Why does a fiber laser leave burr on stainless steel?
Updated:
Short answer
Burr on stainless cut with nitrogen almost always means the melt is not being blown out fast enough: cutting speed too low for the power, nitrogen pressure or purity too low, a worn or off-centre nozzle, or focus sitting too high in the sheet. Start with nozzle condition and gas pressure — they explain most burr cases in a shop.
What causes burr on stainless
| Symptom | Likely cause | First action |
|---|---|---|
| Fine, even burr along the whole contour; worse as thickness grows. | Nitrogen pressure too low | Raise to 12–16 bar for 1–6 mm, 16–20 bar for 8–12 mm. Check the pressure at the head, not at the cylinder. |
| Burr on one side of the part, or appears after a few hours of work. | Worn, spattered or off-centre nozzle | Inspect the orifice, replace if oval or spattered, re-centre the beam. A 0.1 mm offset is enough to skew the gas jet. |
| Wide top kerf, narrow bottom, hard grey burr underneath. | Focus too high in the sheet | Move focus down: for nitrogen cutting it sits below the surface, roughly −⅓ to −⅔ of thickness. |
| Heavy, sticky burr plus a wide heat-affected edge and blue tint. | Speed too low for the power | Raise feed until the edge cleans up; slow cutting overheats the melt instead of ejecting it. |
| Yellow or straw-coloured edge and a thin burr that returns after a cylinder change. | Nitrogen purity below 99.95% | Use 99.95%+ (ideally 99.999%) and check the line for leaks that pull in air. |
| Burr appears gradually across a shift, together with a drop in piercing reliability. | Dirty protective lens | Inspect the protective glass; a burned or spattered lens both loses power and shifts the focal plane. |
Cutting parameters for stainless by thickness and gas — inside the app. Open SBM Laser Help →
Or take it with you:
What to check, in order
- Stop and look at the nozzle: orifice round, no spatter, no melt on the tip. Replace before adjusting anything else.
- Verify nitrogen pressure at the cutting head under flow, not on the regulator gauge at rest.
- Run a focus test (a ramp or focus line) and set the plane below the surface for nitrogen.
- Increase feed rate in 10% steps until the underside cleans up; then step back 5% for margin.
- Check protective glass and beam centring — both drift silently and mimic every other cause.
- Only then change the parameter set: power, frequency, gas ramp at corners.
Nitrogen cutting on stainless — typical starting ranges (6 kW fiber)
| Thickness | Nozzle | Nitrogen pressure | Focus vs surface | Speed |
|---|---|---|---|---|
| 1 mm | 1.4–1.5 mm double | 12–14 bar | −0.5 mm | 30–40 m/min |
| 3 mm | 2.0 mm double | 14–16 bar | −1.5 mm | 10–14 m/min |
| 6 mm | 2.0–2.5 mm double | 16–18 bar | −3 mm | 4.5–6 m/min |
| 10 mm | 2.5–3.0 mm double | 18–20 bar | −5 mm | 2–2.8 m/min |
| 12 mm | 3.0 mm double | 18–22 bar | −6 mm | 1.5–2.2 m/min |
Ranges for a clean beam path and 99.95%+ nitrogen. Machine builders differ — treat this as the starting window, not the final recipe.
Related questions
- Can I cut stainless with oxygen instead to avoid burr?
- You can, and the burr usually drops, but the edge oxidises: it turns dark, loses corrosion resistance at the cut and needs grinding before welding or painting. Oxygen on stainless is normal for thick plate where edge finish is not critical.
- Why does burr appear only on small contours and corners?
- On short segments the head never reaches the programmed feed, so the effective speed is far below the parameter set. Use corner power ramping or a lead-in, and check the acceleration settings rather than the gas.
- Does burr mean my laser is losing power?
- Not by itself. Power loss shows up first as unreliable piercing and slower penetration in thick material. If piercing still works normally, look at nozzle, gas and focus before suspecting the source.