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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

A study of gas flow pattern, undercutting and torch modification in variable polarity plasma arc welding

A study on the plasma and shield gas flow patterns in variable polarity plasma arc (VPPA) welding was undertaken by shadowgraph techniques. Visualization of gas flow under different welding conditions was obtained. Undercutting is often present with aluminum welds. The effects of torch alignment, shield gas flow rate and gas contamination on undercutting were investigated and suggestions made to minimize the defect. A modified shield cup for the welding torch was fabricated which consumes much less shield gas while maintaining the weld quality. The current torch was modified with a trailer flow for Al-Li welding, in which hot cracking is a critical problem. The modification shows improved weldablility on these alloys.

Mcclure, John C.↗
NASA NTRS1992

Gas Contamination In Plasma-Arc-Welded Aluminum

Document describes experimental investigation on visible and tactile effects of gaseous contaminants in variable-polarity plasma arc (VPPA) welding of 2219 T-87 aluminum alloy. Contaminant gases (nitrogen, methane, oxygen, and hydrogen) introduced in argon arc and in helium shield gas in various controlled concentrations. Report represents results of experiments in form of photographs of fronts, backs, polished cross sections, and etched cross sections of welds made with various contaminants at various concentrations. Provides detailed discussion of conditions under which welds made.

Mcclure, John C.↗
NASA NTRS1987

Alternating-Polarity Arc Welding

Brief reversing polarity of welding current greatly improves quality of welds. NASA technical memorandum recounts progress in art of variable-polarity plasma-arc (VPPA) welding, with emphasis on welding of aluminum-alloy tanks. VPPA welders offer important advantages over conventional single-polarity gas/tungsten arc welders.

Schwinghamer, R. J.↗
NASA NTRS1992

Heat flow in variable polarity plasma arc welds

The space shuttle external tank and the space station Freedom are fabricated by the variable polarity plasma arc (VPPA) welding. Heat sink effects (taper) are observed when there are irregularities in the work-piece configuration especially if these irregularities are close to the weld bead. These heat sinks affect the geometry of the weld bead, and in extreme cases they could cause defects such as incomplete fusion. Also, different fixtures seem to have varying heat sink effects. The objective of the previous, present, and consecutive research studies is to investigate the effect of irregularities in the work-piece configuration and fixture differences on the weld bead geometry with the ultimate objective to compensate automatically for the heat sink effects and achieve a perfect weld.

Abdelmessih, Amanie N.↗
NASA NTRS1990

Physics Of Variable-Polarity Plasma Arc Welding

Report describes experimental study of some of the physical and chemical effects that occur during variable-polarity plasma arc (VPPA) keyhole welding of 2219 aluminum alloy. Comprised three major programs: (1) determination of effects of chemical additions (i.e., impurities) on structure and shape of bead and keyhole; (2) determination of flow in regions surrounding keyhole; (3) development of analog used easily to study flow in keyhole region.

Walsh, Daniel W.↗
NASA NTRS1985

Unique variable polarity plasma arc welding for space shuttle

Since the introduction of the Plasma Arc Torch in 1955 and subsequent to the work at Boeing in the 1960's, significant improvements crucial to success have been made in the Variable Polarity Plasma Arc (VPPA) Process at the Marshall Space Flight Center. Several very important advantages to this process are given, and the genesis of PA welding, the genesis of VPPA welding, special equiment requirements, weld property development, results with other aluminum alloys, and the eventual successful VPPA transition to production operations are discussed.

Schwinghamer, R. J.↗
NASA NTRS1984

Variable polarity plasma arc welding on the Space Shuttle external tank

Variable 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.

Nunes, A. C., Jr.↗
DOE OSTI2020

Quarterly Management Document – FY20, 1st Quarter, Multi-pass Hybrid Laser Arc Welding of Alloy 740H

During the first quarter of FY20, work focused on implementing a subcontract with Penn State University to collaborate on the project. Significant delays prevented the subcontract from being placed until the end of December. As a result only limited progress was made on the project. Required equipment was researched and ordered during the first quarter but will not be delivered until the middle of the second quarter of FY20. Delays are not expected to adversely impact the schedule of the project.

36 MATERIALS SCIENCE↗
DOE OSTI2020

FY20, 3rd Quarter, Multi-pass Hybrid Laser Arc Welding of Alloy 740H

Although progress has been slowed by telecommuting restrictions at INL and PSU, progress has been made by PSU on modeling and simulation of deep penetration laser welding. Additionally, both INL and PSU has received critical equipment, in the form of high-powered laser wobble heads, needed to verify the modeling and simulation results. The equipment was installed at INL and preliminary tests, based on a test matrix that was developed in this 3rd quarter, will be made early in the 4th quarter. Similarly, the PSU laser wobble head is expected to be installed early in the 4th quarter and preliminary experiments are expected to commence shortly thereafter. Completion dates on a few milestones have been impacted and new dates proposed.

