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The in-mold coating (IMC) as a mass production process offers potential to generate low-cost, high precision surface qualities on polymeric materials for optical applications, such as mirrors and reflectors. The combination of photocurable coating systems and the IMC process provides several advantages, especially short curing durations and reduced plant complexity. This work presents the generation of optical precision surface finishes on highly filled bulk molding compound (BMC) substrates by coating with UV-curable epoxy in a closed mold. The influence of process parameters as intensity, radiation dose and film thickness on surface finish and adhesion to the substrate is analyzed. Methods for adhesion improvement, such as surface pre-treatment, are taken into account as well. The curing behavior during the coating process is detected in-situ via dielectric analysis (DEA).

Mold filling is an injection molding stage of great significance, because many defects of the plastic components (e.g. weld lines, burrs or insufficient filling) can occur during this process step. Therefore, it plays an important role in determining the quality of the produced parts. Our goal is the temporal refinement in the vicinity of the evolving melt front, in the context of 4D simplex-type space-time grids [1, 2]. This novel discretization method has an inherent flexibility to employ completely unstructured meshes with varying levels of resolution both in spatial dimensions and in the time dimension, thus allowing the use of local time-stepping during the simulations. This can lead to a higher simulation precision, while preserving calculation efficiency. A 3D benchmark case, which concerns the filling of a plate-shaped geometry, is used for verifying our numerical approach [3]. The simulation results obtained with the fully unstructured space-time discretization are compared to those obtained with the standard space-time method and to Moldflow simulation results. This example also serves for providing reliable timing measurements and the efficiency aspects of the filling simulation of complex 3D molds while applying adaptive temporal refinement.

The laser transmission welding is one possibility to join parts, which have been produced in the special injection moulding process structural foam-moulding. Besides reduced weight such parts with reduced density show a reduced cycle time as well as improved size accuracy. Up to now there are no empirical values regarding the laser transmission welding of foamed injection moulded parts. For the use of the laser transmission welding process in a larger scale it is important to acquire knowledge in how far the structure of the foam influences the welding process, the bond strength and the structure of the joint. These knowledges allow an application-specific adjustment of the injection moulding process and the joining process. As part of a current research project the dependence of the foam structure to the injection moulding parameters have been determined using a breathing cavity. That way it is possible to produce parts, which have a defined thickness of the surface layer as well as specified average cell size. Therefore the integral foam parts are analysed via light microscopy. It is shown that the mass flow rate (MFR) has a major influence to the cell structure and the injection time has a significant influence on the thickness of the surface layer. Furthermore the opening speed while mould breathing has an influence on the cell size as well. In addition to these researches the transparent parts have been investigated regarding its transmission properties to show, that the cell structure influences the optical path of the laser beam and therefore the intensity distribution. In further researches the welding suitability of foamed parts is investigated. Therefore the energy input into the material is varied to create process windows and to determine suitable process parameters for the welding process. In addition it is necessary to research the welding pressure, because a high pressure can expel the melt from the joining area and destroy the cell structure.

Current simulation of the injection moulding process insufficiently consider the thermal interactions between melt, solidified material and mould. To improve the prediction accuracy in terms of shrinkage and warpage these interactions cannot be neglected and requires a precise observation of the temperature field within the ongoing process. Nowadays temperature measurements at the transition of the polymer melt to the mould or near the surface of the polymer melt are applicable and do not allow either a non-invasive analysis or a determination of the temperature field. In the approach of ultrasound tomography, presented here, an ultrasound beam is emitted into the melt and the time-of-flight (TOF) is detected by a set of transducers, which are radially arranged around the melt. Subsequent the measurement is repeated from different directions. Using algebraic reconstruction techniques, a distribution of the ultrasound velocity can be calculated based on the TOF-dataset. With additional information about th...

