The Influences Of Die Clearance And Cooling System On Hot Stamping Deformation And Microstructure Transformation

Nowadays, as the global ecological crisis explodes and the serious energy crisis increases, it is imperative to lightweight vehicles. Hot stamping parts application in vehicle body manufacture is believed to be an effective way to achieve it, the problems such as high deformation resistance and serious springback in cold stamping process are well solved, the mechanical properties steels are improved as well. While still, new problems were found such as large temperature difference during cooling.Based on the B brace, taking high strength 22MnB5 steel stamping into U shape part as the research object, the study on high-strength steel hot stamping process is developed by the methods of theoretical analysis、numerical simulation and experimental tests.Firstly, the hot stamping finite element model of U-shape part is established and simulated in DEFORM V11.0, The rationality of finite element model is confirmed in analyzing the deformation process, temperature field, stress & strain fields, phase transformation and thinning ratio of blank during hot stamping process.Secondly, With the method of numerical simulation, the contact between the workpiece and the dies% the thickness of the workpiece、the temperature field and the phase transformation impacts from die clearance were analyzed. The results indicate that the thinning radio of the workpiece is 10% below as the die clearance is in the range of 0.95t to 1.00t, the contact condition is rather good, each part of the workpiece cools more uniform, the transformation ratio of martensite is rather high. In this paper, the mechanism and low of the temperature impact of the hot stamping workpiece from cooling system are analyzed; a new method for decreasing the maximal surface temperature difference of the workpiece by local water flow speed control is proposed. The results indicate that the cooling system increases the temperature gradient inside the dies, the thermal flow speed up, the temperature of the work surface of the dies decreases, the temperature of the workpiece changes. Proper speeding up the water flow can promote the workpiece cooling; proper speeding up local water flow decreases the maximal temperature gap of the workpiece.Finally, the hot stamping experimental test were taken. The temperature、the microstructure and the mechanical properties of the workpiece were measured and analyzed. The results indicate that, the data form simulation and experimental test are well agreed, the microstructure of the workpiece is mainly martensite, the tensile strength of the steel improved into 1400-1600MPa. The veracity and the reliability of the simulation are verified. The simulation results will provide important guiding significance for hot stamping production. This paper will provide guiding significance for hot stamping production.