A Constant Cutting Power Adaptive Control for Rough and Fine Turning

Summary

In industrial applications the ACC controls which have reached the widest diffusion, are constant cutting power adaptive controls: in fact they are enough simple and reliable and allow the user to obtain economic advantages as machining time reduction and uniform utilization of machine tool power. This paper describes a particular strategy, studied for a copying lathe but useful for a NC lathe too, which controls both rough and fine machining of a workpiece keeping the cutting power at a constant value. The studied and tested software obtaines the constant cutting power by a constant cutting speed, whose value is optimized by means of cutting data present in a data bank in a minicomputer, and by a constant cutting force whose value is chosen upon the basis of desired cutting power and specific cutting force of workpiece material, computed during the first seconds of cutting. An automatic loop gain control strategy is used in controlling the cutting force in order to prevent oscillatory phenomena caused by variations of cutting depth and workpiece hardness. Fine machining is also controlled at constant cutting power: such a strategy allows to obtain a constant roughness, below a desired value, on every workpiece surface.