Welding speed

Definition
Welding speed refers to the length of the weld completed per unit time. For example, in actual welding operations, the ratio of the length to the time is the welding speed.

Factors affecting welding speed
Welding methods
Different welding methods have significantly different welding speeds. Generally speaking, manual arc welding is slow, with a welding length of 10-20mm per minute; semi-automatic welding is slightly faster, with a welding length of 50-80mm per minute; automatic welding is faster, with a welding length of more than 100mm per minute. This is because manual arc welding relies on manual operation and is limited by human reaction speed and operation accuracy; semi-automatic welding is partially assisted by machinery, and its efficiency is improved; automatic welding is completed automatically by the machine, and can maintain a high speed continuously and stably.

Welding materials
When welding different metal materials, the welding speed will be different. When welding stainless steel, high-temperature alloys and non-ferrous metals, in order to avoid spatter and obtain a high-density weld, a lower welding speed is usually used, and sometimes a step seam welding process is used to form a molten core. This is because these materials have special physical and chemical properties, and high-speed welding may lead to a decrease in weld quality.

Plate thickness
The thicker the plate, the lower the welding speed is usually required. Thick plate welding requires more heat to ensure the penetration of the weld. If the welding speed is too fast, the plate may not be fully melted, resulting in defects such as incomplete penetration.

Welding skill level
Skilled welders can control the welding process more accurately and may have a faster welding speed than novice welders while ensuring welding quality. They have a better grasp of the adjustment of welding parameters and the stability of operation.

Welding quality requirements
If the quality requirements for the strength, appearance flatness, and density of the weld are high, it is often necessary to appropriately reduce the welding speed to ensure a more stable welding process and reduce the occurrence of defects.

The influence of welding speed on welding quality
Weld formation
Penetration depth and width: In laser arc hybrid welding, when the welding speed increases, the heat input per unit length decreases, resulting in a faster cooling rate of the molten pool. Experiments show that when the welding speed increases from 0.6m/min to 1.2m/min, the weld penetration depth decreases by about 30%, while the width increases by 15%.
Residual height control: Low-speed welding (such as 0.4m/min) is prone to violent evaporation of metal vapor due to heat input accumulation, resulting in a significant increase in weld residual height (up to 1.2mm or more); when the speed is increased to 0.8m/min, the residual height can be reduced to below 0.5mm, and the surface flatness is improved by 40%.
Heat-affected zone (HAZ): High-speed welding (1.0m/min) reduces the width of the HAZ to within 1.5 times the thickness of the parent material, reduces the degree of grain coarsening, and reduces the number of oxide inclusions by 50%.
Droplet transition behavior
Transition mode change: When the speed increases from 0.5m/min to 1.0m/min, the droplet volume decreases from 2.5mm³ to 1.2mm³, the transition frequency increases from 120Hz to 250Hz, and the spatter rate decreases by 70%; high-speed welding (1.2m/min) shortens the contact time between the droplet and the molten pool to less than 0.8ms, the metal vapor interference is weakened, and the arc voltage fluctuation amplitude is reduced by 30%.
Optimization of weld surface quality: The speed increase promotes the precise transition of the droplet along the axial direction of the welding wire, the corrugation spacing of the weld surface is reduced from 0.3mm to 0.1mm, and the roughness Ra value is reduced to less than 3.2μm.
Defect formation
Suppression of porosity defects: The porosity is as high as 8% during low-speed welding (0.4m/min). After the speed is increased to 0.8m/min, the keyhole closing time is shortened by 60%, and the porosity is reduced to below 2%; high-speed welding (1.0m/min) reduces the solidification time of the molten pool to 1.2s, shortens the bubble escape path, and reduces the pore diameter from 0.5mm to 0.1mm.
Bottom hump and crack control: When the speed exceeds 1.5m/min, the insufficient laser energy density leads to unstable penetration, and periodic hump defects are easily formed at the bottom of the weld, with a height of up to 0.8mm.
Recommendations for selecting welding speed under different working conditions
High-frequency straight seam welded pipe working conditions
Under high-frequency straight seam welded pipe working conditions, in order to reduce the reaction between the edge of the tube and oxygen, nitrogen, etc. in the air, reduce the nitrogen and oxide content in the weld, reduce the burning and evaporation of beneficial alloy elements, and improve the weld strength, the welding speed should be increased to allow the weld to quickly leave the heating zone, so that the weld can be quickly crystallized at a large degree of undercooling and the weld grains can be refined.

Laser arc hybrid welding working conditions
Reasonably select the welding speed according to the welding requirements and the characteristics of the weldment. If a deeper weld penetration depth is required, the welding speed can be appropriately reduced; if the weld surface flatness and the reduction of defects such as pores are pursued, the welding speed can be appropriately increased, but care should be taken to avoid defects such as bottom humps caused by excessive speed.