Increasing Mold Temperature Research Articles

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.

Surface Treatments' Influence on the Interfacial Bonding between Glass Fibre Reinforced Elium® Composite and Polybutylene Terephthalate.

This study examines the process of using injection moulding to join two different materials to manufacture bi-component moulded products with improved performance characteristics. The two-component process, which combines the advantages of two different technologies-the high efficiency of the injection moulding process and the excellent mechanical properties of long glass fibre composites produced by resin transfer moulding (RTM) technology-offers a particular advantage and improved applicability of the prepared lightweight products in both the automotive and aerospace sectors. The composite studied here consists of Elium® thermoplastic resin (30%) reinforced with unwoven glass fibre fabric (70%) using the RTM process. The Elium® composite sample is consequently used as an insert overmoulded with polybutylene terephthalate (PBT) homopolymer reinforced with 20% w/w of short glass fibre through injection moulding. The influence of different mould temperatures and surface treatments on the adhesion between the materials used is investigated by evaluating the mechanical performance using tensile shear strength tests. It was found that while an increase in mould temperature from 40 °C to 120 °C resulted in a doubling of the initial average bond strength between untreated Elium® RTM inserts and overmoulded PBT parts (0.9 MPa), sandblasting the inserts ensured a further tripling of the bond strength of the composites to a value of 5.4 MPa.

Study on Rheological Squeeze Casting Process of Ultra-high Strength Al-11Zn-1.8Mg-0.9Cu-0.15Zr-0.15Sc Alloy

7xxx series Al alloys with excellent mechanical properties are widely applied in aerospace, automotive, and defense industries. However, the casting performance of the alloy is relatively poor, and defects such as shrinkage porosity and thermal cracking are easy to occur during the solidification process. In this study, Al-11Zn-1.8Mg-0.9Cu-0.15Zr-0.15Sc alloy with excellent casting and strength performance developed by our research group, was studied by combining numerical simulation with experimental research. The simulation results show that hot joints appear in the thick wall of the wheel parts as the melt temperature increases. The increase of mold temperature and the decrease of squeeze pressure lead to the increase of the existence time of hot joints, which will aggravate the shrinkage and micro-segregation of castings. The experimental results show that electromagnetic stirring melt treatment can significantly improve melt uniformity, refine grain, and a wheel-shaped part with high performance can be obtained when the melt temperature, the mold temperature, the squeeze pressure are chosen as 660 °C, 200 °C, 50MPa, respectively.

Injection Flow Rate Threshold Preventing Atypical In-Cavity Pressure during Low-Pressure Powder Injection Molding

Controlling injection parameters is paramount when it comes to producing high-quality green parts using powder injection molding. This work combines experimental and numerical approaches to study the impact of injection parameters on mold in-cavity pressure and on the overall quality of green parts produced by low-pressure powder injection molding. The properties of two low-viscosity feedstocks (formulated from a water-atomized stainless-steel powder and wax-based binder system) were measured and implemented in an Autodesk Moldflow numerical model to quantify the molding pressures, which were finally validated using experimental real-scale injections. The results confirmed that an increase in mold temperature, an increase in feedstock temperature, and a decrease in solid loading decrease the mold in-cavity pressure, which was correlated with the feedstock viscosity. As a key result, real-scale injections confirmed that a minimum flow rate was required to avoid atypical high in-cavity pressure leading to several visual defects such as weld lines, flow marks, cracks, sinks, and incomplete filling. Due to differences in its thermal transfer properties, this flow rate threshold value decreases as the feedstock solid loading increases. For injection speeds higher than this value, the injection pressure measured experimentally was linearly correlated with the injection flow rate.

Investigating the impact of manufacturing conditions on crack growth rate in nitrile butadiene rubber for enhanced service life – Part 01

Extended service life of components is playing an increasingly important role in society and economy. Accordingly, this also applies to elastomeric materials, which are used for example for tires, seals, and hoses. These are often exposed to cyclic loading, with crack initiation and growth playing a decisive role. Corresponding phenomena have been investigated for many years and are still not fully understood. For the fatigue behavior, the crosslinking state of the material is of particular importance. This is accompanied by various production parameters, such as processing temperature and curing time, which have been of little importance in research to date. For this reason, plain strain test specimens out of nitrile butadiene rubber (NBR) were produced by injection molding at different mold temperatures and crosslinking times in the present work. With the aid of these, the crack growth rate at different crosslinking states under cyclic loading was investigated. It has been shown that a longer crosslinking time toward fully cured specimens results in a 20% reduction in dissipated energy, with a corresponding increase of the crack growth rate by the factor of 100. Furthermore, a 20 K increase in mold temperature during manufacturing of fully cured specimens leads to a four times slower crack growth.

