The aims of this project are to present an understanding in what happens when aluminium-(Al) alloys are welded, and to investigate how the Mg-, Si- and Cr-contents in AA6005A influence the weld strength and cracking susceptibility. It is known that heat from welding affects the mechanical properties (strength) of the material. Different heat cycles during welding are one of the main reasons that the strength varies. Welding can cause various phenomena such as decreased strength, porosity, deformation, cracks and corrosion. To minimize these phenomena one has to have a balance between the welding parameters, alloy composition and welding fixture setup. Al alloys are sensitive to heat from welding because they have high heat conductivity and high thermal expansion coefficient. They also deform easily when the material is heated locally. If the material is deformed too much then cracking easily occurs. This project has examined how the Mg-, Si- and Cr-contents in AA6005A, affect the welded material. A V-joint with MIG welding is used for producing weld samples. For evaluation Vickers micro-hardness, tensile testing, radiography (X-ray), LOM and SEM with EBSD and EDS was used. The evaluation focuses on mechanical properties and microstructure. The results show that small variations of Mg-, Si- and Cr-content do not have any clear effects on the welded material. The results from tensile testing show that all samples have failed in the heat affected zone (HAZ). The tensile strength of all samples are higher than standard but the yield strength are lower than standard (EN ISO 10042:2005). The lowering in hardness and tensile strength in the HAZ are believed to be a result from beta-phase (AlFeSi), lead to transformation and coarsening of the strengthening and metastable precipitate. The HAZ is wide, ranging about 20 mm from the fusion line in 5 mm thick plate. The microstructure evaluation has shown that the grain size in the HAZ has been influenced while welding.  The EDS analysis shows that a small amount of AlFeSi particles occur in the base material and HAZ but not in the weld seam. Future research is suggested to focus on understanding more about ageing, coarsening of beta-phase and precipitation of intermetallic phases.

We investigate the post-weld-shift(PWS) induced fiber alignment shift in butterfly laser packaging. For high-speed laser modules in lightwave communication systems, the butterfly laser modules are widely used. When laser welding is applied to assemble a butterfly package, it is usually necessary to have mechanical elements such as substrates, fiber ferrule, and clip of house materials to facilitate fiber handing and retention within the package. However, during the process, rapid solidification of the welded region and associated material shrinkage often cause a post-weld-shift between welded components. The PWS significantly affects the package yield. A novel measurement and compensation technique employing a high-magnification camera with image capturing system (HMCICS) to probe the post-weld-shift (PWS) induced fiber alignment shifts in high-performance butterfly-type laser module packages is studied. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded butterfly-type laser module packaging can be quantitatively determined and then compensated. The increased coupling efficiency after this PWS compensation was from 3% to 10%. This HMCICS technique has provided an important tool for quantitative measurement and compensation to the effect of the PWS on the fiber alignment shifts in laser module packages. Therefore, the reliable butterfly-type laser modules with a high yield and a high performance used in lightwave transmission systems can be developed.

In this study, shapes of the molten region and transport processes affected by thermocapillary convection in melting or welding pool irradiated by a low-power-density beam are determined from a scale analysis. A low-power-density-beam heating implies no deep and narrow cavity or keyhole taking place in the pool. In this work, the complicated flow pattern in the pool is influenced by an unknown shape of solid-liquid interface, and interactions between the free surface layer, corner regions, and boundary layer with phase transition on the solid-liquid interface. Since Prandtl number is much less than unity while Marangoni and Reynolds number can be more than in melting metals, an appropriate scaling mass, momentum, and energy transport subject to a force balance between viscous stress and surface tension gradient on the free surface account for distinct thermal and viscous boundary layers in these regions of different length, velocity, and temperature scales. The results find that shapes of the fusion zone, free surface velocity and temperature profiles are determined by Marangoni, 104 i Prandtl, beam power, Peclet, and Biot numbers, and solid-to-liquid thermal conductivity ratio. The predications agree with numerical computations.

In this study, shapes of the molten region and transport processes affected by thermocapillary convection in melting or welding pool irradiated by a low-power-density beam are determined from a scale analysis for the first time. A low-power-density-beam heating implies no deep and narrow cavity or keyhole taking place in the pool. A quantitative determination of the fusion zone shape is crucial due to its close relationship with the strength, microstructure, and mechanical properties of the fusion zone. In this work, the complicated flow pattern in the pool is influenced by an unknown shape of solid-liquid interface, and interactions between the free surface layer, corner regions, and boundary layer with phase transition on the solid-liquid interface. Since Prandtl number is much less than unity while Marangoni and Reynolds number can be more than in melting metals, an appropriate scaling mass, momentum, and energy transport subject to a force balance between viscous stress and surface tension gradient on the free surface account for distinct thermal and viscous boundary layers in these regions of different length, velocity, and temperature scales. The results find that shapes of the fusion zone, free surface velocity and temperature profiles are determined by Marangoni, Prandtl, beam power, Peclet, and Biot numbers, and solid-to-liquid thermal conductivity ratio. The predications agree with numerical computations.

