Thermoplastic Injection Moulding Research Articles

Influence of plasticisation during foam injection moulding on the melt viscosity and fibre length of long glass fibre-reinforced polypropylene

Abstract The processing of long glass fibre-reinforced thermoplastics results in considerable fibre damage, particularly during plasticising. By using thermoplastic foam injection moulding (FIM) with a constant blowing agent atmosphere, fibre damage during plasticisation can be reduced. This can be attributed to the reduction of the melt viscosity on the one hand and the influence of the melting behaviour on the other. Therefore, the influence of the FIM and the process parameters on the fibre length and the fibre length distribution are analysed and compared with the influence of the process parameters on the melt viscosity.

Injection Molding of Thermoplastics for Low-Cost Nanofluidic Devices

Thermoplastic micro- and nanofluidics are increasing in popularity due to their favorable chemical and physical properties as an alternative to poly(dimethyl siloxane) (PDMS)-based devices, which are more widely used in academia. Additionally, their fabrication is compatible with industrial processes, such as hot embossing and injection molding. Nevertheless, producing devices with sub-micrometer channel heights and low roughness while retaining high-throughput molding remains challenging. This article details the combination of grayscale e-beam lithography (g-EBL) and injection molding as a fabrication route for capillary 3D thermoplastic nanofluidic devices with unprecedented accuracy in the sub-micrometer range. We employed g-EBL to pattern the device profile in a poly(methyl methacrylate) (PMMA)-based resist, which served as a substrate for the subsequent fabrication of a negative nickel mold by using electroforming. These molds are used to fabricate devices in PMMA and cyclic olefin polymers (COP) using injection molding. We show that the 3D height profile of the nanofluidic devices is maintained throughout the entire replication cycle within very tight tolerances, retaining its nanoscale topography on a millimeter-length scale. Moreover, somewhat surprisingly, the roughness in the inflow section of the devices was significantly reduced, which we attribute to the nickel mold fabrication. Last, we show that the capillary-driven devices can be used to size-dependently trap nanoparticles of various sizes in a reliable and facile manner while only requiring a 4 μL sample volume. The presented device and fabrication procedure paves the way for applications in various scientific fields, ranging from immunology to neurology and material science, in a cost-effective manner.

MAYA – MAnufacturing of the lining panel using hYbrid technologies; Additive manufacturing, injection moulding and thermoforming

MAYA aims at developing innovative manufacturing routes integrating standard thermoplastic processes (such as injection moulding) and additive manufacturing to produce fuselage composite lining panels. These panels basically consist on sandwich structures with sheets reinforced with fibre-glass hold to the aircraft frame by a set of brackets. The high productivity rate of thermoplastic injection moulding associated to the design freedom of 3D printing will lead to an enhancement of the manufacturing process of the panel-bracket assembly resulting in lighter and less expensive panels with improved overall performance. The work carried out by the research group AMADE focuses on the experimental analysis for interface characterisation, material selection and validation of designs. The first stage of the experimental campaign includes the initial characterisation of the interface bonding of dissimilar materials with different thicknesses obtained by direct 3D printing on the composite skin or by using adhesives under mode I, static and fatigue, and mode II, static, to obtain the best material candidates and design properties. The second part of the work is based on the experimental analysis of the union between the composite skin and small-scale brackets under pull-out and shear-out conditions. Lastly, the final designs of the brackets, both for injection moulding and additive manufacturing, and the corresponding interface bonding with the sandwich panels are validated in large-scale tests under static and fatigue conditions simulating the in-use forces applied to the panels. In this work, the characterisation of the interface bonding of dissimilar materials is presented.

