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Topic Incoming Material SPC Tests – Rubber

Incoming Material SPC Tests – Rubber

Home Forums General Forums Tools & Templates Incoming Material SPC Tests – Rubber

This topic contains 6 replies, has 5 voices, and was last updated by  Chris Butterworth 1 month, 3 weeks ago.

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    I am looking for some help on a new goods in area we are setting up.

    I am looking at introducing SPC but am wondering on what limits I should use for each of the different tests:

    Shrinkage – the % an O-ring shrinks in relation to a known tool size (especially this one)
    Hardness – How hard to raw compound is (this is probably in the spec)
    Rheometer – the cure rate of the compound

    We currently only currently measure Rheometer so I could use past data to work the limits out for this.

    Any help would be appreciated.


    @andybryce Why are you doing a control chart? What are you controlling at Incoming Inspection?


    Hi Mike,

    We are trying to control the results for the 3 tests that I mentioned. hey are important to the outcome of our final product. Shrinkage is especially important as it control how mucht he material shrinks and therefore the final size of the product. The rheometer test is also important as that shows how well the produc tis going to cure. Therefore I thought it would be a good idea to monitor the results as they come in.

    If there are any beter ways then i am all ears.



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    @Pen I think you responded to the wrong question.


    Andrew, did you do a gage R&R on those measurements?

    SPC limits are based on process variation with well defined values so not sure what is intended by the question. Remember, SPC is the voice of the process–not the voice of the customer.

    However, be sure to do a gage R&R. You’ll need to get measurements on shrinkage and hardness before being able to calculate limits BUT please do a gage R&R across all shifts to confirm the ability to understand variation and make your SPC even more powerful.


    Chris Butterworth

    Hi Andrew,
    I don’t think SPC is the right tool for this. The value in SPC is that it provides “real-time” insight into process behaviour through measurement data. When you find data that lands outside of control limits you will not know what process parameter caused the shift – only your supplier can know that. Additionally, you may have a hard time knowing the order of the parts you received. For example, if you have ten boxes, which was manufactured first, second etc.

    So it seems reasonable to stick with acceptance sampling rather than SPC.

    And Chris Seider’s comment about Gauge R & R is important. The first thing that you should do in any problem solving assignment is assure yourself that the measurement system is suitable.


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