| Automobile panel dies are very basic equipments in the automotive industry, which decide the forming of more than 90% of auto parts. Traditionally stamping dies are manufacturered by surfacing welding method and die insert method which can't satisfy the actual demand. How to develope new technology and process for auto moulds is an urgent problem for current die industry.In this paper, double metal automobile panel die is prepared by liquid-liquid compound casting, the working part of which is made of 7CrSiMnMoV, while the rest is made of HT300. Foundry method scheme and casting technique parameters were optimized by ProCAST software and related theory. Multi-steps samples with typical structure of mould were cast to research the effect of pouring interval time on the formability and casting quality of those multi-steps samples. The microstructure of transition layer, mechanical properties, the thickness of transition layer and formation mechanism, bonding mechanism of the interface formation, were characterized by using scanning electron microscope(SEM), energy dispersive X-ray spectroscopy(EDS), instron-3382 tensile testing machine and micro hardness tester.(1)The casting method of auto trimming die prepared by lost foam liquid-liquid compound casting is that modeling method with "iron up steel down", resin-bonded sand moulding, perpendicular pouring method, designing two sets of gating system. Low alloy steel cast first and then molteniron poured. Bottom gating system and side gating system are selected for blade section and mold base, respectively. The ingate of mold base and the overflow of the trimming die both should be designed at the interface of the bimetal. The casting process is reasonable and feasible.(2)The best casting process decided by ProCAST software and related theory is that pouring time interval locate within the scope of 50-120 seconds, low alloy steel cast at 1530-1550?, and gray cast iron poured at temperature of 1350-1380?. The best pouring interval time for multi-steps sample with typical structure of mould is 90 seconds. The sample manufactured by this process has a high quality interface with a zigzag structure, and no obvious shrinkage hole, shrinkage and other casting defects are detected.(3)Bimetals are composed of three parts:the steel matrix, the transition region and the iron matrix. The best thickness of transition layer is about 400?m and the transition region has a zigzag structure, and Cr and Si elements near the interface are in gradient distribution. Corresponding mechanisms belong to metallurgical bonding, supplemented by diffusion bonding mechanism.(4)The hardness gradually decrease across interface from the side of HT300 to the side of 7CrMnSiMoV and tensile strength of the bimetal reaches 339 MPa. Fracture Locations appear on the side of HT300, which testify the tensile strength of the bimetal is higher than that of HT300.(5)Two sets of typical automobile trimming dies were successfully prepared by liquid-liquid compound casting, which were evaluated by dye inspectiong and destructive test, respectively. The main results show that:castings with high quality, no obvious casting defects appear, such as shrinkage cavity, shrinkage porosity and cavity, which confirm the accuracy of the related parameters. |
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