During fiber laser transmitter parts processing, the formation of microcracks can significantly impact component reliability and service life. Their formation is closely related to material properties, process parameters, and environmental control. Material purity is a fundamental influencing factor. Impurities such as sulfur and phosphorus, which have low melting points, can form brittle phases at grain boundaries, reducing the weld's crack resistance. Therefore, high-purity raw materials must be selected and impurities removed through vacuum melting or electroslag remelting before processing. Direct processing of highly reflective materials such as copper and aluminum should be avoided. Surface sandblasting or phosphating can be used to increase laser absorption and reduce thermal stress concentration.
Optimizing process parameters is crucial for preventing microcracks. Excessive laser power can lead to an expanded heat-affected zone (HAZ), localized overheating, and thermal stress. Excessive power can lead to incomplete fusion, resulting in incomplete penetration defects. Experimentation is required to determine the optimal power range to ensure a uniform and moderately heated molten pool. The welding speed must be matched to the power. Too high a speed can lead to insufficient fusion of the molten pool, while too low a speed can cause localized overheating, both of which increase the risk of cracking. Furthermore, adjusting the defocus can optimize the weld pool shape. Negative defocus increases penetration, while positive defocus expands weld width. Choosing the appropriate value depends on the part structure. Selecting the spot size is also crucial. Small spots are suitable for precision welding of thin plates, while large spots are suitable for high-speed welding of thick plates. Avoiding excessive energy concentration that can lead to localized overheating is crucial.
Weld seam structural design is crucial for crack control. Deep, narrow welds can easily lead to centerline segregation, increasing the tendency to thermal cracking. Improving the ratio of weld width to weld depth (shape factor) can improve crystallization conditions. For example, adopting V- or U-shaped weld designs can avoid right-angle transitions and reduce stress concentration. Welding path planning should avoid repeated heating of the same area. For complex structures, symmetrical welding or segmented back-welding can be used to distribute stress. For example, long welds can be welded in sections from the center to the ends to reduce restraining stress. When joining dissimilar materials, a transition layer is needed to mitigate differences in thermal expansion coefficients. For example, when welding titanium alloy to stainless steel, a nickel-based alloy transition layer can be added to reduce thermal stress.
Heat treatment processes can significantly improve the internal stress distribution of a part. Preheating before welding can reduce temperature gradients and shrinkage stresses. The preheating temperature should be determined based on the material's properties. For example, steel parts are typically preheated to 100-300°C. Annealing or tempering after welding can eliminate residual stresses and improve weld microstructure. For example, high-temperature tempering of high-strength steel can improve toughness and reduce the risk of cold cracking. For crack-prone materials, such as high-carbon steel or aluminum alloys, a filler wire matched to the base material's composition can be added to dilute centerline segregation and hardened microstructure. The weld chemistry can also be adjusted, such as by adding manganese for desulfurization or titanium or niobium for grain refinement.
Environmental control is equally important for crack prevention. The welding workshop must maintain a stable temperature to avoid sudden temperature fluctuations that can cause large temperature differences between the inside and outside of the material and induce internal stress. Humidity control can prevent moisture from penetrating the weld area, leading to hydrogen embrittlement. High-humidity environments require the use of desiccant or dehumidification equipment. During the processing of fiber laser transmitter parts processing, infrared thermometers or thermal imagers should be used to monitor the temperature of the weld area to ensure that heat input remains within an acceptable range. Welding stresses are monitored using strain gauges or fiber Bragg grating sensors, allowing timely adjustments to parameters or processes to avoid stress concentration.
Post-processing quality inspection of fiber laser transmitter parts is the last line of defense for crack control. Ultrasonic testing, X-ray testing, or penetrant testing can be used to promptly detect cracks and other defects. Small cracks can be polished and repaired with welding, while larger cracks require re-welding and process optimization. For example, the welding of lithium battery casings requires a hermetic seal to prevent moisture infiltration and lithium reactions. Welding processes must strictly control spatter and porosity to ensure weld mechanical strength and impact resistance.
Preventing microcracks in fiber laser transmitter parts processing requires the coordinated efforts of multiple steps, including material selection, process optimization, structural design, heat treatment, environmental control, and quality inspection. By systematically controlling these factors, the quality and reliability of fiber laser transmitter parts processing can be significantly improved, meeting the demands of high-precision and high-performance applications.
