calibration of gauges

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    I am an engineer in an automobile manufacturing company and I am in the Metrology department. The metrology deptt calibrates nearly 24,000 gauges per year and the gauges are classified as A, B and C class depending upon the tolerance for which they are used and also on the criticality of the component. The frequency schedule are 15 days for A gauges, 25 days for B gauges and 90 days for C gauges. Now I am having a doubt whether we are over calibrating the gauges so I want to revise the frequency schedule. I am having the wear pattern of the gauges over its period of calibration. Can anyone help in this regard
    Thanks in advance


    Amit Puri

    I suggest
    Since you are calibrating 65 gaguges on an avergae daily,
    First  – you should take data for waht fraction the non conformance at the time of receiveing you are getting.
    Second – try to do a straightification of the data over a peroid. Why I am saying this becasue in my prevoius organisation I was having a simmilar sitiuation but most of the non conforming gauges I used to get from ONE area. (the usage conditons were different in that area from rest of the shop floor)
    Third – Before asking the question whether or not you are doing a over calibration, acheive a situation where none of the gauge should found non conforming either any of its frequency for calibration.
    This is my guess you may have to relook in to the design of the gauge or for the family of the gauges and over come the problem of non conformances, rather than looking for frequency change.
    Amit Puri



    Hi Ganesh
    Try the control chart method for stability (refer QS9000 manual), you could deduce the frequency of caliberation required.
    If you need any info please let me know. hope this helped



    Have you done a chart of the “As Found” results? If not, this should be a rather simple task in the calibration software you are using. Based on the As Found result and the acceptable region, you MIGHT be able to increase your calibration interval and still get an acceptable As Found result. This would save time & money.



    Hello Ganesh,
    If the objective is to increase the interval of testing the gages then you need to also look at more criteria;
     1. Gages on a static (non portable) system do not recieve as much shock and damage as do gages on a dynamic (portable) system. You can therefore take this into account.
    2. Gages on pneumatic and or hydraulic systems at times need and do not have “pulsation dampners” or “surge protectors” in line between the gage and system, I have run into this in the past, the installation of the dampener extended the life of the gage and reduced the number of adjustments required.
    Has the calibration interval of your reference standard also been reduced? Make sure and make that a concern if you do a trend analysis, some of the error may be the standard and not the test instrument (gage).
    Kind Regards


    Chip Hewette

    Please discuss the risk to production quality with the business leaders before making any changes.  What would happen if the gage calibration interval were expanded, and a gage were found out of calibration after this longer period of time?  What financial impact would this have?  What ‘safety nets’ exist in current gaging practice?  What is the reaction plan for segregating components, subassemblies, or final assemblies?  What lot control do you have to be able to recall items at risk?
    Key question is not how to save money, but how to ensure customers are delighted.

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