This thesis presents an experimental study on how to track zero gaps between metal sheets to be joined by laser beam butt welding. Automated laser beam welding is gaining interest due to its ability to produce narrow and deep welds giving limited heat input and therefore less distortions compared to other processes, such as arc-welding. The automated laser beam welding process is however sensitive to how the high power laser is positioned with regards to the joint position. Deviations from the joint position may occur due to inaccuracies of the welding robot and fixturing, changes in joint geometry, process induced distortions, etc. Welding with an offset from the joint position can result inlack of sidewall fusion, a serious defect that is hard to detect. This work develops and evaluates three monitoring systems to be used during welding in order to be able to later control the laser beam spot position. (i) A monitoring systemis developed for three different photo diodes, one for the visual spectrum of the process emissions, one for the infrared spectrum, and one for the reflected highpower laser light. The correlation between the signals from the photodiodes and the welding position relative to the joint is analysed using a change detection algorithm. In this way an indication of a path deviation is given. (ii) A visual camera with matching illumination and optical filters is integrated into the laser beam welding tool in order to obtain images of the area in front of the melt pool. This gives a relatively clear view of the joint position even during intense spectral disturbances emitted from the process, and by applying animage processing algorithm and a model based filtering method the joint positionis estimated with an accuracy of 0.1 mm. (iii) By monitoring the spectral emissions from the laser induced plasma plume using a high speed and high resolution spectrometer, the plasma electron temperature can be estimated from the intensities of two selected spectral lines and this is correlated to the welding position and can be used for finding the joint position.

The research presented here investigates the effects of laser trimming on the state of stress in alumina Al₂O₃ hybrid microelectronics substrates. Evaluation of stress was performed using x-ray diffraction residual stress analysis and dynamic strain measurements using strain gages before and after laser trimming. X-ray diffraction measurements were carried out in both the longitudinal and transverse directions on the front and back sides of the substrates. The dynamic strain measurements were performed in situ with strain gages attached to the bottom of the substrates while the substrates were trimmed with a 400 watt YAG laser. The substrates were characterized using optical microscopy, scanning electron microscopy / energy dispersive x-ray analysis (SEM/EDAX), electron probe microanalysis (EPMA) and electron spectroscopy for chemical analysis (ESCA). The results from these characterization steps gave results for fractography (optical), surface and bulk composition (SEM/EDAX), chemical composition (ESCA) and phase analysis (EPMA). Results show that laser trimming produces stress gradients which are generally tensile in nature and could have deleterious effects on the mechanical integrity of the substrates if used in hybrid microelectronic applications. Furthermore the stress distribution across the substrates was found to be uniformly distributed showing no peak stresses near the heat affected zone (HAZ) boundary. Phase analysis determined that the substrates contained a magnesium aluminum spinel phase (MgAl₂O₄) and that the glass and pore phases are randomly distributed in the substrates. This could have some overall effect on the state of residual stress in the substrates after they have been laser trimmed. / Master of Science

Since the development of thick film hybrid microelectronic processing, there has been a need for methods to adjust for tighter tolerances for electrical components through a trimming process. Components/elements, as produced, show a tolerance of the order of ±10% due to the variability of the screen printing process associated with film curing conditions. The methods that have arisen from this need encompass a variety of technologies and techniques. The usefulness of each method is based on its operation, flexibility, repeatability, and post-trim effects on the resistor's reliability. The work in this thesis concerns the laser trimming of resistor components to a tight tolerance. It is the objective of this thesis to address the performance of an Nd:YAG laser operation and interface with a computer. The first task involves a computer hardware system to be interfaced to the laser control system, this task includes both design and implementation. The second task consists of a software operating environment to be flowcharted, written, and tested. The third task involves the computer interface driving the laser in the process of trimming resistor components using different types of cuts. The trimmed resistor performance is evaluated as part of the study. / Master of Science

