Tig Ac Welding; Procedure; Mma Welding; Maintenance - Telwin TIG 222 Manuel D'instructions

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. 5) 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. 4) shows suggested values for welding on aluminium; the most
suitable electrode is a pure tungsten electrode (green band).

6.1.4 Procedure

- Regulate the welding current to the wanted value through the knob; if necessary,
adjust during the welding operation to the actual heat transfer necessary.
- Press the torch pushbutton verifying the correct gas outflow from the torch; calibrate,
if necessary, the PRE GAS and POST GAS timings: these timings must be adjusted
in keeping with the operative conditions. In particular, the gas delay must be such
as to permit, at the end of the welding, the cooling off of the electrode and the
weld pool without them coming into contact with the atmosphere (oxidations and
contaminations).
TIG mode with 2T sequence:
- Press completely the torch pushbutton (P.T.), strike the arc and keep a distance of
2-3mm from the piece to be welded.
- In order to interrupt the welding operation, release the torch pushbutton allowing
the gradual zeroing of the current (if the END SLOPE function is active) or to the
immediate switching off of the arc with subsequent post gas.
TIG mode with 4T sequence:
- When the pushbutton is first pressed it strikes the arc with a I
releasing the pushbutton, the current rises up to the welding current's value; this
value is maintained also with pushbutton released. When the pushbutton is pressed
again, the current reduces according to the END SLOPE function until I
reached. The latter is maintained until the release of the pushbutton that ends the
welding cycle, starting the POST GAS period. Instead, if the pushbutton is released
during the END SLOPE function, the welding cycle ends immediately and the POST
GAS period starts.
TIG mode with 4T and BI-LEVEL sequence:
- When the pushbutton is first pressed it strikes the arc with a current I
releasing the pushbutton, the current rises up to the welding current's value; this
value is maintained also with pushbutton released. With every subsequent pressing
of the pushbutton (the time lapse between the pressing and releasing must be very
short) the current will vary between the value set in the BI-LEVEL I
the value of main current I .
2
By keeping the pushbutton pressed for an extended time, the current drops until
I . The latter is maintained until the release of the pushbutton that ends the
minima
welding cycle, starting the POST GAS period (FIG. M). Instead, if the pushbutton is
released during the END SLOPE function, the welding cycle ends immediately and
the POST GAS period starts.

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
- 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 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).
current. Upon
Start
minima
. Upon
Start
parameter and
1
Welding current (A)
min. max.
25 50
40 80
60 110
80 160
120 200

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 couple the electrode holder clamp, the gas diffusor calibrated with the
diameter of the selected electrode in order to prevent overheating, poor diffusion of
the gas and relative malfunctions.
- Before every use, check the state of wear and the correct assembly of the terminal
parts of the torch: nozzle, electrode, electrode holder clamp, gas diffusor.

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
is for damage to the insulation.
- 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.
Use all the original washers and screws when closing the casing.

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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