Molten Resin Research Articles

Resistance Welding of CF/PEI Composites by a Novel Implant of Flame-grown Carbon Nanotubes Grafted Carbon Fibers

Objective: Interface enhancement between resin and fiber has been a longstanding goal for manufacturing composite material. Using carbon nanomaterials in combination with macro-materials for composite materials is an important application of advanced manufacturing technology. Methods: This study examined the use of carbon nanotubes (CNTs) wrapped carbon fibers (CFs) (CFs@CNT), a cross-scale composite component incorporating CNTs and CFs, as an implant for resistance welding of composites containing carbon-fiber-reinforced polyetherimide (CF/PEI). Results: The correlation of growth time (tg) on growth morphology of CNTs on implant and strengths of joints were studied. The surface of CF was gradually covered by CNTs and finally completely wrapped, and CNTs appeared as multi-walled CNTs. The interface structure of resistance welded joints and their mechanical properties were evaluated. The PEI resin was sufficiently melted and obtained a perfect bonding joint with stronger mechanical properties when tg was 2min and 3min. The cracks were found at the edge of the bonding interface and a collapse first appeared in joint when tg was 4min and 5min, respectively. The defects were caused by the accumulation of amorphous carbon at the top of the CNTs. The strength of joint welded by CFs@CNT implant increased to 37.8MPa compared with the joint obtained by pure CFs implant alone only 24.2MPa when tg was 3min. Conclusion: The purpose of strengthening the joint was achieved by improving the wettability of PEI resin on CFs@CNT lead to the CFs was fully wrapped by molten resin during welding process.

Evaluation of thermal contact resistance of molten resin–mold interface during high-thermal-conductivity polyphenylene sulfide filling in injection molding

Evaluation of thermal contact resistance of molten resin–mold interface during high-thermal-conductivity polyphenylene sulfide filling in injection molding

Shape Deviation Network of an Injection-Molded Gear: Visualization of the Effect of Gate Position on Helix Deviation

The purpose of this study is to develop an evaluation method for assessing the relative relationship between gear tooth shape deviations on every gear tooth using network theory. Our previous study introduced a method for representing the phase difference between each helix deviation as a network, demonstrating that it is possible to identify the relative relationship between gear tooth deviations. However, there has been no in-depth analysis of the impact of injection molding on the gear’s phase difference network. In this paper, we begin by measuring the gear tooth shape deviation, calculating the correlation coefficient, and expressing it as an adjacency matrix. When the adjacency matrix was visualized and displayed as a pixel plot, a periodic pattern was formed. The relationship between the position of the gate used to inject molten resin material into the injection mold and the pixel plot were then investigated in detail, and it was confirmed that the helix deviation network of a gear manufactured with the injection molding process is useful as a new indicator for the manufacturing error of injection-molded plastic gear.

Molten resin flowing state identification, inner-mold thermal analysis, and final product quality determination in a complex thermal-regulated mold: Full-scale prototype establishment and validation

Complex system analysis is of great significance in the precision engineering of polymer processing. The compositions of thermal regulation units and multiple devices pose challenges for inner-mold analysis and increase investment in sensing technology in injection molding. This study proposes a mold–product thermally regulated integration (MPTI) methodology for the first time to establish a full-scale prototype and achieve accurate polymer flow, energy transfer, and product-forming state identification in injection molding. The numerical analysis results were compared with the experimental data and verified. The filling duration and pressure drop at the velocity/pressure switchover position were measured at injection velocities of 100–150 mm·s−1. The thermal effects of heat conduction at the inner surface of the mold and the viscous dissipation of the molten resin were experimentally validated by adjusting the hot-runner system and cooling unit. The accuracies of MPTI for the filling duration, pressure variation, and temperature detection were 7.7 %, 9.9 %, and 4.1 %, respectively. The final product deformations in MPTI were 7.8 % and 3.7 % smaller in the x and z directions, respectively. Our method merges polymer flow-state identification, energy transfer analysis, and product quality verification, with the potential for modeling complex thermal molds in manufacturing applications.

