October 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 | O C T O B E R 2 0 1 9 3 1 PART SIZE In principle, robocast parts can be up to 1 m in diameter and up to 10 cm high. However, it should be noted that a dense part this size would need 100 liters of slurry and would take 115 days to print at 10 mm/s and 1 mm resolution. Economically com- petitive manufacturing is more typical for parts of 1-200 mm in diameter and 40 mm high, with extrudates ranging from 0.3 to 3 mm in diameter. MATERIALS Technically speaking, any ceramic powder with a size of about 5 microns can be 3D printed by these methods. In practice, however, the powder qual- ity is more important than in casting methods, as any agglomerate is like- ly to block the nozzle. The ability to achieve good flow at high volume frac- tions is quite sensitive to particle ge- ometry, with highly irregular particles being unsuitable. MACHINES Robocasting machines are custom built (Fig. 1). Simple versions of the ma- chine for experimental use have step- per motors, but servos are preferred for speed and precision. As noted previous- ly, the machines should be quite rigid, with a flat and carefully aligned sub- strate to allow high resolution. Mixing heads may be incorporated to facilitate discrete deposition of mul- tiple materials or graded mixing. Ver- sions of the machines have also been made with multiple heads to make sev- eral parts at once (Fig. 2). Conformal printing on curved surfaces is tricky but feasible. COMMERCIAL PRODUCTION At the outset, 3D printers were sold to large companies and service bureaus to produce nonfunctional look-and-feel prototypes. As materials improved, functional prototypes and one-off parts such as molds could be made. Now these high-priced machines are pushing the cost crossover point between printed parts and convention- al molded parts up into the hundreds or thousands of identical units. At the same time, the availability of inexpen- sive plastic 3D printers has led to wide- spread use by hobbyists. Robocasting Enterprises LLC was set up mainly to produce alumina filters for molten metals; several million of these have been shipped over the last 10 years (Fig. 3). We believe this is one of the few examples of the use of ceram- ic 3D printing for large production runs. In this case, printing allowed geome- tries that improved performance but could not be made by other methods. In addition, the company has made a range of small-number parts in various ceramics and sinterable metals (Fig. 4). As students of technical ceramics, we were told, “Ceramics are the materi- al of the future, and always will be.” This notion arose from the high processing costs and difficulty of making complex shapes with ceramic materials. Perhaps 3D printing methods will help us break these barriers. ~AM&P For more information: Joe Cesarano, president and founder, Robocasting Enterprises LLC, 5660 Pino Ave. NE, Al- buquerque, NM 87109, 505.883.0555, jcesarano@robocasting.com . References 1. T.D. Ngo and A. Kashani, et al., “Additive Manufacturing (3D Printing): A Review of Materials, Methods, Ap- plications and Challenges,” Composites Part B: Engineering, Vol 143, p 172-196, 2018. 2. Z. Chen and Z. Li, et al., 3D Printing of Ceramics: A Review, Journal of the European Ceramic Society, Vol 39, p 661- 687, 2019. 3. J.A. Lewis, J.E. Smay, J.N. Stuecker, and J. Cesarano III, Direct Ink Writing of Three-Dimensional Ceramic Struc- tures, J. Am. Ceram. Soc., Vol 89(12), p 3599-3609, 2006. 4. M. Jafari, W. Han, F. Mohammadi, A. Safari, S. Danforth, and N. Langrana, A Novel System for Fused Deposition of Advanced Multiple Ceramics, Rapid Prototyping Journal, Vol 6, p 161-175, 2000. 5. J.W. Halloran, Ceramic Stereolith- ography: Additive Manufacturing for Ceramics by Photopolymerization, Annual Review of Materials Research, Vol 46, p 19-40, 2016. 6. J. Cesarano III, and P.D. Calvert, Free- forming Objects with Low Binder Slurry, U.S. Patent #6,027,326, Feb. 22, 2000. Fig. 3 — Several differently shaped 3D-printed alumina filters manufactured via the robocasting technique. Fig. 4 — Robocast parts showing the capability to fabricate simple and intricate parts from oxides, mixed oxides, carbides, andmore.