copyright @ csir 2005 cmm audit programme - results and lessons learnt speaker : f. j. van der walt...

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CMM AUDIT PROGRAMME -RESULTS AND LESSONS

LEARNT

Speaker : F. J. van der WaltE-mail: [email protected]

Tel.: (012) 841- 4799

07 September 2005


3D Coordinate Measuring Machine (CMM)

DEA Global Image CMM


Why a CMMaudit programme ?

1. To identify/analyse CMM capabilities.

2. To establish measurement traceability for CMM measurements.

3. Assess the influence of environmental conditions on CMM measurements.

Scientific Research Council Act (Act No 46 of 1988, as amended by Act 71/1990)


Audit Part

Material = 7075-T6

CTE = 23,6 x 10-6 K-1


Top view

A

A

( 6 H O L E S E Q U A L L Y S P A C E D )

0.010 B

0.010

X+

Y+


Section A - A

0.015

Z+

X+


Evaluation of Measurements

• All the measurements from the participating laboratories were recorded and evaluated. It was found that:

a. Length measurements and Diameter measurements are acceptable.

b. Roundness, angle, and concentricity measurements are cause for concern.


Length Measurement

Distance (250 mm) (Ref 7.4.8)

250.034250.033

250.034

250.020

250.034

250.024

250.031

250.027

250.040

250.034

250.000

250.010

250.020

250.030

250.040

250.050

NML LB 01 LAB 02 NML LAB 03 LAB 04 NML LAB 05 (1) LAB 05 (2) LAB 05 (3) LAB 06 NML

Dis

tan

ce M

easu

red

(m

m)

0,031 131,381


Roundness Measurement

Roundness of Bore (Ref 7.4.4)

0.011

0.031

0.005

0.011

0.004

0.03

0.011

0.033

0.014

0.020

0.0100.011

0.0035

0.0085

0.0135

0.0185

0.0235

0.0285

0.0335

NML LB 01 LAB 02 NML LAB 03 LAB 04 NML LAB 05 (1) LAB 05 (2) LAB 05 (3) LAB 06 NML

Ro

un

dn

ess

Mea

sure

d (

mm

)


Error Sources

1. Spatial errors are errors in the measured position of a point on the surface of the workpiece, and are caused by:

a. guideways, scales, probing system, etc.

b. environmental conditions. c. probing strategy. d. workpiece characteristics.


CMM Errors

Lxx

Lyy Positional errors (3)

Lzz

Lxy, Lxz

Lyx, Lyz Linearity errors (6)

Lzx, Lzy


CMM Errors (continued)

Rxx, Rxy, Rxz

Ryx, Ryy, Ryz

Rzx, Rzy, Rzz

9 Rotation Errors


CMM Errors (continued)

Qxy

Qyz

Qzx

Squareness errors (3)


Error Sources (continued)

2. Computation errors are errors in the estimated dimensions and form deviations for the measured points on the surface of the workpiece, caused by:

a. software used to estimate the geometry.

b. the precision of the computer used.

c. the number and position of the measured points.

d. the extent to which the geometry departs from the

ideal geometrical form.


CMMCMM

ComputerComputer

TransformationTransformation

CorrectioCorrectionn

ComputatioComputationn

EvaluationEvaluation

ControllingControlling

Tasks performed by the computer of the CMM


Causes ofMeasurement Errors

• Probe system used.• Parameter settings.• Environmental conditions.• CMM errors.• Metrologist/operator skills.


• The measured value for a distance of 5,0 mm was reported as 12,207 mm

• The measured value for the overall length of 250 mm

was reported as 131,381 mm

• The measured value for the overall length of 250 mm was reported as 0,031 mm.

Operator Skills

NEGLIGENCE, CARELESSNESS, ………..???


Uncertainty ofCMM Measurements

• Machine Specification: ± (1,9 + 3L ) µm

• Very few participants reported the uncertainty of measurement or even their machine spec!

• Can not perform conformance testing without machine spec or estimated uncertainty.

MAJOR CONCERN !!


Conclusion

• Length and diameter measurements are acceptable.• Inconsistency of roundness, angle and concentricity

measurements.• CMM operators must know/estimate the uncertainty

of measurement.• Need for CMM metrologist/operator training.• Participants with poor results should implement

corrective actions.• Participate again.


Upcoming CMM Course

Presenter: Mr. Kostadin Doytchinov

NRC Canada

Venue: Pretoria and Port Elizabeth

Date: November 2005


Thank you for attending this presentation.

Have a nice day.

copyright @ csir 2005 cmm audit programme - results and lessons learnt speaker : f. j. van der walt...

Documents

lzy slide

roundness measurement

computation errors

z x slide

rotation errors

spatial errors

cmm capabilities

causes of measurement