Measurement Systems Analysis

with

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The House of Qualitypresents

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This demonstration uses Data from The AIAG MSA Manual June 2010At tolerance and Process Capability is used to simulate a capable production process (Cp= >1.33) (Tol +/- 5 & SD 1.15)

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Repeatability Reproducibility R & R Discrimination Part Variation Total Variation

more > Analysis.more > Competencemore > Control more > Compliance

< less Input, < less Training, < less Confusion.< less Cost

R&R INNOVATOR LitePrinciples of MSA Innovator

Measurement System Uncertainty is the combined effect of all short and long term Causes of

Measurement Uncertainty

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Measurement System Uncertainty is quantified by various types of measurement variation

Principles of MSA Innovator

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Getting Started

The Study Index accesses

Two demonstration Studies one of which uses the information in the AIAG MSA Reference Manual

These are locked and cannot be edited.

History AchieveUnlimited Historical Studies can be achieved (Logistics Report).Once archived they cannot be edited and only the Logistics Report can be

viewed.

New Studies are also raised from the Indexup to 10 Live Studies can be raised, edited and saved as required by the user.

Note: Up to 10 study's can be active (in progress) at one time.Unlimited study's can be archived.

Note: See slide referring to Archiving completed studies for further information.

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Getting Started1. Open a New Study

2. Complete the DATA ENTRY

Lock trials and the Data Entry fields will automatically be locked.

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One, Two or Three Appraisers can be evaluated.Note: If only One is selected, Reproducibility cannot be evaluated.

One, Two or Three Trials can be conducted.Note: If only One is selected, Repeatability cannot be evaluated.

5 – 10 Samples can be utilised.Note: Min 5 to ensure statistical validity

1 – 5.15 or 6 SD can be utilised.Note: in conjunction with Maximum Acceptable Error.

Required if measurements used for Process Control.Note: Industry Norm requires Cp 1.67 for Short Term Control.

Parameters to be applied for the Study

The Responsible Person must decide on what Logistical & Statistical Parameters will be applied during the Study.

Note 2 : -A basic understanding of Statistical Methodology is required to establish procedures for the selection of statistical parameters.

Industry Norm suggests Maximum Acceptable Error. 10% max for Critical Values. 30% for non-critical Values

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The Study should encompass a typical minimum Sample Data Range that would normally be found in 6 SD of a Process with a long term capability of Cp=>1.33. Data representing >80% of expected process variation is an industry norm.

Note 1:- The sequence or timing of Production from which samples are extracted are not required in consecutive sequence such as used in a Process Capability Study.

Note 2:- R&R uses the variation in the Process Samples to generate a Part Variation value, however this should NOT be used as a measure of Process Capability.

Part Variation can be used to evaluate if the Samples represent sufficient of the Process Tolerance / Spread to ensure the Study is valid throughout the potential Measurement

Range.

5 – 10 Samples can be utilised.Note: Min 5 to ensure statistical validity

Sample CollectionFull Study

Ideally the Sample Values should be distributed evenly through the Tolerance Band.

In practice this is not always easy as it infers preliminary measurement must be made

in order to select the Products with the appropriate measurements.

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Appraiser - Data Collection

5 – 10 Samples will have been collected to be used for the Study.

Decisions will have been made as to How many Appraisers will be used & how many Trials will be used

Procedure

Print data Collection Sheet.Number the Samples discreetly 1 - ??

Appraiser 1 measure samples in random order & record.

Subsequent Appraisers independently measure samples & record.

Enter Appraiser Details in Data Entry Sheet

Appraiser 1 & Subsequent Appraisersrepeat and record the sample measurements,dependent on the number of Trials required.

using the equipment and method

nominated in the Product Control Plan.

See Data collection W.I for collection and recording

method.

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Appraiser - Data Entry

Enter the Appraiser Datainto the applicable Fields.

Note: this Data can be copied and pasted from any other Excel Based Data sheet.

Paste Special MUST be used in order to avoid changing the Formatting.If a mistake is made Copy a Blank set of cells from another study then repeat the Paste – using Paste Special

Once this Data is entered - that’s it – All the Test Results will appear on the Logistics Report.

If the Results are not acceptable – or suspect-Numerous Analysis Data is available to analyse the potential causes

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Repeatability = Equipment Variation (EV)

Representing the SPREAD of the variation (Precision)

Principles of MSA Innovator

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RepeatabilityOnce Data Has been collected…

1 Enter into Data Entry (Appraiser A)

Repeatability analysis can be established using One Appraiser only.

This is useful for measurements

that are NOT influenced by the Appraiser.

i.e. “hands off” measurements.

On Hands Off measurements there is NO point in conducting Reproducibility Tests. Reproducibility assesses the error BETWEEN different Appraisers and on Hands Off measurement there IS NO between Appraiser Error .

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Repeatability - statistical test - using Range1 The Range of the 2/3 trials of each Appraiser is

calculated.

4 Appraiser Range Chart is constructed

2 Average of the Ranges is calculated

3 Upper Control Limit is calculated

Note: MSA Innovator will automatically identify points exceeding the Range upper control limit.

This should be investigated and corrected prior to continuing with the analysis.

Appraiser Range/s that exceed the control limit or a run of >5 consecutive readings indicates “special cause variation”.

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Repeatability – calculation – 3 Appraisers1. Calculate the Average Range of each Appraiser.

2. Using a “factor” to estimate Std Dev.

Multiply the Rbar by the appropriate “factor”to establish the Repeatability.

