Metal additive manufacturing is a family of processes rather than one, and the family members are not interchangeable. Some melt powder with a laser, some glue it and sinter it in a furnace, some feed wire or powder into a moving melt pool. Each produces different density, different accuracy and a different bill for what has to happen after the machine stops.
The three families worth knowing
Powder bed fusion melts thin layers of powder with a laser or electron beam and gives the best combination of resolution and properties. Binder jetting prints a binder into powder and then debinds and sinters, which is faster and cheaper per part but shrinks in the furnace and needs that shrinkage designed for. Directed energy deposition feeds material into a melt pool and suits large parts and repair rather than fine detail.
Why the part price is not the machine price
A metal printed part arrives welded to a build plate on a forest of supports, full of residual stress, with an as built surface nobody would accept on a sealing face. Stress relief, plate removal, support removal, hot isostatic pressing where properties matter, and machining of the critical features are all normal and all priced. Printing is often the smaller half of the invoice.
Where it genuinely wins
Internal channels that no cutter can reach, such as conformal cooling in tooling. Assemblies consolidated into one part. Topology optimised structures where weight is expensive, which is why aerospace adopted it first. Spares for equipment whose tooling no longer exists. Anywhere the part count drops, the case is usually strong even when the unit price does not look it.
Where machining still wins
Simple prismatic or round geometry. Anything where certified wrought material properties are required and nobody wants to qualify a new process. Larger parts, where build volume and build time punish you. And anything in quantity, because the printer's cost per part barely falls with volume while machining's does.
Questions people ask about metal 3d printing
Which metals can be printed?
Commonly stainless steels, tool steels, aluminium alloys, titanium alloys, nickel superalloys and cobalt chrome. Copper and precious metals are printable with the right machine. The alloy list per process is narrower than the list overall.
Are printed metal parts as strong as machined ones?
Properties are comparable and sometimes better in one direction, but they are anisotropic and depend heavily on parameters and post processing. Where strength is critical the process has to be qualified, not assumed.
How accurate is metal printing?
Good enough for most geometry, and not good enough for bearing fits, sealing faces or threads. Those features are printed with stock and machined afterwards, which is normal practice rather than a failure.
Is it cheaper than machining?
Rarely on a simple part, often on a complex one, and almost always when it removes an assembly. Compare the finished, post processed part against the finished machined assembly rather than machine time against machine time.