Consideration 3: Formed metal that is not laying flat and 90 degrees to the cutting direction results in trim lines having knife edges, irregular cut lines, and irregular shaped holes. Also, punching and trimming surfaces off angle result in high maintenance. Holes on angled surfaces that must be round require a separate cam operation be incorporated

Maintain amount of surface with holes to an absolute minimum. Also, try to maintain these planes with 15 degrees of trim direction to avoid added dies and/or cams

Consideration 4:Formed Sheet metal has a normal tendency to spring back to its original position. For parts that require specific wall angles, cam dies or additional die processes are required. Minimum angle varies from 6 degrees upwards depending on part geometry, depth of draw, and other parameters. Also, open angles reduce the tendency for the metal to split or fracture during forming

Roll Forming

The following design recommendations are relevant to the family of roll forming processes.

Bending Radii

Radii for both inside and outside corners should be as big as possible. Minimum radii are prefered to be equal to one or two stock thickness. Smaller radii can be achieved. This requires sharp corners on the forming roll, reducing the roll life significantly.

Part Line

It is preferable to form the stock in long lengths and to cut to length after forming. As a rule of thumb, consider that parts shorter than 3 times the centerline spacing of rolls of the machine employed will not feed or form satisfactorily.

Depth of Form

It is important for the designer to know that different diameters of forming rolls have different peripheral speeds and thus exert different amounts of pull on the stock. Hence, frictional heat, roll wear, and possibitlity of scoring the stock might occur as a result of slippage. These problems are reduced by minimizing the depth of the form. The maximum form depth that has been established for average-size forming machines is 100 mm (4 in ).

Wide Sections

As thin, wide parts may have the tendency to show waviness, it is a good practice to form a longitudinal stiffening rib in the wide area. This helps avoiding irregularities and making the component more rigid.

Symmetrical or Balanced Forms

The most satisfactory shapes for roll forming are shapes symmetrical about a vertical centerline. If symmetry is not possible, it is desirable to have approximately the same amount of bending on each side of the centerline. It is worth mentioning that completely nonsymmetrical forms are also entirely possible.

Source: Bralla, Design for manufacturability Handbook