By Jean Feingold
Introduction: The Basics of Rapid Prototyping
When engineers and designers want to develop new parts and products or improve existing ones, they usually make prototypes. Today this is often done through a high tech method called rapid prototyping or RP. In his book “Better Be Running! Tools to Drive Design Success,” Ronald L. Hollis, Ph.D., P.E. defines rapid prototyping as “automated machine technology that quickly fabricates physical 3D parts from electronic 3D data by building the part in layers” to make a prototype. Various types of CAD software, usually employing the STL file format, are used to transfer the design to an additive manufacturing machine. This machine produces a prototype of the needed part allowing it to be tested to see if it works as desired.
“The purpose of rapid prototyping is to get expert input on your design early in the product development process to reduce failures that are likely to happen,” Hollis explained. How long it takes to create a part using rapid prototyping depends on the size, mass, and complexity of the part, but compared to building prototypes by hand, rapid prototyping is often much faster and less expensive. Hollis said prototyping validates the design prior to producing the tooling, launching marketing programs, and mass producing the parts. It lets the designer know that what they have envisioned is what the part really is.
Main types of rapid prototyping and their uses
Three main methods of rapid prototyping are available. Each employs a different type of manufacturing process. They are Stereolithography (SLA or SL), Selective Laser Sintering (SLS), and Fused Deposition Modeling (FDM). Based on the design information provided through the CAD software, the chosen material is deposited inside the machine in a series of thin layers. Plastic, wax, resin, ceramic, metal, or other materials in powder, liquid, or solid form can be used depending on the nature of the intended part and the type of machine. Each layer is solidified before the next layer is stacked on top of it. This process continues repeatedly until the part is built. Although the general principles remain the same, each process operates in a somewhat different manner. Depending on the method used, the completed part may require hand finishing to remove excess materials and smooth the surface. This could be followed by sanding and painting.
A newer technology gaining in popularity is called inkjet-like 3D printing. This technology operates in a way very similar to inkjet printers for computers, except it involves depositing layers of resin instead of ink. This process is also frequently referred to as PolyJet, which is a brand name for such printers made by Objet.
Companies such as Malco Products use the PolyJet process for form and fit testing. Malco can rapidly produce parts and even moving assemblies in a single build. The PolyJet process is fast and creates highly accurate parts. Using the Polyjet process has allowed Malco to reduce development time while improving design accuracy.
Malco Products had such good success with Objet technology that they began offering rapid prototyping through their service business, the Malco Design and Deliver Group (www.MalcoD2group.com).
Examples of products for which rapid prototypes are made include medical devices, dental appliances, high end jewelry, machine parts, furniture, parts for automotive, aviation and aerospace uses – and even 3D printers themselves. Jos Scheepers, owner of MaukCC in the Netherlands, used rapid prototyping and additive manufacturing to make 40 percent of the parts of the 3D printer he built. “It took me a year to design my printer on my own,” he said. “A team of ‘normal’ designers would have taken three years.”
Engineers and product designers can buy additive manufacturing equipment and do rapid prototyping in-house or they can hire an outside rapid prototyping company (also called a service bureau) to do it for them. In either case, it is important to understand the capabilities of the process in question and whether what it can do fits with the desired end product.
Rapid prototyping is a powerful tool, but only if it is used correctly. As with many technological processes, the possibility of things going awry is large.
Here are some of the more common mistakes people have encountered while using rapid prototyping to develop new parts.
1. Inadequate communication and coordination between the designer and the rapid prototyping company
Lack of adequate communication and coordination between the rapid prototyping fabricator and the designer can almost guarantee the rapid prototype will not be what the designer envisioned and needs. Sharing expectations is critical when working with service providers. Designers must thoroughly understand the process and parameters before cutting a purchase order to the service bureau.
“Designers must remember the variables, as part production can be more of an art than a science,” Hollis pointed out. “Many times customers don’t know what they don’t know. They end up getting exactly what they asked for, which is not at all what they really wanted.”
Portland, OR-based model and prototype maker Bruce Willey agrees, saying, “Everybody needs to communicate expectations and requirements and capabilities very clearly, just like for any other fabrication process.” If the rapid prototyping provider fails to determine the level of quality the client needs, or if the company promises higher quality than they are prepared to provide, the result will be disappointment for the designer, he added.
Providing correct information via the CAD software is crucial. “Rapid prototyping or additive manufacturers fail to explain their requirements in terms of file integrity,” said Spanish additive manufacturing specialist Carlos Garcia Pando. “All layered manufacturing technologies require files that depict a watertight solid. Not all CAD packages work with solids, but with surfaces, and users are not aware of the need of a solid for manufacturing.”
To avoid communication problems, Ryan Law, Senior Manager, Development Engineering, for Philips Healthcare in Gainesville, FL, encourages “an honest discussion of the risks and what is most important (to the designer) between cost, quality, and time. Sometimes you have to sacrifice one.” Having a good relationship with the rapid prototyping manufacturer can also be beneficial in resolving any issues with post-delivery prototype quality.
2. Overestimating users’ knowledge of rapid prototyping
Service bureaus often assume the engineer or designer knows more about how the rapid prototyping process works than they really do, noted Law. “Rapid prototyping is still a new industry,” he said. “I have been using it for 10 years, but the evolution has been so fast, I have found I often needed a good refresher of the rapid prototyping options and their benefits.”
