Patent Publication Number: US-2022212249-A1

Title: Fabrication of lattice structures with a three-dimensional printer

Description:
TECHNICAL FIELD 
     The present teachings relate generally to three-dimensional (3D) printing and, more particularly, to systems and methods for building (e.g., printing) an object with a 3D printer having lattice structures with large strut diameters. 
     BACKGROUND 
     A 3D printer builds (e.g., prints) a 3D object from a computer-aided design (CAD) model, usually by successively depositing material layer upon layer. For example, a first layer may be deposited upon a substrate, and then a second layer may be deposited upon the first layer. One particular type of 3D printer is a magnetohydrodynamic (MHD) printer, which is suitable for jetting liquid metal layer upon layer to form a 3D metallic object. Magnetohydrodynamic refers to the study of the magnetic properties and the behavior of electrically conducting fluids. 
     In MHD printing, a liquid metal is jetted out through a nozzle of the 3D printer onto a substrate or onto a previously deposited layer of metal. When building engineered lattice structures via droplet jetting of this manner, it generally results in weak or fragile struts due to relatively cold weld joints between droplets that make up each cylindrical strut. Furthermore, the diameter of these lattice struts is effectively limited by the diameter of the droplets being jetted. Thus, a suitable method is needed to produce vertical or vertically angled support free struts having any desired diameter and greater strength. 
     SUMMARY 
     The following presents a simplified summary in order to provide a basic understanding of some aspects of one or more embodiments of the present teachings. This summary is not an extensive overview, nor is it intended to identify key or critical elements of the present teachings, nor to delineate the scope of the disclosure. Rather, its primary purpose is merely to present one or more concepts in simplified form as a prelude to the detailed description presented later. 
     A three-dimensional (3D) printer is disclosed. The three-dimensional printer also includes an ejector having a nozzle, a heating element configured to heat a solid in the ejector, thereby causing the solid to change to a liquid within the ejector, a coil wrapped at least partially around the ejector, a power source configured to supply one or more pulses of power to the coil, which cause one or more drops of the liquid to be jetted out of the nozzle, and a substrate configured to support the one or more drops as the one or more drops solidify to form a 3D object and advance along a path defined by one or more arcuate contours, where the one or more arcuate contours define a first layer of a strut. 
     In another embodiment, the 3D printer includes a substrate which is further configured to advance along a path defined by the one or more arcuate contours to print a plurality of layers of the strut onto the first layer of the strut. Each of the plurality of layers of the strut may be laterally offset from the first layer of the strut and may follow a spiral path. The strut may begin at a node where the strut meets a second strut. The 3D printer may print a strut where the strut may include at least one layer between the first layer of the strut and the node of the strut. The strut is printed from the first layer of the strut to the node of the strut. In various embodiments, the one or more struts may be hollow, solid, vertical, or angled and the one or more struts may combine to fabricate a lattice structure including one or more vertical struts and/or one or more angled struts, where the one or more vertical struts may include one or more nodes, the one or more angled struts may include one or more nodes and at least one of the one or more nodes of at least one of the one or more vertical struts intersects with at least one of the one or more nodes of at least one of the one or more angled struts. 
     A method for printing a three-dimensional (3D) object using a 3D printer is disclosed. The method includes jetting one or more drops of a liquid metal through a nozzle of the 3D printer, where the one or more drops land on a substrate, and where the one or more drops cool and solidify to form the 3D object, moving the substrate while the one or more drops are jetted to support the one or more drops as the one or more drops solidify to form a 3D object, and advancing the substrate along a path defined by one or more arcuate contours. The disclosed method also includes defining a first layer of a first strut. and printing a plurality of layers of the first strut onto the first layer of the first strut along the path defined by the one or more arcuate contours. 
