In most cases, metal prototyping costs more than making an equivalent part in plastic, so our first question is, does it really have to be metal?
We need to be confident that the app will cost extra. It might be worth considering some interesting RP applications/materials such as metal coating stereolithography. They may be able to offer suitable alternatives and we would be happy to discuss these options with you.
We also need to understand if a specific material is being looked for, or if a generic metal is okay.
We can usually reference from the stl file, but this won't contain any surface finish, thread or tolerance information. In most cases, metalworking requires a tolerance drawing with all relevant annotations. This must be provided when quoting as it affects process selection and cost.
Most parts are designed in production as CNC, casting or die casting, although as DMLS capabilities continue to increase, we are starting to see some projects specifically designed to take advantage of layer-based manufacturing.
Metal prototyping of parts designed to be produced this way using CNC or DMLS would be the obvious starting point. However, protomold company has to consider the volume and schedule you need as they will have a huge impact on the price.
DMLS is best for highly complex small parts. That said, it's capable of producing some amazing parts right down to the limits of size (usually 250mm x 250mm, although starting with bigger machines). At these dimensions, the geometry of the part will drive the decision, as the premium over CNC will be very significant.
When considering DMLS, we must remember that some supports must be removed after construction. These are usually wire cuts from the part or CNC machined, so the geometry of the underside of the part can have a big impact on this operation.
CNC machining offers the widest range of material options and the best potential accuracy, but is limited by tool range and geometry. However, we continue to push CNC to its limits with incredible results.
The amount you need will influence the decision-making process. CNC requires pre-programming time, which needs to be amortized into the part count. As a result, unit prices tend to fall initially and then stabilize.
With DMLS, quantity is an optimization of land area and part geometry. So just because 100 parts are required, DMLS doesn't have to be ruled out as a solution. Assuming they can all fit in a compact area and require minimal support.