Injection-molded Parts Research Articles

An Experimental Study on Color Shift of Injection-Molded Mobile LGP Depending on Surface Micropattern.

In the display industry, the LCD backlight unit (BLU) module is variously used in mobile phones, notebook computers, monitors, and TVs. The light guide plate (LGP), which is one of the core parts of a BLU, is getting bigger and thinner consistently. Conventional injection methods and injection processes like injection compression molding (ICM) are becoming more complex and harsher with high-speed injection at high mold and melt temperatures. These approaches lead to a change in physical properties and a decrease in optical properties such as yellowing and color shift in injection-molded parts. In the present study, an injection molding experiment was conducted to understand the effect of surface patterns and major injection process conditions like mold and melt temperatures on the color shift in injection-molded mobile LGP. Optical properties obtained by the direct and total transmittance and CIE xy chromaticity diagram for injection-molded mobile LGP were measured with a UV–visible spectrophotometer. From the measurement of patternless LGP, it was found that total or direct transmittance was not affected by molding process variables. It was also found that yellow shift, , occurred as much as 0.00111 ± 0.00014, and a color shift angle, of 43.05 ± 2.44° was recorded in CIE coordinates for all nine experimental cases. From the measurement of total transmittance of patterned LGP, and were found to be almost the same as those of patternless LGP for the locations of low and medium density of the pattern for the LGP, T1 and T2. The measured data of direct transmittance of patterned LGP showed that additional yellow shift due to scattering caused by surface micropattern. Interestingly, of patterned data remained 43.05 ± 2.44°, which was almost the same as that found in the case of patternless LGP.

Silane-Functionalized Sheep Wool Fibers from Dairy Industry Waste for the Development of Plasticized PLA Composites with Maleinized Linseed Oil for Injection-Molded Parts.

Poly(lactic acid) (PLA) was plasticized with maleinized linseed oil (MLO) and further reinforced with sheep wool fibers recovered from the dairy industry. The wool fibers were firstly functionalized with 1 and 2.5 phr of tris(2-methoxyethoxy)(vinyl) (TVS) silane coupling agent and were further used in 1, 5, and 10 phr to reinforce the PLA/MLO matrix. Then, the composite materials were processed by extrusion, followed by injection-molding processes. The mechanical, thermal, microstructural, and surface properties were assessed. While the addition of untreated wool fibers to the plasticized PLA/MLO matrix caused a general decrease in the mechanical properties, the TVS treatment was able to slightly compensate for such mechanical losses. Additionally, a shift in cold crystallization and a decrease in the degree of crystallization were observed due to the fiber silane modification. The microstructural analysis confirmed enhanced interaction between silane-modified fibers and the polymeric matrix. The inclusion of the fiber into the PLA/MLO matrix made the obtained material more hydrophobic, while the yellowish color of the material increased with the fiber content.

Mold-Face Heating Mechanism, Overflow-Well Design, and Their Effect on Surface Weldline and Tensile Strength of Long-Glass-Fiber-Reinforced Polypropylene Injection Molding.

Long-fiber polymers offer the advantage of a lower production cost because specific tool designs are required for conventional injection molding equipment to produce long-fiber polymer parts. The use of long fibers allows relatively high fiber aspect ratios to be obtained, thereby enhancing composite stiffness, strength, creep endurance, and fatigue endurance. However, the multigate design of the injection-molded part can result in weldline formation during the molding process, which reduces the structural strength of the molded part. Therefore, in this study, the surface quality, fiber compatibility, and structural strength of long-glass-fiber-reinforced polypropylene (PP/LGF) injection-molded samples were compared in the use versus nonuse of a mold-cavity overflow-well area and the mold-face infrared heating method. The experimental results indicate that the mold-cavity overflow-well area more greatly improved the surface roughness of the PP/LGF molded samples. Moreover, the infrared heating of the mold-face decreased the weldline depth of the samples. Optical-microscopy images and mold-cavity pressure distributions indicated that the weldline tensile strength and the interface compatibility between fibers and melts at the weldline region during the molding stage were higher in the use than in the nonuse of the mold-cavity overflow-well and mold-face infrared heating method.

A simulation-based approach for assessment of injection moulded part quality made of recycled olefins

To produce plastic parts of high geometrical quality and dimensional stability through injection moulding process there are several key variables that must be considered. These include processing parameters such as packing time, cooling time, packing pressure, melt temperature, mould temperature and the intrinsic melt flow characteristics of polymeric materials used to produce the part. The challenge of producing high quality part is further compounded if the input polymer material is of reclaimed waste streams with inherent inconsistency in their nature. In this work, significant number of simulation-based studies are conducted using Autodesk Moldflow software to delineate the contributing issues pertinent to the part quality and achieve topological optimization by reducing critical parameters of shrinkage and warpage while ensuring overall cycle time viable for industrial production rates. Key simulation variables were obtained through experimental characterization of flow and thermal properties of the recycled olefin plastics. Different gate locations were simulated, and the best gate locations were selected for a two-gate system. These gates were provided with gate valve controllers for controlling the polymer flow to create cascaded injection moulding scenarios. Such scenarios were iterated with the objective of reducing the pressure required for cavity filling and thereby reducing the clamp force required. Optimized melt and mold temperatures of 245 °C, 20 °C were used for all the simulations performed. The result obtained from the most optimized simulation showed an average cycle time of 10.42 secs, volumetric shrinkage of 5.08%, warpage of 1.05 mm and clamp force of 79.81 tonne would be required to produce a part of 200 mm*100 mm*1.5 mm dimensions. Following a cascaded injection setup, it was shown that the clamp force could be reduced by 60.57%.

Micromechanical modeling of bamboo short fiber reinforced polypropylene composites

In recent years, there has been a growing interest in injection moulded Fiber Reinforced Polymer (FRP) composites, particularly with the natural fiber reinforcement due to their renewability and eco friendliness. In many of the applications, stiffness and strength are of prime importance in designing of injection moulded engineering parts. Determination of elastic modulus will give the designer flexibility to design the part geometry depending on stiffness requirement for particular application. This paper discusses micromechanical modeling of bamboo short fiber reinforced polypropylene composites. Bamboo polypropylene composites (BPC) were prepared by reinforcing polypropylene homopolymer matrix with short bamboo fibers. Composites with five different reinforcement percentages (10, 20, 30, 40, and 50 wt%) were prepared and tensile test samples were injection moulded. Tensile elastic modulus and strengths of bamboo composites were measured according to ASTM standard. Various micromechanical theoretical models were studied to find best possible model that correlates well with the experimental results. Elastic Modulus predicted by “Halpin-Tsai” model was in close agreement with the experimentally measured values. Strength predicted by “Kelly-Tyson” model also matched very well with the experimental values. Micromechanic-based semi analytical model “Mori–Tanaka” in Digimat-MF (mean-field homogenization) and numerical finite-element modeling (FEM) of BPC using the concept of representative volume element (RVE) have also been studied and results are compared with experimentally measured values.

Scanning acoustic microscopy investigation of weld lines in injection-molded parts manufactured from industrial thermoplastic polymer

Scanning acoustic microscopy (SAM) is used to characterize welds in a thermoplastic polymer (ABS) manufactured by injection-molding, particularly at the locations of weld-lines known to form as unavoidable significant defects. Acoustic micrographs obtained at 420 MHz clearly resolve the weld lines with morphological deformations and microelastic heterogenity. This is also where terahertz (THz) measurements, carried out in support of the SAM study, reveal enhanced birefringence corresponding to the location of these lines enabling verification of the SAM results. Rayleigh surface acoustic waves (RSAW), quantified by V(z) curves (with defocusing distance of 85 μm), are found to propagate slower in regions close to the weld lines than in regions distant from these lines. The discrepancy of about 100 m/s in the velocity of RSAW indicates a large variation in the micro-elastic properties between areas close to and distant from the weld lines. The spatial variations in velocity (VR) of RSAWs indicate anisotropic propagation of the differently polarized ultrasonic waves.

Quality Prediction for Injection Molding by Using a Multilayer Perceptron Neural Network.

Injection molding has been widely used in the mass production of high-precision products. The finished products obtained through injection molding must have a high quality. Machine parameters do not accurately reflect the molding conditions of the polymer melt; thus, the use of machine parameters leads to erroneous quality judgments. Moreover, the cost of mass inspections of finished products has led to strict restrictions on comprehensive quality testing. Therefore, an automatic quality inspection that provides effective and accurate quality judgment for each injection-molded part is required. This study proposes a multilayer perceptron (MLP) neural network model combined with quality indices for performing fast and automatic prediction of the geometry of finished products. The pressure curves detected by the in-mold pressure sensor, which reflect the flow state of the melt, changes in various indicators and molding quality, were considered in this study. Furthermore, the quality indices extracted from pressure curves with a strong correlation with the part quality were input into the MLP model for learning and prediction. The results indicate that the training and testing of the first-stage holding pressure index, pressure integral index, residual pressure drop index and peak pressure index with respect to the geometric widths were accurate (accuracy rate exceeded 92%), which demonstrates the feasibility of the proposed method.

Investigation of the interfacial adhesion of glass bead-filled multicomponent injection moulded composites

Polymeric materials are often combined with fillers and reinforcements, which modify their properties. The goal can be for example the improvement of thermal and mechanical properties or a reduction in costs. On the other hand, these materials can have negative effects too. In multicomponent injection moulding or in the case of products with weld lines, bonding problems can occur. In this research project, we analysed the effect of glass fibre and glass beads, and the most important technological parameters, melt temperature and holding pressure on the bonding strength between multicomponent injection moulded parts. The test samples were produced with a special injection mould, and the tear-off tests were performed on a tensile testing machine with a grip we developed.

Dynamically vulcanized blends of UHM-EPDM and polypropylene: Role of nano-fillers improving thermal and rheological properties

The effect of the addition of various types of nano-fillers on the viscoelastic properties of the dynamically vulcanized ultra-high molecular weight EPDM (UHM-EPDM)/Polypropylene (PP) was studied in details. The authors have studied the molten state viscoelastic properties at 180 °C by dynamic strain sweep (SS) and also stress relaxation (SR) through Rubber process Analyzer (RPA). The results of the SS and SR indicates that due the addition of the nano-silica to the blends resulting higher Storage modulus (Gʹ) and slower rate of relaxation than the pristine blend and nano-clay added blends. In the parallel plate rheometer frequency sweep study (FS), authors have noticed that nano-silica added blends are showing similar trends like SS study (in RPA) and all the blends are following pseudoplastic type flow behaviour. In the Cole-Cole plot, it is found that there is no semi-circular nature of the ηʹʹ vs ηʹ curve, and it indicates the immiscibility of the blends. In the thermal characterization, it is observed that there is a change in temperature in the thermal degradation study (TGA) about ̴ 5 °C and as the nano-filler amount are increasing the degradation temperature also improving. This special type of UHM-EPDM based TPVs exhibit superior physico-mechanical properties over conventional EPDM based TPVs and in presence of nano-fillers, they show even better physical properties. These newly developed TPVNs can be applied in aesthetic seals/strips, smaller injection moulded parts and 2K-moulds with PP in automotive.

Fiber Orientation Distribution Predictions for an Injection Molded Venturi-Shaped Part Validated Against Experimental Micro-Computed Tomography Characterization

Fil: Quintana, Maria Camila. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingenieria. Instituto de Investigaciones en Ciencia y Tecnologia de Materiales; Argentina

Injection-Molded Parts of Partially Biobased Polyamide 610 and Biobased Halloysite Nanotubes.

This works focuses on the development of environmentally friendly composites with a partially biobased polyamide 610 (PA610), containing 63% biobased content, and a natural inorganic filler at the nanoscale, namely, halloysite nanotubes (HNTs). PA610 composites containing 10, 20, and 30 wt% HNTs were obtained by melt extrusion in a twin screw co-rotating extruder. The resulting composites were injection-molded for further characterization. The obtained materials were characterized to obtain reliable data about their mechanical, thermal, and morphological properties. The effect of the HNTs wt% on these properties was evaluated. From a mechanical standpoint, the addition of 30 wt% HNTs gave an increase in tensile modulus of twice the initial value, thus verifying how this type of natural load provides increased stiffness on injection molded parts. The materials prepared with HNTs slightly improved the thermal stability, while a noticeable improvement on thermomechanical resistance over a wide temperature range was observed with increasing HNTs content. The obtained results indicate that high biobased content composites can be obtained with an engineering thermoplastic, i.e., PA610, and a natural inorganic nanotube-shaped filler, i.e., HNTs, with balanced mechanical properties and attractive behavior against high temperature.

Polarization modulated infrared spectroscopy: A pragmatic tool for polymer science and engineering

In the area of polymer crystallization, the most widely used techniques to quantify structure, morphology and molecular orientation are fundamentally based on light or X-ray scattering and absorption. In particular, synchrotron X-rays are used for detailed studies on the semicrystalline structure in polymeric materials. The technical requirements for such techniques, especially when high spatial resolution is essential, make the application of X-ray diffraction not straightforward. Direct information on the chain orientation in different semicrystalline morphologies requires rather complex sampling and analysis procedures. Surprisingly, a simple yet versatile technique based on infrared spectroscopy is hardly applied in the field of polymer crystallization. By modulating the polarization of the incident light, local anisotropy can be studied in real time on a submolecular length scale. In this article, we provide the relevant details of the polarization modulated infrared microspectroscopy technique for the study of semicrystalline materials from an engineering perspective. We demonstrate the essence of the method using as model systems spherulitic and transcrystalline morphologies and present its applicability to polymer/fiber composite technology and the study of injection-molded parts. The results provided in the present work serve to illustrate the applicability of this informative technique in the field of semicrystalline polymer science.

Evaluating the growth of candida albicans on removable complete dentures bases manufactured using CAD/CAM designed metal (Co-Cr casted from milled wax patterns) and injection molded resin

Acrylic resin processed by compression molded technique had been used to manufacture the removable complete dentures bases for many years. However there are many disadvantages connected to the use of this material with the ordinary compression molding as a denture base, the reason that made the researches try to find a better alternatives whether by changing the processing technique: like in the case of using acrylic resins processed by injection molded technique which proved to be a better choice in many aspects, on the other hand some researchers preferred to use another material so they used metal bases as replacement for the ordinary acrylic denture base. There are many ways to make patterns for metal bases casting in partial and complete dentures. Recently many researchers and practitioners used CAD-CAM technologies to make patterns for metal casting and facilitate the work, and save time. This study compares the candida albicans colony formation on the two materials mentioned above as an advantage to the material studied.Purpose: The purpose of this study is to compare the growth of candida albicans on removable complete dentures bases manufactured using CAD/CAM designed metal (Co-Cr casted from milled wax patterns) and injection molded acrylic resin. Materials and Methods: Split-palate maxillary complete dentures were fabricated for 10 edentulous patients. one-half of the palate was made in acrylic resin and the other half in Co-Cr metal palate that was casted from CAD-CAM milled patterns for each patient in this study. specimens were collected at 1, 3, and 5 months using a modified imprint culture method. Speciation of Candida albicans was performed using a chromogenic culture medium. Two-sample t-test was employed to determine effects and significant interactions between the acrylic and the metal groups. Results: Significant differences were observed in the candida albicans colony counts between both materials during the first, the third, and the fifth month. The Colony forming unit(CFU)/cm2 means were significantly less on the Co-Cr casted metal denture bases than CFU/cm2 means on the injection molded acrylic resin. Conclusions: The metal base proved to be effective in decreasing the candida albicans growth typically present in complete dentures. Colony counts of Candida albicans were higher in the injection molded acrylic resin part of denture bases of the patients in this study.

Optimization and prediction of volume shrinkage and warpage of injection-molded thin-walled parts based on neural network

Warpage and volume shrinkage are important indicators of the quality of thin-walled parts during injection molding. In this study, the optimization goals are warpage and volume shrinkage. Design parameters include mold temperature, melt temperature, injection time, holding time, cooling time, and holding pressure. Based on the orthogonal experimental design and response surface experimental design, the MoldFlow software is applied to the simulation of the thin-walled part injection molding process. The importance of various parameters on warpage and volume shrinkage was analyzed by using analysis of variance. Based on the simulation results, a two-layer hidden-layer back propagation (BP) neural network model is established and the genetic algorithm (GA) is used to optimize the weights and thresholds of the back propagation neural network (BPNN) model to reduce warpage and volume shrinkage by optimizing the design parameters significantly. A support vector machine (SVM) combined with GA-BP was used to build a prediction model for predicting warpage and volume shrinkage. Taking the automobile wire harness protection frame as an example, and verified by numerical simulation, the GA-optimized two-layer hidden-layer BP neural network combination method is an effective method for injection molding to reduce warpage and volume shrinkage of thin-walled parts. SVM-BP-GA can accurately provide predictions for optimization goals; the amount of warpage and the volume shrinkage were 0.93% and 1.9%, respectively.

Improvement of warpage prediction through integrative simulation approach for thermoplastic material

In the injection-molded parts, prediction of accurate warpage at initial level becomes mandatory to avoid iterative work of mold modifications. Simulation teams of many organizations are using existing commercial programs for process simulations. Material models in existing simulation technologies are having certain limitations and assumptions, which can regularly result in up to 50% variation of warpage results as compared to the actual physical warpage measurement. The commonly used Moldflow simulation model, for example, ignores temperature-dependent mechanical properties and the stress relaxation spectrum for viscoelastic materials. These assumptions affect the accuracy of the warpage prediction results significantly. To decrease these kinds of variations, BASF extended its Ultrasim® tool which is based on integrative simulation technology. Recently, a newly developed thermomechanical material model with temperature-dependent nonlinear mechanical properties and stress relaxation behavior was added in the Ultrasim. This model has been used in this work to consider the complete transient description of the warpage, which starts at packing phase of the part inside the mold, followed by actual cooling and ejection. In this article, unreinforced semicrystalline polybutylene terephthalate polymer material (Ultradur® B4520) is considered for warpage correlational study. The accuracy of the warpage prediction is compared between the integrative simulation approach, existing warpage simulation method, and the actual experimental inspection results. The result exhibits that the accuracy of the integrative simulation (Ultrasim)-based warpage simulation is relatively better than existing simulation technologies and closer to the actual measurement.

A study on the response of PLGA 85/15 under compression and heat-treatment testing cycles

Poly(lactic-co-glycolic acid) (PLGA) is one of the most prominent bioresorbable materials, currently used in several medical applications (screws, craniofacial plates etc.). Looking to extend the knowledge about the thermomechanical behavior of bioresorbable medical materials, this research presents a series of experiments and results based on nonhomogeneous compression tests for the polymer PLGA 85/15. Instead of focusing on tensile and bending conditions for compression-molded products, such as usually presented in the literature, attention is given to compression tests and samples machined from injection-molded parts. Additionally, PLGA strain rate sensitivity, which is an issue less discussed in the literature, is analyzed. In the current study, this material is tested by observing the main features related to resorbable medical materials. The effects of a material heat treatment that are associated with PLGA shape-memory properties are investigated. Differential scanning calorimetry (DSC) was also employed in the thermal characterization. A finite element analysis of the compression testing provides a complementary overview of the mechanical behavior of PLGA 85/15. Results indicate that PLGA has a linear rate-insensitive response for small strains but presents a strong rate dependence for strains beyond the material yielding. PLGA shows a remarkable post-yielding strain-softening behavior, with a steep descent slope. Samples present significant mechanical changes after heat treatment at temperatures above $T_{g}$, with reduction of 35% in the material elastic modulus and 30% in the upper-yielding stress and no significant changes for further heat-treatment procedures. DSC analysis confirmed the existence of significant residual stress in PLGA specimens. Mechanical deformation and manly heat treatment seem to reduce this residual stress caused by molecular orientation and rapid solidification. Finally, finite element simulations show that the limit of the homogeneity hypothesis is associated with the yield strain, after which highly non-uniform stresses develop.

A dimensional analysis based model to predict completion of solvent debinding step for Metal Injection Moulded parts

ABSTRACT The objective of this study is to develop a mathematical model to predict, for instance, the time for complete debinding of a metal injection moulded (MIM) part, the extent of solvent debinding (%) at any point of time and the debinding rate (g/min). To this end, two feedstocks, one containing carbonyl iron powder and the other made from irregular-shaped metallic particles from the shopfloor grinding sludge (both mixed with an organic binder system) were used to make by MIM, parts of nine different geometries. Each geometry has its own modulus. The effects of powder material, solid loading (influencing the binder content) and debinding temperature on the debinding characteristics were studied for the moduli of the nine parts. Parts with smaller moduli (thin parts) were found to debind faster than those with higher moduli. Parts, made of carbonyl iron feedstock (CI90), debind faster than that made of irregular-shaped particulates. A generalised solvent debinding model based on dimensional analysis has been proposed and verified experimentally. The root mean square error was found to be approximately 4% between experimentally determined and predicted debinding characteristics. These predictions are used to effectively design and curtail the solvent debinding cycles in MIM process.

Blister Formation in Film Insert Moulding.

The formation of blister in the injection moulded parts, especially in the film insert moulded parts, is one of most significant causes of part rejection due to cosmetic requirements or functionality issues. The mechanism and physics of blister formation for molded parts are not well-understood by the state-of-the-art literature. The current paper increases the fundamental understanding of the causes for blister formation. In the experiment, a membrane strip of 5 mm in width was overmoulded with Polypropylene (PP), which formed a disc-shaped part with a diameter of 17.25 mm and a thickness of 500 µm. To investigate the influence of the processing parameters, a full factorial design of experiments (DoE) setup was conducted, including mould temperature (Tm), barrel temperature (Tb), injection speed (Vi) and packing pressure (Pp) as variables. The degree of blistering at the surface was characterized by the areal surface roughness parameters Spk and Smr1, measured with a confocal laser microscope. The measurements were taken on the 10 mm long section of the membrane surface in the centre of the moulded part across the entire width of the film. In addition, the film insert moulding (FIM)-process was simulated and the average shrinkage of the substrate material under the membrane was investigated. Eventually, a method and processing window could be defined that could produce blister-free parts.

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.

Multi-objective optimization of injection-molded plastic parts using entropy weight, random forest, and genetic algorithm methods

Abstract The qualities of injection-molded parts are affected by process parameters. Warpage and volume shrinkage are two typical defects. Moreover, insufficient or excessively large clamping force also affects the quality of parts and the cost of the process. An experiment based on the orthogonal design was conducted to minimize the above defects. Moldflow software was used to simulate the injection process of each experiment. The entropy weight was used to determine the weight of each index, the comprehensive evaluation value was calculated, and multi-objective optimization was transformed into single-objective optimization. A regression model was established by the random forest (RF) algorithm. To further illustrate the reliability and accuracy of the model, back-propagation neural network and kriging models were taken as comparative algorithms. The results showed that the error of RF was the smallest and its performance was the best. Finally, genetic algorithm was used to search for the minimum of the regression model established by RF. The optimal parameters were found to improve the quality of plastic parts and reduce the energy consumption. The plastic parts manufactured by the optimal process parameters showed good quality and met the requirements of production.