SLA frente a FDM:comparación de tecnologías de impresión 3D comunes

La fabricación aditiva, y específicamente la impresión 3D moderna, ha recorrido un largo camino desde su desarrollo inicial en 1983. Las piezas impresas en 3D de hoy en día pueden alcanzar altas resoluciones y tolerancias. Dos de las técnicas más comunes son la estereolitografía (SLA) y el modelado por deposición fundida (FDM). Si bien ambos surgieron en la década de 1980, utilizan formas claramente diferentes de fabricar piezas y, como resultado, cada una de las piezas finales brinda diferentes beneficios.

Las piezas SLA fabricadas con la resina MicroFine Gray™ de Protolabs logran una resolución de precisión micro.

¿Cómo funciona el SLA?

SLA utiliza resinas de fotopolímeros como materia prima para sus piezas. Los fotopolímeros necesitan luz ultravioleta intensa de un láser para fraguar, y esa es la idea central detrás de SLA. La construcción tiene lugar en una plataforma sumergida en resina. Un láser se ubica sobre el tanque y, dirigido por espejos de precisión, fusiona la resina líquida, endureciéndola para lograr la forma deseada de la pieza, una capa a la vez. Las estructuras de soporte son las primeras capas creadas, lo que garantiza que la pieza esté bien sujeta a la plataforma y apoyada adecuadamente. Con cada pasada, una cuchilla recubridora rompe la tensión superficial de la resina sobre la pieza. Luego, la pieza se construye de abajo hacia arriba.

¿Cómo funciona FDM?

Una de las primeras formas de impresión 3D, FDM, fue inventada por uno de los fundadores de Stratasys, Scott Crump. El concepto es simple:es muy parecido a usar una pistola de pegamento caliente. Un filamento termoplástico o carrete de plástico se calienta hasta el punto de fusión. El plástico líquido caliente emerge a través de una boquilla para crear una capa única y delgada a lo largo de los ejes X e Y en la plataforma de construcción. La capa se enfría y se endurece rápidamente. A medida que se completa cada capa, se baja la plataforma y se deposita plástico fundido adicional, lo que hace crecer la pieza verticalmente (a lo largo del eje Z).

Propiedades materiales de SLA y FDM

Proceso	Cómo funciona	Fuerza	Finalizar	Materiales comunes
SLA	Fotopolímero curado con láser	2500-10 000 (psi) 17,2-68,9 (MPa)	Capas adicionales de 0,002-0,006 pulgadas (0,051-0,152 mm) típicas	Fotopolímeros termoplásticos similares al ABS, PC y PP
FDM	Extrusiones fusionadas	5200-9800 (psi) 35,9-67,6 (MPa)	Capas adicionales de 0,005-0,013 pulgadas (0,127-0,330 mm) típicas	ABS, PC, PC/ABS, PPSU,  PEEK, ULTEM

En esta parte de FDM, las líneas de la capa son visibles. Foto:3Dhubs.com

Neither of these techniques creates parts as strong as ones that are injection molded, for example, but they are suitable for rapid prototyping. SLA’s thin layers and strong bonding between the layers makes its parts smoother, with minimal striations along the Z axis, the direction of the build.

SLA Considerations

If details and surface smoothness are important for your part, SLA handily beats FDM. In part, because of its roots in laser technology, SLA parts can offer incredibly fine detail, yet pricing is competitive. Also, the SLA ultraviolet light curing process avoids FDM’s issues caused by heat compressing previously drawn layers. Equally important, SLA offers many additional finishing options, such as dyeing and texturing.

With SLA, there are three resolution levels from which to choose, ranging from 0.004 in. (0.1016mm) to 0.001 in. (0.0254mm) for layer thickness. Choosing one over the other not only affects part quality, but manufacturing time, too. Minimum feature size can be as small as 0.0025 in. (0.0635mm) on the XY plane and 0.008 in. (0.2032mm) on the Z axis.

One important issue with SLA parts is their sensitivity to light. As photopolymers, they can degrade from exposure to UV rays, such as sunlight. Adding a protective coating can slow this process.

MicroFine™ is an exclusive Protolabs material available in gray and green. This micro-resolution, ABS-like material can print layers that are extremely thin:just 0.001 in. (0.0254mm). That kind of precision is a prerequisite for building parts with many small feature details and is regularly used for small and highly accurate medical components.

FDM Considerations

FDM uses engineering-grade materials (see chart above) and offers a range of color options. With some FDM printers, parts can be as large as 427 in. x 153 in. x 172 in. (10,845.8mm x 3,886.2mm x 4,368.8mm). Essentially it depends on the size of the build space. Also, FDM parts are moderately priced, making it ideal for hobbyists, dental offices, and classrooms.

FDM’s tolerance is dependent on how the machine is set up, but can be as small as +/-0.0035 in. (+/-0.0015mm). Layer thickness varies based on the material you’re using, and some printers can print as thin as 0.001 in. (0.0254mm), although this would lead to long print times and may not be possible with larger parts.

Because temperature affects the core material, FDM parts are subject to rippled exterior edges caused as new layers are dropped atop previous layers. These Z-axis issues also cause weakness in the build. So, a part’s strength is entirely dependent on the direction in which it was built.

FDM does not do well with wide, flat areas, and has difficulties printing sharp corners, so adding fillets to your design makes sense. For all these reasons, prototyping with FDM works well when accuracy and surface finish aren't critical.

Although FDM gets the check for cost, SLA is quite competitive, especially for cosmetic prototypes with intricate designs. It’s also a go-to process to create forms for injection molding and casting.

When to Use SLA and FDM

With all of these considerations in mind, here is a list of when to use either method.

Use SLA :

• For rapid, complex prototyping
• When precision and a smooth surface finish is important
• When high resolution, fine detail, and accuracy is necessary
• For creating molds for casting to facilitate mass production
• When strength and durability of the model is not crucial (models made from resin may suffer when exposed to the sun for long periods)

Use FDM :

• For prototyping
• When a selection of colors is needed
• For low-cost models
• When precision and surface finish aren’t crucial
• For hobbyist and maker projects

SLA produced this clear, red taillight with a smooth finish and custom post-production painting.

For additional help, feel free to contact a Protolabs applications engineer at 877-479-3680 or [email protected]. To get your next design project started today, simply upload a 3D CAD model for an interactive quote within hours.