CUTTING FORCE CONTROL FOR BALL END MILLING OF SCULPTURED SURFACES USING FUZZY LOGIC CONTROLLER

Abstract

Productivity and precision in machining is normally limited by the forces emanating from the cutting process. Due to the inherent varying nature of the work piece in terms of geometry and material composition, the peak cutting forces vary from point to point during machining process. In order to increase productivity without compromising on machining accuracy, it is important to control these cutting forces. In this paper a fuzzy logic control algorithm is developed that can be used to limit maximum peak forces in milling of spherical surfaces using ball end mills. The controller can adaptively maximise the feedrate subject to allowable cutting force on the tool, which is very beneficial for a time consuming complex shape machining. This control algorithm is implemented in computer numerical control (CNC) machine.  To demonstrate constant peak force control, the radial depth of cut was abruptly changed from 1.0 to 1.5 mm. As a result, the peak cutting forces increased. In order to counteract this increase and maintain a constant peak force, the  pre-programmed  table feed was decreased by assigning the appropriate override. For the above change in depth of cut, the override was found to be about 78%, which is a drop of table feed from 30 mm/min to 23.4 mm/min.  It has also been demonstrated that the controller developed can provide stable machining and improve the performance of the CNC milling process by varying feedrate in real-time.