Action on processes that are not capable

[Andrews]

During one of the training programmes, a customer representative told us that reducing the tolerance on the component is an action that can be taken if processes are not capable.

Our stand: What is the use of reducing the tolerance? If the process is not capable, it will go out of this reduced tolerance often. Therefore there is no use of reduced tolerance.

We told him that the only way out is to eliminate the commmon cause e.g by changing the machine.This argument was not accepteed by our customer.

What do cove members feel!

 

[Jim Wynne]

During one of the training programmes, a customer representative told us that reducing the tolerance on the component is an action that can be taken if processes are not capable.

Our stand: What is the use of reducing the tolerance? If the process is not capable, it will go out of this reduced tolerance often. Therefore there is no use of reduced tolerance.

We told him that the only way out is to eliminate the commmon cause e.g by changing the machine.This argument was not accepteed by our customer.

What do cove members feel!

If lack of capability is due to common cause variation, then the process must be changed in order to establish an acceptable level of capability. You are right about the tolerance; reducing (or tightening) it will only result in more trouble; that's an undeniable fact. On the other hand, if the tolerance is tighter than it needs to be, expanding the tolerance can be an acceptable method of achieving capability objectives.

 

[Steve Prevette]

Yes, I wonder if there was a language barrier problem here. Could he have really meant loosening the tolerance? One thing to be said - if the process has been stable for a long time, and you have not had any negative outcomes due to routinely violating the specifications (think hard about hidden costs also before answering this, and risks of things that might happen in the future that haven't popped up before), then you might as well change the tolerances to match what the current process is putting out.

 

[Andrews]

How about if the process is unstable? In such a scenario, will reducing tolerance help?

 

[Steve Prevette]

How about if the process is unstable? In such a scenario, will reducing tolerance help?

In this case, I have no way to predict what the future results of the process will be. I may loosen the tolerances to the worst case I have seen so far, but since the process is unstable, it may be yet worse tomorrow. Since I cannot predict the future results of the unstable process, I cannot predict what the future costs related to far-from-specification products.

 

[Andrews]

In this case, I have no way to predict what the future results of the process will be. I may loosen the tolerances to the worst case I have seen so far, but since the process is unstable, it may be yet worse tomorrow. Since I cannot predict the future results of the unstable process, I cannot predict what the future costs related to far-from-specification products.

Hope I have not misguided you. I was talking about tightening tolerance and not loosening tolerance. Will tightening the component tolerance help for an unstable process

 

[Jim Wynne]

Hope I have not misguided you. I was talking about tightening tolerance and not loosening tolerance. Will tightening the component tolerance help for an unstable process

Unstable=unpredictable. So there's no way to tell for sure what might happen.

 

[Andrews]

Thanks JSW05 for the response. Anymore viewpoints?

 

[Steve Prevette]

Unstable=unpredictable. So there's no way to tell for sure what might happen.

And realize that changing the tolerance does nothing to help or hurt the process you have just completed. What it does help or hurt is the downstream processes. Now, if you manage to remove all of the product that will hurt the downstream processes, you will reduce total costs. Do realize that it is more effective to remove all bad product by preventing the creation of bad product in the first place. It is unlikely that inspection will catch and remove ALL bad product.