Prototyping can involve a number of processes of different types of materials but in general it is done for 1 off or small batch production, as such the unit cost is high, it involves a lot of hand work, its quality is much lower than a production piece (as the materials are not the same) and it can be produced much quicker than producing a mass produced product
3D Printing is used for most plastic components, knowing which 3D printers are suitable and with what material is something gained through trial and error but once found, this is an indispensable tool for prototyping
It is important to realize that 3D prints (and prototypes in general) cannot totally follow the thicknesses (or weights) of production materials as their tolerance and material properties are not the same, this can mean significant modifications to wall thicknesses, assembly methods, and internal structures are needed to make the prototype feasible
In addition, 3D printing can also be used (depending on the machine) to produce simple one-off molds for materials to be formed within quickly and accurately
Handwork is expected but small jigs and modified tools can greatly aid in the accurate production of quality components
This is another layer of development in itself which requires a specific understanding of the methods to be used and an appreciation of the difficulty and skill involved, this can only be learned through exposure and without this misunderstandings and differing levels of expectation are expected