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Check fixtures assist bending projects from aerospace to deep space

Ensuring tubular assemblies meet the requirements for suborbital, orbital, and deep space missions

A check fixture is a conventional tool for verifying that a bent tube or tubular assembly conforms to the print. A check fixture also can accommodate tools or equipment for drilling holes, trimming the ends, or in this case, orbital welding.

No planet has captured our imaginations more than Mars. Easily distinguished from other planets by its red appearance—its surface is rich in iron oxide—it has tantalized mankind for generations. Nineteenth-century astronomer Giovanni Schiaparelli detected a series of long, straight lines on the Martian surface, which he called canali (channels). Mistranslated into English as canals, they were thought to be evidence of intelligent life on Mars. Although they were later determined to be mere optical illusions, that discovery was far too late. The quest was underway to find more evidence of life on Mars.

In popular culture, the concept of life on Mars couldn’t be more varied. It takes the form of a Warner Brothers cartoon character, Marvin the Martian, created in 1948; a CBS sitcom, “My Favorite Martian,” which ran from 1963 to 1966; a song written and recorded in 1971 by David Bowie, “Life on Mars?”; “Life,” a 2017 movie about a life form from Mars that ravages the crew of the International Space Station; a series of Lego toys, Mars Mission; and far too many books to count.

Since 1960, scores of spacecraft have been launched to investigate Mars on missions of increasing complexity (flying past, orbiting, landing, and roving). Although about 65 percent of the missions to Mars fail, this hasn’t done much to dampen the enthusiasm to explore the Red Planet. Whether the quest is to gather as much new information as possible or to answer that one question that has been nagging at us for more than 100 years, the quest to learn more about Mars took on a life of its own in 2004 when then-President George W. Bush announced the start of the most ambitious manned U.S. space program in a half century: Journey to Mars. The mission’s goal is to send a team of astronauts to orbit the fourth planet from the sun.

A project like this is vast, almost beyond comprehension. The spaceship comprises a command module, service module, and a launch system (currently a Delta IV heavy rocket), each of which consists of various systems and subsystems, collectively consisting of thousands upon thousands of individual components. A ship destined for Mars must be robust and durable, and therefore so must every component that goes into it. The quality standards are strict.

“Closely related to the quality standards for the components are significant documentation requirements,” said Calvin TenBrink, vice president of sales and marketing for Clark Fixture Technologies Inc., Bowling Green, Ohio. Nobody wants to sign the documentation for a part unless he’s sure, beyond all doubt, that the component has been manufactured to conform to the print.

What sort of tool should suppliers use to check the dimensions of tubes and tubular assemblies? In many cases, a check fixture is the way to go, and for a program such as this, each check fixture itself must meet strict quality standards.

Introduction to Orion

“Our role in the Orion project started with a cold call,” TenBrink said. “An engineer from Lockheed Martin had contacted a few metal fabricators about tubes and tubular assemblies for the spacecraft.” A few initial discussions led to some face-to-face meetings, and it soon became clear that fabricating tube and making assemblies wouldn’t be the end of it.

The engineer noticed that several of the fabricators he visited had check fixtures for verifying tube dimensions and asked about them. Clark’s phone rang a few days later. Getting a cold call from a contractor working on a NASA project might sound more than a little intimidating, but Clark has been involved in aircraft for years, and the two industries overlap. Many of the companies in the supply chain for one are in the supply chain for the other, and Clark had been serving aerospace customers for more than a decade at that point.

“In the aerospace industry, everything is custom, everything is low-volume, and everything has to be right,” TenBrink said. Does this compound the challenges in fabricating a tube that meets aerospace requirements? Not necessarily. Every fabricator has a story or three about an original equipment manufacturer (OEM) that uses dimensions or tolerances that are simply impossible to meet, but engineers in the aerospace industry tend to be savvy about such things.

