Assignment

Welding seams in the motor sector are produced exclusively through electric arc welding. Apart from spot-welding, it is a particularly important method of joining components together in coach-building and for repair work.

Function

The direct current plus terminal is connected to the component, and the minus terminal to the metal electrode. The electric current is particularly high when the arc is struck. During the even melting of the additional filler material the current is lower. If it is to be a joining weld, one starts the filling, layer for layer, at the seam-root between the two components. Very important is the correct pre-heating of the material which, through a higher temperature on the minus terminal, can reach 4200°C, in contrast to the electrode, where 'only' 3600° is reached. At the end, a small raised seam is left (see figure), which is typical for all welding seams, particularly when welding components at a right-angle to each other. If the welding is done too quickly, then the seam-root is not filled correctly. Apart from that, the join can also be inferior due to insufficient pre- heating.

Apart from the correct temperature, the cleanliness of the welding groove is also very important. Slag, influenced by the magnetic fields, can be blown into the welding groove by the direct current electric arc. This can be avoided to a certain extent, by changing the welding direction and slanting the electrode more. Slag is developed through the casing of the electrode and should protect the molten metal from oxygen and nitrogen. In addition, it stabilises the electric arc and makes it's ignition easier. It can contain alloy elements, at the same time protecting those in the component. The finished welding seam is protected against cooling down by the slag layer. This is why, by using a pointed hammer, it should only be removed afterwards.
Instead of having a filler casing, nowadays the use of welding rods made from coiled wire is widespread, a protective gas is used which flows over the electric arc and the components to be welded. The types of welding processes differ, according to which protective gas is used. 11/10