High Mold Temperature Research Articles

The Influence of In-Mould Annealing and Accelerated Ageing on the Properties of Impact-Modified Poly(Lactic Acid)/Biochar Composites.

In the last few decades, a large number of natural additives have been analysed in connection with the improvement of the properties of poly(lactic acid) (PLA) bioplastic materials. This article comprehensively analyses the applicability of a highly stable and progressive multifunctional additive produced from renewable resources-biochar. The effect of biochar on the structural development and various thermo-mechanical properties was evaluated as a function of the biochar size and volume, addition of an impact modifier and in-mould annealing during injection moulding. In addition, the effect of accelerated ageing on the change in properties was also analysed. The evaluated results showed a significant influence of the particle size and biochar content on the properties of PLA biocomposites. However, the crucial aspect was the production process with a higher mould temperature and longer production time. Consequently, the effect of additives with adjusted processing worked synergistically on the performance of the resulting biocomposites. The accelerated ageing process did not induce any significant changes in the mechanical, impact and heat resistance behaviour of neat PLA. On the other hand, significant effects on the behaviour of the modified PLA biocomposites were observed. Impact-modified PLA achieved a toughness of 28 kJ/m2, an increase of 61% compared to neat PLA. Similar observations were made when submicron biochar was incorporated into the PLA matrix (a 22% increase with PLA/5B1). These increases were even more pronounced when injected into a 100 °C mould. Due to the synergistic effect, excellent impact toughness results of 95 kJ/m2 (a 428% increase) were achieved with PLA/IM/5B1. Moreover, these results persisted even after accelerated ageing.

Structural evolution of ultrasonic microinjection molded sterecomplexes of poly(lactide) during heating process

Two stereocomplexes (SCs) with different molecular weights in poly(L-lactide) (PLLA-49k and PLLA-163k) were prepared by mixing equal amounts of poly(D-lactide) (PDLA) and PLLA via the solution method. The exclusive formation of SCs was achieved in SC-PLLA-49k, whereas both homocrystallites (HCs) and SCs were observed in SC-PLLA-163k. Two blends were subjected to further processing via the ultrasonic microinjection molding technique at varying mold temperatures, yielding amorphous samples. As the samples were heated, the heating induced structural reorganization occurs with the concurrent SCs and HCs for all samples at ca. 80 °C. The degree of crystallinity for HCs XHC exhibits a positive correlation with the mold temperature, whereas the degree of crystallinity for SCs XSC shows a negative dependence on mold temperature for both systems. This behavior can be tentatively explained as follows. Firstly, the demixing of enantiomeric PLA chains occurs in the melt state as evidenced by twice heating measurements of blends. The degree of chain segregation is expected to increase with the increase in mold temperature due to lower supercooling, resulting in a decrease of PLLA/PDLA clusters (SC nuclei). Secondly, a high mold temperature is beneficial for the formation of HC nuclei as the chain mobility is improved. The reformulation of SC nuclei is difficult because of a longer diffusion distance required for PLA molecules. The coexistence of SC and HC nuclei causes the simultaneous appearance of SCs and HCs during heating of samples. As HCs start to melt, a transition from HCs to SCs occurs accompanied by a continuous increase in XSC. For both systems, a maximum of XSC is reached when SCs begin to melt followed by a mold temperature independent evolution of XSC upon further heating. Such a maximum is larger in the low molar mass system because it is less entangled. The reservation of SC nuclei is demonstrated by a comparison of the structural evolution and isothermal cold crystallization behavior between the two blends and their ultrasonic microinjection molded samples.

In-situ synchrotron X-ray investigating crystallization of isotactic polypropylene with β-nucleating agent during injection molding

The coupling effects of mold temperature and packing pressure fields on structure evolution of isotactic polypropylene with β-nucleating agent (iPP/β) during injection molding were systematically investigated using high-throughput in-situ synchrotron X-ray diffraction/scattering technology for the first time. A small number of β-crystals are generated in pure iPP and iPP/β due to the shear flow introduced by the filling stage. The formation of β-crystals induced by β-nucleating agent (β-NA) in iPP/β commenced after about 1.8 s of melt filling. The two-stage growth of β-crystals in iPP/β exhibits differences in growth time and orientation. Both the decrease in the lattice spacing and the β-α transition in iPP/β occur at the packing stage and are suppressed at high mold temperatures (≥ 90 °C). The polymorphism competitive growth of iPP/β is revealed, and the effects of coupling external fields on it are well elucidated by combining finite element simulation and classical nucleation theory. Additionally, the scattering intensity and orientation of iPP/β lamellae initially increase to a maximum value and subsequently decrease until reaching the equilibrium with time. Our current work lays a solid foundation to precisely customize the crystal structure of iPP/β in practical processing and thus to produce high-performance iPP products.

