There are four practical ways to get a metal prototype quickly, and they differ in what they prove as much as in how fast they arrive. Choosing between them is a question about whether you are testing the geometry, the material, the process, or all three, because no single route gives you all three quickly.
Machining from solid
The fastest route for most parts and the highest fidelity on material properties, because it uses certified wrought stock. Simple parts in common alloys ship within days. What it does not prove is anything about a casting or forging process, and it hides the draft and section rules those processes impose. It is the default and usually the right one.
Metal printing
The route for geometry that cannot be machined: internal channels, consolidated assemblies, topology optimised structures. Lead times are days to a week or two including post processing. Properties are close to but not identical to wrought, and every accurate feature is machined afterwards, so it is a hybrid rather than a single step.
Sheet fabrication
For anything that will be a sheet metal part in production, this is both the prototype route and the production route, which is unusual and valuable. Laser cut and press braked parts arrive in days with no tooling and are made by exactly the process that will make the production ones.
Rapid casting
Where the production part will be cast, a printed pattern or a printed sand mould gives a real casting in a fraction of the time a pattern would take. That is the only route that proves the casting process itself: how the metal fills, where the porosity sits and how much the part moves. It costs more and takes longer than machining and it answers a question machining cannot.
Questions people ask about rapid metal prototyping
What is the fastest route to a metal prototype?
Machining from solid for most parts, in common alloys, within days. Sheet fabrication is equally fast for parts that will be fabricated in production.
When should I print a metal prototype?
When the geometry cannot be machined: internal channels, consolidated assemblies or topology optimised structures. Expect machining of critical features afterwards.
How do I prototype a casting quickly?
With a printed pattern or a printed sand mould, which gives a real casting in days rather than the weeks a conventional pattern takes.
Does a machined prototype prove a cast part?
No. It proves the geometry and the material, and it hides the draft, section and porosity behaviour that the casting process will impose.