Telwin TIG DC AC/DC HF Manuel D'instructions page 9

current setting will be supplied. At the end of the cycle the current will fall to zero at the
slope down setting.
6.1.2 TIG DC welding
TIG DC welding is suitable for all low- and high-carbon steels and the heavy metals, copper,
nickel, titanium and their alloys.
For TIG DC welding with the electrode to the (-) terminal the electrode with 2% thorium (red
band) is usually used or else the electrode with 2% cerium (grey band).
It is necessary to sharpen the tungsten electrode axially on the grinding wheel, as shown
in FIG. L, making sure that the tip is perfectly concentric to prevent arc deviation. It is
important to carry out the grinding along the length of the electrode. This operation should
be repeated periodically, depending on the amount of use and wear of the electrode, or
when the electrode has been accidentally contaminated, oxidised or used incorrectly. In TIG
DC mode 2-stroke (2T) and 4-stroke(4T) operation are possible.
6.1.3 TIG AC welding
This type of welding can be used to weld metals such as aluminium and magnesium,
which form a protective, insulating oxide on their surface. By reversing the welding current
polarity it is possible to "break" the surface layer of oxide by means of a mechanism called
"ionic sandblasting". The voltage on the tungsten electrode alternates between positive (EP)
and negative (EN). During the EP period the oxide is removed from the surface ("cleaning"or
"pickling") allowing formation of the pool. During the EN period there is maximum heat
transfer to the piece, allowing welding. The possibility of varying the balance parameter in
AC means that it is possible to reduce the EP current period to a minimum, allowing quicker
welding.
Higher balance values give quicker welding, greater penetration, a more concentrated arc, a
narrower weld pool and limited heating of the electrode. Lower values give a cleaner piece.
If the balance value is too low this will widen the arc and the de-oxidised part, overheat the
electrode with consequent formation of a sphere on the tip making it more difficult to strike
the arc and control its direction. If the balance value is too high this will create a "dirty" weld
pool with dark inclusions.
The table (TAB. 4) summarises the effects of parameter changes in AC welding.
In TIG AC mode 2-stroke (2T) and 4-stroke (4T) operation are possible.
The instructions for this welding procedure are also valid.
The table (TAB. 3) shows suggested values for welding on aluminium; the most suitable
electrode is a pure tungsten electrode (green band).
6.1.4 Procedure
- Use the knob to adjust the welding current to the desired value; if necessary adjust during
welding to the actual required heat transfer.
- Press the torch button and make sure the gas flow from the torch is correct; if necessary,
adjust pre-gas and postgas times; these times should be adjusted according to operating
conditions, the postgas delay in particular should be long enough to allow the electrode
and weld pool to cool at the end of welding without coming into contact with the
atmosphere (oxidation and contamination).
TIG mode with 2T sequence:
- Press the torch button (P.T.) right down to strike the arc with a current of I
will increase according to the START SLOPE UP setting to the welding current value.
- To interrupt welding, release the torch button so that either the current gradually
decreases (if the FINAL SLOPE DOWN parameter has been enabled) or the arc is
extinguished immediately, followed by postgas.
TIG mode with 4T sequence:
- The first time the button is pressed it will strike the arc with a current equal to I
the button is released the current will increase according to the START SLOPE UP setting
to the welding current value; this value is maintained even with the button is released.
When the button is pressed again the current will decrease according to the FINAL SLOPE
DOWN setting, until it reaches I . The I
END
released to terminate the welding cycle and start the postgas phase. If, on the other hand,
the button is released while the FINAL SLOPE DOWN function is proceeding, the welding
cycle will terminate immediately and the postgas phase will start.
TIG mode with 4T and BI-LEVEL sequence:
- The first time the button is pressed it will strike the arc with a current equal to I
the button is released the current will increase according to the START SLOPE UP setting
to the welding current value; this value is maintained even when the button is released.
Now, every time the button is pressed (the time between pressure and release should be
short) the current will change between the setting for the BI-LEVEL I
main current value I .
2
- When the button is kept pressed down for a longer space of time the current will decrease
according to the FINAL SLOPE DOWN setting, until it reaches I
be maintained until the button is released to terminate the welding cycle and start the
postgas phase. If, on the other hand, the button is released while the FINAL SLOPE DOWN
function is proceeding, the welding cycle will terminate immediately and the postgas
phase will start (FIG.M).
6.2 MMA WELDING
- It is most important that the user refers to the maker's instructions indicated on the stick
electrode packaging. This will indicate the correct polarity of the stick electrode and the
most suitable current.
- The welding current must be regulated according to the diameter of the electrode in
use and the type of the joint to be carried out: see below the currents corresponding to
various electrode diameters:
Ø Electrode (mm)
1.6
2
2.5
3.2
4
5
6
- The user must consider that, according to the electrode diameter, higher current values
must be used for flat welding, whereas for vertical or overhead welds lower current values
are necessary.
- As well as being determined by the chosen current intensity, the mechanical
characteristics of the welded join are also determined by the other welding parameters
i.e. arc length, working rate and position, electrode diameter and quality (to store the
electrodes correctly, keep them in a dry place protected by their packaging or containers).
