The Metal 3D Printing Laboratory houses the ExOne Innovent+® metal 3D printer to fabricate sintered stainless steel parts or stainless steel parts that are infiltrated with bronze. This binder-jet additive manufacturing technology is well suited for parts with complex geometries and internal cavities that are difficult or impossible to create with traditional machining methods.
The binder-jet fabrication process has several steps, which make it more complex than most 3D printing methods. The parts are formed through the following steps:
- Print the part
- Cure the part
- De-powder the part
- Prepare the crucible (with bronze for infiltrated parts)
- Heat the part in the furnace (sintering or infiltration)
The part is formed by binding layers of powder with an aqueous binder using the print head jet system. The parts are then cured in an oven at 200 C to harden the binder. After curing, all excess powder is removed, leaving “green” parts that are ready to sinter or infiltrate with bronze in a furnace. Parts are heated to 1120 C. To prevent oxidation during heating, the furnace is purged with Nitrogen gas, and Nitrogen flow is maintained throughout the heating cycle. At 600 C, the binder is burned out of the part. If the part is sintered (i.e. no bronze infiltration), the steel powder particles will lightly bond, but there will be voids and porosity in place of the binder. To infiltrate the parts with bronze, the parts must be connected to the bronze powder. This is achieved by including a stilt on the printed part, which is a small bar that connects the part to a printed runner and an upright that is placed directly in the bronze powder. When the bronze is melted in the furnace, it is transferred through the stainless-steel parts through capillary action. Infiltrated parts are approximately 60% steel and 40% bronze infiltrant.
Post-processing may be desired to improve the surface finish of the part and is required to remove an infiltrated part from the runner.
Note: infiltrated parts require a connection to the bronze infiltrant. The part must be removed from the connection runner using a traditional machining method.
Maximum part size: 130 x 65 x 65 mm
Stainless Steel: Alloy 420, 20-50 μm
Bronze: 90% Cu/10% Sn
Material properties of infiltrated parts:
Density: 7.86 g/cm3
Elastic Modulus: 147 GPa
Ultimate Tensile Strength: 682 MPa
Measured in the 3D Metal Printing Lab:
Density: 7.9-8.05 g/cm3
Ultimate Tensile Strength: 577-698 MPa
Minimum void: 0.8 mm*
Minimum wall thickness: 1 mm*
*The feature size limits will depend on the part geometry. If a void is too small with respect to the size of the part, powder may not be able to be removed from the void. For more guidance on part design, see the manufacturing guidelines from ExOne.
Request a print
To request a print, complete the request form and upload a CAD file (.stl format) of the part. For infiltrated parts add a ~3 x 3 x 7 mm stilt to your part to connect to the bronze. No post-processing will be completed by the Metal 3D Printing Lab (e.g. cutting the stilt from the runner or surface polishing). The cost per print is a flat rate of $204.64, which is all-inclusive of material and personnel time. Multiple parts can be made in one print, so long as the parts are contained in the crucible in a 130 x 65 mm area. The metal 3D printer is staffed and operated by graduate students in Prof. Matlack’s lab. Note one print job takes a total of 4 days to print, cure, and sinter.