Understanding the Common Difficulties of Feeding in MIG Welding Aluminum
Knowing the Right Equipment, Set-Up and Feeding Options
By: Jim Harris, Product Manager, The Lincoln Electric Company and Frank Armao, Group Leader, Non Ferrous Applications The Lincoln Electric Company

Aluminum as a fabrication material is now more prevalent than ever, and its use can be traced to a host of industrially designed objects - from vehicles to household items. With this demand, the need to weld aluminum has never been greater. Aluminum is attractive to industrial designers in many fields, due to its lightweight attributes and corrosion-resistant properties. Aluminum fabrication is becoming commonplace in fabrication shops of all sizes, and so must the skills required to weld this often mysterious and difficult metal.

To those experienced in steel welding, aluminum can present some real challenges. Equipment must be adapted specifically to handle the softer aluminum wire and machine settings that normally work fine for steel may not be appropriate. In fact, aluminum wire can easily be damaged by equipment set-up for steel wire. To be

successful, there are some special considerations that must be taken.

In this article, we will look at three areas:
1) set-up and techniques
2) power sources
3) three ways to feed aluminum wire.

Set-Up and Techniques

Those who usually deal with steel need to make the following changes in their equipment and settings in order to effectively weld aluminum:

• Liner
  For steel welding, the usual practice is to use a helically wound steel liner, but for aluminum, this type of liner would scratch the soft aluminum wire and scrape off shavings. So, when welding aluminum make sure to find a liner that is made of nylon or Teflon®. These materials are recommended to reduce friction and eliminate wire shaving.
  
  
• Wire Guides
  Similarly, for aluminum welding, wire guides also should be composed of nylon or Teflon rather than steel. Again, friction is reduced and wire shaving is virtually eliminated.
  
  
• Drive Rolls
  For steel welding, the normal practice is to have a V-shaped groove in the drive rolls. For aluminum, it is recommended to substitute a U-shaped groove so that there are no sharp edges to shave off the aluminum wire. Also, the tension on the drive roll should be reduced compared to the typical setting for steel to prevent crushing of the aluminum wire during feeding.
  
  
• Contact Tips
  Aluminum expands more than steel as it heats up. Therefore, the proper-sized hole in the contact tip is larger for aluminum than for steel. Be sure to purchase contact tips specifically designed for aluminum, or poor electrical contact may result. Warning signs of an improperly-sized contact tip are wire shaving or scratches on the wire, unusual arcing behavior and irregular wire feeding, typically observed as an erratic, varying arc length.
  
  
• Brake Tension
  Be sure the brake tension on the wire spindle is set more loosely than it would normally be set for steel. This way, less force is required to pull the wire off of the spool.
  
  
• Gun Cables
  Because the column strength of aluminum is much less than steel, feeding aluminum wire can be compared to 'pushing spaghetti uphill'. Therefore, be sure to keep the gun as straight as possible to minimize tangling.

Power Sources

When deciding which power source to buy for aluminum welding, an operator needs to ask two basic questions: 1) how often will I will weld aluminum?; and 2) what is the typical thickness of material that needs to be welded? First answering these questions will serve to guide the buyer in the right direction.

• Infrequent Aluminum Welders
  Those who don't plan to weld aluminum on a regular basis should consider a small wire feed welder system in the 130-170 amp range. The only caveat is that this type of system will only weld a limited range of material thickness (usually from 3/32" to 3/16"). Also, a purchaser will need to buy a manufacturer's kit for aluminum to be sure to have the right liners and tips.
  
  
• More Frequent Users
  Those who will weld a variety of aluminum applications on a frequent basis should move up to a larger machine with more amperage and the capability to weld thicker materials.
  
  
• Aluminum Fabricators
  For serious aluminum fabricators, another great feature to look for in a unit is one with pulse welding capabilities. Pulsing can allow the use of a larger diameter wire electrode than otherwise possible, equating to easier feeding and less porosity.

Feeding System Selection

Having the proper wire electrode feeding system for aluminum welding is imperative. There are three main ways to feed aluminum wire - 1) push system, 2) spool gun, and 3) push-pull system. Each method has its advantages and disadvantages, which we will address below.

1. Push
Browse Lincoln Push Wire Feeder / Welders and MIG Power Sources

What is it?
For the push method of feeding aluminum, a high torque, variable speed motor at the wire feeder pushes wire through the liner to the gun.

Recommended for:
Push feeding systems work best feeding larger diameter wires, such as 1/16", as well as stiffer wires like 5356 alloy. Short gun cable lengths of 15 feet or less are preferred for Push feeding systems.

