Development of Hydraulic Bulge Test to Study Effect of Anisotropy on Low Carbon Steel Sheet Metal for a High Effective Strain

Abstract

In sheet hydroforming process, the sheet metal is subjected to a biaxial condition, which has the elongation of more than 60%. As a result, the conventional tensile testing cannot evaluate the forming behavior of materials properly, because the strain value obtained from the tensile test is lower than 30% that is not enough for the actual forming process. A test was performed to simulate the material under biaxial conditions by applying a pressurized fluid through a semi-circular dome test. Pressurized plate will produce two-directional elongation so called the Hydraulic Bulge Test (HBT). However, the test is still under the influence of the anisotropy, resulting in higher flow stress than the actual test. Tensile test for obtaining the anisotropy is required to correct the flow stress, but the strain level is lower than required in the HBT. As a result, the results of simulation are less accurate. The purpose of this research is to develop the molds used in the Hydraulic Bulge Test to determine the influence of the rolling direction of the sheet metal. Using 3D printing technology to produce the molds to reduce costs and to guide the design of sheet hydroforming process using PLA (Polylactic Acid) material. In this test, the SPCC sheet metal was tested at 1.0 mm thickness. Elliptical hydraulic bulge testing die were printed at the aspect ratio of 2.0 with 3D print. The experiment showed that the use of PLA to create the molded metal sheet can be done by designing the appropriate parameters and shapes. When checking the shape of the 3D Print mold, it was found to be in good condition, no bending or distorsion. When examined by statistical process for testing specimens from the variants of similar specimens from metal mold. The SPCC with 1.0 mm thickness test found that, at the same dome height of 21.48 mm, the pressure at 0 degree of the rolling direction, the value was 211.76 bar and in 90 degree of the rolling direction, the value was 215.23 bar, which was different about 3.47 bar. In conclusion, the result of differences in the anisotropy of the material is clearly quite significant and can be used to determine the anisotropy in the future.