How to define and Calculate the DPU, DPMU, DPMO, Yield, Rolled Throughput Yield (RTY)

[billlin]

Dear Sirs,

First, many thanks for your effort and contribution to this Elsmar Cove Forums, So, We have a place to ask question and could get answer from experts.

And Now, I need help on calculating the DPU, DPMO, Yield, Rolled Throughput Yield ( RTY ), Sampling size and Process Capability question.

We are an assembly factory for baby product, and be required to show our
In-Process and Finishing goods with the above Performance ratio.

Our each assembly convey line daily production about 1,000 units, and we have two Quality Control station A and B. per Assemply line - one is located in 1/3 of line for sub-assembly parts 100% inspection and another in the end of Assemlby line for Finishing goods sampling inspection.

We do have a checking list with 40 inspection items and using attribute data for checking each sampling unit, below is data that we collect and need to confirm the correct way to check the performance vs. DPU, DPMO, Throughput Yield, Rolled Throughput Yield ( RTY ) ratio.

Factory with Assembly line: 5 lines
Daily Production units - 1,000 / day / line.
Per Line - TWO (2) QC Station A and B.
QC Station A. - 100% Inspection each sub-assembly part.
In-Process checking list with 20 inspection items

QC Station B. - Random Sampling Inspection finishing units
( Inspect 100 units / per line / per day )
( PS. Checking each unit per 40 inspection items need to
take about 3.0 min. to 4.0 min. )

Example of data below:
Line 1. QC Station A. In-Process, Input 1,000 units, Output 950 units,
Defectsive 50 units, defects = 150
- DPU = 150 defects / 1000 units = 0.15
- DPMO = (150 defects / 1000 units * 20 inspection items ) * 1,000,000
= 7500
- Yield = 1-( 50/1,000 ) * 100 = 95.0%
- RTY = ???

Line 1. QC Station B. End of Line inspection,
Input 950 units, Output 940 units,
Sampling Inspection units - 100 units only
Defectsive 10 units, defects = 50

Question 1. - How to decide the “U” to calcuate DPU ?
“U” shall use Production unit = 1,000 units ?
or Inspection unit - 100 units ?
- DPU =
- DPMO =
- Yield =
- RTY = ???


Line 2. QC Station B. End of Line inspection,
Input 930 units, Output 910 units,
Sampling Inspection units - 100 units only
Defectsive 20 units, defects = 30

Line 3. QC Station B. End of Line, Input 980 units, Output 940 units,
Sampling Inspection units - 100 units only
Defectsive 40 units, defects = 80

Line 4. QC Station B. End of Line, Input 900 units, Output 880 units,
Sampling Inspection units - 100 units only
Defectsive 20 units, defects = 40

Line 5. QC Station B. End of Line, Input 920 units, Output 900 units,
Sampling Inspection units - 100 units only
Defectsive 20 units, defects = 30

How to dertimine Whole factory ( with 5 lines ):
- DPU =
- DPMO =
- Yield =
- RTY =


Question 2. - end of line Inspection Sampling size 100 units vs.
Production 1000 unit -
How to determine What “Risk level” of this Inspection ?
and If we want 98 % sure of Inspection, How to determine How many units need to Inspection at the end of line ( Finishing goods ) ?
Any Chart to refer to find the Risk level of Sampling plan vs. Production units ?

Question 3. - How to determinr the Process Capability from attribute data ?
Question 4. - How many data need to collect of each assembly line to
calculate the Process Capability of attribute data?

Question 5. - When we say DPU, DPMO, Yield, Rolled Throughput Yield
( RTY ) and Process Capability these performance data is for Assembly line ?
or Whole factory ( 5 assemply lines ) ?
( PS. each assembly line could be produced for different Model ? different Production unit, different defects found, different inspection items, diffferent defective unit ???? )

Question 6. - Refer to our Facotry Production and assembly line status, What kind of Performance ratio - DPU, DPMO, Throughput Yield, Rolled Throughput Yield ( RTY ) ratio or Process Capability that is “BEST” data for us to watch the Quality Performance ? So, we are able to set up Performance Scordcard for each assembly line or each assembly factory ?

Question 7. What difference of “dpmu = defective per million unit “ vs. “DPMO = defects per million opportunity ” ? which one we shall use ?

Question 8. Is this correct ? Use DPU, DPMO to show performance of Finishing goods ?
use the Throughput Yield, Rolled Throughput Yield ( RTY ) for In-Process performance ?

A lot of questions to you and hope you can help to answer or someone can help to correct my thinking.

Thank you in advance. bb

Best Regards,
Bill Lin in Hong Kong.

[Sushil]

Hi,

In your calculation of DPMO for Lin1, (as below) -

"Line 1. QC Station A. In-Process, Input 1,000 units, Output 950 units,
Defectsive 50 units, defects = 150
- DPU = 150 defects / 1000 units = 0.15
- DPMO = (150 defects / 1000 units * 20 inspection items ) * 1,000,000
= 7500"

Do you inspect for 20 types of defects or are these Opportunities per product ?.Pls clarify.

Sushil

[billlin]

Dear Sushil,
Thank you,
That 20 inspection items means 20 areas that we will check on products, it could on certain parts of products, workmanship, operation function .. etc. but, these inspection items and defects that we found is not equal to the cause of the defects. if the "Opportunity" means opportunity to cause defects ? We are not sure hot to define it ? the opportunity of defects could come from material, machine, mold, man, methods .....etc.
Thanks for your further explaination.
Bill

[rohinik1980]

Can you please let me know the final answer for the case provided...

Thanks in advance.

Rohini.