| The sheet metal forming limit is influenced by the different loading strain paths, and stamping process program formulated is affected by sheet metal forming limits. In order to reduce the rejection rate of the forming parts of sheet metal and make the most of the material forming performance, the influences of different strain paths on the sheet metal forming limit are discussed in the paper. The research subject is supported by High-level Talents of Higher Education of Guangdong Province-"Research on Precise Design Technology of Multi-position Progressive Die of High Strength Steel Automotive Structural Parts"(No.x2jqN9101140), Production, Teaching&Research Collaborative Project between Guangdong Province and Ministry of Education of China-"Virtual Manufacturing and Industrial Application of High Strength Steel Multi-position Progressive Die"(No.2010B090400094) and The National Natural Science Funds Youth Fund Project "Metal Spinning in the Forming of Damage Evolution and Rupture Mechanism Research"(No.50905062).In this thesis, the variation of strain path during sheet metal forming is realized by the biaxial tensile test method. And based on the DIC (Digital Image Correlation) method, the local instability of the sheet metal in different strain paths was obtained. Combined with finite element analysis of software and experimental research, the influences of the complex strain path on sheet metal forming limit are studied.The main works and conclusions of this paper are as follows:(1) A biaxial tensile test device was designed and the different loading paths were realized. The loading method and force analysis of the biaxial tensile test device were explained.(2) The DIC strain measurement system was built. The extensometer and DIC method were used to do the uniaxial tensile test experiment and the results show that DIC method is reliability. The basic material parameters is obtained by DIC method.(3) With aluminum alloy6061and high strength steel St52, the experiments of biaxial tensile test in different strain paths were done. The results show that:when direction of the principal strain of the prestrain is perpendicular to the principal strain of last step strain path, the sheet forming limits decreased in the prestrain of uniaxial tension and the last strain path of biaxial tension or prestrain of biaxial tension and the last strain path of uniaxial tension, and the sheet forming limits can be decreased in large prestrain, and the equivalent strain strain of forming Limit is less than the sum of each step equivalent strain.(4) The forward and reverse drawing process of the automotive soleplate component parts was selected as the study object, the influences of the the different strain paths on the sheet metal forming performance were studied. The main conclusions are as follows:the stamping forming quality had been influenced greatly by the changes of strain paths; the forming qualities can be improved by changing the strain paths of the dangerous point in stamping; the forming of complex shape parts and multistep progressive forming can be well predicted by using the finite element numerical simulation method. |
