How does one calculate Cpm (Taguchi process capability)

S

si kang

#1
Hello, sir
I am QA engineer who is in charge of SPC activity in the field of semiconductor assembly in korea.
The question is that I heard that there is a new procability capability index not Cpk.
That is Cpm(Taguchi process cability index) which is from A.I.A.G Manual and JMP Statistical software.
Exactly,I know the meaning of Cpm and what the calculation is.
If possible, Could you specify your answer on the above my questions.


Thanks and best rgds.
SI Kang from korea.
 
Elsmar Forum Sponsor
D

Don Winton

#2
I have never heard of 'Taguchi Process Capability Index' but I have heard of Cpm. Process capability index Cpm is used when a target value other than the center of the specification spread has been designated as desirable. Maybe AIAG has modified the Loss Function equations to relate to process capability. Perhaps some QS folks could elaborate as that I stay away from AIAG's stuff as much as possible.

Regards,
Don

------------------
Just the ramblings of an Old Wizard Warrior.
 
B

Batman

#3
As far as AIAG, I know that Cpm is mentioned in the QS9000 SPC manual, but only mentioned. It does not seem to be popular with the automotive folks. I remember reading about it some years ago, but it was not top on the list, so I recall little. Don has more than I remember.

If you need Cpm capability software, my company has used Statgraphics for many years, and it reports Cpm with the capability study module.
 
D

Don Winton

#4
I checked AIAG, Alta Vista and JMP and cannot find any reference to 'Taguchi' and 'Process Capability' anywhere (linked together, anyway). Perhaps you were misinformed.

You can find additional information on Cpm at:

http://Elsmar.com/pdf_files/ Look for CPK.pdf

which may (or may not) help.

Regards,
Don

------------------
Just the ramblings of an Old Wizard Warrior.
 
S

si kang

#5
Hello,
Thank you for your reply on the Cpm.
But I have wondering about Cpm calculation with target value.
If one side spec limit exists, how could the calculation be?
The reason is that Cp=(USL-LSL)/6*SIGMA.
in case of only existing USL or LSL,the index of Cp is not available.
Eventually, Cp can be calculated from having both two sides spec limit such as USL and LSL.
Is there any alternative or not?
To get Cpm for measuring process capability , It is necessary to have two sides spec limit not one side.
And Batman has mentioned Cpm not popular in automotive site for measuring process.
only automotive site or not?

Could you Please confirm the above my questions?

Thanks in advance.
SI Kang from korea.
 
D

Don Winton

#6
If one side spec limit exists, how could the calculation be?
If a one sided specification limit exists, you use Cpk(max), sometimes referred to as Cpku, or Cpk(min), sometimes referred to as Cpkl.

Cpk(max) = (USL-Xbar)/(3*s)

Cpk(min) = (Xbar-LSL)/(3*s)

To get Cpm for measuring process capability , It is necessary to have two sides spec limit not one side.
Correct only in that the calculation for Cpm requires Cp in the numerator. As I mentioned earlier, Cpm is used when the target value is not the center of the specification spread.

Perhaps this will help:

Cp = (USL-LSL)/(6*s); Process capability when Xbar = Specification center

Cpk = Minimum[(USL-Xbar)/(3*s);(Xbar-LSL)/(3*s)]; Process capability when Xbar <> Specification center

Cpk(max) = (USL-Xbar)/(3*s); Process capability for USL only

Cpk(min) = (Xbar-LSL)/(3*s); Process capability for LSL only

Cpm = Cp/[1+((Xbar-T)^2/s^2)]; Where T is the target value. Explained above.

And Batman has mentioned Cpm not popular in automotive site for measuring process.
Cpm is not popular anywhere because it usually means the process is running off-target and the calculation is made to the off-target value rather that the preferred target value.

Regards,
Don

------------------
Just the ramblings of an Old Wizard Warrior.
 
S

si kang

#7
Hello,
Thank you for your continuous and quick response on my question.

You have mentioned that "Cpm is not popular anywhere because it usually means that the process is running off-target value and calculation is made to the off-target value rather that the preferred target value."
I'm really sorry that I don't exactly understand those meanining you have mentioned.
Your more details are needed to me at this time.

