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 is a platform for publication of results from current research in the field of Plastics Technology. The Journal`s aim is to broaden public access to scientifically qualified, German and English contributions from the fields of material, construction and processing of plastics. Downloads are free of charge.

Optically excited Lockin-Thermography is well suited for fast and robust detection of near-surface defects in isotropic and fiber-reinforced plastics. The resulting phase images are driven by the excitation frequency as a measurement parameter and can be analyzed in the one-dimensional case for depth-selective evaluation. For real test specimens, however, diffusive heat conduction processes overwhelm which makes accurate defect characterization from phase images much more difficult. Neural networks are used within this work to evaluate multiple phase values of different excitation frequencies with each other and thus implement for the first time a quantitative defect characterization in isotropic and fiber-reinforced plastics based on a LSTM-CNN hybrid model. It is shown that the already good prediction values of the neural network are again significantly improved by additional training data obtained from heat flow simulations.

Representation of the experimental setup: thermographic camera (bottom left), photodiode (top left), VCSEL array (right), CFRP test specimen (center).

Industrie 4.0 für die Qualitätssicherung

Künstliche Intelligenz für die Qualitätssicherung

Faserverbundwerkstoffe

Polymethylmethacrylat

Defect characterization in isotropic and fiber-reinforced plastics using active thermography and neural networks

This article describes a production process for environmentally friendly and resource-efficient molded parts consisting of innovative wood chip plastic composites (in German: Holz-Kunststoff-Verbunde, HKV).

HKV in a density-specific materials comparison

Duroplastische Werkstoffe

Thermoplaste

Produktentwicklung(sprozess)

Development of a production process for environmentally friendly and resource-efficient molded parts consisting of load-appropriate reinforced wood-plastic composites

A rotating mould core can induce shear in the tangential direction during injection, which superimposes the injection-induced shear. In the case of fibre-reinforced thermoplastics, this results in a reorientation of the fibres in tangential direction. This paper shows how a rotating mould core influences the fibre orientation and bursting strength of short-fibre-reinforced polypropylene and polyamide respectively. Furthermore, different wall thicknesses and fibre contents are investigated at varying rotational speeds. Regardless of the used material and the wall thickness, strength increases of more than 75 %are possible at the appropriate speed.

Schematic representation of the rotational shear rate due to the rotating tool core

Spritzgießen

Werkzeugkonstruktion

Polyamide

Polypropylen

Influencing the fibre orientation of polypropylene and polyamide in the injection moulding process by a rotating mould core

Up to now, the relevant interactions between thermoplastics and metal surfaces at the interface have not been fully investigated. In this article, possible intermolecular interactions between plastics and metal surfaces are described and investigated on injection-moulded composite specimens made of polyamide 6 and polybutylene terephthalate with aluminum as a composite partner. The results of the investigation show that the composite adhesion is mainly based on intermolecular interactions between the composite partners and not on mechanical form-fit. If the polar surface of the aluminum is chemically inactivated without changing its surface topography, then no composite adhesion occurs.

Intermolecular interactions through hydrogen bonds between a carbonyl group in polyamide and a metal hydroxide surface.

Polybutylenterephthalat

Hybridwerkstoffe

Aluminium

Kupfer

Oberflächentechnik

Hybrid-Spritzgießen (Metall / Kunststoff)

Optische Mess- und Prüfverfahren

Intermolecular interactions and their influence on the adhesion between plastics and metal surfaces

With the help of CFD simulations, a nozzle system (top nozzle) for hot gas welding is developed, which encloses the weld seam during heating. The significantly more controlled flow behavior of the hot gas improves the processing window, increases the reproducibility and achieves a significantly more efficient heating time of the polymer weld seam. The CFD simulations used to develop the new nozzle system are validated by temperature measurements in the hot gas welding process with IR camera and thermocouples.

