Effectiveness of Hard Coatings in Reducing Tool Tip Wear

Summary

Titanium nitride coatings applied to tool tips of cemented carbide and high-speed steel are effective in delaying certain types of wear but are less effective in delaying other kinds of wear. Hence the increase in tool life brought about by coating depends on the cutting conditions imposed. Taylor plots of tool life versus cutting speed for various feeds were found to define two areas. For roughing cuts, life diminished with increasing feed. In this area, the wear mechanism was predominantly cratering which depends largely on tool temperature, and the coating had a useful but limited effect. For finishing cuts, life was almost independent of feed. In this area, flank wear was more important. Here, coated tips had about ten times the life of uncoated tips. It is concluded that coatings are very effective, and indeed a practical necessity, when tool tips are used for finish machining.