Reader Response Final
The article “A Review of Stereolithography: Processes and Systems”, written by Huang et al. (2020), provides a comprehensive review of the generations of stereolithography (SLA), its representative system configurations and derivative technologies. Stereolithography, one of the three most widely used approaches to additive manufacturing, utilises ultraviolet (UV) light to cure liquid resin layers (aka Vat Photopolymerisation), thereby forming highly detailed and precise 3D objects.
Though being the earliest form of 3D printing, stereolithography has solidified itself a strong position in the additive manufacturing (AM) market, due to the combination of its accuracy and isotropic properties.
According to Huang et al. (2020), the method has evolved through four significant phases, each having increasing advantages over both its previous iterations and its competitors. They consist of scanning, projection, continuous and volumetric. In that order, the speed of each iteration increases. However, the resolution is the inverse, with scanning being the highest resolution and volumetric being the lowest. Hence, projection-based stereolithography provides a good middle ground between resolution/accuracy and speed and we will mainly be using that as a basis for comparison.
SLA’s primary advantage over its biggest competitors, Fused Deposition Modelling (FDM) and Selective Laser Sintering (SLS), is its print accuracy. As noted by Ngo et al. (2018), stereolithography achieves resolutions as fine as 10 microns, while FDM ranges from 50-200 microns and powder bed fusion (inclusive of SLS) ranges from 80-250 microns. This underscores SLA’s edge over its competitors in producing more geometrically complex designs with high resolutions. Additionally, its surface finish is comparable to that of Numerical Control milling (Pham, 1997), requiring less post-processing due to its smooth surface. In industries like healthcare, aerospace and consumer goods, the production of parts with tight tolerances and fine details are paramount for performance and aesthetics, and being able to make use of AM methods that meet these requirements will significantly reduce production costs and risks. Thus, SLA's capability of achieving exceptionally high resolutions and precision, alongside smooth surface finishes, makes it a top choice in the market as these qualities are highly valued and sought after, even in niche cases.
Beyond print accuracy, another key advantage of SLA is its material properties. While accuracy allows for intricacy, its isotropic properties ensure these designs maintain structural and mechanical integrity under stress. In engineering materials analysis, isotropy refers to the material's ability to maintain the same properties regardless of which direction it is tested in (Merriam-Webster, (n.d.). Because many AM methods such as FDM print line-by-line and layer-by-layer, it naturally results in anisotropic properties where parts are weaker along the layer lines; however because SLA cures entire layers and even volumes at once, it results in greater bonds between layers, allowing for better isotropic properties. SLA's other main competitor with similar isotropic properties would be SLS. In comparison, SLA still possesses the ability to create finer details while maintaining these high isotropic properties. Having parts that exhibit consistent mechanical durability and strength is crucial in applications requiring structural integrity, where the risk of material failure has to be minimised. This is crucial in the aforementioned aerospace industry, as well as automotive and medical devices, ensuring reliability and longer lifespans. This property of SLA makes it valuable to those seeking the perks of the AM market, securing its strong position among AM methods.
Conversely, because the technology primarily relies on the curing of photopolymer materials, it limits the technology’s use-cases. The use of UV curing does improve the mechanical properties of the material, but it results in decreased elongation at failure, meaning it is generally more brittle (Riccio et al., 2021). Despite being able to fail at higher loads, due to this limitation, alternative materials used in other AM methods like thermoplastics may still be more viable in specific situations where elasticity is an important factor. That said, with ongoing advancements in hybrid resins and composite materials, such as researchers in Massachusetts Institute of Technology (MIT) utilising a new machine-learning system to identify new chemical formulations in order to optimise 3D printing material properties, it paints a brighter future for SLA by attempting to bridge this gap in material properties (MIT News, 2021)
To conclude, SLA's combination of high resolution, isotropic properties, and superior surface finish places it as a leading choice within the AM market, especially in industries that value precision and durability. Despite its present reliance on photopolymers, ongoing advancements in hybrid resins promise to expand its applications, allowing for continued relevance alongside other AM technologies.
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