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Unternehmen sind häufig mit Situationen konfrontiert, in denen schnell Entscheidungen bezüglich der Auswahl mehrerer Handlungsalternativen gefunden werden müssen. Mathematische Verfahren können hierbei unterstützen, z. B. für die Ermittlung einer ersten Diskussionsbasis. Verfügbare Softwarelösungen errechnen zwar häufig optimale Ergebnisse, zeigen jedoch Schwächen bei der praktischen Anwendbarkeit. So ist eine Einarbeitung in komplexe Optimierungssoftware für die teilweise sporadisch auftretenden Probleme in der Regel für Unternehmen nicht möglich, unter anderem auch unter Anbetracht der teilweise hohen Kosten der Standardsoftware und dem benötigten hohen Einarbeitungsaufwand. Gerade Problemstellungen in Fachbereichen, die nicht auf mathematische Problemlösung spezialisiert sind, münden daher regelmäßig in Ineffizienzen. Basierend auf den in der Literatur diskutierten Lösungsansätzen wurde ein praxisorientierter Ansatz zur Entscheidungsunterstützung für Rucksackprobleme bzw. 0–1 Probleme mithilfe von Genetischen Algorithmen (GA) entwickelt und technisch in Microsoft Excel® umgesetzt. Ein Praxistest bei einem chinesischen Textilunternehmen belegt erhöhte Effektivität und Effizienz. Die Software kann kostenfrei nach MIT Lizenz unter http://www.solvega.de/ heruntergeladen werden.
In an Enterprise Resource Planning (ERP) system, production planning is influenced by a variety of parameters. Previous investigations show that setting parameter values is highly relevant to a company’s target system. Parameter settings should be checked and adjusted, e.g., after a change in environmental factors, by material planners. In practice, updating the parameters is difficult due to several reasons. This paper presents a simulation-based decision support system, which helps material planners in all stages of decision-making processes. It will present the system prototype’s user interface and the results of applying the system to a case study.
The adaptive input design (also called online redesign of experiments) for parameter estimation is very effective for the compensation of uncertainties in nonlinear processes. Moreover, it enables substantial savings in experimental effort and greater reliability in modeling.
We present theoretical details and experimental results from the real-time adaptive optimal input design for parameter estimation. The case study considers separation of three benzoate by reverse phase liquid chromatography. Following a receding horizon scheme, adaptive D-optimal input designs are generated for a precise determination of competitive adsorption isotherm parameters. Moreover, numerical techniques for the regularization of arising ill-posed problems, e.g. due to scarce measurements, lack of prior information about parameters, low sensitivities and parameter correlations are discussed. The estimated parameter values are successfully validated by Frontal Analysis and the benefits of optimal input designs are highlighted when compared to various standard/heuristic input designs in terms of parameter accuracy and precision.
In a recent study at the National Research Council Canada, the sound transmission in cold-formed steel-framed constructions was investigated. The results of direct sound insulation tests of wall and floor assemblies were reported at EURONOISE 2015 and INTERNOISE 2015. This paper focuses on flanking sound transmission in cold-formed steel-framed constructions. A representative full-scale mock-up specimen was constructed in NRC’s 8-room flanking transmission facility. The specimen consists of four loadbearing walls with 152 mm deep steel studs, four non-loadbearing walls with 92mm deep steel studs, and four floor-ceiling assemblies consisting of steel joists and a composite steel deck with gypsum concrete. Measurements were conducted according to the indirect method described in ISO 10848. The individual flanking paths were measured by a sequence of transmission loss measurements in which other transmission paths were suppressed by shielding. For the bare specimen without linings, the sound transmission for horizontally adjacent rooms with continuous subfloors is dominated by the floor-floor flanking paths. Floor coverings or floor toppings are needed to meet the requirements in the National Building Code of Canada. This paper presents details of the measurements, highlights some of the results and discusses implications.
Das Kommissionieren zählt zu den arbeitsintensivsten Aufgaben in der Logistik. Aus diesem Grund ist es wichtig, möglichst genau die erwarteten Prozesszeiten für diese Aufgabe zu bestimmen. Ein verbreiteter Ansatz für die Bestimmung von Prozesszeiten für manuelle Tätigkeiten beim Kommissionieren ist die Methods-Time-Measurement (MTM). Um eine Vorgabezeit mittels MTM zu bestimmen, müssen Einflussfaktoren spezifiziert werden. Dieser Beitrag zeigt anhand der Greifzeit auf, wie diese Einfluss-faktoren auf Grundlage von Artikelstammdaten bestimmt werden können. Weiterhin wird der Unterschied zwischen einer für jeden Artikel individuell bestimmten Greifzeit und der Greifzeit basierend auf repräsentativen Eigenschaften von Artikelgruppen verglichen. Wesentlich wird dabei die mittels MTM bestimmte Greifzeit durch das Gewicht und die Abmessungen (Sperrigkeit) beeinflusst.
In-plant milk-run systems represent transportation systems, where materials are delivered from a central storage area to several points of use on fixed routes and in short and defined intervals. Milk-run systems generally enable frequent deliveries in low lot sizes with short lead times and low inventories at the points of use. Thus, stable and reliable system operation is crucial to avoid delays and material shortages. In industrial practice, milk-run trains usually share resources, for example, loading areas and technology and use the same tracks, leading to dependencies between routes and possible traffic jams and blockages, which significantly affect cycle times and may lead to instabilities in the system. We present a simulation model to analyse in-plant milk-run systems with a focus on typical traffic situations. We describe its application to a large industrial case study in detail and derive recommendations for designing routes with low risk of delays.
