Rapid Heat Cycle Molding Research Articles

Development of a rapid heat cycle injection molding system using infrared radiation and convection heating and influence on morphology and mechanical properties

Conventional injection molding is widely used to produce plastic parts, mainly in the automotive industry, due to the high production ratios and quality of injection parts. Low mold temperatures are usually employed to decrease cycle molding time and final process costs; however, resulting surface defects include weld lines, sink marks, and warpage. Therefore, plastic parts are often subjected to secondary processes to reduce the surface defects. A dynamic mold heating and cooling control technology, rapid heat cycle molding (RHCM), was employed to optimize the injection molding process. The present study combined convection heating (pressurized water flow) and external infrared heating systems to investigate the effect of dynamic temperature control on the injection molding process. The infrared heating system was custom built to allow studying under controlled conditions the influence of several process parameters on the resulting morphology and mechanical properties. Results show significant gains from using the RHCM technology to optimize the conventional process, namely, at 100 °C no frozen layer is formed while simultaneously increasing the Young’s modulus. Industrial companies struggling with defects resulting from the thermal changes during injection molding can thus consider RHCM as a mitigation strategy and use these results as a guide for tool design and implementation of the technique.

The potential of RHCM technology in injection molding using a simple convention heating and cooling system

In conventional injection molding, low mold temperatures are used; however, the thermal conditions, which vary during the processing, affect the properties of the injection molded parts and the injection molding process parameters. Due to the rapid cooling of the molten polymer against the mold wall, the flow resistance of the molten polymer increases, and the hydraulic injection pressure is directly affected by this. The rapid cooling of the plastic parts affects the quality of the parts, which can result in surface defects.Using the rapid heat cycle molding (RHCM) approach, a simple convection heating and cooling system was added to a conventional injection molding process to study the potential of RHCM technology. We assessed the influence of the mold temperature on the part's morphological features (namely, the frozen layer) and mechanical properties (namely, the Young's modulus), as well as the hydraulic injection pressure.Using RHCM to heat the molding surface up to 100 °C was found to entirely prevent the formation of a frozen layer, with an expected positive effect on the previously mentioned defects. Note that while the decrease of the frozen layer could have been expected to reduce Young's modulus, this did not happen, which is a very positive outcome related to the specific orientation at which the frozen layer is formed and its morphology. The higher the mold surface temperature, the lower the hydraulic injection pressure, which means less strict structural requirements for the mold. These results highlight the potential of RHCM technology in injection molding, namely as a strategy to mitigate or solve molding defects.

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

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

CNT 면상발열체 적용을 위한 다층 구조 사출 금형의 급속가열 성능에 관한 연구

As a heating method for RHCM (Rapid Heating Cycle Molding) various heating technologies such as high frequency induction heating, IR heating, gas heating, and high temperature steamare applied, but these methods are not satisfying high productivity due to low energy efficiency. Research has been actively conducted on RHCM based on planar heating elements with high heating efficiency, such as carbon nanotubes, which are applied. To apply the CNT web film to the RHCM, a heating element must be applied inside the injection mold and power must be applied. As electricity is directly applied to the CNT web film to generate heat, all mold parts in contact with the CNT web film must be insulated, and high heat transfer is required for rapid heating performance. Thus, in this study, a multi-layer structure mold module for insulation and high heat transfer was designed to enable rapid heating by applying a CNT web film as a heat source. To this end, we intend to present a research direction for the commercialization of rapid heating molds, by identifying the main variables of rapid heating through heating experiments by the mold metal and insulator materials, and reflecting them in the mold design.

Design, manufacturing and FEA prediction of the mechanical behavior of a hybrid-molded polycarbonate / continuous carbon fiber reinforced composite component

In this paper, we report a study regarding the design, manufacturing and finite element analysis (FEA) prediction of the mechanical behavior of a thermoplastic matrix/carbon fiber reinforced composite (CFRC) component. The CFRC component is constituted by a continuous carbon fiber laminate impregnated with a polycarbonate (PC) matrix, with edge and ribs overmolded with unfilled PC. The component has been manufactured by the one-step process (composite hybrid molding), with the use of rapid heat cycle molding (RHCM) to improve the surface quality. The flexural behavior has been predicted by an integrated FEA model approach, which considers the mechanical response of the composite laminate and the structural contribution of the overmolded ribs. As a result, a significant reduction of the surface roughness (Ra value decreases from 0.43 to 0.06 μm) was obtained thanks to the use of RHCM process. Moreover, the developed FEA model was able to predict the flexural behavior of the CFRC component with high accuracy (FEA maximum load 1.6% higher than the experimental value).