Thanks & best regards.
SI Kang.
 
D

Don Winton

#8
I'm really sorry that I don't exactly understand those meaning you have mentioned.
My explanation above is not very clear and stems from my personal applications of process capability. No apologies necessary.

I should expound upon the use of Cpm. Most of my references are rather vague on Cpm as it is not a popular measure of process capability. Thus, the following is not from any official reference I could find, but it seems the logical one.

I believe the original concept of Cpm comes from the application of unilateral and bilateral tolerances. A bilateral tolerance expresses the value as a target value and a range, i.e. 2.0cm +/- 0.1 cm, with the target value and the center of the specification being equal. For bilateral tolerances, Cp or Cpk are applicable.

Unilateral tolerances are given as a target value and a single limit, i.e. 2.0cm +0.0cm/-0.1cm. For unilateral tolerances, Cpku and Cpkl are applicable (other expressions are CpU and CpL, respectively).

I believe Cpm came from a variation of the bilateral tolerance. Tolerances are expressed as a target and a nonsymmetrical range, i.e. 2.0cm +0.2cm/-0.1cm. In this case, 2.0 cm is the target but is not the center of the tolerance (2.05cm is the center). From the definition of Cpm above, "…target value other than the center of the specification spread has been designated as desirable." However, nonsymmetrical tolerances are rarely used in these days of CAD, so it appears that Cpm is also rare, thus rarely used.

Suggestion: Forget Cpm all together and use the four basic definitions of process capability. Besides, if it is indeed from the "A.I.A.G Manual," I personally would not put a lot of stock in it.

Regards,
Don

------------------
Just the ramblings of an Old Wizard Warrior.
 
D

Don Winton

#9
si kang,

Did my last reponse answer your questions?

Regards,
Don

------------------
Just the ramblings of an Old Wizard Warrior.
 
S

si kang

#10
Hello,
Pls reconfirmation Cpm formula, the difference is whether denominator has square root or not as below two formula seeming alike. which is correct?
Cpm=(Cp)/[(1+((Xbar-T)**2)/(S**2))]
or
Cpm=(Cp)/{sqrt[(1+((Xbar-T)**2)/(S**2)))]

and today, I have two questions to you.
How does we understand and recognize Cpm in our process?
For example, we have condidered the meaning of Cpk=2.0 as 3.4dpm very easily.
Hence, is there any relations between Cpm and defects.
If yes, What is that?

Another question, how to determine the target value?
any rules exist or not?
if not, is it possible to make use of the past 3 months' data and calculate arithematic average from the indivudual readings?
if the past three months' data is used, will it be do?

Your quick response will be highly appreciated.

Thanks & best rgds.
SI Kang.
 