Enhancing the Fatigue Strength of the Weld Line in Advanced Polymer Injection Molding: Gas-Assisted Mold Temperature Control for Thermoplastic Polyurethane (TPU) Composites.

This study presents an innovative approach to enhancing weld line strength in advanced polymer injection molding through applying gas-assisted mold temperature control, significantly increasing mold temperature beyond typical values observed in conventional processes. We investigate the effects of various heating times and frequencies on the fatigue strength of Polypropylene (PP) samples and the tensile strength of Acrylonitrile Butadiene Styrene (ABS) composite samples at different Thermoplastic Polyurethane (TPU) percentages and heating times. Using gas-assisted mold heating, mold temperatures exceeding 210 °C are achieved, which represents a significant advancement compared to the standard mold temperatures of less than 100 °C. As a result, the fatigue strength of the PP sample with mold heating at 15 s shows a remarkable increase of up to 5.4 times at 5 Hz compared to the sample without mold temperature control. Moreover, ABS/TPU blends with 15 wt.% TPU exhibit the highest ultimate tensile strength (UTS) value of 36.8 MPa, while blends with 30 wt.% TPU have the lowest UTS value of 21.3 MPa. This advancement demonstrates the potential for improved welding line bonding and fatigue strength in manufacturing. Our findings reveal that increasing the mold temperature before injection results in higher fatigue strength in the weld line, with the TPU percentage having a more significant influence on the mechanical properties of ABS/TPU blends than heating time. The results of this study contribute to a deeper understanding of advanced polymer injection molding and offer valuable insights for process optimization.

Characterisation of Polypropylene Composite Reinforced with Chemi-Thermomechanical Pulp from Oil Palm Trunk via Injection Moulding Process.

As the products made from wood-plastic composites (WPCs) become more sophisticated and required more detail profiles, the injection moulding processing method with wood pulp as the reinforcing material is the answer to cater to the rapid change and demands of composite products. The general objective of this study was to study the effects of the material formulation, as well as the injection moulding process parameters, on the properties of a polypropylene composite reinforced with chemi-thermomechanical pulp from oil palm trunks (PP/OPTP composite) via the injection moulding process. The PP/OPTP composite with a material formulation of 70% pulp/26% PP/4% Exxelor PO produced using injection moulding at 80 °C as the mould temperature and with 50 tonnes of injection pressure exhibited the highest physical and mechanical properties. The increment loading of pulp increased the water absorption capacity of the composite. Higher loading of the coupling agent effectively reduced the water absorption capacity and increased the flexural strength of the composite. The increase in mould temperature from unheated to 80 °C prevented excessive heat loss of the flowing material, which enabled the molten material to flow better and filled up all cavities in the mould. The increased injection pressure slightly improved the physical properties of the composite, but the effect on the mechanical properties was insignificant. For the future development of WPCs, further studies should be focused on the viscosity behaviour, as a greater understanding of the processing parameters' effects on the PP/OPTP's viscosity behaviour will lead to improved product design and enable great potential usage of WPCs.

Effect of molding history on molecular orientation relaxation during physical aging of polystyrene injection moldings

Abstract This work examined the effect of changing molding conditions on the physical aging of polystyrene injection moldings. First, we investigated the relationship between the molecular orientation and the molding conditions. The molecular orientation near the surface changed with changing injection rate, so we hypothesized that this molecular orientation might form during the filling stage. Because this molecular orientation did not relax under heat treatment below the glass transition temperature (T g), the oriented molecules near the surface were thought to be elongated owing to the high strain rate during the filling stage. On the other hand, the molecular orientation in the core layer changed with changing holding pressure and relaxed under heat treatment below T g. Thus, the molecules in the core layer might become oriented during the holding stage and not be elongated owing to the slow strain rate. Furthermore, the molecular orientation in the core layer decreased with increasing mold temperature, and the physical heat resistance improved with increasing mold temperature. Meanwhile, the excess enthalpy did not change with changing molding conditions. Therefore, the improvement in physical heat resistance with increasing mold temperature was likely caused by the decrease in the molecular orientation in the core layer. Analyzing the relaxation behavior of the molecular orientation suggested that increasing mold temperature reduced the number of oriented molecules with large deformation in the core layer.

