System and method of making printed articles

Abstract

To provide a system for forming a product with different size particles.SOLUTION: The system comprises at least one print head region configured to retain a first group of print heads configured to additively print a first portion of the product with a first material and a second group of print heads configured to additively print a second portion of the product with a second material. The described system also comprises at least one processor configured to regulate the first group of print heads and the second group of print heads to distribute the first material and the second material. A method of making an object by ink jet printing using the disclosed system is also disclosed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority to U.S. Provisional Patent Application No. 62 / 487,670, filed April 20, 2017, which is incorporated herein by reference.

[0002] The present disclosure generally relates to a system for forming a product having particles of different sizes. In one embodiment, the system includes a print head region holding one or more print heads configured to additively print different sections or portions of the product, and a processor configured to adjust the print heads. The present disclosure also relates to a method of manufacturing a product, such as by using the disclosed system. [Background technology]

[0003] The three-dimensional (3D) inkjet printing process is considered an additive manufacturing process, along with direct metal laser sintering (DMLS) and selective laser sintering (SLS), respectively. Inkjet printing processes are used to print plastic, metal, or ceramic objects. Unlike DMLS and SLS, metal or ceramic bodies printed with inkjet processes are considered "green" bodies, requiring a final sintering step. Because the mechanical properties of the green part are inferior to those of a fully sintered part, 3D inkjet printing of metal or ceramic typically requires the use of at least two materials: a model material and a support material. The model material and support material are inkjet-readable inks. The model material is used to form the desired object, while the support material is used to form the desired support structure for at least part of the object. Such support structures are configured to support the object during printing or until the model reaches adequate mechanical strength to be self-supporting. The use of support materials is particularly desirable if the model contains channels or other voids or needs to be printed at a negative angle. Once the model reaches a freestanding stage, the support structure is removed.

[0004] One of the fundamental challenges in 3D printing is the development of support materials that allow for the printing of support structures that provide the necessary support for the printed model before it reaches a freestanding stage and can then be removed, while minimizing cross-contamination of support materials within the model. Therefore, the support material must be compatible with various properties of the model material. For example, according to one aspect of the present disclosure, it is important that the sintering temperature of the support structure be higher than the sintering temperature of the model material, as described in more detail below.

[0005] The support material must be removed in a post-printing process, either immediately after printing or after sintering. Support removal can be chemical, mechanical, or thermal. Regardless of the method used to remove the support, some post-printing processing steps are required to convert the printed model into a solid metal or ceramic piece. One problem associated with removing the support after the printing stage and before the model reaches the freestanding stage is that the removal process can affect the integrity of the printed part. The printed part can easily be damaged at this stage.

[0006] The combinations of model and support materials for inkjet printing and methods of combining such materials disclosed in the present disclosure address shortcomings of the prior art. The present disclosure also provides novel and inventive methods of making such inks to overcome one or more of the problems described above and / or other problems of the prior art. In particular, the present disclosure relates to adjusting parameters between the model and support inks to aid in the production of products by inkjet printing, improve the results of the final printed model, or both. Summary of the Invention [Means for solving the problem]

[0007] In part to address the aforementioned needs, the present disclosure relates to a system for forming a product. In one embodiment, the system includes at least one print head region configured to hold a first print head group configurable to apply and print at least a first portion of the product with a first material having a first average particle size. The first average particle size is selected to impart a first sintering characteristic. The system described herein also includes a second print head group configurable to apply and print a second portion of the product with a second material having a second average particle size. The second average particle size is selected to impart a second sintering characteristic.

[0008] The systems described herein also include at least one processor configurable to receive information reflecting desired properties of a product and adjust the first printhead group and the second printhead group to dispense the first material and the second material in a layer-by-layer manner to impart different properties to different portions of the product based on the information reflecting the desired properties of the product.

[0009] The present disclosure also relates to a method for manufacturing an object by inkjet printing, such as by using the disclosed system. In one embodiment, the method includes jetting an object material to form a product structure having a first sintering temperature. Simultaneously with or prior to forming the product structure, the method further includes jetting a support material including particles to form a support structure, wherein the support structure is jetted to support the product structure. In one embodiment, the support material has a sintering temperature higher than the sintering temperature of the object material. The jetted object and the jetted support together constitute a green part. The method further includes heating the green part to a temperature equal to or greater than the first sintering temperature and less than a second sintering temperature to at least partially sinter the jetted object without substantially sintering the jetted support, and removing the substantially unsintered support from the at least partially sintered object.

[0010] Apart from the subject matter mentioned above, the present disclosure includes many other features as described below. Both the foregoing and following descriptions are exemplary only.

[0011] The accompanying drawings are incorporated into and constitute a part of this specification. [Brief explanation of the drawings]

[0012] [Figure 1] 1 illustrates an example of an additive manufacturing apparatus according to the present disclosure.

[0013] [Figure 2A-F] An example of an additive manufacturing process according to an embodiment of the present disclosure is shown, including spraying a layer of powder (FIG. 2A), ink-jetting of nanopowder in a desired model area (FIG. 2B), and consolidation of the model area (FIG. 2D). Subsequently, the steps of applying an additional layer of sprayed coarse powder are repeated (FIG. 2E), followed by ink-jetting of nanopowder (FIG. 2F).

[0014] [Figure 3] 1 illustrates a printer head assembly according to an embodiment of the present disclosure that includes multiple printheads that allow for printing colored inorganic materials by inkjet printing.

[0015] [Figure 4A-C] FIG. 4A shows an ink dispersion according to one embodiment of the present disclosure that includes colorant particles such as pigments or pigments mixed with structural particles such as zirconia (FIG. 4B), or pigments embedded in zirconia particles (FIG. 4C). FIG. 4C shows the structural particles removed.

[0016] [Figure 5] 1 shows a colored cube with a white layer underneath the colored layer made in accordance with an embodiment of the present disclosure.

[0017] [Figure 6A] 1 is a graph showing sintering temperature versus grain size of materials. [Figure 6B]1 is a graph showing relative density versus sintering temperature for four sintering stages associated with powder materials.

[0018] [Figure 7] FIG. 1 is a ternary phase diagram of components used to make SiO2-based inks according to the present disclosure.

[0019] [Figure 8] 1 shows a schematic diagram of an in situ laser system with a model and support material.

[0020] [Figure 9A-B] 9A and 9B are schematic diagrams showing particle material before (FIG. 9A) and after (FIG. 9B) dispersant evaporation. FIG. 9A is a schematic diagram showing particles wrapped with dispersant molecules at low temperature. FIG. 9B is a schematic diagram showing particles remaining after losing dispersant molecules at high temperature, but below sintering.

[0021] [Figure 10A-D] 10A and 10B are schematic diagrams showing the packing density of powders with various shapes and sizes, specifically, a mono-size dispersion (FIG. 10A), a multi-size dispersion (FIG. 10B), a mono-size and multi-size dispersion (FIG. 10C), and the mono-size and multi-size dispersion of FIG. 5C after heat treatment (FIG. 10D).

[0022] [Figures 11A-F] 1 is a schematic diagram illustrating separation and deformation of a model part associated with high stresses and strains due to differential shrinkage between support and model materials during sintering.

[0023] [Figure 12A-B] 12A and 12B show objects printed with different materials according to the present disclosure: Figure 12A shows a coating on a bulk material, and Figure 12B shows a coating on an impregnation layer on the bulk material.

[0024] [Figure 13A-B] 1 illustrates an object constructed from a mixture of materials according to the present disclosure.

[0025] [Figure 14] FIG. 1 is a flow diagram for fabricating a composite object according to the present disclosure by infiltrating a model material with a support material. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present disclosure generally relates to adjusting parameters between model inks and support inks to aid in the manufacture of products by inkjet printing. Several integrated techniques and systems are disclosed for beneficially adjusting parameters between model inks and support inks. These include: i) Adjust the sintering temperature so that the model sinters before the support, to facilitate removal of the support after sintering. As explained in more detail below, this can be done through material selection, particle size, particle distribution, or a combination thereof. ii) Controlling shrinkage between the model and the support structure to avoid distortion or cracking of the model over the temperature range from printing through the green stage, brown stage and final sintering. iii) Reducing cross-contamination between the model and the support structure by selecting materials or using additives that help achieve this result. iv) Controlling the particle size of both the model ink and the support ink to quickly and efficiently cover both the model and support areas, thereby improving printing speed.

[0027] The following is a general description of various embodiments described herein, relating in particular to the disclosed printers, printing systems, inks and ink systems, methods of using such systems and / or inks to produce products, and products produced therefrom. Reference will now be made in detail to these foregoing embodiments, implemented in accordance with the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

[0028] [printer] In one embodiment, an additive manufacturing apparatus is disclosed. As used herein, the term “additive manufacturing apparatus” broadly includes any device or system capable of generating an object from a digital model by depositing successive layers of material until the object is created. FIG. 1 illustrates an example of an additive manufacturing apparatus 100 in which various implementations as described herein may be practiced. As shown in FIG. 1 , the additive manufacturing apparatus 100 may include a print region 102, a print head holder 104 supporting at least one print head 106, at least one conduit 108 interconnecting the print head 106 with an ink reservoir 110, an energy source 112, a cooling fan 114, a shield 116, a leveling device 118, and a controller 120.

[0029] The print zone 102 may be used as a base to support an object being built in an additive manufacturing process. The term "print zone" includes an area with a rigid surface capable of holding multiple layers of material dispensed from the additive manufacturing apparatus 100. The terms "print tray" and "print table" may also be used interchangeably in this disclosure with respect to the print zone. In one embodiment, the print zone 102 may include, for example, a thermally conductive material, or the print zone 102 may include a metal tray. In this embodiment, the print zone 102 may be heated to the required object temperature to aid in solidification of the recently printed layer or to promote evaporation of at least a portion of the ink liquid components. In another embodiment, the print zone 102 may include an insulating material. For example, the print zone 102 may include wood, plastic, or an insulating ceramic. In both embodiments, the print zone 102 maintains the object temperature, and heating of the recently printed layer is achieved by direct thermal radiation from above using an energy source 112, such as a halogen lamp, IR lamp, UV lamp, laser, flash lamp, or microwave source.

[0030] In one embodiment, the print zone 102 may be a print tray that can be attached to a tray holder (or "chuck"). The tray holder can include a heating mechanism to heat the tray as needed. The tray holder can include a rigid, flat, heat-conducting surface (optionally heated by heating means under a cover) to which the tray can be attached by any means, including vacuum or a clipping jig. Alternatively, the holder can include a holding frame that surrounds exposed heating means (e.g., radiant lamps that directly heat the tray). In one embodiment, the print tray is replaceable. For example, once printing is finished, an operator can remove the loaded tray from the printer, attach a clean tray to the printer, and begin a new print session.

[0031] In one embodiment, the tray must be rigid. This is necessary to prevent bending when removing the tray from the tray holder. In one embodiment, the tray holder may be flat. This is desirable to allow for good attachment between the tray holder surface and the tray, and to ensure good alignment between the print and the straight leveling device. The tray should be thermally conductive and not too heavy. According to one embodiment, the tray is made of aluminum and has a thickness in the range of approximately 3 to 12 mm.

[0032] The term "printing area" should not be confused with the term "printing surface." The term "printing surface" refers to the surface on which a new layer is printed. At the beginning of the printing process, the printing area 102 may be the printing surface because the first layer is printed directly on it. However, all subsequent layers (such as the second layer) are printed on top of the previously deposited layer. Thus, for the second layer, the first layer is the printing surface, for the third layer, the second layer is the printing surface, and so on. In the example shown in FIG. 1, the printing surface 122 is the previously deposited layer. The new layer 124 is the layer currently being printed on top of the printing surface 122. The new layer 124 is built along the Z direction during every printing pass and is also called the "top layer" or "latest layer."

[0033] According to aspects of the disclosure described herein, the model is printed on a support, which exhibits desirable properties including rigid stability, adequate interfacing with the supporting part material (model), and ease of separation from the tray. According to another aspect, the support structure must also be removable from the tray. Note that according to one embodiment, a support structure is built between the part and the tray. To allow for easy removal of the printed part from the tray, only a few support layers (e.g., 1 to 10) may be different from subsequently deposited layers. In one embodiment, these few layers comprise only the support material.

[0034] In other embodiments, a few layers contain a particular mixture or combination of support material and model material. In one embodiment, the model material may be added to the pillar structure. The mixture of some bottom layers may be different from the mixture of the layer above, and both may be different from the mixture of the support structure near the part. A more detailed description of this structure is provided in U.S. Patent Application No. 15 / 029,815, which is incorporated herein by reference.

[0035] To aid in the integrity of the final print, the print can be cooled evenly and consistently. In one embodiment, this can be done by holding the print tray with the freshly printed object in a cooled environment, such as an insulated cooling box, until the printed object reaches the desired temperature.

[0036] Consistent with embodiments of the present disclosure, reference is again made to FIG. 1 . As shown in FIG. 1 , the additive manufacturing apparatus 100 may include a print head holder 104 for maintaining at least one print head 106 spaced apart from a printing surface 122. The term “print head holder” includes any structure suitable for holding at least one print head 106 at a fixed distance from the printing surface 122 or at a varying distance from the printing zone 102. Because the additive manufacturing process involves depositing successive layers of material, the height of the object gradually grows. In one embodiment, after each layer is deposited, the printing zone 102 shifts slightly lower in the Z direction to maintain the fixed distance between the at least one print head 106 and the printing surface 122. In another alternative embodiment, after each layer is deposited, the print head holder 104 shifts slightly higher in the Z direction to maintain the fixed distance between the at least one print head 106 and the printing surface 122. In one example, the fixed distance between the print head 106 and the printing surface 122 can be any value between 0.5 mm and 5 mm. In another alternative embodiment, after each layer is laid, the print zone 102 moves slightly lower in the Z direction and the print head holder 104 moves slightly higher in the Z direction to maintain a fixed distance between the at least one print head 106 and the printing surface 122. For simplicity, the following description assumes that the print head 106 is moving while the print tray is stationary. However, in alternative embodiments, the print tray may be configured to move underneath the print head 106.

[0037] According to some embodiments, the print head holder 104 may support a single print head 106 or multiple print heads 106. The term "print head" refers to multiple nozzles organized in a linear array or plate and generally manufactured together. When the print head 106 is connected to the additive manufacturing device 100, the multiple nozzles are configured to dispense ink from an ink reservoir 110 to form an object layer-by-layer. At least one print head 106 may include multiple nozzles, including a first group of nozzles for dispensing a first model material and a second group of nozzles for dispensing a second model material different from the first model material. In one embodiment, the print head is characterized by its ability to contain and manage multiple sets of nozzles. However, each print head is supplied with one type of ink, regardless of the model or support. As used herein, the term "object" is used to describe the combination of a model and a support structure. In one embodiment, the model can be printed using a first material and the support can be printed using a second material. A typical case for this embodiment is when the desired object is made of two different materials. In another embodiment, the first material is the object material used to generate the desired object, and the second material is a support material used temporarily during printing, e.g., to support the object's "negative" sloped walls. Typically, the print head 106 can scan the new layer 124 in an X direction substantially perpendicular to the longitudinal axis Y of the new layer 124. Because each object consists of thousands of printed layers, thousands of cycles are typically required. If each cycle involves multiple prints from multiple print heads 106, the number of cycles can be reduced from thousands to hundreds or even less. Additionally, the additive manufacturing system 100 may generate multiple objects in the same run. In one embodiment, different print heads 106 can be used for different printing materials with different nozzle sizes. For example, a first print head can be used to dispense the object material, and a second print head can be used to dispense the support material.As another example, a first printhead may have nozzles of a first size and a second printhead may have nozzles of a second size that is different from the first size.