36 MATERIALS SCIENCE↗
NASA NTRS2004

Plasma Arc Welding: How it Works

The physical principles of PAW from basic arcs to keyholing to variable polarity are outlined. A very brief account of the physics of PAW with an eye to the needs of a welder is presented. Understanding is usually (but not always) superior to handbooks and is required (unless dumb luck intervenes) for innovation. And, in any case, all welders by nature desire to know. A bit of history of the rise and fall of the Variable Polarity (VP) PA process in fabrication of the Space Shuttle External Tank is included.

Nunes, Arthur↗
NASA NTRS1975

Grain refinement control in TIG arc welding

A method for controlling grain size and weld puddle agitation in a tungsten electrode inert gas welding system to produce fine, even grain size and distribution is disclosed. In the method the frequency of dc welding voltage pulses supplied to the welding electrode is varied over a preselected frequency range and the arc gas voltage is monitored. At some frequency in the preselected range the arc gas voltage will pass through a maximum. By maintaining the operating frequency of the system at this value, maximum weld puddle agitation and fine grain structure are produced.

Iceland, W. F.↗
NASA NTRS1974

Grain refinement control in gas-shielded arc welding of aluminum tubing

When sections are being welded, operator varies pulse rate of power supply and simultaneously monitors signal on oscilloscope until rate is found which produces maximum arc gas voltage. Remainder of welding is performed with power supply set at this pulse rate, producing desired maximum weld puddle agitation and fine uniform weld of grain structure.

Iceland, W. F.↗
DOE OSTI2025

Gas tungsten arc welding and post weld heat treatment effects on microstructure and mechanical property of castable nanostructured alloy steel

Here, this paper details the first study of castable nanostructured alloy (CNA) steel gas tungsten arc weldability and the post-weld heat treatment (PWHT) effects. Effects of welding heat input, thermal cycles, and PWHT on microstructures, microhardness distributions, room temperature tensile properties, and fracture characteristics are discussed. Results show that CNA steel exhibits excellent weldability (i.e., no indication of welding defects and reasonable tensile properties). The welded joint exhibited heterogeneous microstructures with δ-ferrite as well as large microhardness variation and fluctuation. The welded joint yield and ultimate tensile strengths were similar to those of the base metal, but the elongations decreased by 30 %. However, with normalization and tempering PWHT, the δ-ferrite was eliminated, microstructure was modified, hardness was unified, and joint ductility was restored. The study indicated that the CNA reduced-activation ferritic-martensitic steel owns excellent weldability, and PWHT is needed for the industrial application of welded structures.

36 MATERIALS SCIENCE↗
NASA NTRS1981

Automatic arc welding of propulsion system tubing in close proximity to sensitive electronic devices

The planned final assembly of the Galileo spacecraft propulsion system tubing, which involves welding in close proximity to sensitive electronics, raised significant concerns about the effects of electromagnetic coupling of weld energy on CMOS and other sensitive integrated circuits. A test program was established to assess the potential of an orbital arc welder and an RF-induction brazing machine to damage sensitive electronic equipment. Test parameters were varied to assess the effectiveness of typical transient suppression practices such as grounding, bonding, and shielding. A technique was developed to calibrate the hazard levels at the victim-circuit location; this technique is described along with the results and conclusions of the test program.

Lumsden, J. M.↗
NASA NTRS1974

On particle motion in an electric welding arc treated with sonic or ultrasonic oscillations

The criteria for the stability of the subharmonic, harmonic, or superharmonic oscillations determine the relation between acoustic field parameters and particle parameters. The derived formulas underlie the destruction of the fragile Widmanstatten structure in weldings and therefore the designing of the generators that must be used for this welding process.

Petru, S.↗
NASA NTRS1973

Study of gas tungsten arc welding procedures for tantalum alloy T-111 (Ta-8 W-2Hf) plate

Methods of eliminating or reducing underbread cracking in multipass GTA welds in thick T-111 plate were studied. Single V butt welds prepared using experimental filler metal compositions and standard weld procedures resulted in only moderate success in reducing underbread cracking. Subsequent procedural changes incorporating manual welding, slower weld speeds, and three or fewer fill passes resulted in crack-free single V welds only when the filler metal was free of hafnium. The double V joint design with successive fill passes on opposite sides of the joint produced excellent welds. The quality of each weld was determined metallographically since the cracking, when present, was very slight and undetectable using standard NDT techniques. Tensile and bend tests were performed on selected weldments. The inherent filler metal strength and the joint geometry determined the strength of the weldment. Hardness and electron beam microprobe traverses were made on selected specimens with the result that significant filler metal-base metal dilution as well as hafnium segregation was detected. A tentative explanation of T-111 plate underbread cracking is presented based on the intrinsic effects of hafnium in the weldment.

Gold, R. E.↗