Study On Mechanical Properties And Influencing Factors Of Drawbead In The Sheet Forming Of Automobile

As an important method used for metal deformation, stamping has been widely used ineach industrial field. In the drawing process of some large sized workpiece such as thecovering parts of automobile body, the flow velocities of the metal in different zone of theblank are often different from each other because of the geometry asymmetry of theworkpiece, which causes the defects such as necking or cracking due to local severe reductionin some zones of the workpiece after the drawing deformation as well as the defects such aswrinkling and rippling due to over less constrain in some zones of workpiece. A certain shapeof drawbeads is often set in some zones of the moulds to control the metal flow in order toprovent the above defects. Because the shape and size influence directly on the beading forceand drawing pressure, they have very important effects on the deformation quality of thedrawn parts. In the recent decades, many scholars have been researched in relevant aspects ofdrawbead widely and have made great progress, but there are also many problems in theaspect of parameter determination.Most of the covering parts of automobile body are made from drawing, and theresistance force is usually adjusted by the drawbead in the drawing process. Drawing fail maybe caused to when a little improper happens in the process of drawbead design, which finallycause the mould to be heavily prepaired or discarded as useless as well as the waste of labourpower and financial resources. Therefore, finite element method combining experiment isadopted to analyze the mechanical properties and influencing factors of the drawbead in thedrawing process of covering parts of automobile body, which can supply necessary theoreticalbasis for the design of moulds and forming process of the covering parts of automobile body.The research contens are as follows:(1) Finit element model of the blank passing through the drawbead was established basedon the elastic-plastic finite element simulation theory. The finite element simulation theorywas used in the process of blank drawing, and successful analysis of blank passing throughthe drawbead was performed by setting suitable contact condition, fiction condition andestablishing reasonable finite element model of drawbead.(2) The stress and strain distribution laws of blank passing through drawbead wereanalized by finite element simulation of blank passing through drawbeads with different cross sections. The analysis results show that the stress and strain distribution laws of blank passingthrough two drawbeads with different shapes is similar. They all distribute symmetricallyalong the middle line of the drawbead at the initial stage of the deformation and the final stageof the drawbead forming. While at other stages, the maximum of the stress and the straindeviates towards to the front end i.e. the direction of drawing deformation. Finally, effectivemeasures controlling the drawig process are put forward based on the analysis results.(3) The influences of structure parameters of drawbead on the mechanical propertieswere analyzed by finite element simulation. The results show that the beading force, thetensile stress in the front end of the blank and the thickness reduction rate of the bland allincrease with the increase of the corner radius of the drawbead groove. The influence laws ofcorner radius on the beading force, the tensile stress in the front end of the blank and thethickness reduction rate of the blank are consistent, but the change is not monotonic increaseor monotonic decrease because there is a infletion point in the curve. The influence of thedrawbead height on the beading force is not heavy, but the influences on the tensile stress inthe front end of the blank and the thickness reduction rate of the blank are evidently. But theinfluencing trends of them are consistent, i. e. they all increase with the increase of thedrawbead height. The influencing law of friction factor is similar to that of the drawbeadheight.(4) The finite element method was used in the process of drawing the head cover ofzhongyi car. The influences laws of shape and size of drawbead on the formability and straindistribution of the head cover were analyzed comparatively by the simulation in formability,strain distribution and forming limit.(5) The optimized forming project of head cover of Zhongyi car was obtained bycombining finite element simulation to experiment, and the head covers with perfect qualitywere formed ultimately.