Laser welding machine: reasons and solutions for cracking of welded joints in spliced welding plates

The main reasons for weld cracking
1. Material characteristics:
Difference in thermal expansion coefficient: When the welded plate is composed of different materials, due to their different thermal expansion coefficients, stress will be generated during heating and cooling, leading to weld cracking.
Material purity: Changes in impurities or alloy composition can affect the melting point and thermal conductivity of the material, thereby increasing the difficulty of welding and making it easier to form cracks.

2. Improper setting of welding parameters:
High or low power: High power can lead to overheating, resulting in a large heat affected zone (HAZ), while low power may not fully fuse the material, both of which can cause cracks.
Inappropriate welding speed: If the speed is too fast, the molten pool will not fully fuse in time, and if the speed is too slow, it will cause local overheating, both of which may lead to weld cracking.

3. Process design defects:
Unreasonable weld design, such as mismatched parameters such as weld width and depth, or poor welding path planning, can affect the quality of the weld.
Insufficient pre-treatment: The surface of the material is not thoroughly cleaned, and residual impurities such as oil stains and oxide layers can weaken the strength of the weld and lead to cracking.

4. Environmental factors:
Severe temperature changes: If the ambient temperature suddenly changes after welding, there will be a large temperature difference between the inside and outside of the material, which can easily generate internal stress and promote weld cracking.
Humidity impact: In high humidity environments, moisture may seep into the welding area, causing hydrogen embrittlement and reducing weld toughness.

Solution and preventive measures
1. Optimize material selection:
Try to use materials with similar thermal expansion coefficients for splicing to reduce stress concentration caused by material differences.
Ensure stable quality of raw materials, strictly control impurity content, and improve material purity.

2. Adjust welding parameters:
Based on the material type and thickness, the optimal laser power and welding speed are determined through experiments to ensure a uniform melt pool without overheating.
Use appropriate defocus amount to optimize the shape of the melt pool and avoid excessive heat affected zone.

3. Improve process design:
Design a reasonable weld structure to ensure that parameters such as weld width and depth meet requirements, while optimizing the welding path to reduce unnecessary stress concentration.
Strengthen material pretreatment to ensure a clean and impurity free surface before welding, and perform preheating treatment if necessary to reduce temperature differential stress.

4. Control environmental conditions:
Maintain a stable ambient temperature during the welding process to avoid the impact of sudden temperature changes on the weld seam.
Control the humidity in the workshop to prevent moisture from entering the welding area, and use desiccants or dehumidification equipment to maintain a suitable working environment.