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Werkstoffgerechte Auslegung von Direktverschraubungen in duroplastischen Formmassen
No full textThe current trends of digitalisation and electromobility have led to a greater demand for electronic systems. Thermosets are increasingly being used to protect sensitive electronics, as they fulfil the required properties such as electrical insulation, high dimensional stability and good bonding to metals. Due to their comparatively low material costs, thermosets are increasingly becoming the focus of series applications. The potential of thermoset moulding compounds can only be used for complex assemblies, if suitable joining methods are available. Direct screw connections are an economical joining method, which also meets the requirements for recycling-friendly designs due to the detachability of the connection. However, so far there are no generally valid design recommendations for the material-specific design of direct screw connections of thermoset moulding compounds. Within the scope of this work, fundamental correlations were developed on the influence of geometry, material and processing parameters on the screw connection quality. In the first part, the influence of the geometry parameters on the screw connection safety, screw connection quality and pre-load decrease was analysed. The results show recommended values of the characteristic tube geometries of dA = (2.25 2.50)∙d1, dK = (0.85 0.90)∙d1, lE = 2∙d1 and tS = 0.4∙d1. Furthermore, a reparability of the screw connection could be demonstrated. In addition, very small decreases in the pre-loading force of approx. 7 % after 5 days can be achieved. Due to the different processing behaviour of thermoset moulding compounds and the mostly high filler content, the influence of the process parameters on the screw connection quality must be analysed. This was dealt with in the second part of the thesis. It was possible to significantly improve both the screw connection reliability and screw connection quality as well as the pre loading force reduction through a suitable selection of the injection moulding parameters. A good pressure transfer of the moulding compound as well as a sufficient compacting of the component show the greatest influence. Furthermore, it was shown that a developing weld line hardly has a negative influence on the screw connection safety. Finally, the results were summarised in the form of design notes in order to enable a process safe application of thermoset direct screw connections. In summary, the results of the study can reduce the concerns of potential users and contribute to the establishment of thermoset direct screw connection as an economical joining method.
Use of process knowledge in thermoforming of packaging
No full textDiese Arbeit untersucht das Herstellen von Verpackungen im Thermoformverfahren auf Rollenautomaten. Im Rahmen der Arbeit konnte gezeigt werden, dass durch die Überwachung von Prozessgrößen nützliche Informationen beim Thermoformen gewonnen werden können. Der Schwerpunkt lag dabei auf der Verarbeitung von Polypropylen, welches aufgrund seiner Eigenschaften und seines Preises einen Anteil von ca. 20 % an allen Verpackungen besitzt. Zur Überprüfung der Ansätze auf andere Thermoformwerkstoffe wurde amorphes Polyethylenterephthalat in die Untersuchung mit aufgenommen. Die Arbeit ist in zwei Kernthemen untergliedert. Im Ersten werden die Einflüsse der Einstellparameter und der Anlage auf die Produktmerkmale untersucht. Dazu wurde eine Einflussparameteranalyse durchgeführt, die Anlagensteuerung überarbeitet und Peripheriegeräte wie die Vorheizung optimiert. Im Zweiten wird gezeigt, wie mit Hilfe von Prozessgrößen Betriebszustände der Anlage überwacht und Qualitätsmerkmale der Formteile prognostiziert werden können.
Die Einflussparameteranalyse wurde anhand der Formteilmerkmale Wanddickenverteilung, Stauchdruck, Masse, Siegelrandgeometrie und geometrischer Größen des Formteils durchgeführt. Dabei zeigte sich, dass die Umformtemperatur und die Geometrie des Vorsteckers die größten Einflussfaktoren bei der Wanddickenverteilung sind. Die Einstellungen von Niederhalter und Formdruck, sowie Verstreckgeschwindigkeit des Vorstreckers haben einen um circa Faktor vier geringeren Einfluss auf die Wanddickenverteilung bei Ausnutzung des maximalen Variationsbereichs. Dies ist auch darauf zurückzuführen, dass für das Thermoformen optimierte Halbzeuge verwendet wurden. Diese sind in der Regel nukleiert und besitzen eine geringe Abhängigkeit des Dehnverhaltens von der Dehngeschwindigkeit. Nicht betrachtet wurden bei dieser Untersuchung die Stempeltemperatur und deren Einfluss auf die Reibpaarung Halbzeug Vorstrecker.