We study the limited data problem of the spherical Radon transform in two and three-dimensional spaces with general acquisition surfaces. In such situations, it is known that the application of filtered-backprojection reconstruction formulas might generate added artifacts and degrade the quality of reconstructions. In this article, we explicitly analyze a family of such inversion formulas, depending on a smoothing function that vanishes to order k on the boundary of the acquisition surfaces. We show that the artifacts are k orders smoother than their generating singularity. Moreover, in two-dimensional space, if the generating singularity is conormal satisfying a generic condition then the artifacts are even k+1/2 orders smoother than the generating singularity. Our analysis for three-dimensional space contains an important idea of lifting up space. We also explore the theoretical findings in a series of numerical experiments. Our experiments show that a good choice of the smoothing function leads to a significant improvement of reconstruction quality.
The generation of multi-material components using Laser beam melting (LBM) is a challenge which requires the invention of new coating devices for the preparation of arbitrary powder patterns. One solution is the usage of vibration-controlled nozzles for selective deposition of polymer powders. Powder flow can be initiated by vibration even when using powders with low flowability. In this report, the selective deposition of polymer powder by vibrating nozzles is investigated with respect to their application in LBM machines. Therefore, a steel nozzle attached to a piezo actor is applied, whereas the nozzle itself features internal channels which allow the precise control of the powder temperature using heat transfer oil. The setup is used to study the influence of temperature on the powder mass flow. The results show that, next to the vibration mode, the temperature strongly influences the powder mass flow which is done by affecting the moisture and thus the particle-particle adhesion forces. This shows that a precise control of the powder temperature inside the nozzle is required in order to achieve a constant mass flow and thus a successful application of vibrating nozzles inside LBM machines.
Simultaneous laser beam melting (SLBM) allows the direct realization of multi-material components consisting of different polymer materials by a single Additive Manufacturing (AM) process. To achieve a high compound strength between different materials by adhesive bonding, a common boundary zone based on diffusion of the macromolecules is necessary and thus, both materials needs to be compatible regarding their specific adhesion compatibility. However, by SLBM also incompatible polymers can be processed to multi-material parts. If two incompatible polymers are processed, a positive locking between the different materials is necessary to achieve a connection between the materials. The positive locking results of a random mixture process of the different powder materials during the powder deposition process by a two chamber recoater system, which leads to the forming of undercuts of one material in the other during the melting and recrystallization. In this paper, thermoplastic elastomer (TPE) and polypropylene (PP) powders, which are incompatible, are processed to multi-material specimens. By qualifying basic material properties, their influence on the process and especially on the forming of undercuts in the boundary zone is analyzed. To also allow the analysis of the influence of both material and process parameters on the resulting part properties, tensile test specimens are built and their tensile strength is determined. Additionally, cross sections of the boundary zone are prepared and analyzed by microscope images.
Simultaneous Laser Beam Melting of polymers (SLBM) allows the generation of multi-material components,consisting of different thermoplastic polymers, within one additive building process. Besides the common advantagesof conventional Laser Beam Melting (LBM), multi-material components built by SLBM can fulfill different productrequirements like different chemical resistances or haptic material properties within a single part. To achieve suchparts, different powder materials are deposited next to each other and preheated a few degrees below their meltingtemperatures by infrared emitters and laser radiation (λ = 10.60 μm), before in the last step the preheated powdersare molten simultaneously by an additional laser source (λ = 1.94 μm). In this paper, different polymer powders likepolypropylene (PP) and polyamide 12 (PA12) are used for the generation of multi-material specimens. By varyingdifferent building parameters according to a specified design of experiments, their influence on the part properties isanalyzed. Important building parameters are the intensity and the irradiation time of the laser beam used for meltingthe preheated powders. Besides using tensile tests to determine the tensile strength and the elongation at break, theaverage part height in dependence of the energy input is analyzed. The overall aim is to specify the correlationbetween different building parameters regarding the energy deposition on the resulting part properties.
Companies often use specially-designed production systems and change them from time to time. They produce small batches in order to satisfy specific demands with the least tardiness. This imposes high demands on high-performance scheduling algorithms which can be rapidly adapted to changes in the production system. As a solution, this paper proposes a generic approach: solutions were obtained using a widely-used commercially-available tool for solving linear optimization models, which is available in an Enterprise Resource Planning System (in the SAP system for example) or can be connected to it. In a real-world application of a flow shop with special restrictions this approach is successfully used on a standard personal computer. Thus, the main implication is that optimal scheduling with a commercially-available tool, incorporated in an Enterprise Resource Planning System, may be the best approach.
The generation of multi-material components by laser beam melting (LBM) is a challenge which requires the invention of new coating devices for preparation of arbitrary powder patterns. One solution is the usage of vibration-controlled nozzles for selective deposition of polymer powders. Powder flow can be initiated by vibration enabling a start-stop function without using any mechanical shutter. In this report, the delivery of polymer powder by vibrating nozzles is investigated with respect to their application in LBM machines. Therefore, a steel nozzle attached to a piezo actor and a weighing cell is used in order to measure the stability and time-dependence of the powder mass flow upon vibration excitation with the usage of different kind of powder formulations. The results show that precompression of the powder inside the nozzle by vibration excitation is essential to realize a reliable start-stop function with reproducible discharge cyles and to prevent a initial flush of powder flow. Moreover, the use of different powder materials showed that mass flow is even possible with powders which are not optimized regarding flowability, but is readily enhanced with a factor of 2 to 3 by admixing Aerosil® fumed silica.
