The Stability Evaluation Of Continuous Stamping Of Large-sized And Deep-drawing Parts Based On Thermal-mechanical Coupling

With the development of science and technology, sheet stamping has been widelyapplied in industrial production due to high efficiency, high material utilization,excellent part quality, good process adaptability, etc. Dies are the main tool for sheetstamping, and their design and manufacturing would directly influence the formabilityof sheet stamping and the quality stability of sheet parts. Automobile body structureconsists of most of sheet metal forming parts, and the majority of the parts arefabricated through cold stamping. During cold stamping with deep drawing, thefriction work between die surface and sheet surface is transferred into an amount offrictional heat, which would be transmitted to die and lead to a small increase of thedie temperature. For continuous stamping by automation, the die temperature wouldobtain a significant raise because die increasely accumulates an enough great amountof frictional heat with the frequency of stamping increasing. The change of dietemperature results in the deviation of die face due to thermal expansion and thereduction of the die clearance, which would directly affect the quality of cold formingstamping. This issue has not been focused in by engineers and researchers yet.In this thesis, the stamping stability of typical large-sized and deep-drawing partsin continuous stamping process is investigated through firstly establishing the relevantintrinsic thermal-mechanical coupling model via abstract hypothesis and thenanalyzing the variation of die clearance via finite element simulation andmathematical analysis.Based on a large cylindrical deep-drawing model, the following processes in onestamping cycle are modeled through general finite element software ABAQUS, whichinvolve sheet forming and frictional heat generation via thermal-mechanical couplingsimulation, heat exchange between dies, sheet and surrounding air and heatconduction inside dies and temperature field of dies via thermal analysis, and diethermal deformation due to variation of temperature field via thermal deformationanalysis. Based on the analysis results for different original die temperatures, the increasing law of die temperature during continuous stamping is analyzed throughmathematical analysis, and then the variation of die clearance during continuousstamping is investigated via thermal deformation analysis. Finally, the dependences ofstamping stability during continuous stamping on process parameters are assessed byaltering the level of process parameters, which includes initial die clearance, filletradius of dies and friction coefficient between die surface and sheet surface.These results indicate during continuous stamping the heat absorbed by diemainly originates from friction heat between die surface and sheet surface, and theheat transferred from deformed sheet is negligible, where the deformation work ofsheet is converted to heat, resulting in an increase of sheet temperature. Dietemperature is raised from room temperature and die clearance is reduced withstamping frequency increasing. In initial stage of continuous stamping, dietemperature increases sharply, and then gradually becomes flat, and finally trends to astabilized magnitude and the die clearance is reduced into its minimum amount. Thereduction of die clearance suggests a degradation of stamping stability. A comparisonof the dependences of stamping stability on different process parameters indicates thefriction coefficient is the most crucial factor, the initial die clearance has relativelygreat influence, and the influence of fillet radius of dies is relatively insignificant.