Es konnte zudem gezeigt werden, dass die Formteilmerkmale, werden definierte Grenzen der Einstellparameter eingehalten, nicht signifikant von den Toleranzen des Prozessablaufs beeinflusst werden. Dadurch konnte bewiesen werden, dass die wesentlichen Störungen, die die Formteilmerkmale in einer laufenden Produktion beeinflussen, entweder durch die Temperaturführung des Halbzeugs oder die Halbzeugeigenschaften verursacht werden. Aus diesem Grund werden Möglichkeiten aufgezeigt, wie die Temperaturführung optimiert, überwacht und geregelt werden kann.
Um Störungen in der Temperaturführung zu identifizieren und darauf zu reagieren wurde in Erweiterung zum Stand der Technik neben der Temperatursensorik ein Verfahren zur Identifizierung des Materialverhaltens erarbeitet. Dieses Verfahren basiert auf der Messung der Umformkraft des Vorstreckers, die in einigen Veröffentlichungen zur Identifizierung der Thermoformbarkeit oder zur Beschreibung des Arbeitspunkts der Thermoformanlage herangezogen wurde. Dadurch können Veränderungen im Materialverhalten festgestellt werden, die durch Veränderungen des Heizprozesses, der Umgebungsbedingungen oder des Halbzeugs selbst verursacht werden. Insbesondere bei teilkristallinen Polymeren, wie Polypropylen und Polyethylenterephthalat bietet sich die Messung der Verstreckkraft, des Moments des Vorstreckermotors oder der Schließkraft des Werkzeugs eine Alternative zur Temperaturmessung durch optische Sensoren. Vorteile dieser Messung ist die Unempfindlichkeit gegenüber optischen Eigenschaften des Halbzeugs und Strahlungsquellen in der Umgebung.
Durch eine zyklusweise Kennwertbildung aus den Prozessgrößen ergeben sich Prozesswerte, die sich gut zur Identifikation und zur Regelung des Betriebspunktes eignen. Dies ist im Speziellen die Verstreckenergie, die während des Vorstreckens aufgewendet wird. Eine Regelung der Formteilmerkmale durch die Verstreckenergie ist nur sinnvoll, wenn bei der Inbetriebnahme nachgewiesen ist, dass mit dem verwendeten Halbzeug und Vorstrecker die geforderte Formteilqualität erreicht werden kann. Zudem muss dass qualitätsbestimmende Formteilmerkmal von den temperaturabhängigen Materialeigenschaften abhängig sein. Im Rahmen der Arbeit konnte gezeigt werden, dass eine Regelung der Verstreckenergie das Einschwingen der Thermoformanlage verkürzen kann. Zudem ergänzt die Verstreckenergieregelung die Temperaturregelung dahin gehend, dass ein absoluter Kennwert für ein Material unabhängig von Farbe, Umgebungstemperatur oder Emissionsgrad besteht.
Abschließend konnten die im Labor aufgestellten Hypothesen überprüft und Regelungsstrategien getestet werden. Es konnte nachgewiesen werden, dass es möglich ist, durch die Überwachung des mechanischen Versteckvorgangs, Änderungen in den Materialeigenschaften zu identifizieren. Im Labor wurde dies bei verwandten Einschichtpolypropylenfolien nachgewiesen, bei einem Verarbeiter konnte es für einen unbekannten coextrudierten Mehrschichtverbund aus Recyclingmaterialien ebenfalls bestätigt werden.The study investigated the production of packaging in thermoforming processes to roll machines. As part of the study, it can be shown that the monitoring of process variables can obtain useful information in the thermoforming process. The focus was on the processing of polypropylene materials, which due to its characteristics and price has a share of about 20% of all packaging. To compare to other thermoforming materials, amorphous PET was included in the study. The paper is divided into two main subjects. First, the influence of the setting parameters of the system at the product features is examined. The control of the system was revised and peripheral systems such as preheating were optimized. The second part shows how to use process variables to monitor operating conditions of the system and predict quality characteristics of the molded parts.
The analysis of influencing factors on the molded part was performed based on the characteristics of the molded part such as wall thickness distribution, compression strength, mass, sealed-edge geometry and geometrical parameters of the part. It could be shown that the deformation temperature and the geometry of the plug are the biggest influencing factors on the wall thickness distribution. The influences of the settings of the blank holder, molding pressure, as well as the speed of the plug on the wall thickness distribution are smaller by about a factor of four at using the maximum utilization of variation range. This is also due to the fact that for the thermoforming, optimized materials were being used. These are nucleated and the stretch behavior generally has a low dependence of the strain rate. Not considered in this study were the plug temperature and its influence on the friction coefficient.