Shrinkage and Warpage Mechanism of Overflow Water-Assisted Injection Molding Short Fiber-Reinforced Polymers

Experimental study on the shrinkage of short fiber-reinforced polymer injection molding products during the overflow water-assisted injection molding (OWAIM) process, and and analysis of the influence of process parameters with the computer-aided engineering (CAE) were performed. The investigation shows that the shrinkage of the product increases linearly along the melt flow with the increase of water injection pressure. The shrinkage of products is on the rise with the increase of water injection pressure, melt temperature, and mold temperature, but it is decreasing with the increase of flow delay time and fiber mass content. Based on the Taguchi orthogonal array design, an experiment study was conducted to characterize the effect of processing parameters on the shrinkage of OWAIM pipe. The results show that decreasing the mold temperature and increasing the fiber mass content can effectively reduce the shrinkage and warpage of products, thus improving the product quality.

Effect of Zn content on hot tearing susceptibility of LPSO enhanced Mg–Znx–Y2–Zr0.06 alloys with different initial mold temperatures

The critical temperature (Thci) corresponding to the load relaxation measured during the solidification of alloy in a ‘T′-shaped mold is introduced into the Clyne-Davies’ model, so that it can be used to predict the hot tearing susceptibility (HTS) of alloy under non-equilibrium cooling. Then, the improved model is applied to study the HTS of Mg–Znx–Y2–Zr0.06 (x = 0.5, 1 and 1.5 at%) alloys under two initial mold temperatures, i.e., two cooling rates. It is found that HTS is very sensitive to both Zn content and initial mold temperature, and the increase in Zn content or initial mold temperature can reduce HTS of the alloy. However, their micro mechanisms are different. The reason for the decrease in HTS with the increase in Zn content is the decrease in the dendrite coherency temperature. Specifically, the ratio of unconstrained feeding stage to intergranular feeding stage increases, and the intergranular liquid phase with eutectic composition increases in the later stage of solidification. The HTS decreases with the increase in the initial mold temperature because the solidification shrinkage stress is relieved. Consequently, the residual liquid phase between the grains can be fed in a more timely manner.

Effect of surface curing temperature on depth-specific physical properties of poly(urethane-isocyanurate) foam panels in relation with local chemical composition and morphology

Processing low density poly(urethane-isocyanurate) (PIR) rigid foam boards still remains challenging, especially for high thickness panels with the spontaneous formation of two-dimensional wrinkles. Increasing the double-belt conveyor temperature (mold temperature in this work) was regarded as a way to increase the rigidity of the foam base material and, ultimately to increase the stiffness of the PIR foam under the facing. For that purpose, PIR foam samples simulating real panels were prepared at different mold temperatures and were chemically analyzed using ATR-FTIR spectroscopy while a Shore durometer (type OO) was used to estimate the foam rigidity in various locations of the model panel. Obviously, the isocyanurate content of the foam under the facing was found to increase with the increase in mold temperature but surprisingly the Shore hardness demonstrated the reverse effect. This result was explained by the decrease in the density of the foam layer under the facing as the mold temperature increases, thereby counteracting the probable increase in stiffness of the foam base material itself. In addition, foam characterizations at different depths (rise direction) indicate that the chemical and mechanical gradients occurring in the first 20–30 mm tend to disappear as the mold temperature increases.

Preparation of CCF/PEEK filaments together with property evaluation for additive manufacturing

Additive manufacturing technology has been increasingly applied to fabricate continuous fiber reinforced thermoplastic composites for its potential in fabricating complex structures. Owing to the limited thermal and mechanical properties of the matrix, it is a critical trend to develop high-performance thermoplastics to widen engineering applications. This study aims to comprehensively investigate the properties of the prepared CCF/PEEK filaments together with their printed composites. The filaments were fabricated via a thermo-mechanical coupling process and were characterized by micromorphology observation, thermal and mechanical test. It was found that the impregnation behavior, thermal stability and mechanical performance of the filaments were improved with the increase of mold temperature and decrease of traction speed. The performance of printed specimens was evaluated by mechanical test and fracture analysis. It was concluded that the additive manufacturing process promoted the secondary impregnation behavior of the filaments. Higher nozzle temperature and bed temperature together with lower layer thickness and printing speed enhanced the tensile strength of printed specimens with maximum value reached 509.56 MPa. Besides, the analysis of failure mechanism indicated that filament fracture, horizontal cracks and filament pullout together with fiber breakage, fiber pullout, unimpregnated fibers and pores were the dominant failure modes for all printed specimens.