Influence of Injection Moulding Parameters on Electrical Conductivity of Polypropylene-Graphite Composite Bipolar Plates for Hydrogen Fuel Cells

News on Green Energy and Green Hydrogen is spread on popular and academic media. When energy is obtained from sunlight, wind or water, we call it Green Energy. When hydrogen is obtained from electrolysis with Green Energy, we call it Green Hydrogen. Hydrogen Fuel Cells are electrochemical devices that convert hydrogen and oxygen s chemical energy into electricity and heat energy with high efficiency and contribute to the decarbonisation of the power supply. Bipolar plates, essential components of the fuel cells, made in polymer-carbon composites, are an economical alternative to the stainless steel, titan and graphite, traditional materials. Our experiments have used a polypropylene matrix filled with graphite with a total inorganic content of 87%, which contributes to high electrical and thermic conductivity but strongly influences the viscosity, flow, pressures, temperatures, and then challenging to process. Injection Moulding of thermoplastics is a technology widespread in all fields of activities and considerable potential. In this paper, the experiments design is highlighted in choosing the factors. A debate regarding the filling, packing, holding pressures, and the last decades approach and optimisation of injection moulding parameters with the Taguchi Method is presented. Conclusions on the injection moulding process of the bipolar plate made of a polypropylene-graphite composite, the parameters influence with direct effects on the fuel stack s performance are presented. The combined melt and mould temperatures influence most electrical conductivity by better contacting the electrically conductive particles through the polymer s melted layer. The injection pressure influences the mass and thickness of the product and the electrical conductivity by better packing. Furthermore, we suggest an adapted formula to predict the injection pressure considering the inorganic content and the process temperatures in agreement with the experiments.

Thermoplastic foam injection moulding of sandwich structures with short fibre-reinforced skin layers

Sandwich structures, consisting of a short glass fibre–reinforced polypropylene film as skin layer and chemically blown polypropylene as the core material, were produced via injection moulding. The skin layers of the sandwich structures, which contain polypropylene as well as 30 wt% and 50 wt% of glass fibres namely polypropylene–glass fibres 30 and polypropylene–glass fibres 50 respectively, were produced by film extrusion using a coat hanger die. The properties of the films were investigated by dynamic mechanical analysis. Furthermore, the influence of different glass fibre contents in the skin layers and chemical blowing agent contents in the core material of sandwich structures was studied to compare them with the compact polypropylene and the polypropylene foams. The sandwich structures were characterized with regard to density, microstructure, weight reduction, surface roughness and bending properties. In general, distinctive reinforcement effect was achieved by use of the short glass fibre with the strong influence of processing direction of the film. For the sandwich structures, it was found that a good adhesion between the skin layers and the core material can be achieved during injection moulding. The microstructure and the bending properties of the sandwich structures depend on the glass fibre–reinforced film and the chemically blown core. It was found that the use of the skin layers led to lower cell intensity in the foam core. Nevertheless, a high modulus and strength to weight ratio could be accomplished by a high stiffness of the glass fibre–reinforced film and a low density of the chemically blown core. Additionally, it was found that the surface roughness of the films could be reduced due to processing in injection moulding.

Analysis of the No-Flow Criterion Based on Accurate Crystallization Data for the Simulation of Injection Molding of Semi-Crystalline Thermoplastics

Abstract It is well known in practice that the shape and dimensions of injected parts are highly dependent on the packing-holding stage. A major problem in semi-crystalline polymers is the prediction of the solidified layer, whose thickness has an important effect on shrinkage and warpage. We propose a pragmatic approach based on the concept of no-flow temperature. This temperature should be related to crystallization temperature, but the choice is not easy because it depends on cooling rate and pressure which are functions of time and position. The objective of the work is to evaluate the sensitivity of an injection molding computation to the no-flow temperature and to evaluate the relevance of its choice. The crystallization temperature of an isotactic polypropylene is determined as a function of cooling rate and pressure in laboratory experiments. The pressure dependence is measured using the original Cristapress cell. As a case study, we simulate the filling and post-filling of a plate mold using Rem3D, a 3D code for injection molding. Three no-flow temperatures and two sets of parameters for temperature dependence of viscosity are tested. Their respective influences on the pressure evolution are shown, and the crystallization temperature calculated a posteriori using the experimental material data is compared to the “arbitrary” no-flow temperature.

