Wolfgang Nendel

New Biocomposites for Lightweight Structures and their Processes

The development of new biocomposites and efficient manufacturing methods that are suitable for series processing is the purpose of the current sub-project C4 of the Excellence Cluster MERGE, sponsored by DFG (Deutsche Forschungsgemeinschaft). Two different types of materials are combined: bio-based thermoplastic polymers such as bio-polyethylenes or bio-polyamides and renewable reinforcing materials such as thin wood veneer or unidirectional flax fibers. To achieve a high-efficiency in terms of mass-production, reproducibility and flexibility, it is required to perform several steps in the realization of semi-finished and final products. The improvement of the adhesion at the interface of the components, the implementation of continuous processes, in order to increase energetically the yielding, and the final design, through several methods, for future potential applications are so many perspectives to achieve.

Initial Stress Behaviour of Micro Injection-Moulded Devices with Integrated Piezo-Fibre Composites

Based on an increasing demand for function integration in small components, micro injection moulding offers a highly productive solution to combine plastic structures with additional electronic and mechatronic features. Particularly two-component micro injection moulding allows embedding of active elements as well as the application of electric contacts in one process step by using insolating and conductive compounds, respectively. The study outlines major effects on the thermo-mechanical compatibility of active modules comprising several stacked piezo fibre composite beams. With regard to material properties, geometry of the module, machine set up and processing parameters a structural and strength analysis including process induced residual stress is used to predict favourable material combination and composite design.

Polypropylene Based Piezo Ceramic Compounds for Micro Injection Molded Sensors

Polymer matrix compounds based on piezo ceramic and electrically conducting particles within a thermoplastic matrix show distinctive piezoelectric and dielectric effects which can used for sensor applications. The electrical and mechanical properties can be adjusted in a wide range by varying the ratio of active filling particles and the matrix materials. The sensor effect of the compound is generated by the ceramic particles. A large ratio of piezo ceramic powder facilitates a high sensitivity. The electrical permittivity of the otherwise insulating matrix polymer can be adjusted by the amount of conductive filler. An aligned permittivity leads to a stronger electrical field in the ceramic particles. In contrast, too many conductive particles create a conductive network in the compound which short-circuits the sensors. The piezo ceramic compounds can be processed via micro injection molding for application as ceramic sensors. This offers a wide range of new sensor design variants, notably three-dimensional and highly complex geometries. However, there are two main demands for a highly sensitive sensor, which are conflicting. On the one hand the filler content of piezo ceramic particles in combination with electrical conductive carbon nanotubes must be very high, on the other hand the wall thickness should be as thin as possible. For filling cavities with a high aspect-ratio in an injection molding process, low viscosity polymer melts are necessary. These process characteristics conflict with the increasing viscosity by filling the melt with the particles. The sensor measuring area has to be designed as thin walled as possible. In order to overcome this obstacle a dynamically tempered mold design is applied to avoid solidification of the melt, before the mold is completely filled. The mold can be tempered by Peltier elements. The fully electric tempering is cleaner, more precise and more reliable than conventional water or oil tempering.

Process Combination of Hydroforming and Injection Moulding for the In Situ Manufacturing of Metal and Plastic Composite Structures

The use of lightweight structures is a major trend in the reduction of fuel consumption and CO2 emissions, especially in transport. Metal plastic hybrid structures are an efficient solution to use the best material at every point in the design space. In the state of the art production technologies, the metal parts are produced separately from the plastic parts. The injection moulding process is only used for forming the plastic parts and for joining. These process chains are very extensive. The article shows the development of new process combinations. The aim is a combination of metal forming and injection moulding in one die and one process. One part should be produced with every single stroke of the press.In the first step, deep drawing, injection molding and media based forming with the plastic melt were successfully merged in one tool and one process. It was possible to integrate the injection moulding process into a deep drawing machine. In the next step, it was possible to successfully combine hydroforming and injection molding. For this process combination the hydroforming process is integrated into an injection moulding press. Different surface structures of the metal tubes, such as sandblasting, knurling and laser structuring, were systematically tested regarding to their properties as an adhesion promoter. The target is to establish a purely mechanical connection between the hydroformed metal component and the injection moulded component from glass fibre reinforced plastic instead of the chemical bonding agents often used previously, such as Vestamelt®.

