Radius bending punches
Large-radius press-brake punches, insert systems, springback, multi-breakage and bounded die-opening relationships.
Tags: tooling, sheet-metal, press-brakes, bending
On this page
For bending to approximately 90°, WILA's radius-tool guideline gives a minimum V = 2.5(R + s). With an assumed 20 mm bar radius and 2 mm sheet, that gives 55 mm. Its separate relation Rmax = 0.7V − 2s gives 34.5 mm for that opening. These geometric comparisons leave actual unloaded radius, forming force and capacity unresolved. WILA radius-tool FAQ.
Purpose and forming method
WILA uses dedicated rounded punches where ordinary air or step bending cannot achieve the form. WILA generally describes a large inside radius as at least eight sheet thicknesses. WILA large-radius bending
For ordinary air bending, WILA ties the natural inside radius mainly to die opening and advises a tip radius near or below that value. A broad radius punch changes contact geometry. WILA air-bending FAQ
Specify included angle and tangent locations as well as inside radius. The outer surface alone cannot confirm a circular inside contour.
Replaceable inserts and holders
Mate's June 22, 2016 article describes 25 radius inserts from 7 to 50 mm, in non-hardened and hardened-surface versions. Its holder choices include straight, gooseneck, short and tall profiles for European precision, bevel-tang and Wila-Trumpf tooling styles, with 415 and 835 mm lengths. These are dated Mate offerings, not a universal radius range or proof of interchangeability between brands. Mate radius insert/holder system
Engineering synthesis: a replaceable insert separates the working profile from its supporting holder. The complete assembly still has a mounting tang, seating surfaces, retention mechanism, installed height and load limit. Similar insert radii do not establish that two holders share those interfaces. A gooseneck holder changes flange clearance without defining the resulting radius or permissible force.
Mate's press-brake FAQ notes that a larger die opening may be needed to accommodate a large-radius punch. That physical space requirement is additional to the opening chosen for an ordinary air bend. Mate die-opening explanation
Springback and loss of punch contact
Mate's July 6, 2020 article distinguishes two effects:
| Effect | Described behavior | Implication |
|---|---|---|
| Springback | After unloading, the angle opens and inside radius increases | Tool radius need not equal finished radius |
| Multi-breakage, also called advance bending | Sheet separates from the rounded punch during forming; the center develops a smaller radius | A single nominal punch radius does not guarantee a circular arc |
Mate presents urethane counterpressure and a modified flat-tip radius punch as ways to reduce the latter behavior. These are different tooling arrangements, not a claim that every radius tool accepts a pad or tip modification. Mate springback and multi-breakage
Interpretation: springback is a change on unloading, while multi-breakage describes contact and curvature during loading. Their effects can coexist. Material condition, thickness, forming geometry and support determine the outcome; a generic springback percentage does not supply a production punch size.
A scoped die-opening relationship
For bending to approximately 90°, WILA publishes Rmax = 0.7V − 2s and a minimum-opening guideline V = 2.5(R + s), where V is die opening, s is sheet thickness and R is the radius of the bar used. These are its radius-tool relationships, not a machine-independent force or feasibility calculation. WILA radius-tool FAQ
Original substitution into that guideline: with an assumed R = 20 mm bar and s = 2 mm, V = 2.5 × (20 + 2) = 55 mm. The other relation then gives Rmax = 0.7 × 55 − 2 × 2 = 34.5 mm. This checks only those stated geometric comparisons; it does not establish the final part radius, required force or tooling capacity.
Worked geometry: arc and chord
Original idealized arithmetic: assume an exactly circular inside profile of radius 20 mm spanning a 90° central angle. Its inside arc length is:
Arc = Rθ = 20 × π/2 = 31.416 mm
Chord = 2R sin(θ/2) = 40 × sin 45° = 28.284 mm
Difference = 3.132 mm
The chord is the straight distance between arc endpoints, not material length along the curve. Neither value is the neutral-axis bend allowance for a 2 mm sheet. Blank development requires the actual bend profile and neutral-axis model, while springback can change the final radius and angle. The calculation establishes no press setting.
Coverage and source dates
The Mate insert article explicitly carries June 22, 2016, and its large-radius article July 6, 2020. No issue dates were established for the cited WILA pages or Mate FAQ; website copyright dates are not technical editions.
This reference covers press-brake radius punches and selected insert systems. It does not establish universal tonnage, minimum die angle, material bendability, radius tolerance, surface finish or mounting compatibility. Dedicated radius tooling, step bending, and roll bending have different contact paths and capability limits. Manufacturer examples do not establish the equipment or approved forming parameters of a particular shop.