Study On Gas Penetration Behavior Based On Numerical Simulation And Foam On Gas Channel Wall In Gas-assisted Injection Molding

In this paper, based on numerical simulation technology, Influencing factors of gas penetration behavior for Gas-assisted injection molding have been investigated. Taguchi and BP Artificial Neural Network are applied for the optimization of gas-assisted injection molding process parameters in sense of gas penetration behavior. The effects of the gas penetration behavior in the gas-assisted injection molding on the gas fingering defect of the part were investigated. The different geometric dimension of products on the relationship between gas penetration behavior and the equilibrium flow of molten mass in the both sides base plate of gas passage was researched. Finally, an experiment was carried out to study the effects of the molding conditions on foam formation in the gas-assisted injection molding using quantitative analysis method.The main results are as follows:1. The three typical polymer materials (ABS, HDPE, PP) are applied to study the relationship between the processing conditions (melt temperature, short-shot size, mold temperature, gas delay time, gas injection pressure, gas injection time) and the gas penetration behavior under the different process conditions of the gas-assisted molding. The results show "blowing out" and "short shot" occur more easily by using ABS, but " gas fingering" more seriously by using PP. The experimental results also suggest that "gas fingering" decreases with the higher short-shot size, the longer gas delay time, the shorter gas injection time, the lower pressure, the lower melt temperature and mold temperature.2. Taguchi and BP Artificial Neural Network are applied for the optimization of gas-assisted injection molding process parameters in sense of gas penetration behavior. Based on CAE technology, the best level combination of different factors can be obtained with fewer experiments by Taguchi technique. Then, the results obtained from Taguchi technique are used to train BP model. With the BP model trained, it can predict the optimal gas-assisted injection molding process parameters.3. The influence of gas channel configuration and product structure in gas channel quality were studied. Under the same short-shot size, In the case of the semicircular channel, a minimum "gas fingering" was observed when the gas channels equivalent radius is largest, but "blowing out" and "short shot " occur more easily. Under the same process conditions, the greater shape factor, the maximum "gas fingering". The study showed that the modification of the flat plate dimensions can affect the equilibrium flow of molten mass in the both sides base plate of gas channel. The greater difference of flat plate wall thickness and width in the both sides base plate of gas channel, the greater difference of melt pressure gradient and "gas fingering"4. The relationship between the processing conditions and foam on the gas channel wall was studied in order to find the origin of the foam formation on gas channel wall. The high pressure gas such as N2 comes to a supercritical state, diffusing into the polymer melt and solution. After holding the pressure and cooling, the N2 in the polymer melt reaches a super saturation state. The N2 close to the internal remains in the polymer melt to form the cellular bubble blemish gradually. As the melt temperature, the gas injection pressure, the holding pressure and the holding time increase, the number of foam in unit area on the gas channel wall increase.