Sheet metal design

Sheet metal design is the design of parts made from flat sheet by cutting (laser, waterjet, punching) and forming, most often by bending on a press brake. Typical results are covers, enclosures, electrical cabinets, brackets, mounts, frames and instrument chassis. Common thicknesses range from about 0.5 mm to several millimeters.

In CAD systems, sheet metal parts are modeled in a dedicated sheet metal environment. The designer sets the thickness, the inside bend radius and a rule for calculating the flat pattern, usually the K-factor. The K-factor gives the position of the neutral axis (the layer that neither stretches nor shortens during bending), measured from the inside of the bend and expressed as a fraction of the sheet thickness. It typically falls between 0.3 and 0.5. CAD then generates the flat pattern for cutting and a drawing with the bends automatically.

The design has to respect the process. On a press brake, the inside bend radius depends on the die opening, and for common structural steel it is roughly equal to the sheet thickness. Harder aluminum alloys, for example in the T6 temper, need a larger radius, otherwise the bend cracks. A flange must have a minimum length so it can rest on the die, and holes too close to a bend get distorted. Where a bend ends at an edge or runs into another bend, a bend relief (a small cutout) is added to prevent tearing.

Sheet metal parts are joined by welding, riveting, screws into clinch nuts, or self-locating tab-and-slot joints. A well-designed bent part can often replace a multi-piece weldment, saving time and post-weld straightening. For high volumes, laser cutting and press brake bending give way to stamping in progressive dies.

Sheet metal suits thin-walled parts that need stiffness at low weight and a reasonable price even for single units: machine guards, electronics enclosures, brackets, mounts, shelves, frames and protective covers. Compared with milling from solid, a sheet metal part is usually much cheaper and faster, and compared with plastic injection molding it needs no expensive mold.

Consider sheet metal design when optimizing existing weldments or machined brackets as well. Replacing several welded pieces with one bent part often cuts cost and weight.

A common mistake is a part that unfolds in CAD but cannot be bent: flanges that are too short, bends right next to each other, collisions between the part and the tooling when bending closed shapes, or holes right at the bend. The flat pattern from CAD is also based on a generic K-factor, which the manufacturer usually adjusts to their own tooling. Dimension functional features on the formed part, not on the flat pattern.

Specify realistic tolerances: dimensions across one or more bends are usually held to tenths of a millimeter, not hundredths. Standardize bend radii and thicknesses across the whole product so the parts can be made with a single tool set. In your request for quote, state the exact material (for example DC01, S235, 1.4301 or EN AW-5754), the surface finish, burr requirements and grain direction. Also check whether the part has hanging holes for powder coating or zinc plating.