Friction Stir Weld Tooling Development for Application on the 2195 Al-Cu-Li Space Transportation System External Tank

Friction Stir Welding (FSW) is a new and innovative solid-state joining process which can be applied to difficult-to- weld aluminum alloys. However, the large forces involved with the process have posed a production tooling challenge. Lockheed Martin Michoud Space Systems has overcome many of these challenges on the Super Lightweight External Tank (ET) program. Utilizing Aluminum-Copper-Lithium alloy 2195 in the form of plate and extrusions, investigations of FSW process parameters have been completed. Major loading mechanisms are discussed in conjunction with deflection measurements. Since the ET program is a cryogenic application, a brief comparison of cryogenic material properties with room temperature material properties is offered for both FSW and fusion welds. Finally, a new approach to controlling the FSW process from a load perspective is introduced. Emphasis will be put on tooling development, as well as the impact of tooling design and philosophy on Friction Stir Weld success probability

Tool For Friction Stir Tack Welding of Aluminum Alloys

A small friction-stir-welding tool has been developed for use in tack welding of aluminum-alloy workpieces. It is necessary to tack-weld the workpieces in order to hold them together during friction stir welding because (1) in operation, a full-size friction-stir-welding tool exerts a large force that tends to separate the workpieces and (2) clamping the workpieces is not sufficient to resist this force. It is possible to tack the pieces together by gas tungsten arc welding, but the process can be awkward and time-consuming and can cause sufficient damage to necessitate rework. Friction stir tack welding does not entail these disadvantages. In addition, friction stir tack welding can be accomplished by use of the same automated equipment (except for the welding tool) used in subsequent full friction stir welding. The tool for friction stir tack welding resembles the tool for full friction stir welding, but has a narrower shoulder and a shorter pin. The shorter pin generates a smaller workpiece-separating force so that clamping suffices to keep the workpieces together. This tool produces a continuous or intermittent partial-penetration tack weld. The tack weld is subsequently consumed by action of the larger tool used in full friction stir welding tool

Controlling Force and Depth in Friction Stir Welding

Feedback control of the penetration force applied to a pin tool in friction stir welding has been found to be a robust and reliable means for controlling the depth of penetration of the tool. This discovery has made it possible to simplify depth control and to weld with greater repeatability, even on workpieces with long weld joints. Prior to this discovery, depths of penetration in friction stir welding were controlled by hard-tooled roller assemblies or by depth actuators controlled by feedback from such external sensors as linear variable-differential transformers or laser-based devices. These means of control are limited: A hard-tooled roller assembly confines a pin tool to a preset depth that cannot be changed easily during the welding process. A measurement by an external sensor is only an indirect indicative of the depth of penetration, and computations to correlate such a measurement with a depth of penetration are vulnerable to error. The present force-feedback approach exploits the proportionality between the depth and the force of penetration Unlike a depth measurement taken by an external sensor, a force measurement can be direct because it can be taken by a sensor coupled directly to the pin tool. The reading can be processed through a modern electronic servo control system to control an actuator to keep the applied penetration force at the desired level. In comparison with the older depth-control methods described above, this method offers greater sensitivity to plasticizing of the workpiece metal and is less sensitive to process noise, resulting in a more consistent process. In an experiment, a tapered panel was friction stir welded while controlling the force of penetration according to this method. The figure is a plot of measurements taken during the experiment, showing that force was controlled with a variation of 200 lb (890 N), resulting in control of the depth of penetration with a variation of 0.004 in. (0.1 mm)