     In another embodiment, the method includes printing a plurality of layers from the first layer of the first strut to a node of the first strut. The method may also include advancing the substrate along a path defined by a second of one or more arcuate contours to define a first layer of a second strut, printing a plurality of layers of the second strut onto the first layer of the second strut along a second path defined by the second one or more arcuate contours, and printing the plurality of layers from the first layer of the second strut to the node of the first strut to form a lattice structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present teachings and together with the description, serve to explain the principles of the disclosure. In the figures: 
         FIG. 1  depicts a schematic cross-sectional view of a 3D printer (e.g., a MHD printer and/or multi-jet printer), according to an embodiment. 
         FIG. 2A  illustrates a schematic top view of a first example of the 3D object on the substrate, according to an embodiment. 
         FIG. 2B  illustrates a schematic side view of a first example of the 3D object on the substrate, according to an embodiment. 
         FIG. 3  illustrates a photograph of the first example of the 3D object of  FIGS. 2A and 2B , according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments of the present teachings, 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, similar, or like parts. 
     In 3D printing, and in particular, printing with liquid metal jetting, the fabrication of engineered lattice structures generally results in weak or fragile struts or other structural framework elements due to the relatively cold weld joints between droplets that make up each cylindrical strut. Furthermore, the diameter of the lattice struts is effectively limited by the diameter of the droplets being jetted. According to embodiments described herein, a method is provided to produce vertical and/or angled support-free struts having any desired diameter and greater strength. The proposed printer and printing method described in the embodiments may be capable of producing stronger struts or cylindrical beams and is based on printing spiral layers or a plurality of disks of a given diameter. Each printed spiral can have any desired outer diameter, thus allowing 3D printed struts of any desired diameter. In some embodiments, partially overlapping droplets follow a spiral toolpath which can continue until a disk or layer of any desired diameter has been printed. 
       FIG. 1  depicts a schematic cross-sectional view of a 3D printer  100 , according to an embodiment. The 3D printer  100  may include an ejector (also referred to as a body or pump chamber)  120 . The ejector  120  may define an inner volume (also referred to as a cavity). A printing material  130  may be introduced into the inner volume of the ejector  120 . The printing material  130  may be or include a metal, a polymer, or the like. For example, the printing material  130  may be or include aluminum or aluminum alloy (e.g., a spool of aluminum wire). 
     The 3D printer  100  may also include one or more heating elements  140 . The heating elements  140  are configured to melt the printing material  130 , thereby converting the printing material  130  from a solid state to a liquid state (e.g., liquid metal  132 ) within the inner volume of the ejector  120 . 
     The 3D printer  100  may also include a power source  150  and one or more metallic coils  152  that are wrapped at least partially around the ejector  120 . The power source  150  may be coupled to the coils  152  and configured to provide an electrical current to the coils  152 . In one embodiment, the power source  150  may be configured to provide a step function direct current (DC) voltage profile (e.g., voltage pulses) to the coils  152 , which may create an increasing magnetic field. The increasing magnetic field may cause an electromotive force within the ejector  120 , that in turn causes an induced electrical current in the liquid metal  132 . The magnetic field and the induced electrical current in the liquid metal  132  may create a radially inward force on the liquid metal  132 , known as a Lorenz force. The Lorenz force creates a pressure at an inlet of a nozzle  122  of the ejector  120 . The pressure causes the liquid metal  132  to be jetted through the nozzle  122  in the form of one or more liquid drops  134 . 
     The 3D printer  100  may also include a substrate  160  that is positioned proximate to (e.g., below) the nozzle  122 . The drops  134  may land on the substrate  160  and solidify to produce a 3D object  136 . In one example, the 3D object  136  may be or include a strut, which may be part of a lattice structure. A strut is a structural piece or element of a lattice structure that provides support or structural definition to the lattice structure. 
     The 3D printer  100  may also include a substrate control motor  162  that is configured to move the substrate  160  while the drops  134  are being jetted through the nozzle  122 , or during pauses between when the drops  134  are being jetted through the nozzle  122 , to cause the 3D object  136  to have the desired shape and size. The substrate control motor  162  may be configured to move the substrate  160  in one dimension (e.g., along an X axis), in two dimensions (e.g., along the X axis and a Y axis), or in three dimensions (e.g., along the X axis, the Y axis, and a Z axis). In another embodiment, the ejector  120  and/or the nozzle  122  may be also or instead be configured to move in one, two, or three dimensions. In other words, the substrate  160  may be moved under a stationary nozzle  122 , or the nozzle  122  may be moved above a stationary substrate  160 . In yet another embodiment, there may be relative rotation between the nozzle  122  and the substrate  160  around one or two additional axes, such that there is four or five axis position control. In certain embodiments, both the nozzle  122  and the substrate  160  may move. For example, the substrate  160  may move in X and Y directions, while the nozzle  122  moves up and/or down in a Y direction. 
