7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Coupled computational models of the arc plasma and the metal in wire-arc
additive manufacturing

Anthony B. Murphy1, Yun H. Kim1, Dayalan Gunasegaram1, Paul W. Cleary2, Fiona F. Chen1,David G. Thomas2
1
CSIRO Manufacturing, 2 CSIRO Data61
e-mail (speaker): tony.murphy@csiro.auWire–arc additive manufacturing (WAAM) is a form ofmetal 3D printing in which an arc plasma melts a wire,
depositing metal layer-by-layer [1]. WAAM is used toproduce large parts with dimensions up to 1 m or more.
Computational modelling of WAAM is challenging
because of the many physical processes involved and thelarge difference between the part's dimensions and thoseof the arc and melt pool. The most widely adopted
approach is to solve the heat transfer equation in thesolid metal using finite element analysis (FEA). An
artificial heat source is used to approximate the influenceof the arc and the melt pool. While this approach isstraightforward, calibration of the heat source requires
costly experiments for every significant change inprocess parameters (e.g., arc current, travel speed, metalalloy); the heat source also changes from layer to layer.
In addition, the height and width of each layer have to beestimated.
We present two multiscale approaches that substantiallyreduce the requirements for experimental calibration. In
both approaches, we use a three-dimensional
magnetohydrodynamic (MHD) model of the wire, arcand melt pool to calculate the heat transfer to theworkpiece. The MHD model can also predict the shapeof each added layer and the size and temperature of themetal droplets produced when the arc melts the wire. The
model is an extension of a previously developed
MIG/MAG welding model [2] and is run in steady-statemode to reduce computational time.
In the first approach, the heat flux and layer geometry
predicted by the MHD model are coupled to an FEA
model that calculates the heat transfer and residual stressin the workpiece. An example of the heat flux is shownin Figure 1, and an example of the residual stress is given
in Figure 2. Combining the MHD and FEA approaches
allows time-dependent modelling of the production oflarge parts.
In the second approach, the heat flux and the droplet size
and temperature are used as the input to a smoothed
particle hydrodynamics (SPH) model of the melt pooland workpiece. SPH can simulate the time-dependent
impact of the droplet on the melt pool, and the flow
dynamics and solidification of the molten metal.
The benefits of each approach will be assessed, and thepredictions will be compared with experimental resultsin the literature.

Figure 1: Calculated distribution of the heat flux to theworkpiece surface during deposition of the fourth layer
for the parameters of Zhao et al. [3]. The contour lines
indicate the build height above the original substratesurface in mm. The arc is moving in the –y direction.

Figure 2: Von Mises stress distributions predicted by the
coupled MHD-FEA model after deposition of the firstlayer. The scale is from 0 to 270 MPa in 27 MPa
increments. The substrate is 51 mm long × 21 mm halfwidth × 6 mm thick.
References[1] J. Norrish, J. Polden, I. Richardson, J. Phys. D: Appl.
Phys. 54 473001 (2021).
[2] A. B. Murphy, F. F. Chen, J. Xiang, H.-P. Wang, D.
G. Thomas, Y. Feng, J. Manuf. Process. 61 111-127(2021).
[3] W. Zhao, Y. Wei, J. Long, R. Liu, W. Ou, Weld. World
65 1571-1590 (2021).