How to solve the problem of edge burning in fiber laser cutting machines? Edge burning (over-burning) is a common challenge in fiber laser cutting, particularly when dealing with carbon steel or sharp corners. It occurs when excessive heat accumulates in a small area, causing a runaway exothermic reaction with the oxygen assist gas.
Here is a comprehensive guide to solving edge burning through parameter adjustment and technique:
1. Optimize Corner Handling
Corners are the most frequent sites for edge burning because the machine decelerates, allowing the laser to dwell on a single point for too long.
- Lead-in and Lead-out: Ensure the laser enters the path from a “lead-in” line outside the actual part. For sharp corners, use a circular or “loop” lead-in to maintain a constant speed.
- Power Ramping (Slope): Configure the laser to reduce power automatically as the cutting head slows down for a corner and increase it as it accelerates.
- Corner Cooling: Some software allows for a “Cooling Point” or “Micro-joint” at sharp vertices, briefly pulsing the laser or pausing to let the metal cool before continuing.
2. Adjust Gas Parameters
The assist gas is your primary tool for thermal management.
- Switch to Nitrogen: If you are cutting thin mild steel with Oxygen and getting burnt edges, switching to High-Pressure Nitrogen (Fusion Cutting) will eliminate the exothermic reaction entirely, as Nitrogen is inert.
- Gas Pressure: If sticking with Oxygen, increase the gas pressure slightly. More gas flow helps cool the area surrounding the cut, though too much can cause turbulence.
- Nozzle Selection: Use a smaller diameter nozzle for thin materials to concentrate the gas flow precisely where the beam hits, blowing away molten slag faster.
3. Modify Laser Parameters
- Pulse vs. Continuous Wave (CW): Switch to Pulse Mode when cutting intricate details or sharp corners. Pulsing delivers energy in bursts, allowing the material to cool slightly between pulses.
- Focus Position: If the focus is too deep inside the material, heat builds up. Try moving the focus point upward (closer to the surface) to broaden the kerf slightly and allow gas to penetrate more effectively.
- Power Level: Simply lowering the peak power can help, but you must balance this with cutting speed to avoid “dross” (slag) at the bottom.
4. Material and Path Management
- Part Spacing (Nesting): Avoid placing small parts too close together. The heat from one cut can “pre-heat” the adjacent part, making it highly susceptible to burning.
- Film-Coated Metal: If cutting stainless steel with a protective film, use a “Pre-light” or “Evaporation” pass to melt the film along the cut line first, preventing the film from trapping heat or interfering with the gas flow.
Summary Checklist for Troubleshooting
| If you see… | Try this… |
| Melting at sharp corners | Add a “Cooling Point” or use “Power Ramping.” |
| Rough, burnt edges on straight lines | Increase gas pressure or increase cutting speed. |
| Complete blowout on small holes | Switch to Pulse Mode for the entire hole. |
| Burnt top edge | Move the focus position higher. |