Selective Laser Sintering (SLS) is an additive manufacturing technique whereby a laser melts polymer powder layer by layer to generate three-dimensional parts. It enables the fabrication of parts with high degrees of complexity, nearly no geometrical restrictions, and without the necessity of a tool or a mold. Due to the orientation in the building space, the processing parameters, and the powder properties, the resulting parts possess an increased surface roughness. In comparison to other manufacturing techniques, e.g. injection molding, the surface roughness of SLS parts results from partially melted powder particles on the surface layer. The actual surface roughness must thus be characterized with respect to the part's eventual application. At the moment, there is no knowledge regarding which measuring technique is most suitable for detecting and quantifying SLS parts' surface roughness. The scope of this paper is to compare tactile profile measurement methods, as established in industry, to optical measurement techniques such as Focus Variation, Fringe Projection Technique (FPT), and Confocal Laser Scanning Microscope (CLSM). The advantages and disadvantages of each method are presented and, additionally, the effect of tactile measurement on a part's surface is investigated.
Powder based Additive Manufacturing technologies offer huge potential for building parts with almost no geometrical restrictions, but both the process controlling as well as the part properties are strongly dependent on different material characteristics of the material, like the flowability. In this work, different weight percentages of nano-scaled silica dioxide particles (Aerosil®) are admixed to pure polyethylene and polypropylene powder and the resulting flowability is determined. Besides using the Hausner ratio as standardized value, the degree of coverage is introduced as a new characteristic to quantify the powder flowability. The degrees of coverage are compared to the Hausner ratios to allow a discussion and evaluation about the different characteristic values. Additionally, tensile bars consisting of polypropylene are generated to determine the porosity by cross sections and the mechanical part properties by tensile testing. As mechanical part properties, the tensile strength and elongation at break are determined and the effects of different powder flowability on these properties are analyzed.
This study increases the basic understanding of optical material properties of polymer powders used in selective laser sintering (SLS). Therefore, different polymer powder materials were analyzed regarding their optical material properties with an integration spheres measurement setup. By the measurements a direct connection between the absorption behavior of the solid material and the overall optical material characteristics of the same material in powdery form could be shown. The results were used to develop an advanced explanation model for the optical material properties of powders. At present, existing explanation models only consider the occurring of multiple reflections in the gaps between the particles to explain the overall optical material properties of powder materials. Thus, by also considering the absorption behavior of the single particles, the basic understanding of the beam-matter interaction and their effect on the optical material properties of powder materials can be expanded.
Magneto-active Polymers (MAP) are closely related to magneto-rheological fluids in that they contain magnetic micro-particles. However, instead of being freely suspended in a carrier fluid they are physically bound within a highly elastic polymer-matrix. The application of an external magnetic field allows changes in the mechanical properties, such as elastic and shear moduli, of the composite material to be achieved. The colossal magneto-rheological effect has been shown to demonstrate changes in Young's modulus by over 1E6 %. Current research concentrates on controllable compliance and the resulting shape memory properties of MAP. This paper deals with recent advancements in this respect, including tubular magneto-active devices with potential applications in medical and other technology.
Die 3D-Daten, die bei der Fertigungsplanung in CAD/CAM-Systemen vorliegen, bilden häufig auch die Spannsituation des Werkstücks ab. Mit einer vom LFW der OTH Regensburg entwickelten Software lassen sich die Konturen direkt auf den Rüstplatz projizieren. Im Rahmen des durch das Bayerische Staatsministerium für Bildung und Kultus, Wissenschaft und Kunst geförderte F&E-Projekt "AutoRüst" entwickelt das LFW Bausteine zum automatisierten Generieren von Rüstinformationen. Im Wesentlichen geht es dabei um zwei Schwerpunkte: erstens das datenbankgestützte Verwalten von Spannsituationen inklusive der Unterstützung und Überprüfung beim Aufbau sowie zweitens die bedarfsgerechte Visualisierung des Programmablaufs für die Einfahrprozedur an der Werkzeugmaschine. Bei beiden Themenkomplexen werden bereits vorhandene Daten (3D-Spannsituation, NC-Programm mit Maschinenraumsimulation) genutzt, um konfigurierbare Rüstdokumente zum Spannen und Einfahren zu erzeugen. Im Idealfall muss der NC-Programmierer also nur wenige bis gar keine zusätzlichen Eingaben tätigen. Neben der reinen Zeitersparnis wird so auch eine deutlich gesteigerte Prozesssicherheit beim Übertragen der virtuellen Welt in die reale Fertigungswelt erreicht. Das vom LFW entwickelte Modul zur Visualisierung der Spannsituation kann flexibel in den Fertigungsbetrieben integriert werden. Gerüstet werden kann sowohl in der Maschine, auf einer zweiten Palette als auch auf einem externen Rüstplatz. Einzige Randbedingung ist, dass der Laserprojektor auf den Tisch projizieren kann, idealerweise senkrecht von oben. Die Software analysiert in einem ersten Schritt die vorhandene 3D-Baugruppe und erzeugt anhand der Lage der Bauteile eine Montagereihenfolge, die natürlich angepasst werden kann. Ebenso können Einzelteile gruppiert werden, sodass diese bei der späteren Projektion auch als Gruppe projiziert werden. Unwichtige Baugruppenteile wie beispielsweise die Stützen der Spannpratzen oder die Muttern mit den Unterlegscheiben können vom weiteren Prozess ausgeschlossen werden. Auf der so geschaffenen Grundlage erzeugt die Software Projektionslinien auf dem zu positionierenden Bauteil mit einem einstellbaren Abstand (hier: 1 mm) zur Bauteilkante. Als Ergebnis wird eine Ausgabedatei im dxf-Format erstellt, die vom Laserprojektor verarbeitet werden kann. Die in der dxf-Datei auf Layern gruppierten Projektionslinien können dann ferngesteuert in der zuvor definierten Reihenfolge durchgeklickt werden, um die Spannelemente zu positionieren. Die Vorteile des Visualisierungsmoduls im Überblick: (1) Senken der Rüstzeit; (2) Erhöhen der Prozesssicherheit beim Rüsten (Positioniergenauigkeit der Spannelemente < 1 mm) und damit Kollisionsvermeidung; (3) Nutzen bereits vorhandener 3D-Informationen entlang der Prozesskette CAD/CAM-Fertigung; (4) Konturerzeugung direkt im CAM-System OPUS oder über unabhängige Software.
