roughing followed by 3D-5D finishing. Modern production floors have adopted high speed CNC2 machine tools to execute part programs, developed by CAD/CAM3 systems, to manufacture the final workpiece. The overall productivity of the milling process depends on the choice of cutting conditions and the toolpath. Current CAD/CAM systems do not provide any guidance to select cutting conditions due to the unavailability of models of the complex physical and dynamic interaction of machine tool and workpiece systems. Moreover, toolpath generation by CAD/CAM packages is purely geometric in nature and results in engagement angle variation along the toolpath. The selection of cutting conditions and toolpath rely solely on the part programmer’s experi- ence, CAD/CAM systems, handbook guidelines or specifications provided in the catalogues of cutting tools and machine tools. Their poor selection often causes chatter, high fluctuation of cutting forces, and/or violation of the available limits of power and torque of the machine tool. These phenomena result in poor surface finish, workpiece damage, high cutting tool wear, violation of tolerance limits, additional cost, unwanted waste and significant reduction in machine tool working life. In order to avoid these problems, part programs need to be verified iteratively using trial and error experiments and often conservative cutting conditions are selected. These practices lead to long preparation time of part programs and lower machining performance, which in a nutshell significantly lower overall productivity. Moreover, machine tool capabilities are not fully utilized due to the conservative selection of cutting conditions. In order to address these challenges, a genetic algorithm (GA) based optimal milling (OptMill) system is developed for optimal selection of cutting conditions and/or toolpath for a given set of inputs of machine tool/spindle/tool holder/cutting tool and workpiece system. Operational constraints of the machine tool, such as spindle speed and feed limits, available spindle power and torque, chatter vibration4 limits due to the dynamic interaction between cutting tool and workpiece, permissible limits of bending stress and deflection of the cutting tool and clamping load limits of the workpiece system are embedded. The developed system is applied to different industrial use cases: (i) Minimization of pocket milling time considering one-way toolpath (ii) minimization of machining time for multi-feature prismatic parts with the imple- mentation of pre-processing modules: extraction of too