Additive Manufacturing of Functionally Graded Ceramic Materials by Stereolithography

Additive Manufacturing of Functionally Graded Ceramic Components by using lithograph free-based ceramic manufacturing technologies can help to develop innovative function optimized medical implant structures. The main advantage of this additive manufacturing technique is it's high resolution. The fabrication of ceramic components using stereolithography based methods delivers high precision and high density parts.

For this procedure, use high purity ceramic powders with amine particle size of less than 0.5 micrometers, a narrow particle size distribution, and a specific surface area of about seven square meters per gram. In a grinding bowl, combine the powder and absolute ethanol in an 80 to 20 mass ratio. Add one to two millimeter diameter mill balls in an equal mass to the powder.

Then, add about 0.5 to 2%by weight of dispersing agent, depending on the quantity of powder. Mill the mixture for 2 hours at 250 RPM in a planetary ball mill. Afterwards, remove the mill balls using a siv, with 500 micrometer openings.

Let the suspension dry at room temperature in a fume hood for 12 hours, and then dry it further at 110 degrees Celsius, for 24 hours. Grind the dry material through a siv with mesh openings of 100 to 500 micrometers to obtain the deagglomerated functionalized powder. Next, in the can of a high speed planetary ball mill, mix together a photoinitiator activated at the wave length used in the printing device, organic cross linkers and binders, and a plasticizer.

Add five to 10 mill balls made of the ceramic material with diameters of five to 10 millimeters. Homogenize the mixture for four minutes at 1000 RPM. Then, introduce the powder to the mixture and homogenize it four minutes at 1000 RPM, 45 seconds at 1500 RPM, and 30 seconds at 2000 RPM.

Cool the can with water afterwards. If the mixture appears inhomogeneous, repeat the process. Next, place about 1 milliliter of the ceramic filled resin slurry on the plate of a rheometer, configured for a rotational test.

Increase the shear rate from 0.1 to 1000 reciprocal seconds at a constant temperature of 20 degrees Celsius while measuring the torque. Confirm that the suspension shows shear thinning behavior with a dynamic viscosity below 600 pascal seconds, for a shear rate of 0.1 reciprocal seconds, and below 10 pascal seconds for shear rates of 10 to 300 reciprocal seconds. Lastly, evaluate the curing behavior by taking oscillating measurements before, during, and after curing by exposure to UV light.

Set up a digital light processing stereolithography printing device. Confirm that the curing depth is at least the same as the chosen building layers, and preferably several times thicker. Then, generate a 3D model file of the component with computer aided design software.

Slice the component model into layers of the appropriate thickness, and save the file in a sereolithography contour format. Transfer this file to the printing device by network, or USB. Create a printing program and set the curing time per layer, casting speed, building platform speed, and other parameters.

Then, fill the printing device reservoir about half way with the prepared ceramic resin slurry. Pump the slurry through the system until it starts refilling the reservoir. Attach a metal printing plate to the building platform by vacuum suction, and start the printing program.

Refill the reservoir as needed during the printing process. When finished, turn off the vacuum while holding the printing plate to retrieve the component. Use isopropyl alcohol, or another mild organic solvent, to clean away any remaining slurry, and then let the component dry at room temperature in a ventilated area.

De-bind and sinter the component afterwards, to finish the fabrication. This high purity alumina powder was deagglomerated and functionalized with disperant. Upon drying, the functionalized powder reagglomerated, but was evenly re-dispersed in polymeric resin.

For suspension compositions with different powder contents, di, and tetra-functional cross linker ratios, and overall binder cross linker ratios, were evaluated. All four suspensions had the desired shear thinning behavior, but only composition one exhibited the optimal suspension flow behavior. If the dynamic viscosity is too high, it could hinder casting thin slurry layers, owing to a lack of flow.

A too low dynamic viscosity could result in the slurry flowing freely under the casting blade, or in an unstable suspension. Prior to exposing the ceramic resin suspension to light, the shear storage modulus remained roughly constant. The optimal curing time to achieve the minimum necessary strength without over curing was two to three seconds.

Exposure for longer than four seconds could result in brittleness from over curing. Using optimal aluminus slurry composition and exposure times, this test component, with a dense outer shell, and a porous bone-like central core, was fabricated defect free, with an extremely low porosity and high density in the bulk areas. The technique presented in this article is designed to handle viscose ceramic resin mixtures in order to reach the high precision necessary in the fabrication of functionally graded materials.

The present technique paves the way for results in ceramic manufacturing to develop photo reactive ceramic suspensions. They can be used in Lyrica free-based ceramic additive manufacturing to produce high quality ceramic components.