Additive manufacturing technologies through resin polymerization

There are several additive manufacturing technologies capable of producing high-definition parts, with a high level of detail and practically perfect finishes, through resin polymerization.

  • Stereolithography (SLA) is a technology that cures layers of photocurable resin by applying a laser on them. It was invented and patented by Chuck Hull in 1986.
  • Digital Light Processing (DLP) is the technology commonly used to project digital images. EnvisionTEC developed the technology whereby this technology could be used to, like SLA, cure layers of light-curing resin to manufacture three-dimensional parts.
  • Digital Light Manufacturing (cDLM). Just as DLP is an advance over SLA, especially in terms of speed, cDLM technology innovates over DLP by multiplying its printing speed and bringing 3D printing using photocurable resins to the field of mass manufacturing of the final part.

Note: SLA technology is typically used by immersing the platter in a VAT, from top to bottom, and DLP by suspending the part in the air, bottom to top. However, both technologies occasionally use both techniques. The only difference ever, between SLA and DLP, is the light source (a traveling laser or a full surface projection).

Stereolithography or SLA

How it works?

In a container of photocurable or photopolymeric resin (VAT), it is submerged layer by layer. In each layer, a zenithal laser cures said resin, joining the first cured layer to the plate and the subsequent ones to each previous layer. In this way, when printing ends, the printed part is submerged in the bottom of the VAT.

Strengths

  • Produce parts with high definition.
  • Permite la fabricación de piezas de gran tamaño (hasta 1,5 metros)

Weaknesses

  • Since the laser has to travel to draw the section of the part at each layer, just like an FDM printer does when depositing material, it is a very slow technology.
  • Since the VAT is large, and SLA resins densify over time, the entire contents of the VAT must be discarded periodically and replaced with fresh resin. This makes the technology much more expensive to use than initially estimated.
  • For the same reason, the size of the VAT and its high resin content, using different resins for different applications is complex and expensive.
  • It is only possible to print parts as tall as the depth of the VAT. The greater the height of the desired part, the greater the volume of resin that the VAT must contain, with all that it entails.
  • The post-processing of the printed pieces includes a wash in isopropyl alcohol and the manual removal of the supports that held them during the printing process.

References

Digital Light Processing o DLP

How it works?

Similar to SLA technology, this technology cures resin layers. However, the light for curing is emitted from the bottom, up, and using a DLP projector, and the plate rises into the air layer by layer. In this way, when the printing ends, the piece is in the air, suspended from the plate.

Strengths

  • Dado que se utiliza un proyector capaz de «iluminar» la bandeja de impresión de una sola vez, en apenas unos segundos, es una tecnología muy rápida.
  • Al sustituir el láser por un componente tan estandarizado como un proyector DLP, esta es una tecnología con un bajo coste de inversión inicial y de mantenimiento futuro.
  • Al elevarse la pieza desde la bandeja, en lugar de sumergirse en ella, el VAT pasa a ser una bandeja de poca altura. Esto implica una inversión inicial muy reducida en resina.
  • Por el mismo motivo, es sencillo utilizar diferentes resinas para diferentes aplicaciones, y cambiar entre ellas sin apenas coste y esfuerzo, ofreciendo una solución extremadamente versátil.
  • También por el mismo motivo, y dado que el plato se eleva en el aire hasta la distancia que se desee, no hay limitación virtual en la altura de la pieza a imprimir.

Weaknesses

  • Since the part is suspended from the plate, large printers tend not to be produced to avoid the complexity of safely supporting its weight.
  • The post-processing of the printed pieces includes a wash in isopropyl alcohol and the manual removal of the supports that held them during the printing process.

References

Continuous Digital Light Manufacturing o cDLM

How it works?

This technology is virtually identical to DLP except that it uses an oxygen-permeable membrane as the bottom of the resin tray. This technology ensures that the piece, as it cures layer by layer, is never really in contact with said bottom of the tray. As a consequence, there is no adhesion factor between the part and the tray, nor is a separation process necessary, which greatly speeds up the printing process.

It is not about the projector projecting and curing faster. It is that the movements around said curing process are carried out in much less time, making prints that used to take hours to be made, now be made in minutes.

Strengths

  • All the DLP strengths
  • Extreme printing speed that allows this technology to be considered for mass manufacturing of the final part, in addition to its traditional capacity for prototyping and tooling.

Weaknesses

  • All DLP weaknesses

References

  • Nuestra web sobre el inventor de la tecnología cDLM, EnvisionTEC.
  • Manufacturer website: EnvisionTEC (web externa, en inglés).
  • La única impresora con tecnología cDLM es la Envision One, de EnvisionTEC.

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