Deformation Characteristics Of Solidified Layer In External Gas-assisted Injection Molding

External gas-assisted injection molding(EGAIM)introduces gas with pressure between the mold and the polymer during the packing and cooling.The gas pressure pushes the solidified layer and compensate polymer shrinkage,thereby reducing warpage and sink marks.Some researchers have studied the EGAIM process and optimized process parameters.The results have also been extended application insome specific products.However,the aforementioned work has not involved the core problem of how the gas pressure pushed the solidification layer and compensate shrinkage,which is very important for the promotion and application of EGAIM.To solve the problem,this study dicussed the deformation characteristics of the solidified layer in EGAIM,which provides a basis for analyzing the motion deformation of the solidified layer under the action of gas and is of great significance for the promotion and application of EGAIM.The deformation characteristics of the solidified layer wer studied by theory,experiment and simulation method based on the definition of solidification layer and the mechanical properties of polymer materials.The main research results of this paper were shown as following:(1)Analysis of stress-strain behavior of different solidified layers.The solidification layer is defined by analyzing the mechanical properties of the polymer material on the basis of experimental tests,combining the dynamic mechanical properties of the material and the simulation of the molding process.The analytical model of the deformation characteristics of the solidified layer was constructed by the mechanical analysis method of multi-layer composites.The stress-strain curves of the solidified layer at different times were further studied by numerical simulation.(2)Establish temperature-dependent polymer material stress-strain constitutive equation based on experimental and theoretical analysis.Firstly,the tensile experiments at different temperatures were carried out.Based on the analysis of the stress-strain curves at different drawing temperatures,the constitutive models of the materials in the glass state and the high elastic state were constructed.Then,a temperature-dependent stress-strain constitutive equation is established by introducing a temperature factor into the constitutive model.(3)The stress calculation model of the solidified layer in different deformation stages is established and the deformation characteristics of the solidified layer are analyzed.By calculating the stress-strain curve of the solidified layer at different times,it is found that the part of the solidified layer in the process of high elastic state contributes less to the deformation of the whole solidified layer,and the part in the glass state dominates.Finally,the tensile test was carried out using a tensile sample with a temperature gradient,and the tensile test curve was compared with the stress-strain curve calculated by the analytical model.It is found that the characteristics of the two are in good agreement,thus verifying the reliability of the analysis model of the deformation characteristics of the solidified layer.In summary,this paper studies and analyzes the deformation characteristics of the solidified layer,and provides a basis for analyzing the motion deformation of the solidified layer under the action of gas,which is beneficial to the promotion and application of EGAIM.