What each process actually is
Laser melts and blows material away along a focused beam. Modern fibre lasers dominate sheet metal work: fast on thin gauge, narrow kerf, repeatable, and clean enough that many edges go straight to welding or powder coating. Capability falls off as plate gets thick, with roughly 25 to 30 mm in steel the practical ceiling for most job shops, and reflective materials like copper needing the right machine.
Waterjet erodes material with a high-pressure water and abrasive stream. It does not care what the material is, glass, stone, titanium, hardened steel, stacked sheets, and it puts no heat into the part at all. The price is speed: it is the slowest of the three, and machine time is what you pay for.
Plasma cuts conductive metal with an electric arc through ionised gas. It is the economical way through thick steel plate, faster than waterjet and cheaper than laser at thickness, with a wider kerf, more taper and a larger heat-affected zone. For structural work that gets welded and painted, that trade is often exactly right.
The comparison side by side
| Laser | Waterjet | Plasma | |
|---|---|---|---|
| Materials | Steels, stainless, aluminium; reflective metals need the right machine | Anything, including glass, stone, composites, hardened steel | Conductive metals only |
| Sweet-spot thickness | Thin to ~20-25 mm steel | Any, including very thick | Medium to very thick plate |
| Precision | High; narrow kerf, fine detail | High, with slight taper on thick cuts | Lower; wider kerf, more taper |
| Heat input | Small heat-affected zone | None | Largest heat-affected zone |
| Edge quality | Clean, often weld-ready | Sandblasted texture, no hardening | Dross and hardening possible; may need dressing |
| Relative cost | Low on thin sheet at volume | Highest per part | Lowest on thick plate |
Figures and rankings here are deliberately conservative; exact limits vary by machine and operator. The pattern does not.
The three questions, in order
1. What is the material? Non-metal, or a metal that must not see heat: waterjet, and the decision is over. Conductive structural steel plate: plasma enters the running. Standard sheet steels, stainless and aluminium: laser is the default.
2. How thick? Under 20 mm steel, laser is usually fastest and cheapest. Past 25 mm the laser advantage fades: plasma wins on cost, waterjet wins on precision and edge, and the choice between them is question three.
3. What must the edge do next? If the edge is a weld prep under paint, plasma's roughness is fine and dressing is cheap. If the edge is a sealing face, a fatigue-critical feature, or in a heat-treatable alloy where a hardened zone causes trouble downstream, waterjet's cold edge or a laser's clean one earns its money. And if the profile later gets machined anyway, the cheapest adequate cut wins, because the mill removes the evidence.
Why this choice is usually not yours to make alone
Most profiles do not leave the workshop as profiles. They get folded, welded, machined, coated. The right cutting process depends on that downstream route, which is why the honest answer to "laser or waterjet?" is often "what happens to the part next?"
That is how TrueNorth runs sheet metal and fabrication work: cutting, forming, welding, machining and finishing as one coordinated order through vetted UK shops, with the process choices made against the finished part rather than per operation. You send the drawing and the function; the DFM review comes back within 48 hours with the route and one price for the delivered, inspected part. If your job is a bare profile run at volume, a dedicated laser house such as those in our buying-routes comparison may be the better call, and we will say so.