Dissertations / Theses on the topic 'Robotic friction stir welding'
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1
De, Backer Jeroen. "Feedback Control of Robotic Friction Stir Welding." Doctoral thesis, Högskolan Väst, Avd för automationssystem, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-6043.
Abstract:
The Friction Stir Welding (FSW) process has been under constant developmentsince its invention, more than 20 years ago. Whereas most industrial applicationsuse a gantry machine to weld linear joints, there are applications which consistof complex three-dimensional joints, requiring more degrees of freedom fromthe machines. The use of industrial robots allows FSW of materials alongcomplex joint lines. There is however one major drawback when using robotsfor FSW: the robot compliance. This results in vibrations and insufficient pathaccuracy. For FSW, path accuracy is important as it can cause the welding toolto miss the joint line and thereby cause welding defects.The first part of this research is focused on understanding how welding forcesaffect the FSW robot accuracy. This was first studied by measuring pathdeviation post-welded and later by using a computer vision system and laserdistance sensor to measure deviations online. Based on that knowledge, a robotdeflection model has been developed. The model is able to estimate thedeviation of the tool from the programmed path during welding, based on thelocation and measured tool forces. This model can be used for online pathcompensation, improving path accuracy and reducing welding defects.A second challenge related to robotic FSW on complex geometries is thevariable heat dissipation in the workpiece, causing great variations in the weldingtemperature. Especially for force-controlled robots, this can lead to severewelding defects, fixture- and machine damage when the material overheats.First, a new temperature method was developed which measures thetemperature at the interface of the tool and the workpiece, based on the thermoelectriceffect. The temperature information is used as input to a closed-looptemperature controller. This modifies primarily the rotational speed of the tooland secondarily the axial force. The controller is able to maintain a stablewelding temperature and thereby improve the weld quality and allow joining ofgeometries which were impossible to weld without temperature control.Implementation of the deflection model and temperature controller are twoimportant additions to a FSW system, improving the process robustness,reducing the risk of welding defects and allowing FSW of parts with highlyvarying heat dissipation.
2
Zhang, Cheng. "Robotic 3D friction stir welding : T-butt joint." Thesis, Högskolan Väst, Avd för automationssystem, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-8250.
Abstract:
This Master Thesis was performed in terms of robotic three dimensional friction stir welding with T-butt joint. Friction stir welding (FSW) is a solid state welding method that achieves the weld temperature by friction of a rotating non-consumable tool with the workpiece. Science and technology fast developing requires for higher seam quality and more complex welding joint geometry like 3D welds. In order to acquire high productivity, capacity and flexibility with acceptable cost, robotic FSW solution have been proposed. Instead of the standard FSW machine, using a robot to perform complicated welds such as, three-dimensional. In this report, a solution for weld a 3D T-butt joint, which located in an aluminium cylinder with 1.5 mm thickness using a robot, was developed. Moreover, two new paths were investigated in order to avoid the use of two welds to perform this type of joint. The paths were tested on 2D and on 3D (with a 5050 curvature radius) geometries. Both paths had good results. What is more, the parameter developing methods of FSW process, which is composed of necessary parameter setting, positional compensation was introduced. Specially,the study demonstrates how complicate geometry can be welded using a robot. Also,it shows that TWT temperature control is able to acquire high quality 3D welds. In addition, an analysis of the 2D welding and 3D welding was performed, which exposed that, keeping exactly the same welding conditions, higher lateral forces on the tool were found during 3D welding. Basis on the special case in this paper, when the tool goes like "climbing" the sample, the suffering force of tool decreasing with increasing the height(Z position); nevertheless, when the tool goes like "downhill", the suffering force of tool decreasing with decreasing the height (Z position). What is more, in 2D weld, increasing the downforce (Fz) results increasing the lateral forces which can be Fx and/or Fy. Finally, the future works suggestions were presented in terms of (1) performing the new paths into a real cylinder, (2) performing tensile test on the paths and comparing it with conventional path which weld twice, (3) researching how the downforce (Fz) influence the Fx and Fy during welding of different 3D geometries, (4) how the cooling rate of backing bar influence the seam quality when it is use the same welding parameters and (5) the effect of performing welds in the same welding temperature achieved with different combination of the tool rotational speed and downforce on the material properties
3
De, Backer Jeroen, and Bert Verheyden. "Robotic Friction Stir Welding for Automotive and Aviation Applications." Thesis, University West, Division of Production Engineering, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-2171.
Abstract:
Friction Stir Welding (FSW) is a new technology which joins materials by using frictional heat. Inthe first part of this thesis, a profound literature study is performed. The basic principles, therobotic implementation and possibilities to use FSW for high strength titanium alloys areexamined. In the next phase, a FSW-tool is modelled and implemented on an industrial robot in arobot simulation program. Reachability tests are carried out on car body parts and jet engineparts. By using a simulation program with embedded collision detection, all possible weldinglocations are determined on the provided parts. Adaptations like a longer FSW-tool and amodified design are suggested in order to get a better reachability. In different case studies, thenumber of required robots and the reduction of weight and time are investigated and comparedto the current spot welding process.
4
Magalhães, Ana. "Thermo-electric temperature measurements in friction stir welding : Towards feedback control of temperature." Licentiate thesis, Högskolan Väst, Avdelningen för produktionssystem (PS), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:hv:diva-9982.
Abstract:
Friction Stir Welding has seen a fast uptake in many industry segments. Mechanical properties superior to fusion welding, the ability to weld "unweldable" aluminium alloys and low distortion are often described as the main reasons for the fast industrial implementation of FSW. Most existing applications consist of long straight welding joints. Applications with complex weld geometries, however, are rarely produced by FSW. These geometries can induce thermal variations during the welding process, thus making it challenging to maintain a consistent weld quality. In-process adaptation of weld parameters to respond to geometrical variations and other environmental variants allow new design opportunities for FSW. Weld quality has been shown to be reliant on the welding temperature. However, the optimal methodology to control the temperature is still under development.The research work presented in this thesis focuses on some steps to take in order to reach the improvement of the FSW temperature controller, thus reach a better and consistent weld quality. In the present work different temperature methods were evaluated. Temperature measurements acquired by the tool-workpiece thermocouple (TWT) method were accurate and fast, and thereby enhanced suitable for the controller. Different environmental conditions influencing the material heat dissipation were imposed in order to verify the controller effect on the joint quality. In comparison with no controlled weld, the use of the controller enabled a fast optimization of welding parameters for the different conditions, leading to an improvement of the mechanical properties of the joint.For short weld lengths, such as stitch welds, the initial plunge and dwell stages occupy a large part of the total process time. In this work temperature control was applied during these stages. This approach makes the plunge and dwell stages more robust by preventing local material overheating, which could lead to a tool meltdown. The TWT method was demonstrated to allow a good process control during plunging and continuous welding. The approach proposed for control offers weld quality consistency and improvement. Also, it allows a reduction of the time required for the development of optimal parameters, providing a fast adaptation to disturbances during welding and, by decreasing the plunge time, provides a significant decrease on the process time for short welds.
5
Guillo, Mario. "Commande en effort robuste et compensation de trajectoire en temps réel pour les robots industriels sous fortes charges : application au soudage par friction malaxage robotisé (RFSW)." Thesis, Rennes, INSA, 2014. http://www.theses.fr/2014ISAR0020/document.