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

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

Optimization of process parameters in rapid heat cycle molding using heater system

Plastic injection molding (PIM) is a manufacturing technology to plastic products. In PIM, weldline that affects the strength and surface quality of products, and it is then important to determine the optimal process parameters for the weldline reduction. Rapid heat cycle molding (RHCM) is an attracted PIM technology for weldline reduction that by heating up the mold temperature, the melt plastic is smoothly flowed into the die cavity and consequently the weldline is well reduced. In RHCM, since various heating systems are adopted but which have problem that long cycle time. In this paper, to quickly heat up the mold temperature, a heater system is newly introduced and the process parameters in the RHCM using heater system are optimized. A multi-objective optimization for minimizing both weldline and cycle time is considered, and the ratio of mold temperature to injection time is maximized for the weldline reduction, whereas the cycle time is minimized for high productivity. Sequential approximate optimization that the response surface is repeatedly constructed and optimized is adopted for the design optimization, and the pareto-frontier is identified. Based on the numerical result, the experiment is also conducted to examine the validity of the proposed RHCM.

Regional temperature control in ceramic injection moulding: An approach based on cooling rate optimisation

The injection moulding of ceramic components with uneven wall thickness presents challenges due to differential cooling rates developing in the injected parts, which cause premature solidification of the feedstock at thin features and lead to detrimental defects, worsening in components from green to sintered states. To cope with this, suitable mould thermal control approaches have to be selected and validated, as current control methods are based on the achievement of a uniform cavity surface temperature, which is not tailored to such complex geometries. In this work, a novel thermal control system is proposed, based on regional mould temperatures, implemented with the use of Peltier modules, which locally and independently heat and cool different cavity features according to their thickness. The regional temperature profiles are optimised over time with the use of a coupled Finite Element - Particle Swarm Optimisation (FE-PSO), to achieve uniform cooling rates throughout the moulded components. The performance of this approach is compared to both constant ambient mould temperature and Rapid Heat Cycle Moulding (RHCM) techniques, which instead aim at achieving uniform temperatures throughout the mould cavity surface. Results show that the novel proposed method, based on regional temperature control and uniform cooling rates, promotes the simultaneous solidification of features with a 10-times difference in surface-to-volume ratio. Due to this, in terms of components quality, the novel method brings the advantages of higher dimensional control and reduction of differential shrinkage compared to the other analysed approaches, thus increasing the capability to use injection moulding to manufacture ceramic components characterised by non-uniform wall thickness.

Warpage Prediction of RHCM Crystalline Parts Based on Multi-Layers.

Warpage is a typical defect for injection-molded parts, especially for crystalline parts molded by rapid heat cycle molding (RHCM). In this paper, a prediction method is proposed for predicting the warpage of crystalline parts molded by the RHCM process. Multi-layer models were established to predict warpage with the same thicknesses as the skin-core structures in the molded parts. Warpages were defined as the deformations calculated by the multi-layer models. The deformations were solved using the classical laminated plate theory by Abaqus. A model was introduced to describe the elastic modulus with the influence of temperature and crystallinity. The simulation process was divided into two procedures, before ejection and after ejection. Thermal stresses and thermal strains were simulated, respectively, in the procedure before ejection and after ejection. The prediction results were compared with the experimental results, which showed that the average errors between predicted warpage and average experimental warpage are, respectively, 7.0%, 3.5%, and 4.4% in conventional injection molding (CIM), in RHCM under a 60 °C heating mold (RHCM60), and in RHCM under a 90 °C heating mold (RHCM90).

Crystallization and Mechanical Properties of Glass Fiber Reinforced Polypropylene Composites Molded by Rapid Heat Cycle Molding

The crystalline behavior and mechanical properties of PP/GF (glass fibers) composites molded by rapid heat cycle molding (RHCM) and conventional injection molding (CIM) were compared. SEM, DSC and XRD were utilized to study crystallization behavior of PP and PP/GF composites. Furthermore, universal testing machine was employed to investigate the mechanical properties. Results proved that higher degree of crystallinity and larger crystal size can be obtained in RHCM in comparison to CIM. GF can induce more crystal nuclei and then reduce the crystal size due to shear stress which is generated in polymer matrix around fibers. Nucleating agent (NA) has a positive effect on refine grains. The average crystal diameter of PP/NA/30 %GF is about 1.7 µm which is one-tenth of PP/30 %GF (14 µm) in RHCM. XRD tests illustrated that α-form crystal is the main crystal type for PP and PP/GF composites in RHCM and CIM. However, there is a little β-form crystal in RHCM for PP/GF composites without NA. NA accelerates the formation of α-form crystal and restrains the emergence of β-form crystal. The plastic parts obtained in RHCM exhibited higher strength and modulus compared with that obtained in CIM for both tensile and flexural tests.

