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MAPP Plastics Discussion Forum

The MAPP Plastic Industry Discussion Forum allows members to rapidly communicate with each other. Post both questions and answers to questions that other MAPP members have about any industry topic from material and process issues to R&E Tax Credits and other business issues.

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Posted:  14 Dec 2011 23:24
We are working on a project where we need to insert mold a glass lens at the bottom of a polypro vial.  The tolerance on the thickness of the glass is .010"  In our limited exposure we have seen where the variance between pieces of glass in a lot is about .001" and the variation between lots is .010".  Diameter of the glass is .787"
Anyone have suggestions on spring loading a core pin to adjust for variation in thickness or possibly suggest a glass vendor with tighter tolerances.  Volume could be significant if we can overcome this problem.  Customer is ntrying to keep the cost of the lens below $.25 per piece.
Posted:  21 Dec 2011 18:01
More information is required to answer this question.  The part design requirements must be understood.  There are a few design concepts to consider though.  What is the geometry of the contact seal surface to the glass?  Will the glass be loaded in pure compression at this seal?  Does the glass need to support injection pressure?  What is the compression strength of the glass?  Is the lens flat?  Can the seal be designed such that the injection pressure supports the seal as opposed to forcing it open? 

Erich Spraetz
Posted:  22 Dec 2011 19:01
Eric,
Thanks for feedback.  Will get back to you with answers to your question.

Daniel
Posted:  23 Dec 2011 05:15
With the information you provided i would say that a spring loaded corepin would be a possibility, as long as there is no projected area on the core pin. Meaning that the corepin shuts off on the glass insert and the resin flow can not push the pin back. Are you going to mold resin on both sides of the lens, around the edge of the lens?
You could also experiment with a pneumatic cylinder pushing the corepin to create a shut off. You would be able to regulate the core pin force in order to find the balance between damaging the lens and creating a shut off. Are you going to load the lens in the mold with a robot and keep it in place with vacuum?

Peter Blaas

Peter Blaas
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