Introduction
The hot wire process is a method of forming a deposited
metal by passing current through, and thus heating, the
filler wire. As indicated in “Consumable Electrode Arcless
Electric Working” the title of the patent for which Manz
and others in the U.S. applied1 in 1962, essentially, the
filler wire can be melted independently of the arc heat
source which melts the base metal; thus, the distinctive
features are that the deposition rate is controllable and
a high deposition rate is also feasible.
As well as the the TIG arc2, this hot wire process was
formerly employed in combination with the submerged
arc3 and the plasma arc4; most recently, combination with
lasers5 was also anticipated. During common TIG welding
which employs a “cold” wire through which there is no
current passed, the deposition rate is slow; consequently,
there have been many cases where the hot wire process
has been employed to advantage. However, there have
been some problems outstanding from aspects of
workability; consequently, there are some areas for which
this process cannot be described as being technically
established and in general use.
Figure 1 shows the principle of the arrangement of a
hot wire TIG welding machine which consists of a wire
torch to supply the current to the wire and a wire heating
power source in addition to the TIG welding power source,
TIG torch and wire feeder.
The principle problem of hot wire welding is that the
arc can be deflected to the hot wire side or the opposite
side of the hot wire due to the interaction of
electromagnetic forces between the wire current and the
arc current. This “magnetic arc blow” phenomenon
destroys the arc directivity and complicates welding
operations. When the hot wire TIG welding process was
first developed it was recommended that the wire should
be heated by means of commercial frequency AC supply.2
It is thought that the reason for this is probably that
when the wire is heated by AC current the arc becomes
in an oscillating state and the welding operation is
facilitated.
In Japan, equipment which heats the wire with DC,
where the wire side is selected as ‘+’ pole, have been
developed, such as welding equipment6 with the
characteristic of deflecting the TIG arc to the direction
of the welding progress by taking advantage of this
magnetic arc blow in the reverse direction and welding
equipment7 which embodies compact and low cost power
sources where the arc current from the arc power source
is partly distributed to the wire for heating. Furthermore,
equipment which employs a wire heating current where
the wire side is selected to be the ‘–’ pole have come on
the market from overseas manufacturers.8 In addition to
these, equipment in which the filler wire is heated by
passing the current between two electrical connections
have also come onto the market.
Furthermore, in recent years, a technique has been
developed such that two wires are inserted at the front
and the back of the arc, in the direction of the welding
progress and a direct current is passed between those
wires.10 The purpose of this technique is to support the
molten metal which tends to droop during horizontal
position (three o’clock) welding by means of the
interaction of the arc current and the hot wire current
flowing transversely through the molten pool.
For the hot wire TIG welding process, including the
equipments just described, to date both AC and DC
continuous waveform current has been employed for wire
heating, but heating of the wire with pulsed current has
not been investigated, either at home or abroad.
The authors and others previously developed a hot
wire switching TIG welding process in which a low pulsed