Direct-metal and plastics-based prototyping processes enable manufacturers to quickly produce parts and tooling
By Patrick Waurzyniak
Direct-metal processes for rapid manufacturing are catching on in the rapid prototyping industry, joining more traditional plastics-based additive prototyping methods including fused deposition modeling (FDM), stereolithography (SLA), selective laser-sintering (SLS), and 3-D printing techniques. Medical and aerospace applications are taking center stage using some of the newer direct-metal methods for producing parts from titanium and other metal alloys, as well as using FDM to produce engineered thermoplastic prototypes.
With some of the advanced direct-metal techniques like the electron-beam melting (EBM) process from Arcam AB (Mölndal, Sweden), which is distributed exclusively by Stratasys Inc. (Minneapolis) in North America and Mexico, and the direct-metal laser-sintering (DMLS) process from EOS GmbH (Munich), manufacturers are now making more metal tooling and shortrun production parts with CAD-based direct-metal rapid manufacturing systems.
Demand for additive fabrication/rapid prototyping systems grew at a healthy 14.6% rate in 2005 to an estimated $808.5 million market, up from $705.2 million in 2004, according to the Wohlers Report 2006. "The industry has remained solid after a spectacular 2004," notes Terry Wohlers, president of Wohlers Associates and principal author of the Wohlers Report. "Systems, materials, and services experienced double-digit growth in 2005, although growth was not as strong as the previous year."
While interest in less-expensive 3-D printers still drives the majority of prototyping machine sales, rapid manufacturing continues to grow and capture attention, Wohlers adds, as manufacturers in the aerospace, motorsports, medical, dental, and consumer products industries are using additive processes to manufacture high-value parts in comparatively low volumes. Wohlers Associates expects that rapid manufacturing will eventually grow to become the largest application of additive fabrication.
Direct-metal rapid manufacturing processes recently have won converts among the aerospace and medical manufacturers seeking fast, accurate production of net-shape parts made of titanium and other high-strength metal alloys with Arcam's EBM process In Arcam's patented "CAD-to-Metal" additive process, titanium and other metalalloy powders are melted in a vacuum in the EBM machines, producing 100% dense metal parts suitable for many aerospace applications and in medical uses that include implants for hips and other joints, as well as metal meshes used for bone regeneration.
In December, Stratasys installed its first Arcam EBM S-400 system at Medical Modeling LLC (Golden, CO), which plans to use the system to provide surgeons and medical device manufacturers with titanium models for improved surgical planning and implant development. "We looked for years for a technology provider that could help us create complex metal models in titanium, allowing us to meet a unique market niche," says Andy Christensen, president of Medical Modeling. "We believe that use of EBM technology will allow many manufacturers of medical devices the ability to reduce or eliminate nondigital technologies in the process of taking a design to a fully functional metal part." Benefits of minimizing nondigital technologies include streamlined production times and less waste, he notes, translating into more efficient manufacturing.
Medical Modeling provides rapid prototyping services for the medical industry. Using specific patient data acquired from computed tomography (CT) or magneticresonance imaging (MRI) scans, the company creates highly accurate, 3-D anatomical models of bone structures, such as the skull, pelvis, spine, and soft tissue, including the brain and internal organs. Using the EBM system with titanium material, Medical Modeling can create fully dense, fully functional models of surgical instruments, guides, and potentially implantable devices.
Until recently, Arcam's EBM process used titanium powders including Ti6AI4V Titanium, the most widely used titanium alloy; Ti6Al4V ELI (Extra Low Interstitial), which offers improved ductility and fracture resistance at low temperatures, and is considered advantageous for medical uses; and CoCrMo (Cobalt-Chrome). In December, Stratasys also announced that its EBM systems can now use ASTM F-75 Cobalt Chromium, a new alloy said to be ideal for biomedical and aerospace applications requiring high strength, low weight, and excellent wear and corrosion resistance. Stratasys says the Cobalt Chrome alloys are widely used in orthopedic implants in Europe, particularly in total-hip or knee arthroplasty, as well as in metal-on-metal bearings in total-hip arthroplasty.
"The availability of this alloy opens up new possibilities for direct manufacturing of orthopedic implants and prosthetics," says Kirby Quirk, Stratasys EBM channel manager. "By using Cobalt Chrome with Arcam EBM technology, metal parts can be produced three-to-five times faster than other metal additive-fabrication methods, allowing for new design solutions and greater geometric freedom."
Direct-metal laser-sintering with EOS' DMLS systems has been combined with cryogenic processing by CPM Fastools (Lusby, MD), a subsidiary of Chesapeake Plastics Manufacturing Inc., which produces production molds using both conventional and rapid tooling processes. By combining the DMLS system with cryogenic processing, CPM Fastools' approach to toolmaking slashes time and cost for production molds.
"We were seeking an innovative approach to make our company more competitive, says Mark McGrath, coowner of CPM Fastools, who along with co-owner Steven Moore founded the company in 2005. "What we found is that the consolidation of domestic toolmakers, due to overseas competition, has led to lead times of 8–12 weeks or longer. With the EOS DMLS technology and cryogenic processing, we're filling the need for fast-turn, low-cost production molds."
