Melt Flow Direction Research Articles

Fabrication of electrically conductive microparts by constructing carbon black-rich network under high shear conditions in microinjection molding

Microinjection molding (μIM) is an important technique to fabricate microparts for applications in the fields of automotive and microelectromechanical systems. However, the prevailing high shear conditions in μIM are unfavorable for constructing intact electrically conductive networks because the added fillers tend to be preferentially aligned along the melt flow direction. In this work, a series of polypropylene/polyamide 6/carbon black (PP/PA6/CB) composites with a selective localization of CB in the PA6 phase were used as the model system to prepare electrically conductive microparts. The prevailing high shearing and extensional flow effects in μIM were utilized to deform CB-rich phase with an aim to in situ construct electrically conductive network, thereby improving the electrical conductivity (σ) of subsequent moldings. The results indicated that a higher σ was achieved for PP/PA6/CB microparts when compared with their PP/CB and PA6/CB counterparts, at a lower filler content (<10 wt%). The influence of blending sequence of various components (i.e., PP, PA6, and CB) and annealing treatment on the σ of microparts was also studied. This work provided an approach to the design and preparation of electrically conductive microparts that can be potentially used in high-tech sectors.

Heat transfer in β-Ga2O3 crystal grown through a skull melting method

Heat and mass transfer in β-gallium oxide crystals grown via a skull melting method were numerically studied. Specifically, we calculated the temperature and velocity distributions in a furnace for the skull melting method. The distributions covered the entire system: the growing crystal, melt, raw material, basket, and coils generating heat through the radio frequency electromagnetic field. We determined the dependences of temperature and melt flow velocity distributions on the coil position.The results indicate that the melt flow direction is opposite to that in the Czochralski method and that a descending flow exists near the periphery of the melt. The results also show that the maximum temperature of the melt, which affects the overheating conditions of the melt, depends on the position of the coil.

Microstructure Evolution during Cooling Slope Rheoprocessing of Novel Al-15Mg<sub>2</sub>Si-4.5Si Composite

In this study, microstructure evolution during cooling slope casting of Al-15Mg2Si-4.5Si composite is studied considering a test case of melt pouring temperature of 650°C. The shear force exerted by the flowing melt on the evolving primary Mg2Si and α-Al grains facilitates their fragmentation and subsequent spherodisation. After leaving cooling slope, the composite slurry is kept isothermally within a holding furnace for different time duration i.e., 8, 16, 24 and 32 minutes. Increasing trend in grain size values is observed with the increasing slurry holding time, whereas sphericity value decreases after initial increase till 8 minutes of slurry holding. The slurry samples are scooped from chosen locations of the slope as well as from isothermal slurry holding bath and rapidly quenched in oil to study their microstructure and mechanical properties. Simultaneous spherodisation of both the primary phases i.e., primary Mg2Si and α-Al during cooling slope processing is evident from optical microscopy and Scanning electron microscopy of quenched slurry samples. Whereas increasing sphericity of P-Mg2Si and α-Al phases, along the melt flow direction over the slope, is found to accompany with the increasing micro hardness values.

Hygromechanical Behavior of Polyamide 6.6: Experiments and Modeling.

This paper investigates water absorption in polyamide 6.6 and the resulting hygroscopic swelling and changes in mechanical properties. First, sorption and swelling experiments on specimens from injection molded plates are presented. The observed swelling behavior is dependent on the melt flow direction of the injection molding process. Additionally, thermal analysis and mechanical tensile tests were performed for different conditioning states. The water sorption is accompanied by a decrease in the glass transition temperature and a significant reduction in stiffness and strength. Next, a sequentially coupled modeling approach is presented. A nonlinear diffusion model is followed by mechanical simulations accounting for swelling and concentration-dependent properties. For the mechanical properties, the notion of a "gap" temperature caused by the shift of the glass transition range due to water-induced plasticization is employed. This model enables the computation of local moisture concentration fields and the resultant swelling and changes in stress-strain behavior.

