WELCOMETO

MSA

TRAINING PROGRAM

OBJECTIVE To provide Basic concept of measurement system Detail application methodology of all

statistical studies for variable and attribute data

Methods to meet QS9000 & ISO/TS-16949 requirements

IntroductionUses of measurement data are Decision to adjust a manufacturing process Determine the significant relationship

between two or more variables using statistical studies

The result of analytical studies is depends upon the Quality of data produced by measurement system

Why MSA required?

Defect prevention

Prediction

Statistics

Data

Inspection

SPC

MSA is mandatory prior to SPC

PURPOSE OF MSA Quantify Variation present in the

Measurement system Compare the Consistency of

inspectors Provide methods for Validation of

Measurement System

Measurement Systems Process to assign a number or decision to a characteristic Process

Appraiser Checking Method Instrument Environment

E.g, OD checking, Concentricity checking

Terminologies

Standard Effective resolution Location variation Width variation Uncertainty

Statistical properties of MS

Ideal Measurement system is the one Which produces always only the

correct measurements Always agree with the standard Statistical data produced over time

Statistical properties of MSProperties of “GOOD” Measurement Systems : Adequate discrimination & Sensitivity System is always under statistical control Variability of the measurement system is

small compared to Manufacturing process variation and Tolerance

Criteria for MS design selection Team members Purpose of use Frequency of use Part specification Sensitivity required Contact? Non contact/ Auto? Manual?………………

Statistical properties of MSClassification Measurement system errors are: Bias Linearity Stability Repeatability Reproducibility

Statistical properties of MSDetermination of these errors will help us to: Criteria to accept new MS Compare one against another To evaluate a suspect gage To evaluate the effectiveness of repair

QS9000 / ISO-TS16949 Requirements

Define a process for implementation of MS Identify all types of measurement systems Cover all systems covered in Control Plan Perform Appropriate statistical study Use MSA ( or Customer approved) Manual Obtain Customer approval for use of

methods other than MSA manual

QS9000 / ISO-TS16949 Requirements

Types of MS is based on L.C Range Construction Parameter Manufacturer

QS9000 / ISO-TS16949 Requirements

Vernier

L.C – 0.02 mm

Range – 0 – 200mm

Construction- Ordinary

Parameter- O.D

Vernier

L.C – 0.02 mm

Range – 0 – 200mm

Construction- Ordinary

Parameter- Width

Is it Same or different type of MS ?

QS9000 / ISO-TS16949 Requirements

Bore Dial Gage

L.C – 0.001 mm

Range – 18-35 mm

Construction- Ordinary

Parameter- Bore

Air gage

L.C – 0.001 mm

Range – ---

Construction- Dial

Parameter- Bore

Discrimination Ability to detect the small changes in

process Traditional rule

1/10th of Tolerance 1/3rd Considering the cost/ criticality

MSA/ SPC requirement 1/10th of Process variation Resolution 1/10th of Process variation

ACCURACY & PRECISION ACCURACY Closeness to reference

or master value Required where two or

more MS measuring a same characteristic

Same parameters are checked at Suppliers end or at Customer end

PRECISION Ability of MS to repeat

the same reading Required where MS is

repeatedly used to assess and adjust the process

In process inspection as per control plan

ACCURACY & PRECISIONACCURACY

Captured by

BIAS LINEARITY STABILITY

PRECISION

Captured by

REPEATABILITY REPRODUCIBILITY

BIAS – WHAT IT IS ?

X bar

Ref. Value BIAS= X bar -

Ref.Value

BIAS - STEPS1. Capture reference value

• Use masters calibrated traceable to standards

• Measure by better instrument than the instrument being measured

• By Layout inspection

2. Measure the part/ master by Min. 10 times

BIAS - STEPS3. Calculate BIAS for individual reading &

draw histogram

4. Calculate , bias, t limits

APPENDIX C t distribution table

ACCEPTANCE CRITERIA

Zero must lie between t Limits of Bias distribution or

Bias should be within acceptable gage error as defined in Calibration Proc.

