September 2008 Edition

Welding

Core Strength

Switching to metal-cored wire for its welding operations increased both quality and productivity for a manufacturer

Fabricating dozens of subassembly components for top-tier OEM manufacturers of cranes, aerial work platforms, mining, and other heavy equipment requires keen attention to both quality and productivity.

For Miller Welding and Machine Co., Brookville, PA, one of the keys to ensuring both has been equipment standardization. As much as possible, Miller has set up its 140 semi-automatic and 10 robotic welding cells with the same welding processes, guns, gas, and wire.

After using mostly flux-cored welding wire, with a few cells using solid wire, Miller converted most of its cells to metal-cored wire, specifically Tri-Mark Metalloy 76 from Hobart Brothers, Troy, OH.

Since converting to Metalloy 76 two years ago, Miller has increased its semi-automatic and automatic welding productivity by 20 percent. Just as importantly, the quality of its welds far exceeds those produced with either flux-cored or solid wire.

One of the keys to the company’s success has been a willingness to take on jobs from start to finish regardless of quantity or size.

"We’re a one-stop, turnkey operation," Dave Miller Sr., founder of the company, said. "From a rough sheet of steel to the finished product, and all along the way, we do it all. We don’t set a limit that says an order needs to be within a certain size or quantity, or else we won’t take it. We have parts that weigh more than 10 tons, and parts that weigh less than 10 oz."

Wired for Growth

Another key to Miller’s success has been the foresight to recognize the long term benefits of investing in cost-saving technology. Miller’s Production Supervisor, Dave Moore, saw the opportunity to improve the company’s overall quality and productivity through investing in metal-cored wire.

Consisting of a hollow metal tube filled with a blend of metal, mineral, and chemical powders, metal-cored wire offers many advantages over both solid and flux-core wire. The majority of the powder core is iron, with varying amounts of other materials which reduce oxidation and provide higher impact strengths, among other benefits.

Metal-cored wire does not produce a slag coating over the top of the weld, which can reduce weld clean-up time by 75 percent or more.

Other key features of metal-cored wire are that it creates high deposition rates and a visually appealing weld bead. Combined, these features increase first-run productivity and reduce the need for clean-up and rework.

Because the electrical current flows almost entirely through the outer metal tube, it produces a softer, conical arc cone that results in a wider weld bead and less turbulent arc.

Moore decided to give metal-cored wire a try after one of Miller’s biggest customers made the switch for its welding operations and was pleased with the results.

Cleaning up . . . from the Metalloy 76 takes operators one-quarter the time

"We brought in several different brands of wire for testing," Moore said, "and the Tri-Mark Metalloy 76 outperformed everything else we tried. The wetting action and spatter levels were clearly superior to the other wires we tested."

Classified under AWS A5.18 E70C-6M H4, the Metalloy 76 is a versatile, all-purpose wire that can be used in spray, short arc, or pulsed processes, and contains added deoxidizers that let it tolerate mill scale and other surface contaminants better than most other wires.

Miller integrated the Metalloy 76 into as many welding cells as possible. The company was able to replace nearly all of its flux-cored wire, but it still uses solid wire with a pulsed MIG process for a few assemblies, primarily when the customer requires it, and for the majority of its tacking.

At just one of its three facilities, Moore said the company is using over 30,000 lb of wire per month. Miller feeds its wire from 750 lb drums, which reduces the company’s per-pound cost and also reduces the amount of time spent changing wire.

The Metalloy 76 wire is used with a traditional MIG waveform, paired with a 92 percent Argon, 8 percent CO₂ shielding gas. The company uses a variety of positioners that rotate the assemblies so that the operators weld in the flat position as often as possible – the position in which metal-cored wire achieves the highest deposition rates.

The assemblies are fabricated using A36 mild steel as well as high-strength, low-alloy steel for several life-critical components, both of which the Metalloy 76 is able to weld successfully.

Higher Productivity and Better Quality

Overall, Moore said he couldn’t be happier with the results.

"Conservatively, I would estimate that the Metalloy 76 has increased our productivity by 20 percent in our semi-automatic operations," Moore said. "It provides higher deposition rates than our solid and flux-cored wires, and the excellent wetting action and low spatter greatly reduce our clean-up and rework. It costs a lot to put the weld in there the first time, but it costs a heck of a lot more to take it out and put it in there a second time."

The quality of the welds has also improved dramatically.

"The Metalloy 76 gives us a much higher quality weld deposit all the way around in all the different ways you want to measure it," Moore said. "From tensile strength, to elongation, to impact values, however you want to measure it, it’s giving us the weld quality we’re looking for."

These benefits are especially important for the company’s life-critical applications.

"Some of our parts are critical components used in aerial work platforms that go up to 150'," Miller Sr. said, "and when the wind is blowing and things are vibrating, the guys up there want to be able to look down at their basket and see a nice, strong weld.

Easy Decision

Although metal-cored wire costs roughly 33 percent more than solid wire, Moore said the decision was easy once he saw the productivity improvements it could yield.

"When you look at the total cost of producing a fabricated part, the cost per pound of filler metal is a very slim piece of that pie," Moore said. "If you can reduce your post-weld clean-up and rework or increase your deposition rates, you will more than justify the additional cost of the wire."

Moore estimates that cleaning up the minimal spatter that results from the Metalloy 76 takes his operators one-quarter the time it took them to clean the welds from their flux-cored wire.

The Metalloy 76, and most metal-cored wire, is much more forgiving to use than solid and flux-cored wire, which reduces the time it takes to get new welders trained and also allows mid-level welders to produce visually appealing welds.

Using metal-cored wire has also let Miller step up from a 0.045" to a 0.052" diameter wire, resulting in increased deposition rates while still allowing the company to weld material anywhere from 1/4" to 2" thick.

"We’ve programmed four different schedules into our feeders," Moore said, "and the 0.052" wire has a wide enough tolerance that we can dial it down for the thinnest material we weld or dial it up for the thickest."

The ability to weld different material thicknesses with the same wire also saves the company considerable time because it does not have to move the assemblies to separate welding cells or switch wires to weld different material thicknesses on the same part.

"In our community," Dave Miller Jr., Miller’s president, said, "there is a great deal of metal working going on, and all of the companies here are competing for the same skills sets. The metal-cored wire and our robotic welding cells both mitigate our reliance on a very limited labor pool." Hobart Brothers

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