Engineering topics

Mcclure, John C.

Publications and source records attributed to Mcclure, John C..

4 records

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 NTRS1993

Measuring Weld Parameters By Spectroscopy

Optical-emission spectrometric apparatus used to monitor variable-polarity plasma arc welding of aluminum alloys. Spectrometer incorporated into control system to ensure quality of weld because in keyhole, arc fully penetrates weld joint and impurities flushed out. Apparatus helps ensure high quality of weld by monitoring such contaminants as oxygen and hydrogen in shield gas, detecting inadequate flow of shield gas, and sensing changes in temperature of arc with changes in arc current and voltage.

Nunes, Arthur↗

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 NTRS1989

The effect of impurity gasses on variable polarity plasma arc welded 2219 aluminum

Variable polarity plasma arc (VPPA) welding has been used with considerable success by NASA for the welds on the Space Shuttle External Tank as well as by others concerned with high quality welded structures. The effects of gaseous contaminants on the appearance of VPPA welds on 2219 aluminum are examined so that a welder can recognize that such contamination is present and take corrective measures. There are many possible sources of such contamination including, contaminated gas bottles, leaks in the gas plumbing, inadequate shield gas flow, condensed moisture in the gas lines or torch body, or excessive contaminants on the workpiece. The gasses chosen for study in the program were nitrogen, oxygen, methane, and hydrogen. Welds were made in a carefully controlled environment and comparisons were made between welds with various levels of these contaminants and welds made with research purity (99.9999 percent) gasses. Photographs of the weld front and backside as well as polished and etched cross sections are presented.

Mcclure, John C.↗