1. Solid Freeform Fabrication of Stainless Steel Using Fab@Home Maxim Lobovsky 1, Alexander Lobovsky 2, Mohammad Behi 2, and Hod Lipson 1 1 Sibley School of Mechanical and Aerospace Engineering, Cornell University 2 United Materials Technologies, LLC Cornell Computational Synthesis Lab - http://www.mae.cornell.edu/ccsl | United Materials Technologies, LLC - http://www.unitedmt.com | Fab@Home – http://fabathome.mae.cornell.edu A slurry of the type used in powdered metal injection molding processes is deposited in a layer-by-layer fashion, and then sintered. We demonstrate this process using a 17-4 PH stainless steel slurry deposited via robotically controlled syringe in the low-cost Fab@Home rapid prototyper. Completed parts had densities as high as 90% volume fraction and tensile strength as high as 35% of the pure solid. Details of the process as well as a number of samples of different geometries are shown below. 2—Printing Pelletized feedstock is melted and degassed and loaded into syringe Syringe is mounted in Fab@Home printer Variety of nozzle diameters down to 0.016 in. print well At 0.016 in. diameter tip, print rate is ~0.4 cu. in./hour Material use rate of nearly 100% is achievable and recycling green parts is easy Print quality is very negatively affected by gas in feedstock as gas compression affects the volumetric control of printing fluid Uneven drying can cause curling. This can be mitigated by using a highly water- absorbent substrate like plaster. An absorbent support material would be even better Fab@Home printing with heated syringe Failed gear print due to air bubbles 1—Feedstock Preparation Feedstock was prepared at United Materials Technologies in a proprietary process and contains –17-4 PH stainless steel powder, average size 12μm, 45-55% by volume of total mixture –Polysaccharide binder –Water –Silicate or borate compounds Mixed in high shear mixer at 80-95°C for 15-30 min Viscosity can be adjusted by varying water content Feedstock is degassed and loaded into syringe with custom heater set to 85°C Custom syringe heater and filled syringe 3—Sintering Samples sintered in 1.5 in. ID tube furnace –6% Hydrogen, 94% Argon atmosphere –Sinter temperature 1350-1370°C –Total cycle ~8 hours Controlled atmosphere tube furnace Results Volume fraction of sintered piece of solid feedstock is 95% while printed parts are ~90% due to gaps created by printing process Tensile tests were conducted on several printed tensile bars approximately 0.5 in. x 0.25 in. x 0.125 in. –Best achieved tensile strength 53 ksi or 35% of solid 17-4 PH Shrinkage in linear dimension from printed to sintered part is 17% 17% Future Work This process is capable of using many different metal or ceramic powders with no changes to the process except for the sintering schedule Potential materials include –Ni and Co Super alloys –Titanium alloys –Tungsten alloys Multi-material prints with co- sinterable materials can allow for material gradients or intricate multi-material parts. Abstract Curling due to uneven drying