When you shoot a spaceship into space the rocket can only carry so much weight. Astronauts need careful planning to make sure they will have all the equipment they might need.
International Space Shuttle (ISS) commander Barry 'Butch' Wilmore needed a wrench. They did not have it with them and waiting for a resupply mission is kind of time consuming, not to mention expensive.
This is where the awesomeness of 3D printing comes in. You can just email someone a physical object.
Fortunately, the ISS had a 3D printer on board, design specifically for zero gravity environment by the company, Made in Space. And they printed the wrench.
ISS astronaut uses 3D printer to make socket wrench in space
3D printing has another benefit, it can create geometries that would be hard or impossible to make with traditional manufacturing that is usually subtractive - it removes material. 3D printing is additive manufacturing. It builds up objects layer by layer.n
cloud of points and wire frame
slices of layers
While usual consumer 3D printers just work with cheap PLAplastic... this technology has matured to suite industrial production.