     The 3D printer  100  may also include one or more gas-controlling devices, which may be or include gas sources (two are shown:  170 ,  172 ). The first gas source  170  may be configured to introduce a first gas. The first gas may be or include an inert gas, such as helium, neon, argon, krypton, and/or xenon. In another embodiment, the first gas may be or include nitrogen. The first gas may include less than about 10% oxygen, less than about 5% oxygen, or less than about 1% oxygen. 
     In at least one embodiment, the first gas may be introduced at a location that is above where the second gas is introduced. For example, the first gas may be introduced at a location that is above the nozzle  122  and/or the coils  152 . This may allow the first gas (e.g., argon) to form a shroud/sheath around the nozzle  122 , the drops  134 , the 3D object  136 , and/or the substrate  160  to reduce/prevent the formation of oxide (e.g., aluminum oxide). Controlling the temperature of the first gas may also or instead help to control (e.g., minimize) the rate that the oxide formation. 
     The second gas source  172  may be configured to introduce a second gas. The second gas may be different than the first gas. The second gas may be or include oxygen, water vapor, carbon dioxide, nitrous oxide, ozone, methanol, ethanol, propanol, or a combination thereof. The second gas may include less than about 10% inert gas and/or nitrogen, less than about 5% inert gas and/or nitrogen, or less than about 1% inert gas and/or nitrogen. The second gas may be introduced at a location that is below the nozzle  122  and/or the coils  152 . For example, the second gas may be introduced at a level that is between the nozzle  122  and the substrate  160 . The second gas may be directed toward the nozzle  122 , the falling drops  134 , the 3D object  136 , the substrate  160 , or a combination thereof. This may help to control the properties (e.g., contact angle, flow, coalescence, and/or solidification) of the drops  134  and/or the 3D object  136 . 
     The 3D printer  100  may also include another gas-controlling device, which may be or include a gas sensor  174 . The gas sensor  174  may be configured to measure a concentration of the first gas, the second gas, or both. More particularly, the gas sensor  174  may be configured to measure the concentration proximate to the nozzle  122 , the falling drops  134 , the 3D object  136 , the substrate  160 , or a combination thereof. As used herein, “proximate to” refers to within about 10 cm, within about 5 cm, or within about 1 cm. 
     The 3D printer  100  may also include a computing system  180 . The computing system  180  may be configured to control the printing of the 3D object  136 . More particularly, the computing system  180  may be configured to control the introduction of the printing material  130  into the ejector  120 , the heating elements  140 , the power source  150 , the substrate control motor  162 , the first gas source  170 , the second gas source  172 , the gas sensor  174 , or a combination thereof. As discussed in greater detail below, in one embodiment, the computing system  180  may control the rate at which the voltage pulses are provided from the power source  150  to the coils  152 , and thus the corresponding rate at which the drops  134  are jetted through the nozzle  122 . These two rates may be substantially the same. 
     In another embodiment, the computing system  180  may be configured to receive the measurements from the gas sensor  174 , and also configured to control the first gas source  170  and/or the second gas source  172 , based at least partially upon the measurements from the gas sensor  174 , to obtain the desired gas concentration around the drops  134  and/or the object  136 . In at least one embodiment, the concentration of the first gas (e.g., nitrogen) may be maintained between about 65% and about 99.999%, between about 65% and about 75%, between about 75% and about 85%, between about 85% and about 95%, or between about 95% and about 99.999%. In at least one embodiment, the concentration of the second gas (e.g., oxygen) may be maintained between about 0.000006% and about 35%, between about 0.000006% and about 0.00001%, between about 0.00001% and about 0.0001%, between about 0.0001% and about 0.001%, between about 0.001% and about 0.01%, between about 0.01% and about 0.1%, between about 0.1% and about 1%, between about 1% and about 10%, or between about 10% and about 35%. 