Advantages/benefits:
Push systems are lower cost than other aluminum feeding methods since they only require one motor at the wire drive. In general, they work best for wire greater than 3/64". They also have the advantage of offering a compact gun to fit into tight spaces for providing better accessibility to the weld. Also, typical push wire feeders have the capacity to hold a common 12" outer diameter spool of aluminum electrode.

Limitations:
A push system is typically not used for long gun lengths as the operator is likely to experience birdnesting or wire tangling. It also should not be used for smaller diameter wires.

2. Spool Gun
Browse Lincoln Spool Guns

What is it?
A spool gun is a self-contained gun that is equipped to feed wire electrode from small spools mounted on the gun. Typically, these spools 4" in diameter, weighing 1 pound for aluminum. With this set-up, the distance from the wire to the contact tip is a very short, usually less than 12". A spool gun typically makes it easy to feed soft aluminum wire.

Recommended for:

Spool guns should be used for smaller diameter, softer wires. In addition, users that switch frequently between steel and aluminum welding typically find it convenient and cost effective to use a spool gun for aluminum wire electrode and a common push MIG gun for steel wire electrode. Depending on the power source capability, both guns can often be connected to a single power source at the same time.

Advantages/benefits:
Spool guns are fairly simple to use and also have the benefit of being relatively inexpensive. For operators who don't want to be limited to welding within a short distance of the power source, a spool gun has the ability to reach as far as 50 ft. away.

Limitations:
Because a spool gun is larger than a push gun, it can sometimes be difficult to get close access to the weld. Also, a spool gun can only hold a 1 pound spool of aluminum wire electrode, so changeovers are frequent. In addition, these small spools typically are not the most economical way to purchase wire.

3. Push-Pull
Browse Lincoln Push-Pull Systems

What is it?
A push-pull system utilizes dual motors: an assist motor that pushes the electrode from the feeder, and a primary motor that is located in the gun that pulls the electrode.

Recommended for:
This is the most flexible system of the three discussed in this article, and it can accommodate any type of aluminum wire - even soft 4043 - without tangling problems. Wire sizes that work well on a push-pull system run the gamut from .030" to 1/16".

Advantages/benefits:
This type of system offers the best of both worlds - the feeding performance of a spool gun with many of the advantages of a compact push system. A push-pull system provides the most uniform feeding and can hold larger spools of wire up to 8" in diameter (approximately 20 lbs). The gun can be taken long distances from the power source (up to 50 ft.). In addition, this system does not require the costly 1-lb. spools of the spool gun method and has a comfortable, ergonomic gun that fits into tighter places

Limitations:
Typically, the greatest disadvantage of a push-pull system is that it requires the most number of components and is the most expensive. But as we will explain later, this is not always the case as some of the latest technological innovations have addressed these concerns.

Types of Push-Pull Systems:
There are three types of push-pull systems, which are briefly highlighted below:

1) Separate, dedicated slave cabinet
This type of system requires the greatest number of components, including a special pull gun, welding power source and separate wire feed cabinet.

2) Add-on pull torch with an assist motor
Some manufacturers offer an add-on gun for standard push wire feeders systems. These unusual guns contain an assist motor in the gun. However, the potential drawback to this type of push-pull system occurs if the wire feeder motor pushes the wire at a faster rate or with greater torque than the assist motor in the gun, increasing the likelihood of birdnesting or tangling of wire.

3) Self-contained power source/wire feeder

These systems consist of a combination all-in-one power source and wire feeder unit with a motor that is easily switched to operate as a single push motor or behave as an assist motor in the classic push-pull system. A true push-pull gun acting as the primary motor is used with these systems to provide all of the advantages of the classic push-pull component system.

However, this is the best option in the push-pull category, since it provides true push-pull behavior with fewer components. Instead of three pieces, this system only requires two - the combination wire feeder/power source and the push-pull gun. Purchasers save nearly $1,500 in equipment costs, since they don't need to purchase a separate wire feeder cabinet.

Some models, such as Lincoln Electric's Power MIG™: The Professional Choice, 300, offer the benefit of full pulsing capabilities with tailored welding waveforms designed for aluminum that can be programmed into the machine for difficult-to-weld applications, such as particularly thin material. Self-contained power sources/wire feeders also provide the versatility of easily switching between steel and aluminum wire since operators can choose push only or push-pull operation.

Conclusion
Armed with the knowledge presented in this article, a welding operator should be able to distinguish between the many MIG aluminum set-ups on the market today and be able to decide which one is best for a given application.