Forward thinking companies are exploring the use of rapid prototyping (RP) machines for the production of final manufactured parts. As obstacles are overcome and companies demonstrate success, an increasing number of organizations will view RP technology as a viable method of manufacturing. There is even speculation that the application will become so widely used that RP will no longer mean rapid prototyping but rather rapid production.

Key Barriers
As the RP industry explores the prospect of applying its technologies to production applications, it is faced with a number of challenges, including, but not limited to, material properties, surface finish and speed. Current research and development suggests that it is possible to overcome these challenges. In the meantime, these limitations create barriers that can stifle the development of rapid production.

Speed
The fastest RP machines cannot compete with high volume production processes like plastic injection molding or die casting. In production environments, cycle times are measured in seconds and minutes. With RP, cycle times are measured in hours and days. Long-term success will hinge on the ability to reduce the time to produce parts on an RP system.

Rather than wait for change, it may be wiser to look for opportunities. Considering the entire cycle time for today's part production, tool design, tool construction, sampling and machine setup, it can take months to create the first 1,000 parts. Whereas, in that same time an RP system can reasonably produce a small part at a rate of 30 per day. Over three months, this would equal 6,300 parts. Not only can RP lead in production volumes over the short run, it could offer the design team the option of modifying the design after creating each batch of RP parts.

Another option is to fine-tune an RP machine to a specific manufacturing application to reduce production time. Align Technology (Santa Clara, CA) - the company that offers the revolutionary Invisalign orthodontic system - has doubled the speed of its SLA 7000s by tuning them to the company's specific needs, according to Len Hedge, vice president of Manufacturing at Align Technology. "We have optimized the 7000s to the unique characteristics of the parts we build, thus doubling the throughput of the machines," Hedge says.

Post processing
Many RP systems require additional time and expense in the form of labor for post processing. For example, stereolithography (SL) and fused deposition modeling (FDM) require support structure removal and selective laser sintering (SLS) and Z Corp's Z402 machine require the removal of residual powder that surrounds the parts. Each of these tasks consumes valuable human resources and slows the throughput of the process.

Companies have found methods that streamline these operations, but they still take time, require special equipment and can be messy and even hazardous.

Surface finish
Without benching, the surface finish of RP parts cannot match that of molded plastic or die cast metal. Even those processes that produce a smooth surface are limited by the layered nature of RP construction. Some technologies allow layers as thin as 25 microns (0.001 inch), but the stairstepping effect is still detectable. Surface finish can be greatly enhanced with hand-finishing, but this is not a good option for production applications because of the time involved and potential problems with repeatability.

The initial success in rapid production will be found in the abundance of components that are critical to function, but not sensitive to cosmetic appeal or surface smoothness. In each automobile, aircraft or electronic device, one can find hundreds of components that do not demand a high surface quality.

Another consideration is that there are production techniques with inherent surface roughness. Sand casting is an obvious example. If it's possible to use such a process for production applications, there is an opportunity to apply RP without any improvement in surface quality.

Accuracy
If compared to precise manufacturing processes, RP machines cannot achieve these standards of performance. This is especially true when considering dimensional repeatability across all parts.

Designed for prototype applications, today's RP systems lack consideration for elements critical to production equipment. In a one-off environment, process controls, feedback loops and repeatability are not prime concerns in the design and development of the system. As rapid production takes hold, companies must design their equipment with a manufacturing mentality, similar to the way companies design injection molding and die cast machines.

Yet, it is possible to use the technology today for components that do not demand +/- 0.125 mm (0.005 inch) tolerances. As with the surface finish barrier, production processes exist and are acceptable even though they produce near net shape parts.

Material properties
The range of materials in RP is no match to the wide selection of thermoplastics and metals that companies routinely extrude, mold, stamp and form. For most applications, finding an RP material that delivers the exact properties of a production material is unlikely.

Material development is the most requested demand for RP system advancement, and the vendors have responded. DSM Somos (New Castle, DE) and Vantico (East Lansing, MI) have greatly improved the durability of stereolithography polymers. Stratasys (Eden Prairie, MN) offers ABS plastic for its FDM machines. DTM (Austin, TX) continues to offer functional materials, like DuraForm, for its SLS systems. This effort to expand the range and properties of RP materials will increase the likelihood of rapid production applications.

The greatest opportunity to apply RP to manufacturing may be not in developing materials that match those that already exist, but rather in creating parts that can benefit from the unique properties created in the RP environment. For example, photopolymers are used for dentistry and vision care. If these applications can take advantage of the unique properties of light curing materials, there must be other opportunities to benefit from the unique properties delivered from RP. Some RP processes also promise to offer graded materials - something that is impossible to achieve with most of today's manufacturing processes.

