Two dimensional printing has been around for many decades now. Anyone that had a printer in the 80's and early 90's probably remembers those printers that had peel away tracks. Before the days of computers there were typewriters and hand printing presses. Its hard to imagine that designs were drawn by hand and yet engineers were able to design the unthinkable. Printing three dimensional parts has been unheard of until now and now nearly anyone can get a part printed.
With that there are many different types of 3D printing methods. Our company uses a printing technology called Fused Deposition Modeling (FDM). Imagine taking two cartridges of a material similar to weed whacker wire and feeding it separately into a melting pot. This ABS wire is .07" in diameter when comes out of the cartridges. Once melted in the print head, which contains two needle like nozzles the material is then able to be extruded precisely. These needle like nozzles produce .01" or .013" diameter extrusions. A model material is extruded from one of these nozzles and a second material called support material is extruded out the second nozzle. The model material is what a printed model is made out of, while the support material is used to support areas of a part while being built. Once a part is finished the support material is then broken away from the part and disposed. After the support material is broken away the model is then ready to be used. The model can also be go through several different post-processes including painting, patching, or even attaching two smaller models together to make one large model.
If I were making a 2" high part it would contain exactly 200 .01" thick layers or 154 .013" thick layers. It is recommended that each part sent to the printer has a minimum wall and floor thickness of .04". It is possible to create smaller layers, however; strength of the part greatly reduced and some details may not be printed or break off. The more model and support material the longer they model takes to build. Models start off being built on a black ABS plastic build tray which is has a texture that parts will stick to. The first thing the machine does before building a part is to "home" and calibrate the X, Y, and Z axis. Once completed the machine then warms the head to 270 degrees Celsius or 518 degrees Fahrenheit. The build chamber is also heated to 70 degrees Celsius or 158 degrees Fahrenheit. After the machine warms up to temperature the build commences building its first layer. The first few layers of the part consist of support material. This support material is used as a base to the model.
For information on the differences of a solid versus a sparse model please visit this page.