Natural unidirectional sheet processes for fibre reinforced bioplastics

Technical natural fibre semi-finished products are mainly used in lightweight automotive components as random fiber mats which are often combined with petrochemical matrix resins for large series production process. However, random fiber arrangement and limited fiber length restrain the complete utilization of the material-inherent strength reserves of natural fibers. With high-levels of petroleum-based plastics (about 20-50 wt -%) in the structure, these applications have a clear potential in terms of eco-friendliness and sustainability. The development of new fully bio-based composites and efficient manufacturing methods suitable for series processing is the purpose of the current sub-project C4 “Flexible textile / plastics processes with renewable raw materials” in the framework of the Excellence Cluster MERGE EXC 1075, funded by DFG (Deutsche Forschungsgemeinschaft). A high-efficiency in terms of mass-production, reproducibility and flexibility requires the performance of successive steps in the manuf...

Natural Fibre Reinforced Bioplastics - Innovative Semi-Finished Products for Series Production

The development of innovative bio-based composites with efficient manufacturing processes is the purpose of the current project C4 in the framework of the Excellence Cluster MERGE EXC 1075, funded by DFG (Deutsche Forschungsgemeinschaft). Efficiency in terms of mass-production, reproducibility and flexibility requires the performance of successive steps in the manufacture of semi-finished and final bio-based products. About bio-based materials, natural fibres composite (NFC) prepregs have been recently investigated as a potential cost-efficient semi-finished product. By means of continuous production processes, prepreg rolls can be manufactured with unidirectional natural fibres (flax) fabrics as reinforcement and thermoplastic biopolymers films as matrix. The used natural fibre non-crimp fabrics are made of high twisted yarns. For a better impregnation and higher stiffness properties, non-crimp fabrics with non-twisted yarns, which have been lastly developed by natural fibres suppliers, represent an appropriate solution. A second suitable option is the substitution of the biopolymer films, whose impermeability does not facilitate the release of humidity from the natural fibres while the impregnation, by produced low cost thermoplastic spunlace fabrics with a higher permeability and lower reachable surface weights. With these material developments and innovative process optimizations suitable to natural fibres, NFC prepreg properties tend to be improved. From prepregs to finished parts can be implemented by discontinuous processes, with compression molding and back-injection molding, or by continuous processes, with devices gathering several stages such as cutting, stacking, points welding, pre-heating and back injection molding. By stacking, a multi-axial orientation of prepregs can be performed in order to optimize the placement of reinforcing yarns according to the possible load path of future products. The mechanical properties profile of the combination of non-crimp natural fibres fabrics with thermoplastic films or thermoplastic spunlace fabrics has been here studied in detail with press-engineered samples and has confirmed the potential as an alternative to glass fibre-reinforced composite.

The Development of Lead-Free Sliding Contacts Based on Bronze-Graphite Composites through Powder Injection Moulding

Sliding electrical contacts are traditionally produced by conventional compacting technologies. Employing the powder injection moulding process (PIM) as a new manufacturing method can offer several advantages such as the fabrication of complex net-shaped parts, cost-effectiveness and high volume productions. The PIM process route consists of the following steps: powder processing, compounding, injection molding, debinding and sintering. A two-stage process consisting of solvent debinding and thermal debinding is often used to remove the moulding binder. In the present paper, the suitability of the powder metallurgical processes: mechanical alloying and powder mixing for the preparation of bronze-graphite powder mixtures for the compounding and injection moulding of sliding contacts is discussed. The use of a suitable binder is of central importance for the preparation of injection-moldable feedstocks. For this purpose, two commercial ready-to-use binder systems were utilized and evaluated. The essential challenge of the process route is to optimize all parameters of the subprocesses to achieve a damage-free debinding and sintering of the injection-moulded parts. First results on the influence of the graphite content, the binder fraction, the debinding and sintering parameters are presented and discussed.

