Single Minute Exchange of Die (SMED) is a lean manufacturing concept that originated in the late ’50s and early ’60s to improve manufacturing efficiency by reducing or eliminating bottlenecks caused by process change-overs.
The SMED concept was developed by Japanese industrial engineer Shinego Shingo while working with Toyota. Mr. 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 reduced that time from more than 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 it also offers a number of side benefits:
• Setup errors and trial runs are eliminated, which reduces defect rates.
• Operating conditions are fully regulated to improve quality.
• Setups are simplified to increase safety.
• Housekeeping is simplified by using fewer tools and better organization.
• Setup expense is lowered.
• Skill requirements are lower because changes can be designed into the process.
• Production can be mixed to provide flexibility and further inventory reductions.
The same concept is being mirrored in today’s inspection rooms to ease gaging change-overs and increase productivity 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.
It is important to have the correct fixturing to stage parts so they can be efficiently gaged. This is valuable on the shop floor to improve gage performance and reduce operator error, and it is also valuable in the lab for measuring very precise forms or surface finishes in the lab.
Unfortunately, in many cases, part fixturing is either ignored or overlooked. Many form systems are equipped with universal expanding three- or six-jaw sets. These universal fixtures hold any part and eliminate the need for special tooling. However, these universal tools cause the same kinds of problems with the inspection process that complicated die change-overs caused with the manufacturing process:
• The fixturing has to be removed, switched over to another fixture and realigned every time the part setup is changed. This takes time and requires a specially skilled operator.
• Universal fixturing, such as a six-jaw chuck, is operator influenced. There is no way to ensure the same clamping pressure, which can influence shape, especially with thin-walled parts.
• Each fixture style is a little different. Even though it may be universal to fit on the table, it 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 it may not be as tight as the tolerances for parts being measured on the form machine. In order to get the most repeatable readings—and pass gage repeatability and reproducibility (GR&R) studies—the gage has to ensure that different operators always mount the part in the same way. Any variation could influence the characteristics being calculated.
SMEF’s goal 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.
• Aligns fixtures to the machines automatically, with no operator skill required.
• Clamps parts into position with precise force to hold and prevent slipping without distorting.
Successful implementation of an SMEF strategy has provided many of the same benefits noted for SMED, including:
• JIT inspection drives inventory turnover rates.
• Setup errors and trial runs are eliminated, which reduces defect rates.
• Operating conditions are fully regulated to improve quality.
• Setups are simplified to increase safety.
• Housekeeping is simplified by using fewer tools and better organization.
• Setup expense is reduced.
• Skill requirements are reduced because changes can be designed into the process rather than requiring skilled judgment.
• Production can be mixed to provide flexibility and further inventory reductions.
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.
Despite enhancements to manufacturing technology, there are still issues today that can cause programs to fail. These failures can cause lost time, scrapped parts, damaged machines and even injured operators.
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