1. What Is Focal Position in Laser Processing
The focal position is the distance between the laser head's focusing lens and the material surface at which the beam reaches its smallest diameter and highest energy density. This point delivers the most effective energy transfer during cutting or welding.
There are three common focal positions:
Negative focus: the focal point is below the material surface
Zero focus: the focal point is exactly on the surface
Positive focus: the focal point is above the surface
Each position has a different effect depending on material type, thickness, and the desired result.
2. How Focal Position Affects Cutting and Welding
For Cutting:
Too High (Positive Focus):
Leads to reduced energy at the cutting point, wider kerf, poor edge quality, and possible incomplete cuts.
Too Low (Negative Focus):
Results in deeper but narrower focus. It can cause slag adhesion or overheating on thick materials.
Correct Position:
Ensures the smallest spot size, maximum energy density, smooth kerf, and efficient penetration with minimal heat-affected zone (HAZ).
For Welding:
Off-focus (Too High or Low):
Causes incomplete fusion, porosity, or undercutting, especially in thin materials.
On-focus (Zero Focus):
Maximizes depth of penetration and energy efficiency, producing strong, clean welds.
3. Influencing Factors of Focal Position
Several variables affect the ideal focal position and how it impacts processing:
a. Material Type and Reflectivity
Highly reflective materials like aluminum or copper may require slight negative focus or green/blue lasers, which absorb better and compensate for energy loss.
b. Material Thickness
Thicker materials often benefit from a slightly negative focal point to allow deeper penetration. Thin sheets require precise focus to avoid burning or distortion.
c. Laser Power
Higher power lasers can tolerate slight focus offsets, but incorrect focal settings still reduce efficiency and quality.
d. Nozzle Distance and Alignment
If the nozzle is misaligned or the standoff distance is incorrect, it shifts the focal spot, affecting energy delivery and gas flow.
e. Optical Lens Condition
Dirty or damaged lenses distort the beam focus, so regular cleaning and inspection are essential.
f. Motion Speed
Faster speeds may require slight focus adjustments to maintain energy concentration along the cutting or welding path.
4. Best Practices for Managing Focal Position
Use automatic focus systems or capacitive height sensors for consistent focal control.
Regularly calibrate the focus during equipment setup or when changing materials.
Adjust focal position based on trial results to optimize cut quality or weld strength.
Monitor for symptoms of poor focus, such as burrs, slag, incomplete penetration, or uneven welds.
Conclusion
Focal position is a key parameter in laser processing that directly influences quality, efficiency, and outcome. Whether cutting or welding, ensuring proper focus is critical for delivering precision, minimizing defects, and extending machine lifespan. Understanding and adjusting focus based on material type, thickness, and other factors is essential for achieving the best processing results.
- Rayther Laser Lyra Zhang