Patent Publication Number: US-2022219238-A1

Title: Metal drop ejecting three-dimensional (3d) object printer and method for preparing the metal drop ejecting 3d object printer for printing

Description:
CROSS-REFERENCED APPLICATION 
     This disclosure cross-references U.S. patent application Ser. No. ______, which is entitle “A Removable Vessel And Metal Insert For Preparing A Metal Drop Ejecting Three-Dimensional (3D) Object Printer For Printing,” which was filed on Jan. 13, 2021, and which is hereby incorporated in its entirety in this co-pending application. 
     TECHNICAL FIELD 
     This disclosure is directed to three-dimensional (3D) object printers that eject melted metal drops to form objects and, more particularly, to the preparation of such printers for object printing operations. 
     BACKGROUND 
     Three-dimensional printing, also known as additive manufacturing, is a process of making a three-dimensional solid object from a digital model of virtually any shape. Many three-dimensional printing technologies use an additive process in which an additive manufacturing device forms successive layers of the part on top of previously deposited layers. Some of these technologies use ejectors that eject UV-curable materials, such as photopolymers or elastomers. The printer typically operates one or more extruders to form successive layers of the plastic material that form a three-dimensional printed object with a variety of shapes and structures. After each layer of the three-dimensional printed object is formed, the plastic material is UV cured and hardens to bond the layer to an underlying layer of the three-dimensional printed object. This additive manufacturing method is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling. 
     Recently, some 3D object printers have been developed that eject drops of melted metal from one or more ejectors to form 3D objects. These printers have a source of solid metal, such as a roll of wire or pellets, that is fed into a heating chamber where the solid metal is melted and the melted metal flows into a chamber of the ejector. The chamber is made of non-conductive material around which an uninsulated electrical wire is wrapped. An electrical current is passed through the conductor to produce an electromagnetic field that causes the meniscus of the melted metal at a nozzle of the chamber to separate from the melted metal within the chamber and be propelled from the nozzle. A platform opposite the nozzle of the ejector is moved in a X-Y plane parallel to the plane of the platform by a controller operating actuators so the ejected metal drops form metal layers of an object on the platform and another actuator is operated by the controller to alter the position of the ejector or platform in the vertical or Z direction to maintain a constant distance between the ejector and an uppermost layer of the metal object being formed. This type of metal drop ejecting printer is also known as a magnetohydrodynamic (MHD) printer. 
     The ejector used in MHD printers includes internal components that need periodic replacement to maintain the operational status of the printer. Some components require replacement approximately every eight hours. After the components are replaced, the printer must go through a start-up process before it can be used for object production again. A portion of this start-up process is the filling of the ejector with melted metal. In the wire-fed MHD printer discussed above, this part of the process is lengthy as enough wire has to be fed into the heated portion of the ejector and melted. In some MHD printers, ten minutes or more may be required to melt enough wire to fill the ejector. Other aspects of the start-up process need about twenty minutes to perform. Thus, the overall start-up process can require an half-hour or more with one-third of that time being consumed by the refilling of the ejector with melted metal. 
     The time required for wire melting to fill the ejector cannot be reduced by simply increasing the rate at which the wire is fed to the heated chamber of the ejector. Increasing the feed rate results in the tip of the wire impacting the wall of the heated chamber because the wire encounters the wall above the level of the melted metal present in the chamber. The ejector is typically made of high temperature ceramic material, which is sensitive to the impact of the solid wire tip and may be damaged by this contact. Being able to reduce the time for filling the ejector of a MHD printer at start-up without risking damage to the heated chamber would be beneficial. 
     SUMMARY 
     A new method of operating a 3D metal object printer reduces the time required for filling the ejector of a MHD printer without damage to the heated chamber. The method includes placing solid metal into a receptacle of a removable vessel, installing the removable vessel into the metal drop ejecting additive manufacturing apparatus, and activating a heater in the metal drop ejecting additive manufacturing apparatus to a temperature that melts the solid metal within the removable vessel. 