Investigation of Mold Flux Entrapment in Deep Oscillation Mark of Interstitial-Free Steel Shell Using Mold Simulator.

The slag entrapment defect has become a big issue for the IF steel casting process. In this study, the mechanism of mold flux entrapment in deep oscillation mark of an IF steel shell was studied by a high-temperature mold simulator. Results show that both temperature and heat flux in a copper mold become lower when mold flux B with lower melting and viscosity is used, compared with these when mold flux A with higher melting and viscosity is used. The average thickness of the slag film for mold fluxes A and B is 1.31 mm and 1.63 mm, and the consumption of them is 0.33 kg/m2 and 0.35 kg/m2, respectively. The shell for mold flux A exhibits sharper oscillation marks, while the shell for mold flux B has shallower oscillation marks. These deeper oscillation marks capture the mold flux by overflow of molten steel at the meniscus, which finally produces the slag entrapment defect in the shell.

Preparation and Characterization of Functionzliaed Silicone Oil for High Temperature Mold Release Agent

Silicohydrogen addition method was utilized to prepare long-chain alkyl silicone oils using high hydrogen-containing silicone oil, α-methylstyrene, and 1-tetradecene as raw materials and chloroplatinic acid as catalyst. FTIR and 1H-NMR were used to characterize the structure of the products, and the effects of reaction temperature, reaction time, catalyst dosage, and n(Si-H): n(C=C) on the Si-H conversion were investigated experimentally to determine the optimal reaction process. The experimental results showed that the optimized process conditions were n(Si-H): n(C=C) =1:1.1, reaction time of 6 h, reaction temperature of 150 °C, catalyst dosage of 2 ppm, and the Si-H conversion of the product was 96.3%.

Preparation of PLA/PBAT blends with high performance via the synergistic effect of high mold temperature and strong shear field

As a bio-based polymer with excellent mechanical properties, good biodegradability and biocompatibility, polylactic acid (PLA) displays considerable potential to replace traditional petrochemical-based polymers for application. However, poor toughness and heat resistance restrict its wide application. In this work, PLA based PLA/PBAT blends with excellent comprehensive performance were prepared through the synergistic effect of high mold temperature as well as strong shear field. SEM, DSC and WAXD were conducted to characterize the crystal and micro-morphology of the samples. The results show that highly oriented shish-kebab and hybrid shish-kebab structures are observed in VIM-H sample. The crystallinity increases dramatically, which can reach 48%. Besides, the toughness, strength and heat resistance of VIM-H all markedly improve. The Vicat softening temperature (VST) reaches up to 149.2 °C, while the tensile strength and impact strength increase to 89.07 MPa and 10.36 kJ/m2, respectively. This study proves the synergistic enhancement of the properties for PLA/PBAT blends by high mold temperature as well as strong shear field, which provides a new method to obtain high-performance PLA materials and is beneficial for the wider application of PLA products.

Effect of mold temperature on the solidification process and microstructure of Zr-based metallic glasses during casting

To explore the relationship between mold temperature and the formation of large-size metallic glasses, the influence of mold temperature on the solidification process and microstructure evolution of amorphous melts was investigated. It was found that increasing the mold temperature to 623 K contributes to improving the solidification time from ∼1.79 s to ∼2.32 s without affecting the solidification behavior of amorphous melt. However, the duration of the supercooled liquid state was prolonged by the excessively high mold temperature, resulting in a considerable increase in the glass transition time from ∼12.78 s to ∼145.7 s and a decline in the cooling rate from 27.6 K/s to 2.1 K/s, which ultimately leads to the crystallization of the sample. In addition, it has been observed that the 573 K mold temperature is not only the optimal mold temperature to ensure the amorphous nature of the sample but is also beneficial to improve the internal temperature gradient of the sample, thereby reducing the risk of deformation or cracking. Appropriate control of mold temperature can provide valuable guidance for large-size amorphous castings and associated process parameters.

