Metal fabrication methods compared

At a glance

HAZ: heat-affected zone. Detail is for stainless steel (IMOA, 2020): ask the partner about other metals. No prices.

Edges first: what each cut leaves behind

Choose the method from the edge you will see. TWI defines the heat-affected zone as a non-melted area of metal that has undergone changes in material properties, and says shearing and waterjet cutting do not create one because they do not heat the metal. Laser cutting creates a small one, plasma an intermediate one, and oxyacetylene cutting the widest, because of its high heat, slow speed and flame width.

• Laser. In stainless, the laser melts the metal while a nitrogen jet blows it out of the kerf, which prevents oxidation and loss of corrosion resistance. IMOA says laser edges can typically be used without further edge preparation, and TWI lists a high-quality cut needing no finishing as a benefit.
• Plasma. TWI says a conventional plasma edge is like an oxyfuel one, with top edge rounding, poor squareness or a bevel. IMOA says as-cut stainless edges can have reduced corrosion resistance, that oxygen-bearing gases should be avoided, and that if the cut face discolours, pickling or edge milling restores it: see pickling, passivation and electropolishing.
• Waterjet. No heat-affected zone, and edges are normally of high quality, though the bevel angle of the cut face can be an issue on thick sections. It is not cost effective for thin sheet, but stacks of thin sheets can be cut together (IMOA).
• Shearing and punching. The edge has zones: a rolled-over top, a burnished band, a fractured band and a burr. IMOA says sheared edges are cold worked, and the burrs can hold microcracks, so forming after shearing can crack the edge. Grinding, filing, polishing or electropolishing removes the burr and the hardened layer. Smeared overlapping metal where a dull tool pierced a hole is a crevice-corrosion risk.
• Brass, copper and aluminium. The detailed edge guidance read is for stainless steel. TWI says fibre lasers can cut copper, brass and aluminium without fear of back reflections damaging the machine, and that aluminium reflects more than steel. Ask the partner which method it uses on each metal.

Which method runs out first: thickness

The chart shows the thickness ranges the sources state. EN ISO 9013 states the ranges its scope covers: laser 0.5 to 32 mm, plasma 0.5 to 150 mm and oxyfuel 3 to 300 mm. The practical figures for stainless are lower: TWI and IMOA both give about 12 mm for laser cutting stainless, and IMOA calls plasma the most common method for stainless plate 25 mm thick and heavier. Both stainless figures date from before today's higher-power fibre lasers, so treat them as the lower bound and ask the partner for its machine's envelope.

Waterjet and shearing have no lower thickness in the sources read, so their bars are dashed. What decides between them is usually the edge and the heat: where heat tint or a heat-affected zone would show, or the metal is thick, waterjet; where the cut is straight, shearing.

Cut quality: what EN ISO 9013 lets you write down

EN ISO 9013 classifies thermal cuts: oxyfuel, plasma and laser. It applies when a drawing or order refers to it, and applying it to other processes needs separate agreement. From its contents page, it grades the quality of the cut surface by the perpendicularity or angularity tolerance (u) and the mean height of the profile (Rz5), sets dimensional tolerances for parts without finishing and with finishing, including a machining allowance, and says how to indicate the quality and the tolerance class on a drawing. An informative annex lists the cut qualities each process can achieve.

We have not read the standard's text and quote no class value. The useful move is to name the standard, ask the partner which quality range it achieves on test cuts in your metal and thickness, and write that range into the specification. For an edge that shows, also say how it is dressed, because a dressed edge, not an as-cut one, is what the eye sees. The general tolerance to put beside it is in tolerances for visible metalwork. For patterns cut right through, see perforated, laser-cut and expanded metal.

Forming: bend radius, spring-back and the flat pattern

A fold cannot be sharp. The metal needs an inside radius, and IMOA's minimum for press-brake forming of standard austenitic stainless rises from 0.5 to 1.5 times the thickness in the annealed state to 4 to 6 times when full hard (Table 10). The harder the temper, the larger the radius. The same guide says austenitic steels spring back, so the part is overbent: for an annealed 300 series with a radius ten times the thickness, a 90° part needs a bend of about 100.8°. Euro Inox adds that austenitic grades need about 50 per cent more power than carbon steel and are overbent by about 5° to compensate.

