3D printers

I got pretty into 3D printing in 2022. Here are some things I've learned. Be aware that the industry moves very quickly, and this information is likely to go out of data within a few years.

Types of 3D printers

The printing techniques one is likely to see in personal use are almost all material extrusion (FDM) or vat polymerization (MSLA and DLP). There are numerous other methodologies (see this All3DP article), but these make up the vast majority of printers intended for the home. Sadly, all known methodologies are cursed. Also, you'll see the word "fusion" a lot, but despite my earnest prayers it never means nuclear fusion.

• Fused Deposition Modeling printers push filament (usually thermoplastic) through a hot nozzle to melt it. It is then extruded, where it cools and solidifies. The nozzle is moved in the xy plane until a layer is completed, at which point it moves up to deposit the next layer. The printing proceeds from the bottom to the top of the model, with the bottom resting on the buildplate (which stays at the same height throughout).
• Masked StereoLithogrAphy (sometimes just SLA) and Digital Light Processing printers shine light into a vat of photoactive resin (a photopolymer), using e.g. a laser or an array of LEDs. The original SLA traced each xy layer using a laser and mirrors. DLP likewise uses mirrors, but they form a mask allowing a plane to be drawn as a single unit. MSLA uses an LCD mask, eliminating the need for a mirror layer (the light is blocked wherever the mask is activated; where it gets through, it solidifies the resin). The light source is underneath the mask, which is underneath the vat. The printing proceeds from the bottom to the top of the model, with the bottom attached to the buildplate. This buildplate rises as printing continues, so the bottom of the model ends up the furthest away from the vat (and thus at the highest point of the print).

Note that in both methodologies, problems can arise when a layer occupies part of the xy plane unoccupied by the layer underneath it. In the FDM case, material extruded into such areas is likely to fall to a lower z coordinate. In the case of vat polymerization, if the area is similarly isolated in the xy plane (i.e. disconnected from all elements below it or at the same layer), the solidified material is unlikely to rise along with the rest of its layer, settling instead to the bottom of the vat.

Other methodologies include powder bed fusion (SLS, SLM, EBM, MJF), material jetting (including DOD), binder jetting, and direct energy deposition (LENS, EBAM). Some of these get pretty esoteric. Some of them are practically welding. LENS spot-fuses titanium alloy powder using a multi-kilowatt laser in an atmosphere of monatomic argon to build jet engine blades. It is not cheap even before one considers the logistics of ensuring a regular supply of bulk-tanked CGA-680 Ar (and avoiding asphyxiation thereby).