Effects Of Anisotropy On Spring-back Of Stainless Steel Cylinder Deep Drawing Parts

The phenomenon of spring-back, as one common defect in sheet metal stamping, directly affects the precision of the size of the stamping parts. Because stamping and spring-back are the cumulative effect of the whole forming history, which are related closely to the material property, sheet initial shape, process condition, loading history, die geometric shape and other factors in the forming process. The calculation of spring-back becomes particularly difficult and has low accuracy, especially in the condition that anisotropy appears after the rolling and preforming of the sheet metal. Since the study in the spring-back of sheets with anisotropy can not meet the standards for practical industrial application, spring-back has been the important study in the fields of industry and academy in recent years. This article, by finite element method and experimental method, aims to study the effect of anisotropy on the cup drawing formability, especially the resilience of the sheet metal, and with related study in the anisotropy and spring-back value of SS304 to provide evidence to companies for making related systems for reference and evaluation. The main content of this article is as follows:1)Analyze the stress state in the cup drawing formability with Hill’48, and verify the analysis with numerical simulation techniques to get the effects of the material anisotropy, especially the Lankford coefficient (r00、 r45、r90), on the thickness distribution, earing distribution and limit deep drawing height in the forming process. It is concluded that when the greater the different between r45 and r00=r90, the less thinning to the straight wall and the more benefit to the cup drawing formability, but the earing will be more apparent.2)Design an orthogonal test with interaction to explore the effect of the Lankford coefficient on the spring-back value of the cup drawing formability, and conduct the stimulation study of forming and spring-back with numerical simulation techniques. Analyze the data from the stimulation results with the method of ANOVA to get the the lankford coefficient, and the impact significance of its interaction on the spring-back value of the cup drawing formability and as well analyze the effect of the fluctuation of the lankford coefficient on the spring-back value of the sheet metal. The conclusions are as follows:The greatest influence to spring-back of bottom radius is r90, next is r45, and the minimum impact is r00. When the interaction of Lankford coefficient is taken no account, the increase of r00、r45 and r90 can cut down the spring-back value of bottom radius. And when the interaction of Lankford coefficient is taken into account, on the whole, larger r90×r45 and r45×r00 can increase the spring-back value while larger r90×r00 can reduce the spring-back value.3)Conduct the experiment of cup drawing on Sheet SS304. Then measure the coordinate dimensions of the work-pieces obtained from the experiment with coordinate measuring machine and collect all the data obtained to study the effects of the Lankford coefficient on the spring-back value of cup drawing, especially on the spring-back values of the flange, the straight wall and the bottom radius of the formed parts. And the effects of different blank holder forces and deep drawing heights on the spring-back value of the straight wall of the formed parts.The conclusions are as follows:In the the place of bottom radius, the spring-back value of r45’s location can be cut down while increasing in r45’s and r90’s location with larger r00、 r45 and r90. In the flange part, the wrap of flange is most serious where minimum Lankford coefficient(r90) is, however, the average value appears where maximum Lankford coefficient(r45) is. In the straight wall of deep drawing, material thickness is the most and the spring-back value is the smallest where maximum Lankford coefficient(r45) is. However, in the straight wall of shallow drawing, the are not significant differences in different directions.In this study, the rule of the effects of the the Lankford coefficient on the spring-back values of the flange, the straight wall and the bottom radius of the formed parts of anisotropy sheet SS304 with the methods of numerical stimulation and experiment. The result of this paper can have an important academic significance and engineering application value for further designing scientifically reasonable die and improving the accuracy of the formed parts of cup drawing of anisotropy sheet metals.