Various welding processes use Direct Current Power Supply as a power source. In the case of DC polarity, current flows in one direction only, which is either from the base to the electrode or from the electrode to the base metal. In multiple arc welding procedures, you will hear the term DCEP being used. If you’ve ever wondered, “what does DCEP mean in welding?” then keep reading to find out.
What Does DCEP Mean?
DCEP stands for Direct Current Electrode Positive or Direct Current Reverse Polarity. In this process, you connect the base metal to the negative terminal of the power source and the electrode to the positive terminal. The electrons are freed from the base metal and flow to the electrode tip, as current always travels from positive to negative.
The presence of a difference in potential causes the electrons from the base plate to accelerate and strike the electrode at a very high velocity. Upon impact, the kinetic energy converts into thermal energy, which generates heat near the tip of the electrode. Using DCEP has some advantages and some disadvantages to it.
- An increased metal deposition rate
- Reduced distortion level
- Reduced residual stress and complete cutting
- Ideal for joining copper and aluminum
- Improved arc cleaning
- Reduced inclusion of defects
In DCEP processes, around 66% of the heat is generated near the electrode and only 33% near the base plate. Thus, the electrode melts faster, increasing the metal deposition rate of the process. Electrons flowing from the base plate remove excess oils on the surface. They also remove corrosion, dust particles, coating, and oxide layers. It is called the oxide cleaning process and reduces the chances of the inclusion of defects.
DCEP is suitable only for welding together thinner plates or metals with lower melting points as it has lower penetration levels.
- Shorter electrode life
- A higher level of reinforcement is needed
- Insufficient melting
- Low penetration levels
- Incomplete fusion
- Not suitable for thick plates
- Unsuitable for metals with high melting points
Since only 33% of the heat is concentrated near the base metal, the metal doesn’t heat fast enough in processes using DCEP, which can result in incomplete fusion. It can also result in a lack of penetration and increased reinforcement rates in the welding process. Low levels of heat make it unsuitable for use on thicker plates or metals with high melting points. For them, we suggest you choose either DCEN or employ Alternative Current instead.
What Does DCEN Mean?
DCEN means Direct Current Electrode Negative or Direct Current Straight Polarity. In this process, the base metal is connected to the positive terminal and the electrode is connected to the negative terminal of the power source. It is the exact opposite of the DCEP process and is used in procedures where DCEP may prove inefficient.
- Sufficient fusion of metals
- High penetration levels
- Low reinforcements
- Suitable for metals with high melting points
- Can be used for joining of thick plates
In DCSP, the major portion of heat is generated towards the base plates, which increases the penetration levels. The high penetration levels make it ideal for use on thicker sheets of metal and metals with higher melting points.
- No arc cleaning
- High levels of distortion
- Residual stress
- Lower deposition rate
- Unsuitable for thin plates
Since the electrons flow from the electrode to the base, you will not witness any oxide cleaning during the process. There are high chances of inclusion of defects due to the lack of oxide cleaning.
There is also a larger heat affected area as most of the heat is directed near the base metals, which produces higher distortion levels and residual stress. High penetration levels make it unsuitable for use on thinner plates, especially combined with a low metal deposition rate. The low metal deposition rate also significantly reduces productivity levels.
Direct Current Power Supply
In Direct Current power sources, current flows in one direction only. It will either flow from positive to negative or the other way round. Smaller devices like batteries, phones, flashlights or remote control use DC.
In welding, we use both the positive to negative as well as the negative to the positive supply. Both have their pros and cons as described above. However, using a DC supply is beneficial as compared to using an Alternate Current supply, despite the cons of the former.
Using a Direct Current power source for the welding procedure has the following advantages:
- Ideal for welders who require faster deposit rates
- Low spatter production
- Smooth weld
- Higher production yield
- A stable and consistent electrical arc
- Costly, as it requires the use of special equipment like internal transformers
- Not recommended for aluminum
- Unsuitable for tasks requiring high-intensity heat production
- High-risk procedure
When using Direct Current power sources, take extra care. There are chances of a magnetic field building up, which can cause the arc to blow up.
Alternating Current Power Supply
You can also use an Alternate Current power source if you want the advantages of both DCEP and DCEN and only a few of their drawbacks. By using an AC power source, you will alternate the current flow around 120 times per second depending upon the frequency of the supply. At the start of the cycle, the current will flow in one direction to the other, and halfway through, it will switch to the other direction.
- Some arc cleaning
- Compatible with most electrodes
- Good fusion
- Good penetration levels
- Supports a few types of welds like heavy plates, aluminum TIG weld, and even fast-fill
- Can be used for magnetized metal welding
- Allows welding in higher temperatures
- Great for repair work
However, one major drawback of using an AC power supply is its directional instability, which directly affects product yield.
Polarity and Welding Performance
Polarity directly affects the production yield as it affects the efficiency rate of the process. There are multiple factors that the current flow directly influences. You must choose which current flow to use before you start the process. To make the right choice, consider the following factors:
- Required metal deposition rate – Direct Current Electrode Positive provides the maximum metal deposition rate as can be determinable via current flow.
- Weld Penetration – DCEP or Reversed polarity gives bad weld penetration levels, which is why it is unsuitable for use on thicker slabs of metal. For weld jobs that require a high penetration level, using DCEN polarity increases production efficiency.
- Oxide Cleaning – To reduce the chances of the inclusion of defects, you should opt for DCEP as it cleans the base plate during welding. DCEN does not, so if you go for straight polarity instead, then thoroughly clean the plate before use.
- Reinforcement – Weld jobs using DCEP produce a wider and globular metal transfer, thus producing higher reinforcement levels, which directly affects production efficiency.
- Heat Affected Zone – In DCEN, you must adjust the speed as you go; otherwise, the Heat Affected Zone broadens and produces higher distortion levels.
- Weld Bead Appearance – To have better control over weld bead appearance, you should use an AC supply. However, several other factors affect the appearance of the bead.
Which polarity should you use?
A good weld depends on many factors besides the current used. There is no right or wrong answer to this question. Consider all the pros and cons listed in this article as well as the material you will be working with and the type of weld you are making before you choose a polarity.
Which stick to use for AC and DC polarity?
You can use both 6011 and 6010 welding rods for both AC and DC polarities. They have high cellulose potassium type coating and are fast freezing rods. They both work especially well with rusty, dirty, or older base metals and come in handy when making repairs.
What happens when you weld with the wrong polarity?
Polarity directly affects the production yield and efficiency. Using the wrong polarity can be costly and prove a lot more work-intensive than need be. It can also significantly affect the quality of the weld produced.