In situ flow state characterization of molten resin at the inner mold in injection molding

AbstractOnline viscosity information on processing lines can reflect the material flow resistance and offer valuable guidance for manufacturing across various industries. Considering the accuracy, devices, and processes involved in injection molding, characterizing the melt's flow state during material processing poses a significant challenge. To reduce investment in viscometers, avoid influencing the components' surface aesthetics due to the installation of sensors, and make the flow state detect online in mold, this study designs a rheometric mold with cylindrical runners for identifying the in situ viscosity of molten resin during injection molding. The detection conditions of injection speed and cavity pressure variations, the entrance effect, and the viscous dissipation for Polycarbonate are analyzed under various conditions. The in situ viscosity is identified and compared with the standard cross‐WLF model. The result shows that the melt velocity and cavity pressure variations during the filling process create a stable environment for in situ rheological characterization and the detected viscosity is related to the shear rate, melt temperature, and channel dimension in injection molding. The designed mold with cylindrical runners for determining the in situ thermal‐rheological behavior of polymer is distinguished successfully and exhibits prospects for the development of low‐cost, nondestructive, and inner‐mold measurement in manufacturing applications.

Comparative study of micro-sized Al particles enhancing the thermal joining of aluminum alloy-PA66 without or with reinforcement

The huge thermal difference between the aluminum alloy and polymer led to a low interface bonding strength, hindering the application of hybrid joints in the industries. Micro-sized aluminum (Al) particles were introduced into the polyamide 66 (PA66) resin substrates to improve the laser thermal joining of aluminum alloy to PA66 considering the heat conduction of metal particles. Results indicated the resin was physically reinforced after adding Al particles, enhancing the melting point and decomposition temperature due to the constraint on the polymer chain movement. The surface energy of PA66 resin was also increased because of the increase of polar functional groups, resulting in an enhancement of adhesion force between the aluminum alloy and resin. Furthermore, 3D thermally-conductive network formed between particles and resin substrates owing to the thermal vibration caused by Al electrons during the heat conduction, thereby strengthening the thermal conductivity of resin. This improved the thermal microscopic conductance at the interface, and the joining area at the interface dependent on the molten resin was thus enlarged. Finally, the tensile-shear force and strength of joints after adding Al particles were both significantly improved, reaching 1.35 times and 1.44 times of those without Al particles under the optimal heat input, respectively. This was achieved by a synergetic strengthening effect of enhanced adhesion force and joining area, providing a new method to obtain the high-quality joints.

Precise temperature calibration for visualized high-thermal-conductivity PPS in injection molding during filling process

High-thermal-conductivity polyphenylene sulfide (PPS) is expected to be used to manufacture various products because of its light weight, strength, high heat dissipation, and low CO2 emissions during manufacturing compared with aluminum die casting. However, this has a unique filling behavior owing to rapid cooling during the filling process, and is likely to cause hesitation and short shots, which must be suppressed. To address this issue, simulations are used to accurately predict the filling behavior and optimize the product shape. However, the thermal behavior of the molten resin in the mold is complex and not yet fully understood, which limits the accuracy of the simulation. In previous research, we built a thermal imaging visualization system to understand thermal behavior. We selected sapphire glass as the transparent material for infrared transmittance, strength, and thermal conductivity. The sapphire glass was made thicker to withstand the high injection pressure and thermal stress during molding of the high-thermal-conductivity PPS, which resulted in a large interference due to infrared attenuation and radiation inside the sapphire glass, affecting the temperature measurement results. In addition, changes in reflectance caused by changes in the state of contact between the sapphire glass and resin due to shrinkage of the resin in the mold also affected the temperature measurement. In this study, we propose a new temperature calibration method to convert the radiance distribution acquired using the visualization system into an appropriate temperature distribution. The developed system successfully visualizes the temperature of the filling process. The temperature measurement results were verified by comparing with the results from thermocouple temperature measurements.

The Effect of the Plasticization Process in Injection Molding on the Molten Resin State

In injection molding, the melt state of the resin after the plasticization process has a significant influence on the quality of the molded product. However, the plasticization process did not allow visualization of the conditions inside the heat barrel, making it difficult to accurately grasp the melt state of the resin. The purpose of this paper is to establish a method to evaluate the resin melt state during the plasticization process. For evaluation, the resin pressure in the nozzle and the data obtained during the plasticization process in injection molding were analyzed. The data were then compared with the values obtained from the flow analysis. As a result, the screw moving speed in the ideal resin melt state could be calculated from the pressure loss at the check ring, and the evaluation method was established.

Experimental Investigation and Numerical Simulation of a Self-Wiping Corotating Parallel Octa-Screw Extruder.