Prediction of morphology development within micro–injection molding samples

The understanding of the mechanisms that determines mechanical performances during micro-injection molding is crucial to meet the increasing demand for advanced plastic products with improved durability and performance. These depend on the morphology developed during the process, which, on its turn, is determined by the complex thermomechanical history experienced by polymer chains. Thus, the ability to correctly predict morphology opens the possibility to forecast final part properties. Semi-crystalline polymers parts show a morphology mainly composed of spherulites in the core and fibrils close to the sample walls. In this work, a commercial software for injection molding simulation was adopted for describing the thermomechanical history experienced by polymer chains during micro–injection molding tests, whereas a crystallization model was introduced for the description of the two morphologies mentioned above. The molecular stretch parameter was adopted as the main variable for describing the effect of flow on the molecular arrangement. A threshold mechanism based on the molecular stretch was also introduced in the crystallization model for controlling the growth of fibrillar morphologies. Different micro-injection molding tests were conducted in an end-less cavity with the aim of testing the capability of the model in predicting the morphology developed along the sample thickness. The proposed model was able to predict the formation of fibrils in the regions close to the sample wall, furthermore, the reduction of fibrillar layer thickness with the mold temperature increase was consistently described.

Application of Selective Induction Heating for Improvement of Mechanical Properties of Elastic Hinges.

Injection molding is a polymer processing technology used for manufacturing parts with elastic hinges. Elastic hinges are widely used in FMCG (Fast Moving Consumer Goods) packaging (e.g., bottle closures of shampoos, sauces) and in the electrical engineering industry. Elastic hinge is a thin film that connect two regions of the injection molded part, where significant shear rates are present, which can lead to the degradation of polymers and the decrease in mechanical properties. Selective induction heating is the method that improves the flow of the polymer melt through thin regions by the local increase in mold temperature. In this study, selective induction heating was used to improve mechanical properties of elastic hinges by the reduction of material degradation due to high shear rates. To verify the change of shear rates, selective induction heating simulation and injection molding simulations were performed. The linear relation between mold temperature and maximum shear rate in the cross-section was identified and the mechanical tests showed significant differences in hinge stiffness, tensile strength and elongation at break.

Electromagnetic-thermal coupling behaviors and thermal convection during two-phase zone continuous casting high strength aluminum alloy tube

In this paper, the two-phase zone continuous casting (TZCC) technique was used to prepare 2D12 aluminum alloy tubes and a 3D model of TZCC was established to investigate the electromagnetic-thermal coupling as well as fluid flow behaviors under different mold temperatures. The calculated temperature in the induction heated mold agrees well with the measurement. It was found that the heat flux from the mold to the melt leads to a convex isoliquid fraction line of dendrite coherency point and circular thermal convection in front of the mushy zone. The velocity of the transverse flow increases remarkably with increasing mold temperature while the upward flow velocities at the outer wall are nearly constant. Experimental results indicate that the surface exudations with segregated solute appear at the surface of tubes when the mold temperature is higher than 883 K, and their size and quantity increase with increasing mold temperature. The serious solute redistribution and the thermal convection lead to solute segregation at the surface of tubes. Further, the residual liquid with segregated solutes flows to the surface of the tube and forms the surface exudation due to its lower freezing point than the Al matrix.

Investigation on Microstructures and Mechanical Properties of Isotactic Polypropylene Parts Fabricated by Different Process Conditions with Different Aging Periods.

Polymeric parts have been increasingly used in various engineering fields. The performance of polymeric parts is significantly affected by working-environment-induced aging. In this paper, an ultrasonic-vibration-assisted injection molding system was designed and utilized to fabricate polymeric parts from isotactic polypropylene (iPP) using different processing conditions. The natural aging experiments were performed to age the fabricated iPP parts for one year. The effects of key process parameters as well as ultrasound power on the microstructures and the mechanical properties of the iPP parts after aging were systematically investigated using X-ray diffraction analysis, Fourier transform infrared analysis, scanning electron microscope imaging, and tensile testing. It is found that both the microstructures and the tensile strength of the iPP parts deteriorate with the increasing aging time. In addition, the crystallinity and the tensile strength decrease with the increasing melt temperature but increase with the increasing mold temperature in a given range and holding pressure. The increase in ultrasound power leads to an increase in crystallinity. However, when the ultrasound power is over 200 W, the tensile strength of the aged iPP parts decreases, which indicates that high ultrasound power may not form optimal condensed microstructures with excellent anti-aging capacity.

