3D Printing in Plastic: Jello, Chocolate, Gummi Bears and Layer Cake
While there are dozens of trademarked processes for producing 3D parts in plastic, these methods can conceptually be organized into a simple dessert buffet. Each dessert nicely illustrates how a raw material is turned into a solid objects.
Let’s start with Jello. Jello is fundamentally a chemical reaction that takes a liquid and turns it into a solid. In the same way, light based 3D printers consist of selectively hardening a chemical liquid by exposing it to light. These methods include stereolithography (SLA), Polyjet, Direct Light Processing (DLP) and Continuous Liquid Interphase Printing (CLIP). All materials must be light responsive resins, but many are formulated to simulate other plastics. These processes can produce parts with incredible detail and a smooth finish but are not necessarily strong or chemically resistant.
Next to the Jello is the Chocolate. Just like a chocolatier squeezing molten chocolate out of a piping bag, Extrusion printers push the raw material through a heated nozzle, melting it, then distributing it in gradually cooling layers. If some of the upper layers extend out over the base of the part, support material is needed to prevent material from “drooping” as it cools. Any material that can be softened when heated, then cooled and hardened could theoretically be printed with this method. The process of choice for many hobby 3D printers, Extrusion machines are technologically the simplest, but also produce the roughest parts.
Then, on to the cake. While less widely spread than Jello and Chocolate, these “Layer Cake” parts are assembled by stacking thin sheets of plastic or paper (cake) alternating with layers of glue (frosting). Laminated Object Manufacture (LOM) and Selective Deposition Lamination (SDL) both use this method. Individual sheets are cut via laser or a precision metal cutting blade as they are added to the stack. The primary benefit of these machines is that they are true “office” printers. They do not outgas chemicals and (in some machines) use standard printing paper as the raw material. While relatively weak mechanically, they can produce beautiful full-color models suitable for product mock-ups.
Finally, there’s the bag of gummi bears left in the backseat of a hot car. For those who have not had this experience, a bag of individual lumps of gummi becomes a porous wad of fused bears after exposed to high temperature. This is the fundamental process of “Sintering” based 3D printers. A laser is scanned across the top layer of a box full of metal or plastic particles, fusing them together in a pattern. A fresh layer of particles is spread over the fused layer, and the laser fuses the second layer to itself and the first layer. Eventually, the entire build chamber inside the printer is a block of powder, with a fused part embedded inside. The part is broken free in a shower of build materials. Because the part is embedded in layers of powder as its built, incredibly thin, delicate parts are possible. This process also produces some of the strongest 3D printed parts, with nylon or metal parts nearly as strong as their machined or molded counterparts.
When thinking about 3D printing, remember it’s a buffet of processes. Sometimes you feel like cake, sometimes you need to go with the Jello.