The design and manufacture of profile extrusion dies is characterised by costly running-in trials. Significant cost and time savings can be achieved by replacing the experimental running-in trials by virtual ones. A simulative optimisation, however, often leads to complex, free-formed flow channels. A feasible manufacture of such dies is only possible with additive manufacturing processes such as the Selective Laser Melting (SLM). Against this background, the manufacture of profile extrusion dies by SLM is investigated. A major challenge is to ensure a specific surface quality of the extruded plastics profiles. The roughness of SLM surfaces does not meet the high demands that are placed on the surface quality of extrusion dies. Therefore, in case of the SLM die a concept for the surface finishing of the flow channel is required, which can be applied to arbitrarily shaped geometries. For this purpose, plastics profiles are extruded both with a conventionally and an additively manufactured die. In case of the SLM die only the die land of the flow channel was reworked by polishing. The comparison of PP profile surfaces shows that the SLM die with polished die land leads to the same surface quality of the extruded profile as the conventional die (Ra ≈ l μm). Another important task in the design of profile dies by SLM is the optimisation of the die topology. The efficiency of the SLM process largely depends on the volume of the part being produced. To ensure the highest possible efficiency, it is necessary to adapt the die geometry to its mechanical loads and minimise its mass. For this purpose, the internal pressure in the die was numerically calculated and used for a first optimisation of the die topology. The optimisation, however, leads to a free-formed outer die wall so that the die cannot be tempered with heating tapes anymore. This problem is solved by using the high potential of SLM for functional integration and integrating contour adapted tempering channels into the extrusion die.The design and manufacture of profile extrusion dies is characterised by costly running-in trials. Significant cost and time savings can be achieved by replacing the experimental running-in trials by virtual ones. A simulative optimisation, however, often leads to complex, free-formed flow channels. A feasible manufacture of such dies is only possible with additive manufacturing processes such as the Selective Laser Melting (SLM). Against this background, the manufacture of profile extrusion dies by SLM is investigated. A major challenge is to ensure a specific surface quality of the extruded plastics profiles. The roughness of SLM surfaces does not meet the high demands that are placed on the surface quality of extrusion dies. Therefore, in case of the SLM die a concept for the surface finishing of the flow channel is required, which can be applied to arbitrarily shaped geometries. For this purpose, plastics profiles are extruded both with a conventionally and an additively manufactured die. In case of t...

Thermoplastic materials are extensively used as a light weight replacement for metal alloys, especially in automotive applications. Furthermore polymer materials can be used to enhance the safety of passengers and pedestrians in a car accident. The state of the art design process for plastics parts is based on Computer Aided Engineering (CAE). Using Finite Element Analysis (FEA), highly dynamic systems can be simulated with a very high accuracy. Considering crash applications, the influence of strain rate on the mechanical behaviour is of paramount importance. To determine the effect of strain rate on the mechanical behaviour, tensile impact tests are conducted at different haul-off velocities. With an increase of the haul-off velocity, the force-oscillation phenomenon becomes significant. The force-oscillation phenomenon is an artifact caused by the dynamic load application in highly dynamic tests. It can be monitored as a superimposition of measured force data with oscillations which increase in amplitude to higher impact velocities.This study looks at the phenomenon of force oscillation in tensile impact testing on viscoelastic materials and its dependency on longitudinal stress wave propagation. Aside a detailed analysis of its origin, a new approach is presented to measure a nearly oscillation free force signal in tensile impact testing on polymer materials, basically independent of the considered haul-off velocity. For this purpose a modification of a standard dumbbell specimen was designed.Thermoplastic materials are extensively used as a light weight replacement for metal alloys, especially in automotive applications. Furthermore polymer materials can be used to enhance the safety of passengers and pedestrians in a car accident. The state of the art design process for plastics parts is based on Computer Aided Engineering (CAE). Using Finite Element Analysis (FEA), highly dynamic systems can be simulated with a very high accuracy. Considering crash applications, the influence of strain rate on the mechanical behaviour is of paramount importance. To determine the effect of strain rate on the mechanical behaviour, tensile impact tests are conducted at different haul-off velocities. With an increase of the haul-off velocity, the force-oscillation phenomenon becomes significant. The force-oscillation phenomenon is an artifact caused by the dynamic load application in highly dynamic tests. It can be monitored as a superimposition of measured force data with oscillations which increase in amplitu...

For the production of composite components made of long-fibre reinforced thermoplastics (LFT) the economic compression moulding process is well established. However, the low temperature of the compression mould during processing leads to a significant increase in both the material viscosity and in the compression force in particular for thin-walled components. In addition, low surface qualities result which prevent the application of such components in visible areas. To overcome these disadvantages, a variothermal compression moulding process has been developed at the Institute of Plastics Processing (IKV) at RWTH Aachen University. With the variothermal mould technology a reduction of the viscosity of the moulding compound during processing is achieved. This results in a reduction of compression force by about 60 %. Additionally, moulding compounds with higher fibre contents (up to 60 % by weight) can be processed and the surface quality of LFT compression moulding components can be significantly increas...

Although various technologies are capable of producing plastics/metal hybrid parts for electrical applications, they all have disadvantages due to several manufacturing steps and limitations in productivity or the level of achievable geometrical part complexity. In addition, the material groups are often regarded separately, particularly when it comes to the materials-related forming processes. One approach to overcome these disadvantages, which is currently examined at the Institute of Plastics Processing (IKV) and the Surface Engineering Institute (IOT) at RWTH Aachen University within the scope of the Cluster of Excellence “Integrative Production Technology for High-Wage Countries”, is to combine the plastics injection moulding and the thermal spraying of metals to create a new multi-integrated process enabling the production of plastics/metal hybrid parts.The In-Mould-Metal-Spraying (IMMS) is intended to enable the integration of metallic coatings on plastics parts. In the first step, a metallic layer is applied to specific areas of the mould’s surface using thermal spraying, which is immediately followed by the plastics injection. During this second step, the metallic coating is transferred onto the plastics part. The plastics part including the transferred partially metallic coating is then removed from the mould.A strong, permanent connection between the plastics and the metallic coating and an exact outline replication of the metallic coating in the pre-assigned areas are to be realised. To develop and improve the new technology, the influence of different plastics types on the transferability of the metal coating onto the plastics part has been investigated systematically. Furthermore, the influence of the surface structure on the component design is investigated with the help of a test sample featuring a wide range of different surface structures. The results provide valuable information on the favourable process configurations and plastics/metal combinations.

