Arc welding power sources can supply either AC or DC or both forms of current. In case of DC polarity, current flows only in one direction; whereas, in case of AC, current flow direction reverses in every cycle (number of cycles per second depends on the frequency of supply). Now, in arc welding, base metals are connected with one terminal and the electrode is connected with other terminal. Under presence of sufficient potential difference, continuous flow of electrons between them through a small gap constitutes the arc (prime source of heat in arc welding). Based on the connections, DC power can provide two polarities, as provided below:
- Direct Current Straight Polarity (DCSP) or Direct Current Electrode Negative (DCEN)—When electrode is connected with the negative terminal of the power source and base metals are connected with the positive terminal.
- Direct Current Reverse Polarity (DCRP) or Direct Current Electrode Positive (DCEP)—When base metals are connected with the negative terminal of the power source and electrode is connected with the positive terminal.
Both DC Straight Polarity and DC Reverse Polarity have respective pros and cons. Difference between Direct Current Straight Polarity (DCSP) and Direct Current Reverse Polarity (DCRP) are tabulated below. For better understanding, you may read:
- Direct Current Straight Polarity (DCSP) in Arc Welding
- Direct Current Reverse Polarity (DCRP) in Arc Welding
Difference between straight polarity and reverse polarity
| Straight Polarity | Reverse Polarity |
|---|---|
| Electrode is connected with the negative terminal of the power source and base metals are connected with the positive terminal. | Base metals are connected with the negative terminal of the power source and electrode is connected with the positive terminal. |
| Under sufficient potential difference, electrons liberate from the tip of the electrode and strike the base plate surface. | Here electrons liberate from base plate surface and strike the electrode tip. |
| 2/3rd of the total arc heat is generated near base plate and rest is generated at electrode tip. | 2/3rd of the total arc heat is generated at electrode tip and rest is generated near base plate. |
| Proper fusion of the base metal can be achieved easily. So it eliminates the lack of fusion and lack of penetration defects. | Due to less heat generation near base plate, incomplete fusion of the base plate may occur. |
| In case of consumable electrodes, filler metal deposition rate is quite low. | Filler metal deposition rate is quite high as greater portion of heat is generated at electrode tip. |
| Arc voltage and arc stability does not depend on work material emissivity. | Arc voltage and arc stability significantly depend on work material emissivity. |
| Arc cleaning action (oxide cleaning) is poor. | Arc cleaning action is good. |
| Inclusion defects may arise if base plate surfaces are not cleaned properly prior to the welding. | Due to good arc cleaning action, tendency of inclusion defects reduces. |
| DCSP may cause high distortion and broader HAZ in the welded component. | Distortion is less with DCRP and also HAZ is narrow. |
| DCSP is not suitable for welding thin plates. | DCSP is suitable for welding thin plates. |
| Metals with high melting temperature (such as stainless steel, titanium) can be suitably joined by DCSP. | Metals with low melting temperature (such as copper, aluminum) can be suitably joined by DCSP. |