Differential flow velocities control method for push-bending of the thin-walled tube with a 0.9D bending radius by differential lubrication

Abstract

The smaller the relative bending radius of the bent tube, the more difficult the tube blank is to be bent. In this paper, the push-bending process for the aluminum tube with a relative bending radius of 0.9D was analyzed through simulation. There was tangential tensile stress concentration occurring at the front endpoint of tube intrados, which increased the risk of cracking. That is because the bending tube's extrados moves less angular distance than its intrados by the uniform lubrication method, causing excessive deformation of the cross-section. Therefore, a differential lubrication method using the lubricant with a larger friction coefficient at intrados and the lubricant with a smaller friction coefficient at extrados was proposed to increase the angular velocity of the tube's extrados. It was found that the differential lubrication method helped avoid excessive thinning at the front endpoint of tube intrados through simulations. Furthermore, push-bending experiments of 5A02 aluminum alloy with a relative bending radius of 0.9D were carried out to investigate this effect. The experimental results showed that the differential lubrication method effectively avoided cracking, which agreed with the simulation results.

Inhibiting thinning in tube bending by a superposition effect under a boosting movement

“…This further suggests that, besides weakening the deformation by reducing the stress, the boosting effect can compensate by pushing part of the material directly from the feed section to the reduced outer wall thinning in the bend section. To continue to explore the mechanism of improving the quality of the outer wall of the tube under the condition of pushing the die, finite element simulation was used to regulate the parameters affecting the effect of the pressure-assisting die, such as the pressure-assisting velocity v, the friction coefficient μ between the pressure-assisting die and the tube and the relative bending radius R/d [31],…”