- The properties of the weld also depend on the ARC-FORCE value (dynamic behaviour) of
the welding machine. The setting for this parameter can be made either on the panel or
using the remote control with 2 potentiometers.
- It should be noted that high ARC-FORCE values achieve better penetration and allow
welding in any position typically with basic electrodes, low ARC-FORCE values give a
softer, spray-free arc typically with rutile electrodes.
. The current
START
current will be maintained until the button is
END
parameter and the
1
. The I current will
END END
Welding current (A)
Min. Max.
25 50
40 80
60 110
80 160
120 200
150 280
200 350
The welding machine is also equipped with HOT START and ANTI STICK devices to
guarantee easy starts and to prevent the electrode from sticking to the piece.
6.2.1 Procedure
- Holding the mask IN FRONT OF THE FACE, strike the electrode tip on the workpiece as if
you were striking a match. This is the correct strike-up method.
WARNING: do not hit the electrode on the workpiece, this could damage the electrode
and make strike-up difficult.
- As soon as arc is ignited, try to maintain a distance from the workpiece equal to the
diameter of the electrode in use. Keep this distance as much constant as possible for the
duration of the weld. Remember that the angle of the electrode as it advances should be
of 20-30 grades.
- At the end of the weld bead, bring the end of the electrode backward, in order to fill
the weld crater, quickly lift the electrode from the weld pool to extinguish the arc
(CHARACTERISTICS OF THE WELD BEAD - FIG. N).
7. MAINTENANCE
WARNING! BEFORE CARRYING OUT MAINTENANCE OPERATIONS MAKE SURE
THE WELDING MACHINE IS SWITCHED OFF AND DISCONNECTED FROM THE
MAIN POWER SUPPLY.
7.1 ROUTINE MAINTENANCE
ROUTINE MAINTENANCE OPERATIONS CAN BE CARRIED OUT BY THE OPERATOR.
7.1.1 Torch
- Do not put the torch or its cable on hot pieces; this would cause the insulating materials
to melt, making the torch unusable after a very short time.
- Make regular checks on the gas pipe and connector seals.
- Accurately match collet and collet body with the selected electrode diameter in order to
avoid overheating, bad gas diffusion and poor performance.
- At least once a day check the terminal parts of the torch for wear and make sure they are
assembled correctly: nozzle, electrode, electrode-holder clamp, gas diffuser.
7.2 EXTRAORDINARY MAINTENANCE
EXTRAORDINARY MAINTENANCE MUST ONLY BE CARRIED OUT BY TECHNICIANS
WHO ARE EXPERT OR QUALIFIED IN THE ELECTRIC-MECHANICAL FIELD, AND IN FULL
RESPECT OF THE IEC/EN 60974-4 TECHNICAL DIRECTIVE.
WARNING! BEFORE REMOVING THE WELDING MACHINE PANELS AND
WORKING INSIDE THE MACHINE MAKE SURE THE WELDING MACHINE IS
SWITCHED OFF AND DISCONNECTED FROM THE MAIN POWER SUPPLY OUTLET.
If checks are made inside the welding machine while it is live, this may cause serious
electric shock due to direct contact with live parts and/or injury due to direct contact
with moving parts.
- Periodically, and in any case with a frequency in keeping with the utilisation and with the
environment's dust conditions, inspect the inside of the welding machine and remove
the dust deposited on the electronic boards with a very soft brush or with appropriate
solvents.
- At the same time make sure the electrical connections are tight and check the wiring for
. When damage to the insulation.
START
- At the end of these operations re-assemble the panels of the welding machine and screw
the fastening screws right down.
- Never, ever carry out welding operations while the welding machine is open.
- After having carried out maintenance or repairs, restore the connections and wiring as
they were before, making sure they do not come into contact with moving parts or parts
that can reach high temperatures. Tie all the wires as they were before, being careful to
keep the high voltage connections of the primary transformer separate from the low
voltage ones of the secondary transformer.
. When Use all the original washers and screws when closing the casing.
START
8. TROUBLESHOOTING
IN CASE OF UNSATISFACTORY FUNCTIONING, BEFORE SERVICING MACHINE OR REQUESTING
ASSISTANCE, CARRY OUT THE FOLLOWING CHECK:
- Check that the welding current is correct for the diamter and electrode type in use.
- Check that when general switch is ON the relative lamp is ON. If this is not the case then
the problem is located on the mains (cables, plugs, outlets, fuses, etc.).
- Check that the yellow led (ie. thermal protection interruption- either over or undervoltage
or short circuit) is not lit.
- Check that the nominal intermittance ratio is correct. In case there is a thermal protection
interruption, wait for the machine to cool down, check that the fan is working properly.
- Check the mains voltage: if the value is too high or too low the welding machine will be
stopped.
- Check that there is no short-circuit at the output of the machine: if this is the case
eliminate the incovenience.
- Check that all connections of the welding circuit are correct, particularly that the work
clamp is well attached to the workpiece, with no interferring material or surface-
coverings (ie. Paint).
- Protective gas must be of appropriate type (Argon 99.5%) and quantity.
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