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SMEF: Gaging's Version of SMED
George Schuetz, Mahr Federal Inc.
Single Minute Exchange of Die (SMED) is a lean manufacturing concept
(or goal!) that was originated in the late 1950s and early 1960s to
improve the efficiency of manufacturing by reducing or eliminating
bottlenecks caused by process changeovers. The SMED concept was
developed by Japanese industrial engineer Shinego Shingo while working
with Toyota. Shingo saw that Toyota's biggest bottleneck was the time it
took to change the dies on the large transfer-stamping machines that
produced car vehicle bodies. Using a variety of methods, he was able to
reduce this time from over 12 hours to less than 10 minutes,
dramatically reducing machine overhead cost, and improving product flow.
SMED is considered one of the essential precursors for Just-in-Time
(JIT) manufacturing, and also offers a number of side benefits:
• Elimination of setup errors and trial runs reduces defect rates
• Improved quality from fully regulated operating conditions
• Increased safety from simpler setups
• Simplified housekeeping from fewer tools and better organization
• Lower expense of setups
• Operator preference due to ease of use
• Lower skill requirements since changes are now designed into the process
• Ability
to mix production which provides flexibility and further inventory
reductions as well as opening the door to revolutionized production
methods
The same concept is being mirrored in today's inspection
rooms to make gaging changeovers easier and more productive when
switching between parts. It's called Single Minute Exchange of Fixturing
(SMEF) and the idea is to apply the same engineering principles that
speeded die changes to the staging of parts for quality inspection.
We have talked before about how important it is to have the correct
fixturing to stage parts so they can be best and most efficiently gaged.
This is important when bringing measurements to the shop floor to
improve gage performance and make the operator's job virtually error
free, and it is also valuable for staging parts when doing very precise
form or surface finish measurements in the lab.
Unfortunately,
in many cases, the fixturing to hold parts is either never thought of or
simply ignored. Many form systems are provided with universal expanding
3 or 6 jaw sets. These universal fixtures are thought to hold any part
and, thus, eliminate the need for special tooling.
However,
these universal tools cause the same kinds of problems with the
inspection process that complicated die changeovers caused in
manufacturing:
• Every time the part setup is changed, the
fixturing has to be removed, switched over to another fixture and
realigned. This takes time and requires a specially skilled operator.
• Universal
fixturing, such as a 6 jaw chuck, is operator influenced. There is no
way to ensure the same clamping pressure, which can influence shape,
especially with thin walled parts.
• While the
fixturing may be universal to fit on the table, each style is a little
different and may set one part height different from the next. This
requires more alignment time and the calculation of different part
program parameters to begin the part run.
• Universal fixturing is
made to tight tolerances, but not necessarily as tight as the
tolerances for some of the parts being measured on the form machine. In
order to get the most repeatable readings—and pass GR&Rs—the gage
has to ensure the part is mounted the same way every time by different
operators. Anything else could influence the characteristics being
calculated.
The goal of SMEF is to design and use fixturing that:
• Has a fixed base plate with positioning tabs that lock in interchangeable fixtures.
• Requires no tools to change fixtures.
• Allows fixtures to be automatically aligned: no operator skill required to align the fixture to the machine.
• Clamps parts into position with the precise force to hold them and prevent slipping, but not distort the parts.
Successful implementation of a SMEF strategy has provided many of the same benefits noted for SMED, including:
• JIT inspection, which drives inventory turnover rates
• Increased gaging system work rates from reduced setup times even if the number of changeovers increases
• Elimination of setup errors and trial runs, which reduces defect rates
• Improved quality results from fully regulated operating conditions
• Increased safety from simpler setups
• Simplified housekeeping from fewer tools and better organization
• Lower expense of setups
• Operator preference due to ease of use
• Lower skill requirements since changes are now designed into the process rather than requiring skilled judgment
• Ability
to mix production, providing flexibility and further inventory
reductions, as well as opening the door to revolutionized production
methods
Sounds familiar, doesn’t it? When there is a need to
increase inspection throughput in measurement centers, tooling changes
and the lessons learned from the shop floor can have a significant
effect on process improvement.
SMEF designed tooling consists of two components, a base fixture which
is permanently mounted on the machine, and interchangeable fixturing
which holds the parts being measured. Note the tooling balls that help
position the part fixture on the base very precisely.
Another SMEF-designed fixture for a different part, or for a different
area on the same part, which attaches to the base plate very quickly,
precisely and repeatably.
