Rozprawy doktorskie na temat „Welding-Techniques”

Prediction of residual stresses and distortion induced by welding is relevant to many industries involved with the manufacture and assembly of thin plate structures. The ability to predict these unwanted effects on such structures subjected to welding processes is important to minimise costs associated with rework and other corrective actions. The main challenge is to model the complex and at times indeterminate nature of the welding process, preferably in a simple and transparent manner. The present work dealt with the development, validation and application of advanced simulation techniques for the prediction of welding induced residual stresses and distortions. Current literature presents a wide-ranging number of approaches, which vary in complexity and purpose, but at times fail to present a clear methodology for numerical based analysis. In the current work a commercial finite element software package was used to develop thermo-elasto-plastic models suited for this application. The proposed methodology was developed by initially analysing simple set-ups, validated through the use of experimental measurement techniques for both residual stresses and distortions predictions. This provided confidence in the application of the numerical models, which were then used to investigate more complex cases of particular interest to the shipbuilding industry. This part of the project dealt with ancillary operations, namely the initial application of tack welds and restraints on the structure, for which little attention is usually given due to their apparent insignificance compared to the final welding process. Their effects are in fact substantial and were investigated by using the thermo-elasto-plastic models together with experimental trials. A better understanding of their influence was hence illustrated, providing a basis for the establishment of a best industrial practice.

Le soudage par friction et malaxage (SFM) est un procédé d'assemblage innovant à l'état solide qui a été inventé en 1993 et qui présente des avantages significatifs par rapport aux techniques de soudage par fusion. En raison des grandes forces appliquées sur l'outil et la nécessité de maintenir un angle constant sur tout le chemin de soudage (angle d'inclinaison), ce processus est normalement effectué sur des machines coûteuses conçues spécifiquement à cette fin. La présente thèse est une tentative de faciliter l'application de soudage par friction malaxage sur les centres d'usinage CNC très communément rencontré en industrie. Une variante peu connue et peu développée de ce processus, à savoir le soudage par friction et malaxage à angle droit dans lequel l'axe d'outil est toujours perpendiculaire à la surface de la pièce a été étudié de près dans cette thèse. Des outils spéciaux pour le soudage par friction et malaxage qui sont appropriées pour cette nouvelle orientation ont été développés et les paramètres de fonctionnement de ces outils ont été mis en place. En outre, des techniques ont été investiguées pour réduire la force axiale par optimisation de la conception de l'outil et des paramètres de soudage. De plus, l'une des principales difficultés qui pourraient survenir durant les applications industrielles du soudage par friction et malaxage est l’alignement horizontal et vertical des pièces pour le soudage de joints aboutés. Une méthodologie est aussi proposée pour effectuer le soudage par friction et malaxage sur des contours 3D. La Méthode Taguchi a été utilisée pour la conception d'expériences et des modèles de réseaux neuronaux artificiels ont été formés pour l'analyse des résultats des expériences et pour l’optimisation. Il a été démontré que le soudage par friction et malaxage à angle droit a la capacité de faire des soudures saines avec limites ultimes acceptables en utilisant des valeurs plus basses de force axiale d’environ 50% par rapport au soudage par friction et malaxage typique. En outre, les plages utilisables des paramètres de conception de l'outil et des paramètres de fonctionnement ont été trouvées. Elles conduisent à la réduction de la force axiale du soudage par friction et malaxage à angle droit. Les erreurs de placement de pièces dans des joints aboutés ont aussi été investiguées conduisant à une définition des plages acceptables d’erreur avec la méthode de soudage à angle droit. Les techniques développées ont aussi été validées dans la mise en œuvre du soudage par friction et malaxage pour les joints 2D et 3D. De plus, la méthodologie proposée pour le soudage sur contours 3D a été validée avec succès en soudage sur une pièce particulière en utilisant une machine CNC à 5 axes dans les deux configurations de joints aboutés et superposés.
Friction stir welding (FSW) is an innovative solid state joining method invented at the end of twentieth century and having significant advantages over fusion welding techniques. Due to the high amount of forces applied on the FSW tool and the need to keep a constant angle all over the welding path (tilt angle), this process in normally performed on costly machines designed specifically for it. The present thesis is an attempt to facilitate the implementation of friction stir welding on common CNC machining centers. A less considered variant of this process, namely right angle FSW in which the tool axis is always perpendicular to the surface of workpiece has been closely studied and investigated. Special FSW tools which are appropriate for this new orientation have been developed and operating parameters for these tools have been established. In addition, techniques were developed to reduce the axial force through optimization of tool design and welding parameters. Moreover, one of the major difficulties which could be encountered during industrial applications of FSW, joint fit-up issues have been explored and attempts were made to manage these issues. A methodology has been proposed for FSW over 3D contours. Taguchi method has been used for design of experiments and artificial neural network models have been trained for analysis of results of experiments and optimization. It has been shown that the right angle FSW have the capacity of making sound welds with acceptable UTS employing lower values of axial force in comparison to typical FSW. Furthermore, workable ranges of tool design and welding parameters were found that leads to reduction of axial force within right angle FSW. To tolerate for joint fit-up issues, regions of operating parameters were established that could manage typical values of gap and mismatch. The developed techniques have also been validated and implemented for joining on 2D and 3D paths. In addition, the 3D methodology has been successfully validated in welding a complex part using a 5 axis CNC machine in both butt and lap configurations.