Abstract:
Le soudage par friction malaxage (FSW) est un procédé de soudage innovant pour les matériaux à bas point de fusion (aluminium, cuivre…). Il a été breveté en 1992 par l’organisme anglais The Welding Institute (TWI). Depuis plusieurs années, celui-ci se développe dans l’industrie en cherchant à réduire son coût d’investissement. Le principe du FSW est de réaliser un cordon de soudure grâce à un outil animé d’un mouvement de rotation et d’avance. Les niveaux d’efforts et de précision requis contraignent à l’utilisation de machines cartésiennes de grande envergure. L’utilisation des robots industriels est un moyen de réduire les coûts, mais ils ne sont pas conçus pour ce genre d’applications et leur inconvénient majeur réside dans leur manque de rigidité. Ainsi, lorsque l’outil entre en contact avec les pièces à assembler, celui-ci peut dévier de plusieurs millimètres dans différentes directions de l’espace, rendant la mise en oeuvre d’une compensation de la trajectoire du robot obligatoire afin d’obtenir des soudures sans défauts. Le but de cette thèse a été de développer un procédé robotisé robuste. Le premier objectif est la mise en oeuvre d’une commande en effort robuste. En effet, en FSW, le maintien d’un effort axial constant est obligatoire. Le contrôle de cet effort permet de compenser la déviation axiale de l’outil et les défauts de mise en position des pièces à souder. Ainsi, une démarche d’identification et de modélisation afin de créer une commande en effort a été mise en oeuvre. La commande est définie de manière robuste afin d’éviter les réglages de l’asservissement lorsque les outils, les paramètres de soudage ou les trajectoires du robot changent. Une validation expérimentale complète a été réalisée dans le contexte du FSW. Le second objectif de cette thèse a été de développer une compensation de la déviation latérale de l’outil. Contrairement à l’objectif précédent, il n’y a pas d’effort à maintenir pour compenser cette déviation latérale. Dans l’industrie, cette déviation peut être compensée à l’aide d’un système de vision, mais ce dernier comporte de nombreux inconvénients en FSW (réflexion de l’aluminium, non visibilité du joint, coût, mise en oeuvre complexe). Ainsi, dans cette partie, un algorithme de compensation temps réel de la déviation latérale de l’outil a été mis en oeuvre. Celui-ci repose sur l’identification d’un modèle élasto-statique du robot. L’algorithme de compensation de la déviation latérale de l’outil a été couplé à la commande en effort et validé expérimentalement en FSW. La différence avec la majorité des travaux de recherche dans ce domaine est que les procédures d’identification n’utilisent pas de système de mesure 3D (photogrammétrie CCD ou laser de poursuite) dont le coût est un frein indéniable pour beaucoup d’industriels. La démarche est simple à mettre en oeuvre sur un robot industriel du marché actuel, et applicable pour d’autres procédés à contact comme l’usinage ou le polissageFriction Stir Welding (FSW) is an innovative welding process for materials with a low melting point (aluminium, copper…). It was patented in 1992 by the English organization The Welding Institute (TWI). For many years, an effort is done to reduce the investment cost for industrial applications. FSW process involves a rotating tool advancing along a path. Currently, gantry-type CNC systems are using for FSW manufacturing. These machines offer a high stiffness and can tolerate the forces during FSW in order to carry out a good weld quality. Industrials robots can reduce the investment cost; however they are not design for these applications. The main limitation is the low stiffness of the robot structure. Consequently, the robot deformation under the high process forces causes tool deviations about several millimeters. The robot path has to be compensated in order to obtain a good weld quality. The aim of this thesis is to develop a robust robotized process. The first goal is to realize a robust force control. During FSW, a constant axial forging force should be applied. Axial tool deviation is compensated with the force control approach. In this way, a modeling and identification method is done in order to design a force controller. The force controller is robust because no tuning is required, even if welding parameters or robot paths change. An experimental validation in FSW is done. The second goal is to realize a compensation of the lateral tool deviation. Unlike the axial deformation, there is no force to maintain for compensate this deviation. In industry, the lateral tool deviation could be compensated with a camera or laser sensor in order to track the weld seam path during welding. However, the cost of a seam tracking device, the aluminium reflexion and the lack of visibility in lap joint configuration are significant drawbacks. In this chapter, a compensation algorithm is designed. An elastostatic model of the robot is used to estimate in real time the deflection of the robot TCP. The compensation algorithm is coupled with the force controller defined previously. Compare with others research works about this topic, identification methods don’t need a 3D measurement system (CCD camera or laser tracker). The cost of such system is a main drawback for industrial applications. In this thesis, identification methods are easy to implement in an industrial robot and available for others processes like machining or polishing
6
Colegrove, Paul Andrew. "Modelling of friction stir welding." Thesis, University of Cambridge, 2004. https://www.repository.cam.ac.uk/handle/1810/240576.
Abstract:
This thesis investigates the modelling of friction stir welding (FSW). FSW is a relatively new welding process where a rotating non-consumable tool is used to join two materials through high temperature deformation. The aim of the thesis is the development of a numerical model to improve process understanding and to assist in the design of new tools. The early part of the thesis describes the process, defines the modelling problem and describes why a computational fluid dynamics package (FLUENT) was selected for the subsequent work. A systematic series of friction stir welding experiments in 7075 aluminium alloy, used to provide validation data for a numerical model of the process, are described in chapter 2. The trials examined how the welding conditions and tool type affected the weld temperature and heat input. From this data a thermal model of the welds was developed that included the convective heat flow due to material mixing. Chapters 3 to 6 describe the model development, from a preliminary model of a standard tool, to a detailed analysis of 2 dimensional profiles incorporating a novel slip boundary condition, and finally to a full 3 dimensional model of a new tool design, including material slip. The preliminary model with a standard tool assumed that the material stuck to the tool surface and included features such as the tool tilt, heat generation and heat flow. The model captured many of the real process characteristics, but gave poor predictions of the welding forces and heat generation. This identified the need for a more complex treatment of the tool-material interface that allowed material slip. The slip model was first implemented in a 2 dimensional study of flow around profiled tooling (chapter 4). This enabled a first order visualisation of the flow and the quantitative comparison of different 2 dimensional pin profiles. In chapter 5 an optimised 2 dimensional pin profile was determined by selecting the shape that minimised the traversing force. Two prototype tools based on this profile were manufactured: the plain 'Trivex™' and the threaded 'MX-Trivex™'. These were tested against a conventional 'MX-Triflute™' tool with the results showing that the traversing force was reduced by 18-25%. Chapter 6 describes 3 dimensional models of the 'Trivex™' and 'Triflute™' tools, which extended the slip model to 3 dimensions. The model correctly predicted that the Trivex™ tool had lower traversing and down forces than its Triflute™ counterpart, as observed experimentally. The thesis successfully demonstrates the application of fluid dynamics modelling to friction stir welding, enhancing visualisation of the flow, and guiding the development of new tooling.
7
Badarinarayan, Harsha. "Fundamentals of friction stir spot welding." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2009. http://scholarsmine.mst.edu/thesis/pdf/Badarinarayan_2009_09007dcc807d7f97.pdf.
Abstract:
Thesis (Ph. D.)--Missouri University of Science and Technology, 2009.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed July 16, 2010) Includes bibliographical references (p. 175-181).
8
Wang, Tianhao. "Friction Stir Welding of Dissimilar Metals." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1404577/.
