additive manufacturing isn't green, and it isn't efficent.
It's pretty much the opposite of both, when you look at the entire process from producing the special raw materials needed, to the actual manufacturing process, to the additional finishing process needed in a lot of cases.
for example lets consider a piston produced using SLS, SLM, EBM, or maybe BJ.
- Produce the metals you want to use.
- reduce the metals to fine accurately sized particles.
- produce the piston with the additive manufacturing method of choice.
- post process the piston if needed for the process of choice.
- machine the piston so that the critical dimensions are withing tolerance.
steps, 2,3,& 4 are on top of what you would need for traditional manufacturing. Not to mention all but a few of the additive manufacturing processes are very slow any energy hogs.
The real benefit of additive manufacturing, is that you can produce things not possible with traditional methods. for example a piston that is mostly hollow with a honeycomb support matrix inside.