When available, the force feedback data from Friction stir welding (FSW) can be very useful for analyzing weld quality. Friction Stir Welding Analysis Tool software (FSWAT), a new process based non-destructive evaluation (NDE) technique developed at the South Dakota School of Mines and Technology, is designed to analyze any specified section of FSW in real time (with a slight computational delay). With this software, a trained operator or inspector can detect where potential flaws may exist. Another powerful NDE technique is ultrasonic phased array (UPA), which is well known for its capability to detect different kinds of friction stir welding indications and defects. The purpose of this study is to compare the defects identified in a round robin investigation using UPA and electromagnetic radiation X-ray inspection with the defects identified by the FSWAT software data analysis program. In addition, actual destructive tests are used to correlate the identified defects with actual defects. A probability of detection (POD) analysis is carried out to evaluate the wormhole-detection performance of the different NDE methods applied currently in industry. By correlating this software with UPA and X-ray inspection, the time and expense associated with 100% inspection of parts could be considerably reduced. The ultimate goal of this research is to support the development of real-time quality control to minimize the cost of inspection.
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering.

This thesis describes the advancements of the application of thermal tensioning techniques to different weld geometries in order to eliminate buckling distortion. The main goal of this work is to better understand these techniques through experimental and numerical investigation and increase their technological maturity to aid industrial implementation. The thermal tensioning techniques investigated in this work are Thermal Tensioning by Cooling and Thermal Tensioning by Heating. The investigation for both techniques encompasses thermal source characterisation, application to different weld geometries and residual stress measurements and analysis of both butt and fillet welded samples. A detailed technology transfer study of Thermal Tensioning by Cooling was carried out in which different aspects of the application of TTC to arc welding (Gas Metal Arc Welding and Gas Tungsten Arc Welding) was examined. This study focused on the influence of both the liquid CO2 delivery system installation and welding tooling and jigging on the effectiveness of Thermal Tensioning by Cooling in reducing buckling distortion. Experimental and numerical cooling source characterisation was also carried out in the Thermal Tensioning by Cooling work to investigate the characteristics of the cooling source under different cooling conditions. The Thermal Tensioning by Cooling work was then concluded with welding trials and residual stress measurement and analysis. The results of the Thermal Tensioning by Cooling study show that the installation of the liquid CO2 delivery system as well as the welding tooling and jigging has a major influence on the effectiveness of Thermal Tensioning by Cooling in reducing buckling distortion. The cooling source characterisation work reveals that the most important parameter of the cryogenic nozzle delivery system used in this work is the Air Entrainment Gap. A description of a control system of Thermal Tensioning by Cooling is suggested based on controlling the Air Entrainment Gap. The residual stress analysis shows a reduction in the Applied Weld Load and minor changes in the tensile peak of the residual stress distribution of both butt and fillet welded panels. The Thermal Tensioning by Heating investigation includes heat source characterisation, application of Thermal Tensioning by Heating on butt and fillet welds, utilisation of alternative heat sources and residual stress analysis. The results of these investigation show that Thermal Tensioning by Heating is also highly effective in eliminating buckling distortion in butt, fillet and overlapped panels. The applied heating temperature in this work is typically in the range of 160-250 °C but not greater than 330 °C. The residual stress measurements reveal that the additional heating of Thermal Tensioning by Heating generates a positive stress gradient at the location of heating.

With the widespread use of zinc coated steels in the manufacture of high volume spot welded assemblies, such as the automotive body-in-white, there is a need to address the inherent difficulties in welding this particular product. The presence of the zinc coating increases the rate of degradation of the welding electrodes, and so there is a need for frequent electrode maintenance to combat the deterioration in weld quality associated with electrode wear. This results in short production runs and reduced productivity. Pre-programmed current stepping of the welding current may be used to compensate for the reduction in weld size with electrode wear, and so extend electrode life. However, this open-loop technique is difficult to optimise, particularly when welding zinc coated steel. In order to develop a feedback control system for current stepping, it is necessary to relate the weld diameter to some measurable parameter, in order to perform continuous monitoring of the weld quality. In view of the difficulty of deriving a suitable mathematical description of the physical process, on which to base a control algorithm, alternative techniques for spot weld quality monitoring and control have been examined. A neural network based model of the spot welding process has been produced, to predict weld quality from the measured electrical data. Guidelines have been developed for selecting the ideal network parameters for maximising the prediction performance over the life of the welding electrodes. In order to overcome the difficulties observed in optimising the pre-programmed current stepping control system, the feasibility of using a rule based fuzzy logic controller has been assessed. Rules were defined for determining the required step change in welding current to maintain weld quality, given the diameter of the previous weld and the estimated electrode tip diameter.