Neste trabalho estudou-se as propriedades obtidas em juntas soldadas pelo processo de soldagem a laser do tipo estado sólido de onda contínua guiado por fibra, e os resultados foram comparados com juntas soldadas pelo processo feixe de elétrons. O material utilizado foi o aço maraging 350 - ASTM A 538 Grade C. As soldas realizadas com o processo feixe de elétrons possuem um procedimento de soldagem aprovado. A junta selecionada para a elaboração do trabalho foi do tipo sobreposta com material de base de espessuras diferentes, respectivamente iguais a 1,00 e 0,78 mm. As juntas soldadas foram avaliadas por: ensaio de cisalhamento, dureza Vickers e caracterização microestrutural das diversas regiões das juntas soldadas. Foram realizadas análises por microscopia óptica e microscopia eletrônica de varredura usando espectrometria de energia dispersiva (MEV/EDS). Foi realizado o teste de hipótese como técnica para a análise dos dados provenientes dos ensaios experimentais. Nas juntas soldadas com ambos processos não foi verificada a presença de descontinuidades, poros e depressões na superfície do cordão. Os resultados indicam que as condições usadas em ambos os processos de soldagem foram satisfatórias e possibilitaram a soldagem do aço maraging 350 atendendo aos requisitos necessários. / In this work, the welds made by a continuous wave diode pumped solid state laser guided by fiber were studied and the results were compared with welded joints of electron beam welding. The material used was maraging 350 steel ASTM A 538 Grade C. The welding process performed with electron beam welding has a approved welding procedure. The joint chosen for the preparation of the work was the lap joint type with different thicknesses base material respectively equal to 1,00 and 0,78 mm. The welded joints were evaluated by mechanical tests like shear test, Vickers hardness and microstructural characterization of the various regions of the welded joints. Analyzes were performed by optical microscopy and scanning electron microscopy using energy dispersive spectrometry (SEM/EDS). The hypothesis test technique was done for the analysis of data from experimental tests. For both welding process was not detected in the welded joints the presence of discontinuities, pores and depressions on the weld fillet surface. The results indicate that the conditions used for both welding process were satisfactory and allowed the welding of maraging 350 steel meeting necessary requirements.

Les procédés de fabrication additive ont connus un fort essor dans les dernières décennies et entament aujourd'hui leur phase d'industrialisation pérenne. L'industrie, dans un souci d'améliorer sans cesse le ratio masse/rigidité des systèmes qu'elle produit (notamment l'industrie aéronautique), a pris conscience du potentiel de ces technologies à produire des structures plus complexes que les procédés classiques. Elle cherche aujourd'hui à tirer profit de ce potentiel pour alléger encore plus les pièces produites en utilisant notamment des géométries de type réseaux ou alvéolaires (Lattice en anglais). Les travaux présentés dans ce manuscrit ont pour but de proposer une méthodologie, des modèles et des outils permettant la conception, le dimensionnement et l'optimisation de telles structures en vue de leur fabrication par procédés additifs. Le framework proposé peut être résumé par les huit étapes ci-dessous:- Importation de l'espace de conception, comprenant également les cas de chargement.- Optimisation topologique sur l'espace de conception.- Reconstruction de la géométrie, appelée primitive, qui servira de support à l'insertion du réseau.- Calcul par éléments finis qui peut être réalisé pour s'assurer de la bonne tenue mécanique.- Définition de la topologie du réseau, par l'intermédiaire d'un graphe 3D.- Déformation du réseau et optimisation mécanique du réseau.- Reconstruction des volumes.- Préparation des fichiers de données et impression 3D. / Additive manufacturing processes have been quickly growing those past decades and are now getting to their sustainable industrial. Industry has been caring about the mass to rigidity ratio of the structures it produces (especially in aeronautics), and is now acknowledging the potential of additive processes to produce more complex shapes than classical processes. Industry is now trying to take advantage of this potential by designing highly complex structures like lattices or metal foams. The work that is presented in this document propose a methodology, models and numerical tools allowing the conception, dimensioning and optimization of such structures through additive manufacturing. The proposed framework can be describe through the height following steps:- Importing the design space and the technical requirement (load cases).- Topology optimization of the design space- Geometry reconstruction to create a primitive which will be the lattice insertion area.- Finite elements computation to ensure that the structure meets the requirements.- Lattice topology definition using 3D graphs.- Lattice deformation and optimization.- Creation of the volumes around the lattice.- Printing file creation and 3D printing.