     The 3D printer  100  may also include an enclosure  190  that defines an inner volume (also referred to as an atmosphere). In one embodiment, the enclosure  110  may be hermetically sealed. In another embodiment, the enclosure  110  may not be hermetically sealed. In one embodiment, the ejector  120 , the heating elements  140 , the power source  150 , the coils  152 , the substrate  160 , the computing system  170 , the first gas source  180 , the second gas source  182 , the gas sensor  184 , or a combination thereof may be positioned at least partially within the enclosure  190 . In another embodiment, the ejector  120 , the heating elements  140 , the power source  150 , the coils  152 , the substrate  160 , the computing system  170 , the first gas source  180 , the second gas source  182 , the gas sensor  184 , or a combination thereof may be positioned at least partially outside of the enclosure  190 . 
       FIG. 2A  illustrates a schematic top view of a first example of a first layer of the 3D object  136  on the substrate  160  that is formed when the 3D printer  100  operates according to an embodiment. To form the 3D object  136 , the power source  150  may transmit a plurality of voltage pulses to the coils  152 , which may cause a corresponding plurality of drops (fifteen drops are shown:  134 A to  134 Q, note that  134 I and  134 O are not used to avoid confusion with the numerals  1341  and  1340 , respectively) to jet through the nozzle  122 . The drops  134 A to  134 Q may be jetted at a predetermined frequency that allows each drop (e.g., drop  134 A) to land on the substrate before the next drop (e.g., drop  130   4 B) is jetted from the nozzle  122  and deposited on the previous drop  134 A or the substrate  160 . The predetermined frequency may be from about 10 Hz to about 500 Hz, which may cause from about 10 drops to about 50 drops to be jetted through the nozzle  122  per second. In the embodiment illustrated in  FIG. 2A , the substrate  160  is configured to advance along the path defined by one or more arcuate contours, in this embodiment the arcuate path  200  or arcuate contour forms a spiral pattern that creates a disk or disk-shaped layer. The disk forms a foundational layer for a strut. An arcuate path or arcuate contour is defined as a curved outline or boundary shape that is followed by the advancing substrate during a jetting operation with the 3D printer  100 . As the 3D printer  100  continues to operate, and subsequent drops  134 B- 134 Q are jetted through the nozzle  122 , the substrate continues to move along this arcuate path  200 , in this case moving from the center  200 C of the spiral path in a clockwise direction  202  outward towards a radial edge  200 E from the center  200 C of the spiral path  200 . As the substrate  160  moves or advances along the arcuate path  200 , a first layer  135 A is deposited onto the substrate  160  in a spiral path. This first layer  135 A is the first layer of a strut which is continuously formed as additional layers are deposited onto the first layer  135 A. After the first layer is deposited onto the substrate  160 , the substrate continues to advance along a similar path defined by the one or more acute contours to print or build the second layer upon the first layer in a spiral pattern. In the embodiment shown, the first drop  134 A may be deposited onto the substrate  160 , the second drop  134 B may be deposited onto the first drop  134 A, and so on as the substrate  160  advances. The drops  134 B- 134 Q may not be in contact with the substrate  160 . The drops  134 A- 134 Q may be jetted such that each drop (e.g., drop  134 B) is horizontally offset from the previously jetted drop (e.g., drop  134 A) by less than a width of the previously jetted drop (e.g., drop  134 A). This may result in the 3D object  136  being oriented at an initial angle with respect to the substrate  160  where the angle may be from about 20° to about 70° or from about 30° to about 60° (e.g., about 45°). In another embodiment, the arcuate path may be formed by the substrate moving or advancing in a continuous path of one or more arcuate contours, or alternatively the substrate may move in a noncontinuous path of one or more arcuate contours. In yet another embodiment, the drops may be deposited in such a manner that the substrate  160  advances in such a manner that the spiral path  200  begins at a radial edge  200 E of the spiral path  200  and moves inward toward the center  200 C of the spiral path  200 . In another embodiment, the diameter of the spiral path  200  as measured from the center  200 C to the radial edge  200 E, is larger than the diameter of the one of the one or more drops after solidification. In certain embodiments, the tubular or cylindrical structure, or strut formed by this printing method to build a 3D lattice structure may be hollow, solid, or a combination of hollow and solid. Cylindrical struts formed in this manner may also be vertical or angled, and some structures may have a mixture of vertical and angled struts in certain embodiments. In another embodiment, an entire strut is printed up to a node location where two or more struts converge prior to the next strut being printed, distinguishing this approach from standard layer-by-layer 3D printing. 