“They understand tolerances, and they tend to tolerance each dimension appropriately,” he said. “They don’t use a one-size-fits-all approach for every dimension on a drawing.”

Figure 1
A closeup of a check fixture shows some of the various features that can be incorporated to verify the dimensions of specific points along the tube’s length and the locations of specific features.

So far, so good, but how does the fabricator or the contractor verify the dimensions on a manufactured part? Many measurement tools are available, but it’s a matter of matching the tool to the application.

For many manufactured products, checking dimensions in a few critical areas is sufficient, especially when evaluating sheet metal components with flat or gently contoured surfaces. Some auto body parts, such as hoods and trunk lids, are good examples. When evaluating a symmetric part with a few features, checking a few key dimensions often is the most efficient way to go, and the evaluation is thorough enough for the application.

A tubular assembly doesn’t usually have consistency or symmetry along its surfaces; it has straight lengths, simple and compound bends, fittings, weldments, and radiuses rather than flats. Checking a few dimensional points on a complex tube assembly can be problematic, according to TenBrink. He recalled one instance in which a Tier 1 supplier used a tool to verify a few critical points on tubular components, and the assemblies passed the inspection; the OEM later rejected nearly 100 percent of the shipment. The fabricator could have developed a more thorough inspection, but each additional measurement location adds time to the measurement cycle.

A check fixture takes just a few moments to use (see Figure 1). The operator sets the tube into the fixture; if it slips into the fixture and isn’t held up by any interference, it’s a good part. Some fixtures have toggle clamps that the operator closes and pins that the operator slides to contact the tube (see Figure 2). If the clamps close without effort and the pins slide into place, the tube passes the inspection.

“The fixture replicates the print, so it’s a full geometric capture,” said Clark General Manager Jeff Schumaker. It’s also a diagnostic tool.

“A check fixture shows that a part is bad, and where it’s bad, so you can go back and adjust the manufacturing process to make a good tube,” he said.

Eventually a representative from the John C. Stennis Space Center (often abbreviated SSC) visited Clark to review its processes and its quality control mechanisms. It turned out that one of the contractors that supplied parts to Stennis had big plans that hadn’t yet been revealed.

“Initially they wanted to verify each tube’s orientation and clocking,” TenBrink said. “Then they wanted to do orbital welding in the fixture.” This was new to Clark. The company wasn’t accustomed to making fixtures to accommodate orbital welding equipment, but it doesn’t shy away from challenges, so it moved forward with this new and unusual application.

A few of the Clark staff drove to Picayune, Miss., to visit SSC and train the staff in how to use the fixtures and to answer any questions. When that was done, the big moment was at hand. The Clark staff had concerns about the welding process and the heat that likely would distort the assembly. The tolerances were already tight, so any distortion would make removing the tubes from the fixture difficult and perhaps impossible.

To Clark’s relief and surprise, the assembly came out easier than it went in, according to TenBrink.

Figure 2
A check fixture for a tubular assembly captures nearly every linear inch of tube—bends, straights, elevations, and end points. After inserting the assembly into the fixture, the operator slides the various pins into place to contact the tube. It provides quick feedback on an interference with the fixture body or pins.

An Exclusive Club

The Clark staff’s visit to SSC illustrated the nature of this project. It entailed more than a supply chain that connected a fabricator to Lockheed Martin to NASA. At the top tier, it’s not so much a supply chain as it is a supply network.

“Each big company is part of an ecosystem,” TenBrink said, describing a business environment characterized both competition and cooperation: competition for contracts and cooperation after contracts are awarded.

That ecosystem is overseen by Exostar® LLC, a service provider that helps highly regulated industries collaborate securely and mitigate risk. It deals in healthcare, financial services, energy, commercial aviation, aerospace, and defense. Membership in the Exostar network is akin to certification in the National Aerospace and Defense Contractors Accreditation Program (Nadcap) or ISO/TS 16949 certification: It provides recognition that the member company’s products have met the quality criteria for an entire industry, not just one company.

