Digital three-dimensional manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital data model. Polyjet three-dimensional printing, for example, is an additive process in which one or more material applicators expel successive layers of material on a substrate in different shapes. The substrate is supported either on a platform that can be moved three dimensionally by operation of actuators operatively connected to the platform, or the one or more material applicators are operatively connected to one or more actuators for controlled movement of the one or more material applicators to produce the layers that form the object. Three-dimensional printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling.
One process for producing three-dimensional objects with a three-dimensional printing system 10 is illustrated in FIGS. 4A-4D. As shown in FIG. 4A, at the beginning of a printing operation, a member 14 and at least one material applicator 18 are positioned such that the at least one material applicator 18 is spaced vertically above the member 14 by the height H, and the member 14 is to the left of the at least one material applicator 18.
As shown in FIG. 4B, as the member 14 and the at least one material applicator 18 then move relative to one another, the member 14 moves toward the right relative to the at least one material applicator 18. As the member 14 passes underneath the at least one material applicator 18, material 22 is expelled from at least one expulsion element 26, such as a nozzle, ejector, or extruder, of the at least one material applicator 18 toward various locations of the member 14 to form a first layer 30 of an object 34.
Next, as shown in FIG. 4C, when the first layer 30 of the object 34 has been completed, the at least one material applicator 18 and the member 14 are moved relative to one another such that the at least one material applicator 18 is spaced above the first layer 30 by the height H. In other words, the at least one material applicator 18 and the member 14 are moved vertically apart from one another to accommodate a thickness T of the object 34 atop the member 14. Additionally, the member 14 is again positioned to the left of the at least one material applicator 18.
As shown in FIG. 4D, as the member 14 and the at least one material applicator 18 then move relative to one another, the member 14 again moves toward the right relative to the at least one material applicator 18 in the same manner as described above. As the member 14 passes underneath the at least one material applicator 18, the material 22 is expelled from the at last one expulsion element 26 of the at least one material applicator 18 toward various locations of the member 14 to form a second layer 38 of the object 34 atop the first layer 30. Accordingly, the thickness T of the object 34 is increased by the material 22 of the second layer 38. This process can be repeated as many times as necessary to form the object 34.
This three-dimensional object printing process is an additive process, and material 22 is repeatedly added to the object 34 such that the thickness T of the object 34 increases throughout the process. Accordingly, to accommodate the increasing thickness T of the object 34, the height H of the material applicator 18 relative to the member 14 is also increased after each layer is added to the object 34 and before another layer is added. In other words, the material applicator 18 and the member 14 are moved vertically apart from one another after each layer is added to the object 34.
One issue that arises in the production of three-dimensional objects with a three-dimensional object printer in the manner described above is the possibility that independent expulsion elements 36 within a single material applicator 18 or independent material applicators 18 eject varying amounts of material 22. In other words, the three-dimensional object printer may expel variable volumes of material 22 from different expulsion elements 36 or from different material applicators 18. As the object 34 is formed, variable volumes of material 22 produce height variation within each layer, which result in a cumulative height variation within the object 34. Thus, some previously known three-dimensional object printers level the top surface of an object 34 to correct for height variations in each layer of the object to produce a more precisely shaped object.
In these previously known three-dimensional object printers that level the layers in objects being formed by the printer to correct for height variations, the removal of material that has been separated from the object during leveling can be problematic. To prevent contamination of the object, the separated material must be moved away from the object and the elements that come in contact with the object. Accordingly, a three-dimensional object printer capable of removing material which has been separated from the object during leveling would be advantageous because such a three-dimensional object printer would be able to produce an object with less contamination.