Modern Machine Shop

SEP 2017

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Page 77 of 220 September 2017 MMS 75 FEATURE tolerance band around each feature to determine when that feature is likely to pass inspection later. Now, in the probing routines at the machining centers, each feature essentially has two toler- ance bands. The first tolerance band describes whether the feature is in or out of specification. If the latter, the process stops. The second, tighter tolerance band indicates whether the feature is trending out of specification, or depar ting from the performance of a good day. If it is, the operator is alerted, he gets either Mr. Smathers or Ms. Morlacci to come assist with diagnosing t h e p r o b l e m, a n d m e a nw h i l e, t h e p r o c e s s keeps running. The process keeps running. That part is key. Catching errors before they occur requires catch- ing errors well before they occur, while there is still time to diagnose the problem and respond. Mr. Smathers or Ms. Morlacci's first response, when being told that a process has broken out of its range of previously established "good" probing measurements, is typically to let that process keep running with no changes. Will the trend continue? How quickly will it advance? Seeing this helps them in their educated guess as to what the cause might be and how big of a correction to make. L&S's primary customer for nuclear components strongly approves of this process and would like to see it go further. That is, the customer would like to see a process that initiates a response to the data automatically, without human beings having to make a response. This would be a more tightly closed-loop process, and a more advanced, futuristic response to the challenge of repeatable machining. But the problem is this, says Mr. DiNardi: Errors don't happen often enough. For all of the sources of error that happen even some- what frequently, the shop has already developed a safeguard within its process, such as probing catching setup mistakes. The infrequent errors are what remain. At a cer tain point, a human making a judgment really is the most efficient and least trouble-prone way to proceed. Ms. Morlacci and Mr. Smathers are seen here with L&S President Rob DiNardi. Getting away from QA as a final check on machining is not possible for L&S, he says, because of the requirements of the nuclear industry. But L&S owns another shop serving other markets. The process control system L&S developed might actually go further there.

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