As such, the successful run-off of the fixtures at SSC led to an expedited order for fixtures for Kennedy Space Center, Cape Canaveral, Fla., which further demonstrated the strength of the network.

“At Lockheed Martin, these fixtures are for just one or two assemblies,” TenBrink said. “We have sold more than 100 to SSC and many to Cape Canaveral,” he said.

More was in store.

“The engineer who originally contacted us was given new responsibilities and now works at Kennedy Space Center,” TenBrink said. He called about check fixtures for use in a clean room. Conventional materials for check fixture bases are wood, usually mahogany, and medium-density fiberboard. A chief benefit is that they resist warping in humid conditions, but a drawback is that they shed particulates. NASA’s next step involved metal fixtures for use in the room in which the space capsule was under construction (see Figure 3).

Suddenly this project took on new meaning at Clark. At first, it was something abstract—tubes for assemblies for systems to be installed somewhere, who knows where, to do who knows what, somewhere deep within a vast system preparing for a launch in two decades or so. An order for metal fixtures for work on the capsule itself was much more tangible.

These check fixtures are used on tubes that are going to support the astronauts on the journey to Mars? Yes, Mars.

From Moon to Mars in 70 Years

On May 25, 1961, President John F. Kennedy announced the plan to send an astronaut to the Moon before the end of the decade. The Soviet Union had launched into space the first artificial satellite, Sputnik I, in 1957, which took the U.S. by surprise. On April 12, 1961, the Soviet Union achieved another breakthrough when it launched the first man into outer space. Although the U.S. had been sending animals into space since the 1940s, successfully sending insects or a monkey into outer space doesn’t have the public relations impact of a human being orbiting Earth.

Figure 3
Cleanroom operations have little tolerance for particulate matter. Clark Fixture Technologies furnished a check fixture specifically for this application, one made of metal to prevent introducing particles to this environment.

Although the Mercury and Gemini programs suffered a few setbacks, they didn’t suffer many, and they ushered in the Apollo era, which put the first man on the moon on July 20, 1969, just a little more than eight years after the initial announcement. The space race was so ambitious that, to date, just one additional nation has developed a space program that launched a person into space (China), and no other country has ventured to the moon.

How long will it be until the Mars mission is ready? It’s hard to tell. Preparing for a Mars mission in the modern era doesn’t have a lot to do with planning a moon mission in the 1960s decade. Although the space shuttle program and the International Space Station have provided continuous improvements and additions to NASA’s knowledge about space travel, a trip to Mars is an entirely different venture from a lunar landing.

The moon is 239,000 miles away; at its closest, Mars is 34.8 million miles away. Apollo 11 made the trip to the moon in a little more than three days; the orbiters and landers sent to Mars take around 300 days to make the trip. It’s an ambitious goal, certainly more grand than the mission to the moon. Like the lunar landing, NASA’s plan to visit Mars has distinct stages, this time just two: an initial visit to Phobos or Diemos, the moons that orbit Mars, by 2025, followed by a manned spacecraft sent to orbit Mars before 2040.

What will that success hinge on? Thousands upon thousands of manufactured products, big and small, sophisticated and simple, flashy and plain, each made to precise standards and needed to perform a critical role, from the most sophisticated and advanced central processing unit in the spacecraft’s computer system to the simplest tubes and tubular assemblies throughout the spacecraft.

And one thing is sure: From the computer systems to the tubular assemblies, everything will have been tested, measured, checked, and verified before it goes into the spacecraft and sent into deep space.

Clark Fixture Technologies Inc., 410 North Dunbridge Road, Bowling Green, Ohio 43402, 419-354-1541, sales@clarkfixtures.com, www.clarkfixtures.com.

About the Author
FMA Communications Inc.

Eric Lundin

2135 Point Blvd

Elgin, IL 60123

815-227-8262

Eric Lundin worked on The Tube & Pipe Journal from 2000 to 2022.