Abstract
Laser metal deposition (LMD) is a manufacturing
process, which can be used to manufacture a complete, fully
functional part by building it up layer-by-layer using the data from a
Computer-Aided-Design (CAD) file. The layer-by-layer addition can
also be used to rebuild worn-out sections of existing parts, as well as
to deposit protective coatings to protect parts in surface engineering.
The process involves laser heating a substrate, on which a metal
powder is deposited. The powder solidifies, when mixed with the
substrate, thereby creating a metallurgical bond. In order to produce
parts with high geometrical tolerances and desirable material
properties, the process parameters have to be carefully controlled.
Since the LMD process requires the interaction of parameters, it is
not always easy to predict the output geometry. In this paper, the laser
metal deposition process was modelled in ANSYS Parametric-
Design-Language (APDL), using a transient thermal analysis, in
order to determine the geometrical properties of the clad, that is, the
width and the height of the resulting clad. The simulated results were
then compared experimentally by depositing Commercially Pure
(CP) titanium powder onto a Ti-6Al-4V substrate, in order to verify
the simulation. The varying parameter in the experimental process
was the powder flow rate, which was varied between 0.5-2.5g/min.
In addition to the geometrical properties, the microstructure,
microhardness; and the porosity levels of the deposited clads were
also analyzed, in order to better determine the clad quality and
integrity. The model showed good agreement in predicting both the
height and the width of the clads. Porosity was noticed in all the
samples with the exception of the clad deposited at the lowest powder
flow rate setting of 0.5 g/min. An increase in the powder flow rate
also led to a smaller fusion zone, due to a lower laser-material
interaction period, which was the result of the increase in the quantity
of powder causing attenuation of the beam, and less laser power being
absorbed by the substrate. The smaller fusion zone meant that the
clads could not bond to the substrate properly, which led to the clad
in the sample produced with the highest powder flow rate falling off
the substrate. There was a significant increase in the microhardness
of the clad zone, which was due to a combination of alloying with Ti-
6Al-4V and a change in the microstructure to an acicular alpha
martensite microstructure; while the Heat-Affected-Zone (HAZ) in
the substrate only showed a slight increase in microhardness.