The study was also able to show that the molding characteristics cannot be significantly affected by the tolerances of the process flow if the limits of the setting parameters are defined. Thus, it could be shown that variations of the properties of the molded part in a current production are either caused by the temperature control or sheet properties. For this reason, opportunities are identified related to how to optimize, to monitor, and to control temperature setting.
To identify faults in the temperature control, as an extension to the prior method in addition to the temperature sensor, a method for the identification of the material behavior was developed. This method is based on measuring the deformation force of the pre-stretcher, which was used in some publications to identify the thermoforming or description of the operating point of the thermoforming machine. In this research it was shown that the Verstreckkraft and its course is an indication of the ability to process a semi-finished product or can be used to describe a point of operation. This allows the detection of changes in the material properties, which are caused by changes in the heating process, the environmental conditions or the semi-finished product itself. In particular in semi-crystalline polymers such as polypropylene and polyethylene terephthalate the measurement of the plug force, the torque of the motor and the tool clamping force are an alternative to the temperature measured by optical sensors. An advantage of this measure is its insensitivity to optical properties of the material and radiation sources in the environment.
By calculation of the cycle based parameters, values are derived from the process variables, which are well suited for the identification and control of the process point. This is in particular the energy of the plug being spent during the pre-stretching. A control of the molding characteristics by the energy of the plug is only useful if it is proven that with the used semi-finished product, pre-stretch quality can be achieved, and the corresponding molding feature is dependent on the temperature-dependent material properties. As part of the study showed, a control of energy of the plug can shorten the oscillation of the thermoforming machine. Looking ahead, a review of the control in a production environment in order to identify long-term behavior is necessary. The temperature control also complements the energy of the plug so that an absolute value for a characteristic material regardless of color, ambient temperature or emissivity consists.
Finally, the laboratory hypotheses and control strategies can be tested. It has been proven that it is possible to identify by monitoring the pre-stretching changes in material properties. In the laboratory, this has been demonstrated in related single-layer films; the hypotheses could also be confirmed for unknown coextruded multilayer composite made from recycled materials
Berührungslose Erfassung der Vorformlingsgeometrie und -wanddicke beim Extrusionsblasformen
No full textProcess monitoring of parison extrusion is necessary in order to be able to measure process variation. Existing systems do not measure the extrusion in its entirety or have high measurement uncertainties. The aim of the presented work was to develop a monitoring system for the extrusion of parisons, which makes it possible to determine both the temperature of the parison and its geometric dimensions. For this purpose, a measuring system based on an LWIR camera was developed and tested in this dissertation, which allows the full and contactless monitoring of the parison extrusion. Based on extensive process investigations, it could be shown that the measuring system can reliably and accurately determine the geometry and temperature of the parison. The length, speed and centring of the preform are particularly suitable for evaluating the quality of the parison extrusion. Process fluctuations can be reliably detected using this measured variable. The parison diameter or the absolute parison temperature are not suitable for measuring process fluctuations around the operating point, as the influence of the process parameters on these measured variables is not significant.Modelling the parison wall thickness based on the parison temperature difference allows to determine the wall thickness within the experimental space for carbon black filled plastics with an average error of 4.84 % for PE-HD and 10.48 % for PE-LD, with an absolute error of 0.12 mm on average. For transparent parisons, the prediction quality of the model improves with a deviation of 3.30 %, since the temperature in the centre of the parison is also taken into account in the measurement. In the case of deviations from the operating point, such as a change in the cycle time, the model can only calculate the wall thickness with high errors. In summary, the results show that monitoring of preform extrusion can determine both the geometry and the temperature of the preform and that process deviations can be reliably detected from the combination of several measured variables. In industrial production, the developed measuring system can be used to detect process fluctuations and thus reduce defective products. In the future, it is conceivable to develop a closed loop control strategy that uses the measurement data to compensate for any fluctuations that occur
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Experimental investigations on injection molded parts of mechanically recycled offcuts from the production of continuous fiber-reinforced thermoplastic sheets
Full text linkDispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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