The flat pattern follows from geometry. Bend allowance is the length of the neutral axis through the bend, and the factor K says how far inside the sheet that axis sits. K depends on the metal, the tooling and the bend, so the fabricator sets it from a trial. The worked example uses K = 0.4 as a placeholder only, checked by script:

Two things come from the drawing, not the shop. A cut that crosses a bend line must be placed from the flat pattern, and a visible grain must run the way it will be seen after the fold: say which on the shop drawing. Rolling and spinning follow the same logic. IMOA says roll forming gives dimensions that vary with the strength of the batch, and that spinning needs a ductile metal with low work hardening, sometimes with annealing between stages.

Matching method to job, and what to ask the partner

• Fine patterns and lettering in thinner sheet: laser, with the edge dressed where it shows.
• Thick plate, base plates and large cut-outs: plasma then machine or grind the edge, or waterjet if heat must not show.
• Heat-sensitive, coloured or finished metal: ask first. A heat-affected edge on finished metal will show, and forming after coating needs a bend test (see coloured stainless steel options).
• Straight blanks: shear, then dress the edge before folding.
• Boxes, door skins and channels: press-brake folding, from the flat pattern.
• Bowls, shells and bases: spinning.

Ask the partner workshop for its machine envelope: largest sheet and thickest cut by method and metal, the cut quality it achieves on test cuts, minimum hole and slot sizes, press-brake length and tooling, and the roll and spinning limits. Our steel fabrication page lists the methods without limits, and this sheet adds the ones published.

Profiles cut by [laser / waterjet / plasma] from [metal, thickness]. Thermally cut edges classified to EN ISO 9013 (edition [to be confirmed]): perpendicularity or angularity range [__] and mean profile height range [__], dimensional tolerance class [__], as shown on the partner's test cuts [ref. __]. Stainless steel laser cut with [nitrogen] assist, edges free of dross and heat tint. Visible edges [ground / dressed / polished] to match approved sample [ref. __]. Burrs removed from every sheared or punched edge before forming.

Bends: inside radius not less than [__] x thickness for [grade and temper]; bend lines [parallel / across] the grain as the shop drawing shows. Flat pattern and bend allowance by the fabricator from a K-factor trial [__]. Fold angle [90] degrees within [__] degrees, spring-back compensated. First-off bend sample approved before production.

Punched holes: diameter not less than [thickness plus one gauge size], spacing not less than [half the hole diameter]; panels levelled after punching, flatness [__] mm over [__] mm. Dense or irregular patterns by [laser / waterjet]. Spun parts: [metal and temper], approved sample [ref. __].

Standards and sources

• EN ISO 9013:2017 (+A1:2024): thermal cuts; BS EN ISO 9013:2017 current, under review (BSI). Text not read.
• IMOA, Practical Guidelines for the Fabrication of Austenitic Stainless Steels, 2nd ed. 2020: stainless only.
• TWI job knowledge (laser cutting, plasma arc cutting, heat-affected zone); Euro Inox Vol. 1 (2005)

Questions we are asked

Laser, waterjet or plasma: which should I specify?

Say what matters, not the machine: the edge, whether heat can show, and the thickness. Laser suits fine work in thinner sheet, waterjet adds no heat and handles thick sections, and plasma suits heavy plate where the edge is machined or hidden. Let the partner choose within a stated cut quality.

Why is a laser-cut or plasma-cut edge discoloured?

Heat and oxygen. IMOA says nitrogen assist keeps laser-cut stainless free of oxide, that oxygen-bearing gases should be avoided in plasma cutting, and that a discoloured plasma edge needs pickling or edge milling to restore corrosion resistance.

Can brass, copper or aluminium be laser cut?

TWI says fibre lasers can cut copper, brass and aluminium without fear of back reflections damaging the machine, and that aluminium reflects more than steel. Ask the partner which method it uses for your metal and thickness.

What is the minimum bend radius?

It depends on the metal and temper. For standard austenitic stainless in press-brake forming IMOA gives 0.5 to 1.5 times the thickness annealed, rising to 4 to 6 times when full hard. Ask the partner for its own figures for brass, aluminium and mild steel.

Why does a folded flange not come out at exactly 90 degrees?

Spring-back. The metal returns part-way when the press lifts, so the fabricator overbends. For an annealed 300 series stainless at a radius ten times the thickness IMOA's example is a bend of about 100.8 degrees for a 90 degree part.

What tolerance can I expect from a cut?

EN ISO 9013 grades thermal cuts by perpendicularity or angularity and by mean profile height, but we have not read its classes. Ask the partner what it achieves on test cuts, then write that range into the specification.