The effect of microstructure on the tensile and impact behaviour of short-glass fibre-reinforced polyamide 6.6 as assessed by micro-computed tomography

Injection moulding of short-fibre-reinforced thermoplastics opens a new dimension in the field of mass production of complicated net-shaped parts with accurate dimensions and the new challenge is to produce parts with tailored properties. However, the layered structure frequently observed in these composites strongly affects their mechanical behaviour and constitutes the main difficulty in transferring the results of tests performed on standard specimens to actual components and parts. In addition, to use injection-moulded composite materials safely, their mechanical behaviour under different loading conditions must be well understood. In the present work, the effect of microstructure, in terms of fibre length and orientation, on the tensile and impact behaviour of injection-moulded short-glass fibre-reinforced polyamide 6.6 was investigated. Digital reconstruction of the three-dimensional structure of samples, differently oriented with respect to the melt flow path, was obtained by the high-spatial-resolution non-destructive technique of synchrotron radiation micro-computed tomography (micro-CT). Automatic evaluation of the fibre length distribution was developed by a global method based on the mean fibre length distribution, computed from the star length distribution (SLD). The results of uniaxial tensile tests and Izod impact experiments were successfully correlated with morphological analysis of fractured surfaces and the results of SLD. These studies revealed important changes in fibre orientation distribution when the sample orientation is changed with respect to melt flow direction, which also strongly influenced the composite mechanical response.

Effect of High Molecular Mass Tail in the Mol Mass Distribution of Polypropylene on Injection Molding

Abstract The effect of high molecular mass (MM) tail in the molecular mass distribution (MMD) of polypropylene (PP) on injection molding has been studied using injection molded tensile bars from a commercial PP resin and two samples of the above resin deprived of the high MM tail in different degrees by controlled degradation during extruder reaction with an added processing aid named Promax. The central portions of the tensile bars were studied by polarizing microscopy of microtomed sections parallel and perpendicular to the melt flow direction, and by density and birefringence profiles across the thickness of the bar. Mechanical properties and acoustic emission behavior in stretching of these injection molded tensile bars are also discussed. The experimental results show that by stripping off the high MM tail in the MMD the injection molded tensile bar has smaller degree of crystallization, less frozen orientation, improved uniformity across the thickness and the thickness of the skin part is greatly reduced. Better quality of the fabricated articles is to be expected by using Promax with PP for injection molding.

Three-dimensional characteristics of turbulent flow and heat transfer in Czochralski silicon melt with different cusp magnetic field configurations

Three-dimensional unsteady simulations are performed for the turbulent flow and heat transfer in a Czochralski silicon melt for 300 mm crystal growth. The influence of the horizontal symmetry plane in the cusp magnetic field on the melt flow, temperature field, and crystal/melt interface is systematically analyzed. The numerical results show that the melt velocity and its fluctuation near the interface decrease, while the temperature and its fluctuation increase gradually with the downward horizontal symmetry plane position. For each horizontal symmetry plane position, the oscillation frequencies of melt temperature and velocity consist of a basic frequency and its integer multiple frequencies. Thermal waves with a regular shape rotate on the melt-free surface, and the rotational direction is consistent with the crucible rotation. The interface shape is strongly associated with the heat transfer near the interface, which depends on the melt flow direction and velocity magnitude as well as the temperature gradient below the crystal. In addition, the oscillation of interface temperature is affected by the melt flow below the crystal, changing from high-frequency small fluctuation to low-frequency large fluctuation with the horizontal symmetry plane moving down.

Quasi Static and Fatigue Properties of Long Carbon Fiber Reinforced Polyamide

In this experimental work, the quasi static and fatigue properties of a 40 wt.% long carbon fiber reinforced partially aromatic polyamide (Grivory GCL-4H) were investigated. For this purpose, microstructural parameter variations in the form of different thicknesses and different removal directions from injection-molded plates were evaluated. Mechanical properties decreased by increasing misalignment away from the melt flow direction. By changing the specimen thickness, no change in the general fiber distribution pattern transversal and normal to the axis of melt flow was observed. It has shown that with increasing specimen thickness the quasi static properties along the melt flow direction decreased and vice versa resulting in superior properties normal to the melt flow axis. At around 5 mm, an intersection suggests quasi-isotropic behavior. In addition, the fatigue strength of the material was significantly higher in the flow direction than normal to the flow direction. No change in fatigue life was observed while changing specimen thickness. The Basquin equation seems to describe the effect of stress amplitude on the fatigue strength of this composite. Scanning electron microscopy was used to investigate fracture surfaces of tested specimens. Results show that mechanical properties and morphological structures depend highly on fiber orientation.

Effect of gas pressure on the microstructure of parts foamed with the novel microcellular injection molding technology Ku‐Fizz™

AbstractThe increasing demand for lightweight and economical automotive components boosts investigation of advanced materials and new lightweighting technologies. This work employs the novel microcellular injection molding technology Ku‐Fizz™. The process introduces gas with granulates at moderate low pressures into the feed zone of the injection molding machine. Ku‐Fizz is controlled by gas pressure; thus, a simple plate geometry was molded and the effect of various gas contents on the microstructure was analyzed. The material used was a chemically coupled glass fiber‐reinforced polypropylene compound. Optical microscopy was employed to measure the foam microstructure. Microcomputed tomography was used to quantify the fiber volume fraction and the orientation tensors. Results of the fully characterized microstructure showed cell density increasing and cell size decreasing with gas pressure and melt flow direction. Fiber length increased with gas content. Cell growth displaced fibers from the center of the part towards the mold surface, changing the fiber concentration and global fiber orientation.

