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Re: Calculation of PPM What is a total number of produced parts in a specific period? i.e. in a year, in a month etc. Let's say in 2006 you have produced 100.000 parts and you have 900 rejects. So 900/100000 = .009 x 1,000000 = 9000 PPM in 2006 So your PPM for a last year was 9000. This is a simplest calculation of PPM.
Oct 23, 2008. #1. I have a few questions for you gurus out there. I am going to pose a made up scenario of a certain process and I need to understand the correct approach to calculating scrap ppm. BOM. Plastic Door Substrate -1 Piece cost 50.00. Release Handle -1 Piece cost 10.00. Speaker Grill -1 Piece cost 2.00. Impact Foam -1 Piece cost 2.00.
Disposition of Accept Lot = 1 PPM. Disposition of Sort = Actual quantity found from sorting. Return to supplier = Quantity against PPM is based on the calculated number defective in the lot from the receiving inspeciton sample. We give the supplier the opportunity to adjust this quantity based on their sorting results.
Oct 20, 2010. #4. debyang said: When Cp=1.6 and Cpk=0.3, it means your low Z value=3x0.3=0.9 or -0.3x3=-0.9, find the normal distribution probability for z=0.9 is 0.81594, so your estimated defect ratio is 1-0.81594=0.18406 ( or Z=-0.9 probability 0.18406), and in terms of ppm will be 0.18406x1,000,000=184060 ppm. Thanks for the calculation, Deb.
Strictly speaking, no. But, a case could be made that if the AQL was, in fact, 0.065%, then the PPM might be 650. The problem is, AQL is an Acceptable Quality level, not the Actual Quality Level. AQL is the quality level that would be detectable under a certain sampling plan. Also strictly speaking, the LTPD * 10,000 = PPM nonconforming. Regards,
Its easy: Cpk is commonly used as a process capability measure for normally distributed populations. The Cpk value is directly related to both the Sigma and the 'distance'of the pop.average to the closest specification limit. Cpk=|limit-AVG|/ (3*sigma) Thus Cpk=1 --> average 3 sigma from limit. Cpk=1.33 --> average 4 Sigma, andsoforth.
Which ever number you use, the next calculation seems wrong. 9.93e-9 failures/hr * 4.38e7 hr = 0.43 failures (not 43 failures). if I multiply by 22, I get 9.6 failures per year for 5000 devices. In either case, this is way more than 14 failures in a few week for 100 devices.
Dec 21, 2009. #8. Re: Quality PPM (parts per million) tracking. DrM2u said: It depends from organization to organization if the PPM is a good indicator. Sometimes you'll have to consider other metrics, like the value of internal and external failures, the value of internal and external delays, the value of obsolete product, etc..
You would have to look at many more to be a 99% sure than you would have to look at to be 50% sure. Another complication is the sample size to discriminate between 200 ppm and 100,000 ppm will be much smaller than the sample size to discriminate between 200 ppm and 1,000 ppm. As Mike and Dave indicated, this is not a simple question, it ...
leftoverture said: I see PPM as a flawed metric, though, for two primary reasons: 1) It is very dependent on how many parts you actually produce and/or ship. So if you have a low shipping month, for instance, a relatively small rejection can result in an unusual spike in the metric. "Dependent" sounds negative here.