This guide walks through the design decisions that matter most for bent parts: material selection, bend radius, flange length, hole placement, bend reliefs, tolerances, and finishing. It also explains how a factory like DIAN STAMPING turns your 2D drawing, 3D data, or physical sample into production-ready parts.

Material grade and thickness drive almost every other bending decision, so settle them before you start modeling. Mild steel is the most forgiving and cost-effective choice for most parts. Stainless steel adds strength and corrosion resistance but springs back more and needs a larger bend radius. Aluminum is light and easy to form, though softer alloys are best for tight bends. High-strength steels and multiphase steels give you more strength per millimeter but are harder to bend and more prone to cracking at small radii.

Thickness matters just as much. Thicker sheets need larger bend radii and longer flanges; thin sheets can take sharper bends but distort more easily. Most industrial sheet metal falls between 0.5 mm and 6 mm thick. DIAN STAMPING regularly processes multiphase steel, aluminum, custom rolled and welded plate, and stainless steel for automotive OEMs and their suppliers. If you are unsure which grade fits your application, describe the part's function and load and we will recommend a material that balances strength, formability, and cost.

The most common design mistake is a bend radius that is too tight. As a general rule, the inside bend radius should be at least equal to the material thickness, so a 2 mm steel sheet gets a 2 mm radius. Aluminum can sometimes go tighter, around 0.5 to 1 times the thickness, while stainless steel typically needs 1.5 to 2 times the thickness to avoid cracking.

In your CAD model, always enter the inside radius, not the outside. Many programs default to sharp corners, which will not survive the press brake. A consistent radius across the whole part also matters: mixing different radii in one part forces multiple tool setups and adds cost without any functional benefit. This is one of the first things a manufacturer checks during a sheet metal part design review.

A flange that is too short cannot be formed accurately because the press brake tooling has nothing to hold onto. As a baseline, keep flanges at least three to four times the material thickness. For a 2 mm sheet, that means a minimum flange of about 6 to 8 mm. Anything shorter risks the tooling slipping, the bend wandering, and inconsistent results in production.

If your design genuinely needs a very short flange, flag it during the design review. In many cases the geometry can be adjusted or a different tooling setup can be used, but it is far cheaper to catch this in CAD than after a prototype fails.

Holes placed near a bend line are a classic source of scrap. As the material stretches during forming, a hole too close to the bend will distort into an oval, or the surrounding material will crack. Keep holes at least two to three times the sheet thickness away from the bend line. For a 2 mm sheet, that means at least 4 to 6 mm of clearance.

The same thinking applies to slots, cutouts, and notches. If a hole must sit closer to a bend, a relief slot or a post-bend machining step may be needed. Both add cost, so it is worth reviewing the layout early.

Where two bends meet at a corner, the material tends to bunch up and tear. A small bend relief, a slot cut at the bend line, prevents this. Reliefs are most important when flanges are short, bends are tight, or the material is less ductile, like stainless steel or high-strength steel.

As a rule of thumb, make the relief width about equal to the material thickness and the length at least equal to the bend radius. A tiny slot in CAD costs nothing but prevents corner cracks, cosmetic flaws, and uncontrolled shop-floor fixes.

Every additional bend adds springback variation, tolerance stack-up, and tool access constraints. A single bend is easy to control; four or more bends in close succession often cause real problems. Flanges spaced too close together can block the tooling, and each bend at one degree of variation can shift the overall geometry by the same amount, enough to misalign mounting holes.

Keep the design as simple as the function allows. If a part needs many tight bends, consider splitting it into two pieces joined by welding. A welded subassembly can often deliver the same function more reliably and at lower cost. This is where a manufacturer with in-house welding experience, like DIAN STAMPING with its welding jigs and welding assemblies, can help you find the right balance.

No bend forms exactly as drawn. As a baseline, expect about one degree of variation on bend angles and 0.25 to 0.5 mm on linear dimensions in production. Stainless and high-strength steels spring back more than aluminum, sometimes by one to two degrees. On a long panel, even a one-degree deviation can shift a hole pattern by several millimeters.

Design with this variation in mind. Use slotted holes where bends locate fasteners, add alignment tabs, and avoid assemblies that depend on perfect 90-degree bends. Only specify tight tolerances on features that are critical to function, because calling out tight limits everywhere makes a part unnecessarily expensive.

Coatings applied before forming, such as powder coating, anodizing, or plating, tend to crack, chip, or flake along the bend line. The tighter the radius, the higher the risk. Powder coat is especially brittle and almost always shows chipping if bent after coating.

The reliable sequence is bend first, finish second. If you must use pre-finished material, design with a larger bend radius and keep the bend away from cosmetic-critical surfaces. Tell your manufacturer about the intended finish early so the process can be planned correctly.

The cheapest time to fix a design problem is before tooling is cut. Send your CAD model or drawing to the manufacturer during the design phase, not after you have locked the geometry. A good design-for-manufacturability review will flag risky bend lines, short flanges, and tight hole clearances while they are still cheap to change.

DIAN STAMPING is a factory, not a trading company, with more than 20 years of experience serving automotive OEMs including KIA, BYD, Toyota, Honda, Suzuki, and Geely. We accept customization from 2D drawings, 3D data, or physical samples, and we offer prototype services before mass production. Our in-house die designers, press lines, and checking fixtures mean your bent sheet metal parts are verified against the design before they ship, so the part you receive is the part you designed.

Designing a custom sheet metal part for bending is mostly a matter of following a few proven rules: choose the material first, keep the bend radius at least one material thickness, keep flanges long enough, keep holes clear of bend lines, add reliefs at corners, and design for real tolerances. Get these right and your part will form cleanly, fit the assembly, and stay within budget.

If you are working on a new part and want a manufacturability review, send your drawing or 3D data to DIAN STAMPING. We will review the design, suggest improvements, and provide a quote for tooling and production.