Assembly Of Flat Elements Research Articles

Simulation Strategy of the Final Dimension in the Glass Pressing Process

The simulation of the final dimension in the glass pressing process is presented in this paper, in which the part contraction and mold deformation are considered as important factors. A thermorheologically simple thermoviscoelastic material model is used to calculate the residual stress. The model for the analysis of contraction is proposed based on the theory of shells, as an assembly of flat elements. The numerical model for the mold deformation is based on a three‐dimensional thermoelastic boundary element formulation. Finally, an application example of the picture tube panel is used to verify the presented models and simulation methods.

Dimensional precision simulation of the formed picture tube panel

In the forming process of picture tube panel, the accumulated residual stresses cause the formed part to shrink, and the thermal and mechanical loads cause the mold blocks to deform. These two factors result in large deviations on the dimensions of the formed panel, which are both modeled and simulated in this paper. For residual stresses analysis, a thermo-rheologically simple viscoelastic material model is introduced to consider the stresses relaxation effect and to describe the mechanical behavior according to the temperature change. The shrinkage of formed parts induced by the residual stresses is calculated based on the theory of shells, represented as an assembly of flat elements formed by combining the constant strain and the discrete Kirchhoff triangular elements. A thermoelastic model is presented to predict the deformation of the mold blocks during pressing, which is based on the steady mold temperature field and thermoelastic boundary element method. The integrated simulation results suggest the amounts that the mold cavity should be machined by, and have been verified by comparing the dimensional precision of the panels produced by the mold considering a uniform part shrinkage and mold expansion or the mold considering the predicted ununiform part shrinkage and mold deformation.

Modeling and Simulation of Shrinkage During the Picture Tube Panel Forming Process

The accurate prediction of residual stresses and shrinkage of the formed picture tube panel is important to achieve high quality and precision of the final product. In this paper, the numerical simulation of shrinkage of molded panels was carried out in consideration of the residual stresses accumulated during both the packing and free-to-contract stages. For residual stress analysis, a thermorheologically simple viscoelastic material model was introduced to consider the stresses relaxation effect and to describe the mechanical behavior according to the temperature change. The deformation of molded parts induced by the residual stresses was calculated based on the theory of shells, represented as an assembly of flat elements formed by combining the constant strain and the discrete Kirchhoff triangular elements. The simulation results of the developed program were side verified by comparing the dimensional accuracy of the panels produced by the molds, which compensated for a uniform part shrinkage or the predicted ununiform part shrinkage.

Numerical prediction of process-induced residual stresses in glass bulb panel

A numerical simulation model for predicting residual stresses which arise during the solidification process of pressed glass bulb panel was developed. The solidification of a molten layer of glass between cooled parallel plates was used to model the mechanics of the buildup of residual stresses in the forming process. A thermorheologically simple thermoviscoelastic model was assumed for the material. The finite element method employed was based on the theory of shells as an assembly of flat elements. This approach calculates residual stresses layer by layer like a truly three-dimensional calculation, which is well suited for thin pressed products of complex shape. An experimental comparison was employed to verify the proposed models and methods.

Residual Thermal Stresses Simulation of Television Panel in the Forming Process. Part 1: Modelling

Internal residual stresses in glass-pressed components such as television panel are mainly frozen in thermal stresses because of inhomogeneous cooling when surface layers stiffen sooner than the core region as in free quenching. Additional factors in pressing are the effects of melt pressure history and mechanical restraints of the mould. The solidification of a molten layer of glass between cooled parallel plates is used to model the mechanics of the buildup of residual stresses in the pressing process. Flow effects are neglected, and a thermorheologically simple thermoviscoelastic material model is assumed. The equilibrium thermomechanical properties of the material and the shift function can be temperature- and pressure-dependent. The finite-element method employed in the numerical simulation is based on the theory of shells, as an assembly of flat elements. The approach allows the prediction of residual deformations and residual stresses layer by layer like a truly three-dimensional calculation while reducing the computational cost significantly.

Numerical Simulation and Experimental Study of Warpage of Injection-Molded Parts

: The accurate prediction of warpage of injection-molded parts is important to achieve successful mold design and processing parameters settings with high precision. A numerical simulation model for predicting residual stress and warpage that arise during the injection molding of thermoplastic polymers in the packing and cooling stages has been developed. A thermorheologically simple viscoelastic model was used for the calculation of residual stress. The finite element method for warpage simulation was based on the theory of shells as an assembly of flat elements that are formed by combining the constant strain and the discrete Kirchhoff triangular element. This theory is well suited for thin injection-molded products of complex shape. Experiments on a flat plate were also carried out to study the effect of processing parameters on warpage. The simulation results were also compared with the experimental data for verification of the developed program. It was found that the predictions were in agreement with experimental data, especially in qualitative analysis.

Residual stresses, shrinkage, and warpage of complex injection molded products: Numerical simulation and experimental validation

AbstractA numerical simulation model for predicting residual stresses and residual deformations which arise during the injection molding of thermoplastic polymers in the post‐packing stage has been developed. A thermoviscoelastic model with volume relaxation is used for the calculation of residual stresses. The finite element method employed is based on the theory of shells as an assembly of flat elements. This theory is well suited for thin injection molded products of complex shape. The approach allows the prediction of residual deformations and residual stresses layer by layer like a truly three‐dimensional calculation, while reducing the computational cost significantly. The hole drilling technique is used to measure the residual stresses across the thickness of the product. A three‐dimensional laser digitizing system, an image processing technique and a dual displacement transducer system are used to measure the warpage. Experiments are carried out on polycarbonate and high density polyethylene parts. Numerical results are in qualitative agreement with experimental observations, i.e., the skin of the box is surrounded by a compressive region while the core region is in traction. The trend of both the experimental and the predicted residual stress profiles is close. Different examples are presented to illustrate the influence of the geometrical complexity of the shape on the final deformations and residual stresses. The influence of the mold temperature on residual stresses and warpage is also analyzed.