Figure 2
Rockford Process Control uses an inline
gauge to verify part dimensions—bend angle,
bend location, part length, and so forth. The
workcell’s configuration and pace enable RPC
to audit 100 percent of the parts without
affecting the production rate.
STAMPER, WELDER,
FABRICATOR, COATER
A proprietary product manufacturer and
component supplier, RPC is no stranger
to the intricacies of dealing with suppliers
and OEMs. Founded in 1983 by
entrepreneurs Paul Colloton and Richard
Gleichman, the company initially provided components to the automotive
industry. In 1987 it acquired a cabinet
hardware product line from another
Rockford-based manufacturer, and suddenly it was a multifaceted company.
It provided parts for the auto industry and
hinges, knobs (or pulls as they are
known), and other hardware for the
cabinetry and casework industry. It also
developed a line of wire doors, the type of
doors often used on school lockers.
The company’s main manufacturing
activity was stamping. No one-trick
pony, it expanded its capabilities to
include robotic welding, tube bending,
and machining, turning itself into a
contract manufacturer of fabricated
components and assemblies. It also has
powder-coating capabilities.
Although the company is well-positioned for contract manufacturing work,
some contracts require a little more care
than others. One such project landed in
the lap of Rick Williams, a manufacturing engineer with decades of experience.
It was a high-visibility project from the
start. Not only did it involve one of
RPC’s largest customers, it also was
an existing part that the customer
was having trouble incorporating
into an assembly. Complicating
matters was the material itself,
rectangular tubing, which RPC had
limited experience in fabricating
(see Figure 1).
MANAGING VARIABLES OR
MANUFACTURING PARTS?
Some manufacturing processes are
straightforward, such as using a saw to
cut a tube to length or a drill to put a hole
in a length of barstock. Adding more
processes multiplies the variables and the
number of things that can go wrong.
Introducing forming processes, those that
force the metal to flow, makes manufacturing all the more tricky.
This project was a frame rail for a golf
cart manufacturer. The previous supplier
delivered a component that seemed to
meet the OEM’s specifications, but the
OEM had an occasional problem with it.
The specific nature of the problem was
elusive. It seemed that no matter who
Williams asked—manufacturing engineers, quality control personnel,
purchasing agents—he got a different
answer. Eventually he worked his way
through the company and talked to the
equipment operator, the person who
actually loaded the part into the robotic
welding cell. The problem turned out to
be a gap between the frame rail and
another component, a cross member. The
gap varied; on many parts it was small
and the welding process went without a
hitch. Occasionally it was too large for a
good weld. Williams gathered that the
OEM had made some changes in the
final assembly fixture to accommodate
the variations in the frame rail.
Williams’ detective work left him with
a couple of questions. What was causing
the gap to vary? If RPC manufactured
parts that conformed to the OEM’s
specifications, would they fit into the
final assembly fixture?
CREATING A NEW PROCESS
In its simplest form, manufacturing a
component means taking a series of steps
that make changes to a workpiece.
Manufacturing a component successfully
requires strict control over any variable
that can affect the outcome. In the case of
the frame rail project, the manufacturers
had the luxury of starting from scratch.
“We knew the goal, and those of us in
the supply chain got to start with a clean
sheet of paper to see how we could most
cost-effectively get there,” said Chuck
Kuhn, president of GL Precision Tube,
the tube supplier for this project.
“Everybody’s process has limitations
in the factors that can be controlled,”
Kuhn said. “If you’re hitting the mean
objective, things often go fine,” he said,
referring to the center of the tolerance
band, regardless of the specification—the
material’s chemistry, the workpiece’s cut
Figure 3
Depending on the tube and the process,
distortion in the bend area can be substantial.
Although this part fits neatly into the inline
gauge and meets the customer’s requirements
for fit and function, improper use of a CMM
would lead to erroneous data about the part’s
dimensions.
