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The typical injection molding screw has the same outer diameter along the entire length of the screw. When measuring for wear, the highest amount of shear, and wear, typically occurs in the transition and metering zone.

I have seen some cases where a company may use variying clearances in the metering zone for mixing, or adjust the clearance in the feed zone to accomodate specific feed issues.

Some manufacturers, especially those for micro-molding, will occasionally use a tapered barrel to facilitate material conveyance in the feed zone.

Keep in mind… if you are using a barrier screw, you will have two melt channels in the transition zone with one flight having more clearance than the other. 

-Andy

The biggest problem I see is that you have set you tolerances for both the inputs and outputs which relate directly to each other. Although LCPs are highly crystalline and have a very sharp melting point, their ability to flow into the mold is highly dependent on the rate of injection. As a result, any shift in molecular weight, molecular weight distribution, or additives during lot changes will result in a non-compliance. Eventually, you need to re-evaluate your tolerances.

Ultimately, it appears your issues are not related to variations in your machine, but a lack of flexibility in your process resulting in variation.

Such a process often requires a short shot with a high packing pressure to complete mold filling.  This will ensure that there is always enough pressure available to fill the part completely.

I have a few questions to address this week, but I intend to post a blog about high-pressure molding next week. This should help you better understand how to establish such a process.

-Andy