Preventing Robotic Indigestion

Choosing the right welding wire spells downtime relief.

By Jim Harbaugh

To test wire cast, place several feet of wire on a clean, flat surface. The optimum diameter (the cast) of the circle formed by solid carbon steel wire should be 35 to 55 inches.

Automatic welding equipment is a good production investment—when it's welding. The second the arc starts to wander, the minute there is too much spatter, the more often liners need cleaning out, you start to lose money to downtime. You have a case of robotic “indigestion,” and with an average labor and burden rate of at least $35.00 an hour, you need relief now. That relief starts by taking a look at your choice of welding wire.

Fabricators who shop for price rather than for the best wire for their applications often spend more money later on non-scheduled reworks and off-line time. To save on cost and to keep downtime to a minimum, informed fabricators balance the following criteria when purchasing weld wire.

Know the Wire Chemistry and How It Is Derived
Wire chemistry impacts the weld quality and the parts rejection rate. The American Welding Society (AWS) publishes the AWS A5.18, a widely used guide with chemistry tolerances on mild carbon steel weld wires. Most wire manufacturers adhere to these specifications. However, some manufacturers adjust or tighten tolerances on certain elements of the chemistry to enhance performance, while others use the full range of the AWS specification.

The helix is the distance one strand of wire rises off a flat surface. In automatic weld applications, the best performance comes from wires with a helix of 1 inch or less.

There are also variations in how manufacturers verify that their products meet the various chemistry requirements. One may provide customers with “typical,” or the average, chemical composition of the batches or “heats” of weld wire analyzed over a year. Another manufacturer may provide the actual chemical analysis for each heat, which is more precise. Certain alloys create more stable, stronger welds with better puddle fluidity, lower spatter and less potential for porosity formation than other alloys. For the most part, wires with higher manganese and silicone content can be used with less expensive CO2 shielding gas; however, maximum properties are more easily achieved with mixed gases.

Insist on Optimal Cast and Helix
Improper wire cast and helix also can increase reject rates and downtime. The cast is determined by measuring the diameter of a circle formed by a strand of weld wire lying on a flat surface. Ideally, the wire cast for automatic welding equipment should fall within the 35" to 55" diameter range. A cast that is too small can create feedability problems, excessive tip wear, and arc wander specifically in fully automated and robotic welding. A cast that is too large can cause inconsistent current pickup at the contact tip and burnbacks. By using wire with a cast that falls within the optimal range, you are less likely to experience these issues.

The photomicrograph of conventional copper-coated wet-drawn weld wire (left) illustrates the poor copper adhesion to the wire. The copper flakes off inside liners and contact tips, requiring frequent cleanings and replacements. The copper-free wire (right) features a nontoxic coating that eliminates copper flaking and improves feedability.

Wire helix is the distance one end of a strand of weld wire rises off a flat surface. Welders using solid carbon steel wire can expect the best performance from a wire with a helix of 1" or less.

Eliminate Sources of Indigestion
Some wires, because of manufacturing processes, can clog welding equipment more frequently than others. Copper-coated wires with poor copper adhesion often produce copper flakes that plug cable liners, drive rolls and tips. Wire feeding equipment that is in poor condition can also cause the wire's surface to be scraped. Metal particles are then deposited in cable liners, drive rolls and tips. These issues all cause downtime and reduce the efficiency you try to gain with automated or robotic equipment.

One solution to the copper flaking problem is to use non-copper coated wires. These wires typically use a nontoxic chemical coating that improves feedability and lowers downtime costs.

“Dirty” wire is another cause of erratic arcs, clogged liners and tips and, in some cases, weld porosity. The problem stems from the manufacturer not carefully removing the drawing residuals from the wire before shipping.

Reduce Wire Spool Changes
Spool changes can take a welding station off-line for 15 to 20 minutes. Small spools must be changed more often in high-volume, automatic welding stations. To eliminate the high costs of changing spools, fabricators often specify large bulk wire packaging. Because bulk packages come in sizes ranging from 300 to 1,000 pounds, it is not always possible to locate these packages in the welding cell. Some bulk packages are capable of feeding from up to 150 feet without slave motors. This placement makes it easier to service the packaging.

Before installing your bulk packaging, consult with the manufacturer or its distributor representative to insure proper wire placement and optimal feeding conduit alignment to your automatic or robotic station.

Any wire that meets all or most of these criteria saves fabricators more money in the long run. If the wire manufacturer backs the wire with strong technical resources in metallurgy and chemistry, as well as with a support staff that solves special problems quickly, you'll likely get the best source for wire at the best total cost time after time.