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Sökning: db:Swepub > Övrigt vetenskapligt/konstnärligt > Högskolan Väst > Licentiatavhandling > (2012)

  • Resultat 1-8 av 8
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1.
  • Carlsson, Henrik, 1979- (författare)
  • Reliable Virtual Commissioning
  • 2012
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Virtual commissioning is a technique for programming, optimising and verifying industrial automated production, such as robot controllers and programmable logic controllers (PLC), off-line in a simulated environment. Compared with traditional robot off-line programming and simulation, the scope is wider and can include an entire production cell.Robot simulation is a well-established technique and widely used in industry today, much thanks to the RRS interface that enables simulated robot control systems to be integrated in the simulation software. A more general interface for industrial control system integration is OPC that has been an industrial de facto standard for connection between industrial control systems and regular PCs. State-of-the-art production simulation tools often include the possibility to connect an industrial control system via OPC. However, OPC suffers a major drawback when it comes to production simulation, there is no mechanism that synchronises the industrial control system with the simulation and this could lead to unreliable results from the simulation.Another obstacle for virtual commissioning is the amount of time that needs to be spent during the simulation model building phase, since virtual commissioning includes more signals. This does not only take more time, but it is also an error prone process that might lead to unreliable results.In this thesis problems related to the OPC interface and the modelling process are discussed, and suggestions how these issues can be solved are presented so reliable virtual commissioning can be achieved.
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  • Curry, Nicholas, 1984- (författare)
  • Design of Thermal Barrier Coating Systems
  • 2012
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Thermal barrier coatings (TBC’s) are used to provide both thermal insulation and oxidation protection to high temperature components within gas turbines. The development of turbines for power generation and aviation has led to designs where the operation conditions exceed the upper limits of most conventional engineering materials. As a result there has been a drive to improve thermal barrier coatings to allow the turbine to operate hotter for longer.The focus of this study has been the development of a new generation of TBC system for industrial implementation. The goal for these new coatings was to achieve lower conductivity and longer lifetime than those coatings used today. The route taken to achieve these goals has been twofold. Firstly an alternative stabiliser has been chosen for the zirconium oxide system in the form of dysprosia. Secondly, Control of the powder morphology and spray parameters has been used to generate coating microstructures with favourable levels of porosity.Samples have been heavily characterised using the laser flash technique for evaluation of thermal properties. Measurements were performed at room temperature and at intervals up to 1200°C. Samples have also been tested in their as produced state and after heat treatments of up to 200 hours.Lifetime evaluation has been performed using the thermo-cyclic fatigue test to expose coating systems to successive cycles of heating and cooling combined with oxidation of the underlying metallic coating.Microstructures have been prepared and analysed using SEM. An image analysis routine has been used to attempt to quantify changes in microstructure features between coating types or coating exposure times and to relate those changes to changes in thermal propertiesResults show that dysprosia as an alternative dopant gives a reduction in thermal conductivity. While small at room temperature and in the as produced state; the influence becomes more pronounced at high temperatures and with thermal exposure time. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levels of porosity.In relation to lifetime, the target of double the thermo-cyclic fatigue life was achieved using a coating with engineered porosity. Introducing a polymer to the spray powder helps to generate large globular pores within the coating together with a large number of delaminations. Such a structure has shown to be highly resistant to TCF testing.
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  • De Backer, Jeroen, 1987- (författare)
  • Robotic Friction Stir Welding for Flexible Production
  • 2012
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Friction Stir Welding (FSW) is a modern welding process that joins materials by frictional heat, generated by a rotating tool. Unlike other welding processes, the material never melts, which is beneficial for the weld properties. FSW is already widely adopted in several industries but the applications are limited to simple geometries like straight lines or circular welds, mostly in aluminium. The welding operation is performed by rigid FSW machines, which deliver excellent welds but puts limitations on the system in terms of flexibility and joint geometries. Therefore, several research groups are working on the implementation of the FSW process on industrial robots. A robot allows welding of three-dimensional geometries and increases the flexibility of the whole system. The high process forces required for FSW, in combination with the limited stiffness of the robot brings some extra complexity to the system.  The limitations of the robot system are addressed in this licentiate thesis.One part of the thesis studies the effect of robot deflections on the weld quality. A sensor-based solution is presented that measures the path deviation and compensates this deviation by modifying the robot trajectory. The tool deviation is reduced to an acceptable tolerance and root defects in the weld are hereby eliminated. The sensor-based method provided better process understanding, leading to a new strategy that uses existing force-feedback for path compensations of the tool. This method avoids extra sensors and makes the system less complex. Another part of this work focuses on the extra complexity to maintain a stable welding process on more advanced geometries. A model is presented that allows control of the heat input in the process by control of the downforce. Finally, the robot’s limitations in terms of maximal hardness of the materials to be welded are investigated. Parameter tuning and implementation of preheating are proposed to allow robotic FSW of superalloys.
