High-volume MIG welding, like the kind performed by many OEM and Tier 1 automotive manufacturers, can be a grueling race against time to meet tight deadlines and strict quality standards. In order to deliver quality parts on time, the wire must first be delivered to weld those parts. The wire delivery system, however, is often one of the most overlooked areas of the welding process, and an improper delivery setup can cause productivity issues.
There are seven key variables in weld wire dispensing to keep in mind when optimizing a delivery system. The first variable is the wire type.
In the automotive industry, the four wire types used include solid steel, cored steel, aluminum and silicone bronze. The key point to remember with wire type is that non-ferrous wire should at no point touch ferrous wire. This means the weld wire conduit can only be steel lined when using ferrous wire (solid or cored), while non-ferrous wire should only use polymer conduit throughout the wire delivery system.
Using a steel-lined conduit with aluminum or silicone bronze can contaminate the wire and cause serious weld quality issues. Another important factor to remember is that not all wire bends the same. Softer wire, such as aluminum, as well as cored wire is particularly sensitive to a tight bend radius.
To make these tight bends, there are solutions, like the Wire Guide Module from Wire Wizard, where all wire types can benefit when making 45-, 90- and even 180-degree turns where necessary in the wire delivery system. The modules use a series of rollers that allow the wire to coast around turns, eliminating skid friction and reducing pull force on the feed motor.
Without the Wire Guide Module, skid friction compounds at each turn in the wire delivery system, resulting in a significant workload for the feed motor as well as an unstable wire feed. Figures 1 and 2 illustrate how much the skid friction compounds at each bend in the conduit and also the improvements that come from leveraging the module.
With the Wire Guide Module installed on the wire delivery system, the skid friction is eliminated because the wire is not dragging along the interior of the conduit. Several pounds of pull force at the feed motor are reduced to only ounces.
The module provides an ideal solution for manufacturers delivering wire from above the weld cell. This is becoming a more common configuration because it saves valuable floor space.
Wire diameter and conduit length
The second variable is the wire diameter. For most automotive applications, this is rarely over 0.052 in. (1.3 mm) dia., and 0.045-in.-dia. (1.1-mm) wire is common. Therefore, most applications use 0.300-in. (7.6-mm) ID conduit, although it is still critical that the correct conduit is used based on the wire type. Fortunately, automotive industry manufacturers do not have to deal with the monster 5/32-in. (4-mm) wire used in submerged arc welding, which brings a whole new set of wire feeding challenges.
The third variable is the length of the conduit run. The longer the run, the heavier the workload on the wire feeder. Applications that require a longer run to the wire feeder can benefit from using a Wire Guide Module and pneumatic wire feed assist unit. A wire feed assist unit provides a push-pull system to get the wire from the source to the feeder. A pneumatic motor with two drive rolls eliminates the drag on the wire. Using this method allows the wire source to be located more than 150 ft. (46 m) away from the arc, which means the wire packages for multiple weld cells could be located in a central location.
The pneumatic wire feed assist unit is also recommended for feeding aluminum and lighter wire subject to “birdnesting” at the feeder. Birdnesting is essentially the tangling of wire that prevents wire from being fed. Because the wire feed assist unit eliminates the workload on the feeder motor, it allows for more accurate adjustment of drive roll tension – a leading cause of birdnesting and critical when feeding lighter wire.
Wire cast and helix
Wire cast and wire helix are the next two variables that can affect a wire delivery system. Wire cast refers to the curvature of one strand of wire, measured as the diameter of the circle formed by a strand laying on a flat surface. The wire cast varies based on the wire packaging and the amount of wire remaining.
A tighter cast, such as when the wire is down to the inner portion of a spool, creates a smaller contact area between the contact tip and the surface of the wire, causing potential current transfer issues as well as excessive contact tip wear and arc wander. A larger radius cast can cause intermittent arcs due to poor contact with the ID of the contact tip.
