Assisted Injection Moulding Research Articles

Water Penetration Stability in Water Assisted Injection Molded Symmetric Ribs

AbstractWater assisted injection molding technology has received extensive attention in recent years, due to its light weight, relatively lower resin cost per part, faster cycle time, and its flexibility in the design and manufacture of plastic parts. However, there are still some unsolved problems that confound the overall success of this technology. Unstable water penetration in molded symmetric channels is one of them. This report was to study the water penetration behavior in the water assisted injection molded symmetric cavity. Experiments were carried out on an 80-ton injection-molding machine equipped with a water injection unit. A plate cavity with symmetric water channels was used. The materials used were amorphous polystyrene and semi-crystalline polypropylene. Various processing variables were studied in terms of their influence on the water penetration behavior inside the symmetric parts: melt temperature, mold temperature, melt fill speed and fill pressure, short-shot size, water temperature and water pressure, and water injection delay time and water hold time. The effect of channel layout was also investigated. Tapered channels were found to mold parts with better penetration stability than flat channels. In addition, the penetration behaviors of water and gas in molded symmetric parts were also compared. The experimental results suggested that water penetration stability is more stable than that of gas in molded symmetric parts.

Gas Assisted Injection Molding of an Industrial Part: 3D Simulation Provides Virtual Molding Trials

Abstract Techniques developed for three-dimensional simulation of gas assisted injection molding of thermoplastics are here extended to a complex industrial application, a car door handle, providing uniquely detailed insights into the molding process. Handling of the three stages of the process – plastic filling, and primary and secondary gas penetration – is described in terms of the boundary and initial conditions applied. Predictions for plastic filling patterns are compared successfully with molding results, and provide detailed forewarning of potential problems due to weld surfaces and air-traps. Particular emphasis is placed on accurate modeling of secondary gas penetration, which is also validated against practical results. A further novel feature is the export of an STL model of the gas core, providing a CAD model of the finished molding for subsequent in-service analysis.

An approximation to the PTT viscoelastic model for gas assisted injection moulding simulation

An approximation to the Phan-Thien Tanner (PTT) constitutive model is developed with the aim of giving low-cost simulation of Gas Assisted Injection Moulding (GAIM) while incorporating important viscoelastic characteristics. It is shown that the developed model gives a response typical of full viscoelastic models in transient and steady-state uniaxial and constant shear rate deformations. The model is incorporated into a 3D finite element GAIM simulation which uses the ‘pseudo-concentration’ method to predict residual polymer, and applied to published experimental results for a Boger fluid and a shear-thinning polystyrene melt.It is shown that the simulation gives a very good match to published results for the Boger fluid which show increasing Residual Wall Thickness (RWT) with increasing Deborah number. Against the shear-thinning polymer, the quality of match depends upon which of two ‘plausible’ relaxation times is chosen; qualitatively different results arise from two different means of estimating a single relaxation time. A ‘multi-mode’ approach is developed to avoid this uncertainty. It is shown that the multi-mode approach gives decreasing RWT with increasing Deborah number in agreement with the published experimental results, and avoids the issues that arise from estimating a single relaxation time for a molten polymer.

Macroscopic and mesoscopic simulation of viscoelastic free surface flow in gas‐assisted injection moulding process

AbstractIn this work, an improved simple coupled level‐set and volume of fluid (S‐CLSVOF) method is proposed to trace the moving interfaces in gas assisted injection moulding (GAIM) process based on the viscoelastic FENE‐P model. Firstly, the Kreisselmeier‐Steinhauser (KS) function constructed by means of Boolean operations is adopted as the shape level set (LS) function to precisely represent the complex mould cavities. Then, the benchmark problem of two‐dimensional deformation is used to verify the ability of the S‐CLSVOF method for capturing the moving interfaces. The stress birefringence is calculated and compared with the experiment result. Finally, the proposed method is further applied to the mould filling and gas penetration processes in GAIM. The macroscopic bubble appearance, temperature distribution, and the behaviour of the mesoscopic molecular orientation are shown and analyzed in detail. Due to the complexity of the gas‐liquid interaction, the phenomenon of asymmetrical gas flow is clearly observed in the gas penetration process. The influences of the macroscopic parameters on the macroscopic gas flows and mesoscopic molecular orientation are also discussed, such as insert positions, melt temperatures, and gas delay time. The numerical results illustrate that the coupled method can be applied to the multiscale numerical simulation of viscoelastic flows with complex free surfaces and provide significant guidance for the GAIM process.