     A new 3D metal object printer reduces the time required for filling the ejector of a MHD printer without damage to the heated chamber. The 3D metal object printer includes an ejector head having a removable vessel with a receptacle within the movable vessel, a heater configured to heat the removable vessel while the removable vessel is in the ejector head to a temperature sufficient to melt solid metal within the receptacle of the removable vessel, a platform positioned opposite the ejector head, at least one actuator operatively connected to at least one of the platform and the ejector head, the at least one actuator being configured to move the at least one of the platform and the ejector head relative to one another, and a controller operatively connected to the heater, the ejector head, and the at least one actuator. The controller is configured to operate the heater to melt solid metal within the receptacle of the removable vessel, operate the ejector head to eject drops of melted metal toward the platform, and operate the at least one actuator to move the ejector head and the platform relative to one another while the ejector head is ejecting melted metal drops toward the platform. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing aspects and other features of a method of operating a 3D metal object printer and a new 3D metal object printer with a new removable vessel configured for receiving a metal insert that reduces the time required for filling the ejector of a MHD printer without damage to the heated chamber are explained in the following description, taken in connection with the accompanying drawings. 
         FIG. 1  depicts a new 3D metal object printer that reduces the time required for filling the ejector of a MHD printer without damage to the heated chamber. 
         FIG. 2A  is a side view of a two part removable vessel used in the 3D metal object printer of  FIG. 1  with the metal insert used in the removable vessel to reduce the time required for filling the ejector of a MHD printer without damage to the heated chamber. 
         FIG. 2B  is a side view depicting the metal insert after one end of the insert has been installed into an upper housing of the removable vessel shown in  FIG. 2A . 
         FIG. 2C  is a side view of the assembled removable vessel with the installed metal insert. 
         FIG. 2D  is an end view of the assembled removable vessel with the installed metal insert. 
         FIG. 2E  is a cross-sectional view of an alternative embodiment of a single piece removable vessel for use with the printer of  FIG. 1 . 
         FIG. 3  is a side view of the metal insert for use with the two piece embodiment of the removable vessel shown in  FIG. 2A  to  FIG. 2D . 
         FIG. 4  is a flow diagram for a process that uses the removable vessel and metal insert of the 3D metal object printer of  FIG. 1  to fill the removable vessel with melted metal during the start-up process for the 3D metal object printer. 
         FIG. 5  is a flow diagram for a process that reconditions the removable vessel of  FIG. 2A . 
         FIG. 6A  is an illustration of a thermal reconditioning station that can be used in the process of  FIG. 5 . 
         FIG. 6B  is an illustration of a chemical reconditioning station that can be used in the process of  FIG. 5 . 
         FIG. 6C  is an illustration of an abrasive reconditioning station that can be used in the process of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     For a general understanding of the environment for the 3D metal object printer and its operation as disclosed herein as well as the details for the printer and its operation, reference is made to the drawings. In the drawings, like reference numerals designate like elements. 
       FIG. 1  illustrates an embodiment of a new 3D metal object printer  100  that reduces the time required for filling the ejector of a MHD printer without damage to the heated chamber of the ejector head. In the printer of  FIG. 1 , drops of melted bulk metal are ejected from a removable vessel  104  having a single nozzle  108  and drops from the nozzle form swaths for layers of an object on a platform  112 . As used in this document, the term “removable vessel” means a hollow container having a receptacle configured to hold a liquid or solid substance and the container as a whole is configured for installation and removal in a 3D metal object printer. As used in this document, the term “bulk metal” means conductive metal available in aggregate form, such as wire of a commonly available gauge or pellets of macro-sized proportions. A source of bulk metal  116 , such as metal wire  120 , is fed into a wire guide  124  that extends through the upper housing  122  in the ejector head  140  and melted in the removable vessel  104  to provide melted metal for ejection from the nozzle  108  through an orifice  110  in a baseplate  114  of the ejector head  140 . As used in this document, the term “nozzle” means an orifice in a removable vessel configured for the expulsion of melted metal drops from the receptacle within the removable vessel. As used in this document, the term “ejector head” means the housing and components of a 3D metal object printer that melt, eject, and regulate the ejection of melted metal drops for the production of metal objects. The level of the volume of melted metal in the removable vessel  104  is maintained at the upper level  118  of the removable vessel. The removable vessel  104  slides into the heater  160  so the inside diameter of the heater contacts the removable vessel and can heat solid metal within the receptacle of the removable vessel to a temperature sufficient to melt the solid metal. As used in this document, the term “solid metal” means a metal as defined by the periodic chart of elements or alloys formed with these metals in solid rather than liquid or gaseous form. The heater is separated from the removable vessel to form a volume between the heater and the removable vessel  104 . An inert gas supply  128  provides a pressure regulated source of an inert gas, such as argon, to the ejector head through a gas supply tube  132 . The gas flows through the volume between the heater and the removable vessel and exits the ejector head around the nozzle  108  and the orifice  110  in the baseplate  114 . This flow of inert gas proximate to the nozzle insulates the ejected drops of melted metal from the ambient air at the baseplate  114  to prevent the formation of metal oxide during the flight of the ejected drops. 