[0038] In some embodiments, the additive manufacturing apparatus 100 can include at least one conduit 108 interconnecting the print head 106 with the ink reservoir 110. The term “conduit” generally refers to a body having a passage for the transport of a liquid or gas. The at least one conduit 108 can be flexible to allow relative movement between the print head 106 and the ink reservoir 110. In some embodiments, the at least one conduit 108 can include a supply conduit interconnecting the ink reservoir 110 to the print head 106 to supply ink to the print head 106, and a return conduit (not shown) interconnecting the print head 106 with the ink reservoir 110 to circulate at least a portion of the ink not ejected from the print head 106 back to the ink reservoir 110. The term “ink reservoir” includes any structure configured to store ink before being delivered to the print head 106. In some embodiments, the ink reservoir 110 may include one or more tanks and an ultrasound-based element configured to deliver ultrasound or shock waves to the ink to prevent agglomeration of solid particles in the ink or to break up agglomerates if agglomerates are already present in the ink. Additionally, the additive manufacturing apparatus 100 may include a plurality of valves (not shown) operated by the controller 120 and disposed along the at least one conduit 108 to control the pressure within the at least one print head 106, the at least one conduit 108, and / or the ink reservoir 110. A more detailed description of a similar ink system is described in U.S. Patent Application Serial No. 15 / 921,279, which is incorporated herein by reference.

[0039] While it is typical to use a single printhead dispensing a single ink, and multiple printheads for a particular ink, it is also possible to use multi-nozzle array inkjet heads dispensing different inks, where each ink is present in a separate nozzle array.

[0040] [Third printhead used in inkjet printing additives] In various embodiments, one or more additive materials may be added to the ink to improve the properties of the final object, such as the color or mechanical properties of the print, to aid in the processing of the final product, such as the printing or sintering step, or to be printed from a separate head. In one embodiment, there is at least one separate head dedicated to dispensing additives alone or dissolved in a suitable solvent. As used herein, this head is used to deposit materials other than the model or support printed using the two separate print heads and is referred to as the "third print head" or "additive head." More details about the types of additives are provided below. Because the additives are printed from a separate head, there is no issue of the additive dissolving in the target ink, which may be incompatible with the additive. Furthermore, the additive head allows different amounts of additive to be dispensed to different zones of the object.

[0041] Printer heat source According to some embodiments, as shown in FIG. 1 , the disclosed additive manufacturing apparatus 100 can include an energy source, such as energy source 112. The term “energy source” includes any device configured to supply energy to an object printed by the additive manufacturing apparatus 100. For example, energy can be supplied in the form of radiation or heat to the new layer 124 to vaporize the dispersant material and other organic additives and, optionally, initiate at least partial sintering between object particles. In one example, the energy source 112 includes a small-spot-size energy source, such as a lamp or laser, configured to illuminate or scan a line along the new layer 124 to cause in-situ debinding or sintering, or at least partial sintering, of the newly formed layer 124. In another example, the energy source 112 can include a flash lamp configured to cover an area of the newly formed layer 124 to initiate partial or complete in-situ debinding or sintering. According to this aspect of the present disclosure, the energy source 112 can be configured to selectively sinter only the model ink to avoid sintering the support ink. Such selectivity can be achieved by irradiating the new layer 124 with a wavelength that is more absorbed by the model ink than by the support ink, and / or by adding pigments to the model ink that increase energy absorption at the irradiation wavelength.

[0042] In a first embodiment, the energy source 112 can be integrated into the print zone 102 to form a warming tray. When a print is heated from below, heat constantly flows to the new layer 124, creating a temperature gradient (along the Z axis) where the bottom of the object is hotter and the top of the object is cooler due to the material's resistance to heat flow. The temperature of the warming tray is controlled according to the virtual height of the object being printed to maintain a constant temperature in the upper layer. A drawback of this procedure is that heating the lower layer to high temperatures can adversely affect organic molecules, such as those found in dispersants and other additives, potentially causing the organics to decompose into carbon and other residues. Another drawback is that residual liquid remaining in the lower layer can evaporate, creating high gas pressures that can cause the material to crumble or crack. Creating temperature differences between layers after drying is generally not recommended, as this can lead to cracking due to differential thermal expansion of the layers.

[0043] In a second embodiment shown in FIG. 1 , a radiant energy source 112 may be positioned above the object to be printed. Direct heating by the energy source 112 can ensure a constant temperature of the new layer 124. The energy source 112 can be positioned to the side of the print head 106 and can generate thermal radiation, e.g., electromagnetic radiation. The porous body below the temporary final layer absorbs some of the liquid carrier, making layer-by-layer drying of the final layer difficult. Therefore, the intensity of the heat source must increase as a function of the intermediate height Z of the final layer. Alternatively, the heat source must be moved slowly along the X or Y direction as a function of the object height.

[0044] In a third embodiment, the energy source 112 can include an aperture configured to blow a stream of hot air at an angle onto the new layer 124. The use of hot air not only raises the temperature of the new layer 124, but also reduces the partial pressure of the evaporated carrier liquid above the last layer, aiding in the evaporation of the liquid carrier (and possibly dispersant and other organic materials) from the new layer 124. Additionally, any combination of the first, second, and third embodiments can be used to maximize heating and / or evaporation performance.

[0045] cooling device As mentioned above, warming the new layer 124 can be part of the additive manufacturing process. However, in some embodiments, the remainder of the printed object should not be maintained at the same temperature as the new layer 124. Therefore, the additive manufacturing apparatus 100 can include a cooling fan 114 to dissipate heat stored in the recently printed layer into the surrounding air. One reason for cooling the recently printed layer is that if an ink droplet reaches a surface that is higher than the boiling point of the carrier liquid (e.g., 30°C), it may explode rather than adhere to the surface (e.g., when a water droplet reaches a surface that is 120°C). Therefore, the remainder of the object does not need to be maintained at the same temperature as the new layer 124, but only at a constant, uniform temperature. For example, if the previously printed layer is maintained at a relatively low temperature using the cooling fan 114 (e.g., about 230°C), the new layer 124 may be warmed to a temperature above the boiling temperature of the carrier liquid (e.g., the new layer 124 is warmed to about 500°C).

[0046] heat shield In some embodiments, the additive manufacturing apparatus 100 can also include a thermal buffer, such as a shield 116. In the context of this disclosure, a thermal shield refers to a plate that partially covers the nozzle array and has openings that facilitate printing from the nozzles to the print zone. Because the printed object is relatively hot (e.g., about 230°C) compared to room temperature (e.g., about 25°C), the print head 106 should be protected from the heat and fumes emanating from the print zone. In one embodiment, the shield 116 is maintained at a relatively low temperature (e.g., 10-50°C) compared to the temperature of the object being printed, providing a thermal barrier between the print head 106 and the printed object.

[0047] Leveling device Due to variations in process conditions, including different jetting powers of different nozzles, the new layer 124 may not be perfectly flat. As a result of the surface tension of the liquid, the edges of the layer may not be perfectly sharp. Therefore, the additive manufacturing apparatus 100 may also include a leveling device 118 to flatten the new layer 124 and / or sharpen one or more edges of the new layer 124. In one embodiment, the leveling device 118 may include a vertical or horizontal grinding roller or cutting roller. In another embodiment, the leveling device 118 may include a dust pump and dust filter 126 that suctions dust output from the leveling process. During the printing process, the leveling device 118 may operate on the new layer 124 while the layer is being dispensed and solidified. In one example, the leveling device 118 may peel off approximately 5% to 20% of the material of the top layer height. In some embodiments, the leveling device 118 contacts the ink after the carrier liquid has evaporated and the new layer 124 has at least partially dried to a solid state.

[0048] Control and Processing Unit The described additive manufacturing apparatus 100 can generate any object from a digital model. To do so, the additive manufacturing apparatus 100 can include a processing device, such as a controller 120, for controlling the operation of different printing components. According to some embodiments, the controller 120 can include at least one processor configured to determine how the additive manufacturing apparatus 100 should operate. The at least one processor can constitute any physical device having electrical circuitry that performs logical operations on inputs. For example, the at least one processor may include one or more integrated circuits, microchips, microcontrollers, microprocessors, all or part of a central processing unit (CPU), graphics processing unit (GPU), digital signal processor (DSP), field programmable gate array (FPGA), or other circuitry suitable for executing instructions or performing logical operations. The instructions executed by the at least one processor can be pre-loaded into a memory integrated with or embedded in the controller 120, for example, or stored in a separate memory. Memory may include random access memory (RAM), read-only memory (ROM), a hard disk, an optical disk, a magnetic medium, flash memory, other permanent, fixed, or volatile memory, or other mechanism capable of storing instructions.

[0049] In some embodiments, the memory is configured to store information representing a product associated with the visual code. In some embodiments, the controller 120 can include multiple processors. Each processor may have a similar structure or different structures that are electrically connected or disconnected from one another. For example, the multiple processors may be separate circuits or integrated into a single circuit. When multiple processors are used, the processors can be configured to operate independently or in concert. The multiple processors may be coupled electrically, magnetically, optically, acoustically, mechanically, or by other means that enable interaction.

[0050] Printed Sensor The described additive manufacturing apparatus 100 can include one or more sensors to verify that the printing process is proceeding as planned. For example, the additive manufacturing apparatus 100 can also include an imager, such as image sensor 128. The terms "imager" or "image sensor" refer to a device that can detect and convert optical signals in the near-infrared, infrared, visible, and ultraviolet spectrums into electrical signals. The electrical signals can be used to form an image or video stream (i.e., image data) based on the detected signals. The term "image data" includes any form of data obtained from optical signals in the near-infrared, infrared, visible, and ultraviolet spectrums. Examples of image sensors include semiconductor charge-coupled devices (CCDs), complementary metal-oxide semiconductors (CMOS), or N-type metal-oxide semiconductor (NMOS, live MOS) active pixel sensors. In some cases, the image sensor 128 can be part of a camera configured to capture the print area 102.

[0051] The following describes compositions and methods the inventors have discovered to improve the final printed model, including compositions and methods for adjusting sintering temperature, shrinkage between the model and support structure, and cross-contamination between the model and support structure.

[0052] [Ink composition] The additive manufacturing apparatus shown in FIG. 1 (100) can be configured to print multiple types of inks. The term "ink" includes any fluid intended to be deposited in a desired pattern on the printing surface 122. Thus, the term "ink" includes materials for printing models, supports, or additives from a third printhead, if present. These different inks may also be referred to as "model materials," "support materials," "additive manufacturing materials," "printing materials," and "printing fluids." These terms are used interchangeably herein.

[0053] Printing multiple model inks on a given part is a unique and very important attribute of jet printing vs. selective laser sintering printing. This combination can be done as a fine mix on a pixel scale (where you actually get a uniform mix of materials) or on a macroscopic scale by creating different areas of the part containing different materials. In composite printing, the printer has multiple IDSs (ink supply systems) and multiple heads, at least one head for each material being jetted. This approach is described in [PCT_Friedman_3D Particle Printing_4619 / 20_Chapter 17], which is incorporated by reference. Consistent with this disclosure, some examples of suitable inks may include the following attributes:

[0054] Particle size, material and shape The inks described herein may comprise dispersions of solid particles of any desired material, including, but not limited to, metals (e.g., iron, stainless steel, copper, silver, gold, titanium, etc.), ceramic materials, metal oxides, oxides (e.g., SiO, TiO, ZrO, BiO), metal carbonates, metal carbides, carbides (e.g., WC, AlC, TiC), metal alloys (e.g., stainless steel, titanium, Ti64), nitrides, inorganic salts, polymer particles, and combinations thereof in a carrier liquid. In one embodiment, the solid particles comprise metals and metalloids selected from silicon, aluminum, titanium, yttrium, cobalt, copper, iron, zinc, magnesium, zirconia, and combinations or alloys thereof.

[0055] In various embodiments, the particles are desirably micron-sized (about 0.5 μm to about 50 μm) or nano-sized (about 5 to about 500 nm) to maintain the required spatial resolution during printing, maintain the required material properties (after sintering), or meet the limitations of the dispensing head; for example, if the dispensing printhead includes a 30 μm diameter nozzle, the particle size is desirably 2 μm or less. In the context of this disclosure, the terms "model material" or "model ink" generally refer to solid materials or particles used to build a model, while "support material" or "support ink" generally refer to materials or solid particles used to build support structures that are usually temporarily attached to the model.

[0056] Particle size is important for high print resolution. Generally, particle size should not exceed about 1 / 4 of the pixel size of the printed image map, but some clumping (of about 10 particles) is expected, so particle size should not exceed 1 / 10 pixel size. For example, if the pixel size is 15 microns, the particles should be smaller than 1.5 microns. This ratio should be consistent with the other pixel and particle sizes.

[0057] In one embodiment, the solid particles in the model typically have a continuous, multimodal particle size distribution. However, in special cases, the distribution may be discrete, such as a bimodal distribution. In one embodiment, the solid particles in the support material have a unimodal particle size distribution. Such a distribution has the limited advantages over a multimodal distribution, such as improved flow through piping and heads (reduced head clogging) and reduced tendency to sinter at high temperatures. The particle sizes described herein are average particle diameters determined using standard measurement techniques. For example, in one embodiment, the average particle size is determined by examination of the dried model powder using a scanning electron microscope (SEM). The average particle diameter may be the average of the diameters of randomly selected particles, where the particle diameter is the Feret diameter measured in a fixed direction.

[0058] Adjusting particle size to increase printing speed In one embodiment, we attempted to use large, inexpensive particles (1-5 μm) to achieve inkjet printing featuring high-speed printing that covers both the model and support regions, followed by printing of small nanoparticles in a binder only in the model regions. As shown in Figure 2, we found that using a combination of large, micron-sized powder (Figure 2A) jetted with smaller, nano-sized ink (Figure 2B) allowed for faster, more cost-effective printing. In this embodiment, the use of large, inexpensive 1-5 μm particles allowed for high-speed printing of both the model and support regions, followed by printing of small nanoparticles in a binder only in the model regions.

