Metal drop ejecting three-dimensional (3D) object printer and method of operation for facilitating build and release of metal object from build platform

Abstract

To provide a three-dimensional (3D) metal object manufacturing apparatus providing a liquid silicate application system to apply liquid silicate to a surface of a build platform prior to manufacture of a metal object.SOLUTION: The liquid silicate layer is permitted to air-dry and then the platform is heated to its operational temperature range for formation of a metal object with melted metal drops ejected by the apparatus. The liquid silicate layer forms a glassy brittle layer on which the metal object is formed. This brittle layer is removed relatively easily with the object after the object is manufactured and the build platform is cooled. The silicate layer improves the wetting of surfaces of build platforms made of non-wetting materials, such as oxidized steel, while preventing metal-to-metal welds using wetting materials, such as tungsten or nickel.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure is directed to three-dimensional (3D) object printers that eject molten metal droplets to form objects, and more specifically, to the formation of a base layer of a metal object on the build platform of such a printer.

Background Art

[0002] Three-dimensional printing, also known as additive manufacturing, is a process of creating three-dimensional solid objects from digital models of virtually any shape. Many three-dimensional printing technologies use a layering process in which a layer-forming device forms successive layers of a part on top of previously deposited layers. Some of these technologies use ejectors that eject ultraviolet-curable materials such as photopolymers or elastomers, while other technologies melt elastomers and extrude thermoplastic materials into object layers. Printers typically operate one or more ejectors or extruders to form successive layers of a plastic or thermoplastic material to build three-dimensional printed objects having various shapes and structures. After each layer of the three-dimensional printed object is formed, the plastic material is ultraviolet-cured and solidified, bonding the layer to the underlying layer of the three-dimensional printed object. This additive manufacturing method is distinguishable from conventional object formation techniques that mostly rely on the removal of materials from workpieces by subtractive processes such as cutting or drilling.

[0003] Recently, several 3D object printers have been developed that form 3D objects by ejecting droplets of molten metal from one or more ejectors. These printers have a solid metal source, such as a roll of wire or pellets, which supplies solid metal to a heated containment in a container within the printer where the solid metal is melted, filling the containment. The containment is made of a non-conductive material around which electric wire is wound to form a coil. As electric current passes through the coil, it generates an electromagnetic field, which causes the meniscus of molten metal at the nozzle of the containment to separate from the molten metal in the containment and propel it out of the nozzle. A build platform is positioned to receive the molten metal droplets ejected from the ejector nozzle, and this platform is moved in an XY plane parallel to the plane of the platform by a controller-operated actuator. These ejected metal droplets form a metal layer of the object on the platform, and another actuator, operated by the controller, changes the distance between the ejector and the platform to maintain an appropriate distance between the ejector and the immediately adjacent printed layer of the forming metal object. This type of metal droplet printer is also known as a magnetohydrodynamic (MHD) printer.

[0004] During the printing process in MHD printers, the first layer of an object must adhere securely to the surface of the build platform. Without this adhesion, the base of the object becomes unstable as its size increases. The high surface temperature of the build platform can cause the surface to oxidize very highly. This oxide layer can interfere with the adhesion of the object's base layer to the build platform, causing the object to detach prematurely from the build platform surface during printing. In addition, the oxide layer can cause the base layer of the object to form uniformly, resulting in a base layer that is more porous than required for printing a stable object layer.

[0005] However, oxidation of the build platform surface is not the only issue affecting proper adhesion of an object to the build platform. A relatively clean build platform surface can result in excessive adhesion of the base layer of the object to the build platform surface. While the manufacturing of the object proceeds smoothly due to the very stable base of the object, removal of the object at the end of the process can be extremely difficult. In some cases, the attachment of the object to the build platform becomes so secure that removal of the object causes damage to the object, the build platform, or both. It is beneficial to be able to sufficiently adhere the base layer to the build platform and form that layer uniformly and with appropriate porosity without securely attaching the object to the build platform to such an extent that removal causes damage to the object, the platform, or both. [Overview of the Initiative]

[0006] A novel method for operating a 3D metal object printer allows for sufficient adhesion of the base layer of a metal object to the build platform, forming the layer uniformly and with appropriate porosity, without requiring the object to be securely attached to the build platform to such an extent that its removal would damage the object, the platform, or both. The method includes operating a dispenser to apply a silicate to a planar member, and after the liquid silicate has been applied to the planar member, operating an ejector head to eject molten metal droplets onto the planar member.

