Volume 36, Issue 6

The integration and combination of known technologies to one-step-processes is a promising way to implement enhancements to existing processes and products, as well as to new product developments. This approach is followed by two integrative process technologies that were developed by the Institute of Plastics Processing (IKV) at the RWTH Aachen University and the Surface Engineering Institute (IOT) at the RWTH Aachen University as part of the Cluster of Excellence “Integrative Production Technologies for High-Wage Countries”. In these processes, pure metals or metal alloys are joined to the injection moulded part, which potentially results in particular advantages referring to the electrical properties of the product. The integrated metal/plastic injection moulding (IMKS) represents the combination of injection moulding and metal die casting. The in-mould metal spraying (IMMS) combines the injection moulding with the thermal spraying of metal. In the following, the level of development of both methods is presented and future potentials are shown.

Nowadays, the injection molding of optical components is becoming more and more important. A process which constructs the injection-molded part in layers offers considerable potential for productivity increases in the manufacturing of thick-walled optical components. The so-called multilayer injection molding, also known as overmolding technology enables a considerable reduction of the normally long cycle times and improves the optical properties. It is even possible to increase the molding accuracy due to the lower shrinkage potential of the single layers. Contrary to experience, the influence of the mold temperature on the bonding strength is very low. So, the temperature control of the mold can be adapted to the process consideration in regard to optical characteristics.

Due to their wide range of applications and their complex material properties, it is desirable to be able to predict the behaviour of injection moulded parts with the help of simulation tools. For semi-crystalline materials, this can only take place with considerable accuracy if the inhomogeneous material properties are taken into account. Because of this, it is necessary to calculate the microstructure of the solidified melt and to incorporate these findings in the simulation. We present an integrative, multiscale simulation approach in which the manufacturing process is calculated on a macroscale and the solidification process on a mesoscale. A multiphase filling and cooling simulation is done to calculate temperature and velocity fields, which are used as boundary conditions for the calculation of the spherulite distribution in the part. We present the used nucleation and growth model and shortly describe the parallelisation approach of the mesoscale simulation.

Micro structured optical plastics components are intensively used, i.e. in consumer electronics, for optical sensors in metrology, innovative LED-lighting, or laser technology. Injection molding has been proven successful for the large-scale production of these parts. However, the production of these parts still causes difficulties due to challenges in the molding and demolding of plastics parts created with laser-structured mold inserts. A complete molding of the structures often leads to increased demolding forces, which then cause a breaking of the structures and a clogging of the mold. An innovative approach is to combine physical vapor deposition (PVD)-coated, laser-structured inserts and a variothermal molding process to create functional micro structures in a one-step process. Therefore, a PVD coating is applied after the laser-structuring process in order to improve the wear resistance and the anti-adhesive properties against the plastics melt. In a series of molding trials with polycarbonate (PC) and polymethyl methacrylate (PMMA) using different coated molds, the mold temperature during injection was varied in the range of the glass transition and the melt temperature of the polymers. Subsequently, the surface topography of the molded parts was evaluated by digital three-dimensional laser-scanning microscopy. The influence of the molding parameters and the coating of the mold insert on the molding accuracy and the demolding behavior were analyzed. It was shown that micro structures created by ultra-short pulse laser ablation can be successfully replicated in a variothermal molding process. Due to the mold coating, significant improvements could be achieved in producing micro structured optical plastics components.

To make functional surface effects on plastic components usable on an industrial scale, new processes have to be developed. The in-mould graining (IMG) process is a variant of the thermoforming enabling the manufacture of micro-structures. One advantage of the IMG process is that the surface structure is formed to the final shape of the part. Recent investigations show that the forming accuracy of a flat mould can be extended by applying a variothermal mould heating in the IMG process. As high mould temperatures lead to high forming accuracies but also increase the cycle time of the process, a conflict of interests follows. In this paper, it is investigated to what extent high moulding accuracies can be achieved to form three-dimensional parts by using the IMG process extended by a variothermal mould heating. The results show that forming accuracies of micro-scaled structures of >90% can be reached on the bottom and the side walls of a cup-shaped mould. To address the conflict of interests between high moulding accuracy and long cycle times, the influence of the mould temperature is investigated in detail. To analyse the micro-forming behaviour of the processed material, analyses of the rheological behaviour with a rotational rheometer are carried out.