Die Anwendung von Kaizen ist in vielen Firmen ein selbstverständliches Element geworden. Dennoch variiert die Ausprägung eines kontinuierlichen Verbesserungsprozesses stark von Unternehmen zu Unternehmen. Ein wesentliches Hindernis, gutes Kaizen umzusetzen, ist der Mangel an Realisierungsmöglichkeiten. In Zeiten von Industrie 4.0 bestehen inzwischen zahlreiche Möglichkeiten, Ideen schnell und kostengünstig für eine Produktion zu generieren und damit nachhaltig die Produktivität zu steigern. Zentrales Element von Kaizen ist das zielgerichtete Experimentieren. Es werden Hypothesen aufgestellt und diese werden durch Experimente überprüft, so dass man aus den Ergebnissen lernen kann. Entscheidend ist die Fähigkeit, tatsächlich Experimente in einer Produktion ausführen zu können. Das heißt, Produktionsanlagen müssen mit unterschiedlicher Intensität verändert werden können. In erfolgreichen Unternehmen ist ein Betriebsmittelbau in der Lage, diese Experimente zügig durchzuführen. Häufig sind aber auch hier die Möglichkeiten einer schnellen Gestaltung eingeschränkt. Jede Form von Verbesserung führt zu optimierten Prozessen und einer besseren "Business Excellence". Innovationen, die zum Beispiel durch den Produktionsanlagenhersteller eingebracht werden, führen häufig zu einer sprunghaften Verbesserung. Diese Verbesserungen sind in jedem Fall wichtig, aber auch häufig für den Wettbewerb verfügbar, wenn das Wissen nicht bei einem hauseigenen Anlagenhersteller entsteht. Wenn zudem kleine Verbesserungen zu den Innovationen hinzukommen, können die Prozesse zusätzlich optimiert werden. Sind die Verbesserungen eher kurz- als langzyklisch liegt es auf der Hand, dass ein schnelles Erreichen des Verbesserungsniveaus erfolgt. Neben dem Zeitgewinn ist eine kurzzyklische Vorgehensweise deutlich inspirierender und erschließt das volle kreative Potenzial des Verbesserungsteams.
Kaizen is state of the art for high efficient optimization used by many companies. Nevertheless the variations of this method differ from company to company. A big obstacle to realize good kaizen is due to the lack of possibilities to generate different devices. In times of smart factories and increasing digitalization plenty of possibilities can be used to make ideas happen. This is the opportunity to optimize manufacturing systems in a short cyclic and fast way.
Projektmanagement mit Excel
(2016)
Professionelle und erfolgreiche Projektarbeit ist keine Hexerei! Allerdings scheitern viele Projekte am Einsatz der richtigen Software, denn teure Projektverfolgungs-Software ist nicht immer vonnöten. Hier zeigen die Autoren, wie man diese Aufgabe mit Excel löst. Ein Projekt komplett geplant, budgetiert und gesteuert - Am Beispiel eines inzwischen real existierenden Golfplatzes zeigen die Autoren praxisnah, wie ein Projekt komplett geplant, budgetiert und gesteuert wird. - Dabei kommt keine teure Projektverwaltungssoftware zum Einsatz. Die Autoren zeigen, wie diese Arbeit mit Hilfe von Excel und VBA automatisiert werden kann. Sie verknüpfen Excel intelligent mit Outlook und anderen Programmen. Mit diesem Buchtitel verlieren Terminpläne, Budgetüberwachung und Projekt-Reporting ihren Schrecken.
Purchasing is an important and at the same time critical function in multinational enterprises. Challenges are besides the growing purchasing volume the widespread distribution of organizational units and often a lack of coherence in those processes involving various organizational units. This becomes most evident in strategic procurement. Maturity assessments are a vital tool to create coherence in processes. In this contribution we provide a framework for the development of maturity assessments in strategic procurement for multinational enterprises. This framework covers all important aspects and topics to consider when developing a new procurement maturity assessment program for multinational corporations. From our company-background we also provide some casespecific examples how the framework can be brought to live.
Dieses Buch beschreibt anwendungsorientiert die Grundlagen, Methoden und Instrumente des Prozessmanagements in Einkauf und Logistik. Außerdem stellt es mit Lean Management, Industrie 4.0 und Global Sourcing aktuelle Konzepte zur Optimierung von Prozessen vor. Zahlreiche Beispiele und Fallstudien ermöglichen einen anschaulichen Einblick in die praktische Umsetzung.
