3.1 COMET: FEM Simulation for Additive Manufacturing

A software development on the simulation platform optimised for AM process simulation for understanding of the consequences induced by the  AM fabbrication technology.

The Thermal and stress analysis is enabled by the computational framework for the numerical simulation of the metal deposition process by additive manufacturing using the Selective Laser Melting (SLM) technology. The objective is to estimate the residual stress field and distortions induced by the AM process on the manufactured parts.

The final goal is to provide a simulation tool enabling the optimization of the product design, allowing for the minimization of residual stresses and distortions induced by this kind of fabrication technology. The distortions are critical because they increase the manufacturing costs and delivering times as well as the number of wastes and scraps due to dimensional inaccuracies. Therefore, a priori prediction and correction loop at design stage is preferred to the trial and error strategy usually employed to solve such problems.

Using SLM technology, parts are built on a layer by layer basis by focusing a power source (laser, in our case) to the powder bed. The material is rapidly heated above its melting temperature and then allowed to solidify and cool down to form a new solid layer.

A typical printing process with powder-bed technologies, such as SLM, occurs in a closed chamber with an argon-controlled atmosphere and consists of the following steps

1. A powder layer of typically 30-60 microns is spread over the building platform
2. A laser melt the region of powder that belongs to the first cross section
3. The building platform is lowered to accommodate a new layer
4. A new layer of powder is spread over the previous layer with the levelling blade
5. Steps 2 to 4 are repeated until the whole component is created
6. Loose unfused powder is removed during post processing

The peculiarities of this technology are:

1. The scanning speed is very high (≈1000 mm/s): more than 10 time faster compared to blown-powder and even 100 time faster than in wire-feeding technologies (≈10 mm/s);
2. The layer thickness is very small: in wire-feeding  the metal deposition layers  are 1-2 mm thick (1000-2000 microns); in blown-powder the thickness is reduced to (200-300 microns), while in SLM the layer thickness is 20-30 microns, only. Hence, the laser spot and the Heat Affected Zone (HAZ) are very small compared to other AM technologies.
3. SLM is characterized by the powder spreading and recoating time (≈10 s) allowing for the cooling of each new layer to an average temperature field below the annealing temperature. Hence, the thermal stresses due to the thermal contraction of the new layer can develop summing their effects to the rest of previously deposited layers.

The mentioned peculiarities make the numerical simulation of the SLM process very challenging. The High-Fidelity (HF) transient thermo-mechanical model has already been successfully applied and validated in order to predict the thermal field and the mechanical behaviour of AM processes [1, 2]. Nevertheless, these approaches are unaffordable when applied to SLM due to the computational time requirements. On the one hand, the small thickness of the metal deposition layer as well as the reduced size of the laser spot make necessary the use of extremely fine FE meshes. On the other hand, the huge number of hatching necessary to fulfil the complete layer sintering requires a tremendous number of time-steps to afford the HF transient thermo-mechanical analysis.

Information

Reference Web-Page CIMNE
Reference Web-Page COMET
Personal Web-Page Michele Ciumenti
Publication Web-Page
CAxMan D4.1 Specification for Thermal and Stress Analysis
CAxMan D4.2 Thermal Analysis Framework for MD Process
CAxMan D4.3 Validation Strategy for Thermal Analysis
CAxMan D4.4 Coupled Thermo-Mechanical Analysis for the MD Process
CAxMan D4.5 Validation of Residual Stresses model QC
CAxMan D4.6 Heat Treatment Analysis and its Validation QC
(a) Publication : Residual stresses and distortion of rectangular an S-shaped Ti-6Al-4V Laser Solid Forming parts: modelling and experimental calibration          X. Lu, X. Lin, M. Chiumenti, M. Cervera, Y. Hu, X. Ji, H. Yang and W. Huang Additive Manufacturing, (2018) Submitted
(b) Publication: Modeling of microstructure evolution in Additive Manufacturing processes of Ti-6Al-4V          E. Salsi, M. Chiumenti and M. Cervera Metals - Open Access Metallurgy Journal, (2018) Submitted
(c) Publication: Empirical methodology to determine inherent strains in additive manufacturing          I. Setien, M. Chiumenti, S. van der Veen, M. San Sebastian, F. Garciandía and A. Echeverría  Computers and Mathematics with Applications, (2018) in press
(d) Publication: A phenomenological model for the solidification of eutectic and hypoeutectic alloys including recalescence and undercooling          M. Chiumenti, M. Cervera, E. Salsi and A. Zonato Journal of Heat Transfer, 8(140) (2018)
(e) Finite element analysis and experimental validation of the thermomechanical behavior in laser solid forming of Ti-6Al-4V          X. Lu, X. Lin, M. Chiumenti, M. Cervera, J. Li, L. Ma, L. Wei, Y. Hu and W. Huang Additive Manufacturing, 21 (2018) 30–40
(f) Publication: Numerical Modelling and Experimental Validation in Selective Laser Melting          M. Chiumenti, E. Neiva, E. Salsi, M. Cervera, S. Badia, J. Moya, Z. Chen, C. Lee, and C. Davies  Additive Manufacturing,18 (2017) 171–185
(g) Numerical simulation and experimental calibration of Additive Manufacturing by blown powder technology. Part I: thermal analysis M. Chiumenti, X. Lin, M. Cervera, W. Lei, Y. Zheng and W. Huang Rapid Prototyping Journal, 23(2) (2017) 448-463
(h) Numerical modeling of the electron beam welding and its experimental validation M. Chiumenti, M. Cervera, N. Dialami, B. Wu, J. Li and C. Agelet de Saracibar. Finite Elements in Analysis and Design, 121 (2016) 118-133
Finite element modeling of multi-pass welding and shaped metal deposition processes M. Chiumenti, M. Cervera, A. Salmi,  C. Agelet de Saracibar, N. Dialami and K. Matsui Computer Methods in Applied Mechanics and Engineering, 199 (2010) 2343-2359.

Additional Information

Originator: Michele Chiumenti (CIMNE)
Technology Readiness Level: 5
Environment: 2 SaaS