Rapid heating injection moulding: An experimental surface temperature study

Rapid heat cycle moulding (RHCM) is a recent set of injection technologies that allow a full temperature control in a mould.Between all technologies available in terms of heating and cooling, electrical resistance heating and water cooling were chosen for this study.The mould design has a capital importance in terms of process efficiency. Thermal and mechanical key points must be addressed together. Temperature distribution in moulding cavity and quality part run together.Before mould machining, a full mechanical, thermal and rheological simulation was carried out. Due to transient thermal complexity, thermal simulation was validated using infrared thermography on a dummy tool fitted with both heating and cooling devices.All this previous work is usual for each new tool. When a new process is suggested for new part requirements, it is necessary to understand injection physical bases in order to prevent unexpected failures. This work introduces the mould temperature curve to realize how RHCM works, and compare its results with conventional moulding.The influence of cavity temperature map was studied with a cavity pressure and temperature sensor helped with near infrared thermography. At the same time, the relationship with parameters which control both heating and cooling periods was considering.Simulation and experimental results are compared, and RHCM process highlights could be well understood to improve future new injection parts development.

Numerical study on the influence of RHCM on the basic parameters of filling the cavity

Injection molding is a very popular processing technology of polymeric materials. In the conventional injection molding, the low constant temperature of the mold is used for efficient heat removal. However, low mold temperature is not feasible for thin-walled and micro-featured parts. For these kinds of parts the RHCM (rapid heat cycle molding) technologies were developed, where the temperature of the mold is increased to above transition temperature of the polymer before the filling phase starts.In this paper, the influence of processing parameters and part thickness on maximum flow length was investigated with numerical simulations for thin-walled geometry manufactured with RHCM technology. Obtained results showed strongly nonlinear relations between maximum flow length, part thickness, and volumetric flow rate, whereas the relation between flow length, injection pressure, and cavity surface temperature was linear. Surprisingly, the cavity surface temperature had the smallest influence on maximum flow length, which may result from the velocity flow rate high enough to prevent the part from excessive solidification befor the maximum injection pressure is reached.

Microstructure, Tensile Property, and Surface Quality of Glass Fiber-Reinforced Polypropylene Parts Molded by Rapid Heat Cycle Molding

The microstructure of a molded product considerably influences its macroscopic properties. In this study, the influence of molding process on microstructure, tensile property, and surface quality was explored on the glass fiber-reinforced polypropylene (GFRPP) parts molded by rapid heat cycle molding (RHCM) and conversion injection molding (CIM). Tensile strength and surface gloss were chosen to measure macroscopic properties of the molded parts. The microstructure including multilayer, fiber orientation, crystallinity, and fiber-matrix bonding strength were analyzed by simulations, scanning electron microscopy, wide-angle X-ray diffraction, and dynamic mechanical analysis. The relationship between the macroscopic properties and microstructure of the RHCM samples was also discussed. The results indicate that as the mold cavity surface temperature increases, the tensile strength increases firstly and decreases thereafter. The tensile strength of RHCM parts reached the maximum at the mold heating temperature of 60°C. It is also observed that the surface gloss of the sample increases as the mold cavity surface temperature rises, and the increase of surface gloss decreases distinctly with the mold heating temperature higher than 90°C.

Process Parameters Optimization in Rapid Heating Cycle Molding

Process Parameters Optimization in Rapid Heating Cycle Molding

A quantitative evaluation of the appearance quality of weld lines in RHCM parts

The appearance quality of plastic parts in weld lines can be improved significantly through the rapid heating cycle molding (RHCM) process. However, there is no evaluation method for measuring the appearance quality of weld lines to determine whether they are in a good or bad condition. In this study, RHCM parts were molded with electric heating and the total color difference dE of the Commission Internationale de l’Eclairage (CIE) Lab system was employed as the quantitative evaluation method for the appearance quality of weld line. The dE of weld lines under different heating temperature conditions was analyzed. The results indicate that the mold heating temperature significantly influences the appearance quality of weld lines and the CIE Lab system accurately assesses the appearance quality of weld lines. Moreover, the experimental results further demonstrate that the lightness difference ΔL has a significant influence on the dE of weld lines in plastic parts, whereas the color differences Δa and Δb have only a slight influence.

