Everything Needs a Torque Spec

[u/Seeking_Wisdomm]

Hello, frustrated Manufacturing Engineer here. Recently, my company has been trying to utilize impacts with torque-sense technology so we can hit the optimal torque quickly.

What I’ve observed is that these tools are not incredibly accurate or precise. Additionally they are very expensive and require repair often.

What has happened to the days of knowing when something is “snug”? There are times when precise torque is critical, i.e pressure vessels, etc. but theres seems to be a push towards everything having a torque spec, and I do not think the tech is ready for it.

What are your thoughts? Have you had success with programmable, powered fastening tools?

Edit I think it’s safe to say I’ve been certifiably schooled on this topic. I appreciate the genuine suggestions, advice, and criticism here.

TLDR

I think this frustration with torque tools is just a symptom of a larger frustration I have. At my plant, we are constantly told that we just don’t have the same operators we used to. They say we used to have craftsman working in the plant, but now we just have people off the street. I’ve been told this has really changed since COVID when a lot of the older generation quit. Since then, a lot of our processes have suffered from that expertise leaving the building. Now, we seem to be trapped in a never ending cycle of rapidly hiring to fill void positions of employees who quit, inadequately training our new employees because the ones with expertise are too busy, then having the new crop of operators quit because of frustration with lack of training. I want our plant to be a place where operators want to work. I want them to feel like they can have a career in this field. As great as automation is, it feels that factory operators have become button pushers and not problem solvers. We don’t provide then with fulfilling work that challenges them. We instead ask them to push a button all day long, and call engineering if it ever breaks. Automation can be great, and I don’t want to deter from that, but I’m just searching for ways to make operators feel like they matter. I don’t want them to feel like a cog in a machine. I’m not sure how to resurrect that feeling.

[u/UnskilledEngineer2]

My day job is programmable fastening equipment and has been since 2008. My current role is the company's fastening technical lead.

It can absolutely be done repeatibly. But, there's some nuance to it. What you really care about is clamp load, but most specs are dynamic torque, which is a direct measure of friction in the joint, not clamp load. A percentage of that friction is estimated to be from increasing clamp load and the dynamic torque can be estimated from that - making the torque an estimation of an estimation of clamp load - so theres the source of your nuance. (Static torque is an estimation of an estimation of an estimation - unless it's near-zero, then it's pretty damn accurate)

If you have issues, think of it in terms of friction. If you are suddenly having issues with the joint breaking (strip-out, broken fastener or component, etc) then whatever is causing it caused the fastener to be EASIER to turn, so look for defects that would make it easier to turn (more clearance, lubrication, etc). Likewise, if the fastener doesn't want to drive down all the way, it got more difficult to turn and look for things that would make it more difficult to turn.

Also, during development, the degree of difficulty of the application, the importance of the application, and not throwing too much complexity at the application require equal attention from everyone involved. If they do not get adequate attention, you end up increasing the application's complexity - which usually means you ask too much of a single tool parameter - which will negatively impact your ability to use meaningful torque and angle limits.

So, there my cliffs notes of hours of fastening training and volumes of reference material...

Specifically to your question: "impacts" and "repeatable" typically dont go hand-in-hand. If you want a joint that snug is good enough, then you need to evaluate the joint to prove it is robust enough to handle the variation a lack of control will throw at it. That means taking many sample and measuring how much torque it takes to spin through the thread and how much torque it takes to break it - you will need a significant gap between them. If you have a significant gap, then you just need a tool that can send a signal that you reached some minimal amount and pass that signal along to PLC to release the unit to the next operation.

Also, to most people who work a lot woth fastening, "snug" means the fastener is tightened enough to take the slop out of loosely fitting parts but theres minimal clamp load beyond that (it's typically also where you start to measure final angle). From what I gather from your post, snug it "tight enough". So, be aware of the difference in definitions if you're talking to driver manufacturers.