An octa-screw extruder (OSE) is equipment for pelletizing, blending, and mixing polymers and composites. In this study, the degree of resin filling, residence time distribution (RTD) of molten resin, and temperature profile in the octa-screw extruder were evaluated both experimentally and numerically. An intermeshing corotating parallel octa-screw kneading extruder was used for the experiments. For the comparison study, the results obtained from this extruder were compared with the twin-screw extruder. High-density polyethylene was selected as the material for extrusion. Meanwhile, a numerical code, based on a 2.5 D finite element method derived from the Hele–Shaw flow model, was developed to simulate the octa-screw extrusion process. The empirical outcomes suggest that octa-screw extrusion exhibited a narrower RTD of the molten resin compared with the twin-screw extrusion, suggesting better extrudate quality. The octa-screw extrusion also showed a lower temperature profile than twin-screw extrusion. The results of the simulation were also found to be in good agreement with experimental measurements. Experimental and numerical investigations of an OSE enable detailed comprehension and visualization of resin distribution in the entire length of the OSE, thus providing advantages in terms of process optimization.

Extraction of viscosity feature quantities using an in-mold sensor and evaluation of temperature dependence

Plastic is a material for which resource circulation should be strongly required, and the replacement of virgin materials with recycled materials is accelerating. Controlling the viscosity of molten resin is important during material changes in the injection molding process. In this study, the technology to extract the feature quantities that correlate with resin viscosity by using an in-mold sensor has been developed to expand the application of recycled materials. Several feature quantities were extracted from pressure sensor data. By evaluating the response of those features to changes in the temperature of the molten resin, the integral value of the pressure from the start of injection to the peak time was clarified to have the highest validity. It was confirmed that there was a positive correlation between the selected feature quantity and measured viscosity by a capillary rheometer, and that it represents differences in intrinsic viscosity between resins.

Controlled Degradation of Commercial Resin for Meltblown Nonwoven Fabric Sheet Production.

Manufacturing meltblown nonwoven fabrics requires special grades of resin with very low viscosity, which are not dealt with so much on market and cost quite high compared to the standard grades. We propose a high-shear rate processing method that can quickly and easily produce such low-viscosity resin from the commercial one without using organic peroxides. In this method, we apply high-shear stress to molten resin by using a high-shear extruder, which is a single screw extruder with high screw rotation speed, and the resin is thermally decomposed of its shear-induced heat which is quickly generated. We found that polypropylene with a value of melt flow rate over a thousand, which was required for the meltblown process, was produced from the standard grade with the high-shear extruder at the screw rotation speed of 3600 min and the barrel temperature over 300 C. Using the degradated polypropylene, a meltblown nonwoven fabric sheet was successfully fabricated. We also developed a numerical simulator of the high-shear extruder which can handle a wide range of the screw rotation speed and barrel temperature by the Nusselt number modulated with the operational conditions. The experimental values of the zero-shear viscosity and temperature at the exit of the extruder agreed well with the simulation results. Our high-shear rate processing method will enable us to quickly and easily produce various meltblown nonwoven fabric sheets at low costs.

Effects of a Twin-Screw Extruder Equipped with a Molten Resin Reservoir on the Mechanical Properties and Microstructure of Recycled Waste Plastic Polyethylene Pellet Moldings.

Each year, increasing amounts of plastic waste are generated, causing environmental pollution and resource loss. Recycling is a solution, but recycled plastics often have inferior mechanical properties to virgin plastics. However, studies have shown that holding polymers in the melt state before extrusion can restore the mechanical properties; thus, we propose a twin-screw extruder with a molten resin reservoir (MSR), a cavity between the screw zone and twin-screw extruder discharge, which retains molten polymer after mixing in the twin-screw zone, thus influencing the polymer properties. Re-extruded recycled polyethylene (RPE) pellets were produced, and the tensile properties and microstructure of virgin polyethylene (PE), unextruded RPE, and re-extruded RPE moldings prepared with and without the MSR were evaluated. Crucially, the elongation at break of the MSR-extruded RPE molding was seven times higher than that of the original RPE molding, and the Young’s modulus of the MSR-extruded RPE molding was comparable to that of the virgin PE molding. Both the MSR-extruded RPE and virgin PE moldings contained similar striped lamellae. Thus, MSR re-extrusion improved the mechanical performance of recycled polymers by optimizing the microstructure. The use of MSRs will facilitate the reuse of waste plastics as value-added materials having a wide range of industrial applications.

