3D printing or additive manufacturing is a process of creating three dimensional solid objects from a digital file using additive methods. An additive method involves the making of an object by laying down successive layers of a particular material- a layer at a time- until the entire object is created. The objects are built up without any cutting; drilling or machining- which is why the industrial version of 3D printing is also called additive manufacturing (AM). Each constructed layer can be seen as a thinly sliced horizontal cross-section of the eventual object.
The process of additive manufacturing or 3D printing starts off by making a virtual design of the object that is to be created. This virtual design is made in a CAD (Computer Aided Design) file using a 3D modeling program or with the use of a 3D scanner. A 3D modeling program is used for the creation of a totally new object while a 3D scanner is used to copy an existing object. The digital file of the virtual design of the object is uploaded in the 3D printer which creates the object layer by layer.
All 3D printers do not use the same technology to create their objects. However, most 3D printing technologies, as of now, have been additive, differing mainly in the way layers are build to create the final object. Some methods use melting or softening material to produce the layers. Selective laser sintering (SLS) and fused deposition modeling (FDM) are the most common technologies using this way of printing. Another method of printing is to lay liquid materials that are cured with different technologies. The most common technology using this method is called stereolithography (SLA) in which photopolymerization is used to produce a solid part from a liquid.
If the history of manufacturing is taken into account, it would become evident that subtractive methods have ruled the roost so far. The generation of machine parts with high precision was generally a subtractive affair, from filing and turning through milling and grinding. Subtractive manufacturing, such as CNC milling and turning, uses a block of a particular material and removes unnecessary and excess substance until only the required shape remains.
The difference between additive and subtractive manufacturing lies in complexity of the parts they are able to create in a limited timeframe. For parts with complex geometries or intricate designs, additive manufacturing methods can produce far superior results than subtractive methods can. However, the real integration of the newer additive technologies into commercial production is essentially a matter of complementing subtractive methods rather than displacing them entirely.