Injection-molded Parts Research Articles

Ageing of laser sintered glass-filled Polyamide 12 (PA12) parts at elevated temperature and humidity

Additive manufacturing is traditionally used to manufacture either prototypes or very small-scale demonstrators. In recent years though, it is being increasingly used to make low volume parts for the aeronautical and defence industry. One concern with laser sintered parts is that their relatively porous nature, means that they may be more susceptible to ageing than injection moulded parts. Parts were aged for 6 months in at different temperatures (18°C, 40°C, 50°C, 60°C, 80°C and 100°C) and in a humidity chamber at 60°C and 80% relative humidity. Each month samples were removed for characterisation. The testing included tensile testing, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and gas pycnometry. During ageing the samples displayed visible discolouration and embrittlement over the 6-month test period. This embrittlement was not observed in those samples aged at room temperature or an elevated humidity. The observed yellowing in the samples aged above ambient temperature is likely a result of the build-up unsaturated degradation products. No significant differences as a result of ageing were observed via DSC, TGA, SEM or gas pycnometry.

Comparing Performance of 3D-Printed and Injection-Molded Fiber-Reinforced Composite Parts in Ring-Spinning Traveler Application

Fiber-reinforced 3D printing (3DP) technology is a recent addition to the material extrusion-based 3DP process unlocking huge potential to apply this technology for high-performance material fabrication with complex geometries. However, in order to take the full advantage of this technology, a comparative analysis with existing technologies targeting a particular application is necessary to understand its commercial applicability. Here, an applied composite part, ring-spinning travelers, has been developed using the unique design features of fiber-reinforced 3DP technology that is beyond the capability of the currently used technology; the injection molding, quality, and performance of the printed and molded travelers were investigated and compared. The results demonstrated that fiber-reinforced 3DP is a promising technology that offers a lot of flexibility regarding reinforcement patterns and materials including both short and continuous fibers to tailor the performance, although the printed travelers showed poorer surface characteristics and wear resistance than the molded travelers. Based on the present analysis, a number of recommendations have been proposed on the design of the traveler to apply the technology effectively and use the printer to improvise and manipulate the performance of the travelers.

Enhancement of multilayer perceptron model training accuracy through the optimization of hyperparameters: a case study of the quality prediction of injection-molded parts

Injection molding has been broadly used in the mass production of plastic parts and must meet the requirements of efficiency and quality consistency. Machine learning can effectively predict the quality of injection-molded part. However, the performance of machine learning models largely depends on the accuracy of the training. Hyperparameters such as activation functions, momentum, and learning rate are crucial to the accuracy and efficiency of model training. This research aims to analyze the influence of hyperparameters on testing accuracy, explore the corresponding optimal learning rate, and provide the optimal training model for predicting the quality of injection-molded parts. In this study, stochastic gradient descent (SGD) and stochastic gradient descent with momentum (SGDM) are used to optimize the artificial neural network model. Through optimization of these training model hyperparameters, the width testing accuracy of the injection product is improved. The experimental results indicate that in the absence of momentum effects, all five activation functions can achieve more than 90% of the training accuracy with a learning rate of 0.1. Moreover, when optimized with the SGD, the learning rate of the Sigmoid activation function is 0.1, and the testing accuracy reaches 95.8%. Although momentum has the least influence on accuracy, it affects the convergence speed of the Sigmoid function, which reduces the number of required learning iterations (82.4% reduction rate). In summary, optimizing hyperparameter settings can improve the accuracy of model testing and markedly reduce training time.

Experimental Determination of Coefficients for the Renner Model of the Thermodynamic Equation of State of the Poly(butylene succinate) and Wheat Bran Biocomposites.

