Have you ever wondered when was 3D Printer invented? 

The first concept was invented in 1980 where a photosensitive liquid polymer would cure by shedding UV light through a masked transparency. The process is called "Solid Ground Curing"  

It was "Chuck Hull" who revolutionized 3D printing by inventing a process called Sterolithography in 1984. He then started "3D Systems" (a company of 3D printing machines) 

Sterolithography (SLA) is a process where a computer controlled laser beam moves around on a thin layer of liquid polymer. Liquid cures only where laser hits it. Then new layer of polymer is deployed on the top of the cured one and laser-beam moves around and cures the next layer. Process continue until the model is fully built.

See image and video below.

Want to know more about the history of 3D printing? Read it here

Wiki 3D_printing

Refrences:
Image from "Sniepview.com" and "i.materialize.com"
Video from "3D Systems"
Web "Wikipedia"