The Numerical Simulation And Experimental Study Of Gas-assisted Co-injection Molding

Gas-assisted co-injection molding (shortened as GACIM) is an advanced polymer molding technique. This technique has the advantages of both co-injection molding technique and gas-assisted injection molding technique, and it is the environmental friendly molding technique by which high performance, low cost goods are produced. So the technique is regarded as one of the most advanced polymer molding techniques by which the future important problems of engineering material will be resolved. Up to the present, few of researches on GACIM technique have been reported at home and abroad. Based on the inconsistency between the advance and research shortage of GACIM, the numerical and experimental researches on GACIM are implemented in this paper, which yield the following main achievements:To the flowing characteristics of GACIM and on the basis of polymer rheology and fluid dynamics, reasonable assumptions were put forward, and 3D unsteady isothermal viscoelastic theoretical model is established to describe the GACIM polymer melt filling process.Based on the of the mixed finite element stable discrete techniques of Mini-Element method, penalty function method, Galerkin method and DEVSS/SU method etc., stable finite element numerical models is established for 3D GACIM viscoelastic polymer melt filling process. And By means of time dependent moving Lagrange interface technique, the tracing, regenerating and update of gas moving front interface were implemented successfully. Based on the numerical simulation code of the research, the numerical simulations of gas penetration during viscoelastic polymer melt were implemented. the distributed rules of variable fields for velocity, pressure and stress of gas penetration during viscoelastic polymer were given.By means of 3D numerical simulations of gas penetration during viscoelastic polymer melt, the influencing rules of relaxation time and polymer melt viscosity on coating layer thickness of the polymer left on the wall were studied. The fractional coverage was found to be strong dependent of shear rate and polymer melt viscosity. At low shear rate region, relaxation time increased, the fractional coverage increased. But at high shear rate, increasing of relaxation time resulted in a reverse trend of fractional coverage. It was in accordance with Yijie Wang's work in which experiments on gas penetration during non-Newtonian fluids was conducted. Moreover, polymer melt viscosity increased, fractional coverage increased.By means of experiments of GACIM, the influencing rules of process parameters such as polymer melt temperature, gas pressure, gas filling volume and delay time etc. on GACIM were studied. The influencing mechanisms were disclosured by theoretical analysis.