Development of Tensile Properties and Crystalline Conformation of Recycled Polypropylene by Re-Extrusion Using a Twin-Screw Extruder with an Additional Molten Resin Reservoir Unit

Plastic mechanical recycling is an attractive method for reducing the amounts of waste plastics. However, the alterations in the mechanical properties (degradation) in recycled plastics is a limitation to the material’s mechanical recycling. In this study, the mechanical recycling was enhanced by the addition of a “molten resin reservoir” unit at the end of the twin-screw extruder. Recycled polypropylene (RPP) obtained from a household was re-extruded with this developed extrusion unit. The tensile properties, type of crystalline, and conformation of polypropylene polymorphs were evaluated and compared for virgin polypropylene (VPP), recycled polypropylene (RPP) without extrusion (RPP-original), and RPP with extrusion by using a new type of extruder (RPP-extrusion). It could be found that the tensile properties of RPP-extrusion were improved, so as to be similar to those of VPP. In addition, the conformation of RPP-extrusion was similar to that of VPP by increasing the ratio between the helix and parallel band. This study succeeded in regenerating the tensile properties and inner structures in recycled PP, which could prolong the used lifetime and decrease the amount of waste from single-use plastic.

A study on the optimal mould design method for the prevention of weld-line by injection moulding CAE

ABSTRACT A weld-line is known as a representative defect in the field of plastic injection moulding, and also as a cause of inferior mechanical propensities and poor appearance. Heating and cooling mould systems, which cost extremely high, are a typical technology to prevent the weld-line. It is important to avoid weld-line defects easily and efficiently during the moulding process. Therefore, low cot design methods that enable to prevent weld-lines are demanded. A weld-line usually is generated at a meeting point of two or more flow fronts of molten resin in a mould, where the flow fronts are solidified and not fully contacted. The authors investigated the effect of the sub-gate which was designed to stir the meeting point and to suppress the weld-line using CAE. Since it is relatively easy to predict weld-line occurrence points by CAE, it is realistic to locate a sub-gate. This study intends to report on the following relevances: ‘Weld-line length and sub-gate geometrical conditions’, ‘Weld-line length and temperature conditions’ and ‘Occurrence trend of weld-lines and flow patterns’.

가정간편식 용기용 바이오매스 기반 발포구조체의 특성에 관한 연구

A series of foamed plastic sheets containing biomass (as HMR container) were developed via different foaming process temperatures, and their density, porosity, WVTR, and pore morphology were evaluated. Thermal stability of samples during re-heating the food in oven, change in morphology, density, porosity, and WVTR were investigated using a simulated thermal shock process according to MIL-STD-883E assay. As such, the pore size of samples was generally increased with increasing temperature of the foaming process. It can be explained that as foaming temperature increased, the viscosity of molten resins and the repulsive force against pore expansion decreased. In addition, an increase in the thermal shock cycle reduced the pore size and WVTR, while density increased because high temperature treatment that softened the sheet matrix was followed by a low temperature incubation, which contracted the matrix, thereby changing the physical and morphological properties of samples. However, an insignificant change in density was observed and WVTR tended to be decreased, indicating that as-prepared foamed plastic sheets could be used as a high thermal stable container for HMR application. Therefore, it found that the properties of newly developed HMR containers containing biomass were dependent on the foaming process temperature. Moreover, to better understanding of these newly developed containers, further investigations dealing with foaming process temperature based on various food items and cooking conditions are needed.

Braid-press forming for manufacturing thermoplastic CFRP tube

Braid-press forming was developed for manufacturing hollow tube parts made of carbon fiber reinforced thermoplastic (CFRTP) tape. The CFRTP tapes were braided to make a tube, which was consolidated under pressure and heat in the press forming process. Internal pressure was applied to the braided CFRTP tube by a silicone rubber rod inserted in the tube using axial compression. The reason for using a silicone rubber rod was to apply a high internal pressure until the molten resin solidified, which cannot be achieved in bladder molding and pultrusion, and to obtain good consolidation quality and high mechanical properties. As a result, up to 7 MPa press pressure was successfully applied and the tube made contained no voids and had good flexural properties. The study of the pressure showed that the higher press pressure (from 4.1 MPa) produced tubes with higher flexural properties. The estimation of wall thickness after press forming using the braiding architecture agreed with the measured value. Subjects to be addressed in future studies are productivity improvements and continuous tube manufacturing by the serial joining of braiding and press forming. It can be concluded that braid-press forming is a desirable method for the manufacturing of tubes for structural applications and can be used in future mass-production.