Abstract:
Dissimilar metals joining have been used in many industry fields for various applications due to their technique and beneficial advantages, such as aluminum-steel and magnesium-steel joints for reducing automobile weight, aluminum-copper joint for reducing material cost in electrical components, steel-copper joints for usage in nuclear power plant, etc. The challenges in achieving dissimilar joints are as below. (1) Big difference in physical properties such as melting point and coefficient of thermal expansion led to residual stress and defects. (2) The miscibility issues resulted in either brittle intermetallic compound layer at the welded interface for miscible combinations (such as, aluminum-steel, aluminum-copper, aluminum-titanium, etc.) or no metallurgical bonding for immiscible combinations (such as magnesium-copper, steel-copper, etc.). For metallurgical miscible combinations, brittle intermetallic compounds formed at the welded interface created the crack initiation and propagation path during deformational tests. (3) Stress concentration appeared at the welded interface region during tensile testing due to mismatch in elastic properties of dissimilar materials. In this study, different combinations of dissimilar metals were joined with friction stir welding. Lap welding of 6022-T4 aluminum alloy/galvanized mild steel sheets and 6022-T4 aluminum alloy/DP600 steel sheets were achieved via friction stir scribe technology. The interlocking feature determining the fracture mode and join strength was optimized. Reaction layer (intermetallic compounds layer) between the dissimilar metals were investigated. Butt welding of 5083-H116 aluminum alloy/HSLA-65 steel, 2024-T4 aluminum alloy/316 stainless steel, AZ31/316 stainless steel, WE43/316 stainless steel and 110 copper/316 stainless steel were obtained by friction stir welding. The critical issues in dissimilar metals butt joining were summarized and analyzed in this study including IMC and stress concentration.
9
Reilly, Aidan. "Modelling of friction stir spot welding." Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/244946.
Abstract:
Friction stir spot welding (FSSW) is a solid-state welding process which is especially useful for joining precipitation-hardened aluminium alloys that undergo adverse property changes during fusion welding. It also has potential as an effective method for solid-state joining of dissimilar alloys. In FSSW, heat generation and plastic flow are strongly linked, and the scale of the process in time and space is such that it is difficult to separate and control the influence of all the relevant input parameters. The use of modelling is well-established in the field of welding research, and this thesis presents an analysis of the thermal and mechanical aspects of FSSW, principally using the finite element (FE) technique. Firstly, a thermal FE model is shown, which is subsequently validated by reference to experimental temperature data in both aluminium-to-aluminium and aluminium-to-steel welds. Correlations between high-quality welds and temperature fields are established, and predictions are made for peak temperatures reached under novel welding conditions. Deformation and heating are strongly linked in FSSW, but existing modelling tools are poorly suited to modelling flow processes in the conditions extant in FSSW. This thesis discusses the development and optimisation of two novel techniques to overcome the limitations of current approaches. The first of these uses greatly simplified constitutive behaviour to convert the problem into one defined purely by kinematics. In doing so, the boundary conditions reduce to a small number of assumptions about the contact conditions between weld material and tool, and the model calculation time is very rapid. This model is used to investigate changes in the slip condition at the tool to workpiece interface without an explicit statement of the friction law. Marker experiments are presented which use dissimilar composition but similar strength alloys to visualise flow patterns. The layering behaviour and surface patterns observed in the model agree well with observations from these experiments. The second approach extends the FE method to include deformation behaviour without the need for a fully-coupled approach, guided by the kinematic model. This is achieved using an innovative sequential small-strain analysis method in which thermal and deformation analyses alternate, with each running at a very different timescale. This technique avoids the requirement to either remesh the model domain at high strains or to use an explicit integration scheme, both of which impose penalties in calculation time and model complexity. The method is used to relate the purely thermal analysis developed in the work on thermal modelling to welding parameters such as tool speed. The model enables predictions of the spatial and temporal evolution of heat generation to be made directly from the constitutive behaviour of the alloy and the assumed velocity profile at the tool-workpiece interface. Predictions of the resulting temperature history are matched to experimental data and novel conditions are simulated, and these predictions correlate accurately with experimental results. Hence, the model is used to predict welding outcomes for situations for which no experimental data exists, and process charts are produced to describe optimum welding parameters. The methods and results presented in this thesis have significant implications for modelling friction stir spot welding, from optimising process conditions, to integration with microstructural models (to predict softening in the heat-affected zone, or the formation of intermetallics at the interface in dissimilar welds). The technique developed for sequential small strain finite element analysis could also be investigated for use in other kinematically constrained solid-state friction joining processes.
10
Merry, Joshua D. "Performance evaluation of discontinuous friction stir welding." Thesis, Wichita State University, 2011. http://hdl.handle.net/10057/5188.
Abstract:
Friction stir welding has been shown by previous investigators to have many advantages
over traditional metal joining practices. Friction stir lap welds and friction stir spot welds have
been shown to be stronger than rivets when joining materials of the same thickness.
Substructures containing continuous lap welded joints have demonstrated increased load carrying
capabilities over their riveted counterparts. In full-scale structures, however, continuous welds
are not always an option. Welds may be interrupted by fixturing limitations, tooling restrictions,
or stiffening members that cross the weld path. In these situations, a discontinuous lap weld
would be necessary. The principal problem with a discontinuous weld is that the tool plunge and
exit locations cannot be eliminated with a run-off tab, as in continuous welded structures. These
plunge and exit locations are then subjected to operational loads. In fatigue applications, it has
been demonstrated that cracks will initiate in the exit hole of a discontinuous weld. The purpose
of this study was to investigate techniques to terminate a lap weld without compromising the
structure by leaving an unprotected exit hole.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering.
11
Peel, Matthew J. "Friction-stir welding of dissimilar aluminium alloys." Thesis, University of Manchester, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.488339.
12
Zhou, Xingguo. "Friction stir welding simulation, optimization and design." Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25244.
Abstract:
Friction stir welding is an advanced welding technology mainly used to join aluminum alloys but with potential for other materials like steel, titanium and its alloys. The aim of this work is to provide a combination of numerical and experiment tools to understand the mechanisms of friction stir welding, optimizing the friction stir welds and characterizing the material properties for welds. The thesis is broadly divided into three themes. In the first theme, an automatic procedure to estimate friction stir welding model parameters, particularly those difficult to measure directly, is proposed and developed. The proposed methodology is seen to predict heat input power from the welding tool and contact conductivity between the workpiece and its supporting plate in good agreement with experimental temperature history data. In the second theme, discontinuous and distributed cooling methods, which use periodical and non-uniformly distributed cooling medium flow to cool the welding workpieces, are proposed to reduce the residual stress of friction stir welds and investigated using multi-physics numerical simulation to predict transient temperature field, residual stress and mechanical performance of welds. The discontinuous cooling method is found to be more effective than conventional active cooling, leading to a lower drop in induced welding temperature and reduced residual stress. The distributed cooling provides another method to balance residual stress and welding temperature for butt welding. The effect of discontinuous cooling on microstructure is evaluated using the multi-physics model. The third part presents small punch beam testing method to characterize material properties of base material, welded material and material property distribution. The small punch beam test utilizes miniaturized specimen and is therefore suited to measuring material properties in local regions of structure, such as the friction stir welding nugget.
13
Bagaitkar, Harish. "Design for manufacturing for friction stir welding." Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/Bagaitkar_09007dcc805a2c42.pdf.
Abstract:
Thesis (M.S.)--Missouri University of Science and Technology, 2008.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed December 2, 2008) Includes bibliographical references.
