Latest approaches enable rapid manufacturing of metal parts for industrial use
By Patrick Waurzyniak
Rapid manufacturing techniques encompassing several direct-metal manufacturing methods promise to offer manufacturers substantial savings in compressing time-to-market on new product development cycles and lower costs for expensive tooling. In recent years, such rapid technologies have gained converts, particularly for aerospace and medical manufacturing, as the direct-metal approaches, seen as futuristic just a few years ago, have become more practical for rapid tooling and rapid manufacturing of low-volume and production-level metal parts.
Several rapid manufacturing suppliers have devised innovative methods for making direct-metal tooling and parts for lower-volume production applications, including laser-sintering and electron-beam melting of parts from powdered metals, and ultrasonic consolidation or solid-state layered bonding of metals to create production metal parts.
The prospects for rapid manufacturing are on the upswing, as rapid prototyping industry observers forecast stronger growth for that portion of the overall rapid prototyping industry in the coming years. Rapid manufacturing has shown an interesting, though not totally unexpected, upward growth trend, notes Terry Wohlers, president of Wohlers Associates Inc. (Fort Collins, CO). According to the Wohlers Report 2005, organizations that use additive processes to manufacture end-use parts indicate that activity has increased from 3.9% in 2003 to 6.6% in 2004, and to 8.2% in 2005. Wohlers Associates expects that rapid manufacturing will grow to become the largest application of additive fabrication in the future.
Direct-metal approaches most recently have made inroads for applications including rapid development of tooling and for shorter-run low-volume production parts (see "Rapid Metal" in the November 2003 issue of Manufacturing Engineering.) With refinement of some of the latest techniques, proponents of direct-metal rapid manufacturing contend that the processes will greatly benefit aerospace, medical, and automotive manufacturers seeking to lower costs, speed time-to-market, and even develop entirely new types of products with these rapid manufacturing techniques.
With its patented electron beam melting (EBM) system, Arcam AB (Mölndal, Sweden) has developed a rapid manufacturing technique that is said to use free-form fabrication technology to form fully dense parts melted from metal powder, built up layer-by-layer in the company’s "CAD-to-Metal" additive process. Arcam’s technology has won over customers in the aerospace and medical field for its ability to melt titanium and other metal alloys into dense, void-free parts that can be used for prototypes or production applications. Arcam aerospace customers include Boeing Phantom Works in St. Louis, which is using an Arcam EBM S12T system configured to build titanium parts for aerospace applications, and NASA, which earlier this year ordered an EBM S12 system for the NASA George C. Marshall Space Flight Center (Huntsville, AL), for use in direct-metal manufacturing of parts from titanium and other high-end alloys.
The Arcam EBM process also has garnered significant attention from medical implant manufacturers, and early this year, Arcam added two new materials, CoCrMo (Cobalt-Chrome) and Ti6Al4V ELI (Extra Low Interstitial), for use with its EBM process. In March, the Swedish manufacturer also signed an agreement with rapid prototyping/rapid manufacturing supplier Stratasys Inc. (Minneapolis) under which Stratasys became the exclusive distributor of Arcam EBM systems throughout North America and Mexico. "The US is Arcam’s largest market and also the market with the best potential," notes Magnus René, Arcam CEO. "Today there are nine systems installed or on order for US customers. Stratasys is clearly the leading company in the business and this agreement brings a perfect partner to accelerate our growth in the important North American market."
Aerospace and medical are among the industries most interested in deploying EBM technology to both speed time-to-market on new product designs and save the tremendous investment made annually in expensive dies and tooling. "We’re really departing somewhat from rapid prototyping per se," notes Stratasys’ Kirby Quirk. "We’re seeing new people and getting involved with metals people, who actually have to install components onto an aircraft, or implant a device into a person in the form of custom implants.
"What they’re looking for is a way to eliminate millions of dollars worth of tooling a year that they spend money on for molds," adds Quirk. "And if tooling costs $100,000, the more important thing is that they can save the 15–20 weeks to obtain that tooling. It’s a huge thing. Time-to-market is everything."
By eliminating time and tooling costs, direct-metal production of parts can offer a big payoff. "If you go out to the F-16 plant, say they’ve got 10 aircraft for the Israeli Air Force and they need 10 brackets each for a certain radar package that goes on the aircraft," Quirk says. "They only need 10 of those, and that’s all they’ll ever need. If they can eliminate the tooling, and the wait, which may be 10, 12, 15 weeks, and the cost, say $30,000–$40,000, if they can do those parts overnight or in a couple of days, and have them out on the line to mount directly on the airframe, that’s huge."
Medical applications likewise can benefit greatly from fast turnaround on rapidly manufactured parts, he says. "I was at a medical instrumentation company the other day, and they had a particular piece that would cost about $35,000 for the tooling—just for a core and cavity—and it took about 20 weeks turnaround time. Now if they find one problem with that, guess what? It’s another whole cycle time."
Manufacturers of metal implants used in hip or knee-replacement surgeries and makers of surgical instruments are also looking at the direct-metal rapid manufacturing technology. "They have huge interest in this—you name them, they’re all excited about this," Quirk states. "Facial cranial reconstruction, bone scaffolding, we can basically do all those kinds of things. With the scaffold, what you’re doing is replacing bone, growing two pieces of bone together where you insert a titanium scaffold in the shape of the bone, and then it grows together through the scaffold itself. It looks like a kind of mesh, and we can do it in any kind of a sculptured shape, with a number of titanium fibers running through kind of a sponge."
Implant manufacturers can use the EBM technology to produce standard implants in production batches, or just as easily produce small lots or custom designs. Arcam says its system can also use computer tomography (CT) scan data in building custom implants that perfectly match the shape of the patient’s bones, a method that can be used to custom orthopedic devices as well as bone plates for severe bone fractures and lost bone from cancer resections.