Variothermal Foam Injection Molding - Dimensional Stability with High Surface Quality

Thermoplastic foam injection moulding offers various advantages for both processing and product design. Despite its many benefits, the moderate surface quality still constitutes a major disadvantage of this process. The mould temperature can be controlled dynamically to improve the surface quality. Different dynamic temperature control strategies are employed and analysed regarding their effectiveness and scope of application. Mould temperatures above the specific material transition temperatures allow the surface defects to be cured and enable the production of foamed thermoplastic parts with surface qualities comparable to those of the compact reference samples. The high mould temperatures during the injection phase alter the foam structure and the skin layer thicknesses, which impacts the mechanical properties.

Morphology Development During Micro Injection Moulding of Thermoplastics

Micro injection moulding is a key process in the field of micro manufacturing especially in the production of medical devices. Micro injection molding technology involves the injection of the whole material with the result of a high degree of efficiency due to the material saving process. In comparison with conventional large injection moulding, the volume of material is very much reduced and as a consequence the flow and temperature profiles are considerable different to macro injection moulding. This work focuses on the impact on the structure, morphology and properties of parts prepared using micro injection moulding of these changes flow and temperature profiles. We have used small-angle X-ray Scattering techniques to evaluate the semicrystalline morphology and we have discovered that the nature of the process has led to changes in the morphology. We have supplemented the small angle scattering technique with wide-angle x-ray scattering as well differential scanning calorimetry.

Microcellular Foam Injection Molding of Thermoplastics Using Green Physical Blowing Agent

The microcellular injection molding technology, commercially offered by Trexel Inc. and other manufacturers, is primarily a close cell foaming technique. This process is capable of offering light weight non-porous thermoplastics moldings. The foaming of thermoplastics with open cellular morphology has got various high end applications among others like tissue engineering and membrane separation. Some of the researchers were successful in synthesis of open cellular thermoplastics at laboratory scale via solid state batch process. The growing demand for microporous thermoplastics, especially the biodegradable plastics (e.g. Polylactic acid), motivated the researchers develop a specialized microcellular injection molding process for processing of open cell thermoplastics using physical blowing agents such as supercritical nitrogen or carbon dioxide gas. A brief of theoretical and conceptual treatment of microcellular injection molding is presented.

Rheological properties of wood polymer composites at high shear rates

This paper presents the rheological properties of wood-polymer composites (WPC) with a polypropylene (PP) matrix in the corrected shear rate range from approx. 20 s−1 to 150 000 s−1. Tests were conducted using a capillary rheometer and a rheological head of the author's construction, for which the working element is a thermoplastic injection moulding machine. The constructed tool was found to be very useful, especially for the determination of the processing characteristics of WPC composites containing a large particle-size filler. It was observed that the rheological properties of wood-polymer composites in the shear rate range of up to several thousand s−1 significantly depended on the filler content of the polymer matrix; at the same time, at higher shear rate, a clear decrease in the effect of the wood filler content on the viscosity of the composites and on the flow behaviour, as described by the power law, took place.

A study on the role of wetting parameters on friction in injection moulding

In the injection moulding of thermoplastics, hot polymer melt wets a cold mould surface during filling. In contrast, ejecting can be considered as de-wetting a solid polymer from a solid mould surface. In ongoing research, we suggest that the interfacial tension γ12 predicts the resistance of a solid polymer being separated from a solid mould, i.e. low γ12 indicates elevated ejection friction and vice versa. The aim of this study was to validate this assumption for polymer PA6 and the mould surfaces M333_IP, M268_VMR, MoN, and CrC/a-C:H. To calculate γ12, we determined the five solids surface energies at 90°C. Therefore, we conducted contact angle measurements using bromonaphtalene and ethylencarbonate and applied the OWRK method. In succeeding friction experiments, we used a friction-test injection mould to determine the ejection friction of the same material combinations at 90°C. To conclude, the four mould coatings ranked in friction to PA6 as γ12 suggested.

