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5.
Periodically check that the earth clamp pads are not damaged and that the
welding cables (torch and earth) are not cut or burnt which could impair
efficiency.
4.4
STAINLESS STEEL WELDING
MIG Welding of 300 series (austenitic) stainless steel must be carried out with a
shielding gas that has a high Argon content and a small percentage of O2 to stabi-
lise the arc. The most commonly used mixture is AR/O2 98/2.
- Never use CO2 or AR/CO2 mixtures.
- Never touch the wire.
The filler material used must be of a higher quality than the base material and the
welding zone must be completely clean.
4.5
ALUMINIUM WELDING
To MIG weld aluminium, use the following:
1.
100% Argon shielding gas.
2.
Filler wire with a composition suited to the base welding material. To weld
ALUMAN and ANTICORODAL use 3-5% silicon wire.To weld PERALUMAN
and ERGAL use 5% magnesium wire.
3.
Use a torch designed for aluminium welding.
4.6
WELDING WITH CORED WIRE (WITHOUT GAS) FCW
For welding with cored wire without gas, the polarity inside the machine must be
changed. Connect the mass to the positive pole.
FAULT
UNEVEN LEVEL
EXCESS THICKNESS
INSUFFICIENT METAL
OXIDISED BEAD
INSUFFICIENT
PENETRATION
OVER PENETRATION
LACK OF FUSION
CHANNELS
6.0 WELDING PROCESS
6.1
TIG PROCEDURE
1.
Connect the earth cable connector to the positive (+) pole on the power
source and the terminal to the piece in the point nearest to the welding area.
MIG WELDING FAULTS
Figure 2.
4.7
SPOT WELDING
This type of welding is used for spot welding two
overlapping sheets, and requires the use of a special gas nozzle.
Fit the spot welding gas nozzle, press it against the piece to be welded. Press the
torch button; note that the welder will eventually detach from the piece. This time
interval is determined by the spot welding control and must be set according to
the thickness of the sheet to be spot-welded.
5.0 MIG WELDING FAULTS
FAULT CLASSIFICATION AND DESCRIPTION
MIG welds may be affected by various defects, which are important to identify.
These faults do not differ in form or nature from those encountered during manual
arc welding with coated electrodes. The difference between the two applications
lies rather in the frequency of defects: porosity, for example, is more common in
MIG welding, while inclusion of slag is only encountered in welding with coated
electrodes.
The causes and prevention of faults are also quite different.
The following table illustrates the various faults.
APPEARANCE
- Poor preparation.
- Align edges and hold during spot welding.
- No-load voltage or welding speed too low.
- Incorrect torch inclination.
- Wire diameter too large
- Welding speed too high.
- Welding voltage too low for welding application.
- Weld in the channel if using a long arc.
- Regulate voltage.
- Wire is bent or over-protruding from the wire guide tube.
- Incorrect wire feed speed.
- Incorrect torch inclination.
- Irregular or insufficient distance.
- Wire guide tube worn.
- Wire speed too slow for voltage used or for welding speed.
- Wire speed too high.
- Incorrect torch inclination.
- Excessive distance.
- Distance too short.
- Rough out or grind the weld, then repeat.
- Welding speed too high.
(This fault is easily detected on sight by the welder, and should be
corrected immediately.)
2.
Connect the TIG torch power connector to the negative (-) pole on the
power source.
3.
Connect the TIG torch gas hose to the pressure reducer outlet connected to
the argon gas cylinder.
(GB) 8
CAUSE AND REMEDY
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