Robust, repeatable recommendations: Fill Time

08/02/2012

The foundation to any robust process, in my opinion, is based on choosing the correct fill time. If you are familiar with any form of scientific injection molding, regardless of the name, then you know one of the first steps is performing a viscosity curve study. A viscosity curve is developed using calculations of the fill time and plastic pressure at transfer, at multiple injection speed settings.

This study should be completed with zero hold pressure and the parts should be filling to about 95%. (Remember visual shorts.) I recommend starting at the fastest injection speed possible and repeating at lower fill speeds until a minimum of 12 data points is collected. Make sure you cover the spectrum as far as injection speeds are concerned; slow injection speeds are just as important during this study as faster speeds.

So, once you have completed the viscosity curve study the next step is choosing a fill time from the curve...right?...
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