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SPC for tablet/capsule weights. Can it be done?

Discussion in 'SPC - Statistical Process Control' started by Jennie, Jan 22, 2016.

  1. Jennie

    Jennie Member

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    We manufacture tablets and capsules in our facility. For the past few decades, we've been using run charts with spec limits as our monitoring tool for tablet/capsule weights. Contrary to popular belief-100% online inspection isn't available for this operation. We're planning on shifting over to use SPC. Here lies the problem; the operators who use the tablet presses must frequently adjust the pressure, speed, and fill cams to compensate for the product flow going into the presses amongst other things. I'm positive that some of these adjustments are unnecessary but I'm assuming that some of them are. With all the operator adjustments, can we even implement SPC in faith? What would you do? My first reaction is that this is an uncontrolled process and it can't be done.
     
  2. Miner

    Miner Moderator Staff Member

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    Try the following first:
    1. Run the process with zero adjustments for a defined period of time that overlaps at least one material lot change. Record the weights, pressure, speed and fill cam values. Plot the data in time sequence on an individuals control chart. This will help you understand how stable the process is.
    2. If the process is unstable, run a DOE on the pressure, speed and cam settings to understand their impact on weight and how tightly they must be controlled.
    The greatest benefit from SPC that I ever saw was when we implemented it on an incapable process that operators constantly adjusted. Once we explained the concept and operators stopped adjusting, we found that the process was stable and capable. All it took was stopping the "tampering".
     
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  3. Bev D

    Bev D Moderator Staff Member

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    Miner is correct. My experience is the same. if you implement control charts in the manner in which they were intended, you stop the tampering, increase your process understanding and reduce the variation.
    There is no process that won't benefit from control charting.
     
  4. Jennie

    Jennie Member

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    What if it actually needs tampering periodically? Recalculate control limits after the adjustment?
     
  5. Bev D

    Bev D Moderator Staff Member

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    no.
    tampering is random adjustment - no matter how well intended.
    necessary adjustment is take when the control limits are violated (signaling a real change that can be corrected)
    you only change the control limits when you have fundamentally improved the process such that it will now reliably and repeatedly run with less variation.
     
  6. Jennie

    Jennie Member

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    OK-bing, the lightbulb just went on for me. Thanks!
     

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