How does the cold extrusion process improve the strength and precision of the parts of the seat belt locking device of the car?
Publish Time: 2025-04-15
As an advanced plastic forming technology, the cold extrusion process has shown significant advantages in the manufacturing of the parts of the seat belt locking device of the car. Through the coordinated optimization of the microstructure and macroscopic performance of the metal material, a double breakthrough in strength and precision is achieved.In terms of strength improvement, the cold extrusion process uses the plastic deformation characteristics of the metal material under the three-dimensional compressive stress state to form a dense fiber streamline structure inside the part. Taking the retractor ratchet, a key part in the seat belt locking device, as an example, during the cold extrusion process, the material flows along the mold cavity in a directional manner, the grains are refined and work hardening occurs, and the dislocation density is significantly increased. The interaction between dislocations effectively hinders the subsequent deformation, so that the tensile strength of the parts is increased by more than 30% compared with traditional cutting. In addition, the residual compressive stress field formed by cold extrusion can offset part of the external load and delay the fatigue crack growth rate. According to actual measurements, the fatigue life of the cold extruded ratchet is 2-3 times longer than that of the forging process.In terms of precision control, the cold extrusion process relies on the synergy of high-precision molds and presses to achieve micron-level control of part size. By optimizing the mold cavity design through finite element simulation technology, the dimensional accuracy of the seat belt locking device shell can be stabilized, and the surface roughness Ra≤0.8μm. During the cold extrusion process, the metal material undergoes viscous flow under high pressure, and the micro-texture of the mold cavity can be accurately replicated on the surface of the part to form a functional structure with a specific friction coefficient. This structured surface improves the locking sensitivity of the seat belt while reducing noise and wear during use.Precise control of process parameters is the key to the coordinated improvement of strength and precision. Dynamic balance of metal flow can be achieved. For example, in the cold extrusion molding of the seat belt pin, the phosphating-saponification composite lubrication process is adopted, combined with the precision control of the 3,000-ton hydraulic press, so that the coaxiality of the pin is ≤0.02mm and the verticality is ≤0.01mm, meeting the millisecond-level response requirements of the seat belt emergency locking.The optimization of material utilization and production efficiency further highlights the competitiveness of the cold extrusion process. Compared with traditional cutting, the material utilization rate of cold extrusion process is increased by more than 60%, and the production cycle of a single piece is shortened to 15-20 seconds, which is particularly suitable for large-scale production of high-precision parts such as seat belt locking devices. Dongfeng Commercial Vehicle has increased the material utilization rate of the seat belt retractor ratchet from 45% to 85% through patented cold extrusion molding process, while making the hardness uniformity of the parts (HBW135-145) reach the strict standard of ±3.The cold extrusion process achieves a coordinated improvement in strength and precision in the manufacturing of automotive seat belt locking device parts through metal streamline reconstruction, residual stress regulation, precision mold design and process parameter optimization, providing technical support for the lightweight and high-performance of automotive passive safety systems.
