On the difference between DLP and LCD based SLA printers

Laser, LCD, and DLP are three distinct methods of exposing a light-sensitive resin in layers to cause a cross-linking of liquid polymers, curing the liquid into a solid object. All of these are used within SLA printers, a term used to refer to the stereolithography process. There has been a disturbing trend to refer to LCD printers are “DLP” printer that started when lower price-point manufactures began to use the already-taken “DLP” term for marketing purposes and claiming it was ok because their LCD does light processing using digital signals. Doing so, however, is like calling a gasoline-engine car an electric vehicle – something that it is not – just to confuse consumers into thinking that they are getting something often seen as more desirable but at a lower price.

Laser, (originally L.A.S.E.R as an acronym for Light Amplification by Stimulated Emission of Radiation) uses galvanometer scanners to direct a light beam via vector and raster scanning. The process is fast for smaller object, but get progressively slower when it must draw out more objects. The advantage is a smooth surface finish and compatibility with resins high in polymer content for the strongest resulting parts. An example of desktop laser-based SLAs are the Peopoly Moai and the Formlabs Form-2 printer.

LCD is a variation of SLA that uses a Liquid Crystal Diode display, the same as in most laptops and mobile phones, as a mask. It is also known as MSLA, or masked SLA. A light source is placed on one side, and the resin on the other. Because the entire layer can be exposed at the same time, they are generally faster for printing more or larger objects. Example of LCD-based SLA printers are the Anycubic Photon, Wanhao Duplicator 7, and the EPAX-3D 1X. One reason why LCD still remains on the low end, because the fact that they can simply be manufactured for less cost, is that there is a limited amount of light that can pass through the LCD panel before it overheats and self-destructs. This limits the speed at which printing can take place. To help make up for this lower amount of light exposure, the resin makers increase the monomers and photo-sensitive initiators, with a resulting increase in potential for shrinkage and weaker parts. In reality though, due to advances in resin such as Siraya Labs Blu (the strongest LCD resin I have tested) and eSun Bioresin (the strongest solid-color LCD resin I have tested), some very strong parts can be made – just as strong, if not stronger, than PLA and ABS parts on FDM printers.

DLP uses a digital micro-mirror device in which light is reflected through a projector lens and onto a tank of resin. Because this matrix of mirrors can be well cooled, a lot more light can be directed than with LCD, thus making it the choice of larger, faster, and more expensive printers that can still make use of less sensitive and stronger resins normally reserved for laser. The downside being a higher price point, taller printer size, and sometimes lower resolution because DLP chips tend to max out at 1080P.

But you may ask – why is it not ok to refer to my LCD-based printer as “DLP” when the manufacturer says it has light processing and is digital? The answer is because the term DLP was already taken for a digital micro-mirror projector device, and there would be no distinction between the technologies, both of which are used in resin printers, if you used the same term for both.

Here is a video showing a DLP chip in action:



This is TI explaining their DLP reference design. Notice how it does not make use of an LCD:

Examples of some DLP printers are:

Chimera:

https://www.instructables.com/id/Chimera-60-DLP-resin-3d-printer/

Ember:

https://www.fabbaloo.com/blog/2014/12/28/see-autodesks-ember-3d-printer-in-action

Milkshake 3D:

https://www.milkshake3d.com

Carbon-3D

Moonray

G3D T-1000

https://www.g3dsys.com/product/t-1000-dlp-3d-printer/

FlashForge Hunter:



References:

See https://en.wikipedia.org/wiki/Digital_micromirror_device

https://en.wikipedia.org/wiki/Digital_Light_Processing






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