The following acronyms are used in various publications on friction stir welding and its variants. Some of them have a double-meaning:
FSC — Friction Stir Channeling: (a) Specifications on probe thread profile for FSC of a AA5083-H111 plate (dimensions in mm); (b) The assembled FSC-tool with shoulder and probe; (c) Clamping jig used for the making FSC samples in the laboratory
Friction Stir Channelling (FSC) is a solution for producing internal closed channels along a desired path with a constant or continuously modified shape along the path in a single manufacturing step. The channels are formed by continuous extraction of part of the plasticised workpiece material into the external flash.
FSC — Friction Stir Channeling: Macrograph of the cross-section of the channel with the metallurgical zones of interest: 1—top corner of retreating side, 2—middle part of the ceiling, 3—top corner of the advancing side, 4—bottom corner of the advancing side, 5—middle part of the bottom and 6- bottom corner of the retreating side
FSE — Friction Stir Extrusion of ultra-thin wall biodegradable magnesium alloy tubes
Friction stir extrusion (FSE) was used in 2020/21 to produce thin-walled biodegradable tubes, which corrode from the outside after being implanted into the body of a human or animal. Biodegradable tubular structures such as stents are routinely deployed for various short-term medical interventions. The biodegradability can eliminate the need for secondary procedures associated with conventional stents.
The coronary stents manufacture require defect-free, high-quality tubes with thin walls (0.1 mm – 1 mm) as a precursor. Fully consolidated, structurally sound ultra-thin walled (∼ 400 μm) AZ31 Mg alloy tubes by friction stir back extrusion (FSE) — a process used typically to manufacture thick metallic tubes and rods.
The tube cross-sectional microstructure was layered and consisted of a severely deformed stir zone with refined grains near the inner edge, a back-extruded zone with small grains near the outer edge, and a thermomechanically affected zone (TMAZ) with coarse grains develop within the central region. The inner tube surface microstructure had an average grain size of 4.1 ± 1.9 μm and a strong basal texture. In comparison, the outer tube surface microstructure was coarse, with an average grain size of 13.3 ± 6.4 μm with no preferred orientation.
Upon exposure to Hank’s balanced salt solution at 37 °C, microgalvanic coupling resulting from the gradient through-the-thickness grain size and texture differences between the tube inner and outer surfaces, and residual strain arising from the FSE process, promoted a localized attack that preferentially initiated on the outer tube surface and progressed inwards. The study established that FSE is a viable single-step process to manufacture ultra-thin Mg alloy tubes suitable for degradable precision tubular applications.
PFSW — Plasma Assisted Friction Stir Welding with a 500kg payload COMAU robot NJ5000, a bespoke FSW spindle and a Hyperterm Powermax 1250® 80 A plasma cutter
Experimental trials were conduced in Brasil on using Plasma Assisted Friction Stir Welding (PFSW*) for dissimilar material combinations of joining 3 mm thick SAE 1020 carbon steel sheets to 3 mm thick 5052 H34 aluminum sheets using an offset of 0 or -2.5 mm. The plasma torch was used to preheat the steel to 250 °C, 350 °C or 450 °C. Further parameter development trials are recommended to improve the weld quality and reduce tool wear.
PFSW — Pinless Friction Stir Welding
© Yu Ni, Yue Mao, Dingqiang Qin, Xuan Xiao and Li Fu (Xi’an, China), CC BY 4.0
Pinless Friction Stir Welding (PFSW*) was used for instance by Zhenlei Liu et al in 2016 for making thin wall structures from Alclad 2A12-T4 alloy. Yu Ni et al later conducted successfully a study on μFSW of 0.5 mm thick AA7075-T6 sheets with a thickness of 0.5 mm in Xi’an, China in the butt joint configuration. The influence of the welding process on the thermal cycles and deformations of μFSW was systematically studied through experiments. They concluded that "in comparison to the pin tool, the joint fabricated by the pinless tool experienced a lower peak temperature, a shorter elevated-temperature exposure time, and a larger temperature gradient within the shoulder range under the same shoulder penetration depth."
Reciprocating friction stir welding is particularly useful for welding plastics, as shown in the first patent of Wayne Thomas at TWI
Courtesy of TWI Ltd.
Closed-loop temperature control can be used in Robotic Friction Stir Welding (RFSW) for modifying the spindle rotation speed to maintain a constant welding temperature. For industrial applications this will reduce the programming time and increase the robustness of the process. By measuring the ohmic resistance between the tool and the work piece it is possible to assess the processing temperature without the need for thermocouples inside the tool. The method can be used used to control both plunging and welding.
RT-FSW: Combined rotation and translation of the tool axis (Com-stir™)
Wayne Thomas, the inventor of friction stir welding, developed and published also
Com-stir™, a compound motion for FSW and machining, using a rotary motion in combination with an orbital motion.
The benefits of this motion have been confirmed by several researchers, and Cabibbo et al. described this as an "approach in which welding pin was forced to slightly deviate away from the joining centreline (defined by authors as RT)", i.e. an "innovative approach to the conventional FSW process, defined by authors as RT-type configuration, in which the welding motion of the pin tool was obtained by combining two different movements occurring simultaneously:
(i) the rotation of the pin axis around an axis, perpendicular to the sheet blanks and belonging to the welding line, with a radius equal to R, and
(ii) the translation of the pin axis along a direction parallel to the welding line."
UAFSW — Ultrasonically assisted friction stir welding concept and device[10, retouched]
Ultrasonic vibration promotes the flow of metal at the interface, enlarged the size of the stirred zone (SZ), and reduced the angle between the hook defect and the interface. It was observed that, under otherwise identical conditions, UAFSLW joints can withstand a greater fracture shear strength than FSLW joints, as ultrasonic vibration helps to mix the material at the interface, thus, enlarging the SZ and diminishing the cold lap defects.
Viblade™ Welding — In-line Reciprocating Friction Stir Welding: Schematic, photo and macrosections of some of the first welds made in 9 mm thick polypropylene sheet
Courtesy of TWI Ltd.
VFSW — Vortex Friction Stir Welding: Principle, tool and shematic side view
For Vortex Friction Stir Welding (VSFW) the tool is partially made from the same material as the workpiece material. The process depends on a vortex material flow to make the weld. The weld macro- and micro-structures look similar to those of conventional FSW. However, in VSFW a lug boss is left at the end of the weld instead of an exit-hole as in conventional FSW. The mechanical properties are similar or even identical to those in conventional FSW.
VFSW — Vortex Friction Stir Welding: Metallographic section of lug boss at end of weld
* Acronyms marked with an asterisk are synonymously used for several variants, and their use is therefore disencouraged without an explanation. The P in the acronym PFSW can, for instanstance, be interpreted as penetrating, pinless, plasma or portable.
** Some variants can be abreviated by several acronyms, e.g. EFSW and EAFSW for Electrically Assisted Friction Stir Welding.
A Scialpi, M Troughton, S Andrews and L A C De Filippis: In-Line Reciprocating Friction Stir Welding of
Plastics. Joining Plastics/Fügen von Kunststoffen. Magazine, Issue 1, May 2007.
A Scialpi, M Troughton, S Andrews and L A C De Filippis (deutsche Übersetzung von Stephan Kallee):
Rührreibschweissen von Plastik mit einer vibrierenden Vorwärts- und Rückwärtsbewegung des Werkzeugs. Joining Plastics/Fügen von Kunststoffen. Magazine, Issue 1, May