# How to Calculate RPN in Design FMEA (DFMEA) vs. Process FMEA (PFMEA)

N

#### nsraj

Hi,

In FMEA normally we'll calcualte the RPN as Sev x Occ x Det,

but recently I came to know that in DFMEA the RPN calculation method is slightly difference. i.e.

First Calulate RPN for Failure Mode (RPN FM = Sev (Max) x Occ X Det(FM))

and then RPN for causes,

but in calculating RPN for causes, I was told the formula as

RPN C = Sev (max) x Occ x Det (Min (FM, Causes)

Example

Assuming
for Failure mode RPN FM = 5 X 5X 3 = 125

for cause 1 suppose if i get Sev = 5, Occ=5 and Det = 4,

I normally calculate as 5 x 5 x 4,

but i was told to calculate as 5 x 5 x 3(Det of FM)

is there any reference to this method???

nsr

V

#### Valeri

Re: How to Calculate RPN in Design FEMA (DFMEA) vs. Process FMEA (PFMEA)

Good morning,

I'm not quite sure where you found/heard that calculation for RPN but it should be the same (S)x(O)x(D)=RPN (severity x occurrence x detection = risk priority number) no matter if it's a DFMEA or PFMEA. Then again, maybe I'm not understanding the question

#### Jim Wynne

Re: How to Calculate RPN in Design FEMA (DFMEA) vs. Process FMEA (PFMEA)

Hi,

In FMEA normally we'll calcualte the RPN as Sev x Occ x Det,

but recently I came to know that in DFMEA the RPN calculation method is slightly difference. i.e.

First Calulate RPN for Failure Mode (RPN FM = Sev (Max) x Occ X Det(FM))

and then RPN for causes,

but in calculating RPN for causes, I was told the formula as

RPN C = Sev (max) x Occ x Det (Min (FM, Causes)

Example

Assuming
for Failure mode RPN FM = 5 X 5X 3 = 125

for cause 1 suppose if i get Sev = 5, Occ=5 and Det = 4,

I normally calculate as 5 x 5 x 4,

but i was told to calculate as 5 x 5 x 3(Det of FM)

is there any reference to this method???

nsr

I've never seen anything like it, and it seems to be a needless overcomplication of an already dubious practice.

N

#### nsraj

Hi Jim

Thanx for the reply, me too thought the same, but wanna know if realy anything is there like that or not. If anybody come across such info pls pass it on

and Valeri,

let me put it in other way, do we need to calculate RPN for "Failure mode" Separately and RPN for its "causes" separately???

#### Jim Wynne

Hi Jim

Thanx for the reply, me too thought the same, but wanna know if realy anything is there like that or not. If anybody come across such info pls pass it on

and Valeri,

let me put it in other way, do we need to calculate RPN for "Failure mode" Separately and RPN for its "causes" separately???

You said that you "came to know" this method--from where? Unless you have a customer that requires it or you can find some utility in it in your own application, I would just stick to the SxOxD method and be done with it.

P

#### parallel

Hi

I have a slightly different doubt about RPN:

RPN=S x O x D

If S is more which is bad, is given maximum rating.
If O is more which is bad, is given maximum rating.
If D is more, which is good (prevents failure from reaching the customer), should we not give minimum rating?

This way priority will have balanced scale.

I know my thought does not tally with our conventional method of calculating RPN.

#### Chennaiite

##### Never-say-die
Trusted Information Resource
Hi

I have a slightly different doubt about RPN:

RPN=S x O x D

If S is more which is bad, is given maximum rating.
If O is more which is bad, is given maximum rating.
If D is more, which is good (prevents failure from reaching the customer), should we not give minimum rating?

This way priority will have balanced scale.

I know my thought does not tally with our conventional method of calculating RPN.

Without getting into the semantics, please refer whichever rating criteria you have. I am sure it says 'lower the better' for Detection rating as well.

P

#### parallel

Thank you. However my doubt still remains.

#### Chennaiite

##### Never-say-die
Trusted Information Resource
If D is more, which is good (prevents failure from reaching the customer), should we not give minimum rating?

AIAG FMEA rating criteria does provide minimum rating if the detection control is good. In other words, if D is more, it is not good i.e. the defective part will be undetected and will in all probability reach the Customer. If possible, please share the rating criteria you are referring to, this will help us clarify better.

A

#### amit_rd

Hi

I have a slightly different doubt about RPN:

RPN=S x O x D

If S is more which is bad, is given maximum rating.
If O is more which is bad, is given maximum rating.
If D is more, which is good (prevents failure from reaching the customer), should we not give minimum rating?

This way priority will have balanced scale.

I know my thought does not tally with our conventional method of calculating RPN.

There is no scope for this doubt as what you think is how the rating is to be done. The ratings for severity and occurrence go 1 to 10 whereas for Detection, it is 10 to 1 which mean better the detection control lower the rating. I hope it is clear for you now.