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  • Tano, Ingrid (författare)
  • Contributions to multivariate process capability indices
  • 2012
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The work presented in this thesis considers multivariate process capability indices (MPCIs) with focus on confidence intervals and tests for MPCIs. It also includes a case study, where multivariate statistical analysis and MPCIs are applied to data from a thermal spraying process at Volvo Aero Corporation. A process capability index measures the ability of a process to satisfy customers’ demands. Since the knowledge about the process performance is based on a random sample, it is important to be able to handle the uncertainty this implies. If the uncertainty is not dealt with and the estimated index is used directly without considering, e.g. a confidence interval, an erroneous conclusion may be drawn about the process capability.The thesis consists of a summary and of three papers, one of which has been presented at an international conference, one has been accepted for publication in an international journal, and the third has been submitted for publication.In Paper I, multivariate statistical analysis is used for screening and tentative model building to describe the relationship between the porosity and the heat conductivity in the thermal spraying process. Object-oriented finite element analysis (OOF) is subsequently used for verification of the statistical model. The new approach functions well and confirms the findings from the statistical model.Paper II reviews and compares four different MPCIs with confidence intervals, requiring multivariate normal distribution. MPCIs are needed when the quality characteristic of interest is multivariate, i.e. when the quality characteristic consists of several correlated variables. The review shows that more research is needed to obtain an MPCI with a confidence interval or a test that works properly. In particular, it is required that a stated value of the MPCI at least limits the probability of non-conformance in a known way. A drawback is also elucidated with existing MPCIs based on principal component analysis.Paper III presents some method development with the purpose of meeting the deficiencies identified in Paper II. A new index together with a confidence interval and a decision procedure is developed that converts a multivariate situation into a familiar univariate situation. Well-known statistical theory for univariate process capability indices can then be used. Properties, like significance level and power, of the pro¬posed deci¬sion procedure is evaluated through a simulation study in the two-dimen¬sional case. A comparative simulation study between our new MPCI and an MPCI pre¬viously suggested in the literature is also done. These studies show that our proposed MPCI with accompanying decision procedure has desirable properties and is worth to study further.
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7.
  • Wanner, Bertil (författare)
  • Strategies for Reducing Vibrations during Milling of Thin-walled Components
  • 2012
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • Factors such as environmental requirements and fuel efficiency have pushed aerospace industry to develop reduced-weight engine designs and thereby light-weight and thin-walled components. As component wall thickness gets thinner and the mechanical structures weaker, the structure becomes more sensitive for vibrations during milling operations. Demands on cost efficiency increase and new ways of improving milling operations must follow.Historically, there have been two “schools” explaining vibrations in milling. One states that the entry angle in which the cutting insert hits the work piece is of greater importance than the exit angle. The other states that the way the cutter leaves the work piece is of greater importance than the cutter entry. In an effort to shed some light over this issue, a substantial amount of experiments were conducted. Evaluations were carried out using different tools, different tool-to-workpiece offset positions, and varying workpiece wall overhang. The resultant force, the force components, and system vibrations have been analyzed.The first part of this work shows the differences in force behavior for three tool-to-workpiece geometries while varying the wall overhang of the workpiece. The second part studies the force behavior during the exit phase for five different tool-to-workpiece offset positions while the overhang is held constant. The workpiece alloy throughout this work is Inconel 718.As a result of the project a spread sheet milling stability prediction model is developed and presented. It is based on available research in chatter theory and predicts the stability for a given set of variable input parameters.
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  • Resultat 1-8 av 8

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