Basic Knowledge of Sheet Metal Processing

A formed part starts as a flat blank, not as a block of material. The blank is cut to a developed shape, then bent, then joined or finished. Every operation changes the geometry slightly, and the next operation inherits that change. This is why a drawing that looks simple can still be hard to hold.

The usual order runs: blanking, forming, joining, finishing, inspection. Blanking sets the outside profile. Forming creates flanges, bends and stiffening ribs. Joining adds hardware, rivets, welds or clinch nuts. Finishing coats or textures the surface. Inspection checks what the earlier steps did.

Tolerances stack along that chain. A ±0.1 mm blank tolerance plus a 1° bend angle error can push a hole out of position by more than ±0.3 mm on a long flange. Engineers who understand the stack can set realistic callouts. Engineers who do not often over-specify and pay for it.

Thickness matters more than most people expect. A 0.8 mm panel springs back differently than a 3 mm one, and the bend radius that works for one will crack the other. We look at thickness first when we review a formed part.

Cold-rolled steel SPCC is the default for brackets and enclosures. It bends cleanly, takes powder coat well, and costs less than stainless. It rusts if left bare, so plan a finish from the start. Hot-rolled SHCC is thicker and rougher, used for heavy frames where surface appearance does not matter.

Galvanized sheet SECC and SGCC carry a zinc layer that resists corrosion without painting. The zinc is soft and can flake at a tight bend, so keep the inside radius at least equal to thickness. Welding galvanized steel releases zinc fumes; we prefer rivets or clinch joints on those parts.

Aluminium 5052 is the best forming grade in the common range. It bends without cracking and holds a radius well. Alloy 6061 bends less gracefully and is better left for machined details. Alloy 1060 and 1010 are soft and used for cosmetic panels. Copper and brass form easily but cost more and tarnish.

Stainless 304 and 316 resist corrosion and take a brushed or mirror finish. They work-harden, so a bend that starts fine can crack on a second hit. 301 and 430 are used where springback is wanted. Titanium and Inconel are possible but slow, and usually end up on a mill instead.

• 1
  Thickness under 1 mmWatch springback and handling dents.
• 2
  Thickness over 3 mmBend radius grows; consider machining.
• 3
  Coated stockProtect the coating at every step.

Laser cutting holds ±0.1 mm on thin stock and leaves a clean edge. It costs more per part than punching but needs no tooling, so it suits prototypes and low runs. Punching wins above a few thousand parts because the tool amortizes. Waterjet cuts thick plate and heat-sensitive alloys without a heat-affected zone.

Bending is where most design problems surface. The inside radius should be at least equal to thickness for mild steel, and larger for aluminium and stainless. A hole placed too close to a bend will distort; keep it at least 2.5 times thickness away, plus the radius. Counterbores and slots near a bend need the same clearance.

Springback is the material pushing back after the punch lifts. Mild steel springs back about 1°, stainless and aluminium more. We compensate by over-bending or by coining, and we check the first part before running the rest. A bend angle callout of ±1° is realistic; ±0.25° usually is not.

Hardware insertion adds another step. Clinch nuts, standoffs and studs press into the sheet and need a flat area around them. Put them at least 1.5 times the nut diameter from an edge. Rivets work on thinner stock. Welded studs are stronger but distort thin panels.

Sheet metal tolerances are looser than machining tolerances, and that is normal. A formed part might hold ±0.2 mm on a hole pattern and ±0.5 mm on an overall length. When a feature truly needs ±0.005 mm, it usually belongs on a machined insert rather than the sheet itself.

Finish choice follows function. Anodizing suits aluminium and comes in clear, color, hardcoat and conductive versions. Electroless nickel and zinc plating protect steel. Powder coat gives a thick, durable color layer but adds 0.05–0.1 mm per side, which can close a tight fit. Black oxide is thin and mainly cosmetic.

Bead blasting and brushing give a matte or directional look. Polishing brings stainless to a mirror. Laser marking handles part numbers and logos, with a minimum character height of 1.5 mm so the mark stays legible after coating.

We inspect 100% of parts before shipment. That covers raw material checks, in-process monitoring and a final dimensional pass. Reports are available on request, and qualification rate on our lines sits at 99.99%.

Keep bends away from each other. Two bends closer than 3 mm make the tooling awkward and the second bend can pull the first out of shape. Space them by at least the material thickness plus the radius, and more if you can.

Standardize hole sizes and hardware across a product family. Fewer tools, fewer setup changes, lower cost. If a prototype uses M4 clinch nuts, keep M4 on the production version unless there is a real reason to change.

Avoid sharp inside corners on the blank. A small fillet at an internal corner spreads stress and stops a crack from starting. This matters most on stainless and aluminium, which crack more readily than mild steel.

Think about grain direction on rolled stock. Bending across the grain gives a cleaner result than bending with it. On parts that will be formed hard, note the grain direction on the drawing so the shop can nest accordingly.