Reducing the Burn Marks on Injection-Molded Parts by External Gas-Assisted Injection Molding

A burn mark is a sort of serious surface defect on injection-molded parts. In some cases, it can be difficult to reduce the burn marks by traditional methods. In this study, external gas-assisted injection molding (EGAIM) was introduced to reduce the burn marks, as EGAIM has been reported to reduce the holding pressure. The parts with different severities of burn marks were produced by EGAIM and conventional injection molding (CIM) with the same molding parameters but different gas parameters. The burn marks were quantified by an image processing method and the quantitative method was introduced to discuss the influence of the gas parameters on burn marks. The results show that the burn marks can be eliminated by EGAIM without changing the structure of the part or the mold, and the severity of the burn marks changed from 4.98% with CIM to 0% with EGAIM. Additionally, the gas delay time is the most important gas parameter affecting the burn marks.

Effect of Aluminum Flakes on Mechanical and Optical Properties of Foam Injection Molded Parts

Injection research using aluminum flakes has been conducted to realize metallic textures on the surface of plastic products. Several studies have focused on the effect of the orientation and quality of the flakes when using conventional injection molding methods; however, limited studies have focused on the foam injection molding method. In this study, we examined the orientation of aluminum flakes through foam injection with an inert gas and observed the changes in texture using a spectrophotometer and a gloss meter. The mechanical properties were also studied because the rigidity of the product, which is affected by the weight reduction that occurs during foaming, is an important factor. The results demonstrate that under foam injection molding, reflectance and gloss increased by 6% and 7 GU, respectively, compared to those obtained using conventional injection molding; furthermore, impact strength and flexural modulus increased by 62% and 15%, respectively. The results of this research can be applied to incorporate esthetic improvements to products and to develop functional parts.

Warpage Prediction of RHCM Crystalline Parts Based on Multi-Layers

Warpage is a typical defect for injection-molded parts, especially for crystalline parts molded by rapid heat cycle molding (RHCM). In this paper, a prediction method is proposed for predicting the warpage of crystalline parts molded by the RHCM process. Multi-layer models were established to predict warpage with the same thicknesses as the skin-core structures in the molded parts. Warpages were defined as the deformations calculated by the multi-layer models. The deformations were solved using the classical laminated plate theory by Abaqus. A model was introduced to describe the elastic modulus with the influence of temperature and crystallinity. The simulation process was divided into two procedures, before ejection and after ejection. Thermal stresses and thermal strains were simulated, respectively, in the procedure before ejection and after ejection. The prediction results were compared with the experimental results, which showed that the average errors between predicted warpage and average experimental warpage are, respectively, 7.0%, 3.5%, and 4.4% in conventional injection molding (CIM), in RHCM under a 60 °C heating mold (RHCM60), and in RHCM under a 90 °C heating mold (RHCM90).

Effects of Three Different Injection-Molding Methods on the Mechanical Properties and Electrical Conductivity of Carbon Nanotube/Polyethylene/Polyamide 6 Nanocomposite

Morphological evolution under shear, during different injection processes, is an important issue in the phase morphology control, electrical conductivity, and physical properties of immiscible polymer blends. In the current work, conductive nanocomposites were produced through three different injection-molding methods, namely, conventional injection molding, multi-flow vibration injection molding (MFVIM), and pressure vibration injection molding (PVIM). Carbon nanotubes in the polyamide (PA) phase and the morphology of the PA phase were controlled by various injection methods. For MFVIM, multi-flows provided consistently stable shear forces, and mechanical properties were considerably improved after the application of high shear stress. Shear forces improved electrical property along the flow direction by forming an oriented conductive path. However, shear does not always promote the formation of conductive paths. Oscillatory shear stress from a vibration system of PVIM can tear a conductive path, thereby reducing electrical conductivity by six orders of magnitude. Although unstable high shear forces can greatly improve mechanical properties compared with the conventional injection molding (CIM) sample, oscillatory shear stress increases the dispersion of the PA phase. These interesting results provide insights into the production of nanocomposites with high mechanical properties and suitable electrical conductivity by efficient injection molding.

