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)

17

## corrective approaches to increase process potential

###
increase the specification limits

reduce the process spread

18

## 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

--£££

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