Pando said service bureaus take for granted that customers know the rules, restrictions, improving factors, materials, properties, and dimensional tolerances of the layered technologies. As a result of these assumptions, rapid prototyping providers don’t explain the requirements and limitations of their equipment adequately to potential designer clients.
Some engineers and designers lack even general familiarity with the advancements in rapid prototyping. “Older designer/engineers know of prototyping parts as being expensive and fragile,” said Tony Byrd, Owner of Louisville, KY-based New South 3D Printing. “That’s really no longer the case.”
3. Thinking everything can be built using rapid prototyping
It seems a certain amount of overpromising by rapid prototyping companies has led to the false idea that any object can be built using rapid prototyping. “For me, the source of 90 percent of all mistakes engineers and designers do is the industry claim that everything is possible, that there are no limits but the designer’s /engineer’s imagination,” Pando said. “They say, ’If you can dream it and draw it, it can now be manufactured.’ They have been using this to attract interest and have brought a number of false expectations and disappointed customers.” These dissatisfied customers will not only avoid trying rapid prototyping again, they will tell many others of their bad experiences.
When size matters, rapid prototyping may be too expensive or not viable, Pando cautioned. “Rapid prototyping machines are limited in size and cost greatly increases with the size of the part,” he said. In addition, for some products, there are regulations requiring load, electrical, or other tests that must be done using the end part’s actual material and manufacturing processes. Rapid prototyping cannot substitute for that.
4. Expecting prototypes to be perfect the first time
Prototypes let designers identify potential flaws before incurring the dramatically higher costs of re-tooling and rework. This reduces some of the risk and expense involved in introducing new products.
But the first prototype produced using rapid prototyping may not function as expected. “We all feel that our designs should work and we have foreseen all obstacles involved in the project,” said Byrd. “When we are developing something that not only needs to work, fit, function, and look pleasing to the consumer, it also must be easy to assemble, handle, and work with other manufactured parts.” That might happen with the first prototype, but it is possible it might not.
While designers may be disappointed when the initial prototype does not perform as desired, using the knowledge gained from it will allow them to tweak their design to correct the problems and make a new prototype. Even if several rapid prototypes must be made before the part meets the designer’s needs, this should still take less time and money than building parts without prototyping or creating the prototype by hand.
5. Using the wrong process or materials
Each type of rapid prototyping process has its own strengths and weaknesses. For example, the size of the machine may limit how large a part it can produce. This must be taken into account in the design process.
Parts made using SLA based machines can have thin walls, fine features, and support structures. FDM can include support structures, but thin walls don’t work well using SLS or at all with FDM. SLA made parts don’t like heat and could even be damaged in shipping because of it; SLS and FDM parts can handle higher temperatures. “For FDM parts, interlayer strength is quite weak which is a real pain,” noted Andrew Rodger, Engineering Consultant at the Centre for Smart Product in New Zealand. Law pointed out that some rapid prototyping methods produce prototypes that are easier to finish than others, so designers should describe the texture and color they desire on their product when choosing a rapid prototyping method.
“Not every rapid prototyping process can solve every problem,” Byrd noted. If the designer needs to test different plastics together, the different types of additive manufacturing machines cannot each produce parts from every material. Some metal objects can be produced in plastic using rapid prototyping but in other situations the object needs to be an actual metal part, he said.
6. Selecting a vendor whose capabilities don’t match your needs
Because industrial quality additive manufacturing machines are expensive, some service bureaus may own only one or two types of machines. Before selecting a vendor, designers need to know and be able to communicate how they plan on using the prototype. Using that information, designers can ask service bureaus what their rapid prototyping capabilities are and whether they can make the prototype needed. “If they can only do FDM, they will tell you it is always best,” Law said. He recommends choosing a company with several rapid prototyping options and staff who can guide you to the right method based on your application.
Law suggests starting by asking the service bureau, “What process do you recommend for making this prototype and why?” Think about whether the prototype is just for show or needs to be functional. Does it require finishing and painting? Does it have any sliding contact surfaces or flexible or snap-fit features?
“It is perfectly fine to go with a supplier that only has one type of machine as they may specialize in the process that fits your needs best,” Law said. “However, I recommend discussing the project with at least one supplier that can offer a wider selection of equipment to determine if there is a more suitable alternative.”
Rapid prototyping isn’t just about designing a new part or product. Being able to obtain a prototype quickly can help with marketing the product, Byrd suggested. Since designers have experience with the products they manufacture all the time, it’s sometimes hard to prove to them that a prototype part could benefit their supervisors, the marketing department, and end consumers by helping these audiences understand the product better.
When senior engineers, marketing staff, and customers see the design working correctly and that it feels and fits the way they wanted it to, the prototype demonstrates the new design’s advantages in a convincing way. As Pando puts it, “If an image is worth a thousand words, a prototype is worth a thousand rendered images.”
8. Building more than is necessary
When designers think about making a prototype, they usually think about building the whole thing even if their issue with the existing part is limited to certain aspects of it. “The big thing that I try to tell inventors is you don’t need the whole part remade if only a section of it is off unless it is integral to the whole design,” said Byrd. In some cases, he said it is possible to make a prototype for just a section of a part, only the area with problems, instead of making the whole part.
Another option he suggests is to make the prototype to a smaller scale, say one-half or one-quarter size, to test the idea. Either option would reduce the cost of the rapid prototyping process.
By recognizing and understanding the common mistakes of rapid prototyping, designers, engineers, and service bureaus will be better able to avoid them. That will enable them to work together productively in producing effective rapid prototypes.