       FIG. 2B  illustrates a partial side view of subsequent layers, of the 3D object  136  formed on the substrate  160  in the manner described in regard to  FIG. 2A , in this case a partial side view of a strut, according to an embodiment. The drops  134 A- 134 Q may not be in contact with the substrate  160  in certain embodiments but may be built upon other structures or 3D objects previously printed by the 3D printer  100 . As the 3D printer  100  continues to jet drops in the next disk or layer  135 B, drops  136 A- 136 Q, of which only drops  136 A- 136 C and  136 N are visible in this view, the drops  136 A- 136 Q are jetted along a path defined by the same one or more arcuate contours as followed in the first foundational layer  135 A of the strut. A path similar to path  200  is then followed repeatedly to print a plurality of layers  135 C,  135 D, and up to  135 N of the strut on top of the first layer of the strut. In the embodiment shown, layer  135 N is a node point, or a position along the length of a strut where it meets or joins or insects with a node or node point of another strut or structural element of the 3D object  136 . Struts printed in the manner described in regard to  FIG. 2B  are printed with at least one layer between the foundational primary layer  135 A and the node layer  135 N of a strut. A strut according to an embodiment is printed continuously from the first layer  135 A of the strut to the node layer  135 N of the strut. As shown in  FIG. 2A , the strut may be printed as a hollow strut, although alternate embodiments may print solid, vertical, angled struts, or combinations thereof. According to an embodiment, an outer diameter of the struts may be limited by or defined by the diameter of the drops jetted in the printing fabrication of the struts, after solidification. Drop diameter according to the embodiment shown may be from about 0.05 mm to about 1 mm, from about 0.1 mm to about 0.5 mm, or from about 0.25 mm to about 0.5 mm. Layer  135 B and subsequent layers  135 B- 135 N are deposited vertically upon foundation layer  135 A, although the drops in layers  135 B- 135 N may alternatively be jetted such that each layer (e.g., drops  136 A- 136 Q forming layer  135 B, and so on) is horizontally offset from the previously jetted layer (e.g., layer  135 A) by less than a width of a previously jetted strut layer. This may result in the 3D object  136  being oriented at an initial angle with respect to the substrate  160 , for example, the angle may be from about 20° to about 70° or from about 30° to about 60° (e.g., about 45°). As shown the angle of layers  135 A- 135 N relative to one another is approximately 0° with respect to the substrate  160 . 
       FIG. 3  illustrates a photograph of the first example of the 3D object fabricated as described in  FIGS. 2A and 2B , according to an embodiment. The lattice structure  300 , is a structure fabricated from one or more vertical struts  302 , and one or more angled struts  304 . Each of the vertical struts  302  in the lattice structure  300  defines a node  306  or node point (a connection point between one or more struts in a lattice structure) along the length of the vertical strut  302 . Each of the angled struts  304  defines a node  308  or node point along the length of the vertical strut  304 . According to an embodiment, the lattice structure  300  shown in  FIG. 3  has multiple vertical struts  302  spaced apart and connected or coupled with several angled struts  304 , in this embodiment shown as an “X-shaped” support, where each angled strut  304  is coupled to a vertical strut  302  at a node point  306  on the vertical strut  302 . The “X-shaped” support structure is fabricated from four angled struts  304  meeting at a center node  308 . 
