| Nowadays,light weight, energy conservation and high efficiency has become the development trend of various industrial fields. Many industries(such as automobiles, aviation, medical equipment, electric power fittings) have increasingly high demands for new material and new technology, especially in the development of China's electric power industry. In the next few decades, high-voltage transmission line field of our country will meet the unprecedented development opportunity, but also bring great challenges to the manufacturing technology of transmission line fitting parts. So the demand for developing new material, improving strength of the material, and reducing weight in electric power fittings has become increasingly prominent.The traditional high-voltage transmission line fittings such as Clevises are mainly produced by casting and other complex process, the shortcomings are obvious: coarse and thick appearance, heavy weight, much metal consumption, poor bearing performance and the fittings' own weight will increase the load of line tower. Based on the hot stamping technology, the multilayer high strength steel hot forming new process has been proposed in this paper. Considering the advantages of strength performance and lightweight, the traditional Clevis-Clevis body is replaced by multilayer stack of ultra-high strength boron steel sheet which produced by hot stamping, to achieve the purpose of realization of high performance and lightweight electrical power fittings.According to the new processing technology of multilayer stack high strength steel sheets, thermo-mechanical-metallurgical coupled numerical simulation of the deep U-shaped hot stamping component has been completed in this paper. Based on the simulation, good contact heat conduction between the sheet and die is the assurance of obtaining full martensitic ultra-high strength steel. And finite element analysis combining the experimental data is also used to predict the mechanical performance and electromagnetic property of the new connection fitting, which verifies the use reliability of the new multilayer stacked Clevis-Clevis. The results show that, the multilayer structure can help to reduce the electromagnetic loss of current carrying fittings, and the new connection fitting with four or five stack layers has greatly improved stress distribution and deformation deflection, when rigid and secure constraint is applied at the laminated layers in practical application.Through the basic experimental research on the hot stamping of double layered and three layered plates, it has found that the heat transfer process of the multilayer sheet is greatly influenced by the interfacial contact pressure. Both inner and outer layers of the multilayer sheet which formed in different contact pressure show great difference in strength and ductility characteristics. And the scanning electron microscope(SEM) observation has found that the microstructural evolution of outer layer is stronger than that of inner layer. Then tempering experiment has been conducted on the quenched multilayer parts, an optimized tempering treatment scheme aiming to improve the strength and plastic comprehensive performance is summarized in this paper. On the basis of the experimental results, a set of multilayer sheet hot bending die has been designed according to the characteristic of deep U-shaped multilayer structure. Through experimental trial, high dimensional precision, high strength and uniform performance multilayer parts have finally been obtained, which lay a solid foundation for the actual production and engineering application of the lightweight, high performance electric power fittings. |
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