SPH275 arrives with a dark oxide layer from the hot rolling process. This scale absorbs laser energy differently than bare metal. Compared to cutting pickled or cold-rolled material, SPH275 typically needs either slightly higher power or reduced feed rates—usually 10-15% slower than equivalent thickness of descaled steel. Some shops keep a separate SPH275 cutting table in their CAM library to avoid manual adjustments job to job.
For thinner gauges up to 3mm, 1kW to 2kW fiber lasers run well at 3 to 5 meters per minute using nitrogen assist. Edge oxidation stays minimal, and dross formation rarely appears with proper focal position.
Moving to 4mm to 8mm plate, 2kW to 4kW at 1.5 to 2.5 meters per minute delivers consistent results. Oxygen assist becomes more common at these thicknesses, with pressures around 0.6 to 0.8 bar producing clean, weld-ready edges.
Above 8mm up to 12mm, 4kW to 6kW lasers running oxygen assist at 0.4 to 0.6 meters per minute handle SPH275 reliably. The key becomes managing heat input—too slow and the kerf widens; too fast and incomplete penetration leaves parts attached.
The mill scale affects focus behavior. Starting with focal position at the material surface works for thinner gauges. For thicker plates, dropping focus 1-2mm below the surface improves edge squareness and reduces dross on the bottom side. Running a small test grid with varied focal positions saves material compared to guessing on production parts.
Above 6mm, standard piercing can create large spatter that contaminates the scale surface. Using ramp piercing or longer pierce delays allows heat to penetrate without explosive blowback. Maintaining higher pierce pressure than cut pressure prevents material ejection from the pierce hole.
Laser-cut SPH275 produces edges that weld directly for most applications. Light oxidation near the cut face from oxygen assist isn't a problem. If dross appears, increase oxygen pressure slightly or decrease feed rate in 5% increments until it clears up.