External gas-assisted mold temperature control and optimization molding parameters for improving weld line strength in polyamide plastics.

In this study, we present a novel approach to injection molding, focusing on the strength of weld lines in polyamide 6 (PA6) composite samples. By implementing a mold temperature significantly higher than the typical molding practice, which rarely exceeds 100°C, we assess the effects of advanced mold temperature management. The research introduces a newly engineered mold structure specifically designed for localized mold heating, distinguishing it as the 'novel cavity.' This innovative design is compared against traditional molding methods to highlight the improvements in weld line strength at elevated mold temperatures. To optimize the molding parameters, we apply an Artificial Neural Network (ANN) in conjunction with a Genetic Algorithm (GA). Our findings reveal that the optimal ultimate tensile strength (UTS) and elongation values are achieved with a filling time of 3.4 seconds, packing time of 0.8 seconds, melt temperature of 246°C, and a novel high mold temperature of 173°C. A specific sample demonstrated the best molding parameters at a filling time of 3.4 seconds, packing time of 0.4 seconds, melt temperature of 244°C, and mold temperature of 173°C, resulting in an elongation value of 582.6% and a UTS of 62.3 MPa. The most influential factor on the PA6 sample's UTS and elongation at the weld line was found to be the melt temperature, while the filling time had the least impact. SEM analysis of the fracture surfaces revealed ductile fractures with rough surfaces and grooves, indicative of the weld line areas' bonding quality. These insights pave the way for significant improvements in injection molding conditions, potentially revolutionizing the manufacturing process by enhancing the structural integrity of the weld lines in molded PA6 samples.

Influence mechanism of injection process parameters on iridescent pattern defects on optical molded parts

AbstractIridescent patterns are insufferable molding defects during mass manufacturing of polymer optic devices by using injection molding (IM) technique and seriously affect the appearance and imaging performance of parts. However, at present, the research on the factors affecting iridescent pattern defects is lacking, resulting in the difficulty of obtaining effective methods to weaken iridescent pattern defects. This article aims to clarify the correlation mechanism between injection process parameters and iridescent patterns and provide a theoretical basis for reducing iridescent pattern defects. Based on the process characteristics of IM and the optical mechanism of iridescent patterns, the correlation between iridescent patterns and influencing factors such as optical characteristics and the material structure is established. The influence mechanism of process parameters on iridescent patterns is further clarified by experiments. The results show the iridescent pattern color is related to the retardation, while the iridescent pattern brightness is affected by the retardation and transmittance. Process parameters change the retardation and transmittance by varying factors such as the thickness, birefringence, and crystallinity. Higher mold temperature, reasonable melt temperature, injection speed, and holding pressure are conducive to reducing the colorful fringe area and iridescent pattern brightness, thereby weakening the iridescent patterns on the part.

Formation and prediction of the multi-layered crystalline structures in micro-injection molded small modulus gears

Due to the temperature difference between mold and melt, micro-injection molded products, such as small modulus gears, inevitably exhibit stratification. The presence of multi-layered crystalline structures with different mechanical properties can adversely affect the kinematic stability and service life of gears. In response to this problem, the distribution and property of multi-layered crystalline structures in micro-injection molded small modulus gears was analyzed based on experiment detection. The results indicate that higher mold temperature is advantageous to manufacture gears with more homogeneous and robust structure. Furthermore, a simulation was carried out to obtain melt thermal history. It can be found that the specific crystalline structure in gears has similar cooling curves regardless of mold temperature. This similarity can be represented by the initial cooling rate. Therefore, the initial cooling rate can be used as an indicator to predict the distribution of multi-layered crystalline structures. Besides, the additional heat dissipation of top land accelerates the cooling process of the melt at the corresponding position. Therefore, the non-core layer near top land is thicker than that near flank. Similar phenomenon is speculated to appear in the other injection molded microstructures with a similar length-width ratio.

Analysis of Weld Lines in Micro-Injection Molding.