14
Liechty, Brian C. "Material Flow Behavior in Friction Stir Welding." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2403.pdf.
15
Russell, Michael Jonathan. "Development and modelling of friction stir welding." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621984.
16
Norton, Seth Jason. "Ferrous friction stir weld physical simulation." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1143252009.
17
Soron, Mikael. "Robot System for Flexible 3D Friction Stir Welding /." Örebro : Universitetsbiblioteket, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-1675.
18
Li, Hongjun. "Coupled thermo-mechanical modelling of friction stir welding." Thesis, University of Strathclyde, 2008. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=23481.
Abstract:
Friction Stir Welding (FSW) is a new welding technique for joining and processing metals. The object of this thesis is to develop the numerical models based on scientific knowledge and to provide a useful tool for predicting field variables and understanding the FSW process at a fundamental level. The thesis is focused on developing a continuum solid mechanics-based, fully coupled thermo-mechanical numerical model of FSW using the finite element method to simulate coupling between the welding tool movement, material deformation and movement, energy dissipation and heat transfer in the welding system. The model can simulate the whole welding process.
19
Minton, Timothy J. "Friction stir welding of commercially available superplastic aluminium." Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/4247.
Abstract:
A series of Friction Stir Welds (FSW) has been produced in order to optimise tool designs and weld/process variables to minimise flaws in the weld and obtain the best possible microstructure for superplastic Forming (SPF). Therefore the main goal is to produce friction stir welds which do not fail during subsequent SPF processes. The friction stir welds have been created using novel tools which are oversized for the material thickness used; this creates a wider weld region of fine equiaxed grains which are suitable for SPF. These original tools have been compared to tools which are already in mainstream FSW production. The welds created for this investigation also represent an evolution of friction stir welding by starting with a milling machine; a very basic piece of engineering workshop equipment. This was then replaced by a modified milling machine with force monitoring capabilities and finally using a state of the art dedicated FSW machine for the final welds. Room temperature properties are not usually a good indicator of high temperature response; however in this thesis the room temperature properties are closely linked to the FSW microstructure and have been used to assess the suitability of the weld structure for subsequent superplastic forming operations. The welds created for this thesis have been completed using hot and cold welding conditions, evaluated for room temperature properties and microstructural stability. The results have then been used to assess the welds and select the most suitable structure for cone testing, which is used to test the welds‘ performance during SPF. Friction stir welds were then recreated and cone tested which reveals the different levels of deformation occurring across the entire weld section and the unaffected parent material. Specimens in the as-welded, post-weld annealed and post-SPF have been analysed using standard microscopy techniques and Electron Back-Scattered Diffraction (EBSD). Welds in Aluminium Alloy (AA) 2004 with excellent room temperature properties have been created and shown to be capable of superplastic deformation achieving strain greater than 200%. Welds in AA5083, although producing excellent room temperature properties are unable to deform superplastically due to the difference in strengthening mechanisms employed by the different alloys. AA2004 contains Al3Zr which effectively pins the microstructure allowing grain boundary sliding to occur, AA5083 lacks this grain refinement element and so suffers from abnormal grain growth leading to early failure.
20
Thorn, Graeme John. "Mathematical and computational modelling of friction stir welding." Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426545.
21
Strand, Seth R. "Effects of Friction Stir Welding on Polymer Microstructure." Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd338.pdf.
22
Hovanski, Yuri. "Temporarily alloying titanium to facilitate friction stir welding." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Spring2009/y_hovanski_041709.pdf.
Abstract:
Thesis (M.S. in mechanical engineering)--Washington State University, May 2009.Title from PDF title page (viewed on Apr. 13, 2010). "Department of Mechanical Engineering." Includes bibliographical references (p. 35-38).
23
Stratton, Daryl A. "Characterizing the Frictional Interface in Friction Stir Welding." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1757.pdf.
24
Olsen, Eric. "Friction stir welding of high-strength automotive steel /." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1911.pdf.
25
Olsen, Eric Michael. "Friction Stir Welding of High-Strength Automotive Steel." BYU ScholarsArchive, 2007. https://scholarsarchive.byu.edu/etd/951.
Abstract:
The following thesis is a study on the ability to create acceptable welds in thin-plate, ultra-high-strength steels (UHSS) by way of friction stir welding (FSW). Steels are welded together to create tailor-welded blanks (TWB) for use in the automotive industry. Dual Phase (DP) 590, 780, and 980 steel as well as Transformation-Induced Plasticity (TRIP) 590 steel with thicknesses ranging from 1.2 mm to 1.8 mm were welded using friction stir welding under a variety of processing conditions, including experiments with dissimilar thicknesses. Samples were tested under tensile loads for initial determination if an acceptable weld had been created. Acceptable welds were created in both TRIP 590 and DP 590 at speeds up to 102 centimeters-per-minute. No acceptable welds were created in the DP 780 and DP 980 materials. A series of microhardness measurements were taken across weld samples to gain understanding as to the causes of failure. These data indicate that softening, caused by both excessive heat and insufficient heat can result in weld failure. Not enough heat causes the high concentration of martensite in these materials to temper while too much heat can cause excessive hardening in the weld, through the formation of even more martensite, which tends to promote failure mode during forming operations. Laser welding is one of the leading methods for creating tailor-welded blank. Therefore, laser welded samples of each material were tested and compared to Friction Stir Welded samples. Lower strength and elongation are measured in weld failure while the failure location itself determines the success of a weld. In short, an acceptable weld is one that breaks outside the weld nugget and Heat Affected Zone (HAZ) and where the tensile strength (both yield and ultimate) along with the elongation are comparable to the base material. In unacceptable welds, the sample broke in the weld nugget or HAZ while strength and elongations were well below those of the base material samples.
26
Ali, Khaled Yousif. "Friction Stir Welding Between Similar and Dissimilar Materials." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1513857047779233.
27
Marrero, Robert L. Jr. "Analysis of Variable Insensitive Friction Stir Welding Parameters." ScholarWorks@UNO, 2017. http://scholarworks.uno.edu/td/2385.
Abstract:
Friction Stir Welding (FSW) was used to perform a Design of Experiment (DOE) to determine the welding parameters effects on yielding consistent mechanical properties across the length of the weld. The travel speed was varied across set forge force and RPM conditions, to find a dataset that will yield consistent mechanical properties independent of the travel speed. Six different welds were completed on two different aluminum panels, the advancing side being Aluminum alloy 2195-T8 at a thickness of .350”, with the retreating side being Aluminum alloy 2219-T851 with a gauge thickness of .360”. A Left-hand Right-hand self-reacting pin tool was used for each weld. The mechanical properties of interest are the Ultimate Tensile Strength, Yield Strength, Elasticity and Hardness. The strengths were evaluated by tensile testing, with the Elasticity being measure post break. Specimens were then polished where macrograph and micrograph analysis was completed. Micro-hardness testing was then completed on the weld nuggets.
28
Pothier, Raymond Peter. "Closed-loop temperature control of friction stir welding." Thesis, Nelson Mandela Metropolitan University, 2015. http://hdl.handle.net/10948/10362.
