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The Laser-Sintering Effect

Thu, 02/06/2014 - 10:41am
Lindsay Hock, Managing Editor

C. J. Howard climbing with his laser-sintered rock climbing prosthetic. Photo: Mandy OttExposed on a vertical face, rock climbers rely on their instincts and experience just as much as their equipment for survival. Depending on the climb, an assortment of gear is used for a successful ascension to the top—carabineers, cams, harnesses, specialized climbing shoes. Different styles of footwear are used for finessing cracks, balancing on small toeholds or smearing sloping slabs, the choice depends on individual preference.

Rock climbing is hard enough for the average human or athlete, but, the terrain gets even harder for amputees. For C.J. Howard, a northern Calif.-based climbing enthusiast, shoes are important. But as a lower-leg amputee, even more important is his customized prosthetic foot that he designed with climbing partner and environmental/aerospace engineer Mandy Ott.

Once an athlete and a distance runner for the Univ. of California, Irvine (UC Irvine), Howard was diagnosed with osteosarcoma, a type of bone cancer, which resulted in the amputation of his left leg just below the knee. But this did not hinder his love for climbing. Instead, it inspired him to engineer a prosthetic that would further his love for adventure and the activity.

Howard started out climbing with his standard artificial foot fitted to a climbing shoe, but the prosthesis’ generic shape didn’t work. It wore out the specialized footwear too quickly. So Ott suggested an additive manufacturing (AM) process called Direct Metal Laser Sintering (DMLSä) that she encountered in her work at an aerospace company. With the help of Morris Technologies, an Ohio company that specialized in AM and DMLS, Howard was fitted with a customized prosthetic. (Morris has since been acquired by GE Aviation.)

Unlike traditional metal-forming techniques that remove or subtract material from a solid block, DMLS builds an object layer-by-layer out of metal powder in an additive manner. Ott’s digital CAD model of the prosthesis served as the 3-D blueprint to guide the process. The material that Morris engineers chose was a commercial-grade titanium (Ti64).

Fabricating the approximately 6-by-3-by-2-in, smooth-edged foot took about 40 hours and started with uploading the CAD file to the DMLS system, an EOSINT M 270, where it was converted to a 2-D sliced file. Titanium in powder form was deposited on a platform in the build chamber of the system—a unit manufactured by EOS, developer of the DMLS technology. A focused 200-W laser traced the first cross-sectional slice of foot, melting and solidifying the metal powder at high heat into a solid replica of the digital data. Fresh powder was then reapplied and the next layer of the CAD model was outlined by the laser, fusing it to the first. As the process repeated, the foot grew one 20-µm layer at a time.

Now, Howard is climbing as much as three times a week thanks to his new DMLS customized prosthetic.

The history of DMLS
DMLS is used in various medical applications. In addition, the technology as a whole has evolved to where it is now accepted as a manufacturing process as opposed to just a rapid prototyping technology. And there are numerous industries riding this trend, such as aerospace, tooling, dental, consumer, and automotive. DMLS allows for the creation of complex geometries, part consolidation, light-weighting, electronic warehousing, and mass customization.

Laser sintering (LS)—also known as plastic laser sintering—was developed in 1989 at the Univ. of Texas by Carl Decker under the sponsorship of the Defense Advanced Research Projects Agency (DARPA) and commercialized by DTM Corp. (now 3D Systems Corp.).

In parallel, Dr. Hans Langer, the founder and CEO of EOS, Munich, Germany, developed a plastic laser-sintering technology in Europe under an R&D budget from BMW, says Andrew Snow, regional director, EOS North America, Novi, Mich. EOS subsequently developed DMLS.

Direct Metal Laser Sintering relies on metal powder, such as titanium, Inconel, aluminum, stainless steel and cobalt chrome, and uses a high-powered Yb-fiber optic laser to melt metal powder into a solid part. Parts are built up additively layer by layer—typically in 20-µm layers. Highly complex geometries can be created directly from 3-D CAD data in hours, without any tooling, says Snow.

DMLS offers benefits over other conventional manufacturing techniques, including no tooling requirements and more design freedom.

A laser-sintered UAV. Image: Univ. of SouthamptonOne of the common misconceptions in the marketplace, according to Snow, is that EOS doesn’t have open parameters to meet the needs of universities and research institutions to develop technologies further. At the recent EuroMold meeting in Frankfurt, a detailed review of EOS’ architecture and graphical interface showed that EOS’ software and build parameters were far more open than customers thought. With options such as standard parameters and pre-defined part property profiles, an editing function and custom-build parameter, EOS’ technology appeals to those looking to build standard or custom parts.

DMLS flies high in aerospace applications
Aviation history has been made before in Southampton, U.K.: It was in this city that Reginald Joseph Mitchell developed the Spitfire, a famous British fighter aircraft in WWII. Today, engineers at Southampton Univ. have taken an innovative step in implementing their idea of an experimental, unmanned aerial vehicle (UAV). The team developed a UAV using plastic laser sintering and, in the summer of 2013, flew the first 3-D printed unmanned plane, made entirely of nylon and known as the Southampton Univ. Laser Sintered Aircraft (SULSA).

Laser sintering offers structural freedom, meaning designers can think in new ways. The design team from the Univ. of Southampton wanted to build a UAV that was light and sturdy, with no structural restrictions in either design or production. Laser-sintering technology enabled the team to use forms and structures in the construction of the aircraft that would’ve been impossible or prohibitively expensive using other manufacturing techniques.

To implement the plan, designers from the university partnered with 3T RPD, who undertook the manufacturing and detailing of the design, as well as supplying laser sintering knowledge and expertise. The structural components were manufactured via EOS’ large-frame plastic laser-sintering technology, the EOSINT P 730. Nylon 12, PA 2200, was chosen as the material as it minimizes the weight of the aircraft while offering a high degree of structural rigidity. By the end of the process, the team successfully produced their aircraft according to plan, cheaply and quickly.

The UAV is comprised of four parts plus a component tray, which simply clip together. The aircraft can be prepared for flight in no more than 10 min. Clip fasteners for the internal components—of which there are only ten—are integrated in the fuselage.

Sustainability is also of importance in the aerospace industry, and the major organizations are looking to reduce the overall carbon footprint of airplanes by re-designing jet engine fuel nozzles. According to Snow, aerospace OEMs have identified well over 100 components on jet engines that are candidates for EOS’ DMLS technology. Through re-design efforts, the aerospace organizations look to reduce the weight of their engine to ultimately reduce fuel costs.

By using EOS’ DMLS to re-design a jet engine fuel nozzle, one aerospace company has demonstrated five times more durability and 25 percent less weight in the engine. They took a 20-piece design where extensive brazing and welding was needed and consolidated steps into a one-piece design.

So what is the future of AM and DMLS? Snow says it’s toward bigger, faster and multi-laser systems that will have an eye on manufacturing complex parts in a single design.

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