Which materials are weldable?
Since the possibility of welding and welding safety can be strongly influenced by machines and aids, the consideration of the basic weldability of a substance is usually most important. It may happen that a substance that is not suitable for fusion welding, can be very well suited for a pressure welding. The weldability can therefore always be evaluated only in relation to a welding process .
Weldability of components
The weldability of components is decided on the basis of three criteria.
Weldability is the ability of the fabric to be inseparably linked to the same or different fabric when using a welding technique. The possibility of welding refers to adequate equipment for carrying out the planned welding process, ie it is aimed at a suitable workplace.
Welding reliability weighs the likelihood of deformation or other errors due to welding influences.
Which properties should a weldable material have?
“Weldability is available if, under consideration of qualitative and economic aspects, a spot welding meeting the requirements can be produced.”
The most important ability of a substance is that it regains its strength after welding and after cooling. At the same time, however, high hot workability is beneficial for good welding results.
In fusion welding processes , the melting temperatures of the substances to be welded should be as close as possible to each other. Too large differences in the melting temperatures make the process difficult or even impossible.
Low thermal conductivity simplifies the process because less heat must be applied. If the substance has a high thermal conductivity, significantly more heat must be applied to the material due to heat dissipation from the weld. However, fabrics with extremely low conductivity (glass, plastic) often tend to crack and break.
The role of chemistry in welding
By heating up to the melting point or the large force, the affected areas of the workpieces are changed in their chemical composition. This change can lead to a serious deterioration of the mechanical properties of some materials and disqualifies these materials for welding.
For steels, weldability is strongly related to carbon content. For a steel with a carbon content above 0.2% precautions should be taken as they tend to crack. This risk is significantly reduced by preheating and stress relief annealing.
Caution is advised when welding alloys, since even a small amount of alloy of a few percent can significantly change the properties of the substance. Thus, the weldability of the substance may change due to the alloy, which makes a different welding process more suitable than for the substance in its pure form.
Which materials are suitable for welding?
All substances whose heating is associated with a risk of fire or explosion are not suitable for fusion welding. Examples are containers in which flammable liquids are or were located. The same applies to work in the vicinity of such hazardous substances. In fusion welding, there is always an open ignition source that can ignite liquids or gas mixtures in the vicinity.
In general, all metals are suitable for welding, as they have a ductility. This means that metals can bend rather than break. This applies regardless of whether it is steel, other ferrous metals or non-ferrous metals.
Furthermore, with some welding processes also plastics and even glass can be welded. In these materials, however, the lowest possible and targeted heat input is important because glass tends to crack at large temperature differences and plastics are only partially fireproof.