Sintering simulation framework for 316L stainless steel components manufactured by binder jetting
Doctoral thesis, 2024

Binder Jetting (BJT) is an additive manufacturing (AM) technology allowing mass-production of small to medium-size metal components. BJT is a multi-step AM technology, where the geometrical shape of components is provided during the printing step, and the final properties are achieved through a second consolidation step - sintering. The sintered properties are achieved through densification of the porous (~40-60%) BJT parts, resulting in large volumetric shrinkages during the process. Furthermore, shape distortions are common due to sintering at high temperatures, close to the melting point of the metallic powder.

The first part of the thesis focusses on establishing an experimental characterization procedure for the sintering of BJT parts. The dimensional evolution from dilatometry experiments reveals the anisotropic sintering shrinkages with larger shrinkages along the building direction. Debinding does not induce substantial shrinkages (< 0.5%) or shrinkage anisotropy. Density fluctuations along the building direction related to the printing layer thickness of 42 µm were revealed, which decrease during sintering. An increase in shrinkage rate above ~1310°C was observed, related to the formation of
δ-ferrite phase detected in samples sintered at 1370 °C.

The second part of the thesis focusses on the development and implementation of a phenomenological model of sintering based on experimental input from the first part. The model is based on the continuum theory of sintering and describes the particularities of the 316L stainless steel BJT components during sintering. The bulk viscosity dependency on porosity is studied by using different expressions with and without fitting constants. Also, a new material shear viscosity expression is proposed, which explicitly accounts for the effect of δ-ferrite formation on the sintering behavior.

The last part comprises the implementation of the model expressions in a commercial FEA software and the sintering simulation of BJT geometries that showcases predictions with less than ~1 mm deviation on the shape distortions due to gravity. Demonstrator components were designed, including overhang structures that lead to large shape deformations. Different sintering models’ results are compared, where the ROH (Rios-Olevsky-Hryha) sintering model shows the best performance revealing small deviations of ~0.56 mm related to the isotropic assumption of the model.

This works paves the ground for its expansion to component manufactured using different BJT printers and stainless steel powders. Moreover, it has a high application potential to other sinter-based manufacturing technologies.

Sintering

sintering modelling

additive manufacturing

binder jetting

stainless steel.

dilatometry

Virtual Development Laboratory (VDL-room), Chalmers Tvärgata 4C, Chalmers University of Technology in Gothenburg
Opponent: Adjunct Professor Susanne Norgren, AB Sandvik Coromant, Sweden

Author

Alberto Cabo Rios

Chalmers, Industrial and Materials Science, Materials and manufacture

Sintering anisotropy of binder jetted 316L stainless steel: part I–sintering anisotropy

Powder Metallurgy,; Vol. 65(2022)p. 273-282

Journal article

Elisa Torresani, Alberto Cabo Rios, Thomas Grippi, Andrii L. Maximenko, Marco Zago, Ilaria Cristofolini, Eugene A. Olevsky. Sintering Simulation and Experimental Validation of 316L Pipe Tee Connectors Printed by Binder Jetting Additive Manufacturing.

Alberto Cabo Rios, Mats Persson, Eduard Hryha, Eugene A. Olevsky. Modelling of gravity-affected sintering of additively manufactured stainless steel components.

The present and future of additive manufacturing holds exciting possibilities, and binder jetting (BJT) is at the forefront of this revolution. The process of manufacturing BJT components involves shaping metallic particles, like building a sandcastle on the beach but in a layer-by-layer process, then consolidating them by heating at high temperatures (sintering). But, during this consolidation process the volume and geometry of the parts change substantially.

This research explores in detail how the BJT 3D printed components change during the sintering process. Not only the geometrical changes but also the internal porous structure, until a solid part is achieved. BJT components do not shrink homogeneously due to the layer-by-layer printing process. Also, their geometrical shape deforms during sintering, caused by the components exhibiting a viscous behavior under the high sintering temperatures.

The prediction of these changes is crucial to achieve the desired geometry without extensive trial-and-error iteration and can be used to re-design the 3D geometry to compensate for these distortions. Therefore, a simulation tool was developed that predicts the evolution of BJT 3D components during the sintering process. The simulation was validated with real sintering experiments using 316L stainless steel. Furthermore, it could be expanded and applied to other steel materials and sintering-based 3D printing technologies.

Subject Categories

Metallurgy and Metallic Materials

Areas of Advance

Materials Science

ISBN

978-91-8103-028-0

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5486

Publisher

Chalmers

Virtual Development Laboratory (VDL-room), Chalmers Tvärgata 4C, Chalmers University of Technology in Gothenburg

Online

Opponent: Adjunct Professor Susanne Norgren, AB Sandvik Coromant, Sweden

More information

Latest update

3/7/2024 8