Effect of gas on the polymer temperature in external gas-assisted injection molding

The introduction of gas is the principal difference between external gas-assisted injection molding (EGAIM) and conventional injection molding. In this study, the effects of gas thickness and gas delay time on polymer temperature were discussed. A modified one-dimensional transient heat conduction model of polymer was established to reveal the relationships between polymer temperature and gas thickness and gas delay time in EGAIM. The temperature histories of polymer were obtained by the simulation methods, including Moldflow and ANSYS, and were verified by comparing the experimental data to numerical simulation results. The effects of gas thickness and gas delay time on the temperature histories of polymer will be discussed in detail. The results showed that the polymer temperature is strongly affected by the heat preservation of gas, which in turn, increases with the increase of gas thickness and delay time. This paper provides quantitative methods and theoretical guidance for the study of the effects of gas on the polymer temperature in EGAIM.

Comparative study of crystallization and lamellae orientation of isotactic polypropylene by rapid heat cycle molding and conventional injection molding

The crystallization and orientation of isotactic polypropylene (iPP) molded by rapid heat cycle molding (RHCM) and conventional injection molding (CIM) were studied. Due to the varying cooling rates and shearing, the molded parts exhibited a multilayered structure (skin, shear and core) across the part thickness, reflecting different degrees of crystallization and lamellae orientation of iPP. The morphology evolution of RHCM products was discussed based on the comparative research of morphology and structure at multiple sites on the RHCM and CIM specimens. Scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD) were used to analyze the thickness, crystallinity and lamellae orientation of these three distinct layers. The crystallization and lamellae orientation of iPP correlated strongly with the multilayered structure. In the RHCM process, one side of the mold is equipped with the rapid heat cycle function. The thickness and lamellae orientation next to the heated surface were less than that of the opposite skin layer without heating. Meanwhile, the crystallinity was greater than that of the opposite skin layer.

Dual-Scale Modeling and Simulation of Skin Layer Thickness in Injection Molding with Variable Mold Temperatures

Compared with the constant mold temperature in conventional injection molding (CIM), injection molded parts with variable mold temperatures undergo a different thermomechanical history. As a result, the microstructure—for example, the skin–core structure found often in CIM—can be changed. However, unlike conventional injection molding, there have been few studies on the microstructure of injection molding with variable mold temperatures (IMVMT), possibly because the experimental control of variable mold temperatures remains difficult. In this paper, the skin layer thickness of CIM and IMVMT under different mold temperatures was carefully investigated by optical microscope. The higher mold temperatures and longer holding times during the injection flow stage caused a thinning of the highly oriented skin layer, and vice-versa. A dual-scale modeling was then proposed based on the prediction of crystal dimensions, and it was further used to predict the thickness of the skin layer. The predicted results were in agreement with the experimental observations under the different mold temperatures during IMVMT processing, and the proposed model proved to be effective.

In situ nano-fibrillation of microinjection molded poly(lactic acid)/poly(ε-caprolactone) blends and comparison with conventional injection molding

During microinjection molding, there are highly oriented PCL nanofibrils in situ formed, while during conventional injection molding, there are oriented microfibrils in situ formed.

The Influence of Temperature Dependant Parameters in Plastic 0.0nd Metal Injection Molding using Taguchi Method

Injection molding is a promising manufacturing process because of several advantages. Conventional injection molding was dominated by plastic as the raw material, but for better engineering properties feasibility, metal injection molding (MIM) has been given special attention. However, because of different properties and rheology, processing parameters for both processes must be treated accordingly. In this paper, the most influencing process parameter is identified for both processes using the state of the art Taguchi method. Simulation using Moldflow software is conducted with various process settings. From the study, it is proven that due to rheological behaviour, all the input parameters influence the MIM process while only one parameter is dominating during the injection molding of polypropylene.