The use of graphene as a filler in thermoplastics has already been investigated extensively. The mechanical properties as well as electrical and thermal conductivity of thermoplastics can be improved due to graphene. However, these studies were carried out in experimental scale, which allows a good dispersion of graphene because of a long residence time during melt mixing and because of the use of almost ideal graphene, which has a high specific surface and low number of layers. In this study the scientific findings are transferred into industrial practice. For that purpose, a co-rotating intermeshing twin screw extruder with limited residence time and limited shear energy input is used to produce graphene based polyamide 6 composites and short carbon fibre reinforced graphene based polyamide 6 composites. These composites are further processed by injection molding to produce specimens in order to determine the mechanical properties. In addition to the scale-up to industrial production, two types of graphene platelets are used, which are commercially available. This investigation reveals that the addition of 1 wt.-% commercially available graphene platelets to polyamide 6 improves Younǵs modulus and tensile strength. Compared to pure polyamide 6 an improvement up to 20 % with regard to Younǵs modulus and up to 15 % with regard to tensile strength can be achieved. The combination of short carbon fibre with graphene platelets in polyamide 6 enables an increase of Younǵs modulus, which is higher than the additive effect.

Due to intensive research in the field of material development considerable progress in terms of processing and performance characteristics could be achieved during the last years. Therefore, bio-based plastics are increasingly being used for the production of durable injection moulded components. Several applications can be found in the automotive sector, in the field of consumer electronics or the sports industry. For an economic production, joining technology often plays a key role to realise modular designed components. Detachable connections, which are frequently used in plastics processing (e. g. snap hooks or screw connections), often reach their limits with respect to reliability and tightness of the joint. In order to meet the increasing requirements on the joint, plastics joining processes can allow suitable component assembly. Bio-based plastics may differ from conventional plastics regarding their processing properties, such as the melting and solidification behaviour. For these reasons, inves...

Weld lines lead to a significant reduction of the mechanical properties of injection moulded parts. To provide a reliable method for the mechanical design of parts with weld lines, a calculation concept must be developed to predict the weld line strength. For this purpose, a semi-empirical model to describe a reduction factor depending on relevant process influences will be derived from the results of a variety of experimental investigations on stagnating and flowing weld lines. A simulation chain is developed to employ the model in an integrative simulation chain for injection moulded parts.

Light Emitting Diodes (LED) conquer the growing global market of lighting technologies. Due to their advantages, they are increasingly used in consumer products, in lighting applications in the home and in the mobility sector as well as in industrial applications. Particularly, with regard to the increasing use of high-power LED (HP-LED) the materials in the surrounding area of the light emitting semiconductor chip are of utmost importance. While the materials behind the semiconductor chip are optimized for maximum heat dissipation, the materials currently used for the encapsulation of the semiconductor chip (primary optics) and the secondary optics encounter their limits due to the high temperatures. In addition certain amounts of blue UV radiation degrade the currently used materials such as epoxy resins or polyurethanes for primary optics. In the context of an ongoing joint research project with various partners from the industry, an innovative manufacturing method for high precision optics for LED applications made of liquid silicone rubber (LSR) is analyzed at the Institut of Plastics Processing (IKV), Aachen. The aim of this project is to utilize the material-specific advantages of high transparent LSR, especially the excellent high temperature resistance and the great freedom in design. Therefore, a high integrated injection molding process is developed. For the production of combined LED primary and secondary optics a LED board is placed in an injection mold and overmolded with LSR. Due to the integrated process and the reduction of subcomponents like the secondary optics the economics of the production process can be improved significantly. Furthermore combined LED optics offer an improved effectiveness, because there are no losses of the light power at the transition of the primary and secondary optics.

