What is the Difference Between AC and DC Welding?

electric weldingArc welders use both AC and DC current.? In order to make the best welds a welder must understand what alternating current (AC) and direct current (DC) signify on the welder as well as on electrodes. AC and DC are terms that refer to the polarity of the electrical current that is created by the welder and runs through the electrode.

The strength of a weld depends on selecting an electrode with the correct polarity because the polarity of the electrode can significantly affect both the strength of the weld as well as the quality of the weld.

What Is Welding?

Welding is a process used to join metals together by melting the parts and using a filler to form a joint.? Welds can be accomplished using different energy sources from a gas flame or electric arc to a laser or ultrasound.

The welding processes used currently include arc welding which is done through the use of electrical current; gas welding which is most commonly used in the repair of pipes and tubes; resistance welding which uses additional sheets of metal to encase the workpieces that will be joined together; and energy beam welding or laser beam welding which is fast and accurate but very expensive.

Welding cannot be done with all types of metals. For example, stainless steel is prone to cracking and distortions when it is overheated.? Alloys are often a problem because it is difficult to know the exact chemical composition of the metal.

An interesting fact about welding is that welding can be done under unusual conditions such as underwater and in outer space.

What Is Polarity?

Every electrical circuit has a negative and positive pole.? Direct current flows in a single direction resulting in a constant polarity. Alternating current or AC current flows in one direction half of the time and in the opposite direction the other half. AC current changes its polarity 120 times per second with a 60 hertz current.

Electrode positive or reversed polarity (AC current) results in deeper penetration while electrode negative (DC) or straight current provides faster deposition rates because there is quicker melt-off of the electrode.? There are different types of electrodes and electrode shielding that can alter these basic conditions. Some kinds of shielded electrodes function using either polarity while others only operate on one polarity.

In order to achieve proper penetration, uniform beading and good welding results the correct polarity must be used when welding with any given metallic electrode. Using incorrect polarity results in poor penetration, irregular bead shapes, excessive splatter, overheating, lack of arc control and quick burning of the electrode.

Most arc welders have clearly marked terminals or directions for how the welder can be set to either polarity. Some welding machines use a switch to change polarities and others require changes be made to the cable terminals.

Welding with AC Current

Welding with AC is ideal for the following AC arc welding machinetypes of welds:

  • Downhand heavy plate
  • Fast fill
  • Aluminum TIG welding with Hi frequency

Carbon arc torches have two types of AC current: a smooth arc for general purpose welding and a force arc for carbon arc, TG attachments and new fabrications.

Welding with DC is best used for:

  • Hard facing
  • Single carbon brazing
  • Build-up of heavy deposits
  • Stainless steel TIG welding
  • Cutting tap

DC Reverse Polarity

In DC reverse polarity the electrode is positive and the current flows from the workpiece to the electrode. Welding with reverse DC polarity is ideal for:

  • Overhead welding
  • Vertical welding
  • Cast iron welding
  • Heavy aluminum
  • Rivet welding
  • Sheet metal
  • Low hydrogen welding
  • Arc bronze rod

Advantages of DC Welding

DC tig welderWhen it comes to stick welding applications DC welding offers certain advantages over AC.? Generally, starts are easier, there are fewer arc outages and sticking, there is less spatter, welds have a better appearance, welding vertically or overhead is much easier and DC current is the best ways for beginners to learn “how to weld”.? DC welding also provides a smoother arc and DC straight polarity welds a lot of thinner metals better than AC.

Advantages of AC Welding

The main advantage of AC output welding is that it enables one to weld on magnetized materials because the current alternates between polarities.? DC output does not work on magnetized materials because of “arc blow” which is when the magnetic field blows molten filler metal out of the weld puddle.

Welding Machines and Safety

Many cities and states require welders to be trained and certified in order to operate welding machines.? There are also requirements for personal safety equipment and fire-prevention measures that welders must follow.

Welding fumes can cause breathing problems in welders. Some problems are short term and others may be long term illnesses like asthma.? Welding fumes are also internationally classified as possible carcinogens.? There are specific methods for reducing the exposure to fumes.? Contact OSHA or the American Welding Society for more information.

Burns are probably the most common injury associated with welding.? Personal protective clothing can significantly reduce the risk of burns.? Personal protective equipment for welders includes fire-resistant clothing, safety glasses, shoes, gloves,? hood and welding helmet and leathers.? Synthetic clothing should never be worn because it melts when exposed to extremely high heat.? Wool is a better choice because it is durable and resistant to fire.

Pants and shirts should not be rolled up because sparks can get deposited in the folds. Pants should also be worn outside of shoes or work boots to protect particles from falling inside the shoes or boots.? Safety goggles should always be worn under the welding helmet. If safety glasses are used instead of goggles they should also have side shields.

Conclusion

AC And DC welding are both needed to accomplish certain tasks.? DC welding generally has more advantages over AC welding but the most important thing for a welder to understand is how polarity works so that the welder can choose the proper electrode with the right polarity for the job.

Best Welder For The Job

MIG WeldingWelding is defined as the joining of two individual pieces of metal together with the use of heat produced by an “arc” (aka: electrical current).

MIG (Metal Inert Gas) welders are continuously fed wire and gas. The inert gas is used as a protective shield, from the area that is being welded, from other gases present.

Gas Metal Arc Welding (GMAW), also known as a type of MIG welding, is an electrical welding process that allows long stretches of metal to be joined continuously.

