The Research Of Sheet Metal Multi-point Composite Incremental Forming Fracture Defects

Combined with the advantages of single point incremental forming(SPIF) and multi-point forming(MPF), the multi-point composite incremental forming(MPCIF) has been an advanced dieless sheet metal forming method. The sheet mental has a higher forming limit and better forming quality as MPCIF can effectively improve its formability. However, MPCIF also has some forming defects, such as fracture, wrinkling, forming indentation, bottom inward convex and springback, especially fracture has the most important influence on the appearance and functions of the parts among them. Therefore, the research was focus on the fracture process of MPCIF, and carried out by FEM analysis and experiments.In order to prevent or reduce fracture defects in the process of MPCIF, the research was carried out by combined with theoretical analysis, FEM analysis and experiments. The main worker: the ductile fracture criterion for MPCIF based on Lemaitre damage theory was derivated and the material parameters was determined; the fracture FEM of the MPCIF was established and the fracture characteristics of MPCIF was studied; the process parameters effects on the fracture were researched and the threshold of ductile fracture was seeked; the fracture prediction model of maximum forming depth was established by RSM(Response Surface Methodology).Main research results of this paper:(1) Based on Lemaitre damage theory, the ductile fracture criterion for MPCIF was derivated. With 1060 aluminum alloy as test material, the material parameters in the guidelines was determined by hybrid test method.(2) Based on the MPCIF forming principle, the major structure of the MPCIF tester was designed, and the FEM was established accordingly. The fracture visualization of MPCIF was realized through the redevelopement of MSC.Marc. Meanwhile, in order to study the fracture characteristics of MPCIF, the distributions of stress, strain, thickness and ductile fracture value in different areas were analyzed.(3) The process parameters’ effects on the fracture were researched by single factor test methods, such as forming angle, feed rate, tool head size, forming speed and sheet mental initial thickness. Meanwhile, the threshold of ductile fracture was obtained by the simulation and experimental research of 1mm 1060 aluminum alloy fracture process of Mf PCIF.(4) According to single factor test results, the multiple regression fracture prediction model of maximum forming depth was established by RSM. Through the optimization design and forming experiments, the correctness of the finite element model and fracture prediction model were verified. Meanwhile, the advantages of vibration on delaying fracture and improving forming limit were confirmed with the introduction of vibration in the process of MPCIF.The reasearch shows that the study of the fracture forecast will have an important significance on the actual production and application of MPCIF.