In order to reduce cycle times, increase functional integration and automation further, the innovative gap impregnation process and mold technology was developed at the Institute of Plastics Processing at RWTH Aachen University (Germany) in collaboration with industry partners. The novel process enables an automated production of continuous fiber-reinforced sandwich composite structures in integral design with high surface quality in short cycle times, which is demonstrated by manufacturing a carbon fiber-reinforced plastic (CFRP) engine hood. For the first time, the gap impregnation and mold technology makes it possible to manufacture large-scale, three-dimensionally shaped sandwich components in one shot and in short cycle times at similar mechanical properties compared to the reference steel hood. Furthermore, a weight reduction of about 60% to only 5 kg was achieved for the CFRP engine hood. This paper focuses on the systems engineering of the RTM-related gap impregnation process. The focus is on the utilized mold concepts for the pressurized air-assisted ejector pins, vacuum-tight sealing, the motion concept of the mold halves, resin traps, sensors for process control and the specially treated mold surfaces for class A surface components. Additionally, the main procedures, capabilities and characteristics of this innovative process are discussed.

Injection moulding is a widespread large-scale production technology for the manufacturing of thermoplastic parts, with small wall thicknesses limiting the feasible flow length. Introducing microthermoforming into the injection moulding process with dynamic mould temperature control enables the production of film-based, plane microstructured parts with further three-dimensional functional structures (e.g. for handling or for fitting in devices/assembly groups). Investigations show that considerable forming is possible with pressures up to 140 bar and forming temperatures far below the glass transition temperature of 50-μm-thick polycarbonate films in cycle times of <3 min. Generally speaking, the novel technology is expected to allow for multifunctional, thin-walled microstructured parts at large scales with short cycle times.

Dynamic vulcanization is an eminent industrial process to enhance the physical, thermal, and rheological properties of polymer composites. The present experimental study comprised the formation of polystyrene (PS) and styrene butadiene rubber (SBR) composites using three different types of fillers, namely, kaolin, talc, and rice husk powder (RHP), whereas dicumylperoxide was added as a cross-linking agent. Further, the filler loading was varied from 0 to 20 parts per hundred of resin (phr) for all types (i.e. RHP). The mechanical (i.e. tensile strength, elongation at break, and impact strength), thermal (i.e. melting point and softening point index), and dynamic mechanical properties of each composite were measured and compared with each other. The results indicate that kaolin-based vulcanizate showed better mechanical, thermal, and dynamic mechanical properties compared to that of talc and RHP vulcanizate. Furthermore, it can be observed that the mechanical, thermal, and dynamic mechanical properties of PS/SBR vulcanizates are the function of filler loadings for all three types of fillers (i.e. kaolin, talc, and RHP). In addition, high-temperature storage properties (i.e. loss modulus and storage modulus) were also investigated for better design and material optimization. The study may be helpful to the tribological applications in material selection and design.

The main aim of this study was to improve the mechanical properties of the recycled poly(ethylene terephthalate)/poly(ethylene 2,6-naphthalate) (r-PET/PEN) blends by enhancing the miscibility between PET and PEN with the usage of chain extenders. This idea was novel for the recycled PET-based r-PET/PEN blends, as investigation of the effects of the chain extender usage on the properties of r-PET/PEN blends has not been studied in the literature, according to our knowledge. 1,4-Phenylene-bis-oxazoline (PBO), 1,4-phenylene-di-isocyanate (PDI), and triphenyl phosphite (TPP) were selected as chain extenders. The maximum tensile strength value was observed for the 1.0PDI sample. Moreover, PDI-based blends exhibited better Izod impact strength when compared with all other samples. The miscibility and degree of crystallinity values of all blends were discussed by means of thermal analysis. 1 H-nuclear magnetic resonance ( 1 H-NMR) analysis was carried out to determine transesterification reaction levels. According to 1 H-NMR results, the increase in the level of transesterification was around 40% with the usage of PDI. The optimum loading level for selected chain extenders was determined as 1 wt.%, and PDI-based blends exhibited better properties when compared with those of the blends based on PBO and TPP at this loading level.

