Modeling of Powder Bed Fusion Additive Manufacturing
Mattia Moda
Department of Civil and Industrial Engineering, University of Pisa Largo Lucio Lazzarino 2, 56122 Pisa PI, Italy
Email: mattia.moda@ing.unipi.it
PhD program Industrial Engineering
Curriculum Mechanical Engineering
Cycle XXXIII (11/2017–10/2020)
Supervisors Prof. Leonardo Bertini Prof. Bernardo D. Monelli
Summary
Designing and producing additively manufactured parts entails expensive and time-consuming trial and error procedures. This is partially due to process-induced stresses and distortions affecting the integrity and functionality of 3D printed components. Process simulation may thus be an efficient and effective approach to identify suitable or, preferably, optimal parameters and printing configurations based on the desired geometry and the adopted material.
The first part of the research concerned the development and validation of a multi-scale simulation method aimed at predicting residual stresses and distortions induced by Powder Bed Fusion (PBF) Additive Manufacturing (AM) processes. This led to the implementation of an integrated software application currently in use at Nuovo Pignone International S.R.L. – Baker Hughes, whose TPS Innovation Department funded the research project and thus holds the patent on the designed scaling strategy.
Besides simulation, validation, and patenting activities, the final year was devoted to the study of the Rosenthal solution for a moving point heat source in steady state on a semi-infinite solid, which led to the development of a theoretical framework for the analysis and optimization of melting processes that use focused moving heat sources (including welding and PBF). Among the most significant findings are a closed-form procedure to determine the optimal operating condition given two geometric constraints on the melt isotherm and a quasi-analytical method to compute the residual stress field associated with the Rosenthal solution under the linearity assumption. The above framework provided a general dimensionless perspective on welding and AM processes, which allowed to appreciate the remarkable similarities between the reframed operating conditions1for many different materials and identify hot cracking as possibly the main
hindrance to productivity for AM technologies on aluminium alloys. As for the structural quasi-analytical method, it outperforms any numerical alternative of comparable accuracy – and, perhaps more importantly – showcases the potential of the misfit strain (i.e., the inelastic strain induced by the gradient of thermal expansion at solidification), which could prove to be an instrumental expedient for modeling solidification in solid mechanics.
Courses
Name Hours Organizer Professor(s) Evaluation
Academic English C1 30 CLI – University of Pisa J. Spataro Excellent Fundamentals of Optimization 25 University of Pisa G. Pannocchia Positive Scientific Programming 40 Scuola Normale Superiore J. R. M. Bloino Positive Fundamentals of artificial neural
networks and genetic algorithms 10 University of Pisa B. Lazzerini N/A Academic English C1+ 30 CLI – University of Pisa J. Spataro Excellent Fundamentals of Multi-objective
Optimization 20 University of Pisa
A. Artoni
F. Pistolesi N/A Metal Additive Manufacturing Scenario
Research and Industrial Experience 37 CISM – Udine N/A N/A
Conferences and seminars
Name Hours Date Location Attended as
GdL AIAS – Metal Additive Manufacturing 16 13–14/02/2018 Parma Contributor An introduction to propulsion 2 29/05/2018 Pisa Participant
DMLM numerical simulation 4 19/06/2018 Florence Lecturer
Pisa Gears 2018 4 21/09/2018 Pisa Participant
Additive Manufacturing, lo stato dell’arte nell’industria meccanica italiana,
casi di applicazione e sfide future
6 22/02/2019 Florence Contributor
BHGE AM Summit 2019 4 08/04/2019 Florence Contributor
BHGE AM Global Workshop 2019 16 22–24/07/2019 Celle (DE) Contributor
BH AM Symposium 2020 4 03/06/2020 Online Contributor
vAIAS 2020 12 02–04/09/2020 Online Contributor
External research activities
Company/Institution Time frame Description
Nuovo Pignone International S.R.L.
Baker Hughes, Florence 11/2017–10/2020
Experimental and benchmarking activities aimed at validating the developed PBF simulation methods and assessing their performances (also in relation to the available commercial solutions)
KU Leuven (BE) 05/2020–09/20202 Experimental validation of the developed PBFsimulation methods and implementation of simplified
strategies for modeling complex support structures
2Planned but canceled due to the COVID-19 emergency.
Tutoring and supplementary teaching activities
Supplementary lecturer for the course of Machine Design (ING-IND/14) – MSc in Energy Engineering (LM-30), 15 hours. Master’s thesis supervisor for Matteo Benassi (graduated in Mechanical Engineering with the final mark of 110/110 cum laude) and Camilla Riscossa (ongoing).
Publications
• L. Bertini, F. Bucchi, F. Frendo, M. Moda, B. D. Monelli, Residual stress prediction in selective laser melting, International Journal of Advanced Manufacturing Technology 105 (2019) 609–636. doi:10.1007/s00170-019-04091-5. • M. Moda, B. D. Monelli, L. Bertini, M. Benassi, M. Palladino, P. Tozzi, Scaling Method Based on a Pointwise Superposition
Procedure and System thereof, Italian Patent No. 102020000017164 (2020).
• M. Moda, B. D. Monelli, M. Benassi, M. Palladino, Validation of a multi-scale simulation strategy based on the Pointwise Strain Superposition Method, IOP Conference Series: Material Science and Engineering 1038 (2021) 012022. doi:10.1088/1757-899X/1038/1/012022.
• M. Moda, B. D. Monelli, L. Bertini, M. Palladino, The Pointwise Strain Superposition Method: A scaling strategy for simulating Powder Bed Fusion processes, Additive Manufacturing (Submitted).
• M. Moda, A. Chiocca, G. Macoretta, B. D. Monelli, L. Bertini, Linear thermo-structural analysis of a moving point heat source in steady state on a semi-infinite solid, International Journal of Engineering Science (Submitted).
