| Advanced high strength steel (AHSS) has become main materials inlight weight body-in-white structures for its high specific strength, goodsafety and low cost compared to traditional steel, aluminum alloy andnew composite materials. However, In order to reduce the spring-backproblem of AHSS pressed part, a smaller corner radius and a largerblank-holder force are often used in stamping process, which leads tosevere surface damage of the pressed part and tool wear as a result ofincreased interface the contact pressure between the blank and theforming tool. The surface damage defect and the wear phenomenon resultin tool maintenance and production interruption. Therefore, it is necessaryto investigate the wear behavior on the contact interface between theblank and the die during AHSS stamping process, and to seek a suitabledie material for AHSS stamping production.In this paper, the wear performance and characteristics between heattreated die materials against advanced high strength dual-phase steels isinvestigated based on the U-shaped stretch-bending test method. Thefollowing three aspects are performed:(1)Tribo-tester prototype design based on the U-shaped test methodIn order to simulate a more real wear process during AHSS stampingin the laboratory, a semi-industrial test method-the U-shaped stretch-bending test method, was adapted. In this paper, a U-shaped stretch-bendingdie and a Tribo-tester prototype were completed. The U-shaped stretch-bending die is designed using by the structure of insert with different corner radii. Based on the U-shaped stretch-bending test method above,the Tribo-tester prototype, which can simulate not only the process of thestretch-bending but also the horizontal stretching process, wasdeveloped. In addition, the test results showed that the all tested inserts had good geometry and property quality.(2) Study of wear resistance of die material in dual-phase steel bare sheetstampingThe wear tests between heat treated die materials against the bare dual-phase steels, DP780and DP980, were conducted. The four die materials, V4E(TD, Thermal Diffusion Carbide Coating Process), XW-42(TD),DC53(TD), SKD11(TD), DC53(VT, vacuum heat treatment) is tested.The results showed that the die materials with TD coating had a goodwear resistance, while the die material with VT, namely DC53(VT), hada worse performance. The Wear region on the insert is mainly distributedalong with the corners, which was related to the interfacial contact pressure distribution in the stamping. For the DP780bare sheet stamping, thedie materials-V4E, XW-42, DC53, SKD11with TD coating are suitable,and for bare DP980stamping, the wear resistance of V4E with TDcoating was the best, XW-42and DC53with TD coating were good, andSKD11with TD coating was the worst.（3）Study of wear law in galvanized dual-phase steel stampingWear characteristics between galvanized sheet and bare sheet weredifferent, so wear test for galvanized sheet of DP980were conductedbased on U-shaped stretch-bending method above. Some pressed samplesand all inserts were analyzed using metallographic examination andsurface profiler. The results showed that: the thickness of zinc layer onthe pressed samples decreased, the surface was flattened, and zinc powderwas adhered on the die corner. Compared with bare sheet above, die wearwas less serious. V4E, XW-42and DC53with TD coating had a goodwear resistance property, while SKD11with TD coating had a poorperformance.Through the above research, the wear law of the die materialsagainst the dual-phase steels has revealed and some suitable die materialswith high wear resistance has obtained, which provides support to the selection of die materials and surface quality control in AHSS stampingproduction. |
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