Väitös (konetekniikka): DI Joni Reijonen
Aika
10.1.2025 klo 13.00 - 17.00
DI Joni Reijonen esittää väitöskirjansa ”SOURCES OF VARIABILITY IN METAL ADDITIVE MANUFACTURING: Effects of machine architecture-defined process parameters in PBF-LB AM” julkisesti tarkastettavaksi Turun yliopistossa perjantaina 10.01.2025 klo 13.00 (Turun yliopisto, Natura, X-luentosali, Turku).
Vastaväittäjänä toimii professori Milan Brandt (The Royal Melbourne Institute of Technology -yliopisto, Australia) ja kustoksena professori Antti Salminen (Turun yliopisto). Tilaisuus on englanninkielinen. Väitöksen alana on konetekniikka.
Väitöskirja yliopiston julkaisuarkistossa: https://urn.fi/URN:ISBN:978-952-02-0022-0 (kopioi linkki selaimeen).
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Tiivistelmä väitöstutkimuksesta
Additive manufacturing, so-called 3D printing, has matured from rapid prototyping into an industrial manufacturing technology used to produce critical components even for demanding applications. However, the high variability in the quality of the manufactured parts is a major hindrance to further advancement and wider adoption of this potentially revolutionary manufacturing technology.
This dissertation has identified the root causes behind the quality variation in the laser powder bed fusion process and determined their impact on the properties of the manufactured parts. The study focused on machine architecture-defined process parameters. These are the shielding gas flow, the re-coater blade type and the laser beam focal point position. The effect of these parameters has been scarcely studied and they have been often inadequately described in the methods of previous studies. This work also investigated the variability in mechanical properties of stainless steel specimens produced using different machines and powders, including exploration of the potential of using post-process heat treatments to reduce variability. Additionally, the thesis presents strategies for in-situ process monitoring for quality assurance purposes.
The results show that the shielding gas flow, the re-coater blade type and the laser beam focal point position have a significant effect on the quality of parts produced. Practical guidance is provided on how these parameters should be considered in additive manufacturing procedure specifications or similar process control approaches aimed at assuring repeatable material properties. Post-processing with hot isostatic pressing reduced variability in most of the studied properties, but at the cost of an associated significant reduction in absolute properties. This is due to the loss of the strengthening features in the stainless steel microstructure generated during the laser powder bed fusion process. This work showed that photodiode-based melt pool monitoring and contact-image sensor-based powder bed imaging are effective means of direct and continuous monitoring of the state of the actual fundamental unit processes in the PBF-LB process: the spreading of the powder layer and the ive laser melting of it.
Vastaväittäjänä toimii professori Milan Brandt (The Royal Melbourne Institute of Technology -yliopisto, Australia) ja kustoksena professori Antti Salminen (Turun yliopisto). Tilaisuus on englanninkielinen. Väitöksen alana on konetekniikka.
Väitöskirja yliopiston julkaisuarkistossa: https://urn.fi/URN:ISBN:978-952-02-0022-0 (kopioi linkki selaimeen).
***
Tiivistelmä väitöstutkimuksesta
Additive manufacturing, so-called 3D printing, has matured from rapid prototyping into an industrial manufacturing technology used to produce critical components even for demanding applications. However, the high variability in the quality of the manufactured parts is a major hindrance to further advancement and wider adoption of this potentially revolutionary manufacturing technology.
This dissertation has identified the root causes behind the quality variation in the laser powder bed fusion process and determined their impact on the properties of the manufactured parts. The study focused on machine architecture-defined process parameters. These are the shielding gas flow, the re-coater blade type and the laser beam focal point position. The effect of these parameters has been scarcely studied and they have been often inadequately described in the methods of previous studies. This work also investigated the variability in mechanical properties of stainless steel specimens produced using different machines and powders, including exploration of the potential of using post-process heat treatments to reduce variability. Additionally, the thesis presents strategies for in-situ process monitoring for quality assurance purposes.
The results show that the shielding gas flow, the re-coater blade type and the laser beam focal point position have a significant effect on the quality of parts produced. Practical guidance is provided on how these parameters should be considered in additive manufacturing procedure specifications or similar process control approaches aimed at assuring repeatable material properties. Post-processing with hot isostatic pressing reduced variability in most of the studied properties, but at the cost of an associated significant reduction in absolute properties. This is due to the loss of the strengthening features in the stainless steel microstructure generated during the laser powder bed fusion process. This work showed that photodiode-based melt pool monitoring and contact-image sensor-based powder bed imaging are effective means of direct and continuous monitoring of the state of the actual fundamental unit processes in the PBF-LB process: the spreading of the powder layer and the ive laser melting of it.
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