- 21 December 2024
Why is aluminum harder to weld than ordinary steel or even alloy steel? It's all about the temperature difference required to melt the top oxide layer and weld the metal itself. The top layer has a melting point of 2044 degrees, while aluminum and its alloys have a melting point of 660°C.
It should be remembered that aluminum has a high thermal conductivity. As a result, the heat affected zone becomes very hot and deforms. If you weld aluminum in one place for a long time, the metal will simply deteriorate. At the same time, the release of hydrogen contributes to the formation of pores and loss of tightness. Welding aluminum is also made more difficult by the fact that aluminum has increased fluidity and it is difficult for the welder to control the weld pool. Often the seam turns out to be flaccid and uneven in width.
There are only three ways when it comes to welding aluminum. Each of them has its obvious advantages and disadvantages.
The biggest problems when welding aluminum, arise from its increased thermal conductivity, through which there is a risk of burning through thin objects and the oxide layer on the metal. MIG welding eliminates these risks to some extent.
To prevent warping and burn-through, thin aluminum parts are welded with a pulsed arc or short, low voltage and low welding current. This not only reduces heat input. The short arc is easier to control during welding.
For thick-walled aluminum parts, drop flux transfer MIG welding is used at higher welding voltage and current. The size of the welding current, the arc voltage depend on the alloy grade. This is due to the difference in thermal conductivity, which can be significant. Particularly noteworthy is the position of the torch. When welding, keep the arc length within 12-15 mm, move the torch away and do not change the angle with respect to the surface.
TIG welding involves the use of a non-fusible tungsten electrode in an inert gas (argon). The current source is an inverter. The current itself can be either direct or alternating current, with reverse polarity, but it is believed that with alternating current the seams are much better.
TIG welding is carried out with the torch inclined at an angle of 45-80 degrees, which follows the wire. The current intensity is selected according to the thickness of the material at a rate of 25 A for every 1 mm. Note that this method requires an initial gas for 2 s and a final gas at intervals of up to 6 s. To stretch the width of the seam, slight lateral movements are allowed with the torch. The advantages of this method are the high density of the seam, the absence of pores, and the lack of subsequent processing.
Spot welding has been somewhat forgotten in recent decades. Traditional technologies have been replaced by those that allow the welding process parameters to be changed programmatically during the formation of the welded joint, according to calculation data or depending on the conditions of the welding process itself. Technologies have emerged - adaptive automatic resistance welding (smart welding). The emergence of new technologies and equipment in the field of resistance welding was due to the following reasons:
- The use of new materials.
- Increasing quality requirements.
- The use of robotic technology due to the mass nature of production;
Still, "spot welding" has its supporters. The shape and dimensions of the parts to be joined and the position of the points must be such that the parts at the points of contact are pressed against each other without obstruction. The thickness of welded parts should not exceed three times the difference. Due to the high thermal conductivity of the material, there are restrictions on the types of electrodes used. The material for their production must have good electrical conductivity (more than 85%), heat resistance and hardness. These are copper electrodes, the composition of which is selected depending on the type of alloy to be welded.
