Co-injection Moulding Research Articles

Interface development and numerical simulation of powder co-injection moulding. Part. I. Experimental results on the flow behaviour and die filling process

Powder co-injection moulding (PCM) was carried out by using two feedstocks, 316L(60%) and 316L(40%), as core and skin feedstocks, respectively. The effects of processing parameters such as the pre-filling volume of skin feedstock, the injection temperature of core feedstock and the injection rate of skin feedstock on the profiles of the two feedstock layers were studied. It was found that the interface between core and skin feedstocks exhibited an arched shape in the transverse plane and a V shape in the longitudinal plane. There is a “maximum thickness” of core feedstock in the longitudinal direction. The penetration length and maximum thickness depended on the injection parameters. The formation mechanism of the interface was studied on the basis of rheological theory. This research provided an experimental base for the simulation work of PCM processes.

Interface development and numerical simulation of powder co-injection moulding. Part II. Numerical simulation and experimental verification

A numerical model was proposed to predict the co-injection step of the powder co-injection moulding (PCM) process. Several assumptions were established for the purpose of simplifying the physical models. The melt front was traced by a modified control volume method, in which the maximum thickness of core feedstock was taken into consideration. Such modification can overcome the shortage of Hele-Shaw equitation in predicting 3D flow behaviour. By using this model, the movement of the skin melt front and core/skin interface, and the profile of temperature and pressure fields were obtained. The simulations were in good accordance with the experimental results. The thickness and the penetration distance of the core feedstock were accurately predicted. The deviation between the simulated and experimental results was due to the uneven shrinkage of the green part during cooling.

Numerical simulation and experimental study on physical mechanism in multiple component moulding

Multiple component moulding (MCM) is one of the great methods to fabricate the modern injection products. Due to many procedure combinations, it is very difficult to know the detailed process. Besides, because of its complicated nature and the unclear physical mechanism, using trial-and-error method cannot realise and manage the mechanism effectively. In this study, we will review various MCM technologies, including over-moulding, and co-injection moulding, and study these two applications in more details. Results show that the product geometries, process condition, and moulded materials will affect the product quality. The physical mechanism of warpage in a sequential over-moulded part is due to the unbalance between the volumetric shrinkage during filling/packing and the thermal unbalance from cooling. The warpage behaviour for co-injection moulding is more complicated because of the uncertain interface. However, one of the keys to manage the warpage is the control of the core penetration.

Opportunities for In-mould Painting at TVS Motor Company Ltd

TVS Motor Company is the third largest manufacturer of two-wheelers in India and one of the top ten manufacturers in the world. The company manufactures 1.5 million two-wheelers for both its domestic and overseas requirements. The company's manufacturing process involves painting of plastic, metal and aluminium components to enhance their appearance and performance properties. The company currently uses a conventional post painting process for its moulded plastic panels. However the conventional post painting process causes a huge impact on the environment through flue gas emissions from baking ovens, solvent emission from paint booths and ovens, sludge generation from paint booths and wastewater generation from paint booths and pre-treatment processes. The volumes of waste and cost for part attached to the painting process for TVS Motor Company are detailed in this paper. Paint shop replacement technologies in relation to current in-mould decoration technologies such as pigmented plastics, in-mould film, co-injection moulding and in-mould spray painting (INSPIRE) are considered. Based on current specifications and requirements for painted plastic components, INSPIRE is found to be the most advantageous paint shop replacement technology for current TVS Motor Company Ltd production as it uses a thermoset, matching current specifications. A design of experiments is performed using a polyester skin and ABS substrate to optimise part coverage for a sample part. Using statistical analysis spray time and spray pressure are found to be the most important process parameters for paint coverage. Paint coverage could be greatly improved compared to that which has been previously reported.

Feasibility Study on Producing Components with Embedded Channel by Powder Injection Moulding

Feasibility study on producing components with embedded channel by powder injection moulding (PIM) is conducted in this paper. The base plate with open channel was produced by co-injection moulding of polymeric material and ceramic feedstock. The polymeric material acted as the sacrificial material to fill the channel feature. A cover plate was then over-moulded onto the base plate to form green assembly, which was then debinded and sintered. The embedded channel was created when the sacrificial material was removed during the debinding and sintering stage. This process eliminates the need for additional joining process required by conventional manufacturing process which could cause misalignment and leakage under harsh working environment such as high pressure and high temperature. Joining was found between the cover plate and the base plate in over-moulding stage. Temperature and time during solvent debinding played important roles in order to obtain defect free component. Low temperature and short time in solvent debinding resulted in insufficient wax loss which led to various types of defects. A fair good sintered component was obtained under optimal debinding condition at 50 °C for 48 hours. The embedded channel was observed clearly by x-ray inspection without blockage by foreign particles. The shape of the channel was well retained and perfect bonding was formed in the central area of the two plates.

