| For the traditional hot stamping automobile parts, even though they can improve the performance of the vehicles in the crash considerably, but the high tensile strength and hardness are beyond the bearing of current cutters in the factory. So it would bring a lot of difficulties in the process of cutting these parts. In consideration of the shortness above, there comes a new technology called Tailored Tempering Process based on the traditional hot stamping technology, which can be used to produce auto parts suitable for the load distribution. In this technology, different measures are taken to change the cooling rates in different regions of a whole blank, so the phase transformation would be influenced, and the auto parts with tailored mechanical properties would be manufactured.In this paper, three main factors of the manufacturing of the S rail beam using the high strength steel with the tailored tempering technology are investigated. Those are the tool temperature, contact pressure and stress on the blanks in the stamping process. The S rail model in the experiment is designed and developed by our research team. And the model is composed of three parts, two parts on the both ends are heated by the electric resistance, the temperature of which could be400℃. The middle part is separated from the heated parts by the asbestos fiber cloth. During the experiment, the tool temperature and contact pressure are controlled to change the cooling rates in different regions of the whole blank. As a result, the S rail beam with tailored mechanical properties are produced.The conclusion demonstrates that:(1) Tool temperature:the changes of tool temperature can considerably influence the hardness and metallographic organization of the forming parts. When the tool temperature is20℃, the hardness for this region of the forming part can be as much as531.45HV, and the metallographic organization is the fully martensitic structure. When the tool temperature is raised to400℃, the hardness could be declined to268.15HV, and the metallography is mainly made up of bainite. At the same time, the middle part of the S rail model is cold enough to guarantee the metallography in this region is fully martensitic structure.(2) Contact pressure:more contact pressure would be needed to produce an S rail beam with good quality, when the temperature of the model is lower. As to the mechanical properties of the forming part, when it is fully martensitic or mainly bainitic structure, the contact pressure would have a little effect on the hardness, while the tool temperature is the main factor on the mechanical properties in this situation. However, if the metallographic organization is combined of the martensite and bainite, the contact pressure would have an important impact on the mechanical properties. When the tool temperature is20℃, the martensitic volume would expend with the increasing of the contact pressure, and the hardness would get higher. If the tool temperature is above200℃, the bainitic volume would expend with the decreasing of the contact pressure, and the hardness would get lower.(3) Stress on the blanks:the stress on the blanks in the region of inside wall or outside wall in the fillet is different during the stamping process. The effect of the compressive stress would hinder the martensitic transformation, but the tensile stress would improve the transformation.Through the experiment in this paper, the traditional hot stamping technology has been improved. The tool temperature, contact pressure and stress on the blanks have been investigated. And the S formed parts with mechanical properties are successfully manufactured by the tailored tempering process technology. The experiment has laid a great foundation for the tailored tempering process technology being used in the automobile industry. |
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