The Case for DIY Approach to High End 3-D Printing
Over the last year I have been working on creating a wristwatch using modern manufacturing methods. The watch industry sees novel applications of materials and methods in a variety of places but rapid prototyping and rapid designing are usually limited in their scopes. Most watch prototypes are visual prototypes rather than functional, failing to make use of the wealth of modern prototyping methods available in the 21st century. One such method, SLA 3D printing, is an ultra-high resolution 3D printing method that lends itself to rapid prototyping of a watch because of its high surface finish quality and high detail. SLA printing also has one drawback: the medium is a sticky and “soapy” resin that requires substantial post-processing.
The resin used in SLA 3D printing is a suspension of monomers and pigments in which crosslinking is induced by focused UV exposure. That’s a verbose way of saying that the resin is a plasticky soup that, when hit with a UV laser, becomes solid: the little bits of plastic cling to each other on a molecular level when they are exposed to the UV light. This differs greatly from more standard methods of 3D printing in which plastic is extruded or otherwise melted together. These little bits of plastic will cling to each other strongly after being exposed to the laser but are fairly weak to any sort of mechanical disturbance due to the fact that the monomers are not entirely crosslinked into polymers.
In order to complete crosslinking the finished SLA printed watch part must be bathed in UV light. The exposure to UV light can be low intensity but long duration (e.g. leaving a part out in the sun) or the exposure can be high intensity and low duration. The latter can be achieved in a curing chamber in which UV lights expose the part from all directions at high intensity for just a few minutes. These curing chambers, sold commercially, can run several hundreds of dollars. Cheaper solutions include UV nail curing stations but those are often less effective than a proper solution due to the fact they are not designed to provide uniform exposure of printed parts.
Many difficult problems in 3D printing can be solved via DIY methods and post-curing SLA prints is no different. In order to cure my SLA printed watch parts, I made a chamber that satisfies all the requirements for proper and expedited crosslinking of the resin. The chamber (pictured below) is a low tech solution to a complicated problem, consisting of a glass jar wrapped in UV-emitting LEDs, then wrapped in reflective foil. The jar is filled with water in which the part is submerged, isolating it from oxygen, speeding up the curing process. The aluminum foil serves to keep heat in and reflect UV light back towards the part, further speeding the curing. The foil also shields the user from UV light, which can be damaging to the eye.
The end result is a sub-10-minute post-cure for a fairly inexpensive sum: only about $30. By satisfying the chemical requirements of the resin curing process, the $30 curing chamber is even able to beat out many other high end curing stations, producing smooth parts with high durability.