Some Aspects of Adaptive and Computer Control Applied to a Milling Machine

Abstract

Typical objective functions concerning turning, drilling and milling are presented, with their derivatives, and have been reduced to functions of speed, feed rate and depth of cut, Series of cutting tests were carried out on a Cincinnati vertical milling machine fitted with an E.M.I. tape command control. End milling using various types of cutters has been employed and it was noted that down-cut milling, for roughing operations, was more suitable than up-cut machining. Some aspects of Adaptive Control Optimisation (A.C.O.) were investigated and relevant machining parameter equations obtained analytically and experimentally. No suitable sensing elements for on-line tool-wear measurements are satisfactory so an Adaptive Control Constraint (A.C.C.) system investigation was undertaken. Deflection of the cutter was the sensing element used to adaptively control the feed rate and it was found possible to retrofit an existing numerically controlled machine tool, though the experimentations are peculiar to this machine tool. The transfer function of the feed rate-cutter deflection workpiece interface was obtained and a simple adaptive controller designed and fitted. This A.C.C. system was used primarily for roughing operations, the feedrate limiter being set to the deflection constraint associated with the largest depth of cut, but as soon as cutting commenced, the feedrate reduced accordingly. Considerable time was saved, especially when "air" gaps were encountered. Machining errors were found to be almost constant along the length of the test piece though the surface finish was generally poor. Preliminary work was considered on geometric A.C. using correlation techniques to see if there was any relationship between vibration and surface finish. Some aspects and developments of Computer Numerical Control was undertaken and Direct Numerical Control (D. N.C.) investigated using a simulation program to see the viability of such systems. Finally a small digital computer (16K core storage) was coupled via a Digital-to-Analogue interface to the N.C. machine tool.