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Lesson 4.1DeformChapter 4 · Sheet and tube forming

Sheet metal bending

A press brake folds sheet along straight lines

Sheet metal bending folds a flat sheet along a straight line to make an angle, a channel or a box. Your computer case, an electrical cabinet and a shelf bracket were all bent this way. Most bending happens on a press brake, a long, narrow press built for the job, using cheap standard tools.

Sheet metal bending: a real photo
Photo: GaspariniIndustries, CC BY-SA 4.0, via Wikimedia Commons
A punch pushes the sheet into a V-die; the stroke depth sets the angleAir bending on a press brake, seen from the end of the bend lineBefore the strokeThe sheet lies flat on the die,pushed against the stopRamPunchV-dieBedSheetBackgauge12Bottom of the strokeThe sheet touches only atthe 3 dots; a deeper strokegives a sharper bend3After releaseThe bend opens a little;the press overbends tomake up for it4Sheet (workpiece)Tools and machineSheet under load (springback exaggerated)
air bending on a press brake · 3 stagesThe three panels follow one bend from start to finish, with springback exaggerated; circled numbers match the steps below.

How it works

  1. Set the sheet. You lay the flat blank (the sheet, already cut to size) across the V-die, the lower tool with a V-shaped groove. Then you slide it back against the backgauge, a set of stops that fixes where the bend line falls.

  2. Press. The ram (the press brake's moving upper beam) drives the punch, the upper tool, down along the bend line. Hydraulic cylinders or electric servo motors supply the force, often tens to hundreds of tonnes.

  3. Bend in the air. In air bending, the most common method, the sheet touches only the punch tip and the two edges of the V. The deeper the punch goes, the sharper the angle, so one tool set can make many angles.

  4. Release. When the punch lifts, the metal springs back a few degrees; this springback is the elastic part of the bend recovering. So the press bends slightly past the target, then you turn the part for its next bend.

Key facts

Materials
Steel, stainless steel, aluminum, copper and brass sheet, typically about 0.5 to 6 mm thick; heavy press brakes bend plate over 20 mm
Typical parts
Brackets, enclosures, cabinets, chassis, channels, panels, ducts
Part size
From small clips to bends about 3 to 4 m long on common machines; linked (tandem) machines go longer
Precision
Angles about ±0.5° to ±1° and flange lengths about ±0.2 mm on a CNC (computer-controlled) press brake
Surface finish
Same as the incoming sheet; the die edges can leave faint lines beside the bend
Batch size it suits
One-offs to tens of thousands of parts; much bigger runs often move to stamping
Tooling and machine cost
Standard punches and dies: hundreds to a few thousand dollars; CNC press brakes: roughly tens of thousands to several hundred thousand dollars
Speed
A few seconds per bend; a part with several bends takes about a minute including handling

Strengths and limits

Strengths

  • No dedicated mold: standard tools make many shapes
  • Quick to set up, so prototypes and small batches stay cheap
  • Sheet thickness stays almost unchanged
  • A CNC press brake repeats each bend accurately

Limits

  • Only straight bends; curved 3D shapes need stamping or other processes
  • Springback must be corrected, more so in high-strength steel and aluminum
  • Too tight an inside radius cracks the outside of the bend
  • Short flanges and holes close to a bend distort; every bend is a separate stroke

Where it's used

  • Electronics and ITServer racks, computer cases, electrical cabinets
  • ConstructionFlashing, trim, door frames, cable trays
  • TransportTruck bodies, trailer parts, brackets, battery boxes
  • MachineryMachine guards, frames, control-box housings
  • Home and officeAppliance panels, kitchen hoods, steel shelves, office furniture

How to recognize it

  • Straight, crisp folds with a small, even inside radius, often close to the sheet thickness.
  • The same thickness everywhere, even at the corners: the metal was folded, not stretched.
  • Small notches or gaps at box corners where two flanges meet (bend reliefs), instead of a seamless corner.
  • Faint lines on the outer face, parallel to the bend, left by the die edges.

Compare with

Stamping and deep drawing4.2a matched die forms a whole 3D shape in one stroke; far faster per part, but the die costs far more.Metal spinning4.3makes round, hollow shapes by rotation instead of straight folds.Laser cutting6.2usually cuts the flat blank and its holes before the sheet is bent.

Watch it

Muniac LLC · The basic principles of bending, explained for beginners

WoodchuckTinman · Hands-on press brake use: tooling and the backgauge

Adam Deuling · Real shop-floor bending on a CNC press brake

SigmaTEK Systems, LLC · How a bent part unfolds into a flat blank: bend allowance and K-factor

See real photos

Remember

  • A punch presses the sheet into a V-die; in air bending, stroke depth sets the angle.
  • Metal springs back a little, so the press always bends slightly past the target.
  • Cheap standard tools make bending ideal for straight folds, from one-offs to large batches.

More in Sheet and tube forming

All 100 processes
4.2ShortStamping and deep drawingMatched dies cut and press sheet into shape, often in a secondOpen the lesson4.3Metal spinningA roller presses a spinning disc over a formOpen the lesson4.4Flow formingRollers stretch a spinning tube thinner and longer over a mandrelOpen the lesson4.5HydroformingFluid pressure pushes tube or sheet into a dieOpen the lesson4.6Incremental sheet formingA round tool traces contours into clamped sheet, with no dieOpen the lesson4.7Superplastic formingHot gas blows a superplastic sheet into one dieOpen the lesson4.8Electromagnetic formingA magnetic pulse throws metal onto a fitting, without contactOpen the lesson4.9Explosive formingAn underwater blast pushes sheet into one dieOpen the lesson4.10Laser peen formingLaser shots stretch one face so a plate curvesOpen the lesson

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