     The ejector head  140  is movably mounted within z-axis tracks for vertical movement of the ejector head with respect to the platform  112 . One or more actuators  144  are operatively connected to the ejector head  140  to move the ejector head along a Z-axis and are operatively connected to the platform  112  to move the platform in an X-Y plane beneath the ejector head  140 . The actuators  144  are operated by a controller  148  to maintain an appropriate distance between the orifice  110  in the baseplate  114  of the ejector head  140  and an uppermost surface of an object on the platform  112 . 
     Moving the platform  112  in the X-Y plane as drops of molten metal are ejected toward the platform  112  forms a swath of melted metal drops on the object being formed. Controller  148  also operates actuators  144  to adjust the vertical distance between the ejector head  140  and the most recently formed layer on the substrate to facilitate formation of other structures on the object. While the molten metal 3D object printer  100  is depicted in  FIG. 1  as being operated in a vertical orientation, other alternative orientations can be employed. Also, while the embodiment shown in  FIG. 1  has a platform that moves in an X-Y plane and the ejector head moves along the Z axis, other arrangements are possible. For example, the actuators  144  can be configured to move the ejector head  140  in the X-Y plane and along the Z axis or they can be configured to move the platform  112  in both the X-Y plane and Z-axis. 
     The controller  148  can be implemented with one or more general or specialized programmable processors that execute programmed instructions. The instructions and data required to perform the programmed functions can be stored in memory associated with the processors or controllers. The processors, their memories, and interface circuitry configure the controllers to perform the operations previously described as well as those described below. These components can be provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits can be implemented with a separate processor or multiple circuits can be implemented on the same processor. Alternatively, the circuits can be implemented with discrete components or circuits provided in very large scale integrated (VLSI) circuits. Also, the circuits described herein can be implemented with a combination of processors, ASICs, discrete components, or VLSI circuits. During metal object formation, image data for a structure to be produced are sent to the processor or processors for controller  148  from either a scanning system or an online or work station connection for processing and generation of the signals that operate the components of the printer  100  to form an object on the platform  112 . 
     Among these components are the switches  152 . One switch  152  can be selectively operated to provide electrical power from source  156  to the heater  160 , while another switch  152  can be operated to provide electrical power from another electrical source  156  to the coil  164  for generation of the electrical field that ejects a drop from the nozzle  108 . Because the heater  160  generates a great deal of heat at high temperatures, the coil  164  is positioned within a chamber  168  formed by one (circular) or more walls (rectilinear shapes) of the ejector head  140 . As used in this document, the term “chamber” means a volume contained within one or more walls in which a heater, a coil, and a removable vessel of a 3D metal object printer are located. The removable vessel  104  and the heater  160  are located within this chamber. The chamber is fluidically connected to a fluid source  172  through a pump  176  and also fluidically connected to a heat exchanger  180 . As used in this document, the term “fluid source” refers to a container of a liquid having properties useful for absorbing heat. The heat exchanger  180  is connected through a return to the fluid source  172 . Fluid from the source  172  flows through the chamber to absorb heat from the coil  164  and the fluid carries the absorbed heat through the exchanger  180 , where the heat is removed by known methods. The cooled fluid is returned to the fluid source  172  for further use in maintaining the temperature of the coil in an appropriate operational range. 