Effect of Magnetic Field on the Distribution and Orientation of Magnetic Particles in Co-injection Moulding

This paper presents a study of the effect of an external magnetic field on the distribution and orientation of magnetic particles in co-injection moulding. The orientation of the magnetic particles was determined using optical microscopy and image analysis techniques. The external magnetic field was placed in the tool cavity and used to magnetize the particles and to generate the necessary magnetic field gradient to manipulate them. The ferromagnetic nickel particles remained magnetic enough to overcome the strong drag forces imposed on them by the polymeric fluid matrix and to be orientated by the permanent magnet in the tool.

In mould painting using thermoset powder coating and thermoplastic substrate in closed tool injection moulding

In mould decoration (IMD) is attractive because a fully, or partially, decorated component is produced directly from the moulding process, with reduced emissions at lower process costs when compared to traditional techniques. A new IMD process has been developed to produce a painted component direct from the injection moulding tool. This incorporates the pressure spraying of thermoset powders through a valve into a closed mould. The residual heat of the tool initially softens the thermoset. The high temperature of thermoplastic polymer injected in a standard injection moulding subsequently cures the thermoset. The resultant product combines both thermoplastic and thermoset in a single injection moulding cycle. This paper presents frames from high speed video capture of powder mould filling and the results of INSPIRE (in mould spray painting, impact reduced on the environment) initial injection moulding using thermoset polyester and acrylonitrile butadiene styrene (ABS). The parameters that affect material distribution are examined and discussed. Similarities to the coinjection moulding process are noted.

Numerical investigation of the flow front behaviour in the co-injection moulding process

This paper presents a three-dimensional (3D) solution algorithm for solving the sequential co-injection moulding process. The flow of skin and core materials inside a rectangular cavity is investigated both numerically and experimentally. A 3D finite element flow analysis code is used to solve the governing equations of the non-isothermal sequential co-injection moulding. The predicted flow front behaviour is compared to the experimental observations for various skin/core volume ratio, injection speed, injection temperature, and core injection delay. Simulation results are in good agreement with experimental data and indicate correctly the trends in solution change when processing parameters are changing. Solutions are also shown for the filling of a spiral-flow mould. The numerical approach is shown to predict the core expansion phase during which the flow front of core and skin materials advance together without breakthrough. Breakthrough phenomena is also predicted and the numerical solution is in good agreement with the experiment. Copyright © 2005 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

Controlled delivery achieved with bi-layer matrix devices produced by co-injection moulding.

The aim of this study was to design new soy protein-based bi-layered co-injection moulded matrix systems aimed to achieve controlled drug delivery. The devices consisted of a drug-free outer layer (skin) and a drug-containing core. The systems overcame the inherent disadvantage of non-linear release associated with diffusion-controlled single-layer matrix devices by providing additional releasing area with time to compensate for the decreasing release rate. As expected, the bi-layer devices presented a significant decrease in drug release rate when compared with a correspondent single layer matrix system. The skin thickness and the degree of crosslinking of the core appeared to be very important tools to tailor the release patterns. Furthermore, due to the amphoteric nature of the soy protein, the developed devices evidenced a pH-dependent behaviour. The mechanisms of drug release were also elucidated at two different pH values: i) pH 5.0, near the isoelectric point of soy (low matrix solubility); and ii) pH 7.4, physiological pH (high matrix solubility). Consequently, changing the release medium from pH 5.0 to pH 7.4 after two hours, led to an abrupt increase in drug release and the devices presented a typical controlled drug delivery profile: slow release/fast release. These evidences may provide for the development of individual systems with different release onsets that in combination may exhibit drug releases at predetermined times in a pre-programmed way. Another possibility is the production of three-layer devices presenting bimodal release profiles (fast release/slow release/fast release) by similar technologies. Scanning electron micrograph of a developed bi-layer device.

Sandwich Injection Moulding of Thermosetting Materials. Part I: Initial Experiments

Thermoset co-injection moulding is a novel technology that might be an alternative for thermoset recycling. This paper describes some experiments on the sandwich moulding of two polyesters, a powder coating and a BMC using a new special design thermoset co-injection machine and manifold system. The first thermoset sandwich moulding has been made and a number of initial moulding problems are presented and discussed.

Development and design of double-layer co-injection moulded soy protein based drug delivery devices

Novel double-layer delivery devices based on soy protein derived materials were designed and produced using an innovative two material co-injection moulding technique. It was demonstrated that the viscosity ratio between core and skin layer materials played an important role in the formation of the interfacial shape, namely the skin thickness and uniformity of the bi-materials. The adequate selection of the materials used and the optimisation of the respective processing conditions enabled an accurate control of the relative thickness of the layers of the device. The preliminary results confirmed the potential of these systems to achieve a controlled drug delivery.

