To understand the differences between AC and DC welding types, we must first understand the fundamentals of arc welding.
The process arc of welding involves the use of a power supply to produce an electric arc between an electrode and the job intended to be welded to melt the metals at the joint.
The arc provides heat energy at the joint to weld the metals.
The power supply used for the purpose could either supply (DC) or alternating (AC) current.
AC or DC defines the polarity of the electrical current that a welding machine creates for the arc and runs through the electrode.
The difference in current input gives rise to various possibilities as both types have their own takeaways.
There can be many types of welding jobs each having its own unique characteristics.
The user has to keep in mind the requirements for the same as the same technique might not work for all the jobs.
The market has a wide variety of machines that work with AC, DC or both types of current.
Overview of AC Welding
AC or Alternating Current is a form of electric current that switches its direction back and forth, this change in direction also leads to a periodically reversing voltage.
An AC current usually changes its polarity 120 times a second with a 60-hertz frequency.
One can find typical AC currents from electrical outlets in a household, these are often used for higher voltage devices such as domestic appliances including refrigerators, microwaves, and others.
The primary use of AC current falls in welding magnetic materials as DC current is not capable of performing the process on magnetic metals.
Furthermore, AC current is also preferred when a deeper penetration is required on certain material be it due to rust or material thickness.
There are also no deflections in welding processes when using an AC current since the current and the magnetic field of the arc reverse direction many times a second.
- AC current based welding is ideal for the following applications –
- Down-hand heavy plate
- Fast fill welds
- Aluminum with high-frequency TIG welding
- Magnetic materials
AC current is also the preferred for welding aluminum with TIG, this is because the AC current supports welding at a higher temperature.
It also utilized for making repairs on machinery due to the inevitable presence of a magnetic field in the machinery.
The machinery may also have rust or a layer of any impediment that may need higher penetration.
The use of AC current is also prevalent in seam welding in shipbuilding because the current output is required to be higher so that deeper penetration of the plates can be achieved.
The use of AC current, however, brings certain shortcomings too. The quality of a weld is often not as good, the user needs to be more skilled to achieve a substantial quality of welds.
The quality of welds suffers primarily due to periodically switching nature of the current which translated to a less smooth arc.
This periodic nature of the welder also results in more splatter during the welding process.
- Stable arc
- No deflections while welding
- Deeper penetration
- Can weld magnetic metals
- Supports higher temperature
- Supports higher current parameters
- More splatter
- Arc is not as smooth
Overview of DC Welding
DC or Direct Current is a type of current flowing through with a constant direction and possessing a voltage with a constant polarity which can either be positive or negative.
DC current applications can be found in current in a number of batteries and are often implemented in low voltage devices such as cell phones and remote controls.
During a welding process, an electrode negative (DC current) or better known as a straight current provides better deposition rates due to the faster melting of the electrode, and the electrode positive results in penetration.
A DC current in welding is best applicable for –
- Overhead or Vertical Welding
- Single Carbon Brazing
- Stainless Steel by TIG Welding
- Cutting Tap
DC current is preferred for welding due to many reasons and the first being that the arc produced is easier to use.
This is particularly important when novice welders select the current types.
The DC current produces a smoother weld arc and less spatter is encountered, both of these characteristics are due to the constant linear direction of the current.
Another important consideration and fact that should be considered are that welders and accessories using DC current are generally cheap and more accessible to use.
As the DC current supports a constant current, it also facilitates a better weld on thinner materials.
However, there are some drawbacks to using DC type current in welding processes. The arc produced by DC current is more vulnerable to an arc blow.
The arc blow can hurt the integrity of the weld joint.
Furthermore, DC currents are rarely supplied by power grids, so the equipment would need an internal transformer to switch the current to AC for use.
- Smoother welding arc
- Low splatter
- Easy to use arc
- Welds thinner metals better
- Better quality of welds
- Low skill requirement
- Greater potential for an arc blow
- Transformer required
- Cannot product high-intensity heat
Key Differences between AC vs DC Welding
Due to DC current’s characteristics of maintaining a constant and non-flickering arc, it is easier to handle and more reliable than AC current, especially for beginner welding users.
A DC current based arc can weld thinner metals better than an AC current.
An arc blow occurs when a magnetic field is present in the vicinity where the welding job is being prepared to weld a joint of two metal components.
The quality and strength of a weld can be spoiled by a magnetic disturbance, which might occur due to the interaction of the magnetic field in the welding current with the residual magnetic field leftover in the material.
In AC current, the current changes direction and is not affected by magnetism and thus is never subjected to an arc blow.
The use of a generator is necessary at times with a DC current, as power grids do not provide DC current from the get-go, this makes it expensive to use. Weld strength, however, is almost independent of the usage of two arcs.
The different current type needs to be selected for different jobs as no one type is perfect for all jobs.
In the End…
Both the types have their own advantages and disadvantages, each current type caters to different needs.
The user would require equipment needed for conversion from AC to DC, thus increasing the investment for DC welding.
AC welding has no deflections and also provides deeper penetration which increases welding capacities for the user.
The other primary advantage of using AC welding is that it allows the operator to weld on magnetized materials. Arc blow is also not prevalent in AC current arc.
Another reason against the use of DC current is that the current cannot always produce a high amount of heat for certain materials.
It is not effective for use in welding aluminum due to the current’s inability of producing high-intensity heat.