Note i ..Repeatability is referred to as Equipment Variation (EV).Because the common factor in the analysis is the Equipmenti.e. the effect of individual Appraisers is nullified with the Rbar being the average of all Appraisers

Note ii ..An industry Norm for maximum EV % is <10% for Critical and <30% for standard tolerances

Note iii ..AIAG use 1SD and then state Spec or Process SD should be used as Appropriate.HoQ Innovator reports directly on the parameters of Product Spec & Process Capability

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Repeatability (ONE Appraiser)

Repeatability analysis can be established using One Appraiser only.

This is useful for measurements that are NOT influenced by the Appraiser. i.e. “hands off” measurements. Note: Where there is no Appraiser influence “Reproducibility” results serve no purpose.

This example indicates “no assignable variation” in the ranges of Appraiser A.

If Assignable Variation existsit invalidates the repeatability results and should be investigated and corrected.

Upper Range Control Limit

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Reproducibility = Appraiser Variation (AV)

Representing the Location of the variation (Accuracy)

Principles of MSA Innovator

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Reproducibility - calculation

1 Calculate the Average reading of each Appraiser.

2 Calculate the Range of the average readings of each

Appraiser.3. Using a “factor” to estimate Std Dev.

and using the formulae below calculate the Reproducibility

Note: An industry Norm for maximum EV % is <10% for Critical tolerancesAnd

<30% for standard tolerances

Note: Reproducibility is referred to as Appraiser Variation (AV) … .. because the common factor in the analysis is the Appraiseri.e. the effect of the instrument is nullified using the Average Range of all Appraisers.

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Repeatability (EV) & Reproducibility (AV).

Representing the combination of Spread & Location variation.

Principles of MSA Innovator

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Note: An industry Norm for maximum R&R % is <10% for Critical and <30% for standard tolerances

Repeatability (EV) & Reproducibility (AV)

At first glance it may seem obvious that Repeatability & Reproducibility would be a simple equation of adding the two together.

This requirement OVERRIDES the individual maximum values given for Reproducibility & Repeatability

Based on the theory of Statistical Tolerancingit is possible

to predictably merge the two distributions.(manipulating the data with Square and Square Root)

Whilst there is statistical theory that 1 + 1 does not equal 2, a more understandable theory is that the possibility of making an Equipment Error at the same time, as making an Appraiser error is statistically remote

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Repeatability, Reproducibility & R&R - summary

The Acceptable Error % is designated according to the criticality of the Product Characteristic.

The Std Dev is taken from the historical Process Capability.

The Tolerance is according to the product / design Specification.

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Discrimination & ResolutionResolution should be 10%> of tolerance.

Discrimination = number of distinct categories (ndc)and should be 5+ when this formulae is applied.

To ensure that Data used in the study is valid

On anXbar Chart >50%; should be “out of control”

Factor of 1.41 is based on a 95% confidence level

The theory indicates that Data Points “in-control” are due to Measurement Error (noise) and those “out of control” are due to Process Variation. i.e. The Process Variation should contribute > 50% to the overall Variation.

To ensure that the Measurement System is adequate for Product evaluation.

To ensure that the Measurement System is adequate for Process Control (SPC)

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Part Variation & Total Variation

Part Variation applies to

the variation in the samples used in the Measurement Analysis.based on calculating the Std Variation of the samples.

The K3 Factor depends on the Degree of Confidence required, ( 5.15 or 6 sigma ) and the, number of samples, used in the analysis.

Part Variation of the samples used should be >80% of the Tolerance or Process Capability which will ensure that the full potential spread of measurements are analysed.

Because of the small sample size (5-10) and the fact that the samples were “selected” the Part Variation of the samples serves little other value.

If the samples were selected from normal production, a figure of +100% would indicate that the process is not capable ( a low Cp value).

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Part Variation (based on 10 samples) & Total Variation

Total Variation considers the Part (sample) Variation + The Measurement Error.previously discussed as of little value other than to ensure that the study covered the expected measurement range.

In this examplePart Variation inthe 10 samples used =66% of Product Tolerance.96% of Process Variation (samples)

Because the variation in the 10 samples--(based on SD estimate) is 6.63 mm Total Variation (Part Vr + Measurement Error) =

69% of Product Tolerance100% of Process Variation (samples)

In this exampleThe R&R has acceptable influence if used to assess Product Acceptance.

Despite a R&R value of 1.8 mm or 18% of the Tolerance measurements used to evaluate if product is in or out of tolerance will have acceptable effective measurement error(providing the process is centred on the nominal value)

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Part Variation (based on historical Process Capability – Cp) & Total Variation

(True) Total Variation considers the Part (Historical Cp) Variation + The Measurement Error.

Historical Cp is calculated from (6x) the known Process SD (standard deviation)divided by the Tolerance Band (10)

In this examplePart Variation inthe 10 samples used =66% of Product Tolerance.96% of Process Variation (samples)

Because the variation in the 10 samples--(based on SD estimate) is 6.63 mm Total Variation (Part Vr + Measurement Error) =69% of Product Tolerance100% of Process Variation (samples)

True Total Variation(with a Cp of 1.449 (SD 1.15) =

71% of Product Tolerance103% of Process Variation (historical SD)

In this exampleThe R&R has a marginal influence if used to assess Process Control.

Despite a R&R value of 1.8 mm or 18% of the Tolerance measurements used to evaluate if process is in or out of statistical control will have marginal effective measurement error(providing the process is centred on the nominal value)

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R&R Lite has the facility to have up to 10 Studies “live” at any one time.Thereafter the Logistics Report of unlimited studies can be filed in a History Archive.

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R&R Lite has the facility call on pre-determined databases – or – enter details, on the fly, during the study.