Abstract:
This study develops and presents a friction stir weld (FSW) quality assurance tool based on control of weld zone temperature. Apart from correct tool geometry, tool tilt angle, traverse speed and forge force during welding, one important requirement is that the weld material be sufficiently plasticised (softened). The level of plasticisation is related to weld zone temperature which is primarily dependent on spindle speed, traverse speed and forge force. When all other conditions are correct, sufficiently plasticised material flows around and consolidates behind the tool without the production of voids in the weld. Typically, weld temperature varies along the weld length which may result in variations in weld quality. Weld zone temperature control makes constant weld zone temperature possible. In this study, thermocouple sensors were embedded in the FSW tool and a weld zone temperature control algorithm was developed. Spindle speed was the actuating mechanism for controlling weld temperature. The system was modelled and controllers were designed using Matlab tools. The system was simulated and the performance was compared to the system performance during welding. The control system ensures that the weld zone temperature can be maintained irrespective of the presence of thermal disturbances. Tensile testing was conducted which confirmed a range of temperature in which the welds resulted in consistent strength.
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Kandaswaamy, Sakthivael Payton Lewis Nathaniel. "Thermal field mapping technique for friction stir process." Auburn, Ala., 2009. http://hdl.handle.net/10415/1980.
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Ratanathavorn, Wallop. "Hybrid Joining of Aluminum to Thermoplastics with Friction Stir Welding." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-93144.
Abstract:
Hybrid structures including aluminum-thermoplastic and aluminum-reinforced thermoplastic composite are increasingly important in the near future innovations due to its lightweight and high strength-to-weight ratio. A critical point for metal-polymer application is that sound joining of these materials is difficult to achieve owing to a large difference in surface energy and dissimilar structure between metal and polymer. In practice, two major joining methods for hybrid structures are mechanical joining and adhesive bonding. However, there are some drawbacks of these conventional methods such as stress concentration, long curing time and low reliability joints. A new novel metal-polymer hybrid joining is required to overcome these issues as well as manufacturing and cost perspectives. To this end, this work aims to develop a general methodology to apply friction stir welding techniques to join a wide range of thermoplastics with and without fibers to aluminum alloy sheets. The present work proposed an experimental study to attain insight knowledge on the influences of welding parameters on the quality of hybrid joints in term of the maximum tensile shear strength. This includes the role of tool geometries, welding methodology as well as material weldability in the investigation. The results showed that friction stir welding is a promising technique for joining of thermoplastic to aluminum. Microstructural observation showed that a good mixing between aluminum and thermoplastic as well as defect-free weldments were obtained. Tool geometries and welding speed are two factors that significantly contribute to the quality of friction stir welded hybrid joints. The results also demonstrated that weld fracture modes are associated with material mixing as well as interfacial bonding between aluminum and thermoplastic. An evaluation of the joint strength was benchmarked with the relevant literatures on hybrid joining. The results of proposed technique showed that the maximum tensile shear strength of friction stir welded joints were the same order of magnitude as the joints welded by laser welding.
31
Owen, Charles Blake. "Two Dimensional Friction Stir Welding Model with Experimental Validation." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1200.pdf.
32
Källgren, Therese. "Friction stir welding of copper canisters for nuclear waste." Licentiate thesis, KTH, Materials Science and Engineering, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-318.
Abstract:
The Swedish model for final disposal of nuclear fuel waste is based on copper canisters as a corrosion barrier with an inner pressure holding insert of cast iron. One of the methods to seal the copper canister is to use the Friction Stir Welding (FSW), a method invented by The Welding Institute (TWI).
This work has been focused on characterisation of the FSW joints, and modelling of the process, both analytically and numerically. The first simulations were based on Rosenthal’s analytical medium plate model. The model is simple to use, but has limitations. Finite element models were developed, initially with a two-dimensional geometry. Due to the requirements of describing both the heat flow and the tool movement, three-dimensional models were developed. These models take into account heat transfer, material flow, and continuum mechanics. The geometries of the models are based on the simulation experiments carried out at TWI and at Swedish Nuclear Fuel Waste and Management Co (SKB). Temperature distribution, material flow and their effects on the thermal expansion were predicted for a full-scale canister and lid. The steady state solutions have been compared with temperature measurements, showing good agreement.
Microstructure and hardness profiles have been investigated by optical microscope, Scanning Electron Microscope (SEM), Electron Back Scatter Diffraction (EBSD) and Rockwell hardness measurements. EBSD visualisation has been used to determine the grain size distribution and the appearance of twins and misorientation within grains. The orientation maps show a fine uniform equiaxed grain structure. The root of the weld exhibits the smallest grains and many annealing twins. This may be due to deformation after recrystallisation. The appearance of the nugget and the grain size depends on the position of the weld. A large difference can be seen both in hardness and grain size between the start of the weld and when the steady state is reached.
33
Källgren, Therese. "Friction stir welding of copper canisters for nuclear waste /." Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-318.
34
Sued, Mohammad Kamil. "Fixed bobbin friction stir welding of marine grade aluminium." Thesis, University of Canterbury. Mechanical Engineering, 2015. http://hdl.handle.net/10092/10729.
Abstract:
PROBLEM - The bobbin friction stir welding (BFSW) process has potential benefits for welding thin sheet aluminium alloy. The main benefits of friction stir welding over conventional thermal welding processes are minimisation of energy usage, no need for consumables, potential for good weld quality without porosity, no fumes, minimal adverse environmental effects (green), minimal waste (lean), and reduced threats to personal health and safety. The BFSW process has further advantages over conventional friction stir welding (CFSW) in the reduction of welding forces, faster welding, and less fixturing. It is especially attractive to industries that join thin sheet material, e.g. boat-building. The industrial need for this project arose from the desire to apply the technology at a ship manufacturing company, INCAT located in Hobart, Tasmania, Australia. However there are peculiar difficulties with the specific grade of material used in this industry, namely thin sheet aluminium Al6082-T6. Early efforts with a portable friction stir welding machine identified the process to have low repeatability and reproducibility, i.e. process-instability. There are a large number of process variables and situational factors that affect weld quality, and many of these are covert. This is also the reason for divergent recommendations in the literature for process settings. PURPOSE - The main purpose of this research was to identify covert variables and better understand their potentially adverse effects on weld quality. Therefore, this thesis investigated the hidden variables and their interactions. Developing this knowledge is a necessity for making reliable and repeatable welds for industrial application. APPROACH - An explorative approach that focused on the functional perspective was taken. An extensive empirical testing programme was undertaken to identify the variables and their effects. In the process a force platform and BFSW tools were designed and built. A variety of machine platforms were used, namely portable friction stir welding, manual milling machine and computer numerical control (CNC) milling machine. The trials were grouped into 14 test plans. These are tool shoulder gap, spindle and travel speed, tool features, machines, tool fixation, machinery, welding direction, plate size (width and dimension), support insulation, tool materials, substrate properties and fixation. For the welded plates besides visual inspection of the weld, current, force, and temperature were measured. The Fourier transform was used to analyse the frequency response of machines. Also the welded samples were tested to the maritime standards of Det Norske Veritas (DNV). A number of relationships of causality were identified whereby certain variables affected weld quality. A model was developed to represent the proposed causality using the IDEF0 systems engineering method. FINDINGS - From these trials six main variables have been identified. These are tool features, spindle speed, travel speed, shoulder gap compression, machine variability, tool and