Jürgen Tröltzsch

On the numerical simulation of injection molding processes with integrated textile fiber reinforcements

In the present article, the polymer melt impregnation of textile fiber reinforcements in an injection molding process is explored theoretically and experimentally. Simplifying the numerical simulation of the thermoplastic melt flow behavior a specific mold with integrated single-glass fiber bundle was developed and used for experimental fill studies with thermoplastic melt. The polymer melt impregnation of the fiber bundle in the injection molding process is modeled and calculated with Complex Rheology Polymer Solver (CoRheoPol), a simulation tool developed at Fraunhofer Institut fŭr Techno- und Wirtschaftsmathematik by the present authors. Navier-Stokes and Navier-Stokes-Brinkman equations are used to describe the melt flow in a pure fluid region and porous media, considering the non-Newtonian flow behavior of thermoplastic melts. Experimental and numerical results are compared determining the filling fronts and fiber impregnation of the injection molded test samples. A clear relationship between the degree of impregnation, verified by magnified photomicrograph, and the position of flow front can be detected. A good correlation of simulated and experimental flow fronts against the degree of filling of the mold is observed too. The differences in macroscopic flow behavior between the cavity with and without an integrated fiber bundle with respect to the impregnation process can be simulated with high accuracy.

Computational modelling of the complex dynamics of chemically blown polyurethane foam

This study presents computational analysis of the complex dynamics observed in chemically blown polyurethane foams during reaction injection molding process. The mathematical formulation introduces an experimentally motivated non-divergence free setup for the continuity equations which reflects the self expanding behaviour observed in the physical system. The foam growth phenomena which is normally initiated by adequate pre-mixing of necessary reactant polymers, leading to an exothermic polymerization reaction, bubble nucleation, and gas formation, is captured numerically. We assume the dependence of material viscosity on the degree of cure/polymerization, gas volume fraction, and temperature as well as non-dependence of mixture density on pressure. The set of unsteady nonlinear coupled partial differential equations describing the dynamics of the system are solved numerically for state variables using finite volume techniques such that the front of the flow is tracked with high resolution interface captu...

CAPAAL and CAPET – New Materials of High-Strength, High-Stiff Hybrid Laminates

The natural resources available for national and international economic development are limited. A gentler and more efficient use of available energy and materials in all sectors is essential. In mobile applications in particular, in which large masses are moved and accelerated (e.g. automotive, railway, aircraft and in machinery and equipment), a consequent lightweight construction is necessary for a significant saving of energy.

Mechanical properties of polymer melt-impregnated fiber tape sandwiches using injection molding technology

In this study, the direct melt impregnation of unidirectional glass fiber tapes in an injection molding process is investigated. The simple textile structures were used for a load-adapted reinforcement of injection-molded parts, determining the impregnation quality by mechanical tests. A sandwich layer construction was made with an outer unidirectional fiber layers and an inner injection-molded layer with pure or additionally short fiber-reinforced polypropylene (PP). The glass fiber tapes were produced in a continuously working fiber–foil process where the aligned fiber bundles have been fixed with one side on a PP foil under temporarily acting pressure and temperature. A special bundle spreading device reduced the number of individual fiber layers, which ensured the direct melt impregnation in the injection molding process. The mechanical properties of the sandwich structures were determined using a three-point bending flexural test as well as Charpy and puncture impact tests to investigate the energy absorption. The results were compared to unreinforced and globally short fiber-reinforced test samples. The local reinforcement, designed for bending stiffness and energy absorption, led to a considerable reinforcement effect with minimal mass increase in comparison with the short fiber-reinforced samples. The fiber masses required to achieve commensurable properties were significantly reduced. Thus, when using the fiber tapes, only one-third of the fiber mass necessary for reinforcement with short glass fibers was required.

