| In recent years,thin-wall injection molding technology has received more and more attention and research in order to meet users’ demands for light,thin,short and small plastic products.thin-walled products can reduce the size,reduce weight,save materials,compression costs.But the thin-walled plastic products also make it extremely difficult to form,often short-shot,residual stress is too large and too much distortion and other defects,the quality is difficult to guarantee.In this paper,Moldflow software is used to study forming characteristics of the super-thin lunch box cover on the injection molding,through various means to solve short and weld marks defects,optimize the amount of warpage,to ensure that the super-thin lunch box cover molding quality.The main contributions are as follows:1)Filling simulations were carried out in three thicknesses(0.5mm,0.3mm,0.2mm)using four different materials(PP,PP+PE,PS,HIPS)with Moldflow software.With the change of different materials cover thickness,the influence of four process parameters(injection temperature,injection temperature,melt temperature and injection pressure)on the filling rate was analyzed by single factor method,and the conclusion was drawn.And the relative optimum material of forming 0.2mm thick cover is PP.2)The injection molding of 0.2mm thick lunch box cover with PP material was optimized to solve the molding defects.The feasibility of 0.2mm thick lunch box cover injection molding was verified.By increasing the injection rate,mold temperature and melt temperature,adjusting the number and location of the gate method,as far as possible to reduce the maximum injection pressure circumstances,short shot of the 0.2mm thick cover of the lunch box in injection molding is solved.Hot runner valve gate sequence control method is used to eliminate the weld line.The amount of warpage decreased from 11.19 mm to 1.949 mm by the use of two-stage pressure-holding mode.3)Aiming at the problem that the injection pressure and the amount of warpage are still large after the optimization of the 0.2mm thick super-thin lunch box cover inthe conventional injection molding,Rapid Heating Cycle Molding is applied to the injection molding of the super-thin lunch box cover.So that the injection pressure decreased from 195 MPa to 153 MPa,the amount of warpage decreased from1.949 mm to 0.8448 mm.4)Based on two-stage pressure-holding mode,A five-factor four-level orthogonal experiment was performed in the 0.2mm thick super-thin lunch box cover with Rapid Heating Cycle Molding.The degree of impact of process parameters on the warpage is: mold temperature> holding time 1> melt temperature> holding pressure 2> holding pressure 1.And the optimum combination of process parameters is A3B2C3D2E4,the first section holding pressure 168MPa、the first section holding time 1s、the second section holding pressure 92MPa、the mold temperature 140 ℃、the melt temperature 280 ℃.Using this optimum combination,the warpage analysis was conducted again,with a result of 0.6345 mm,which was smaller than the minimum warp amount of 0.8448 mm before the orthogonal experiment,the amount of warpage decreased by 0.2103 mm. |