Importance of Melt Flow Direction during Injection Molding on Polymer Heat Sinks' Cooling Efficiency.

Polymers with highly conductive fillers could possibly replace standardly used materials, such as aluminum and copper alloys, for passive cooling purposes. The main problem of the composite polymer-based heat sinks is that their high thermal conductivity is uneven. The orientation of this anisotropy is set according to the position of the highly thermally conductive filler. Its orientation is influenced by the melt flow during the polymer heat sink molding process. This article shows that change of the melt flow inside the mold cavity can improve the overall cooling efficiency of a polymer heat sink, which leads to lower temperatures on the heat source used. Two polymer heat sinks of identical geometries were produced. Their high thermal conductivity was given by the use of graphite flakes as the filler. The only difference between the heat sinks was in the position of the fan gate during their production. Different temperatures of the heat source between the two heat sinks were observed for the same measurement conditions. The measurements were conducted at Heatlab, BUT.

Effects of Heating and Cooling of Injection Mold Cavity Surface and Melt Flow Control on Properties of Carbon Fiber Reinforced Semi-Aromatic Polyamide Molded Products.

Fiber reinforced thermoplastics (FRTP), reinforced with glass or carbon fibers, are used to improve the mechanical strength of injection-molded products. However, FRTP has problems such as the formation of weld lines, the deterioration of appearance due to the exposure of fibers on the molded product surface, and the deterioration of the strength of molded products due to the fiber orientation in the molded products. We have designed and fabricated an injection mold capable of melt flow control and induction heating and cooling. This mold can both heat and cool the injection mold. It can also control the melt flow direction using a movable core pin. In this study, the above-mentioned mold was used for the molding of carbon fiber reinforced semi-aromatic polyamide. As a result, we found that increasing the heating temperature of the mold and increasing melt flow control volume contribute to the prevention of the generation of a weld line and the exposure of fibers on the molded product surface, as well as to the formation of a flat surface and increased bending strength. The relationships of these results with the carbon fiber orientation in the molded products and the crystallization of semi-aromatic polyamide were also examined in this study.

Melt flow regularity and hump formation process during laser deep penetration welding

In this study, the relationship between melt flow and hump formation was directly revealed during laser deep penetration welding of transparentmaterial. In partial-penetration welding, the melt flowed obliquely upwards along the bottom of the keyhole to the rear surface of the molten pool. And its flow rate increased first and then decreased with the increase of the welding speed. There was a one-to-one correspondence between the humps formed on the weld surface and the fluctuation of the inclination angle of the front keyhole wall (FKW) near the Brewster angle. The maximum eruption rate of the laser-induced vapor on the FKW exceeded 30 m/s. In full-penetration welding, the melt flow direction changed and humping was suppressed. The laser-induced vapor on the FKW surface can act on the rear keyhole wall, and this is the main reason for melt flow. When the inclination angle of the FKW is close to the Brewster angle, the amount of laser-induced evaporation on the FKW will increase to form a high speed jet of vapor which will drive melt flow in the molten pool behind the keyhole, and this is the main reason for hump formation on the rear surface of the molten pool.

Experimental investigation of quenching behavior of simulant material CaO-Fe2O3 under bottom flooding with the effect of melt volume

In a severe accident of a nuclear reactor, the termination and stabilization of the melt pool are necessary for the safety of the reactor. To address this issue, melt pool coolability plays a significant role in severe accident scenarios. In the context of this coolability measures, there are three major techniques i.e. top flooding, bottom flooding, and indirect cooling were used in the past and also in the present scenario to analyzed the actual phenomena occurred during a severe accident in a nuclear reactor with numerous simulant material of different composition and melt volume. This is because of extremely difficult to use the prototype material and conditions. Among the various strategy of melt coolability, it has been found that the melt coolability with the bottom flooding technique is very efficient to quench the material within a few minutes. In this regard, the present paper has involved the study of quenching phenomena of melt pool using bottom flooding at a small scale with a simulant material CaO-Fe2O3 at two different melt volume i.e. 1 l and 2 l. The simulant material is melted into an electric furnace at 1420 °C (~200 °C superheat) and poured into the test section where it has been quenched through water induction by a nozzle (12 mm) from the bottom side. Temperature history has been analyzed along the radial and axial direction of melt flow and further particle size and porosity of debris were measured. The size of debris was measured in the range of 0.4 to 40 mm although this debris was so fragile in nature. The average porosity was measured as 56% and the result was found in good agreement with literature.