Since implementing the rapid-tooling process, the company has doubled its revenues while gaining speed and efficiency advantages using direct metal laser-sintering with cryogenic processing compared with conventional CNC milling of aluminum molds. CPM Fastools' process uses EOS DMLS technology to produce fully dense metal-core and cavity inserts. The inserts, and all mold components, are cryogenically processed to relieve residual stress and increase wear resistance. The company says its production molds are ideal for resins that are difficult to injection-mold and cause rapid tooling wear. "We have made production tools for molding tough resins like polyphenylsulfone and glass-filled engineering plastics," adds Moore.
More traditional prototyping processes using plastics for rapid prototyping purposes include FDM, stereolithography, and 3-D printing, methods which continue to account for the majority of prototypes built for industry. Stratasys, which according to the Wohlers Report shipped 34% of all prototyping systems worldwide in 2005, now markets its patented FDM systems and the new EBM direct-metal rapid-manufacturing systems, after deciding to discontinue offering the PolyJet systems made by Objet Geometries Ltd. (Rehovot, Israel) at the beginning of this year.
With its FDM systems, Stratasys offers benefits derived both from the FDM process and the high-strength materials used in making FDM prototypes, according to Fred Fischer, technical manager, FDM products. The company's FDM process uses ABS plastic, polycarbonate, and polyphenylsulfone (PPSF) to produce functional models from any 3-D CAD program that can be used as prototypes or in rapid manufacturing and rapid-tooling applications.
"What we are doing is not differentiating between rapid manufacturing or rapid tooling; we call both of them direct digital manufacturing," Fischer notes. "It's irrelevant what you're manufacturing—whether it's a tool or an end-use part, or whether it's a wheel, a gear, or a handle. You're manufacturing them directly from digital files, so there's no tooling or machining involved. It's just built on the system, and it's done.
"With the FDM technology, we can produce parts that can be used right off the system that don't necessarily require additional machining, polishing, sanding, painting," he adds. "FDM has great material strength. The product and materials direction that we have will allow us to expand the applications that we are suitable for."
Adding direct-metal capabilities with the nascent EBM process broadens the application base Stratasys can deliver, he adds. "There are more than 20 installations globally. Like many other metal and RP technologies, it certainly has somewhat of a defined niche, and that tends to be the medical and aerospace markets. That's mostly because of the material it uses to build parts.
"EBM indeed will continue to expand the materials offered. They're looking at a variety of different materials right now that probably will come to market somewhere in 2007," notes Fischer. "The materials are yet to be determined but, like with FDM, it will continue to expand the applications and markets that EBM is a solution for. They realize they're in a niche right now with titanium, in the medical and aerospace industries, and they want to broaden out into more consumer products, automotive, business machines—areas in which they might use metals like aluminum, steel, and other alloys."
Making functional models for medical tooling, Medtronic Inc.'s (Minneapolis) Sofamor Danek prototype lab uses Stratasys' FDM rapid prototyping systems to produce working prototypes of new surgical instruments. The lab, a leader in spinal and cranial medical technologies, produces prototypes of new medical tools at its locations in Memphis, TN, and Rossi, France.
"We often see one or two VIP surgeons per day," says design engineer Richard Franks. "They come in with a problem to solve in the morning. They explain their need to an engineer, the engineer will model a solution on ProEngineer, and then make a rapid prototype. Often by the next morning, we'll have a prototype in their hands. Sometimes we even deliver the same day. Having the FDM machine inhouse really makes it easy for us to design products."
Sofamor Danek engineers recently designed a ratcheting counter-torque instrument that surgeons use to fasten setscrews to a corrective implant on a patient's vertebrae. After the screws are fixed in place, the tool shears off the screw heads at a pre-set torque level. The existing method required surgeons to use separate tools, working them in opposing directions, using both hands. The result was often a violent impulse that occurred at the moment the screw head sheared off, and the surgeons wanted to eliminate that.
"The tool we developed combines the two existing tools into a single unit," notes Franks. "As the surgeon squeezes two handle pieces together, the ratchet tightens the screws." The engineers produced a working polycarbonate ratchet strong enough to withstand testing on stainless steel setscrews and durable enough to survive an autoclave. "Surgeons are really rough on these prototypes while trying them out," adds Troy McDonald, senior engineering manager, "so we have got to have tough material. FDM gave us the strength and durability we needed."
Medical technologists advancing surgical techniques appreciate the impact of FDM technology, McDonald adds. "FDM turned out to be an important tool for us," he says. "The benefits of functional prototypes also extend to communication. Being able to use the rapid prototypes has really cut down on miscommunication." After sending the counter-torque ratchet out to three hospitals, Sofamor Danek learned that the tool design could be improved by rotating its handle 90°, information it might not have learned without working prototypes.
The cost savings of using FDM technology in the prototype lab are evident to McDonald. "Now we can refine our designs more before we start cutting metal, which is where the dollars start going up exponentially." McDonald sees savings mount as more prototypes are made in-house. "We have several divisions, and each one has its own dedicated engineering staff that comes to our RP lab with modeling requests. Except for display items, almost everything that comes off the FDM machine is for functional evaluation. That saves the company a lot of money.
"At Medtronic-Sofamor Danek, cutting-edge medical technology takes new shape, thanks in part to FDM rapid prototyping technology," McDonald adds. "The cost of sending out work versus doing it in-house is easy to capture, and we can justify owning the FDM system via reducing that cost alone, but the intangibles—like timing issues, communication, and the value-added services—are where we see the greatest benefits."
This article was first published in the February 2007 edition of Manufacturing Engineering magazine.