Fiber Laser CNC Machine Guide

• 1
  What a fiber laser CNC machine does to metal
• 2
  Fusion cutting, oxidation cutting and the limits of each
• 3
  Reading a cut edge to judge the process
• 4
  Design rules that keep laser parts cheap
• 5
  Where laser cutting fits in a CNC shop
• 6
  Fiber laser cutting compared with other cutting processes

A fiber laser CNC machine generates light inside a doped glass fiber, then delivers it through that same fiber to a cutting head. The active medium is ytterbium, which lases at about 1,070 nm. That wavelength is roughly one tenth of a CO2 laser's 10,600 nm, and it is absorbed far better by steel, stainless and aluminum.

The beam leaves the fiber, passes a collimating lens, then a focusing lens that squeezes it to a spot 0.1–0.3 mm across. Power density at that spot reaches 10^6 W/cm² or more. Metal does not get pushed aside. It is heated past melting, and in most cutting regimes past vaporization, while a coaxial gas jet blows the molten and vaporized material out of the kerf.

Movement comes from the CNC gantry and the cutting head. A gantry machine moves the sheet under a fixed head; a galvo head moves the beam with mirrors instead. Gantry machines dominate sheet cutting because they hold position over a 3,000–4,000 mm bed without losing focus.

The key engineering consequence: this is a thermal process, so every parameter you change alters the heat input. Focus position, gas pressure, feed rate and duty cycle all trade against each other. There is no single correct setting, only a window that produces a clean edge.

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  Wavelength matters1,070 nm is absorbed well by metals, poorly by organics.
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  Spot size sets the kerf0.1–0.3 mm spot gives a kerf of roughly 0.15–0.5 mm.
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  Gas does two jobsIt shields the lens and ejects molten material.

Fusion cutting uses nitrogen or argon at 10–20 bar. The gas is inert, so the cut edge stays free of oxide and appears bright. Mild steel up to about 6 mm and stainless up to the full thickness range are usually cut this way. The trade is gas cost and slower feed rates on thick plate, because inert gas carries less energy into the kerf than an exothermic reaction does.

Oxygen cutting uses O2 at 0.5–3 bar. Iron burns in the oxygen jet, and that reaction supplies a large share of the cutting energy. Feed rates on 6–20 mm mild steel roughly double compared with nitrogen. The edge comes out with a thin oxide layer, acceptable for structural parts and usually removed before painting anyway.

Thickness limits scale with source power, not linearly. A 6 kW source cuts mild steel to about 20–25 mm, stainless to about 20 mm, and aluminum to about 15 mm. A 12 kW source pushes mild steel past 30 mm, but the useful edge quality thins out well before the machine stops cutting. Below 1 mm, thin sheet distorts easily; a 1–2 kW source with high feed rates beats a 12 kW source here.

Copper and brass reflect near-infrared light at room temperature, which is why they were hard to cut for years. Once the surface melts, absorption climbs steeply, so a high-power source with good beam quality cuts them cleanly. Titanium cuts well but needs argon, because nitrogen reacts with hot titanium and leaves a brittle edge.

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  NitrogenClean edge, higher gas cost, best for stainless and visible parts.
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  OxygenFaster on mild steel, oxide edge, good for structural work.
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  Compressed airCheap, acceptable on thin mild steel, not on stainless.

A good laser edge has fine, near-vertical striations and a small heat-affected zone, typically 0.05–0.2 mm on steel. Drag lines that lean noticeably in one direction mean the feed rate is too high for the available power or the focus is too deep. Vertical striations that become coarse at the bottom of the cut mean the gas jet has lost energy before it reaches the exit.

Dross is the most common defect. On mild steel, hard dross that sticks usually means focus is too low or oxygen pressure is too high. On stainless, soft dross on the underside points to focus too high or feed too slow, so the melt pool grows and gravity pulls it through. Neither is fixed by turning power up.

Taper is the change in kerf width from top to bottom. It runs 0.02–0.1 mm on a well-tuned machine and grows with thickness. If your part needs a press-fit hole, taper is often more important than kerf width itself, because the hole is smaller at the bottom than the top.

Tolerance on laser-cut sheet is typically ±0.1 mm on thin material and ±0.25 mm on thick plate. Cutting does not hold the ±0.005 mm that milling holds. That gap is why laser blanks often feed a second milling operation rather than shipping as finished parts.

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  Vertical striationsFeed and focus are balanced; edge is ready to use.
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  Leaning striationsFeed too fast or focus too deep for the power available.
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  Hard drossFocus too low or oxygen pressure too high on mild steel.

Hole diameter should stay at least equal to sheet thickness. A 2 mm hole in 3 mm stainless will cut, but taper and dross make it unreliable. If the design needs a small hole, cut it undersize and drill or ream it after. The same logic applies to slots narrower than the thickness.

Corner radii should be at least half the sheet thickness. A sharp internal corner forces the machine to slow down, dumps heat into one spot, and often leaves a burned tip. Adding a 0.5 mm radius on thin sheet costs nothing and removes the problem.

Nesting drives material cost more than cutting speed does. A part rotated 15 degrees often fits a standard 1,220 × 2,440 mm sheet better than the same part aligned to the edges. On a 10,000-part run, a few percent of sheet utilization is real money.

Keep features that need tight tolerance out of the laser profile. Threaded holes, bearing bores, sealing faces and anything held to ±0.05 mm should be milled after cutting. Laser gets you a near-net blank fast; milling finishes the critical features. That split is how most production parts are actually made.

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  Hole ≥ thicknessSmaller holes need drilling or reaming afterward.
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  Corner radius ≥ half thicknessAvoids burn-through at sharp internal corners.
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  Nest before you quoteRotation and shared edges change material cost.

Laser cutting and CNC milling solve different problems, and most metal parts need both. A bracket starts as a laser-cut blank, then goes to a 3-axis or 5-axis mill for bores, counterbores, tapped holes and face flatness. Cutting alone cannot produce a bearing seat. Milling alone wastes stock and time on a flat profile.

At GreatLight we run 127 high-precision CNC machines across three plants, including 16 simultaneous 5-axis machining centers and a maximum processing size of 4,000 mm. That range covers both the flat blank and the finished part, so a job does not bounce between suppliers and lose tolerance stack-up at each handoff.

Material choice interacts with the process. Aluminum 6061 and 7075 cut quickly and cleanly. Stainless 304, 316 and 17-4PH cut well with nitrogen. Titanium TC4 (Ti-6Al-4V) and Inconel need argon and slower feed rates, and the cut edge may need a light mill pass before finishing. Copper and brass cut fine at higher power.

Post-processing decides whether the laser edge matters. Anodizing shows every striation, so a bead blast or light face mill usually precedes it. Powder coating hides most edge marks. If the part gets black oxide or electroless nickel, the oxide layer from oxygen cutting must be removed first or the coating will not adhere evenly.

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  Blanks from laserFlat profiles cut fast with no tool wear.
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  Features from millingBores, threads and flatness come off the CNC.
• 3
  Finishing follows bothAnodizing, plating and coating change edge requirements.