Hot gas welding station (left) and flow field of the investigated process (right)

Düsen, allgemein

Simulation Schweißen

Thermisches Fügeverfahren

Analysis of two different nozzle systems for hot gas welding using CFD simulations and measurement results

The occurrence of process-specific defects in the wet filament winding process requires an oversizing of the components which leads to high additional material costs, especially for 700 bar type-IV pressure vessels. This paper presents the development of a quality control together with an image processing algorithm based on an industrial camera with which manufacturing deviations in the cylindrical area of the vessels can be determined.

An industrial camera is used to inspect a pressure vessel for manufacturing deviations during the infeed of fiber slivers.

16:9

Bildverarbeitungs-Software

Qualitätssicherung

Wickelmaschinen

Qualitätssicherung Kunststoff

Use of an industrial camera for quality control in the production of the cylindrical area of type-IV pressure vessels in the wet filament winding process

This paper presents a new method for in situ deformation and wear measurement of polymer gears under operating loads. This new approach is based on the highly accurate measurement and tracking of time differences in the index pulses of encoders on the driving and driven side of a gear test rig.

Example pairing of two gears for the determination of elastic, plastic and wear deformation components

Zahnräder

Verschleißprüfgeräte

Tribologie

Getriebe

Test Rig for the In Situ Measurement of the Deformation Characteristics of Polymer Gears

In this research project an algorithm is developed and tested, which enables the automated optimization of dynamic mixing elements. For this purpose, selected geometry parameters are optimized by a genetic algorithm on a parameterized spiral shear mixer in such a way that flow conditions that favor mixing are established. In order to avoid manual evaluation of the flow results, quality criteria are introduced which are automatically calculated. A total of nine different quality criteria are used, which not only assess the potential of the flow field to implement distributive and dispersive mixing mechanisms, but also include processing aspects such as the fluid change effectiveness of the system. The results of the test show that an automated optimization can be carried out with the selected quality criteria and further improvement measures for the algorithm can be derived.

Automated optimization of dynamic mixing elements

In the present study, the pressure-dependent orientation relaxation was investigated by varying the mold temperature and cavity pressure in the context of a new injection-compression molding process with dynamic mold temperature control. For this purpose, isothermal pvT measurements were used to define a process window around the pressure-dependent glass transition region within which the injection-compression molding experiments were carried out. Initially, orientations were systematically introduced into the component via the filling phase, and their pressure- and temperature-dependent relaxation was observed during an isothermal and isobaric holding phase by means of photoelasticity images and path difference measurements. A clear pressure and temperature dependence of the orientation relaxation could be found, whereby with increasing mold temperature and decreasing cavity pressure, smaller path differences could be measured as a result of lower orientations.

Spritzprägen

Dynamische / variotherme Temperierung

Pressure-dependent orientation relaxation in injection compression molding with dynamic mold temperature control

Leakage in vacuum bags for fibre composite production is a frequently occurring defect, especially in the manufacture of components using the open mould process. The previous limit values for assessing the leak tightness of a vacuum set up are mostly historical and based on empirical values. In this paper, the effects of leaks that have been introduced in a defined manner into a vacuum bag are investigated. The physical processes that occur during curing within the leaking vacuum structure are analysed optically as well as by means of ultrasonic testing and thickness measurement and a better understanding of the effects on laminate quality is generated. It is found that there is a difference between leakages in the vacuum bag only and leakages that affect both the vacuum and release film.

Verbundwerkstoffe / Werkstoffverbunde

Influence of leaky vacuum bags on the quality of composite parts made from prepreg material

The process stability of injection moulding is negatively influenced by disturbing influences. An adaptive, close-phase process control strategy, which defines the reference curve for a subordinate cavity pressure control, should enable constant part quality. The influences of the cyclical changes are analysed for different control strategies by evaluating the process variable curves and the part weight during the start-up process. Up on that, it is evaluated whether the examined process variables are relevant for process control and therefore cyclical adjustments of the cavity pressure reference are necessary.