Interfacial instabilities in multimaterial co-injection mouldings: Part 2 - Interfacial mixing in transparent mouldings

Previous research in co-injection moulding has produced viscosity ratio guidelines for skin and core components, which must be followed if good core distribution is to be achieved. However, by examining two phase systems of PMMA-PC, which fall within the recommended viscosity range, this work shows that viscosity matching of materials is not a sufficient requirement for interfacial stability. The transparency of the materials allows areas of interfacial mixing to show up as streaks in the mouldings, so that factors affecting stability can be determined. One system is found to be more stable than the others. Explanations for such effects are given by consideration of interfacial mixing, viscosity, tooling geometry, injection speeds, interfacial stresses and shear in multilayered mouldings.

Interfacial instabilities in multimaterial co-injection mouldings Part 1 – Background and initial experiments

Interfacial adhesion between the skin and core is vital for successful co-injection moulding. This is the first paper in a series, which introduces and describes an in mould method of mixing that is applicable regardless of the compatibility of the materials. It works by inducing turbulent mixing at the interface between the skin and core materials. It makes use of the change that occurs from laminar to turbulent flow at high injection speeds in co-injection moulding. This novel approach takes advantage of the moulding parameters already available within the co-injection system to offer an expanded range of material combinations for multimaterial moulding. Comparisons are made between multimaterial mouldings made with miscible polymers, immiscible polymers with no compatibiliser, and immiscible polymers bonded by compatibilisers.

Development in Powder Co-Injection Moulding

Powder co-injection moulding (PCIM), is a novel technique for the surface engineering of PIM components. The process uses two moulding feedstocks which are injected into a mould sequentially, so that one feedstock forms the surface layer of the component and the other forms the core. Work to date has shown that the injection moulding time and the viscosity ratio of the two feedstock materials are critical in determining the surface layer profile. This has been confirmed through finite element modelling predictions of the skin layer thickness distribution which correlate well with experimental observations.

Vegetable fibres in automotive interior components

This paper gives a brief status of the state of the art of the use of plastic/vegetable fibre composite materials for interior car parts and the technologies to realise such parts (injection moulding, low pressure injection moulding, thermoforming, thermocompression and co-injection moulding). The development activity on composite plastic-wood materials to be used in the automotive sector performed by J.C.A. is also presented, in particular the research lines performed on several kinds of vegetable fibres (eucalyptus, jute, flax, kenaf) to be applied on semi-finished products: granules (short vegetable fibre) for injection moulding, and extruded sheets (long and short vegetable fibre) for thermoforming.

Surface engineering by powder coinjection moulding

Intricately shaped surface engineered components have been produced using the technique of powder coinjection moulding. Powder coinjection moulding is the combi nation of two processing methods, polymer sandwich moulding and powder injection moulding, and has been used to produce metal or ceramic surface engineered components using several model material systems. Surface engineering was achieved by the addition of rigid non-sinterable particles or alloying particles. Modelling of the coinjection moulding process using a commercial finite element computer program, C-Mold, has demonstrated the ability to predict the skin thickness and distribution as a function of processing conditions and material properties. The ability to engineer surfaces as part of the powder injection moulding cycle provides a further incentive for the additional exploitation of the powder injection moulding process.

Control of surface layer thickness in metal co-injection moulding: J.R.Alcock et al. (Cranfield University, UK.)

Control of surface layer thickness in metal co-injection moulding: J.R.Alcock et al. (Cranfield University, UK.)

Surface engineering by co-injection moulding

A novel process, powder co-injection moulding (PCM), a development of powder injection moulding is described. A twin-barrel injection moulding machine has been used to inject two different powder/binder mixtures sequentially into a mould. The new process allows surface engineering during powder injection moulding rather than as a post-production stage in the manufacturing cycle. Two examples of co-injection moulding are described. The first considers a polymer component having a particulate or fibre-reinforced skin layer. The second discusses the production of dense, layered ceramic or metal components having a corrosion- or wear-resistant surface layer. Modelling of the PCM process is being undertaken using a commercial finite-element modelling program, C-Mold and an example of how this may be used to predict coating thickness is presented.

Metal co-injection moulding

Metal co-injection moulding

Food packaging materials and radiation processing of food: A brief review

Food is usually packaged to prevent microbial contamination and spoilage. Ionizing radiation can be applied to food-packaging materials in two ways: (i) sterilization of packaging materials for aseptic packaging, and (ii) radiation processing of prepackaged food. In aseptic packaging, a sterile package is filled with a sterile product in a microbiologically controlled environment. In irradiation of prepackaged food, the food and the packaging material are irradiated simultaneously. For both applications, the radiation stability of the packaging material is a key consideration if the technology is to be used successfully. To demonstrate the radiation stability of the packaging material, it must be shown that irradiation does not significantly alter the physical and chemical properties of the material. The irradiated material must protect the food from environmental contamination while maintaining its organoleptic and toxicological properties. Single-layer plastics cannot meet the requirements of either application. Multilayered structures produced by coextrusion would likely satisfy the demands of radiation processing prepackaged food. In aseptic packaging, the package is irradiated prior to filling, making demands on toxicological safety less stringent. Therefore, multilayered structures produced by coextrusion, lamination or co-injection moulding could satisfy the requirements.