At present, the common sheet metal pressing method for body-in-white is hemming. Hemming usually has two forms of implementation: hemming and hemming. Hemming refers to traditional mold hemming. Use a press or some cylinders to drive the pressing block to compress the hemming and wrap another part to achieve the purpose of assembly. The hemming roller (usually driven by a robotic arm) is used to fold the hemming and wrap another part to achieve assembly.

                                             

1. Flanging height
The hemming length has a certain relationship with the hemming height of the outer panel. Generally speaking, the definition of the hemming height directly determines the feasibility and appearance quality of the hemming. According to the empirical value, when the four-door and two-cover panels are pressed together, if the pressing section is a flat straight edge, the numerical parameters of the hemming.

In other places, such as drainage holes (generally there are three in the front door and 2 to 3 in the rear door), the hemming length is also different from that of general parts, and the hemming length here is changed by less than 30% of the normal hemming length.

2. Feasibility of inner and outer panel assembly
Before the four-door and two-cover panels are pressed together, the inner and outer panels need to be assembled, that is, the inner panel is placed in the outer panel, but due to the shape or some other needs, the outer panel has a large angle in the shape, and it is difficult or impossible to assemble the inner and outer panels at this time.

The stamping die door cover hemming process is the last process of the assembly of the four-door and two-cover product assembly. Its hemming quality directly affects the overall appearance and sealing performance of the product. After assembly, it is necessary to maintain a uniform assembly gap with the surrounding parts to achieve good appearance and interchangeability.

1. Size

Gap indentation (roll-in) refers to the end position of the hemming being inside the ideal position. It is caused by the change in the size of the outer layer plate due to the movement of the hemming edge during the hemming process. It generally occurs in the final hemming process.

Due to the complex shape of the hemmed parts, the hemming process produces different roll-in values ​​in different areas. At the straight edge of the plane, the roll-in value is basically the same, while at the corners and where the curvature changes sharply, the roll-in value changes greatly.

The roll-in value directly determines the assembly gap of the panel and affects the appearance quality of the whole vehicle. According to the different hemming processes, the roll-in value also varies. The roll-in value of the die hemming is usually 0.5mm, and the roll-in value of the rolling hemming is usually 0.2~0.3mm.

2. Appearance

The car door is the exterior assembly of the car body. After assembly, it is required to maintain a uniform door gap and good shape surface difference with the surrounding parts. Door hemming is a relatively special process method in the manufacture of car door assemblies. After hemming, the assembly surface is required to be smooth, flat and free of external defects such as crushing, convexity and concave. It is also necessary to ensure that the overall size of the door shape surface and the periphery is accurate and stable. Therefore, the requirements for equipment and tooling are also very high. At the same time, the requirements for related parts such as the outer and inner panels of the car door are very high, so that high-quality car door assemblies can be manufactured. In order to obtain good body assembly accuracy and appearance quality, the hemming and pressing process of the car door requires not only good tooling, equipment and high-precision inner and outer sheet metal parts of the car door, but also accurate and advanced manufacturing processes.