O conjunto de tubos denominado sistema pneumático, tem a função de conduzir o ar quente pressurizado desde o motor até os pontos de utilização pelos sistemas ambientais da aeronave. A ocorrência de falhas em serviço de peças desse sistema soldadas pelo processo TIG (Tungsten Inert Gas), motivou o estudo da substituição desse processo pelo de soldagem a laser. Foi utilizado um laser a fibra de 2 kW de potência e tubos de titânio comercialmente puro grau 2, de 0,5 mm de espessura e 50 mm de diâmetro. Para efeito de comparação foram realizadas soldas pelo processo TIG, semi-automático, cujos parâmetros foram obtidos junto a uma empresa fabricante de aviões. Os tubos de titânio foram soldados em cheio, sem adição de arame, e o argônio foi utilizado como gás de proteção. Os parâmetros de soldagem a laser selecionados foram 200 W e 2000 mm/min e, 250 W e 300 mm/min. Os tubos soldados a laser apresentam cordões com aproximadamente 1 mm de largura e grãos de Ti-CP ?, enquanto que as soldas TIG resultam em cordões de 5 mm e grãos grosseiros serrilhado de Ti-CP ?. O refinamento microestrutural observado nas amostras soldadas a laser, em relação à TIG, deve-se a alta taxa de resfriamento, que no laser foi cerca de 70 vezes maior do que no TIG. Os tubos soldados a laser e TIG foram ciclados na bancada pneumática, 44.000 vezes, a 350 oC, sem fraturarem ou iniciarem uma trinca que comprometesse os testes de pressurização cíclica. Os resultados de fadiga evidenciaram uma maior resistência mecânica da solda a laser na condição de 200 W e 2000 mm/min, quando comparado com as demais condições de soldagem. As avaliações microestruturais e mecânicas dos cordões de solda evidenciaram as vantagens do processo de soldagem a laser para substituir o TIG, em junções do sistema pneumático de aeronaves. / The engine bleed air system, also known as pneumatic system, conducts the pressurized hot air from the engine to the environmental systems of aircrafts. In-service failures of the arc welded pneumatic parts have driven further developments of laser beam welding as an alternative method. Here, a fiber laser with 2 kW power had been employed to weld commercial purity titanium alloy tubes with 0.5 wall thickness and 50 mm diameter. For comparison purposes, semiautomatic TIG welding was realized, based on the previous experience of an aircraft company. All the welds were autogenous, bead-on-plate, and under protective argon atmosphere. The chosen parameters speed and laser powers for laser welding were 200 W - 2000 mm/min and 250 W - 300 mm/min. The laser welded tubes presented 1-mm wide weld beads composed by grained ?-Ti. The TIG welded tubes showed 5-mm wide beads composed by acicular ?-Ti grains. These observed differences had been associated to the cooling rate, which is seventy times higher in the laser case. Both laser and TIG welded tubes were cycled 44.000 times in a pneumatic bench at 350 oC without failures or cracks that could break the internal pressure. The condition 200W-2000mm/min presented superior fatigue resistance values compared to other welding conditions, and being similar to the tubes in the unwelded condition. On the other hand, the condition 250W-3000mm/min presented the highest dispersion for the fatigue lives. The microstructural and mechanical results shown that the current laser technology could replace with advantages the arc welding for the joining of the titanium tubes in the aircrafts pneumatic system.

Haynes alloy 282 is a new gamma prime (γ’) precipitation strengthened nickel-base superalloy developed for high temperature applications in land-based and aero turbine engines. Joining is a crucial process both during the manufacturing of new components and repair of service-damaged turbine parts. Unfortunately, the new superalloy cracks during laser beam welding (LBW), which is an attractive technique for joining superalloys components due to its low heat input characteristic that preclude the geometrical distortion of welded components. This research is therefore initiated with the goal of studying and developing an effective approach for preventing or minimizing cracking during LBW of the new superalloy Haynes 282. Careful and detailed electron microscopy and spectroscopy study reveal, for the first time, the formation of sub-micron grain boundary M5B3 particles, in the material. Microstructural study of welded specimens coupled with Gleeble thermo-mechanical physical simulations shows that the primary cause of weld heat affected zone (HAZ) cracking in the alloy is the sub-solidus liquation reaction of intergranular M5B3 borides in the material. Further weldability study showed that the HAZ liquation cracking problem worsens with reduction in welding heat input, which is normally necessary to produce the desired weld geometry with minimum distortion. In order to minimize the HAZ cracking during low heat input laser welding, microstructural modification of the alloy by heat treatment at 1080 - 1100oC has been developed. The pre-weld heat treatment minimizes cracking in the alloy by reducing the volume fraction of the newly identified M5B3 borides, while also minimizing non-equilibrium grain boundary segregation of boron liberated during dissociation of the boride particles. Further improvement in resistance to cracking was produced by subjecting the material to thermo-mechanically induced grain refinement coupled with a pre-weld heat treatment at 1080oC. This approach produces, for the first time, crack-free welds in this superalloy, and the benefit of this procedure in preventing weld cracking in the new material is preserved after post-weld heat treatment (PWHT), as additional cracking was not observed in welded specimens subjected to PWHT.

