In most cases, rapid metal prototyping is much more expensive than making the same part in plastics. So should your part or prototype really have to be metal?

The application should warrant the extra costs. Sometimes, it may be worth considering some other interesting rapid prototyping materials, like metal-coated Stereolithography. In this article, we will present you common metal prototyping techniques a specialized prototype factory can offer and some factors needed to be considered when choosing the technique.

What data should you offer to the prototype factory?

The professional factory can offer a quote according to an STL file. But such a quote does not include any information about the surface finish or tolerance. If it is the rapid metal prototyping you require, then it is necessary to provide a tolerance drawing. It is because the tolerance requirement can impact the cost as well as the selection of process.

What rapid metal prototyping techniques are available in a prototype factory?

Most metal parts are manufactured using casting or Die-casting even though with the continuous development of DMLS technology. Using CNC machining or DMLS to create metal prototypes may have many advantages. But the required quantities and turnaround times can dramatically impact the cost. What's more, casting allows the manufacturing of prototypes or parts with rather complex geometries. There are many casting processes for creating metal parts, such as plaster, sand, or investment. Creating metal parts using the casting method can be an excellent solution. But the post-processing will further increase costs.

DMLS is ideal for manufacturing small parts of highly complex geometries. It is able to manufacture stunning parts up to the limit of the bed size, usually 250mm*250mm, which drives this technology as the premium over CNC machining. And DMLS is able to tackle the geometry that would need EDM and CNC to create.

When using DMLS for rapid metal prototyping, what will happen with the support structures should also be considered. The supports have to be removed post-processing and the removal process is not as simple as that of Stereolithography. In DMLS, the supports are wire cut from the printed parts. Thus the geometry of the printed parts can significantly affect the operation.

CNC machining offers the widest range of material choices and the best possible precision. However, limited by the reach and geometry of the tool, it is hard to machine geometrically complex parts. But with five-axis machining, it is possible to chase out materials progressively until the desired shape is got. This process is costly in both time and money, but the result is an incredibly precision piece.

What impact the best selection of the rapid metal prototyping method?

Quantity

The number of metal parts you want to manufacture will affect the best choice of rapid metal prototyping technique. There is the upfront programming time in CNC machining. Thus initially, the more parts you make, the lower the unit price can be. But since the materials cost and machining time become fixed, this tendency will finally stabilize at high quantities. It is not an economical option for scale production.

As for DMLS printing, the quantity is about optimization of part geometry and printing platform area. It can be economical even if you require only 100pcs of parts.

The higher the quantity, the more suitable for casting solution, even though post-processing is required. Like CNC machining, casting also has some fixed upfront costs. But once the upfront costs are covered, the unit price could be exceptionally attractive.

Time

Time is also always an essential factor in assessing which metal rapid prototyping solution to take. DMLS may be the quickest solution. CNC machining needs a certain time to produce tooling before the production of parts can start.

Material

Speaking of material, most metal prototypes are made from stainless steel or aluminum. DMLS offers different options, including titanium, Inconel, and cobalt chrome. If the purpose of creating metal prototypes is to emulate the mechanical properties of the finished parts, then the process should be matched as well. For instance, the grain flow in casting will not be found in CNC machined parts.

Material limitation can significantly impact the choice of metal prototyping solution thereby influencing the time and cost to prototype metal prototypes.

Geometry

The features of desired metal prototypes like thin walls, sizes, surface finish, dimension accuracy, internal sharp edges also have a great impact on the selection process. That said, when you want to make prototypes of complex geometry or many details, you should be open for close communication with your prototype factory. The geometric feature is pretty important in determining which process is the most appropriate, which materials are available, how many quantities are economical, as well as how much time is required.

The above are not only factors that you should consider when making a decision but also factors that a prototype factory will consider before offering you a quotation for a metal prototype. Let your prototyping partners have easier access to your requirements will greatly increase their efficiency of realizing your project.