In arc welding, the base plates are connected with one terminal of the power source, while the electrode is connected with other terminal. When sufficient potential difference is applied, electrons flow from negative terminal to the positive terminal in the external circuit. Avalanche of flow of electrons constitutes the electric arc, which is prime source of heat. Polarity in arc welding decides the direction in electron flow between base plates and electrodes. Arc welding power sources provide either AC or DC power; however, depending on the connection made, DC power can provide two polarities – straight polarity and reverse polarity, 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. So with DCSP polarity, electrons emit from electrode and flow towards base plates.
- 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. Thus with DCRP polarity, electrons emit from base plates and flow towards electrode.
Both DC Straight Polarity and DC Reverse Polarity have respective pros and cons. Similarities and differences between Direct Current Straight Polarity (DCSP) and Direct Current Reverse Polarity (DCRP) are tabulated below. For better understanding, you may read following articles.
- Direct Current Straight Polarity (DCSP) in arc welding.
- Direct Current Reverse Polarity (DCRP) in arc welding.
- AC polarity in arc welding.
- Comparison among AC, DCRP, and DCSP.
Similarities between DCSP and DCRP polarities in arc welding
- Both DCSP and DCRP can be applied for joining of two or more components together; however, the result may be substantially different.
- Both the polarities constitute electric arc (prime source of heat in arc welding).
- Both occur repeatedly one after another in every cycle in case of AC supply.
Differences between DCEN and DCEP polarities in arc welding
|In Direct Current Straight Polarity, electrode is connected with the negative terminal of the power source and base metals are connected with the positive terminal.||In Direct Current Reverse Polarity, 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.|
|Almost 2/3rd of the total arc heat is generated near base plate and rest is generated at electrode tip.||Here, 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 lack of fusion and lack of penetration defects.||Due to less heat generation near base plate, incomplete fusion plate may be encountered.|
|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.|
|Oxide cleaning action by arc is poor.||Oxide cleaning action by arc is good.|
|Inclusion defects may arise if base plate surfaces are not cleaned properly prior to 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 quite thin.|
|DCSP is not suitable for welding thin plates as it may cause cutting instead of welding.||DCRP 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.|
- Book: Manufacturing Technology: Foundry, Forming and Welding by P. N. Rao (Tata McGraw Hill Education Private Limited). Buy this book
- Book: A Text-Book of Welding Technology by O. P. Khanna (Dhanpat Rai Publications). Buy this book
- Book: Welding Metallurgy by S. Kou (Wiley India). Buy this book
- Book: Welding Processing and Technology by R. S. Parmar (Khanna Publishers). Buy this book