Nozzle and Hot Runner Systems for Injection Moulding Machines for the Manufacturing of Moulded Thermoplastic Composite Parts with Skin-Core Structure (Sandwich Mouldings)

Injection moulding of thermoplastic melts is based on the source flow. This principle allows for the production of mouldings in skin-core structure: the core enclosed on all sides by skin material may consist of a different or modified thermoplastic material. Generally, this method is referred to as co-injection or also sandwich injection moulding.Known applications of this method include processing of recycled material in the core and new material for the surfaces, foaming (chemically and physically) of the core material, processing of filled core material, e.g. Glass fibres and unfilled material for the surfaces. Other combined methods, e.g. with gas and water injection, are possible.The report describes the nozzles and hot runners developed by A&E Produktionstechnik Co. for the application of this method. Sample mouldings, produced and developed by customers and research cooperation partners, demonstrate the potentials and limits of the procedure in regard to the combination of different thermoplastic melts in a moulded part.

CATPUAL - An Innovative and High-Performance Hybrid Laminate with Carbon Fibre-Reinforced Thermoplastic Polyurethane

In consideration of environmental aspects and limited availability of resources, the focus of automotive and aerospace industry lies on significant weight optimisations especially for moving loads. In this context, innovative lightweight materials as well as material combinations need to be developed. A considerable potential for lightweight structures can be found in fibre- or textile-reinforced semi-finished products. Due to their specific characteristics and extraordinary structural diversity, thermoset and thermoplastic matrix systems can be used. In particular, carbon fibres as reinforcing components combined with a thermoplastic matrix polymer are able to create new high-performance applications. Besides the significant lightweight characteristics of the fibre-plastic-composites, in some instances contrary requirements must be satisfied in many areas, such as strength and ductility. In this field, the combination of fibre-reinforced polymers with aluminium or titanium sheets creates unique composite materials, so called hybrid laminates, which fulfil the unusual expectations.The focus of the current study lies on the development of a new thermoplastic hybrid laminate named CATPUAL (CArbon fibre-reinforced Thermoplastic PolyUrethane/ALuminium laminate). The structure of the laminate is an alternating sequence of thin aluminium sheets (EN AW 6082-T4) and fibre-reinforced thermoplastic polyurethane (TPU). The individual layers are consolidated to each other by using a hot pressing process. First results showed that the impregnation capability of thermoplastic polyurethane surpasses any other commercially available hybrid laminates. Furthermore, the mechanical properties regarding bending strength and interlaminar shear strength are exceeding the state of the art drastically.

Ultrasonic-Impregnation for Fiber-Reinforced Thermoplastic Prepreg Production

Fiber-reinforced thermoplastics have a high potential for big scale light weight process applications due to low processing times and recyclability. Further advantages are the low emissions during the manufacturing process and beneficial handling and storing properties of the semi finished materials. Thermoplastic composites are made of reinforcement fibers and a thermoplastic polymer matrix by applying two essential sub processes: (1) melting of the matrix-material and (2) impregnating the textile component with molten matrix-material. At present state of art both sub-processes are applied by using double-belt-presses, characterized by high processing temperatures and high processing forces. Therefore, a large amount of energy is needed to create the necessarily high compaction forces and temperatures with hydraulic cylinders and electric heating. Convection, infrared-radiation and the cooling (dynamic) of tempered machine parts leads to a significant dissipation of energy. Especially the process for generating the hydraulic pressure has a low level of efficiency. Therefore, in respect to economic and ecologic reasons, novel energy-efficient impregnation processes need to be investigated and developed. The represented novel impregnation process is based on ultrasonic technology. A stack of polymer film (outer layers) and a textile ply (inner layer) is formed and the energy is applied with an ultrasonic sonotrode. The efficient, fast and strongly concentrated energy application into the thermoplastic films allows the development of novel and highly flexible machine concepts. These can be used for development of small scale up to large scale production processes. The ultrasonic-technology allows a continuous impregnation of the textile component with molten matrix-material. A custom-designed prototype was developed. First material samples were produced and the technological parameters studied. A characterization of the experimental results, material samples, prototype machine and process is the focus of this paper.