The image segmentation algorithm is the most challenging step and requires more computer processing power than the boundary filtering, and the Cullen et al's method, which used the Cullen et al's method to determine the electrodes tip width automatically in the automotive industry in real time. Spot welding is used extensively in the automotive industry. The quality of an individual spot weld is a major concern due to the heavy reliance on their use in the manufacture of motor vehicles. The main parameters that control the quality of a spot weld are current, voltage, welding force, welding time, and the quality of welding electrodes. The condition of the welding electrodes plays a major part in determining the quality of a spot weld. For example, excessive electrode wear can occur during the welding process and can cause weakening in the weld nuggets. As the number of welds increases, the electrode tip wears down and so the contact area between electrode tip and work piece increases. In order to determine the quality of the welding electrodes, a machine vision approach is employed, where images of the electrode tips in real time are captured and are processed using various image-processing algorithms. These algorithms can be used to automatically measure the electrode tip width and hence assess the quality of the electrodes tip in real time. The quality of two types of spot welding electrode tips, namely flat-shaped and dome-shaped tips, is assessed here using image processing techniques. For each tip type, a database of 250 images is used to test the performance of the tested algorithms. Also the tip width in these 250 images is determined manually by counting the number of pixels using an image editor such as Microsoft Paint. An excellent agreement is found between these manual and automatic methods. The tip width for an electrode is measured by first grabbing an image showing the electrode. The electrode in the image is then extracted using an image segmentation algorithm. Then the boundary of the electrode is determined and filtered. The Cullen et aI's method is subsequently applied, which uses the filtered boundary to determine the tip width. A number of image segmentation and boundary filtering algorithms have been used to determine the tip width automatically. For flat tip electrode, the combination of the region growing image segmentation, Minimum Perimeter Polygon, and Cull en et al's techniques was capable of automatically determining the tip width for 250 images with a root mean square error of 7.5 % of the tip width. For dome-shaped electrodes, the combination of the Snake segmentation algorithm, Fourier transform, and the Cullen et al's method was capable of automatically determining the tip width for 250 images with a root mean square error of2.9 % of the tip width. The author has proposed and built an active illumination system that captures a backlit image of the electrode's shadow, this system has different camera with same time then above. The image is then processed using a simple image segmentation method, such as the Canny filtering algorithm to locate the boundary of the electrodes tip. Then the boundary is processed using Minimum-Perimeter Polygon approach and Cull en et aI's method to automatically determine the tip width for 200 experiments images. The proposed system is capable of determining the tip width automatically with a root mean square error of 3.2% of the total tip width for flat tips and 3% for dome tips.

The main aims of this study are to generate a methodology for the optimisation of welding procedures for plasma welding of thin sheet aluminium alloys and to investigate weld quality modelling. Emphasis is focused on the recognition and evaluation of the consecutive stages of welding procedure development and on the formulation of a generalised procedural methodology that is potentially applicable to other processes and materials. The materials under investigation were 1.6 mm thick sheet 6013, 2024 and 7475 alloys, representing the major medium and high strength heat treatable aluminium groups used in the aerospace industry. Initial experimentation generated procedures relating to specimen and equipment pre-weld preparation. Bead on plate and square butt joint trials were performed in the downhand position. The plasma keyhole mode was operated autogenously while filler wire addition was employed for the melt-in mode. Arc monitoring techniques were used to log the arc voltage and welding current values. The effect of background and control parameters on process performance and joint quality was studied and used to generate operating envelopes and reveal optimum welding conditions. Geometrical data from the melt-in joints of all alloys were employed to build joint geometry prediction statistical models. Numerical algorithms, based on the information generated by the statistical models, were used to create joint geometry optimisation techniques. Calorimetric experiments and x-ray examination of joints revealed the relationship between major operating parameters and arc efficiency and the incidence of porosity, suggesting desired welding conditions that were incorporated in the optimisation process. Finally, two software tools for Joint Geometry Prediction and Welding Procedure Optimisation were developed, incorporating the knowledge and information created during the modelling and optimisation stages. These provide the end user with a means of process parameter selection and visualisation of the influence of parameter variation on weld bead geometry.

Welding is the main joining method used in shipbuilding. A multi-electrode submerged arc welding is usually applied to long joints of massive components since the early 1950s.

The problem of welding stresses and deformations arose almost simultaneously with the introduction of welding as a joining method. In 1892 Slavianov, in his works, mentioned about "harmful stresses in metal" appearing during welding. Despite tremendous development in welding technology since that time, this problem is still present.

This dissertation presents the development of an experimental, numerical and analytical approach to the analysis of weldability. Focus is placed on the investigation of transient and residual welding stresses and distortions in thick-walled ship hull structures. The investigation mostly relies on the finite element analysis. Some recommendations about mitigation techniques for reducing their negative influence on welded structure efficiency are given.

A number of simulation systems for the sequentially coupled thermo-mechanical analysis of welding process, taking into account the welding conditions during the butt welding of thick-walled steel panels, are developed. Two welding techniques are investigated. The three-electrode one-pass welding process and the one-electrode multipass process are compared in terms of the joint characteristics and transient stresses and deformations.

