The effect of inner assisted gas length on the gas-assisted extrusion forming of plastic micro-tube

The effect of inner assisted gas length on the gas-assisted extrusion forming of plastic micro-tube was numerically studied in this paper. The 2D geometric models with different lengths of inner assisted gas were established. Under the same boundary conditions and material parameters, the profile changes of extruded plastic micro-tubes were obtained. To ascertain the reasons of profile changes induced by different lengths of inner assisted gas, the radial and axial flow velocities, shear stress and the first normal stress differences of melt were all obtained. Numerical results show that the diameter swell or shrinkage phenomenon occurs when the inner assisted gas length mismatches the outer assisted gas length. The deformations are generated by the unbalance axial flow velocity of melt induced by the mismatch of two assisted gases lengths, especially at the outlet of assisted gases. At the same time, the shear stress focus and first normal stress difference focus of melt are also existed at the outlet of assisted gases. In practice, the lengths of two assisted gases should be equal in the gas-assisted extrusion of plastic micro-tube.