What is built-up edge?
Built-up edge is an accumulation of material that is deposited on and adheres to the cutting edge of the tap during machining. This deposit modifies the effective profile of the tool, making cutting irregular and increasing the likelihood of thread defects.
This phenomenon is particularly common in materials that tend to “stick” to the cutting edge, such as low-silicon aluminum, copper and austenitic stainless steels.
Signs that indicate the presence of built-up edge
- thread with an irregular or torn surface;
- tap tends to “scratch” instead of cutting;
- short, compressed or deformed chip;
- increased cutting torque;
- sudden drops in thread quality;
- abnormal chip coloration, a sign of overheating.
Why built-up edge forms: the main technical causes
Built-up edge is the result of a combination of factors related to the material, tap geometry and cutting parameters. The most common causes include:
- Materials with high ductility, such as aluminum with Si < 10%, copper and austenitic stainless steels, which tend to adhere to the cutting edge.
- Inadequate cutting speed, which generates heat and promotes material adhesion.
- Insufficient lubrication, which does not sufficiently reduce friction between chip and cutting edge.
- Tap geometry unsuitable for the material being machined.
- Inadequate or absent coating, which does not protect the cutting edge from adhesion.
UFS solutions to eliminate built-up edge
To prevent built-up edge, it is essential to work on the tool, coating and cutting parameters. The most effective UFS solutions include:
- Use anti-adhesion coatings such as XP or TXC, designed to reduce material adhesion to the cutting edge.
- Choose specific geometries for light alloys, such as AZ geometry, for example E24M AL AZ, optimized for aluminum and copper.
- Optimize cutting speed to reduce heat and friction.
- Improve lubrication with fluids suitable for the material and hole depth.
- Check pre-hole quality to avoid overloading the cutting edge.
Best practices to prevent built-up edge
- use specific coatings for ductile materials;
- avoid cutting speeds that are too high on aluminum and copper;
- prefer geometries with ample chip space;
- regularly monitor the condition of the cutting edge;
- ensure constant and adequate lubrication;
- choose taps designed for materials at risk of adhesion.