Cracks and porosity are common defects in spin welding, and their formation is closely related to factors such as materials, processes, and environment. Cracks usually originate from welding stress concentration or insufficient material toughness, while porosity is mostly caused by the failure of gas to escape from the molten pool in a timely manner. Considering the characteristics of spin welding machines, a comprehensive approach is needed, including material pretreatment, process parameter control, environmental management, equipment debugging, operating procedures, post-processing, and quality inspection, to effectively avoid the formation of cracks and porosity.
Material pretreatment is fundamental to preventing defects. Before spin welding, the base material and filler material must be rigorously cleaned to remove impurities such as oil, rust, and oxide films. These impurities decompose at high temperatures, generating gas and increasing the risk of porosity; simultaneously, the presence of impurities reduces the purity of the weld metal, weakening its crack resistance. Furthermore, for easily cracked materials such as high-carbon steel and alloy steel, preheating treatment can reduce welding stress and decrease the tendency to crack. The preheating temperature must be reasonably selected based on the material thickness and welding method to avoid excessive temperature leading to material performance degradation.
Precise control of process parameters is crucial. During spin welding, parameters such as current, voltage, and welding speed directly affect the morphology of the molten pool and the conditions for gas escape. Excessive current can lead to overheating of the molten pool and increased metal fluidity, but rapid cooling may prevent gas from escaping, resulting in porosity. Insufficient current results in insufficient penetration, poor weld formation, and defects such as incomplete fusion. Excessive voltage causes an excessively long arc, allowing air to easily enter the molten pool and increasing the risk of porosity; insufficient voltage leads to an unstable arc, affecting weld quality. Welding speed must be matched with current and voltage. Too fast a speed can cause the molten pool to cool too quickly, making gas escape difficult; too slow a speed results in excessive heat input, potentially causing cracks. Therefore, the optimal range of process parameters must be determined through experimentation based on material thickness, welding position, and the specific model of the spin welding machine.
Environmental management is also crucial. During spin welding, environmental humidity and wind speed have a significant impact on weld quality. Excessive humidity can cause welding rods and flux to absorb moisture, generating a large amount of hydrogen gas during welding and increasing the risk of hydrogen-induced cracking. High wind speeds can disperse the protective gas, exposing the molten pool to the air and causing porosity. Therefore, the welding environment must be kept dry, with humidity controlled within a reasonable range. When working outdoors, a windproof shelter must be erected to ensure effective coverage of the protective gas.
Equipment debugging and maintenance are crucial. The performance stability of the spin welding machine directly affects the welding quality. Regularly check the wear of each component and replace worn electrodes, contact nozzles, and other vulnerable parts promptly to ensure stable arc combustion. Simultaneously, the spin welding machine's rotation mechanism must be calibrated to ensure the concentricity of the upper and lower workpieces, avoiding stress concentration due to eccentricity, which can lead to cracks. Furthermore, regularly clean the inside of the equipment of dust, welding slag, and other impurities to prevent them from affecting normal operation.
Following operating procedures is paramount. When welding with a spin welding machine, welders must strictly follow the operating procedures, maintaining a stable welding speed and arc length, avoiding frequent arc initiation and extinguishing, reducing the number of weld joints, and lowering the risk of cracking. Simultaneously, it is necessary to carefully observe the shape and color of the molten pool and adjust welding parameters promptly to ensure full fusion of the molten metal and smooth gas escape.
Post-treatment and quality inspection are the last line of defense. After spin welding, the weld must undergo post-heat treatment to eliminate residual welding stress, improve the microstructure of the weld metal, and enhance its crack resistance. At the same time, comprehensive inspection of the weld must be conducted using methods such as visual inspection, radiographic testing, and ultrasonic testing to promptly detect and address defects such as cracks and porosity, ensuring that the welding quality meets standard requirements.
