11 - Sheet-Forming Analysis

Summary

Sheet-metal forming is one of the most important manufacturing processes for mass production in industry. It is inexpensive in large quantity production, but a great deal of time and expense are devoted to the design and production of reliable stamping dies. Since the mid-1970s, important advances have been made in the development of computer simulation codes for deformation modeling during sheet-metal forming.

Typical sheet-forming operations carried out in standard presses are characterized by quasi-static loading, principal loading by in-plane tension (with some bending influence), irregularly shaped and continuously changing contact surfaces, and large relative movements of material on the contacting surfaces. Nearly all FEM nodes in the sheet mesh will come into contact with the tooling at some stage of the simulation. (This contrasts with forming or bulk forming, in which the majority of mesh nodes are internal.) Therefore, sheet forming is in general much more dependent on friction and contact than most other forming operations. It is essential to handle contact and friction accurately and consistently in sheet-forming analysis; otherwise, large errors can accumulate. Furthermore, contact algorithms must be sufficiently stable that small perturbations do not induce numerical divergence and instability into the techniques.

Current numerical research focuses on whole-part analysis by FEM. The principal obstacles remain stability, time, knowledge of physical boundary conditions and friction, and limited experimental verification. While contact is more complex for sheet forming, the process offers some simulation advantages in terms of the possibility of neglecting through-thickness stresses and, in some cases, bending stresses.