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International Journal of Bioprinting Advancements in 3D printing

the movement trajectory of the nozzle. These limitations adaptable for multiple functions, including prototype
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present challenges to the innovative application of DIW. design models, master dies for die casting, investment
casting molds, and casting shells and cores.
2.4. Selective laser sintering
Selective laser sintering is a 3D printing methodology Several technical limitations of SLS are depicted
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that employs an infrared laser to fuse powder materials as follows :
together. The process commences by depositing a layer (i) Elevated raw material expenses and procurement
of powder material using a powder roller (Figure 2C). costs: The materials employed in SLS, especially
Subsequently, the powder is heated to a temperature just metal powders, can be costly. Additionally, sourcing
below the sintering threshold by a temperature control and acquiring these materials can prove to be
mechanism within the printing apparatus. A laser beam demanding and expensive.
is then directed onto the powder layer, elevating the
temperature of the irradiated powder above its melting (ii) Metal parts produced through SLS often exhibit
point. This triggers sintering, causing the powder unsatisfactory or limited mechanical properties,
particles to fuse and establish a bond with the previously such as heightened porosity and suboptimal
consolidated layer beneath. As each layer is sintered, mechanical attributes. The joining of low-melting-
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the printing platform descends by a layer thickness, and point powder with high-melting-point powder
the powder application system overlays a fresh layer of results in reduced elongation and restricted
powder onto the platform. Subsequently, the laser beam is suitability for manufacturing functional metal
precisely controlled to irradiate the new layer for sintering. components.
This cyclical procedure is reiterated layer by layer until the
entire 3D object is successfully printed. (iii) Utilizing varied materials in SLS might
necessitate supplementary and intricate auxiliary
SLS demonstrates versatility in printing diverse procedures. For instance, raw materials may need
materials, spanning polymers, ceramics, metals, and extensive pretreatment, including heating, which
composite substances. Additionally, it facilitates the increases overall production time and expenses.
generation of intricate and distinct structures. The merits Additionally, finishing surfaces may entail powder
of SLS encompass a few crucial aspects : cleaning.
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(i) SLS technology is compatible with a broad spectrum 2.5. Digital light processing
of materials, encompassing nylon, polystyrene, Digital light processing is a technology harnessing
various polymers, metals like iron and titanium, digital processing to project image signals, yielding a
alloys, ceramics, and coated sand. This material final product. The DLP apparatus (depicted in Figure
diversity facilitates the creation of diverse prototypes 2D) comprises a reservoir containing photopolymer,
and components.
which can be solidified through ultraviolet light exposure
(ii) One notable advantage of SLS is its heightened at a specific wavelength. Positioned below the liquid
manufacturing efficiency. Unlike certain additive reservoir is the DLP imaging system, with its imaging
manufacturing processes that fully melt the powder, surface situated at the bottom. Through the curing of
SLS solely sinters it, thereby speeding up the a thin layer of photopolymer possessing a predefined
production times. Furthermore, SLS demonstrates shape and thickness corresponding to the cross-sectional
remarkable material utilization efficiency. Unfused configuration extracted from prior slicing, a 3D structure
powder can be reclaimed for use, minimizing is incrementally assembled layer by layer. Above the
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material wastage and saving cost in comparison to liquid reservoir, a lifting mechanism elevates the cured
other techniques. resin, detaching it from the bottom surface and causing

(iii) Diverging from FDM and stereolithography it to adhere to the lifting plate or the preceding mold’s
processes, SLS does not necessitate auxiliary support resin layer. This integration of projection mechanisms
structures. Unfused powder can inherently support contributes to the compact sizing of the equipment, as
the model’s cavities and overhangs, negating the the layer curing and forming function module is more
requirement for supplementary support design. This compact. The molding traits of DLP technology are
enables the direct fabrication of intricate prototypes concisely summarized as follows 2,29 : (i) elevated curing
and components. The versatility of SLS technology speed due to heightened light efficiency at 405 nm; (ii)
extends to an array of applications. Leveraging a cost-effectiveness; (iii) high-resolution output; and (iv)
variety of formable materials, sintered components are enhanced reliability.

Volume 10 Issue 2 (2024) 48 doi: 10.36922/ijb.1752