1. What Is Focal Depth?
Focal depth refers to the distance along the Z-axis (up and down) where the laser beam remains sufficiently focused to perform effective cutting. The most intense energy is at the focal point, but there's a small range above and below where the beam can still cut efficiently. This range is called the focal depth or focus tolerance.
2. Why Focal Position Matters
The laser's focal point must be precisely aligned with the material's surface or interior, depending on the material type and thickness. Proper focal positioning ensures:
Maximum energy concentration
Narrower kerf (cut width)
Minimal slag or burr
Cleaner and faster cutting
3. Effects of Improper Focal Depth
If the focus is too high: The laser beam diverges before hitting the material, resulting in wider kerf, more slag, and poor penetration.
If the focus is too low: The beam loses sharpness and energy by the time it reaches the surface, causing incomplete cuts or rough edges.
For thicker materials: A slightly deeper focus may improve penetration but may require higher power.
4. Interaction with Material Types
Thin materials (e.g., stainless steel <3 mm): Set the focal point on or just below the surface.
Thick materials (e.g., mild steel >10 mm): The focus should be deeper into the material for stable cutting.
Reflective materials (e.g., aluminum, copper): Require careful focusing and possibly shorter-wavelength lasers (e.g., blue or green) to reduce reflection losses.
5. Other Influencing Factors
Lens cleanliness
Beam quality and spot size
Automatic focus adjustment systems
Machine calibration
Conclusion
Focal depth is a key factor that determines laser cutting efficiency, quality, and reliability. Correctly setting the focal point helps minimize defects like slag, burrs, and incomplete cuts. For best results, operators should routinely check focus alignment, maintain optics, and understand the material-specific needs.
-- Rayther Laser Lyra Zhang