The study of short‐shot water‐assisted injection molding of short glass fiber reinforced polypropylene

Abstractwater penetration length and fiber orientation (along the melt flow direction) are important indicators for water‐assisted injection molding products of the fiber‐reinforced polymer. The effects of melt short shot size, water injection delay time and water injection pressure on these two important indexes are analyzed theoretically and experimentally. The study found that with the increase of the melt short shot size, the extension of the water injection delay time and the increase of the water injection pressure, the water penetration length changed from 216 to 96 mm, 170 to 210 mm, and 215 to 180 mm, respectively. Therefore, it can be known that melt short shot size has the greatest influence on water penetration length, followed by water injection delay time, and finally water injection pressure. Meantime, due to the fiber orientation and change degree of water‐assisted injection‐molded products along the melt flow direction, the fiber orientation in the water channel layer along the melt flow direction has the highest and lowest change degree, followed by the wall layer and finally the core layer. It can be known that the melt short shot size has the greatest influence on the fiber orientation and the degree of change along the melt flow direction, followed by the water injection delay time, and finally the water injection pressure.

Numerical Simulation during Short-Shot Water-Assisted Injection Molding Based on the Overflow Cavity for Short-Glass Fiber-Reinforced Polypropylene

Compared with water penetration condition of short-shot water-assisted injection molding with or without overflow cavity, it can be known from theory and common knowledge that short-shot water-assisted injection molding with overflow cavity has many advantages, such as it can save materials and energy. Then, the effects of melt short shot size, water injection delay time, melt temperature and water injection pressure on the penetration of water after penetration, and the orientation distribution of short fibers during water-assisted injection molding of the overflow cavity short-shot method were studied. It is found that the melt short shot size had the greatest influence on it, followed by water injection pressure, water injection delay time, and finally, melt temperature. With the increase of the melt short shot size, the thickness of the residual wall of the whole main cavity becomes thinner, the orientation of short fiber along the melt flow direction becomes higher, and the degree of fiber orientation changes becomes lower. In the front half of the main cavity, with the decrease of water injection pressure, the delay time of water injection, and the melt temperature, in the front part of the main cavity, the residual wall thickness becomes thinner, the fiber orientation along the melt flow direction becomes lower, and the fiber orientation changes degree becomes higher; in the latter half of the main cavity, the influence of the water penetration and the orientation distribution of short fibers along the melt flow direction are not significant.

Joining of Contact Pins and Conductive Compounds via Injection Molding – Influence of the Flow Situation on the Electrical Contact Resistance

Abstract While a lot of research can be found in the field of bulk resistance of carbon filled polymers, comparatively few papers focus on contact resistance between compound and metal contacts. Due to that small number of researches that deal with contact resistances, studies of the influence of injection molding conditions and parameters on the contact resistance are also very rare. In contradiction to that, these influences on bulk resistance have been studied. The objective of this work was to investigate the electrical contact resistance of overmolded tinplated copper contacts after modifying flow situations and molding conditions by procedural and constructional methods in contact areas. Metal pins were overmolded with a polypropylene compound containing 45 vol.% graphite, utilising an insert injection molding process. To affect the flow situation at the contacts, several processing parameters, such as mold temperature and injection speed, were modified. In addition, the contact alignment related to melt flow direction was varied. Electrical properties were studied and related to macroscopic and microscopic connection properties and flow situations in contact regions. It was found that the contact resistance is a significant factor while examining electrical resistances of overmolded samples. Furthermore, it was shown that the various flow situations had an essential impact on contact resistances. Weld lines at the position of the contact caused a decreased contact resistance. The correlation of the weld line effect, the filler orientation and contact resistance were successfully investigated by μ-CT. Regarding processing parameters, it was observed that a high mold temperature of 120 °C increased not only bulk conductivity, but also had a positive impact on contact conductivity. Macroscopic and microscopic connection mechanisms of contact surfaces were interpreted and connected to the experimental observations.