The accuracy of each finite element models is evaluated based on experimental results and the results of the analytical solution.

Several techniques allowing to reduce residual stresses and deformations are investigated. Both, obtained results and governing phenomena, are studied and explained based on physical principles.

The first part of the thesis is a significant part of the work. Its purpose is a deep analysis of the thermo-mechanics of welding allowing better understanding of the complicated phenomena.

A inspeção visual de imagens radiográficas de soldas e tubulações é uma tarefa difícil para o ser humano, devido a sua característica repetitiva. Desta forma, a partir da digitalização dessas imagens radiográficas, é possível o desenvolvimento de ferramentas de inspeção automática, reduzindo os erros cometidos por inspeção visual. Este trabalho apresenta uma metodologia que tem o objetivo de automaticamente segmentar os defeitos em soldas e tubulações e extrair características que permitam o reconhecimento destes defeitos. Os resultados obtidos com o uso da metodologia desenvolvida neste trabalho mostram que é possível segmentar os defeitos em imagens radiográficas de soldas e levantar as características desses defeitos de forma automática, mesmo que tais defeitos sejam de difícil visualização. O trabalho também propõe o uso de parâmetros para calibrar o método proposto, sendo que tais parâmetros conferem uma maior maleabilidade ao método. Desta forma o método proposto para segmentar os defeitos foi testado com dois grupos de imagens, cada grupo proveniente de origem diferente, e obteve resultados satisfatórios conseguindo segmentar os defeitos em quase todas as imagens. Para extrair as características utilizou-se a rotulação das regiões segmentadas fechadas, este algoritmo coloca um label em cada possível defeito e assim permite levantar os seus parâmetros de forma automática. Por sua vez o método de segmentação de cordões de solda também se mostrou visualmente robusto conseguindo segmentar os cordões mesmo em imagens onde haviam outros objetos inseridos.
The visual inspection of radiographic images of welds and pipelines is a very repetitive task, very hard for humans. However, using digital radiographic images, it is possible to develop computational tools to be applied in the inspection process and to decrease the risks of inconsistent evaluations. This work presents a methodology to be applied in the automatic segmentation of defects in welds and pipes radiographic images, as well as to extract characteristics for the defects recognition. The tests and results, using the proposed methodology, show that it is possible to automatically perform the defect segmentation and characteristic extraction. As a result, some defects, difficult to be visually detected, were automatically segmented by the proposed method. Using some adjusting parameters, also proposed in this work, it is possible to adjust the method performance, obtaining more flexibility in the method applications. Two groups of images, originating from different sources, were tested and the results were satisfactory, since the defects, in almost all images, were segmented by the proposed method. A connected region labeling algorithm was used in order to make possible the automatic characteristics extraction for each detected defect. Besides, the proposed methodology shows to be robust also in some situations where other undesirable objects are presented in the image.

O objetivo desta dissertação é escrever sobre a técnica de ultra-sonografia, aplicada na inspeção da soldagem por resistência a ponto, e demonstrar as vantagens desta técnica em relação aos ensaios destrutivos convencionalmente normalizados e utilizados na inspeção de solda a ponto até meados de 1999, quando a técnica de ultra-som começou a ser aplicada no Brasil. Para tanto foram realizados dois procedimentos experimentais, sendo o primeiro deles utilizando a técnica de ultra-som a-scan (transdutor de simples elemento), onde foram estudados os efeitos da indentação do ponto de solda, um dos parâmetros que pode ser detectado com extrema facilidade por esta técnica. O segundo experimento visa demonstrar a capacidade de detecção da técnica de ultra-som b-scan (transdutor matricial), onde a metodologia foi aplicada visando correlacionar os resultados obtidos pelo equipamento com os resultados encontrados nas técnicas de arrancamento (peel test) e nos ensaios macrográficos convencionalmente conhecidos. Com estes experimentos, foi possível comprovar a confiabilidade e repetibilidade desta técnica, mostrando uma maior precisão em relação aos ensaios normalizados conhecidos, além da avaliação quantitativa que pode ser feita, tornando possível a coleta estatística de dados. Foi também notada grande dificuldade em interpretar os sinais gráficos emitidos pelos equipamentos, bem como atestar sua confiabilidade e capacidade de detecção de defeitos, surgindo a necessidade de intensificar o treinamento dos operadores desta técnica. De qualquer forma, esta técnica representa o estado da arte na inspeção de solda por resistência, e foi o principal motivador deste estudo.
The aim is to describe the ultrasound technique, applied to the inspection of the resistance spot welding, and to demonstrate the advantages of this technique over the conventionally standardized destructive tests used in spotweld inspections until mid 1999, when the ultrasound technique began to be applied in Brazil. For this, two experimental procedures were organized, the first using the a-scan (single element transducer) ultrasound technique, in which the effects of the indentation of the spotweld were studied, one of the parameters that can be easily detected by this technique. The second experiment seeks to demonstrate the detection capacity of the ultrasonic b-scan technique (matrix transducer), in which the methodology was applied to seek the correlation between the results obtained by the equipment with the results found in the peel test and also in the macrographic results conventionally known. With these experiments, it was possible to prove the reliability and reproductibility of this technique, showing an increase in precision when related to the normalized known tests, besides the quantitative evaluation that can be made, allowing the statistical collection of data. A great difficulty was also noticed in interpreting the graphic signs emitted by the equipment, as well as in attesting the reliability and capacity of defects detection, raising the need of operators training. In any way, this technique represents the state of the art in the resistance spotweld inspection, and this was the main motivator of this study.

