Modern Machine Shop and MoldMaking Technology present ADDITIVE MANUFACTURING, a quarterly supplement reporting on the use of additive processes to manufacture functional parts. More at additivemanufacturinginsight.com.
Issue link: https://am.epubxp.com/i/542042
8 — AM Supplement F E A T U R E of this head, heating helium carried through chan- nels surrounding the fre. On previous Stirling engines, this component would have been an assembly. Tubing to conduct the helium would be cut and bent into shape. However, the circular profle of off-the-shelf tubing is demonstrably not the best choice for thermal ef- fciency. Through additive manufacturing, company engineers have been able to grow heater head forms in which the passages carrying helium pres- ent profles to the fame that achieve better heat transfer. Adding fns to the design, both inside and outside the channels, has also helped with this. Every such improvement in thermal effciency is important, because greater effciency ultimately re- sults in a smaller engine to transport into a remote location, and less fuel for people in that location to burn to obtain a given amount of power. In fact, a presumed disadvantage of additive manufacturing is actually a plus here. Within the tubes made additively, the rough surface charac- teristic of additive manufacturing helps to transition the helium from laminar to turbulent fow. This is a positive change, because the turbulent fow also enhances heat transfer. Initially, heater heads were made from Inconel 625. That still might be the material that is ultimately used. But Mar-M 247, which is even better than In- conel at retaining its strength at high temperatures, might permit a more compact or effcient design. If this alloy is to be used, then additive is essential, because building the head through traditional as- sembly would not be possible. Machining the metal is so diffcult, says Lanigan, that off-the-shelf tubing made of this material cannot be obtained. Actually growing the part in this material will not be any more diffcult than growing it in Inconel, he says. The challenge instead will relate to post- processing. As yet, it is unclear whether or how a Mar-M 247 heater head can be treated to make it helium-tight. Helium is a tiny atom—effectively even tinier than hydrogen, because hydrogen exists as a molecule. With Inconel, Deka has found that hot isostatic pressing could be applied to enable the additively grown heater head to contain helium. Can a similar process do the same for the less Another part produced additively is the burner throat. Air and fuel mix at the fange end and fre comes out the spout end. The teardrop forms on the fange end, a feature developed and modifed through various additive builds, help to encourage and regulate the air and fuel mixture. familiar alloy? Deka is seeking the answer to that question. Off the Grid Other questions will follow, says Lanigan. Even after the problems of design and manufacturing are worked out, he says, commercialization will be a challenge. After all, the intended benefciaries of this engine—the most poor—obviously lack fnancial means. To fund the full-scale manufacturing of the en- gine, Deka therefore hopes to fnd additional markets for it in wealthier economies. One possibility is people wishing to live off the grid in the United States. The need to face this very question arguably highlights the difference between the inventor and the engineer, because for inventors, the challenges continue even after the engineering is done. But success in one area ought to contribute to success in the other. For Deka, the hope is that the engine de- sign made possible through additive manufacturing will also make the engine attractive to those consum- ers who have the means to cover its costs. e r