Material Options: An Absence or Abundance?

For some, it is easy to forget that material can make the difference between success and failure when prototyping. Would Stratasys be as successful as it’s been if its machines produced parts in wax only? It’s the durability of ABS plastic that has helped carry the company to where it is today. The same can be said about the thermoplastics for laser sintering from 3D Systems and EOS.

By Terry Wohlers

"Viewpoint" is a monthly column authored by Terry Wohlers for Time-Compression Technologies
This column was published in the March/April 2005 issue.

An impressive range of materials are available for stereolithography (SL), laser sintering (LS), and fused deposition modeling (FDM), and processes from Solidscape, Z Corp., Objet Geometries, and other companies. A month seldom goes by without hearing about a new material product or upgrade. Over the years, it’s been interesting to watch DSM Somos and Huntsman raise the bar on what’s achievable with photopolymers. In the mid-1980s, when photopolymer was first applied to SL, few would have anticipated how far it would come.

Tom Mueller of Express Pattern (Buffalo Grove, IL) is an industry veteran that has spent considerable time with prototypes produced in photopolymer. He led the work at Baxter Healthcare in 1987 when it received the first commercial SL machine, the SLA 1, from 3D Systems (Valencia, CA). Most recently, he has developed a deep understanding of how photopolymers can be used to predict the performance of injection-molded parts. Mueller explained that some photopolymers are advertised to be similar to common injection-molded plastics such as polypropylene and ABS. Despite the availability of improved materials, however, he said that it is very difficult for users to answer two basic questions:

• If the prototype passes testing, will the production part pass, and
• If the prototype fails testing, will the production part fail?

According to Mueller, much can be done to answer these two questions, even if it is impossible to match all the properties of a production plastic. In any prototyping situation, a limited number of material properties control the performance of a part.

Mueller uses an example of a simple injection-molded part such as a plastic coat hanger. Only two properties significantly affect the ability of the hanger to do its job:

• Stiffness, which determines how much the hanger deflects under load, and
• Strength, which determines how much load the hanger can withstand before it fails. 

RP Material

If an RP material matches both the stiffness and the strength of the production plastic, one could build a prototype hanger in that material and it would behave exactly like the injection-molded production hanger. It doesn’t matter whether the RP material matches other properties of the production material such as hardness, impact strength, or heat deflection temperature. It is only necessary to match the key material properties for the prototyping situation to predict the performance of the production part. With all the accomplishments in new materials development, there is still work to be done. Consider the range of thermoplastics that could be processed by LS, and the powders that one could solidify by jetting a binder onto them. Also, consider the small handful of materials that are currently available for new generation technologies such as the Eden PolyJet machines from Objet Geometries (Rehovot, Israel) and the InVision machines from 3D Systems. Both offer tremendous opportunity for the future, but not without the availability of a broad family of materials.

Metal

One the most exciting developments in this industry is that of direct metal part production. No fewer than 12 companies worldwide are producing machines that build metal parts. Many of them use a laser melting approach to produce parts layer by layer.

It has been exciting to watch these systems develop, although many of them are years away from maturity. The annual EuroMold trade fair in Frankfurt, Germany has become a showcase for witnessing their progress from year to year.

European system developers currently lead the development of metal parts systems. Arcam, EOS, F&S/MCP, Phoenix Systems, and Trumpf—all from Europe—have successfully processed titanium alloys for the production of medical or dental implants. At EuroMold 2004, Concept Laser, another European company, displayed some impressive parts in aluminum. And EOS had on display small LS parts produced from gold powder.

Work in metals has not been limited only to Europe.

Solidica (Ann Arbor, MI), led by former Ford scientist Dr. Dawn White, is taking its ultrasonic consolidation process to new levels. Aluminum is the material of choice, although White and her team have experimented with a number of other metals including copper, silver, titanium, and nickel. Meanwhile, Extrude Hone’s ProMetal Division (Irwin, PA) is focused mostly on using 316L and 420 stainless steels, which are brought to full density through the infiltration of bronze. The final part is about 60% steel and 40% bronze.

Optomec (Alboquerque, NM), with its Laser Engineered Net Shaping (LENS) machine, can process a wide range of materials including 316 and 304 stainless steels, nickel-based superalloys such as Inconel 625, 690, and 718, H13 tool steel, cobalt-chromium, and Ti-6Al-4V titanium alloy. Meanwhile, competitor POM, with its Direct Metal Deposition (DMD) process, is concentrating mostly on tool steels such as H13 but is capable of processing nickel superalloys (Inconels, Hastalloys, and others), cobalt superalloys, tungsten-based alloys, copper-based alloys, cermet alloys, and precipitation-hardened steels. A titanium material system is under development.

The challenge for all the companies that produce metal-based machines is to uncover new applications for their machines. This means offering materials that meet the needs of those applications.

Research & Development

Most of photopolymer R&D has come from DSM Somos (New Castle, DE), Huntsman (West Depford, NJ), and 3D Systems. In Japan, Asahi Denka, JSR Corp. (formerly Japan Synthetic Rubber), and Takemoto Yushi have developed a wide range of resin products that compete with the best. However, many companies in the business of manufacturing machines choose to develop materials in parallel with their processes because it’s difficult to separate the two. EOS, Objet Geometries, Solidscape, and Stratasys, as well as most of the companies producing metal-based machines, are developing the materials themselves.

A number of universities are also working on new material formulations. The University of Applied Sciences (St. Gallen, Switzerland) is credited with developing the DuraForm polyamide (PA 12) and CastForm polystyrene LS powders for 3D Systems. The same team, led by Professor Gideon Levy, is currently developing an LS material that offers interesting elastic properties. The parts that I’ve seen are impressive. Down under, the University of Queensland (Australia) has been developing for some time an aluminum powder for LS from 3D Systems. Research and development has not been limited to the established companies and universities. A relatively new company, 3Dimensional Resins

(Pompano Beach, FL), is launching new urethane-acrylate resins for stereolithography. An example is a new photopolymer that is flame retardant, according to 3Dimensional Resins’ Jim Harrison.

With all the materials that are available, one could argue that there are an abundance of options available. However, this is anything but the case. New and better materials is one of the top requests among users of the machines. This is especially true among customers of some of the latest generation 3D printing processes. Without materials that meet the needs of the application, you can’t use the machines.

Improved materials for the existing RP processes will open the floodgates for prototyping and manufacturing applications. A growing opportunity is emerging for short run production parts directly from these machines. The direct production of parts in metal is on the verge of tapping the market for low volume castings and machined parts. A lot of work is ahead to make these materials—plastics, metals, ceramics, composites, and other formations—meet the minimum requirements for series production applications. When they do, brace yourself: It will become big—very big. The current RP market will pale in comparison. And much of this hinges on the development and commercialization of new materials.

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