Inert gas electric arc welding process and torch for use therein

An inert gas electric arc welding process is described in which the refractory electrode of the welding torch is rotated about its own axis throughout the welding operation so that the electric arc produced at the end of the electrode rotates and agitates the surface of the melt pool locally and continuously.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to an inert gas electric arc welding process and to a 
torch for use in the process. 
2. Discussion of the Background 
Electric arc welding is carried out in most industrial fields, especially 
the aerospace, aeronautical and nuclear industries, and is often performed 
by an automatic welding system. 
In TIG arc welding processes an electric arc is produced between a 
stationary refractory electrode and two metal articles which are to be 
welded together, and a melt pool is formed by transfer of energy from the 
arc into the material of the metal articles. The arc and the melt pool are 
protected by surrounding them with an inert gas. The welding operation is 
performed progressively either by moving the articles past the stationary 
arc or by moving the arc over the articles, which remain stationary. 
However, because of the movement of the arc relatively to the articles, 
the melt pool has a temperature spread which may cause weld defects. These 
defects can be blowholes formed by gases trapped in the weld, or an 
unsatisfactory surface texture of the weld bead. Blowholes have a 
particularly adverse effect on the mechanical strength of the weld since 
they produce porosities which weaken the weld. These weld defects are even 
worse when the weld is formed between two articles made of different 
metals or between very thick articles. 
SUMMARY OF THE INVENTION 
It is an object of the invention to overcome these problems and improve 
weld quality by providing an electric arc welding process which reduces or 
eliminates blowholes and facilitates the welding of very thick articles 
and articles made of different metals. 
Accordingly, the invention provides a process for welding two metallic 
articles together using an inert gas electric arc welding torch comprising 
a torch body and a refractory electrode disposed in said torch body, 
wherein an electric arc is produced between said refractory electrode and 
said two metal articles to be welded, and said arc is moved relatively to 
said metal articles to progressively weld said articles together, said 
process including the step of continuously rotating said refractory 
electrode about its own axis during the welding operation while keeping 
said torch body stationary relative to said axis. 
The electric arc thus rotates with the electrode and acts to agitate the 
melt pool surface locally and continuously so that a homogeneous 
temperature is produced at the weld point, whereby the quality and surface 
texture of the weld are improved. The agitation of the melt pool also 
helps to remove gases and eliminate blowholes. 
The invention also provides an inert gas electric arc welding torch 
comprising a torch body having a longitudinal axis, a refractory electrode 
disposed in the torch body on the longitudinal axis for producing an 
electric arc between two metal articles Lo be welded together, a shaft 
secured to said refractory electrode and disposed longitudinally in said 
torch body coaxially with said longitudinal axis, and means mounting said 
shaft for rotation about said longitudinal axis within said torch body 
whereby said shaft is adapted to rotate said refractory electrode about 
said longitudinal axis while said torch body remains stationary relative 
to said axis. 
Preferred features and advantages of the invention will become apparent 
from the following description of the preferred embodiment, given by way 
of non-limitative example, with reference to the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The drawings show a welding torch for inert gas welding with a tungsten 
electrode, called TIG welding, the torch comprising a cylindrical torch 
body 1 having a longitudinal axis XX' and, at one end near the welding 
plane, an inert gas discharge nozzle 2. A refractory electrode 3 is 
disposed in the torch body on the longitudinal axis XX' and is held in 
position by means of a clamp 4. The electrode 3 has a tip 5 for producing 
an electric arc which creates a melt pool between two metal articles to be 
welded. 
The electrode 3 is rigidly connected to a shaft 6 for rotating the 
electrode about its axis, i.e. the longitudinal axis XX', the shaft being 
disposed longitudinally in the torch body 1 and mounted for rotation about 
the axis XX' by bearings 7. One end 8 of the shaft 6 extends beyond the 
torch body 1 and is adapted to be connected to drive means (not shown) for 
rotating the shaft. 
On commencement of a welding operation, the shaft 6 is rotated about the 
axis XX' and thus drives the electrode also to rotate about said axis, the 
torch body 1 remaining stationary relative to the axis. 
The electrode is rotated throughout the welding operation, and the standing 
electric arc produced at the end of the rotating electrode thus rotates on 
itself and agitates the surface of the resulting melt pool locally and 
continuously. The melt pool surface is therefore in a state of vibration 
which boosts the capillarity of the pool, improves the homogeneity of the 
melt zone and accelerates degassing of the pool. The surface texture of 
the resulting weld bead is even and the junctions between the melt zone 
and the metal of the welded articles are progressive. 
The invention is, of course, not limited to the particular embodiment 
described. For example, a torch and electrode assembly which rotates 
axially can be used, although this causes problems with electrical 
connections between the torch and the welding installations to which the 
torch is connected, as well as problems with supplying the torch with 
inert gas and cooling fluid.