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April 05, 2010

Additive Manufacturing - Direct Laser Sintering of Titanium and other Metals

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Direct Laser Sintering of Titanium will make aerospace components cheaper and with less waste

What is direct metal laser-sintering (DMLS), and does titanium pose any unique technical challenges for this technology?

A: DMLS is an emerging technology for rapid, additive manufacturing of metal parts. Among other applications, it is well suited to production of high-strength, low-weight components at low manufacturing volumes. As such, it has exciting potential for aerospace and often involves less cost than conventional manufacturing processes.

Laser-sintering prototypes and fixtures already achieves significant cost and time savings over other processes, but more importantly, DMLS offers a new age of innovative design freedom. Engineers no longer need to be concerned with draft angles, parting lines, corner radii, and the minutiae of turning complex models into matter.

Laser-sintering offers the potential for design-driven manufacturing – the creation of a component based solely on a vision of its ultimate function, without the compromises imposed by process limitations. Instead, designers can focus on creating products that most efficiently and effectively meet the utmost performance goals.



DMLS is an ”additive” technology that works by sintering very fine layers of metal powders layer-by-layer from the bottom up until the build is complete. The process begins by sintering a ”first layer” of 20 micron (0.0008") powder onto a steel platform. The platform then lowers by 20 microns, a fresh layer of powder is swept over the previously sintered layer and the next layer is sintered on top of the previously built one. A powerful 200W Yb-fibre laser is precisely controlled in the X and Y coordinates allowing for exceptional tolerances to be held (+/-0.001"/inch)(0.0254 mm). The latest technology takes advantage of a ”dual spot” laser allowing feature sizes as small as 0.203mm to be built. With a machine build envelope of 250 x 250 x 215mm (9.84" x 9.84" x 8.46"), many medium to small parts and inserts can be constructed in hours and days versus days and weeks using traditional processes. Once started, the machine builds unattended, 24 hours a day. Parts and inserts that come out of the machine typically will go through a series of ”post” steps, including support removal, shot peening, etc.

DMLS starts with a 3D digital model divided into cross-sections by control software. A thin layer of powdered metal is deposited on a build platform in a sealed chamber. The software then guides a laser on a path dictated by the cross-section, melting the metal powder. The process repeats, layer-by-layer, with a high degree of precision, until the part is complete.

Because titanium is highly reactive in its molten state, it requires a low, controlled oxygen content in the metal powder lots and an inert gas (argon) for a processing atmosphere. Apart from these considerations, titanium is as easy to laser-sinter as other proven metals.

Q: What special benefits does laser-sintering a titanium alloy present over traditional molding and machining processes?
A: Since DMLS is an additive technology, it dramatically reduces material waste in comparison with traditional processes. Investment casting of titanium, for example, is difficult and often has a high scrap rate. Currently, many titanium aerospace components are machined from solid stock, often cutting away 90% or more of the original material – a time-consuming, costly operation that is completely eliminated with DMLS.

DMLS also has lower labor costs since it is a nearly automatic process that involves minimal programming and no “hands-on work” or supervision during part manufacture.

Finally, some of the characteristics that make titanium ideal for aerospace applications also make it difficult to machine. Its hardness and low heat conductivity reduce tool speeds and life, require a great deal of liquid cooling during machining, and limit the producibility of certain shapes, such as thin walls. Laser-sintered titanium, however, retains the beneficial properties of the metal and involves no tool-wear or coolant costs. In addition, nearly any geometry, including thin walls, can be created with laser-sintering.

Q: How do you see the use of DMLS for titanium parts in aerospace expanding, and what will drive the expansion?

A: The expanded use of laser-sintered titanium parts will follow the same route as composites are traveling now, and as aluminum did before. Aerospace companies are mainly appraising manufacturing applications for DMLS through proprietary projects and small studies. These early adopters often begin by re-creating titanium part designs previously made by machining or casting. They then discover cost reductions from the elimination of tooling, scrap, and waste. The success of these early projects will promote a gradual review of other existing parts.
At the next stage, as engineers become familiar with laser-sintering technology, they can fully implement design-driven manufacturing to achieve more innovation in new part designs. In particular, the complex geometries possible with DMLS enable the engineer to integrate several parts from a previous design generation into one, eliminating manufacturing and assembly operations and attaining still greater weight and cost reductions. Such breakthroughs will naturally lead to greater reliance on DMLS.

Q: Are there other laser-sintered metals that you see having a strong role in aerospace going forward?

A: EOS CobaltChrome MP1, which is a CoCrMo alloy, is already in use at several aerospace companies. Recently introduced nickel-based superalloys such as EOS NickelAlloy IN718 (which corresponds to Inconel 718) and NickelAlloy IN625 (which corresponds to Inconel 625) will also have a growing presence in aerospace. The recently introduced EOS Aluminum AlSi10Mg found good response-specifically in the satellite and space industry. In the long term, DMLS will likely support manufacturing with novel alloys that cannot be effectively used in conventional processes. These will open up new applications in aerospace, and in other fields as well.

North America's leading supplier of DMLS parts and inserts is Morris Tech

* Morris Technologies was the first company in North America to acquire this technology in 2003
* With five (5) alloys currently available, including the Super Alloy Cobalt Chromium (CoCr) and Stainless 17-4 PH, Morris Technologies remains at the leading edge of this advanced technology.
* Applications are wide ranging and include inserts for plastic injection molding and die casting, as well as direct parts for a variety of applications and industries, including Aerospace, Automotive, Medical, Electronics and many others.
* Morris Technologies has seen the technology used primarily for smaller, complex parts that would be time consuming and expensive to make using other, more traditional methodologies.
* New alloys are constantly in development, including Titanium and Inconel 718.
* Morris Technologies is one of four e-MP companies worldwide, with a specific emphasis on the DMLS technology.






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