The most important thing in PVD coating process is the clamping method, which will determine the thickness and uniformity of the coating. And there is no doubt that the thickness of the coating affects its service life. However, it is not the thicker the coating, the better its life expectancy. On the same workpiece, different application requires different thickness. And different workpiece also needs different thickness. So, the thickness control of the coating is important.
The thickness of the coating is mainly determined by the coating procedure. Certain procedures have a certain range of coating thickness, and the thickness of the coating varies substantially within this range. However, the clamping method of the workpiece also greatly affects the thickness of the coating. Under improper clamping, the thickness of the coating will exceed the range set by the program.
The rotation dimension of the workpiece affects the thickness of the coating. The workpieces must be rotated in the chamber while being coated. There are three ways of rotation of workpiece: single-dimension rotation, two-dimensional rotation and three-dimensional rotation. For same coating procedure, the more rotation dimensions, the thinner coating. The thickness of the two-dimensional spin coating is approximately 5 times the thickness of the three-dimensional spin coating, and the thickness of the one-dimensional spin coating is approximately 1.5 times the thickness of the two-dimensional spin coating. Assuming a coating thickness of a three-dimensional rotating is 2um, and then the coating thickness of two-dimensional rotating workpiece is about 3um, while the coating thickness of single-dimensional rotating spin can reach 4.5um or more.
When clamping the workpiece, the density of the workpiece also affects the thickness of the coating. The coating thickness of the workpiece where clamped intensively is small, and the coating thickness of the workpiece where clamped sparsely is great.
The figure above shows the thickness distribution of the coating on a single tooth of a hob. The figure below shows the thickness distribution of the coating at different positions of a drill.
Thus it can be seen that the thickness of different parts of the tool is greatly affected by the clamping, so we must determine the clamping method based on experience.