An experimental study of the effect of cutting speed on chip breaking

Abstract

Advanced carbide tooling for turning operations have been proposed for some time by several cutting tool manufacturers. When machining continuous chip-forming materials, several sintered chip-breaker geometries are available in the market. They are usually classified according to the their application range, defined by the classical depth of cut/feed areas where chip-breaking occurs and an acceptable chip form is obtained. Usually, no information is available, from the cutting tool manufacturer, on the quantitative effect of cutting speed on their chip-breaking efficiency areas. In this paper, research work carried out at Instituto Superior Técnico (IST) is presented, on the effect of cutting speed on chip-breaking when using advanced carbide tooling with sintered chip-breakers. Several commercially available chip-breakers were used. The preliminary results obtained show that an increase in the cutting speed reduces the area of efficient chip-breaking since it increases the minimum feed for chip-breaking. As expected, an increase In shear angle with cutting speed was observed. Consequently, when comparing the efficiency of several types of chip-breakers, observing the chip-breaker diagrams provided by the manufacturers, one can incur a considerable error since no standard cutting speed was used for the establishment of the presented data: a wider application range chip-breaker can have a poorer performance (usually at the lower feeds) than the apparently more restricted chip-breaker. Due to the effect of cutting speed on minimum feed for chip-breaking, when machining a continuous chip-forming material, a chip-breaker with a wide application range should be selected. From the optimised set of cutting conditions (mainly feed and depth of cut), the selection of a chip-breaker should take into consideration that the use of conditions lying on the boundaries of the chip-breaker application range can have a negative effect on machining process control mainly due to variations in chip behaviour with changing cutting conditions.