A 3D printer works in a similar way to a conventional printer except that instead of ink it uses a liquid material which is applied in an additive process by creating successive layers in thin horizontal slices until the object is formed. Once the form has been achieved the material hardens. The object is built up from the bottom layer as if you were creating a loaf of bread by applying the individual slices until complete and it turns into a single loaf. 

 Create a Virtual Design using Software

Using suitable 3D modeling software you design the object you want to make in a CAD (Computer Aided Design) file or animation modeling software (both WYSIWYG graphics editors). Alternately you can use a 3D scanner to scan an existing object's image into your computer and the 3D modeling program. You will have created a virtual blueprint. 

Once you are happy with your design on the computer screen the 3D modeling program prepares the digital file for printing by converting the design into thin horizontal 2D slices which will then be combined into the final 3D object. 

The Digital File is Uploaded into the 3D Printer 

Once the file has been uploaded to your 3D printer you select the desired material depending on your printers capabilities – rubber, plastic, polyurethane materials, metals etc. The printer reads the program's information about each 2D slice and proceeds to create each slice one on top of the other. The final product bears no sign that the process involved layers; it appears as one integral whole. 

Printing Technologies of 3D Printers

Not all 3D printers use the same technology but with the most common form of 3D printing the material is squeezed out of a nozzle and transferred to the printer platform where the object takes shape in successive layers. After each layer is placed the printer platform moves down a fraction.

The additive process uses molten ink (melted plastic, liquid concrete, chocolate etc) which is printed while soft but solidifies when it exits the printer head and becomes a layer in the design object. Some 3D printers feed solid plastic into the 3D printer where it is melted. The melted plastic becomes the "ink" and is ejected from the printer nozzle. As each layer is placed in position the printer platform is lowered to allow room for the next layer. Like a conventional inkjet printer the printer nozzle passes back and forth as it deposits the successive layers each approximately 0.1 millimeters thick. 

The finished object

The successive layers are fused together automatically during the printing process and they dry into a single 3D object. 

Other methods of 3D printing include the use of material in its powered form which is then bound together with a bonding agent or fused together by heat. Lasers have also being used in the 3D printing world. Hopefully this gives you an overall understanding of how 3D printers work.