Laser welding machines are a crucial tool in modern manufacturing, known for their efficiency, precision, and high degree of automation. They are widely used in industries such as aerospace, automotive manufacturing, and electronic information. However, the issue of welding cracks during the laser welding process remains a significant challenge for engineers. This article will delve into the causes of welding cracks in laser welding machines, influencing factors, and coping strategies.

I. Causes of Welding Cracks
1. Thermal cracks:
Thermal cracks occur during the welding process due to the high temperature in the weld and its vicinity, causing material volume shrinkage and stress concentration during cooling. These typically occur at the center of the weld or near the heat-affected zone (HAZ).
Material Thermal Conductivity and Thermal Expansion Coefficient
The thermal conductivity and thermal expansion coefficient of the material directly affect the formation of thermal cracks. Materials with high thermal conductivity can dissipate heat quickly during welding, reducing heat accumulation and thus lowering the risk of cracks. Conversely, materials with high thermal expansion coefficients tend to generate larger shrinkage stresses during cooling, increasing the risk of cracks.
Welding Parameter Settings
Welding current, voltage, speed, and other parameters directly affect the heat input to the weld. Excessive or insufficient heat input can lead to uneven temperature distribution in the weld area, causing thermal cracks.
2. Cold cracks:
Cold cracks mainly form during the cooling process after welding, usually occurring in the HAZ of the weld. The formation of cold cracks is closely related to the hardness of the material, welding stress, and environmental humidity.
Welding Stress
Welding stress is one of the primary causes of cold cracks. During the welding process, the metal material undergoes thermal expansion and cooling contraction, generating stress. If these stresses are not effectively relieved, they can lead to cracks during cooling.
Environmental Factors
Environmental humidity and temperature have a significant impact on the formation of cold cracks. High humidity environments can cause the weld area to absorb moisture, leading to hydrogen embrittlement and increasing the risk of cold cracks.
II. Factors Influencing Welding Cracks
1. Material selection:
Different materials exhibit varying sensitivity to cracks during laser welding. High-strength steels, aluminum alloys, and titanium alloys are more prone to cracks due to their unique physical and chemical properties.
High-Strength Steel
It due to its high hardness and brittleness, is prone to welding cracks during the welding process. Particularly during cooling, if welding stress is excessive, cold cracks are likely to form.
Aluminum Alloy
Aluminum alloys, with their high thermal conductivity and thermal expansion coefficient, are prone to thermal cracks in the weld area during welding. Additionally, aluminum alloys tend to react with oxygen in the air at high temperatures, forming an oxide film that further increases the risk of cracks.
2. Welding process:
Different welding processes significantly affect the occurrence of cracks. Reasonable welding parameter settings and welding method selection can effectively reduce the occurrence of cracks.
Welding Parameters
Reasonable settings of welding current, voltage, and speed can control the heat input to the weld, thereby influencing the temperature distribution in the weld and HAZ areas, reducing the risk of cracks.
Preheating and Post-Heating Treatment
These processes can effectively reduce welding stress and minimize the occurrence of cracks. Preheating can evenly heat the weld area, making it more uniformly heated during welding, while post-heating treatment can release residual stress generated during welding, preventing the formation of cold cracks.

III. Prevention and Coping Measures
1. Material modification:
Improving welding quality through material modification is one of the important means of preventing welding cracks. For example, adding trace alloy elements to high-strength steel can enhance its crack resistance.
Microalloying
Adding small amounts of elements such as titanium and niobium to steel can refine grains, improve the toughness of the steel, and reduce the likelihood of cracks.
2. Process optimization:
Optimizing welding process parameters and procedures is key to reducing crack formation. This includes controlling welding heat input and reasonably arranging preheating and post-heating treatments.
Controlling Heat Input
By reasonably setting welding current, voltage, and speed, controlling the welding heat input, and avoiding excessive heat concentration in the weld area, the risk of thermal cracks can be reduced.
Proper Preheating and Post-Heating Treatment
Appropriately preheating the workpiece before welding and slowly cooling and post-heating treatment after welding can effectively reduce welding stress and prevent cracks.
3. Environmental control:
Controlling the humidity and temperature of the welding environment is also crucial in reducing welding cracks. Avoiding welding operations in high humidity environments and taking moisture-proof measures during the welding process can effectively lower the risk of cracks.
Moisture-Proof Measures
Using dry protective gases during welding to prevent the weld area from contacting moisture and preventing hydrogen embrittlement can reduce the occurrence of cracks.
4 Detection and repair:
Timely detection and repair of welding cracks are important steps to ensure welding quality. Advanced detection technologies such as ultrasonic testing and X-ray testing can detect welding cracks early and facilitate repairs.
Ultrasonic Testing
Ultrasonic testing technology can penetrate the interior of the weld to detect hidden cracks, allowing for timely repair and preventing crack propagation and weld structure failure.
X-Ray Testing
X-ray testing technology can visually display the internal structure of the weld, helping engineers identify crack locations and severity, and develop effective repair plans.

Final Thoughts
The occurrence of welding cracks in laser welding machines is the result of multiple factors, including material properties, welding process parameters, and environmental conditions. Through material modification, process optimization, environmental control, and timely detection and repair, welding cracks can be effectively prevented and addressed, improving welding quality and structural reliability. In the future, with the continuous development and innovation of laser welding technology, significant breakthroughs in preventing and treating welding cracks are expected.