3D printing has been around longer than most people realise. The idea was first patented in 1984, but it took another 20 years to really get off the ground. What makes 3D printing so special is that it’s a additive process - material is added to more material to create one whole part, as opposed to what’s normally a subtractive process. A chair made traditionally out of one big block of wood would be made by cutting away unrequired bits of wood from the greater block. In 3D printing, a material is molded together to make a whole.
This is normally done by taking a thermoplastic like ABS or PLA and heating it till it’s amorphous (able to be molded into a shape). The amorphous plastic is then injected over a build surface, layer by layer, until the product is formed. The injection point behaves according to the computer model of the product. In our chair example, the computer would give specific instructions to the syringe to first make four legs, then the seat, then the backrest. This would all form one seamless whole, without any separate parts. ABS and PLA are popular plastics, but there are many others available.
An important distinction to remember when discussing 3D printing is the difference between an additive process and a constructive process: an additive process is different from a constructive process precisely because one seamless whole is formed. A house, although it forms a whole, is built brick by brick, and each is distinguishable from the other. Therefore, it is not built additively.
The truly amazing thing about 3D printing is that with enough filament (and a big enough printer) anything could be made from a technical specification. A computer-modelled version of your house could easily be programmed, and so (again, with enough filament and a big enough printer) your entire house could be built additively, down to the knives and forks in their draws. This is what makes 3D printing so exciting - genuinely anything can be made, if the digital model - known as a virtual blueprint - can be made first.
The lifeblood of 3D printers is their virtual blueprints - these are used to provide instructions to the printer, so it “knows” where to inject over a surface. Freeware virtual blueprints for almost anything are available over the web, and should be easy to get hold of. These blueprints are already a real threat for many businesses, as they could make many products freely available to anyone with a 3D printer.
The printers, although expensive, will in upcoming years become invaluable to a household, as many products that would otherwise cost money could be printed at home at a fraction of the cost. One of the greatest challenges facing scientists in the field is making a plastic that is easily printable and affordable, but able to withstand high temperatures such as those required for cooking implements, kettles etc. etc. Once this is achieved, a 3D printer would be able to offset vast costs for consumers everywhere; all they would need to make a new knife and fork set, for example, is some freeware knife and fork blueprints, a printer, and enough filament to make them.
Generally, a printer uses a collection of 2-dimensional specifications to form a whole. An injection syringe will print an entire level without moving up or down, then move up 1/10th of a millimeter and print another level. This continues until the product is finished. The size of each level is determined by the resolution of the printer - most printers on the market have maximum resolutions of about 1/10th of a millimeter. There is software like Slic3r available on the market that takes a 3D blueprint and slices it into many two-dimensional blueprints, which are then converted into x- and y- axis instructions for the syringe.
Some printers are able to build supports during the additive process, which can then be dissolved after printing. These supports are used to hold structures in place during the process until the model is finished.
It should be pointed out that on most printers, it’s not just the injection syringe that moves, but the build platform as well. This allows for greater maneuverability and protects the delicate syringe from any avoidable damage.