Improvement of Welding Rate in Aluminum Alloy Using Friction Stir Welding with Heating
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The Friction Stir Welding (FSW) with heating of A5052-H34 aluminum alloy, which is a narrow welding condition material in FSW, was conducted to clarify the improvement of welding rate by heating effect. At first, the FSW with heating on temperatures of 150 and 300°C was examined at welding rates of 600 to 900mm/min. And the joint integrity was evaluated by observation of appearances of welded part and its cross section. Good joints in FSW with heating were obtained at welding rate up to 700mm/min for heating of 150°C, and up to 900mm/min for heating of 300°C. In addition, the hardness profile and tensile strength of joints by FSW with heating showed a good level as much as non-heating one with low welding rate. As the result, welding rate in FSW with heating could expand a conventional welding rate. Therefore, the improvement of welding rate in FSW with heating clarified would be feasible.Keywords:
Friction Stir Welding
Cold welding
Friction Welding
For CO2 laser welding of large output, when a deep penetration welding in single pass is done in the ambient atmosphere, it is known that blowholes may occur because of the in-keyhole gas being entrapped in molten metal. Keeping this problem in mind and changing the parameters, we conducted welding tests with full-penetration bead-on-plate welding, and checked by radiographic test for welding defects.The experimental results demonstrated that the larger is the specimen thickness, the more frequently occur welding defects, and that generation of welding defects depends upon the amount of welding heat input.Welding defects such as blowholes remain in metal, because the gas once entrapped into keyhole floats up in molten metal, and it is enclosed in the course of solidification. From this, we can verify the theory that a larger welding heat input, in the case of the full-penetration bead-on-plate welding, may be favorable for preventing welding blowholes. It can be assumed, therefore, that a larger heat input may hinder cooling of molten metal, and need a longer time for metal solidification; in this longer span of time, in-molten metal gas may escape while the metal is sufficiently heated.
Keyhole
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Cold welding
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Spot welding
Cold welding
Electrogas welding
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Upset welding
Flash welding
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In order to avoid splash when large amount of heat of resistance spot welding is input for hot stamping high strength steel and meet the strict requirements for assembly under laser spot welding,a new welding process that is combination of resistance spot welding and laser spot welding is proposed.The welding joints were obtained through the combination of resistance and laser spot welding process.The microstructures of various regions for welding joints were analyzed with scanning electron microscopy.The micro-hardness distribution of welding joints was tested by micro-hardness testing.The mechanical properties of welded joints under different welding process were obtained by using universal tensile machine,and the fracture mode and fracture mechanism were analyzed.The results show that the welding area under process of combination of resistance and laser spot welding is composed of resistance welding zone and laser welding zone.The microstructure of laser nugget zone and base metal are lath martensite.The heat affected zone locates outside of laser ring and near the base metal,and the nug-get of original resistance spot welding are tempering organization.The hardness of laser nugget zone is the same as that of base metal,and the hardness of softening zone corresponding to the tempering zone decreases to 60% of that of base metal.The softening zone outside of laser ring is the weak region for tensileshear fracture.The obtained welding joints by this combination process have better load carrying capacity and toughness than those by individual resistance spot welding or laser welding.
Spot welding
Tempering
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For the demand of low heat input,high quality welding technology,the repair welding experiment using CMT welding technology have been examined in thick aluminum alloy plate welding. The multiple repair welding was performed for hot cracking test in thick aluminum alloy plate. The results have shown that the hot crack susceptibility of CMT welding is lower than the pulsed MIG welding process. The test showed that CMT welding temperature field was lower,and the microstructure of welding joint was improved significantly compared to the joint welded bypulse MIG welding.
