Performance of oxide PVD-coatings in dry cutting operations

Dry cutting processes effect increased economic efficiency and at the same time fulfil ecological requirements. However, elimination of coolants involves absence of their positive influences on the metal cutting process such as lubrication, heat dissipation and chip evacuation. This leads to high adhesive, abrasive and tribo-chemical tool wear. Innovative oxide coatings meet the sophisticated demands of dry cutting applications such as high wear resistance and the reduction of friction, which minimises the thermal load. The oxide materials provide a high resistance against adhesive wear, due to the high binding energy. Furthermore, the friction coefficient can be decreasing with increasing temperature, and a high hardness even at elevated temperatures is provided. This paper shows the performance of the deposited Al2O3 and ZrO2 coatings in dry drilling of high strength spheroidal graphite cast iron (SGI70). Influences of the coating composition on the tool wear behaviour, the cutting forces and the chip flow are highlighted. Additionally the coatings are evaluated by determination of the absolute temperature on the cutting edge of the drilling tool. Therefore, a suitable measuring technique was developed.