Acrylonitrile-butadienestyrene (ABS)/poly(methylmethacrylate) (PMMA)/ethylene methacrylate (EMA) composites were prepared with different blending sequences. All ABS/PMMA/EMA copolymers were designed to achieve the same total chemical composition, in which ABS/PMMA was equal to 80/20 and EMA was fixed at 6 wt%. The effects of different blending sequences on the mechanical and optical properties of ABS/PMMA/EMA blends were investigated. Results indicated that the tensile strengths of ABS/PMMA/EMA blends with different blending sequences were slightly affected, whereas the Izod impact strength of blends significantly varied. The impact toughness of the blends, in which PMMA/EMA was initially blended and then combined with ABS, was approximately twice that of the other blends. This blending sequence also had surface glossiness that was superior to those of the other blends. Differential scanning calorimetry and scanning electron microscopy further revealed that blending sequence influenced the phase miscibility and dispersion of the blends, which led to different mechanical and optical properties.

Fabrication of superhydrophobic films of polypropylene and of three different types of polyethylene was performed using a facile hot-press lamination and peeling process, which successfully fabricated a superhydrophobic film of linear low-density polyethylene (LLDPE). The water contact angle on the superhydrophobic reached as high as 160°, and the roll-off angle decreased to below 7°. The superhydrophobicity of the LLDPE film was attributed to a special surface morphology comprising micron- and submicron-sized fiber-like structures fabricated on the film surface by the hot-press lamination and peeling process. The method is based on the mutual adhesion and interdiffusion of polymer chains at the film interface during hot-press lamination and on the subsequent unzipping of the morphology during the peeling at room temperature. The effects of varying hot-pressing temperature and time on the surface morphology and wetting characteristics of the fabricated LLDPE films were also investigated.

Phenolic composites containing three different types of agricultural waste fillers (i.e. oil palm shell flour, rice husk flour, and coconut shell) have been prepared consecutively using the two-roll milling and hot pressed methods. The resulting granules were compression molded before mechanical testing. Mechanical properties of the agro-fillers/phenolic composites were investigated by means of flexural test, impact test, and heat distortion temperature measurement. Flexural test was conducted following ASTM D790, impact test was carried out according to ASTM D-256, while heat distortion temperature was measured using ASTM D648. The stiffness of the composites is insensitive to the increasing of the filler loading. The incorporation of the three different types of agro-waste fillers into the phenolic matrix produced composites with better heat distortion temperature as compared to that of the neat resin. Overall, coconut shell flour was superior in improving the flexural strength of the composites, while oil palm shell composites exhibited the most apparent improvement in heat distortion temperature.

The objective of this work is to use techniques such as Raman analysis and Raman mapping to confirm that graphene-based polyvinylidene fluoride (PVDF) composites can be used in strain sensing industrial applications. The I d / I g ratio is used to predict the defect level of unstrained graphene-PVDF films with respect to strained graphene-PVDF films. By analyzing the intensity variations of band in the spectra, the defect level present in strained graphene-PVDF films compared with that of unstrained graphene-PVDF films can be predicted. Area mapping is also conducted to correlate the defect variation between unstrained and strained graphene-PVDF films. Raman results were compared with defect level and in turn with induced strain. As expected, results are in concurrence with one another, thereby providing complementary and confirmatory analysis of the results to measure strain.