Using 4943 Filler Metal to Weld Critical Medical Devices for the U.S. Military

The critical medical devices manufactured by Fort Defiance Industries LLC (FDI; Loudon, TN) are used by the U.S. military and disaster relief operations in life and death situations where the stakes are high. Product quality and reliability are critical. “In everything we do, we really try to exceed expectations and deliver excellence,” says Chris Yerger, the chief executive officer of FDI. Launched 12 years ago, they have steadily grown and added product offerings at their Loudon facility, becoming known as the “can-do company” for their ability to solve problems for customers, especially the U.S. Department of Defense (DoD). “If the military had an issue, we said ‘we can do it, we’ll help you solve that problem,’” adds Yerger. “So that reputation was developed early on.”

While they manufacture a variety of equipment – from water systems to pumps and electrical panels – a key offering is an automated field steam sterilizer produced for the DoD. These units can sterilize 36 lb of surgical instruments per load and process 100 loads using only ten gallons of water. They’re also designed for easy transport and setup. The steam sterilizers undergo rigorous quality testing to ensure high reliability in remote and harsh environments. Choosing MaxalTig® 4943 aluminum filler metal from Hobart Brothers LLC (Troy, OH) for manufacturing the sterilizers resulted in significantly better weld strength compared to other options FDI considered. “We wanted to do everything we could to still have good weldability, really good aesthetics, but also have as strong a weld as we possibly could,” explains Ken Owens, the welding team leader at FDI. “It was clear the 4943 would give us increased strength.”

QUALITY: THE TOP PRIORITY
The autoclave sterilizer, which contains a pressure chamber where the sterilization happens, is fabricated from 6061 aluminum alloy, so it’s lightweight for portability but also very strong and rugged for field conditions. The design uses a variety of weld joints, including full penetration v-groove joints and various sizes of fillet welds. The autoclave design is unique because it’s automated and also features a closed-loop system with water recovery capabilities, making it more efficient and reliable. Previous field steam sterilizer designs used almost two gallons of water with every cycle and they were manual, which required someone to monitor the system and adjust valves for the sterilization process to work properly.

Because the application requires leak-tight welds with high strength, FDI manufactures the sterilizers to ASME Section VIII Division 1 welding code for boiler and pressure vessels. All of their welding operators are also X-ray and 6g pipe welding certified. FDI is also certified to ISO 13485 standards, which are stringent regulatory requirements for medical devices. Using welding procedures and filler metals that reduce the risk of porosity is another key factor in the success of producing this equipment. “We’ve got to stay focused on the quality of our welds. If we don’t do this well, we have something that could rupture and potentially cause harm,” notes Yerger. “We have to follow very strict procedures.”

INCREASED WELD STRENGTH
In bidding for the contract to produce the field sterilizers, FDI had to quickly develop a prototype that was reliable, durable and stood up to rigorous testing. It was clear that selecting the right filler metal was an important part of the equation to ensure the necessary weld quality and strength. FDI compared the 4943 aluminum filler metal with a 4043 filler metal, using in-house tensile testing. They also sent the welds to outside certified labs for extensive testing. “The tensile strength was the biggest thing,” says Owens. “We saw about 2,000 psi bump in tensile strength with the 4943.” It was also important for them to choose a filler metal with consistent weldability, a fluid puddle and one that produces proper aesthetics in the finished product. “It’s just an all-around good rod. We get the extra strength we’re looking for, and it has great weldability,” says Tim McKee, a welder at FDI. “We have a little bit of everything on this pressure vessel, all kinds of different welds. We don’t have to go back and do a lot of fixing because it’s right the first time.”

A Hobart representative helped FDI adjust welding parameters with the 4943 rod, including recommendations for the best way to prevent porosity in the application. Using the 4943 filler metal, FDI has manufactured about 180 steam sterilizers and will produce hundreds more to satisfy the government contract they secured. They also hope to expand to more international military customers.

THE RIGHT ROD – AND A VERSATILE MACHINE
Fort Defiance Industries requires a welding power source that offers the flexibility to weld very thin sheet metal up to one inch thick materials. They turned to Miller Electric Mfg. LLC (Appleton, WI), a welding equipment manufacturer also owned by Hobart parent company Illinois Tool Works Inc. (ITW; Glenview, IL). The Dynasty® machines from Miller that FDI chose to use in the manufacturing operation are programmable, so operators can pre-program their preferred settings and easily cycle through them with the touch of a button to make changes. This helps save time in setup and parameter changeover. “The speed between jobs is a benefit,” states Owens. “You don’t have to come back to the machine and dial in settings. They’re already there and you know what program to use, so each welder can tailor the arc to his needs.”

These machines also deliver a more focused arc for better penetration. The ability to dial in the arc is especially helpful in tight weld joints. “We can really fine-tune to get into that tight joint or to help us out on the porosity side, to where we have little or no porosity,” adds McKee. The machine’s wireless foot pedal also helps improve productivity, maneuverability and reliability by eliminating the control cable, saving time in cable management and reducing clutter in the work area. “I love the wireless foot pedal,” says McKee. “They’re great machines. We can focus it in and do a really good job.”

Hobart was a partner in the welding process from the beginning, helping FDI assess and determine the right procedures and filler metal for the job. “It’s been a very positive experience,” states Yerger. “They have been very helpful and supportive of what we’re doing here. We knew we would get extra strength from the 4943 and that gave us a lot of peace of mind. It’s a big deal from a safety standpoint, so that increased strength was the primary reason we went with that filler metal.”

“We’re building something for our military,” adds McKee. “You don’t want it to fail.”

Fort Defiance Industries LLC, 2411 Maremont Parkway, Loudon, TN, 37774-1066, 865-408-0100, www.fortdefianceind.com.

Hobart Brothers LLC, 101 Trade Square East, Troy, OH 45373, 937-332-4000, hobart@hobartbrothers.com, www.hobartbrothers.com.

Miller Electric Manufacturing LLC, 1635 West Spencer Street, PO Box 1079, Appleton, WI 54912-1079, 920-734-9821, www.millerwelds.com.