Werkzeuginnendrucksensoren

Prozesssimulation

Effects of cyclical process influences on the cavity pressure curve and part quality in the injection moulding process

The article presents a process simulation environment for the additive fused layer modeling process. It allows the simulation of an extruded melt strand as a function of process parameters which are specified by the machine in additive manufacturing and whose influence cannot currently be predicted and computer-aided determined. The challenge here is the implementation of pressure and temperature dependent properties, since these are not provided for in common CFD environments in terms of fluid mechanics. The validation of the process simulation developed in OpenFOAM is based on experimental thermographic analysis.

Verfahren für die additive Fertigung

Development of a Computer-Aided Approach for Modelling the Strand Deposition in Extrusion-Based Additive Manufacturing

For simulations of the mechanical behavior of short-fiber reinforced plastics, a variety of commercial software tools are available. The planning of modern product development processes makes a decision regarding the selection of a suitable tool necessary. Therefore, a suitable methodology is necessary for this selection. Using the methodology presented in this study, the mechanical behavior of a PP-GF30 is simulated using four commercial tools. It turns out that there are significant difference between the tools used, particularly with regard to material failure under multiaxial load. The presented methodology creates a reliable basis for the application-dependent selection of the most suitable software.

Evaluation methodology of commercially available homogenization software for the optimized simulation of the mechanical behavior of short fiber reinforced plastics

In addition to the previous state of the art in science and technology, in this publication spruce fibres from a thermo-mechanical pulping process were directly compounded with polypropylene and coupling agent using an injection moulding compounder. An increasing wood fibre content of up to 30 wt.% was investigated in direct single-stage processing. The characterisation of the material combinations is carried out by tensile tests, melt-flow-rate measurements, density determination, microscopy and impact tests. An increase in tensile properties, viscosity and density is observed with increasing wood fibre content. The impact strength is lower compared to the unchanged base polymer, but remains constant within the standard deviation with increasing wood fibre content.

Reinforcement of polypropylene with wood fibres by direct compounding

Conventional additive manufacturing processes such as Fused Layer Manufacturing (FLM) technology make it possible to produce any structures from a wide variety of materials without tools in a very short time. In addition, layer-by-layer processes hardly make use of the technical manufacturing degrees of freedom with regard to the filling strategy and existing anisotropy. Therefore, in the present publication an optimality strategy for 2.5D-FLM structures shall be presented which is based on a principal normal stress analysis. The goal is to generate a structure design that is suitable for the requirements and production process by means of simulation-based methods. In addition to the methodical imple-mentation, experiments on generic open hole plates with different filling strategies serve to validate and first confirm the method.

Application of a principle normal stress oriented filling strategy for Fused Layer Manufacturing structures

Currently, a nozzle consisting of a series of round tubes (round nozzle) is used as standard for hot gas welding. A newly developed nozzle (top nozzle), which surrounds the weld joint during heating, enables a reduction of the heating time of the resin by up to 60 % during the hot gas welding process. For PA66-GF35, for example, the heating time can be reduced up to 15 s compared to a round nozzle system. In addition, the melting of the resin is much more uniform and does not have a crater-like structure on the surface. The reduction of the heating time leads to lower process gas consumption and ultimately to a reduction of the total energy consumption and thus lower process costs.

Reduction of the heating time for hot gas welding

Air inclusions in fiber reinforced plastics (FRP) are among the most common imperfections that can affect both the resulting stiffness and strength. For the calculation of the stiffness of a perfect UD layer, semi-empirical mixing rules can be used which show good agreement with experimental data. Since the content of air inclusions is generally low compared to the constituents of an FRP, the Mori-Tanaka scheme can be exploited in a following step to homogenise the perfect phase and air inclusions. By introducing a geometry function into Mori-Tanaka scheme, influence of air inclusions’ appearance can be investigated.