The Measurements of the Shear Stress Distribution at the Cavity Surface during Melt Filling in an Injection Mold

Measurement of shear stress distribution is important for examining phenomena occurring in the interface between the mold cavity surface and molten resin in injection molding. The authors developed a high precision measurement technique for shear stress distribution using a movable block and 3-component force transducer. In this study, we analyzed the influence of resins, cavity surface properties, and cavity thicknesses on shear stress distribution. The results are summarized below：

Enhancement of Injection Molding Consistency by Adjusting Velocity/Pressure Switching Time Based on Clamping Force

Abstract The velocity/pressure (V/P) switching time, the transition from the filling phase to the holding phase during the injection molding cycle, plays a crucial role in ensuring the quality of the injection molding. Improper settings can lead to a variety of defects, including oversize/undersize, excessive residual stress, flash, warpage, and the like. There are currently many V/P switching methods to choose from. For example, when the injection time or the screw position reaches a prescribed value, that is, when a specified percentage of the cavity is filled with the molten resin, the switching time can be started. These traditional V/P switching methods should work well using precision injection molding machines to ensure accurate and repeatable motion control. However, the quality of shot-to-shot injection molding still varies with environmental changes, such as varying mold/melt temperatures. In this study, we propose a V/P switching adjustment method involving part weight or maximum clamping force increments. It was found that the weight of the injection molded part was highly correlated with the maximum clamping force increment and the V/P switching time. Experimental verification by considering various settings such as V/P switching time, injection speed and holding pressure show that the adjustment method is a feasible means of assuring quality consistency.

Application of Network Analysis to Flow Systems with Alternating Wave Channels: Part A (Pressure Flows).

Wave-dispersion screws have been used industrially in many types of extrusion processes, injection molding, and blow molding. These high-performance screws are constructed by replacing the metering section of a conventional screw with a melt-conveying zone consisting of two or more parallel flow channels that oscillate periodically in-depth over multiple cycles. With the barrier flight between the screw channels being selectively undercut, the molten resin is strategically forced to flow across the secondary flight, assuring repeated cross-channel mixing of the polymer melt. Despite the industrial relevance, very few scientific studies have investigated the flow in wave-dispersion sections in detail. As a result, current screw designs are often based on traditional trial-and-error procedures rather than on the principles of extrusion theory. This study, which was split into two parts, was carried out to systematically address this issue. The research reported here (Part A) was designed to reduce the complexity of the problem, exclusively analyzing the pressure-induced flows of polymer melts in wave sections. Ignoring the influence of the screw rotation on the conveying characteristics of the wave section, the results could be clearly assigned to the governing type of flow mechanism, thereby providing a better understanding of the underlying physics. Experimental studies were performed on a novel extrusion die equipped with a dual wave-channel system with alternating channel depth profiles. A seminumerical modeling approach based on network theory is proposed that locally describes the downchannel and cross-channel flows along the wave channels and accurately predicts the pressure distributions in the flow domain. The solutions of our seminumerical approach were, moreover, compared to the results of three-dimensional non-Newtonian CFD simulations. The results of this study will be extended to real screw designs in Part B, which will include the influence of the screw rotation in the flow analysis.

In-mold and Machine Sensing and Feature Extraction for Optimized IC-tray Manufacturing.

Injection molding is a mature technology that has been used for decades; factors including processed raw materials, molds and machines, and the processing parameters can cause significant changes in product quality. Traditionally, researchers have attempted to improve injection molding quality by controlling screw position, injection and packing pressures, and mold and barrel temperatures. However, even when high precision control is applied, the geometry of the molded part tends to vary between different shots. Therefore, further research is needed to properly understand the factors affecting the melt in each cycle so that more effective control strategies can be implemented. In the past, injection molding was a “black box”, so when based on statistical experimental methods, computer-aided simulations or operator experience, the setting of ideal process parameters was often time consuming and limited. Using advanced sensing technology, the understanding of the injection molding process is transformed into a “grey box” that reveals the physical information about the flow behavior of the molten resin in the cavity. Using the process parameter setting data provided by the machine, this study developed a scientific method for optimal parameter adjustment, analyzing and interpreting the injection speed, injection pressure, cavity pressure, and the profile of the injection screw position. In addition, the main parameters for each phase are determined separately, including injection speed/pressure during the mold filling phase, velocity-to-pressure switching point, packing pressure and time. In this study, the IC tray was taken as an example. The experimental results show that the method can effectively reduce the warpage of the IC-tray from 0.67 mm to 0.20 mm. In addition, the parameters profiles obtained by parameter optimization can be applied for continuous mass production and process monitoring.