Arc pulse concept for orbital welding

The arc pulse involves the use of welding power sources to rapidly displace the welding current from a high (peak current) to a lower value (background current). This creates an overlapping weld line. This reduces heat input to the substrate and can also allow for increased welding speed.

This welding technique brings many benefits to the welding process, often improving weld quality and repeatability. In some cases, poor materials and joints will be difficult to successfully weld with pulseless welding, but can easily be welded with pulsed arc technique. The result is improved weld quality and increased welding productivity.

The concept of arc pulse

In orbital welding, the arc pulse also provides an advantage due to the fact that gravity pulls the weld pool in different directions as the welds are created around the tube. When the pulse is at peak current, the base material will melt and flow into each other, at lower current (background current) the weld puddle can solidify before becoming liquid at the next peak current pulse.

This reduces the effect of gravity on molten welds, minimizes sag at the 12 o'clock and 6 o'clock positions, and reduces fusion puddles that drop downhill at the 12 o'clock positions. at 3 o'clock and 9 o'clock, affecting the distance from the electrode (welding needle) to the welding puddle. Such a pulsed arc technique becomes more profitable because increasing tube thickness leads to a larger weld pool.

Arc pulse parameters: The arc pulse is related to four welding parameters: peak current, background current, duty cycle, and pulse frequency. ) .

It is important to understand how to choose the starting parameters for convenient weld development and the effect on the welds by varying each parameter.

The main purpose is to utilize the benefits of pulse welding to improve weld quality and productivity.

Peak current/background current ratio: This ratio basically provides the ability for the welding current to pulse from one arc to another (a circle around a pipe divided into 4 arcs, for example). The industry often uses ratios that vary from 2:1 to 5:1 billion. A good starting point is to use a 3:1 ratio, make the required welds and check other parameters to see if any results are found.

Pulse frequency: The pulse frequency depends on the required overlapping spot position. A good starting point is to try to get the overlay to 75%. The pulse rate for thin pipes is usually equal to the welding speed measured in ipm (5 ipm = 5 pps).

Pulse Width: The pulse width (percentage of time spent for maximum welding current) depends on the thermal sensitivity of the material and the welding current available from the power supply. Higher thermal sensitivity requires a lower pulse width x % of peak current. The standard pulse width is typically 20% to 50%. A good starting parameter would be to set the pulse width to 35%.

Benefits of pulsed arc for orbital welding

Benefits of the arc pulse:

Reduce the heat supplied to the workpiece.

Improved weld width/depth ratio.

The arc pulse can increase penetration while maintaining the minimum weld width. Or the weld width can be reduced but still give the same penetration.

Controlling the welding puddle from the arc generated, the convection from the weld puddle is controlled, so it limits the pitting in the weld, the weld puddle is hardened faster, minimizing or eliminating the possibility of the weld puddle. out to the sides during the welding process change position continuously.

The pulse is stable, the arc is less prone to deflection or problems with the surface tension of the weld pool.
Improved weld quality, uniformity, reduced heat affected zone (HAZ), reduced dilution between heterogeneous materials,

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