     The controller  148  of the 3D metal object printer  100  requires data from external sources to control the printer for metal object manufacture. In general, a three-dimensional model or other digital data model of the object to be formed is stored in a memory operatively connected to the controller  148 , the controller can access through a server or the like a remote database in which the digital data model is stored, or a computer-readable medium in which the digital data model is stored can be selectively coupled to the controller  148  for access. This three-dimensional model or other digital data model is processed by a slicer implemented with the controller to generate machine-ready instructions for execution by the controller  148  in a known manner to operate the components of the printer  100  and form the metal object corresponding to the model. The generation of the machine-ready instructions can include the production of intermediate models, such as when a CAD model of the device is converted into an STL data model, or other polygonal mesh or other intermediate representation, which can in turn be processed to generate machine instructions, such as g-code, for fabrication of the device by the printer. As used in this document, the term “machine-ready instructions” means computer language commands that are executed by a computer, microprocessor, or controller to operate components of a 3D metal object additive manufacturing system to form metal objects on the platform  112 . The controller  148  executes the machine-ready instructions to control the ejection of the melted metal drops from the nozzle  108 , the positioning of the platform  112 , as well as maintaining the distance between the orifice  110  and the uppermost layer of the object on the platform  112 . 
       FIG. 2A  is a side view of the removable vessel  104  of the printer  100 . This embodiment of the removable vessel  104  is of two piece construction that includes an upper housing  204  and a lower housing  208 . As used in this document, the term “housing” means a structure having a portion of a receptacle within it and that is configured to be secured to another structure to form a removable vessel. The lower housing  208  includes the nozzle  108  (shown in  FIG. 1 ). Upper housing  204  is longer than lower housing  208  and includes a collar  228  having an external circumference that is equal to the external circumference of lower housing  208 . The opening of the lower housing  208  that is opposite the nozzle in the lower housing  208  has a flange that extends from the opening and that has a circumference that is less than the circumference of the interior circumference of the collar  228 . Collar  228  has an instep that is recessed from the end of the upper housing  204  that is secured to the lower housing  208  by a distance that corresponds to the distance the flange of the lower housing extends from the lower housing. Thus, the flange of the lower housing slides within the collar  228  until it contacts the instep of the upper housing  204  to fit within the internal circumference of the collar  228 . When the upper housing  204  and the lower housing  208  are assembled, they form a receptacle having a shape that corresponds to the metal insert  212 . Metal insert  212  is a solid piece of metal having an elongated and rounded stem  216  and a bulbous portion  220  that terminates in a pointed end that fits within the nozzle  108 . As used in this document, the term “elongated” means structure that is longer than it is wide and the term “rounded” means structure that has at least a partial cylindrical shape. As used in this document, the term “bulbous” means structure having a conical shape along at least a portion of its longitudinal axis. Upper housing  204  also is formed with a guiding flange  224 . This flange fits within a groove in the ejector head  140  to orient the removable vessel  104  correctly within the printer  100  and hold the vessel in its correct orientation after the vessel is installed in the ejector head  140 . 
     The upper housing  204  is formed with boron nitride and the lower housing  208  is formed with graphite. Both of these materials are high temperature ceramics. In one embodiment, the upper and lower housings are heated to temperatures in the range of about 800° C. to about 850° C. for periods of eight hours or longer. The receptacle within the removable vessel  104  can be coated with suitable anti-oxidant retardant materials that help attenuate the formation of oxides on the metal insert. As used in this document, the term “anti-oxidant retardant” means any material that attenuates the formation of a metal oxide on the type of metal placed in the receptacle of the removable vessel. The boron nitride forming the upper housing is not electrically conductive so it does not interfere with the generation of the electric fields used to eject melted metal drops from the receptacle through the nozzle  108  and the orifice  110 . The overall dimensions of the assembled removable vessel are 55 mm with the length of the upper housing being 40 mm and the length of the lower housing being 15 mm. The circumference of the upper housing at the collar  228  is about 50 mm with a diameter of about 16 mm and the circumference at the widest portion of the lower housing is about 50 mm with a diameter of about 16 mm. 
