The Rapid Manufacturing You Didn’t Know About

Despite its anticipated success, rapid manufacturing’s (RM) use is well below most predictions. While RM applications may be short of expectations, additive fabrication technologies and indirect rapid manufacturing have quietly been adopted and found solid acceptance in the manufacture of a number of products.

Rapid manufacturing (RM, also referred to as direct digital manufacturing) is most often defined as the direct manufacture of an end use product using an additive fabrication (AF) process and has been one of the hottest buzzwords in the rapid prototyping world over the last few years. Consider:

• At least two European conferences were dedicated to the topic in the last year.
• It has earned prominent positions on the agendas of a number of other technical conferences related to additive fabrication over the last several years. The recent SME conference RAPID 2008 dedicated three sessions on the topic.
• Terry Wohlers has dedicated a chapter of his annual report on Additive Fabrication for the last several years.
• A Google search on the term brings up 777,000 references.
• It is a topic in Wikipedia

There is no question that the concept of RM has generated a great deal of interest. Proponents claim it has tremendous potential and that the number of applications is growing. Some applications have been very successful. For example:

• Hearing Aids—The majority of hearing aids are now produced using a shell manufactured with additive fabrication processes. It allows fast and economical manufacture of a shell custom fit to the ear canal of the customer and provides a significant advantage over the manual process previously used.
• F18 Fighter Jet Air Duct—Laser sintering is used to create a complex air duct for the jet, replacing the multiple piece assembly formerly used. That assembly required several tools and manual labor to assemble. The RM part resulted in a significant cost savings. In spite of these successes, RM use is well below most predictions. A recent estimate was $30 million per year, far short of where most proponents thought it would be. While RM applications may be short of expectations, AF technologies have quietly been adopted and found solid acceptance in the manufacture of a number of products, but not in a manner that fits the generally accepted definition of RM.

Indirect Rapid Manufacturing

In these products, instead of creating the end product, AF technology is used to create an intermediate step in the creation of the part. Such processes, which might be called indirect rapid manufacturing, create one AF component for each end component created.

In each case, it allows a conventional manufacturing process to be used without requiring that tooling be built to create the intermediate step. An example is investment casting an AF pattern to create a metal casting. The AF process does not create the end use part, but does create a component which is necessary to create the end use part.

For each casting created, one pattern is required and the need to create a tool is eliminated. In most cases, AF technology is used to create an intermediate step that was formerly created with tooling.

Indirect rapid manufacturing (IRM) has found applications in a number of industries.

Investment Casting

The use of AF patterns in investment casting has increased steadily over the last several years. More importantly, their use has grown beyond prototype castings. Many AF patterns are now used to create production castings. Production applications include low volume projects such as military components, custom orthopedic implants and replacement parts for equipment for which drawings and tooling no longer exists.

The greatest current use, however, is to create limited amounts of production castings while wax pattern tooling is being built. Using AF components, foundries can deliver initial castings in two to three weeks, allowing their customers to do initial builds while the tooling is being built. As a result, customers can get initial units to market weeks or even months earlier than would otherwise be possible. They will then ramp up to full production once the tooling is completed. Foundries have learned that customers place a high value on the early delivery of even limited amounts of castings and are willing to pay significantly more money for these castings than they will for the castings provided after tooling is completed. Consequently, foundries are making more money per casting on those castings created from AF patterns than they do from castings made from wax patterns. Several foundries have now made AF patterns a central part of their business strategy.

There is also growing acceptance of using investment casting with AF patterns for short-run jobs. In the past, the cost of tooling made investment casting economically unfeasible and short runs of parts were typically machined instead. The ability to use AF patterns now allows investment casting to compete very favorably with machining and the industry is finding new markets in low volume parts that were previously machined.

An estimated 100,000 AF patterns are cast each year by investment foundries and approximately 50,000 of those are for production rather than prototype castings. The value of those production castings now exceeds $250 million annually and is growing more than 25 percent annually. While still a small part of the total market for investment castings, IRM is changing the landscape of the industry.

Dental Applications

“Mass customization” is a phrase frequently used to describe applications of RM and refers to its use to make a basic product, each of which is customized for the end user. Dental applications present an excellent example. No two sets of teeth are alike, and every dental product must be customized to the customer. This unique nature of teeth has prevented the large scale manufacturing of dental products such as braces, bridges, crowns, etc. The dental area has been a prime area for IRM applications:

• Align Technologies is the manufacturer of the Invisalign™ brand of dental appliances, which is a series of individual forms which gradually move the patients teeth from their current position to a more desirable position. To create the appliance, Align scans a patients teeth and uses specialized CAD software to determine the desired configuration of the patients teeth and then to determine a number of steps in moving the teeth from their current position to the desired one. A set of stereolithography teeth is created for each one of the steps and the form is vacuum formed over the SLA pattern. In 2007, Align sold more than $280 million worth of braces, every one created using an SLA master.
• Solidscape, Envisiontec and 3D System’s Invision systems are all used to create patterns for crowns, bridges, conventional brace components and other dental hardware, which are then investment cast. An estimated $30 million worth of components are created in this fashion.

