Different problems arise from choice of setting technological parameters during welding of alluminium alloys. Choice of welding method, welding speed and material influence mechanical properties of welds. During welding of alluminium alloys come difficulties due to oxidation of thin surface layer of material. One of ways how to overcome this obtacle is to use hybrid laser-TIG welding method. In this diploma thesis is described influence of welding processes on mechanical properties of two alluminium alloys(EN AW-5754 H22, EN AW-6082 T6) and change in their microstructure during welding.

The master thesis summarizes the critical situation of the lack of a cobalt used in different industry branches. Due to its increasing price, it will not be possible to use in existing applications. One of these applications is production of cobalt alloys where the replacement of this element is impossible. This type of material keeps mechanical properties at high temperature. However, a suitable choice of technology can achieve at least its savings. In the field of welding, the alloys are joined without any use of an additional material. The possible solution could be the use of hybrid technologies or electron beam. Verification of weldability of both methods was realised in experimental parts and evaluated by destructive methods. The investigation was performed on wear resistant alloy Stellite 6B.

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.

Scania Ferruform AB is an independent affiliate of the truck- and bus manufacturer Scania AB which produces rear axle housings among other chassis components for said vehicles. The banjo part, i.e. the base of the rear axle housings undergoes processes which have issues both in terms of exceeded technical life span and insufficient production capacity. These three processes consist of both milling and welding operations. In order to resolve these issues the discussion of future investments arise. As this is discussed, the question whether alternative technologies could be of interest, specifically the performance of welding- and cutting operations with the use of laser technologies. By reviewing state-of-the-art literature, studying the present production conditions and interviewing experts within academia as well as parties active in developing and supplying industrial laser systems it has been shown that a laser arc hybrid welding technique would be the most suitable replacement, while laser nitrogen cutting would be the most suitable cutting technique. This project presents the theoretical outcome of implementing laser arc hybrid welding as a replacement to the present and conventional gas metal arc welding, as well as the possibility of using laser nitrogen cutting as a replacement to a set of milling processes. The study has shown that by implementing these technologies in a manner which also alters the balance in performed operations achieves a cycle time below the future goal for each production section. Cycle time values, quantities and costs are expressed with an indexed value of t, n and k respectively due to confidentiality. The first investment scenario results in an annual saving of consumption costs by 4 738k SEK, with a total investment cost of 112 743k SEK and 6,9 years pay-off time. The second scenario results in an annual saving of consumption costs by 5 018k SEK, with a total investment cost of 114 843k SEK and 5,2 years pay-off time. The third scenario is similar to the second in terms of the manufacturing processes, but it is the alternative of the lowest investment cost. This scenario would result in the same sum of annual savings as the second scenario, but with an investment cost of 89 843k SEK and 0,2 years pay-off time.

Ces travaux présentent une recherche sur la physique du soudage hybride. La revue littéraire décrit les principaux processus physiques se produisant au cours de la combinaison Laser-arc, les principales réalisations et les problèmes rencontrés lors de l'analyse de ces processus. Les processus ont été étudiés pendant l'assemblage de matériaux de fortes épaisseurs. Deux configurations ont été utilisées. La première est le soudage d’un acier Superduplex en un seul passage, par Laser et arc distanciés. La seconde configuration est le soudage multipasse de l'acier 18MND5, où le faisceau Laser défocalisé intercepte le plasma d'arc électrique. Avec l'aide de la planification d'expérience, l'imagerie vidéo rapide, l'enregistrement des signaux électriques, la détermination de la température et des distorsions de l’assemblage ont permis d’expliquer le rôle de chaque source thermique et l'influence de leur combinaison sur la création du bain fondu, l'identification du mode de transfert métallique et la répartition de la chaleur dans la plaque soudée. Les relations entre les signaux électriques et la géométrie de l'arc, les dimensions du bain et la distribution de chaleur sont analysées à différentes échelles de temps. L'analyse thermique présentée montre que l'hypothèse de stationnarité, qui est largement utilisé par les simulateurs, est vraie seulement sur une courte période et pour une longueur donnée de soudure. L’analyse macrographique montre, quant à elle, l'effet de la variation des paramètres d'entrée sur la structure et la géométrie de la soudure. / An investigation on hybrid welding physics is presented in the current work. A literature review describes main physical processes occurring during Laser-arc combination and shows main achievements and problematics met during process analysis. Physical processes were studied during joining of very thick materials. Two configurations were used. The first configuration is welding of Superduplex steel in one pass by Laser and arc that are far apart. The second configuration is multipass welding of 18MND5 steel, where defocused Laser beam intercepts arc plasma. With a help of experiment’s design, fast video imaging, electric signals recording, determination of temperature and workpiece distortion, were explained the role of each thermal source and influence of their combination on arc behaviour, molten pool creation, metallic drop transfer evaluation and heat distribution into welded plates. The relationships between electric signals and arc geometry, bath dimensions and heat distribution have been analyzed at various time scales. Thermal analysis, presented in this work, shows that hypothesis of stationarity, which is commonly used in numerical modelling, is true only during a short welding period and for a given weld length. Macrographic analysis shows effect of input parameters variation on weld’s structure and geometry.