MIG welding uses electricity to melt and join metal pieces together, and this type of welding is considered to be one of the easiest types to learn.

The 110v MIG welder and the 220v MIG welder differ only by the power they use, and the power they output. 110 MIG welders are portable and convenient because it fits into any U.S. standard 3-prog outlet. 220 volt versions may require custom electrical outlets.

Safety Tips Regarding 100v and 220v MIG Welders

These include head to toe safety gear to avoid serious burns (and potentially other types of injuries). Welding safety gear includes: leather gloves, long sleeves, long pants, boots and a protective hood.

If you do not invest in proper (and quality) safety welding gear, it is possible that you are putting yourself at risk for inhaling toxic gases and experiencing painful flash or UV burns.

In addition to wearing welding safety gear, it is also important to survey the immediate area and remove any items that can potentially catch fire due to a welding spark.

Some advantages of MIG welding include:

  1. Easy to learn.
  2. Produces high quality output at a faster rate.
  3. Weld splatter is minimal.
  4. Capable of welding in many positions.
  5. A variety of material can be welded together.

Considerations Regarding the Best MIG Welder For Your Needs

MIG WelderA couple considerations would be cost, type of material you plan to weld and frequency of use.? Don’t necessarily go for a cheap MIG welder, but concentrate on top quality for the amount of money you are willing to spend on this piece of machinery.

A portable MIG welder usually weights under 40 pounds, as it can easily be transported in a mini-van. Larger units can weigh in an excess of 75 pounds. Even with smaller units, it is advised to use a wheeled cart when moving the unit around a warehouse or shop.

The basic components of a MIG welder include:

  1. Control switch
  2. Wire feed
  3. Power source
  4. Gun/welding torch
  5. Wire source/electrode

Also, a MIG rod oven is available for safely storing electrodes.

It is important to note that if you are planning to weld aluminum that a spool gun attachment is necessary to avoid aluminum electrode wires clogging up the wire feeder. A spool gun feeds the aluminum wire directly into the torch to provide you with a smooth/uninterrupted welding experience.

The duty cycle refers to how many minutes the MIG welder can run within a ten minute period without needing to “rest”. For example, a duty cycle may be 20% when run at 90AMPS, this basically means that the machine will continuously weld for two minutes, and then it needs to rest for eight minutes before the welding process can continue.

In the same manner, at 30% duty cycle means that you will have three minutes of welding time before the machine needs to rest for a seven minute period.

Because welders are major financial investments and require quite a bit of electricity, it is never advised to purchase a cheap MIG welder unless you are sure it is of high quality. Always do your homework and purchase a quality, positively reviewed welder whether buying new or used.

Proper Maintenance For Welders and Welding Equipment

Welder
Welder

Welders and Welding Equipment

Welding equipment is often used in construction, automotive, fabrication, farming and other industries where dirt and oils are present and equipment usage can be tough. Routine maintenance on welders is often overlooked, but is extremely important to ensure the longevity of the equipment.

Not only is operation efficiency compromised without proper maintenance, but operator safety is also at risk if routine maintenance is ignored. For this reason, some proper welder maintenance and safety concerns will be covered in the following paragraphs.

Operating Welders Safely

The most important thing to do with any piece of equipment is to get to know your machinery by reading the operator’s manual included with it. Safety precautions will always be in a section of its own.
When in doubt, contact the manufacturer.

Basics For Efficient Welding Equipment Maintenance

Grounding the welder is important for both operator and the welding equipment safety. If the machinery is not properly grounded, there is great risk of electrical shock to the operator. The first thing to remember is to avoid water and wet working conditions because water is an excellent conductor of electricity; even using welders when sweating excessively can be dangerous for the same reason. Standing on a rubber mat or wooden surface is the best possible scenario. When working outdoors, standing on dirt or concrete can also work well as long as the surface is dry.

Loose connections and bare spots on cables are a hazard and should be inspected daily.

Grounding the equipment itself can be accomplished by connecting one end of the grounding cable to a metal stud on the machinery. The other end should be connected to a metal stake, driven into the earth.

Inspection of welder components is important to ensure proper operation and avoidance of a number of potential safety issues.

Cables should be inspected daily for leaks or signs of excessive ware. Worn or leaking cables should be replaced immediately.

Wire feeders should be inspected to ensure the electrode drive rolls are clean and free from dirt or debris. They should be inspected, cleaned, adjusted or changed only when the equipment is off. Inlet and outlet guides should also be inspected, cleaned and replaced in the same manner.

Torch and gun assembly should be inspected routinely by a trained professional. This is to ensure the proper mixing of gasses and pressure. The condition of the gun should always be inspected by the operator, before each use. Any issues should be reported to maintenance right away.

Welder power sources should be disconnected from the power source and either blown or vacuumed out approximately every six months under moderate usage conditions.
Electrode holders should be fully insulated and should not have protruding screws.
Fully insulated lock type connectors should always be used when connecting welding cables.

Electrodes used in MIG welders, arc welders and TIG welders can get hot when the power source is switched on. The electrode wire should never be touched when the power is on – or for a period of time after powered off.

Electrical safety devices such as circuit breakers and interlocks should be connected and inspected routinely only when power is off.?Terminals and electrical parts should all have insulated covers.

Gas Cylinders and regulators should be inspected daily for damage and leakage. Any faulty components found, should be replaced immediately by trained professionals.

Proper maintenance of all machinery utilized in industrial applications is the job of the operator, supervisors and the maintenance department. Welders and welding equipment are not exempt.