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Thread: Insert molding metal terminals

  1. #1
    Join Date
    Jan 2022
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    2

    Insert molding metal terminals

    I have a question about a part I am designing. The part is a flange that must possess a female electrical connection on both the top and bottom of the part. There are two terminals that must connect the two connectors on the opposite sides of the flange. Because of the part's exposure to diesel fuel, hostaform c 13031 xf seems like a good fit for the material. Also, creating a seal is critical, so leak pathways in the part (along the terminals) must be minimal.

    However, I fear that the insert mold method may damage the electric terminals (copper alloy with tin plating) and deform them during the process since they are only .8 mm thick and will be in contact with the melt. I feel creating a smaller part to insert mold the terminals and then insert molding this small part with the terminals already in it to the*larger part may work since it will reduce the time the terminals are exposed directly to the high temperature. Will the POM bond to itself in the insert molding process? Or should I not worry about the terminals being deformed and instead just insert mold them directly?

    Thanks for any help or advice.

  2. #2
    Join Date
    Aug 2011
    Location
    Upstate of South Carolina
    Posts
    689

    Re: Insert molding metal terminals

    I believe you will need to tweak the terminal design to ensure the melt flow and cavity pressure doesn't damage them. But, if not properly supported in the mold; they can move and may get twisted or bent in the process. Does the terminal need to be flat or can it be round in shape? This helps with resin flow around it. Also you might should design some stepped rings into the insert so that the resin can fill these smaller areas and give you maximum sealing around the insert.

    I over-molded inserts into a PP-GF bottle and a PE extrusion grade resin bottle in the past. They had these rings in the terminals plus O-rings that were over-molded into the part. Another job molded the bottle and a snap in insert with O-rings was pressed into the top of the bottle. So you may want to do a prototype tool and test all of these points before commiting to building a mold and ordering inserts!

    Copper is NOT to be used with POM! I think that is your first problem to resolve! They will react in a NOT favorable way to one another! POM can be rough since it can/does out gas some of the formaldehyde from the melt. Now your choice may be the best one but you still should be careful.

    Mold temp for the resin should be very hot which could reduce fill pressure. BUT, the injection gate must stay open long enough to pack the shrinkage out of the part as the resin shrinks while in the cavity. So you should end up with a long hold time/higher pressure and short cooling time. I don't think you want to mold the inserts into a part and then try to over-mold/bond it into a part.
    Rick

  3. #3
    Join Date
    Jan 2022
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    2

    Re: Insert molding metal terminals

    I greatly appreciate the response Rick.

    Unfortunately, the terminal has to be flat to mate with the connector. I already had added some steps into the terminals to help with the sealing. The terminals are currently designed to have a tin plating, do you think this sufficient to minimize the reaction between the terminals and the POM?

    Also, I had considered doing a snap in connector for the part. However, the connector isn't one that is available for purchase so that would mean I would have to custom produce it, leading to the same problems, or buy go with a standard one that snaps in, which would require multiple connector harnesses and significantly raise the price of each part.

  4. #4
    Join Date
    Aug 2011
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    623

    Re: Insert molding metal terminals

    Wow! I learnt something from Rick. Those are some good suggestions. Did not know about POM - Copper. Thanks.

    Just to answer one question about POM - POM bonding,: Yes, they will bond well. It is best to have them the same grade. Also make sure the premold is resin rich. This is in case you decide to take the premold - overmold route.

    Suhas

  5. #5
    Join Date
    Dec 2012
    Location
    Serbia
    Posts
    102

    Re: Insert molding metal terminals

    For sealing terminals did you considered silicone seals?
    Something similar we using on connectors that we overmold with TPE.
    If tool desined properly and you dont use some exsesive injection preassure melt wont damage terminals.
    There is also possibility to do potting than overmold, but that will increase price of part for sure.

    Do you plan to make insert molding manual by worker or automatic by robot?

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