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For several decades friction welding technology has found broad application in many fields of the metal and plastic connection industry. The fabricated joints are laminar or punctiform depending upon the shape of the parts to be welded. The work presented here deals with the application of this technology to wood connection. Its application to the material wood is still very young and the process is to a large extent unexplored. The type of connections investigated in this study is of laminar shape. The wood in the contact zone is heated by means of frictional energy. This causes a thermal alteration of the wood cell structure, which leads to the formation of a viscous layer. After cooling, the material in this layer forms the connection. The welding machine used for these investigations applies a circular movement to the parts to be welded. Within the scope of the work presented here the behaviour of the material during the welding process is examined. Measurement of the frictional force and interfacial temperature during the welding process shows that this process bears distinct resemblance to friction welding of metals and thermoplastic synthetics. As with metals and plastics, this process can be divided into different phases by means of measuring the frictional force. These phases reflect the particular states of the interface (dry friction, transition phase, viscous state). The influences of the machine settings, welding frequency and welding pressure, on the process cycle are examined by means of the friction force and the interfacial temperature as a function of welding time and welding displacement. To investigate the influence of the annual rings and their orientation these investigations are carried out for samples with different cut direction. Welding frequency and welding pressure affect the welding duration as well as the friction force in a distinct manner. The results show that circular friction welding is influenced by the orientation of annual rings in a significant way. The moisture content of the material is part of the investigations as well. Its influence on the behaviour of the material and the resistance of the connection is of substantial importance. This result arises from investigations on test pieces welded with different moisture contents. In accordance with the experiments carried out, the atmosphere of the welding environment (ambient air, argon atmosphere) seems to be not very important with regard to the process flow. Investigations concerning the evolution of the interfacial resistance showed that the welded connections do not meet the resistance achievable by conventional glues. However, the relatively high initial resistance permits a continuous welding of multilayered laminates. The initial strength of the newly formed connection clearly exceeds the load applied by the newly introduced vibration. Therefore the existing joint is not damaged by welding of an additional layer. Microscopic examinations reveal that the cell structure at the contact layer is completely destroyed. It becomes apparent that the decomposed wood forms a viscous layer during the welding process. This layer encloses the adjacent cell structure, embeds the cell walls, and contributes in this manner to the adhesion. Thermal degradation of the adjacent cell structure occurs only within a thin layer close to the contact zone. This is due to the good insulation properties of wood. The thermal influence becomes evident by a visible dark discoloration of the cell structure. The joint consists of a consolidated mass of thermally-altered wood decomposition products. This is also reflected in the results of chemical analyses carried out within the scope of this research. This study shows that the main components of wood (cellulose, polyoses and lignin) experience a thermal degradation. Within the material, which forms the interfacial layer the cellulose was detected to remain in a relatively high proportion. Due to its predominantly crystalline structure the cellulose behaves in a thermally relatively stable manner. Polyoses are thermally significantly less stable. Compared with thermally unchanged spruce wood, polyoses remain only in a small percentage in the joint substance. The molecular structure of lignin, the third chemical compound, experiences distinct changes. However, its total mass stays relatively stable. The investigations indicate reactions between the decomposition products of polyoses and cellulose and the thermally altered units of lignin, which could lead to a cross-linking of the joint material and thus contribute to cohesion. Advantages of this technology are seen particularly in the rapidity of the joint formation. In addition, wooden compounds, which are fabricated by this method consist of natural wood and thermally altered wood only. Compared to glued compounds where the adhesives usually contain solvents, this leads to advantages with regard to environmental compatibility. With respect to machining, welded connections offer advantages when compared to traditional methods used for wood connection. Disadvantages result from the resistance of the joint, which is significantly less stable than the resistance of most conventional glues. One application of this new method is seen in the fabrication of solid wood elements with rather small stress loads at the interface.
Friction Welding
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Friction Stir Welding is a novel green solid state joining process particularly used to join high strength aerospace aluminum alloys which are otherwise difficult to weld by conventional fusion welding. Unlike other solid state joining technique, in Friction stir welding a third body contact by tool will generate the additional interface surfaces and finally all the surfaces are coalesced with each other by applied pressure and temperature and form solid state weld. This review paper addresses the overview of Friction stir welding which includes the basic concept of the process, microstructure formation, influencing process parameters, typical defects in FSW process and some recent applications. The paper will also discuss some of the process variants of FSW such as Friction Stir Processing, Friction Welding processes
Friction Stir Welding
Fusion welding
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For CO2 laser welding of large output, when a deep penetration welding in single pass is done in the ambient atmosphere, it is known that blowholes may occur because of the in-keyhole gas being entrapped in molten metal. Keeping this problem in mind and changing the parameters, we conducted welding tests with full-penetration bead-on-plate welding, and checked by radiographic test for welding defects. The experimental results demonstrated that the larger the specimen thickness, the more frequently welding defects occur, and that generation of welding defects depends upon the amount of welding heat input. Welding defects such as blowholes remain in metal, because the gas once entrapped into keyhole floats up in molten metal, and it is enclosed in the course of solidification. From this, we can verify the theory that a larger welding heat input, in the case of the good appearance full-penetration bead-on-plate welding, may be favorable for preventing welding blowholes. It can be assumed, therefore, that a larger heat input may hinder cooling of molten metal, and need a longer time for metal solidification; in this longer span of time, in-molten metal gas may escape while the metal is sufficiently heated.
Keyhole
Cold welding
Penetration (warfare)
Plastic welding
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Abstract With the rapid development in the technological, industrial, and defense industries, the joining of metallic materials used becomes very important. Various problems may arise in metallic materials joined by traditional fusion welding methods. The friction welding technique, which is one of the solid-state welding types that contains minimum welding defects and creates minimum internal stresses after welding, can be used in order to reduce the negativities in different steel joining. Thus, the negativities in fusion welding methods are reduced. The friction welding is a plastic deformation and extrusion process that uses heat to convert mechanical energy generated by friction between the interfaces of these two material pairs as a result of one material rotating at a stationary speed and the other rotating at a rotary speed into thermal energy. The heating phase (friction phase) is the time until the end of the welding process. During this time, the surfaces are under pressure. The formation of temperature in steel is between 900 and 1300 °C, and this temperature is reached in a very short time. Thus, parts are joined together by the pressing force. Materials that are very difficult to join with fusion welding can be joined more easily by friction welding.
Fusion welding
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