Laser welding equipment uses high-energy laser pulses to focus and melt the target metal, thereby welding the workpieces.
The new welding technology has a positive effect, however, if not handled correctly, it can result in hot or cold cracking.
What causes welding cracks on a laser welding machine?
Metallurgical factors
The rapid unbalanced heating and cooling during laser welding creates a complex stress state in the joint, which is a mechanical factor contributing to cracking.
Laser welding is a series of unbalanced processes, leading to uneven component distribution and a hardened structure with poor crack resistance during rapid solidification. This constitutes a metallurgical factor that promotes crack initiation.
Mechanical factors
There are three types of cracks that can occur during the welding process of a laser welding machine: product cracks, liquefaction cracks and reheat cracks.
Crystal cracking is the result of non-uniform composition in the weld macroregion.
The central area of the weld is where liquid phase crystallization last occurs and where the columnar crystals on both sides of the weld meet.
Unfortunately, a large number of impurities with low melting points also accumulate in this area, resulting in centerline segregation that weakens bond strength.
Under certain mechanical conditions, cracks may occur in this location.
Therefore, it is important to promptly identify and resolve any cracks that occur.
So, what can be done to reduce the occurrence of welding cracks on a laser welding machine?
There are two main measurements:
Changing Laser Welding Machine Parameters
The main causes of thermal cracking during pulsed laser welding are due to the solidification of the weld after the laser welding process. During this process, the weld passes through a temperature range with low plasticity, called the brittle temperature zone.
The crystallization of the weld metal is influenced by tensile stress, which is caused by the difficulty in retracting the welded metal.
This tensile stress results in elastic-plastic deformation in the weld.
If the weld metal is in the brittle temperature zone and the plastic deformation exceeds the plasticity of the metal, cracking will occur.
Reasonably improve the alloy system of the material according to the nature of the crack
The causes of cold cracking during pulsed laser welding occur during the cooling process. A martensitic structure forms near the seam and welding stresses as well as microstructural stresses are generated.
Metal with martensitic structure has high strength, but low plasticity and residual stresses remain in the weld metal during the cooling process.
In the case of ferritic or austenitic hardened steel, the stress state of welded joints is characterized by the formation of longitudinal compressive stresses close to the weld area. This is caused by the martensitic transformation that occurs in this area during welding.
These types of stresses can result in the formation of cold cracks.
Causes of thermal cracking:
The occurrence of thermal cracks during laser welding depends on several factors, including the chemical composition of the weld metal and the surrounding area, the conditions and characteristics of the crystallization process, the extent of chemical and physical microheterogeneity, the size of the deformation, and the rate at which the strain grows.
Currently, the formation mechanism of crystalline cracks is described below:
During the solidification process of a sheet metal bending machine, the weld from the laser welding machine passes through a temperature range with low plasticity, called the brittle temperature zone.
The crystallization of the weld metal is influenced by tensile stress, which is caused by the difficulty in retracting the welded metal.
The presence of tensile stress leads to elastic-plastic deformation in the weld.
If the weld metal is in the brittle temperature zone and the plastic deformation exceeds the plasticity of the metal, a crack will form.