Micro-injection molding (µIM) is a widespread process for the production of plastic parts with at least one dimension, or feature, in the microscale (conventionally below 500 µm). Despite injection molding being recognized as a robust process for obtaining parts with high geometry accuracy, one last occurrence remains a challenge in micro-injection molding, especially when junctions are present on the parts: the so-called weld lines. As weld lines are crucial in determining mechanical part performances, it is mandatory to clarify weld line position and characteristics, especially at the industrial scale during mold design, to limit failure causes. Many works deal with weld lines and their dependence on processing parameters for conventional injection molding, but only a few works focus on the weld line in µIM. This work examines the influence of mold temperature on the weld line position and strength by both experimental and simulation approaches in µIM. At mold temperatures below 100 °C, only short shots were obtained in the chosen cavity. At increased mold temperatures, weld lines show up to a 40% decrease in the whole length, and the overall tensile modulus doubles. This finding can be attributed to the reduction of the orientation at the weld line location favored by high mold temperatures. Moldflow simulations consistently reproduce the main features of the process, weld line position and length. The discrepancy between experimental and simulated results was attributed to the fact that crystallization in flow conditions was not accounted for in the model.

Rapid mold temperature rising method for PEEK microcellular injection molding based on induction heating

As a high-performance polymer, Polyether ether ketone (PEEK) and its injection-molded products are widely used as an ideal metal replacement. The production of ideal PEEK injection molded products, including microcellular injection molded, requires the support of high mold temperatures that can be maintained. Given this, a rapid mold temperature rising technology based on induction heating was designed to take advantage of the ultra-high heating rate of induction heating, which effectively met rapid increase and maintenance of high mold temperatures for PEEK injection molding. Both finite element analysis and experimental results showed, compared to the electric heating method, the induction heating method increased the efficiency to 5600% when the mold temperature rise from 150 to 180 °C compared to electric heating. All heating methods were used for the validation tests of injection molding PEEK, microporous injection molding PEEK, and micro-open microporous injection molding PEEK. The experimental results showed that the surface quality of PEEK samples molded by induction heating was 9.8%–61.2% higher than that of the oil heater heating, while the mechanical properties were more than 18%. Besides, the adaptability to longer holding times for micro-open microcellular injection molding suggested it can effectively broaden the possibilities of developing higher-performance PEEK foam products. The pioneering design and analysis of heating methods in this work had important guidance for promoting high-performance polymer injection molding and the lightweight of its foamed products.

Characterisation of microneedle replication and flow behaviour in ultrasonic micro-injection moulding through design of experiments

This research investigates the impact of process parameters on ultrasonic micro-injection moulding (u-μIM) by studying microneedle replication efficiency, temperature evolution during moulding, melt flow consistency and sonication behaviour. The experimentation comprises of a full-factorial design of experiments using three process variables: sonication time, mould temperature and injection force. The current study presents that; (i) mould temperature was found to be the most influential parameter to tune and optimise micro-feature replication, (ii) consistent ultrasonic micromoulding flows can be achieved using higher mould temperatures, (iii) injection force is a key parameter influencing sonication frequency, a critical aspect of the ultrasonic method to obtain a repeatable manufacturing process. These outcomes will be a datum during development of the manufacturing processes for specific products using the ultrasonic method. The research presented here takes a unique approach to characterise the ultrasonic method for the development of this novel technique, particularly for microneedle patch and medical device production. With this increased level of understanding of u-μIM process characteristics, the method can become an energy efficient and cost-effective alternative to conventional micro-injection moulding processes for delivering high-quality, miniature components.

The effects of cooling rate (mould temperature) on HDPE gears produced through injection moulding

