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Additive Manufacturing – A New Tool in the Manufacturing Toolbox Part 3

Blog Written by: Hutch Hutchison, Principal, Technology & Engineering, FuzeHub
As Promised, this week we will take a look at Additive Manufacturing of metal parts. Last week I suggested I would cover Selective Laser Sintering, but there have been so many methods of 3-D printing metal parts, I thought I would cover them all.
SELECTIVE LASER SINTERING (SLS)
This process is the first of many, all fitting into the category of “Powder Bed Fusion”. The basic idea consists of our now-familiar CAD file, once again determining the layer structure of the part to be created. The machine consists of an elevator platform on which to build the part, a hopper containing metal powder, a brush or roller system to distribute an even layer of metal powder on the build layer, and a ”print head”, consisting of a powerful laser, typically CO2, delivered by a fiber optic, to achieve a focused, small beam.
The operation of the machine starts with a uniform layer of the metal powder being spread over the build platform. The tightly focused laser head then melts the powder, fusing its particles into a melt, according to the layer information from the cad file to determine the shape. The melt hardens as the laser moves from the spot. When the layer is completed, the elevated platform drops by the specified layer thickness amount, on the order of 20µm. The next layer of powder is distributed to the build platform, and the layer is melted by the laser. The process continues until the part is complete.
The part is supported during the build by the un-fused, and re-usable powder, which drops with the part as the build platform is lowered. When the part is complete, the powder can be blown or otherwise washed away from the part, which is then removed from the build platform.
This video, while an unabashed advertisement for a prototype company, clearly shows how the process works:
Laser Sintering of Metal
The part that results from the SLS process may be suitable as a finished part, according to the design specification. However, the specification may call for a finish finer than the SLS capability, or a hardness that is not inherent in the build. Note that the SLS process produces fully dense metal, similar to a forging or casting, but often that process does not yield suitable final parts. Traditional means, such as Computer Numerically Controlled (CNC) mills, lathes, grinders, and. or drills may be used to achieve final finish or shape, and conventional heat treating may be required to achieve appropriate metallurgy.
Laser Sintering is also known by other names in this rapidly growing AM field: Direct Metal Laser Sintering (DMLS), Powder Bed Fusion, Direct Laser Melting, and others, being coined as quickly as other processes are conceived. The first company and still the largest to commercialize this process was EOS, a German company.
Without re-titling the section, I call out an alternative to the laser being used as the fusing device on the print head, that being directed energy melting. A small company from Sweden, ARCAM AB, has substituted an electron beam, and called it Electron Beam Melting (EBM).  The use on metal is somewhat obvious, in that the e-beam requires a conducting medium, such as metal, to properly fuse powders. Contrast this process to one that has been used for years as a metal forming process, Electric Discharge Machining (EDM), where material is removed using electric sparks. (Subtractive Manufacturing!)
Here is a video of how the Arcam Machine works:
ARCAM EBM
Among the many beautiful features of metal AM is the ability to fuse a variety of materials, making these processes very attractive to aerospace/aviation and automotive industries.  With Titanium and Aluminum alloys available, as well as a variety of steels, such as maraging (tool) steel, and cobalt, tantalum, inconel and magnesium, the ability to produce parts that are both strong and lightweight, with the further capability of a lattice structure under a solid skin that was heretofore un-manufacture-able, applications for metal AM are expanding very rapidly, but more on this in subsequent articles…
As we are on the topic of E-Beam, yet another metal AM system has been created by Sckiaky, in Chicago. They call their system Direct Manufacturing (DM). Instead of the powder bed, DM consists of a moving, articulated e-Beam welding head, fed by an opposing metal wire feed head. DM takes an approach of welding in place, guided by the CAD file, to produce parts, large ones at that.  Sciaky’s DM has a standard build envelope of 19′ x 4′ x 4′! The parts produced, as in the case with all metal AM, will most likely need additional finishing and heat treating, but, once again, AM provides a means to make otherwise un-manufacture-able parts, fitting into the tool box nicely. Here’s a video of the DM process:
Direct Manufacturing (E-Beam Welding)
Yet other powder fusion devices exist, where a jet of metal powder is aimed at the laser spot, which creates a melt pool, which is formed as the jet and laser are guided by the CAD file for that layer.
BINDER JETTING
Yet another method of AM with metal is the process of binder jetting. EXOne, a company from Pittsburgh, PA, has pioneered binder jetting, with a large variety of materials, including sand (for investment cast molds) and metals. The process is similar to what we have learned so far, a bed of metal powder, spread uniformly over a build platform, but now the print head prints a binder material, to join the particles of metal via bond. The part drops as with SLS, new powder spread and a new layer put down for the binder print.
The process is not as complete as with SLS, in that the density is not as SLS parts, due to the binder. Typically the binder jetted part is then infused with bronze. There are many applications which call for this process, especially for large parts. EXOne has machines with huge build volumes.
ULTRASONIC ADDDITIVE MANUFACTURING
Fabrisonic, a subsidiary of EWI Inc., of Ohio ( Formerly Edison Welding Institute), has come up with another method of additively manufacturing, which is hybrid. It combines additive, layer manufacturing with tradional machining techniques. The process uses ultrasound to weld metal tapes, layer by layer, and machining internal features using conventional (milling, grinding, etc.) techniques to achieve the net shape. The beauty of this process is that dissimilar metals can be added to each build, such as copper, titanium, and steel. Here is how this process works:
Ultrasonic Additive Manufacturing
So we’ve covered metals, at least up until this year.  I believe, by the time this is published, that even more processes will be released, perhaps hybrids like the Fabrisonic process. Given the ability to manufacture parts that are un-manufacture-able or complex, this field is sure to enjoy the tremendous growth it has undergone so far. A milestone will be surpassed this year as the fundamental patents on powder bed fusion expire – opening up avenues for lower-cost alternatives to enter the market. Wow!
Tune in next week, when we take a look at 3-D Printing. I know I said that 3-D Printing was synonymous to Additive Manufacturing, but we are going to look at Polyjet printing, that most closely resembles our model- inkjet printing. We will see how Objet, now merged with Stratasys, prints with multiple materials – up to 14 different cartridges – to make a single part.
 

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