Tool Wear: Plastic Deformation

indexable cutting tools

This article is part of a 9-part series on tool wear and how to manage it. For insights into other wear mechanisms and how to address them, be sure to read the rest of the series.

Tool wear is arguably the most disruptive event—and a major cause of missed production time—on the manufacturing floor. It is also a key factor driving overall tooling spend. On most machines, production comes to a complete stop during tool changes. Additional time is lost when test cuts and offsets are made to reset the dimensional position of the cutting edge. Add inspection time and scrapped components due to wear or tool breakage—and all of this is before even addressing the time spent solving tool wear issues.

Of course, cutting tools don’t last forever, and while we can never fully eliminate the costs associated with tool wear, its disruptive effects can be reduced through an improved understanding of the various wear mechanisms—and by taking appropriate corrective actions.

Plastic Deformation

What it is:

Plastic deformation occurs when the cutting edge or geometry of the insert deforms. This can appear as warping along the edge line or compressive deformation along the flank. Depending on the tool style and the severity of the deformation, magnification may be required to verify that plastic deformation is present.

Why it happens:

This type of wear is caused when temperatures in the cutting zone exceed the insert's thermal capabilities. Excessive heat weakens the material’s structural integrity, allowing the tool to deform from its intended shape.

How to Correct:

The most effective correction is to reduce heat levels in the cutting zone. The specific action depends on the direction of the deformation:

If the tool appears to deform downward (the clearance flank is compressed), reduce the cutting speed.
If the tool appears to deform upward (the rake face is pushed up), reduce the feed rate.

In addition, the following measures may help resolve the issue: