Conventional Injection Moulding Research Articles

Crystallographic Texture Evolution in 3D Printed Polyethylene Reactor Blends.

In this work, crystallographic texture evolution in 3D printed trimodal polyethylene (PE) blends and high-density PE (HDPE) benchmark material were investigated to quantify the resulting material anisotropy, and the results were compared to materials made from conventional injection molded (IM) samples. Trimodal PE reactor blends consisting of HDPE, ultrahigh molecular weight PE (UHMWPE), and HDPE_wax have been used for 3D printing and injection molding. Changes in the preferred orientation and distribution of crystallites, i.e., texture evolution, were quantified utilizing the wide angle X-ray diffraction through pole figures and orientation distribution functions (ODFs) for 3D printed and IM samples. Since the change in weight-average molecular weight (Mw) of the blend was expected to significantly affect the resulting crystallinity and orientation, the overall Mw of the trimodal PE blend was varied while keeping the UHMWPE component weight fraction to 10% in the blend. The resulting texture was analyzed by varying the overall Mw of the trimodal blend and the process parameters in 3D printing and compared to the texture of conventional IM samples. The printing speed and orientation (defined with respect to the axis along the length of the samples) were used as the variable process parameters for 3D printing. The degree of anisotropy increases with an increase in the nonuniform distribution of intensities in pole figures and ODFs. All the highest intensity major texture components in IM and 3D printed samples (0° printing orientation) of reactor blends are observed to have crystals oriented in [001] or [001̅]. Overall, for the same throughput, 3D printed samples in the 0° orientation showed greater texture evolution and higher anisotropy compared to IM samples. Most notably, an increase in 3D printing speed increased the crystalline distribution closer to the 0° direction, increasing the anisotropy, while deviation from this printing orientation reduced crystalline distribution closer to the 0° direction, thus increasing isotropy. This demonstrates that tailoring material properties in specific directions can be achieved more effectively with 3D printing than with the injection molding process. Change in the overall Mw of the trimodal PE blend changed the preferential orientation distribution of the crystal planes to some degree. However, the degree of anisotropy remained the same in almost all cases, indicating that the effect of molecular weight distribution is not as significant as the printing speed and printing orientation in tailoring the resulting properties. The 3D printing process parameters (speed and orientation) were shown to have more influence on the texture than the material parameters associated with the blend.

Modelling Fatigue Crack Growth in High-Density Polyethylene and Acrylonitrile Butadiene Styrene Polymers.

Prior studies into fatigue crack growth (FCG) in fibre-reinforced polymer composites have shown that the two methodologies of Simple-Scaling and the Hartman-Schijve crack growth equation, which is based on relating the FCG rate to the Schwalbe crack driving force, Δκ, were able to account for differences observed in the measured delamination growth curves. The present paper reveals that these two approaches are also able to account for differences seen in plots of the rate of crack growth, da/dt, versus the range of the imposed stress intensity factor, ΔK, associated with fatigue tests on different grades of high-density polyethylene (HDPE) polymers, before and after electron-beam irradiation, and for tests conducted at different R ratios. Also, these studies are successfully extended to consider FCG in an acrylonitrile butadiene styrene (ABS) polymer that is processed using both conventional injection moulding and additive-manufactured (AM) 3D printing.

Effect of microstructure tuning by rapid heat cycle molding on the photodegradation behavior of isotactic polypropylene

AbstractRapid heat cycling molding (RHCM) is an injection molding technique that improves the product quality of isotactic polypropylene (iPP) by tuning the microstructure, but its effect on the photodegradation stability remains to be investigated. In this work, the effect of RHCM tuned microstructure on the photodegradation behavior of iPP was investigated and compared with conventional injection molding (CIM). Differential scanning calorimetry (DSC), x‐ray diffraction (XRD), Fourier transform infrared spectrometer (FTIR), atomic force microscopy (AFM), and shore durometer (D scale) were used to examine the photodegradation behavior of iPP samples. The results showed that RHCM increased the crystallinity, crystal size, and β‐crystal content of iPP samples. With the increase of photodegradation time, iPP samples injected with RHCM showed higher stability in terms of microstructure and surface quality. The relative changes in CI and Ra of RHCM90 were reduced by 48% and 40% after 800 h of UV irradiation, respectively. In addition, the combined results of dynamic mechanical analysis (DMA) and UV–visible absorption spectrum showed that RHCM promoted the development of crystalline structure and reduced the mobility of the surface chain segments as well as UV absorption coefficient. These combined effects contributed positively to its photodegradation stability.

Determination of mechanical performance of boric acid filled polypropylene based polymer composites

Polypropylene (PP) polymer, which is one of the indispensable materials of our daily life and stands out with its lightness, low cost and chemical resistance properties in the industry, was used. In industrial applications where the properties of polymers without additives are not sufficient, composite materials are produced by adding some additives to the polymer. In this experimental study, the mechanical properties of composites produced by adding boric acid (BA) to PP polymer at 5 wt.% (PP/5BA), 10 wt.% (PP/10BA) and 15 wt.% (PP/15BA) ratios were investigated. the effect of both BA filler and optimum BA filler ratio on mechanical properties were investigated. In the production of PP/BA composites, granules were first produced in an industrial twin screw extruder. Then, PP/BA composite tensile and impact test specimens were moulded on a conventional injection moulding machine. As a result, it was observed that the tensile modulus, tensile and yield strength of the composite materials decreased with increasing boric acid filler content in PP polymer. Depending on the boric acid filler content, the tensile strength decreased by an average of 18.3% and the breaking strength decreased by 14.8%. The lowest tensile modulus was obtained with a value of 2713 MPa at 10wt.% boric acid filler addition. The impact strength increased slightly at 5 wt.% boric acid filler addition and decreased at 10wt.% and 15wt.% boric acid filler addition.

Shape recovery behavior of polylactic acid/thermoplastic polyurethane polymer blends

Polylactic acid (PLA) and thermoplastic polyurethane (TPU)-based blends were prepared by twin-screw extruder and conventional injection molding (CIM) machine at various weight ratios of PLA/TPU, that is, 90/10, 80/20, and 70/30. The prepared blends were investigated for their shape memory properties by performing shape deformation and recovery experiments at various temperatures and bending angles. During the deformation process, TPU acted as a toughening agent that prevented the PLA/TPU blends from distortion. Hence, the temporary shape can be kept as the internal stress was stored in the blends. On heating above the glass transition (Tg) temperature of PLA, the deformed parts recovered their original shapes quickly along with the release of the stress. The prepared blends were found to exhibit significant shape memory properties at the TPU content of 10 wt%. The recovery rate was found to reach up to approximately 95%. Such shape memory polymers found fascinating applications in aerospace engineering, engineering plastics, biomedical implant materials, and textiles.

Mechanical characterisation of Aerosil-polycarbonate-based ceramic nanocomposites: 3D printing versus injection moulding technology

The 3D printing of composite materials especially, nanocomposites, is an essential step in exploring new perspectives for the applications of organic matrix composite materials for industrial applications. In this work, the effect of ceramic nanofillers on the mechanical properties of a thermoplastic matrix is studied using different wt% of nanofillers (AEROSIL). The results showed that the increase in the wt% of AEROSIL resulted in an increase in the mechanical properties in terms of hardness, stiffness, ductility, and tensile strength. Moreover, these samples were 3D printed and were compared with the samples prepared by conventional injection moulding. The comparison characterized the influence of the manufacturing method on the mechanical performance of materials. Although there was very little behavior difference in both samples, the 3D-printed samples showed a weight reduction. This has broadened the possible applications of this material and technique in areas where weight is of utmost significance.

Large Scale Vat-Photopolymerization of Investment Casting Master Patterns: The Total Solution.

The material properties and processing of investment casting patterns manufactured using conventional wax injection Molding and those manufactured by vat photopolymerization can be substantially different in terms of thermal expansion and mechanical properties, which can generate problems with dimensional accuracy and stability before and during ceramic shelling and shell failures during the burn-out of the 3D printed casting patterns. In this paper and for the first time, the monofunctional Acryloyl morpholine monomer was used for 3D printing of casting patterns, due to its thermoplastic-like behavior, e.g., softening by heat. However, the hydrophilic behavior of this polymer led to an incorporation of up to 60 wt% of Hexanediol diacrylate, to control the water absorption of the network, which to some extent, compromised the softening feature of Acryloyl morpholine. Addition of a powdered wax filler resulted in a delayed thermal decomposition of the polymer network, however, it helped to reduce the thermal expansion of the parts. The dimensional accuracy and stability of the wax-filled formulation indicated an excellent dimensional tolerance of less than ±130 µm. Finally, the 3D printed patterns successfully went through a burn out process with no damages to the ceramic shell.

Improving the weld lines mechanical properties by combining alternate dynamic packing and rapid heat cycle moulding

This is the first study that investigates the combined effect of alternate dynamic packing and rapid heat cycle moulding (RHCM) on the weld line mechanical properties of glass fibre reinforced thermoplastics. In conventional injection moulding, the outer layers rapidly solidify leaving a superficial weld line that do not recover when applying the dynamic packing. The results show that the thermal effect of RHCM reduces the thickness of the solidified skin layer and allow the alternate dynamic packing to reorient the fibres along the flow direction even in the outer layers. With reference to conventionally moulded tensile specimens made of 35% glass fibre reinforced polypropylene and having a front weld line, the proposed technological combination increased specimens’ strength and stiffness by 201% and 46%, respectively.

Comparison of Conventional Pressure-packed and Injection Molding Processing Methods for an Acrylic Resin Denture based on Microhardness, Surface Roughness, and Water Sorption.

Polymethyl methacrylate (PMMA) is a widely used material in prosthetics and is used to fabricate denture bases. The main disadvantage of this material is its polymerization shrinkage which causes clinical problems during use. The present study aimed to investigate and compare the microhardness, surface roughness, and water sorption of a commercial acrylic resin denture, which were processed by two different methods including conventional and pressure-packed injection molding techniques. A total of 60 polymethyl methacrylate samples were prepared in two groups: conventional acrylic resin (vertex) for the compression molding method and injection acrylic resin (vertex) for the injection molding method (10 samples of each material per test). The microhardness test was performed using a Vickers microhardness test device, the surface roughness test was performed by using a profilometer, and the water sorption test was performed using a digital scale. Data were analyzed using an independent sample t-test with Statistical Package for the Social Sciences (SPSS), version 17. The significant level was considered to be 0.05. According to the results, there was a significant difference between microhardness, surface roughness, and water sorption of the samples in the two groups. The results of the independent t-test showed that the microhardness of injection vertex acrylic resin samples was significantly higher than that of conventional pressure-packed vertex acrylic resin samples (P value<0.05). Also, the surface roughness and water sorption of injection vertex acrylic resin samples were significantly lower than those of conventional pressure-packed vertex acrylic resin samples (P value <0.05). According to the obtained results, denture fabrication by the injection molding method can improve the quality and durability of dentures due to the increased microhardness, the decreased surface roughness, and the decreased water absorption of the denture base compared with the conventional method.

Processing Effects on the Through-Plane Electrical Conductivities and Tensile Strengths of Microcellular-Injection-Molded Polypropylene Composites with Carbon Fibers.

Polymers reinforced with conducting fibers to achieve electrical conductivity have attracted remarkable attention in several engineering applications, and injection molding provides a cost-effective way for mass production. However, the electrical performance usually varies with the molding conditions. Moreover, high added content of conducting fibers usually results in molding difficulties. In this study, we propose using microcellular (MuCell) injection molding for polypropylene (PP)/carbon fiber (CF, 20, and 30 wt%) composites and hope that the MuCell injection molding process can improve both electrical and mechanical performance as compared with conventional injection molded (CIM) parts under the same CF content. Both molding techniques were also employed with and without gas counter pressure (GCP), and the overall fiber orientation, through-plane electrical conductivity (TPEC), and tensile strength (TS) of the composites were characterized. Based on the various processing technologies, the results can be described in four aspects: (1) Compared with CIM, microcellular foaming significantly influenced the fiber orientation, and the TPECs of the samples with 20 and 30 wt% CF were 18–78 and 5–8 times higher than those of the corresponding samples molded by CIM, respectively; (2) when GCP was employed in the CIM process, the TPEC of the samples with 20 and 30 wt% CF increased by 3 and 2 times, respectively. Similar results were obtained in the case of microcellular injection molding—the TPEC of the 20 and 30 wt% composites increased by 7–74 and 18–32 times, respectively; (3) although microcellular injection molding alone (i.e., without GCP) showed the greatest influence on the randomness of the fiber orientation and the TPEC, the TS of the samples was the lowest due to the uncontrollable foaming cell size and cell size uniformity; (4) in contrast, when GCP was employed in the microcellular foaming process, high TS was obtained, and the TPEC was significantly enhanced. The high foaming quality owing to the GCP implementation improved the randomness of fiber orientation, as well as the electrical and mechanical properties of the composites. Generally speaking, microcellular injection combined with gas counter pressure does provide a promising way to achieve high electrical and mechanical performance for carbon-fiber-added polypropylene composites.

Comparing the Replication Fidelity of Solid Microneedles Using Injection Compression Moulding and Conventional Injection Moulding.

Polymer surfaces are increasingly being functionalized with micro- and nano- surface features using mass replication methods such as injection moulding. An example of these are microneedle arrays, which contain needle-like microscopic structures, which facilitate drug or vaccine delivery in a minimally invasive way. In this study, the replication fidelity of two types of solid polycarbonate microneedles was investigated using injection compression moulding and conventional injection moulding. Using a full factorial design of experiments for the injection moulding process, it was found that the volumetric injection rate had the largest positive effect on the replication fidelity. The mould temperature and holding pressure were also found to have a positive effect, while the effect of the melt temperature was found to be insignificant for the considered temperature range. For the injection compression moulding process, it was found that a larger compression stroke resulted in a better replication fidelity. A comparison between the replication fidelity for the injection moulding and injection compression moulding indicated that the injection compression moulding process resulted in a higher and more uniform replication fidelity. Using finite element flow simulations, a higher and more evenly distributed cavity pressure was observed compared to the conventional injection moulding process.

Optimization of composite extrusion modeling process parameters for 3D printing of low-alloy steel AISI 8740 using metal injection moulding feedstock

Composite Extrusion Modeling (CEM) is an advanced material extrusion additive manufacturing technique for low-cost rapid production of complex parts. In this work, a conventional Metal Injection Moulding (MIM) feedstock is used for 3D printing of low alloy-steel AISI 8740 via CEM. This steel is widely used in aircraft, aerospace, and MIM industries. However, it has, so far, not been processed using CEM-based 3D printing. The influence of four printing parameters, extrusion multiplier, extrusion temperature, nozzle velocity, and layer thickness on green density and surface roughness was explored following the feedstock's investigation. Full-factorial and face-centered response designs were utilized to study the influence of printing parameters and their optimization to achieve maximum green density and minimum surface roughness. The optimized parameters were found to be an extrusion multiplier of 107.6 %, extrusion temperature of 180 °C, nozzle velocity of 20 mm/s and layer thickness of 0.050 mm through a multiple response optimization process. The dense green part with relative densities of ≥ 98 % was achieved with minimum surface roughness of Ra = (2.3 ± 0.1) μm and Rz = (16.1 ± 1.1) μm. Moreover, a scanning electron microscope was utilized to study the surfaces of green parts. The parts printed with optimized printing parameters showed the best quality with minimized printing voids and smooth extrusion.

Potential of Rapid Tooling in Rapid Heat Cycle Molding: A Review.

Rapid tooling (RT) and additive manufacturing (AM) are currently being used in several parts of industry, particularly in the development of new products. The demand for timely deliveries of low-cost products in a variety of geometrical patterns is continuing to increase year by year. Increased demand for low-cost materials and tooling, including RT, is driving the demand for plastic and rubber products, along with engineering and product manufacturers. The development of AM and RT technologies has led to significant improvements in the technologies, especially in testing performance for newly developed products prior to the fabrication of hard tooling and low-volume production. On the other hand, the rapid heating cycle molding (RHCM) injection method can be implemented to overcome product surface defects generated by conventional injection molding (CIM), since the surface gloss of the parts is significantly improved, and surface marks such as flow marks and weld marks are eliminated. The most important RHCM technique is rapid heating and cooling of the cavity surface, which somewhat improves part quality while also maximizing production efficiencies. RT is not just about making molds quickly; it also improves molding productivity. Therefore, as RT can also be used to produce products with low-volume production, there is a good potential to explore RHCM in RT. This paper reviews the implementation of RHCM in the molding industry, which has been well established and undergone improvement on the basis of different heating technologies. Lastly, this review also introduces future research opportunities regarding the potential of RT in the RHCM technique.

Numerical and experimental investigations on the mechanism of flow‐induced fiber orientation in short‐shot water‐assisted injection‐molded short‐glass‐fiber‐reinforced polypropylene

AbstractIt is a critical requirement to have an insight into the mechanism of flow‐induced fiber orientation in short‐shot water‐assisted injection molding (SSWAIM) of fiber‐reinforced polymer for improving the structural rigidity and service life of molded parts. However, this mechanism is still unclear, which stunts the development of SSWAIM. In this work, the mechanism of flow‐induced fiber orientation in SSWAIM parts of short‐glass‐fiber‐reinforced polypropylene (SGF/PP) was clarified through numerical research and experimental verification. The results showed that the difference of fiber orientation distribution at different positions both in the radial direction and along the flow direction between SSWAIM parts and conventional injection molding (CIM) parts was mainly due to the strong flow field caused by the high‐pressure water penetration in SSWAIM. Moreover, fiber orientation in the SSWAIM part depended not only on its position both in the radial direction and along the flow direction, but also on the processing parameters. At the front of SSWAIM part, fiber orientation changed greatly in the radial direction and presented an obvious “shell layer‐core layer‐water channel layer” hierarchical structure across the part thickness, whereas this phenomenon became more inconspicuous with increasing the distance of the selected position from the water injection inlet. Short‐shot size is the principal parameter affecting the fiber orientation, and within the range of investigated processing parameters, smaller short‐shot size, shorter water injection delay time, higher water pressure, and lower melt temperature could significantly facilitate fiber orientation across the part thickness.

Conventional and Microcellular Injection Molding of a Highly Filled Polycarbonate Composite with Glass Fibers and Carbon Black.

Conventional solid injection molding (CIM) and microcellular injection molding (MIM) of a highly filled polycarbonate (PC) composite with glass fibers and carbon black were performed for molding ASTM tensile test bars and a box-shape part with variable wall thickness. A scanning electron microscope (SEM) was used to examine the microstructure at the fractured surface of the tensile test bar samples. The fine and uniform cellular structure suggests that the PC composite is a suitable material for foaming applications. Standard tensile tests showed that, while the ultimate strength and elongation at break were lower for the foamed test bars at 4.0–11.4% weight reduction, their specific Young’s modulus was comparable to that of their solid counterparts. A melt flow and transition model was proposed to explain the unique, irregular “tiger-stripes” exhibited on the surface of solid test bars. Increasing the supercritical fluid (SCF) dosage and weight reduction of foamed samples resulted in swirl marks on the part surface, making the tiger-stripes less noticeable. Finally, it was found that an injection pressure reduction of 25.8% could be achieved with MIM for molding a complex box-shaped part in a consistent and reliable fashion.

A Review on Material Extrusion Additive Manufacturing of Metal and How It Compares with Metal Injection Moulding

Material extrusion additive manufacturing of metal (metal MEX), which is one of the 3D printing processes, has gained more interests because of its simplicity and economics. Metal MEX process is similar to the conventional metal injection moulding (MIM) process, consisting of feedstock preparation of metal powder and polymer binders, layer-by-layer 3D printing (metal MEX) or injection (MIM) to create green parts, debinding to remove the binders and sintering to create the consolidated metallic parts. Due to the recent rapid development of metal MEX, it is important to review current research work on this topic to further understand the critical process parameters and the related physical and mechanical properties of metal MEX parts relevant to further studies and real applications. In this review, the available literature is systematically summarised and concluded in terms of feedstock, printing, debinding and sintering. The processing-related physical and mechanical properties, i.e., solid loading vs. dimensional shrinkage maps, sintering temperature vs. relative sintered density maps, stress vs. elongation maps for the three main alloys (316L stainless steel, 17-4PH stainless steel and Ti-6Al-4V), are also discussed and compared with well-established MIM properties and MIM international standards to assess the current stage of metal MEX development.

Mechanical Properties of Isotactic Polypropylene with Oriented and Cross-hatched Lamellae Structure

Abstract The mechanical properties of injection moulded unreinforced isotactic, polypropylene depend on the crystalline structure and lamellae orientation. Push-pull processing is an injection moulding technique that allows the user to produce parts with oriented structures. Mostly applied for short fibre reinforced thermoplastics in order to align fibres parallel to the flow direction, this technique can also be used to orient the polymeric matrix of LCP and polypropylene. A comparison of mechanical properties as well as investigations on morphology between the samples produced using conventional injection moulding and push-pull processing are presented trying to improve the knowledge about this so far rather unknown technique.

Improved process moldability and part quality of short-glass–fiber-reinforced polypropylene via overflow short-shot water-assisted injection molding

Abstract Water-assisted injection molding (WAIM) is a promising molding process developed based on conventional injection molding (CIM). It has been a research hotspot in recent years and is still receiving extensive attention from many scholars and industries because of its significant potential advantages in practical applications. However, compared with CIM, since the additional water-related parameters are involved, the process moldability of thermoplastics is significantly reduced, especially for fiber-reinforced thermoplastics, which stunts the development of WAIM process. In this work, short-shot WAIM with an overflow cavity (OSSWAIM) was developed to address the problems and broaden the application scope of WAIMs. The results showed that compared with overflow WAIM (OWAIM) and short-shot WAIM (SSWAIM), OSSWAIM could significantly improve the process moldability and part quality of fiber-reinforced thermoplastics, especially for thermoplastic composites with a high fiber weight fraction. Besides, it was also found that water penetration had a slight influence on the fiber orientation near the water inlet, but had a significant influence on the fiber orientation near the end of mold cavity. Finally, three processing parameters affecting the water penetration, i.e., water pressure, melt temperature, and water injection delay time were investigated in terms of their influences on the fiber orientation within OSSWAIM.

Analysing Powder Injection Moulding of a Helix Geometry Using Soft Tooling.

Freeform injection moulding is a novel technology for powder injection moulding where a sacrificial 3D printed mould (i.e., a soft tooling) is used as an insert in the injection process. The use of 3D printed moulds enable a higher geometrical design flexibility as compared to the conventional injection moulding process. However, there is still very limited knowledge on how the sacrificial soft tooling material and powder suspension handles the increased geometrical complexity during the process. In this study, a stainless steel powder suspension is injected into a geometrically challenging sacrificial mould (viz. a helix structure) that is produced by vat photopolymerization additive manufacturing. Computed tomography is used to quantify the geometrical precision of the mould both before and after injection. In addition, a new numerical model that considers the suspension feedstock is developed to investigate the powder injection moulding process. The numerical results are found to be in qualitative good agreement with the experimental findings in terms of pinpointing critical areas of the structure, thereby highlighting a new pathway for evaluating sacrificial inserts for powder injection moulding with a high geometrical complexity.

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.