This paper presents the assumptions of a thermodynamic equation of state for polymers according to the Renner model. The experiments involved extruding a biocomposite based on poly(butylene succinate) that was filled with ground wheat bran with its size not exceeding 200 μm. The biocomposite was produced in pellet form with three different contents by weight of wheat bran, i.e., 10%, 30% and 50%. All specimens were examined for their thermodynamic p-v-T characteristics. Taking advantage of the SimFit module of Cadmould 3D-F, experimental results were used to determine the coefficients of thermodynamic equation of state for the tested biocomposite according to the Renner model. The coefficients were then used to calculate transition temperature and to create diagrams illustrating the relationship between pressure, temperature and specific volume for the tested biocomposite. The obtained results can serve as a basis for assessing the suitability of the biocomposite for injection molding, selecting technological parameters of this process, as well as for analyzing shrinkage and defects of injection-molded parts.

Parametric optimization of plastic injection moulding for FMCG polymer moulding (PMMA) using hybrid Taguchi-WASPAS-Ant Lion optimization algorithm

In this fast growing world, the demand for fast-moving consumer goods (FMCG) and half of the goods are manufactured through the use of plastic. To cater to those, plastic goods are manufactured using different types of moulding process. Plastic injection moulding (PIM) is a technique of injecting molten plastic into a mould to form it. They are widely used to manufacture FMCG products like containers, remote cases, or other small, complex profiles. But sometimes these complex profile mouldings lack dimensional accuracy. The current study provides an understanding of the clear thermoplastic Polymethyl Methacrylate (PMMA) material moulding for FMCG items utilizing an injection moulding machine. The transparent top sheath used in male/female deodorants can be considered in this investigation. For the purpose of minimizing weld-line width and sink-marks depth during injection moulding of commercial grade transparent thermo-plastic (Polymethyl Methacrylate), eight plastic injection moulding criteria were considered, namely melting temperature, mould temperature, cooling time, injection pressure, back pressure, holding pressure, ambient temperature, and holding time. In accordance with Taguchi's Design, the 27 experiments were piloted, and the factors were optimized using the Taguchi-based WASPAS method (Weighted Aggregated Sum Product Assessment), the Ant Lion optimization algorithm, and analysis of variance to determine the most dominant parameter in the minimization of weld-line width and sink-mark depth of the plastic injection moulded part. It was discovered that the cooling time of the plastic injection moulded component is the most important element affecting the weld-line width as well as the depth of the sink-mark on the surface of the part.

Creep study of glass reinforced polypropylene: Effect of temperature and presence of notches

Short fibers reinforced injection molded parts are commonly used in the applications under sustained loads. This requires creep resistance and creep behavior predictions under both short- and long-term service conditions.This article studies the creep behavior of injection molded polypropylene with short glass fibers at different temperatures and in the presence of a notch. The produced samples were analyzed by means of FT-IR (Fourier-transform infrared spectroscopy) and TGA (thermogravimetric analysis) to obtain and indication on microstructure and fiber content, respectively. Visible light microscopy was used to analyze the fiber orientation. Mechanical properties were measured using tensile testing. Tensile creep testing in an internally fabricated lever-type creep machine at a controlled constant temperature was conducted on plain specimens and specimens with machined notch. Fracture surfaces were analyzed by means of SEM (Scanning Electron Microscopy).Both creep strength and time to failure decrease with increasing temperature following the power law models. Norton’s power law and Monkman-Grant’s relationship can estimate the time to rupture not only of plain specimens, but also notched, if the stress is amplified by the stress concentration factor. These results can potentially estimate lifetime of injection molded parts with stress concentrations at elevated temperatures.

Injection Molding and Near-Complete Densification of Monolithic and Al2O3 Fiber-Reinforced Ti2AlC MAX Phase Composites.

Near-net shape components composed of monolithic Ti2AlC and composites thereof, containing up to 20 vol.% Al2O3 fibers, were fabricated by powder injection molding. Fibers were homogeneously dispersed and preferentially oriented, due to flow constriction and shear-induced velocity gradients. After a two-stage debinding procedure, the injection-molded parts were sintered by pressureless sintering at 1250 °C and 1400 °C under argon, leading to relative densities of up to 70% and 92%, respectively. In order to achieve near-complete densification, field assisted sintering technology/spark plasma sintering in a graphite powder bed was used, yielding final relative densities of up to 98.6% and 97.2% for monolithic and composite parts, respectively. While the monolithic parts shrank isotropically, composite assemblies underwent anisotropic densification due to constrained sintering, on account of the ceramic fibers and their specific orientation. No significant increase, either in hardness or in toughness, upon the incorporation of Al2O3 fibers was observed. The 20 vol.% Al2O3 fiber-reinforced specimen accommodated deformation by producing neat and well-defined pyramidal indents at every load up to a 30 kgf (~294 N).

