The wear process of PVD coated HSS taps - a preliminary study

Abstract

The purpose of this study is to investigate wear processes and wear mechanisms on PVD coated high speed steel taps. The tested taps are Dormer Tools E395 M8 with spiral point geometry for through holes. All tested taps are coated with a TiAlN PVD coating and tested in different operation intervals at a cutting speed of 30m/min. SEM photographs of the tested taps indicate an early loss of coating on the edge. An initial wear arises after just a few threaded holes, mainly as flank wear on the cutting edge. The flank wear on the cutting egde tends to be S-shaped with an initial wear, a steady state phase and a fast increasing wear just before tap breakage. Workpiece material adheres in grinding scratches on the rake face. Adhered workpiece material rips off parts of the coating as the fiction between the chip and the adhered workpiece material increases. The tests indicate that the wear process on the outer diameter is exponential and the flank wear process tends to be S-shaped.