Systematic Approach to Optimize Injection Molding and Microstructural Analysis of Fiber Reinforced Resins for Anisotropic Mechanical Characterization

Fiber reinforced resin materials are increasingly being used in aviation, automotive, mass transportation and healthcare industries. Engineers are keen to explore new design concepts with such materials, since these materials promises to offer high strength to weight ratio, elimination of secondary operations and ease in process ability to form complex shaped parts through injection molding. The mechanical properties of molded parts made from such materials depends on the orientation of the reinforcing fibers. Such orientation occurs in fiber-reinforced plastics, since the fibers in the plastic melt during processing, will orient in different directions under the influence of shear forces that are driven by flow pattern. This paper provides details on systematic and abusive injection molding of test specimens and characterizing anisotropic mechanical data that can be used for fiber orientation predictions in computer aided engineering programs. Systematic molding as compared to abusive molding, identifies optimum molding parameters that reduces part–to-part variation during injection molding, thereby reduces part rejections. It provides optimum part performance during application and the process settings are repeatable and reproducible. The intention of this paper is to share widely such a method to make this process less of a skill or art. The mechanical properties covered here are elastic, shear modulus and poisson ratio. Scanning electron microscopy (SEM) analysis revealed that most of the fibers are aligned in melt flow direction for systematic molded plaques, leading to higher stiffness and strength characteristics as compared to transverse to melt flow.

Effects of high-efficiency infrared heating on fiber compatibility and weldline tensile properties of injection-molded long-glass-fiber-reinforced polyamide-66 composites

AbstractGlass fiber composites are prevalent molded materials used in various fields, including aviation engineering, automobile manufacturing, and medical equipment production. The length of a glass fiber affects the mechanical properties of a glass fiber composite. Studies have reported that breakage occurs in long fibers subjected to screw plasticization, injection processes, and geometrical changes in injection molding. Moreover, multigate injection molding can result in weldlines on the final product, consequently reducing its strength. Further exploration is required to determine how product strength is affected by weldlines generated through injection molding with glass fiber composites and how product tensile properties associated with weldlines can be improved. Therefore, this study designed a mold with a vent area and a plug-in mold-surface-heating device to examine changes in the weldlines and tensile properties of long-glass-fiber composite specimens fabricated through injection molding using two melts. The results revealed that fiber length decreased with increasing screw speed; such declines in fiber length affected the tensile strength of the long-glass-fiber-reinforced polyamide-66 composites. In addition, because the arrangement and distribution of the glass fibers were affected by the melt flow rate, melt flow direction, and changes in mold cavity volume, the weldline tensile strength varied with the depth of the vent area. Mold surface heating improved the specimen surface roughness by 5.79% and effectively improved the interfacial adhesion between the fibers and melts, thereby resulting in more favorable weldline tensile strength. This also notably reduced the depth of weldlines produced by the adhesion of two melts.

Microstructure and tensile properties of injection molded thermoplastic polyurethane with different melt temperatures

ABSTRACTThe use of injection molding technology to prepare heterogeneous interlayer film of laminated glass holds strong applicable potential. This article aims to investigate the effects of melt temperature and melt flow on the microstructure evolution and tensile properties of thermoplastic polyurethane (TPU) specimens during the injection molding process. The tensile properties of the TPU specimens show dependency on the melt temperature and melt flow direction. The results of birefringence indicate that melt flow and lower melt temperature induce higher stretching deformation of the molecular chain network. Small‐angle X‐ray scattering analysis approves that besides the melt temperature and flow direction, the testing position on the cross section of the specimen has great influence on the microstructure of the TPU sheet. Further analysis and conclusions can be made using wide‐angle X‐ray scattering method. The above results demonstrate that both the tensile properties and microstructure of the injection molded TPU specimens tend to be isotropic with the increase of melt temperature. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48891.

Transformation mechanisms and governing orientation relationships through selective dissolution of Ni via liquid metal dealloying from (FeCo)xNi100−x precursors

Liquid metal dealloying (LMD) is a promising technique that can be used to synthesize non-noble porous materials by preventing oxidation through using a metallic melt. However, the phase transformation behavior between a parent grain and synthesized ligaments surrounded by penetrating liquid metal channels remains unknown, despite its importance on the final physical properties. In this study, the temperature effect on the transformation mechanisms during the LMD process is investigated. At a low temperature of 600 °C, a fcc grain of (FeCo)xNi100−x precursors transforms to bcc FeCo ligaments by following unique orientation relationships (ORs), which differ from the well-known ORs like Bain, Kurdjumov-Sachs and Nishiyama-Wassermann. A few select variants are generated in the proposed ORs, and the formation of coincident site lattice boundaries is shown to play a crucial role in the variant selection to reduce the internal energy of the initial nanostructure. However, at a higher temperature of 800 °C, the crystal orientation of ligaments prefers to align in the <111> direction, which is parallel to the flow direction of Mg melt, owing to a strong interaction between the melt and ligaments. Ligaments are elongated along with the fiber texture, and this transformation behavior is irrelevant to the parent orientation.