Assessment of the thermal effects on chip surfaces

Cermets not only possess the advantage of high hot hardness, but they are a lso chemically stable, which effects high wear resistance as well as good s urface quality of the workpiece. However, owing to their disadvantages of h igh brittleness and low thermal resistance, there have been many attempts t o improve their service life by means of the disposition of wear-resistant coatings. Various techniques have been used to evaluate the cutting performance of al l of these coatings. A common method to evaluate the temperature at the too l-chip contact zone is done by using a tool-work thermocouple, an embedded thermocouple technique or by infra-red scanning. These techniques are diffi cult to be implemented, especially for low thermal conductivity and brittle tool materials such as cermets. This paper describes the chip-colour approach to analyse the effects of the thermal behaviour of coated cermet tools. This approach is useful, in part icular, to overcome the limitations of the other methods described earlier. It was observed that different colours will be produced in the chip when u sing different tool inserts. With experiment results, the obtained, a chart with chip colours and lightness as a function of the cutting temperature w as plotted. The cutting temperature for different cutting conditions can th en be assessed by the lightness and the colour of the chip. (C) 2000 Elsevi er Science S.A. All rights reserved.