Reliability Prove-out, Pass-Fail Testing

[JayGreen]

I have only 15 samples of a fuse available. Each fuse is 6" long, containing a type of powder. The object is to prove with high reliability and confidence (~99%R/95%C) that the powder will burn continuously and not snuff or fizzle out.
To achieve this reliability and confidence is difficult. The only response seems to be pass/fail. Logistic regression seems a logical choice, but the independent variable may be difficult to decide upon (say, % binder, or amound of another ingredient). Even if the independent variable is determined, samples are limited to 15. With logistic regression, proving margin gets one the most bang for the buck, but replication at numerous inputs would be needed for most high reliabilities & confidence combinations.
DOE doesn't appear an option. I'd think the high reliability & confidence would be more difficult to prove out with multiple factors changing.
I see engineering confidence being shown, but not statistical confidence.
I know this is a bit vague, but I'd appreciate any ideas. There will likely be 1 or 2 input factors that can change.
More could be addressed (long term vs. short term lot production; homogeneity of the powder, more), but this seems enough for now.
Appreciate your input.

 

[Marc]

A quick "Bump". My Thanks in advance to anyone who can help with this one.

 

[JayGreen]

Thanks for the bump, Marc.

Sorry if my earlier note was a bit rushed and vague. What can be done in an experiment is not completely defined yet. Let me try and clarify a few things, though.

A total of 60 fuses will exist for qualification.

Two main objectives exist: (1) proving that the chosen powder (the composition chosen for qualification) will burn continuously/uniformly and not snuff; (2) determine a model to predict the fuse burn time with a precision of +/-10%.

I’d have to say that requirement #1 is more of a continuous burning. As the powder will be inside a metal tube, the uniformity of the burning would be difficult judge. It should be more of a judgment of whether it’s continuous or not (and no snuffing seen).

The non-snuffing requirement is new. Originally, there was only the objective to model burn time. 45 fuses have already been dedicated for modeling the burn time (the experiment’s target is a certain # of minutes +/- 10%). These 45 fuses will all be made of the powder composition that is eventually chosen. Each of these 45 fuses will have the same powder composition (binder, ingredients, homogeneity – should be as all will be made from one lot). Based on the historical variability of other powders (which are most likely more variable than the powder we’re testing), this 45 run test matrix will give adequate precision. There are only two factors involved in this 45 run experiment: temperature and conditioning time. The response here is certainly a variable one (burn time).

There shouldn’t be any reason why these 45 fuses can’t also be used to prove that the powder will burn continuously/uniformly and not snuff.
The response for the snuffing prove-out, though, is likely a pass/fail response (snuff / no snuff). I’d like to have a critical Y which is variable for acceptance/failure. Chances are slim, though. This will be discussed early this week and confirmed or not, but my hopes are not high.
15 additional fuses will be available that can be 100% dedicated for determining if the powder will burn continuously and not snuff. It may be advantageous to change a powder ingredient (if one is thought to be correlated to the chance of snuffing) in the testing of these 15 fuses. This is something that should be discussed early this coming week with the team involved. If an ingredient is changed, then it seems that these 15 additional fuses would become separated from the first 45 fuses due to the composition of the 45 fuses being the same, while the composition of the additional 15 fuses would be mostly different (vs. the 45 fuses).

If a single factor can be used, then possibly enough margin can be shown via logistic regression to show a high reliability of not snuffing with this ingredient/factor in a certain range. Not sure yet if a correlation like this exists – again, a discussion for early this week.

The fuse is actually about 6 inches in length (sorry – rushed and poor typing earlier). One of the criteria for success will be the continuous and complete burn of a fuse’s powder. Since a fuse would need to burn completely, I don’t see our being able to split a fuse into multiple fuses (as shorter fuses would not prove a full 6 inch burn).

Hope this clarifies things a bit better. I’d like to have 60 samples which I could test in a logistic regression manner with only one factor. That might get me to the reliability I want (not considering lot to lot variation). Not sure that this scenario will exist, though.


I appreciate your input,

Jay