THREE-DIMENSIONAL PRINTING
In an example three-dimensional printing method, individual layers of a metal-based build material are patterned, based on a 3D object model, with a binding agent to form an intermediate structure. A case-hardened portion of a 3D object is also patterned (based on the object model) by selectively depositing a hardening agent to deliver a predetermined concentration of a hardening element to at least one of the individual layers, wherein the individual layers are maintained below a vaporization temperature of the hardening agent during the selectively depositing. The intermediate structure is heated at a first rate to a temperature that aids in diffusion of the hardening element, and is held at the temperature for a predetermined time. The intermediate structure is cooled at a second rate. The intermediate structure, with the patterned case-hardened portion, is then sintered at a sintering temperature of the metal-based build material.
1 . A method for three-dimensional printing, comprising:
based on a 3D object model, patterning individual layers of a metal-based build material with a binding agent to form an intermediate structure, the binding agent including water and polymer particles;
based on the 3D object model, patterning a case-hardened portion of a 3D object by selectively depositing, using an inkjet printhead, a hardening agent, which is separate from the binding agent, to deliver a predetermined concentration of a hardening element to an outermost layer of the individual layers, wherein the individual layers are maintained below a vaporization temperature of the hardening agent during the selectively depositing;
heating the intermediate structure at a first rate to a temperature that aids in diffusion of the hardening element;
holding the intermediate structure at the temperature for a predetermined time based on a diffusion rate of the hardening agent;
cooling the intermediate structure at a second rate;
wherein the heating, the holding, and the cooling together are a thermal cycle;
repeating the thermal cycle to create a gradient profile of the hardening element throughout a predetermined depth of the intermediate structure; and
sintering the intermediate structure with the patterned case-hardened portion at a sintering temperature of the metal-based build material.
2 . (canceled)
3 . The method as defined in claim 1 , further comprising controlling the inkjet printhead to selectively deposit the hardening agent over a number of printing passes.
4 . The method as defined in claim 1 , further comprising selectively depositing, using a second inkjet printhead, a second hardening agent to deliver a second predetermined concentration of a second hardening element to the outermost layer of the intermediate structure.
5 . The method as defined in claim 1 wherein:
the metal-based build material is a stainless steel, and the hardening element is selected from the group consisting of molybdenum, tungsten, and boron; and
the method further comprises performing the sintering in a reducing atmosphere.
6 - 15 . (canceled)
16 . The method as defined in claim 1 wherein de-binding of the intermediate structure occurs during the heating of the intermediate structure.
17 . The method as defined in claim 1 wherein the cooling of the intermediate structure includes cooling the intermediate structure to room temperature.
18 . The method as defined in claim 3 , further comprising setting the number of printing passes based on the predetermined concentration of the hardening element to be delivered, a concentration of the hardening element in the hardening agent, a diffusion coefficient of the hardening element, and the predetermined time.
19 . The method as defined in claim 1 wherein the metal-based build material is a stainless steel, and wherein the hardening element is selected from the group consisting of carbon, molybdenum, tungsten, copper, and boron.
20 . The method as defined in claim 1 wherein the metal-based build material is titanium, and wherein the hardening element is gold.
21 . The method as defined in claim 1 wherein:
the first rate ranges from about 20° C. per hour to about 200° C. per hour, and
the second rate ranges from about −20° C. per hour to about −200° C. per hour.
22 . The method as defined in claim 1 wherein cooling the intermediate structure involves bringing the intermediate structure to a second temperature that is at least below the vaporization temperature of the hardening agent.