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Little bit OT, Are shielding methods still required if welding in a vacuum?

steve-l

Titanium
Joined
Mar 2, 2012
Location
Geilenkirchen, Germany
I know of no tests currently being performed to determine how to weld in space. I guess that does not mean they are not being done, it just means I don't know about them. Perhaps oxidation is not an issue, but maybe rapid weld cooling is. Thoughts?
 
Electron beam welding is performed in a vacuum. At pressures below 1 millitorr (760 torr = 1 atmosphere) the electron beam standoff from the work piece can be 16 inches or more away from the welded joint. Butt welds can be more than 6 inches deep in some materials. Electron beam welding is used when the joint design requires a narrow heat affected zone.

There are electron beam welding processes that can be done at higher pressures. The higher pressures cause the beam to expand and produce a wide weld with low penetration.The beam standoff distance is less than a inch and welding depth is limited to sheet metal at 760 torr.

Electron Beam Welding Process, Applications and Equipment | PTR-Precision Technologies, Inc.

When a arc is struck in a vacuum there is no longer a vacuum. The evaporated metal vapor becomes the surrounding atmosphere. It is still in the millitorr range. This has a number of useful applications. Almost all production thin film coating machines for cutting tools use vacuum arc sources. The pure metal arc targets supply the metal vapor and the background high purity feed gas in the chamber supplies the oxygen, nitrogen, or carbon (from methane) which produces the carbides, nitrides and oxides on the tool surface. The chemical reaction occurs on the tool surface rather than in the vapor cloud.

High purity alloys of high strength steels, stainless steels, and titanium are processed in vacuum arc remelt furnaces. The arc melting releases gas and low temperature melting point metals into the vacuum chamber which are then pumped out. The high temperature oxides and nitrides float to the surface of the melt and are cutoff from the completed billet.

Removing the contaminants increases the fatigue life of the high strength materials. Stainless steel destined for vacuum chamber construction is processed this way to remove inclusions that will cause vacuum leaks. This is important when working at pressures below 1* 10 exp-7 torr

Vacuum arcs are a problem when designing high voltage switch gear used in power transmission. A switch that is opened when conducting thousands of amps will continue conducting electrons even when the contacts are several feet apart. The conducting medium is the vapor cloud.

The arc can be extinguished using a high pressure air blast or, in the case of vacuum switch gear, by using magnetic fields.

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I wouldn't expect cooling to be more rapid in vacuum. Perhaps a little less rapid actually as there is no atmosphere to carry away any of the heat.

Regards.

Mike
 
This question was not so OT. I just read an article that has stated that there are now contracts being generated by NASA to build construction robots, including welding robots to build new permanent facilities on the moon. Hence, my question.
 








 
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