Numerical Simulation and Experimental Research on Rubber Flexible-Die Forming Limitation with New Position-Limited Back Pressure Mechanism

The forming limitation and the wall thickness distributions are the two main parameters for estimating the forming quality of T-shaped tubes. In this paper, the effects of three key factors on the forming limitation and the wall thickness distributions are investigated, which are punch front distance l1, reverse height h1, and the matching relationship between rubber hardness and axial feed Δl. A new position-limited backpressure mechanism is proposed, which is made up of the rigid position-limited lever, the flexible backpressure medium, and the rigid spacer. The simulations and experiments are carried out. Both results show that the thinning rate of the wall thickness decreases first and then increases, and the thickening rate decreases gradually with the increase of l1. The branch reaches the highest with the l1 of 5mm under the requirements of thinning rate and thickening rate. With the rise of reverse height h1, the bigger h1 is beneficial to the wall thickness thinning suppress at the top of the branch, and the branch reached the highest when h1 is 7mm. When Δl is fixed, the rubber hardness has a significant influence on the forming defects. The exorbitant rubber hardness causes the branch to rupture, and the excessive axial feed causes the wall to wrinkle. When rubber hardness is fixed, the thickening rate decreases with the increase of Δl. The best forming limitation and thickness distribution are achieved with the punch front distance l1 of 5mm, the reverse height h1 of 7mm, the rubber hardness of 75HA, and the axial feed Δl of 24mm.