Ductile failure of structural metals is relevant to a wide range of engineering scenarios. Computational methods are employed to anticipate the critical conditions of failure, yet they sometimes provide inaccurate and misleading predictions. Challenge scenarios, such as the one presented in the current work, provide an opportunity to assess the blind, quantitative predictive ability of simulation methods against a previously unseen failure problem. Rather than evaluate the predictions of a single simulation approach, the Sandia Fracture Challenge relies on numerous volunteer teams with expertise in computational mechanics to apply a broad range of computational methods, numerical algorithms, and constitutive models to the challenge. This exercise is intended to evaluate the state of health of technologies available for failure prediction. In the first Sandia Fracture Challenge, a wide range of issues were raised in ductile failure modeling, including a lack of consistency in failure models, the importance of shear calibration data, and difficulties in quantifying the uncertainty of prediction [see Boyce et al. (Int J Fract 186:5-68, 2014) for details of these observations]. This second Sandia Fracture Challenge investigated the ductile rupture of a Ti-6Al-4V sheet under both quasi-static and modest-rate dynamic loading (failure in 0.1 s). Like the previous challenge, the sheet had an unusual arrangement of notches and holes that added geometric complexity and fostered a competition between tensile- and shear-dominated failure modes. The teams were asked to predict the fracture path and quantitative far-field failure metrics such as the peak force and displacement to cause crack initiation. Fourteen teams contributed blind predictions, and the experimental outcomes were quantified in three independent test labs. Additional shortcomings were revealed in this second challenge such as inconsistency in the application of appropriate boundary conditions, need for a thermomechanical treatment of the heat generation in the dynamic loading condition, and further difficulties in model calibration based on limited real-world engineering data. As with the prior challenge, this work not only documents the 'state-of-the-art' in computational failure prediction of ductile tearing scenarios, but also provides a detailed dataset for non-blind assessment of alternative methods.
The authors study the relation between workers' age and their productivity in work teams, based on a new and unique data set that combines data on errors occurring in the production process of a large car manufacturer with detailed information on the personal characteristics of workers related to the errors. The authors correct for non-random sample selection and the potential endogeneity of the age-composition in work teams. The results suggest that productivity in this plant which is typical for large-scale manufacturing does not decline at least up to age 60. (C) 2016 Published by Elsevier B.V.
We consider the generalized Radon transform (defined in terms of smooth weight functions) on hyperplanes in R-n. We analyze general filtered backprojection type reconstruction methods for limited data with filters given by general pseudodifferential operators. We provide microlocal characterizations of visible and added singularities in R-n and define modified versions of reconstruction operators that do not generate added artifacts. We calculate the symbol of our general reconstruction operators as pseudodifferential operators and provide conditions for the filters under which the reconstruction operators are elliptic for the visible singularities. If the filters are chosen according to those conditions, we show that almost all visible singularities can be recovered reliably. Our work generalizes the results for the classical line transforms in R-2 and the classical reconstruction operators (that use specific filters). In our proofs, we employ a general paradigm that is based on the calculus of Fourier integral operators. Since this technique does not rely on explicit expressions of the reconstruction operators, it enables us to analyze more general imaging situations.
Magnetoactive elastomers (MAEs) are composite materials comprised of micrometer-sized ferromagnetic particles in a nonmagnetic elastomermatrix. Asingle-particle mechanism ofmagnetostriction in MAEs, assuming the rotation of a soft magnetic, mechanically rigid particle with uniaxial magnetic anisotropy in magnetic fields is identified and considered theoretically within the framework of an alternative model. In this mechanism, the total magnetic anisotropy energy of the filling particles in the matrix is the sum over single particles. Matrix displacements in the vicinity of the particle and the resulting direction of the magnetization vector are calculated. The effect of matrix deformation is pronounced well if the magnetic anisotropy coefficient K is much larger than the shear modulus mu of the elastic matrix. The feasibility of the proposed magnetostriction mechanism in soft magnetoactive elastomers and gels is elucidated. The magnetic-field-induced internal stresses in the matrix lead to effects of magnetodeformation and may increase the elastic moduli of these composite materials.
Transient magnetorheological response of magnetoactive elastomers to step and pyramid excitations
(2016)
Transient rheological response of magnetoactive elastomers is experimentally studied using dynamic torsion at a fixed oscillation frequency in temporally stepwise changing magnetic fields and oscillation amplitudes. For step magnetic-field excitations, at least three exponential functions are required to reasonably describe the time behavior of the storage shear modulus over long time scales (>10(3) s). The deduced characteristic time constants of the corresponding rearrangement processes of the filler network differ approximately by one order of magnitude: tau(1) less than or similar to 10(1) s, tau(2) similar to 10(2) s, and tau(3) similar to 10(3) s. The sudden imposition of the external magnetic field activates a very fast rearrangement process with the characteristic time under 10 s, which cannot be determined more precisely due to the measurement conditions. Even more peculiar transient behavior has been observed during pyramid excitations, when either the external magnetic field was first stepwise increased and then decreased in a staircase manner at a fixed strain amplitude gamma or the strain amplitude gamma was first stepwise increased and then decreased in a staircase manner at a fixed magnetic field. In particular, the so-called "cross-over effect'' has been identified in both dynamical loading programs. This cross-over effect seems to be promoted by the application of the external magnetic field. The experimental results are discussed in the context of the specific rearrangement of the magnetic filler network under the simultaneous action of the external magnetic field and shear deformation. Striking similarities of the observed phenomena to the structural relaxation processes in glassy materials and to the jamming transition of granular materials are pointed out. The obtained results are important for fundamental understanding of material behavior in magnetic fields as well as for the development of devices on the basis of magnetoactive elastomeric materials.