Haynes alloy 282 is a new gamma prime (γ’) precipitation strengthened nickel-base superalloy developed for high temperature applications in land-based and aero turbine engines. Joining is a crucial process both during the manufacturing of new components and repair of service-damaged turbine parts. Unfortunately, the new superalloy cracks during laser beam welding (LBW), which is an attractive technique for joining superalloys components due to its low heat input characteristic that preclude the geometrical distortion of welded components. This research is therefore initiated with the goal of studying and developing an effective approach for preventing or minimizing cracking during LBW of the new superalloy Haynes 282. Careful and detailed electron microscopy and spectroscopy study reveal, for the first time, the formation of sub-micron grain boundary M5B3 particles, in the material. Microstructural study of welded specimens coupled with Gleeble thermo-mechanical physical simulations shows that the primary cause of weld heat affected zone (HAZ) cracking in the alloy is the sub-solidus liquation reaction of intergranular M5B3 borides in the material. Further weldability study showed that the HAZ liquation cracking problem worsens with reduction in welding heat input, which is normally necessary to produce the desired weld geometry with minimum distortion. In order to minimize the HAZ cracking during low heat input laser welding, microstructural modification of the alloy by heat treatment at 1080 - 1100oC has been developed. The pre-weld heat treatment minimizes cracking in the alloy by reducing the volume fraction of the newly identified M5B3 borides, while also minimizing non-equilibrium grain boundary segregation of boron liberated during dissociation of the boride particles. Further improvement in resistance to cracking was produced by subjecting the material to thermo-mechanically induced grain refinement coupled with a pre-weld heat treatment at 1080oC. This approach produces, for the first time, crack-free welds in this superalloy, and the benefit of this procedure in preventing weld cracking in the new material is preserved after post-weld heat treatment (PWHT), as additional cracking was not observed in welded specimens subjected to PWHT.

O conjunto de tubos denominado sistema pneumático, tem a função de conduzir o ar quente pressurizado desde o motor até os pontos de utilização pelos sistemas ambientais da aeronave. A ocorrência de falhas em serviço de peças desse sistema soldadas pelo processo TIG (Tungsten Inert Gas), motivou o estudo da substituição desse processo pelo de soldagem a laser. Foi utilizado um laser a fibra de 2 kW de potência e tubos de titânio comercialmente puro grau 2, de 0,5 mm de espessura e 50 mm de diâmetro. Para efeito de comparação foram realizadas soldas pelo processo TIG, semi-automático, cujos parâmetros foram obtidos junto a uma empresa fabricante de aviões. Os tubos de titânio foram soldados em cheio, sem adição de arame, e o argônio foi utilizado como gás de proteção. Os parâmetros de soldagem a laser selecionados foram 200 W e 2000 mm/min e, 250 W e 300 mm/min. Os tubos soldados a laser apresentam cordões com aproximadamente 1 mm de largura e grãos de Ti-CP ?, enquanto que as soldas TIG resultam em cordões de 5 mm e grãos grosseiros serrilhado de Ti-CP ?. O refinamento microestrutural observado nas amostras soldadas a laser, em relação à TIG, deve-se a alta taxa de resfriamento, que no laser foi cerca de 70 vezes maior do que no TIG. Os tubos soldados a laser e TIG foram ciclados na bancada pneumática, 44.000 vezes, a 350 oC, sem fraturarem ou iniciarem uma trinca que comprometesse os testes de pressurização cíclica. Os resultados de fadiga evidenciaram uma maior resistência mecânica da solda a laser na condição de 200 W e 2000 mm/min, quando comparado com as demais condições de soldagem. As avaliações microestruturais e mecânicas dos cordões de solda evidenciaram as vantagens do processo de soldagem a laser para substituir o TIG, em junções do sistema pneumático de aeronaves. / The engine bleed air system, also known as pneumatic system, conducts the pressurized hot air from the engine to the environmental systems of aircrafts. In-service failures of the arc welded pneumatic parts have driven further developments of laser beam welding as an alternative method. Here, a fiber laser with 2 kW power had been employed to weld commercial purity titanium alloy tubes with 0.5 wall thickness and 50 mm diameter. For comparison purposes, semiautomatic TIG welding was realized, based on the previous experience of an aircraft company. All the welds were autogenous, bead-on-plate, and under protective argon atmosphere. The chosen parameters speed and laser powers for laser welding were 200 W - 2000 mm/min and 250 W - 300 mm/min. The laser welded tubes presented 1-mm wide weld beads composed by grained ?-Ti. The TIG welded tubes showed 5-mm wide beads composed by acicular ?-Ti grains. These observed differences had been associated to the cooling rate, which is seventy times higher in the laser case. Both laser and TIG welded tubes were cycled 44.000 times in a pneumatic bench at 350 oC without failures or cracks that could break the internal pressure. The condition 200W-2000mm/min presented superior fatigue resistance values compared to other welding conditions, and being similar to the tubes in the unwelded condition. On the other hand, the condition 250W-3000mm/min presented the highest dispersion for the fatigue lives. The microstructural and mechanical results shown that the current laser technology could replace with advantages the arc welding for the joining of the titanium tubes in the aircrafts pneumatic system.

