Enhancement of Incremental Sheet Metal Forming Technology by Means of Stretch Forming

Incremental Sheet Forming (ISF) is a relatively new flexible sheet metal forming process mainly oriented to small batches production and prototyping. The technology has been conceived to enable flexible forming of sheet metal parts based on CNC governed punch movements, being the use of conventional milling machines possible if vertical maximum force is controlled. During the process, a simple shape punch is moved against the surface of the sheet, such that a localised deformation is caused, and the use of spatial punch movements enables the forming of complex 3D shapes. However, the process has some drawbacks: high geometrical inaccuracies, an emphasised problem in complex non-axisymmetric parts, poor final surface quality due to the friction between the punch and the blank, limitations to obtain steep walls and the need of large process times due to the nature of the process. In this paper, the stretch forming is used together with the Incremental Sheet Forming in order to overcome the process limitations, aiming to optimise the material flow and minimise the thinning. Numerical, Finite Element Modelling, and experimental results are presented using a real case study.