Page 95 - ESAM-1-2

Engineering Science in
Additive Manufacturing Impact of machine factors on PBF part surface quality

Laser-based PBF of metals, commonly known as following factors are important in determining the final
selective laser melting (SLM) or direct metal laser sintering, surface quality built by PBF: Material feedstock (type, size,
is an AM process capable of producing near-net-shape and quality), surface orientation concerning the process,
metal components for research and industrial applications. support interface, and key processing parameters. In
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The process begins with a computer-aided design model recent years, the effect of machine factors on Ra variation
configured with process parameters and sliced into layers has also received attention.
using specialized software. During fabrication, metal A variety of process parameters influence print quality
powder is deposited onto a build plate layer-by-layer with in AM, including laser power, scanning speed, hatch
a predefined layer thickness. The laser selectively melts
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the powder in each layer, fusing it to form the final part. spacing, layer thickness, scanning strategy, spot size, and
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PBF enables the rapid fabrication of metal components pre-heat temperature. In addition, other factors, such
with complex geometries, offering good quality and as gas flow rate and raw material properties, can impact
dimensional accuracy. It enhances design freedom by process stability and overall print quality. These parameters
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eliminating many of the geometric constraints imposed collectively affect mass and heat transfer within the melt
by conventional machining methods. In addition, PBF pool, thereby influencing melt pool behavior and the
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supports part integration, which can reduce manufacturing resulting part quality. Meanwhile, heat treatment such as
costs and improve overall component performance, annealing also has a major effect on the fracture toughness
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making it well-suited for meeting industrial demands. and the threshold for fatigue crack initiation. Two other
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Parts are built layer-by-layer with the thickness of each parameters to be considered are scanning strategy and
layer at 20 – 100 μm. Ideal metal powder is spherical, build orientation. 18
medium-sized, with a narrow particle distribution. The main characteristics of 1.2709 tool steel are
Oxygen level is controlled at <500 ppm. The platform can characterized by high hardness and high ductility. 19-22 Its
be heated up to 200°C. PBF technology is compatible with specific mechanical properties allow usage in high-stress
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many materials, highly efficient, and capable of producing components due to its high wear resistance. 23-25 Lasers
complex end-products of high precision. Companies can also be used to diminish the Ra of 1.2709 tool steel
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such as General Electric, Airbus, Boeing, and Rolls-Royce PBF parts up to 41% and increase their hardness up to
are all at the forefront of using more metal AM in their 88%. The maximum operating temperatures can further
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production line. 9-11 reduce wear. It is commonly used for applications such as
Key advantages of the PBF process include greater conformal cooling systems for mold devices. 27,28 Various
design freedom, enhanced functionality, reduced build strategies were developed to optimize the printing
tooling and setup costs, lightweight structures, mass process of 1.2709 tool steel. 29-33 In hybrid manufacturing
customization, and overall cost savings. However, various applications, 1.2709 tool steel (ASTM A276/M300) is
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post-processing steps, such as heat treatment, secondary widely used and adopted. 34-36 Its performance can also
machining, and polishing, are often necessary to improve be enhanced via various heat treatment methods, such
the quality of parts produced by the PBF process further. as solution annealing and aging after the PBF fabrication
Components fabricated using PBF can exhibit superior process. 37,38 Its microstructure change during heat
properties compared to those made by conventional treatment was investigated to obtain the optimal heat
methods, largely due to the refined microstructures treatment process. 39-42
formed during the rapid cooling and solidification cycles, This study aims to produce high-quality PBF parts and
with cooling rates ranging from 10 to 10 °C/s. Despite its
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potential for producing near-net-shape components, PBF investigate the machine factors affecting the surface quality
technology has yet to be widely adopted across industries. of as-built parts from the PBF process, such as inert gas
A key barrier to broader implementation is the need for flow and the position of parts relative to the location of the
additional post-processing to achieve the surface quality laser spot center.
required for many applications. 12 2. Data and methods
The surface roughness (Ra, the arithmetic mean
deviation of the assessed profile) of metal additive 2.1. Material and manufacturing
manufacturing (AM) components varies between 5 and This study used 1.2709 tool steel (ASTM A276/M300)
50 μm, depending on the material used. At present, (Nikon SLM Solutions AG, Germany). As shown in
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additional post-processes such as computer numerical Figure 1, the powder has a spherical morphology
control milling and turning, grinding, and polishing are according to the standards of the German Institute
implemented to achieve <1 μm Ra. In addition, the for Standardization (DIN), European Standard (EN),
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Volume 1 Issue 2 (2025) 2 doi: 10.36922/ESAM025240014