[0007] The new 3D metal object printer securely adheres the base layer of a metal object to the build platform, forming the layer uniformly and with appropriate porosity, without requiring the object to be attached to the build platform to such an extent that its removal would damage the object, the platform, or both. The new 3D metal object printer comprises an ejector head having a container, the container having a containment portion configured to hold molten metal within the container, and an applicator configured to apply a silicate material onto a planar member to receive molten metal droplets ejected from the ejector head. [Brief explanation of the drawing]

[0008] A method for operating a 3D metal object printer that securely adheres the base layer of a metal object to a build platform without securely attaching the object to the build platform to such an extent that its removal would cause damage to the object, the platform, or both, thereby forming the layer uniformly and with appropriate perforation, and the aforementioned embodiments and other features of a 3D metal object printer that implements the method are described below in conjunction with the attached drawings.

[0009] [Figure 1] This represents a novel 3D metal object printer that securely adheres the base layer of a metal object to a metal foil layer on a build platform, forming the layer uniformly and with appropriate perforation, without requiring the object to be attached to the build platform to such an extent that its removal would damage the object, the platform, or both. [Figure 2] This is a schematic diagram of a process that provides sufficient adhesion of building materials to the build platform for a reliable base for building parts, without securely attaching the object to the build platform to such an extent that its removal would damage the object, the platform, or both. [Figure 3]Figure 1 is a flowchart of the process for operating the system, which provides sufficient adhesion of building materials to the build platform for a reliable base for building parts, without securely attaching the object to the build platform to such an extent that its removal would damage the object, the platform, or both. [Figure 4] This is a schematic diagram of a prior art 3D metal printer that does not include an applicator for applying a silicate layer to the surface of a build platform before forming a base layer of a metal object on the build platform. [Modes for carrying out the invention]

[0010] For a general understanding of the 3D metal object printer and the environment for its operation disclosed herein, as well as the details of the printer and its operation, refer to the drawings. In the drawings, similar reference numbers represent similar elements.

[0011] Figure 4 shows one embodiment of a known 3D metal object printer 100 that ejects droplets of molten metal to directly form a metal object on a build platform. In the printer of Figure 4, droplets of molten bulk metal are ejected from a housing of a removable container 104 having a single nozzle 108, and the droplets from the nozzle form a base layer of the object by swath applied directly to the build platform 112. As used in this document, the term “removable container” means a hollow container having a housing configured to hold a liquid or solid substance, and the container as a whole is configured for installation and removal within a 3D metal object printer. As used in this document, the term “container” means a hollow container having a housing configured to hold a liquid or solid substance, which may be configured for installation and removal from a 3D metal object printer. As used in this document, the term “bulk metal” means conductive metal available in aggregate form, such as commonly available standard-size wires, macro-size ratio pellets, and metal powders.

[0012] Referring further to Figure 4, a bulk metal source 116, such as a metal wire 120, is supplied to a wire guide 124 extending through the upper housing 122 within the ejector head 140, where it is melted in the housing of a removable container 104 to provide molten metal for ejection from the nozzle 108 through an orifice 110 in the base plate 114 of the ejector head 140. As used herein, the term “nozzle” means an orifice fluidly connected to the volume in the housing of the container containing molten metal, configured to eject molten metal droplets from the housing in the container. As used herein, the term “ejector head” means the housing and components of a 3D metal object printer that melts, ejects, and controls the ejection of molten metal droplets for the manufacture of metal objects. The molten metal level sensor 184 includes a laser and a reflection sensor. The reflection of the laser from the molten metal level is detected by the reflection sensor and generates a signal indicating the distance to the molten metal level. The controller receives this signal and determines the level of the molten metal volume in the removable container 104 so that it can be maintained at the appropriate level 118 within the removable container's housing. As the removable container 104 slides into the heater 160, the inner diameter of the heater comes into contact with the removable container, allowing the solid metal in the housing of the removable container to be heated to a temperature sufficient to melt the solid metal. As used in this document, the term “solid metal” means a metal as defined in the periodic table of elements, or an alloy formed by these metals in a solid form rather than a liquid or gas. The heater is separated from the removable container, forming a volume between the heater and the removable container 104. The inert gas supply unit 128 provides a pressure-regulated source of an inert gas, such as argon, to the ejector head through the gas supply pipe 132. The gas flows through the volume between the heater and the removable container and exits through the orifice 110 in the ejector head and base plate 114 around the nozzle 108. This inert gas flow close to the nozzle insulates the ejected molten metal droplets from the surrounding air of the base plate 114, preventing the formation of metal oxides during the flight of the ejected droplets.The gap between the nozzle and the surface on which the ejected metal droplet lands is intentionally kept small enough so that the inert gas escaping from around the nozzle does not dissipate before the droplet in the inert gas stream lands.

