Cause Analysis of Bad Weld Formation

Influence of welding current on weld formation

Under other certain conditions, with the increase of arc welding current, the weld penetration and residual height increase, and the weld width slightly increases

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 heat conduction to the depth of the weld pool and increases the penetration. The penetration is approximately proportional to the welding current, that is, the penetration h of the weld is about km × I, where km is the penetration coefficient (the number of MM that the welding current increases by 100a) It is related to the method of arc welding, the diameter of welding wire and the type of current.

2.the melting speed of the welding core or wire is proportional to the welding current. With the increase of welding current, the melting speed of the welding wire increases, and the melting amount of the welding wire increases approximately in proportion, but the melting width increases less, so the weld residual height increases.

3.With the increase of welding current, the diameter of arc column increases, but the depth of arc penetration into the workpiece increases, and the moving range of arc spot is limited, so the increase of weld width is small. When gas shielded metal arc welding, the welding current increases and the weld penetration increases. If the welding current is too large and the current density is too high, finger penetration is easy to occur, especially when welding aluminum.

Effect of arc voltage on weld formation

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

At the same time, because the welding current is constant and the melting amount of welding wire is basically the same, the weld residual height is reduced. In order to obtain the proper weld forming, that is to say, to maintain the appropriate welding forming coefficient φ, the arc voltage should be increased appropriately while the welding current is increased, and the arc voltage and welding current should be properly matched. This is more common in the welding of molten electrode.

Effect of welding speed on weld formation

Under certain other conditions, increasing the welding speed will lead to the decrease of welding heat input, resulting in the decrease of weld width and weld depth. Because the deposition amount of wire metal on the unit length weld is inversely proportional to the welding speed, it also leads to the decrease of weld reinforcement.

The welding speed is an index to evaluate the welding productivity. In order to increase the welding productivity, the welding speed should be increased. But in the structural design, in order to ensure the required weld size, the welding current and arc voltage should be increased while the welding speed is increased. These three quantities are interrelated. At the same time, the welding current, arc voltage and welding speed should be considered When the welding speed is increased (i.e. high power welding arc and high welding speed welding), it is possible to produce welding defects, such as undercut and crack, in the process of forming molten pool and solidification of molten pool, so increasing the welding speed is limited.