Research On The Distribution Of Bubble Structure And Warpage In The Process Of Microcellular Foaming And In-Mold Decoration Combined Injection Molding

Warpage is an important factor that affects the dimensional accuracy of plastic injection molded products.Compared with traditional injection molding,microcellular foam injection molding has a large number of microporous structures inside the molded products,which can suppress and improve the occurrence of warpage and deformation to a certain extent.Microcellular foam in-mold decorative molding（MIM/IMD）is a new process for molding high apparent quality,lightweight plastic products,but the decorative film creates an unbalanced temperature field in the mold cavity and changes the structure and distribution of the bubble pores,which aggravates the warpage and deformation of the products.Therefore,this paper investigates the effect of bubble structure and distribution on warpage and deformation under this new process.A mathematical model of vesicle growth under asymmetric temperature field is developed.Based on the assumptions of the cell model,the growth process of vesicles in the flowing melt is analyzed based on the continuity equation,the equation of motion and the energy equation,and the growth control equation is constructed by combining the polymer melt intrinsic structure,gas diffusion and heat conduction equations;the structure and distribution of vesicles in the asymmetric temperature field are analyzed by numerical simulation.To study the warpage of MIM/IMD under asymmetric temperature field.Using the tensile sample as the research object,orthogonal experimental design and flow simulation calculations are used to analyze the influencing factors of product warpage in MIM/IMD under asymmetric temperature field,and to obtain the best combination of process parameters with minimum warpage.The simulation results of warpage in X,Y and Z directions for MID/IMD,in-mold decorative injection molding（IMD）,microcellular foam injection molding（MIM）and conventional injection molding（CIM）are also compared to analyze the changes of warpage in different directions,bubble radius and density of different molding processes,and explore the influence of microcellular structure and distribution on warpage deformation.In order to eliminate the influence of asymmetric temperature field on the bubble structure and distribution of products,a new method of decorative composite molding（d-MIM/IMD）is innovatively proposed for the inner surface of double-side laminated microcellular foam molds.and d-MIM/IMD,and investigate the influence of bubble structure and distribution on warpage under d-MIM/IMD process.The results showed that the bubble radius and number density distribution in the thickness direction of dMIM/IMD process were more balanced than those of MIM/IMD,and the maximum warpage deformation was 0.970 mm.In order to further suppress the occurrence of warpage and reduce the amount of warpage,the fiber-reinforced phase（GF）was introduced into the base material,and the changes of bubble radius and number density and distribution of fiber-reinforced thermoplastic composites under the conditions of MIM/IMD and d-MIM/IMD processes were analyzed at 0 %,20 % and 40 % of fiber content,respectively,to study the mechanism of their changes on warpage,and the mechanical properties of the molded samples with different processes and fiber contents were analyzed.The mechanical properties of the molded strips with different processes and fiber contents were analyzed.The results showed that when the fiber content is 20 %,the d-MIM/IMD process is beneficial to the generation and growth of bubble holes,and the increase of bubble number density and delayed growth reduces the warpage to 0.338 mm,and the mechanical properties improve significantly with the increase of fiber content.