[0013] The ejector head 140 is mounted to move within a Z-axis trajectory to accommodate the movement of the ejector head relative to the platform 112. One or more actuators 144 are operably connected to the ejector head 140 to move the ejector head along the Z-axis and to the platform 112 to move the platform in the XY plane below the ejector head 140. The actuators 144 are operated by a controller 148 to maintain an appropriate distance between the orifice 110 in the base plate 114 of the ejector head 140 and the surface of the object on the platform 112. In some modifications of the system 100, the build platform is made of oxide steel in essence, and in other cases, the oxide steel has a tungsten or nickel top coating. The oxide steel version of the platform is less likely to bond so strongly to the base layer of molten aluminum because it is not easily wetted by molten aluminum. This platform is advantageous for removing objects after manufacturing, but may not be strong enough to support the formation of objects throughout the entire process. To address this issue, other versions of the platform add tungsten or nickel surfaces to the platform to improve wetting of the build surface with molten aluminum. However, these versions of the platform can adhere firmly to the base layer of the metal object, resulting in intermetallic welds that can damage the object, the build platform surface, or both when the object is removed.

[0014] By moving the platform 112 in the XY plane so that droplets of molten metal are ejected toward the platform 112, a swath of molten metal droplets is formed on the object being created. The controller 148 also operates the actuator 144 to adjust the distance between the ejector head 140 and the layer most recently formed on the substrate, facilitating the formation of other structures on the object. The molten metal 3D object printer 100 is shown in Figure 4 as operating in a vertical orientation, but other alternative orientations can be employed. Also, the embodiment shown in Figure 4 has a platform that moves in the XY plane and the ejector head that moves along the Z axis, but other arrangements are possible. For example, the actuator 144 can be configured to move the ejector head 140 in the XY plane along the Z axis, or it can be configured to move the platform 112 in both the XY plane and along the Z axis.

[0015] Controller 148 operates switches 152. One switch 152 may be selectively operated by the controller to provide power to a heater 160 from a power source 156, and another switch 152 may be selectively operated by the controller to provide power to a coil 164 from another power source 156 to generate an electric field for ejecting droplets from the nozzle 108. Because the heater 160 generates a large amount of heat at a high temperature, the coil 164 is positioned within a chamber 168 formed by one or more walls (linear) of the ejector head 140 (circular). As used in this document, the term “chamber” means a volume contained within one or more walls in a metal droplet ejection printer, in which the heater, coil, and removable container of the 3D metal object printer are located. The removable container 104 and the heater 160 are located within such a chamber. The chamber is fluidically connected to a fluid source 172 via a pump 176 and is also fluidly connected to a heat exchanger 180. As used in this document, the term “fluid source” refers to a container of liquid having properties useful for absorbing heat. The heat exchanger 180 is connected via a return to the fluid source 172. Fluid from the source 172 flows through the chamber, absorbing heat from the coil 164, and the fluid carries the absorbed heat through the exchanger 180, where the heat is removed by known means. The cooled fluid is returned to the fluid source 172 for further use in maintaining the coil temperature within a suitable operating range.