The wire helix (also known as wire pitch) is defined as the rise of a single strand of wire when placed on a flat surface (how high the wire springs off the floor). This is measured horizontally for ferrous wire and vertically for aluminum wire. Think of it as the “spring” in the wire.
Wire helix can be a problem if it is inconsistent, which can cause tracking issues along the weld seam. Ideally, the wire cast and helix should remain consistent throughout the life of the wire package. A poor cast and helix can cause the wire to twist and spin out of the contact tip at varying degrees. Figure 3 (on the following page) illustrates wire cast and helix.
Wire straighteners, however, can serve as an excellent tool for fine tuning the wire cast and helix and can increase the overall welding consistency by stabilizing the wire feed. They are most often installed at the wire feeder to straighten or recast the wire before it is fed to the welding gun.
Some wire may be exempt from the next variable, wire drawing compounds (or otherwise dirty wire). However, most wire is covered with at least some drawing compounds. These drawing compounds are used in the wire manufacturing process or applied to the wire to inhibit corrosion. Sometimes, they can make a mess of a wire delivery system.
As part of the maintenance schedule, a wire delivery system should be checked and cleaned periodically for drawing compounds and other debris. If the wire package is uncovered, an oily buildup in the conduit or connection points from the industrial environment may also appear. In the most severe cases, some manufacturers have resorted to wrapping rags around the wire at the source to attempt to clean the wire. Wood reel packaging is especially susceptible to getting dirty, but this can be prevented by using a protective cover over the reel.
Choosing the right conduit
Perhaps the most important variable to examine is the welding application itself. Robotic arc welding applications, with an emphasis on speed and efficiency, are the most demanding on the wire delivery system. Choosing the right conduit for the application is critical.
With semi-automatic welding, the conduit can typically be polymer, except in some high-volume applications with flux-cored wire where steel-lined conduit may be used. In robotic applications, the wire delivery system requires a high degree of mobility inside the weld cell. In a typical robotic wire delivery system, polymer conduit is used from the wire source to the outside of the weld cell. Inside the weld cell, steel-lined conduit is usually recommended unless the wire is non-ferrous.
With non-ferrous wire and some steel wire robotic applications, polymer conduit should be crosslinked to reduce the risk of breakage. Crosslinked polymer conduit has been treated with radiation to strengthen the polymer molecules and provide better durability and crack resistance. Just like a superhero created by radiation, crosslinked conduit can save the day by reducing downtime and outlasting non-crosslinked conduit by a wide margin.
In addition to the conduit, torch liners also play a critical role in the wire delivery system on the other side of the wire feeder. Many torch liners are manufactured with steel wire that can be abrasive and shave the weld wire. They can also cause excess friction that can make the wire vibrate.
Wire vibration can actually cause micro-arcs inside the contact tip (similar to a wire EDM), resulting in poor welding performance and increased burn backs. Each burn back is like blowing a tire. It will set you back while the competition speeds ahead.
To reduce burn back, wire vibration must be eliminated. Torch liners designed with a coated elliptical wire provide a smoother, more consistent wire feed that eliminates the wire vibration in the contact tip, resulting in less burn backs and reduced downtime.
Continuous wire delivery
In auto racing, in order to win it’s important to make as few pit stops as possible. Some of those stops are due to problems, others like refueling and changing tires, however, are routine. In either case, optimizing the car for the track usually means less stops and a much better chance of winning.
In MIG welding, it’s just as important to optimize a weld cell for the application. Essentially, the fuel is the wire, and with high-volume robotic welding applications fuel runs out more often. That’s where continuous wire delivery systems come into play.
Continuous wire feeding means production doesn’t have to stop to change out a wire package. Wire Wizard’s Non-Stop Wire System is one option for a continuous wire delivery system that uses a butt welder to join the end wire from one drum with the start wire from the next drum. The process of joining the wires only takes a couple of minutes, and the reduction in downtime alone can add up to thousands of dollars in savings over the course of a year.
So clearly, an optimized wire delivery system is a key component to building a high-performance weld cell and winning the race to maximum quality and productivity. See you at the finish line!