Metal Parts Follow Tough Plastics Act
Data drive additive manufacturing processes in parts production
By Jim Lorincz
When you walk into the Redeye On Demand facility in Eden Prairie, MN, you enter into one version of the factory of the future. There you will see a bank of 100 high-end Fortus fused-deposition modeling (FDM) machines from Stratasys that provide the capacity to build real, functional parts with production-grade thermoplastics directly from CAD data. It's the fulfillment of the quest for direct-digital manufacturing in which Redeye's motto — "design one, prototype ten, manufacture one thousand" — is being realized.
Welcome to the world of additive manufacturing. AM is based on technologies that cure, sinter, lase, laminate, print, and weld materials including plastics, paper, and metals to produce prototypes, working models, jigs and fixturing, and, now increasingly, parts in low-production (serial) volume. Parts are produced directly from CAD data, eliminating the need to machine, mold, form, or cast parts. Instead, parts are built up in layers using liquid, powder, or sheet materials bonded, melted, or fused and deposited in cross sectional layers to replicate complex designs from virtual CAD representations.
AM processes have the advantage of dramatically reducing the time and costs associated in producing workpieces with conventional material removal processes, or traditional casting and molding processes that require mold and die tooling. Part design is freed from the limitations of traditional machining and the costs and lead time required to produce tooling.
Redeye's Tim Thellin outlines the benefits of manufacturing with Stratasys FDM:
- Designs are data driven, no tooling is required, and leadtimes are shorter.
- Digital files are easy to modify for design or engineering changes, and multiple parts can be run on any of the 100 or so machines available in the Eden Prairie facility. Redeye has another 23 Fortus systems operating in Europe and Australia providing manufacturing capacity.
- Designs are based on functional or aesthetic needs of parts rather than the manufacturing constraints of traditional material-removal or forming processes.
"Companies are now seeing the advantages of direct digital manufacturing for custom manufacturing, replacement parts, and low-volume production," says Thellin. As the technology continues to evolve, it's increasingly providing competition to traditional manufacturing practices, such as injection molding. With its network of 100 systems, RedEye can build up to 5000 parts in two weeks, depending on their size and readily switch from one-off production requirement to low-volume production by changing out data files.
Stratasys' DDM Consulting Services group advises manufacturers on how to employ direct digital manufacturing to produce tooling, jigs, and fixtures in a fraction of the time and cost of conventional tooling. In one case, an ABS plastic hand-held tool replaced an aluminum tool on an automotive assembly line reducing repetitive stress injuries for operators.
FDM uses production-grade thermoplastics, including ABS, polycarbonates, polyphenylsulfone and Ultem—materials typically used for injection-molded parts because of their accuracy, durability, and stability. In operation, a thermoplastic filament is fed into a head where it's melted to a semiliquid state and then extruded from a nozzle. The extrusion head moves in the X and Y axes, following a toolpath, defined by the CAD file. The part is built up, one layer at a time, and then the table moves down in position, so the extrusion head can build the next layer.
Unlike other service bureaus, RedEye's large capacity and FDM thermoplastic output targets applications traditionally dominated by rapid tooling. Industries include aerospace, automotive, consumer products, electronics, government/military, and medical device.
In addition to FDM, AM technologies include SLS (selective laser sintering), SLA (stereolithography), LOM (laminated object manufacturing, EBM (electron beam melting), and 3-D Printing. Several AM processes, including SLM (selective laser melting), Direct Metal Laser Sintered (DMLS), and Laser Engineering Net Shaping (LENS) continue to expand the use of metals for repairing high-value workpieces and, increasingly, for customized parts production, especially for medical and dental device applications, aerospace, and consumer products like jewelry.
Laser deposition technologies applied to metals have had considerable success in repairing high-value components, especially where exotic metals are required. Laser Engineered Net Shaping (LENS) technology from Optomec Inc. (Albuquerque, NM) and developed by Sandia has been used since 2000 to repair tank-engine parts for Anniston Army Depot, as well as high-value workpieces like gas turbine components and integrally bladed rotors (IBRs or blisks).
Richard Grylls, LENS product manager, explains why repair was a good place to start for additive manufacturing with metals: "The process with laser and powder is relatively straight forward. In repairing things, you are adding material in a place where it has already disappeared, and as a result qualification of the work is much simpler. For repairing blisks, a high-quality process was needed to repair the whole blisk. That meant the ability to get in between blisk blades with a narrow deposition head, being able to repair leading edges, trailing edges, and tips, and filling in features on the hub."
Optomec's success with the LENS process during the last six years of development work has been recognized by the government for its cost effectiveness with the awarding of a new Phase II SBIR (Small Business Innovative Research) contract from the US Navy to continue to develop new repair capability for restoring aircraft blisks. The Phase II contract brings the total amount of funding to $900,000. Optomec's Phase I and Phase II proposals for funding were supported by Pratt & Whitney.
In the current project, the LENS process will be used to repair nickel-based superalloy blisks, which are difficult to weld, typically suffering from extensive cracking when welded. The LENS process has eliminated these problems. "We are implementing an upgraded control system that enables the production of improved microstructures that will enable the LENS process to make repairs with outstanding properties for many high-strength superalloys, and also expand the capability of LENS to repair titanium IBRs. This new capability will find applications beyond IBR repair, including other airfoil repairs in aerospace and industrial gas-turbine applications," says Grylls.
LENS technology, which is capable of working with titanium alloys, nickel-based alloys, stainless, and cobalt alloys, is able to produce fully dense structures directly from 3-D CAD solid models. LENS systems use energy from a high-power fiber laser to build up structures one layer at a time directly from powdered metals. The resulting components are said to have mechanical properties that can be equivalent or even superior to wrought materials, and the LENS systems can be used throughout the entire product lifecycle for applications ranging from functional prototyping to rapid manufacturing and repair.
