What Is Resin 3D Printing?
Resin 3D Printing or stereolythography, machines use an ultra-violet light. This builds models by changing liquid resin solid. The process is called: photopolymerization. Mirrors direct the laser beam across each axis on the build platform. The process is repeated layer by layer until the solid model is complete.
In Addition, highly intricate detail, can be achieved in a short space of time. These two factors make resin 3D printing great for prototyping parts with tiny features. Furthermore, SLA prints are also the closest in form to an injection molded part. There are two types of resin printers: bottom-up and top-down.
SLA 3D printing and Design
This form of printing can help designers, produce a prototype, that feels like the injection molded final product. Primarily, used for the final prototype, once all forms and fittings have been signed off. Perfect for showcasing the final look and feel of the product. All before investing in a mold tool.
Here is an example of where SLA has been used in the design process. The image is an enclosure designed to house components for a motion detector. With this we can ensure all components fit snug inside. Furthermore you can see how everything is interacting when the shell is fixed. Ultimatly, this is the closest you can get to touching a final product, before buying a mold tool.
3D Printing Resins
SLA 3d printing machines uses UV light and photopolymers to build models. The fine UV beam turns the viscous liquid solid. Ranging around $50 per litre, for Standrd Resins. Whereas, high detailed and castable resins can exceed $400. In addition, color variation is limited. Furthermore, SLA resins have a limited shelf life of one year.
UV curing of parts in stereolithography is paramount. Otherwise parts will not achieve thier top properties. Correct UV exposure times are listed with each type of polymer.
Printing Resin Properties
Standard
High detail, smooth finish. Becomes brittle over time. Perfect for making precise prototypes.
Transparent
Same as standard, only transparent/ transluscent. Great for fluid and electric housing prototypes.
Castable
Still achieves high detail and smooth finishes. Used mostly for jewelery and dental products.
Durable
Most mechanically sound out of the resin family. Will continue to bend and absorb force.
High Temp.
Takes 3-5 x more heat than other resins. Prints same resolution. Ideal for heated prototypes.
Flexable
Perfect for erganomic parts of multi body prototypes. Not ideal for high resolution parts.
Resin 3D Printing Perameters
Stereolithography printers have 3 varying perameters. Each affecting either Resolution, print speed or ease of post processing, if changed manually. Otherwise, these are pre-set for different types of resin.
-Layer hieght
-Light source resolution
-Part orientation/ Support location
Resin Printers achieve layer heights of 25, 50 and 100 microns. Therefore, giving them the smoothest finish, as well as, matching the highest detail in 3d printing.
Resin 3D Printing Supports
Photopolymarization uses supports like other 3D printing processes. However, parts are printed at an angle. This is to combat the peeling stage. Each new layer is pulled from the vat to allow it to harden. After which it is dipped back in, ready for the next layer. In addition, the print fails if the build plate can not be seperated from the vat.
Support structures must usually be removed by hand. This is because the are printed in the main build material.
Resin 3D Printing Limitations
Resin 3D prints are liable to curling or warping, much like FDM 3D printing. Large flat surfaces bearing the most risk. Supports are key in fixing prints to the build plate and thus, mitigating warpage. In addition, SLA prints are printed at an angle to further prevent this issue.
Furthermore, deviation occurs in the seperation stage. The image shows the forces causing a print to bend, due to each cooling layer having shrunk slightly. The effect builds layer by layer to cause warpage. This effect makes flexable resins not suited for high resolution prints.
Post-Processing
SLA 3D printers can achieve feature sizes as small as 0.3mm. However, most prints need supports to be removed. These are added automatically by the slicing software. A good printing technician will optimise the orientation. Positioning supports in the least significant areas.
Many finishes can be achieved in resin 3d printing. One can go further than just sanding and support removal. Such as: painting, pollishing or perhaps a mineral oil finish.
Support Removal
Resin supports consist of the same material as the model. Thus, they need to be removed by hand. Usually achieved, using mini pliers. Supports are printed with a thin tip for easy removal. Even so, support marks will still be visible.
UV Curing
The curing process optimised your 3d printing resins’ mechanical properties. For instance, makeing them stronger and/or more flexable. It depends on which resin is being used. This effect happens as photo-polymarisation is still happening.
Sanding
Sanding down support marks is neccesary for an all over smooth finish. 600 grit paper is a good start. However, 800-1000 is better if you would like to have an injection mold style finish. Moreover, wet sanding is advised before painting.
Resin 3D Printing Conclusion
Stereolithography’s best features are the high levels of detail that can be achieved along with a smooth finish. Making them ideal for injection mold like prototypes. In addition, resin prints are also used in dentistry and jewelery.
In Contrast, SLA’s largest pitfall is the materials mechanical properties. Resins are usually brittle. and therefore not suited for end use. Furthermore they degrade over time, becoming more brittle and losing shade/color, through being photo sensetive. Coatings can be added, however this will only slow the process.