substrate fixation. A rigid system is required for a consistent weld results. Under this condition, full pin features (threads and flats) need to be used to balance the adverse effects of individual features. It has been shown that fabricated bobbin tools with sharp edges can cause cuts and digging thus this feature should be avoided. Additionally, the substrate should have continuous interaction with the tool so the shoulder interference needs to be fixed and well-controlled. It is found that the compression generated by the shoulder towards the substrate helps material grabbing for better tool-substrate interaction. It is also shown that tool entry causes ejection of material and hence an enduring mass deficit, which manifests as a characteristic tunnel defect. The new explanation of the formation, origin and location of this defect has been explained. Material transportation mechanisms within the weld have been elucidated. It is also found that the role of the travel speed is not only to control heat generation but also for replacing the deficit material. Additionally, heat supplied to the weld depends not only on thickness, but also the width of the plate. Different types of machine cause an interaction in the material flow through their controller strategies. Jerking motion can occur at a slow travel speed, which also alters the way material is being transported. The Fourier transform (FFT) has been used to identify the characteristics of good and bad BFSW welds. This has the potential to be expanded for real-time process control. IMPLICATIONS - Tool deflection and positioning, material flow and availability are identified as affecting weld quality through stated mechanisms. The impact is even more severe when involving thin-plate aluminium. For the industry to successfully adopt this technology the process typically needs tight control of shoulder gap, tool strength and stiffness, feature fabrication, substrate and tool fixation. Additionally spindle and travel speed need to be adjusted not only based on the type of materials and thickness, but also the width, type of machine and method of tool entry. ORIGINALITY - New data are presented, which lead to new insights into the welding mechanics, production settings, material transportation and weld defects for BFSW on thin sheet material. The conventional idea that the welding tool has a semi-steady interaction with the substrate is not supported. Instead the interaction is highly dynamic, and this materially affects the weld-quality, especially in the difficult-to-weld material under examination. Factors such as shoulder gap, tool and substrate fixation compliance and machine types emerge as variables that need to be given attention in the selection of process parameters. The causal relationships have been represented in a conceptual model using an IDEF0 system approach. This study has made several original contributions to the body of knowledge. First is the identification of previously hidden variables that effect weld formation for the fixed gap BFSW process. The second contribution is a new way of understanding the material transportation mechanics within the weld. This includes the flow around the pin in the plane of the weld, the vertical transportation of material up the pin, the formation of turbulent-like knit lines at the advancing side, and the formation of tunnel defects. Also included here is a new understanding of how material deficit arises at tool entry and exit, and from flash/chips, and how this contributes to the tunnel weld defect. In addition, new understandings of the role of feed rate have been identified. Related to the material transportation, the work has also identified the importance of an interference fit between the substrate and tool. A third contribution is the identification of the dynamic interaction between tool and substrate. This identifies the important role rigidity plays. Associated with this is the identification of frequency characteristics of the motors under load. The fourth contribution is identification of the specific process settings for the difficult-to-weld material of AL6082-T6. The fifth contribution is the development of a novel method of fabricating bobbin friction stir welding tools as embodied in a patent application.
35
Hartman, Trent J. "Friction Stir Spot Welding of Ultra-High Strength Steel." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3302.
Abstract:
Friction stir spot welding (FSSW) is quickly becoming a method of interest for welding of high strength steel (HSS) and ultra high strength steel (UHSS). FSSW has been shown to produce high quality welds in these materials, without the drawbacks associated with fusion welding. Tool grade for polycrystalline cubic boron nitride (PCBN) tools has a significant impact on wear resistance, weld quality, and tool failure in FSSW of DP 980 steel sheet. More specifically, for a nominal composition of 90% CBN, the grain size has a significant impact on the wear resistance of the tool. A-type tools performed the best, of the three grades that were tested in this work, because the grain size of this grade was the finest, measuring from 3-6 microns. The effect of fine grain size was less adhesion of DP 980 on the tool surface over time, less abrasive wear, and better lap shear fracture loads of the welds that were produced, compared to the other grades. This is explained by less exposure of the binder phase to wear by both adhesion and abrasion during welding of DP 980. A-type tools were the most consistent in both the number of welds per tool, and the number of welds that reached acceptable lap shear fracture loads. B-type tools, with a bimodal grain size distribution (grain size of 4 – 40 microns) did a little bit better than C-type tools (grain size of 12-15 microns) in terms of wear, but neither of them were able to achieve consistent acceptable lap shear fracture load values after the first 200 welds. In fact only one out of five C-type tools was able to produce acceptable lap shear fracture loads after the first 100 welds.
36
Martinez, Nelson Y. "Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc862775/.
Abstract:
The Al-Zn-Mg-Cu (7XXX series) alloys are amongst the strongest aluminum available. However, they are considered unweldable with conventional fusion techniques due to the negative effects that arise with conventional welding, including hydrogen porosity, hot cracking, and stress corrosion cracking. For this reason, friction stir welding has emerged as the preferred technique to weld 7XXX series alloys. Aluminum 7449 is one of the highest strength 7XXX series aluminum alloy. This is due to its higher zinc content, which leads to a higher volume fraction of eta' precipitates. It is typically used in a slight overaged condition since it exhibits better corrosion resistance. In this work, the welds of friction stir welded aluminum 7449 were studied extensively. Specific focus was placed in the heat affected zone (HAZ) and nugget. Thermocouples were used in the heat affected zone for three different depths to obtain thermal profiles as well as cooling/heating profiles. Vicker microhardness testing, transmission electron microscope (TEM), and differential scanning calorimeter (DSC) were used to characterize the welds. Two different tempers of the alloy were used, a low overaged temper and a high overaged temper. A thorough comparison of the two different tempers was done. It was found that highly overaged aluminum 7449 tempers show better properties for friction stir welding. A heat gradient along with a high conducting plate (Cu) used at the bottom of the run, resulted in welds with two separate microstructures in the nugget. Due to the microstructure at the bottom of the nugget, higher strength than the base metal is observed. Furthermore, the effects of natural aging and artificial aging were studied to understand re-precipitation. Large improvements in strength are observed after natural aging throughout the welds, including improvements in the HAZ.
37
Reese, Gregory A. "Dissimilar Friction Stir Welding Between Magnesium and Aluminum Alloys." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc955097/.
Abstract:
Joining two dissimilar metals, specifically Mg and Al alloys, using conventional welding techniques is extraordinarily challenging. Even when these alloys are able to be joined, the weld is littered with defects such as cracks, cavities, and wormholes. The focus of this project was to use friction stir welding to create a defect-free joint between Al 2139 and Mg WE43. The stir tool used in this project, made of H13 tool steel, is of fixed design. The design included an 11 mm scrolled and concave shoulder in addition to a 6 mm length pin comprised of two tapering, threaded re-entrant flutes that promoted and amplified material flow. Upon completion of this project an improved experimental setup process was created as well as successful welds between the two alloys. These successful joints, albeit containing defects, lead to the conclusion that the tool used in project was ill fit to join the Al and Mg alloy plates. This was primarily due to its conical shaped pin instead of the more traditional cylindrical shaped pins. As a result of this aggressive pin design, there was a lack of heat generation towards the bottom of the pin even at higher (800-1000 rpm) rotation speeds. This lack of heat generation prohibited the material from reaching plastic deformation thus preventing the needed material flow to form the defect free joint.
38
Pehkonen, Henri. "Design of Gas Shield for Friction Stir Welding Machine." Thesis, Linköpings universitet, Maskinkonstruktion, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-126605.
