The use of gas-assisted technology is very popular in injection molding for its significant effect of improving mechanical properties and quality of products.Accordingly

the demand of gas-assisted CAE technology is also in the rising.In current CAE technology the compressibility of gas is neglected and gas or air pressure is usually imagined as a constant

such as a given value of the pressure at the inlet.But in fact

gas is strongly compressible and its pressure changes from a low value of zero to a high one before it is stabilized.It leaves unknown if these facts have any influence on the quality or mechanical properties of products.The objective of this paper is to study the complex behavior of compressible gas flow in the gas-assisted injection molding process.For simplification the real 3D flow was reduced to a 2D one based on certain assumption.A numerical simulation model of 2D transient compressible gas flow based on the characteristic-based-split method (CBS) was presented and a corresponding software with VC++ was established.Using this software a real simulation work was done.Its results could be taken as base data in further filling simulation.In addition

a pressure testing experiment was also done

and the comparison between simulation and experiment showed that the model presented in this paper was feasible.