Warpage Of Injection Molded Parts Research Articles

Shrinkage and Warpage Minimization of Glass-Fiber-Reinforced Polyamide 6 Parts by Microcellular Foam Injection Molding.

Shrinkage and warpage of injection-molded parts can be minimized by applying microcellular foaming technology to the injection molding process. However, unlike the conventional injection molding process, the optimal conditions of the microcellular foam injection molding process are elusive because of core differences such as gas injection. Therefore, this study aims to derive process conditions to minimize the shrinkage and warpage of microcellular foam injection-molded parts made of glass fiber reinforced polyamide 6 (PA6/GF). Process factors and levels were first determined, with experiments planned accordingly. We simulated designed experiments using injection molding analysis software, and the results were analyzed using the Taguchi method, analysis of variance (ANOVA), and response surface methodology (RSM), with the ANOVA analysis being ultimately demonstrating the influence of the factors. We derived and verified the optimal combination of process factors and levels for minimizing both shrinkage and warpage using the Taguchi method and RSM. In addition, the mechanical properties and cell morphology of PA6/GF, which change with microcellular foam injection molding, were confirmed.

The influence of cavity deformation on the shrinkage and warpage of an injection-molded part

As soon as the gate solidifies or the nozzle is closed, the amount of melt inside a cavity remains constant. At this moment, the cavity deformation affects the final product shape and size. A set of simulation procedures has been developed in this study to estimate the cavity deformation which arises during an injection-molding process. A mold-filling program was applied to calculate the molding variables. The estimated cavity pressure, temperature distribution, and clamping force were employed as the boundary conditions in the mold-deformation analysis. A structural analysis program was developed to predict the cavity deformation. Molding experiments were carried out for polymethyl methacrylate (PMMA) wedge-shaped parts. To verify the structural analysis, a strain gauge was installed on the sidewall of the mold. The measured strains agreed with the simulated results. A commercial simulation software package was also used to predict the shrinkage and warpage of injection-molded parts. Numerical results showed the improvement in predicting the shape and size of a final product by taking the cavity deformation into account. The influences of the packing pressure, mold temperature, or melt temperature on shrinkage and warpage were also investigated.

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.

Prediction of shrinkage and warpage in consideration of residual stress in integrated simulation of injection molding

The accurate prediction of shrinkage and warpage of injection molded parts is important to achieve successful mold design with high precision. In this study, the numerical analysis of shrinkage and warpage of injection molded parts made of amorphous polymers was carried out in consideration of the residual stresses produced during the packing and cooling stages of injection molding. The temperature and pressure fields were obtained from the coupled analysis of the filling and post-filling stages. For residual stress analysis, a thermo-rheologically simple viscoelastic material model was introduced to consider the stress relaxation effect and to describe the mechanical behavior according to the temperature change. The effect of the additional material supply during the packing stage was modeled by assigning the reference strain. The deformation of injection molded parts after ejection induced by the residual stress and temperature change was analyzed using a linear elastic three-dimensional finite element approach. In order to verify the numerical predictions obtained from the developed program, the simulation results were compared with the available experimental data in the literature. In the case of residual stress, it was found that the present simulation results overpredicted the tensile residual stresses at the surface of injection molded parts. However, the predicted shrinkage was found to be reasonable to describe the effects of processing conditions well. Finally, an analysis of the shrinkage and warpage was successfully extended for a part with a more complex curved shape.

Variation of Part Wall Thicknesses to Reduce Warpage of Injection-Molded Part: Robust Design Against Process Variability

This article introduces a concept for deliberately varying the wall thicknesses of an injection-molded part within prescribed dimensional tolerance to reduce part warpage. The “warpage” described is measured from warpage simulation so as to represent various deformation behaviors of the molded part. Considering the variation in molding process as noise factors, a wall thickness model that minimizes the effect of these noises on warpage characteristics is obtained using the Taguchi method. The warpage characteristics of this model are compared with those of the constant-wall-thickness models that comply the general rule of an uniform wall thickness in part design. Each wall thickness model is then simulated for plausibly small process fluctuations against the best process conditions of each model that would occur in the actual molding operation. It is seen that varying wall thicknesses obtained by the present study exhibits better warpage characteristics in terms of warpage mean and variance against this mean, compared to the constant wall thicknesses.