What are my options for metal prototyping?

We need to be confident that the application warrants the additional cost. It might be worth considering some of the interesting RP applications/materials out there, such as metal coated Stereolithography. They might be able to deliver a suitable alternative and we’d be happy to talk you through the options.

We also need to understand if a specific material is being sought, or whether a generic metal will do. 

What data do I need to provide?

We can usually quote from an stl file, but this won’t contain any surface finish, threads or tolerance information. In most instances going to metal will require a toleranced drawing with all the associated call outs. It is imperative that this is available at the time of quotation as it impacts both process selection and cost.

From a production perspective

Most parts are designed as either CNC, Castings or Die castings in production, although as the capability of DMLS continues to improve we are starting to see some items designed especially to take advantage of layer based manufacture.

Using CNC or DMLS to prototype a part designed to be produced this way would be the obvious starting point. However we would have to take into consideration your required quantities and timescales as they will have a dramatic effect on price.

From a process perspective

DMLS is best suited to highly complex, small parts. That said, it is capable of producing some stunning parts up to the limit of the bed size (usually 250mm x 250mm although larger machines are starting to become available). At these kinds of sizes the geometry of the part will drive the decision as the premium over CNC will be significant. 

When considering DMLS we must remember there will be supports that have to be removed post build. These are usually wire cut from the part or CNC machined, hence the geometry of the parts lower surface can have a big impact on this operation.

CNC machining offers the greatest range of material options and the best potential accuracy, but is limited by cutter reach and geometry. However, we continue to push CNC to its limits with incredible results. 

How does quantity affect my choices?

Your required quantities will influence the decision making process. CNC requires upfront programming time that needs to be amortised into the number of parts. Hence unit prices tend to fall initially, and then stabilise.

With DMLS, quantity is all about optimisation of platform area and part geometry. Hence just because 100 parts are required, DMLS does not have to be ruled out as a solution – assuming they can all fit in a compact area and that minimal supports are required.

Is time an issue?

Time is always a factor in assessing which route to take and available capacity will affect your time limits.

CNC machining has the biggest advantage here as it may be possible to drip feed parts, as opposed to alternative processes that require a time to manufacture tooling before part production can commence.

Material choice

When it comes to material, the level of flexibility is linked to the application. Most metal prototypes are in aluminium or stainless steel, however DMLS offers options such as Cobalt Chrome, Inconel and Titanium. If the purpose is to emulate the mechanical properties of the production part then this will require that the process be matched as well. 

Constraining the material to a particular grade or standard is likely to have a significant impact on the process options and hence time to produce the prototypes.

And finally, what affect will the geometry of the part have on my choices?

Features such as thin walls, internal sharp edges, aspect ratio of the features, part size, surface finish, accuracy etc. all have a significant affect on the selection process. Internal sharp edges are the classic scenario that can add time and cost when the only reason they are on the data is that no one has thought to add a radius.

What else?

The following information will also be extremely useful in helping us find the best solution for your part:

• Can we apply different options to different shipments? For example, can the first 10 be produced with CNC and the balance cast and post machined?
• How critical is the material call out and how flexible can this be?
• Have you got the correct control drawings in place to control what you purchase?
• Do we have the flexibility to only call up tight tolerances where really required and allow some fluidity of form where it is not so important? (Note a 0.5 mm radius can make a big difference form a machining perspective!)

Allowing us early access to your requirement and the opportunity to develop the prototyping solution with you can make a huge difference in achieving a cost effective solution. Get in touch today and let’s begin looking at finding the best solution for your part.