Poor Capability - Electric torque screwdriver

T

the_joker

#1
Hi all,

Well need a bit of help and finally bit the bullet and just posted as I couldn't find the information I need.

First a bit of background, the project I'm working on is for an Aerospace application. The objective is to screw in small screws into a box at 7 - 9 lbf-in (.6 - .75 ft lb). This is a new process for us and the prints only specify a torque value (doesn't specify if the value is break or applied). No ISO / ASTM / Customer spec to give guidance on installation past the torque range.

We've purchased electric screwdrivers with torque control chucks but I'm seeing quite a bit of variation in break torque. Generally I'm seeing about 1 lbf-in of variation (about .13 ft lbf).

First, I'm looking for some guidance about what my expectations should be at this kind of a low level torque. I mean my repeatability is up near 50% showing something is really wrong (method, equipment, etc), but with my limited experience I'm not sure if a 2 lbf-in range is so tight that I won't be able to do better, or if there is truly something wrong. At this level I'm also seeing similar variation in a single person GR&R just repeatedly torquing into the same hole. This leads me to believe it is either equipment or something very minor in method.

Second, the screws are going into helicoils. So, I'm also not sure if this could be the culprit or at least part of the problem. (Yes, I'm also new to using helicoil inserts in Al products.)

Third, should I be meeting a break torque or an applied torque by default? Is there an ISO / ASTM standard that may give me some kind of guidance on this?

Oh, and finally, before you all say, "ask the customer" about some of the items above, please be aware that I have. I'm not getting a response or guidance, but am being expected to supply parts. Gotta love being in QC. The references on the prints and in all customer-supplied documentation aren’t giving me enough to decide that the design is at fault.

So, basically, I'm using this forum as more of a sanity check on what I should expect given existing equipment on the market and the limitations on the spec range I've been supplied.

Any help would be appreciated... Thanks!
 
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Hershal

Metrologist-Auditor
Staff member
Super Moderator
#2
Re: MSA - Electric torque screwdriver

I am not a GR&R expert, but some on here are and they will likely reply soon.
 

Miner

Forum Moderator
Staff member
Admin
#3
Capability Problems - Electric torque screwdriver

This is not an MSA issue. A torque driver is a process, so a capability study would be appropriate. An MSA could be performed on a torque analyzer, which is a measuring device, but not on a driver.

I am renaming this thread and moving it to a more appropriate forum to improve your responses.
 
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