A recent method in aero engine production is to fabricate components from smaller pieces, rather than machining them from large castings. This has made laser beam welding popular, offering high precision with low heat input and distortion, but also high productivity. At the same time, the demand for automation of production has increased, to ensure high quality and consistent results. In turn, the need for sensors to monitor and control the laser welding process is increasing. In laser beam welding without filler material, the gap between the parts to be joined must be narrow. Optical sensors are often used to measure the gap, but with precise machining, it may become so narrow that it is difficult to detect, with the risk of welding in the wrong position. This kind of problems can cause severe welding defects, where the parts are only partially joined without any visible indication. This thesis proposes the use of an inductive sensor with coils on either side of the gap. Inducing currents into the metal, such a sensor can detect even gaps that are not visible. The new feature of the proposal is based on using the complex response of each coil separately to measure the distance and height on both sides of the gap, rather than an imbalance from the absolute voltage of each coil related to gap position. This extra information allows measurement of gap width and misalignment as well as position, and decreases the influence from gap misalignment to the position measurement. The sensor needs to be calibrated with a certain gap width and height alignment. In real use,these will vary, causing the sensor to be less accurate. Using initial estimates ofthe gap parameters from the basic sensor, a model of the response can be used to estimate the measurement error of each coil, which in turn can be used for compensation to improve the measurement of the gap properties.The properties of the new method have been examined experimentally, using a precise traverse mechanism to record single coil responses in a working range around a variable dimension gap, and then using these responses to simulate a two coil probe. In most cases errors in the measurement of weld gap position and dimensions are within 0.1 mm.The probe is designed to be mounted close to the parts to be welded, and will work in a range of about 1 mm to each side and height above the plates. This is an improvement over previous inductive sensors, that needed to be guided to the mid of the gap by a servo mechanism.

No description available.

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.

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.

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.

The demand for high energy battery assemblies is growing in sectors such as transportation. Alongwith it is the need for reliable, efficient and cost-effective ways to electrically connect the batteries toensure their performance. Battery cells are most often put into modules or packs when produced forelectrically driven vehicles. The variable of greatest influence when welding battery packs is thecontact resistance between the cell and the connection tab. It is crucial to minimize this variable asmuch as possible to prevent energy loss in the form of heat generation. The purpose of this project is to conduct a comparative literature study of different weldingtechniques for welding batteries. The compared techniques are resistance spot welding, laser beamwelding and ultrasonic welding. The performance was evaluated in terms of numerous factors such asproduction cost, degree of automation and weld quality. All three methods are tried and proven to function in the production of battery applications. Eachmethod has separate strengths and limitations which makes them complement each other. Thus, it isimportant to look at several factors when deciding which welding technique is the most suitable forthe desired application. The scale of production, economical aspects as well as battery cell geometrywere concluded to be the most important in making this decision.