BIAS – VARIOUS CASES

X bar

Ref. Value

Ref. Value

BIAS – VARIOUS CASES

X bar

Ref. Value

Ref. Value

CAUSE OF LARGE GAGE BIAS

• Error in Master

• Instrument

- Worn

- Made to wrong dimension

- Measuring wrong characteristic

- Improper use by operator

- Improper calibration

APPLICABILITY OF GAGE BIAS• Not a Problem like R&R

• Required where Accuracy to be captured

• Being Carried out as part of Calibration

• Applicable for Gages designed by the Organization

LINEARITY Difference in Bias over the Operating range of the Gage

- ve Bias+ve Bias

X bar X bar

Linearity – Steps 1. Collect 5 parts / masters over the operating range of the gage through process variation

2. Capture reference value for the 5 parts3. Measure at least 12 times in a random manner to cover all 5 parts

4. Measure at least 12 times in a random manner to cover all 5 parts

Linearity – Steps 5. Calculate Average, BIAS and enter the data in a Spread sheet

6. Draw Best fit line for the average, Lower limit and Higher limit of Bias

Linearity – Acceptance criteriaZERO LINE MUST BE CONTAINED WITHIN THE TWO LIMIT LINES OR WITHIN ACC.CRITERIA OF CAL ERROR

0

+ VE

- VE

Upper t limits

Lower t limits

Is this MS acceptable ?

LINEARITY - CASES

0 0

Causes for Gage Linearity•Error in Master

•Instrument

-Worn

-Made to wrong dimension

-Measuring wrong characteristic

-Improper use by operator

-Improper calibration

Applicability of Gage Linearity• To Capture Accuracy over the operating range to assure its suitability of gage for the entire process variation

• Required for Special gages designed by the Organization

• Can be performed as part of Calibration

Stability study – What?Variation of Bias w.r.t time when measured over a Same Master

T 1

T 2

T 3

Stability – How?No.of Samples/ Masters

1 or 3 at Minimum, Mid and Higher Specification limits

Subgroup Size 1 or 3 times over a period in the Morning, Noon and Evening

Frequency Daily,Weekly, Monthly based on the stability assessment of instrument

Charts One chart for each sample, X-MR , or X bar& R or X bar & S

Stability – Acceptance criteria• No out of Control conditions in Control charts with careful interpretation

• No drift

• No trend

• Zero must lie within two limits of bias variation

Stability – Applicability• To compare two or more measurement

systems measuring a same characteristic

e.g Bore dial gage & Air gage

• To establish or evaluate the Calibration Frequency

Constitution of total variation Total variation

Manufacturing process variation Part to part variation Within part variation

Measurement system variation Appraiser variation Equipment variation Appraiser part interaction

Methods to capture variationElements of Variation

Range Method

X bar & R Method

ANOVA Method

TV

PV

WIV

AV

EV

App & part interaction

Repeatability & ReproducibilityRepeatability

• One Appraiser

• One Equipment

• Same part

• Several trials

This Variation is represented by Equipment

Reproducibility

• Same equipment

•Same Parts

•Several trials

•Different AppraiserThis Variation is represented by Appraiser

Range method

No.of Samples 5 nos. gives 80 % chance of detecting a wrong MS.

10 nos gives 90% chance

No.of Appraisers Min. 2

Formula Sigma = R bar / d2*

Range method - ExerciseAppraiser

A1. 15.032. 15.043. 15.024. 15.055. 15.02

Appraiser B

15.0515.0415.0315.0515.02

Range

0.02

0.00

0.01

0.00

0.00

Tol = 0.05, TV(SPC)= 0.120

Range method - Exercise

Average R = 0.006

Std.deviation = 0.006 / 1.128 = 0.0053

where n=2 d2 is1.128, n=3 d2 is 1.693R&R ( 1 sigma) = 0.0053

% R&RTV = (0.0053)/ (0.120/6) * 100 = 26.5

Interpretation = MS IS NOT ACCEPTABLE

% R&RTOL = (0.0053)/ ( 0.050/6) * 100= 66.5

Range method - Exercise

COMPARE AGAINST TOLERANCE WHEN

• TV IS MORE THAN TOLERANCE

• WHERE SPC IS NOT IMPLEMENTED

COMPARE AGAINST TOTAL VARIATION WHEN

• TV IS LESS THAN TOLERANCE

• WHERE SPC IS IMPLEMENTED

Range method – Acceptance criteria

% R&R < 10 % OF TOL OR TV

% R&R 10 – 30 % OF TOL OR TV ACCEPTABLE SUBJECT TO ANALYSIS AND JUSTIFICATION W.R.T COST OF REPAIR AND CRITICALITY

Range method – Applicability

Being the Short study this can be used for Periodic verification of R&R to detect any changes rather than average range method

Being the short study it is suitable for studying MS where it is time consuming to measure one measurement e.g Concentricity, R/O

Average & Range MethodNo.of Samples 10 nos. Randomly selected

representing actual process variation

No.of Appraisers 3 From personnel actually performing on a day to day operation

No.of trials Min 2 . Preferably 3

Average & Range Method- steps for conducting study

1. Identify the parts from 1 – 10

2. Mark the Place where to check to eliminate Within part variation

3. Communicate the purpose of the study to all appraisers

4. Conduct the study in a Random manner covering all parts for required no.of trials through all appraisers 5. Monitor all appraisers are following the same method

