Simulation And Optimization Of Process Parameters In Gas Assisted Injection Molding For Flat-pannel With Ribs

Gas-Assisted Injection Molding technology (shortened as GAIM) was a process developed for the purpose of conquering the localizations of conventional injection molding and blow molding. The GAIM technology was an innovation and a new molding method of plastics products in plastic producing. The technique is still at the quick growing stage.GAIM comprises a partial injection of polymer melt into the mold cavity, followed by an injection of compressed gas (usually nitrogen gas) into the polymer melt. The compressed gas will drive the melt filling the mold cavity, then make a hollow bore in the part section, and accomplish post-filling with pneumatic pressure. This method has been used widely with many good points such as improving surface quality of products, increasing intensity, reducing shrinkage and warpage, less material consumption, and increasing productivity. At the same time, plastics melt flow becomes more complexly than traditional injection molding with gas injection. In GAIM, gas still brings some new limitations, which will have important influence to the quality and performance of the plastic products.On the research of gas-assisted injection molding process, the key technologies of injection molding were discussed and the general principles of designs of the gas-assisted injection part and mold were analyzed and summarized in this thesis. A more systematic guide lines were set including the reference of wall thickness, structure, layout and the size of gas runner, mold and the process, etc.. Take a salver of electric apparatus as an example; the original process was modified to improve the gas penetration. Orthogonal experiments were applied on the study of law about process parameter on gas penetration affected by mold and melt temperature, gas delay time, gas injection pressure and gas injection time. Finally, the optimized process parameters, melt temperature 270℃, gas delay time 0.8s, gas injection pressure 4MPa and gas injection time 6s were found out.Furthermore, established on common model, the orthogonal test was applied in searching the impact of process parameters to the quality of GAIM part, which were: gas delay time > gas injection time > gas injection pressure > diameter of gas runner > melt pre-injection volume >melt temperature. the effect of processing parameters on gas penetration were studied. And the optimum technological combination of larger penetration was found: diameter of gas runner 7mm, melt temperature260℃, melt pre-injection volume 94%, gas delay time1s, gas injection pressure12MPa, and gas injection time8s.Finally, response surface method was successfully applied in searching the law about process parameters on gas penetration with two main impact factors, delay time and gas injection time, to guide for the GIAM.