[0059] Referring to Figure 2A, a process is described in which the first step involves spraying / dusting a dispersion of 1-5 μm-sized powder, for example, via an inkjet printhead with a larger nozzle, air, fluid, or electrospray, or by wire rod coating, or by another method. As shown in Figure 2B, at this stage, a tray is coated with the powder dispersion, and then the dispersion is evaporated. After the dispersion has evaporated, the nano-sized powder is inkjet printed onto the model, as shown in Figure 2C. This is followed by a curing step, shown in Figure 2D, by thermal curing using a binder or a partial sintering process, which can be in situ. The deposition step is repeated as many times as necessary to obtain the desired thickness and profile, as shown in Figures 2E and 2F.

[0060] According to one embodiment, the dispersion of powders with sizes between 1 and 5 μm, the large particle dispersion, may contain the same material as the small nanoparticle ink. As a few non-limiting examples, the large and small particles can be stainless steel, such as 316, silica, alloys, zirconia, or other metal or ceramic materials. According to this embodiment, during the debinding or pre-sintering step, the small particles tend to create necking, creating green or brown areas in the model area to provide some hardening or other mechanical properties. As a result, the model area is freestanding, while the large-particle-only support area remains a more separable structure. According to another embodiment, the large and small particles can be of different materials. One non-limiting example is a dispersion of large zirconia particles and stainless steel or copper nanoparticles. According to another non-limiting example, the large particles can be WC, and the small particles can be stainless steel or copper.

[0061] Supporting ink The support materials described herein may remain an integral part of the finished product, forming a multi-component material. Alternatively, once the object is printed, the support material is removed prior to post-printing processes, which typically involve heat treatments such as sintering. Alternatively, the support structure printed with the support ink may remain on the printed object during post-printing processes. In these cases, the support structure of the support ink must remain sufficiently soft and / or brittle to allow removal after the sintering process. The metal composition of the final object will be similar or close to that of the initial ink, but in some embodiments may differ from the starting composition due to loss of some material during the printing process.

[0062] A detailed description of support materials is provided in WO2015056232A1 (Patent Application No. PCT / IB2014 / 065402), which is incorporated herein by reference. Support inks according to embodiments disclosed herein include chemicals including solid particles dispersed in a carrier vehicle, dispersant, and additives, such as those described herein.

[0063] Solid particles for supporting inks In one embodiment, the support material comprises particles of one or more types of material and / or particle size. For example, in one embodiment, one or more types of particles can be mixed together. Particle size is indicated by diameter, but not specifically indicated. As described, particle diameters range from nanometer scale, e.g., (about 10 nm to less than 500 nm, e.g., 400 nm, 300 nm), to submicron (about 0.5 μm to about 1 μm), to micron (50 μm or less), providing the general function of a support. Optionally, the solid particles are miscible or at least partially soluble in water, basic, or acidic aqueous solutions.

[0064] In various embodiments, the particle size of the solid particles of the support material is 1.0 micron or greater, at least 2.0 microns, at least 10.0 microns, at least 20.0 microns, or up to 50.0 microns. In one embodiment, the particle size of the solid particles of the carrier material ranges from 1.0 micron to 50 microns, such as from 1.0 micron to 5.0 microns. Additionally, the particle size of the solid material in the model ink is 0.5 microns or less, such as 0.4 microns or less, 0.3 microns or less, 0.2 microns or less, 0.1 microns or less, or 10 nm. In one embodiment, the particle size of the model particles ranges from 10 nm to 0.5 microns.

[0065] In various embodiments, the solid particles comprise one or more metal or ceramic materials, oxides, carbides, nitrides, or carbonates. Non-limiting examples of such oxides and carbonates that can be used as solid particles include silicon oxide (silica - SiO), aluminum oxide (AlO - alumina), titanium oxide (TiO - titania), yttrium oxide (YO - yttria), cobalt oxide (CoO), copper oxide (CuO), iron oxide (FeO), zinc oxide (ZnO), magnesium oxide (MgO), zirconium oxide (ZrO - zirconia), iron carbonate (FeCO), and organic or inorganic salts.

[0066] In one embodiment, the support material comprises FeCO3 particles. FeCO3 is a brittle material that thermally decomposes into iron oxide and CO2 at temperatures between 500 and 700°C. To provide a support structure for iron-containing model inks, FeCO3 powder can be dispersed in a solution to form a jettable ink that can be deposited onto a substrate from an inkjet printhead. FeCO3 particles can be dispersed in a carrier liquid using commercially available dispersants. Another advantage associated with the use of FeCO3 is its reduced size during chemical decomposition to iron oxide. Not only is the iron oxide easily removable, but any iron oxide contaminants in the model are converted to metallic iron during sintering. This results in model pieces with mechanical properties that are unaffected by contamination.

[0067] Salt Support In another embodiment, the support comprises the same model particles mixed with other materials or particles that prevent sintering of the support particles, such as silica or organic or inorganic salts. The advantage of this support material is that any residual support material that inadvertently contaminates the model will contain the same model material. Salt-based support materials have many advantages, including the fact that they can be easily washed with water due to the high solubility of water per salt. Indeed, if support removal is performed before sintering (green or brown stage), the part is porous, allowing water to flow throughout the model material (not just the outer surface) and wash away contaminating salts within the bulk of the part. Thus, contamination is prevented. In one embodiment, inorganic salts may be preferred over organic salts to facilitate support removal in the green stage, since organic salts can be damaged at high temperatures.

[0068] In another embodiment, the support contains only salt. If additional model material is required, it is added during printing based on the print map. Mixing is then performed either uniformly by interlacing model and support pixels, or non-uniformly by printing islands of model pixels in a support matrix. This technique not only simplifies support material production, but also eliminates the need to manufacture individual supports for each model material to be printed. Another advantage of this approach is the flexibility in determining the ratio of salt to model material in the support, including the possibility of controlling the ratio as a function of distance from the printed part.

[0069] The salt support can be implemented as either a salt solution or a salt particle dispersion in a liquid. In one embodiment, the salt can be a combination of particles such as silicate nanoparticles and inorganic or organic salt particles or solutions thereof.

[0070] In one embodiment, the support ink contains insoluble salt particles, which can be inorganic or organic. The particle size of these inorganic or organic salts may range from 10 to 800 nm, e.g., 50 to 600 nm, or 100 to 500 nm. Insoluble salt particles mean that they are insoluble in neither water nor the ink-solvent mixture (both the model and the support). In other words, the salt-support ink is characterized by a first solvent in which the salt is insoluble. To remove such supports, a second solvent in which the salt dissolves is used, either before or after sintering. The second solvent, the salt-support removal solvent, may be applied in different forms, such as by spraying, jetting, or immersing the printed part in an aqueous bath. The aqueous bath containing the second solvent can enhance support removal by a mechanical element configured to increase the flow of the aqueous medium at the printed part, or by generating mechanical vibrations or pulses to the aqueous medium. According to another aspect, the printed part may be placed on a vibrating tray to enhance support removal.

[0071] Carrier Liquid The particles can be dispersed in a carrier liquid, also known as a "carrier" or "solvent." According to one embodiment, the carrier liquid evaporates immediately after printing, allowing subsequent layers to be dispensed onto the solid material underneath. Therefore, the temperature of the top layer of the object being printed should be comparable to the boiling point of the carrier liquid. To reduce heat output during printing, it is desirable for the boiling point not to be too high. To enable jetting capability, the ink viscosity, which primarily depends on the viscosity of the carrier liquid, must not be too high. Additionally, the surface tension of the liquid must match the requirements of the jetting head. In one embodiment, a suitable carrier liquid has a boiling point between 100 and 250°C, a viscosity between 3 and 30 at 24°C, and a surface tension between 20 and 70 millinewtons per meter.

[0072] In another embodiment, the temperature of the top layer is much higher than the boiling temperature of the liquid carrier, thereby promoting evaporation of other organic materials, such as dispersants or various additives, in the carrier liquid.

[0073] Dissolving Model Materials At least a portion of the solid material in the form of micro- or nano-sized particles used to construct the object can be dissolved in the carrier liquid. For example, a dispersion of silver (Ag) particles contains, in addition to the Ag particles, a portion of an Ag organic compound dissolved in the carrier liquid. After printing and during firing, the organic portion of the Ag organic compound evaporates, allowing the metallic silver atoms to be sufficiently dispersed. Inks containing dissolved silver are readily available, such as DYAG100 conductive silver printing ink, available from Dyesol Inc. (USA) (638 5th Street, CA 95617).

[0074] Dispersants To maintain particle dispersion, dispersants help disperse particles in the carrier liquid. Dispersants are known in the art and are often a type of polymer molecule. Generally, dispersant molecules attach to the surface of solid particles (i.e., they encapsulate the particles) and inhibit particle aggregation. When multiple types of solid particles are dispersed in a dispersion, it is preferable to use the same dispersant for all solid particle types to avoid compatibility issues between different dispersant materials. The dispersant must also be soluble in the carrier liquid so that a stable dispersion can be formed.

[0075] The dispersant must also be compatible with the liquid carrier for stability purposes. For example, in aqueous inks, stabilization can be achieved by appropriately controlling the surface properties, such as by changing the pH of the dispersion. It is important to note that the stabilizer (i.e., dispersant) is bound to the surface of the particles by covalent bonds or physical adsorption.

[0076] An additional role of dispersants is realized during printing. During printing, after jetting and drying, dispersants help particles adhere and bond to each other. Note that this is the opposite role of a dispersant when particles are dispersed in a liquid carrier. If additional bonding is required, special bonding additives are added to the ink dispersion.

[0077] Non-limiting examples of dispersants that can be used herein include Disperbyk 180, Disperbyk 190, and Disperbyk 163 from BykChemie; Solsperse 39000, Solsperse 33000, and Solsperse 35000 from Lubrizol; Rheosperse 3020, 3450, and 3620 from Coatex (Arkema); and Efka 7701, Efka 7731, and Efka 7732 from BASF. Ionic dispersants include, for example, SLS (sodium lauryl sulfate), CTAB (cetyltetraammonium bromide), AOT (dioctyl sulfosuccinate), and fatty acids such as oleic acid. Conventional particle inks are readily available, such as SunTronic Jet Silver U6503, available from Sun Chemicals Ltd. (485 Berkshire Ave, Slough, UK).

[0078] The aforementioned dispersants can be found in amounts ranging from 1 to 10% by weight of the model particles. The exact amount of dispersant also depends on the dispersing power of the agent and the quality of the mixing tool, as well as the adhesion characteristics of the dry material. All of these can affect ink properties such as viscosity.

[0079] Dispersant removal The dispersant must also be such that it can be removed from the print before or during any desired post-processing steps, specifically during thermal treatment of the print, such as pre-sintering or sintering. Partial removal of the dispersant may occur during printing in the high temperature environment of the printer. In this case, partial sintering occurs, replacing the dispersant's binding power. A more detailed discussion of various issues related to sintering is provided below.

[0080] Surface Modifiers Surface modifiers are substances that affect properties such as surface tension, scratch resistance, and interfacial properties with the print. Exemplary surface modifiers include cellulose-based polymers such as ethyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, and cellulose acetate. Other surface modifiers may include polybutyral (manufactured by Butvar). As discussed in more detail below, surface modifiers impart desirable properties to the finished model, such as adding color or abrasion resistance. Surface modifiers may also improve processing of the print, such as by facilitating separation of the support from the model or by providing a barrier between the support and the model to reduce cross-contamination.

[0081] If present in the support ink, the surface modifier may be from about 0.1 to about 5% by weight of the support ink, depending on the desired ink properties such as viscosity.

[0082] Additives used as modifiers As used herein, "additive" refers to a material added to an ink to assist in printing target particles, harden raw parts, or prevent adverse phenomena during the printing and sintering process. In various embodiments, one or more additive materials can be added to the ink to assist in the processing of the final product, such as the printing or sintering step, or in the properties of the final object, such as the color or mechanical properties of the print. In one embodiment, there is at least one separate print head dedicated to dispensing additives alone or additives dissolved in an appropriate solvent. As used herein, this head used to deposit materials other than the model or support is referred to as an "additive head." In this case, there is no issue of dissolving the additive in the target ink, which may be incompatible with the additive. Furthermore, the additive head can be used to dispense different amounts of additive to different zones of the object.

[0083] Additives used to color the surface of a model In various embodiments, one or more additive materials may be deposited on the surface of the print to impart a desired color. For example, one zone that may benefit from the addition or overuse of an additive is the peripheral area of the model. The additive may be a specific color that is only needed at the periphery.

[0084] [System for forming products with particles of different sizes] In one embodiment, a system for forming a product containing particles of different sizes is described. The system includes at least one print head region configured to hold a first group of print heads configurable to apply and print at least a first portion of the product with a first material having a first average particle size, where the first average particle size is selected to impart an initial structural characteristic upon sintering. In one embodiment, the first portion comprises a core or essential portion of the printed product. For example, when printing an artificial tooth, the core or essential portion of the printed tooth constitutes the tooth core, as opposed to an outer layer.

[0085] The system also includes at least a second group of printheads configurable to print at least a second portion of the product with an additive second material having a second average particle size, where the second average particle size is selected to impart a second structural characteristic upon sintering that differs from the first structural characteristic. In one embodiment, the second portion comprises a peripheral portion of the printed product. For example, if an artificial tooth is being printed, the peripheral portion of the printed tooth constitutes the outer layer of the tooth, as opposed to the core structure.

[0086] In one embodiment, the first material and the second material are substantially the same, such as the same chemical or crystalline structure, except for having different average grain sizes and different sintering temperatures. In another embodiment, the first material and the second material are substantially different, such as having different chemical and / or crystal structures from one another, but have substantially the same sintering temperature.

[0087] The system further includes at least one processor configured to receive information reflecting desired properties of the product and to adjust the first printhead group and the second printhead group to non-uniformly dispense the first material and the second material layer by layer to thereby impart different structural properties to different portions of the product based on the information reflecting the desired properties of the product. In one embodiment, the at least one processor is configured to determine a distribution of the first and second materials to achieve the desired properties of the product.

[0088] As used herein, "interlace" means that the first and second materials intersperse with each other during deposition to form a single structure rather than being separated in different parts of the product. The single structure may contain different amounts of the first and second materials by weight or volume. For example, the ratio between the different materials throughout the interlace may vary in different parts of the product depending on the desired characteristics of the product. In one embodiment, the print heads do not randomly interweave the first and second materials, but deposit such materials to achieve a specific effect. For example, at least one processor may configure the first and second print head groups to digitally interlace the first and second materials with each other to achieve a printed product with desired characteristics.

[0089] In one embodiment, the systems described herein deposit materials such that at least one of the materials penetrates the other, forming one or more strings, such as a web of strings, that are formed in a printed product by wicking the first material into the second material, or vice versa.

[0090] Desired properties can be achieved by varying the amount and / or distribution of the first and second materials in each layer. For example, the at least one processor may be configured to determine the distribution of the first and second materials such that the first layer includes more of the first material than the second material, and the second layer includes more of the second material than the first material. Varying the amount and / or distribution of the first and second materials in each layer enables printing of a first portion comprising the core of the object and at least a second portion comprising the periphery of the object.

