Rapid Prototyping Cuts Time to Market30 Apr, 2001 By: Mark Huxley,Steven Weisberg Cadalyst
Rapid prototyping is an automated process that quickly builds physical prototypes from 3D CAD files composed of surface quilts or solid models.
Rapid prototyping is an automated process that quickly builds physical prototypes from 3D CAD files composed of surface quilts or solid models. The vast majority of projects we work on involve an RP (rapid prototyping) model of some sort. A variety of rapid prototyping machines are made by fewer than ten highly competitive United States vendors and just more than a dozen internationally. According to respected industry observer Terry Wohlers, author of Wohlers Report, an annual look at the state of the RP industry, RP machines vary in process technology, price ($7,500$800,000), and quality, with some interesting overlaps.
Companies that produce sufficient prototypes to warrant the capital expenditure may buy one or even several rapid prototyping machines.
|PHOTO IMAGE: These three parts are all interior automotive air vents. From left to right are a standard SL (stereolithography) prototype part for design verification, a QuickCast SL master pattern for investment casting, and the final production part made from the investment casting mold. (Courtesy of 3D Systems Corp) A concept for a desktop stereo developed by Volan Design LLC for Dataplay Inc.'s CES debut. 1a. CAD model of the assembly. 1b. The STL output with a detailed view of a triangulated corner. 1c. Finished prototype.|
Many others outsource their RP needs to specialized service bureaus. RP service bureaus are very competitive, and they vary in expertise and capabilities. We've found prices at different bureaus to vary by three times for the same part, so it definitely pays to shop around. You can find a worldwide directory of RP service bureaus on the web.
In the not-too-distant past, Chuck Hull, founder and chief technology officer of 3D Systems Corp., introduced a relatively simple idea that involved solidifying a liquid polymer via exposure to UV light. After more than seven years of part-time development devoted to proving the concept workable, he was granted a U.S. patent. The SLA (stereolithography apparatus) was born, and a billion-dollar industry was created. See Common steps to make an SLA model.
STL as prototype data
3D Systems developed the STL file format to transfer geometry to the SLA machine. STL files are faceted representations of data composed of triangles. The data for the STL file can come from a variety of sources: a solid CAD model, a sewn (air-tight) surface quilt, MRI (magnetic resonance imaging) and x-ray data, and laser and digitizing arm scans.
|Figure 1. This long-term exposure of a section trace from an automobile rim built in 3D Systems' RP machine.|
The SLA preprocessing software uses the STL file to generate sections of the part that are on the order of 0.005" thick. These sections are then successively traced by the laser to build or "grow" parts (figure 1). Problematic geometry and topology in the native CAD system may result in an unusable STL file. However, CAD model quality and translation is another topic altogether.
Alternatives to SLA
During the past 13 years, technologists have developed many variants of SLA technology. The most popular are:
- FDM (fused deposition modeling). The least like SLA. A polymer filament is fed into the head, melted, and deposited. It cools to form the part. It's similar to MIG (metal inert gas) welding, but on a smaller scale.
- LOM (laminated object modeling). Similar to SLA in that the models are built up from sections or layers. Paper is the building block with this method.
- SLS (selective laser sintering). Most closely related to SLA, this
process uses a powder instead of a liquid photopolymer.
For more on different variations, see our "Pros and cons" summary.
One particularly interesting company, Objet of Israel, shows great promise. Its Quadra system, set for mid-2001 delivery, acts like a 3D inkjet printer. It uses a 1,536- jet printhead to distribute a proprietary photopolymer that quickly builds accurate parts with a great surface finish. Why is Objet's technology so intriguing when 3D Systems Corp., has done something similar for more than a decade?
The Quadra, priced at $39,000, could end up competing with machines that cost 20 times as much. "Designed to be office friendly, Objet's technology is suitable for both the high-production environments of model shops and service bureaus and the fast-paced office area of the design team," explains Wohlers.
STL files are used in situations other than RP machining. One company's software (Magics Communicator from Materialise) uses STL files for real time conferencing. It lets geographically separated people conference via the Internet and simultaneously view, measure, and mark up models dynamically. The software pays for itself in one use when you factor in travel expenses and time saved.
Why don't you use RP?
|Figure 2. The cost of changes increases dramatically as products get closer to market. Different products can have significantly different slopes to their graphs, although the cost of a change always increases as the cycle progresses. Courtesy of John Krouse, Krouse Associates.|
Those who have tried RP have realized the benefits of reduced cycle times and increased innovation. When you use MCAD and RP models, they synergistically improve your ability to get the right product to market faster and thus improve your profits through increased revenues. This is made possible by catching mistakes and making changes earlier in the product development cycle (figure 2).
A phenomenon known as the TALC (technology adoption lifecycle) describes
the acceptance of new developments (figure 3). While MCAD approaches its
early majority phase, RP has yet to bridge the chasm between the early
adopters and the early majority described in the well-regarded book, Crossing
The Chasm, by Geoffrey Moore. Nevertheless, RP is not a bleeding-edge
technology that is limited to use by adventurers with money to burn. RP
is reliable and affordable enough to warrant your use today.
|Figure 3. The technology adoption lifecycle traces how people adopt technology. Where does your company lie on the graph with respect to RP?|
The proverbial napkin sketch serves as the most popular means of transferring
knowledge from one person to another. However, the napkin/paper can leave
a lot to be desired when developing and com municating complex 3D parts
and assemblies to colleagues. Software, computers, and virtual reality
produce more advanced versions of the napkin sketch, but we all have much
more experience dealing with the physical world (figures 4 and 5).
