Welding techniques

The best welding choice depends on many factors, not only from metallurgical but also from an economic and logistic
point of view. MMA Welding Technique fits for welding with a high quantity of material deposit. For example,
it is particularly suitable in case of modifying a mold shape for a variation in piece design.

Furthermore, because of its easy transportability, welding can be performed on site with no need of dismantling and transporting the mold. This technique generates a remarkable thermic supply in the areas adjacent the welded spot, therefore it is necessary to take good care of pre-heating and stress relieving procedures.

TIG technique is suitable for smaller repairing of mold, than the MMA technique and it generates a lower thermic supply. Such a technique is not as easily transportable as the MMA, because of its jet shielding system and the torch cooling system. LASER technique is suitable for welding repairing with minimum material deposit. It is advisable to use it when the required deposit thickness is from 0.2 mm to 1-1.5 mm and with a size related to the welded thickness.

MMA TECHNIQUE

MMA (Manual Metal-Arc Welding) technique is probably the most well known.

The welding process is obtained creating a voltage difference between the electrode and the work piece to be welded. Putting the two parts in contact a short circuit is created with a subsequent local overheating caused by Joule effect on the electrode. This starts to melt and to deposit material on the work piece. Under these conditions a modest tension is sufficient to strike an electric arc for the welding process.

The electrodes used with MMA technique have a surface layer that protects from contamination by air, deoxidizes and purify the molten pool, enriching it of alloy elements too. Arch welding is recommended in many and diverse situations, especially when an elevate quantity of filler material deposit is needed.

TIG TECHNIQUE

TIG (Tungsten Inert Gas) welding technique is an autogenous process, where the heat is generated by the arch between the non consumable tungsten electrode and the work piece. The tungsten is a material that mostly its this kind of application because of its very high fusion temperature and of its excellent thermionic properties. The welding is executed in protected atmosphere by an inert gas shielding, for example Argon.

By means of this process, it’s possible to weld with or without filler material, as in the case of thin thickness. The electrode is made of a circular section with dimensions and chemical analysis compatible with the base metal.

LASER TECHNIQUE

LASER technique is utilized for micro-welding to adjust machining errors in tool making, to modify the worpiece design, to recover damaged toolings during service and to repair incidental surface defects.

The main advantages of the laser technique are the following:

– To operate on small areas with minimum filler material
– Minimum “invasive” effect on the areas surrounding the welded spot.
– Rapidity of execution, because usually there is no need of massive heat treatment before and after welding
– High polishability and photoetchability on the welded area

LASER (Light Amplification by Simulated Emission of Radiation) is an electromagnetic waves beam, moving in the same direction and producing very high specific powers (107 – 109 W/cm2).

Unlikely other welding techniques, laser technique can be executed without filler material.
In case of tool steel, Laser welding is always executed with filler material, namely a wire with chemical analysis compatible with the base material and with 0,2 – 0,8 mm diametric section.
The predominant heat transmission mechanism is the conduction. The possibility of focusing its action on a very restricted area is one of the most interesting features of Laser welding.
It is possible to operate on smallest areas, even smaller than 1 mm2 width. So micro-welding can be carried out in order to remedy even smaller defect than a tenth of a millimetre derived from the mechanical grinding.