Whether for prototyping or low-quantity production, choosing the right technology to implement can prove vital in minimizing product development cycles.
By Jeff Reinke, Editorial Director
Size hurts, quickness kills. At least that’s what my high school football coach told me. It’s a saying that seems to apply not only to undersized defensive ends, but also to those at the forefront of product design. Facing greater demands to reduce time-to-market processes has led to more prominence being placed on the use, development and understanding of prototyping and rapid manufacturing technologies. Although haste should not create waste in this situation, it can if the wrong application is selected.
 Digital prototypes, like this one of helicopter blades or the transmission shown above, can help reduce the amount of money spent on physical prototypes during the design process. |
According to Fred Fischer at Stratasys, the
prototyping market as a whole is growing at about a four percent annual clip. It’s an interesting climb for methodologies that are far from mature in either their use or scope of capabilities. Each approach we’ll discuss here offers its own benefits and obstacles to universal acceptance, but each seems to have found its niche, and as you get faster and more accurate, the price goes up. There’s really no wrong answer, just a better one depending on the situation.
Something To Build On
Stereolithography (SLA), often abbreviated as SLA, was one of the first, and remains one of the most popular methods for creating prototypes or models. Developed by 3D systems, this technology applies a liquid resin photopolymer in layers that is cured and solidified by a UV laser in creating a part. Because it is the most mature of processes, it stands to reason that it is also among the least expensive outside of 3D printing, and its popularity stems from the fact that very little needs to be done from a finishing perspective once the part has been completed. This is probably a good thing because these prototypes can be less durable, and if left out in UV light, they can warp, offering an inaccurate representation of the product being analyzed.
Additionally, because of the layered process, these models usually have a surface composed of stair steps, which can be removed by sanding if the aesthetics are important. However, this can be a risk due to the nature of the curing and layering process, and the very dynamics of the part’s composition. This stepping effect can also be minimized by orienting longer elements of the part so that they’re built vertically instead of horizontally. The trade-off is that this will add to production times.
In terms of materials, Accura 60 is among the most popular rigid epoxy resin being used, but, Accura 25 and Somos 9110 have also been used when looking to duplicate part properties more closely associated with injection molding. The fourth resin, Somos 11120, is similar to ABS in helping to add to a prototype’s durability.
Evolving from SLA has been the SLS, or selective laser sintering process. This approach, also developed by 3D Systems, improves the durability and accuracy of SLA. Basically, instead of curing photopolymers, it uses a laser to fuse an ABS-type plastic powder together in a controlled process chamber, layer by layer, in building the part. The added durability and wider range of material usage involved with this approach allows for rapid manufacturing applications when production quantities are less than 1,500. The advantages here also revolve around time, as neither tooling nor molding needs to be done before producing a prototype or a low-quantity run of parts.
Although not always as fast as SLS, fused disposition modeling, or FDM, represents 42 percent of the rapid manufacturing market. More than capable in producing working prototypes as well, FDM also takes an additive approach by feeding material in layers, where it is melted. The operational aspects are similar to stereolithography, but the plastic is hardened immediately in producing a more durable product with improved accuracy. Fisher states that Stratasys FDM machines can produce parts that are accurate to within 0.005” 95 percent of the time. So not only is the result repeatable, but stacks up well with injection molding products that are accurate to within 0.003” of CAD drawing specifications. This accuracy is significant when working with larger parts that have to snap together, or in realizing the time savings versus machining or injection molding set-ups.
From a material perspective, early prototypes produced with this technology actually used wax. From there the move was made to ABS, and recently RedEye RPM, a sister company of Stratasys involved with the actual production of parts and prototypes, unveiled ABS M30, a 25 - 70 percent stronger plastic option. Stratasys FDM systems also use polycarbonates, PPSF (polyphenylsulfones) and additional blends that aid in the feel and functionality of prototypes or rapid manufactured parts.
In evaluating which approach might best suit a designer’s individual needs, FDM will take a little longer, but offer a higher quality part. These systems, however, are also more expensive when compared to SLA or SLS.
Going Digital
In addition to reducing the amount of time involved with the design process, there’s always an interest in reducing cost as well. That’s where recent developments in CAD software come in with their digital prototyping capabilities. Digital prototyping allows for examining parts and simulating performance criteria with the aims of reducing the number of physical prototypes that are needed, which will therefore save both time and money in the process.
