Laser Assisted Incremental Forming

Single Point Incremental Forming (SPIF) is a flexible sheet forming process which is characterized by the continuous stepwise forming of a blank sheet through the movement of a small forming tool. In contrast to processes such as spinning and shear forming, incremental sheet forming (ISF) can create both symmetric and asymmetric shapes. Customized three-dimensional parts can be made by the CNC-controlled motion of a hemispherical tipped tool over a metal, polymer or composite sheet. Using the incremental forming method, small series production of sheet components with high customization is possible within short lead times. In this dieless forming technology the time and cost of designing, manufacturing and storing dies for small series production of sheet metal parts can be reduced. 

In order to allow processing high strength materials or materials with limited formability a Laser Assisted variant of SPIF has been developed (LASPIF). In this process a warm spot is generated in the vicinity of the contact between the forming tool and the workpiece. By creating a local hot spot around the contact point between tool and sheet, process forces can be reduced while forming limits are increased for most materials. Furthermore, a local hot and ductile spot in a rigid cold sheet results in more local deformation of the sheet and therefore increased control and accuracy. The LASPIF process has proven to offer advantages in terms of increased formability, reduced inaccuracy due to undesirable elastic springback and reduced process forces.

However, the use of a laser beam adds several degrees of freedom to the forming process in comparison to single point incremental forming at room temperature. Enhancing the formability and accuracy achievable with LASPIF requires a strategic choice for the many process parameters involved. The work reported in this dissertation aims to investigate the relations between the different process parameters and the resulting process output in order to better understand the process mechanisms under heat-assisted forming conditions. For this purpose, it is necessary to model the process and to explore the influence of the respective process parameters. Apart from finite element modelling, a design of experiments (DOE) is used to define optimal laser scanning and laser-tool offset conditions to maximize formability of the material. Moreover, an in-depth study on the use of tailored microstructures through local, thermally induced hardening or softening transformations to influence the LASPIF process performance has been performed. Furthermore, the possibility of using a laser for post stress relief-annealing of SPIF formed parts to remove residual stresses of SPIF formed part was investigated.