Basic Knowledge of Laser Cutting for Sheet Metal Parts

The beam lands on a spot a few tenths of a millimeter wide. Power density at that spot is high enough to melt or vaporize metal, and a coaxial gas jet blows the molten material out of the kerf. The head then travels along the toolpath. That is the whole process in one sentence. Everything else is control of focus, power, speed and gas.

Two laser sources dominate sheet metal work. CO2 lasers run at 10.6 μm and cut mild steel, stainless, acrylic and wood well, but they reflect off copper and aluminium alloys. Fiber lasers use a shorter wavelength near 1 μm, which couples far better into reflective metals. That is why fiber machines now handle most stainless and aluminium work, and why thick mild steel cutting has moved away from CO2.

Cutting is not a thermal free-for-all. The kerf stays narrow, usually 0.1–0.5 mm depending on material and thickness, and the heat-affected zone is small. A 1 mm stainless sheet may show a HAZ under 0.1 mm with nitrogen assist. On thicker steel the zone widens and the edge color shifts. Watching the cut edge tells you whether the parameters are right: a clean silver-grey edge on stainless means good gas coverage and correct focus.

Flat parts with profiles cut from sheet are the natural fit. Brackets, covers, mounting plates, gaskets and busbar shapes come off the bed ready to form or weld. No tooling cost, no minimum order quantity, and the first part is the same price as the thousandth. For a prototype or a low-volume run, that beats a stamping die by a wide margin.

Speed is another factor. A fiber laser cutting 1 mm mild steel runs at several meters per minute; the same part on a mill needs a tool change and multiple passes. When the geometry is 2D and the tolerance is not tighter than about ±0.1 mm, laser wins on time. Thin sheet is where it is strongest.

The process is also easy to nest. Odd-shaped blanks that would waste material on a mill can be packed tightly on a 4,000 mm bed. That matters on 316L or titanium where scrap cost is real.

There is a limit. A laser cuts through the sheet, so it cannot produce a blind pocket, a thread, or a counterbore. Those features need a mill or a tapped insert afterward.

Edge quality drops as thickness climbs. A clean cut in 1 mm stainless is routine; at 6 mm the kerf widens, dross can form on the underside, and the edge may need grinding. If the drawing calls for Ra 0.8–1.6 μm on the cut face, plan a finishing pass.

Tolerance is the other constraint. A laser positions well, but thermal movement, sheet flatness and the kerf itself add up. Typical achievable tolerance on a laser-cut profile is looser than the ±0.005 mm we hold on a CNC mill. If your part needs a bearing bore or a sealing face, cut it oversize and machine it.

Taper is a quiet problem. The kerf is not perfectly parallel through the thickness; on thick plate the top edge can be wider than the bottom by a few hundredths of a millimeter. For a locating tab that gap matters. Design the mating feature with clearance rather than counting on a press fit.

Reflective and highly conductive metals behave differently. Copper and brass absorb less of the beam at 1 μm, so they need higher power and often a different assist gas. Aluminium cuts fine, but it conducts heat away fast, so thick sections can be slow.

Lasers also struggle with sharp internal corners. The beam has a finite diameter, so the smallest inside radius you can cut is roughly half the kerf. A square internal corner is not possible. Add a radius on the drawing and the part gets cheaper and cleaner.

Start with the smallest hole you need. The practical rule is that hole diameter should be at least equal to the sheet thickness, and no smaller than about 1 mm on thin stock. A 0.5 mm hole in 3 mm steel is possible but slow and inconsistent. If the part needs a small hole, expect to drill it after cutting.

Keep the profile simple where you can. Every corner adds travel time and every narrow bridge between two cuts risks distortion. A tab 1 mm wide in 2 mm stainless will bow from residual stress. Make it 2 mm and it holds shape.

Spacing between parts matters too. Nested parts should sit at least one sheet thickness apart so the heat from one cut does not soften the edge of its neighbor. On thin material the scrap skeleton can warp and lift, which ruins the next pass.

If the part will be bent after cutting, put the bend line away from the cut edge. The HAZ is slightly harder and less ductile than the base metal. A bend right on a laser-cut edge can crack. Leave 2–3 mm of flat stock between the cut and the bend radius.

Finally, mark the drawing with the cut path you expect. Laser cutting is a 2D process, so a clear flat pattern with bend lines and hole callouts saves a round of questions. We review every upload and send back a DFM note within 12 hours.

Waterjet cuts thicker stock and leaves no HAZ, but it is slower and the abrasive stream tapers more on thick plate. For 1–4 mm sheet, laser is faster and cheaper. For 20 mm stainless, waterjet is the better call.

Plasma is cheaper per meter on thick mild steel but the kerf is wide and the edge needs cleanup. It is a fabrication tool, not a precision one. A part with a ±0.1 mm profile will not come off a plasma table.

CNC milling removes the thickness limit and holds tighter tolerance. It also adds features a laser cannot: pockets, threads, counterbores, 3D contours. When a part is thick, needs tight tolerance, or has features in the Z direction, milling is the answer. Many of our jobs combine both: laser-cut blank first, then 5-axis machining for the critical bores.

The decision usually comes down to three questions. Is the part flat? Is the tolerance looser than about ±0.1 mm? Is the thickness under 6 mm? Three yes answers point to laser. Any no sends the job to a mill or a waterjet.