Cette étude s’inscrit dans une démarche de réduction des coûts dus à l’utilisation croissante d’alliages de titane pour des applications structurelles, via des procédés d’assemblage à l’état solide, comme le soudage par friction linéaire (LFW). Cependant, les chargements thermomécaniques transmis au matériau au cours du LFW engendrent d’importantes transformations microstructurales pouvant affecter sévèrement la durabilité mécanique de l’assemblage. Ces transformations sont dépendantes à la fois de l’histoire thermomécanique du matériau et de ses éléments d’alliage. Ainsi, la compréhension des mécanismes régissant ces transformations en lien avec l’impact des configurations procédé et/ou de traitements thermiques sur ces dernières apparaît comme nécessaire pour des applications industrielles. Les travaux présentés dans ce document se focalisent sur la caractérisation/optimisation microstructurale de deux joints obtenus à partir de deux alliages sensiblement différents : le β-métastable Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) et le quasi-α Ti-6Al-2Sn-4Zr-2Mo (Ti6242). Une analyse détaillée des mécanismes impactant les transformations microstructurales et la résorption des défauts sera exposée en s’appuyant sur des études multi-techniques et multi-échelle. Ces campagnes expérimentales ont conduit à l’élaboration d’un traitement thermique permettant d’obtenir des comportements mécaniques quasi-homogènes au sein des structures soudées. De plus, les effets des principaux paramètres de LFW sur les microstructures ont été déterminés fournissant ainsi à la littérature des données essentielles pour la dissipation des défauts et le contrôle des textures de déformation
The present study follows up two major development axes focusing on the increase in use of Ti-alloys for structur applications through the use of solid-state joining processes such as Linear Friction Welding (LFW). Yet, the therm mechanical loads involved during LFW result in remarkable microstructural changes deeply affecting the associate mechanical performances. These changes are concomitant with the thermo-mechanical processing history and the alloyin compositions of the welded Ti-alloys. Hence, a correct understanding of the microstructure transformation mechanism induced by LFW is required as well as identifying the influence of the process conditions and/or complementary he treatments on these changes. This dissertation is endeavored at characterizing and optimizing the microstructures of two butt-joints of significantl different Ti-alloys: the ß-metastable Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti17) and the near-α Ti-6Al-2Sn-4Zr-2Mo (Ti6242). The extensive microstructural investigations will focus on identifying the mechanisms responsible for transforming the microstructures and for the formation/resorption of welding defects. These investigations will combine temperatur measurements, micrographs, crystallographic/chemical analysis, hardness/tensile tests. The resulting comprehension the microstructural changes will enable designing a heat treatment capable of a quasi-homogenization of the tensil behavior across the assemblies. Moreover, identifying the effects of the main process parameters on the microstructur will provide the literature with valuable insights on tailoring the process duration, the recrystallization/textur development, and the defect removal

Le travail présenté dans cette thèse concerne la modélisation et la commande robuste en force de robots manipulateurs industriels à articulations flexibles utilisés pour le procédé FSW. Afin de réduire les temps de calcul et l'occupation de la mémoire, une approche basée sur la méthode par intervalle est proposée en vue de la simplification des modèles dynamiques des robots industriels, et contribue à identifier les paramètres d'inertie qui sont négligeables. Des études de cas sur trois types de trajectoires de test et l’analyse des couples moteurs ont démontré l'efficacité et les bonnes performances de la méthode de simplification. Ensuite, la modélisation dynamique et l'identification des paramètres du procédé FSW ont été effectuées. Les paramètres des modèles linéaires et non-linéaires de forces axiales sont identifiés. Sur la base de la modélisation du procédé FSW qui considère simultanément la cinématique du système complet, le modèle de déplacement du robot rigide, les flexibilités des articulations et le modèle dynamique de la force axiale, un contrôleur robuste en force est obtenu par la méthode de réglage fréquentielle. En outre, un simulateur du procédé FSW robotique est développé et les résultats de simulation montrent les bonnes performances du contrôleur en force. L'oscillation de la force axiale dans le procédé FSW peut être simulée en utilisant un modèle de perturbation de la position verticale de référence
The work presented in this thesis focuses on the modeling and robust force control of flexible joints industrial robot manipulators used for FSW process. In order to reduce computation time and memory occupation, a novel interval-based approach for dynamic model simplification of industrial robots is proposed, which applies to arbitrary trajectories of whole robot workspace and contributes to obtaining negligible inertia parameters. Cases studies have been carried out on three kinds of test trajectories and torques analysis of robot dynamic equation, demonstrating the effectiveness and good performance of the simplification method. Then, the dynamic modeling and identification of robotic FSW process is performed, and the parameters of linear and nonlinear dynamic axial force process models are identified by using the plunge depth and its derivative. On the basis of the modeling of robotic FSW process which simultaneously considers the complete kinematics, the rigid robot displacement model, the joint flexibility and the dynamic axial force process model, a robust force controller can be obtained by using the frequency response approach. Besides, a simulator of robotic FSW process is developed and simulation results show good performance of the force controller. The oscillation of axial force in FSW process can be simulated when a disturbance model of initial vertical reference position is proposed and used in the simulation