[0091] Typical desirable product properties that can be modified or imparted include thermal, mechanical, chemical, or physical properties. Non-limiting examples of thermal properties include sintering temperature, coefficient of thermal expansion, coefficient of contraction, thermal conductivity, and thermal diffusivity. Non-limiting examples of desirable mechanical properties include wear resistance, brittleness, ductility, elasticity, stiffness, toughness, and yield strength. Non-limiting examples of physical properties include density, hardness, and color. Non-limiting examples of chemical properties include stability, corrosion resistance, and oxidation resistance. As used herein, chemical "stability" means that a material does not react specifically with the environment or during normal use. For example, a material is considered stable if it is inert to air, water, moisture, heat, solvents, etc. under expected application conditions. Similarly, a material may be considered unstable if it is likely to corrode, decompose, polymerize, burn, or explode under expected use conditions or normal environmental conditions. By alternating first and second materials and the amounts of each, any combination of the above can be imparted to a printed product.

[0092] As mentioned above, the desired properties of the product may include various chemical or mechanical properties, particularly the shrinkage coefficient of the product or only certain portions of the product. In one embodiment, it may be desirable to reduce or eliminate dimensional shrinkage between the printed model part and the printed substrate, such as by adjusting the sintering temperature and / or shrinkage coefficient. In one embodiment, the difference in dimensional shrinkage between the printed model and the printed substrate is less than 15%, such as less than 10%, or less than 5%.

[0093] In one embodiment, at least one of the support ink or the model ink includes solid particles having a chemical composition, particle size, particle size distribution, or a combination thereof that causes the printed model part to sinter at a lower temperature than the support material. For example, in one embodiment, the printed model part sinters at a temperature at least 100° C. lower than the temperature of the support structure, such as at least 150° C. lower, or even at least 200° C. lower than the temperature of the support structure.

[0094] The particle size, particle size distribution, or a combination thereof, of the solid particles in the support ink and the model ink may be modified to allow the printed model to sinter at a temperature lower than that of the support material. For example, the particle size of the solid material in the support ink is larger than that of the solid material in the model ink. In one embodiment, the particle size of the solid material in the support ink is 1.0 microns or greater, and the particle size of the solid material in the model ink is 0.5 microns or less. In one embodiment, the support ink includes solid particles having a unimodal particle size distribution, and the model ink includes solid particles having a multimodal particle size distribution. Similarly, the support ink may include solid particles having a packing density lower than that of the solid particles in the second ink.

[0095] As previously mentioned, inks that can be used in accordance with the present disclosure include one or more support inks for inkjet printing support structures comprising one or more solid particles of an oxide or carbonate of a metal or semi-metal, such as silicon, aluminum, titanium, yttrium, cobalt, copper, iron, zinc, magnesium, zirconia, or a combination or alloy thereof, and a model ink for inkjet printing model parts, wherein at least one of the support ink or model ink exhibits properties that reduce or eliminate differences in dimensional shrinkage between the printed model and the printed substrate. In one embodiment, the one or more solid particles of an oxide or carbonate of the support ink comprise SiO2, Al2O3, TiO2, YO3, CoO, CuO, ZnO, MgO, ZrO2, FeCO3, and combinations thereof.

[0096] In one embodiment, the model ink comprises solid particles made from metals selected from iron, copper, silver, gold, and titanium; metal oxides selected from SiO2, TiO2, and BiO2; metal carbides selected from WC, Al4C3, and TiC; and alloys of metals selected from stainless steel and titanium-based composites.

[0097] In one embodiment, at least one of the support ink or the model ink further comprises an additive selected from a dispersant, a rheological agent, a binder, or a combination thereof, wherein the additive is present in an amount sufficient to control the void space between solid particles contained in the ink.

[0098] In one embodiment, the print head region of the described system is configured to hold a third group of print heads, which can be configured to print with a removable support material to temporarily support the first and second prints. As noted above, one or more additive materials can be added to the ink to aid in processing the final product, such as printing or sintering steps, or printed from a separate head to improve the properties of the final object, such as the color or mechanical properties of the print.

[0099] Methods of forming products with particles of different sizes using the disclosed system Also disclosed herein are methods for manufacturing products by inkjet printing using the described systems. For example, the methods for making objects by inkjet printing described herein can include jetting an object material containing particles to form an object structure having a first sintering temperature. Simultaneously with or prior to forming the product structure, the method further includes jetting a support material containing particles to form a support structure, where the support structure is jetted to support the product structure. In one embodiment, the support material has a sintering temperature higher than the sintering temperature of the object material. The jetted object and the jetted support together constitute a green part. The method further includes heating the green part to a temperature equal to or greater than the first sintering temperature and less than the second sintering temperature to at least partially sinter the jetted object without substantially sintering the jetted support, and removing the substantially unsintered support from the at least partially sintered object.

[0100] As used herein, "substantially unsintered" means that the support particles remain substantially separate or easily separated, even if there is some adhesion between the support particles, as long as the support particles have not yet fused together to form a dense solid piece.

[0101] As noted above, the one or more solid particles that can be used in the disclosed methods, among others, include SiO2, Al2O3, TiO2, YO3, CoO, CuO, ZnO, MgO, ZrO2, FeCO3, and combinations thereof. Similarly, the model inks that can be used in the disclosed methods include solid particles made from a metal selected from iron, copper, silver, gold, and titanium; a metal oxide selected from SiO2, TiO2, and BiO2; a metal carbide selected from WC, Al4C3, and TiC; a metal alloy selected from stainless steel and titanium-based composites.

[0102] The method further includes sintering the printed model at a temperature below the sintering temperature of the support material, such as sintering the printed model at least 100° C. below the sintering temperature of the support material.

[0103] In one embodiment, sintering may be performed in a single step, multiple steps, or by the use of a laser. When sintering occurs using a laser, laser sintering further includes at least one external energy source in combination with the laser, such as by an external energy source including microwave energy, plasma energy, or a high-energy lamp.

[0104] In one embodiment, the method further includes heat treating the green body at a temperature and time to form a partially sintered model having a density in the range of 70-85% of theoretical density.

[0105] Additives used to modify surface properties In one embodiment, the method further includes adding at least one additive to the support or model, the additive being deposited with the support ink or model ink or using a separate printer head. The additive can be deposited on the surface of the model with a separate printer head to modify at least one property of the final model, the at least one property being selected from the color or mechanical properties of the print. For example, the additive deposited on the surface of the model can form at least one wear-resistant layer comprising a metal or a polymer. Non-limiting examples of metals include cobalt, titanium, tungsten, and their carbides, and polymers include sol-gel-derived silica and a hybrid film of tetraethoxysilane (TEOS) and 3-glycidyloxypropyltrimethoxysilane (GLYMO).

[0106] In one embodiment, the additive may include a polymer that forms a composite with the finished model and is added to the printed model material by adding it to the ink during printing or by capillary action during subsequent infiltration. For example, the polymer may include polyaniline alcohol (PAN) and the printed model may include a metal carbide.

[0107] In one embodiment, the method further includes forming an interface layer between the support material and the model material, the interface layer comprising a combination of the support material and the model material, for example, the interface layer comprises FeCO.

[0108] In one embodiment, the method further comprises removing the support structure from the model material by at least one mechanical, chemical, or thermal treatment step.

[0109] As mentioned above, the additive head assembly may include several heads as shown in Figure 3, or may include one head that accepts and ejects several ink types. The inks required for this head assembly may include several ink types, each stored in several ink tanks and piping.

[0110] Systems and methods for creating colored printed parts In one embodiment, the inks must optionally include inks for the bulk material, which are structural material inks, white inks, and colored inks. As shown in FIG. 4, the inks must include dispersions of solid particles in a carrier liquid, with the exception of colored inks, which include colorants dissolved in a solvent. As an example, referring to FIG. 4A, in one embodiment, the bulk ink can include a zirconia dispersion in a carrier liquid. The colored inks can include zirconia mixed with yellow, red, and blue inorganic pigments. As shown in FIG. 4A, the ink dispersion can include colorant particles (pigment), pigment mixed with structural particles (zirconia), or pigment embedded in zirconia particles (see FIG. 4B).

[0111] In another example, the bulk material includes steel, the white ink includes zirconia, and the colored inks include the four CMYK inks used in color printing: cyan, magenta, yellow, and key (black). In this embodiment, the CMYK particle pigments may be mixed with glass particles, which upon sintering form a glossy, transparent coating. Referring to Figure 5, a roll of structural particles in the colored ink dispersion is used to create the appropriate solid volume fraction of ink needed to achieve the same layer thickness in the colored versus bulk areas. In this embodiment, the structural particles can be considered fillers.

[0112] In one embodiment, a method for adding color to a model surface includes: Creating or receiving a 3D digital representation of any desired object, including its shape and surface color. The color may vary from point to point on the surface and can be expressed in the Munsell color system (hue, saturation, lightness), CIE XYZ (tristimulus values) or CIELAB (a*, b*, L*) or numbered code systems, or any other color system. Separating colors into a set of ink colors available to the printer (CMYK subtractive system colors, or spot colors, or whatever). Calculate the number and relative proportion of colored pixels that make up a color spot on the surface of an object. As shown in Figure 5, pixels close to the surface of the object are digitally assigned different shades of color. Determine the orientation of the object on the material being printed and digitally add any necessary support structures. Slice digital objects. Print the object layer by layer (slice), with each head firing according to the ink type assigned to each pixel. Note that the layer thickness of the surrounding colored areas must be similar to, and in some cases identical to, the thickness of the bulk of the layer. The printed object is called the "green object." And The green object is baked in an oven until the material in the object is completely sintered.

[0113] In an alternative embodiment where the bulk material making up the object is not white, the method involves adding a white layer to the periphery of the object beneath the colored pixels. If saturated colors are required, or if the color varies from spot to spot on the surface of the object, it is desirable that at least the layer behind the colored layer be white (Figure 5). It may also be essential that the structural particles of the colored ink (if present) be transparent.

[0114] In one embodiment, the color shade includes an inorganic colorant (pigment) that is compatible with the firing temperature of the object being sintered. Additionally, the colored ink may include a colorant mixed with a colorant or building material. The building material may be the same as or different from the bulk building material, such as zirconia. For example, if the bulk includes steel, the colored ink may include glass.

[0115] If the colored outer layer contains a different material than the bulk (e.g., if the bulk is metal and the colored layer is ceramic), the size of the particles comprising the ink can be adjusted so that the sintering temperature of both materials is the same, within the required tolerance. If the colored ink contains glass particles and the glass contains a homogeneous mixture of various oxide molecules, the composition of the glass itself can be formulated to have the same sintering temperature as the bulk. For example, glass made by adding small amounts of lead oxide to silica material reduces the sintering temperature of silica from 1600°C to 1300°C.

[0116] In one embodiment, the printing color ink and the structural ink are in pixels of the same color to ensure uniform layer thickness throughout the layer. In addition to or instead of the color ink, a clear gloss ink can be deposited after sintering to add gloss to the manufactured object.

[0117] Systems and methods for creating colored prostheses The described process may benefit the dental industry, for example, for fabricating artificial teeth. In one embodiment, the typical color of an artificial tooth or crown is a dull color, such as off-white or brownish-white. To match such colors, the artificial tooth or crown can be printed using the disclosed method, such as using a zirconia-based ink, where the colored ink includes a pigment mixed or embedded with zirconia. In one embodiment, an artificial tooth or crown manufactured using the disclosed process and colored as described herein, as depicted graphically in Figures 3-5, is described.

[0118] System for fabricating artificial teeth In view of the foregoing, a system for additively manufacturing a body implant or prosthesis, such as an artificial tooth part, is also described. In its simplest embodiment, the system includes at least one print head region and at least one processor. The print head region is configured to hold a first group of print heads configured to additively print a three-dimensional metal core from a first ink containing metal particles, and a print head configured to additively print an outer ceramic coating surrounding the metal core from a second ink containing ceramic particles. Additionally, the at least one processor is configured to receive instructions for printing a customized artificial tooth part composed of metal and ceramic. The processor controls the first group of print heads and the second group of print heads such that the first group of print heads additively prints the three-dimensional metal core in the print region, while the second group of print heads additively prints the outer ceramic coating in the print region.

[0119] In one embodiment, the received instructions include three-dimensional data representing an entire actual tooth, and the at least one processor is configured to accurately replicate the actual tooth. For example, in one embodiment, the processor is configured to control the dispensing of the first print head group and the second print head group such that the ceramic outer coating of the artificial tooth portion has the same dimensions as the entire actual tooth.

[0120] Additionally, the at least one processor can be further configured to control the first printhead group and the second printhead group such that the height of the metal core is greater than the height of the ceramic outer coating.

[0121] Additionally, the at least one processor can be further configured to control the first printhead group and the second printhead group such that the metal core has a threaded metal portion protruding from the ceramic outer coating.

[0122] The described processors enable flexibility in printing the various materials described herein. For example, the processor can configure the print heads to print metal and ceramic in the same layer or separate, distinct layers. In one embodiment, the at least one processor is further configured to print a layer of ceramic outer coating corresponding to the layer of three-dimensional metal core before the next layer of three-dimensional metal is deposited. In one embodiment, the at least one processor is further configured to cause the first print head group and the second print head group to digitally interlace the metal and ceramic with each other.

[0123] An additional printhead is also described that can be used to print the threads on the artificial teeth. In this embodiment, at least one print head region is configured to hold a third group of print heads that can be configured to add and print a removable support material to produce the threaded metal part.

[0124] Also described is a method for printing a ceramic layer after the metal has solidified. In this embodiment, the described system may further comprise a heat source configured to provide heat to the print area to solidify the recently deposited ink, and the at least one processor is further configured to print a layer of ceramic outer coating corresponding to the layer of three-dimensional metal core after the layer of three-dimensional metal core has at least partially solidified.

[0125] To avoid thermally induced stress issues, the metal core and the ceramic outer coating layer share the same or substantially the same sintering temperature. As previously mentioned, this can be achieved by manipulating the particle size of the inks used to print various portions of the final product, such as using different particle sizes for the metal and ceramic materials. In one embodiment, the average particle size of the ceramic particles may be larger than the average particle size of the metal particles, allowing the metal core and the ceramic outer coating to substantially share a common sintering temperature or shrinkage coefficient.

[0126] The processor used in this embodiment receives instructions including three-dimensional color information regarding coloring of the artificial tooth portion. The processor is further configured to cause the multiple print heads to print the ceramic outer coating such that a different color is deposited for each pixel to simulate the color distribution of a real tooth. In one embodiment, the multiple print heads are configured to print ceramic in different colors, and at least one processor is further configured to control the deposition of the ceramic in different colors according to the three-dimensional color information. For example, the multiple printheads are configured to print non-structural pigments, and the at least one processor is further configured to control the distribution of the non-structural pigments on the ceramic outer coating according to three-dimensional color information, such as the CMYK inks described above.

[0127] In one embodiment, the multiple print heads described herein may be further configured to deposit materials that provide mechanical or aesthetic improvements, for example, in one embodiment, the multiple print heads are further configured to deposit materials to provide a glossy, transparent coating after sintering, such as by depositing glass on the surface of the artificial tooth.

