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Thread: Clamp force calcualtion

  1. #1
    Join Date
    Oct 2017

    Clamp force calcualtion

    I am looking for advice on calculating clamp force. I have tried some cool phone apps, and online calculators but they all ask for information I cant seem to find. FIMM TECH has a really nice app with all the tools you could ask for but it still ask's for "required tonnage per sq. area". I have no clue where to get this number since the material supplier doesn't give that information. The material I use is TPE and I would be fine using a "generic" number for TPE if there is one but I have no clue what that number is.

  2. #2
    Join Date
    Jul 2014
    Lincoln, NE

    Re: Clamp force calcualtion


    Here is a list I had compiled about a year ago of common resins and High and Low Tonnage factors, these are all Tons/sq. in.

    For your TPE question, Depending on wall thickness and what not, the range would be between 3 and 6 Tons/ sq. in. A lot of this information is not provided by resin suppliers, but some deep google searching and free time allowed me to create this reference.

    However, the best way I found for a more accurate calculation is if you have Cavity Pressure Transducers in your tools.

    That formula is

    Proj. Area X # of Cavities = Total Proj. Area

    [Total Proj. Area (sq. in.) X Max Cavity Pressure (psi)]/ 2000 (lb/Ton) = Tonnage required.

    Tonnage Required X 1.3 (safety factor of 30% for viscosity changes) = Your Set Tonnage.

    Let me know if you have other questions. Keep on molding!

    Click image for larger version. 

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  3. #3
    Join Date
    Feb 2016
    San Francisco Bay Area, CA

    Re: Clamp force calcualtion

    Amount of pressure exerted on parting line depends on fill speed, melt temperature, and pack pressure. Surely if you pack parts at 1,000 psi the effective pressure at end of fill is much less in most cases!

    3 tons per square inch is a good starting point

    If there's a tricky 3 plate mold, mechanical slides, or core pulls clamping a little tighter isn't a bad idea!

    A sound method is to start at high tonnage, and slowly come down until you see very minor flash, then add 10% or so of that final tonnage.
    I've found it's best to set tonnage somewhat on the lighter side of the window so when tooling adjustments are made you can always come up in tonnage if needed.


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