Stamping is the first of the four technologies, and its importance can be imagined. The quality of stamping products will lay a reliable foundation for the appearance and performance of the vehicle. Therefore, the quality assurance of stamping parts has always been a very important issue for automobile manufacturing enterprises.
According to the practical experience of quality management in our stamping factory, this paper summarizes the causes and Countermeasures of common problems in the production process of metal stamping parts, hoping to provide some useful reference for improving the quality of stamping parts in the same industry.
1 Why do metal stamping parts appear distortion?
Stamping parts in progressive die, by punching the periphery of stamping parts to form the shape of the stamping parts. The main cause of stamping and twisting is punching force. In blanking, due to the existence of blanking clearance, the material is stretched on one side of the die (material warped upward), and compressed on the side of the punch. When the unloading plate is used, the material is pressed by the unloading plate to prevent the material on the side of the concave die from warping upward. At this time, the material’s stress state changes correspondingly. The material near the punch side is stretched (the compressive force tends to decrease) and the material on the die surface is compressed (the tensile force tends to decrease) with the increase of the pressure on the discharging plate. The rollover of stamping parts is due to the tensile strength of the material on the die surface. Therefore, pressing and compressing material during blanking is the key to prevent the material from turning and twisting. Causes and Countermeasures of stamping and twisting during stamping.
The punching edge is caused by blanking. We need to study the punching edge, and pay attention to check whether the blanking clearance is reasonable.
The turning and twisting deformation of the punched parts have occurred during blanking, resulting in poor forming after bending, which should be solved by blanking workstation.
The instability of stamping parts is caused by bending. Mainly for U and V bending. To deal with this problem, the key points are the guide position before bending, the guide position during bending, and the pressing material to prevent the stamping parts from slipping during bending.
2 why do metal stamping parts cause tear?
The common form of tearing and skewing for metal stamping parts is blanking and punching – punching incision – flanging forming – incision – flanging. There are various forms of tearing and skewing in the forming process of the intermediate face shield bracket. The tearing parts are mainly distributed at the pass of the part, the junction of R arc and neck at the corner of the side wall and so on. Tearing can be either a one-off plastic tear or a tear caused by the development of a fatigue crack, i.e. an invisible crack.
According to the actual situation on the spot and by checking the tearing position, fracture morphology and the degree of extrusion, it is considered that the tearing and skewing behavior of the workpiece is mainly reflected in the flanging forming process. The causes of this process phenomenon are as follows:
The forming process parameters are not in place. In the forming process, the concave die, the pressing core and the two parts must be tightly bonded together, and the plastic deformation of the sheet metal is compressed when the slider of the machine tool slides. But now, the quality of the pressed parts is unstable, which shows that the machine pressure is in an unbalanced state in the production process. The main reason is that the processing technicians did not adjust the machine pressure in time according to the requirements of process specifications at this stage, or did not communicate with each other in the handover of each shift pressure stability information, resulting in unstable parts quality.
The design of flanging die is defective. The mold is a common one with double cavity left / right parts. Because of the contents of this process, besides the flanging, it also has the shape forming content, and the parts are special and complex, and the bending surface is narrow. The forming requires the concave die core to match the forming face, which results in the large forming stroke and small pressing area of the mold. In the initial mold design, the designer only considered the small blank surface, but neglected the sliding stroke of the core forming.
3 why is the surface quality of metal stamping parts bad?
There are many reasons for the surface quality problems of stamping products. The surface quality of coil, sheet metal and die will affect the quality of final stamping parts. The operation in stamping process and the clamping and unloading of workstation tools may also damage the surface quality of stamping parts. Therefore, the surface quality of stamping parts should be fully considered in every step of the whole manufacturing process. Consider details, try to avoid quality problems and affect the final appearance of products.