The effects of mould temperature (cooling temperature) on molten HDPE (Hostalen GC 7260) during manufacture, is evaluated in this paper. HDPE gears were produced at varying mould temperatures using Injection Moulding. Optimised injection values for melt temperature, injection volume, hold pressure, and hold time were obtained, and then held constant while the mould temperature was altered.Analysis on how the mould temperature affected peak melting points and crystallinity were then carried out using differential scanning calorimetry (DSC). These revealed that crystallinity improved as the mould temperature was increased from 22 °C to 65 °C. Gears produced at similar cooling temperatures were then meshed on a gear test rig and run at 1000 rpm, using different torque loadings. Their wear rates, and modes of failure were then analysed, and comparisons were made to ascertain how the differing mould temperatures employed during the injection moulding manufacturing process affected their wear characteristics. Topographical analysis of worn gear teeth was performed using scanning electron microscopy (SEM). It was noted that gear tooth wear and failure was dependent on the mould temperature employed during the manufacturing process. Gears produced at 65 °C showed improved tooth surface wear resistance at lower loads (0.5 Nm and 1 Nm) compared to those produced at 22 °C, but were more likely to fail through tooth fracture at the pitch line due to excessive material removal. Gears produced at lower mould temperatures, on the other hand, exhibited better wear resistance for higher loads (3 Nm and 4 Nm), compared to those produced at higher mould temperatures, and were more likely to fail due to material flow. The results show a correlation between mould temperature, crystallinity, and gear performance. Based on wear rate responses of gears produced at differing mould temperatures to the application of varying torque loadings, a Mould Temperature to Torque Reference Chart for HDPE is presented.

Study on the Influence of Microinjection Molding Processing Parameters on Replication Quality of Polylactic Acid Microneedle Array Product

Biodegradable microneedles with a drug delivery channel have enormous potential for consumers, including use in chronic disease, vaccines, and beauty applications, due to being painless and scarless. This study designed a microinjection mold to fabricate a biodegradable polylactic acid (PLA) in-plane microneedle array product. In order to ensure that the microcavities could be well filled before production, the influences of the processing parameters on the filling fraction were investigated. The results indicated that the PLA microneedle can be filled under fast filling, higher melt temperature, higher mold temperature, and higher packing pressure, although the dimensions of the microcavities were much smaller than the base portion. We also observed that the side microcavities filled better than the central ones under certain processing parameters. However, this does not mean that the side microcavities filled better than the central ones. The central microcavity was filled when the side microcavities were not, under certain conditions in this study. The final filling fraction was determined by the combination of all parameters, according to the analysis of a 16 orthogonal latin hypercube sampling analysis. This analysis also showed the distribution in any two-parameter space as to whether the product was filled entirely or not. Finally, the microneedle array product was fabricated according to the investigation in this study.

A simple melt blending method for preparing PP/HMSPP foaming composites with superior surface appearance and mechanical performance

AbstractIncreasing mold temperature is effective to improve the surface quality of injection molding foamed products, but high mold temperature often leads to deteriorative cellular quality. Based on this, the polypropylene/high melt strength polypropylene (PP/HMSPP) composites with temperature insensitivity were prepared by a simple melt blending method, the rheological behavior and crystallization behavior of PP/HMSPP composites were studied by rotational rheometer and DSC at different cooling rates, respectively. In addition, foamed PP/HMSPP composites were prepared by chemical foaming injection molding, and their cellular quality, surface quality, and mechanical properties were analyzed. The results showed that when the content of HMSPP came to 50 wt%, the effect of the cooling rate on the rheological behavior of PP/HMSPP composites could be ignored. Furthermore, when the mold temperature increased from 60 to 120°C, the surface quality increased significantly, with the average cell diameter only increasing from 15.92 μm to 19.03 μm, and the cell density decreasing from 2.3 × 107 cells/cm3 to 1.9 × 107 cells/cm3. The tensile strength, bending strength, and impact strength were maintained at 24.15 MPa, 38.11 MPa, and 3.24 kJ/m2, respectively. This temperature‐insensitive PP/HMSPP composite foaming material can be used as guidance for the industrial stable production of PP injection molding chemical foaming. And this work suggested new thinking for future research on the modification of other polymer foam products at a high mold temperature.

Experimental investigations on thermo-stamping of carbon fiber reinforced polyamide 6 hat-shaped components with self-resistance electrical heating: Influence on microscopic and macroscopic properties from temperature related processing parameters

