Can an assembly process produce 2 PPM (Parts Per Million)?

[jackylpt]

I heart a middle size company (Tier 1) which have several assembly processes said it's PPM is 2.0. I want to know is it truth.

As I know one or two assembly process probably get very low PPM, but whether the PPM of a finished parts(have 5 assembly processes)can reach 2PPM? Becuase if only 2PPM, how is it's six sigma level?


thanks

Michael

[Jim Wynne]

Originally Posted by jackylpt

I heart a middle size company (Tier 1) which have several assembly processes said it's PPM is 2.0. I want to know is it truth.

Right this minute? Who knows? It's possible, but it's also probable that A) the number will change, and B) it most likely bears no real-world relationship to what would happen after actually making 1,000,000 things.

[Claes Gefvenberg]

Originally Posted by JSW05

Right this minute? Who knows? It's possible, but ..

Agreed, it is not impossible, merely improbable. An exceedingly simple assembly process would help too.

/Claes

[D.Scott]

Another consideration is the way the PPM is determined. If, for example it is the number of actual rejects per million parts as JSW05 says, that's one thing, but consider this:

If the number is based on Cpk values determined from a standard "fall-out chart", 2.0 PPM represents a Cpk of 1.6 assuming the process is centered, stable and never shifts. If, however, the 1.6 Cpk is viewed assuming a normal 1 1/2 sigma shift over a given time period the expected fall-out will jump to 460,000 PPM (illustrating the "B" scenario in JSW05's post). This is why a six sigma program is so critical to a process. With a 6 sigma process, even counting the normally expected swing of +/- 1 1/2 sigma, there would only be an expected fall-out of 3.4 PPM.

Dave

[Caster]

Originally Posted by jackylpt

I heart a middle size company (Tier 1) which have several assembly processes said it's PPM is 2.0. I want to know is it truth.

As I know one or two assembly process probably get very low PPM, but whether the PPM of a finished parts(have 5 assembly processes)can reach 2PPM? Becuase if only 2PPM, how is it's six sigma level?

Michael

One can imagine zero defects even in a complex assembly process <BIG IF> a serious product and process design effort was done and serious poka yokes were put in place. And no, I have never seen it done.

We came close in a simple operation for one characteristic with an effective poka yoke. Zero defects for that charactersitic for 18 months followed by 100% defective. Turns out the poka yoke was re assembled wrong after maintenance. So we poka yoked the poka yoke and went back to zero defects. However this was one characteristic on a simple operation.

Surely someone, somewhere has done well on more complex processes?

I sure hope NASA has complex assemblies under control for the sake of the next team to fly the shuttle.

[Claes Gefvenberg]

Originally Posted by Caster

We came close in a simple operation for one characteristic with an effective poka yoke. Zero defects for that charactersitic for 18 months followed by 100% defective. Turns out the poka yoke was re assembled wrong after maintenance. So we poka yoked the poka yoke and went back to zero defects. However this was one characteristic on a simple operation.

Whups .Well, there we go. Nothing is ever 100% foolproof, but nigh on everything can be improved... Good tale, Caster. Something to remember.

/Claes

[IEGeek]

98.5% of all our produced parts are hand built. We have enjoyed the status of being able to claim a PPM of 18 or less for the past 3 years from our OEM customers.

While the processes are not perfect and we do make mistakes, being a hand built operation we have the luxury of correcting prior to final assembly and shipment to the customer. One true measure of our quality system at this time is our level of produced parts vs. labor hours. We know that one team member can make .92 parts per hour. If on any given day we have a team member that only made 7 parts or less we know there was an issue that needs investigation.

Just some thoughts.....

[Jim Wynne]

Originally Posted by IEGeek

While the processes are not perfect and we do make mistakes, being a hand built operation we have the luxury of correcting prior to final assembly and shipment to the customer.

This highlights another of my objections to the whole PPM concept. If I'm the customer and I ask for PPM data (and feel free to shoot me if I do), I want to know about the output of the process, not outgoing quality level. I know that if a supplier has to make 10 units in order to yield 9 good ones, I'm going to wind up paying for the tenth one anyway, one way or another.