Molecular Mechanism Research into the Replication Capability of Nanostructures Based on Rapid Heat Cycle Molding

Aimed at the molding of polymer nanostructure parts, the interface model between long- and short-chain polycarbonates (PC) and nickel mold inserts was established by the molecular dynamics method. The molecular mechanism of the replication capability of polymer nanostructure part molding was discussed by analyzing the migration and diffusion of the molecular chain, concentration profile, filling morphology evolution, interface binding energy, and filling rate of conventional injection molding (CIM) and rapid heat cycle molding (RHCM). The results show that nanostructures are filled mainly during the packing stage. A short-chain PC system has a low glass transition temperature (Tg) and viscosity, good fluidity, and a high filling rate, so the replication capability of its nanostructures is good. A long-chain PC system has a fast cooling rate in CIM, its molecular chain motion is blocked, the filling rate is low, and the interface binding energy is small, and so its nanostructures have poor replication capability. However, the high temperature at the nanostructures can be maintained for a long time in RHCM, which promotes Brownian motion in the molecular chains. Under the action of packing pressure, molecular chains can overcome entanglement barriers and viscous resistance. Thus, the polymer concentration profile and filling rate increase with increasing packing pressure, which can produce more van der Waals energy. Furthermore, the evolution process of polymer filling morphology is realized by the Brownian motion of chain segments under packing pressure; that is, the diffusion motion of the molecular chain along the direction of a tube composed of other chains around it. With the increase of temperature or pressure, the migration and diffusion of the molecular chain can be promoted; thus, the replication capability of nanostructure parts for mold cavities can be enhanced.

Optimization of mold temperature profile and process parameters for weld line reduction and short cycle time in rapid heat cycle molding

Weld line reduction is one of the major concerns in plastic injection molding (PIM) that results in high surface appearance and high strength of a plastic product. To resolve this issue, rapid heat cycle molding (RHCM) has attracted attention as an innovative PIM technology. In the RHCM, the mold temperature profile plays a crucial role in weld line reduction. On the other hand, high productivity as well as high surface appearance is also required in the PIM, and the trade-off between them will be observed. To achieve weld line reduction and high productivity simultaneously, it is important to adjust both the mold temperature profile and other process parameters in RHCM. A trial and error method is so widely used to adjust them, but it is much time-consuming task. In this paper, the mold temperature profile and several process parameters are optimized for the weld line reduction and the short cycle time. Therefore, multi-objective design optimization is performed. Numerical simulation in PIM is so intensive that a sequential approximate optimization using radial basis function is adopted to identify the Pareto frontier with a small number of simulations. The trade-off between the weld line reduction and the cycle time is clarified through the numerical result. Based on the numerical result, the experiment using a PIM machine (GL100, Sodick) is carried out. It has been confirmed through the numerical and experimental result that the proposed approach in RHCM is valid for the weld line reduction and the short cycle time.

On the effect of mould temperature on the orientation and packing of particles in ceramic injection moulding

Particle packing and orientation in Ceramic Injection Moulding are caused by shear rate variations along the part, which are complicated by cooling rates and depend on material properties and process parameters. This work studies particle orientation and packing for a ceramic feedstock in relation to mould temperature, with a focus on the influence from Rapid Heat Cycle Moulding (RHCM). A sample part consisting of bars having different thicknesses (0.4 mm to 6 mm) was injection moulded using first ambient mould temperature and then a rapid heating approach; subsequently, green part microstructure was analysed to detect particle orientation and packing. Results show a more uniform orientation at thick sections using RHCM, with a 15% enlargement of a core layer characterised by randomly oriented particles, as well as a higher homogeneity of powder packing between thin and thick sections. Thus, this study demonstrates that not only can RHCM be used to enhance feature replication capability, but also has the potential to improve critical microstructural properties of green components, which highly influence sintered parts quality.

금속 열순환 성형에서 수지의 점도와 윤활유가 유리 섬유 강화 고분자의 기계적 물성과 표면에 미치는 영향

Conventional injection molding (CIM) and rapid heat cycle molding (RHCM) methods are used to prepare ABS and (acrylonitrile-butadiene-styrene)/glass fiber copolymer (ABS/GF) plastic parts. Pentaerythritol stearate (PETS) and silicon particles are chosen as lubricants. Effect of resin viscosity and lubricants on properties of plastic parts was investigated. The results show that resin viscosity has some effect on surface quality of plastic parts in CIM process but no effect in RHCM process. ABS/GF plastic parts molded in RHCM process exhibit higher tensile, higher flexural strength and lower impact strength. Silicon is more effective in RHCM process than in CIM process.

Modeling and characterization of crystallization during rapid heat cycle molding

Rapid heat cycle molding (RHCM) is an injection molding process that has been developed in recent years. Recent studies of RHCM have mainly focused on heating technologies and process optimization. Few studies have examined the evolution of crystallization behavior. In this study, a novel method is proposed to determine the crystallization evolution information of polymers during the RHCM process. The influence of temperature and shear rate on crystallization was considered. The non-isothermal crystallization process was first divided into a series of isothermal processes. Next, mathematical model parameters were obtained through isothermal crystallization experiments, and then the crystallization information during the RHCM process could be determined. Finally, for comparison, the degrees of crystallinity for the final product in different positions were measured using wide-angle X-ray diffraction (WAXD). Experimental results showed that the proposed method is both accurate and effective. It is also simple and has broad application prospects in characterizing crystallization information during the molding process.