     Prior to installation in the ejector head  140  of the printer  100 , the metal insert  212  is loaded into the removable vessel  104 . This is done by either pushing the stem  216  of the insert  212  into the portion of the receptacle in the upper housing  204  ( FIG. 2B ) or by pushing the pointed end of the bulbous portion  220  into the lower housing. A few spots of cyanoacrylate glue, sometimes more commonly known as “super glue,” are applied to either the instep of the lower housing  208  or the inner circumference of collar  228  and then the instep of the lower housing  208  is slid within the inner circumference of collar  228  to secure the lower housing and upper housing together as shown in  FIG. 2C . This glue is removed by the heat applied from the heater  160  during operation of the printer so the two housings can be separated for printer maintenance. As shown in  FIG. 2D , the stem  216  is visible through an opening in the upper housing. This opening is opposite the wire guide  124  to receive wire  120  once the metal insert  212  has been melted in the removable vessel  104 . Inert gas source  128  is coupled to the upper housing to supply insert gas to the receptacle within the removable vessel so the environment within the removable vessel does not cause the melted metal within the receptacle of the vessel to oxidize. A thermocouple (not shown) is placed in the opening  232  to provide a signal indicative of the heat in the removable vessel so the controller can regulate the operation of the heater  160 . 
       FIG. 2E  is a cross-sectional view of an alternative embodiment of the removable vessel. This vessel  104  is an integral structure. That is, the vessel has a single housing with a nozzle at one end and an open end at the other. To fill this embodiment, the metal insert  216  is comprised of pelletized solid metal or solid metal powder, which is poured through the opening that receives the wire. In a similarly manner, the embodiment of the removable vessel  104  shown in  FIG. 2A  to  FIG. 2D  can be assembled first and then pelletized solid metal or solid metal powder poured through the opening in the upper housing to fill the vessel. The guiding flange  224  slides within a mounting groove in the ejector head  140  to orient the removable vessel during installation and to maintain that orientation in the printer. 
     As noted in the description of the removable vessel presented above with regard to  FIG. 2A  to  FIG. 2D , the metal insert  212  is a solid piece of metal having an elongated and rounded stem  216  and a bulbous portion  220  that terminates in a pointed end that fits within the nozzle  108 . After the metal insert is manufactured, it is stored in a container  222  as shown in  FIG. 3 . The container  222  is sealed with a lid  226  having a self-sealing hole that is connected to a vacuum  230  so air can be removed from the container before shipping. Removal of the air helps impede the formation of oxide on the solid metal. As the conduit connecting the vacuum to the interior of the container  22  is removed, the self-sealing hole closes to retain the vacuum in the container. The metal insert  212  is dimensioned to slide easily into the receptacle formed by the upper and lower housings. Thus, for the embodiment described above, the length of the stem  216  from the junction with the bulbous portion  220  to the end of the stem is 32 mm and the circumference of the stem is 8.5 mm, which narrows slightly towards its end so the stem fits easily in the horizontal cross-sectional area of the receptacle in the upper housing. The circumference of the bulbous portion near the junction with the stem  216  is about 37.7 mm with a diameter of about 12 mm and the length of the bulbous portion from the junction with the stem to the pointed end is 19 mm. In some embodiments, the metal insert is coated with various coatings to impede oxidation, such as paraffin wax or the like. The metal insert is made of solid metal, such as bulk aluminum or other known metals that can be used in metal drop ejecting printers. 