Geometric Replication Integrity of Micro Features Fabricated Using Variotherm Assisted Micro Injection Moulding

The geometric surface integrity of micro patterns is critical for functionality of polymeric micro devices, e.g. replication accuracy for micro channels and individual lens for the element of a compound eye lens. Micro injection moulding has been used widely for mass production of these devices. However, achieving high replication integrity is a critical challenge. In the present work, we developed a variotherm assisted micro injection moulding process to replicate a micro droplet and ellipse feature arrays in order to study the deformation behaviour of sickled blood cells. The effects of warm circuit temperature and cold circuit temperature on replication integrity, including filling depth, profile and morphology, were characterized based on moulding process monitoring, measurement and imaging. We have found that the warm circuit temperature is critical for feature filling due to its influence on the polymer-mould interface temperature, and that too high a warm circuit temperature can cause significant adhesion of polymer to a micro cavity. The cold circuit temperature controls shrinkage of polymer melts and the mould, and subsequently influences demoulding. Both temperatures need to be optimized to achieve the best replication of micro features.

Three‐dimensional simulations of non‐isothermal flow for gas penetration in complex cavity during gas assisted injection moulding process

AbstractIn this paper an R‐function is employed to construct the shape level set (LS) function for representing the complex mould cavity in a gas‐assisted injection moulding (GAIM) process. With the shape LS function, the continuity, momentum, and energy equations can be extended for solving the gas‐liquid two‐phase flows using the finite volume and immersed boundary methods. Firstly, an improved simple coupled level set and volume of fluid (S‐CLSVOF) method is proposed to track the moving interfaces of gas‐liquid interface and polymer melt front. Then the benchmark problems of the two‐ and three‐dimensional deformation tests are carried out to verify the ability of the improved S‐CLSVOF method. At last, the gas penetration processes are simulated in two different complex mould cavities. The numerical results show that the improved S‐CLSVOF method has higher accuracy than the S‐CLSVOF method, and the coupled numerical framework can successfully depict the asymmetry phenomenon of gas flow, racetracking, and fountain phenomena, which has great significance in determining processing conditions and designing mould cavities.

Water Assisted Injection Molding for Single and Multi-branched Tubular Components

To produce hollow polymeric parts with complex geometries the Fluid Assisted Injection (FAI) technology is currently used. In this technology water and gas can be employed with or without the aid of a projectile. The process consists in the injection of water at high pressures, after the closing of the mold and polymer injection, and up to the filling of the whole molding zone. The injection of water at high pressures will force the polymer from the core to be expelled to a reservoir. This material expulsion is possible, not only thanks to the high water pressures, but also because the polymer is still in a viscous state, thus facilitating the evacuation. Even though the FAI technology is by direct injection of water/gas or with aid of a projectile, there is a common limitation, which is the inability to produce hollowed parts with forking channels. However, even if creating these branches is possible, there is the impossibility of them being geometrically complex and/or extensive. In these cases, the branches are created with inserts inside the mold, meaning that they will always be limited by a molding insert, and not controlled by the water jet. For cases where it is desired to add complex and/or extensive ramifications, subsequent steps of production and assembling must be added, influencing the overall production time. This work aims, therefore, at studying a new approach for the production of hollow parts with extensive branched channels and complex geometries within a single injection cycle, and thus eliminating subsequent processes that are currently required. The first approach is the application of several water injectors, guided towards the respective branches where hollow sections are intended to be produced. This innovation will have an impact on the serial production of high complexity tubular type parts, reducing the production time with the elimination of subsequent processes. Furthermore, a saving of raw materials is achieved by eliminating the necessity of a creation of additional molds. In this work, a detailed experimental study of the water assisted injection process was done to serve as a knowledge base to the concept of the new process named Multi-Path.H2O.

