‘Microparts’ Interest Group Workshop 28. to 29. October 2009, NPL, Teddington Ulrich Neuschaefer-Rube, Markus Bartscher, Marko Neukamm, Frank Härtig PTB Physikalisch-Technische Bundesanstalt, Braunschweig und Berlin, Germany Karsten Ehrig, Andreas Staude, Jürgen Goebbels BAM Bundesanstalt für Materialforschung und –prüfung Berlin, Germany Dimensional Measurements with Micro- CT -Test Procedures and Applications 20 mm 10 mm 1 mm 2 mm
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Ulrich Neuschaefer-Rube, Markus Bartscher,
Marko Neukamm, Frank Härtig
PTB Physikalisch-Technische Bundesanstalt,
Braunschweig und Berlin, Germany
Karsten Ehrig, Andreas Staude, Jürgen Goebbels
BAM Bundesanstalt für
Materialforschung
und –prüfung Berlin, Germany
Dimensional Measurements
with Micro- CT
-Test Procedures and Applications20 mm
10 mm
1 mm
2 mm
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
1. Introduction
2. Test procedures
and error correction
3. Application examples
4. Conclusions
Content
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Set-up of industrial computed tomography (CT)Measurement object on rotary table between X-ray source and X-ray detector
Micro-CT: Cone-beam and area detector
Scale factor dependent on the distances between X-ray source, measurement object
and detector
Introduction
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
geometry fittingwall thickness
analysis
result report
measurement object
threshold process
CT measurement
voxel data
surface datareference data
(e.g. CAD model)
actual/nominalcomparison
Introduction
Flow chart of typicaldimensional CTmeasurement processes
�Each step contributes
to the measurementuncertainty of CT
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Introduction
Structural resolution depends on:Size of X-ray focus
Minimal distance between X-ray source and measurement object
Second:Measure the flanks with gear specific software Gear Pro.Orientation of the x-axes is unknown!
Tooth flanks
Define coord. system
Define Zeiss F25 CMM workpiece
coordinate system
Best fit alignment with restricteddegrees of freedom
Probe radius correction
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Example 1 – Micro spur-gear study
Deviation of CT measurement (data-set 1 of 6)
Distribution of deviations without strong outliers
me
asure
me
nt err
or
in m
m
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Example 1 – Micro spur-gear study
Histogram of all 6 assessed measurements
Analysis of deviations
95% of all observed absolute deviations are less 0.0037 mm
Due to the statistics of 6 measurements (correction with t-distribution) a value of 0.0048 mm can be attributed as a first measureof the uncertainty of measurement
0
500
1000
1500
2000
2500
3000
3500
-0.006 -0.004 -0.002 0 0.002 0.004 0.006
measurement error in mm
freq
uen
cy
0
500
1000
1500
2000
2500
3000
0 0.001 0.002 0.003 0.004 0.005 0.006
absolute value of measurement error in mm
freq
uen
cy
0%
20%
40%
60%
80%
100%
cu
mu
lati
ve p
erc
en
tag
efrequency
cumulative %
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Example 2 – Internal micro gear study
No. of teeth 40
Normal module mn 0.12 mm
Pressure angle α0 20°
Addendum modification coefficient x
-0.79
Base circle radius rb 2.615 mm
Helix angle β0 0°
Tip circle diameter da 4.8 mm
Root circle diameter df 5.23 mm
Internal micro gear
made from steel
lengthca. 11 mm
� Reference measurement with micro CMM
Werth VideoCheck HA 400 with tactile-optical probe
Probe diameter: 61 µm
Modus of operation: single point probing
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Reproducibility test of CMM measurement (7 measurements)Result of gear analysis: Profile deviations (example: tooth 10, left flank, z = -0.4 mm)
Reproducibility better than 1 µm in analysis interval
Example 2 – Internal micro gear study
-0.005
-0.0025
0
0.0025
0.005
0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3
length of roll in mm
pro
file
dev
iati
on
in
mm
tooth tip tooth rootanalysis interval
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Synchrotron CT measurement
at BESSY BAMLine
Report
Object
Threshold
Voxel data
Surface
Comparison
Reconstruction
Segmented slice data
Gear analysis
CMM meas.
Gear analysis
Example 2 – Internal micro gear study
Energy: 60 keV
Voxel size: (2.2 µm)3
Detector: GdOS scintillator,
CCD-camera
(3209 x 801 pixel)
Exposure (each): 3 s
No. of angles: 2500 (0°-180°)
Projection
Point data
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
Comparison of CT and CMM dataResult of gear analysis: Profile deviations (example: tooth 10, left flank)
Deviations < 2 µm in analysis interval
Example 2 – Internal micro gear study
-0.005
0
0.005
0.01
0.015
0.9 0.95 1 1.05 1.1 1.15 1.2 1.25 1.3
length of roll in mm
pro
file
de
via
tio
n i
n m
m
CT, z = -0.4 mm
CT, z = -0.6 mm
CMM, z = -0.4 mm
CMM, z = -0.6 mm
tooth tip tooth rootanalysis interval
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington
� Complete dimensional measurements of microparts possible with micro-CT
� Smallest voxel size without optics approx 0.5 µm
� Successful application of material standards
� Standardization of dimensional CT:
- VDI/VDE 2617 Sheet 13 = VDI/VDE 2630 Sheet 1.3
available as Draft
- Work item CT in ISO TC 213
� Achieving traceability of CT measurements
is still a challenge
First results: measurement uncertainties of several
micrometer for small complex objects
� Vision in future:
CT is a fully accepted measurement technique
which is used coequal to conventional coordinate metrology
Conclusions
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‘Microparts’ Interest Group Workshop28. to 29. October 2009, NPL, Teddington