Screw connection is a process used to connect two thinner parts with through holes on the connected parts. The parts are tightly connected through the threaded connection of bolts and nuts. In order to facilitate the actual operation, there is a certain gap between the screw and the hole. Clearance, simple structure, convenient loading and unloading, is a commonly used connection method in the automotive industry.
According to structural forms, material differences, and functional requirements, there are seven main types of screw connection structures.
1. Ordinary bolt + ordinary nut
The bolts and nuts of this structure and the connected parts are independent at the beginning, which facilitates disassembly, and has stronger flexibility in the selection of bolts and nuts.
Screw connection structure diagram
Sheet metal opening: usually the size of the first layer of sheet metal opening is bolt diameter + 0.5, and the second layer is an additional 1mm based on the first layer of opening size. (Different OEMs have certain differences in openings due to production capacity)
Cross-section drawing of screw connection
2. Projection welding nut + bolt
The projection welding nut of this structure and the sheet metal are pre-composed of components, as shown in the section below, the protruding points of the projection welding bolt will be integrated with the sheet metal, and then connected with the bolt.
This type of structure is mainly used in areas where there is no space on one side or where it is difficult to install on one side, such as the four-layer board of the top cover, the seat beam and other areas. The sheet metal opening method is the same as that of structure form 1
Object and cross-section drawing of projection welding boltThe sheet metal opening method is the same as that of structural form 1.
3. Projection welding bolt + nut
Projection welding bolts are divided into end projection welding bolts and bearing surface projection welding bolts. The bearing surface projection welding bolts need to be opened. The bottom hole of the projection welding bolts is uniformly set as (M+0.5), which is suitable for the tight fitting of the mounting parts and the sheet metal. Components, end projection welding bolts do not require sheet metal openings, and are suitable for components that do not need to be closely attached to the sheet metal. Some models of projection welding bolts are used in the front wall, front longitudinal beam and other positions.
Projection welding bolt diagram
With the application of body aluminum, thermal connection cannot be achieved, and the current screw connection of aluminum structure cannot be achieved by projection welding. There are mainly the following.
4. Pressure riveting nut + bolt
The nut is pressed into the sheet metal preset hole by pressure in advance. The hole diameter of the preset hole is slightly smaller than the embossing teeth of the pressure riveting nut. Then the bolt and the pressure riveting nut are combined to make the sheet metal connection structure. The connection strength is pressure riveted. The form of the nut has a greater influence.
Features: one side of the sheet metal is flat, one side protrudes larger (threaded side)
Detailed drawing of pressure riveting nut
5. Blind rivet nut + bolt
Blind rivet nuts are pre-assembled with sheet metal according to Hooke’s law, and then combined with bolts to achieve a structural form of connection. Blind rivet nuts are usually M-0.5mm in sheet metal holes and are used in various parts of the aluminum car body.
Features: The sheet metal on both sides is uneven, and the screwed side protrudes by about 1.5mm.
6. Pressure riveting bolts + nuts
This structure is the same as Structure 4, except that the pressure riveting nut is replaced by a pressure riveting bolt. The choice of bolts and nuts mainly depends on the functional requirements and the requirements of the counterpart.
Detailed drawing of pressure riveting bolts
7. Rivet bolt + nut
This structure is the same as Structure 5, except that the blind rivet nut is replaced with a blind rivet bolt. The choice of the bolt and nut mainly depends on the functional requirements and the requirements of the counterpart.
Blind rivet bolt detail drawing
In car body applications, the number of pull riveting is always greater than that of pressure riveting. Why?
The main reason is that pull riveting can be applied to finished and semi-finished products, while pressure riveting must be applied to thin plates. After the finished product, the riveting cannot be used. There are fewer limiting factors for pulling riveting in the body assembly process, and the operation is more convenient and the functions are satisfied. The quantity is always more surplus riveting. (Following a detailed introduction to the difference between pull riveting and pressure riveting)
Ordinary screw connection is not affected by the material, but requires sufficient space on both sides, and is mainly used in large parts such as anti-collision beams.
For projection welding fasteners, which are widely used in steel areas, only one side space is required to meet the requirements, which is convenient for the installation of various components in the final assembly process. With the development of body materials, pressure riveting fasteners and Riveting applications are gradually increasing, but pressure riveting requires more space, while pulling riveting only requires one-sided space, which occupies a particularly important position for pulling riveting in a closed structure or a narrow area under a space.
For the seven structural forms, they are applied in different areas according to various factors such as function, material, production, space and so on.