Digitalization of design for support structures in laser powder bed fusion of metals

327 Pages·2023·12.888 MB·English

by  Katharina Bartsch

Light Engineering für die Praxis
Katharina Bartsch
Digitalization of design
for support structures
in laser powder bed
fusion of metals
Edited by Claus Emmelmann
123
Digitalization of design for support structures in
laser powder bed fusion of metals

Vom Promotionsausschuss der
Technischen Universität Hamburg
zur Erlangung des akademischen Grades
Doktor-Ingenieurin (Dr.-Ing.)

genehmigte Dissertation

von
Katharina Lisa Bartsch

aus
Hamburg

2023
Betreuer: Prof. Dr.-Ing. Claus Emmelmann
1. Gutachter: Prof. Dr.-Ing. Claus Emmelmann
2. Gutachter: Prof. Dr.-Ing. Benedikt Kriegesmann
Tag der mündlichen Prüfung: 29. September 2022
Light Engineering für die Praxis
Reiheherausgegebenvon
ClausEmmelmann,Hamburg,Deutschland
Technologie- und Wissenstransfer für die photonische Industrie ist der Inhalt dieser
Buchreihe. Der Herausgeber leitet das Institut für Laser- und Anlagensystemtechnik an
derTechnischenUniversitätHamburgsowiedieFraunhofer-EinrichtungfürAdditivePro-
duktionstechnologien IAPT. Die Inhalte eröffnen den Lesern in der Forschung und in
UnternehmendieMöglichkeit,innovativeProdukteundProzessezuerkennenundsoihre
Wettbewerbsfähigkeit nachhaltig zu stärken. Die Kenntnisse dienen der Weiterbildung
von Ingenieuren und Multiplikatoren für die Produktentwicklung sowie die Produktions-
und Lasertechnik, sie beinhalten die Entwicklung lasergestützter Produktionstechnolo-
gien und der Qualitätssicherung von Laserprozessen und Anlagen sowie Anleitungen für
Beratungs- und Ausbildungsdienstleistungen für die Industrie.
Katharina Bartsch
Digitalization of design
for support structures
in laser powder bed fusion
of metals
KatharinaBartsch
iLASInstitutfürLaser-und
Anlagensystemtechnik
TUHHTechnischeUniversitätHamburg
Hamburg,Germany
ISSN2522-8447 ISSN2522-8455 (electronic)
LightEngineeringfürdiePraxis
ISBN978-3-031-22955-8 ISBN978-3-031-22956-5 (eBook)
https://doi.org/10.1007/978-3-031-22956-5
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2023
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Abstract
The digital transformation of the manufacturing sector is among the most important meg-
atrends in the global value creation. Additive manufacturing, with laser powder bed fusion
of metals presenting the most mature technology for the production of metal end-use prod-
ucts, is considered an essential technology for digital production and is increasingly ap-
plied in industry. The design freedom allows for highly complex parts optimized for per-
formance and efficiency, while the nature of additive manufacturing – being based on a
digital model of the part and requiring no tools – enables decentralized on-demand pro-
duction as well as customization of parts without additional cost. However, several barri-
ers towards the broad industrial application exist. Among the most crucial challenges are
the associated cost and the required experience regarding the manufacturing process. A
possible approach to reduce production cost and eradicate the need for user experience lies
in the complete digitalization of the value creation process, including design and manu-
facturing. A digital, automated support structure design procedure addresses most of the
process steps lacking. Support structures are essential to the successful manufacturing by
laser powder bed fusion, but require design experience because the automation of their
generation is limited currently. As they do not belong to the final product, though, they
increase production cost without adding value to the product.
In order to advance today’s additive manufacturing towards first-time-right production
with no need of extensive user knowledge as well as to reduce support structure-induced
production cost, this thesis digitalizes the support design process by developing an algo-
rithm-based, automated process for part-specific support structure design. In the first step,
process simulation determines the actual load cases of the support structures. Then, using
the space colonization method from algorithmic botany, the support structures are gener-
ated, which have a tree-like topology. The algorithm includes specific design rules for the
tree shape, which have been derived from a systematic topology optimization study. The
support structure design procedure is validated experimentally by applying a benchmark
approach specifically developed to compare support structures in terms of their technical
and economic performance. The whole thesis is based on the titanium alloy Ti-6Al-4V,
for which a complete model of the thermo-physical, optical, and mechanical material prop-
erties is presented.
The validation demonstrates the procedure’s capability to design support structures tai-
lored to a specific part without the need of user experience. This enables the adoption of
laser powder bed fusion even in smaller companies, who cannot afford to build up expe-
rience over several years. Furthermore, by advancing the digitalization of the manufactur-
ing process, the possibility of the digital transformation of manufacturing companies is
eased. Although the support structure volume is significantly reduced, and therefore the
production cost, no significant savings in support structure-induced cost is achieved at the
level of single-lot production due to the numerical efforts required. However, with the on-
going efforts to introduce laser powder bed fusion to serial production, significant cost
savings could be pointed out at larger production scale, as the influence of the support
structure design on the support structure cost is dimished. By this, the technology adoption
barrier is lowered, contributing to the current efforts of achieving broad industrial appli-
cation for fully digital production by additive manufacturing.
Table of content

1 Introduction 1
2 Digital production by additive manufacturing 5
2.1 Laser powder bed fusion of metals (PBF-LB/M) .............................................5
2.1.1 Technical process ................................................................................5
2.1.2 Digital transformation of (additive) manufacturing ............................9
2.2 Digitalization of part design by topology optimization.................................. 12
2.2.1 Topology optimization methods ....................................................... 14
2.2.2 Numerical challenges ........................................................................ 21
2.2.3 Physics addressed in topology optimization ..................................... 23
2.2.4 Solver algorithms .............................................................................. 25
2.2.5 Topology optimization for additive manufacturing .......................... 26
2.3 Digitalization of PBF-LB/M process ............................................................. 28
2.3.1 Process modeling .............................................................................. 28
2.3.2 Material modeling ............................................................................. 34
2.4 Support structures in PBF-LB/M ................................................................... 44
2.4.1 Integration of supports in the manufacturing process ....................... 44
2.4.2 Challenges in the application of supports ......................................... 48
2.5 Support structure optimization ....................................................................... 49
2.5.1 Support structure avoidance .............................................................. 53
2.5.2 Optimization of available support structures .................................... 56
2.5.3 Development of novel support structures.......................................... 60
2.5.4 General characteristics of optimization approaches .......................... 64
2.5.5 Optimization goals ............................................................................ 65
2.5.6 Quantification of optimization success ............................................. 66
2.5.7 Automated support structure removal ............................................... 69
2.6 Economic evaluation of additive manufacturing ........................................... 71
2.6.1 Cost calculation ................................................................................. 73
2.6.2 Cost prediction .................................................................................. 76
3 Research Hypothesis and Methodology 79
4 Material Model of Ti-6Al-4V Alloy in Laser Powder Bed Fusion 83
4.1 Thermo-physical properties of Ti-6Al-4V ..................................................... 84
4.1.1 𝛽-transus temperature ....................................................................... 85
4.1.2 Solidus temperature .......................................................................... 90
4.1.3 Liquidus temperature ........................................................................ 90