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
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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
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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
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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.
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