Material Selection and Process Configuration for Free-Form, Voluminous and Textile-Based Multi-Material-Design by the Example of a Bucket Seat

Hybrid textile-based composites possess an enormous potential for energy and resource efficient large-scale production, with freedom in and high specific mechanical properties. This paper covers the connection of available and established production processes for textiles in a differential process chain for the manufacturing of complex shaped and elastic sandwich components. The technology enables both stiffness and comfort through elasticity.OLU-Preg®-organic sheets, polyurethane foam cores and 3D-spacer fabrics form the targeted properties of demonstrator models. This article refers to the demonstrator part “bucket seat”. To show the benefit of complex composite material, the lightweight and mechanical properties of the sandwich structures are tested in several variations of core and comfort shapes. Absolute and specific improvements of performance are shown in static and dynamic examinations. An Analysis of coupling effects, deformation and failure behavior of the multi-material design (MMD) complete the scientific approach of the structure-property relationships of hybrid composites.

Investigation of Polymer Melt Impregnated Fibre Tapes in Injection Moulding Process

The polymer melt impregnation of glass fibre tapes or rovings is of vital importance for manufacturing textile reinforced thermoplastic composites. In the present paper, the polymer melt impregnation of fibre bundles in injection moulding process is investigated by a specific pull-out test which allows the preparation of the investigated specimen near to process. Several glass fibre roving types with varying appearance and yarn count were placed as a tape insert in a mould for thermoplastic injection process and were impregnated with the injected poly-propylene melt. The fibre bundle pull-out test then was used to determine the quality of melt impregnation which could be verified by magnified photomicrograph. A clear relationship between maximal load in pull-out test and impregnated fibre fraction has been observed. Also a strong influence of the fibre bundle geometry and yarn count on impregnation quality was detected.

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.

Investigation of the specific adhesion between polyurethane foams and thermoplastics to suited material selection in lightweight structures

Lightweight construction combines various materials to create resource efficient components. Thermoplastics (TPs) combined with polyurethane (PUR) foams are increasingly used to create hybrid composites. Optimizing the energy efficiency is one of the main issues in the development of production processes of components. Reducing the number of process steps offers great potential in this respect. PUR foam develops a strong adhesive bond with most materials. This is used for the manufacturing of hybrid composite components by filling complex cavities with PUR foam simultaneously bonded with other TP polymer components. This way, one process step for joining is saved. The interfaces in this composite structures are critical points of the failure. A huge variety of TP is used for the production of hybrid composite components and PUR foam develops varying bonding strengths with all of them. Selecting the suitable TPs for a durable bonding with PUR foam in the desired production process necessarily requires information about the respective specific adhesion. In this investigation, different TPs were processed with PUR foams in order to manufacture sandwich composites. The TP facings are produced in the injection moulding process. Subsequently, the facings are combined with the foam core during reaction injection moulding. The wetting behaviour was examined using the contact angle measurement and the mechanical strength of the interface in the sandwich composite was determined using a tensile test. A precise order of the selected TPs concerning their specific adhesion to PUR foams was achieved with these investigative methods.

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.

Textile-based surface design of thermoplastic composites for microstructural adhesion to polyurethane foams for lightweight structures

ABSTRACT In an effort to reduce the mass of components, sandwich design has become well established above all in the aerospace and the vehicle construction. In these structures, facings and cores made of very different materials are joined using a wide variety of technologies. The challenge in the use of this type of construction frequently results both from generating component joints stable enough to bear loads and the productivity of the manufacturing process. This publication investigates the textile-based surface design of thermoplastic composites which create optimised conditions for the bonding of Polyurethane (PUR) foam cores in the in-situ foaming. The reinforcement layer structure is represented on the surface by varying the layer stack in the production of textile-based thermoplastic composites through pressing. This approach is resource and energy-efficiency because it includes no additional process steps. Two thermoplastic composite variants with differently firmed textile surface structure were manufactured and analysed. In reaction injection moulding, each variant was processed with two different PUR foam cores to obtain sandwich structures. Bonding between the facings and the core was only achieved by means of textile microstructuring, which was demonstrated in the analysis of the basic materials and the microstructure penetration through PUR foam as well. The mechanical capacity of the interface was determined by the sandwich structures in the tensile test. In future studies, a bulky, textile-based lightweight construction material in sandwich design that is both suitable for application and capable of being mass produced will be developed based on these investigations. Graphical Abstract