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Why does the surface of the workpiece appear to be strained or seized when it is formed?


The essence of the strain problem of automobile mold workpiece and the basic measures to solve the strain problem
The problem of strain during the molding process of the workpiece is divided into the following two situations. One is that the macro-mechanical unevenness of the mold or the inclusion of other hard particles between the molded material and the mold will cause mechanical cutting on the surface of the workpiece. This situation may occur in actual production. The solution is to perfect the mold design and make careful grinding of the mold surface, and strengthen the management of the production environment.
Another case of automobile molds is due to the adhesion and wear of the workpiece surface and the mold surface. The resulting strain is also the most common and difficult to solve in production. The following detailed analysis of the occurrence of adhesive wear and some basic measures to reduce adhesive wear.
When the automobile mold forming mold processes the workpiece, the mold and the processed material surface contact each other and slide relatively to form a pair of contact pairs or friction pairs. Since the surface of the material cannot be completely flat, there is always a measurable roughness, so the real contact only occurs on the micro contact surface. The analysis shows that the microscopic real contact area is only a small part of the nominal geometric contact area, and thus a large mechanical stress is generated in the microscopic contact surface range. These stresses will be strengthened due to the relative tangential movement, resulting in the roughness of the load. The surface convex peaks undergo elastic or elastoplastic deformation, so that the adsorption layer or the reaction layer on the surfaces of the friction pair will be destroyed. As a result, the atomic bonds exposed on the surface are more or less strengthened. This phenomenon is called adhesion. . When the friction pair moves relative to each other, the atomic bonds will disengage from each other. The disengagement of the atomic bonds does not necessarily break at the original microscopic contact, but may break near the surface layers of the friction pair. The result is The material is transferred from one side of the friction pair to the other side of the friction pair, which is the so-called adhesive wear [1]. Experiments have proved that the surface of the friction pair with adhesive wear is very rough and has strain. The degree of which is related to the load parameters such as the normal force, the relative movement speed between the friction pairs and the temperature. When the above load parameters exceed the critical value, the adhesive wear suddenly intensifies, and the so-called bonding phenomenon occurs. In extreme cases, the relative movement between the friction pairs stops and seizure occurs. From the above analysis, it can be seen that the surface strain or seizure of the workpiece during forming is the result of adhesive wear.

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