A beginner's guide to resin 3D printing

This post supports and augments my previous post on 3D printing which focused primarily on FDM (Fused Deposition Modelling) printers - see A beginners' guide to 3D printing. In summary, FDM printers apply a series of layers of melted plastic to create an object in three dimensions. By contrast, resin, or SLA (Stereolithography), printers harden a series of layers of light sensitive resin to create a three dimensional object.

Image source:https://jiga.io/resource-center/3d-printing/best-affordable-resin-3d-printers-2021-buyers-guide/

The majority of domestic resin printers now use ultraviolet light projected through an LCD screen to harden small areas of resin at the base of a vat. The higher the resolution of the LCD screen, the more intricate and accurate the detail on the object can become.

The best way to explain how 3D resin printing works is to follow each stage of the process required to create a model.

 

Stage 1 - Creating a 3D image

3D images are created with a 3D Computer Aided Design (CAD) program. Once an images has been created, it is usually saved as a .STL or .OBJ file which can be understood by the slicing software for the 3D resin printer.

3D images can be downloaded from internet sites such as Thingiverse ......

.....or created yourself with 3D CAD software such as SketchUp, Fusion 360 or TinkerCAD.

For more information on downloading and creating 3D images see A beginners' guide to 3D Printing

Stage 2 - Slicing the image

As with FDM printers, SLA printers need to be given instructions to tell them what shape each layer of the 3D print should take. The .STL or .OBJ file of the object which has been exported from the 3D CAD program or downloaded from the internet ........

.... is opened in the slicing program which is usually supplied with the printer.

NOTE: For objects with overhangs, additional supports need to be created by the slicer or other programs

Slicing is achieved with the click of an on-screen button and the set of instructions required by the printer is saved on to a USB stick, SD card or sent to the printer via a cable or Wifi.

Stage 3 - Setting up the printer

Like a FDM printer, the print bed or building platform needs to be levelled in relation to the upper surface of the LCD screen. A sheet of standard A4 paper is positioned between the plate and the screen and screws adjusted and tightened.

The next job is to fill the vat with light sensitive resin. This is usually supplied in a 1kg bottle. 

Care must be taken in handling the resin as it is mildly toxic and so plastic gloves are recommended to avoid contact with the skin.

The vat is then positioned on the printer above the LCD screen and fixed into place. The base of the tank is transparent to allow light to pass through.

Stage 4 - Printing

Assuming object's slicer file has been loaded into the printer via the USB stick, SD card or via the cable or wifi, it can be selected from the printer's user LCD screen.

It is then just a question of waiting. The building platform (or print bed) is gently lowered by the printer into the vat and the first layer exposed through the LCD screen and the base of the vat.

The print bed is then raised a few millimetres before being lowered again, this time a fraction of a millimetre higher to allow the next layer of resin to be hardened. This process is repeated layer by layer until the object has been printed.

The print bed is then raised to its highest point to allow excess droplets of resin to fall back into the vat.

Stage 5 - Washing

The excess resin needs to be thoroughly removed from the outside of the printed object otherwise it will be hardened on to it by natural UV light. This can be done with Isopropyl Alcohol (IPA) either manually or more efficiently using a dedicated washing machine.

The object can be placed into the tank either still attached to the build plate or removed from it if it is large enough not to slip through the mesh of the wire basket holding it in place.

The alcohol is then agitated by the machine for five to ten minutes (time being dependent on the size or complexity of the object) before being removed and allowed to dry off for a few minutes.

Stage 6 - Curing

To ensure the resin is fully hardened it is then exposed to UV light. Again, this can be achieved simply by placing the object in sunlight or more reliably by placing it on a turntable while being exposed to UV LEDs. The process takes five to ten minutes with UV LEDs.

Stage 7 - Tidying-up

The object is now ready for painting or attaching to other parts to form a larger model.

The printer needs to be tidied away. If it is not going to be used for some while then the resin needs to be poured back into its light resistant container. If more parts are going to be printed then the resin can be left in the vat. Resin printers are usually supplied with plastic covers which resist UV radiation and some come with lids to cover the vat. I usually cover my vat with a layer of thick card as an additional protection and also place another large piece of card between the printer and the washer/curer to ensure there is no accidental UV light leakage.

It's very difficult to prevent drops of resin dropping from the build plate or unwashed object as they are being removed from the printer and so I find it useful to have a good supply of paper towels readily to hand.

Conclusion

An that's really all there is to it. The quality of printed object produced by SLA printing is superior to that produced by even the best FDM printers

Left = Resin printed - Right = FDM printed

They are probably similar in upkeep costs but resin printers can be a bit messy to operate and maintain. The build size is also smaller on resin printers, but as they are generally used for the production of small detailed parts that, to my mind, is quite acceptable.