Stabilization of contour milling on CNC machines

Abstract

Contour milling processes are characterized by a quasi-stationary nature, which leads to the need to assign a cutting mode for the entire contour based on the most unfavorable cutting conditions in a particular area. Simultaneously, CNC machines allow for selecting different cutting modes for contour sections, stabilizing cutting conditions along the entire contour, and stabilization is advisable based on the material removal rate (MRR) criterion. The research deals with contour milling on a CNC machine. Since the process is quasi-stationary, the problem arises of stabilizing it by controlling the feed rate and spindle speed. Therefore, the MRR as the main process parameter was considered the research subject. This parameter determines the cutting intensity and is responsible for forming the required surface quality of the part. A computer program was developed to simulate the contour milling process by determining the main characteristic of the MRR process. At the first stage of the developed technology, using the created modeling program and a G-code control program, a digital file of the MRR dependence was created for the part’s contour. Such a file was used in a developed authors’ program to generate a G-code control file, which ensures stabilization of the cutting process according to the MRR criterion. Moreover, control was realized when changing the feed rate to discretize the resulting array with a specified percentage of the change step. This reduced the number of frames for the new control program while maintaining the positive effect of stabilizing the process in terms of MRR. The developed technology was tested for machining the contour with convex and concave sections in the trajectory. Experimental studies were conducted on a CNC milling machine with the workpiece mounted on a dynamometer table. This made it possible to record the cutting force during milling. As a result, the high efficiency of the developed technology was confirmed. Overall, process stabilization increased productivity approximately 3.0 times compared to the process designed in a CAM system at a constant feed rate and spindle speed.