Rührreibschweißen mit einem Industrieroboter unter Berücksichtigung der Einsatzkriterien für die automobile Großserienfertigung

The joining method "friction stir welding" allows production of reproducible high-quality welded joints of different aluminum alloys. This thesis shows that special machines and machine tools are preferably used because of high process forces being at work during the process of production. However, the use of standard industrial robots for friction stir welding as a more cost-effective and more flexible alternative is favored in large-scale automotive production. In the present thesis, performance characteristics of an industrial robot are first analyzed without processing forces. In this context, pose repeatability and path repeatability of industrial robots are quantified for different reference paths in the plane. In this context, it is noted that the robot satisfies the accuracy requirements of the welding process. However, when analyzing the interactions between the process and the robot structure, it becomes clear that the working accuracy of the industrial robot is significantly influenced by the resulting process forces during friction stir welding; without "reteaching" or offline correction of the programmed reference path, the mechanical properties of the welded joint are negatively affected by the lack of the industrial robots working accuracy. During the analysis, it can be demonstrated that the displacement of the tool not only depends on the resulting process forces, but is also significantly influenced by the direction of the vector of the path velocity during path welding. Within the analysis of the static and dynamic system properties of the industrial robot, it is shown that the nonlinear stiffnesses of the robot structure depend significantly on the joint positions and the loading direction. Based on the findings of the system analysis, a model-based offline path correction, that takes considers static compliances and interactions between process and industrial robot, will be developed.Das Fügeverfahren „Rührreibschweißen“ ermöglicht die Herstellung reproduzierbar hochwertiger Schweißverbindungen. Aufgrund der sehr hohen Prozesskräfte werden in der Produktion vorzugsweise Sonder- und Werkzeugmaschinen eingesetzt. In der automobilen Großserienfertigung wird jedoch der Einsatz von Standard-Industrierobotern für das Rührreibschweißen als kostengünstigere und flexiblere Alternative favorisiert. Im Rahmen der Arbeit werden die Leistungskenngrößen des Industrieroboters zunächst ohne Bearbeitungskräfte analysiert. In diesem Zusammenhang werden die Pose- und Bahn-Wiederholgenauigkeit des Industrieroboters an unterschiedlichen Referenzbahnen in der Ebene quantifiziert. Hier ist festzustellen, dass der Roboter den Genauigkeitsanforderungen des Schweißverfahrens genügt. Bei der Analyse der Wechselwirkungen zwischen Prozess und Roboterstruktur wird jedoch deutlich, dass die Arbeitsgenauigkeit des Industrieroboters durch die resultierenden Prozesskräfte beim Rührreib-schweißen signifikant beeinflusst wird; ohne ein „Nachteachen“ oder eine Offline-Korrektur der programmierten Soll-Bahn werden die mechanischen Eigenschaften der Fügeverbindung durch die mangelnde Arbeitsgenauigkeit des Industrieroboters negativ beeinflusst. Bei der Analyse kann nachgewiesen werden, dass die Abdrängung des Werkzeugs nicht nur von den resultierenden Prozesskräften abhängt, sondern auch signifikant durch die Richtung des Vektors der Bahngeschwindigkeit beim Bahnschweißen beeinflusst wird. Bei der Analyse der statischen und dynamischen Systemeigenschaften des Roboters wird gezeigt, dass die nichtlinearen Steifigkeiten der Roboterstruktur maßgeblich von den Gelenkstellungen und der Belastungsrichtung abhängen. Aus den Erkenntnissen der Systemanalyse wird eine modellbasierte Offline-Bahnkorrektur, die Nachgiebigkeiten und Wechselwirkungen zwischen Prozess und Roboter berücksichtigt, entwickelt

Musiklehre und kunstlerisches Bewusstsein. : Zur 'Methode der Musik' bei Adolf Bernhard Marx.

markdownabstract__Abstract__ Worldwide, 600 million jobs are needed over the next 15 years to keep employment rates at their current level. Because most employment in low and middle income countries is in micro-, small and medium-sized enterprises, governments, non-governmental organizations and donors spend on targeted programs and broader policies to enhance employment creation in these firms. But despite these efforts, not much is known about which of these interventions are really effective. This systematic review synthesizes the existing evidence on the employment impact of these programs. The results show that the effects have so far been very modest. Even if many interventions were relatively successful in boosting self-employment, expanding employment in already existing firms is generally more difficult but eventually easier in somewhat larger firms compared to very small firms. This finding is also true in relative terms, but it is probably not fully independent from the contexts in which firms of different sizes have been observed. The effects of finance interventions have on average been weaker than the effects of entrepreneurship training or business development services. Our study also reveals that about a third of the interventions covered by this review are not primarily designed to create employment but rather strive for income stabilization and poverty reduction. A further striking finding is that the study design matters for the impacts found; randomized controlled trials find systematically smaller effects than quasi-experimental studies. A significant shortcoming of the literature is that almost nothing is known about long term effects and cost-effectiveness and many studies fail to provide a detailed analysis of why certain effects occurred or did not occur — making it hard to extrapolate lessons