Metal additive manufacturing is not one technology and not a general replacement for machining. It is a set of processes that make a narrow class of parts possible or cheap, and outside that class it is neither. Knowing which class your part is in is the whole decision, and it can usually be settled in a conversation rather than a trial.
The processes and the powders
Laser and electron beam powder bed fusion melt fine powder layer by layer and give the best resolution and properties. Binder jetting glues powder and sinters it, trading accuracy for throughput. Directed energy deposition feeds powder or wire into a melt pool and suits large parts and repair. Powder itself is a controlled material: particle size distribution, sphericity and oxygen content all affect the result, and reused powder is tracked.
The four business cases that hold up
Consolidating an assembly into one part, which removes fasteners, joints, inspection and inventory. Internal channels that cannot be drilled, above all conformal cooling in moulds. Topology optimised structures where mass costs money for the whole life of the product. And spares for equipment whose tooling no longer exists, where the alternative is not a cheaper part but no part at all.
The cost structure nobody expects
Machine time is charged by build height and by how much of each layer is solid, so nesting decides the rate. Powder is expensive and handling it safely is a real overhead. And post processing is often the larger half: stress relief, plate removal, support removal, hot isostatic pressing where fatigue matters, and machining of every feature that has to be accurate.
Qualification is the real barrier
Properties depend on parameters, orientation, powder lot and post processing, so an additive part is a process as much as a part. In regulated sectors that means a qualification programme, witness coupons and lot traceability. This is why aerospace and medical adopted it in a controlled way and why a casual substitution of a printed part for a machined one is rarely as simple as it looks.
Questions people ask about metal additive manufacturing
Which metals can be printed?
Stainless and tool steels, aluminium alloys, titanium alloys, nickel superalloys and cobalt chrome are the common industrial set, with copper and precious metals available on suitable machines.
Are printed metals as good as wrought?
Comparable when the process is controlled and the part is properly post processed, and anisotropic in ways wrought material is not. Where it matters, the process is qualified rather than assumed.
Is it cheaper than machining?
Rarely for a simple part, often for a complex one, and almost always when it removes an assembly. Compare the finished post processed part against the finished machined assembly.
What is the biggest hidden cost?
Post processing. Stress relief, support removal and machining of critical features routinely cost more than the build itself.