Solutions to Burning and Yellowing Edges in Metal Laser Cutting

Burned edges and abnormal glowing (usually refers to unusual sparks or slag glowing under the cut) are common issues in metal laser cutting. They typically indicate unstable cutting processes or excessive energy input, leading to over-burning and melting. Below is a simplified, step-by-step guide to diagnose and resolve the problem.
I. Key Causes
Burned edges and abnormal glowing stem from excessive heat input or inadequate heat dissipation. Specific causes include:

1. Gas Issues (Most Common)

•  Insufficient gas pressure: Auxiliary gases (O₂, N₂, air) fail to blow away molten metal promptly, causing slag buildup and continuous burning.
•  Low gas purity: Impure N₂ (e.g., with O₂) for stainless steel/aluminum triggers oxidation, leading to extra heat and burning.
•  Wrong gas type: Use O₂ for carbon steel (aids combustion) and high-purity N₂ for stainless steel (prevents oxidation).

2. Process Parameter Errors

•  Excessive laser power: Over-melts materials.
•  Slow cutting speed: Prolongs laser exposure, causing heat accumulation.
•  Incorrect focus position: Reduces energy density, widens cuts, and expands heat-affected zones.
•  Nozzle issues: Mismatched nozzle size, improper height, or damage disrupts gas flow.

3. Equipment/Consumable Problems

•  Contaminated lenses (protective/focus lenses): Reduce laser energy, forcing higher power use (worsens burning).
•  Misaligned nozzle: Gas flow is uneven, failing to remove slag effectively.

4. Material Issues

•  Oil, rust, or coatings on material surfaces: Burn during cutting, generating extra heat.
•  Material composition: High-reflectivity/thermal-conductivity metals (Al, Cu) require specific parameter settings.

II. Step-by-Step Solutions
Follow this order to troubleshoot (start with the simplest, most frequent issues):

Step 1: Check & Optimize Gas Settings (Highest Priority)
1.Gas Pressure

•  Carbon steel (O₂): Adjust to manufacturer’s recommendations (insufficient pressure often causes burning).
•  Stainless steel/aluminum (N₂/Ar): Increase pressure to 1.0–2.0 MPa (or higher, based on thickness) – high pressure is key to removing molten metal.
•  Inspect gas lines: Check for leaks, blockages, or low cylinder pressure.

2. Gas Purity & Type

•  Stainless steel: Use N₂ with ≥99.9% purity.
•  Carbon steel: Use industrial-grade O₂.
•  Aluminum: Use high-purity N₂ or compressed air.

3. Nozzle Maintenance

•  Choose the right size: Thicker materials need larger nozzles (e.g., φ2.0mm/φ3.0mm).
• Replace with a new, undamaged nozzle (old nozzles may have deformed holes).
• Calibrate height: Ensure 0.5–1.5mm distance from the material surface (use auto-calibration if available).

Step 2: Optimize Cutting Parameters
1. Cutting Speed: Increase speed (within the range that ensures full penetration) to reduce heat input. Avoid over-speeding (causes incomplete cuts).
2. Laser Power: Lower power slightly (balance with speed adjustments).
3. Focus Position:

• -Refer to the equipment manual for recommended positions (by material/thickness).
•  Test positions (-2mm to +2mm) to find the one with the smoothest, slag-free cut.

4. Pulse Mode: For thin metals or overheating issues, switch from continuous laser to pulse mode (allows short cooling intervals).
Step 3: Inspect Equipment

•  Clean Lenses: Regularly clean protective/focus lenses; replace damaged ones.
• Check Beam Alignment: Have professionals verify if the laser beam exits the nozzle center (misalignment needs calibration).

Step 4: Prepare Materials
Clean oil, rust, or coatings from material surfaces before cutting.
Quick Troubleshooting Checklist
1. First Priority (Gas)

•  Is gas pressure sufficient? (Boost N₂ pressure for stainless steel!)
•  Is the correct gas type used? (O₂ for carbon steel, high-purity N₂ for stainless steel)
•  Is the nozzle new/undamaged? Is the height calibrated?

2. Second Priority (Parameters)

•  Is the cutting speed too slow? (Try increasing it)
•  Is the laser power too high? (Try lowering it)
•  Is the focus position correct? (Test positions)
•  Can pulse mode be used?

3. Third Priority (Equipment/Materials)

•  Are lenses clean?
• -Is the material surface clean?

Most burned edge issues can be resolved with the above steps. If problems persist, contact your equipment manufacturer for material/device-specific support.