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SPC and Injection Moulding


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Reviving an older thread. It has been many years and I am interested in knowing what people have found since this thread originally started. What have your experiences with SPC in the injection molding industry been lately? My company has just begun the SPC journey, and I am very interested in any benchmarks.



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{{{crickets chirpin}}}

I am interested in any updates in commonly accepted practices for implementing SPC in injection molding (actually we deal with rubber, but data on plastics is welcome as well)...

Can anyone bring us up to date...?


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Hi Ezekiel,

Great name. Love it!

As for SPC, since I posted in 2017 we have made quite a bit of progress but maybe not as much as I hoped. We do X-bar and R charts on many higher volume jobs, but most of our production seems to be in the lower to medium run size. For these we use individuals charts (run charts) and we set guardband limits on those. Our guardband limits typically are a percentage of the total tolerance and serve to help us react before we go out of tolerance.

One thing we found, with the lower volume jobs, is that material lot can be an assignable cause. So, we run for maybe 36 hours, then do not run again for another 3 months. When we run again in 3 months it is a different lot of material. This played havoc with calculated control limits, which is why we switched many of these jobs to calculated guardband limits. This seems to work quite well for us.

I would be happy to stay in touch with you can compare notes and to provide any input I can.

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