The Accuracy Controlled Enterprise (ACE) work quality control method requires a target that is world class performance, a tolerance limit of what is just good enough, and a way to proof test so you know how you are performing.
In the ACE 3T method, how do I define target and tolerance acceptance limits for a single sided spec?
In my current role there are a few challenges I’m facing.
1) Drawings don’t specify screw torque values to aim for—they only specify ‘to be tightened’.
2) Manual assembly only with hand tools.
Judgement on acceptable workmanship is not documented and is pretty subjective; a few orders of magnitude from achieving world class performance.
Currently, the company adopts “Inspecting quality into the product” rather than “building quality into the processes”.
I guess my first challenge would be to benchmark world class performance for screw torque. Perhaps you could help point me to the right direction to begin this journey.
It’s good you provided an example of your situation. There are general comments that I can pass to you in response to your ACE 3T question; plus give you some interesting results of valuable fastener tensioning research done in 1999.
A Target is the range of values that contains those outcomes which are considered to be absolutely brilliant, world class performance, through to a totally perfect result that is impossible to do better. In your situation, what is the totally brilliant through to perfect range of results you wish always occurred?
The Tolerance range is bounded by the worst result you will accept and still use the item or outcome for all its functions and purposes. This point is what anyone doing the work must always deliver as the worst they produce. Anyone who cannot always produce at least this worst allowed performance is in the wrong job.
The Test is the technique to use to prove a particular result is at least within Tolerance.
If you do not know the Target value I suggest you identify the Tolerance value and set the Target value at one magnitude better than the Tolerance Value. This means the Target range is ten times more accurate than the Tolerance range.
Imagine an archery target with its bullseye so much smaller than the target’s outer edge—you want people to hit bullseyes every time! In the ACE 3T method we tell people where the wrok quality bullseye is in a task, and where is the edge of acceptance. By doing that we challenge them to hit a bullseye, to be a world class expert at what they do. Can you imagine the huge swell of pride people will feel when they get bullseyes—it’s wonderful for them to know they are great (and it’s great for our business too!)
You can use this approach to set work quality control limits for every job performance paramater and job task quality variable. All work tasks have more than one criterion for acceptance. There is always its degree of accuracy, which is what ACE 3T was first created to identify, but also there are time, cost, and task specific factors, like safety, which ACE 3T can be used to define.
Using multiple ACE 3T criteria allows you to fully specify what world class performance is in your company for every aspect of every job.
The screen dump below is about the accuracy of various fastener torqueing methods. Hand tightening is the worst way possible to tension fasteners, guaranteeing regular failures.
In all cases you must have a Target torque value to tension up to. This ought be specified by the designer of the item—who else in the world will know what they intended it to be, unless they decide and tell us all what they actually want! As a last resort get the value from the fastener manufacturer.
I hope this information is useful. Let me know if you have more questions on the above.
My best regards to you,
Lifetime Reliability Solutions HQ