Press brake and sheet metal glossary

Air bending

Bending where the sheet bridges the die opening and contacts only the punch tip and die shoulders. The lowest-force bend method; the angle depends on stroke depth and springback correction.

Angle correction

The CNC feature where the operator measures the first bent part and enters the deviation; the machine then applies the correction automatically for that material, tooling and thickness.

Backgauge

The movable fingers that position the sheet for each bend. Axes are labelled X (front-to-back), R (height) and Z1/Z2 (lateral).

Bead

A stiffening ridge rolled or formed into a flat panel so it does not drum under load.

Bend allowance

The developed length of the bend itself — the arc length through the deformation zone — used to calculate the flat blank.

Bend deduction

The difference between the sum of the outside flange dimensions and the developed flat length; the complement of bend allowance.

Bottoming

Bending where the sheet is squeezed into full contact with punch and die. Needs several times the force of air bending but sets the angle mechanically and absorbs most springback.

Box and pan brake

A brake with removable or segmented fingers that let already-formed flanges pass through the tooling — the frame geometry that makes boxes and enclosures possible.

CNC

Computer numerical control: the machine executes a stored program of bend angles and axis positions, rather than an operator setting each bend.

Coining

The highest-force bend method, where the punch penetrates the sheet and thins it at the bend. Produces very tight radii and consistent angles at high force and tooling wear.

Crowning

Compensation for ram and bed deflection under load — a pre-curve in the tooling line, mechanical or hydraulic, that keeps punch and die parallel at rated load.

Daylight

The clear height between ram and bed at full open. Decides how tall a die stack or how deep a box you can close.

Deep throat

A frame with a large distance from the side frame to the tooling centre, letting long flanges reach into the machine.

E21

A class of NC control common on entry-level Chinese press brakes and shears: backgauge positioning and stroke control without programmable bend angles.

Finger tooling

Segmented or removable fingers on punch and die that let formed flanges clear the tooling — required for boxes, enclosures and cable tray.

Gauge

A sheet thickness designation that differs by metal — the same gauge number is a different thickness in steel, stainless and aluminium. Calculations use thickness, never gauge.

Gooseneck punch

A punch profile that clears an already-formed flange, for U-channels and return flanges.

Guillotine shear

A shear where the upper blade moves straight down (or with a small rake) against a fixed lower blade — straighter cuts than a swing beam on heavier stock.

Hemming

Folding a flange back on itself, with a hemming die, to create a folded edge. Needs considerably more force than a single bend.

HS code

The Harmonised System customs classification. Press brakes and shears generally fall under heading 8462, with subheadings that differ by function and by NC versus non-NC.

Hydraulic synchronisation

Keeping two cylinders in step so the ram stays level — by mechanical linkage (torsion bar), by electro-hydraulic servo loop, or by flow division.

K-factor

The ratio locating the neutral axis within the sheet during bending — the position that neither stretches nor compresses. The key input to bend allowance calculations.

Laser cladding

Depositing a wear- or corrosion-resistant layer by melting powder or wire with a laser — used for repair, coating and surface engineering.

Light curtain

A presence-sensing guarding device for the point of operation, sized from the machine's measured stop time plus an approach-speed allowance.

Lockout/tagout

Energy isolation before anyone reaches into the machine: disconnect, bleed, block the ram, verify zero energy by attempting a cycle.

Mandrel

An internal support inserted into tube during bending to stop the section collapsing. The difference between a clean tight-radius bend and a buckled one on thin wall.

Multi-V die

A die body carrying several V-openings, covering a thickness range without changing dies.

NC

Numerical control without programmable bend angles: positions the backgauge and controls stroke for repeat work.

Open height

See daylight — the clear height between bed and ram at full open.

Pan brake

See box and pan brake. The finger geometry, not the tonnage, is what makes boxes possible.

Plate roller

A machine that rolls plate and section into curves with driven rollers — symmetric (four-roll) and pyramid (three-roll) arrangements.

Press brake

A machine that forms sheet and plate by pressing it into a die with a punch — the central machine of sheet metal fabrication.

Punch

The upper tool that descends into the die to form the bend. Profiles include upright, gooseneck, offset, finger, acute, flattening and hemming punches.

Ram

The moving member that carries the punch and delivers the force.

Repeatability

How closely the machine returns to the same position or angle over repeated cycles — the number that matters on production, more than single-shot accuracy.

Retrofit

Upgrading an older machine — CNC control, backgauge axes, tooling clamping — instead of replacing the frame.

Servo valve

An electrically controlled hydraulic valve that meters flow and pressure precisely; the component that makes closed-loop Y1/Y2 angle control possible, and the component most sensitive to dirty oil.

Shear

A machine that cuts sheet and plate with straight blades — swing beam and guillotine (guideway) types.

Springback

The elastic recovery after the punch releases. Depends on the alloy and temper, not the machine — the reason CNC angle correction exists.

Stroke

The travel of the ram, top to bottom.

Swing beam shear

A shear where the upper blade pivots from a rear pivot — economical, with slightly more cut distortion than a guideway shear.

Tandem press brake

Two synchronised brakes working one long part, for bends beyond a single bed.

Throat depth

The distance from the side frame to the tooling centre. Decides how far a flange can reach into the machine — the number that fails more parts than tonnage.

Tonnage

The downward force the ram can apply, per unit length of bend. One of four capacities that decide whether a machine can make your part.

Torsion bar

A mechanical shaft linkage that synchronises two cylinders — the durable, low-cost sync method on conventional WC67K-range brakes.

Turret punch

A punch press with a rotating turret of stations, nibbling and forming sheet with programmed tool selection.

V-die

The die opening, specified by its V width. A common starting point for air-bent mild steel is a V about 8x the material thickness.

Webbing

The distortion of the flat around the bend from compressive stress in the tooling contact zone.

Y1/Y2 axis

The two ram cylinder position axes on a servo brake; closed-loop control on them keeps the angle consistent across the bed.

Z1/Z2 axis

The lateral backgauge finger axes, left and right — the axes that let one program position fingers differently for the same part, which is what boxes need.

Terms worth going deeper on

The entries above are the short version. The ones that change buying decisions have full guides: tonnage, bed length and size, bend allowance and K-factor, tooling systems, bend methods, crowning, and HS codes and duty.

If a term you need is missing, ask — the glossary grows from real questions.