Thread starter Similar threads Forum Replies Date
B How does Forbes calculate networth for their Rich List ? Coffee Break and Water Cooler Discussions 0
T K1, K2 and K3 factors - Does anyone know how to calculate them? Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 1
T Does Excel STDEV calculate in 3 stdev (standard deviation)? Excel .xls Spreadsheet Templates and Tools 12
Z Does anyone have experience with EN ISO 17664 ? IEC 62366 - Medical Device Usability Engineering 2
F Does anyone have an ESD quality/cooler talk to share? Training - Internal, External, Online and Distance Learning 4
A What does this line from MDCG 2020-3 (MDR art. 120 substantial change) mean to you? EU Medical Device Regulations 3
D Change Approval Requirements - Does every change need formal customer approval? Design and Development of Products and Processes 17
T What does AS9100 mean when it says you must establish a process to do X? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 24
L Does a backdate form format can be changed if wrong revision is used? Document Control Systems, Procedures, Forms and Templates 8
B General Motors and Honda Alliance - What does this mean to suppliers? IATF 16949 - Automotive Quality Systems Standard 3
C ISO 13485 :2016 - CAPA - Does every CAPA need to be checked by regulations? ISO 13485:2016 - Medical Device Quality Management Systems 9
A Does ISO 9001:2015 cover all the requirements of ISO 10012:2003? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 6
N FDA UDI - Label vs. Labeling - Does the insert need to include UDI? Other US Medical Device Regulations 0
A Does anyone have a checklist of API Spec 650 13th Edition? Oil and Gas Industry Standards and Regulations 0
D Does Manufacture can submit CE mark application under MDD with NB for his New product after May 2020? EU Medical Device Regulations 3
A What does this sentence "this symbol shall be used in the orientation shown" mean in ISO 780:2015? Other Medical Device Related Standards 4
L Turkish Requirements - Does the Software need to be translated? CE Marking (Conformité Européene) / CB Scheme 2
R Where does IATF 16949 address Process mapping? IATF 16949 - Automotive Quality Systems Standard 3
J Does Pakistan Medical Device Import License allows parallel import? Other Medical Device Regulations World-Wide 0
BeaBea Interesting Discussion Where Does Marketing/ Advertisement of Products fit in to ISO 9001? Process Maps, Process Mapping and Turtle Diagrams 39
P Does anyone have a API Q1 Documentation Package? Quality Management System (QMS) Manuals 1
N What is our product classification? (Does Unclassified classification still exists) Other US Medical Device Regulations 14
C Does a CE mark infer meeting all applicable standards? CE Marking (Conformité Européene) / CB Scheme 4
N Small Company - Internal audit process - Who does the audit? Internal Auditing 16
J Does anyone have an excel IATF 16949 Internal Audit checklist I could use? IATF 16949 - Automotive Quality Systems Standard 7
A Does AS9100 require traceability to operators performing the work? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 4
I Does anybody use Detection in medical device Design FMEA? ISO 14971 - Medical Device Risk Management 18
A EN ISO 14971:2019 does not include the Annex Zs ISO 14971 - Medical Device Risk Management 4
Watchcat Does "Similar Device" = "Predicate"? EU Medical Device Regulations 7
C Document Control Stamps - Does anyone still stamp their documents? Document Control Systems, Procedures, Forms and Templates 24
Y Does Solidworks (2D/3D drafting modules) need validation? Other Medical Device and Orthopedic Related Topics 5
M Definition Open Audit - What does an Open Audit mean? Definitions, Acronyms, Abbreviations and Interpretations Listed Alphabetically 3
I Does training have to be written? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 10
P What does UPH/m² mean? Quality Tools, Improvement and Analysis 3
L "IATF-Compliant" IATF 16949:2016 certification? What does this mean? IATF 16949 - Automotive Quality Systems Standard 13
D Why does Official Journal list superseded standards? EU Medical Device Regulations 6
B Record Management - Does the QMS need to control templates of records? Records and Data - Quality, Legal and Other Evidence 17
MDD_QNA QR Code Standard ISO/IEC 15417:2007 - Does anyone use it? Other Medical Device Related Standards 3
R Does any here use an internal auditing tool that works on different platforms? Internal Auditing 3
Sidney Vianna IAQG SCMH explains "positive risk"..........but does it? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 3
D Where does "as far as possible" stop? FMEA - EN 14971 ISO 14971 - Medical Device Risk Management 29
W Does anyone have an API Q2 checklist for internal auditing? Oil and Gas Industry Standards and Regulations 1
G Does pitch/increment/resolution of a ruled scale apply to measurement uncertainty as line item? Measurement Uncertainty (MU) 10
L External power supplies: How close does the safety report have to match the end-use application? IEC 60601 - Medical Electrical Equipment Safety Standards Series 4
Watchcat Does 820.30 include the manufacturing process? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 2
Watchcat Does ISO 13485 7.3 include the manufacturing process? ISO 13485:2016 - Medical Device Quality Management Systems 14
R When does the FDA consider a component a medical device? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 17
B Does EN ISO 15223-1:2016 include the graphic symbols to be added to software and IFU? Other Medical Device Related Standards 9
DitchDigger Boston Fire Code: Who Does What? (CAL TB 117-2013; CAL TB 133) Occupational Health & Safety Management Standards 2
GreatNate Metrotom - Does anyone have any exposure to the Zeiss Metrotom 800 or 1500? Manufacturing and Related Processes 0

Similar threads

Top Bottom