Current models of the injection moulding process insufficiently consider the thermal interactions between melt, solidified material and the mould. A detailed description requires a deep understanding of the underlying processes and a precise observation of the temperature. Because todays measurement concepts do not allow a non-invasive analysis it is necessary to find new measurement techniques for temperature measurements during the manufacturing process. In this work we present the idea of a set up for a tomographic ultrasound measurement of the temperature field inside a plastics melt. The goal is to identify a concept that can be installed on a specialized mould for the injection moulding process. The challenges are discussed and the design of a prototype is shown. Special attention is given to the spatial arrangement of the sensors. Besides the design of a measurement set up a reconstruction strategy for the ultrasound signals is required. We present an approach in which an image processing algorithm can be used to calculate a temperature distribution from the ultrasound scans. We discuss a reconstruction strategy in which the ultrasound signals are converted into a spartial temperature distribution by using pvT curves that are obtained by dilatometer measurements.

The variothermal extrusion embossing process enables a high quality replication of microstructures in plastics films. In this advancement on regular flat film extrusion a polymer melt is shaped by a flat film die and cast on an embossing roll. The surface of the embossing roll has the negative form of the desired microstructure. A counter pressure roll is used to apply the line force needed for embossing, thereby transferring the microstructure into the polymer melt. The melt stays in contact to the embossing roll allowing for a rapid cooling of the film and a solidification of the microstructures inside the molds on the embossing roll’s surface. At the haul-off point the cooled down film is removed from the roll. The governing process parameters for successful embossing are the melt temperature, the viscosity, the surface temperature of the embossing roll and its rotation speed. By tempering the embossing roll to a low base temperature while using an electrical inductor or a high-power infra-red laser as...

This paper deals with investigations of the mixing behaviour of rubber extruders. The requirement to obtain a high-quality elastomer product is a thermally and materially homogenous rubber mixture. Because of the highly viscous and multicomponent nature of rubber mixture, extruders require a thoroughly distributive and dispersive mixing behaviour. The current state of the art is the pin-type rubber extruder with cylindrical pins which extend radially into the screw channel, causing a constant deformation and reorientation of the rubber melt. As mixing is of crucial importance, the mixing behaviour of pin-type rubber extruders is analysed with the goal of optimising it. The starting point of the optimisation is the current cylindrical pins. Over the course of the investigation, new pin designs and geometrical arrangements are investigated.

Thermoplastic materials are increasingly used as a light weight replacement for metal, especially in automotive applications. Typical examples are frontends and bumpers. The loads on these structures are very often impulsive, for example in a crash situation. A high rate of loading causes a high strain rate in the material which has a major impact on the mechanical behavior of thermoplastic materials. The stiffness as well as the rigidity of polymers increases to higher strain rates. The increase of the mechanical properties is superimposed at higher rates of loading by another effect which works reducing on stiffness and rigidity, the increase of temperature caused by plastic deformation. The mechanical behavior of thermoplastic materials is influenced by temperature opposing to strain rate. The stiffness and rigidity are decreased to higher values of temperature. The effect of thermal softening on thermoplastic materials is investigated at IKV. For this purpose high-speed tensile tests are performed on a blend, consisting of Polybutylenterephthalate (PBT) and Polycarbonate (PC). In preliminary investigations the effects of strain rate on the thermomechanical behavior of thermoplastic materials was studied by different authors. Tensile impact as well as split Hopkinson pressure bar (SHPB) tests were conducted in combination with high-speed temperature measurement, though, the authors struggled especially with temperature measurement. This paper presents an approach which uses high-speed strain measurement to transpire the link between strain, strain rate and thermal softening as well as the interdependency between strain hardening and thermal softening. The results show a superimposition of strain hardening and thermal softening, which is consistent to preliminary investigations. The advantage of the presented research is that the results can be used to calibrate damage and material models to perform mechanical simulations using Finite Element Analysis.

Production efficiency is one of the most important demands in blown film production. In many cases, the cooling power is the limiting factor for an increased output. A possible solution for a better cooling is the use of a cooling sleeve right after the outlet of the die in addition to the conventional air rings and internal bubble cooling (IBC). At the Institute of Plastics Processing (IKV), first tests were conducted to investigate the advantages of the use of a cooling sleeve. Therefore, the influence of several geometries of the cooling sleeve surface and different cooling sleeve temperatures on the process stability and the mechanical and optical film properties is investigated. The cooling sleeve surfaces differ in the tapping between inlet and outlet diameter from 0 % (cylindric) to 10 % (conical). The tests show that a high amount of tapping as well as too high resp. low cooling sleeve temperatures cause process instabilities and an uneven thickness profile of the film. While the mechanical film properties (E-modulus, elongation at break, tensile strength) of the films produced by the use of a cooling sleeve (cs-films) do not significantly differ from the values of the reference films, the haze of the cs-films was higher and therefore worse. A measurement of the bubble temperatures above the air ring shows that the use of a cooling sleeve can significant lower the bubble temperature at this point. Because of this and because of the results of the mechanical tests, the principle of a contact cooling is generally applicable. Further research and development on the geometry of the cooling sleeve surface has to be done to improve the process stability and the haze for a possible industrial application.