In planning and design of engineering projects, engineers are often required to decide upon a course of action irrespective of the completeness and accuracy of available information. With the fast development of computer technology, many numerical analysis tools have arisen to assist engineering decision-making based on complete design information, which is, however, rarely available at most design stages. Little has been done to help engineers make sound decisions when complete design information is not available. Qualitative and Semi- Quantitative Reasoning, a branch in the field of Artificial Intelligence, has the ability of analyzing "ill"-defined problems using sound and clear arguments which are based on facts. This thesis is an attempt to tackle "ill"- defined engineering problems with the above mentioned reasoning techniques. This thesis revolves around the topic of shrinkage and distortion in welded structures. Steel fabrication frequently involves the joining of components by welding. Each component must be fabricated to particular dimensional tolerances. Distortion caused by welding is a frequently occurring problem that makes it difficult to estimate the dimensions of the finished structures and thus increases the fabrication costs. Welding distortion is a poorly quantified phenomenon controlled by many factors that are difficult to describe numerically. The characteristics of the distortion problems make the traditional numerical analysis very arduous and expensive to apply. Due its high complexity, for many years, welding distortion problems have been approached primarily empirically or by trial and error, and uncertain design factors cannot be effectively considered. In this thesis, a computer software tool was developed using qualitative and semi-quantitative techniques, attempting to solve complex welding distortion problems with unclearly specified design factors. With the assistance of this software tool, it is hoped to make the efforts of predicting and controlling welding distortion become more of a science rather than an art.

碩士
華梵大學
工業工程與經營資訊學系碩士班
95
In general, there is no sophiscated formula for the parameter design of plasma arc welding. Usually, welding staffs used to depend on their experience and domain knowledge to determine welding parameters and judge welding quality. Once a case is out of their rule of thumb experience, it becomes difficult to optimize effectively the welding parameter design. Therefore, the relationship among the welding parameters is then hard to be handled. To approach the best performance in the overall welding quality, this research attempts to develop a database for controlling welding parameters in order to reach the required quality and build an automatic welding control system in the future. Therefore, the primary issue of this research is to explore the possibility of applying fuzzy data mining algorithm and fuzzy neural network for the generation of welding parameter association rules in order to construct a fuzzy welding knowledge base. In this research, the experimental material is 304 stainless steel; the welding equipment is plasma arc welding. About the research methodology, this research adopts an advanced AprioriTid data mining algorithm, which is able to mine out linguistic type association rules for welding parameter design; and also the Kosko’s fuzzy neural network model, which was developed as the FuzzyTECH software for generating the fuzzy welding association rules. This experimental results show that both the advanced AprioriTid algorithm and FuzzyTECH can be successfully employed for the generation of welding parameter association rules, but FuzzyTECH presents better performance than the advanced AprioriTid. The reason is that the advanced AprioriTid algorithm uses only the largest linguistic term for each parameter and further produce possible association rules, so that some rules may not be found. The association rules for welding parameter design generated from this research were verified by domain experts about their usability of improving time spent and cost for welding staff to get the relationship among the welding parameters quickly through the knowledge base.

碩士
長庚大學
機械工程研究所
92
Abstract Osteomyelitis has been one of the most common causes of problems and complications after the operation despite the advance in surgical techniques and the availability of newly developed antibiotics. Local antibiotic delivery beads for treatment of various surgical infections had been studied recently especially in orthopedic infection. The report was to develop a novel solvent-free method for the manufacture of biodegradable capsules for a long-term drug delivery. To manufacture an antibiotic capsule, polylactide-polyglycolide copolymers were pre-mixed with vancomycin. The mixture was then injection compression molded to form a cylinder and a cover of 8mm in diameter. After the addition of liquid gentamicin into the core, an ultrasonic welder was used to seal the capsule. An elution method and an HPLC assay were employed to characterize the in-vitro release rates of the antibiotics over a 30-day period. Biodegradable capsules released high concentrations of vancomycin and gentamicin (well above the minimum inhibition concentration) in vitro for the period of time needed to treat bone infection; i.e., 2 to 4 weeks. A bacterial inhibition test was carried out to determine the relative activity of the released antibiotics. The diameter of the sample inhibition zone ranged from 3 mm to 18 mm, which is equivalent to 16.7% to 100% of relative activity. By adopting this novel technique, we will be able to manufacture biodegradable capsules of various medicines for long-term drug deliveries. Keyword: osteomyelitis, polylactide-polyglycolide, vancomycin, gentamicin, capsules, release rate, in vitro elution, bacterial inhibition

