Transcript Document

CMM AUDIT PROGRAMME RESULTS AND LESSONS
LEARNT
Speaker : F. J. van der Walt
E-mail: [email protected]
Tel.: (012) 841- 4799
07 September 2005
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3D Coordinate Measuring
Machine (CMM)
DEA Global Image CMM
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Why a CMM
audit 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)
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Audit Part
Material = 7075-T6
-6
CTE = 23,6 x 10
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-1
K
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Top view
X+
A
Y+
0.010
A
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0.010 B
Section A - A
0.015
Z+
X+
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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.
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Length Measurement
Distance (250 m m ) (Ref 7.4.8)
250.050
250.040
250.040
Distance Measured (mm)
250.034
250.033
250.034
250.034
250.034
250.031
250.030
250.027
250.024
250.020
250.020
250.010
0,031
131,381
250.000
NML
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LB 01
LAB 02
2005
NML
LAB 03
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LAB 04
NML
LAB 05 (1)
LAB 05 (2)
LAB 05 (3)
LAB 06
NML
Roundness Measurement
Roundness of Bore (Ref 7.4.4)
0.0335
0.033
0.031
0.03
Roundness Measured (mm)
0.0285
0.0235
0.020
0.0185
0.014
0.0135
0.011
0.011
0.011
0.011
0.010
0.0085
0.005
0.004
0.0035
NML
LB 01
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LAB 02
2005
NML
LAB 03
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LAB 04
NML
LAB 05 (1)
LAB 05 (2)
LAB 05 (3)
LAB 06
NML
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.
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CMM Errors
Lxx
Lyy
Positional errors (3)
Lzz
Lxy, Lxz
Lyx, Lyz
Lzx, Lzy
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Linearity errors (6)
CMM Errors (continued)
Rxx, Rxy, Rxz
Ryx, Ryy, Ryz
Rzx, Rzy, Rzz
9 Rotation Errors
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CMM Errors (continued)
Qxy
Qyz
Qzx
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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.
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Tasks performed by the
computer of the CMM
Correctio
n
Transformation
Controlling
CMM
Computer
Evaluation
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Computation
Causes of
Measurement Errors
•
•
•
•
•
Probe system used.
Parameter settings.
Environmental conditions.
CMM errors.
Metrologist/operator skills.
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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.
NEGLIGENCE, CARELESSNESS,
………..???
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Uncertainty of
CMM 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 !!
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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.
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Upcoming CMM Course
Presenter:
Mr. Kostadin Doytchinov
NRC Canada
Venue:
Pretoria and Port Elizabeth
Date:
November 2005
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Thank you for attending this
presentation.
Have a nice day.
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