XMT® 350 Inverters with Auto-Line™ Technology Provide Smooth Welding Arc for Equipment Repair Outfit - MillerWelds

XMT® 350 Inverters with Auto-Line™ Technology Provide Smooth Welding Arc for Equipment Repair Outfit

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Dodge Machining, Corp. relies on inverter welding technology from Miller Electric Mfg. Co. to combat dirty power.

Executive Summary

  • Auto-Line™ power management technology eliminates problems caused by dirty power.
  • Increased productivity and improved weld quality.
  • Better inverter reliability when running off generator power.
  • XMT® 350 provides reliability and portability in extreme conditions.

Dodge Machining Keeps Mining Equipment in the Dirt

Service company reduces welding time with Miller, Bortech equipment

Not many people will fix a gear case on a mining truck. It holds half a million dollars of gears, and any problems caused by the welding repair and machining process will create a huge liability. Fortunately for the coal, gold, ore and other mining industries, Dodge Machining Corp., is one of the few companies with the skill, experience, adequate liability insurance and equipment to tackle the job of repairing the world’s heaviest mining equipment.

Power and hydraulics rolled into one, this Hitachi shovel takes as much of a beating as it delivers; scooping tons of ore a day into the mine’s fleet of haulers. Each piece of equipment relies on another in a mining operation
This hauler has the rear left wheel off for repairs. Each wheel is run by its own independent drive motor (seen to the lower right), which has to be removed before any work can be done.

Since mining shovels and trucks operate around turning and pivot points, typical repair work includes rebuilding pins and line borings of bushings, repairing cracks in the boom, stick, bucket and track frame of mining shovels and working on the beds, frames and chassis of mining trucks. Dodge Machining offers these services and more.

When one shovel supplier couldn’t deliver a new backboard for more than a year, Dodge Machining built the mine a new one. When the casting on the end of a stick cracked and spare could not be obtained, Dodge machined a new one from scratch using a piece of 24-in. solid round stock, cut bevels on each side, welded it and stress relieved it…all on site.

“Not many companies or individuals have the will or desire to spend the amount of money required to tool themselves and do the job right,” says owner Derek Dodge. “On top of that, there’s no school that teaches you how to bring machine tools and welders to a job site, set them up and run them properly.”

Derek Dodge (right) founded Dodge Machining more than 25 years ago. With business booming, Dodge enlisted more help, including like Mike Nowell, his nephew and coworker.

Dodge estimates that up to 75 percent of his work results from poor welding and machining practices of others (on both the OEM and field repair side), and sloppy work is something Dodge won’t tolerate. During a recent job for a gold mine in Cripple Creek, Colorado, Dodge took a few minutes from his busy schedule to talk about how welding equipment from Miller Electric Mfg. Co. and Bortech Corporation improves productivity. He also shares some of his best welding practices (see “Inside the Story” at end of article).

Mobile Welding Shops

Derek Dodge founded Dodge Machining more than 25 years ago in the Yukon Territory. Dodge, who was mining gold at the time, bought some small, portable machining equipment from a friend to maintain his own mining equipment. Word got out that he could machine. Soon, he was so busy repairing equipment that he never went back to mining.

This perspective compares the size of a 300-ton hauling truck to that of a standard service truck.

A decade ago, Dodge and his wife moved to Casper, Wyo. to semi-retire. Again, people discovered Dodge Machining’s service and quality, and Dodge delayed his retirement. Today, the company is one of the biggest and busiest players in the business. Five or six welders work full time, with another 20 to 30 added to meet peak demand.

Dodge Machining operates two shops. However, the size of mining equipment often demands working in the mine itself, or at least working in the mine’s maintenance shop. Because no ordinary service truck can haul all the necessary repair equipment, Dodge outfitted two semi-trailers. At the heart of each trailer is a diesel generator that produces up to 180 kW of 480 V, three-phase power (and a transformer to create 120/240 VAC power).

“Because of the wide variety of primary power and power outlet configurations found in different mines, waiting for their electricians to start changing plugs on everything eats up a lot of man hours and slows us down. It’s better if we bring our own power,” Dodge says.

Equipment run off the generator includes Miller’s XMT® 350 and Dimension® 652 welders, Bortech’s model 306-P and 1202 bore welding systems, air compressors, portable milling equipment and heat treating systems for pre-heating and stress relieving welds. Other equipment on the semi-trailer includes flange-facing equipment, a hydraulic-driven magnetic drill that can drill a 3-in. hole, 500-ton hydraulic jacks and huge high-torque torque wrenches.