Modelling of Indirect Laser-induced Thin-film Ablation of Epoxy for Local Exposing of Carbon Fibers

Laser radiation is used as enabling technology for intrinsic joining of high-strength CFRP laminates and fiber-reinforced thermoplastic injection moulding compounds by exposure of surface-near carbon fibers. Short-pulsed NIR laser sources represent an acceptable compromise with respect to ablation performance, remote process capability by use of compact 3D scanner and the capability for closed-loop process control. However, using such a laser source means also minimizing heat-affected zones (HAZ).Based on literature research about laser ablation of thin metal films, heat flow at CFRP and thermo-mechanical behavior in FRP by pyrolysis, an analytical model was generated for thin-film ablation of cured epoxy resins at the surface of CFRP laminates by lift-off of resin chips.A comparison between simulation and experimental results confirms the capability of the model to predict the exposure area and the HAZ with deviations below 15%. Threshold fluences for the HAZ (>1J/cm2) and the resin ablation (>3J/cm2) have been confirmed.

DESIGN CONSIDERATIONS OF CONFORMAL COOLING CHANNELS IN INJECTION MOULDING TOOLS DESIGN: AN OVERVIEW

Design of the cooling system in the thermoplastic injection moulding process is one of the most important steps during mould design. It has a direct influence on the quality of the parts produced, and thereby impinges on the cycle time. Cooling channel design has traditionally been limited to comparatively simple configurations due to the main process for manufacturing being restricted to the drilling of straight holes. Nowadays, with the emergence and rapid uptake of 3D printing, complex shapes are able to be produced with intricate details and more complicated geometries. The objective of this study was to determine the temperature profile along the mould tool cavity wall to improve the cooling system design. Virtual models from a 3D modelling software (such as Solidworks and Moldflow) are used to design a simple artefact and simulate studies to include different cooling systems such as straight and conformal channels. The effects of cooling channel form and location on the temperature distribution of the mould and the solidification degree of polymer are studied. The bulk of the results indicate that in order to improve the productivity of the process, the cooling and cycle times have to be minimised while at the same time a homogeneous cooling is necessary to maintain a consistent quality of product.

Diesel Effect Problem Solving During Injection Moulding

Abstract Study describes principles of diesel effect creation during thermoplastic injection moulding as a consequence of wrong injection conditions and poor venting system design. On real example, study shows sequence of all steps to eliminate this sort of material degradation with minimal costs in phase when mould is already made. As a first, process parameters were optimized by CAE simulation to minimize cavity internal gasses creation. Finally the specific mould modifications were suggested to improve the effectiveness of venting system.

Integration of CAD CAM Techniques in the Development of an Injection Mould for Automotive Parts

Processing by injection is the technological process by that the thermoplastics material is injected, under pressure, in the cavity of a mould, where it cools down and solidifies. This process is the most common method for obtaining plastic materials. Injection moulding of thermoplastics has emerged as the premier vehicle for delivering high quality, value added commercial products. Continued global competitiveness has increased standards for product capability and quality while requiring reduced product development time and unit cost. Despite advanced design methods and new process technologies, it is becoming apparent that the injection moulding process is neither flexible nor robust. This paper presents a design process using CAD-CAM software applied to an injection mould for manufacturing a plastic component that is used in the automotive industry. The component was analyzed, measured and subjected to simulations that will certify the quality of the final product.

