Research On Wall Thinning Of Lattice Shell Based On Modal Flow Analysis

As people pay more attention to air quality and health,the demand for air purifiers is increasing,leading to increasingly fierce market competition.Major manufacturers are committed to the development and production of cost-effective products.For air purifier products,reducing the wall thickness of the raster shell can not only directly reduce the consumption of raw materials,but also improve the processing efficiency of injection molding,which is one of the effective ways to reduce the product cost.The quality of injection molding and the structural strength of finished raster shell must be studied in the thinning of raster shell wall.To this end,this paper adopts Moldflow and Ansys software,through the mold flow analysis and structural stress calculation of the grid shell with different wall thickness,to evaluate the molding quality of the injection molding products and the structural strength and stiffness,to provide a theoretical basis for the air purifier grid shell wall thickness thinning.According to the performance and application requirements of the air purifier,the structure of the grid shell of the air purifier is designed,and the materials used in the injection molding of the grid shell are determined.According to the structure of grid shell,according to the principle of mold design,the forming structure,pouring system,cooling system and ejection system of grid shell mold were established,and the general assembly drawing of the mold was designed.Based on the mold structure and injection process flow,the process parameters of injection molding were determined.Using Moldflow software,a three-dimensional discrete numerical model was established to simulate the injection molding of the lattice shell.Because of the large number of holes distributed in the lattice shell,the size of the global grid side length will directly affect the accuracy and calculation time of the mold flow analysis.In order to balance the contradiction between solving accuracy and computing efficiency,a numerical model of global mesh side lengths with wall thickness of 1.5,1.75 and 2 times was established.By comparing the simulation results of filling time,pressure and temperature fields,it was shown that the main calculation results of the three models with global mesh side lengths were not very different.The maximum filling time and pressure errors are 9.85% and 4.29%,respectively,which meet the requirements of calculation accuracy.Moreover,2 times wall thickness has the advantages of fewer elements and high computational efficiency,so it is determined to be the preferred global grid side length for this model of lattice shell mold flow analysis.Based on the numerical model of global mesh side length with double wall thickness,the numerical model of raster shell with wall thickness of 2.7mm,2.4mm and 2.1mm was established by reducing the wall thickness by 10%,20% and 30%,respectively,and the modal flow analysis was carried out.The simulation results show that the pressure holding pressure of 2.1mm wall thickness reaches 138.5MPa,which exceeds the 130 MPa allowed by the process,and the thinning cannot be realized.The maximum warpage and shrinkage of the raster shell with wall thickness of 2.7mm and 2.4mm are 1.133 mm and 1.214 mm,respectively,and 0.0154 mm and 0.007 mm,respectively.Compared with the original wall thickness of3 mm and 1.080 mm,the maximum warpage and shrinkage of 0.0218 mm are increased and reduced.The number of weld mark butt angles below 75° is basically the same,and the number of air pockets is small and evenly distributed.These factors will not affect the molding quality of the product.The shell with 20% less wall thickness can meet the requirements of injection molding process and product quality.According to the upwind resistance and Darcy formula,the wind loads borne by three kinds of grid surfaces with wall thickness of 3mm,2.7mm and 2.4mm are calculated for the working state of the grid shell under the maximum power of the air purifier.The three-dimensional numerical model of lattice shell structure stress analysis is established by Ansys software,and the numerical simulation of lattice shell structure stress under three kinds of wall thickness is completed.The results show that: The maximum equivalent stresses of the three kinds of shell with wall thickness are 0.36 MPa,0.44 MPa and 0.53 MPa,the maximum tensile stresses are 0.37 MPa,0.43 MPa and 0.52 MPa,and the maximum strains are 0.018%,0.022% and 0.026%,respectively.The maximum deformation values in the thickness direction are 0.23 mm,0.29 mm and 0.37 mm,respectively.Compared with the original wall thickness,the stress safety factor of the lattice shell reduced by 20% and the maximum deformation increased by 37.84%.However,the maximum value is far less than the allowable value,which conforms to the strength and stiffness conditions.The product’s raster shell can reduce wall thickness by up to 20%.