Understanding Tool Wear: Flank Wear, Crater Wear, and Built-Up Edge Explained

Wear is one of the biggest issues when it comes to CNC milling. Each cutting tool will wear out from repeated use, but the knowledge about it will help you to improve the machining process, save money on the production and increase the longevity of your tools.No matter what carbide inserts, end mill, or tool for turning you work with, you should be aware of wear types.

This article will introduce you to three most popular cutting tool wear types - flank wear, crater wear, and BUE (built-up edge).

What Is Tool Wear?

Tool wear is the gradual loss of material from the cutting edge of a tool due to friction, heat, and mechanical stress during machining. As the cutting tool , cutting performance decreases, surface finish becomes poor, and machining accuracy is affected.

Ignoring tool wear can lead to:

• Poor surface finish
• Dimensional inaccuracies
• Increased machining costs
• Unexpected tool failure
• Longer machine downtime

Monitoring wear regularly helps improve productivity and reduces unnecessary tool replacement.

Common Types of cutting tool wear 

The three most common types of cutting wear patterns are:

• Flank Wear
• Crater Wear
• Built-Up Edge (BUE)

Each type occurs in a different area of the cutting tool and has different causes.

1. Flank Wear

Flank wear develops on the side of the cutting tool that comes into contact with the finished surface of the workpiece. It is the most common and expected form of wear in CNC machining.

Causes of Flank Wear

• Continuous rubbing between the tool and workpiece
• High cutting speed
• Hard or abrasive materials
• Insufficient coolant
• Long machining cycles

Effects of Flank Wear

When flank wear increases, it can cause:

• Poor surface finish
• Reduced dimensional accuracy
• Higher cutting forces
• Increased heat generation
• Shorter tool life

How to Reduce Flank Wear

• Maintain the appropriate cutting speed and feed rate.
• Use good carbide inserts.
• Coolant should be used properly while machining.
• Replace carbide inserts before wearing out.
• Select the appropriate tool coating according to the workpiece material.

2. Crater Wear

Crater wear appears on the rake face of the cutting tool where chips slide over the tool surface. It is mainly caused by high temperatures and continuous chip flow during cutting.

Causes of Crater Wear

• High cutting temperatures
• Excessive cutting speed
• Machining tough materials
• Poor chip evacuation
• Long continuous cutting operations

Effects of Crater Wear

Crater wear can:

• Weaken the cutting edge
• Increase the chance of tool breakage
• Reduce machining efficiency
• Affect chip control
• Lower tool performance

How to Prevent Crater Wear

• Reduce cutting speed where possible.
• Use heat-resistant coated inserts.
• Ensure proper chip evacuation.
• Select suitable cutting parameters.
• Maintain effective coolant flow.

What Is Built-Up Edge (BUE)?

Built-Up Edge (BUE) refers to one kind of wear in cutting tool where fine bits from the workpiece attach themselves to the edge of the cutting tool during machining process. These fine bits gradually build up into a temporary deposit on the edge of the cutting tool. As the process of machining is carried out, the deposits get formed and then get separated repeatedly.

The Built-up Edge is generally associated with the machining of soft and ductile materials such as mild steel, aluminum, copper and low carbon steel.

Causes of Built-Up Edge

Several machining conditions can lead to the formation of BUE:

• Low cutting speeds
• High feed rates
• Inadequate coolant or lubrication
• Machining soft or ductile materials
• Dull or worn cutting tools
• High friction between the tool and workpiece

Effects of Built-Up Edge

When BUE forms, it can negatively affect machining performance by:

• Producing a poor surface finish
• Reducing dimensional accuracy
• Increasing cutting forces
• Causing irregular chip formation
• Accelerating cutting tool wear  when the built-up material breaks away

How to Prevent Built-Up Edge

You can minimise BUE by following these best practices:

• Increase the cutting speed within the recommended range.
• Use sharp, high-quality carbide inserts.
• Apply the correct cutting fluid or coolant.
• Choose tool coatings that reduce friction, such as TiN or TiAlN.
• Optimise feed rate and depth of cut according to the workpiece material.
• Replace worn tools before excessive material adhesion occurs.

Why Understanding BUE Is Important

Even though the Built Up Edge is a small problem, it might influence machining processes greatly. If one is able to recognize the symptoms of BUE and choose the correct parameters and tools for the job, one will be able to get good finishes on surfaces, longer tool life and save money.