Reduction of Injection Moulded Plastic Part Warpage Using Advanced Gas Assisted Injection Moulding

Dimensional and shape accuracy are the basic quality criteria of almost every injection moulded plastic part, manufactured in the engineering industry. They are dependent on many production conditions as part and moulding tool design, material structure properties and injection parameters. Generally, it is very difficult to achieve high geometrical accuracy during injection moulding, therefore, dimensional tolerances for plastic parts are usually many times larger than in the case of metals. However, according to requirements of the engineering industry, demands for the plastic parts dimensional accuracy keep growing permanently, what also extends to the growing shape complexity of the produced parts. Due to this tendency, engineers must look for more and more advanced solutions to meet market requirements and keep the competitiveness of their product. In consonance with all this, this paper presents a case study where the progressive gas assisted injection moulding is used as a solution for the plastic part warpage reduction while any other conventional methods failed. The study is performed making use of part from the automotive industry, initially produced with unacceptable deformations. In the first step, the real manufacturing state was studied to determine the warp behaviour. Subsequently, the process parameters and cooling conditions were unsuccessfully modified while trying to reduce deformations. Nevertheless, these were effectively eliminated by the only application of internal gas support to the melt injection phase. A numerical modelling based on Finite Volume and Finite Element Method was also used in the case study in order to mathematically represent the fluid, thermal and mechanical processes during the process of injection moulding.

Mechanical Benefits of Gas Assisted Injection Moulding Application in Design of Structural Parts

Due to of many advantages and specific properties plastics are gradually becoming the most widely used materials in the engineering industry. In the last years, more and more metal parts are converted to plastic, in the cases of mechanically loaded parts as well. However, the usage of plastic is limited by its mechanical properties and production possibilities. Conventional injection moulding as the most productive plastic part production technology mostly enables the manufacturing of thin-wall parts with uniform wall thickness, what restricts full-fledged utilization of plastics. In this study, the benefits of progressive gas assisted injection moulding is investigated in order to produce plastic parts with higher mechanical properties. The paper presents complex study with respect to structures generated in material during gas penetration state, orientation of reinforced short fibres, stress relaxation behaviour, notch effect of rough gas channel surface, producible cross-section profiles with high moment of inertia and undesirable production effects, which can occur during gas aided moulding technologies. Finally, the mechanical properties of specimen produced by conventional and gas-assisted injection moulding were compared using numerical analyses. For comparison, integration of two numerical solver - FVM for fluid analysis of plastic/gas injection and FEM for structural analysis of specimen strength/stiffness were used.

Characterization Methods of Nano-Patterned Surfaces Generated by Induction Heating Assisted Injection Molding

An induction heating-assisted injection molding (IHAIM) process developed by the authors is used to replicate surfaces containing random nano-patterns. The injection molding setup is developed so that an induction heating system rapidly heats the cavity wall at rates of up to 10°C/s. In order to enable the optimization of the IHAIM process for nano-pattern replication, it is necessary to develop robust methods for quantitative characterization of the replicated nano-patterns. For this purpose, three different approaches for quantitative characterization of random nano-patterns are applied and compared. Results show that the use of IHAIM is an efficient way to improve replication quality. All three measurement methods are capable of detecting the trend of the replication quality of the surface changing the process condition.