Abstract:
The research and development of the final disposal of the nuclear waste produced by the nuclear power plants is an important work done by The Swedish Nuclear Fuel & Waste Management Co. (SKB). As the demands on a final disposal increase the laboratory equipment has to be better in order to do valid experiments. Research on how the copper canister for the spent fuel will be manufactured and handled is done at the Canister laboratory in Oskarshamn, Sweden. The work presented in this report was to design a new gas shield for the friction stir welding machine at the laboratory. The welding machine seals the canisters containing the spent fuel which are then transported to the final disposal 500 meter down in basement rock. To minimize the amount of oxide particles in the weld zone SKB have to design a better gas shield that should deliver the required atmosphere around the welding area. The work contains a pre study phase where the important things to consider when designing are collected. Then ideas are generated and concepts created for a new gas shield. These concepts are evaluated by a pair wise comparison method in order to find the most promising concept. The concept chosen is then detail designed to come as close to a manufacturable design as possible.Utvecklingen av ett slutförvar för det urbrända kärnbränslet som blir avfallsprodukten vid framställning av energi via kärnkraft är ett viktigt arbete som drivs av Svensk Kärnbränslehantering AB. Då kraven och bevisningen på huruvida ett slutförvar ska utföras på ett säkert sätt måste experimenten och försöksutrustningen bli bättre för att generera tillförlitliga resultat. Forskning om hur kopparkapseln för det urbrända kärnbränslet ska konstrueras och hanteras pågår vid Kapsellaboratoriet i Oskarshamn. Arbetet som presenteras i denna rapport tar upp konstruktionen av ett nytt gasskydd till friktionsomrörningssvetsningsmaskinen på Kapsellaboratoriet. Svetsmaskinen försluter kapslarna med radioaktivt avfall vilka sedan transporteras 500 meter ner i det svenska urberget. För att minska mängden oxidpariklar kring svetsområdet måste SKB tillverka ett nytt gasskydd vilket bör uppfylla de krav på atmosfären kring svetsområdet som finns. Arbetet består av en forsknings- och informationssamlingsfas där viktiga aspekter och problemområden hittas. Sedan genereras idéer och nya koncept på gasskydd fås fram. Koncepten utvärderas parvis med metoden ”pair wise comparison” för att hitta det mest lovande konceptet. Konceptet detaljkonstrueras och tillslut fås en design vilken är så nära tillverkningsbar som möjligt.
39
Hunt, Johnathon Bryce. "Defect Detection in Friction Stir Welding by Measureable Signals." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8676.
Abstract:
Friction stir welding (FSW) is an advantageous solid-state joining process, suitable for many materials in the energy, aerospace, naval and automotive industries. Like all other welding processes, friction stir welding requires non-destructive evaluation (NDE). The time and resources to preform NDE is expensive. To reduce these costs, nontraditional NDE methods are being developed for FSW. Spectral based defect recognition uses the forces during the welding process to validate weld quality. Although spectral NDE methods have shown promise as an alternative NDE processes, many research welding speeds do not correspond to manufacturing speeds, nor do they explain the relationship between the spectral data and the process. The purpose of this work is to explore the possibility of acquiring additional information about the defect. Namely the defect’s type, location, and magnitude. In this study, welds with “wormhole” defects were produced at 2000, 2500 and 3000 mmpm in 5754 aluminum. The welding process forces and torque were measured and analyzed spectrally. The welded plates were then imaged with x-ray photography, a validated NDE method. It was found that low frequencies (0 – 4 Hz) in the y & z force signals correlate with defect presence in high speed FSW. In addition, the strong correlation between the spectral data and the presence of a defect allowed for defect magnitude predictions. Linear fits were applied to the defect measurements and the spectral data. Large error inhibits the wide use of this prediction method.
40
Blignault, Calvin. "Design, development and analysis of the friction stir welding process." Thesis, Port Elizabeth Technikon, 2002. http://hdl.handle.net/10948/1350.
Abstract:
The development of a CNC-based technology FSW machine to accurately produce friction stir weld samples that can be analyzed for research purposes is implemented and discussed. A process diagnosis and control scheme to improve the process monitoring and weld evaluation capabilities of an FSW machine are proposed and implemented. Basic CNC-based hardware implementation such as optical encoders and inverters for process control are explained and verified. The control scheme and framework of interfaces to the digital I/O cards for PC user interface are explained. An advanced monitoring system which senses process performance parameters such as tool temperature, 3-axis tool forces, torque and spindle speed are explained. Mechanical designs and manufacturing techniques such as tool, clamp and backing plate designs are explained and verified. The process parameters for quality optimization are investigated and optimized by making use of Correlation and Regression Analysis. The statistical data and analytical relationships between welding parameters (independent) and each of the performance parameters (dependent) are obtained and used to simulate the machining process. The weld research samples are tested for strength and integrity making use of various scientific testing techniques. The reliability of the samples are also evaluated and compared to that of other institutions. Process variables and the optimum operating range of the Friction Stir Welding machine is determined and a framework for further research into weld quality optimization is set.
41
Tipaji, Pradeep Kumar. "E-design tools for friction stir welding: cost estimation tool." Diss., Rolla, Mo. : University of Missouri-Rolla, 2007. http://scholarsmine.mst.edu/thesis/pdf/Tipaji_09007dcc8043f642.pdf.
Abstract:
Thesis (M.S.)--University of Missouri--Rolla, 2007.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed February 5, 2008) Includes bibliographical references (p. 29-31).
42
Stephen, Michael George. "Development and analysis of a friction stir spot welding process for aluminium." Thesis, Nelson Mandela Metropolitan University, 2005. http://hdl.handle.net/10948/1351.
Abstract:
Friction Stir Spot Welding (FSSW) has been developed from the conventional Friction Stir Welding (FSW) process, developed at The Welding Institute (TWI). FSSWs have been done without the keyhole being eliminated. Elimination of the keyhole would result in the process being more commercially viable. This dissertation focuses on an attempt of eliminating the keyhole using a retractable pin tool as well as a comparison of the weld integrity of a FSSW to that of a conventional Resistance Spot Weld (RSW). Welds were conducted on aluminium alloy 6063 T4. Comparisons between different weld procedures were done. Further analysis of the weld integrity between FSSW and RSW were conducted, comparing tensile strengths, microstructure and hardness. For the above welding procedure to take place, the current retractable pin tool, patented by PE Technikon, was redesigned. Problems associated during the welding process and the results obtained are documented. Reasons for the keyhole not being eliminated as well as recommendations for future work in the attempt to remove the keyhole are discussed.
43
Oyedemi, Kayode. "Increasing the gap tolerance in friction stir welded joints of AA6082-T6." Thesis, Nelson Mandela Metropolitan University, 2012. http://hdl.handle.net/10948/d1012325.
Abstract:
This research project was conducted to increase weld gap tolerance in Friction Stir Welding (FSW) of 8 mm thick aluminum alloy 6082 – T6. Investigation was done on I-STIR PDS platform and a Johnford milling machine. The research project involved tool-pin design with varying re-entrant features and varying parameters as a method of weld gap closing to produce successful welds. Direction of spindle rotation and dwell time were established as part of a preliminary study. Clockwise spindle rotation with 20 seconds dwell time allows sufficient plasticity and improved material flow which assisted in achieving welds with prior 30 percent weld gap of the plate thickness. Final welds were made using three rotational speeds and feed rates with sufficient plunging to prevent root defects. Analysis of the results were detailed which include vickers microhardness test, tensile test and metallographic observation to access the suitability of the weld structure. From the set of tool-pins designed, the flare tool-pin gave a well-defined weld nugget with improved stirring at the weld root. Also, with a concave shoulder, right hand threaded tool-pin and counterclockwise flutes undergoing a clockwise spindle rotation, plasticized material flow was upward which was beneficial in reducing the amount of plate thinning. The right hand thread counter clockwise flute with a flute machined in the foot exhibited superior tensile strength for welds containing 30 percent weld gap.
