When using a metal plate fiber laser cutting machine, burrs (rough edges) on the cutting surface are a common issue. Many factors affect burr formation, but one of the most important is the cutting focus—where the laser beam is focused during cutting.
What Is Cutting Focus?
The cutting focus is the point where the laser beam meets the metal. Adjusting the focus changes how the laser cuts the material.
Let’s imagine the laser beam like a cone of light. The narrowest part of the cone is the focal point. This point can be set above, on, or below the surface of the metal plate.
- +4 mm focus: The laser focuses 4 mm above the surface.
- +2 mm focus: The laser focuses 2 mm above the surface.
- 0 mm focus: The beam focuses exactly on the surface.
- –2 mm focus: The beam focuses 2 mm below the surface.
- –4 mm focus: The beam focuses 4 mm below the surface.
How Does Focus Affect the Cutting?
We did a test by cutting straight lines at different focus points and compared the cutting seams (gaps).
- From +4 to 0, the cutting seam becomes narrower.
- At 0 mm, the seam is the thinnest.
- From 0 to –4, the seam gets wider again.
This means the best seam usually happens at or near the 0 mm focus. A small shift of ±2 mm is still acceptable, depending on the material.
How Does Focus Affect Burrs?
Next, we cut the same shape at different focus points and compared the burrs:
- +4 mm focus: More burrs
- +2 mm: Fewer burrs
- 0 mm: Very clean cut
- –2 mm: More burrs again
- –4 mm: Rough cut with lots of burrs
This shows that the best results (least burrs) often happen at 0 mm or +2 mm focus.
Common Cutting Issues and How to Fix Them
Problem: Cut Doesn’t Go Through the Metal
If the top of the cut looks clean but the bottom isn’t fully cut, the focus is probably too high. Try lowering it by 1–2 mm.
Problem: Layered or Rough Cutting Surface
If the cut surface looks bumpy or has layered lines, the focus is likely too low (for example, –6 or –8 mm). Try raising the focus slightly. Even a 1 mm change can improve the result.
Conclusion
To get clean cuts with fewer burrs, focus adjustment is key. Start with a focus of 0 mm and adjust slightly up or down depending on the material thickness and the result. A small change in focus can make a big difference in cutting quality.