Representation and Analysis of Polymer Flowing Velocity Distribution Based on Physical Visualized Technology in Ultrasonic Assisted Injection Molding

Representation and Analysis of Polymer Flowing Velocity Distribution Based on Physical Visualized Technology in Ultrasonic Assisted Injection Molding

Characteristics analysis and mold design for ultrasonic-assisted injection molding

Abstract This study investigated the use of ultrasonic technology in assisted injection molding (AIM) and mold design. An ultrasonic device installed in a mold was employed to vibrate a melt, thereby converting kinetic energy into thermal energy. This method enabled maintaining the desired temperature in the melt flow, preventing a high level of shear and the formation of a thick frozen layer surrounding the skin layer; thus, the injection molding efficiency was enhanced and the residual stress inside the injection-molded component was reduced. In this study, a flat sample (75 mm×47 mm×1 mm) of an ultrasonic-assisted injection mold was developed. An ultrasonic oscillation device 45 mm in diameter was placed in the center of the cavity and used to vibrate a polycarbonate melt at a frequency of 20 KHz. In addition, cavity pressure sensors were positioned at the front and rear of the vibration region to analyze the melt flow behavior under ultrasonic-AIM (UAIM) conditions. The results showed that ultrasonic oscillations can reduce the amount of melt pressure lost through the cavity. The pressure loss of the flat sample used in UAIM was approximately 29% lower than that of the sample used in conventional injection molding (CIM; nonultrasonic-assisted injection); the power of UAIM did not yield substantial effects. Direct ultrasonic oscillations destroyed the melt flow and thermal stresses, therefore, the region exhibited a low stress distribution. Compared with using CIM, using UAIM reduced the average residual stress by 27%. Ultrasonic oscillation affected the surface roughness during melt solidification. When the ultrasonic power was <70%, no substantial increase in surface roughness was observed; however, when the ultrasonic power >70%, the surface roughness was 10 times higher compared with that observed using CIM.

Recent Advances on Fluid Assisted Injection Molding Technique

Fluid assisted injection molding (FAIM) technique greatly improves the quality of the molded plastic articles through the introduction of pressurized fluid. The FAIM has two main realizations: the gas assisted injection molding (GAIM) and the water assisted injection molding (WAIM). The characteristics and practical applications of GAIM and WAIM are discussed in detail in this article. Besides that, several optimization techniques of GAIM and WAIM are also briefly introduced, including cooling gas assisted method, vibrated gas-assist molding method, plastic expulsion process (PEP) method, external gas assisted method, and WAIM-GAIM method. For each method, the article quotes one or several patents to illustrate its features. Finally, the future development of the FAIM technique is also discussed.

Gas-assisted compression moulding of recycled GMT: Effect of gas injection parameters

Gas assisted compression moulding (or GasComp) is a novel process based on the injection of nitrogen gas during a conventional compression moulding cycle, a technique originally introduced in the injection moulding industry.The gas is injected into the molten material at a preset gas inlet point, hollowing out the part and thus assisting the compressive force of the press in generating material flow. This paper presents gas injection parameter studies on polypropylene based recycled glass mat-reinforced thermoplastic (GMT). The parameters investigated are gas ramp rate, gas injection delay time, and peak pressure. The size of cavity was found to be inversely proportional to gas injection delay time. Rheological instabilities at the polymer–gas interface were observed; a phenomenon previously noted during the development of gas assisted injection moulding.

디스플레이용 외장패널의 가스사출공정 개발

Gas Assisted Injection Molding is a relatively new low-pressure injection molding technique that provides benefits such as reduced part warpage, excellent surface quality without shrink marks, greater design flexibility, etc. In the gas assisted injection molding process, the injected pressurized nitrogen gas flows through designed gas channels and forms hollow sections within the part. However, due to the characteristics of the gas, the design of the gas channels which are the paths for the injected gas is important in order to avoid defects such as gas blowout, fingering, etc. Therefore, in this study, the gas channel design for gas assisted injection molding of exterior display panels was conducted by examining the results of three CAE analyses. The designed gas channel was verified by conducting tryouts using a 450 ton injection molding machine with 3-stage pressure controlled gas kit. In addition, the hollow shapes which were formed by the gas with the installed gas channels were examined by examining the cross sections of the prototypes that were produced. As a result, it was found that exterior display panels can be produced without any defect by applying the gas assisted injection molding technique.

