Analysis of automobile body parts and requirements for welding

1 Characteristics of auto body parts
The automobile body is generally composed of inner cover parts, outer cover parts and frame parts. The cover parts are generally made of steel plates, and the frame parts are also made of thin plates. Auto parts have the following characteristics: complex structure and shape, difficult composition. The automobile body is a spatial shell welded by sheet metal stamping parts. In order to make the shell have certain rigidity and beautiful appearance, the parts of the automobile body are usually the spatial curved surface body formed by drawing, and the structural shape is quite complex. The rigidity is poor and easy to deform. Because the parts of the automobile body are made of thin plates, the formed thin plate stamping parts have a certain rigidity, and a single large stamping part is easy to deform. Compared with the machined parts, the rigidity is much worse. It has strong stiffness only after welding into the body shell. During the development of China’s automobile industry, the quality management system and technical assurance measures for the processing and production of automobile parts are relatively sound. Combined with the characteristics of automobile body parts, the welding process should be selected according to the characteristics of parts [1].
2 requirements for welding of automobile body parts
In the automobile industry, welding is a key link in the manufacturing of automobile body, which plays a special role of connecting the preceding and the following. At the same time, due to the large number of vehicle models and complex forming structure of automobile products, the gradual specialization and standardization of automobile body parts production, as well as the comprehensive requirements of automobile manufacturing in terms of quality, efficiency and cost, all determine that automobile welding processing is a production process with multi-disciplinary, cross domain and strong technical integration. When choosing the welding process, we should consider the characteristics of auto parts and formulate the welding process according to its characteristics to ensure the welding quality and smooth assembly of the car. In fixture design, one of the key issues to be considered is the distribution of welding spot process. Only when we carefully study the welding process can we well design the welding fixture. Reasonable fixture design can ensure the smooth progress of the welding process. Therefore, only by correctly understanding the characteristics of assembly and welding production such as rebound and deformation of sheet metal stamping parts, can we design a suitable automobile assembly and welding fixture.
Due to the large number of parts of automobile assembly welding and assembly, in order to carry out the welding and assembly process smoothly, fixtures should be used for welding. Most of the welding fixtures of the front wall of the car body are positioned by the shaped platform on the surface, the steps formed by drawing and bending, the outer edge, the assembly holes and the surface shape and process holes of stamping parts. For the parts with good quality, the positioning parts shall be dimensioned according to the coordinates and marked with tolerances. After the body stamping parts are assembled, the resistance welding shall be used, and the workpiece will not be subject to torsional torque. When the gravity of the workpiece is consistent with the pressurization direction during spot welding, the welding pressure is enough to overcome the elastic deformation of the workpiece. The requirements for welding process of parts with good rigidity are relatively loose, because when the thin plate of parts with good rigidity is used as a stamping part, the action point of clamping force acts on the support point, and only the workpiece with good rigidity is allowed to act on the plane composed of several support points for force balance, so as to avoid bending or separation of the workpiece from the positioning reference by clamping force.
Automobile assembly parts form a rigid cavity in the fixture through assembly positioning, and can be maintained in the corresponding coordinate system to resist the deformation of stamping parts on assembly lap. Automobile assembly parts should overcome welding deformation force and mechanical impact force when passing through spot welding. This requires that the welding personnel must weld in strict accordance with the process requirements, so as to avoid the unqualified phenomenon of welding quality such as deformation and out of tolerance caused by inconsistent spot welding sequence.
The accuracy of body product parts depends on the accuracy of body product assembly and welding fixture and stamping parts. Only when the accuracy of body parts and assembly and welding fixture is guaranteed, can the quality and operability of fixture be improved in debugging and production. Our welded body parts play different roles in all parts of the vehicle, and their welding accuracy is also different. The positioning parts should have high welding accuracy, and the clamping parts and base should have sufficient strength and stiffness. Therefore, the functions of automobile body parts are different, and the requirements for welding are also different .
When designing the body assembly and welding fixture, we should consider the degree of freedom of body parts. This restriction depends not only on the mutual restriction between parts, but also on the positioning and clamping device of the fixture. When designing the fixture, we should consider the welding process. The welding process plays a guiding role in the fixture design. The determination of the welding process is the basis of the body fixture design, which determines the universality, flexibility, automation level, subassembly welding fixture and welding assembly line fixture. One factor we must consider in the fixture design and production is the welding process. When designing the fixture, A key issue to be considered is the distribution of solder joint process. Only by carefully studying the welding process can we design the welding fixture well. Reasonable fixture design can ensure the smooth progress of the welding process. Therefore, only by correctly understanding the characteristics of assembly and welding production such as rebound and deformation of sheet metal stamping parts, can we design a reasonable assembly and welding fixture. Ensure the normal welding process and assembly and welding quality. Reduce labor intensity, improve labor conditions, reduce product costs, improve labor productivity, position and clamp the parts of the car body to ensure assembly accuracy. At the same time, the positioning method of the same position rule is correctly understood. The principle of the positioning method is that the parts can always be placed in the same position on the fixture. According to the characteristics of body parts, from the perspective of positioning principle, first of all, the parts should be fixed on the fixture. The form of positioning pin and positioning surface can be used to limit the freedom of components and parts. In order to eliminate the deformation of the workpiece caused by the supporting force of the thin plate, it is essential for the work of the automobile. During assembly, the fixture must make the assembled parts and components obtain the correct position, and the fixture can clamp reliably. During welding, it can reduce and prevent the deformation of weldments. We know that reasonable over positioning can eliminate springback and deformation of parts and ensure more stable and accurate positioning. However, for the interference in the assembly position caused by over positioning, as long as the bearing surface is carefully polished when adjusting the fixture, the adverse effect caused by over positioning can also be controlled within the allowable range of standards and production specifications .

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