Ethnographies of Power

What does it mean to work with radical concepts in our time of rampant inequality, imperial-capitalist plunder, racial/sexual/class violence and ecocide? When concepts from the past seem inadequate, how do scholars and activists concerned with social change decide what concepts to work with or renew? The contributors to Ethnographies of Power address these questions head on. Gillian Hart is a key thinker in radical political economy, geography, development studies, agrarian studies and Gramscian critique of postcolonial capitalism. In Ethnographies of Power each contributor engages her work and applies it to their own field of study. These applied concepts include: ‘gendered labour’ practices among South African workers, reading ‘racial capitalism’ through agrarian debates, using ‘relational comparison’ in an ethnography of schooling across Durban, reworking ‘multiple socio-spatial trajectories’ in Guatemala’s Maya Biosphere Reserve, critiquing the notion of South Africa’s ‘second economy’, revisiting ‘development’ processes and ‘Development’ discourses in US military contracting, reconsidering Gramsci’s ‘conjunctures’ geographically, finding divergent ‘articulations’ in Cape Town land occupations, and exploring ‘nationalism’ as central to revaluing recyclables at a Soweto landfill. Ethnographies of Power offers an invaluable toolkit for activists and scholars engaged in sharpening their critical concepts for the social and environmental change necessary for our collective future

Ethnographies of Power

What does it mean to work with radical concepts in our time of rampant inequality, imperial-capitalist plunder, racial/sexual/class violence and ecocide? When concepts from the past seem inadequate, how do scholars and activists concerned with social change decide what concepts to work with or renew? The contributors to Ethnographies of Power address these questions head on. Gillian Hart is a key thinker in radical political economy, geography, development studies, agrarian studies and Gramscian critique of postcolonial capitalism. In Ethnographies of Power each contributor engages her work and applies it to their own field of study. These applied concepts include: ‘gendered labour’ practices among South African workers, reading ‘racial capitalism’ through agrarian debates, using ‘relational comparison’ in an ethnography of schooling across Durban, reworking ‘multiple socio-spatial trajectories’ in Guatemala’s Maya Biosphere Reserve, critiquing the notion of South Africa’s ‘second economy’, revisiting ‘development’ processes and ‘Development’ discourses in US military contracting, reconsidering Gramsci’s ‘conjunctures’ geographically, finding divergent ‘articulations’ in Cape Town land occupations, and exploring ‘nationalism’ as central to revaluing recyclables at a Soweto landfill. Ethnographies of Power offers an invaluable toolkit for activists and scholars engaged in sharpening their critical concepts for the social and environmental change necessary for our collective future

Integrin-mediated Activation of MAP Kinase Is Independent of FAK: Evidence for Dual Integrin Signaling Pathways in Fibroblasts

Integrin-mediated cell adhesion causes activation of MAP kinases and increased tyrosine phosphorylation of focal adhesion kinase (FAK). Autophosphorylation of FAK leads to the binding of SH2-domain proteins including Src-family kinases and the Grb2–Sos complex. Since Grb2–Sos is a key regulator of the Ras signal transduction pathway, one plausible hypothesis has been that integrin-mediated tyrosine phosphorylation of FAK leads to activation of the Ras cascade and ultimately to mitogen activated protein (MAP) kinase activation. Thus, in this scenario FAK would serve as an upstream regulator of MAP kinase activity. However, in this report we present several lines of evidence showing that integrin-mediated MAP kinase activity in fibroblasts is independent of FAK. First, a β1 integrin subunit deletion mutant affecting the putative FAK binding site supports activation of MAP kinase in adhering fibroblasts but not tyrosine phosphorylation of FAK. Second, fibroblast adhesion to bacterially expressed fragments of fibronectin demonstrates that robust activation of MAP kinase can precede tyrosine phosphorylation of FAK. Finally, we have used FRNK, the noncatalytic COOH-terminal domain of FAK, as a dominant negative inhibitor of FAK autophosphorylation and of tyrosine phosphorylation of focal contacts. Using retroviral infection, we demonstrate that levels of FRNK expression sufficient to completely block FAK tyrosine phosphorylation were without effect on integrin-mediated activation of MAP kinase. These results strongly suggest that integrin-mediated activation of MAP kinase is independent of FAK and indicate the probable existence of at least two distinct integrin signaling pathways in fibroblasts