[0128] With further reference to a system for manufacturing an artificial tooth portion, an interface for receiving three-dimensional data representing an actual tooth is described. In one embodiment, the three-dimensional data includes three-dimensional color information representing the actual coloration of the tooth. The described system includes at least one print head region configured to support at least a first print head group configured to jet a first material of a first color in a carrier liquid and at least a first print head group configured to jet a second material of a second color in the carrier liquid. In one embodiment, the system further includes at least a third print head group configured to jet a third material of a third color in the carrier liquid. At least one of the first material, second material, and third material is configured to allow additional jetted layers to form the artificial tooth portion.

[0129] The systems described herein further include at least one processor configured to access three-dimensional data including three-dimensional color information, which is used to generate a digital representation of the color distribution of the tooth portion, the digital representation comprising instructions for controlling at least one first printhead group, at least one second printhead group, and at least one third printhead group to digitally simulate the color distribution of actual teeth in the jetted artificial tooth portion.

[0130] The at least one processor may be further configured to control the first, second, and third printhead groups to jet the artificial tooth portion. In this embodiment, the processor enables the mixture of colors from the at least one first printhead group, the at least one second printhead group, and the at least one third printhead group to simulate the color distribution of actual teeth. In one embodiment, the printed artificial tooth portion has a metal core digitally interwoven with a ceramic outer coating. It is understood that any or all of the first, second, and third materials may include a ceramic, such as the ceramic materials described herein. In another embodiment, the second and third materials may include a substantially non-structural pigment, as previously described herein.

[0131] Methods for making artificial teeth using the described system A method for additively manufacturing an artificial tooth portion is also described. In one embodiment, the method includes providing a first group of print heads configurable to additively print a three-dimensional metal core from a first ink having metal particles. The method further includes providing a second group of print heads configured to additively print a ceramic outer coating surrounding the metal core from a second ink including ceramic particles.

[0132] In another embodiment, the method receives instructions to print a customized artificial tooth portion comprised of metal and ceramic, and controls a first group of print heads and a second group of print heads such that the first group of print heads prints a three-dimensional metal core in a print area, while the second group of print heads additionally prints an outer ceramic coating in the print area.

[0133] [A third printhead for printing additives to improve the properties of the final product] As mentioned above, one or more additive materials may be added to the ink to aid in the processing of the final product, for example to improve the properties of the final object. Non-limiting examples of properties that may be improved include the color or mechanical properties of the print.

[0134] Adding a wear-resistant layer to the model surface While wear-resistant layers can be described in the context of artificial teeth or orthopedic implants and various industrial components, their use is illustrative only and not limiting or exclusive. In addition to artificial teeth, various printed products can benefit from wear-resistant layers. In one embodiment, an additional head can be used to deposit additive materials that increase the wear resistance of the resulting object. The inventors have discovered that wear-resistant layers can be achieved by incorporating additives into the printed model material. Non-limiting examples include adding WC to stainless steel, adding WS2 or C60 to stainless steel, or using a WC / Co matrix. In one embodiment, WC or WS2 can be added to the matrix as a third phase to reduce friction and wear resistance of the resulting product. Furthermore, WS2 can be added to the print to improve lubricity, adhesion, fracture toughness, and strain energy release rate. In one embodiment, an additional head can print a material containing a dispersion of cobalt particles added to a dispersion containing tungsten carbide.

[0135] In another embodiment, the abrasion-resistant layer may comprise an epoxy / sol-gel composite. To deposit these materials, sol-gel or epoxy combined with a sol-gel precursor is printed onto the surface of the print. These materials harden at temperatures between 100 and 200°C upon losing the solvent. In one embodiment, these materials become ceramic-like when exposed to further heating under certain conditions. Without being bound by theory, such conditions typically result in weight loss of the sol-gel over most of the thermal range. For example, up to approximately 250°C, the initial evaporation of the solvent, which is weakly chemically bonded to the water molecules in the sol-gel matrix, occurs. Further decomposition / thermal decomposition of the cross-linked organic groups / chains occurs at approximately 300°C and continues up to 650°C. Above 500°C, condensation reactions begin to form a 3D Si-O-Si network. This results in a silica coating.

[0136] The GLYMO-TEOS combinations described herein can be used alone or with additives for greater hardening, such as crosslinkers (PVP). The inventors have discovered that these materials are desirable in the disclosed methods because the polymers are relatively easy to jet using inkjet technology and the environment is conducive to the desired end product. In one embodiment, the process involves spraying these polymers onto the hot surface of the print, which accelerates curing and hardening, resulting in a dense, clear, scratch-resistant coating.

[0137] Procedures for preparing these polymer-type materials are described in Wu et al., "Study on Improving the Mechanical Properties of Sol-Gel Coatings for Polycarbonate," Solid Thin Films, Vol. 516, No. 6, 2008, pp. 1056-1062, which is incorporated herein by reference.

[0138] Adding a barrier between the model and the support In another embodiment, an additive head can be used to deposit a buffer / barrier-forming additive to prevent cross-contamination and / or improve support removal. This embodiment was previously described with respect to the use of FeCO3 as an additive. For example, in one embodiment, FeCO3 may be used as a support material for 3D printing of iron-based metal alloys. As previously mentioned, FeCO3 is a brittle material that thermally decomposes into iron oxide and CO2 at temperatures between 500 and 700 °C. To provide a support structure for iron-containing model inks, FeCO3 powder can be dispersed in a solution to form a jettable ink that can be deposited onto a substrate from an inkjet printhead. In addition to jetting and drying, the 3D printing process includes a leveling step to reduce height variations due to variations in build speeds between different nozzles. The leveling step is often performed by rollers, which can cause cross-contamination between the model and the support. Therefore, the support material must be removable during post-printing heat treatment or be able to integrate support contamination into the material matrix.

[0139] In one embodiment, FeCO3 may be used as a support material for iron and iron alloys such as stainless steel. After printing, the support along with the model is placed in a furnace for thermal debinding and FeCO3 decomposition. Because debinding occurs primarily at temperatures below 500 °C, FeCO3 decomposition occurs at a stage when some pore structure is already available for CO2 to leave the printed part. The remaining iron oxide remains small in volume and brittle. After pyrolysis, the support and model part must be cooled to room temperature, and the remaining iron oxide can be easily removed mechanically with a brush or airflow. After removing the support, the model is transported to a sintering furnace.

[0140] As mentioned above, one advantage of the FeCO3 support is that contaminants in the model are converted to iron oxide during the decomposition stage. During sintering in a hydrogen atmosphere or forming gas (5% H2, 95% N2), the iron oxide is reduced to metallic iron. Thus, the contaminants are converted into part of the model material. Because the contaminant concentration is low, adding small amounts of iron (≤2 wt%) does not significantly change the stoichiometry of the model material, such as stainless steels 316, 316L, 17-4, or 314.

[0141] In one embodiment, the thickness of the described barrier / buffer layer can be in the range of 0.1-0.3 μm, thus preventing mixing of the support material and model material on the surface of the object.

[0142] Formation of composite materials by supplying additives to model regions In some embodiments, the additive can be applied uniformly or non-uniformly to the model area, depending on the desired effect. For example, after the printing stage, it may be desirable to add another material to the open pores of the print by capillary action, e.g., in the green or brown areas, before full sintering, to create a composite material.

[0143] In one embodiment, polyaniline alcohol (PAN) polymer is added to the printed model material during printing (by adding it to the ink) or afterward by capillary action using an infiltration method. This particular method uses high-pressure packing, resulting in a composite with higher strength than objects without polymer packing. The PAN participates in the sintering process and carbonizes to create a metal-carbon composite. One non-limiting example of the type of composite created using this process is when PAN is added to a WC printed sample. In this case, the PAN carbonizes without losing carbon to the WC, resulting in a lower density and increased elasticity of the resulting composite.

[0144] Carbon fibers are generally made from PAN, an organic polymer, and are characterized by long strings of molecules bonded by carbon atoms. Fibers are produced through several process steps, including spinning, stabilization, carbonization, and final processing. Before the fibers can be carbonized, they must be chemically modified to convert the linear atomic bonds into more thermally stable ladder bonds. This is accomplished by heating the fibers in air at approximately 200°C for 30–120 minutes. This causes the fibers to pick up oxygen molecules from the air and rearrange their atomic bonding pattern. In the described process, printing is performed at 200°C, so no additional processing steps are necessary when using PAN.

[0145] [Sintering - Adjustment of parameters between model and support] Consistent with the present disclosure, after the printing process is complete, the object can be placed in an oven for sintering. In some embodiments, the object may be fired to a predetermined temperature in the oven until complete. The sintering process includes the following firing steps: an initial warming to burn off any organic materials; additional warming to liquefy inorganic additives, such as cobalt, if present; and a final heating to sinter the particles.

[0146] Some of the heating steps described can include applying a vacuum, applying pressure, adding an inert gas to prevent oxidation, and adding other gases that diffuse into and react with the material (e.g., hydrogen to help remove oxygen from the body).

[0147] The sintering temperature of particles is a function of, among other things, particle size. Because nanoparticles tend to melt at lower temperatures, mixtures of nanoparticles and microparticles can facilitate partial sintering. This is particularly important when designing model inks that sinter at lower temperatures than the support material. By removing the dispersant, sintering between model particles can proceed without interference or contamination from dispersant particles. Furthermore, dispersant removal prevents the formation of "islands" of dispersant particles within the print, which weaken the solidified 3D structure. Polymer dispersants and other non-volatile compounds are typically burned or incinerated in post-printing processes.

[0148] In one embodiment, the present disclosure provides a mechanism whereby the particle size and sintering temperature are selected to ensure sintering of the model before the support, facilitating support removal after sintering. This mechanism, where the sintering temperature between the model and support material is controlled to allow for easy removal of the unsintered support from the sintered model, is exemplified with silica supports. Silica supports are composed of a uniform, large particle size.

[0149] During sintering, the sintered particles substantially adhere to each other, filling the voids located between them and increasing density. The macroscopic result is substantial shrinkage (e.g., 15-60% volume). Therefore, if only one material shrinks at a certain temperature, it will separate from the other material, potentially causing the two materials to separate and at least one of the materials to fracture. To avoid this problem, in one embodiment, the sintering temperatures and shrinkage coefficients of the different materials must be substantially identical.

[0150] Sintering temperature and support material The roll of support material is dual: (a) to support the "negative" wall of the model, and (b) to add a protective envelope around the model. In one embodiment, the support material is not removed from the model prior to sintering it. In this embodiment, in contrast to the aforementioned requirements for composite materials, the support material requires a substantially different (higher) sintering temperature than the model material. Thus, partial or complete sintering of the model material occurs with little or no sintering of the support material, allowing the removal of soft, brittle, or soluble support material from the rigid sintered model material without destroying the model. Again, this embodiment can be achieved by selecting a support material with a sufficiently high melting point compared to the model, or by adjusting the sintering temperature of the individual ink compositions with controlled particle size and / or particle size distribution, or controlled shape irregularities of the different materials.

[0151] An example of a substrate according to the last embodiment is an ink containing spherical silica particles about 1 micron in diameter, which acts as a substrate for stainless steel ink. See materials comparison in Table 1. [Table 1]

[0152] From any perspective, the model sinters at a temperature (approximately 1250°C) well below the sintering temperature of the support (approximately 1560°C). As shown in the table above, the sintering temperature of particles depends on their size and chemical composition. When the particle size is much smaller than 1 micron, such as less than 0.1 microns, the sintering temperature decreases substantially as the particle size decreases. Therefore, if two materials A and B with different melting temperatures need to be sintered at the same temperature, the particle size of at least one material (e.g., material B) can be adjusted to ensure the same sintering temperature for both. Figure 6A graphically illustrates this idea, showing the sintering temperature of a material versus its particle size. Figure 6B graphically illustrates the relative density of a material versus its sintering temperature. In one embodiment, the model material sinters at a temperature at least 100°C lower than the sintering temperature of the support material, e.g., at least 150°C lower, at least 200°C lower, at least 250°C lower, or at least 300°C lower than the sintering temperature of the support material.

[0153] Therefore, one embodiment for achieving the same sintering temperature is to control the particle size and / or particle size distribution of at least one material to achieve a substantially similar sintering temperature as the other material. Another embodiment is to control the particle shape. The more regular the shape (e.g., spherical), the higher the sintering temperature.

[0154] Single-stage sintering As mentioned above, in one alternative embodiment, the inventors have discovered a method for producing prints based on a large difference in sintering temperatures. This allows for a single heating step that is high enough to sinter the model material but not the support material. This method creates a model that is consistent enough to be removed from the underlying (or wrapped) support structure without damage. This embodiment takes advantage of the difference in sintering temperatures between the model ink and the support ink.

[0155] Two-stage sintering Referring again to FIG. 6B, a graph showing the relative density of multiple sintering stages associated with a powder material. In this embodiment, the support material is removed after the model material reaches its pre-sintering stage (the point where powder particles begin to contact each other and neck) but before substantial shrinkage begins. This process is similar to the two-stage debinding and sintering process used in the MIM industry when organic components must be removed from a part before sintering. An exemplary two-stage sintering process includes removing the print from the print substrate; placing the object with a portion of the support structure in a first oven and heating it to a temperature where the object begins to neck between particles (this stage, called pre-sintering, removes the binder from the object); cooling the object and moving the cooled portion to a cleaning port to remove the support structure from the object; and placing the object in a high-temperature oven for the second sintering stage (this stage heats the object to fully sinter it).

[0156] During the early stages of sintering, the powder particles bond together and necking forms between them. At this stage, the material is much harder and less brittle than in the loose powder stage, but little shrinkage has occurred. Furthermore, because of the low temperature, the support material has not yet reached the point where it begins to sinter, making the process of removing it—either mechanically, physically, or chemically—relatively straightforward. Removing the support material during the pre-sintering stage allows for complete removal of the support material using part machining and handling. Removing the support material before the sintering stage also helps prevent cracking. If the support is not removed before the sintering process, the support material may also begin to sinter, making its removal more difficult.

[0157] It is worth commenting that with two-stage sintering, the desire for little or no difference in shrinkage between the model and support materials from room temperature to the temperature of the first-stage oven is limiting. In one embodiment, using a two-stage process can be more economical because the lengthy debinding process can be performed in a relatively inexpensive, low-temperature furnace, leaving the expensive, high-temperature sintering furnace for the fast, high-temperature sintering stage alone.

[0158] As previously mentioned, one way to ensure that the support does not sinter during the debinding step is to use a support material with a larger size, more regular shape, a "narrow" particle size distribution, and a high melting point than the model material. This is exemplified by the use of a support material containing 1-micron spherical silica particles to support an ink containing steel nanoparticles, as previously described. Such a support ink can be produced by a system of chemical reactions that allows the controlled growth of uniformly sized spherical silica particles through the hydrolysis of alkyl silicates and the subsequent condensation of silica acid in an alcohol solution. Ammonia is used as a morphological catalyst. The particle size obtained in this process can be controlled from less than 0.05 μm to 2 μm in diameter. Diameter nonuniformity is less than 10%.

