The Surface-Tension-Transfer Power Source

Figure 1

1.) Background current (T₀ - T₁): This is the current level of the arc prior to shorting to the weld pool. It is a  steady-state current level, between 50 and 100 A.

2.) Ball time (T₁ - T₂): When the electrode initially shorts (at the background current), the "arc voltage" detector provides a signal that the "arc" is shorted. The background current is futher reduced to 10 A for approxiametly 0.75 milliseconds. This time interval is referred to as the ball time.

3.) Pinch mode (T₂ - T₃): Following the ball time, a high current is applied to the shorted electrode in the form of an increasing, dual -slope ramp. This accelerates the transfer of molten metal from the electrode to the weld pool by applying electronic pinch forces. (note that the electrode-to-work voltage is not zero during this period. This is due to the high resistivity of iron at its melting point of 1550° C / 2822° F.)

4.) The dv/dt calculation (T₂ - T₃): This calculation is included within the pinch mode. It is the calculation of the rate of change of the shorted electrode voltage vs. time. When this calculation indicates that a specific dv/dt value has been attained, indicating that fuse separation is about to occur, the current is reduced to 50 A in microseconds. (Note, this event occurs before the shorted electrode separates. T₄indicates the separation has occurred, but at a low current.

5.) Plasma boost (T₅ - T₆): This mode follows immediately the separation of the electrode from the weld pool. It is the period of high arc current where the electrode is quickly "melted back." (The geometry of the melted electrode at this point is very irregular.)

6.) Plasma (T₆ - T₇): This is the period of the cycle where the arc current is reduced from plasma boost to the background current level.

 
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