Practical design for manufacturability guide for bent sheet metal parts. Learn about flange lengths, bend relief, hole placement, and features that simplify bending.
Introduction
Good design is the foundation of manufacturable bent parts. At Fulei Metal, we review hundreds of designs and help optimize them for bending.
Flange Design
Minimum Flange Length
Minimum: 4 times material thickness, or at least enough for back gauge and operator holding. Too-short flanges cannot be bent reliably.
Maximum Flange Length
Limited by machine throat depth and part handling capability. For very long flanges, consider alternative designs.
Bend Relief
Add relief at bend lines near cut edges: width at least 1 thickness, depth at least 1 thickness beyond bend. Prevents tearing and distortion.
Corner Relief
For boxes and enclosures: notch relief prevents overlap. Slot relief allows both flanges to bend. Design appropriate relief for the corner type.
Hole Placement Near Bends
Holes should be at least 2 times thickness plus bend radius from the bend center. Holes too close to bends deform during bending. Slots are more forgiving than round holes.
Bend Direction
Bend across grain for tight radii. If grain direction is unknown, specify across-grain bending. Consider nesting implications.
Consistent Bend Radii
Use the same radius for all bends on a part. This reduces tool changes and setup time. Standard radii: 0.5, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0 mm.
Bend Direction Consistency
Design parts so bends are in the same direction where possible. This reduces part reorientations. Up-bends and down-bends require flipping.
Avoid Impossible Geometries
Ensure all bends can be made without tool interference. Verify with 3D simulation. Consider the tool access for each bend. Avoid bends that require impossibly narrow punches.
Tolerancing
Bend angle: plus or minus 0.5-1.0 degrees. Flange length: plus or minus 0.2-0.5 mm. Avoid over-tolerancing non-critical dimensions.
Assembly Considerations
Consider how bent parts fit with mating components. Design for assembly access. Account for tolerance accumulation. Provide adjustment features where needed.
Conclusion
Designing for bending avoids manufacturing problems and reduces cost. At Fulei Metal, our design review services help clients create parts that are easier to bend, higher quality, and more cost-effective.
The Rules That Most Often Delay a Quote
Most DFM conversations on bent parts come back to the same six rules. None of them restrict what you can design, but following them removes setup time from every unit and from every repeat order.
| Rule | Recommended value | Why it matters |
|---|---|---|
| Keep one bend radius across the part | a single radius wherever possible | each additional radius is a tool change and usually a re-fixturing |
| Keep bend direction consistent | same direction where geometry allows | avoids rotating the part between operations |
| Keep holes clear of the bend line | at least 2 × t + R from hole edge to bend tangent | closer than this and the hole deforms into an oval |
| Respect the minimum flange length | roughly 0.7 × the die opening | a shorter flange slips into the die instead of forming |
| Add bend relief at the ends of a bend | width at least t, extending past the tangent | prevents tearing where the bend meets a free edge |
| Mark grain direction requirements | call it out where cracking is unacceptable | the material grain drives cracking risk, especially on stainless and hard tempers |
It helps to be explicit about which dimensions are inspected. A drawing that calls general tolerances everywhere, including on features that mate, pushes cost up without improving function. Tell us which three or four dimensions actually matter and the rest can run in the standard band — and if you are unsure which are critical at drawing stage, that question is exactly what a DFM review before RFQ is for.
Frequently Asked Questions
Can we keep different radii if appearance requires them?
Yes, and sometimes it is worth the cost. We just want the decision made deliberately, with the extra setup reflected in the piece price rather than appearing later as a surprise.
How close can a hole be before it really matters?
The usual safe rule is 2 × t + R from the hole edge to the bend tangent. Below that the hole starts to ovalise; a relief slot either side usually solves it if the hole position cannot move.
Is it cheaper to laser-cut holes after forming?
Sometimes, for holes that would otherwise be distorted. It adds an operation, so it is worth doing when the feature is critical rather than as a default.
Questions about a specific part are usually faster to answer against the drawing — send it through the review route below.
About these figures. The reference values above come from our own production range; bending service details lists the machines and materials behind them, and what tolerance to specify explains the adjacent steps that change the formed result. For your own part, DFM review before RFQ is the fastest route to a quote — the earlier we see the drawing, the more of it can still be adjusted without cost. The tolerance context is set out in radius choices by material.