The Advanced Telescope for High-ENergy Astrophysics (ATHENA) will observe “the hot and energetic universe,” which was determined as one of the most urgent scientific topics for a major future space mission by The European Space Agency (ESA). One of its three main components is the optical bench, a monolithic titanium structure that accommodates 678 mirror modules and keeps them accurately aligned. The immense but slender structure in the range of 2.5–3 m diameter at a height of 300 mm proves a challenge to manufacturing. A hybrid robot cell is developed using additive buildup via laser welding, combined with high-performance machining and the state of the art process and metrology monitoring and control. The present work focuses on the shielding of the laser induced melt pool, a key concern when processing titanium. The sensitive metal with unusual low heat conductivity requires a large area of high purity atmosphere to prevent embrittlement. However, the large hybrid system prohibits the use of a sealed enclosure, and therefore, a local shielding system is developed for the challenging case of the ATHENA optical bench’s hollow-chamber design. Since the present thin wall design poses a worst-case scenario in terms of heat dissipation and shielding flow for the shielding system, its effectiveness here can be applied to most other geometries enabling the flexibility for lot size one. The key features of the novel approach are the prevention of turbulence while keeping operation economical despite the large shielding area. The first is achieved by means of an integrated honeycomb screen and the latter by employing a layered flow with a higher velocity outer curtain and an air deflecting coflow. This system was numerically optimized, tested, and effectiveness proven by means of visual inspection, microstructural analysis, and measurement of material properties.

1.
E.
Wille
,
M.
Ayre
,
I.
Ferreira
,
S.
Fransen
,
M. J.
Collon
,
G.
Vacanti
,
N. M.
Barrière
,
B.
Landgraf
,
J.
Sforzini
,
K.
Booysen
,
C.
van Baren
,
K.-H.
Zuknik
,
D.
Della Monica Ferreira
,
S.
Massahi
,
F. E.
Christensen
,
M.
Krumrey
,
V.
Burwitz
,
G.
Pareschi
,
D.
Spiga
,
G.
Valsecchi
,
D.
Vernani
,
P.
Oliver
,
A.
Seidel
,
B.
Shortt
,
M.
Bavdaz
, and
P.
Müller
, “Development of the ATHENA mirror,” in Proceedings of Space Telescopes and Instrumentation 2018: Ultra-violet to Gamma Ray, Austin, TX, 2018, edited by
J.-W. A. d.
Herder
,
S.
Nikzad
, and
K.
Nakazawa
(
SPIE
,
Bellingham
,
WA
,
2018
), p.
32
.
2.
M. R.
Ayre
,
M.
Bavdaz
,
I.
Ferreira
,
E.
Wille
,
D. H.
Lumb
,
M.
Linder
, and
A.
Stefanescu
, “
ATHENA system design and implementation for a next-generation x-ray telescope
,” in
Proceedings of SPIE Optical Engineering + Applications: UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XX, San Diego, CA, 2017
(SPIE, Bellingham, WA,
2017
).
3.
European Space Research and Technology Centre
, Statement of Work: TRP IPC T224-004QT Demonstration of an Additive Manufactured Metallic Optical Bench—TRP T224-004QT Appendix 1 to AO/1-8607/16/NL/LvH: TRP IPC T224-004QT Demonstration of an Additive Manufactured Metallic Optical Bench—TRP T224-004QT Appendix 1 to AO/1-8607/16/NL/LvH [2016 (Date of Issue)].
4.
M.
Peters
and
C.
Leyens
,
Titan und Titanlegierungen
(
Wiley-VCH Verlag GmbH & Co. KGaA
,
Weinheim
,
2002
), p.
528
.
5.
I.
Inagaki
,
Y.
Shirai
,
T.
Takechi
, and
N.
Ariyasu
, “Application and features of titanium for the aerospace industry,” Technical Report (Nippon Steel & Sumitomo Metal, Chiyoda, Japan, 2014).
6.
R. R.
Boyer
, “
An overview on the use of titanium in the aerospace industry
,”
Mater. Sci. Eng. A
213
,
103
114
(
1996
).
7.
M. J.
Donachie
,
Titanium: A Technical Guide
(
ASM International
,
Materials Park
,
OH
,
2000
), p.
381
.
8.
G.
Lütjering
and
J. C.
Williams
,
Titanium
(
Springer-Verlag
,
Berlin, Germany,
2007
), p.
413
.
9.
J. L.
Smialek
,
J. A.
Nesbitt
,
W. J.
Brindley
,
M. P.
Brady
,
J.
Doychak
,
R. M.
Dickerson
, and
D. R.
Hull
, “
Service limitations for oxidation resistant intermetallic compounds
,” in MRS Proceedings Library, Symposium on High-Temperature Ordered Intermetallic Alloys–VI, Boston, MA, 1994 (MRS, Pittsburgh, PA,
1994
), Vol. 364, p. 1273.
10.
B. K.
Vainshtein
,
V. M.
Fridkin
, and
V. L.
Indenbom
,
Modern Crystallography 2: Structure of Crystals
(
Springer
,
Berlin
,
2000
), p.
521
.
11.
R. G.
Jones
,
W.
Ando
, and
J.
Chojnowski
,
Silicon-Containing Polymers: The Science and Technology of Their Synthesis and Applications
(
Springer Netherlands
,
Dordrecht
,
2000
), p.
768
.
12.
J. L.
Murray
and
H. A.
Wriedt
, “
The O-Ti (oxygen-titanium) system
,”
J. Phase Equilib.
8
,
148
165
(
1987
).
13.
B.
Sefer
,
J.
Roa
,
A.
Mateo
,
R.
