|M.Sc Student||Bar-Hen Meir Hai|
|Subject||The effect of coating thickness and surface roughness on|
cutting tool's wear
|Department||Department of Mechanical Engineering||Supervisors||Professor Emeritus Izhak Etsion|
|Dr. Yuri Kligerman|
|Full Thesis text - in Hebrew|
The effect of coating thickness and substrate roughness on the tool wear in turning is studied experimentally. During cutting operation, one or more wear types may occur. This research is specifically directed to flank wear type. A useful way of presenting the amount of flank wear is by the parameter VB, which is the width of flank wear.
TiAlN coating of various thicknesses was applied on tungsten carbide (WC) tool substrate having various surface roughnesses.
Turning tests using CNC lathe were performed in a wet cutting environment. Each tool underwent 25 facing passes without being removed from the holder. After the conclusion of all 25 passes, the tool was removed from the holder and its flank wear was measured. Cutting velocity, feed rate and depth of cut were maintained constant.
The general trend of the results was decreasing flank wear VB with increasing coating thickness t. However, the scatter of the results was very large and the goodness of fit was somewhat poor. Additionally, the results show increasing flank wear VB with increasing average radius of curvature of the substrate roughness Rsu (smoother surface). Here the goodness of fit was somewhat better but still poor. Hence, these parameters by themselves are not good candidates for reliable prediction of the flank wear VB.
Based on the experience gained with modeling the resistance to plastic yield of a coated asperity, it was attempted to plot the flank wear vs. the dimensionless ratio t/Rsu. The results showed a very clear trend of decreasing flank wear with increasing ratio t/Rsu. The goodness of fit was excellent, much higher than that of coating thickness or average radius of curvature of the substrate roughness alone.
An attempt was made to examine the results in light of the findings in the models for plastic yield inception of a single spherical asperity of rough surface with hard coating. In these models the effect of the dimensionless coating thickness t/R (where t is the coating thickness and R the radius of the substrate) on the critical load to cause yield inception and on the location of this yield was investigated.
It was found that the tools with maximum flank wear belong to the range where the first plastic yielding occurs in the substrate. The tools with the minimum flank wear belong to the range where the first plastic yielding occurs in the coating. Hence, a good correlation seems to exist between the theoretical results of resistance to plastic yield inception and the present experimental results of resistance to tool flank wear.