The Effects of Traction Velocity on the Gas-assisted Extrusion Forming and Traditional Extrusion Forming of Plastic Microtubes

Abstract

The effects of traction velocity on gas-assisted extrusion (GAE) and traditional extrusion (TE) of plastic micro-tubes (PMTs) were numerically studied in this paper. Under same 3D geometric model, boundary conditions setting and constitutive parameters, the extrudate profile change and swell ratios of GAE and TE were all obtained. The radial and axial flow velocities, shear stress and first normal stress difference distributions of melt under different traction velocities were also gotten and compared. Results show that with the increase of traction velocity, the swell ratio increases first and then decreases. When the traction velocity is less than the axial velocity of melt, the radial velocity of melt outside of die increases, which demonstrates the generation of radial swell. When traction velocity is larger than that of the melt, the negative radial velocity of melt generates, which demonstrates the generation of shrinkage phenomenon. In addition, the changes of shear stress values and first normal stress difference values are not large, and the sudden increase of stresses always generates at the outlet die for the TE. However, the stresses of melt are well removed at the outlet of die, which demonstrates that extrudate swell and melt fracture problems are well eliminated by the GAE during the extruded PMTs dragged by traction velocity.