Generating Multiaxis Tool Paths for Die and Mold Making with Evolutionary Algorithms

Defining tool paths for multiaxis milling is a difficult task that requires knowledge about the process and the behavior of the machine tool. Because of the high risks of multiaxis movements within a real machine, the resulting paths are safe but normally sub-optimal. This article introduces a new method to obtain tool paths, which are free of collisions and optimal in consideration, the machine and its kinematics. The proposed method combines evolutionary algorithms and a newly developed efficient multiaxis milling simulation. The evolutionary algorithm uses multiple criteria for the optimization of a tool path. These criteria are minimized axial movement of the machine, minimal cutting forces and the exclusion of collisions between the workpiece and the non-cutting parts of the cutting tool. The approach uses multi-objective algorithms because minimal or no movement of a machine axis can lead to high cutting forces or multiple collisions. Along with the evolutionary algorithm, this article introduces a simulation for multiple axis milling. This simulation is able to compute the fitness of the given tool paths by considering the engagement condition and collision situation of a cutting tool. 1 Problem Description In multiaxis milling of free formed surfaces for die and mould making, one of the main tasks is a near optimal definition of the tool path. This definition is placed under various constraints, which need to be fulfilled simultaneously. One point is the avoidance of collisions between the non-cutting parts of the cutting tool and the work piece. A second one that is exclusive to multiaxis milling is the task of finding a tool orientation that fulfills all constraints resulting from the used machine. Different milling machines have different constraints imposed upon the movement of their additional axis, which are needed for the more than three axis movement. This can be seen as an additional collision condition between tool and possible movement area of the machine in addition to the collision between tool and free form surface. The third constraint is not exclusively given in multi axis milling; it is also valid for all milling processes. In milling processes, the cutting force on the cutting edge is 1288 K. Weinert and M. Stautner an important factor for a stable and safe process control. The programming of tool paths must lead to a process that is fast and safe to be cost efficient. Resulting from these constraints multiaxis tool path strategies are often designed as an addition to the existing three axis strategies. These paths are planned as a threeaxis movement with an additional two-axis movement, which changes the orientation of the tool to the work piece. This additional rotational movement has to be free of collisions. Therefore, plenty of user experience is needed to design these tool paths. There are some software tools on the market that deliver some kind of collision detection but they are often restricted to three axis milling or only to collision detection against the final geometry and not the actual process geometry of the free form surface. So there is a demand for solutions which provide functions to develop tool paths which are free of collisions and use the possibilities of multi axis tool path programming to gain a fast and safe process course. This article introduces a first prototype of a tool that enables the user to convert given three axis tool paths to collision free multiaxis tool paths.