Metrology
Metrology
SMEF: Gaging's Version of SMED
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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.