Sheet metal bending: how it works, costs and design rules

Flat laser-cut blanks are folded on a press brake into enclosures, brackets, chassis and covers. Bent sheet metal is light, stiff for its weight and cheap in batches.

Typical tolerance

±0.2 mm per bend, ±0.5° angles

Quantities

1 to 10,000+

Lead time

3–10 working days

Materials

Steel, stainless, aluminium (5xxx alloys bend best)

How it works

A punch presses the sheet into a V-shaped die. The operator or a robot positions the blank against back gauges for each bend. The flat size is calculated with a K-factor so that the bent part ends up at the right dimensions.

Benefits

• Light and stiff parts from cheap sheet material.
• Low cost per part with no dedicated tooling.
• Fast changes: a new flat pattern is all that is needed.

Limitations

• Tolerances add up over several bends.
• Minimum flange lengths limit small details.
• Holes close to a bend line distort.

What drives the cost

• Number of bends and changes of tooling.
• Very short flanges or tight bend radii that need special tools.
• Secondary operations such as PEM inserts, welding and finishing.

Design rules

• Use an inside bend radius of at least the sheet thickness, and one radius for the whole part.
• Make flanges at least 4× the thickness long.
• Keep holes at least 2.5× thickness plus the bend radius away from bends.
• Add bend reliefs where a bend meets an edge.

Preparing your STEP file

• Model with your CAD sheet metal tools so the flat pattern is correct.
• Send the STEP of the bent part and a DXF of the flat pattern.
• Tell the shop which K-factor you used or let them unfold it with theirs.

See also the full STEP export checklist and the comparison of all processes.