Numerical Analysis For Local Forming Of Sheet Metal Forming Limit

With the vigorous development of manufacturing in industry, the forming technologywith the characters of energy saving, accuracy and high efficiency becomes one of the currentresearch trends in production manufacturing, and many new forming technologies have gotdeveloped. The incremental forming, by which the complex curved surface sheet part can beformed, is one of the new developed forming technology.In experiment, the phenomenon that the forming limit of sheet part obtained byIncremental Sheet Forming(ISF) was much higher than those by conventional sheet formingwas found. Also in the practical product manufacture process, when using ISF to producesheet part can greatly reduce the cost of parts and shorten the R&D period. But up to now,there were no perfect theories about the forming mechanism to explain why the higherforming limit can be obtained in incremental sheet forming. And even the related researchworks of considering initial defects in numerical analysis for incremental forming process wasnot found. Therefore, the theory research work in ISF is yet to be developed.In this paper, firstly the ISF forming technology and the relative basic forming theorywere introduced. The FEM was used to simulate the incremental forming process andconventional stamping forming by die separately for the same rectangle tapered cup. And thenumerical results of the local plastic strain, the sheet metal thickness change, the finalspringback etc. were studied and discussedThen, two methods were used to consider the initial sheet defect in numerical analysis. Inthe first method, the BAMMAN_DAMAGE materials constitutive model was used, in whichthe initial defects were introduced by the parameter of void rate. In order to consider theinfluence of tool on necking limit, the lateral tool was introduced in the FE model and itsaction was considered through contact and friction. The numerical results showed that theBAMMAN_DAMAGE materials model was not sensitive to the multidirectional loadscondition. In the second method, the initial defect was simply modeled by geometric shape tostudy the effect of lateral tool action on the sheet necking limit. The numerical analysis resultsshow that the reason of higher forming limit in the incremental sheet forming can beexplained reasonably. And further in this paper, the influence of friction coefficient betweenthe tool and sheet metal on the sheet forming limit was studied.