MSA and Process Capability Flashcards Preview

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Flashcards in MSA and Process Capability Deck (22):
1

Measurement Systems Analysis MSA

analysis to determine what variation is from the actual process or the measurement system in place

2

MSA involves

-selecting the correct measurement and approach
-assessing the measuring device
-assessing procedures and people conducting measurements
-assessing any measurements interacions
-calculating the measurement uncertainty of individual measurement devices and/or measurement systems

3

MSA elements

MS - accuracy
. linearity
. Bias
. Stability
- Precision
. repeatability
. reproducibility
, operator
part interaction
, operator

4

accuracy in terms of MSA

the difference between the measurement and the parts actual value

5

precision in terms of MSA

the variation you see when you measure the same part repeatedly with the same gauge

6

True value

theoretically correct value

7

bias

difference between the average value of all measurements of a sample and the true value for that sample

8

stability

stable processes are those that are free from special cause variation

9

Linearity

a measure of any change in accuracy or precision over range of instrument capability

10

repeatability

variability inherent in the measurement system under constant conditions

11

reproducibility

variability among measurement made under different conditions

12

source of poor measurement

poor/nonexistent operational definitions
lack of understanding of the definitions
difficult measures
poor sampling

13

specification limits

-derived from customer requirements
-allowable range of product deviation from the customers requirements that he/she is willing to accept

14

Process Capability

Ability of a process to meet its specifications
- measures the performance of a process
- process must be stable in order to calculate process capability

15

process capability measures

Cp index: measures the process potential
Cpk index: measures the process capability but take into account the of off-centredness of a process

16

Cp equation

(USL-LSL)/(6*deviation)

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corrective approaches to increase process potential

increase the specification limits

reduce the process spread

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limitations of process capability

does not incorporate the process mean or process centring
-process can be capable and still not meet the customer needs
Cpk takes process centring and variation

19

Cpk, process capability index equation

Cpk = min [ ((USL-u)/3sigma), ((u-LSL)/3 sigma)]

20

Desired Cpk

>1

21

Reasons for sampling

to save time, money and effort
-we can draw relatively accurate conclusions about the population from sample (if sample is representative)
--appropriate sampling
method
--appropriate sample size
-impossible to examine all population
--too large
--sampling is destructive
--£££

22

Samping approaches

random sampling
systematic sampling
subgroup sampling
stratified sampling