44
Altenkirch, Jens. "Stress engineering of friction stir welding : measurement and control of welding residual stresses." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505389.
Abstract:
Friction stir welding (FSW) is a maturing welding technique using a rotating tool for simultaneous heating and stir deforming th~ material interface to form a solid bond. Significant tensile residual stresses (RS) and component distortion may be produced even with optimized FSW parameters. Recent stress engineering techniques such as global mechanical or roller tensioning may reduce tensile RS and distortion. This dissertation reports on the first systematic investigation into the efficiency of insitu global mechanical tensioning (IS GMT) as well as roller tensioning applied in-situ (ISRT) and post welding (PWRT) for mitigation of tensile RS and plate distortion in high strength aluminium alloy plates joined by FSW. The techniques were evaluated by measuring the distribution of RS across the weld-line by means of neutron and synchrotron X-ray diffraction as well as' the levels of plate distortion. In each case the weld microstructure and hardness distribution were characterised. The data were rationalised against the ISGMT load and roller tensioning down force respectively. The results have shown that ISGMT and PWRT significantly mitigate longitudinal tensile RS and component distortion. ISGMT was found to decrease the tensile RS by an amount approximately equal to that of the load applied. Consequently, a stress free weld is produced with an ISGMT load equal to the magnitude of the weld-line RS in the as-welded condition~ PWRT decreases the tensile RS as the rolling down force increases and significant compression may be introduced once a certain magnitude is exceeded. ISRT, at least for the range tested, was found to be less effective. The component distortion reduced along with RSÇ'ú mitigation. No effects on the microstructure or hardness distribution due to mechanical stress engineering were observed. Furthermore, it was demonstrated that in order to make accurate stress measurements by diffraction, the effect of precipitation on the stress free lattice spacing must be taken into account for age hardening alloys. In order to complete this study an automated robotic sample manipulation system was developed. Finally, the degree of stress relaxation occurring on cutting down large welds was evaluated by progressively shortening test welds and determining the RS for each length. The amount of stress relaxation for each weld follows the same behaviour and appears to depend on the width of the tensile weld zone only.
45
Coelho, Rodrigo Santiago. "Joining of light-weight materials by friction stir welding and laser beam welding." Berlin Bochum Dülmen London Paris Europ. Univ.-Verl, 2008. http://d-nb.info/994359489/04.
46
Kruger, Grant. "Intelligent monitoring and control system for a friction stir welding process." Thesis, Port Elizabeth Technikon, 2003. http://hdl.handle.net/10948/273.
Abstract:
A Friction Stir Welding machine is proposed and built to allow future research into the process and to provide a framework from which the application of intelligent manufacturing to industrial processes can be investigated. Initially a literature survey was conducted upon which the design of the machine could be based. The conversion of a conventional milling machine into a Friction Stir Welding machine by applying modern monitoring and control systems is then presented. Complete digital control was used to drive actuators and monitor sensors. A wireless chuck mounted monitoring system was implemented, enabling forces, torques, temperature and speed of the tool to be obtained directly from the process. Software based on a hierarchical Open Systems Architectural design, incorporating modularity, interoperability, portability and extensibility is implemented. This experimental setup is used to analyze the Friction Stir Welding process by performing data analysis using statistical methods. Three independent variables (weld speed, spindle speed and plunge depth) were varied and the independent variables (forces, torques, power, temperature, speed, etc) recorded using the implemented software. The statistical analysis includes the analysis of variants, regression analysis and the creation of surface plots. Using these results, certain linguistic rules for process control are proposed. An intelligent controller is designed and discussed, using the derived rules to improve and optimize certain aspects of the process encountered during the experimental phase of the research.
47
Freeney, Timothy Alan. "Friction stir processing of cast magnesium alloys." Diss., Rolla, Mo. : University of Missouri-Rolla, 2007. http://scholarsmine.mst.edu/thesis/pdf/Freeney_09007dcc804a9022_3_09007dcc8055e79b.pdf.
Abstract:
Thesis (M.S.)--University of Missouri--Rolla, 2007.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed June 17, 2008) Includes bibliographical references.
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Sidhar, Harpreet. "Friction Stir Welding of High Strength Precipitation Strengthened Aluminum Alloys." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc862787/.
Abstract:
Rising demand for improved fuel economy and structural efficiency are the key factors for use of aluminum alloys for light weighting in aerospace industries. Precipitation strengthened 2XXX and 7XXX aluminum alloys are the key aluminum alloys used extensively in aerospace industry. Welding and joining is the critical step in manufacturing of integrated structures. Joining of precipitation strengthened aluminum alloys using conventional fusion welding techniques is difficult and rather undesirable in as it produces dendritic microstructure and porosities which can undermine the structural integrity of weldments. Friction stir welding, invented in 1991, is a solid state joining technique inherently benefitted to reduces the possibility of common defects associated with fusion based welding techniques.
Weldability of various 2XXX and 7XXX aluminum alloys via friction stir welding was investigated. Microstructural and mechanical property evolution during welding and after post weld heat treatment was studied using experimental techniques such as transmission electron microscopy, differential scanning calorimetry, hardness testing, and tensile testing. Various factors such as peak welding temperature, cooling rate, external cooling methods (thermal management) which affects the strength of the weldment were studied. Post weld heat treatment of AL-Mg-Li alloy produced joint as strong as the parent material. Modified post weld heat treatment in case of welding of Al-Zn-Mg alloy also resulted in near 100% joint efficiency whereas the maximum weld strength achieved in case of welds of Al-Cu-Li alloys was around 80-85% of parent material strength. Low dislocation density and high nucleation barrier for the precipitates was observed to be responsible for relatively low strength recovery in Al-Cu-Li alloys as compared to Al-Mg-Li and Al-Zn-Mg alloys.
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Bhojwani, Shekhar. "Smoothed particle hydrodynamics modeling of the friction stir welding process." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2007. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Overfield, Norman E. "Feasibility of underwater friction stir welding of hardenable alloy steel." Thesis, Monterey, California. Naval Postgraduate School, 2010. http://hdl.handle.net/10945/5092.
Abstract:
Approved for public release; distribution is unlimitedThe objective of this thesis is to determine whether friction stir welding (FSW) is a feasible welding process for steels in an underwater environment. Specific benefits would be underwater weld repairs on steel alloy piping systems and/or structures, and crack repairs on control surfaces of submarines without the need for strict environment controls or in the submarine's case, for drydocking. A single tool made of polycrystaline cubic boron nitride (PCBN) with a Tungsten-Rhenium binder was used to conduct a series of bead-on-plate FSW traverses, approximately 64 inches (1.6 m) in total length, on 0.25 inch (6.4 mm) thick plates of a hardenable alloy steel. The first series of traverses involved various revolutions per minute (RPM) and inches per minute (IPM) combinations on a dry plate. A second series was conducted while a plate was immersed in water in order to assess the potential for inducing hydrogen assisted cracking (HAC) during FSW of susceptible alloys. All traverses were visually defect-free. The FSW nuggets (stir zone) exhibited refined microstructures and increased hardness relative to the base plate. Based on preliminary findings, FSW of hardenable alloy steel is a feasible process and should be further researched and refined.