“With the stuff we have in this trailer, we have a mobile welding and machine shop on wheels,” states Dodge. “We can repair bores up to 3 ft. with one trailer, and we can repair bores up to 14 ft. with the other.”

Flux Cored Welding for Speed

Dodge Machining’s welding generally falls into two categories: fabrication and repair using the flux cored welding process and rebuilding worn bores using an automated bore-welding (MIG) process. Both processes differentiate Dodge Machining from others, and they improve welding speed.

Many people repairing heavy equipment are stuck on Stick welding because they’re familiar with it. However, Dodge Machining rarely Stick welds because of its low productivity. For example, a 1/16-in. diameter E71T-1 flux core wire, the type Dodge uses most often, deposits 10.9 lbs. of weld metal per hour when run at 325 amps/26.5 volts. Conversely, an E7018 Stick electrode deposits 2.7 to 5.4 lbs./hr, depending on electrode diameter. In other words, the flux cored welding process improves deposition rates by at least 50 percent, and a typical mine repair job requires hundreds if not thousands of pounds of wire.

“Last year on a drag line shoe repair in Montana, five of our welders used 3,700 lbs. of wire in 12 days,” says Mike Nowell, Dodge’s nephew and coworker. “Considering down time for a drag line can be $100,000 a day, our flux cored welding capabilities enable us to offer mines an excellent value proposition.”

Upgrading Inverters

Dodge Machining Corp. is one of the few companies with the skill, experience, liability insurance and equipment (including this Miller XMT 350 welder) that is mobile enough to tackle the job of repairing the world’s heaviest mining equipment. Whether the job is in the U.S. or Africa, Dodge Machining’s equipment trailers can go just about anywhere.

For its welding power sources, the company recently upgraded from older inverters to nine new XMT 350 inverters. While the XMT 350 offers more welding power (350 amps at 60 percent duty cycle) than the previous units, the XMT 350’s Auto-Line™ primary power management technology especially attracted Dodge.

Mines, construction sites, maintenance shops, factories and generators are notorious for dirty power and/or power fluctuations that occur when a large piece of equipment is brought on-line. Miller developed Auto-Line technology to solve this problem. It enables the XMT 350 to operate seamlessly as long as primary power stays within a 190 to 630 V range (+37% and –59% when running on 460 V primary), which solved a major issue of Dodge Machining.

“The problem we had is that our old inverters sometimes failed when someone turned on the generator without first shutting off the breaker that supplied power to the inverters,” says Dodge. “We have not run into that problem with the XMT 350s because of Auto-Line.”

As a generator starts and stops, it produces rated output voltage at low frequencies, which can harm the control power components and cause a failure with older and competitive inverter technology. Good training can solve the generator problem, but, unfortunately, not everyone remembers to shut off the breaker every time.

“After our old inverters got to a certain age, we sold them and upgraded to the XMT 350,” states Dodge. “Because of the new technology, even if we do forget to shut off the breaker, there is less of a problem because Auto-Line works well with generators.”

Nowell says another thing he likes about the XMT is its reliability and portability in extreme conditions, such as an underground mine in Death Valley.

“We’d go 1,600 ft. straight down a shaft and haul those little [80-lb.] XMTs in a mine cart and back into some crevice to repair little haul trucks, graders and continuous miners,” says Nowell. “The mine was ventilated with outside air. Well, when the outside air is 123° F, that’s how hot the mine was. Our Miller equipment gave us no problem.”

For excellent performance in hot conditions, Miller rates the output of all of its equipment at 104° F (compared to 86° F for some competitive units). As a result, Miller welders keep operating in conditions that cause other units to have their output de-rated or shutdown due to thermal overload.

Reduced Borewelding Time

The bore repair process involves depositing weld metal to build up worn bushings and pins to past their original diameter and then machining them to the correct diameter. Traditionally, repair personnel used the Stick or a semi-automatic MIG welding process. However, welding with automated Bortech equipment is 50 to 85 percent faster than hand welding.

A borewelder fixes to the part being welded (Model 306-P) or it can stand independently (the larger Model 1202) and continuously rotates a MIG torch inside the bore. After each 360° rotation, the torch indexes forward to make the next pass. Borewelders need to be paired with a MIG welding power source, and Dodge Machining uses an XMT 350 or a Trailblazer® gas engine drive. Both units provide best-of-class MIG welding capabilities.

While Bortech designed the Model 306-P especially for portable applications (the system weighs less than 100 lbs.), Dodge Machining uses both its 306-P and 1202 systems in the field and the shop. In all instances, the equipment reduces repair time.

