Research on surface quality improvement of an automotive outer panel in single-point incremental forming

The small-volume large-variety production is needed in the automotive after-sales service market (AM) to address the issue of reduced production quantities caused by frequent vehicle model updates in recent years. Single point incremental forming (SPIF) technology can meet the above requirements. SPIF is a low-cost, small batch-forming technology that does not require specialized forming machines or dies. This study determine the parameters needed for incrementally form a 0.3 mm-thick Al1050 sheet into a lab scale automotive hood panel. The CAD files are processed into forming paths via CAM software and input into a CNC machine tool. The forming tool with rounded corners will follow the programmed path to form three-dimensional movements on the sheet metal surface, applying localized plastic deformation to achieve the desired dimensions and shape. The sheet supporting fixtures was manufactured by a 3D printer. The experiment was conducted using a micro- CNC machine. For the analysis, the original G-code path to form the hood panel was imported into the analysis software. Results indicate that the forming limit angle was 57.5 degrees for 0.3mm-thick Al1050 sheet. Large step size can improve formability and save processing time, but the surface appearance of panel is unaccepted. A small step size can achieve excellent surface, but formability is reduced. The control of blank holder force become crucial and longer forming process time is needed. A high spindle speed can improve formability, achieving uniform deformation and improve surface quality. The feed rate is recommended to be increased as much as possible to reduce the processing time when the machine rigidity is sufficient. During the process, it was found that the sheet metal exhibited a reverse twisting phenomenon, which was determined to be caused by changes in the contact area of the forming tool as depth increased, altering the friction stress pattern on the blank surface. The analysis results effectively presented the same thickness distribution trend as the experimental results and significantly reduced computation time. With the combination of optimized process parameters and path planning, this study met the surface quality and formability requirements, proving the feasibility of applying incremental forming technology to automotive outer panels.