Calculation of stiffness for FRP with air inclusions with respect to their geometry

Investigations and prediction of the melting processes in single-screw extrusion have been of scientific interest for many decades. In this study, the melting zone of a high-performance extruder with a continuous helically grooved plasticizing zone is experimentally investigated for the first time. For this purpose, an axially divisible extruder was developed to expose the barrier screw together with the plastic melt. An optical examination of the frozen melt validates assumptions of the existing melting model. In addition, the results of the experimental investigation are compared with those of the analytical model. These investigations confirm the essential mathematical model assumptions and are in good agreement with previous investigations on an axially grooved single-screw extruder.

Investigation of the melting zone of high-performance extruders using a helically grooved plasticizing zone

Contrary to the plastification in injection molding processes, thermoset molding compounds could be more heated in a twin screw extruder due to its stronger shearing effect which leads to the rise of the melting temperature above the initial curing temperature. Besides the screw speed, the screw configuration has an extensive impact on the shear-induced energy input and on the melt temperature profile along the extruder. The aim of this research is the development of an analytical method to investigate the influence of different processing conditions on the flow-curing behavior. Furthermore, possible implications to the resulting properties of the foamed semi-finished parts are discussed.

Analysis of the flow-curing behavior of chemically foamable phenolic molding compounds in the extrusion process

Effects of post-processing thermal treatments of vibration-welded polypropylene and its silica nanocomposite were systematically studied by using a heating cabinet and in-line infrared radiation. Experimental results demonstrate that thermal treatments, independent on the heating sources, exert obviously positive effect on improving the weld quality of polypropylene materials, i.e. stiffness and strength of the weld. Despite the short cycles used for infrared heating, the results are better and the effort is less.

Response of mechanical and thermal properties of a vibration-welded polypropylene/SiO<sub>2</sub> nanocomposite on different thermal treatments

This research work presents a recycling methodology for carbon fibre composites processed with a novel room temperature infusible and curable thermoplastic matrix ELIUM 150 from Arkema. Herein we demonstrate that by dissolving the composites in acetone at room temperature it is possible to separate the matrix from the fibres and to reuse both the matrix and the fibres in form of scrim (preform). A comparison of the thermomechanical, thermal and mechanical properties of the composites shows only marginal performance changes in bulk properties due to the proposed recycling strategy.

Closed-loop room temperature recycling of Elium CFRPs and its influence on the 2nd generation composite properties

Changes in the specific volume during the processing of thermosetting resin systems result in reduced dimensional accuracy of the components due to residual stresses and, in the case of fibre reinforced plastics (FRP), in surface waviness. A specially developed dilatometer is used to characterise the chemical shrinkage close to the process. The tests show a significant influence of the mixing ratio of resin and curing agent, which leads to a reduced chemical shrinkage. An increased moisture content of the resin component tends to lead to a lower chemical shrinkage.

Investigation of the Shrinkage Behaviour of a Fast Curing Epoxy Resin as a Function of Moisture, Gas Content and the Mixing ratio

A flexible air guiding system in blown film extrusion enables a mass throughput increase of more than 60 %. The development encloses the bubble expansion zone and creates a flow gap between the film bubble and a flexible membrane. In this gap, the flow velocity of the cooling air can be increased, resulting in higher heat extraction. As a side effect, the increase in flow velocity creates a local vacuum in the gap, causing the film bubble to open earlier than in the conventional process. Because of this surface enlargement the heat extraction can be improved again. During the extrusion process, the flow gap can be adjusted to the current bubble geometry independent of the process parameters.

Increased cooling capacity when using a flexible air guiding system due to the Venturi effect in blown film extrusion

In this investigation, a possibility for shortening the cycle time in the manufacture of thick-walled optical components by compression induced solidification (CIS) was studied in a numerical manner and experimentally tested for validity. The test specimens produced with a reduced cycle time were compared with the manufacturing processes commonly used for such components, i.e. injection molding, injection-compression molding and conventional CIS, with regard to dimensional accuracy, internal stresses and microstructural impression. It could be shown that by delaying the heating of the mold, the adapting time and thus the cycle time of the process can be reduced by up to 55 %, while maintaining the same high quality of the components.