The surface dilational modulus is a crucial parameter for describing the rheological properties of aqueous surfactant solutions. These properties are important for many technological processes. The present paper describes a fully automated instrument based on the oscillating bubble technique. It works in the frequency range from 1 Hz to 500 Hz, where surfactant exchange dynamics governs the relaxation process. The originality of instrument design is the consistent combination of modern measurement technologies with advanced imaging and signal processing algorithms. Key steps on the way to reliable and precise measurements are the excitation of harmonic oscillation of the bubble, phase sensitive evaluation of the pressure response, adjustment and maintenance of the bubble shape to half sphere geometry for compensation of thermal drifts, contour tracing of the bubbles video images, removal of noise and artefacts within the image for improving the reliability of the measurement, and, in particular, a complex trigger scheme for the measurement of the oscillation amplitude, which may vary with frequency as a result of resonances. The corresponding automation and programming tasks are described in detail. Various programming strategies, such as the use of MATLAB (R) software and native C++ code are discussed. An advance in the measurement technique is demonstrated by a fully automated measurement. The instrument has the potential to mature into a standard technique in the fields of colloid and interface chemistry and provides a significant extension of the frequency range to established competing techniques and state-of-the-art devices based on the same measurement principle.
Um die Lebensqualität und Einsatzfähigkeit von Menschen mit Behinderung oder älteren Menschen zu verbessern, wurde untersucht, inwiefern Gamification-Anwendungen beim Anlernen einer Gestensteuerung geeignet sind. Grundlage des Experiments stellt ein intelligenter Arbeitsplatz (Smart Workbench, SWoB) dar, der Personen bei manuellen Handhabungsaufgaben unterstützt sowie bestimmte Produktionsprozesse teilautomatisiert ausführt. Um die Anlage bedienen zu können, muss im Vorfeld eine Einweisung erfolgen, welche von Menschen oder durch ein Lerntutorial mit Gamification-Elementen zur Motivationssteigerung durchgeführt werden kann. In der Studie wurde untersucht, welche Form des Anleitens aus welchen Gründen von unterschiedlichen Personen eher akzeptiert oder abgelehnt wird.
Precisely aligned high-aspect-ratio (HAR) silicon tip arrays were fabricated using enhanced reactive ion etching with an inductively-coupled-plasma followed by a sharpening oxidation. A gold thin film was then sputtered only on the tips of the HAR structures. Field-emission (FE) properties from Au-coated HAR p-Si tip array cathodes have been systematically investigated by means of field emission scanning microscopy (FESM). A rather high efficiency of the HAR Si structures (71% at 550 V), but limited homogeneous FE with currents of 1-600 nA might be correlated with the varying geometry of the tips and the presence of oxides. I-V measurements of single Au-coated HAR emitters revealed activation effects and the saturation current region at 3 nA. An increase of the saturation current by 4 orders of magnitude was observed during 20 hours of conditioning at constant voltage, which finally resulted in nearly reproducible FN curves with a ß-factor of 473. An excellent stability of the emission current of less than 1 % was obtained during the additional long-time conditioning at constant voltage. Optical switching under halogen lamp illumination resulted in at least 2 times higher saturation currents and showed a linear dependence of the FE current on the light color temperature.
Black silicon structures with integrated gate electrode were realized by using an improved fabrication process. An enhanced insulation layer was achieved by a combination of dry and wet oxidation, and a gold layer was evaporated as gate electrode. The black silicon structures were prepared with a RIE/ICP etching process at room temperature. Arrays of 16 and 100 apertures with buried p-doped black silicon whiskers have been fabricated. These structures have an emitter height of approximately 1.5 μm with tip radii between 5 nm and 30 nm. The whiskers are surrounded by the gate electrode in a distance of 1.5 μm. Integral field emission measurements yielded an onset voltage of 92 V for 16 apertures and 60 V for 100 apertures for an emission current of 1 nA. Maximum emission currents up to 0.2 μA were observed for the array with 100 apertures at a cathode voltage of 200 V. Stability measurements showed a current fluctuation of ± 21% at a mean value of the emission current of 12 nA over a period of 30 minutes for 16 apertures with b-Si whiskers.
A novel three-dimensional epitaxial technique allows on patterned substrates the realization of gallium nitride pillars, also known as nano- and microrods. The typical dimensions of the microrods are in the range of one micron for the radius of the hexagonal footprint and about 10 μm in height. The microrods consist of a semiconductor heterostructure with an n GaN core, a n-GaN shell, a p GaN shell and an intermediate quantum well layer. The field emission properties were investigated in diode configuration by integral field emission measurements in a vacuum chamber at pressures around 10 -9 mbar. The spacer was mica with a thickness of 50 μm. A metallized fine-meshed nitride grid (or a metallized Si-grid) was used as anode. A current of about 1 μA at a voltage of 1250 V (1750 V) was measured. An onset field of about 12.5 MV/m (20 MV/m) and field enhancement factors in the range of 200 to 500 (150 to 300) were found. The investigation with the fine-meshed grid showed an expected pronounced saturation region.
