Obstacles to Rapid Manufacturing

Rapid manufacturing (RM) is the direct production of finished goods using additive fabrication technology. An example is the use of stereolithography (SL) to produce shells for in-the-ear hearing aids. The hearing instrument is small, its shape is complex, and its value is high. No two ears canals are identical in shape and size, so the traditional method of producing a mold for each hearing aid is time-consuming, expensive, and prone to error. The use of laser digitizing, special software, and additive processes result in a custom product that is superior in many ways.

Rapid manufacturing is finding its way into many industries. In the future, RM promises to play a significant role in these and other areas, including personalized sporting goods, jewelry, electronics, education, and entertainment. Also, RM will be applied to a wide range of custom products for the military, defense, security, and personal use. The possibilities seem limitless.

Each year, Wohlers Associates surveys many companies worldwide representing hundreds of customers that benefit from parts produced with additive technologies. They answer questions including "How do your customers use additive parts?" Form, fit, and function applications continue to be the most popular. It may be surprising to some that RM now represents an interesting percentage. In 2003, respondents said that 3.9 percent of their activity was rapid manufacturing. It grew to 6.6 percent in 2004 and 8.2 percent in 2005, which means that RM is now on the "radar screen" at many organizations. However, will this growth continue with so many obstacles in its path--obstacles such as material properties and cost?

Obstacles

Material Cost
Today, the cost of most materials for additive systems is about 100 to 200 times greater than those used for injection molding. This suggests that RM will not replace injection molding any time soon. There are exceptions, such as when production runs are relatively small and when the parts that are being molded are small. The same is true for metal parts that are normally cast or machined.

The cost of additive materials is expected to decline as consumption increases. However, a dramatic increase in consumption is unlikely to occur until RM becomes much more popular. Before RM can increase considerably in popularity--at least for parts that are injection molded--material prices must decline. Material suppliers are faced with the challenge of transiting material pricing for prototypes to pricing for manufacturing.

Material Properties
Improvements in SL resins and other materials for rapid prototyping have been impressive. However, many of these materials remain substandard for manufacturing applications. SL materials, for example, may meet the requirements soon after they have been produced, but the properties of the part change over time. This change is acceptable for most prototyping applications because the life of a prototype is usually very short. When used for part manufacturing, products could fail and lead to customer dissatisfaction or worse.

Thermoplastics from laser sintering (LS) have performed the best for RM applications. However, a limited choice of materials is available. Also, materials for additive processes have not been fully characterized, and consequently, are not completely understood. Companies in aerospace, motor sports, and medicine may characterize and certify one or more materials for their particular company, but this information is usually not made available to others. This presents a costly burden on the part of the customer--a burden that many may not be willing to bear.

Support Material Removal
When production volumes are only a few parts, the removal of support material is usually not a big issue. When the volumes are much higher, it becomes an important consideration. Support material that is physically attached is of most concern. Parts that are buried in powder do not have the same issues, but powder removal and clean up of the parts, as well as the containment of dust, are issues. The manufacturers of hearing aids, air ducts, and other products have been able to deal with these issues successfully. However, parts that contain varying types of geometric features, such as deep holds and slots, present entirely new sets of circumstances.

Solutions to many of these problems will require creativity and some level of partnering between the machine manufacturers and their customers. This also presents an opportunity for third-party companies to offer unique solutions. Traditional manufacturing is faced with the removal of material from parts, such as flash and gating, and the machining of surfaces of cast metal parts, so the problem is not entirely new. Additive processes that have automated the removal of support materials, such as the use of soluble substances, are a step ahead.

Machine Speed and Cost
I have combined machine speed and cost because they go hand in hand. Fewer machines are needed when they are fast and this impacts overall capital equipment costs. Currently, additive processes are many times slower than most conventional manufacturing processes, although it's important to consider the entire start-to-finish process. If you include tooling, time and cost of manufacturing change dramatically. So when you remove tooling from the equation--as is the case with rapid manufacturing--the economics can change impressively in favor of RM.

Loughborough University has done interesting work in this area. An example is the comparison of manufacturing a plastic part for a lawn mower with injection molding and additive processes. The researchers found that it is less expensive using an additive system when volumes are at a particular point. At the time of the study, it was less expensive to produce the part using SL when manufacturing up to about 5,500 parts. For fused deposition modeling (FDM), the break-even point was about 6,500 parts. With LS from EOS, it improved to about 14,000 parts. The conclusion was that if you were manufacturing these kinds of quantities for this particular part, using an additive system would be less expensive than producing a mold and molding the parts.

Nearly every candidate part for rapid manufacturing will require a cost analysis, at least in the beginning. Among the major factors that influence the cost are machine depreciation, speed of the machine, and the cost of material.

Large Parts
The production of large parts is a consideration. With additive fabrication, small parts form faster than large ones. In fact, it is faster to produce a batch of 100 hearing aid shells than one large air duct for a Formula 1 car. With conventional manufacturing processes, the difference in production time between small and large parts is not nearly as great, so the economics are different.

To some, a "large" air duct may seem relatively small. Parts that go into ships, offshore drilling rigs, and heavy industrial and construction equipment are many times larger. Currently, additives systems are unable to produce parts larger than about 1 meter in length. Companies often join together individual parts with fasteners and glue to produce larger prototypes. However, this approach is impractical for many manufacturing applications due to time and accuracy considerations.

Designer Habits
For decades, engineers and designers have been educated and trained to design products that can be manufactured. This means, for example, being able to manufacture and remove parts from molds. Additive processes do not require tooling, which opens up a great deal of freedom when creating new designs. As RM increases in popularity, so will the need for engineers and designers to rethink the way they design new products.

Fortunately, a growing number of schools are including additive processes in their curriculum. My hope is that they introduce the technology not only for prototyping, but also for manufacturing applications. Only then will we produce a workforce that can take advantage of what additive systems have to offer.

Management and Cultural Issues
I have saved this for last, but not because it is the smallest obstacle to overcome. Some believe that it might be the largest. It is my belief that most decision makers at manufacturing organizations that could benefit from RM have yet to consider the possibility of using it. At the same time, I am encouraged somewhat by the growing number of companies that discuss the idea privately. They are beginning to think about it. Some are considering it for the production of personalized products that before were impractical due to the cost of tooling.

Rapid manufacturing has grown over the past few years to more than 8 percent of the activity at companies using additive systems. The people behind the technology are faced with many barriers that could prevent expansion. I am optimistic that most of these obstacles will be overcome as entrepreneurial individuals and organizations recognize the vast opportunities before them and address the barriers one by one. The potential payback is too large for them to ignore it.

Industry consultant, analyst, and speaker Terry Wohlers, is principal consultant and president of Wohlers Associates, Inc. (Fort Collins, CO). For more information visit www.wohlersassociates.com.