     The lattice structure  300  in  FIG. 3  can be printed or fabricated, according to an embodiment, such that a vertical strut  302  within the lattice structure  300  is printed layer by layer from bottom to a top of the structure  300 . Angled or diagonal struts  304  may be printed such that the first layer of one or more angled struts  304  is printed, then a subsequent second layer of the one or more angled struts  304  is printed. The layer-by-layer printing of an angled strut  304  may continue until a node point  308  is reached that would join a vertical strut  302  at its node point  306 . At this time, the 3D printer  100  and the substrate  160  would follow an arcuate path in such a manner that a vertical strut  302  could be completed by repetitive layers vertically on top of one another, or alternatively by forming a spiral disk layer of all angled and/or vertical struts in a lattice structure to another node point before continuing to print the subsequent layers. In this manner, a 3D printer  100  as disclosed herein may fabricate a lattice structure having one or more vertical struts and one or more angled struts, wherein the one or more vertical struts may include one or more nodes, the one or more angled struts comprise one or more nodes. In the fabricated lattice structure, at least one of the one or more nodes of at least one of the one or more vertical struts intersects with at least one of the one or more nodes of at least one of the one or more angled struts. In an embodiment, the lattice structures are fabricated by 3D printing of aluminum or aluminum alloy. In another embodiment, plastic or polymer-based printing materials may be used with the use of alternate methods of 3D jetting and fabrication methods. 
     In certain embodiments, a 3D object  136  such as a lattice structure may be printed using a 3D printer  100  by jetting one or more drops of a liquid metal through a nozzle of the 3D printer, wherein the one or more drops land on a substrate, and wherein the one or more drops cool and solidify to form the 3D object. The substrate may be moved while the one or more drops are jetted to support the one or more drops as the one or more drops solidify to form a 3D object and the substrate is advanced along a path defined by one or more arcuate contours, thereby defining a first layer of a strut. The path defined by one or more arcuate contours may be a spiral path. Next, a plurality of layers of the strut is continuously printed onto the first layer of the strut along the path defined by the one or more arcuate contours until a node point of the strut is reached. In an embodiment, one or more of the subsequent layers are horizontally offset from the location of the first layer of the strut while alternate embodiments may have one or more of the subsequent layers positioned directly onto the first layer. This method of jetting may enable the construction or fabrication of intricate structures having engineered lattice structures. The lattice structures according to an embodiment may further have a solid printed outer skin that encapsulates the internal supporting lattice structure, a formation that is difficult or impossible to make with existing printing methods. 
     While the present teachings have been illustrated with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. For example, it may be appreciated that while the process is described as a series of acts or events, the present teachings are not limited by the ordering of such acts or events. Some acts may occur in different orders and/or concurrently with other acts or events apart from those described herein. Also, not all process stages may be required to implement a methodology in accordance with one or more aspects or embodiments of the present teachings. It may be appreciated that structural objects and/or processing stages may be added, or existing structural objects and/or processing stages may be removed or modified. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. Furthermore, to the extent that the terms “including,” “includes,” “having,” “has,” “with,” or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising.” The term “at least one of” is used to mean one or more of the listed items may be selected. Further, in the discussion and claims herein, the term “on” used with respect to two materials, one “on” the other, means at least some contact between the materials, while “over” means the materials are in proximity, but possibly with one or more additional intervening materials such that contact is possible but not required. Neither “on” nor “over” implies any directionality as used herein. The term “conformal” describes a coating material in which angles of the underlying material are preserved by the conformal material. The term “about” indicates that the value listed may be somewhat altered, as long as the alteration does not result in nonconformance of the process or structure to the illustrated embodiment. The terms “couple,” “coupled,” “connect,” “connection,” “connected,” “in connection with,” and “connecting” refer to “in direct connection with” or “in connection with via one or more intermediate elements or members.” Finally, the terms “exemplary” or “illustrative” indicate the description is used as an example, rather than implying that it is an ideal. Other embodiments of the present teachings may be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present teachings being indicated by the following claims.