As a rule, this creates a material-to-material connection. Historically, there was first of all autogenous welding, in which acetylene was also used as a fuel gas in addition to the oxygen in steel cylinders. The flame must be precisely adjusted according to the mixture of the two gases and reaches around 3,200°C at the top of the blue part.

This type of welding is only very rarely used in body construction. The risk of hardening and, above all, warpage is too great with the thermal stress. By adding significantly more oxygen, the process can also be used for separation. However, it is essential for tinning.

In the automotive sector, weld seams are produced exclusively by electric arcs. Apart from spot welding, it is an important type of connection, especially in body construction and repair.

Direct current is connected with the plus side to the workpiece and the minus side to the metal electrode. The amperage is particularly high when the electric arc is ignited. If the filler material melts evenly, it is lower.

Assuming joint welding, the space between the workpieces is filled layer by layer, starting at the root of the seam. It is important that the material has a well through heating, which is also achieved here by a higher temperature at the negative pole of 4200°C compared to 'only' 3600°C at the electrode.

At the end there is a small elevation (picture), which is typical for every weld seam, especially for workpieces standing at right angles to one another. If the welding speed is too high, the seam will only have filled in the middle and not towards the workpieces. In addition, the connection can be faulty due to insufficient through heating.

In addition to the right temperature, the cleanliness of the weld joint is also very important. The electric arc generated by the direct current can blow cinder into it influenced by magnetic fields. This can be partially prevented by changing the welding direction and partly tilting the electrode more.

Cinder is created by the coating of the metal electrode and is intended to protect the still liquid metal from oxygen and nitrogen. It also stabilizes the electric arc and facilitates its ignition. It can contain alloy components and at the same time protect those contained in the material.

The finished seam is protected from cooling down by the cinder on the weld seam. It should therefore only be removed afterwards with a pointed hammer. Instead of the coating, electrodes made of coiled wire and inert gas are mostly used today. The welding processes are differentiated according to the type of protective gases.

Here we use a TIG welder to weld aluminum. It works with argon as the protective gas and non-melting tungsten as the electrode (Fig. 2). The aluminum sheets to be processed contain 5% magnesium.

They can be connected with and without additional wire. The prerequisite is the cleaning of the oxide layer, e.g. with a wire brush. The actual welding process takes a little longer than with sheet steel.

The electric arc is significantly brighter. It is important not to point it at the weld seam, so as not to increase its temperature. A relatively small angle is maintained between the torch and the bead against the direction of welding (welding with torch directed toward the part of the weld still to be made). In fact, you have to be very careful about the heat development so that the seam does not sink too much. Welding on both sides is not a problem, but only after a certain cooling phase.

Cast knots can also be connected to the corresponding strands using this method. A short time after the welding process you can see how the seam and its surroundings are covered with a new oxide layer. Less corrosion precautions are required, but great care should be taken to avoid contact with other metals with electrochemical series values different from aluminium.

For do-it-yourselfers or vintage car owners who only have a single problem, e.g. a leaking aluminum lid, there are now small welding machines with cartridge burners (camping gas) and additional material that is easy to handle.
Thanks to Georg Kaiser (TraCK, DN)