Comparison: Flank Wear vs Crater Wear vs Built-Up Edge (BUE)

Key Takeaway

• Flank Wear is the most typical and slowest form of cutting tool wear . It primarily impacts the surface finish and accuracy of the cut.
• Crater Wear occurs on the rake face due to high temperature and chip contact. This can eventually lead to the weakening of the cutting edge and failure of the tool.
• Built-Up Edge (BUE) happens when pieces of the work material build up at the cutting edge. This leads to bad surface finish, unstable cutting, and inconsistent performance of the machine.

Proper inspection of the cutting tools and use of appropriate cutting parameters, coolant, and carbide inserts will help to avoid all the three types of wear.

Best Practices for cutting tool wear  Prevention

Preventing insert wear  is essential for improving machining efficiency, extending tool life, and maintaining consistent product quality. By following the right machining practices, you can reduce wear, lower production costs, and avoid unexpected tool failures.

1. Select the Right Cutting Tool

Select a tool that suits the work material and machining process being used. Inserts made from high-grade carbides and coated tools have higher resistance to wear and function well in difficult cutting processes.

2. Use Recommended Cutting Parameters

Always stick to the manufacturer’s suggested cutting speed, feed rate, and depth of cut. Excessive speed creates heat, whereas inappropriate feed rates create friction and contribute to tool wear.

3. Apply Proper Coolant and Lubrication

Using the correct coolant helps reduce heat, friction, and chip adhesion. Proper lubrication also minimizes the chances of flank wear, crater wear, and Built-Up Edge (BUE).

4. Monitor Tool Condition Regularly

Inspect cutting tools at regular intervals for signs of wear. Replacing inserts before they become excessively worn helps maintain machining accuracy and prevents sudden tool breakage.

5. Ensure Efficient Chip Evacuation

Poor chip removal can cause chips to rub against the tool, increasing heat and wear. Use proper chip breakers and maintain effective coolant flow to keep the cutting zone clear.

6. Use Coated Cutting Tools

Coatings like TiN (titanium nitride), TiAlN (titanium aluminum nitride) and AlCrN (aluminum chromium nitride) add hardness, lower friction, and enhance thermal stability, which increases tool life.

7. Secure the Workpiece and Tool Properly

Vibration during machining can damage the cutting edge and reduce machining accuracy. Ensure the workpiece is clamped securely and the tool holder is properly tightened to minimise chatter.

8. Train Machine Operators

Experienced operators can identify early signs of tool wear and make timely adjustments to cutting parameters. Regular training helps improve productivity and reduces unnecessary tool replacement.

Final Tip

Apart from ensuring that your tool life is increased, it will also ensure that there is an improvement in terms of surface finishes and accuracy when carrying out CNC machining. The four things that are essential in achieving efficient and effective CNC machining are tool inspection, proper machining parameters, good tooling, and correct coolant application.

Conclusion

Understanding cutting tool wear helps improve machining quality, extend tool life, and reduce production costs. By identifying flank wear, crater wear, and Built-Up Edge (BUE) early and following the right machining practices, you can achieve better surface finish, higher accuracy, and more efficient CNC operations.

For high-quality carbide inserts, tool holders, end mills, and other CNC tooling solutions, visit at Jaibros and explore reliable products designed to enhance machining performance and productivity.

Frequently Asked Questions (FAQs)

1. What is tool wear in CNC machining?

Tool wear is the gradual deterioration of a cutting tool due to friction, heat, and mechanical forces during machining. It reduces cutting efficiency, affects surface finish, and can lead to poor dimensional accuracy if not monitored.

2. What are the main types of tool wear?

The three most common types of tool wear are flank wear, crater wear, and Built-Up Edge (BUE). Each occurs in a different area of the cutting tool and requires specific preventive measures.

3. What causes Built-Up Edge (BUE)?

Built-Up Edge (BUE) occurs when material from the workpiece sticks to the cutting edge of the tool. It is commonly caused by low cutting speeds, inadequate lubrication, dull tools, or machining soft materials like aluminium and mild steel.

4. How can tool wear be reduced?

Tool wear can be minimized by using high-quality cutting tools, selecting the correct cutting speed and feed rate, applying proper coolant, ensuring efficient chip evacuation, and inspecting tools regularly for signs of wear.

5. Why is monitoring tool wear important?

Regularly monitoring tool wear helps maintain machining accuracy, improves surface finish, extends tool life, reduces production costs, and prevents unexpected tool failures or machine downtime.