When people think about 3D printing, they tend to think in terms of finished objects but have a hard time fathoming how you get from a digital file to an actual thing. So, how, exactly, does a 3D printer work? There are many different ways, but here are three models to consider:
Fused Deposition Modeling (FDM) http://en.wikipedia.org/wiki/Fused_deposition_modeling
FDM is the additive technology many consumer-grade 3D printers are built around. You can think of it as the “smart hot-glue gun” model of rapid prototyping. Plastic (or other material) filament is heated, melted, and extruded through a nozzle and laid down in layers to create an object. Stepper motors drive the nozzle on vertical and horizontal axes and a build plate is lowered on the Z-axis as the layers of extruded filament are built up. Objects printed using this method are not solid but, rather, made up of “shells” that define a surface. Often there is a honeycomb structure which makes up the interior of FDM objects. Makerbots and Rep Rap printers utilize FDM. There are limitations on the number and size of overhangs this process can accommodate, but it is possible to print models with overhangs by using a support structure akin to scaffolding that is printed on the outside of an object. There tends to be a fair amount of post-processing with FDM to get satisfying models.
Granular Materials Binding http://en.wikipedia.org/wiki/3D_printing#Granular_materials_binding
Granular Materials Binding fuses a powder with dots of glue, also in layers and also moving the build-area downwards until an object is built up. Models made with this method have interiors of solid powder, unless you design space into your object, but overhangs are easier to accommodate as you will always have support where you need it from the loose powder outside your object. Granular Materials Binding is faster than FDM and allows for a higher resolution. Color information can be included in models, as color from cartridges can be delivered at the same time as the binder (i.e. glue) and unused powder is never wasted as it can always be reclaimed and color is only included in the binder. Post-processing of models is less time-consuming, but they are heavier than models printed in plastic because they are solid.
Stereolithograpy (SLA) http://en.wikipedia.org/wiki/Stereolithography
SLA is also an additive process that uses light (usually a laser) to cure a liquid (resin) to create a model. There is a $100 3D printer currently being manufactured and beta-tested, the Peachy Printer, that uses this process, and was funded by the crowdsourcing platform Kickstarter.
These additive processes can accommodate manifolds, where every surface is connected to another surface. The surfaces are mesh surfaces, in which every plane can be approximated with polygons. 3D models must be prepared for 3D printing using a software specific to your printer, which translates the digital model into a format your printer understands. This is referred to as “slicing,” where the software slices a model and creates cross-sections which approximate curves. This is how the printer will make shapes. The code behind 3D models is G-code, a numerical control programming language that instructs machines how to move and delineates which paths to follow. There are massive amounts of code that go into creating 3D printed objects.
But how do you make a 3D model to print? Well, that’s another post! Look for that in 3D Printing Primer, part 2.