[0159] As an example, SiO2 particles with a size of approximately 60 nm (polydisperse) sinter at approximately 900 °C. If larger particles, e.g., in the micron range, are used, the particles sinter at 1550 °C, significantly above the sintering temperature of the model part. Thus, a support containing micron-range particles allows the model particles to sinter to form a rigid structure, but the support particles do not. The difference in sintering temperatures, and the resulting microstructure, allows the printed and sintered model to be removed from the support structure without damage.

[0160] Using known wet chemical techniques, micron-sized SiO2 particles can be produced with controlled shape, porosity level, and density, e.g., customized properties such as hollow spheres with reduced density. Non-limiting examples of control parameters that can be used to control particle size include the nature of the Si precursor; the water / ethanol ratio used to produce silica; reaction time and temperature; and the type of pH agent. A process describing the system is described in the literature [W. Stober, A. Fink, E. Bohn, Controlled growth of monodispersed spheres in the micron size range, J. Colloid and Interface Sci. 26 (1968) 62-69], which is incorporated herein by reference.

[0161] To illustrate the effect of Si precursor properties, water content, and ethanol ratio on the particle size of the SiO2 material, we tested several variables within the ternary phase diagram shown in Figure 7. The following reaction conditions were used: temperature 20°C, stirring for 12 hours, pH ~11.

[0162] The SiO2 precursor material contained 9 wt% SiO2 content and exhibited a viscosity of 12.2 cPs at 25°C, a density of 1.12 g / cc, and a surface tension of 32 mN / m.

[0163] Table 2 shows how particle size changed with varying ethanol / water ratio and silica content. [Table 2]

[0164] In-situ debinding and sintering In one embodiment, a method is disclosed that addresses the problems associated with shrinkage during debinding and sintering. In particular, the inventors have discovered an in-situ debinding and sintering process that improves process throughput, both to eliminate cracks in green or brown bodies and to shorten the debinding process after printing.

[0165] In the current process, each printed layer is cured before jetting the successive layer. Curing is typically achieved by evaporating the liquid carrier of the metallic ink, creating a green area. To evaporate the liquid carrier and fix the jetted droplets in specific, precise locations, printing is typically done on a hot surface, and additional heating is used to completely evaporate the liquid carrier. The extra heating is provided by a system consisting of fans, lamps, lighting, and suction.

[0166] When nanoparticles are used in the disclosed process, their melting points are typically in the range of about 200-400°C. Therefore, simple external energy, such as using a heated chuck or lamp, can cause sintering in the substrate or previous layer. However, when micro- and sub-micron particle sizes are used, the melting points of typical metals remain consistent with the bulk material, thus eliminating sintering or even partial sintering using a heated chuck or lamp. In particular, the energy flux (Watt / m 2 ) is insufficient to initiate sintering. As a result, a high energy flux over a short time frame is required to provide a low total energy flux to the sample. This can be achieved by laser, microwave, or flash light sintering. Such systems can provide a high energy flux (watts) in a short time, thereby raising the surface temperature to an appropriate sintering level.

[0167] In one embodiment, a post-printing process consisting of a debinding and sintering procedure can be used to obtain fully sintered parts containing micron and submicron metal particles. An in-situ process can also be used to sinter the powder using a laser line scanner, but this process is limited by low throughput due to scanning times.

[0168] To circumvent these limitations of in-situ sintering, a process is described herein that results in a brown or fully sintered part after the printing process. Unlike existing laser line-scanning techniques, this paper describes line-scanning laser or full-area sintering, which involves flashlight or microwave energy. This process utilizes a model and support where the support does not sinter due to its material properties, such as using a ceramic material for the support and a metal powder for the model. Another example is the use of nanoparticle doping in the model area.

[0169] 8 is a schematic diagram of an in situ laser system with a model and support material according to one embodiment of the present disclosure. The external energy used for sintering can be microwaves, a charged roller rolling over the sample, or plasma generated by a flashlight from a high-energy lamp.

[0170] The disclosed method results in direct selective heating of the printed metal ink layer, which allows for higher process temperatures and therefore better sintering performance in shorter times. The proposed process is as follows: (i) print the ink and the substrate; (ii) remove the liquid carrier with low energy flux using heat from the bottom of the substrate and / or using a blower with a lamp system; (iii) remove the excess organic material using a laser scanner or other energy with a mid-range energy flux (see below for details); and (iv) finally use the same equipment (e.g., a laser) with high energy to briefly heat the particles to the sintering temperature.

[0171] In one embodiment, the debinding process can be performed using a laser as described and exemplified herein, for example, one with low intensity (process speeds up to 10 mm / sec) for a long period of time. The goal of the debinding process is to remove the organic components of the printed ink through pyrolysis. This requires heating the surface of the model to 300-400°C. For short, high-energy sintering times, sintering times must be in the millisecond range to avoid oxidation. During sintering, metal particles begin to connect to each other through surface energy forces. A method has been described for partially removing the organic components, followed by partial sintering to achieve the brown intensity of the sample. This can be followed by furnace sintering to achieve complete debinding and sintering. High-speed sintering in the printing process can eliminate oxidation. However, to ensure an oxidizing environment, inert gases such as nitrogen, argon, or hydrogen, or common combinations of these gases, can be added to the system. For the laser used in this sintering method, approximately 10-20 kW / cm is used. 2 Line array lasers producing 808 nm wavelengths with intensities of 10-100 μm, linewidths of 10-100 μm, and linelengths of 3-300 cm are described. In one embodiment, CW or pulsed lasers with typical pulse durations of 1-20 ms can be used.

[0172] As mentioned above, sintered materials shrink substantially during sintering due to voids between their constituent particles and the compaction associated with the removal of voids. Therefore, if only the model sinters and shrinks at a certain temperature, the model will delaminate from the non-shrinking support material. In one embodiment, this delamination can be used as a means of removing the support from the model. This feature is useful when the support is external to the model body. In contrast, if the support is substantially surrounded by the model, this feature is not an option because the support would prevent the model from shrinking as needed, potentially damaging the model during sintering.

[0173] In other words, in addition to the digital application of different materials per pixel in the various non-limiting examples above, one or more complementary digital heat treatments can be applied to each pixel to achieve desired local or bulk properties, such as controlling the pixel's solidification, evaporation, necking, debinding, or sintering level. According to this embodiment, printed pixels may be processed to become green, brown, sintered pixels, or anywhere in between, such as heated, debinding, necked, partially sintered, or fully sintered. Because different heat treatments can provide different mechanical properties to specific materials, the ability to apply digital heat treatments at the pixel level according to embodiments of the present invention allows for different mechanical property distributions across model structures, support structures, or their interfaces. For example, model pixels may be subjected to an in-situ heat treatment that creates model regions as brown regions, while support pixels may not be subjected to an in-situ heat treatment or may be subjected to a heat treatment that converts these supports to green regions. Alternatively, for example, some support pixels may be subjected to an in-situ heat treatment to turn them brown pixels and strengthen their supports while keeping other support pixels in the green stage. According to another example, pixels in the boundary layer between the support and the model may be subjected to an in-situ heat treatment that turns them into green pixels to facilitate separation between the support and the model or to reduce sensitivity to differences in the contraction coefficients between the support and the model to prevent cracking. According to another example, some model pixels may be subjected to an in-situ digital heat treatment to create these pixels as green pixels that act as strain relief regions in the model, while other model pixels may be subjected to a digital in-situ heat treatment to convert them into brown pixels or partially sintered pixels.

[0174] [Shrinkage - Adjustment of parameters between model and support] Controlling ink shrinkage during processing In view of the foregoing discussion, and in accordance with aspects of the present disclosure, when different model inks are used in the same model, it is advantageous to use model inks that share similar shrinkage coefficients to form a composite or multi-component object. Such similarity in shrinkage coefficients must be within the temperature range along the heating and sintering stages of the part. A first substantial shrinkage occurs during debinding, where the additives evaporate (leaving a vacuum), and a second shrinkage occurs during sintering. In one embodiment, shrinkage is controlled by removing the support in the green state or after the debinding process, where shrinkage is less than 3%, e.g., less than 2%, or even less than 1%.

[0175] Shrinkage during debinding In one embodiment, differential shrinkage during the debinding stage can be prevented by preventing shrinkage altogether. This can be done by maintaining a vacuum in the oven throughout the process. Because of the vacuum surrounding the part, the internal vacuum remaining after the loss of the additive does not create pressure that would cause shrinkage. A second embodiment is based on the proposal that when the additive leaves the object (e.g., by evaporation or collapse and evaporation), the particles move toward each other until they come into intimate contact, thus minimizing the empty volume previously occupied by the additive. However, not all of the volume occupied by the additive is eliminated. This is because there is still a lot of empty space between the nearest neighboring particles, even without the additive. For example, for spherical particles of uniform radius, the empty space between the nearest neighboring particles exceeds 30% of the total volume. If the particles are of different sizes, the empty space may be less. In this embodiment, the amount of additive (e.g., organic material) lost is appropriately controlled so that both materials shrink by the same amount while the additive is lost. If the majority of the additive is a binder, this stage is the debinding stage.

[0176] Shrinkage during sintering Before debinding the binder and other additives, the particles are separated from each other. After debinding, the particles only contact each other at individual points. During sintering, the particles fuse together, the voids between the particle surfaces disappear, and the material shrinks. The amount of shrinkage therefore depends on the amount of open space between the particles before sintering.

[0177] In one embodiment, the particles of each material are substantially identical in size and shape to one another. This embodiment relies on the fact that the ratio of free space to particle volume is invariant with scale. Another embodiment describes size and shape distributions for both materials that are substantially identical except that the scale may be different. Another embodiment relates to controlling the relative free space of the materials by mixing small particles with larger particles to ensure that both materials have the same relative free space. This embodiment relies on the fact that the small particles fill the free space between the larger particles, thereby reducing the free space.

[0178] To prevent breakage and cracking, it is important that the temperature at which the additive is lost is substantially the same for the different materials, so that identical shrinkage occurs at the same time.

[0179] Shrinkage control with additives As mentioned above, in embodiments where it is desirable to sinter two or more model materials at the same temperature, compositional variations can be used to avoid the issue of different shrinkage rates between the materials. For example, it is known that model materials may shrink by different amounts during sintering. This is because the voids between each particle may vary. One parameter that affects void size is the amount of missing material added and mixed into the particles. The missing material evaporates or collapses and evaporates at temperatures lower than the sintering temperature of the particles. Once the missing material evaporates, the particle material leaves large gaps between the particles. During sintering, the particles move closer to each other, closing the gaps and causing the material to shrink. Therefore, the shrinkage coefficient is controlled by the amount of missing material added.

[0180] As mentioned above, different additives, namely, dispersion materials, injection-improving materials, and binder materials, can naturally be included in the ink formulation. One or more of the three materials are generally lost during the heat treatment period before sintering. Typically, all organic materials are lost. Therefore, the amount or size of voids between particles can be controlled by controlling the amount of (additive) material added.

[0181] Figure 9 shows particle material before and after evaporation of the dispersant. Figure 9A shows the particle (902) wrapped with dispersant molecules (904) at low temperature. Figure 9B shows the particle (902) remaining after losing the dispersant molecules at high temperature (lower than sintering), which often include organic materials.

[0182] Controlling shrinkage rate through packing density In one embodiment, the amount of shrinkage can also be modified by changing the physical shape of the particles. For example, there is a different packing ratio (also referred to herein as "packing density") when the particles are cubic compared to spherical particles. The packing limit for spherical particles is approximately 64%. In one embodiment, by selecting a specific particle distribution that allows multiple particles to be packed to a very high packing density, a wide range and mix of particle sizes can be used to increase the packing density to values approaching 100%.

[0183] The packing factor of printed powder depends on the particle shape and size distribution. This is similar to the packing of molecules or atoms in a crystal lattice. Typical packing factors for single-sized loose powders range from 0.5 to 0.7. For example, in a crystal lattice, the packing factor for a simple atomic cube is approximately 0.52; for a body-centered cubic (BCC), it is 0.68; and for a face-centered cubic (FCC), it is 0.74. On the other hand, when powders of various sizes are present, smaller powders fit into the spaces between larger ones.

[0184] Figure 10A shows the low packing density of the model powder associated with only large particles of a single size. In contrast, Figure 10B shows the higher packing density of the model powder associated with a multimodal particle size distribution. In Figure 10B, the smaller particles can fill the voids between the larger particles. As a result of this effect associated with a bimodal particle size distribution, the powder has a higher packing density, which results in printed models with less shrinkage compared to powders with lower packing densities. In one embodiment, the printed model shrinks less than 10% in each axis to maximum density. We have found that by controlling particle shrinkage, packing density, and binder removal, low-strain regions can be obtained. Note that, according to this discussion, the particles comprise a solid target particle embedded in an envelope containing additive material, which is later burned off during the debinding process.

[0185] The inventors have found that using different particle size distributions for the model powder and the support powder results in more desirable shrinkage profiles for the model and support regions, respectively, and reduces the strain area between the model and the support. One embodiment, shown in Figure 10C, describes a model powder with a multimodal particle size distribution that results in a high packing density, and a structural powder with a monomodal particle size distribution that results in a lower packing density. It has been found that using a high-packing-density model material in combination with a low-packing-density support material results in lower stress in the support during debinding. During debinding, the low packing density associated with the support material increases the free volume of the support material as the binder is lost, allowing the support particles to move freely to other locations while the model shrinks. For example, in one embodiment, a support material with substantially the same particle size (to achieve a packing density of approximately 0.5) results in more than 50% free volume once the binder is removed. This allows substantially all stress to be released from the model during sintering. See Figure 10D.

[0186] In one embodiment, a method for neutralizing the shrinkage between the model and support materials of a 3D printing material is disclosed. This method seeks to avoid uncontrolled separation and deformation of the model part, associated with high stresses and strains due to differences in shrinkage between the support and model materials during sintering. In Figures 11A-11F, selecting powder for the model ink with a higher shrinkage rate than the support material results in distortion at the beginning of sintering (see Figure 11A) and uncontrolled separation during sintering, resulting in deformation of the resulting print (see Figure 11C). On the other hand, selecting powder for the model ink with a lower shrinkage rate than the support material again results in distortion at the beginning of sintering (see Figure 11B) and high compressive stresses during sintering (see Figure 11D), resulting in deformation of the resulting print. As a result, in one embodiment, it is desirable to balance and match the shrinkage rates of the model and support materials as closely as possible to minimize stresses during sintering, as shown in Figures 11E and 11F. [Industrial Applicability]

[0187] The disclosed ink compositions, methods for making such compositions, and methods for using such compositions can be applicable to 3D printing objects, such as composites of materials. Such objects and composites can be made by printing a model using multiple model inks according to the present disclosure onto a substrate and removing the support structure in a post-printing process. Another method can include retaining the support structure in the completed object, with the model material infiltrated by the support material, or vice versa.