“I used to have one person in my shop where the major portion of his job was bore welding by hand,” says Dodge. “After I bought Bortech equipment, bore welding became the minor portion of the job, and I could use him for other things.”

Nowell adds that, “In one day, we repaired 28 bores of various sizes. We might have done four or five if we didn’t have Bortech equipment. On a CAT D11 ripper, Derek and I can set up a Bortech and complete the job in a day and a half.”

In addition to reducing welding time, a bore-welder also reduces machining time by up to 50 percent. First, it precisely controls the build-up thickness, eliminating excess machining. Second, its continuous welding capabilities eliminate the hard spots hand welding creates during arc starts and stops. Third, the automated process eliminates the high and low spots associated with hand welding. Cutting through metal with a consistent temper, as well as with a consistent force, speeds machining and extends cutting tool life.

Bortech equipment also improves productivity because, “If you’re good with a Bortech—and we are—one operator can be welding and boring at the same time,” states Nowell. “That is, after he makes the first bore weld, he can set the Bortech unit up on a second bore and then go back to machine out the first bore.”

For many companies, reducing labor costs drives decisions about using new technology. To this end, Bortech offers an online cost analysis wizard. While reducing labor cost isn’t an issue for Dodge Machining, reducing labor time—and total repair time—is a major driver of customer satisfaction.

“Services like borewelding, as well as our overall quality of service, are a step above what everybody else wants to provide,” notes Dodge. “Everything we do comes down to customer service. A quality job on our part keeps equipment in the dirt longer, which lets the mine put more money in the bank.”

Side-bar Story

Welding Advice: Buy Grinders by the Case

“In think the biggest contributor to our success is weld preparation and weld clean-up, which improves the quality of the repair we put in,” says Derek Dodge, owner of Dodge Machining. “Most guys just don’t like to grind because it’s hard and it’s a pain in the backside. But if you don’t clean up a weld properly and prepare for the next pass, something will cause poor fusion. As a result, we buy 5-in. grinders by the case because we burn them up so quickly.”

For those who want to repair their own equipment*, Dodge offers the following advice:

Completely remove (by air carbon arc gouging and/or grinding) any “torn” or otherwise stressed metal. Such metal cannot be restored to appropriate mechanical properties (e.g., tensile and yield strength or hardness).
After air carbon arc gouging, completely grind the joint to remove any carbon residue.
  • Prevent brittleness and hydrogen cracking by pre-heating parts to at least 350 degrees F following the procedure specified by the OEM. For some situations where the OEM doesn’t require pre-heat, Dodge recommends that for the best quality, it’s a good idea to do it anyway using a standard pre-heat or pre-heating to a lower temperature. “When working on thick plate in sub-zero temperature,” says Dodge, ‘the heat of the welding arc gets sucked out of the weld area pretty quickly. That puts a lot of stress on the metal unless you pre-heat it.”
  • Stress-relieve thick weldments when weld quality is critical, even if the OEM makes no recommendations regarding stress relieving. Dodge notes that, “a lot of our repairs on big V-joints are made because the joint cracked in the area right next to the weld (heat affected zone). That is why when we built a mining shovel backboard, which weighed some 60,000 lbs., we put the whole thing in a stress-relieving oven. The procedure wasn’t required by the mine, but we did it and spent the money ourselves to ensure quality.”
  • Machine surfaces perfectly flat. Any imperfection will create unnecessary friction.
  • Grind out the end of every weld. Welds often crack at the end of a weld because of a weld flaw at that point, such as crater cracking.
This weld requires two beads right next to one another as part of a multi-pass process.
“Blend-grind” (Dodge’s term for grinding down a weld so it blends into a seamless looking piece of metal) thoroughly between multiple passes to eliminate any slag inclusions, porosity or undercuts. “On one manufacturer’s equipment, every crack we’ve seen resulted from an undercut weld made at the factory,” explains Dodge.
  • On critical welds, grind off the top of every pass to eliminate slag inclusions, porosity, undercut or other common sources of weld flaws.
  • To prevent a radius from cracking, eliminate stress points in the weld by blend-grinding it. A sloppy looking weld may create stress points, which make the weld more likely to fail.
  • Always think about safety. “The biggest thing to remember is that everything you touch is heavy enough to kill you,” says Dodge. “Even if a hose or cable comes off and slaps you, it can kill you. You have to keep them in mind all the time when working on mining equipment. For example, you can’t expect to tack weld something together and think it will hold. It won’t, because there’s so much mass that any stress on the part causes the tack weld to pop.”

* For those who want Dodge Machining’s speed and quality, call Derek at 702-528-8070