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Control Limits

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  • #53032

    Tierradentro
    Participant

    Could someone tell me how to keep a eight cavity injection mold with five target dimension in control.  It seems to me that if any adjustmenst are made it will affect all the cavities.

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    #187535

    Taylor
    Participant

    John
    Need a little help understanding your question.
    When you talk about adjustments, are you talking about cool time, heat, injection pressure, (process input variables) etc etc? or are you talking about physical dimensions in the mold cavities?

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    #187536

    Tierradentro
    Participant

    Adjustments regarding cool time, pressure and other machine settings, not to the steel.

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    #187540

    Taylor
    Participant

    John
    As you know, injection molding is tricky and you have to optimize each setting to find the best capability for the process. DOE trials is probably the best way to acheive your goal. BUT, first you must have a real clear understanding of your process and already have some idea how each change in the settings will affect your output. My first suggestion is to contact your material supplier and ask them for suggestions on process variable inputs. You may also want to talk with the manufacture of the equipment for their input as well. These guys are usually very willing to help and can give the highs and lows for your input variables. This is real good information to know, that way you don’t have to stuck plastic out of your molds like I have done before.
     

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    #187544

    GB
    Participant

    In support of Chad’s view, I would start at the beginning and characterize the current process capability. IOW, SPC. I would see what the initial data set reveals across all measures and for each cavity to gauge if a problem exists at all. The goal would be to see what’s happening in terms of within/between subgroup variation.
    Once done, then set up a DOE, or even a GR&R of the measurement devices/processes if you smell something fishy.

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    #187641

    Bob Rome
    Participant

    We use a combination of scientific molding & DOE’s.  By scientific molding I mean RJG decoupled molding 2 and eDart cavity pressure monitoring.  I try to get good consistent/balanced fill across all cavities, which will give you long term least variation (stable process).  Then we do screening and optimization DOE’s based on the critical dimensions.  If you don’t achieve a stable process with optimum fill up front, you’ll be chasing your tail doing DOE’s – getting a lot of noise and low Rsq’s.  This also minimizes (or surfaces) the cavity to cavity differences and imbalances.  Because as you know, you need to distinguish between process variation that you control and steel variation that will require a tweak (time & expense).  Measure twice, cut once as they say…
    On the DOE planning, do a detailed planning sheet and have it reviewed by the process experts – work with them.  You’ll learn the molding process and they will learn about variation reduction techniques.  You will also need to look at post molding part handling during cooling – where parts develop warp.  We include factors premold (resin moisture, regringd $, etc.), molding parameters and post molding variables.
    I can be contacted if more help is needed…

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