Torque required to tighten threaded punch

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Discussion Overview

The discussion revolves around the calculation of torque required to install and remove threaded punches in a forging press. Participants explore the factors influencing torque, including gravity, friction, and lubrication, as well as the implications for tool design and operation.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • Sean seeks guidance on calculating the torque needed to screw in punches vertically against gravity and friction, noting a lack of knowledge on thread specifications.
  • Some participants emphasize the importance of ensuring that the press load does not solely rely on the threaded connection, suggesting proper seating of the punch.
  • One participant raises concerns about metal fatigue in high-cycle applications, indicating that bolts can lose significant strength over time.
  • Another participant clarifies that the torque required to remove a punch is generally greater than that needed for insertion due to lubrication redistribution and suggests that removal torque could be about twice the insertion torque.
  • It is noted that the torque wrench must be calibrated according to the punch manufacturer's specifications, and care should be taken to avoid damaging the threads or punch during removal.

Areas of Agreement / Disagreement

Participants express varying views on the factors influencing torque requirements, with some agreement on the importance of proper torque calibration and the effects of lubrication. However, there is no consensus on specific torque values or methods for calculation.

Contextual Notes

Participants mention the need for specifications from the press manufacturer regarding lubrication and tightening torque, indicating that assumptions about these factors may affect the calculations. There is also an acknowledgment of the potential for thread seizing, which complicates the removal process.

Sean_crisp
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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 don't recall learning anything along those lines at university.

Thanks in advance.
Sean.
 
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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?
 
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
 
Baluncore said:
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?


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.
 
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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