A notch clip approach to compensate post-weld-shift(PWS) induced by laser welding process in butterfly type laser module packages is investigated. For high-speed laser modules in lightwave communication systems, the butterfly laser modules are widely used. When laser welding is applied to assemble a butterfly package, it is usually necessary to have mechanical elements such as substrates, fiber ferrule, and clip of house materials to facilitate fiber handing and retention within the package. However, during the laser welding process, rapid solidification of the welded region and associated material shrinkage often cause a post-weld-shift between welded components. The PWS significantly affects the package yield. A notch clip approach and measurements employing a high-magnification camera with image capturing system (HMCICS) to probe the PWS induced fiber alignment shifts and welding compensation on notch in high-performance butterfly-type laser module packages are studied. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded butterfly-type laser module packaging can be quantitatively determined and then compensated. The overall coupling efficiency after this PWS compensation was from 80¢H to 90¢H. This notch approach and HMCICS technique have provided an important tool for quantitative measurement and compensation to the effect of the PWS on the fiber alignment shifts in laser module packages. Therefore, the reliable butterfly-type laser modules with a high yield and a high performance used in lightwave transmission systems can be developed.

Volvo Construction Equipment with headquarters in Eskilstuna is the world's oldest and one of the leading companies in the construction industry with products such articulated haulers, wheel loaders, excavators and skid steer loaders. The main purpose of this study is to create a tool for predicting the production cost of welded structures for the company's articulated haulers, which today is world leading on the market. To succeed, the study has been broken down in three problem areas in which the first one is to completely map out today's manufacturing process of the six basic components of the articulated hauler model A40 (A-Stay front, A-Stay rear, short and long rods and front and rear frame) for both manual and robotic welding. Account is taken to each weld in the manufacturing process and all costs incurred. Various types of welding measurements such as thread consumption for both manual and robotic welding, weld length for both manual and robotic welding is taken account to. The weld metal weight, arc time, robot degree length, deposition rate, price per meter, price per kilo and the total cost for each component has been measured and calculated. Next problem area starts from the identification of the manufacturing process and the purpose is to identify the largest cost culprits to lower manufacturing process costs and making the manufacturing process more efficient. As regards the third and final problem area on basis of the results from the two past problem areas regression is used to generate a mathematical formula that is used to predict the production of welded components for the company's articulated haulers. The final tool that is sought was created in form of a software by embedding the mathematical formula obtained from the regression. Now one can easily predict the production cost of welded structures by using the following tool. The only thing you need to do to predict any production cost of a welded structure is to enter the drawing welding weight, item weight, average welding length, proportion of butt weld percentage and the butt weld length for manual and robot welding. / Volvo Construction Equipment med huvudkontor i Eskilstuna är världens äldsta och en av världens ledande företag vad gäller anläggningsmaskiner som exempelvis dumprar, hjullastare, grävmaskiner och kompaktlastare. Syftet med detta arbete är att skapa ett verktyg för att kunna förutse produktionskostnaden för svetsade komponenter för företagets ramstyrda dumprar som idag är världsledande i sin klass. För att lyckas med projektet har man brutit ner syftet i tre problemområden där man först och främst kartlägger hela dagens tillverkningsprocess av de sex grundläggande delarna för dumpermodellen A40 (A-stag, Vågbalk, kort och långt stag samt fram och bakram) för både manuell och robot svetsning. Hänsyn tas till varje svets i tillverkningen och alla kostnader som uppstår. Man utför även olika typer av svetsmätningar som exempelvis trådförbrukning och total svetslängd för både manuell och robotsvetsning. Man beräknar även svetsgodsvikten, bågtidsfaktorn, robotgradlängden, insvetstalet, pris per meter, pris per kilo och totalkostnaden för varje objekt. Vid nästa steg utgår man från kartläggningen av tillverkningsprocessen och man identifierar de största kostnadsbovarna med syfte att sänka tillverkningskostnaderna och göra tillverkningen mer effektiv. Vad gäller tredje och sista steget med utgångspunkt från tidigare resultaten använder man regression för att generera en matematisk formel som man använder för att kunna förutse produktionskostnaden för svetsade komponenter för företagets ramstyrda dumprar. Det slutgiltiga verktyget som eftersöks skapades i form av en mjukvara för datorer genom att bädda in den matematiska formeln man erhöll från regressionen som bygger på resultaten av kartläggningarna. Nu kan man enkelt förutse produktionskostnaden av svetsade komponenter. Det enda man behöver göra för att förutsäga någon produktionskostnad av en svetsad komponent är att mata in ritningens svetsvikt, objektvikt, medelsvetslängd, andelen stumsvets i procent samt längden manuell och robot stum svets för den komponenten man vill förutsäga priset på. Nyckelord: Svetsgodsvikt, Svetsekonomi, Regression.

