The welding process parameter—speed refers to the speed at which the welding arc or welding wire moves. It is a critical parameter affecting weld quality and welding efficiency. The choice of welding speed directly impacts the formation and maintenance of the weld pool, as well as the physical and chemical properties of the weld joint.
Specifically, the selection of welding speed needs to consider several factors:
Material type and thickness: Different materials require different welding speeds. Generally, faster speeds can be used for welding thin plates, while slower speeds are needed for welding thick plates to ensure sufficient heat input and weld pool formation.
Current and voltage settings: Welding speed is typically directly related to the current and voltage settings. Higher current and lower voltage usually require faster welding speeds, while lower current and higher voltage require slower welding speeds.
Welding position and angle: Different welding positions (horizontal, vertical, overhead) and angles require different speeds to ensure stable weld pool and welding quality.
Reactivity of welding materials: Some materials (such as stainless steel, aluminum alloys) are more prone to oxidation or other chemical reactions at high temperatures, necessitating faster speeds to minimize these effects.
Requirements of the weld joint: Different weld joints require different welding speeds to meet strength and aesthetic requirements.
In practical operations, the optimal welding speed often needs to be determined through testing and adjustment. Correctly choosing welding speed can improve welding efficiency, reduce welding distortion and residual stresses, and ensure the quality and reliability of weld joints.
Welding speed often influences the amount of energy absorbed by the weld per unit time, thereby affecting weld penetration, bead width, and appearance. Below is a brief overview of how welding speed impacts weld quality, providing insights for process optimization.
Speed primarily affects weld penetration and bead width, closely tied to line energy density. Generally, as welding speed increases in laser welding, the fusion zone area and width decrease. This can be understood as follows: higher welding speed in laser welding reduces the dwell time of the laser on the surface of the workpiece. With a shorter dwell time, the heat-affected zone shrinks, leading to smaller fusion zone and heat-affected zone areas.
Additionally, welding speed affects the appearance of the weld. Higher speeds can lead to the formation of "V-shaped" fish scale patterns, rough and uneven weld surfaces, discoloration, minimal or nonexistent weld reinforcement, and lack of fullness in the weld bead.
Improper selection of welding speed can lead to defects in laser welding. Laser welding involves a continuous process of melting and solidification. As the welding speed increases, the cooling rate of the liquid metal also increases. This accelerates the solidification of the liquid metal, making it difficult to spread smoothly. This can result in hump defects, where the hump defect increases with higher welding speeds, effectively limiting the maximum achievable welding speed.
pproach to Resolving Hump Defects:
Use of a laser with a small core diameter or selection of a collimator focusing lens to reduce spot size: Concentrating energy into a smaller spot diameter laser shortens the distance between the laser heat source and the molten metal convergence point, facilitating better spread of the liquid metal and suppressing hump formation.
Adopting a dual-beam laser method (one before and one after), or using a ring-shaped spot, and multi-wavelength fiber-semiconductor composite welding can significantly increase the maximum welding speed without generating hump defects, typically boosting it by more than 40% compared to single-beam laser speeds. In this method, one beam is typically used for preheating and post-processing, while the other is used for deep melting. This setup reduces the cooling rate of the liquid metal around the keyhole, moderates the temperature gradient, decreases surface tension of the liquid metal around the keyhole, and enhances its spreading ability, thereby suppressing the formation of hump defects.
