How does 3D printing work?

https://youtu.be/riy7E4ehldM
3D printing is revolutionizing industry and medicine, and inspiring designers and DIY enthusiasts. The main drawback is how long it takes…
Printing an object the size of a tennis ball can take up to 12 hours. New developments could reduce this to just six or seven minutes.
At present, printers use a layer-by-layer technique
The simplest method is known as filament printing, and tends to be used in mass-market 3D printers. A thread of heated plastic is deposited in successive layers.
Professional applications use stereolithography (SLA) or laser sintering (SLS). These techniques involve applying layers of a special resin or powder with a laser and can take hours or even days.
But inventors hope a new technique could reduce this to just a few minutes.
Continuous Liquid Interface Production uses ultraviolet light to ‘grow’ objects out of a reservoir of liquid resin.
Oxygen enters via a permeable window underneath which ensures the resin in the bottom of the pool remains liquid.
The reaction which causes it to solidify takes place just above this ‘dead zone’.
This process is both high speed and continuous. The object solidifies as it emerges out of the resin bath…like a rabbit pulled out of a magician’s hat!