Assignment 1: Draft 1

Stereolithography has solidified itself a strong position in the additive manufacturing (AM) market due to the combination of its accuracy, isotropic properties and geometrical complexity.

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 light to cure liquid resin layers (aka Vat Photopolymerisation or Photo-Solidification), thereby forming 3D objects with high precision and details.

This method has evolved through four significant phases, with each having increasing advantages over its previous iterations and competitors, that thereby helps secure its spot in the 3D printing world. These iterative changes mainly consist of improvements in precision and resolution (layer thicknesses as fine as 25 microns and feature print sizes as small as 85 microns), smooth surface finish, isotropic properties (Formlabs, n.d.), material versatility (3D Actions, n.d.), and complex geometries (Ultimaker, n.d.).

With the basis of SLA being the curing of photopolymer resins, the main four generations consists of: scanning (the laser traces the layer line by line), projection (the layer is exposed in a single shot, or projected), continuous (light is projected, but through a permeable membrane that allows for curing, layer by layer, but without stopping between layers) and volumetric (multiple light sources that allows for curing of the entire volume). In that order, with each iteration the speed is faster than its predecessor. 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. With that in mind, we will be mainly using that as a basis for comparison.

The first major driving force for seeking SLA would be print 'quality/accuracy'. In a comparison between SLA and its main competitors: Fused Deposition Modelling (FDM) and Selective Laser Sintering (SLS), SLA stands out. T.D. Ngo et al. (2018) shows the resolution range in a comparison between the main methods of AM, with stereolithography at 10 microns, as compared to FDM at 50-200 microns and powder bed fusion (including SLS amongst others) at 80-250 microns. This highlights the difference SLA has in terms of print resolution. Being capable of high print accuracy also allows for higher geometrical complexity. SLA also produces a surface finish that is comparable to that of Numerical Control (NC) milling (Pham, 1997), requiring less post-processing due to its smooth surface finishes. 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 provide these requirements will significantly reduce production costs and risks. Thus, SLA's capability of achieving exceptionally high resolutions and precision makes it a top choice as these qualities are highly valued and sought after, even in niche cases.

The second major driving force would be the print's isotropic properties. Isotropic, in the case of engineering material analysis, refers to the material's ability to maintain the same properties regardless of which direction it is tested in. 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 at once, and sometimes even whole volumes, it results in greater bonds between layers, allowing for better isotropic properties. SLA's other main competitor with similar isotropic properties would be SLS, due to the powders being sintered together. However, SLA still possesses the ability to create finer details while maintaining high isotropy properties. Having parts that exhibit consistent mechanical durability and strength regardless of direction 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 therefore makes it valuable to many seeking the perks of the AM market.

A downside to SLA is its reliance on resin materials, limiting its use-cases due to its general brittleness versus thermoplastics. However, with ongoing advancements in hybrid resins and composite materials, it paints a brighter future for SLA by bridging this gap.

In conclusion, because of SLA's combination of highly sought after properties, many industries still choose to seek it from the AM market, therefore maintaining it a good position amongst its competitors.


References
    1. Formlabs. (n.d.). FDM vs. SLA vs. SLS: How to Choose the Right 3D Printing Technology. https://formlabs.com/asia/blog/fdm-vs-sla-vs-sls-how-to-choose-the-right-3d-printing-technology/

    2. Formlabs. (n.d.). Ultimate Guide to Stereolithography (SLA) 3D Printing. https://formlabs.com/blog/ultimate-guide-to-stereolithography-sla-3d-printing/

    3. Huang, J., Qin, Q., & Wang, J. (2020). A review of stereolithography: Processes and systems. Processes, 8(9), 1138. https://doi.org/10.3390/pr8091138

    4. Ngo, T. D., Kashani, A., Imbalzano, G., Nguyen, K. T. Q., & Hui, D. (2018). Additive manufacturing (3D printing): A review of materials, methods, applications and challenges. Composites Part B: Engineering, 143, 172-196. https://doi.org/10.1016/j.compositesb.2018.02.012

    5. Pham, D. T., & Gault, R. S. (1998). A comparison of rapid prototyping technologies. International Journal of Machine Tools and Manufacture, 38(10-11), 1257-1287. https://doi.org/10.1016/S0890-6955(97)00137-5

    6. Ultimaker. (n.d.). Comparing FFF, SLA, and SLS Technologies. https://ultimaker.com/learn/comparing-fff-sla-and-sls-technologies/

    7. 3D Actions. (n.d.). SLA (Stereolithography). https://3dactions.com/blog/sla-stereolithography/

(Edited 07/10/2024)


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