Gas-Assisted Compression Moulding of Glass Reinforced Polypropylene, Part 1: Scoping Study

A new process of combining gas injection with compression moulding is presented. The process is called Gas Assisted Compression Moulding (or GasComp). The principle is based on the injection of nitrogen gas during a conventional compression moulding cycle. The flow of the material due to the compressive force of the press is assisted by the injection of gas into the centre of the molten material. The gas assists in the flow by coring out the material. An introduction to the process and moulding parameters are presented along with initial scoping studies using GMT, LFT and recycled GMT. Glass architecture was found to be a major factor in the shape and location of the gas cavity produced. This process is shown to be advantageous when compared to gas assisted injection moulding in that long fibre parts can be cored out.

NDT Based Process Monitoring and Control

The old focus on using automation was simply to increase productivity and reduce costs. Today, the purpose of automation has shifted to broader issues. Highly automated processes ensure high quality on a constant level, if it is connected with a high degree of (automated) monitoring and control. Meanwhile, continuous process and quality monitoring by non-destructive testing (NDT) is an accepted procedure to early diagnosis of irregular process conditions, followed by an NDT-based feed back control and optimization. Consequently, the development of process integrated NDT is an important scientific task. Such developments have to fulfil the requirements of today’s industrial production concerning integrability, automation, speed, reliability and profitability. Flat steel production and processing, gas assisted injection moulding and cold joining processes are some examples of a successful application of the processintegrated NDT.

The Cooling Time of Gas Assisted Injection Molding

The mathematical model of solid-liquid interface is obtained by making an idealized hypothesis for parameters of the cooling process in gas-assisted injection molding, and simplifying the mathematical model. And then the cooling time of plastic products in the process is obtained by using two ways of solving the solid and liquid phases. And verified by example the conclusions that some plastic products of gas-assisted injection molding, when the materials and workmanship conditions are constant, cooling time of the airway is proportional to the square of the wall thickness is obtained.

Effect of processing parameters on water penetration in water assisted injection molding of ABS

This study experimentally investigates the effect of processing parameters on water penetration and part hollow-core characteristics (includes wall thickness, core diameter) and shrinkage of the plastic molded part, in Water Assisted Injection Molding process (WAIM) of an amorphous polymer. WAIM has been developed for production of hollow plastic parts and is suitable for weight reduction of large parts with a good internal surface. Other benefits are fast cooling and short cycle time without compromising part quality. In this study acrylonitrile-butadiene-styrene (ABS) was chosen as the candidate amorphous polymer. The selected processing parameters were: water injection delay time, holding time and mold temperature. The mold cavity shaped a branched pipe (two-head) to be cored out via water penetration. Actual factory-like experiments and full shot size were applied during this research. The results showed that the longest water penetration, the least wall thickness differential, the highest uniformity in pipe diameter and the lowest shrinkage are obtained when the process parameters such as holding time and mold temperature are maintained at the highest level and delay time is optimized.

Numerical Simulation of Melt Filling and Gas Penetration in Gas Assisted Injection Molding

The governing equations of two-phase flows including gas and polymer melt are presented, which are solved using finite volume and domain extension methods with SIMPLEC technology. The melt filling and primary gas penetration in gas-assisted injection molding (GAIM) process are simulated, where the Cross-viscosity model is employed to describe the melt rheological behavior, and the CLSVOF(coupled Level Set and Volume of fluid) method is employed to capture the moving interfaces. In order to test and verify the coupled methods, melt filling in a rectangular plate with an insert is simulated, and the numerical results are in good agreement with those of the experiment. As a case study, the melt filling and gas penetration processes in a ring-shaped channel are simulated. The numerical results successfully depict some important phenomena, such as race-tracking effect, corner effect and the flow asymmetry of the gas penetration, which can deepen the understanding and studying of the GAIM process.