Design Tips for Sheet Metal Bending

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Design Tips for Sheet Metal Bending

Sheet Metal Bending · DFM Guide

Design bending features that are easier to manufacture and inspect

Good bending design starts before the press brake is set up. Material, temper, thickness, bend radius, flange length, hole position and cosmetic requirements all affect the manufacturing route.

Hongming Sheng reviews customer drawings for custom brackets, panels, covers, enclosures and welded assemblies—from prototypes to repeat production.

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CNC Press Brake

Prototype to Production

Laser Cutting & Forming

Welding & Finishing

Four Decisions to Make Before Releasing a Drawing

Specify Material and Temper

Stainless steel, aluminum, mild steel and galvanized sheet do not bend in the same way. Include the exact grade, temper and sheet thickness.

Use a Practical Bend Radius

An inside radius near one material thickness is a common starting point—not a universal rule. Alloy, temper, grain direction, tooling and angle must be reviewed.

Define Critical Features

Mark important dimensions, datums, bend directions, tolerances, cosmetic faces and any areas that must remain free of tooling marks.

Provide Both 2D and 3D Data

STEP/STP supports geometry review; PDF or DWG/DXF communicates tolerances, threads, finishes and inspection requirements.

Important: bend allowance and springback depend on the actual material and production setup. Avoid locking the flat pattern unless the bend deduction or K-factor has been agreed with the manufacturer.

Sheet Metal Bending in Production

Common Bending Methods

Air Bending

The punch forms the sheet into a V-die without fully pressing it to the die bottom. It is flexible and widely used, but angle control depends on springback and machine setup.

Bottoming

The sheet is pressed more closely against the die surfaces. Tool angle, die opening and material response must match the required result.

Coining

Higher force plastically sets the bend area. It can improve angular repeatability but requires greater tonnage and is not the preferred route for every part.

Folding & Wiping

Useful for selected panels, edges and flanges. Part size, visible surfaces and the risk of marking should be reviewed.

Joggle Bending

Creates two opposite bends to form an offset. Offset height, tooling access and deformation near adjacent features require attention.

Ten Practical Design Checks

1. Keep Thickness Consistent

Uniform sheet thickness simplifies tooling selection and bend compensation. If several thicknesses or joined materials are involved, identify them clearly in the assembly drawing.

Uniform sheet metal thickness design example

2. Keep Holes and Slots Away from Bends

Features too close to a bend may stretch or distort. As an initial DFM guide, allow about 2.5T from a hole and about 4T from a slot; final clearance depends on radius, die opening and geometry.

3. Standardize Bend Radii

Using consistent radii can reduce tooling changes and setup time. Avoid unnecessarily small radii, especially in hard aluminum, thick sheet or bends across an unfavorable grain direction.

4. Review Curls and Rolled Edges

Curl diameter, opening, straight length and nearby holes need enough clearance for the forming tool. Confirm functional and safety requirements before detailing the edge.

5. Control Countersink Depth

Thin sheet limits countersink depth. Identify the fastener, required seating condition and whether an extruded hole, formed feature or secondary insert is more suitable.

6. Select the Correct Hem

Open, closed and teardrop hems behave differently. Material hardness, return length, inside opening and appearance requirements influence feasibility.

7. Add Clearance at Chamfered Flanges

Chamfers and corners must leave enough material and tool access so the flange does not tear, bulge or interfere during bending.

8. Check the Bending Sequence

Successive bends can trap the part or collide with the punch, die or machine. Provide sufficient flange access and review the sequence before finalizing the design.

9. Position Notches and Tabs Carefully

A useful starting point for notch-to-bend clearance is approximately 3T plus the bend radius. Tab spacing should also allow stable cutting and forming.

10. Use Bend Relief Where Needed

Relief cuts help control tearing and bulging where a bend terminates. Relief width is commonly at least the material thickness, with length extending beyond the bend radius.

Bending Force and Tooling Review

Required press force is influenced by material strength, thickness, bend length, die opening, angle and inside radius. A reference chart is useful for planning, but final tonnage must be confirmed for the actual material and tooling setup.