Tool Wear: Built-Up Edge

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.

Built-Up Edge (B.U.E.)

What it is:

Built-up edge (B.U.E.) occurs when material from the workpiece becomes welded or "built-up" onto the rake face of the cutting tool.

Why it happens:

This wear mechanism is most often caused by cutting at a speed that is too low. When the cutting zone temperature is too low, the workpiece material doesn't fully shear away from the cutting edge and instead adheres to the tool. Once material begins to stick, the build-up can accelerate—layer upon layer welding to the cutting edge. If not corrected, this changes the tool geometry significantly and can lead to catastrophic failure.

Built-up edge can also result from using a cutting geometry that is too negative for the application. The increased cutting forces from too negative a geometry can effectively blunt material onto the edge, creating a friction-welding effect instead of promoting proper chip formation.

This type of wear is particularly common in stainless steels and high-temperature alloys. These materials often contain alloying elements—especially nickel—that resist corrosion and heat, but also promote B.U.E.

In milling applications, built-up edge can be even more problematic. Material adheres to the edge of each insert during each spindle rotation, and that built-up material gets compressed and sheared repeatedly. Eventually, this leads to the entire edge line breaking away.

How to Correct:

Built-up edge can generally be addressed by the following steps, in this order:

1. Increase the cutting speed.
2. Use a more positive cutting edge or freer-cutting tool geometry.
3. If already using a positive geometry, increase the feed rate.
4. Turn the coolant off.
5. In rare cases, increase coolant flow to add lubricity and help prevent material adhesion.