[0016] The controller 148 of the 3D metal object printer 100 requires data from an external source to control the printer for the manufacture of metal objects. Generally, a three-dimensional model or other digital data model of the object to be formed is stored in memory operably connected to the controller 148. The controller can selectively access the digital data model through a server or the like, a remote database where the digital data model is stored, or a computer-readable medium where the digital data model is stored. This three-dimensional model or other digital data model is processed by a slicer implemented with the controller to generate machine-ready instructions that the controller 148 executes in a known manner, thereby operating the components of the printer 100 and forming a metal object corresponding to that model. The generation of machine-ready instructions may include the generation of an intermediate model, such as when the device's CAD model is converted to an STL data model, polygonal mesh, or other intermediate representation, and this intermediate model can then be processed to generate machine instructions, such as G-code, for the printer to manufacture the object. As used in this document, the term “machine-responsive instruction” means a computer language command executed by a computer, microprocessor, or controller to operate the components of a 3D metal object additive manufacturing system to form a metal object on the platform 112. The controller 148 executes the machine-responsive instruction to control the ejection of molten metal droplets from the nozzle 108, the positioning of the platform 112, and the maintenance of the distance between the orifice 110 and the surface of the object on the platform 112.

[0017] A new 3D metal object printer 100' is shown in Figure 1, which uses similar reference numbers for similar components and removes some components that are not used to stabilize the object during formation without excessively rigidly attaching the object to the platform 112. The printer 100' includes a silicate layer coating system 200 and a controller 148' consisting of programmed instructions stored in non-temporary memory connected to the controller. The controller 148' executes programmed instructions to operate the coating system 200 as described below to form a silicate layer that is heated to form a brittle layer suitable for supporting the formation of a metal object by the system. The silicate layer may be a liquid solution or a powder. After the formation of the object, the object and the portion of the brittle layer supporting the object can be removed from the build platform 112 without damaging the object or the platform.

[0018] The coating system 200 includes an articulated arm 204 that holds an applicator 208 located in a reservoir 212. In one embodiment, the reservoir 212 contains a solution of sodium silicate. The applicator 208 is a porous material such as felt or ceramic material that absorbs the solution in the reservoir. Furthermore, the solution or powder can be applied using a brush or sprayer. The articulated arm is operably connected to a controller 148' so that the controller can operate the arm to lift the applicator from the reservoir, apply a layer of liquid silicate to the platform 112, and then return the applicator to the reservoir (Step 1, Figure 2). As used herein, the term “liquid silicate” means an aqueous solution of a conjugate salt of any water-soluble silicate. In one embodiment, the liquid silicate is an aqueous solution of sodium silicate ranging from 1 to 40% by weight of pure sodium silicate, lithium silicate, or potassium silicate. The aqueous solution of liquid silicate may contain a surfactant such as sodium dodecyl sulfate for wetting. The liquid silicate layer is dried in ambient air, leaving a solid silicate hydrate layer (Step 2, Figure 2). Controller 148' operates the resistance heater 212 to raise the build platform temperature to over 100°C, preparing the platform for ejection of molten aluminum droplets. In one embodiment, the build platform is raised to a temperature in the range of about 400°C to about 500°C. This temperature range also causes the remaining water in the silicate layer to be released, condensing the silicate into an insoluble glassy layer (Step 3, Figure 2). The droplets of molten aluminum or aluminum alloy have a temperature of about 660°C. When these molten aluminum droplets encounter the glassy layer, they reactively wet the layer and bond to the brittle silicate layer via a partial redox reaction (Step 4, Figure 2). After the manufacturing of the metal object and the active removal of heat from the build platform, the object and platform are cooled to a temperature of approximately 500°C or less, and as a result, the object and the portion of the brittle silicate layer can be mechanically separated from the build platform without damaging the object or platform 112 (Step 5, Figure 2).

[0019] In the systems and methods described with reference to Figures 1 and 2, the silicate layer promotes the wetting and adhesion of molten aluminum to bonding substrates with low wettability and strength, such as oxide steel, as previously described. It also reduces the degree of bonding between molten aluminum and strong bonding substrates, such as nickel or tungsten, as previously described. Therefore, the silicate release layer promotes wetting and adhesion with build platforms requiring higher wetting and adhesion, and weakens wetting and adhesion with build platforms requiring lower wetting and adhesion. In both types of build platforms, the silicate layer creates an effective fracture surface to facilitate the removal of metal objects from most build platforms.

