Electric drivers / Torque

[DarrellH]

In an electronic assembly environment, our contract manufacturer is using electric drivers with torque settings and High / low speed settings.

Our design engineers are specifying torque based upon torque only and using variable speed drivers (the amount you pull the trigger determines the speed, some designers use the gun full speed / some do not.

Its clear that speed is a significant factor on the "joint" achieved. I need to ensure that our specifications define speeds, BUT, how do I
a) convince designers that their existing specs are worthless, (cap study of loosening force ?)
b) determine the % effect of speed on the "joint" (Gauge R&R on variable drivers versus 2 speed drivers at each setting (hi / low)?)

 

[mhannon]

Its clear that speed is a significant factor on the "joint" achieved.

Can you elaborate on your reasoning for this?
I am not an expert in the torque field, so I may be missing something. I would not think speed has any effect on specifically an electronically controlled torque driver. Or even pneumatic... Once the clutch reaches the preset force, it slips and prevents any more force being applied to the object.

8 lbf.in should be the same whether I slowly walk it in by hand or slam it down with an impact wrench. If this is not true, and you are creating a tighter joint with a higher loosening force, I need to go back and review some of our practices.

 

[ChrisM]

It also depends on what materials are involved. Metal-to-metal won't be as much of an issue as plastic-to-plastic, where the speed of rotation can affect things like slight compression of the material, that affects the torque achieved. I suggest you conduct some studies; I've had to do similar in the past with securing a slightly "soft" plastic part to a metal bracket. The results can be surprising

 

[mattador78]

It also depends on what materials are involved. Metal-to-metal won't be as much of an issue as plastic-to-plastic, where the speed of rotation can affect things like slight compression of the material, that affects the torque achieved. I suggest you conduct some studies; I've had to do similar in the past with securing a slightly "soft" plastic part to a metal bracket. The results can be surprising

Agreed we have a lot of metal to polypropalene or nylon contacts here with the chemical baths and connections and threads can be stripped easily using torque drivers especially at high speed. Heat plays the biggest factor with the friction weakening the tread and the bolt stripping it out.

 

[dwperron]

In an electronic assembly environment, our contract manufacturer is using electric drivers with torque settings and High / low speed settings.

Our design engineers are specifying torque based upon torque only and using variable speed drivers (the amount you pull the trigger determines the speed, some designers use the gun full speed / some do not.

Its clear that speed is a significant factor on the "joint" achieved. I need to ensure that our specifications define speeds, BUT, how do I
a) convince designers that their existing specs are worthless, (cap study of loosening force ?)
b) determine the % effect of speed on the "joint" (Gauge R&R on variable drivers versus 2 speed drivers at each setting (hi / low)?)

The best in class solution is to have the actual user of the tool validate the torque setting on a calibrated torque analyzer/tester, with the proper run down assembly to simulate the joints being made, using the same settings they will be using in the assembly process, prior to them starting the job.

 

[DarrellH]

It also depends on what materials are involved. Metal-to-metal won't be as much of an issue as plastic-to-plastic, where the speed of rotation can affect things like slight compression of the material, that affects the torque achieved. I suggest you conduct some studies; I've had to do similar in the past with securing a slightly "soft" plastic part to a metal bracket. The results can be surprising

We are attaching a plastic connector block to a zintec plate, yes the connector is compressing somewhat and the variables, Screw / plastic / zintec plate and driver are combining to give varying degrees of compression. I naively thought check the torque setting would be a reasonable place to start but then ran into the variables on the screwdrivers - Doh !

 

[DarrellH]

The best in class solution is to have the actual user of the tool validate the torque setting on a calibrated torque analyzer/tester, with the proper run down assembly to simulate the joints being made, using the same settings they will be using in the assembly process, prior to them starting the job.

Hi, thanks for this, can you elaborate on what you mean by "the proper run down assembly to simulate the joints being made" thank you

 

[dwperron]

Hi, thanks for this, can you elaborate on what you mean by "the proper run down assembly to simulate the joints being made" thank you

Run down adapters, sometimes called joint simulators, are devices that simulate the tightening of a screw or nut by a motorized torque tool. This more real life test gives more accurate results that just running a torque tool on a torque analyzer. Some are made up of springs, some have stacks of washers. Here is a paper about run down adapters:

https://mountz.nl/Dokumentatie/RDA_Instructions.pdf