Neste trabalho estudou-se as propriedades obtidas em juntas soldadas pelo processo de soldagem a laser do tipo estado sólido de onda contínua guiado por fibra, e os resultados foram comparados com juntas soldadas pelo processo feixe de elétrons. O material utilizado foi o aço maraging 350 - ASTM A 538 Grade C. As soldas realizadas com o processo feixe de elétrons possuem um procedimento de soldagem aprovado. A junta selecionada para a elaboração do trabalho foi do tipo sobreposta com material de base de espessuras diferentes, respectivamente iguais a 1,00 e 0,78 mm. As juntas soldadas foram avaliadas por: ensaio de cisalhamento, dureza Vickers e caracterização microestrutural das diversas regiões das juntas soldadas. Foram realizadas análises por microscopia óptica e microscopia eletrônica de varredura usando espectrometria de energia dispersiva (MEV/EDS). Foi realizado o teste de hipótese como técnica para a análise dos dados provenientes dos ensaios experimentais. Nas juntas soldadas com ambos processos não foi verificada a presença de descontinuidades, poros e depressões na superfície do cordão. Os resultados indicam que as condições usadas em ambos os processos de soldagem foram satisfatórias e possibilitaram a soldagem do aço maraging 350 atendendo aos requisitos necessários. / In this work, the welds made by a continuous wave diode pumped solid state laser guided by fiber were studied and the results were compared with welded joints of electron beam welding. The material used was maraging 350 steel ASTM A 538 Grade C. The welding process performed with electron beam welding has a approved welding procedure. The joint chosen for the preparation of the work was the lap joint type with different thicknesses base material respectively equal to 1,00 and 0,78 mm. The welded joints were evaluated by mechanical tests like shear test, Vickers hardness and microstructural characterization of the various regions of the welded joints. Analyzes were performed by optical microscopy and scanning electron microscopy using energy dispersive spectrometry (SEM/EDS). The hypothesis test technique was done for the analysis of data from experimental tests. For both welding process was not detected in the welded joints the presence of discontinuities, pores and depressions on the weld fillet surface. The results indicate that the conditions used for both welding process were satisfactory and allowed the welding of maraging 350 steel meeting necessary requirements.

This master thesis deals with surface hardening of steels, especially with rotary flash hardening of 42CrMo4 steel (WNr 1.3563, ČSN 15142). In this method homogenous heating of whole surface occurs during a very fast rotation of the component. In the theoretical part of this thesis the most common methods of surface hardening are described, with focus on laser and electron beam technologies. In the experimental part special device for this application was constructed. Rotary flash hardening was done using different radiation source and experimantal device parameters. The hardened surface layer of maximal thickness of 0,7 mm and width of 5,6 mm was achieved using laser beam. Results with electron beam were way better, because this technology allows to control the distribution of power along the beam width in order to improve the width/thickness ratio of hardened layer. Using this method maximal layer thickness of 1,4 mm and width of 13,4 mm was achieved.

No description available.

Proposed are novel sensors for extreme environment power plants, laser beam analysis and biomedicine. A hybrid wireless-wired extreme environment temperature sensor using a thick single-crystal Silicon Carbide (SiC) chip embedded inside a sintered SiC probe design is investigated and experimentally demonstrated. The sensor probe employs the SiC chip as a Fabry-Perot (FP) interferometer to measure the change in refractive index and thickness of SiC with temperature. A novel temperature sensing method that combines wavelength-tuned signal processing for coarse measurements and classical FP etalon peak shift for fine measurements is proposed and demonstrated. This method gives direct unambiguous temperature measurements with a high temperature resolution over a wide temperature range. An alternative method using blackbody radiation from a SiC chip in a two-color pyrometer configuration for coarse temperature measurement and classical FP laser interferometry via the same chip for fine temperature measurement is also proposed and demonstrated. The sensor design is successfully deployed in an industrial test rig environment with gas temperatures exceeding 1200 C. This sensor is proposed as an alternate to all-electrical thermocouples that are susceptible to severe reliability and lifetime issues in such extreme environments. A few components non-contact thickness measurement system for optical quality semi-transparent samples such as Silicon (Si) and 6H SiC optical chips such as the one used in the design of this sensor is proposed and demonstrated. The proposed system is self-calibrating and ensures a true thickness measurement by taking into account material dispersion in the wavelength band of operation. For the first time, a 100% repeatable all-digital electronically-controlled pinhole laser beam profiling system using a Texas Instruments (TI) Digital Micro-mirror Device (DMD) commonly used in projectors is experimentally demonstrated using a unique liquid crystal image generation system with non-invasive qualities. Also proposed and demonstrated is the first motion-free electronically-controlled beam propagation analyzer system using a TI DMD and a variable focus liquid lens. The system can be used to find all the parameters of a laser beam including minimum waist size, minimum waist location and the beam propagation parameter M2. Given the all-digital nature of DMD-based profiling and all-analog motion-free nature of the Electronically Controlled Variable Focus Lens (ECVFL) beam focus control, the proposed analyzer versus prior-art promises better repeatability, speed and reliability. For the first time, Three Dimensional (3-D) imaging is demonstrated using an electronically controlled Liquid Crystal (LC) optical lens to accomplish a no-moving parts depth section scanning in a modified commercial 3-D confocal microscope. The proposed microscopy system within aberration limits has the potential to eliminate the sample or objective motion-caused mechanical forces that can distort the original sample structure and lead to imaging errors. A signal processing method for realizing high resolution three dimensional (3-D) optical imaging using diffraction limited low resolution optical signals is also proposed.

No description available.