Average & Range Method- steps for conducting study

6. Record the observations in a manner which is not seen by the appraisers – FORMAT-7. If any abnormal readings are observed ask the appraiser to repeat the reading

8. Maintain the samples till the completion of analysis

10. Calculate EV,AV,PV & TV and it Percentage against TOL or TV and ndc

9. Draw R chart and X bar chart and interpret

X bar & R chart Method – Acceptance criteria

% R&R < 10 % OF TOL OR TV

% R&R 10 – 30 % OF TOL OR TV ACCEPTABLE SUBJECT TO ANALYSIS AND JUSTIFICATION W.R.T COST OF REPAIR AND CRITICALITYNo. of distinct data categories

ndc > 5 where SPC is used

ndc >2 where no SPC is used

R chart interpretationCONDITION

One or more than one point of one appraiser out of UCL R

One or more than one point of all appraisers out of UCL R

In one part all appraisers points are out of UCL R

INTERPRETATION His method is

different from others

Measurement System is sensitive to appraisers skill

Part is deformed or Damaged

X chart interpretationCONDITION

More than 50 % of readings are out of control limits

INTERPRETATION

Measurement system is adequate enough to capture process variation

Causes for R&RWhen repeatability is large compared to

reproducibility

     Instrument needs maintenance 

     Redesign gage for more rigidity 

     Improve clamping or location of gauging

Excessive within – part variation

( Conduct R & R with within part variation )

Causes for R&RWhen reproducibility is large compared to

repeatability

   Appraisers need better gage use training 

   Need better operational definition 

Incremental divisions on instrument are not readable 

Need fixture to provide consistency in gage use.

X bar & R method - Applicability• To capture Precision, Mandatory before SPC study

• Measurement Systems which are used repeatedly on line to control the process based on the measurement data

• Where individual readings are affected by the precision of the instrument

• Applicable for all MS used in In process where the MS can be repeated

ATTRIBUTE MEASUREMENT

• COMPARES EACH PART TO A SPECIFIC SET OF LIMITS AND ACCEPTS THE PART IF THE LIMITS ARE SATISFIED

• IS DESIGNED TO ACCEPT/REJECT A SET OF MASTER PARTS

• CANNOT INDICATE HOW GOOD OR HOW BAD A PART IS,ONLY WHETHER THE PART IS ACCEPTED OR REJECTED (PASS/FAIL)

• VISUAL STANDARDS MAY RESULT IN 5 TO 7 DISTINCT

DATA CATEGORIES. MSA MANUAL DOES NOT PRESCRIBE ANY METHOD OF EVALUATION OF THE SAME

• GPC METHOD IS MOST APPROPRIATE ANALYSIS• RISK ANALYSIS METHOD IS CUMBERSOME, BUT IT IS PREFERRED BY SOME CUSTOMERS (Eg, FORD)

Gage performance curve method

LSL USL

I II II IIII

HIGH RISK AREA

GPC KEY INSTRUCTIONS Select the gage to be studied Calibrate the gage to know the actual size of the

gage Understand the distribution and location of the

process Decide the on which side of specifications

samples to be taken and the measurement method Select samples (8) and repeat minimum 20 times

on a random manner and count no.of accepts ( a )

GPC KEY INSTRUCTIONS Select Minimum 8 samples out of that One sample on lower than specification, no.of

accepts a = 0 One sample on higher specification, no of accepts

a = 20 Six parts on the gray area where, a is more than

or equal to 1 and less than or equal to 19 Select sample repeat the study till we meet the

above criteria

GPC KEY INSTRUCTIONS Calculate Probabilities of acceptance using

formulae Plot Probabilities of acceptance as % in

normal probability paper Calculate Bias & Repeatability Conclude the decision on the acceptability

of gage

RISK ASSESSMENT – Key steps Take 50 parts representing entire process

variation having bad, marginally bad, good & marginally good parts

Mark as 1 to 50 Select 3 appraisers Conduct study in a random manner and

record the decisions, 1 as OK and 0 as Not ok

RISK ASSESSMENT – Key steps Get the reference value for all the 50 parts

using layout inspection/ variable instrument and decide its status as 0 or 1

Compare each trial of each inspector with the another inspector for their decision

Complete the cross tabulation table Calculate Kappa for

A Vs B, A vs. C , B Vs C A vs. Ref, B Vs Ref., C vs. Ref.

Risk analysis – Acceptance criteriaDecision Effectiveness

Acceptable for the appraiser

More than 90 %

Marginally acceptable for the appraiser

More than 80%

Unacceptable for the appraiser – Need improvement

Less than 80 %

MSA TRAINING

ANY QUESTIONS ?

Thank YouThank You