[0020] Controller 148' may be implemented using one or more general-purpose or dedicated programmable processors to execute programmed instructions. Instructions and data required to perform programmed functions may be stored in memory associated with the processor or controller. The processors, their memories, and interface circuits constitute the controller to perform the operations described above and below. These components may be provided on a printed circuit card or as circuits in an application-specific integrated circuit (ASIC). Each circuit may be implemented on a separate processor, or multiple circuits may be implemented on the same processor. Alternatively, circuits may be implemented as individual components or circuits provided in a very large scale integrated (VLSI) circuit. Also, circuits described herein may be implemented in combination of processors, ASICs, individual components, or VLSI circuits. During the formation of a metal object, image data of the structure to be manufactured is transmitted to one or more processors of controller 148' from either a scanning system or an online or workstation connection to process and generate signals that operate the components of printer 100' to form the object on platform 112.

[0021] Figure 3 shows a process for operating a 3D metal object printer 100' to form a metallic object on the surface of a silicate layer formed on a build platform 112. In the description of the process, when the process performs several tasks or functions, it means that a controller or general-purpose processor executes program instructions stored in a non-temporary computer-readable storage medium operably connected to the controller or processor in order to perform a task or function by operating data or by manipulating one or more components in the printer. The controller 148' described above may be such a controller or processor. Alternatively, the controller may be implemented with two or more processors and associated circuits and components, each configured to perform one or more tasks or functions described herein. In addition, the steps of the method may be performed in any executable chronological order, regardless of the order shown in the figure or the order in which the processes are described.

[0022] Figure 3 is a flowchart for process 300, which operates the coating system 200 to form a silicate layer on the build platform 112 before the formation of a metallic object by the printer 100'. The controller 148' is configured to execute programmed instructions stored in a non-temporary memory operably connected to the controller in order to operate the coating system 200 for this purpose. After the printer is initialized (block 304), the articulated arm is operated to move the applicator from the reservoir across the build platform surface and back to the reservoir (block 308). An appropriate period of time is waited to allow the liquid silicate layer to air dry so that no silicate hydrate layer remains (block 312). The build platform heater is operated to heat the build platform to a temperature within a range sufficient for the formation of a metallic object (block 316). The heat obtained causes the silicate layer to release any remaining water so that the silicate condenses into a glassy brittle layer. During the object manufacturing process (block 320), molten aluminum reacts to wet and bond to the condensed silicate layer. After the formation of the object is complete (block 324), the heater of the build platform is turned off (block 328), and the object and build platform are cooled to a temperature in the range of approximately 25°C to approximately 500°C, so that the object and the portion of the brittle silicate layer can be mechanically separated from the build platform without damaging the object or platform 112 (block 332).

[0023] It will be understood that variations or substitutions of the features and functions disclosed above and other features and functions may, preferably, be combined into many other different systems, applications, or methods. Various currently unforeseen or unexpected substitutions, modifications, variations, or improvements, which are also intended to be covered by the following claims, may subsequently be made by those skilled in the art.

Claims

1. an ejector head having a vessel with a receptacle within the vessel configured to hold molten metal; a planar member; a heater configured to heat the planar member; a reservoir configured to hold a volume of material; an articulated arm to which the applicator is operatively connected; a controller operatively connected to the ejector head, the articulated arm, and the heater; Equipped with The controller actuating the articulated arm to move the applicator from a first position within the reservoir to a position outside the reservoir and opposite the planar member, moving the applicator across a surface of the planar member to apply the material to the surface of the planar member, and placing the applicator in the first position within the reservoir; After the solution is applied to the surface of the planar member by the applicator, waiting for a predetermined period of time; after the predetermined period of time has elapsed, operating the heater to raise the temperature of the planar member to a temperature that forms an insoluble layer of the material on the surface of the planar member; and operating the ejector head to eject droplets of molten metal from the container toward the insoluble layer of material on the planar member while the heater is operating to maintain the planar member at a temperature equal to or higher than the temperature at which the insoluble layer is formed on the planar member. Metal droplet ejection device.

2. The device of claim 1 , wherein the material is a silicate powder.

3. The device of claim 1 , wherein the material is a liquid silicate.

4. The device of claim 1 , wherein the applicator consists essentially of a porous material.

5. 5. The device of claim 4, wherein the porous material consists essentially of felt or ceramic material.

6. The apparatus of claim 1 , wherein the temperature to which the planar member is heated exceeds 100° C.

7. The apparatus of claim 6, wherein the temperature to which the planar member is heated is within a range of about 400°C to about 500°C.

8. 8. The apparatus of claim 7, wherein the ejector head is configured to eject droplets of molten aluminum or aluminum alloy at a temperature of at least 660°C.

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