Tool Wear: Crater Wear
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.
Crater Wear
What it is:
Crater wear occurs when a crater-like cavity forms on the rake face (top surface) of the insert. This happens as the cutting tool material is gradually pulled away by the chip sliding over the top of the tool.
Why it happens:
Crater wear is caused by diffusion. At the rake face, temperatures become high enough that the cutting tool material begins to migrate onto the passing chip. Once crater wear begins, it typically accelerates, eventually leading to a severely weakened cutting edge. Fortunately, crater wear is less common with modern multi-layer coated carbide grades.
How to Correct:
Crater wear can be effectively managed using one or more of the following corrective actions:
- Switch to a more wear-resistant grade – Ideally, use a multi-layer coated grade that includes a layer of Al2O3 (Aluminum Oxide) coating.
- Reduce the cutting speed – Lower cutting speeds reduce temperature, which helps slow the diffusion process.
- Reduce the feed rate – A lighter feed can reduce the intensity of contact between chip and tool.
- Use a more positive cutting geometry – This reduces cutting forces and helps direct the chip away from the rake face.