Study on the relativity of the variable blank holder force control and the formability of rectangular box drawing

In the paper,at first,the series of the simulation tests were used to find the forming critical conditions of rectangular box drawing during the rectangular box drawing processing when applying constant blank holder forces. According the test results,the reasonable alteration scope of initiative variable blank holder forces (VBHF) was obtained as 1.9t～2.3t. Then,based on the studying on the test productions of blank holder force,applied twelve typical VBHF curves to having the simulation tests by DYNAFORM. The simulation test results obviously showed that VBHF had great effects to drawing formability of hot-galvanized sheet steel during the rectangular box drawing. However,the different VBHF curves were applied to control the whole drawing,it would get great different effects. According the simulation test results,the VBHF had great effects to the maximum thick thinning ratio,but had little effect to the maximum thick incrassation ratio. So,reasonably applied the VBHF would greatly decrease the fractures occurring. When the VBHF profile was as curve L would get the best effect of drawing formability,when it was as curve I would get contrary effect,when it was as the other types of curves would get effects between above two types of VBHF curves. Finally,the actual tests were applied to prove the validity of the simulation tests. The results were shown that the FEM simulation tests were good tools for predicting and optimizing of VBHF.