Effiziente Methode zur Bestimmung von dynamischen strukturellen Belastungen in Großpresswerkzeugen
(2016)
Structural Dynamic Analysis of Thin Composite Plates Using Noncontact Measurement and Excitation
(2016)
Arrays of black silicon field emission pillar structures were fabricated on p-type silicon substrates. Two types of samples with the same number of pillars (arrays of 10 × 10) but different pillar heights (8 and 20 μm) were prepared as well as a black silicon reference sample without pillars. The field emission properties of these cathodes were investigated both by means of integral current-voltage measurements and by field emission scanning microscopy. Samples with a pillar height of 20 μm revealed onset fields as low as 6.4 V/μm, field enhancement factors up to 800, and emission currents up to 8 μA at an applied field of 20 V/μm. Due to the p-type material, a saturation of the emission current for fields above 11 V/μm was observed. This saturation leads to a stable operation with a current fluctuation of less than ±8%. It was found that samples with a pillar height of 20 μm showed improved emission characteristics compared to samples with a pillar height of 8 μm or without pillars. The voltage maps revealed an increased emission homogeneity after a “burn-in” sequence of the sample. The current map showed that a few of the pillars dominate the emission. Integral current stability measurements were performed under different vacuum pressures, in order to investigate altered emission behavior and a potential degradation of the emitters. At pressures above 10−6 mbar, the sample starts to degrade irreversibly. Nevertheless, even after a harsh treatment over 30 min at 5 × 10−5 mbar and at an applied field of 23 V/μm, the cathode was still operating, and did not fail during further operation over 20 h at 5 × 10−8 mbar and at an applied field of 28 V/μm.
We have investigated the properties of black Si field emitter arrays under strong electric fields and laser illumination. A low onset field of 1.8 MV/m for an emission current of 1 nA was obtained. A pronounced saturation region of the dark and photo-enhanced current was observed, which provided a short-term stability of 0.1% at 0.4 μA and 0.7% at 1.0 μA, respectively. As maximum value for the photosensitivity, an on-off current switching ratio of 43 reaching about 13 μA was achieved at a laser power of 15 mW. Electron spectra in the dark and under laser illumination are presented, showing a current and light-sensitive voltage drop across the emitters as well as hints for hot electron emission.
In this paper, the idea of fiber-oriented repair geometries for carbon fiber reinforced plastics (CFRP) is investigated. It considers the differing mechanical properties of unidirectional fiber reinforced material by excluding overlapping regions perpendicular to the fiber direction of the particular layer.
A mechanical and numerical comparison of tensile strength of stepped joints with continuous step lengths per ply and stepped joints with reduced step lengths in plies with fiber orientation differing from load direction is performed.
Finite element simulations show similar shear stresses. Mechanical tests of CFRP laminates with stepped joints show no significant deviation in tensile strength, in spite of a joint length reduction of nearly 40%. This leads to the possibility of a significant reduction of repair area.
An over-the-counter methodology to predict fracture initiation and propagation in the challenge specimen of the Second Sandia Fracture Challenge is detailed herein. This pragmatic approach mimics that of an engineer subjected to real-world time constraints and unquantified uncertainty. First, during the blind prediction phase of the challenge, flow and failure locus curves were calibrated for Ti–6Al–4V with provided tensile and shear test data for slow (0.0254 mm/s) and fast (25.4 mm/s) loading rates. Thereafter, these models were applied to a 3D finite-element mesh of the non-standardized challenge geometry with nominal dimensions to predict, among other items, crack path and specimen response. After the blind predictions were submitted to Sandia National Labs, they were improved upon by addressing anisotropic yielding, damage initiation under shear dominance, and boundary condition selection.
Tightness is often the main requirement for quasi-simultaneous laser transmission welds. However, remaining gaps cannot be detected by the used set-path monitoring. By using a pyrometer in combination with a 3D-scanner, weld seam interruptions can be localized precisely while welding, due to temperature deviations along the weld contour. To analyze the temperature signal in correlation to the progress of gap-bridging, T-joint samples with predefined gaps are welded. The set-path is measured synchronously. Additionally, the temperature distribution and the influence of the thermal expansion of the polymers are studied by a thermo-mechanical FEM-process simulation. On top of that, the melt blow-out of the welded samples is analyzed using μCT-measurements. The experiments have shown that closing of a gap can be identified reliably by the temperature signal and that the squeezed melt flow into the gap and the thermal expansion in the gap zone accelerates gap-bridging. Furthermore the inserted heat can be adapted in the fault zone, in order to avoid thermal damage.
Quasi-simultaneous laser transmission welding is a well-known joining technique for thermoplastics and mainly used in the automotive as well as in the medical industry. For process control usually the so called set-path monitoring is used, where the weld is specified as "good" if the irradiation time is inside a defined confidence interval. However, the detection of small-sized gaps or thermal damaged zones is not possible with this technique. The analyzation of the weld seam temperature during welding offers the possibility to overcome this problem. In this approach a 3D-scanner is used instead of a scanner with flat-field optic. By using a pyrometer in combination with a 3D-scanner no color-corrected optic is needed in order to provide that laser- and detection-spot are concentric. Experimental studies on polyethylene T-joints have shown that the quality of the signal is adequate, despite the use of an optical setup with a long working distance and a small optical aperture. The effects on temperature are studied for defects like a gap in the joining zone. Therefore a notch was milled into the absorbent polymer. In case of producing housings for electronic parts the effect of an electrical wire between the joining partners is also investigated. Both defects can be identified by a local temperature deviation even at a feed rate of four meters per second. Furthermore a strategy for signal-processing is demonstrated. By this, remaining defects can be identified. Consequently an online detection of local defects is possible, which makes a dynamic process control feasible.
