MSA and Process Capability Flashcards Preview

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

Measurement Systems Analysis MSA

A

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

2
Q

MSA involves

A
  • 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
Q

MSA elements

A
MS - accuracy
                       . linearity
                       . Bias
                       . Stability
      - Precision
                       . repeatability
                       . reproducibility
                            , operator 
                         part interaction
                            , operator
4
Q

accuracy in terms of MSA

A

the difference between the measurement and the parts actual value

5
Q

precision in terms of MSA

A

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

6
Q

True value

A

theoretically correct value

7
Q

bias

A

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

8
Q

stability

A

stable processes are those that are free from special cause variation

9
Q

Linearity

A

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

10
Q

repeatability

A

variability inherent in the measurement system under constant conditions

11
Q

reproducibility

A

variability among measurement made under different conditions

12
Q

source of poor measurement

A

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

13
Q

specification limits

A
  • derived from customer requirements

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

14
Q

Process Capability

A

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
Q

process capability measures

A

Cp index: measures the process potential

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

16
Q

Cp equation

A

(USL-LSL)/(6*deviation)

17
Q

corrective approaches to increase process potential

A

increase the specification limits

reduce the process spread

18
Q

limitations of process capability

A

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
Q

Cpk, process capability index equation

A

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

20
Q

Desired Cpk

A

> 1

21
Q

Reasons for sampling

A
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
Q

Samping approaches

A

random sampling
systematic sampling
subgroup sampling
stratified sampling