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
“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.
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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.