Student Number : 9811923K - PhD thesis - School of Mechanical Engineering - Faculty of Engineering and the Built Environment
Methods are presented for obtaining models used for predicting welded sample resistance and effective weld current (RMS) for desired weld diameter (weld quality) in the resistance spot welding process. These models were used to design predictive controllers for the welding process. A suitable process model forms an important step in the development and design of process controllers for achieving good weld quality with good reproducibility. Effective current, dynamic resistance and applied electrode force are identified as important input parameters necessary to predict the output weld diameter. These input parameters are used for the process model and design of a predictive controller. A three parameter empirical model with dependent and independent variables was used for curve fitting the nonlinear halfwave dynamic resistance. The estimates of the parameters were used to develop charts for determining overall resistance of samples for any desired weld diameter. Estimating resistance for samples welded in the machines from which dataset obtained were used to plot the chart yielded accurate results. However using these charts to estimate sample resistance for new and unknown machines yielded high estimation error. To improve the prediction accuracy the same set of data generated from the model were used to train four different neural network types. These were the Generalised Feed Forward (GFF) neural network, Multilayer Perceptron (MLP) network, Radial Basis Function (RBF) and Recurrent neural network (RNN). Of the four network types trained, the MLP had the least mean square error for training and cross validation of 0.00037 and 0.00039 respectively with linear correlation coefficient in testing of 0.999 and maximum estimation error range from 0.1% to 3%. A prediction accuracy of about 97% to 99.9%. This model was selected for the design and implementation of the controller for predicting overall sample resistance. Using this predicted overall sample resistance, and applied electrode force, a second model was developed for predicting required effective weld current for any desired weld diameter. The prediction accuracy of this model was in the range of 94% to 99%. The neural network predictive controller was designed using the MLP neural network models. The controller outputs effective current for any desired weld diameter and is observed to track the desired output accurately with same prediction accuracy of the model used which was about 94% to 99%. The controller works by utilizing the neural network output embedded in Microsoft Excel as a digital link library and is able to generate outputs for given inputs on activating the process by the push of a command button.

Femtosecond laser direct writing in transparent materials such as glass and optical fibers has been used as a versatile tool in order to fabricate various 3-D photonic structures such as active and passive waveguides, couplers, gratings and diffractive optical elements (DOEs). This capability of patterning and refractive index modification in the bulk of transparent materials depends on the nonlinear absorption phenomenon. This practical technique has the potential to be used for cost effective and simplified manufacturing in various applications. This thesis examines three advanced manufacturing techniques that use ultrashort pulse filamentary propagation induced by nonlinear absorption in the transparent materials. First, a new gradient index lens fabrication method using femtosecond laser direct writing is introduced. Light that passes through the lens with refractive index change resulting from localized energy deposition is focused using a beam profiler. Second, wide welding area of glass samples are used to fabricate microfluidic devices with long channels by adopting customized fixture. The fixture making artificial pressure helps the two glass samples have wide optical contact area and the highly intensive pulse filamentation strongly joins glass slides. As an example of a more specific application, microfluidic samples with long grooves sealed by femtosecond laser welding were successfully fabricated as part of this project. Finally, a screw-shaped, long period grating sensor was fabricated by rotating the optical fiber. This technique enables the fiber core to have asymmetric refractive index change, resulting in higher sensitivity compared to conventional long period grating sensors. Also, a new long-period grating sensor with reverse bending effect has been demonstrated by producing complex pitches of refractive index change.
Graduate

