Friction stir welding Wikipedia. Close up view of a friction stir weld tack tool. The bulkhead and nosecone of the Orion spacecraft are joined using friction stir welding. Issuu is a digital publishing platform that makes it simple to publish magazines, catalogs, newspapers, books, and more online. Easily share your publications and get. Friction stir welding FSW is a solid state joining process that uses a non consumable tool to join two facing workpieces without melting the workpiece material. 1 Heat is generated by friction between the rotating tool and the workpiece material, which leads to a softened region near the FSW tool. While the tool is traversed along the joint line, it mechanically intermixes the two pieces of metal, and forges the hot and softened metal by the mechanical pressure, which is applied by the tool, much like joining clay, or dough. 1 It is primarily used on wrought or extruded aluminium and particularly for structures which need very high weld strength. FSW is also found in modern shipbuilding, trains, and aerospace applications. 234567It was invented and experimentally proven at The Welding Institute TWI in the UK in December 1. TWI held patents on the process, the first being the most descriptive. 8Principle of operationedit. Schematic diagram of the FSW process A Two discrete metal workpieces butted together, along with the tool with a probe. B The progress of the tool through the joint, also showing the weld zone and the region affected by the tool shoulder. A rotating cylindrical tool with a profiled probe is fed into a butt joint between two clamped workpieces, until the shoulder, which has a larger diameter than the pin, touches the surface of the workpieces. Supplier of a curated selection of natural stone, porcelain tile, and engineered stone for architects, designers, developers, contractors homeowners. InspectionNon Destructive Testing. This document provides detailed and specific guidance on inspection and NonDestructive Testing NDT in support of the Level 2. The probe is slightly shorter than the weld depth required, with the tool shoulder riding atop the work surface. 9 After a short dwell time, the tool is moved forward along the joint line at the pre set welding speed. Frictional heat is generated between the wear resistant tool and the work pieces. This heat, along with that generated by the mechanical mixing process and the adiabatic heat within the material, cause the stirred materials to soften without melting. As the tool is moved forward, a special profile on the probe forces plasticised material from the leading face to the rear, where the high forces assist in a forged consolidation of the weld. This process of the tool traversing along the weld line in a plasticised tubular shaft of metal results in severe solid state deformation involving dynamic recrystallization of the base material. 1. Microstructural featureseditThe solid state nature of the FSW process, combined with its unusual tool shape and asymmetric speed profile, results in a highly characteristic microstructure. The microstructure can be broken up into the following zones The stir zone also nugget, dynamically recrystallised zone is a region of heavily deformed material that roughly corresponds to the location of the pin during welding. The grains within the stir zone are roughly equiaxed and often an order of magnitude smaller than the grains in the parent material. 1. A unique feature of the stir zone is the common occurrence of several concentric rings which has been referred to as an onion ring structure. 1. The precise origin of these rings has not been firmly established, although variations in particle number density, grain size and texture have all been suggested. The flow arm zone is on the upper surface of the weld and consists of material that is dragged by the shoulder from the retreating side of the weld, around the rear of the tool, and deposited on the advancing side. citation neededThe thermo mechanically affected zone TMAZ occurs on either side of the stir zone. In this region the strain and temperature are lower and the effect of welding on the microstructure is correspondingly smaller. Unlike the stir zone the microstructure is recognizably that of the parent material, albeit significantly deformed and rotated. Although the term TMAZ technically refers to the entire deformed region it is often used to describe any region not already covered by the terms stir zone and flow arm. citation neededThe heat affected zone HAZ is common to all welding processes. As indicated by the name, this region is subjected to a thermal cycle but is not deformed during welding. The temperatures are lower than those in the TMAZ but may still have a significant effect if the microstructure is thermally unstable. In fact, in age hardened aluminium alloys this region commonly exhibits the poorest mechanical properties. 1. Advantages and limitationseditThe solid state nature of FSW leads to several advantages over fusion welding methods as problems associated with cooling from the liquid phase are avoided. Issues such as porosity, solute redistribution, solidification cracking and liquation cracking do not arise during FSW. In general, FSW has been found to produce a low concentration of defects and is very tolerant of variations in parameters and materials. Nevertheless, FSW is associated with a number of unique defects, if it isnt done properly. Insufficient weld temperatures, due to low rotational speeds or high traverse speeds, for example, mean that the weld material is unable to accommodate the extensive deformation during welding. This may result in long, tunnel like defects running along the weld which may occur on the surface or subsurface. Low temperatures may also limit the forging action of the tool and so reduce the continuity of the bond between the material from each side of the weld. The light contact between the material has given rise to the name kissing bond. This defect is particularly worrying since it is very difficult to detect using nondestructive methods such as X ray or ultrasonic testing. If the pin is not long enough or the tool rises out of the plate then the interface at the bottom of the weld may not be disrupted and forged by the tool, resulting in a lack of penetration defect. This is essentially a notch in the material which can be a potential source of fatigue cracks. A number of potential advantages of FSW over conventional fusion welding processes have been identified 1. Good mechanical properties in the as welded condition. Improved safety due to the absence of toxic fumes or the spatter of molten material. No consumables  A threaded pin made of conventional tool steel, e. H1. 3, can weld over 1 km 0. Easily automated on simple milling machines  lower setup costs and less training. Can operate in all positions horizontal, vertical, etc., as there is no weld pool. Generally good weld appearance and minimal thickness underover matching, thus reducing the need for expensive machining after welding. Can use thinner materials with same joint strength. Low environmental impact. General performance and cost benefits from switching from fusion to friction. However, some disadvantages of the process have been identified Exit hole left when tool is withdrawn. Large down forces required with heavy duty clamping necessary to hold the plates together. Less flexible than manual and arc processes difficulties with thickness variations and non linear welds. Often slower traverse rate than some fusion welding techniques, although this may be offset if fewer welding passes are required. Important welding parameterseditTool designedit. Advanced friction stir welding and processing tools by Mega. Stir shown upside down. The design of the tool1. It is desirable that the tool material be sufficiently strong, tough, and hard wearing at the welding temperature.