Application optimized compression induced solidification

For years, proven concepts such as spiral mandrel dies for blown film extrusion, have been used in extrusion die design. However, with today‘s possibilities of additive manufacturing technology, there is potential to optimize this design of the melt-carrying flow channels from a thermo-rheologically point of view.

Blasfolienextrusion

Werkzeuge für die Kunststoffverarbeitung

Additive Fertigung

Novel die designs for blown film extrusion involving additive manufacturing

The MERCUR research project Pr-2017–0003 „Analysis of the product development process in the combination of additive and subtractive manufacturing processes for the manufacture of multi-material products“ combines different manufacturing and post-treatment processes to connect the respective advantages.

Filamente für additive Verfahren

Investigation of the influence of various post-treatment methods on the properties of additive manufactured FDM Nylon 12 samples

The main focus of the current reasearch is the lifetime estimation of continuous fibre reinforced plastics within a layer-based fatigue analysis. In the present paper, the downsizing of the failure envelope due to multiaxial cyclic loads is investigated with regards to variable amplitude loads and change of load directions.

On modeling failure envelopes in residual strength-based fatigue life analyses of cfrp with regard to load direction changes

This article describes two numerical approaches for calculating contact temperatures.

Kunststoffverarbeitung

Numerical estimation of temperatures in simple sliding contacts

Automated lay-up of carbon fiber reinforced polymers is an established method for producing large parts in the aerospace industry. Currently, the quality control for this automated manufacturing process is performed by humans. In the last years, research has focused on increasing productivity of automated lay-up, thus the automation of the quality control has been taken into consideration. The objectives of the paper are to review the requirements for quality control based on an overview of the possible defects in automated lay-up and to evaluate their fulfilment by both visual quality control by humans and automated quality control systems.

A literature review of quality control for automated lay-up processes of CFRP

Poly(lactic acid) (PLA)/silica nanocomposites with different filler loading and two different primary particle size of the filler were prepared by using a twin-screw extruder followed by injection molding. Morphological investigations showed, depending on the filler size and filler content, good dispersion with average agglomerate sizes of 38–60 nm. The spherulite growth and crystallization behavior of the nanocomposites discovers that smaller particles and a low filler loading leads to the fastest crystallization. The behavior can be explained by the fact that the small agglomerates and individual particles, visible in a standard Scanning Electron Microscope (SEM) are most frequently in this case. These particles serve as heterogeneous nucleation agents finally resulting in a fast crystallization of the PLA nanocomposite.

The effect of nanoparticle content and size on the morphology and crystallization behavior of poly(lactic acid)/silica nanocomposites

During injection molding of semi-crystalline thermoplastics, an influence by means of the mold temperature and thus on the cooling behavior of the plastic melt can have a significant effect on the resulting component properties. Within the scope of the present investigations, the influence of the mold temperature on the formation of internal and mechanical properties over the flow path length is investigated with the aim to produce components with homogeneous properties over the entire component geometry. The results show that an increase in the mold temperature leads to a significant homogenization of the component properties over both the component cross-section and the flow path length especially by improving crystalline and mechanical properties far from gate.

Achieving homogeneous properties for thin-walled components through dynamic temperature control

To maintain functionality of gear sets over their lifetime, the occurring wear and temperature development must be considered. Surface structure is one of the most important factors on the run-in behavior. In this paper, the effects of different process-induced surface structures of steel pinions on the thermal and tribological run-in behavior of a steel-polyamide gear set is investigated.

Initial morphology of the PA66 wheel and area for localizing wear

Effect of Surface Structure on Run-in Wear in Steel-Polyamide Gear Sets

The Journal of Plastics Technology is a peer reviewed internet periodical published under the auspices of the Scientific Alliance of Polymer Technology (WAK)