Contouring Accuracy of a Machine Tool: Design of a Performance Test and Optimization of the Jerk

With increasing demand of high feed rates the dynamical characterization of a milling center is becoming a strategic aspect. The contouring accuracy at high feed rates and high acceleration is vital in order to preserve the tolerance integrity of parts produced with high speed machining. The dynamic accuracy is influenced by the velocity, acceleration and Jerk. While the cutting speed depends from technological considerations and the maximum velocity and the acceleration depends from the mechanical structure, what value assign to the Jerk is not well defined. The Jerk has an important impact on the execution time of a tool path in a mould/die production, where there are frequent accelerations and decelerations, and a high jerk leads to a deteriorated surface accuracy and an unsmooth machining process. In this paper, experimental test were conducted on various milling centers in order to define the Jerk value. Firstly, some tool path features are introduced in order to consider the effect of the trajectory. Then a tool path, called STAR, is designed and it has been tested by changing the Jerk. A mathematical model able to estimate the execution time it was prepared. A performance test is designed in order to estimate the contouring accuracy in relation with Jerk for all tool paths. The best value of Jerk is the compromise between high accuracy and high productivity. Then an objective function is introduced in order to optimize the Jerk.