Basic Knowledge of CNC Laser Processing

A CNC laser machine moves a focused beam along a path taken from CAD data. CAM software converts the geometry into G code, and the controller drives mirrors, a gantry or a robot arm to keep the focus point on that path. At the focus, power density is high enough to melt or vaporize metal in a narrow kerf, typically 0.1–0.5 mm wide on thin sheet.

Three things decide the result: wavelength, power and focus position. Wavelength sets how much light the surface absorbs. Power and travel speed set how much energy per millimeter of cut. Focus position decides kerf width and whether the cut edge is square or tapered. Assist gas does the rest. Oxygen adds exothermic heat and speeds up mild steel cutting but leaves an oxidized edge. Nitrogen or argon shields the melt and gives a cleaner, weld-ready edge at a slightly slower speed.

The cut zone is a heat-affected region, not a machined surface. Expect a narrow recast layer and a small taper on thick plate. That is normal. It matters when the edge is a sealing face, a bearing seat or a fatigue-critical feature, because those need a later machining pass.

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  KerfThe slot the beam leaves behind. Size it into your nest layout.
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  HAZHeat-affected zone; hardness and microstructure change near the edge.
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  Assist gasO₂ for speed on steel, N₂ for clean edges on stainless.
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  FocusSet above, at or below the surface to trade kerf width against edge squareness.

Fiber lasers at around 1 μm wavelength dominate metal cutting today. They cut mild steel, stainless, aluminium, copper and brass, and they do it with a solid-state source that needs little maintenance. For most sheet metal work up to roughly 6 mm, a fiber machine is the default answer. Above that, edge quality and dross become the limiting factors, not the source.

CO₂ lasers at 10.6 μm cut non-metals that fiber sources cannot handle well: acrylic, PMMA, wood, MDF, leather, some ceramics and coated board. They also cut mild steel, but the electrode-based resonator has higher running cost. If your part is a plastic display panel with a polished edge, CO₂ is often the better process.

Nd:YAG is the older solid-state option, still found in spot welding, drilling and some marking cells. Its role has shrunk in cutting, but short-pulse variants remain useful for fine holes in turbine and fuel-injector parts. The practical question is not which source is newest. It is which one gives you the edge and thickness you need at a cost you can carry.

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  FiberMetals, thin to medium sheet, low maintenance, fast.
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  CO₂Non-metals and organic materials; good cut edge on acrylic.
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  Nd:YAGWelding, drilling, fine marking; niche in cutting.

Mild steel and stainless are the easy cases. Stainless cuts cleanly with nitrogen assist and gives a bright edge that can go straight into welding. Aluminium cuts quickly but reflects a good share of the beam, so power and focus need tuning, and thick sections tend to show more dross on the bottom edge.

Copper and brass are the harder non-ferrous cases. Their reflectivity and thermal conductivity pull heat away from the cut zone, so you need higher power density and a wavelength-matched source. Thin copper is routine. Thick copper is a job for a high-brightness fiber machine with the right lens and gas setup, and even then cut speed drops sharply.

Titanium and Inconel cut with inert gas and careful parameter control. Titanium needs oxygen kept out of the cut zone to avoid embrittlement, and the cut edge usually needs a mechanical cleanup before service. Plastics behave differently again: they do not melt and blow away the way metal does. They vaporize, and the risk is a heat-affected rim, discoloration or a burnt edge. PMMA and PC cut well on CO₂ with air assist; PVC should be avoided because it releases corrosive fumes.

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  Good fitMild steel, stainless 304/316, aluminium, thin copper, PMMA, PC.
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  Needs tuningThick copper and brass, titanium, Inconel, reflective surfaces.
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  AvoidPVC and other chlorine-bearing plastics; they release acid fumes.

Laser cutting holds position well on thin sheet, but it is not a precision finishing process on its own. Kerf width, taper and the recast layer set a practical limit. If a hole must be a press fit or a bearing seat, cut it undersize and bore it on a CNC mill. That two-step route is common and cheap compared with fighting the laser.

Sheet thickness drives everything. Thin stock cuts fast with a narrow kerf and little taper. As thickness rises, the beam spreads, taper grows, and the bottom edge may show dross that needs grinding. On 10 mm stainless, a laser is still viable for profile work, but the edge will not be a sealing surface.

Milling wins when you need three-dimensional geometry, tight fits, threaded holes, deep pockets or a surface finish below Ra 1.6 μm. Laser wins when the part is flat, thin, has many holes and profiles, and the edge is not a functional seat. Many production parts use both: laser the blank, then mill the critical features on a 3-axis or 5-axis machine. At GreatLight we run that combination on the same floor, so a laser-cut blank can move straight to a 5-axis center for finishing.

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  Laser firstFlat profiles, hole patterns, blanking before machining.
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  Mill firstFits, threads, pockets, sealing faces, tight flatness.
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  BothLaser blank plus milled critical features; one setup plan.