Due to the poor column strength of aluminum, the wire easily bends or twists when pushed through a typical GMAW wire feeder and gun system, causing “bird-nesting.” Here are some ways to prevent this problem.
Poor feedability is one of the most common problems in aluminum welding production, particularly for users who are just starting to weld with aluminum. Due to the poor column strength of aluminum, the wire easily bends or twists when pushed through a typical GMAW wire feeder and gun system, causing “bird-nesting.” This problem often leads to excessive rework and wasted material, as well as increased labor costs and reduced production.
Several things should be considered in the fight against bird-nesting. One is the gun liner. I’ve heard many varying recommendations in this area. The first thing to consider is what size wire is being used. In a push system, the “slop” between the wire and the liner can allow as much as an inch or two (depending on the length and gap) of wire length. This means that when the wire is cut and pulled after a weld or when the ball is removed, the wire can be pulled back and forth. The slack is then taken up when the wire is fed causing a burn-back on start-up. Keeping this gap as small as possible will help prevent this problem.
The type of liner is also important. The ends of steel or brass liners have sharp edges that can easily cut aluminum wire. These should be avoided or, if they must be used, the edges should be polished or ground before use. Some metal liners use plastic coatings but these are often too thin, and there is no way to know if they are worn until shavings develop.
Disqualifying metal liners, this leaves some sort of plastic product. Teflon has a lower coefficient of friction than Nylon, but it is also softer. As the harder of the two, Nylon does not cut as easily, which reduces embedded shavings (such as shop dust/particles). Nylon is also lower in cost than Teflon.
Some manufacturers have developed two-part liners: an outer liner that is stiff and an inner liner that has a lower coefficient of friction. Here you want to examine the characteristics of the part of the liner that actually touches the wire. Composite products have advantages in lubricity although if they cut easily, they still have the potential to embed particles, which can cause further shavings. These are also usually more expensive and may have little advantages in performance, wear and the reduction of shaving buildup.
Another thing to consider is the temperature requirements of the liner. The liner often comes into contact with the contact tip and/or gas diffuser, which can melt plastic liners. Some liners come with a metal coiled “jumper-liner” made from brass, copper or even steel. Metal jumper liners can cause shavings just as easily as those constructed completely from metal. One alternative is a liner cap with a high heat tolerance. These caps simply insulate the hot contact tip or diffuser from the plastic liner.
A second major consideration is to understand the “push” and “pull” qualities of your welding gun. Feeding only 6 ft to 8 ft allows a push style, while feeding wire more than 8 ft requires use of a push/pull gun.
The required force to pull wire is not always consistent. As the spool diameter changes from the top layers, about 12 in (305 mm) diameter, to the bottom, around 6 in (150 mm) diameter, the force to pull the wire changes as well. Say, for example, there is 5 lb of force to pull from the top of the spool (which, by the way, is excessive). By the time the wire reaches the bottom layers of the spool that force has increased four times! This would require 20 lb of force, which certainly would put undue stress on the motor and drive rolls, not to mention causing slippage problems that make the arc erratic.
As you add drive roll force, the opportunity for bird-nesting increases. Most machines include some type of adjustment on the hub that allows the static brake system to be reduced. There should be only enough force on the brake to keep the wire from falling off the spool. Sometimes less is a good thing!
A new patent-pending technology just introduced to the market is a breakthrough device that pushes the welding wire from a drum package to your existing wire feeder. This air-driven system provides delivery of wire to a feeder up to 100 ft (33 m) away. It also converts the typical sine wave shape of drum wire to a circular cast to allow long, continuous seam welds without arc wander and maintains good contact to the tip. Contact me if you would like more information on this new device.
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