Jewelry

Solidscape reports that more than 2,000 of their systems are used to create patterns for jewelry. Furthermore, a survey of their customers found that, on average, each system creates 75 patterns per month, resulting in 1.8 million jewelry patterns per year. Each of these patterns will be used to create a ring or other jewelry component, typically in a precious metal. An additional one million patterns are created each year on Envisiontec’s Perfactory and 3D Systems’ Invision and Viper systems. The estimated value of jewelry created from AF patterns is $700 million per year, not including the value of any precious stones that will be set in the jewelry.

In these three markets alone, IRM is used to create an estimated $1.2 billion worth of product each year, approximately 40 times the value of product created by rapid manufacturing, and more than the revenues of all AF system manufacturers combined.

Clearly, additive fabrication has had a significant impact on manufacturing, but not in the way that most analysts predicted. Two questions come to mind:

1. Why has indirect rapid manufacturing grown so much more rapidly than rapid manufacturing?
2. Why aren’t there more rapid manufacturing applications? The first question is relatively straightforward. For the most part, products created with IRM are virtually indistinguishable from those created using a conventional manufacturing process. They are made from the same materials, and use the same manufacturing process. The only change was in the process used to create the intermediate step of the process. Often, the end customer will not even know that a variation of the conventional process was used. In general, he just knows that he is getting his product faster and for a lower total manufacturing cost than if tooling had been created. That can be a pretty easy sell.

Rapid manufacturing, on the other hand, creates parts in a different manufacturing process and uses different materials than conventional processes. Typically the end customer will have to approve the use of AF processes. Customers may be reluctant to risk a change in process and material.

There are a number of reasons that RM has not been more widely adopted. They include:

• Process limitations—Compared to conventional manufacturing processes such as injection molding, AF systems generally fall short in areas such as accuracy and surface finish. As a result, they are typically limited to non-appearance parts without tight tolerance requirements.
• Material limitations—The range of materials available for AF processes is extremely limited compared to other manufacturing processes. In addition, many of those available have limited life, impact resistance or strength, further limiting the applications for which they can be seriously considered.
• Cost—The cost of most RM parts built with current AF technology is very high compared to what customers are used to paying for conventionally manufactured components. Future machines undoubtedly will increase capacity and speed, enabling lower costs, but for the time being, cost is prohibitive for most applications.

These limitations make it very difficult for RM to compete with conventional manufacturing processes for the vast majority of applications.

There undoubtedly will be significant improvements in AF technology over the next few years which will provide major improvements in all of the above limitations. However, even with such improvements, RM is likely to compare unfavorably with conventional processes for the vast majority of manufacturing applications. It is unlikely that RM will ever be able to make an iPod case at a cost low enough to compete with injection molding.

However, the biggest obstacle to greater use of RM may be that the types of applications best suited for RM are exactly those that designers are trained to avoid. The biggest opportunities for RM lie in applications which strongly use the specific advantages that AF processes offer. With respect to manufacturing, those advantages are:

1. The ability to easily create geometries that are difficult or impossible to create with conventional manufacturing processes. This ability makes it possible to manufacture components in one piece which must be made as assemblies using conventional manufacturing methods.
2. The ability to create geometries without the use of tooling. This makes it possible to manufacture low volumes of product which would be economically unfeasible with conventional manufacturing because of the cost of tooling.

The best applications for rapid manufacturing are those which use one or both of these advantages to manufacture products which are difficult or impossible to create using conventional manufacturing. The fighter jet duct application is an example of exploiting the first advantage while the hearing aid application is an example of exploiting the second.

However, as mentioned previously, these kinds of applications are the ones that designers are most likely to shun. Ease of manufacturing by conventional processes is one of the more important design criteria taught in engineering schools. Designers are taught to minimize hard to manufacture features like undercuts, widely varying wall thickness, etc. because it will significantly increase the cost of manufacture. If they are unavoidable, the component will often be manufactured in sections and joined together to create the complex geometry.

Furthermore, whenever possible, designers avoid low volume applications because they know that the amortized cost of tooling would make the part cost unacceptably high using conventional manufacturing processes. It is no wonder that when we look at existing products, RM rarely is an attractive alternative to conventional manufacturing. Good RM applications have already been filtered out in the design process.

What Role Will AF Play in Manufacturing in the Future?

IRM will continue to grow rapidly as additional applications are identified. Some likely areas include:

• Medical Products—Any product that must be made to fit to an individual body is a good candidate. An obvious application is custom orthopedic implants such as hip and knee joints and implants for bone reconstruction.
• Complex Products—There are a number of potential products that are very difficult if not impossible to manufacture by conventional means but that can be fairly straightforward by IRM. An example is trussed panels. Imagine two thin sheets of metal separated by a tetrahedral framework of thin metal members. The structure would be very light but very stiff. It could be relatively straightforward to manufacture with IRM.

RM applications will undoubtedly grow as more designers learn about its capabilities and move away from the design rules that have been made obsolete by AF technology.

Tom Mueller is partner and co-founder of Express Pattern (Vernon Hills, IL), a supplier of rapid prototyping services and a provider of rapid prototyping patterns for investment casting. Tom’s involvement with rapid prototyping began in the late 1980s at Baxter Healthcare where he headed the first beta test for 3D Systems. After two years there, he and a partner formed Prototype Express, one of the earliest service bureaus.