How is UV light part of the fast-evolving 3D printing technology?

There is no doubt that 3D printing will be a technology to be even further developed and implemented in the future although it has been already be used in industrial application for years.

3D printed skull

Generally spoken: a 3D printer can be used to replicate any figure of any size with high accuracy. The fact it might take several hours to produce one single design (depending on the size), it consumes much less time and is much more cost efficient compared to e.g. prototyping carried out by engineers or product designers. This is due to the fact that 3d prints can be created from a vast selection of materials such as polymers, resins and diverse metals.

A 3D printer works with building up layer by layer of a desired compound (resin, polymer or metal). Until the layers merge into the desired 3d shape. Major preparations have to be done before the printing can be started as the printer relies on a computational generated 3D model.

There are mainly four printing methods: fused deposition modelling (FDM), stereolithography (SLA), carbon CLIP technology (CLIP stands for continuous liquid interface production), and selective laser sintering (SLS). Depending on the type of compound used, the type of drying or curing will be different. From the mentioned techniques, the SLA and CLIP are the ones where photosensitive resins are employed. Generally, lasers or UV-LED lamps are used. Lasers can be used for all materials, while UV-LED lamps are applied for resins, gels and special polymers.

To look into the UV process in more detail: One of the most important factors to have in mind when working with a 3D printer is the curing of the compound, since it is not possible to continue applying raw material if the work’s surface has not dried yet. By irradiating the composite with UV light, the composite hardens as it polymerizes, allowing more material to be applier in further layers.

Depending on the wavelength and the material properties, the UV exposure time determines directly the polymerization process or the curing of the resin. It is also important to consider which resin is the best fit to the printer. The most common polymeric resins used in the UV-curing are thermoplastic polymers, such as acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyamide (PA) and polycarbonate (PC), and thermosetting polymers such as epoxy resins, which requires thermal or UV-assisted curing to complete its polymerization process.

Metal materials usually cannot be cured by UV light sources due to their requirement of a more focused power source which fall upon one small area. Hence, laser technology is more frequent used when working with metals.

Besides the already mentioned curing of the resin while printing, UV is further used in the post-processing of the formed shape. This procedure is carried out to improve the material performance and mechanical properties, minimize shrinkage, increase of resistance or resilience, among others.

But why should an LED be used as a light source in the 3D industry? As it was mentioned before, a LED lamp requires a lower energy source to operate and in the present days where in the industry the price of electricity represents a big share in the operational costs, it is a factor that must be considered. Further LED light sources are very compact and therefore easy to place especially in the smaller set-ups of desktop 3D printing machines.

Wang, X., Jiang, M., Zhou, Z. Gou, J., & Hui, D. (2017). 3D printing of polymer matrix composites: A review and prospective. Composites Part B: Engineering, 110, 442-458; Stansbury, J. W., & Idacavage, M. J. (2016). 3D printing with polymers: Challenges among expanding options and opportunities. Dental Materials, 32(1), 54-64

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