     A process for operating a material deposition 3D object printer to reduce the time required to prepare a removable vessel for printing operations is shown in  FIG. 4 . In the description of the process, statements that the process is performing some task or function refers to a controller or general purpose processor executing programmed instructions stored in non-transitory computer readable storage media operatively connected to the controller or processor to manipulate data or to operate one or more components in the printer to perform the task or function. The controller  148  noted above can be such a controller or processor. Alternatively, the controller can be implemented with more than one processor and associated circuitry and components, each of which is configured to form one or more tasks or functions described herein. Additionally, the steps of the method may be performed in any feasible chronological order, regardless of the order shown in the figures or the order in which the processing is described. 
       FIG. 4  is a flow diagram for a process  400  that uses the removable vessel and metal insert in the 3D metal object printer of  FIG. 1  to fill the removable vessel with melted metal during the start-up process for the 3D metal object printer. The process begins with the removal of the removable vessel  104  from a 3D metal object printer that has been taken offline and allowed to cool (block  404 ). The removable vessel is filled with solid metal. When the removable vessel is the single piece construction embodiment (block  408 ), then the vessel is filled by pouring solid metal pellets or solid metal powder through the opening in the end of the vessel into which the bulk wire is later inserted (block  412 ). In the two piece embodiment of the removable vessel, the vessel is separated into its two parts (block  416 ) and the metal insert is removed from its container that impedes the formation of oxide (block  420 ). The elongated and rounded end of the metal insert is placed in the upper housing of the vessel (block  424 ) and then the bulbous end is inserted in the lower housing (block  428 ). The upper and lower housings are then secured to one another (block  432 ). Alternatively, the two piece embodiment can be filled with metal powder or metal pellets if the housings remained secured to one another. Once the removable vessel is filled with solid metal, it is installed within the heater in the 3D metal object printer (block  436 ) and the printer is closed (block  440 ). The heater is activated to bring the removable vessel to a temperature that melts the solid metal so the vessel is filled with melted metal (block  444 ) and the bulk metal wire is inserted into the wire guide so the end of the wire from the wire supply can be positioned within the melted metal in the removable vessel (block  448 ). The printer can then resume operations for producing metal objects (block  452 ). 
     From time to time, when the vessel is removed from a printer, the vessel needs to be reconditioned. Reconditioning the two-piece removable vessel, as used in this document, means the lower housing is replaced and the upper housing is swabbed with a cleaning solvent to remove hardened aluminum from the chamber within the upper housing. A method of reconditioning a single piece removable vessel is shown in  FIG. 5 . The process  500  begins with the vessel or at least the lower housing of the single piece embodiment of the vessel being placed within one of the reconditioning stations (block  504 ) shown in  FIG. 6A ,  FIG. 6B , or  FIG. 6C . The conditioning station is then operated to remove the solidified metal drops from the external surface of the nozzle (block  508 ). When the removal is complete, the vessel is removed (block  512 ) and filled with solid metal as previously described (block  516 ) and then stored in a container, such as container  222 , that impedes oxide formation on the metal insert (block  520 ). 
     The conditioning station  604  shown in  FIG. 6A  thermally treats the nozzle of the removable vessel to remove the solid metal drops. In this station, a heater  608  is activated to heat the exterior of the nozzle  610  to a temperature sufficient to melt the solid metal drops. Once the drops have melted, an actuator  612  is activated to spin the platform  614  to which the vessel is secured at a speed that produces a centrifugal force that casts off the melted metal drops. The conditioning station  620  shown in  FIG. 6B  chemically treats the nozzle of the removable vessel to remove the solid metal drops. In this station, an applicator, such as a sprayer  624 , applies one or more chemicals to the external surface of the nozzle to etch or otherwise erode the solid metal drops from the nozzle. The conditioning station  630  shown in  FIG. 6C  mechanically treats the nozzle of the removable vessel to remove the solid metal drops. In this station, an actuator  634  is operated to press an abrasive tool, such as a spinning abrasive wheel  638  against the external surface of the nozzle to grind or otherwise polish the solid metal drops from the nozzle. 
     It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements may be subsequently made by those skilled in the art that are also intended to be encompassed by the following claims.