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Analysis of the causes of poor weld formation

The influence of welding current on weld formation

Under certain other conditions, with the increase of arc welding current, the weld penetration depth and the remaining height increase, and the penetration width increases slightly. The reasons are as follows:

1. With the increase of arc welding current, the arc force acting on the weldment increases, the heat input of the arc butt weldment increases, and the position of the heat source moves down, which is conducive to the conduction of heat to the molten pool and increases the penetration depth. The penetration depth is approximately proportional to the welding current, that is, the weld penetration depth H is approximately equal to Km×I, where Km is the penetration coefficient (the number of millimeters that the welding current increases by 100A causes the weld penetration to increase), which is related to the arc welding method , Wire diameter, current type, etc.

2. The melting speed of the core or wire of arc welding is proportional to the welding current. As the arc welding current increases, the melting speed of the welding wire increases, and the amount of welding wire melting increases approximately proportionally, but the melting width increases less, so the weld The residual height increases.

3. As the welding current increases, the diameter of the arc column increases, but the depth of arc penetration into the workpiece increases, and the range of arc spot movement is limited, so the increase in melting width is small. When gas shielded argon arc welding, the welding current If the welding current is too high and the current density is too high, finger penetration is likely to occur, especially when welding aluminum.

The influence of arc voltage on weld formation

Under certain other conditions, the arc voltage increases, the arc power increases accordingly, and the heat input of the weldment increases. The increase of the arc voltage is achieved by increasing the arc length. The increase of the arc length makes the radius of the arc heat source increase and the arc heat dissipation Increase, the energy density of the input weldment decreases, so the penetration depth is slightly reduced and the penetration depth increases.

At the same time, because the welding current is constant, the melting amount of the welding wire is basically unchanged, so that the weld reinforcement is reduced. In order to obtain a suitable weld formation, that is, to maintain a suitable weld formation coefficient φ, while increasing the welding current, it should be appropriate Increase the arc voltage and require a proper matching relationship between the arc voltage and the welding current, which is more common in molten electrode arc welding.

The influence of welding speed on weld formation

Under certain other conditions, increasing the welding speed will reduce the welding heat input, thereby reducing the weld width and penetration. Since the amount of welding wire metal deposition per unit length of the weld is inversely proportional to the welding speed, it also leads to The weld reinforcement is reduced.

Welding speed is an index to uate welding productivity. In order to increase welding productivity, the welding speed should be increased. However, in order to ensure the required weld size in the structural design, while increasing the welding speed, the welding current and arc voltage should also be increased accordingly. These three quantities are interrelated. At the same time, it is necessary to consider that when the welding current, arc voltage and welding speed increase (that is, high-power welding arc, high welding speed welding), it may be in the process of forming a molten pool and Welding defects such as undercuts and cracks are generated during the solidification of the molten pool, so there is a limit to increasing the welding speed. 

 

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