Laser Processing — Engineering Decision Guide

Choose a fiber laser for cutting metals — especially thin-to-medium sheet, stainless, aluminum, brass, and copper — and where speed, running cost, and reflective-metal capability matter. Choose CO₂ for cutting non-metals (acrylic, wood, many plastics) and, historically, for a very smooth edge on thick mild-steel plate, though modern high-power fiber has largely closed that gap.

The ~1µm fiber wavelength is absorbed far better by metals than CO₂'s ~10µm beam, so fiber cuts metal faster, at lower electrical cost, with no laser-gas or beam-path mirrors to maintain, and it can process copper and brass that once reflected CO₂ beams dangerously. CO₂'s longer wavelength couples well into organic non-metals, which fiber cannot cut cleanly — so the two are complementary, not simply old-versus-new.

A fiber laser can't cut acrylic or wood cleanly. A CO₂ laser is slower and costlier per part on sheet metal and struggles with (or is endangered by) reflective copper and brass. Matching source to material family is the first decision, before power or options.

Use oxygen for thick mild/carbon steel — it adds an exothermic burn that boosts speed and thickness capacity, leaving an oxidized edge. Use nitrogen (high pressure) for stainless, aluminum, and any part needing a clean, oxide-free, weld/paint-ready edge. Use compressed air as a low-cost middle option for thin mild steel and aluminum where a light oxide is acceptable.

Assist gas both ejects molten material and sets the edge chemistry. Oxygen reacts with steel and releases heat, so it cuts thicker and faster — but leaves an oxide layer that must be removed before welding or coating. Nitrogen is inert: it blows the melt out without oxidizing, giving a bright, ready-to-finish edge, at the cost of higher gas consumption and pressure. Air is ~80% nitrogen and cheap, a reasonable compromise on thin stock.

Oxygen on stainless leaves an oxidized edge that fails downstream welding or corrodes. Nitrogen on thick mild steel is slow and burns expensive gas for no benefit the job needs. Air where a pristine edge is required leaves a light oxide that still needs cleanup.

Set focus roughly on the top surface for thin material, and progressively into or below the sheet for thicker sections and for nitrogen cutting, so the beam waist and gas do their work through the full kerf. Hold the nozzle standoff tight and consistent (typically ~0.5–1 mm) and keep the nozzle centered on the beam. Follow the machine's material/thickness table as the starting point, then fine-tune on a test cut.

Focus position sets where the beam is smallest and most intense relative to the plate. On thin stock a top-surface focus gives the narrowest kerf; on thick stock or high-pressure nitrogen cutting, driving the focus down keeps enough energy and gas pressure at the bottom of the cut to clear the melt and avoid a wedge-shaped kerf. Standoff sets how effectively the assist-gas jet reaches the kerf — too far and it disperses, too close and it disturbs the melt pool.

Wrong focus leaves a tapered kerf, incomplete cuts, or heavy bottom dross. Inconsistent standoff (a warped or bumped sheet) causes intermittent cutting and crashes. A nozzle off-center to the beam cuts unevenly and burns one kerf wall.

Use annealing (low power, no material removal) for permanent, corrosion-safe black marks on stainless and titanium — medical and tooling parts that must not have a breachable surface. Use engraving (deep material removal) for wear-resistant marks that survive machining, heat, or abrasion. Use etching/foaming (shallow melt) for fast high-contrast marks where depth isn't needed.

Marking methods trade depth, contrast, permanence, and surface integrity. Annealing oxidizes just below the surface to create a color change without breaking the surface — critical where a recess would trap contaminants or start corrosion (implants, surgical tools). Engraving physically removes material for a mark that outlasts surface wear. Etching melts a shallow layer for speed and contrast when the part won't see heavy wear.

Engraving a medical part that needs a sealed surface creates a crevice for bacteria and corrosion. Annealing a part that will be abraded or machined lets the mark disappear. Etching where deep permanence is required fades under wear.

Hard, re-solidified metal (dross) clinging to the underside of the cut, or a rough, burred bottom edge — requiring a secondary deburring operation and, in bad cases, scrapping the part.

Cutting speed too high or too low for the thickness, wrong focus position (energy not reaching the kerf bottom), insufficient assist-gas pressure or a worn/off-center nozzle, incorrect gas for the material, and a dirty or damaged lens/protective window.

1) Tune cutting speed to the material/thickness — dross is often a speed mismatch. 2) Correct focus position so the beam clears the full kerf. 3) Raise assist-gas pressure and replace a worn nozzle; recenter it to the beam. 4) Confirm the right gas (nitrogen for clean stainless/aluminum edges). 5) Inspect and clean the lens and protective window — contamination scatters the beam.

Trouble starting or completing cuts in copper, brass, or shiny aluminum — stalled pierces, inconsistent edges — and, on unprotected machines, back-reflected energy that trips faults or damages the laser source.

High surface reflectivity at the laser wavelength (worst on copper and brass), a mirror-bright unoxidized surface, and starting a pierce on a flat reflective face that bounces the beam straight back up the beam path.

1) Use a fiber laser with back-reflection protection/isolation rated for reflective metals — the primary enabler. 2) Follow the builder's reflective-material pierce settings (ramped power, modulated pulsing to establish a keyhole). 3) Where allowed, a lightly matte or coated surface couples energy better than a mirror finish. 4) Keep power/speed within the machine's reflective-metal window rather than forcing thin-steel parameters. 5) Never run reflective metal on a source not rated for it.