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Stålindustrin står för 7 % av världens koldioxidutsläpp. För att minska industrins miljöpåverkan är ett alternativ att introducera konstruktioner i höghållfasta stål eftersom det ger möjlighet till slankare konstruktioner och därmed mindre materialåtgång. Användning av höghållfasta stål i svetsade konstruktioner kan dock vara problematiskt då de utsätts för utmattningslaster vilket kan leda till oanade brott i konstruktionen. För att förbättra svetsade konstruktioner mot utmattning kan PWT tillämpas.I arbetet undersöktes möjligheterna till implementering av PWT i tillverkningsstadiet samt eventuella hinder till varför metoden inte används. För att bilda en uppfattning om möjligheten till alternativa metoder för att öka utmattningshållfastheten för en svets har gällande myndighetskrav samt normer för utförande av vanliga svetsar undersökts. Genom intervjuer har åsikter från olika aktörer inhämtats för att besvara frågeställningarna.Efter genomförd undersökning konstaterades att den bristande förmågan att kontrollera spänningar i en svets är en bidragande faktor till varför PWT i dagsläget inte används i tillverkningsstadiet inom byggbranschen. Intervjun med Trafikverket resulterade i alternativet att ta fram en särskild kravspecifikation enligt Krav Brobyggande, som vid godkännande skapar möjlighet för implementering av PWT. Krav Brobyggande är Trafikverkets dokument men krav och råd för brobyggande i Sverige. / The steel industry stands for 7 % of the worlds emission of carbon dioxide. An alternative to reduce the environmental impact of the industry is to introduce structures of high strength steel since it provides opportunity for slimmer structures and thereby less material consumption. However, the use of high strength steel in welded structures can be problematic when exposed to fatigue loads, which can lead to unsuspected breaks in the structure. To improve welded structures against fatigue PWT can be implemented.The possibilities for implementation of PWT during manufacturing and possible obstacles as to why it should not be used was investigated in this thesis. To form a perception for the possibilities of alternative welding methods to increase fatigue strength the existing regulations and norms of execution for as welded conditions was examined. Opinions from different participants in the construction process were interviewed to answer the questions at issue.The lacking ability to verify stress in a weld was concluded to be a contributing factor as to why PWT is not currently used during the manufacturing process in the construction industry. The interview with Trafikverket resulted in the alternative to create a specific requirement specification according to demands in Krav Brobyggande. Approval of the specific requirement specification could lead to possibility to implement PWT in the construction industry. Krav Brobyggande is Trafikverkets document with demands and advice for bridge construction in Sweden.

<p>Complete Joint Penetration (CJP) welds are commonly used in many industries such as structural steel-fabrication, pressure vessels, pipelines, nuclear industries, etc. However, CJP weld could be susceptible to defects such as lack of fusion, slag, porosity, etc. The 1994 Northridge earthquake and the 1995 Kobe earthquake revealed that there was a significant loss in the ductility of CJP welded connections due to the presence of defects. There are very limited experimental and numerical studies available to understand the overall behavior and strength of CJP welded connection in the presence of defect. This study aims to bridge this gap. The objective of this study is to understand the influence of defects on ultimate strength and ductility of the CJP welded connection. To achieve this objective, a total of twelve specimens were tested, out of which four specimens were without any defect, while eight specimens had defects in the weld. A process was developed to introduce defects in the CJP weld specimens. A simplified lower bound approach using ductile damage criteria was proposed based on benchmarked finite element models to simulate the weld fracture. Moreover, a parametric study was performed to understand the effects of various parameters such as length and depth of defect, failure criteria, etc. on behavior and ductility of the welded connections. It was found that the welded specimens having no defect were able to reach the ultimate strength and ductility of the base metal. Whereas loss in ductility and strength was observed in the specimens with defects. The loss in ductility as compared to base metal ranges from 30% to 88% for different specimens. The maximum loss in strength was observed to be 12% only for specimens with the worst defect. The study concluded that the depth of defect had significant influence over ductility as compared to length of defect. If the depth of defect (d) is greater than half of plate thickness (d > t/2), it exhibits similar behavior regardless of actual depth. However, no significant influence of defect was observed if the depth of defect was less than t/8.</p>