[0188] 12A and 12B, which show schematic diagrams of objects constructed of different materials. Often, the desired object will include different materials in different parts of the object, such as the core material, and may also include multiple coating layers. In one embodiment, a bulk material 1202 of a first object 1200 and 1201 has a coating material 1204 layered on the outer surface of the first object.

[0189] Referring to FIG. 12B, in one embodiment, multiple layers 1204 and 1206 are present on a bulk material 1202. An alternative technique is to print one layer with one material and another layer with a different material. A special case is impregnation of a coating-like material 1206 on the outer surface of an object, or between the object and the top layer. Such impregnation can involve a gradual decrease in the ratio of impregnation material to bulk material as the distance from the object surface increases. In this way, functionally graded materials can be created that achieve different functions, such as color, thermal, or mechanical properties, as the gradient changes.

[0190] Referring to FIG. 13A, an object constructed from a mixture of materials according to the present disclosure is shown. In this embodiment, object 1300 includes a mixture of two or more materials either over the entire object or over a portion of the object. Object 1300 includes a mixture of a first material (1304) and a second material (1306). Referring to Figure 13B, when a section of object 1300 is zoomed in on (1310), the mixture of materials can be seen such that each pixel (1312 and 1314) is made up of alternating materials 1304 and 1306.

[0191] Methods and systems for printing mixed materials One technique for printing an object with a mixture of materials according to the present disclosure at a given location in a layer can be achieved by dispensing one material in certain pixels of the layer and another material in other pixels. Multiple inks and ink heads can be used to differentiate printing between the object material and the object support. According to one embodiment, one ink can be used to build both the object and the support structure (layer by layer), while another ink is dispensed only in the layer portion belonging to only the object or the support, thereby creating a difference in the mechanical attributes of both materials. This difference can be used to impart improved desired properties to the finished object or to facilitate support removal from the object after printing. For example, a first ink, such as WC particles, can be used to print both the object layer portion and the support layer portion. A second ink, such as cobalt material or particles, can be dispensed only in the object portion of the layer. After printing is completed and the printed composite is baked in an oven, a substantial difference is introduced between both materials (the support, consisting only of WC particles, is not sintered, while the object is sintered or at least formed into a solid matrix of WC in cobalt). This difference allows the support to be removed from the object.

[0192] [System for printing mixed materials] As shown, an additive manufacturing system for forming a composite three-dimensional product from at least two different materials is described. In one embodiment, the system includes at least one print head region configured to hold a first group of print nozzles configurable to additively print a layer of a first object material and a second group of nozzles configurable to additively print a layer of a second object material. In one embodiment, the first object material is a metal and the second object material is a ceramic.

[0193] The system may further include at least one processor configured to receive instructions for printing a composite three-dimensional product and control the first and second printhead groups according to the instructions. For example, in one embodiment, the first and second printhead groups are controlled to sequentially form a product from multiple additive layers, with the first and second nozzle groups depositing a first object material and a second object material, respectively, in a common layer on a pixel-by-pixel basis, and then depositing a first object material and a second object material, respectively, in a subsequent layer. In one embodiment, the subsequent layer includes at least one of a second object material pixel on top of a first object material pixel and a first object material pixel on top of a second object material pixel.

[0194] In one embodiment, the controller is configured to interface the first object material with the second object material.

[0195] In one embodiment, the controller is configured to encapsulate at least a portion of the second object material within the first object material.

[0196] In one embodiment, a first set of nozzles can be configured to print an additive layer of a first object material from a first ink composition, and a second set of nozzles can be configured to print an additive layer of a second object material from a second ink composition. In one embodiment, the first ink composition and the second ink composition are jetted together in liquid form and include a dispersant selected to prevent substantial phase separation or diffusion between the first ink and the second ink when combined.

[0197] In one embodiment, the product is a green part, and the green part comprises a binder in an amount ranging from 2% to 20% by volume, such as from 4% to 15%, or from 5% to 10%.

[0198] In one embodiment, the green portion comprises solid particles in an amount ranging from 50% to 70% by volume, such as from 55 to 65% by volume.

[0199] In one embodiment, the green part has a porosity in the range of 2% to 20%, for example 5% to 10%.

[0200] In another embodiment (see flow diagram in Figure 14), composite materials can be made by using a support that remains an integral part of the finished product. In this embodiment, the support can infiltrate a porous model to produce the composite. Because there is no need to remove the support, this method allows for materials that can be made using a single sintering step, thereby simplifying processing and reducing the cost of making composite materials. Furthermore, the resulting sintered composite materials can exhibit improved physical and chemical properties.

[0201] [Method for forming composites by printing mixed materials] Referring to FIG. 14, an exemplary process 1400 begins with a printing step 1405, which forms a model 1406 on a metal oxide as a support 1408. The next step 1410 involves heating the print to a temperature in the range of 500-800°C, such that oxygen is removed from the metal oxide, reducing it to metal. The decomposition of the metal oxide results in the model being surrounded by another metal. Continued heating at elevated temperatures 1415 causes the model and support particles 1412 to begin sintering without any dimensional change, resulting in the formation of brown areas 1414. Finally, at elevated temperatures 1420, the support metal melts and infiltrates the porous model, thereby forming a composite 1425 of the model material and support metal.

[0202] In one embodiment, a composite is disclosed that includes a model made of tungsten carbide (WC) and a support made of cobalt oxide (CoO). This embodiment takes advantage of the fact that CoO loses its oxide above 500°C in the following way: Co3O4 → CoO → Co. Furthermore, WC is known to begin sintering above 900°C without changing its geometric shape due to its grain shape (sharp edges). In other words, because WC is not circular, grains larger than one-tenth of a nanometer begin to harden at 900°C. This is because the sharp edges of the grains connect to the surfaces of nearby grains, creating physical connections between the grains.

[0203] When the temperature reaches 1400°C, the cobalt infiltrates the inherent porosity of the WC to create a composite material.

[0204] In addition to the one-step sintering process, this method has many other beneficial properties, including the use of support material (as opposed to discarding the support material). The process also allows for the use of many combinations of model and support materials, with no contamination between the support and model materials. For example, it has been found to be very simple to prepare support inks from metal oxides or ferrous carbonate.

[0205] In one embodiment, a model material containing WC and a support material containing ferrous carbonate are disclosed. The ferrous carbonate is known to change state to ferrous oxide at 800°C and lose its oxide above 900°C. Further heat treatment at 1500°C results in iron infiltration into the WC.

[0206] Model materials, including WC, can be used with a variety of support materials, such as metal oxides, including copper oxide and cobalt oxide. Further support options include eutectic oxide materials, such as Fe oxide and Co oxide. At high temperatures (e.g., >500°C), the oxides decompose. As the temperature increases further, infiltration occurs.

[0207] [Additive printing system for simultaneous printing and coloring] As previously mentioned, the disclosed system enables the printing of three-dimensional parts, such as composites, that can be further modified by printing a colored exterior coating to provide a product with a desired color. In this embodiment, an additive printing system for simultaneously printing and coloring a product using colored structural particles is further described.

[0208] [System for simultaneously printing and coloring products] The preceding description is relevant to this embodiment and the following description: In one embodiment, a system is described that includes at least one printhead region configured to hold a first printhead group configurable to apply and print a first colored build material of a first color and a second printhead group configurable to apply and print a second colored build material of a second color different from the first color.

[0209] In one embodiment, the systems described herein further comprise at least one processor configured to receive information reflecting desired structural and color characteristics of the product. Based on information reflecting the desired structural and color characteristics of the product, the first and second printhead groups are adjusted to mix colored particles in controlled proportions to simulate the desired color characteristics as the product is additively formed.

[0210] The systems described herein may further include at least a third group of printheads configurable to apply and print at least a third colored build material of at least a third color different from the first and second colors. In one embodiment, the first colored build material, the second colored build material, and the third colored build material are sinterable to produce a simulated desired color characteristic after sintering.

[0211] In one embodiment, at least a third group of printheads can be configured to apply and print at least a third colored build material and includes multiple subgroups, each subgroup can be configured to apply and print a different colored build material.

[0212] As previously described herein, the first colored structural material, the second colored structural material, and the at least third colored structural material can include ceramic particles, for example, the ceramic particles may be selected from at least one of Al2O3, TiO2, YO3, CoO, CuO, ZnO, MgO, ZrO2, and FeCO3.

[0213] In one embodiment, the first colored structural material, the second colored structural material, and the at least third colored structural material include those described herein above. For example, the first, second, and third colored structural materials may include metallic particles, such as at least one metal, metal oxide, carbide, and metal alloy selected from iron, copper, silver, gold, titanium, SiO, TiO, BiO, WC, AlC, TiC, stainless steel, and titanium-based composites.

[0214] In one embodiment, the first colored structural material, the second colored structural material, and at least the third colored structural material comprise synthetic structural particles as described herein. For example, the synthetic structural particles may comprise a copolymer selected from polyaniline alcohol (PAN) polymer, ethylene vinyl acetate copolymer, cellulose polymer selected from ethyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate, and polybutyral. The copolymer may comprise sol-gel-derived silica, tetraethoxysilane (TEOS), and 3-glycidyloxypropyltrimethoxysilane.

[0215] An additive manufacturing system for forming an object having a desired surface color includes at least one print head region configured to hold a first print head group configurable to print a three-dimensional object having an inner core portion and an outer surface portion, and a second print head group configurable to deposit a color coating on the outer surface portion having a coloration different from the coloration of the core, wherein the second print head group is configured to deposit a plurality of different colors.

[0216] The additive manufacturing system may further comprise at least one processor configured to receive a 3D digital representation of the object including a desired shape of the object and a desired surface coloration with color shading that varies across a surface of the object, and to analyze the desired surface coloration to identify color shading in the desired surface coloration.

[0217] The processor can be further configured to control the first group of print heads to additively form the three-dimensional object, and during additive formation of the three-dimensional object, control the second group of print heads to deposit a mixture of varying colors across a surface of the object to simulate color shades corresponding to desired variable surface coloration across the surface of the object.

[0218] In one embodiment, the at least one processor is configured to analyze the desired coloration for each pixel and deposit various colors on the second printhead group to simulate the desired coloration for each pixel. For example, the second printhead group may be configured to print colored ceramic materials using multiple printheads separated into CMYK (cyan, magenta, yellow, and key (black)) shades.

[0219] In one embodiment, the first printhead group includes a metal subgroup configured to print a core from a metal and a ceramic subgroup configured to print an outer surface adjacent to the metal core from a ceramic material, for example, the metal subgroup includes at least one of stainless steel, titanium, and Ti64, and the ceramic subgroup is configured to print at least one of SiO2, TiO2, ZrO2, and BiO2.

[0220] In one embodiment, the second group of print heads can be configured to deposit a material to provide a glossy, transparent coating after sintering, such as a glass material. In this embodiment, the first group of print heads includes a first subgroup configured to print an inner core and a second subgroup configured to print an outer surface portion. When using an additive manufacturing system to print an artificial tooth, the first group of print heads includes a first subgroup configured to print the inner core of the artificial tooth and a second subgroup configured to print the outer surface portion of the artificial tooth.

[0221] It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed inks and methods of forming titanium parts using inkjet printing technology without departing from the scope of the present disclosure. Alternative implementations will be apparent to those skilled in the art from consideration of the specification and practice disclosed herein. The detailed description and examples are illustrative only. [Explanation of symbols]

[0222] 100 Additive Manufacturing Equipment 102 Print area 106 print head 110 Ink reservoir 120 Controller 122 Printing surface

Claims

1. 1. A system for manufacturing a product, comprising: a first group of printheads configurable to apply and print at least a first portion of the product with a first material having a first average particle size, the first average particle size selected to provide first sintering characteristics; and a first group of printheads configurable to apply and print at least a second portion of the product with a second material having a second average particle size, the second average particle size selected to provide a second sintering characteristic; at least one print head region configured to hold receiving information reflecting desired characteristics of said product; Coordinating the first and second printhead groups to dispense the first and second materials layer by layer to impart different properties to different portions of the product based on information reflecting desired properties of the product. at least one processor configured to Including, the system.

2. The system of claim 1 , wherein the at least one processor is configured to determine a distribution of the first material and the second material to achieve a desired characteristic of the product.

3. The system of claim 2 , wherein the desired property of the product comprises a thermal, mechanical, chemical, electrical, or physical property.

4. 4. The system of claim 3, wherein the desired properties of the product include coefficient of thermal expansion, thermal conductivity, thermal diffusivity, wear resistance, brittleness, ductility, elasticity, stiffness, toughness, yield strength, color, density, hardness, corrosion, oxidation resistance, and combinations thereof.

5. The system of claim 1 , wherein the sintering characteristics include at least one of a sintering temperature and a shrinkage coefficient.

6. 10. The system of claim 1, wherein the at least one processor is configured to coordinate the first and second printhead groups to dispense the first and second materials in different amounts determined by weight or volume.

7. The system of claim 1 , wherein the first material and the second material share at least one element but have different average grain sizes and different sintering temperatures.

8. The system of claim 1 , wherein the first material and the second material have different chemistries but substantially the same sintering temperature.

9. The system of claim 1 , wherein the at least one processor is further configured to interlace the first material and the second material with one another during deposition.

10. The system of claim 9 , wherein the interlaced materials form a unitary structure.

11. The system of claim 10 , wherein the ratio between different materials across the interlace varies in different portions of the product depending on the desired characteristics of the product.

12. The system of claim 11 , wherein at least one of the first material and the second material is wicked into the other to form one or more strings in the other.

13. The system of claim 1 , wherein the at least one printhead region is further configured to hold a third group of printheads.

14. 14. The system of claim 13, wherein the third printhead group is configurable to print with an additional removable support material that temporarily supports the printed first material and the printed second material.

15. The system of claim 1 , wherein the first portion comprises a core of the object and the second portion comprises a periphery of the object.

16. 1. A method for producing an object by inkjet printing, comprising: jetting an object material including particles to form a product structure, the object material having a first sintering temperature; simultaneous with or prior to forming the product structure, jetting a particle-containing support material to form a support structure, the support structure being jetted to support the product structure, the support material having a sintering temperature higher than a sintering temperature of the object material, the jetted object and the jetted support together comprising a green part; heating the green part to a temperature equal to or greater than the first sintering temperature and less than the second sintering temperature to at least partially sinter the jetted object without substantially sintering the jetted support body; removing a substantially green support from the at least partially sintered body; A method comprising:

17. The support particles are SiO ２ , Al ２ O ３ , TiO ２ , Y ２ O ３ , CoO, CuO, ZnO, MgO, ZrO ２ , and FeCO ３ 17. The method of claim 16, comprising at least one of:

18. The solid particles of at least one of the support material and the object material are iron, copper, silver, gold, titanium, SiO ２ , TiO ２ , Bio ２ , W.C., Al. ４ C ３ 17. The method of claim 16, wherein the material comprises at least one metal, metal oxide, carbide, and metal alloy selected from titanium-based composites, TiC, stainless steel, and titanium-based composites.

