Selco WF 115 XP Instrucciones De Uso página 27

Blowholes
Cause Insufficient shielding gas.
Solution Adjust the gas flow.
Check that the diffuser and the gas nozzle of the
torch are in good condition.
Sticking
Cause Incorrect welding parameters.
Solution Increase the welding current.
Cause Incorrect welding mode.
Solution Angle the torch more.
Cause Pieces to be welded too big.
Solution Increase the welding current.
Cause Incorrect arc regulation.
Solution Use a higher setting inductive connection.
Undercuts
Cause Incorrect welding parameters.
Solution Decrease the welding voltage.
Cause Incorrect welding mode.
Solution Decrease the side oscillation speed while filling.
Decrease the travel speed while welding.
Cause Insufficient shielding gas.
Solution Use gases suitable for the materials to be welded.
Oxidations
Cause Insufficient gas protection.
Solution Adjust the gas flow.
Check that the diffuser and the gas nozzle of the
torch are in good condition.
Porosity
Cause Grease, varnish, rust or dirt on the workpieces to be welded.
Solution Clean the workpieces carefully before welding.
Cause Grease, varnish, rust or dirt on the filler material.
Solution Always use quality materials and products.
Keep the filler metal always in perfect condition.
Cause Insufficient shielding gas.
Solution Adjust the gas flow.
Check that the diffuser and the gas nozzle of the
torch are in good condition.
Cause The weld pool solidifies too quickly.
Solution Decrease the travel speed while welding.
Pre-heat the workpieces to be welded.
Increase the welding current.
Hot cracks
Cause Incorrect welding parameters.
Solution Decrease the welding voltage.
Cause Grease, varnish, rust or dirt on the workpieces to
be welded.
Solution Clean the workpieces carefully before welding.
Cause Grease, varnish, rust or dirt on the filler metal.
Solution Always use quality materials and products.
Keep the filler metal always in perfect condition.
Cause Incorrect welding mode.
Solution Carry out the correct sequence of operations for
the type of joint to be welded.
For any doubts and/or problems do not hesitate to contact
your nearest customer service centre.
6 CONTINUOUS WIRE WELDING THEORY
6.1 Introduction
A MIG system consists of a direct current power source, wire
feeder, wire spool, torch and gas.
MIG manual welding system
The current is transferred to the arc through the fusible elec-
trode (wire connected to positive pole); in this procedure the
melted metal is transferred onto the workpiece through the arc
stream. The automatic feeding of the continuous filler material
electrode (wire) is necessary to refill the wire that has melted
during welding.
6.1.1 Methods
In MIG welding, two main metal transfer mechanisms are
present and they can be classified according to the means by
which metal is transferred from the electrode to the work-
piece. The first one, defined "SHORT-ARC", produces a small,
fast-solidifying weld pool where metal is transferred from the
electrode to the workpiece only for a short period when the
electrode is in contact with the weld pool. In this timeframe,
the electrode comes into direct contact with the weld pool
generating a short circuit that melts the wire which is there-
fore interrupted. The arc then turn on again and the cycle is
repeated (Fig. 1a).
Fig. 1a
Fig. 1b
SHORT cycle (a) and SPRAY ARC welding (b)
Another mechanism for metal transfer is called the "SPRAY-ARC"
method, where the metal transfer occurs in the form of very small
drops that are formed and detached from the tip of the wire and
transferred to the weld pool through the arc stream (Fig. 1b).
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