Page 32 - MSAM-4-3

Materials Science in Additive Manufacturing Numerical simulation of plasma WAAM for Ti-6Al-4V

A B measure. This strategy effectively reduced thermal stress,
minimized cracking, and promoted a more uniform
temperature distribution. By increasing the initial
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temperature of the baseplate, pre-heating prevented
the first deposited track from becoming excessively
narrow, promoted better metal spreading, and improved
metallurgical bonding between the deposited material and
C D the baseplate. Beyond thermal management, pre-heating
the baseplate significantly influenced the microstructural
evolution of Ti6Al4V in the WAAM process. The first
layers experienced relatively high cooling rates due to
rapid heat conduction into the cold baseplate, resulting in
steeper thermal gradients. Elevated pre-heat temperatures
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Figure 2. Experimental setup for the heat source calibration. (A) reduced these thermal gradients, slowing cooling rates
M3DP welding system. (B) Experimental setup for the calibration runs.
(C) Thermocouple locations. (D) Micrograph after single bead deposition. and consequently modifying the solidification behavior
Scale bar: 2,000 µm, magnification 5× and phase transformation kinetics. According to Tan
et al., pre-heating of the baseplate contributed to melt
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deposition process took place within a closed, airtight welding pool stabilization, affected grain growth dynamics, and
chamber filled with highpurity argon, providing an inert gas facilitated microstructural homogenization. These effects
atmosphere for adequate shielding. Weldinggrade argon are crucial for reducing columnar grain formation,
(99.99% purity) was used in both the process and as a shielding improving part integrity, and enhancing the overall
gas. Cold Ti6Al4V wire with a diameter of 1.2 mm was mechanical properties of WAAM-produced components.
continuously fed by an automatic wire feeder. Both base plates The most critical process parameters are the welding
and welding wire are commercially available and conform current I, the travel speed of the plasma torch, and the wire
to the American Society for Testing and Materials B265 and feed speed, influencing the deposited metal shape. The
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American Welding Society A5.16 - 07 standards, respectively. specific deposition parameters used in the experiments are
The experimental setup for the heat source calibration shown in Table 1.
is shown in Figure 2B. To minimize heat loss, the baseplate After the experiments, samples were extracted
was supported with carbon fiber composites, and the air along the sectional plane A-A (Figure 2C), embedded
gap between the baseplate and the backing plate was filled in bakelite, ground, polished, and etched with Kroll’s
with alumina wool, which effectively isolated the bottom agent. Metallographic analysis was performed using
surface of the baseplate. This design reduced contact heat an optical microscope (Zeiss, Germany) to evaluate
transfer to the backing plate as well as convective heat loss the microstructure and measure the dimensions of the
through the air gap. Weld beads 170 mm in length are weld and HAZ. An example micrograph of single bead
deposited to establish a steady thermal process. deposition is shown in Figure 2D. From these micrographs,
To characterize the thermal profiles within the workpiece, the width b, depth d, and cross-sectional area A of the weld
thermocouples were positioned at pre-defined measurement bead and HAZ were determined. In this context, the depth
locations on the baseplate (Figure 2C), following the d represents the height of the weld seam.
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methodology described by P. Helbig. These thermocouples 2.3. FE model
recorded peak temperatures and thermal gradients within
the workpiece. Insulated type K thermocouples were inserted Wire arc AM can be analyzed at different scales: macro,
from the bottom of the baseplate into pre-drilled holes, meso, and micro. At the macro-scale, multi-purpose FE
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with direct thermal contact provided by the application of software (Simufact Welding 8.0) was used to simulate the
a thermally conductive paste. Temperature was recorded coupled thermo-mechanical behavior of WAAM parts,
using a PCET 390multi-channel digital thermometer (PCE where a generic heat source model replaces the welding
Instruments GmbH, Germany) with a sampling rate of 1 Hz. torch and electric arc.
In total, three calibration runs were performed: a single pre- Within Simufact Welding 8.0, the welding process
heating pass, a single printing pass, and two pre-heating was modeled based on key manufacturing parameters,
passes with a subsequent printing pass. including the welding process, energy input, welding speed,
To improve adhesion and optimize bead geometry, pre- filler material, metallurgical properties, clamping concept,
heating of the baseplate was applied as a process control components of interest, and the FE mesh configuration.

Volume 4 Issue 3 (2025) 5 doi: 10.36922/MSAM025140021