SHEET METAL FORMING
Description
| Sheet metal forming describes the process by which a material undergoes permanent deformation to produce complex three dimensional shapes. Ease of forming depends primarily on the shape and dimensions of the part and the material. The most important factors that determine a particular material’s formability are its intrinsic mechanical properties. However, success or failure is often determined by the frictional conditions at the tool/material interface. Friction is controlled by such factors as press conditions, lubrication, tool material and surface condition, and strip surface condition. | |
Contacts
www.forming.com
www.me.umn.edu
cybercut.berkeley.edu/mas2/html/processes/forming_sheetmetal/
Characteristics
| Costs (tooling / unit) | Approx. £1,000,000 for the largest cast iron tool sets (car door panels, fenders, etc) |
| Volume (units / day) | Up to 32 parts per minute depending on press type and size of part |
| Possible Materials | Strip steel (uncoated and coated) and aluminium |
| Size / Shape | Limited by the bed size and capacity of the press and the width of strip which can be supplied by the mills (supplier dependent). Design limitations are dependent on the material selected. |
| Mechanical Properties | Yield stress, n value (work hardening exponent) and r value (resistance to thinning). A drawn component requires a high r value: a stretch formed component requires a high n value. |
| Special Remarks | There is no specific material characteristic which will adequately describe performance under the widely varying conditions of forming sheet metal parts. The forming limits of the material must be compared with the strain developed in the part during deformation to be sure of success during volume production. |
Application / Case Study
The photograph shows a typical car door inner, first stage pressing. The part has been manufactured from FeP04 grade mild steel using a double action mechanical press. This is a complex pressing, exhibiting areas of high strain, stretch and draw.
Most of the deformation required is introduced at the first stage, with subsequent operations required to pierce, flange and trim, with a final restrike operation designed to sharpen radii and pull the panel tight over the punch to improve visual appearance.