3D printing, or fast prototyping as it used to be known, is not all its cracked up to be. But, it brings new entirely new possibilities to the table.

I can go and program my milling machine to cut a mold out of aluminum, and then I can make a 100 parts with my plastic injection molder in a day.

Depending on the size, the 3D printer couldn't even compete.

But, that injection molded part is really a 2-1/2D part. It has to come out of the mold. It can't have any internal cavities. It has to have sloped sides.

Also, if I wanted to change the part, I would have to do all the design, and mill a new injection mold.

With a 3D printer, you can make one, and then send me the file and I can make one.

If what you need is a replacement part for your doohicky 3000.1a, then with a 3D printer, you just tell it to print one. With an injection mold, you have to go find it. Of course you are using mold 1d now, so where is that hunk of metal? Did you throw it out?

3D printing can't compete with injection molded parts for cost and speed, but it can do things injection molding can't.