Pederson
, and
M.-L.
Antti
, “
Evaluation of the bulk and alpha-case layer properties in at Ti-6Al-4V micro-and nano-metric length scale
,” in
Proceedings of the 13th World Conference on Titanium, San Diego, CA, 2016
(TMS, Pittsburgh, PA,
2016
), p.
1619
.
14.
C.
Leyens
and
M.
Peters
,
Titanium and Titanium Alloys: Fundamentals and Applications
(
Wiley-VCH
,
Weinheim
,
2005
), p.
532
.
15.
K.-H.
Richter
, Titan und Titanlegierungen, DGM Deutsche Gesellschaft für Metallkunde e.V, Köln (
2018
).
16.
O.
Untracht
,
Jewelry Concepts and Technology
(
Robert Hale
,
London
,
1987
), p.
864
.
17.
L. S.
Smith
and
M. F.
Gittos
, “
Formation of thin bands of interference colours or ‘tramlines’ adjacent to arc welds in titanium and its alloys
,”
Weld. World
58
,
127
142
(
2014
).
18.
F.
Brückner
,
Modellrechnungen zum Einfluss der Prozessführung beim induktiv unterstützten Laser-Pulver-Auftragschweißen auf die Entstehung von thermischen Spannungen, Rissen und Verzug
(
Fraunhofer Verag
,
Stuttgart
,
2012
), p.
152
.
19.
European Space Agency
, see https://www.esa.int/ESA_Multimedia/Images/2019/04/3D_printing_and_milling_Athena_optic_bench for “3D Printing Titanium for ESA’s Athena” (
2019
).
20.
Y.
Koren
,
S. J.
Hu
,
P.
Gu
, and
M.
Shpitalni
, “
Open-architecture products
,”
CIRP Ann.
62
,
719
729
(
2013
).
21.
C.
Brecher
,
Integrative Produktionstechnik für Hochlohnländer
(
Springer
,
Berlin
,
2011
), p.
1177
.
22.
D. L.
Olson
,
T. A.
Siewert
,
S.
Liu
, and
G. R.
Edwards
,
Welding, Brazing, and Soldering
(
ASM International
,
Materials Park
,
OH
,
2000
), p.
1299
.
23.
S.
Jäckel
,
M.
Hertel
,
S.
Rose
, and
U.
Füssel
, “
Qualifizierung und Weiterentwicklung von Schleppgasdüsen für eine verbesserte Schutzgasabdeckung beim Schweißen,
” Technical Report (
TU Dresden
,
Dresden
,
2016
).
24.
A. J.
Nunes
and
P. R.
Gradl
, “Gas shielding technology for welding and brazing,” NASA Technical Reports (NASA, Huntsville, AL,
2012
), see https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201200 15986.pdf (Accessed 22 May 2019).
25.
R. M.
Evans
,
D. C.
Martin
,
R. E.
Monroe
, and
J. J.
Vagi
, “Welding procedures for titanium and titanium alloys,” NASA Technical Reports (NASA, Huntsville, AL,
1965
), see https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/196600 14185.pdf (Accessed 22 May 2019).
26.
M.
Dreher
, “
Numerische und diagnostische Untersuchung der Schutzgasströmung beim Metallschutz-gasschweißen für die Brenner- und Verfahrensentwicklung
,”
Ph.D. thesis
,
TU-Dresden
,
2014
.
27.
D.
Eylon
,
S.
Fujishiro
,
P. J.
Postans
, and
F. H.
Froes
, “
High-temperature titanium alloys—A review
,”
JOM
36
,
55
62
(
1984
).
28.
H.
Oertel
,
M.
Böhle
, and
L.
Prandtl
,
Prandtl—Füh-rer durch die Strömungslehre: Grundlagen und Phänomene: Grundlagen und Phänomene
(
Springer Fachmedien Wiesbaden
,
Wiesbaden
,
2012
), s.l, p.
764
.
29.
S.
Katayama
,
Handbook of Laser Welding Technologies
(
Woodhead Pub
,
Cambridge
,
2013
), p.
654
.
30.
D.
Grevey
,
P.
Sallamand
,
E.
Cicala
, and
S.
Ignat
, “
Gas protection optimization during Nd:YAG laser welding
,”
Opt. Laser Technol.
37
,
647
651
(
2005
).
31.
F.
Caiazzo
,
F.
Curcio
,
G.
Daurelio
, and
F.
Memola Capece Minutolo
, “
Ti6Al4V sheets lap and butt joints carried out by CO2 laser: Mechanical and morphological characterization
,”
J. Mater. Process. Technol.
149
,
546
552
(
2004
).
32.
N. P.
Mikhailova
,
E. U.
Repik
, and
Y. P.
Sosedko
, “
Optimal control of free-stream turbulence intensity by means of honeycombs
,”
Fluid Dyn.
29
,
429
437
(
1994
).
33.
R. D.
Mehta
and
P.
Bradshaw
, “
Design rules for small low speed wind tunnels
,”
Aeronaut. J.
83
,
443
453
(
1979
).
34.
T.
Finaske
, “COAXShield—State of the art titanium processing,” Technical Report (
Fraunhofer IWS
,
Dresden
,
2019
).
35.
André
Seidel
, see https://www.esa.int/ESA_Multimedia/Videos/2019/04/3D_printing_titanium_for_ESA_s_Athena for “3D Printing Titanium for ESA’s Athena” (
2019
).
36.
ARCAM AB, Ti6Al4V ELITitanium Alloy, spec sheet, see http://www.arcam.com/wp-content/uploads/Arcam-Ti6Al4V-ELI-Titanium-Alloy.pdf (Accessed 22 May 2019).
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