(A) study on the adaptive control system for turning process using axial force

Abstract

Adaptive control of machine tools aimes to improve the productivity and economics of the cutting process. This study is concerned with adaptive control of CNC lathe to minimize machining cost. The adaptive control system requires a performance index, in which tool wear rate is involved. The direct on-line measurement of tool wear rate is not feasible at the present state of the art. Thus the axial force is used to represent tool wear rate in online fashion. This necessitates a priori knowledge of the relationship between the tool wear rate and the axial force. This is experimentally obtained for the various cutting speed and feed using SM45C work material with two different carbide tools (P10 and St20E). Experimental results show that the axial force has a linear correlation with the wear rate and that the proportionality constant is approximately the same regardless of the tool materials. Based upon these results, simulation for the process control is done to investigate the effectiveness of this control method. The simulation results indicate that trial and error method is more suitable for this system than steepest ascent method. Futhermore, it is shown that the time interval of controlling cutting speed also influences the optimization of cutting performance. The cutting process variable is only speed since the feedrate for the present study is assumed to be kept at maximum allowable value.