[Discussion] I have heard that 3D printing is good for rapid prototyping, but what about localized manufacturing? What are some advantages/disadvantages of FDM vs injection molded parts?

When it comes to mass manufacturing, inject molding is the undisputed king. 3D print times are measured in hours per part, injection molding is measured in seconds or even milliseconds per part. Injection molded parts also have a smoother surface finish and are generally stronger than 3D prints.

Setting up an injection molding run is expensive and time consuming. You have to design molds (requires specialized design skills) and have them machined (costly in time and materials). Setting up a 3D print just requires slicing a model and sending to the printer, which can be as little as a few minutes.

3D printing can also create geometries that are impossible in injection molded parts. With injection molding, there are quite a few specific design requirements to allow the plastic to flow into the mold, cool, and be ejected. With 3D printing, there fewer restrictions on the design.

So, if you want a huge number of something it's definitely worth it to spend the up front time and money to do injection molding. If you are doing smaller quantities, need to get started fast, or require geometries that are impossible with injection molds, then 3D printing may be a better option.