The LENS process is housed in a machine chamber that is purged with argon, maintaining the oxygen level below 10 ppm so that there is no pickup of impurities. "It's essential to control the size of the melt pool, which is 2–4-mm diam, to maintain the cooling rate of different-sized features. A camera looks down the optical axis at the melt pool, calculates the size of the melt pool, and compares it to the set point, turning down the laser power automatically to ensure constant cooling temperature," Grylls explains. The melt pool sensor optimizes the melt pool size in repairing a component with large, thicker, or thinner areas, to optimize laydown for the shape and quality of the build. Parts may be heat-treated, Hot-Isostatic-Pressed (HIP), machined, or finished in any other manner.
For EOS of North America Inc. (Novi, MI), laser-sintering is the basis for expanding e-Manufacturing in the aerospace, medical/dental device, and tooling industries, among others. The EOS laser-sintering process works with polymers and metals, providing parts where tool-based manufacturing methods are not suitable for meeting the increasing demand for customized products with shorter product life cycles, and lower production volumes are sought.
EOS generative layer manufacturing technology can take any 3-D geometry and build it without tools or milling tool paths, using 3-D CAD data. The required geometry is built up layer-by-layer using a laser that solidifies powder-based plastic or metal. In this sense, laser sintering is a generative, flexible production method, particularly well-suited for industries that no longer need to produce a large volume of identical parts.
The EOS Direct Metal Laser-Sintering (DMLS) process offers the tool and moldmaking industry an alternative to traditional machining processes. DMLS applications range from prototypes to series products and end parts. Metal parts of the most complex geometries are built layer-by-layer directly from 3-D CAD data automatically in hours without any tooling. Parts exhibit excellent mechanical properties, high detail resolution, and a good surface quality. The process melts the powder completely, creating a fine, homogeneous structure, allowing the formation of cavities and undercuts, which conventional methods can produce only with great difficulty.
EOS offers a variety of materials for use in its EOSINT P laser-sintering systems. Plastic materials are based on PA 12 or polystyrene. Polyamide is resistant to most chemicals, and the material itself is not harmful to the environment or health. There is a wide spectrum of materials for the special requirements of different applications. These materials can be distinguished among other things by their filling, for example with aluminum, glass, or carbon fiber.
DMLS metals from EOS vary from bronze-based alloys to tool steel and stainless. Light metals on the basis of titanium and superalloys, for example cobalt-chrome, have already been developed at EOS for use in EOSINT M systems. Such alloys are especially interesting for applications in the medical device industry as well as in aerospace.
For medical devices, laser-sintering technology is used for custom-fitted prostheses or implants. For dental crowns, for example, laser-sintering can produce hundreds of individual dental crowns in one batch. With e-Manufacturing from EOS, dental laboratories can produce bridges and copings directly from CAD data without investment casting.
"Developing new materials for laser-sintering pushes our technology to the next level," says Hans Langer, CEO and founder of EOS. At EuroMold, EOS introduced a new NickelAlloy IN718, a nickel-based heat-resistant superalloy for high-temperature aerospace applications. Corresponding to Inconel 718 alloy, NickelAlloy IN718 offers good corrosion resistance and cryogenic properties, making it a good fit for aerospace applications.
"Meeting the manufacturing challenges and application requirements clients have previously expressed to EOS, we develop newer materials that are ideally applicable to manufacturing requirements," Langer explains.
Selective Laser Melting (SLM) technology from ReaLApril izer GmbH (Borchen, Germany) is continuing to move out of R&D laboratories into production applications for producing parts for applications where material volumes and lot sizes are small, or intricate lattice and honeycomb structures are desired. Typical applications include dental prostheses, functional prototypes from aluminum, titanium, or steel, tool inserts for injection molding or other tools, and prostheses and implants like joint or bone prostheses made from titanium, and individually fitted based on CT or other scanned data.
ReaLizer SLM is a generative production method that applies metal in thin layers of fine powder, and uses a laser to melt onto those areas where the workpiece will be developed. Depending on surface quality and production speed requirements, the powder is automatically applied with layer thicknesses of 20–100 µm. In the next step, a fiber-optic laser selectively melts the designated areas. Sharp focusing provides the laser beam with a high-power density, allowing workpieces to be produced with wall thicknesses from 40 µm on up. When the melting process is finished for the particular layer, the platform is lowered by the respective thickness, and another layer of powder is applied. The layered structure facilitates the production of highly complex lattice or honeycomb structures, minimizing the weight due to optimized material usage.
Functional prototypes for automotive, motorcycle, and aerospace applications can be produced from aluminum, titanium, or steel in near-series production, without producing tooling beforehand. For hip and knee implants, production pieces with intricate lattice structures can be produced into which bone can grow for durable and long-term fusion.
The ReaLizer SLM-100 is designed for the production of smaller components, typically produced using milling centers and in dental laboratories. The machine has a 100-mm-high cylindrical construction area with a diameter of 125 mm. The base area allows the use of optics to focus the diam of the laser beam down to 20µm, enabling the machine to produce components with delicate structures, minimal wall thickness down to 60µm, and high surface quality.
The newest addition to the ReaLizer lineup is the desktop SLM 50 machine, for manufacturing metal components with a diameter to 70 mm and a height to 40 mm. With its small build volume, the SLM 50 is well-suited for gold applications in the dental and jewelry industries. All other materials can be processed as well. Typical dental applications include accurately fitted dental pieces, for example, framework, caps, or brackets made from cobalt-chromium, titanium, or gold.
This article was first published in the April 2010 edition of Manufacturing Engineering magazine.