To get the most out of rapid prototyping, it helps to understand the different methods available for quickly producing a physical model from 3D CAD data. You can also improve your results by listening to what experts have said over the years about working effectively with outsourcers as well as your own in-house machines.
Of course, the first thing you should remember is it all starts with good data:
- Create a robust model. No machine can make your 3D CAD dreams into a real, physical artifact when the digital data contains problems. Prototyping companies say that if you want a successful part on time, watch out for these common design fails before you send a CAD file to the printer:
- Open lines and vertices
- Features with no or little measurable thickness
- Wrong facing surfaces (when an inward surface faces outward, Mobius-strip like)
- Evaluate your supplier carefully. Some companies like to work with rapid prototyping vendors within driving distance, establishing relationships and making it easier to get their finished items fast. Others feel completely comfortable ordering a one-off part over the internet from a company across the country. Both methods can work; just make sure that your prototyping organization can deliver:
- The fabrication method and materials that best suits your need—as discussed in part one of this series.
- On time. Some online providers promise overnight results, while the shop down the street may not deliver for a few days. In Rapid Prototyping Casebook, Chris Ryall writes, “Remember, the sense of urgency and rapidity common to your industry may not be understood elsewhere. Make certain that it is.”
- Excellent customer service, including a dedicated project manager.
- Run through your process once with a non-urgent project. Can you easily convert your CAD files to the STL, STEP, or whatever format your supplier needs? Can the service successfully accept and read your files? You don’t want to find out on the day of the trade show that your display model won’t be forthcoming. In fact, because of the variables and importance of prototypes, Ryall advises that once you have a service provider that you like, it’s best to stick with it, rather than chasing a slightly cheaper or faster model.
- If you’re considering buying your own system, make sure you have the labor and expertise you need! As with traditional machining, some methods of additive manufacturing require very knowledgeable workers. Highly accurate systems, like those used to produce artificial hips, need to work in a closed environment and staff must be well trained to operate the machines. In many cases, they’ll need to perform post-processing steps too, like curing, sanding, machining, and painting. If you’re weighing the value of an in-house machine versus outsourcing the work, make sure you understand all the costs involved.
- Consider induced demand. Induced demand is a term often used by traffic engineers to describe what happens when you add lanes to a highway—more traffic appears! The same thing can happen when you buy a machine for rapid prototyping. Look at this example from Mitsubishi Digital Electronics, as described in a 2004 article in Machine Design magazine:
“’In the year before we brought RP machines in house, our engineers requested funds for 40 models,’ says a company representative. That's understandable because the service bureau they were using charged about $1,200/part and up. ‘But in the first six months of having machines in house, we built over 450 parts.’”
Today’s suppliers typically charge less, but the point is this: when engineers can produce a physical prototype at low cost and overnight, they use it more often. That can mean more ergonomic verification, more form and fit tests, more opportunities for customer feedback, and better quality products.
Mix up your solutions. Throughout this series, we've touched on the different stages of the design cycle where you might pursue a rapid prototype. By now it should be clear that for some applications an inexpensive FDM machine in your own lab could serve your purposes with little overhead. In other cases, a high-quality piece from an expertly outfitted and staffed supplier might be more practical. Many companies successfully use a combination of all these solutions to “maximize what's possible, inspire your consumers and validate the function as quickly and economically as possible.”
A Part Number Anthology 
Part numbering. For most engineers, this two-word phrase is all it takes to conjure up especially strong feelings about what it means to be “right”, and what it means to be very, very “wrong.” We've assembled a handful of our part number greatest hits in this eBook anthology.
