Abstract
Intermittent cutting operation is characterised by mechanical stresses due to cutting load together with thermal stresses arising from cyclic temperature fractuations. This paper presents the results of the cutting tests performed to examine the influence of mechanical stress on the performance of the three cermet tools (TiC simple carbide type, TiN added type, TaC added type) in an intermittent cutting operation. Machining tests were conducted on a lathe by cutting steel bars with narrow slots. Cutting speed was varied from 1. 25 m/s to 4. 17 m/s, but depth of cut (1. 5 mm) and feed rate (0.2 mm/rev) were maintained constant throughout the tests. In this experiment, the tool edge fracture was adopted as the criterion for tool failure. TiN added type tool which has highest bending strength shows the most excellent performance in intermittent cutting operations, but TaC added type tool which has poor bending strength tends to be fractured within a small number of impact times. Plotting the data of failure on the Weibull probability chart indicates that its distribution, could not be considered as the Weibull's probability distribution, but it could be divided into three parts named premature, stationary and final failure region. The increasing cutting speed which is accompanied by the increasing cutting temperature decreases the probability of the tool failure which occurs in the premature failure region, and increases the average tool life.
