Laser, Plasma or Waterjet: Choosing a Cutting Process

Guide

Three processes cover most sheet and plate cutting, and they overlap enough that the choice is rarely obvious. The honest short answer: laser for thin metal and fine detail, plasma for thick steel at low cost, waterjet for anything heat would ruin.

Laser cutting

A focused beam melts a very narrow line through the material. The cut is clean, the kerf is thin, and the edge usually needs no finishing.

• Best for thin to medium steel, stainless and aluminum where edge quality and tight tolerance matter.
• Detail — the narrow kerf holds small holes, fine lettering and intricate decorative patterns that other processes cannot.
• Speed is very high on thin material, which makes it economical for volume.
• Limits — cost per cut rises sharply with thickness, and highly reflective metals like copper and brass are harder to process.

If you are cutting decorative screens or gate panels, this is almost always the process. See laser cutting.

Plasma cutting

An ionised gas jet cuts by melting and blowing metal away. It is fast on thick material and the equipment cost is much lower, so the price per metre on heavy plate is hard to beat.

• Best for thick mild steel — structural plate, base plates, brackets, gussets.
• Speed on thickness — where laser slows down, plasma keeps going.
• Limits — wider kerf, a slight bevel on the cut face, more heat-affected zone, and a rougher edge that often needs grinding before welding or coating.
• Not suited to fine detail or parts where the edge is the finished surface.

For structural work where the part gets welded anyway, the rougher edge is irrelevant and the saving is real. See plasma cutting.

Waterjet cutting

A high-pressure stream of water mixed with abrasive grit erodes through the material. Nothing melts, so there is no heat-affected zone at all.

• Best for thick material, heat-sensitive alloys, and anything where the metallurgy at the edge must not change.
• Material range — it cuts almost anything: steel, aluminum, stone, glass, composites, rubber, and stacks of dissimilar materials at once.
• No hardening at the edge, so parts can be machined or tapped afterwards without fighting a hardened rim.
• Limits — slower than both alternatives and more expensive per metre. Very small holes are limited by the jet diameter.

Choose it when heat is the problem, not when speed is. See waterjet cutting.

How to decide in practice

Work through four questions in order.

• What material and how thick? Thin and non-ferrous points to laser. Thick mild steel points to plasma. Exotic or heat-sensitive points to waterjet.
• Is the cut edge visible or functional? If it is the finished surface, laser or waterjet. If it will be welded or ground, plasma is fine.
• How fine is the detail? Small holes, narrow slots and intricate pattern need laser. As a rule, a hole smaller than the material thickness is difficult on any process, and impossible on plasma.
• What is the quantity? High volume rewards the fastest process even at a higher machine rate. One-offs are usually decided by what is already set up.

What happens after cutting

Cutting is one step. Most parts also need deburring, and many need bending, machining for threads and close-tolerance features, or welding into an assembly. Bends in particular change the flat pattern, so the cutting file has to be developed with the bend allowance already in it — which is why it is worth telling the fabricator the whole scope rather than just asking for a cut.

Send a drawing and we will tell you which process suits it and why. Our drawing preparation guide covers what to include.