Research On Mechanism Of The Solidification Of Material At Packing And Cooling Stage Of External Gas-Assisted Injection Molding

As a new injection molding technology, the external gas-assisted injection molding (EGAIM) has many technical advantages which the conventional injection molding(CIM) doesn’t have. The product’s surface sink marks and warpage can be reduced by this technology. Because the formation mechanism of EGAIM is very complex, now studies on EGAIM mainly stay in the impact of process parameters on the product quality, while research on the relevant aspects of the mechanism of EGAIM is little, so the industrial application of EGAIM is inadequate extensive at present.The quality of products is closely related to the solidification of material in the process of EGAIM, and the difference between EGAIM and CIM is the packing cooling stage, so the research on mechanism and models of the solidification of material at the packing and cooling stage of EGAIM is necessary. The main work and results are as follows:(1) The research on mechanism and model of the solidification of material at the packing and cooling stage of EGAIM. According to the characteristic of packing and cooling stage of EGAIM, the packing and cooling stage is divided into three parts:the impact of gas on the solidified layer, the movement of melt and the phase change of material. The mechanism of these three parts is described respectively, and the corresponding mathematical model is set up. The mechanism of evolution of internal stress is described and the model is set up. Based on the mechanism of the solidification of material and evolution of internal stress at packing and cooling stage of EGAIM, the mechanism of the generation of sink marks and the impact of gas on the sink marks is described.(2) The simulation of the solidification of material at packing and cooling stage of EGAIM. According to the mechanism of the solidification of material at the packing and cooling stage of EGAIM, ANSYS is used to simulate the packing and cooling stage of EGAIM with ribs plate which is made by ABS, verifying the accuracy of the mechanism of the solidification of material at the packing and cooling stage of EGAIM.(3) Experimental verification of the solidification of material at packing and cooling stage of EGAIM. By comparing the sink mark depth, slab thickness, shrink of the reinforcement of the product under EGAIM and CIM, it is verified that compared with CIM, EGAIM can improve the sink marks of the product, and the mechanism and simulation of the impact of gas on the solidified layer and the movement of melt is verified. And the mechanism and simulation of morphological evolution of material at packing and cooling stage of EGAIM is verified by the observation experiment of scanning electron microscope (SEM).