Optimisation of Mould Design for Injection Moulding – Numerical Approach

Computer simulation of injection moulding process is a powerful tool for optimisation of moulded part geometry, mould design and processing parameters. One of the most frequent faults of the injection moulded parts is their warpage, which is a result of uneven cooling conditions in the mould cavity as well as after part ejection from the mould and cooling down to the environmental temperature. With computer simulation of the injection moulding process it is possible to predict potential areas of moulded part warpage and to apply the remedies to compensate/minimize the value of the moulded part warpage. The paper presents application of simulation software Moldex 3D in the process of optimising mould design for injection moulding of thermoplastic casing.

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).

Study about the technique of determining residual stress of loading measuring method

Nondestructive test method for residual stress in a structural member is always an important research subject, as a new technique for measuring residual stress loading measuring method needs to consummate for the convenience of engineering. The paper proves that nondestructive test loading measuring method is effective and accurate when compared with the result from hole-drilling method. Taking the measurement of residual stress of injection-molded part in automotive lamp as example, the residual stresses in the surface of injection-molded parts of automotive lamp measured by the two methods are very close based on the two measuring results. It shows that loading measuring method, a new method is used to measure the residual stress, has enough accuracy and credibility when it is used to measure the residual stress of complicated injection-molded part. It provides a basis for popularization and application of loading measuring method in engineering. The paper discusses the basic principles of loading measuring method and detailed procedure of the measurement of residual stress by loading measuring method; it gives out some advices to reduce the test errors.

Improving appearance quality of injection molded microcellular parts through mold coating of PTFE and zirconia

AbstractThe application of microcellular parts in the field of high appearance quality is limited due to its appearance defects. In order to improve the appearance quality of microcellular parts, low heat transfer coefficient mold coating with PTFE and zirconia was employed in this study. The appearance quality of microcellular was evaluated by the surface roughness of microcellular parts. The numerical and experimental results show that delayed heat transfer between the melt and the mold can be achieved through both mold coatings, which improve the melt fluidity and reduce the shear force of the mold on the melt effectively. It is demonstrated that the PTFE has a better effect of delay heat transfer under thinner coating. The polished zirconia coating shows more conducive to the melt wall slip due to its stable molecular structure and smooth surface, resulting in microcellular parts with better appearance quality.

New insights on the porous network created during solvent debinding of powder injection-molded (PIM) parts, and its influence on the thermal debinding efficiency

Mn-Zn ferrite components were successfully produced using Powder Injection Molding (PIM) from a binder system (11.5 wt%) made of paraffin wax (PW), linear low density polyethylene (LLDPE) and stearic acid. Solvent debinding kinetics of the molded parts depended on n-hexane temperature, on immersion duration and on part’s geometry. The volume to surface ratio of the considered parts were comprised between 1.3 and 4.0. The primary binder (PW) removal created a porous network having a narrow average pores distribution centered on a diameter of about 50 nm. We highlighted by using Archimedes’ principle and mercury intrusion porosimetries that the parts achieved a maximal open porosity disregarding their volume to surface ratio, while it was still possible to remove additionnal PW. This maximal porosity (12.6 %) has proved to be the most relevant parameter for the definition of an optimal solvent debinding duration (∼15−20 h at 40 °C). Using this chemical debinding step, it was possible to reduce our thermal debinding duration by 62.5 % (80 h–30 h) while avoiding the occurrence of structural defects as cracking or deformations on the parts. The sintered PIM parts had a density of about 4.84 g/cm3 (94.9 % of relative density) and a magnetic saturation polarization of about 500 mT what is very similar to parts produced using the conventional fabrication techniques. These results should be useful to understand how to improve the production rate of ferrites fabricated by PIM technology.