Effects of process parameters on semi-solid squeeze casting performance of aluminum alloy scrolls for scroll compressors

The aluminum alloy scroll is one of the key parts of the scroll compressors widely used in the air-conditioning, refrigeration, and heat pump systems. In this work, the semi-solid squeeze casting (SSSC) process was used to fabricate the aluminum alloy scroll. The effects of process parameters including the pouring temperature, mold temperature, and squeezing velocity on the filling and solidification behaviors of the alloys were investigated through simulations based on the power law cut-off (PLCO) material model. Results show that there is a significant increase in the flow velocity of the slurry, and the area of the high-speed region enlarges with the increase of the pouring temperature. The homogeneity of the temperature and velocity fields in the slurry is improved with an increase in mold temperature. Both the filling time and its variation rate decrease with an increase in squeezing velocity. The maximum solidification time exhibits a linear variation with the increase in pouring temperature. The shrinkage area is decreased by increasing the mold temperature. The optimal process parameters of the SSSC process were obtained from simulation analysis, which are the pouring temperature of 595 °C, mold temperature of 350 °C, and squeezing velocity of 0.3 m·s−1. Moreover, the qualified scroll casting was fabricated using the SSSC process under the optimal process parameters.

Effect of Injection Molding Conditions on Crystalline Structure and Electrical Resistivity of PP/MWCNT Nanocomposites.

Polypropylene (PP) / multi-walled carbon nanotube (MWCNT) nanocomposites were prepared by melt-mixing and used to manufacture samples by injection molding. The effect of processing conditions on the crystallinity and electrical resistivity was studied. Accordingly, samples were produced varying the mold temperature and injection rate, and the DC electrical resistivity was measured. The morphology of MWCNT clusters was studied by optical and electron microscopy, while X-ray diffraction was used to study the role of the crystalline structure of PP. As a result, an anisotropic electrical behavior induced by the process was observed, which is further influenced by the injection molding processing condition. It was demonstrated that a reduction of electrical resistivity can be obtained by increasing mold temperature and injection rate, which was associated to the formation of the γ-phase and the related inter-cluster morphology of the MWCNT conductive network.

Evaluation of different strengthening methods in the mechanical and functional properties of soy protein-based bioplastics

The bioplastics manufactured are still not competitive compared to conventional plastics, due to their higher price and poor mechanical properties. For this purpose, different physical strengthening methods have been studied to evaluate the reinforcement of soy protein-based bioplastics: mold temperature increase (from 70 °C to 130 °C), as the application of a dehydrothermal (4 and 24 h at 50 °C) or ultrasound (for 5 and 45 min at 20 kHz) treatment. In this sense, the crosslinking degree, the mechanical properties, water uptake measurements and scanning electron micrographs of the different bioplastics were compared. The results conclude that suitable processing conditions and post-treatments could favor some characteristics of bioplastics (such as maximum stress (∼5 times) or strain at break (∼3 times)), although worsening others (such as water uptake capacity (∼50%)). Specifically, thermal treatments improved the mechanical properties of the structures obtained, whereas the ultrasound treatment leads to the formation of a structure with smaller pores.

Fabrication of highly filled wood plastic composite pallets with extrusion‐compression molding technique

AbstractThe aim of this study was to fabricate highly filled wood plastic composite pallets with extrusion‐compression molding technique and investigate the effects of processing parameters on mechanical performance and production stability. The composites were blended in twin‐screw extruder and subsequently measured by weight with an electronic scale. Before compression, it was divided into pieces and rearranged in the cavities of compression mould according to the mass distribution. The effects of compression pressure and mould temperature on flexure strength, density, water absorption, and dimensional deviation were investigated. The results show that both the flexure strength and density of the pallets increased with compression pressure and remained higher than that of extruded deck when compression pressure exceeded 6.5 MPa. Water absorption and dimensional deviation decreased with compression pressure and remained lower than that of extruded deck after the compression pressure exceeded 6.0 MPa. Compression pressure could increase the final passed yield by improving the composite melt filling state and lowering the buckling deformation, but further increase above 6.7 MPa would result in a decline in final passed yield. Increase in mould temperature contributed to the production stability but an excessive value would extend the molding cycle. The insights gained from this study may be of assistance in optimizing extrusion‐compression processing parameters and expanding the application of highly filled wood plastic composites in complicated and irregular products.