Two basic facts about laser cutting 316L: nitrogen must be used (not oxygen), otherwise the cut edge oxidizes and requires secondary processing; but nitrogen cutting has no exothermic oxidation, relying entirely on molten blow-off, so it is more sensitive to parameter matching — that is how dross arises.
One-sentence diagnosis
Soft dross at the bottom (can be knocked off, sticky) is mostly caused by too slow speed or too high power; hard dross at the bottom (cannot be knocked off, shiny) is mostly caused by too fast speed or insufficient gas pressure. First identify which type it is, then adjust parameters — the adjustment directions for the two are completely opposite.
Why nitrogen for 316L
- Oxygen cutting forms an oxide layer (blackening) at the cut edge, directly damaging the corrosion resistance of the stainless steel cut edge, requiring subsequent pickling or grinding;
- Nitrogen is an inert shield, leaving the cut edge silver-bright with essentially no oxidation, ready for direct welding or use after cutting;
- The cost: no exothermic oxidation, so cutting speed at the same power is slower than carbon steel, especially noticeable on thick plate.
Three forms of dross and adjustment directions
- Soft dross at the bottom (hanging but not falling, can be knocked off): too much molten material. Reduce power, increase speed, or lower gas pressure (excessively high pressure blows the melt pool too wide);
- Hard dross at the bottom (firmly adhered, shiny): molten material solidified before being blown away. Speed too fast or gas pressure insufficient — increase pressure, reduce speed;
- Rough side face, deep striations: incorrect focus position or dirty lens/nozzle. Check focus first, then nozzle.
Parameter ranges (reference, must be trial-cut per machine)
Different power levels and equipment brands vary greatly; the following is only directional reference:
- Gas pressure: nitrogen cutting of 316L commonly uses 10–14 bar (thinner plate can be lower, thicker plate needs higher); insufficient gas pressure is the most common cause of hard dross;
- Focus: 316L commonly uses negative focus (focus below the plate surface, about -1 to -3 mm depending on plate thickness); positive focus causes bottom dross;
- Speed: 30–50% slower than carbon steel of the same thickness; too fast causes hard dross, too slow causes soft dross and overburning;
- Nozzle: diameter must match plate thickness; a dirty nozzle or poor concentricity directly causes one-sided dross.
An on-site diagnostic sequence
- First check cut edge color: blackening indicates impure gas or oxygen contamination (check gas source purity and lines);
- Then check dross form: soft dross — adjust speed/power; hard dross — adjust gas pressure/speed;
- Then check focus and nozzle: try a new nozzle on a test piece, which can eliminate half the problems;
- Only then adjust program parameters: change only one variable at a time, otherwise you will never dial it in.
Common pitfalls
- Switching to oxygen to cut faster: the cut edge oxidizes and must be fully ground before welding, making it slower overall;
- The pressure gauge reading is a 'set value'; actual pressure at the nozzle is affected by lines and the regulator, so verify it;
- Using thick-plate parameters on thin plate (excessively high pressure deforms thin plate);
- Relying on manual grinding to fix dross without investigating the root cause — in mass production, grinding cost will exceed cutting cost;
- Ignoring material surface condition: 2B and BA, cold-rolled hard and annealed states do not use exactly the same cutting parameters.
Tell us your plate thickness, machine power, gas type and target cut surface quality, and we will give recommendations on material surface condition (2B/BA) and leveling accuracy for your process — dross is sometimes not a parameter issue but a matter of plate flatness and internal stress.