Polypropylene/talc foams with high weight-reduction and improved surface quality fabricated by mold-opening microcellular injection molding

Microcellular injection-molded part can save materials usage and reduce energy consumption. However, the part molded by conventional microcellular injection molding often encounters problems of a limited weight-reduction and poor surface quality. Focusing on these problems, this paper adopted mold-opening microcellular injection molding and talc as nucleating agent to prepare foamed polypropylene (PP) part. Different PP/talc composites were obtained by twin-screw extruder compounding, and their crystallization and rheological behaviors were investigated. The results show that talc can significantly promote PP crystallization, and the crystallization temperature changes slightly with talc content. However, the viscoelasticity of PP melt cannot be enhanced by the added talc. Then, the effects of packing time, mold-opening distance and talc content on the foaming behavior of PP were studied. It is found that a high packing pressure for long time can effectively eliminate the cells generated in melt filling process, thus a transparent part is obtained. With increasing packing time, the unfoamed skin layer of the part increases and cell size decreases. With increasing mold-opening distance, cell density increases. At a same mold-opening distance, cell density remarkably increases because of the heterogeneous nucleation of talc, thus cell size decreases. When talc content is 10 wt.% and weight-reduction of the part is 62.1%, the average cell size is 56.5 μm and the cell density reaches 1.54 × 107 cells/cm3. Because the high packing pressure is employed in the mold-opening microcellular injection molding, the surface quality of the part is improved.

Study of an Online Monitoring Adaptive System for an Injection Molding Process Based on a Nozzle Pressure Curve.

Injection molding is a popular process for the mass production of polymer products, but due to the characteristics of the injection process, there are many factors that will affect the product quality during the long fabrication processes. In this study, an adaptive adjustment system was developed by C++ programming to adjust the V/P switchover point and injection speed during the injection molding process in order to minimize the variation of the product weight. Based on a series of preliminary experiments, it was found that the viscosity index and peak pressure had a strong correlation with the weight of the injection-molded parts. Therefore, the viscosity index and peak pressure are used to guide the adjustment in the presented control system, and only one nozzle pressure sensor is used in the system. The results of the preliminary experiments indicate that the reduction of the packing time and setting enough clamping force can decrease the variation of the injected weight without turning on the adaptive control system; meanwhile, the master pressure curve obtained from the preliminary experiment was used as the control target of the system. With this system, the variation of the product weight and coefficient of variation (CV) of the product weight can be decreased to 0.21 and 0.05%, respectively.

Innovative fabrication of diffractive surfaces on plastic parts via textures micromilled on NiP injection moulds

Diffractive microstructured surfaces are nowadays increasingly applied to polymeric parts for aesthetic, security and optical functionalities. However, both the machining of the mould blaze-grating and its replication on plastic are still representing challenging issues, from both the technical and economical points of view. In this work, an innovative process chain based on carbide tools micromilling of mould gratings was developed for mass production of diffractive patterns on injection moulded parts. A micromilling experimental campaign was conducted on a nickel-phosphorus (NiP) thick coating to machine a blaze-grating on the mould surface, evaluating the influence of the cutting parameters on the diffractive surface quality. Subsequently, the microstructures were replicated on ABS, PC and PMMA by injection moulding. The roughness parameters Sk, Spk and Svk were added with the idea that their sum is representative of the polymer replication of regular diffraction grating pattern. Moreover, the effect of the moulded grating surface quality on the optical performance was preliminarily assessed. The obtained results show that the proposed process chain is suitable for low-cost mass production of polymeric parts with diffractive microstructures.

Investigations into performance of conventional and conformal cooling channels of a plastic injection mold.

In this paper, a comparative simulation analysis with traditional, conventional and conformal cooling channels of a plastic injection moulded part with variation in wall thickness has been analysed with the aim of determining which configuration will give better results in terms of part cooling time, volumetric shrinkage and warpage. The objective is to improve the part quality and to reduce the overall cycle time needed to manufacture the part.