With EBM melting the titanium powder in a vacuum at 2400°F (1316°C), the process creates a fully dense titanium part, and it can more easily meet government requirements for certification of implants than some alternative methods, Quirk adds. "As far as we know, it’s probably the only one that has real promise," he says. "A sintered part will not cut it—it’s got to be a fully melted part to get the metallurgy that’s required for certified implants, to meet FDA specification. In this process, we don’t introduce any foreign materials. We keep all the materials pure, it’s fully melted, it’s 100% dense.
"If you look at the metallurgy, and you look at the grain structure, it’s the same as raw billet material—you literally can’t see any difference. The Ti 64 is standard aerospace stuff that was developed on the SR-71. The Ti 64 ELI is better-suited for sterilization—it has somewhat finer properties, and while it’s not quite as strong as aerospace material, it’s spectacular for implanting in the human body, and that’s what it’s adapted for."
In the Arcam system, the EBM machine takes a part designed in 3-D CAD and transfers the file to pre-processing software where the model is sliced into thin layers. Parts are then built by layer with the EBM process in a vacuum chamber, resulting in a complete net-shape part that can be cleaned and finished as needed with conventional machining. The system currently can build parts sized to about 8" (203-mm) square, which Quirk notes would represent roughly 40% of the parts in a typical aircraft. The system, which is said to be at least 3–5 times faster than many competing technologies, can also build several parts at once.
"When you watch a part being built, you can have three, four, five, six parts thats are identical so you’re building all of them at one time," Quirk says, "and the speed in the X-Y extents of the part is basically the same for one as it is all five. We did a whole spinal assembly for measuring spinal impacts in crash-test dummies, and in that assembly, there must have been seven or 10 different bone configurations. There are several different parts in that assembly, and they’re built in the chamber simultaneously."
Solid-state layered bonding of metals takes a distinctly different approach to direct-metal rapid manufacturing. With its ultrasonic consolidation solid-state bonding process in a hybrid system for additive and subtractive formation of metal parts, Solidica Inc. (Ann Arbor, MI) manufactures parts from aluminum, steel, copper, and metal-matrix composites. While bonding metals with the additive ultrasonic consolidation process, Solidica’s Formation systems, which are about the size of a smaller NC mill, function as a subtractive system by removing excess metal.
"A big difference is we don’t melt any metal," says Ken Johnson, Solidica vice president, strategic business development. "It’s completely solid-state which, from a metallurgical standpoint, if you can take out the melting part of any additive metal process, you can do a lot of unique things."
The Solidica Formation systems feature a large tooling envelope and offer high feature-to-feature accuracy of ±0.002 to ±0.005" (±0.051–0.13 mm), similar to some machine tools. "We’ve got an ultrasonic deposition module, and this is what lays down the tape and bonds it," Johnson says. "That is basically anvil-mounted to a conventional CNC platform, so we have no edge effects and there’s no lasers involved. With lasers, if you try to build up to the fringe, you now have focal point issues, it becomes a geometry challenge. For us, it’s completely irrelevant. Literally if the CNC bed was six feet by six feet wide, we could build exactly that big.
"Our accuracy is tooling accuracy," he says. "There are a couple of key things that allow us to have accuracy that’s basically equivalent to what you’d get off a high-speed machining center, for example. Because we don’t melt anything, there are no residual stresses. As a hybrid process, we lay the tape and build it up, and we periodically remove material with a machine tool.
"When we talk to people about things like accuracy and additive manufacturing or rapid prototyping, whatever you want to call it, we say look, ‘Look at nature. In nature, there are no flat surfaces. Everything’s additive in nature, trees grow, grass grows.’ It took man to come along and make smooth surfaces and 90° square, things like that. And so no matter how tiny your droplet or no matter how small your laser spot size, it’s not going to ever allow you to get services that are engineering quality, what people have come to expect."
With the hybrid Formation system, users can quickly build metal parts with the additive process while retaining the accuracies inherent to machine tools, he adds. "Our ‘spot size’ is a 1" [25-mm] wide, 0.006" [0.15-mm] thick tape, so we can lay down material and build things up really fast. We get all the inherent benefits of additive—it’s quick, we build our tools or parts directly onto a base plate, so there’s no fixturing. You just send it to the machine like you would send it to a printer, with its additive benefits, but the part comes off the machine looking identical to a CNC-machined part.
"It’s literally no different than if you had taken a block of metal and you hogged it out, other than the fact that with additive, you’ve got way more geometry freedom, in terms of how deep the channels are, or how fine the features are."
A startup founded in 2000, Solidica has received significant backing from the military and research sectors. In March, Solidica won a contract with the National Science Foundation to collaborate with Clemson University on developing next-generation rapid prototyping and tooling with an advanced support system to expand 3-D metal fabrication. Last year, Solidica was awarded a Navy contract from the Office of Naval Research to develop new smart armor for Marine Corps vehicles including tanks and Humvees, and the company is also working with the Army on a $3.8 million contract to develop uses for Solidica’s UC technology applied to metal-matrix composites.
"On the material side, it’s really a question of what has become a product for the commercial market, and what has been made available to select customers on development efforts," Johnson states. "We’ve built things out of nickel, copper, and silver, and we’ve bonded stainless steel and titanium to different degrees in different ways. There are hundreds of combinations of materials that have been proven to be ultrasonically weldable together. So far, every one that we’ve tried with ultrasonic consolidation, which is like a continuous spot-welding approach in a way, has worked."
This article was first published in the April 2006 edition of Manufacturing Engineering magazine.