Moldmaking technical question: preloading taperlocks
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  1. #1
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    Default Moldmaking technical question: preloading taperlocks

    Good morning all Moldmakers:
    I have a mold build going on right now and I have a technical question for all you experienced designers and builders.

    I need to run two slides for two different parts in one mold.
    The slides are NOT directly opposite each other but are offset by 2 inches to make the mold shorter.
    I always preload the slides and locks by at least 0.002"; more for bigger molds.
    With the slides offset, the preload will want to twist the Hotside relative to the Coldside.
    I'm going to put 4 strip type taperlocks around the periphery of the parting surface to resist this twisting force.

    The question:
    Should I preload the taperlocks that are at the opposite ends of each slide stroke too?
    If I do it I'd obviously do it by shifting the HS lock relative to the CS lock.
    One instinct says YES, the other says NO.

    I know the taperlocks that are oriented parallel to the slides need no preload...but what about those damned end taperlocks??

    Also this mold has a sprung floating HS plate and the slide locks are bolted to the top plate so I need to taperlock those two plates together too.
    (I need to hold the mold closed while the slides start to pull or I'll distort the parts as the cores pop free)
    Do I preload those as well?

    Here is a picture with both HS plates hidden, to help you visualize it.

    All comments will be happily accepted.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    Attached Thumbnails Attached Thumbnails cs-mold-layout.jpg  

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    Not a mold builder, but what strikes me as a solution is a pancake cylinder of the same diameter as the lock cylinder positioned to be in alignment with the opposite lock cylinder. Put the cylinders in series.

    Tom

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    Hi Tom:
    That would be a brilliant solution if this mold had hydraulic slides but it's going to run mechanical cam pins.
    If you are unfamiliar with how they work, a cam (or horn) pin is an angled pin that runs through a hole in the slide body and is attached to the Hotside plate.
    When the mold opens, the angled pins pull the slides back, and when the mold closes they push the slides forward until the locks (the magenta parts in the picture) can take over and force the slides all the way forward.
    If you look at the two big holes in the grey and purple parts just inboard of the magenta parts...those are the cam pin bores in the slide bodies.

    'Twas a great suggestion though.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    We called them pecker pins. So add two more pins.

    Tom

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    I take it from your absence of a reply that the additional pins was ridiculous. Ok, since we are brain storming, put cam blocks on the hot side plate that engages the cavity plate (do I have that correct?) so that just as the side draws lock up, the cams engage the cavity plate. Timing should be not different than the side draws.

    Tom

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    Hi Tom:
    I hadn't had a chance to check out this thread again until now so I was unaware you had commented...my apologies.

    My issue with the mold design is not the forces that act on it when it opens (they are small)...it is the forces that act on it when it is closed and the locks push on the backs of the slides to force the slides forward.
    Since they are not directly opposite one another they will twist the hot side relative to the cold side when the mold closes...more pecker pins (I love that term) will not help that.
    I need to be able to resist those twisting forces to protect the leader pins and bushings.

    The competing theories go as follows:
    If I preload the end taperlocks the twisting force does not occur at all...it becomes naturally balanced and the hotside plate just stretches by 0.004" (0.002" per side) and the taperlocks seat against each other but can never twist.

    If I do not preload the taperlocks the hotside plate can twist in the last 0.006" to 0.008" of the mold closing motion, and then is forced back by the mating of the taperlocks.
    Depending on the lost motion in the system this may be of no consequence and the top plate (that the locks are bolted to) distorts only locally around the area that the main slide locks occupy.

    Preloading the taper locks makes them wear prematurely because their surface area is so small compared to the area of the slide/lock interface.

    Not preloading them make the mold base theoretically go through these complicated twisting and un-twisting motions in the last 0.006" to 0.008" of mold closing stroke as the slides ostensibly come under clamping load before the taperlocks do.
    Depending on the face angle of the taperlocks compared to the slide locks this may not be significant at all because the taperlocks are essentially closed within tenths before the slide locks can create any significant force on the hotside and top plate, so the argument is that I'm totally overthinking this and it doesn't matter so just keep it simple and quit breaking my head.

    That's it in a nutshell, so I'm going "yes I should...no I shouldn't".
    I need to decide soon because I'm almost ready to cut the taperlock pockets.
    The "taperlocks" I'm describing function exactly as you are advocating for the "cam blocks" that you are describing if I preload them.
    They are the turquoise parts in the picture in post #1, and the corresponding hotside mating taperlock parts are hidden so you can see the cold side properly.
    I naively assumed all would recognize them for what they are supposed to represent...mea culpa!

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Not sure But how about making the backs of the locks at a angle so both part are parallel to eachother
    Or less of a angle if parallel would be too much

    Peter

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    I prefer parting line locks that aren't tapered. There are locks that mount on the side in a pocket, and they have a tapered lead-in, but then they are straight, so everything is held in alignment well before the final action of the slides. Easy to install, too. You clamp together the A and B plates and mill the side pockets together, so they are perfectly aligned.

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    Hi MushCreek:
    Yeah I've used those and normally I like them when my only objective is to hold precise alignments between Hotside and Coldside.
    However, what I'm trying to do is counteract twisting forces that I know will be imposed on the plates by the asymmetric location of the slides and slide locks.

    Those non-tapered locks are sensitive to having pretty good alignment already before the mold closes.
    If a sudden side force is imposed before they are home, they tend to lock up and gall.
    I've seen it occur on old molds with worn out leader pins run in crappy presses where parting line locks like these have been installed in an attempt to resurrect a mold that really needed a full rebuild.
    The parting line locks get beat to ratshit in a day or two if the alignment is at all off.

    So for this specific application, I feel that strip taperlocks is the safer bet.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Hi Peter:
    I think I understand what you're advocating...correct me if I'm wrong.
    You are suggesting cutting a compound taper onto the back of each slide and cutting a matching compound taper on the front of each lock to point the forces more toward each other.

    There are two problems with this approach:
    1) it's more difficult to do accurately.
    2) the slides run parallel to each other and are constrained in tee slot rails, so cutting the compound angle does not redirect the forces...it only redirects part of the forces so the slides will be pushed sideways and the slide locks will be pushed sideways in the opposite direction.

    So I don't think it would solve the problem.
    But it is a great out of the box thought experiment, and I appreciate your input.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Dummy scaled smaller with a lower pre-load. Balanced mathematically.
    Attached Thumbnails Attached Thumbnails 169777433.jpg  

  14. #12
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    About 2
    You swap some or all rotating force for side force on the t slots
    This side force hardly travels any distance The T slots need a redisign yes
    I never build a mold Only have seen some

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    Hi David_M:
    So what you're recommending is to tripodize the load so the big slide and lock is pushing between two smaller ones that are pushing the other way.
    Now that is a brilliant idea!

    It doesn't even need to be another slide obviously.
    I could just put in a honking big parting line lock of the kind Mush Creek recommended in post #8. but with taper and preload.

    David, I think you may just have solved my problem for me.
    I owe you one!

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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  17. #14
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    I agree with your parting line taper locks, and I would indeed still preload the slides. Odds are you have a steeper lock on the slides compared to the Parting line locks, so I don't think damage or galling will occur on the PL locks.


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