Size
RP systems are limited in the size of parts that they can produce. Both the build envelope of the machines and the time to construct a large part are barriers. Big parts, especially those that are tall, can take hours, even days, to build. In fact, it can take longer to build a single part - a gearbox, for example - than several hundred hearing aid shells.

Since the inception of RP, there has been very little emphasis on developing machines capable of rapidly producing large parts. And this is not likely to change. Yet, it is possible to construct an endless supply of small components with RP. In the molding industry, custom molders are segmented by the size of parts that they can shoot. In fact, injection molders that can produce parts such as large trash containers are much rarer than shops that can produce much smaller parts on machines such as 300 ton (or less) presses. This is evidence that the biggest demand is likely to come from smaller, more reasonably sized parts.

The other opportunity lies in the application of RP to parts of any size where the production volume is extremely low. Even if it takes days and thousands of dollars to produce one part, it can be much faster and less expensive to produce five or 10 pieces in RP than producing production tooling. This scenario is often found in the aerospace industry.

Cost
RP machines and materials are expensive and therefore cost prohibitive for many companies. Although the prices for systems and materials have not decreased much throughout the past few years, developments have yielded better price to performance ratios that deliver more technology and throughput for the money. Barring unexpected developments, prices for rapid production machines and materials are not expected to decrease in the short term.

As with any purchase of production machinery, price is secondary to the return on the investment. Even though the expense of RP systems may be high relative to commonly used manufacturing equipment, the overall ROI could be better for the right application.

As RP begins to take hold in rapid production, it is likely that both system and material prices will decrease. With greater demand and increased unit sales, machine manufacturers will amortize the development, support and distribution over a broader base, allowing prices to decrease without sacrificing profits. The price decrease for production-specific RP systems could be more dramatic than for their rapid prototyping counterparts. The dramatic decrease would result from the large number of systems installed in production environments versus the smaller potential of one-off prototyping systems.

Skepticism
The biggest barrier is found within individuals and corporations. Long-established traditions, practices and preconceptions within a company will deter the thought that RP can be a powerful option in the production of finished parts. Resistance to change will delay the inevitable.

Visionary individuals and forward thinking companies will lead the masses to rapid production. Pushing the limits of the technologies while trying new ideas and methods, these trailblazers will open the door to the future.

Forward Thinkers
The aerospace industry imposes stringent quality demands. Rigorous testing and certification is necessary before it is possible to use materials and processes for the manufacture of aerospace components. Yet, Boeing's Rocketdyne (Canoga Park, CA) has successfully used RP technology to manufacture hundreds of parts for the International Space Station and the space shuttle fleet. The company also uses RP to manufacture parts for the military's F-18 fighter jet. Using DTM's Sinterstation, Rocketdyne has produced parts in glass-filled nylon. Align Technology has created a new market in the world of orthodontics. Appearance conscious adults can now have straighter teeth without the embarrassment of a mouth full of metal. Using 3D Systems' (Valencia, CA) stereolithography technology, the company produces custom-fit, clear plastic aligners under the proprietary Invisalign process. Launched in July 1999, an astonishing 60 percent of all U.S. and Canadian orthodontists have embraced this revolutionary system. A key component of the process is the company's 11 SLA 7000s. C.R.P. Technology, a division of the Cevolini Group (Modena, Italy), is using laser sintered CastForm PS from DTM to produce patterns for titanium castings. Parts include uprights, suspension supports, clutch boxes, steering boxes and gearboxes. Italy's Minardi Team is using these parts on its race-ready Formula 1 race cars.

Moving Forward
Focus on the opportunities and crowd out the barriers. See the benefits of RP and seek out unique applications. Breakthroughs can come in two forms: (1) improving on an established process or (2) changing the game altogether. With the identified barriers, using RP to improve existing processes without altering expectations will have limited success. So, changing the rules, similar to what Align Technology has done, can be the best opportunity for the success of rapid production in the next few years.

Perhaps change will come when the question asked is, "How could the design change if we were to remove the constraints imposed by tooling?" Could the part be made better, less expensively or faster, if zero draft or undercut conditions do not cause die-lock? With this simple shift in the thought process, companies can unleash the imagination and creativity of the design team.

Consider the challenges of those outside of the product development area and change may be welcomed. By seeing the world through other departments' eyes, new options will surface. Could automated, one-off manufacturing help the plant manager or production scheduler cope with tight labor markets, load balancing or excess inventory? The answer may surprise us.

There are no problems, only solutions and opportunities. Viewing the key barriers to rapid production will highlight the limitations and obscure the potential. Whether the glass is viewed as half full or half empty, RP will become synonymous with rapid production. The thinking of the RP industry will control how soon it will occur.

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