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Influence of Electron Beam
Alignment on Dimensional
Metrology by Computed
Tomography
Gabriel PROBST1, Michele PAVAN1,2,Jitendra RATHORE3, Tom CRAEGHS2,Jean-Pierre KRUTH1, SimoneCARMIGNATO3, Wim DEWULF1
1Department of Mechanical Engineering, KU Leuven, Belgium,Leuven2Materialise NV, Belgium, Leuven3Department of Engineering and Management, University ofPadova, Italy
Digital Industrial Radiology and Computed Tomography (DIR 2015) 22-25 June 2015, Belgium, Ghent - www.ndt.net/app.DIR2015
• Electron beam alignment
o Case study 1
o Case study 2
o Case study 3
• Conclusions
2
Outline
• Schematic of the tube
o Passing current through the X-Y coils steers the electron beam
3
Electron beam alignment
• Sinusoidal current signal
4
Electron beam alignment
Target
Electron beam
5
Electron beam alignment
120 kV ~ 160 kV80 kV ~ 120 kV 160 kV ~ 200 kV 200 kV ~ 225 kV
• Position of the focal spot on the target changes when kV ischanged (center of bouncing changing in the projections)
6
Electron beam alignment
• Objectives
o To characterize the influence of the electron beamalignment of dimensional metrology and quality controlby Computed Tomography
o To develop an intuitive tool which enables the user to
perform the alignment of the electron beam in a fast andaccurate way
• Measurement procedure
o Align the Electron Beam at the alignment conditions
• 220 kV
o Select the Measurement conditions
• 180 kV
o Perform the shading correction
o Do the measurement
o Align the Electron Beam at the measurement conditions
o Perform the shading correction
o Do the measurement
• Magnifications of 50 and 30 times
7
Case study 1
n times
1º
2º
AC Alignment at 220 kV MC Alignment and
Measurement at 180 kV measurement at 180 kV
8
Case study 1
Mis
alig
nm
en
t in
pix
els
Beam alignment
• Influence of the misalignment
o AC Alignment at 220 kV and measurement at 180 kV
o MC Alignment and measurement at 180 kV
9
Case study 1
2,994
2,998
3,002
3,006
3,010
3,014
3,018
Dia
met
er
(mm
)
EBA – Influence on the diameters
R17 - Calibrated value
R17 AC M50
R17 MC M50
R17 AC M30
R17 MC M30
R18 - Calibrated value
R18 AC M50
R18 MC M50
R18 AC M30
R18 MC M304,096
4,100
4,104
4,108
4,112
4,116
4,120
4,124
4,128
Dis
tanc
e (m
m)
Distance between spheres
Calibrated value
Alignment conditions 50M
Measurement conditions 50M
Alignment conditions 30M
Measurement conditions 30M
• Measurement without any previous alignment:
before after alignment at 70 kV
• 10 mm side cube made of thermoplastic-polyurethane (TPU) produced by Laser Sintering
• Goal: to study the porosity added by thesintering process
10
Case study 2M
isalig
nm
en
t in
pix
els
Mis
alig
nm
en
t in
pix
els
Beam alignment Beam alignment
• Slice of the measured cube
aligned not aligned
11
Case study 2
• Red (bottom) Electron beam aligned
• Black (top) Electron beam NOT aligned
12
Case study 2
Big difference in the number of small
pores measured (?)
• Red (bottom) Electron beam aligned
• Black (top) Electron beam NOT aligned
13
Case study 2
Big difference in
the volume relative
to the smaller
pores measured
Shift of the distribution
towards bigger pore
diameters
• Comparison between the interpolation method and theelectron beam alignment at the measurement conditions:
o Object of study: a polymeric micro injection molded part
• The measurands were the diameter of 4 cylinders (D1, D2, D3and D4) and center-to-center distances (C13: between cylinders1 and 3; C24: between cylinders 2 and 4)
Table 1: Comparison between interpolation and single alignment
14
Case study 3
Settings Unit
Interpolation Voltage80
kV150210
Measurement conditions
Voltage 100 kVCurrent 87 µA
Exposure 2000 ms
• Comparison between interpolation and single alignment
15
Case study 3
-0,005
0,000
0,005
0,010
0,015
0,020
Dev
iatio
n fr
om n
omin
al (
mm
)
Influence at a magnification of 40x
Interpolation Single Alignment
-0,005
0,000
0,005
0,010
0,015
0,020
Dev
iatio
n fr
om n
omin
al (
mm
)
Influence at a magnification of 30x
Interpolation Single Alignment
• The influence of electron beam misalignment ondimensional metrology proves significant at highmagnifications
• The influence of electron beam misalignment on porosity
measurements proves significant at high magnifications
• Interpolation of the electron beam alignment between afew aligned settings seems adequate
16
Conclusions
This project has received funding from the European Union’sSeventh Framework Programme under grant agreement No.607817.
17
Acknowledgments
