EN
Multiprocess 175. Operating manual.
Multiprocess 175. Operating manual.
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Cast and helix
The cast and helix of the wire has a major influence on the feedability of
MIG/MAG wire.
If the cast is too large the wire will move in an upward direction from the
tip when welding and if too small the wire will dip down from the tip.
The result of this is excessive tip wear and increased wear in the liners.
If the helix is too large the wire will leave the tip with a corkscrew effect.
Selection of the Correct Power Source
Power sources for MIG/MAG welding are selected on a number of
different criteria, including:
1. Maximum output of the machine
2. Duty cycle
3. Output control (voltage selection, wire feed speed control)
4. Portability
The following table gives an indication of the operating amperage for
different size wires.
Wire sizes
0.8mm
0.9mm
1.0mm
1.2mm
Amperage range (A)
60–180
70–250
90–280
120–340
Selection of the correct polarity on the power source
Many power sources are fitted with an optional reverse polarity dinse
connector.
To achieve the optimum welding it is important to adhere to the
consumable manufacturer‘s instruction to select the polarity.
As a general rule all solid and metal-cored wires are welded on
electrode positive. (Work return lead fitted to the negative connector.)
Some grades of self shielded flux-cored wires need to be welded on
electrode negative. (Work return lead fitted to the positive connector.)
Selection of the Correct Shielding Gas
The selection of the shielding gas has a direct influence on the
appearance and quality of the weld bead.
The thickness of the material to be welded will determine the type of
shielding gas that has to be selected. As a general rule the thicker the
material (C-Mn and Alloy steels) the higher the percentage of CO₂ in the
shielding gas mixture.
Different grades of shielding are required for materials such as stainless
steel, aluminium and copper.
Cast and helix
Cast – Diameter of the circle,
Helix – Vertical height
3. Gas Tungsten Arc Welding (GTAW/TIG).
Shielding gas is directed into the arc area by the welding torch and a
gas lens within the torch distributes the shielding gas evenly over the
weld area. In the torch the welding current is transferred to the tungsten
electrode from the copper conductor. The arc is then initiated by one of
several methods between the tungsten and the workpiece.
During TIG welding, the arc can be initiated by several means:
Scratch start
With this method, the tungsten electrode is physically scratched on the
surface of the workpiece and the arc is initiated at the full amperage
set by the operator. The incidence of the tungsten melting at the high
initiation amperage is high and tungsten inclusions in the weld metal are
quite common.
High frequency start
During High Frequency start, the arc will ‘jump’ towards the workpiece
if a critical distance is reached. With this method, there is no incidence
of tungsten inclusions happening. High Frequency is only available on
certain types of machines and it can affect nearby electronic equipment.
Lift Arc™
During this method of arc initiation, the tungsten is actually touching the
workpiece. This occurs at very low amperage that is only sufficient to
pre-heat, not melt the tungsten. As the tungsten is moved off the plate,
the arc is established. With this method, there is little chance of tungsten
inclusion occurring.
3.3 Process variables
DCEN
When direct-current electrode-negative (straight polarity) is used:
→
Electrons strike the part being welded at a high speed
→
Intense heat on the base metal is produced
→
The base metal melts very quickly
→
Ions from the inert gas are directed towards the negative electrode at
a relatively slow rate
→
Direct current with straight polarity does not require post-weld
cleaning to remove metal oxides
3.1 Introduction
The Tungsten Inert Gas, or TIG process, uses the heat generated by an
electric arc struck between a non-consumable tungsten electrode and
the workpiece to fuse metal in the joint area and produce a molten
weld pool. The arc area is shrouded in an inert or reducing gas shield to
protect the weld pool and the non-consumable electrode. The process
may be operated autogenously, that is, without filler, or filler may be
added by feeding a consumable wire or rod into the established weld
pool.
3.2 Process
1
Shielding gas,
2
Arc,
3
TIG filler rod,
4
Weld pool,
5
Collet,
6
Tungsten Electrode,
7
Workpiece
Schematic of the TIG welding process
1
2
3
4
5
6
7
Direct or alternating current power sources with constant current output
characteristics are normally employed to supply the welding current.
For DC operation the tungsten may be connected to either output
terminal, but is most often connected to the negative pole. The output
characteristics of the power source can have an effect on the quality of
the welds produced.
Cast
Helix