 All of the parts pictured in this article help demonstrate the dynamics of different prototyping and rapid manufacturing technologies involving plastics as well as metal. |
According to Jim Spann, the vice president of marketing at Blue Ridge Numerics, this integration of digital prototyping has increased primarily due to a growing user-base of CAD software. With this increase in use, price points for this technology have also decreased, making it more affordable for a larger audience.
He also adds that, “the high-fidelity, 3D nature of digital prototyping allows engineers to see and experience product performance in ways that will never be possible with a physical model, which leads to higher quality and greater innovation in the design.” And although Spann and others can see the benefits of a digital prototyping approach, they also see the reality of trying to combat the dynamics of being able to physically touch and feel a prototype.
Additionally, although there have been some advancements by Adobe and others in providing programs that allow CAD data to be viewed and shared even if a dedicated seat has not been purchased for that individual, obstacles still exist in sharing prototype-based data with sales, marketing or manufacturing personnel.
“I think less than 10 percent of the companies in the world will ever get comfortable with going into production with a design that has never been tested in the physical realm,” reiterates Spann. “There is still no substitute for holding the product in your hand and watching it do its thing before committing the manufacturing start-up money.” Essentially, digital prototypes seem like a great compliment to other approaches, but simply can’t replace the mechanics of a physical product.
Not So Heavy Metal
When asked about future developments in this arena, Fischer describes metal prototypes and metal rapid manufacturing as the “grail” of the marketplace. While everyone can see the benefits, few are able to join the ranks of early adopters for two main reasons – aesthetics and price.
One option is ARCAM, which uses an electron beam to melt metal powder in building up parts layer-by-layer. The accuracy of this technology is very good, and in handling a variety of titanium, cobalt and chrome alloys, prototypes can provide material characteristics and environmental tolerances that are very close to the target metals that will actually be used. The creation of parts is also relatively quick. This combination of benefits and the ability to read CAD files in greater detail has led to the use of ARCAM in some low-volume manufacturing applications. The composition of these end-products also allows for high-speed machining and grinding after they’re created.
As initially mentioned, the major obstacles with this technology are price and surface finish, as some sort of additional coating will be needed if the part is being presented as an end-product. The external features of these parts are similar to those created with sand casting. Much like CAD software and 3-D printers, as this technology improves, costs and functionality should make it more economical and user-friendly in growing its use and acceptance.
Much like FDM, SLA and SLS offer comparable, but unique options in the plastics arena, ARCAM, which is distributed solely by Stratasys in North America, and DMLS are in a similar situation when it comes to metal prototyping and rapid manufacturing. DMLS (direct metal laser sintering) is a metal-based layer additive technology that also uses metal powders and an electron beam, but it builds in finer layer thicknesses, which distributors and users of the technology feel translates to greater detail and accuracy.
 DMLS (direct metal laser sintering) can be used to create very intricate, yet durable pieces, like these tooling inserts. |
Greg Morris of Morris Technologies, a distributor of DMLS and manufacturing partner of EOS, the German company who pioneered metal sintering, offers this explanation. “Whereas ARCAM builds in 100 micron layers, DMLS builds in 20 micron layers. Also, the laser spot size on the DMLS
system allows for finer detail resolution. ARCAM, however, builds faster than DMLS. I wouldn’t necessarily pit the two technologies against each other because I think ARCAM certainly has its niche, as does DMLS. In fact, I would suggest they are almost complimentary if you want to cover the entire spectrum of applications.”
Morris also offers his perspective on the future of this technology. “DMLS is in its infancy, but here are my projections of what we’ll see in the not-too-distant future:
- “Many new materials will be developed.
- “The machines will get faster. This will allow for an increasingly larger presence as they become more cost-effective.
- “Although the tolerances and detail resolution are already very good, that will also continue to improve.
- “The size of the build area will increase, probably at a minimum of twice what it is today.
- “The ability to sinter different materials in the same build will eventually happen. Say you want good strength in one area of the part, then you want to have a different alloy elsewhere on the same part to meet other needs like wear resistance.”
So which approach is the best? The answer, of course is all of the above, depending on where your priorities lie. The key is to examine the options currently available and then relate them to the production or prototyping result you desire. The benefit with each approach is an ability to more efficiently move the design process along, and get better products to market quicker.
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