Nov_Dec_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | N O V E M B E R / D E C E M B E R 2 0 1 7 7 FEEDBACK are some cradle-to-grave studies on ener- gy consumption of 3D-printed parts and conventionally manufactured parts that have demonstrated this very well. For ex- ample, 3D-printed lattice structures have shown a savings of about 25% in ener- gy as compared to EDM machined struc- tures. Another consideration is that AM enables much greater detail and thinner gages that are not possible with castings. One benefit of AM-built parts is the design freedom for manufacturing and weight savings that can be obtained. This not only saves materials and ener- gy for manufacturing the part, but also saves energy throughout the part’s en- tire life if the part is used in the trans- portation industry. Directmetal printing also allows repair and refurbishment of used components. Refurbishing a used but damaged component not only saves material and money, but also saves the energy that would have been involved in manufacturing a spare part. Another aspect that must be tak- en into account, at least for aerospace applications, is the casting factor—a factor applied to castings that reduc- es strength by a factor of a minimum of 1.25, and typically 1.5 to 2. The strength is divided by the casting factor. Con- sider a casting factor of 1.5, and a cast- ing procured with a tensile strength of 125 ksi. In this scenario, the usable strength of the part is 125 ksi/1.5, or 83.33 ksi. So, the part could be much heavier than it would be for something machined from plate or a forging (this can be negated by design advantag- es for the cast structure). The casting factor takes into account the potential variability of the properties, much of which is due to process variability at dif- ferent foundries. Weld repair of castings is also a concern. Aerospace castings typically have extensive weld repair, which can significantly add to the cost and raise concerns about the possibility of lack of fusion at the bottom of the repair. Mr. Keough also notes the high cost of atomized titanium powder used in the AM process. We should point out that there are a number of emerg- ing techniques for pro- duction of low cost, meltless spherical ti- tanium powder suit- able for AM, such as the hydrogen-assisted process developed by Professor Fang and his group at the University of Utah. In closing, we ab- solutely agree with Mr. Keough that 3D print- ing is not a solution for all problems, but is an- other tool in the tool- box. There are many applications that will save material and en- ergy by using 3D print- ing. We also appreciate Mr. Keough’s insightful comments about 3D printing of molds and pat- terns and its benefits. As engineers cre- ate more demanding and better per- forming designs, the manufacturing industry will advance and 3D printing is expected to help the industry along. A final point. The October issue of AM&P includes an article by A. Pawlows- ki et al. on how AM can be combined with traditional casting to create a hy- brid process to produce a custommate- rial for applications with specific perfor- mance needs. So, the old and the new can work together. F.H. (Sam) Froes, FASM Rod Boyer, FASM Bhaskar Dutta 24-in. diameter Inconel housing for turbine engine built using DM3D Tech- nology’s TransFormAM. We welcome all comments and suggestions. Send letters to frances.richards@asminternational.org.