B Formula to calculate the Process Sigma from an RPN Six Sigma 17
Attribute MSA-AIAG 4th How to calculate sample size IATF 16949 - Automotive Quality Systems Standard 12
How to calculate sample size and sample frequency Statistical Analysis Tools, Techniques and SPC 2
Calculate FPY for Audit Results AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 9
How to calculate the A4 constants in Median/Range control charts? Statistical Analysis Tools, Techniques and SPC 2
How to calculate Effective Number of People for ISO 13485 Certification? General Auditing Discussions 2
Need to calculate tolerance Intervals with a set of non-normal data and 3-Parameter Weibull distribution Using Minitab Software 0
Calculate acceptance of equipment reading after calibration General Measurement Device and Calibration Topics 2
Calculate acceptance of calibration reading Measurement Uncertainty (MU) 1
How would you calculate this? Capability, Accuracy and Stability - Processes, Machines, etc. 4
Bend allowance formula to calculate per degree per radii Manufacturing and Related Processes 2
Commercial excel templates that calculate overhead, hourly rates, fee proposal Excel .xls Spreadsheet Templates and Tools 0
M How to calculate benefits? Moving some developed non controlled software/automation systems Service Industry Specific Topics 2
Calculate number of people in processes, considering cycle time/takt time = quantity of people Lean in Manufacturing and Service Industries 9
How to calculate the maximum allowable hysteresis of a pressure gauge General Measurement Device and Calibration Topics 1
S How to Calculate the producer Risk AQL - Acceptable Quality Level 25
Methods to Calculate Available Production Rate ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 0
Why calculate LCL in P-chart? Statistical Analysis Tools, Techniques and SPC 4
How to calculate CPK with n = 1 Manufacturing and Related Processes 2
Add-On software for VMC to calculate setting time, Idle Time, OEE etc.. Manufacturing and Related Processes 2
L How to calculate the Probability of Deficiency of the AQL of an Inspection AQL - Acceptable Quality Level 16
V How to Calculate Unbiasing Constant C4 Statistical Analysis Tools, Techniques and SPC 1
J How to Calculate OEE Indicator for a Workshop (15 Machines) Lean in Manufacturing and Service Industries 6
R How to calculate UCL (Upper COntrol Limit) and LCL (Lower Control Limit) Statistical Analysis Tools, Techniques and SPC 5
I want to calculate reliability at 750 hours Reliability Analysis - Predictions, Testing and Standards 8
R How To Calculate & Print CDF and Lower Bound CDF value for some t(time) with Minitab? Using Minitab Software 1
N How to calculate the Premium Freight charges Service Industry Specific Topics 4
A How to calculate Mean and standard deviation without sample size in Minitab Using Minitab Software 5
When do I need to calculate Process OEE? Manufacturing and Related Processes 12
How to calculate Thread Pitch Diameter for non standard TPI like 5/8" 17.75 NF3 Manufacturing and Related Processes 3
C Definition and Way to Calculate some Metrics Lean in Manufacturing and Service Industries 6
M How calculate P value for Linearity and Bias using Excel Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 8
N Formula that will calculate the NoGo Major Diameter of an M20 x 1.5 6H Thread gage Inspection, Prints (Drawings), Testing, Sampling and Related Topics 3
M How to calculate Cg and Cgk for a 2-Dimensional Area Gage R&R (GR&R) and MSA (Measurement Systems Analysis) 4
T Calculation Question - Calculate the runner weight for a part Manufacturing and Related Processes 2
M Spreadsheet on How to Calculate SMT Capacity wanted Manufacturing and Related Processes 2
F How to Calculate the unbiased Standard Deviation in Excel using Minitab Formula Capability, Accuracy and Stability - Processes, Machines, etc. 6
S Spreadsheet that will Calculate Audit Duration times based on IAF MD5 and MD11 Excel .xls Spreadsheet Templates and Tools 8
Calculate PPMs by going back to Date of Production or Date Noticed Quality Tools, Improvement and Analysis 7
M How to calculate MTTF (Mean Time to Failure) Reliability Analysis - Predictions, Testing and Standards 1
H How to calculate the Lot Reject Rate Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
L How calculate the number of samples Statistical Analysis Tools, Techniques and SPC 2
A Simple 125 piece part Capabilty Excel .xls sheet to calculate Cpk Capability, Accuracy and Stability - Processes, Machines, etc. 3
R How to calculate MMC when is placed after datum Inspection, Prints (Drawings), Testing, Sampling and Related Topics 4
S Which one is better to calculate, Cpk or Ppk? Statistical Analysis Tools, Techniques and SPC 11
C How to calculate P value on Probability Plot Statistical Analysis Tools, Techniques and SPC 1
S Supplier Disruption Score and how to calculate it Quality Tools, Improvement and Analysis 4
IAQG OASIS - New tool to calculate Audit Time AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 1
M How to calculate dimensions of trapezoid ? Quality Tools, Improvement and Analysis 3
How to calculate Surveillance Audit Days in Corporate Audit Scheme IATF 16949 - Automotive Quality Systems Standard 4