How does 3D printing work?

3D printing works by building up an object layer by layer. There are several 3D printing technologies and they are are all quite different.

One of them Selective Laser Sintering (SLS) works like this:

1. The 3D printer spreads out a layer of fine powder.
2. A laser hardens the powder in that layer that comprises the bottom slice of your part
3. A new layer of fine powder is spread out. The next slice of your part is hardened and joined to the first.
4. The rest of the powder remains loose. This supports the part as it is built up
5. This is repeated many times until your part is built.
6. Then your part is lifted from the loose powder.
7. It is then sandblasted and finished by hand.

An animation and video (disclosure: made by the company I work for) can be found here:

http://www.youtube.com/watch?v=sFpSxX0SzgY

http://www.youtube.com/watch?v=-6ItiCbYFvI

SLS is the process used by 3D Systems and EOS.

Fused Deposition Modeling (FDM) another 3D printing process was invented by Stratasys and also used by the RepRap project and the Makerbot 3D printers works like this:

1. A thin ABS plastic wire is extruded through a nozzle on a printing head.
2. The wire is melted and laid down filling in the bottom layer of a shape.
3. The printing head goes to its starting position and the build platform is lowered.
4. A new layer is laid down and your part is built up like this.

The Stratasys 3D printers have support material. This is later removed and lets you make more complicated structures and overhangs.

A Stratasys 3D printer works like this:

1. A thin ABS plastic wire is extruded through a printing head.
2. The wire is melted and laid down filling in the bottom layer of a shape.
3. The printing head goes to its starting position and the build platform is lowered.
4. A new layer is laid down and your part is built up like this.
5. If there is an overhanging part a second nozzle on the printing head extrudes the support material.
6. For example if you wanted to 3D print a person standing upright. If you've just 3D printed the neck you're going to have a problem 3D printing the jawline because the material has nothing to be built upon. It would just go everywhere. So what happens is that during the print support material is extruded from the second nozzle all around the body of the person. That way this material is in place for when you start to print the overhanging parts.
7. The part is taken from the 3D printer and the support material is removed.