Based on the practical quality management experience of our stamping plant, this article summarizes the causes and countermeasures for common problems in the production of metal stamping parts, hoping to provide useful reference for improving the quality of parts for peers in the stamping industry.
1. Why do metal stamping parts experience flipping and twisting?
Stamping parts are formed in a progressive die by punching away the excess material around the part to create its shape. The main cause of flipping and twisting in stamped parts is the influence of the blanking force. During blanking, due to the presence of the die clearance, the material is stretched on the die side (material warps upward) and compressed on the punch side. When using a stripper plate, it is essential to press the material firmly with the stripper to prevent the material on the punch side from warping upward. At this point, the stress state of the material also changes accordingly. As the pressure from the stripper plate increases, the material on the punch side is stretched (pressure tends to decrease), while the material on the die surface is compressed (tensile force tends to decrease). The flipping of the stamped part is caused by the stretching of the material on the die surface. Therefore, during punching, pressing the material firmly is the key to preventing flipping and twisting. Causes and countermeasures for flipping and twisting during bending of stamped parts.
This is caused by the burrs on the punched parts during blanking. It is necessary to inspect the cutting edges and pay attention to checking whether the die clearance is reasonable.
During the blanking process, the stamped parts experience flipping and deformation, leading to poor forming after bending. This needs to be addressed at the blanking and cutting station.
Stamping parts are unstable during bending, mainly in U-shaped and V-shaped bending. To address this issue, guiding before bending, guiding during the bending process, and pressing the material during bending to prevent the stamped part from slipping are the keys to solving the problem.
2. Why do metal stamping parts tear?
Common tearing and skewing forms in metal stamping parts: The stamping process for the intermediate protection bracket is: blanking and punching – punching and notching – flanging and forming – notching – flanging. During the forming process, the intermediate protection bracket may exhibit various forms of tearing and skewing. The areas prone to tearing are mainly distributed at the hole shapes, the junctions of R arcs and side wall corners, and the wall neck transitions, etc., due to the stamping and forming production. Due to different process conditions, the proportion of each fracture site varies. Tearing can be a one-time formation or a tear caused by the development of fatigue cracks.
Cause analysis: Based on the actual site conditions, by inspecting the tear locations, fracture forms, and extrusion degree of the parts, it is believed that the tearing and skewing behavior of the parts mainly occurs during the flanging and forming process. The reasons for this phenomenon are as follows:
Inadequate execution of forming process parameters: During the forming process of the part, the process requires that the die, the pressure pad core, and the part must be tightly combined, and the plastic deformation of the plate occurs as the machine slide moves downward. However, due to shortcomings such as unstable quality of the pressed parts, the machine pressure is in an unbalanced state of pressure fluctuation during production. The main reason is that the processing technicians did not adjust the machine pressure in a timely manner according to the process requirements at this stage, or during the shift handover process, the machine pressure stability information was not communicated, leading to unstable part quality.
Design defect in the flanging and forming die. This die is a one-mold, two-cavity design shared by left and right parts. Because this operation involves not only flanging but also forming, and the part is particularly complex with narrow bending surfaces, the forming requires the blank holder core in the lower die to match the forming surface, resulting in a large forming stroke and a small blank holder area in the die structure. In the initial die design, the designer only considered the small blank holder surface but overlooked the sliding stroke of the forming guide rail on the blank holder core.
3. Why is the surface quality of metal stamping parts poor?
The causes of surface quality issues in stamped products are multifaceted. The surface quality of coils, sheets, and dies affects the quality of the final stamped parts. Operations during the stamping process and loading/unloading of workstations can also damage parts. Therefore, surface quality should be carefully considered at every stage of the entire manufacturing process, and efforts should be made to avoid quality issues that affect the final product's appearance.
1. Coil material
Common defects in coil material mainly include the following:
Foreign matter mixed on the surface or inside of the steel sheet
Foreign matter peeling off, leaving scar-like marks on the coil
Coil material defects
Edge damage on the coil
Deformation or wrinkling at the edges (20–30 mm) due to uneven stress
Scratches (caused by roller surface or foreign matter)
Caused by roller slippage
Irregular edge damage
Bumps pressed on the back of the coil after foreign matter enters (disappear if the foreign matter falls off)
Roller marks (caused by foreign matter adhering to the roller)
Material defects beyond specification
Deep, visible grooves on the surface caused by foreign matter