A 3D printer builds a part up in thin layers, from plastic or metal powder. The process is also called additive manufacturing, because material is added, instead of being cut away as in a CNC machine. It suits quick prototypes, shapes that are hard to cut, and production where every part differs a little.
The printer reads a 3D model from CAD. Software slices the model into layers. On a plastic thread printer, each layer is usually 0.1 to 0.3 mm thick. Resin and metal printers use thinner layers, often 0.02 to 0.1 mm. A plastic printer melts a plastic thread and lays it down along each layer. A metal printer spreads a layer of fine metal powder and melts it with a laser where the part is solid. Then the printer lowers the part by one layer and repeats.
Consider a startup in Hyderabad that designs the casing of a smart electricity meter. The casing is 40 mm tall. The printer slices it into layers of 0.2 mm, which gives 200 layers. It prints the casing in about five hours. The founders hold it in their hands, find that the button is badly placed, change the model and print another one the next day. Making a mould for this test would have cost lakhs of rupees and taken weeks.
There are three common kinds of printer. The cheapest melts a plastic thread and lays it down, as described above. A resin printer uses light to harden a liquid, layer by layer, and gives a smooth surface, so it suits small detailed parts such as dental models. A metal powder printer costs far more and is used for aircraft and medical parts. After printing, a part usually needs cleaning, and a metal part needs heat treatment and polishing.
Hospitals also use printers. For example, a hospital can print a model of a patient's bone, using data from 3D medical imaging, so that surgeons can plan an operation. Where each printed item is different, the work is called mass customisation with 3D printing.
Printing is slow and, per part, expensive for large numbers. Printed plastic parts can also be weaker than moulded parts. So for thousands of identical plastic parts, injection moulding is used instead. Printing is also offered by on-demand manufacturing platforms.