Simulation of CNC machining using a ball endmill

Abstract

In this thesis, a method for improving the efficiency of NC machining of free-form surfaces through a simulation technique is presented. Traditionally for the machining of free-form surfaces, the NC codes are generated using an NC programming software and sent to the controller of a CNC machine. This process can contain errors. Thus, it is general to perform a test cut before a real machining, and the result of the test cut is used to correct the NC programming errors. This procedure is repeated until a desirable result is obtained. By using the NC simulation software, this expensive and time consumming processes can be elliminated, improving the utilization of machines the leadtime and the machining cost significantly. The errors in NC machining can be categorized as geometrical errors and physical errors. The conventional NC simulation methods were focused on one of these. However, without considering both, the test cut cannot be elliminated from the NC machining procedure. In this study, a method is developed for combining the geometric simulation and the physical simulation. The method is applied for finding out programming errors, predicting the abnormal machining by excessive cutting forces, and determining the optimum cutting conditions for the machining of 3-dimensional shapes with a ball endmill. To interface the geometric simulation with the physical simulation, the tool-workpiece-contact-area is determined geometrically for each instance of machining. Then, the area is used for calculating the cutting forces by the physical simulation. The cutting forces are used in determining the optimum cutting conditions. In general, the cutting conditions for the free-form surface machining are given as fixed values or as variable feedrate with a fixed speed. In this study, both the spindle speed and the feerate are controlled by considering the tool wear rate, the accuracy and the production rate. Since the interaction area between the workpiece and the cutting...