Just as running a marathon requires rigorous, disciplined preparation compared to taking an afternoon stroll in the park, so does managing a high-volume or robotic MIG welding
operation. Where a general fabrication shop can get away with using a “value oriented” solid MIG wire, a high-volume operation cannot because of the high cost of downtime and quality issues. Fortunately, filler metal suppliers listen closely to their customer needs and continue to introduce new products and packaging that improve uptime.
Spatter, porosity and inconsistent quality are big drags on productivity when MIG welding with a solid wire. Instead of sending the part to the next manufacturing step, the part will require post-weld cleaning and inspection, both of which add cost and increase cycle time. Failure to remove excess spatter or silica islands may also cause issues related to paint quality and provide a weak spot for rust to attack.
Filler metal manufacturers have developed a variety of consumables specifically to address these causes of downtime in various applications. These includes filler metals with tighter chemistry tolerances for consistent performance, formulations with better arc stability for lower spatter and chemistries with superior wet-out for a consistently smooth transition at the toe of the weld to create a uniform bead profile.
A classic example is manufacturers moving from an ER70S-3 wire to an ER70S-6 wire. Years ago, manufacturers chose an S-3 wire because it cost less compared to an S-6 wire, which has higher levels of deoxidizers for better performance over dirt, rust, mill scale or pickling oil. They also chose an S-3 wire for low silica island formation. These days, the cost difference is small, and the formulation of today’s S-6 wire addresses many of its previous shortcomings (such as silica island formation), and provides low spatter and other benefits that lower total welding cost.
An ESAB distribution partner in Europe recently conducted a side-by-side comparison of premium versus value-oriented wires and consumables. They connected a structural steel fabricator’s mixed-brand welding fleet to the InduSuite WeldCloud Productivity online application to monitor the number and duration of weld sessions and voltage and amperage. The bottom line: the data proved that a premium ER70S-6 wire could increase speed by 10 percent because it provides a stable arc at high welding currents with extremely low levels of spatter.
Another good example is wire formulated to weld galvanized steel. Zinc melts at temperatures much lower than steel. As a result, the heat of the welding arc releases zinc vapor around the weld pool, which affects arc stability and contributes to excess spatter. If trapped in the weld pool, the vapor causes porosity as the weld solidifies. Through tightly controlled micro-alloying elements in its formulation, wire, such as the OK AristoRod 38 Zn, controls surface tension in the weld pool in a manner that allows the zinc vapor to escape, greatly reducing spatter and the chance for porosity.
Coated or uncoated?
MIG wire is available in coated and uncoated versions. Historically, manufacturers applied a copper coating to enhance feeding properties through improved current transfer between the electrode and the contact tip and not, as is often claimed, to protect against rust. Because current transfer determines a large part of the actual feeding force needed, the copper coating, primarily, enhances wire feedability. A favorable side-effect is that the copper coating in a premium wire can reduce contact tip bore wear, which is a primary factor in uptime, arc stability and spatter generation.
The drawback of a copper-coated wire lies in the fact that copper is a soft alloy and sensitive to mechanical damage during feeding. Copper particles chip off and contaminate the feeding system. They gradually clog the liner and gun and melt into the contact tip (arcing), increasing feed resistance and, eventually, leading to burnback of the wire to the tip, halting the welding process.
The severity and speed of contact tip wear and gun liner contamination depends on several factors, and electrode quality is one of the main influences. Creating an optimal copper coating is a complicated process with several critical production steps. Cleanliness and degree of roughness before coppering, for example, are extremely important. They determine how well the copper coating adheres to the electrode surface and resists being rubbed off during feeding.
Equally important is the thickness of the layer – it has to be thick enough to provide the necessary benefits, but thin enough not to chip off during feeding. Electrodes such Purus, an ER70S-6 wire for high-volume welding, have been developed specifically to address all these considerations.
As an alternative, manufacturers have developed non-copper-coated MIG wire with advanced surface characteristics that provide consistent welding performance, a stable arc with low feeding force, trouble-free feedability, excellent arc ignition and extremely low spatter level. In side-by-side tests, a wire such as OK AristoRod 12.50, a non-copper-coated ER70S-6 wire, can reduce the number of contact tip changes and the related downtime because it generates fewer particles and enables a longer runtime between scheduled maintenance and liner and tip replacement.
The number of production variables and the different wire technologies explains why there is such a broad quality spectrum of electrodes and associated differences in contact tip wear and generation of flaking that clogs liners and tips. Of course, arc starting, arc stability and spatter generation are also factors. The best solution is to continuously evaluate new filler wire options and, ideally, conduct the evaluation using an online welding application to measure arc-on time and possibly real-time monitoring using a quality assurance system.
Packaging and delivery
MIG wire packaged on spool or basket typically weigh 33 to 60 lbs. Given a deposition rate that could range from 3 to 15-plus lbs./hour (depending on wire diameter and parameters), operators would need to change spools several times per shift, losing perhaps 10 min. of productivity every time.
Shifting to a bulk wire drum is an easy way to gain productivity. Drums contain anywhere from 250 lbs. of wire for smalls drums to 1,100 lbs. for the new Marathon Pac Ultra, which holds 100 lbs. more than competitive drums and 22 percent more than the previous Marathon Pac. An extra 100 lbs. equates to 18,416 ft. of 0.045-in. wire or 30,417 ft. of 0.035-in. wire, providing an additional 8 to 16 or more hours of welding time before needing to rethread the drum, depending on the process and parameters.
Drums themselves continue to evolve. Instead of just a solid corrugated drum with a wire ring, drums now feature ports to view wire level, built-in slots for a forklift lifting yoke and reinforced side walls to better stabilize the wire during transit and also enable stacking drums to reduce storage space. Once the wire is depleted, every element of the drum can be disassembled and recycled (excepting the conical hood).
High-volume fabricators understandably tend to adopt the “don’t fix what isn’t broken” mantra. However, achieving new heights of productivity requires trying new solutions. For companies consuming tens or hundreds of thousands of pounds MIG wire annually, increasing arc-on time just a few percentage points adds up to putting more parts out the door without adding more resources.