Tool life characteristics were investigated for tungsten carbide cutting tools coated with TiC and with TiC plus $Al_2O_3$. A low carbon steel workpiece was turned on a lathe at a feed rate of 0.206-0.410 mm/rev. and a depth of cut of 0.1-0.5 mm for cutting velocities between 100 m/$\min$ and 250 m/$\min$.
Data was analyzed using both Taylor's tool life equation and Wu's tool life method. Results were similar for both methods but Wu's method seemed to give more consitent results. Compared to an uncoated tungsten carbide tool, tool life of both the coated tools were from 5 to 7 times longer and the improvement was greater at higher cutting speeds.
The TiC plus $Al_2O_3$ coated tool was slightly superior to the TiC coated tool.
The wear mechanism and a possible explanation of increased tool life for the coated tools was discussed.
대한 중석에서 구입한 P20S tool을 화학 증착법으로 증착하여 TiC coated tool과 $TiC+Al_2O_3$ coated tool을 얻은 후 turning test 를 하여 Taylor's method와 Wu's method를 이용하여 공구수명을 구하였다.
그 결과, coating을 하면 공구수명이 5∼8 배 증가하며, 고속절삭일수록 $TiC+Al_2O_3$ coated tool이 TiC coated tool보다 수명이 더 증가 하였다.
또, Wu의 방법으로 구한 공구수명식이 Taylor방법으로 구한 공구수명식보다 더 실용적이라고 생각된다. 그리고, Wu의 공구수명식의 의미를 Reduced parameter를 사용하여 정확히 해석하고자 하였으며, machinability에 영향을 미치는 Removed Metal Volume을 각 tool의 경우에 비교하였다.
$TiC+Al_2O_3$ coated tool의 경우에 공구 수명이 가장 증가하기 위한 $Al_2O_3$ coating의 증착두께는 3∼5 μm 이었다.
마지막으로, wear mechanism을 종합적으로 고찰하고, 열역학과 고체역학적으로 공구수명증가 방법을 제시하였다.
