Appliance Design - May 2008 - (Page 15)

NEW & NOTABLE Another distinction is that this volumetric printing method produces a “green” part that must be fired after it’s built to sinter the materials. But the most notable difference between the EoPlex process and RP is that EoPlex produces functional production parts, not models. After firing, the parts produced by EoPlex will perform in the intended application. While the EoPlex concept sounds simple in theory, it was extremely challenging to perfect, and required the development of numerous proprietary processes, materials, and equipment designs. Pivotal to the concept was the formulation of what has become known as the “secret sauce,” which serves as the basis for the “inks” that are used in the process. The secret sauce is a thick liquid similar in consistency to toothpaste, and it serves as the carrier medium for the different materials used to build the parts. For example, when making a ceramic part with this process, a specific ceramic material would be rendered into powder form and then mixed in with the paste to a certain percentage to create the ceramic “ink” that will be used to build the layers of the part. The characteristic that makes this paste so special and so secret is that it disappears completely during the firing process, leaving behind only the intended part material. In the previous example, the heat would cause the paste to slowly disappear and the ceramic particles it carried would be sintered together, yielding a sintered ceramic part. That, too, sounds simpler that it really is because the carrier paste must disappear at a controlled rate – it must hang around just long enough to hold the part together, but no longer. “There’s a whole lot of chemistry involved in making that,” says Arthur L.Chait, president and CEO of EoPlex. “We use about 15 different ingredients in there to make it work.” The secret sauce is also the secret to one of the most novel aspects of the process, one that gives a design engineer a previously impossible level of flexibility in designing part geometry. The paste can also be formulated in an empty or negative version, that is, not containing any build materials. EoPlex refers to this version of the paste as a “fugitive ink,” because it disappears during firing. When used in this fashion, the paste is used to fill interior voids and spaces within the part geometry, providing support for layers being applied above. One could, for example, design a honeycomb, or a three-dimensional mesh. After printing, still in its green stage, the part would like a solid block. During firing, the fugitive ink www.applianceDESIGN.com Component at left shows how a conventionally fabricated part would require secondary operations to include any additional functional features. The component at right contains additional structural features and electrical elements, all of which are formed simultaneously with the fabrication of the larger part. would disappear from the interstices, leaving behind the honeycomb or mesh structure. What makes the fugitive ink even more fascinating is that it does not require any type of drain hole or vent hole to escape. The fugitive material vaporizes and passes through the pores in the walls of the build material. One could, for example, design a small ceramic maraca containing metals balls. After printing the green part, the interior space of the maraca would be filled with the fugitive ink, which in turn would contain the green version of the metal balls, embedded like dinosaur bones in clay. During firing, the fugitive ink would slowly escape through the walls of the maraca, leaving no ash or residue behind. The ceramic maraca would then sinter, as would the metal balls inside. That is clearly one of the trickiest aspects of the whole process. “The fugitive paste has to gently diffuse through the walls while they’re still porous and without disrupting anything,” Chait notes. “The walls will sinter to high density, so the fugitive paste has to go first. But it has to go at a very controlled rate. If it escapes too fast, the part will blow up or collapse. If it moves too slowly, it won’t get out in time.” Another unique feature of the secret sauce is its ability to carry a blend of materials. When mak- ing a part out of multiple materials, the key issue is compatibility. To date, the maximum number of different materials EoPlex has used to make a single part has been seven. Chait isn’t yet sure of the ultimate maximum number of materials that can be combined into a single part, but he does know that the issue has less to do with the EoPlex process and more to do with the compatibility of materials. “A lot of materials are not meant to go together,” Chait says. “They might have different coefficients of thermal expansion, for example, or different sintering characteristics. One limit is a big difference in sintering temperatures, like say tin and tungsten. Tin would melt and flow away just when tungsten is getting warmed up.” One way to mitigate the compatibility issue is to create transition zones between two different materials. So instead of having a sharp, abrupt change from one material to another, the carrier paste permits a gradual transition from one material to another simply by altering the proportions. In other words, instead of switching abruptly from 100 percent material A to 100 percent material B, the transition zone can be designed to go from 90/10 to 70/20 to 50/50, and so on. Here again is where the printing analogy works. Take out a magnifying glass and look at a black-and-white photograph in a newspaper and you see that it is merely a composition of black applianceDESIGN May 2008 15 http://www.appliancedesign.com

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Appliance Design - May 2008 Contents Editorial Shipments/Forecasts News Watch New and Notable Displays & Indicators Elastomers Quality & Standards Indoor Air Quality IHHS Highlights New Products Classifieds Design Marts Advertiser’s Index Association Report: PSMA

Appliance Design - May 2008

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