How to prevent the occurrence of thermal cracks in laser welding?

How to prevent the occurrence of thermal cracks in laser welding?

Welding cracks are a very serious defect. The destruction of the structure starts from the cracks. All necessary measures should be taken to prevent cracks during the welding process, and various methods should be used to check whether there are cracks after welding. Once cracks are found, they should be cleaned. Then repair, welding cracks are divided into hot cracks and cold cracks.

• The cracks produced during the crystallization process of the weld metal from liquid to solid are called thermal cracks. The reason for the thermal cracks is that there are impurities with low melting points in the weld pool. Due to the low melting point of these impurities, the crystallization solidifies later, and the plasticity after solidification And the strength is low. During the solidification process or shortly after solidification, these low melting point impurities in the molten pool are pulled apart, resulting in intergranular cracking. When the weldment and welding rod contain more impurities such as sulfur and copper, hot cracks are prone to occur .

  
  

Measures to prevent thermal cracking during laser welding include:

   1. Strictly control the welding process parameters, slow down the cooling rate, appropriately increase the shape factor of the weld seam, and use low-current multi-layer multi-pass welding as much as possible to avoid cracks in the center of the weld seam.

   2. Conscientiously implement the process regulations, choose a reasonable welding process, and reduce welding stress.

•  During the cooling process or after the weld metal is cooled, the cracks that appear at the base metal or at the junction of the base metal and the weld are called cold cracks. It can occur immediately after welding or within a long time after welding, so it is also called delayed crack.

Measures to prevent cold cracks in laser welding include:

  1. Choose low-hydrogen electrodes to reduce the content of diffusible hydrogen in the weld.

  2. Strictly abide by the storage, baking and use system of welding materials (welding rods and fluxes), and strictly prevent them from getting damp.

  3. Carefully clean up the oil, water and rust on the side of the tank to reduce the source of hydrogen.

  4. Adopt a reasonable welding process, adopt segmental stripping method, etc., to reduce welding stress.

What is the welding purpose of non-standard laser welding processing?

  1. Fusion welding - heat the workpiece to be welded to form a molten pool, and weld after the molten pool is cooled and solidified. If necessary, fillers can be added. It is suitable for welding various metals and alloys without pressure.

  2. Pressure welding - the welding process needs to exert pressure on the weldment, which belongs to the processing of various metal materials and some metal materials.

  3. Brazing - the metal material with a melting point lower than the base metal is used as a brazing filler metal, the liquid brazing filler metal wets the base metal, fills the joint gap, and diffuses with the base metal to realize the connection weldment, which is suitable for various materials Welding is also suitable for welding of dissimilar metals or dissimilar materials.