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Torque required to tighten threaded punch

  1. Jul 23, 2014 #1
    Hi guys
    Im new to the site and was hoping for some information.
    Im currently working on a design to interchange different punching tools in a forging press. These tools are screwed into the punching piston and then the press forges metal objects.

    My question is this:
    I am tasked with installing a hydraulic torque wrench to screw new tools vertically (against gravity) into the piston head. How can i calculate the amount of torque required to overcome the weight from gravity and, more importantly, the resistance of the friction of the two threads meshing? I assume the specs of the threads have something to do with it but I dont recall learning anything along those lines at university.

    Thanks in advance.
    Sean.
     
  2. jcsd
  3. Jul 24, 2014 #2

    Baluncore

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    Science Advisor

    Welcome to PF.

    It will be important to tighten the thread to the point where when being pressed the press load does not take all pressure from the thread.

    It is best to locate and seat the punch to the piston so that the pressing force does not travel along the inner threaded section. Is that the case here?
     
  4. Jul 24, 2014 #3

    Bandit127

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    Gold Member

    It is also a good idea to know about metal fatigue in such applications.

    A high tensile bolt can loose more than half of its initial strength over 106 cycles. That is 4 months for a 10 second cycle running 24x7.

    http://www.unbrako.com/docs/engguide.pdf Fatigue Strength, p.54
     
  5. Jul 27, 2014 #4

    Sorry, that is not really what i was looking for. Let me give some more background, the press and punch have both been designed a while ago and are in full operation so there are no issues with the design side of the punch and the piston. However, what I would like to do is use a hydraulic torque wrench to remove the punches from the piston in a quick fashion rather than doing it manually (the punches have hexagonal sides) but I need to know how much torque is required to unscrew the punch so that I can choose the correct type of torque wrench. I do not want to select a torque wrench that is too powerful which could result in damaging the threads or punch. That is why I was queering about how much torque is required to screw in a punch.
     
  6. Jul 27, 2014 #5

    Baluncore

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    When a threaded punch is screwed in, it will tighten onto a lubricated thread and alignment surface. During use, redistribution of the lubrication by pressure on the thread, will increase removal torque. So it will usually be harder to remove a threaded punch than to insert it.

    The torque needed to overcome gravity will not be important. The torque needed to elastically “stretch” the thread sufficiently to ensure punch retention will be specified somewhere. I would expect the press manufacturer to specify the state of lubrication and punch tightening torque. From experience, I would expect the removal torque to be about twice the insertion torque.

    The torque wrench used to install the punch must be accurately calibrated to the punch manufacturers specification. The removal process must be capable of greater torque. If the thread is seized, removal torque must be limited to prevent damage to the punch or wrench.

    Finding the answer to a question often involves rewriting the question.
     
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