Intermittent metal cutting at small cutting depths—1. Dead zone phenomena and surface finish

Abstract

Chip formation in intermittent metal cutting at small cutting depths was investigated by single edge experiments. Single cutting strokes were performed in a modified Charpy pendulum tester which offers force measurement, accurate selection of cutting speed and feed in the ranges typical of many intermittent high speed steel (HSS) tool operations. The pendulum is also provided with an excellent quick-stop mechanism. The cutting performance of HSS tools in three widely used steel grades (including one plain carbon, one quenched and tempered and one austenitic stainless steel) was studied. A number of double rake micro geometries, with primary rake angles ranging from +20° (parrot bill) to −60°, all with a prepared 0.1 mm wear land were tested. The performance of the different edge geometries was investigated with respect to class of dead zone developed on the cutting edge, and its relation to chip curl and finish of the cut surface. The results are visualized in a dead zone map. The influence of cutting length, cutting speed, cutting depth and TiN-coating was treated specifically. Among the most important observations were: — the micro geometry of the edge influences the dead zone formation mechanism and hence the class of dead zone, — the surface finish is strongly dead zone class dependent, — the chip curl is determined by edge micro geometry and dead zone class. The relationships between the varied parameters, generated dead zones and resulting cutting forces are presented in part 2 of this paper.