|Figures 4 and 5. These painted SLA, SLS, and cast urethane models from Dataplay and Volan Design were developed for the January 2001 CES (Consumer Electronics Show). RP technology enabled Volan Design to produce more than 60 models in just 8 weeks. The models were particularly helpful in demonstrating potential applications of the technology.|
Physical prototypes are helpful to just about everyone involved in developing products. They pay for themselves in many ways:
- communicating desired form, fit, and function;
- providing feedback about ergonomic and aesthetic requirements;
- driving home a design proposal for a client;
- providing an example to a vendor for quotation;
- facilitating quick changes in a design (especially true for castings, as shown in figure 6); and
- some combination of these benefits.
|Figure 6. DaimlerChrysler used the QuickCAD stereo-lithography part (right) as a pattern for the tooling of the actual engine block casting (left).|
Other benefits of rapid prototypes include:
- They can be used as intermediary models to develop or modify tooling (indirect tooling). Text can now be incorporated into an SLA mold master.
- You can build mold components directly from the CAD geometry (direct tooling). These first two points are possible for both prototype and production tooling. More than 20 types of technologies used today build direct and indirect tooling.
- Some RP parts cost as little as a few cents to producehandmade parts can't beat them in performance and price.
Companies that don't take advantage of rapid prototyping are at a great disadvantage against those who do. Wohlers found that "most of the 3,000 foundries in the United States don't take advantage of rapid prototyping." This is a shame because those who use RP see truly remarkable productivity gains. By one English company's estimate, casting production cycles were reduced from 1224 weeks to 24 weeks.
Ways to use RP
You can use RP in numerous creative ways. Audi performance racing used RP to create mold masters that in turn produced turbocharger intakes and exhausts. An architectural project in Phoenix, Arizona, used RP to produce scale versions of 80- to 90-story buildings to demonstrate how the buildings' appearance mimicked the area's mountain ranges. Recent dental devices have met with uncharacteristic wide-ranging acceptance in the medical community partially because RP models enabled better feedback and assistance in production.
RP has also been used in forensic analysis. A murder victim's skull was
prototyped to preserve the original as evidence (figure 7). A forensic
artist then rebuilt the facial region and created a composite sketch.
The sketch of the victim was instrumental in finding the perpetrator.
Sandia Labs is developing the world's smallest autonomous robot chassis. RP is the only realistic way to manufacture some of the parts. See Sandia Lab's web site for more information. RP may be used to build parts in space or on other planets.
In existence for just 13 years, RP is still in its infancy. As a result, some limitations exist within RP, such as
- Size envelopes. Some machines offer parts with maximum sizes of 3" cubed. Others aren't as restrictive at 32" 22" 20" , but large parts usually must be built separately and connected manually. Larger parts can be quite expensive.
- Limited material properties. Many argue that RP doesn't equal or rival injected molded parts. There have been some significant developments in this area lately, but RP can't solve everyone's problems,
- Varying accuracy between the x-, y-planes and the z-plane. Because parts are built in sections, the properties may not be very isotropic. This is worse for some technologies than others (unacceptable in SLA but significant in 3DP and LOM).
- Surface finishes that require subsequent finishing labor. This is due in part to the accuracies of the technologies and can sometimes be caused by using too coarse an STL file.
RP vendors continue to make significant strides in material development. During the past year, researchers used water to build RP models out of ice. This could prove very interesting because you can make a casting mold and simply melt the core away.
Both Chinese and United States teams are growing "bones," or more accurately, porous frames for cell adhesion, made from PLA (polylactic acid). These frames develop properties very similar to real bone. A French company is using a paste for raw material that requires fewer support structures. Others are experimenting with suspending ceramic material within a photopolymer that produces extremely stiff components.
Rapid prototyping pioneer Chuck Hull recently stated, "The major innovation on its way is direct manufacturing or rapid manufacturing applications, where we use the same kind of solid imaging technology. In order to get closer to that, we're working on improving the materials and processes and applying them in a manufacturing situation, either in place of injection molding or where it's a product or process we haven't thought of before."
Terry Wohlers believes many changes face the industry in the near future. He notes that attrition and consolidation will continue to reduce the number of RP vendors. Machine prices will drop dramatically, partially as a result of large corporations (Fortune 500) getting involved in the manufacture of rapid prototyping systems. This will make the technology much more viable for many more end-users.
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Todd Grimm with Accelerated Technologies Inc. says that the future will be "difficult to navigate," which comes as no surprise when confronted by the vast areas of use for the RP technologies. He feels that system suppliers will be taking focused yet divergent paths. The high-end prototype market will likely dwindle as companies such as Objet snatch up clients. Manufacturers of RP devices that target specific markets, such as concept modeler, rapid manufacturer, or high-end prototype, will flourish. Vendors that try to be everything to everyone won't succeed. Finally, demand for RP services will increase once production levels and technology transfer make the systems more affordable.
With wide-ranging benefits and fairly low costs, RP models can provide major returns via increased innovation and reduced production costs. Still, RP doesn't fit every application. You have to use your engineering skills to evaluate if the limitations in material properties, part size, and cost are applicable to your project and product.
You might propose an RP model for your next project, where appropriate, or simply use one of the "newer" technologies that you didn't know existed until now. Who knowsmaybe you or someone you tell about RP will come up with the next big variant.
Terry Wohlers, Wohlers Associates
Todd Grimm, Accelerated Technologies Inc
About the Author: Mark Huxley
About the Author: Steven Weisberg
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