General
Fusion welding of Aluminium is mainly done with the MIG (Metal Inert Gas) Process if the quantity of deposited material is put into calculation. Besides of the MIG process also TIG (Tungsten Inert Gas) has a greater significance for pressure vessels and plate thicknesses below 2 mm. Presently a substitution of TIG by the MIG process occurs with materials below 2 mm thickness. The reason is the fast progress of MIG pulse arc welding which makes it possible to extend the working range of MIG into thin materials.
The TIG and the MIG process have in common the inert shielding gas (Argon, Helium or mixtures of Argon and Helium) and the weld bead. The main differences are in the electrode and the required power source. While with MIG welding the filler wire is the electrode itself and a constant potential power source is used, with TIG welding the electrode is made of Tungsten and the power source is constant current.
The MIG process can be easily mechanized (robotic) which is not as simple with TIG welding. Because of this fact and the generally higher deposition rate of MIG welding it will show an increasing significance in the future.
Filler metals
The selection of the proper filler metal can be made with the material calculator. These aids cannot consider all constructional and metallurgical characteristics and the conditions of the base metal. Due to this reason separate investigations and trials are required before production in many cases. The quality and the stability of the process are in an immediate relation with the quality of the filler metal.
MIG welding
Filler metals from MIGAL.CO have an outstanding purity and enjoy a special surface treatment. With MIG-welding the fi ller wire is the electrode at the same time. The wire is fed from the spool through a wire-feed system into a hose pack and finally the contact tip by means of an automated system. The welding current is given to the electrode only short before the arc.
The gliding characteristic and the purity of the surface are essential for a trouble free wire feeding. MIGAL.CO wires are optimised for this purpose and provide a stable and safe arc ignition as well as low friction in the liners. A favourable side effect of the surface purity is the low formation of welding fumes, which occurs substantially by evaporation of the surface impurities. Welds made with wires from MIGAL.CO show lowest porosity and highest strength.
The wire feed unit must be equipped according to the manufacturers specifi cations. These concerns the shape of the wire feed rolls, the use of plastic or Teflon liners and the selection of the contact tips.
In opposite to steel wires the inner diameter of the contact tips bore must be larger. For instance it has been proven that a bore diameter of 1.6 mm is suitable for a 1.2 mm wire diameter. Greatest care has to be taken that the wire electrode does not scratch on any metal part on its way from the spool to the arc and that its surface remains undamaged. Furthermore it has to be considered that pure Aluminium and Aluminium-Silicon alloys are softer than Aluminium-Magnesium alloys and that the liner length should not exceed 3 m. With Aluminium-Magnesium alloys a length of 4 m should be possible. With mechanised or robotic welding processes a hose pack length of 1.5 to 2 m should not be exceeded and in the full interest of a trouble free welding process a pull-wire feed system (wire drive in the welding torch) or combined systems (push-pull) are recommended.