19. 17. The method of claim 16, wherein the object material has a sintering temperature that is at least 100°C less than the sintering temperature of the support material.

20. 17. The method of claim 16, wherein the sintering step is a single step or multiple steps and is carried out in an oven or with laser energy, microwave energy, plasma energy, or high energy lamps.

21. 17. The method of claim 16, wherein the support particles have at least one of a particle size, particle size distribution, or material that causes the support to sinter at a higher temperature than the body particles.

22. The method of claim 16 , wherein at least one of the support material and the object material is selected to be a dopant of the other.

23. 1. An additive manufacturing system for forming a composite three-dimensional product from at least two different materials, comprising: a first group of print nozzles configurable to eject a first object material; and a second group of nozzles configurable to jet a second object material; at least one print head region configured to hold receiving instructions for printing the composite three-dimensional product; controlling the first group of printheads and the second group of printheads to sequentially form the product from a plurality of additive layers in accordance with the received instructions; at least one processor configured to Additive manufacturing systems, including:

24. 24. The additive manufacturing system of claim 23, wherein the first group of nozzles and the second group of nozzles each deposit, for each pixel, the first object material and the second object material in a common layer before depositing the first object material and the second object material, respectively, in a subsequent layer, the subsequent layer including at least one of a second object material pixel on top of a first object material pixel and a first object material pixel on top of a second object material pixel.

25. 24. The additive manufacturing system of claim 23, wherein the first object material is a metal and the second object material is a ceramic.

26. 24. The additive manufacturing system of claim 23, wherein the processor is configured to interface the first object material with the second object material.

27. 24. The additive manufacturing system of claim 23, wherein the processor is configured to encapsulate at least a portion of the second object material within the first object material.

28. 24. The additive manufacturing system of claim 23, wherein the first set of nozzles is configurable to additively print a layer of the first object material from a first ink composition, and the second set of nozzles is configurable to additively print a layer of the second object material from a second ink composition.

29. 30. The additive manufacturing system of claim 28, wherein the first ink composition and the second ink composition further comprise a dispersant.

30. 30. The additive manufacturing system of claim 29, wherein the dispersant is selected such that when jetted together in liquid form and combined, there is substantially no phase separation and diffusion between the first ink and the second ink.

31. 24. The additive manufacturing system of claim 23, wherein the product is a green part, and the green part comprises a binder in an amount ranging from 2% to 20% by volume.

32. 32. The additive manufacturing system of claim 31 , wherein the green part comprises binder in an amount ranging from 5% to 10% by volume.

33. 33. The additive manufacturing system of claim 32, wherein the green portion comprises solid particles in an amount ranging from 50% to 70% by volume.

34. 24. The additive manufacturing system of claim 23, wherein the green portion has a porosity of between 2% and 20%.

35. 35. The additive manufacturing system of claim 34, wherein the green portion has a porosity of between 5% and 10%.

36. 1. An ink composition configured to be jetted through a printhead to form a three-dimensional object, comprising: a plurality of ceramic particles, each of which has a dimension less than 30 microns; binder material; pigments; dispersants; and a removable carrier that is mixed and configured to carry the ceramic particles, the binder material, the pigment, and the dispersant during ejection through the printhead; wherein the carrier is formulated for evaporation removal by drying after jetting.

37. The ink composition of claim 36, wherein the ink composition is formulated such that, after drying after jetting, the carrier substantially evaporates and the binder material substantially does not evaporate.

38. 37. The ink composition of claim 36, wherein the binder and the dispersant are the same material.

39. 37. The ink composition of claim 36, wherein the structural particles comprise at least one of metallic particles, ceramic particles, and synthetic particles.

40. The structural particles are SiO ２ , Al ２ O ３ , TiO ２ , Y ２ O ３ , CoO, CuO, ZnO, MgO, ZrO ２ , or FeCO ３ 40. The ink composition of claim 39, comprising at least one of:

41. The at least one metal particle is selected from the group consisting of iron, copper, silver, gold, titanium, SiO ２ , TiO ２ , Bio ２ , W.C., Al. ４ C ３ 37. The ink composition of claim 36, comprising metal oxides, carbides, and metal alloys selected from titanium, TiC, stainless steel, and titanium-based composites.

42. 37. The ink composition of claim 36, wherein the dispersant is present in an amount of 1 to 10% by weight of the ceramic particles.

43. 37. The ink composition of claim 36, wherein the pigment is mixed with or embedded in structural particles.

44. 1. An additive manufacturing system for an artificial tooth portion, comprising: a first group of printheads configurable to apply and print three-dimensional metal cores from a first ink including metal particles; and a second group of printheads configurable to print from a second ink containing ceramic particles an outer ceramic coating surrounding the metal core; at least one print head region configured to hold receiving instructions for printing a customized metal and ceramic prosthetic tooth portion; controlling the first printhead group and the second printhead group to add and print the three-dimensional metal core in a print area, and simultaneously controlling the second printhead group to add and print the ceramic outer coating in the print area; at least one processor configured to Including, the system.

45. 45. The system of claim 44, wherein the received instructions include three-dimensional data representing an entire actual tooth, and the at least one processor is configured to control the distribution of the first group of print heads and the second group of print heads such that the ceramic outer coating of the artificial tooth portion has the same dimensions as the entire actual tooth.

46. 45. The system of claim 44, wherein the at least one processor is further configured to control the first group of print heads and the second group of print heads such that a height of the metal core is greater than a height of the ceramic outer coating.

47. 45. The system of claim 44, wherein the at least one processor is further configured to control the first printhead group and the second printhead group such that the metal core has a threaded metal portion protruding from the ceramic outer coating.

48. 45. The system of claim 44, wherein the at least one print head region is configured to hold a third group of print heads configurable to add and print a removable support material to produce a threaded metal part.

49. 45. The system of claim 44, wherein the at least one processor is further configured to print a layer of the ceramic outer coating that corresponds to a layer of the three-dimensional metal core before a subsequent layer of the three-dimensional metal is deposited.

50. 45. The system of claim 44, wherein the at least one processor is further configured to cause the first group of printheads and the second group of printheads to digitally interlace the metal and the ceramic with one another.

51. 45. The system of claim 44, further comprising a heat source configured to apply heat to a print area to solidify recently deposited ink, and wherein the at least one processor is further configured to print a layer of the ceramic outer coating corresponding to the layer of three-dimensional metal core after the layer of three-dimensional metal core has at least partially solidified.

52. 45. The system of claim 44, wherein the average particle size of the ceramic particles is larger than the average particle size of the metal particles, but the metal core and the ceramic outer coating substantially share a sintering temperature.

53. 45. The system of claim 44, wherein the received instructions include three-dimensional data representing a tooth portion configured to be bonded to a real tooth, and the at least one processor is configured to control dispensing of the first group of printheads and the second group of printheads such that a ceramic outer coating of the artificial tooth portion has the same dimensions as the tooth portion.

54. 45. The system of claim 44, wherein the received instructions include three-dimensional color information regarding the coloring of the artificial tooth portion, and the at least one processor is further configured to print the ceramic outer coating with multiple print heads such that different colors are arranged pixel by pixel to simulate a color distribution of actual teeth.

55. 55. The system of claim 54, wherein the plurality of printheads are configured to print ceramic in different colors, and the at least one processor is further configured to control deposition of the ceramic in different colors according to the three-dimensional color information.

56. 55. The system of claim 54, wherein the plurality of printheads are configured to print a non-structural pigment, and the at least one processor is further configured to control the distribution of the non-structural pigment on the ceramic outer coating according to the three-dimensional color information.

57. 55. The system of claim 54, wherein the plurality of printheads are further configured to deposit a material to provide a glossy, clear coating after sintering.

58. 1. A system for manufacturing an artificial tooth part, comprising: an interface for receiving three-dimensional data representing actual teeth, said three-dimensional data including three-dimensional color information representing actual coloration of the teeth; a first group of printheads configured to eject a first material of a first color in a carrier liquid; a second group of printheads configured to jet a second material of a second color in a carrier liquid; a third printhead group configured to jet a third material of a third color in a carrier liquid; at least one print head region configured to support a first material, a second material, and a third material, wherein at least one of the first material, the second material, and the third material is in a structure that allows additional jetted layers to form the artificial tooth portion; accessing three-dimensional data including three-dimensional color information; generating a digital representation of the color distribution of the tooth portion using the three-dimensional color information; controlling the first printhead group, the second printhead group, and the third printhead group to jet the artificial tooth portion such that a mixture of colors from the first printhead group, the second printhead group, and the third printhead group simulates a color distribution of actual teeth; wherein the digital representation comprises instructions for controlling the first group of printheads, the second group of printheads, and the third group of printheads to digitally simulate a color distribution of actual teeth in the jetted artificial tooth portion; Including, the system.

59. 59. The system of claim 58, wherein the printed artificial tooth portion is a digitally interlaced metal core with a ceramic outer coating.

60. 59. The system of claim 58, wherein the first material comprises a ceramic.

61. 59. The system of claim 58, wherein the second material and the third material comprise ceramic.

62. 59. The system of claim 58, wherein the second material and the third material are substantially non-structural pigments.

63. 1. A method for additive manufacturing of an artificial tooth portion, comprising: providing a first group of printheads configurable to add and print three-dimensional metal cores from a first ink having metal particles; providing a second group of printheads configurable to print from a second ink including ceramic particles an outer ceramic coating surrounding a metal core; receiving instructions for printing a customized artificial tooth portion comprised of metal and ceramic; controlling the first printhead group and the second printhead group so that the first printhead group applies and prints the three-dimensional metal core in a print area, and simultaneously the second printhead group applies and prints the ceramic outer coating in the print area; A method comprising:

64. 1. An additive printing system for simultaneously printing and coloring a product using colored particles, comprising: a first group of printheads configurable to apply and print a first material of a first color; and a second group of printheads configurable to apply and print a second material of a second color different from the first color; at least one print head region configured to hold receiving information reflecting desired structural and color characteristics of said product; at least one processor configured to control the first and second printhead groups based on information reflecting desired structural and color characteristics of the product such that, as the product is additively formed, particles of different colors are mixed in controlled ratios to simulate the desired color characteristics; and 1. An additive printing system comprising:

65. 65. The additive printing system of claim 64, further comprising a third printhead group configurable to additively print a third colored build material of a third color different from the first color and the second color.

66. 66. The additive printing system of claim 65, wherein the first colored build material, the second colored build material, and the third colored build material are sinterable to achieve the simulated desired color characteristics after sintering.

67. 66. The additive printing system of claim 65, wherein the third printhead group configurable to additively print at least a third colored build material includes multiple subgroups, each subgroup configurable to additively print a different colored build material.

68. 66. The additive printing system of claim 65, wherein the first colored build material, the second colored build material, and the third colored build material comprise ceramic particles.

69. The ceramic particles are SiO ２ , Al ２ O ３ , TiO ２ , Y ２ O ３ , CoO, CuO, ZnO, MgO, ZrO ２ , or FeCO ３ 69. The additive printing system of claim 68, comprising at least one of:

70. 66. The additive printing system of claim 65, wherein the first colored build material, the second colored build material, and the third colored build material comprise metal particles.

71. The metal particles are selected from the group consisting of iron, copper, silver, gold, titanium, and SiO ２ , TiO ２ , Bio ２ , W.C., Al. ４ C ３ 71. The additive printing system of claim 70, comprising at least one metal, metal oxide, carbide, and metal alloy selected from TiC, stainless steel, and titanium-based composites.

72. 66. The layered printing system of claim 65, wherein the first colored build material, the second colored build material, and the third colored build material comprise synthetic build particles.

73. 73. The additive printing system of claim 72, wherein the synthetic structural particles comprise a cellulose polymer selected from polyaniline alcohol (PAN) polymer, ethylene vinyl acetate copolymer, ethyl cellulose, carboxymethyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate, and a copolymer selected from polybutyral.

74. 74. The additive printing system of claim 73, wherein the copolymer comprises sol-gel derived silica, tetraethoxysilane (TEOS), and 3-glycidyloxypropyltrimethoxysilane.

75. 1. An additive manufacturing system for forming an object having a desired surface color, comprising: a first group of printheads configurable to print a three-dimensional object having an inner core portion and an outer surface portion; and a second group of printheads configurable to deposit a coating material having a coloration different from the coloration of the core on the outer surface portion; at least one print head region configured to hold receiving a 3D digital representation of an object, the 3D digital representation including a desired shape of the object and a desired surface coloration with color shading of the object; analyzing the desired surface coloration to identify the color shades in the desired surface coloration; controlling the first group of printheads to additively form a three-dimensional object; controlling at least one of the first group of printheads and the second group of printheads to deposit a mixture of colors during additive formation of the three-dimensional object, thereby simulating a color shade corresponding to the desired surface coloration across the surface of the object; at least one processor configured to Additive manufacturing systems, including:

76. 76. The additive manufacturing system of claim 75, wherein the desired surface color varies across the surface, and wherein the at least one processor is configured to control the first group of printheads and the second group of printheads to deposit a mixture of colors that vary across the surface of the object.

77. 76. The additive manufacturing system of claim 75, wherein the second group of printheads is configured to deposit a plurality of different colors, and wherein the at least one processor is configured to control the first group of printheads and the second group of printheads to deposit a varying mixture of colors across a surface of the object.

78. 76. The additive manufacturing system of claim 75, wherein the at least one processor is configured to analyze a desired coloration for each pixel, and wherein the second group of printheads is configured to deposit different colors to simulate the desired coloration for each pixel.

79. 76. The additive manufacturing system of claim 75, wherein the first group of printheads comprises a metal subgroup configured to print a core from metal and a ceramic subgroup configured to print an exterior surface from a ceramic material adjacent to the metal core.

80. 76. The additive manufacturing system of claim 75, wherein the second printhead group is configured to print colored material using multiple printheads separated into CMYK [cyan, magenta, yellow, and key (black)] shades.

81. 81. The additive manufacturing system of claim 80, wherein the coloring material comprises a ceramic material.

82. 82. The additive manufacturing system of claim 81 , wherein the ceramic material is transparent.

83. 76. The additive manufacturing system of claim 75, wherein the outer surface portion is substantially white.

84. The metal subgroup is configured to print at least one of stainless steel, titanium, and Ti64, and the ceramic subgroup is configured to print SiO ２ , TiO ２ , ZrO ２ , Bio ２ 76. The additive manufacturing system of claim 75, configured to print at least one of:

85. 76. The additive manufacturing system of claim 75, wherein the second group of printheads is configurable to deposit a material to provide a glossy, clear coating after sintering.

86. 86. The additive manufacturing system of claim 85, wherein the glossy transparent coating comprises one of a glass or a transparent ceramic.

87. 76. The additive manufacturing system of claim 75, wherein the first group of printheads comprises a first subgroup configured to print the inner core and a second subgroup configured to print the outer surface portion.

88. 88. The additive manufacturing system of claim 87, wherein the first group of printheads comprises a first subgroup configured to print an inner core of an artificial tooth and a second subgroup configured to print an outer surface portion of an artificial tooth.

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