How do you define Preventive Action Items in the Manufacturing Sector?

Kevin Mader

One of THE Original Covers!
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Yes it does. Your response is leading to something I have been considering for a while now.

Trends of 4, 5, 6 or seven above the grand average but below the upper control limit or above the lower control limit suggest that the process has drifted (dependent on the organization’s protocol for adjustment), and is out of control. While the process may have not yield a defect, action is necessary to prevent the possibility of producing a defect.

My question for the group is this: are actions taken corrective or preventive? Remember, a defect (out of the specification limits) has not been produced.

Regards,

Kevin
 
A

Al Dyer

Kevin,

I have to go with:

1: No nonconformance, no corrective action.

2: Process adjustment to prevent the possibility of a nonconformance equals a preventive action.

We have had heated discussions at work concerning trends and the 7 points above or below process average.

In this instance I argue that because perishable tooling is a major cost center we set-up the process to run up and down between 4 sigma. The Cp and Cpk's do not look great but we have the initial data to back up our decision and currently have 0 external PPM and an internal scrap rate of appx. 0.67% (over a 1 year period) in an industry that typically runs between 5% & 7%.

And tooling costs are optimized.

It is a fine line, and getting buy-in from quality, engineering, and manufacturing can be hard to overcome.

I guess it all comes down to having an effective APQP/Product Realization process.

A Long Winded ASD...
 

Kevin Mader

One of THE Original Covers!
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Al,

Great response! There is good value in the information you presented in your post for folks following this thread.

I also feel it is a Preventive Action. Same heated discussions here. Many argue that we are fixing an special cause such as tool wear, so it is corrective in nature. True enough I suppose and I'll concede that it is a corrective action to the process, but a preventive action to the production of a nonconforming product (out of tolerance).

Optimization is the key to your answer. You have nice balance between cost of tool replacement and cost of producing nonconforming product. Now if we can only optimize all the other processes........

Regards,

Kevin
 
A

Al Dyer

Kevin,

Just my point of view, but I would not consider tool wear a special cause. (I don't believe you do either) I believe tool wear to be inherent to the process and controllable by many means. We use Mean Time Between Failure, or tool life studies.

ASD...
 

Kevin Mader

One of THE Original Covers!
Leader
Admin
Al,

It is inherent, hence the 1.5 sigma shift for the Six Sigma folks. Still when viewing a SPC chart, the operator will detect a trend or shift based on the data. Something caused the shift or trend, perhaps a heavy hand, change of operator, or perhaps tool wear (dull turning tool). As you correctly point out, there are many means to prevent a worn tool, preventive and predictive maintenance being highly popular. While it is a common cause (it has not caused a 'flyer' outside of the limits), it is still assignable.

Common cause is attributable for the random up and down activity between the UCL and LCL. My question is this: if you have trends or shifts on the chart, displaying an out of control situation, do we attribute this to common or assignable (special) cause?

Regards,

Kevin
 
A

Al Dyer

Kevin,

We are currently is a situation where we have integrated SPC in our process that makes the operator assign an inherent cause to that particular reason. If the inherent cause type is not available as a choice the operator can't continue processing until he/she or a group investigate the problem.

As I said before, we had a good APQP process and pretty well defined the inherent causes and removed the special causes. This is not to say that they don't occur, only that when they do, we have a robust response process available.

Now to answer your last question:

If I detected an uncommon pattern (i.e. other than the expected up & down between 4 sigma) on the chart I would suspect a special cause and investigate.

I wish I had a way to post a visualization, but we expect a basically straight line (45 degree) from the lower 2nd sigma to the top 2nd sigma. Any variation (such as a horizontal line over 4 or 5 readings) causes me concern and the notion that a special cause has been detected.

ASD...
 

Kevin Mader

One of THE Original Covers!
Leader
Admin
Al,

Nice approach. I would be interested to hear how the operators like it.

I was thinking along these lines, in reference to Control Charts. Tell me what you think (and anyone else following this thread).

Corrective Action: action taken against the cause of a 'flyer', something outside of the control limits but perhaps within the Specification Limits (treatment of a Special Cause). The process is not in statistical control, unpredictable, and creating a nonconformance.

Preventive Action: action taken against the cause of a shift or trend within the control limits. The process is not in statistical control because of the shift or trend but no 'flyers' are present. The process has not produced a nonconformance. (How would we feel about flyers not beyond the specification limits? Still preventive?)

Continuous Improvement: the action taken against common causes of variation in the process, which is both stable and predictable (statistical control).

Regards,

Kevin
 
A

Al Dyer

Kevin,

Our operators like it.

Some because it is an automated system and is less labor intensive.

Some because the good parts they make can be attributed to them. (i.e. review time)

I suspect some don't like it because their production, scrap, and performance is traceable. Time will tell.

As to your question:

Agree with all except corrective action (maybe semantics?). I would say we all need to define when a "formal" corrective action is required and when we just "tweak" the process. It is a fine line, but I would not issue a CA for a "flyer" that is in specification but out of "typical" control limits. I say this to you with the thought that there would be some type of action on any "flyer".

Also, I would not typically consider action on a "flyer" a continuous improvement.

100% agree with your definition of preventive action as it applies to control charts.

ASD...

[This message has been edited by Al Dyer (edited 23 May 2001).]
 

Kevin Mader

One of THE Original Covers!
Leader
Admin
I am glad to hear that it is mostly positively received! I think the rest will come to appreciate it.

Good input. Anyone else out there willing to contribute to defining the three?

Regards,

Kevin
 
D

dbulak

Thankyou for all your responses. It is a real thrill to have so many respond. But another question on the same subject. Would increasing the capacity of a machine be a preventive action? My thought is that the machine now has a larger capacity to produce product where new orders can be taken by sales. Sales will not be lost because of a limited capacity. Please, any ideas on this.
 
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