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Variable polarity plasma arc welding on the Space Shuttle external tankVariable polarity plasma arc (VPPA) techniques used at NASA's Marshall Space Flight Center for the fabrication of the Space Shuttle External Tank are presentedd. The high plasma arc jet velocities of 300-2000 m/s are produced by heating the plasma gas as it passes through a constraining orifice, with the plasma arc torch becoming a miniature jet engine. As compared to the GTA jet, the VPPA has the following advantages: (1) less sensitive to contamination, (2) a more symmetrical fusion zone, and (3) greater joint penetration. The VPPA welding system is computerized, operating with a microprocessor, to set welding variables in accordance with set points inputs, including the manipulator and wire feeder, as well as torch control and power supply. Some other VPPA welding technique advantages are: reduction in weld repair costs by elimination of porosity; reduction of joint preparation costs through elimination of the need to scrape or file faying surfaces; reduction in depeaking costs; eventual reduction of the 100 percent-X-ray inspection requirements. The paper includes a series of schematic and block diagrams.
Document ID
19840065754
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Nunes, A. C., Jr.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Bayless, E. O., Jr.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Jones, C. S., III
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Munafo, P. M.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Biddle, A. P.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Wilson, W. A.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Date Acquired
August 12, 2013
Publication Date
September 1, 1984
Publication Information
Publication: Welding Journal
Volume: 63
ISSN: 0043-2296
Subject Category
Mechanical Engineering
Accession Number
84A48541
Distribution Limits
Public
Copyright
Other

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