Oggi, la velocità con cui vengono sviluppate tecniche di produzione innovative è sempre più crescente e nuove tecnologie o sviluppi di processi già esistenti vengono raggiunti in un tempo minore. Sebbene, queste nuove tecnologie debbano affrontare e risolvere i nuovi problemi e le questioni relative alla novità dei processi stessi, tuttavia molte volte, devono affrontare anche vecchi problemi noti da più di un secolo. Uno di questi problemi è quello delle tensioni residue. Queste ultime sono stati tensionali "congelati" che esistono in materiali o strutture, essenzialmente a causa dei processi di fabbricazione, indipendentemente che qualsiasi carico esterno sia stato applicato alla struttura o al materiale. Combinandosi con i carichi esterni, gli effetti delle tensioni residue possono essere sia positivi che negativi, a seconda della grandezza, dal segno e dalla distribuzione delle sollecitazioni. In questa tesi, sono state studiate due tecniche innovative in due diversi campi che devono affrontare i problemi relativi alle tensioni residue: Friction Stir Welding (FSW) e Fused Deposition Modelling (FDM). Poiché il materiale nella FSW non raggiunge il punto di fusione, si può pensare che i valori delle tensioni residue possano essere bassi. Tuttavia, poiché la FSW è principalmente un processo di saldatura meccanico, a causa delle elevate forze in gioco e delle importanti forze di serraggio utilizzate, le tensioni residue non possono essere considerate basse in generale. Infatti, i vincoli imposti alle piastre da saldare, impediscono la contrazione del materiale durante il raffreddamento generando tensioni residue. Nella tecnica FDM, il modello è costruito come una deposizione strato per strato del materiale base. A causa di questo approccio, la parte stampata si raffredda strato dopo strato durante la deposizione e, di conseguenza, si creano variazioni termiche e diverse velocità di raffreddamento da un livello all'altro. Questo produce tensioni interne tra gli strati, ritrazione irregolare, problemi di destratificazione, deformazioni e i problemi ad esse associati in particolare con pezzi di grandi dimensioni. Per effettuare questo studio, le due linee di indagine sono state divise sostanzialmente come segue. Per quanto riguarda le tensioni residue nella saldatura FSW, è stato sviluppato il setup sperimentale per misurare il campo di temperatura durante il processo di saldatura sia nella FSW e che nella Laser Assisted FSW. Questo permette di avere una mappa di temperatura a campo intero durante il processo di saldatura. Questo ha permesso di studiare l'influenza sulla temperatura della distanza spot laser – utensile FSW e della potenza della sorgente laser. Inoltre, sono state effettuate le misure sperimentali delle tensioni residue in nuove tecniche derivate dalla FSW e in nuovi materiali per la FSW, cioè LAFSW, l'in-process cooled FSW e giunti a sovrapposizione alluminio-titanio. Infine, i risultati sperimentali termografici e della misura delle tensioni residue sono stati impiegati per validare i modelli numerici per FSW e LAFSW. Questi modelli sono in grado di prevedere la temperatura e le tensioni residue cambiando i parametri di processo e il setup dei vincoli. Per quanto concerne le tensioni residue nella FDM, è stato eseguito prima uno studio preliminare sul comportamento meccanico dei pezzi FDM al fine di dimostrare che questi mostrano un comportamento ortotropo sia a carichi statici che dinamici. Questi studi sono stati utilizzati al fine di avere una migliore conoscenza delle parti FDM e stabilire il comportamento appropriato da impiegare al fine di creare il modello numerico per eseguire il calcolo delle tensioni residue. Questo modello permette di correlare gli spostamenti sperimentali misurati dall’Electronic Speckle pattern Interferometry (ESPI) durante la foratura e le tensioni residue.
Nowadays, the speed whereby innovative manufacturing techniques are developed is more and more increasing and new technologies or developments of already existing processes are achieved in a smaller time. Though these innovative technologies have to face and resolve new difficulties and issues related to the novelty of the processes, however, many times they have to tackle old problems known for more than a century. One of these problems is the residual stresses issue. Residual stresses are �frozen� stresses that exist in materials or structures, essentially due to the manufacturing processes, independently that any external load has been applied on the structure or materials. Combining with the external loads, the effects of residual stresses may be either beneficial or detrimental, depending upon the magnitude, sign, and distribution of the stress. In this thesis, two innovative techniques in different fields that have to face to residual stress issues have been addressed: Friction Stir Welding and Fused Deposition Modelling. In the Friction stir welding (FSW), the material is not led to fusion and this helps to decreases the residual stresses values. However, because FSW is mainly a mechanical welding process, due to the high force involved in the weld and, thus, the rigid clamping used, the residual stresses are not low in general. Indeed, the constraints avoid the contraction of the materials during cooling in both longitudinal and transverse directions producing residual stresses. In the Fused deposition modelling (FDM), the model is built as a layer-by-layer deposition of a feedstock material. Due to this approach, the part cools down layer by layer during the deposition and, consequently, there is thermal variation and different cooling rates from one layer to the other. This produces internal stresses between layers, uneven shrinkage, de-layering problems, warping, and the relatively associated problems especially with large parts. In order to carry out this study, the two lines of investigation are basically divided as follow. For residual stress in Friction stir welding, the experimental setup to measure the temperature field on both FSW and LAFSW during the welding process has been developed. This allows to capture the whole temperature fields during the welding process and to study the influence on the temperature of the distance laser spot - FSW tool and of the laser source power. Moreover, the experimental measurements of residual stresses in new developed FSW techniques and materials, i.e. Laser Assisted FSW, the in-process cooled FSW, and lap-joint of aluminium-titanium have been carried out. Finally, the thermographic experimental results and the residual stresses measurements have been employed to validate the numerical models for FSW and LAFSW. These models can predict the temperature and residual stresses changing the process parameters and clamping configuration. For residual stress in fused deposition modelling, a preliminary study on the mechanical behaviour of FDM parts has been done in order to prove that FDM parts show an orthotropic behaviour on both static and dynamic loads. These studies are useful in order to have a better knowledge of the FDM parts and establish the appropriate behaviour of the material to employ in order to create the numerical model to carry out the residual stress calculation. This model allows to correlate the experimental displacements measured by Electronic Speckle Pattern Interferometry (ESPI) during hole drilling and the residual stresses.