Thermo-stamping is a widely used forming process for automotive components made from fiber reinforced thermoplastic composites, but it still suffers from a variety of challenges such as long cycle time and high energy consumption. In this paper, self-resistance electrical (SRE) heating, an internal efficient heating method with the advantages of rapid heating speed and low energy consumption, was introduced into thermo-stamping for the rapid manufacturing of carbon fiber reinforced polyamide 6 (CFR-PA6) hat-shaped components. The impacts of the temperature related process parameters, preheating temperature (90 °C ∼ 220 °C) and mold temperature (20 °C ∼ 130 °C) on the shape accuracy, surface quality, microscopic morphology and mechanical properties of obtained hat-shaped components were investigated through experimental characterization. Besides, the energy-saving effect of SRE heating was also revealed compared with radiant heating, an external heating method. It is found that the defects such as fiber bundle cracks, matrix cracks and interface cracks caused by SRE heating are more serious than those caused by radiant heating, which is attributed to the effect of Joule heating, Lorentz force and dielectric breakdown. However, a high mold temperature can reduce these defects owing to the reconsolidation behavior of the hat-shaped component during the thermo-stamping process. The results show that the hat-shaped components possess a good formability and forming quality at a preheating temperature at 200 °C and mold temperature at 130 °C. Moreover, the total cycle time of thermo-stamping with SRE heating is less than 1 min and the energy consumption by SRE heating is about 9.86 % ∼12.09 % compared with radiant heating, which provides a more energy-efficient option for industrial production.

Strong and high void fraction PP/CNS nanocomposite foams fabricated by core‐back foam injection molding

AbstractPolypropylene/carbon nanostructure (PP/CNS) nanocomposite foams with a void fraction as high as 78% were successfully prepared by foam injection molding (FIM) with core‐back operation. Rheological curves and differential scanning calorimetry results showed that the added CNS significantly improved the melt strength and accelerated the crystallization process of PP, respectively. A high mold temperature was applied to overcome the adverse effect of CNS, which had a high thermal conductivity and went against the preparation of high void fraction (VF) products. Thus, adding CNS could dramatically increase cell density by three orders of magnitude. With a CNS loading of 5 wt%, the PP/CNS nanocomposite foam with a cell size of about 60 μm, cell density over 107 cells/cm3, and a void fraction of 78% was obtained. More interestingly, the specific flexural modulus of the PP/CNS composite foam with 50% void‐fraction was increased by 37% relative to the neat solid injection‐molded PP. PP/CNS composite foams with adjustable cell structure and good mechanical properties show great potential for electromagnetic interference (EMI) shielding and sensors applications.

Tool wear mechanisms and surface quality assessment during micro-milling of high entropy alloy FeCoNiCrAlx

High entropy alloys (HEA) are widely used in high-strength tools, high-temperature molds, and corrosion-resistant components. This work focused on tool wear and surface quality during micro-milling HEA FeCoNiCrAlx (x = 0.1, 0.5, 1) with different Al element content. Tool wear appeared more severe with the increase of Al element content. Tool wear patterns mainly included flank wear, adhesive material, micro-chipping, coating peeling, substrate tearing and edge fracture. The combined effects of adhesive wear, mechanical shock damage, abrasive wear, and oxidative wear were the primary reasons of tool wear mechanisms, while the diffusion wear was less noticeable. Moreover, the surface qualities including surface roughness, surface defects and edge burrs changed worse with the increase of Al element content and tool wear.

Fabrication of Microcellular Injection‐Molded Polypropylene with Super High Expansion Ratio by Precision Mold Opening Technology

AbstractIn this study, microcellular injection molding with the combination of the precision mold opening and rapid heat cycle mold technology is conducted to fabricate the 30% glass fiber reinforced polypropylene (PP/GF30) foam. By optimizing supercritical fluid, mold temperature, mold opening distance, and other process conditions, the injection‐molded PP/GF30 foam with a super high expansion ratio, density of 0.32 g cm−3, and porosity of 75%, is fabricated. The crystallization and rheological properties of the PP/GF30 samples are tested to determine the suitable injection molding parameters. The results show that glass fiber promotes the crystallization of polypropylene (PP) while improving its storage modulus and complex viscosity. The fiber distribution and orientation as well as the cellular structure are investigated by scanning electronic microscopy (SEM) and X‐ray computed tomography. Due to the high mold temperature, the shear effect and melt cavity filling are greatly changed. The oriented fibers in the core layer are randomly moved by the cell growth and presented as a scaffold to support the cell wall structure. The glass fiber increases the PP melt stiffness and avoids cell collapse so that the cellular structure with small cell size and even cell distribution is fabricated. The compression properties, surface roughness, and thermal conductivity are examined.