Friction stir welding
[13] The probe is slightly shorter than the weld depth required, with the tool shoulder riding atop the work surface.
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.
[16] The solid-state nature of the FSW process, combined with its unusual tool shape and asymmetric speed profile, results in a highly characteristic micro-structure.
The micro-structure can be broken up into the following zones: The solid-state nature of FSW leads to several advantages over fusion welding methods, as problems associated with cooling from the liquid phase are avoided.
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.
Hot-worked tool steel such as AISI H13 has proven perfectly acceptable for welding aluminium alloys within thickness ranges of 0.5–50 mm [23] but more advanced tool materials are necessary for more demanding applications such as highly abrasive metal matrix composites[24] or higher-melting-point materials such as steel or titanium.
An example is the "whorl" design that uses a tapered pin with re-entrant features or a variable-pitch thread to improve the downwards flow of material.
The Triflute design has a complex system of three tapering, threaded re-entrant flutes that appear to increase material movement around the tool.
The Triflute tool uses an alternative system with a series of concentric grooves machined into the surface, which are intended to produce additional movement of material in the upper layers of the weld.
Work is continuing to better understand the effects of tool material's composition, structure, properties and geometry on their performance, durability and cost.
On the other hand, an excessive plunge depth may result in the pin rubbing on the backing plate surface or a significant undermatch of the weld thickness compared to the base material.
The researchers used a combination of thin copper strip inserts and a "frozen pin" technique, where the tool is rapidly stopped in place.
Detailed material flow field during friction stir welding can also be calculated from theoretical considerations based on fundamental scientific principles.
Calculation of material flow fields in friction stir welding can be undertaken both using comprehensive numerical simulations[34][35][36] or simple but insightful analytical equations.
[37] The comprehensive models for the calculation of material flow fields also provide important information such as geometry of the stir zone and the torque on the tool.
[42] The heat generation is often assumed to occur predominantly under the shoulder, due to its greater surface area, and to be equal to the power required to overcome the contact forces between the tool and the workpiece.
A major difficulty in applying these equations is determining suitable values for the friction coefficient or the interfacial shear stress.
In 1997 two-dimensional friction stir welds in the hydrodynamically flared bow section of the hull of the ocean viewer vessel The Boss were produced at Research Foundation Institute with the first portable FSW machine.
[citation needed] The Sea Fighter of Nichols Bros and the Freedom-class Littoral Combat Ships contain prefabricated panels by the FSW fabricators Advanced Technology and Friction Stir Link, Inc.
[56] BRÖTJE-Automation uses friction stir welding for gantry production machines developed for the aerospace sector, as well as other industrial applications.
[58] In Japan FSW is applied to suspension struts at Showa Denko and for joining of aluminium sheets to galvanized steel brackets for the boot (trunk) lid of the Mazda MX-5.
Friction stir spot welding is successfully used for the bonnet (hood) and rear doors of the Mazda RX-8 and the boot lid of the Toyota Prius.
[59] Rear seats for the Volvo V70 are friction stir welded at Sapa, HVAC pistons at Halla Climate Control and exhaust gas recirculation coolers at Pierburg.
[citation needed] The front subframe of the 2013 Honda Accord was friction stir welded to join aluminum and steel halves.
[failed verification][63] Japanese commuter and express A-trains,[64] and British Rail Class 395 trains are friction stir welded by Hitachi,[65] while Kawasaki applies friction stir spot welding to roof panels and Sumitomo Light Metal produces Shinkansen floor panels.
Bizerba meat slicers, Ökolüfter HVAC units and Siemens X-ray vacuum vessels are friction stir welded at Riftec.
[68][69] Pressure vessels from ø1 m semispherical forgings of 38.1 mm thick aluminium alloy 2219 at Advanced Joining Technologies and Lawrence Livermore Nat Lab.
