Factors and relation of skin melt formation under isothermal condition have been analyzed during gas-assisted injection molding in a tube.This research shows that thickness ratio of skin melt is about0.3 which is close to the experimental values 0.34~0.37

and that the ratio value (<0.3) of non-Newtonian fluid is less than the value0.38of gas-assisted injection molding.The difference factors are analyzed under nonisothermal condition

which shows that shear stress at the gas/melt interface and the pressure gradients existing at the gas and melt fronts are two very important contributing factors forming skin melt thickness in addition to melt temperature

mold temperature and gas delay time

which were recognized as the important influence parameters on the skin melt formation.