In recent years, a considerable amount of interest has arisen for scheduling problems with technological restrictions. For example, no-buffer flow-shop scheduling problem are well investigated. Here a real world flow shop with a transportation restriction is regarded. It has to produce small batches, very often with a lot size of one, with short response times. Thus, scheduling algorithms are needed to ensure that under the constraint of a high average load of the flow shop, the duedates of the production orders are met. This transportation restriction reduces the set of feasible schedules even more than the nobuffer restrictions discussed in the literature in the case of limited storage. Still this problem is NP-hard. Due to the transportation restriction, the duration of a job A on the flow-shop depends on the other jobs processedon the flow-shop in the same time frame which is called a cycle. Realistic processing times are achieved by a simulation of the scheduling of A which includes the next jobs until A has left the flow-shop. The usage of such realistic processing times instead of net processing times improves the priority rules by around 16%. There are pools of jobs where a large variance of the cycle times is beneficial and pools of jobs where a small variance is better. This is partially detected by agenetic algorithm. This improves the performance by another 34%.
Production planning and production control mainly focus on optimising the entire production system of a company. On the basis of hierarchical planning as a suitable method for solving this task, this paper shows - besides the economic dimension taken into account so far - that there are also social and ecological effects which will have to be considered in the process of planning. For this purpose, we would like to indicate here which social and ecological parameters can be or have already been taken into account for master production scheduling, for lot sizing and resource scheduling. As a result, an overview has been created which presents the existing concepts of sustainable production planning and production control as well as the existing deficits regarding the sustainability perspective.
Bei der Produktionsplanung steht die Optimierung des Produktionssystems eines Unternehmens im Vordergrund. In diesem Beitrag wird auf Basis der hierarchischen Produktionsplanung aufgezeigt, dass neben ökonomischen und ökologischen Aspekten insbesondere auch soziale Effekte bei der Entscheidungsfindung zu berücksichtigen sind. Dazu werden für die Hauptproduktionsprogrammplanung, die Losgrößenplanung und die Ressourcenbelegungsplanung dargelegt, welche sozialen Größen berücksichtigt werden können beziehungsweise bereits berücksichtigt sind. Überdies wird ein Modellansatz zur Hauptproduktionsprogrammplanung vorgestellt, der auf die Beseitigung identifizierter Forschungslücken abzielt.
The rising energy prices – particularly over the last decade – pose a new challenge for the manufacturing industry. Reactions to climate change, such as the advancement of renewable energies, raise the expectation of further price increases and variations. Regarding the manufacturing industry, production planning and controlling can have a significant influence on the in-plant energy consumption. In this paper, we develop a scheduling method as a linear optimization model with the objective to minimize energy costs in a job shop production system.
Lean Management wurde in den letzten Jahren in den deutschen Produktionsbetrieben immer populärer. Die daraus resultierende Umstrukturierung bringt meist eine höhere Wirtschaftlichkeit, Produktivität und große Einsparpotenziale mit sich. Im Zuge dessen sollen bei der Produktion der Kühlbehälter (IsoTec) der Gebhardt Logistic Solutions GmbH in Cham Potenziale und Maßnahmen aufgedeckt werden, um die Prozesse zu verbessern. Großes Augenmerk liegt dabei, in der Anwendung eines der bekanntesten Methode des Lean Managements, dem Kanban-Prinzip, zur Optimierung der Materialbereitstellung, den Lagerbeständen und den Durchlaufzeiten. Damit verbunden ist die Verkürzung der Lieferzeiten gegenüber dem Kunden. Durch die Nutzung der eigenen Kompetenzen rund um die Transportbehälterfertigung wird die Bereitstellung und der Transport der benötigten Materialien für die Montage neu geplant und umgesetzt.
Companies often use specially-designed production systems and change them from time to time. They produce small batches in order to satisfy specific demands with the least tardiness. This imposes high demands on high-performance scheduling algorithms which can be rapidly adapted to changes in the production system. As a solution, this paper proposes a generic approach: solutions were obtained using a widely-used commercially-available tool for solving linear optimization models, which is available in an Enterprise Resource Planning System (in the SAP system for example) or can be connected to it. In a real-world application of a flow shop with special restrictions this approach is successfully used on a standard personal computer. Thus, the main implication is that optimal scheduling with a commercially-available tool, incorporated in an Enterprise Resource Planning System, may be the best approach.
This paper proposes a scenario-based two-stage stochastic programming model with recourse for master production scheduling under demand uncertainty. We integrate the model into a hierarchical production planning and control system that is common in industrial practice. To reduce the problem of the disaggregation of the master production schedule, we use a relatively low aggregation level (compared to other work on stochastic programming for production planning). Consequently, we must consider many more scenarios to model demand uncertainty. Additionally, we modify standard modelling approaches for stochastic programming because they lead to the occurrence of many infeasible problems due to rolling planning horizons and interdependencies between master production scheduling and successive planning levels. To evaluate the performance of the proposed models, we generate a customer order arrival process, execute production planning in a rolling horizon environment and simulate the realisation of the planning results. In our experiments, the tardiness of customer orders can be nearly eliminated by the use of the proposed stochastic programming model at the cost of increasing inventory levels and using additional capacity.