Design must consider which operations are performed before forming and which after forming.

Considerations for the sequence in the manufacturing process—where bending must come first, followed by hole machining—include:

Round holes, square holes, oblong holes, threads, etc., located very close to a bend edge require special treatment during blanking. If the blank is produced directly as per the expanded view, subsequent processing may become impossible. For instance, oblong holes may stretch during bending, and threaded holes may become impossible to tap with standard taps.

Design must determine which features can be formed from sheet metal and which cannot.

Consider the minimum bend radius: The minimum bend radius for sheet metal depends on the material. The table below lists the minimum bend radii for common sheet metal materials.

Consider whether machine positioning can be used directly. If not, reserve two small tabs for positioning, which can be removed after bending.

Consider the bending direction relative to the material grain: This is especially important for non-ferrous metals like aluminum and copper sheets. Bending should be perpendicular, not parallel, to the rolling grain direction to avoid cracking at the bend.

Allow clearance for springback compensation: When a sheet metal part has flanges that fold over other bends, one surface becomes the "enclosing" flange and the other the "enclosed" flange. When creating the flat pattern, include clearance to account for bend springback. As sheet metal tends to spring back after bending to 90 degrees, over-bending beyond 90 degrees is often necessary to compensate. Therefore, clearance must be预留 to accommodate this springback.

Account for cumulative errors in multiple bends: Bending accuracy is generally not very high, typically controlled within 0.2 mm. Accuracy decreases with increasing bend height. When there are mounting holes, threaded holes, press-fit screws, or press-fit nuts on bent surfaces, cumulative machining errors must be fully considered. Use oversized clearance holes or design mounting holes as slots to accommodate installation errors and facilitate assembly.

Consider the issue of holes for press-fit screws or nuts being too close to a bend edge: During bending, both bending deformation and stretching deformation occur simultaneously. If a hole or notch is too close to the bend edge, it will experience stretching deformation. Generally, if the distance from the bend edge is at least 4.5 times the material thickness, bending deformation issues can be avoided.

The above outlines the bending-related issues that must be considered in sheet metal design. Sheet metal design must fully account for bending processes, understand them thoroughly, and ensure the design can be manufactured into a viable product. The limitations of sheet metal bending processes cannot be ignored.