Friction Stir Welding Alter a Decade of Development
By 1995, FSW had matured to a point where it could be transitioned and implemented into the U.S. aerospace and automotive markets. The many advantages of FSW compared to conventional arc welding have repeatedly been demonstrated with both improved joint properties and
performance. Often, production costs are significantly reduced. Other times, FSW enables new product forms to be produced or skilled labor freed to perform other tasks. Research and development efforts over the last decade have resulted in improvements in FSW and the spin-off of a
series of related technologies.
W. J. Arbegast
An Analysis of Resistance Spot Welding
The resistance spot welding (RSW) process has been widely employed in sheet metal fabrication because of its high speed and suitability for automation. In this process, two metal sheets are compressed between a pair of water-cooled copper-alloy electrodes by an external applied force, then an electric current is passed through the sheets via the two electrodes to generate concentrated Joule heating at the contact surface. This results in a molten nugget forming at the intersection of the two sheets. After the current flow ceases, the electrode force is maintained for a short duration to allow the workpiece to rapidly cool and solidify.
Z. Hou et al.
Friction Stir Welding Vs. Fusion Welding
Friction stir welding (FSW) is a proven nonferrous metal joining process in which base metal melting, filler metal, and shielding gases are absent. Because it is a solid-state joining process, friction stir welding eliminates most of the ill effects associated with resolidification inherent to conventional fusion welding. The process also can be applied in all welding positions.
Evaluating the Pros and Cons
Three important features outline friction stir welding’s advantages over conventional fusion welding processes: high production output, low production costs, and the ability to effectively join aluminum alloys that are difficult or impossible to weld by conventional fusion methods. Of course, each of these claims must be evaluated in order to best determine friction stir welding’s potential advantage or disadvantage.
Investigating Resistance and Friction Stir Welding Processes for
International interest in developing lighter, more fuel-efficient automobiles has resulted in the introduction of a new round of alternative construction materials. Of recent interest has been the exploitation of magnesium (Mg) alloys. Magnesium, with a density of 1.74 g/cm3, has roughly that of Al, and one-fourth that of steel. With proper alloying, the strength-to-weight ratio of Mg-based products is similar to many Al alloys, as well as many common grades of automotive sheet steels. Magnesium is particularly of interest for automotive applications given its natural corrosion resistance and ease of casting. Magnesium has seen limited use in automotive applications since the 1920s.
J. E. Gould and W. Chuko
Friction Stir Welding Flies High at NASA
Welding at NASA’s Marshall Space Flight Center (MSFC), Huntsville, Ala., has taken a new direction during the past 12 years. In 1994, fusion welding processes, namely variable polarity plasma arc (VPPA) and gas tungsten arc (GTA), were the cornerstone of welding development in the Space Flight Center’s welding laboratories, located in the part of MSFC known as National Center for Advanced Manufacturing (NCAM). Developed specifically to support the Space Shuttle’s external tank and later the International Space Station’s manufacturing programs, VPPA was viewed as the paragon of welding processes for joining aluminum alloys. A major change began in 1994 when NASA’s Jeff Ding brought the friction stir welding (FSW) process to NASA. At that time, FSW was little more than a lab curiosity.
J. Ding et al.
A Look at Rocker Arm Spot Welding Machines
Rocker arm spot welding machines (Fig. 1) are commonly used to assemble sheet metal parts, wire displays, make repairs to electrical motors and starters, weld nuts to sheet metal parts, and join numerous other assemblies. The name ‘rocker arm’ comes from the pivoting arm used to apply the force to the electrodes during welding.
The welding force is applied to the electrodes when the rocker arm is lifted. Commonly, the lifting is applied by either a spring compressed by means of a foot treadle (foot kicker), or a double-acting air cylinder. The air cylinder is controlled by a fourway solenoid air valve with an air regulator.
A Review of Postweld Heat Treatment Code Exemptions
This article compares and contrasts the current rules and guidelines present in various fabrication standards (mainly U.S. and UK) regarding the postweld heat treatment (PWHT) requirements of welds and the limits for as-welded construction made in pipes, pressure vessels, and structures, including bridges, buildings, and offshore structures, as discussed below. It is recognized that some codes now include provision for repair without PWHT (Refs. 1–3), and that there have also been investigations aimed at providing recommendations for acceptable thickness limits for the as-welded condition for general structural conditions (Refs. 4, 5). It is noted that steel making technology has changed over the last thirty years or so (although steels are also produced in parts of the world where steel making technology lags behind best practice). However, the fabrication codes were generally devised for older, normalized steels with higher carbon contents (Refs. 6, 7), and often with no toughness requirement.
D. J. Abson et al.
WELDING RESEARCH SUPPLEMENT
*Design of Experiment Analysis and Weld Lobe Estimation for Aluminum Resistance Spot Welding (.pdf)
Process parameters, fitup, and misalignment were examined as to their effects on
Y. Cho et al.
Behavior and Melting Rate in the VP-GMAW Process (.pdf)
Element Modeling Predicts the Effects of Voids on Thermal Shock
Reliability and Thermal Resistance of Power Device (.pdf)
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WELDING JOURNAL - March 2005, Volume 85, Number 3