Patent GB-1304021-A (GB)
Inventor: LEDERGERBER A
IPC: B23Q5/34
Filed: 1970-05-19
Abstract: 1304021 Programmed control of machine tools WERKZEUGMASCHINENFABRIK GILDEMEISTER AND CO AG 19 May 1970 [31 Oct 1969] 24249/70 Heading G3N An automatic lathe is numerically controlled by electric means which store the desired contour of a part to be machined and compare it with the actual machined profile. For rough machining the lathe is programmed to keep the torque at a maximum permissible value, while the tool cuts a zig-zag path in the workpiece. Feed rates in the longitudinal, or ŒZ directions, and transverse, or ŒX directions are constrained to lie always between extremes ŒZ' min , ŒZ' max ; ŒX'  min , ŒX' max  unless the tool is not cutting, when rapid feeds are provided. The tool feeds into the workpiece, Fig. 4, at a reduced rate, Fig1a (not shown) until the maximum torque Md  per . is reached whence feed in the -Z direction ceases and that in the +X direction commences, and continues at a decreasing rate X' keeping the torque Md  per  always constant until X'  min  is reached when the feed rate +Z' min  is introduced so that the cutting depth is decreased, and X' increases until X'  max  is attained when the Z feed stops and feed in X alone is present until X'  min  is attained whence the procedure repeats, Figs. 1a, 2a (not shown). When the tool point reaches a radius r+ detected by a drop in the torque,  Fig.4a, where the cutting edge just penetrates the outersurface of the workpiece a feed in the  -Z direction is introduced, and if, due to increasing workpiece radius -Z'  min  is attained, a feed +X' is actuated, feed -Z' increasing to -Z'  max , whence the X feed stops the ratio of X' to Z' is chosen so that a secondary cutting edge of the tool never touches the workpiece and the process continues iteratively. The rotation speedof the workpiece is determined by the allowable cutting speed for the particular workpiece and tool and may either be inversely proportion to the cutting radius or be constant, related to the maximum turning diameter. Further cuts are taken as above until desired material would be removed whence finishing cuts are taken, Figs.7, 7a, 7b and Figs. 8, 8a, 8b; 9, 9a, 9b (not shown) until the desired contour with possibly an oversize for final finishing is attained. A finish machining tool is provided in the latter case. For face machining only, the tool is programmed to cut right out when r+ is reached, and for rough inside machining the feed -X' may be constant, the torque decreasing Figs, 5, 5a, 3, 3a (not shown). When (r++ Fig. 5 (not shown) is reached, the tool may be programmed to cut out, Fig. 6, 6a (not shown), or may proceed into the workpiece to machine the inner surface, with additional and intermittent feed in the -X direction if -Z'  min  is attained. If Z'  min  and X'  min  are attained simultaneously the machine stops, indicating a blunt tool. The system can be used for boring, only Z' feed being needed. Machining commences with at least one revolution at the minimum feed rate, in case the workpiece is not flat. If a programmed valve of the ratio dx'/dt:dx/dt is exceeded the lathe stops, and transducers, such as quartz transmitters or strain-gauges are mounted on tools or tool carriers and can serve to measure the torque or tool chatter. The lathe stops or feed rates are changed if tool chatter frequency reaches a given value. In taking successive cuts, Fig. 7 parts of the prophile already finished are passed over at rapid feed speeds.