【正文】 and 90176。 but the application of excessive tensile stresses leads to failure by tearing. Hence, the blankholder force must lie within a narrow range, above that necessary to suppress wrinkles on the one hand, and below that which produces fracture on the other. This narrow range of blankholder force is difficult to determine. For wrinkles occurring in the central area of a stamped part with a plex shape, a workable range of blankholder force does not even exist.In order to examine the mechanics of the formation of wrinkles, Yoshida et al. [1] developed a test in which a thin plate was nonuniformly stretched along one of its also proposed an approximate theoretical model in which the onset of wrinkling is due to elastic buckling resulting from the pressive lateral stresses developed in the nonuniform stress field. Yu et al. [2,3] investigated the wrinkling problem both experimentally and analytically. They found that wrinkling could occur having two circumferential waves according to their theoretical analysis, whereas the experimental results indicated four to six wrinkles. Narayanasamy and Sowerby [4]examined the wrinkling of sheet metal when drawing it through a conical die using flatbottomed and hemisphericalended punches. They also attempted to rank the properties that appeared to suppress wrinkling.These efforts are focused on the wrinkling problems associated with the forming operations of simple shapes only, such as a circular cup. In the early 1990s, the successful application of the 3D dynamic/explicit finiteelement method to the sheetmetal forming process made it possible to analyse the wrinkling problem involved in stamping plex shapes. In the present study, the 3D finiteelement method was employed to analyse the effects of the process parameters on the metal flow causing wrinkles at the draw wall in the stamping of a tapered square cup, and of a stepped rectangular part.A tapered square cup, as shown in Fig. 1(a), has an inclined draw wall on each side of the cup, similar to that existing in a conical cup. During the stamping process, the sheet metal on the draw wall is relatively unsupported, and is therefore prone to wrinkling. In the present study, the effect of various process parameters on the wrinkling was investigated. In the case of a stepped rectangular part, as shown in Fig. 1(b),another type of wrinkling is observed. In order to estimate the effectiveness of the analysis, an actual production part with stepped geometry was examined in the present study. The cause of the wrinkling was determined using finiteelement analysis, and an optimum die design was proposed to eliminate the wrinkles. The die design obtained from finiteelement analysis was validated by observations on an actual production part.Sketches of (a) a tapered square cup. Sketches of(b) a stepped rectangular cup.Fig. 1.2. FiniteElement ModelThe tooling geometry, including the punch, die and blankholder,were designed using the CAD program PRO/ENGINEER. Both the 3node and 4node shell elements were adopted to generate the mesh systems for the above tooling using the same CAD program. For the finiteelement simulation,the tooling is considered to be rigid, and the corresponding meshes are used only to define the tooling geometry and are not for stress analysis. The same CAD program using 4node shell elements was employed to construct the mesh system for the sheet blank. Figure 2 shows the mesh system for the plete set of tooling and the sheetblank used in the stamping of a tapered square cup. Owing to the symmetric conditions, only a quarter of the square cup is analysed. In the simulation, the sheet blank is put on the blankholder and the die is moved down to clamp the sheet blank against the blankholder. The punch is then moved up to draw the sheet metal into the die cavity.In order to perform an accurate finiteelement analysis, the actual stress–strain relationship of the sheet metal is required as part of the input the present study, sheet metal with deepdrawing quality is used in the tensile test has been conducted for the specimens cut along planes coinciding with the rolling direction (0176。 Stepped rectangular cup。機(jī)械行業(yè)電子類文獻(xiàn)原文作者：日期：Int J Adv Manuf Technol (2002) 19:253–259? 2002 SpringerVerlag London LimitedAn Analysis of DrawWall Wrinkling in a Stamping Die Design. Chen and . LiaoDepartment of Mechanical Engineering, National Taiwan University, Taipei, TaiwanWrinkling that occurs in the s