In this article, you will learn:

1. Turning – Overview

2. Turning – Types of Tool Damage

3. Turning – Built-Up Edge Formation

4. Turning – How to Reduce Built-Up Edge

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Overview

In turning operations, the tool remains stationary while the workpiece rotates in a chuck or collet fixture. Many machining processes are performed on a lathe, and the correct tool geometry and cutting parameters must be used according to the material being machined. If these parameters are not properly applied, built-up edge (BUE) or other damage modes may occur. These damage modes negatively affect tool performance and can ultimately lead to scrapping the entire workpiece.

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Common Forms of Turning Tool Damage

When inspecting tools under a microscope or magnifier, several types of turning tool failure modes can be observed. Some of the most common include:

Flank wear:
The only acceptable form of tool wear, caused by normal aging of a used tool and found on the cutting edge. This abrasive wear results from hard particles in the workpiece material. It is predictable and provides stable tool life, allowing further optimization and improved productivity.

Crater wear:
Deformation that appears on the rake face of the tool. This mode is a chemical and thermal failure occurring in the rake face area of the insert or toolholder. It is caused by a chemical reaction between the workpiece material and the tool and is intensified by cutting speed. Excessive crater wear weakens the cutting edge and may result in edge failure.

Chipping:
Breakage along the cutting edge that causes rough, inaccurate cutting. This is a mechanical failure commonly seen in interrupted cuts or unstable machining setups. Causes include machine collisions, poor rigidity, and toolholder issues.

Thermo-mechanical failure (thermal cracking):
Cracks caused by significant fluctuations in temperature during machining. Both excessive and insufficient heat can cause problems, but rapid thermal cycling (repeated heating and cooling of the edge) is especially harmful. These cracks usually appear evenly spaced and perpendicular to the cutting edge.

Built-up Edge (BUE):
Occurs when chips adhere to the cutting tool under high heat, pressure, and friction. BUE is the easiest type of tool wear to identify—even without magnification—because the machined material is pressure-welded onto the tool's rake or flank face.

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Problems Caused by Built-Up Edge

This condition leads to many machining issues: reduced tool life, poor surface finish, dimensional inaccuracies, and other quality defects. These problems occur because the material welded onto the tool alters the cutting edge location and tool geometry. As BUE grows worse, other failure modes—and even catastrophic tool failure—may occur.

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Causes of Built-Up Edge in Turning

Incorrect tool selection:
BUE often results from using a tool with improper geometry for the material. Sticky materials like aluminum or titanium require extremely sharp cutting edges, free-cutting geometry, and polished rake and flank faces. These features improve chip flow and reduce material adhesion.

Using worn tools:
Even with proper geometry, BUE can still occur as the tool dulls. As the edge becomes rounded, material begins to accumulate on the tool surface. Randomly inspecting the cutting edge during the tool’s service life helps identify early-stage failure and root causes.

Insufficient heat generation:
Running tools at poor cutting parameters may trigger BUE. Most commonly, BUE happens when speed or feed is too low. Heat generation is critical in machining—too much heat affects the workpiece, but too little heat prevents efficient chip removal.

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Four Methods to Reduce Built-Up Edge in Turning

01. Choose the Right Chipbreaker and Tool Geometry

Select free-cutting, sharp geometries with highly polished surfaces. Using chipbreaker geometry helps divide the chip and remove it from the cutting zone. This ensures freer cutting and better control of chip formation.

02. Proper Speeds and Feeds

Even experienced machinists should regularly verify correct speeds and feeds. Ensure the machine is in optimal condition; avoid overloading it, and schedule regular maintenance. Use speeds and feeds recommended by tool manufacturers and avoid exceeding machine capability.

03. Use Coolant Effectively

Coolant helps evacuate chips and prevents high-temperature welding on the cutting edge. When coolant is properly directed at the cutting zone and concentration is sufficient, BUE is less likely to occur.

04. Tool Coating Selection

Choose coated inserts when appropriate (note that some non-ferrous materials may not require coatings). Coatings are designed to handle specific materials and reduce common machining problems. They minimize cutting forces and prevent tool damage. Operators must select the proper coating for the material to maximize tool life.