Ultrasonic Activated Injection Used on Manufacturing Thin Wall Plastic Parts

Processing by injection is the technological process by that the thermoplastics material is injected, under pressure, in the cavity of a mould, where it cools down and solidifies. This process is the most common method for obtaining plastic materials. Injection moulding of thermoplastics has emerged as the premier vehicle for delivering high quality, value added commercial products. Continued global competitiveness has increased standards for product capability and quality while requiring reduced product development time and unit cost. Despite advanced design methods and new process technologies, it is becoming apparent that the injection moulding process is neither flexible nor robust. This paper presents a set of experiments that focused on particular processing conditions of injection through narrow section, thin-wall injection and microinjection. In these cases, the ultrasonic activation does not play an important role as single influence factor but could amplify or strengthen the influence of classical setting parameters of the process: mould temperature, injection pressure and temperature

Variable Distance Adjustment for Conformal Cooling Channel Design in Rapid Tool

During thermoplastic injection moulding process, the gradual increase of the coolant temperature along the conformal cooling channel (CCC) inside the rapid tool reduces the rate of heat transfer from the polymeric melt to the cooling channel surface at the outlet portion. Injection moulded defects such as irregular warpage of the part between the coolant inlet and outlet cannot be avoided. Rapid tooling (RT) technology offers a speedy and automatic method for rapid tool design and fabrication integrated with complex internal structure such as CCC. This paper presents a novel adjustment method for cooling distance modification between the CCC and its mould cavity (or core) surface along the cooling channel. The proposed method can compensate the gradual increase of the coolant temperature from the coolant inlet to the coolant outlet. More heat can be transferred from the mould surface near the coolant outlet to the proposed variable distance conformal cooling channel (VDCCC). In this study, the cooling channel distance modification relies on two adjustment attributes: (1) the adjustment direction and (2) the adjustment amount, between the mould cavity (or core) surface (terrain) and the cooling channel axis (polyline) after the linearized approximation. A computer-aided melt flow analysis tool of moldflow plastics insight is employed in the case study in order to demonstrate the feasibility of the proposed method. The cooling performance of the proposed VDCCC design can be verified.

Monitoring of Injection Moulding of Thermoplastics: Adopting Pressure Transducers to Estimate the Solidification History and the Shrinkage of Moulded Parts

In this work, a series of injection moulding tests were conducted using a general purpose PolyStyrene, PS, and changing the holding pressure, injection temperature and cavity dimensions. The pressures at the interface with the mould at several positions along the flow-path were measured by means of pressure-temperature transducers. The samples were measured after moulding to determine dimensional accuracy, which was taken to be the target quality parameter. The pressure profiles obtained were then analysed using a recently developed procedure that is able to estimate the local solidification history from pressure measurements. The local average solidification pressure, namely the average along the thickness direction of the pressures at which each layer solidifies, could thus be estimated. This parameter is known to correlate well with shrinkage and thus a master-curve can be created that can be adopted to monitor the quality of the moulded part on line.

Differential Molding System for Micro Injection Molding of Thermoplastics

Abstract A differential molding system for micro injection molding of thermoplastics was designed and fabricated. As the core part, a planetary gear pump was integrated into the molding module and used for metering, delivering and supercharging. The molding system was installed in the stationary platen beside which a servo motor was connected to the transmission shaft of the pump through a coupling. A traditional injection molding machine which was equipped with this module could be upgraded to a precise micro injection molding machine and realized the function of multiple micro injection molding machines. A process study was first performed to verify the machine performance and to determine the influence of the main process parameters. It has been proved by experiments that the differential molding system could realize the manufacture of fine and precision parts with micro structures in one step with high efficiency at low cost.

Design and fabrication of an adhesion force tester for the injection moulding process

During the injection moulding process, serious adhesion effects can occur at the interface between the specimen and tool surface during ejection, causing distortions or cracks in the samples, especially for resins such as PMMA, PC and TPU. However, ejection force measurement is not able to measure adhesion force accurately for elastomeric resins during the injection moulding process. A tensile mode adhesion force tester was fabricated to measure the adhesion force between the sample and tool surface during the thermoplastic injection moulding process, especially for elastomeric resins, which have adhesion problems that are both serious and difficult to measure. In addition, three different types of TPU are examined, with their temperature and viscosity being the main factors that affect the adhesion force. Engineers can use the measurements obtained in this work to better understand adhesion and work to reduce it.