Metrologia
Metrologia
Calibrating For Quality
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Calibrating For Quality

 Just as you need to calibrate a gage in order to make accurate measurements, so a complete and ongoing program of machine calibration is a necessary prerequisite to any quality program.

 Machine tool calibration is often seen as too complicated and too time consuming to be worth the bother.  And many shop owners reason, if the factory can’t set a machine right, how can they?  So they continue to purchase machines without a thorough check of their full range of motion, they set them up and run them -- sometimes for years -- without recalibration, and then continually complain about their “inability to hold tolerance.” 

 First and foremost, set at the factory does not mean set in your shop.  Too many things can happen during shipment and installation to even hope a new machine will be in spec without calibration.  Second, once set does not mean always set.  Strange things can and do happen to machine tools: an errant shaft of sunlight heating up a lead screw, or a minor lubrication problem in the ways, can throw a very expensive machine all out of position. You need to recheck that machine and its environment on a regular basis to ensure its ability to produce good parts.  The good news, though, is that with the advanced equipment and software available today, calibration is not the bear it used to be.  And most important, an ongoing calibration program in your shop can pay hefty dividends.

 The most obvious of these is better quality parts.  This means fewer rejects, reduced scrap, and less rework.  But, there are other, more subtle, benefits as well.  One of these is in part and program editing.   One of the “miracles” of the CNC revolution is supposedly the ability to program part routines and run them on different machines.  This sounds good in theory, but in practice, it usually requires untold hours of programmer and operator time editing routines to accommodate machine peculiarities.  Calibration minimizes this programming and editing time, so one program really can serve several machines.  This can make a major difference in the ability of a shop to respond in a JIT environment. 

 Another often overlooked benefit is the ability to document quality.  This is valuable not only for vendor certifications programs, but also as a marketing tool to help sell your capability.   But the most important benefit of an ongoing calibration program is the increased understanding you gain about your machine’s performance and your overall production environment.  Calibration not only tells the good from the bad, it tells you how good your machines are, and how you can make them better, where they are best, and when you can expect them to give you trouble.

 This knowledge can pay off in a number of ways.  Scheduling, for example, knowing in a very precise way what your machines are capable of will not only help you optimize production, it can also help you do things you didn’t know you were capable of.  Sometimes machines have “sweet spots,” ranges in which they perform way beyond their stated accuracy specification.  If you know where they are, you may be able to take very profitable advantage of them.  Maintenance and troubleshooting are another.  Machines usually don’t break overnight.  There are warning signs.  Monitoring performance on a regular basis can put you in the driver’s seat.  You will know when readjustments are necessary.  You will be better able to schedule regular maintenance.  And, you stand a better chance of being forewarned of major problems and avoiding the inevitable, middle-of-a-rush job breakdown.

 Finally, regular calibration can help you determine when a favorite old machine has, shall we say, passed its peak.  And when the time comes to replace it, the understanding you will have gained from ongoing calibration will make you a much wiser and better buyer.  And help you prove it.