Assessing the Suitability of Freeform Injection Molding for Low Volume Injection Molded Parts: A Design Science Approach

Low-volume manufacturing remains a challenge, especially for parts that need to be injection-molded. Freeform injection molding (FIM) is a novel method that combines elements from direct additive manufacturing (DAM) and injection molding (IM) to resolve some of the challenges seen in low-volume injection molding. In this study, we use a design science approach to explore the suitability of FIM for the manufacturing of low volume injection-molded parts. We provide an overview of the benefits and limitations of traditional IM and discuss how DAM and indirect additive manufacturing (IAM) methods, such as soft tooling and FIM, can address some of the existing drawbacks of IM for short series production. A set of different parts was identified and assessed using a design science-based approach to demonstrate how to incubate FIM as a solution to address the challenges faced in short series production with IM. This initial process innovation was followed by solution refinement, involving the optimization of the FIM processes. Finally, a “cross-case” analysis was conducted using the framework of context, intervention, mechanism and outcomes to generate insights about the generalizability of the results. It is concluded that FIM combines the short lead-times, low start-up costs and design freedom of DAM with the versatility and scalability of IM to allow manufacturers to bring low volume products to the market faster, more cheaply and with lower risk, and to maintain the relevance of these products through easy customization and adaptations once they have been launched.

Personalized Mass Production by Hybridization of Additive Manufacturing and Injection Molding.

The new trend in the composites industry, as dictated by Industry 4.0, is the personalization of mass production to match every customer’s individual needs. Such synergy can be achieved when several traditional manufacturing techniques are combined within the production of a single part. One of the most promising combinations is additive manufacturing (AM) with injection molding. AM offers higher production freedom in comparison with traditional techniques. As a result, even very sophisticated geometries can be manufactured by AM at a reasonable price. The bottleneck of AM is the production rate, which is several orders of magnitude slower than that of traditional plastic mass production technologies. On the other hand, injection molding is a manufacturing technique for high-volume production with little possibility of customization. The customization of injection-molded parts is usually very expensive and time-consuming. In this research, we offered a solution for the individualization of mass production, which includes 3D printing a baseplate with the subsequent overmolding of a rib element on it. We examined the bonding between the additive-manufactured component and the injection-molded component. As bonding strength between the coupled elements is significantly lower than the strength of the material, we proposed five strategies to improve bonding strength. The strategies are optimizing the printing parameters to obtain high surface roughness, creating an infill density in fused filament fabrication (FFF) parts, creating local infill density, creating microstructures, and incorporating fibers into the bonding area. We observed that the two most effective methods to increase bonding strength are the creation of local infill density and the creation of a microstructure at the contact area of FFF-printed and injection-molded elements. This increase was attributed to the porous structures that both methods created. The melt during injection molding flowed into these pores and formed micro-mechanical interlocking.

Articulated Pneumatic base for injection moulding parts

Articulated Pneumatic base for injection moulding parts

A Novel Multiscale Methodology for Simulating Droplet Morphology Evolution during Injection Molding of Polymer Blends.

The morphology of polymer blends plays a critical role in determining the properties of the blends and performance of resulting injection-molded parts. However, it is currently impossible to predict the morphology evolution during injection molding and the final micro-structure of the molded parts, as the existing models for the morphology evolution of polymer blends are still limited to a few simple flow fields. To fill this gap, this paper proposed a novel model for droplet morphology evolution during the mold filling process of polymer blends by coupling the models on macro- and meso-scales. The proposed model was verified by the injection molding experiment of PP/POE blends. The predicted curve of mold cavity pressure during filling process agreed precisely with the data of the corresponding pressure sensors. On the other hand, the model successfully tracked the moving trajectory and simulated morphology evolution of the droplets during the mold-filling process. After mold-filling ended, the simulation results of the final morphology of the droplets were consistent with the observations of the scanning electron microscope (SEM) experiment. Moreover, this study revealed the underlying mechanism of the droplet morphology evolution through the force analysis on the droplet. It is validated that the present model is a qualified tool for simulating the morphology evolution of polymer blends during injection molding and predicting the final microstructure of the products.