Lincoln Electric SQUARE WAVE TIG 255 IM520-B - Manual (Page 20)

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TABLE 2
RECOMMENDED POLARITY
SETTINGS FOR TIG WELDING
Type of Welding
Electrode
Polarity
High Frequency
Setting
Stainless Steel
Aluminum & Magnesium
Other Metals
DC-
AC
DC-
START
CONTINUOUS
START
OPERATION
WELDING OPERATION
TIG Welding
Familiarize yourself with the Controls and Display
Section before attempting operation of the Square
Wave TIG 255.
TIG Welding Guidelines
TIG welding can be done in either the TIG 2-Step or
the TIG 4-Step Weld Mode. TIG 2-Step is typically
used with Hand or Foot Amptrols, with Remote
Current control. TIG 4-Step is typically used with Arc
Start switches and Local Current Control, because it
provides a very brief current upslope, and a 5-second
current downslope. TIG 4-Step also functions like a
trigger interlock, making it unnecessary to hold down
the Arc Start switch during a weld. Note, on later
versions, TIG 4-Step was made available for use with
Remote Current Control with the release of ROM
version S21228-4 (initiated on Control board G2150-3
on codes 10022 and higher). This feature requires
that the remote control devise in use must have
separate Arc Start and Output Control mechanisms.
Read the TIG Welding Sequence of Operation
sections for more details on 2-Step and 4-Step
Operation.
HAND AND FOOT AMPTROL ACCESSORY
OPERATION
Both the Hand and Foot Amptrol work in a similar
manner. They are meant to be used for remote current
control when Remote Current Control is selected.
The TIG 2-Step mode must be selected when using
an Amptrol for remote current control. As explained
below, Amptrols can also be used as arc start
switches if Local Current Control is selected.
For simplicity, the following explanation will refer only
to “Amptrols”, meaning both Foot and Hand models.
The term “minimum” refers to a Foot pedal in the “up”
position, as it would be with no foot pressure, or a
Hand Amptrol in the relaxed position, with no thumb
pressure. “Maximum” refers to a fully depressed Foot
Amptrol, or a fully extended Hand Amptrol.
The Amptrol is capable of controlling the output
current from 5 amps to the preset current displayed on
the ammeter. For example, if the ammeter is preset
for 200 amps and the Current Control switch is in the
REMOTE position, the Amptrol, when depressed just
past its minimum position, will cause the Square
Wave TIG 255 to weld at 5 amps. At the Amptrols
maximum position, the output would be near 200
amps.
It is important to note that, for many applications, the
tungsten will not start an arc at only 5 amps. To start
an arc reliably, it is important to depress the Amptrol
far enough so that the machine output current is near
the tungsten operating range. In the example above, a
3/32” tungsten may be used on DC- to weld near 200
amps. To start the weld, the operator may have to
depress the Amptrol approximately 1/4 of the way
down, or to nearly 50 amps, in order to start the arc.
Merely depressing the Amptrol to its 5 amp minimum
position will not start the arc.
If the Current Control switch is set to the LOCAL
position, an Amptrol can be used as an arc start
switch. Depressing the Amptrol just past minimum will
cause the Amptrols built-in arc start switch to close,
and backing off completely causes the built-in start
switch to open. The Amptrol will have no effect on the
welding current when used as an arc start switch.