Patent Application
20230034213
This disclosure is directed to three-dimensional (3D) object printers that eject melted metal drops to form objects and, more particularly, to the vessel in which the metal is melted in such printers.
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 to construct 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 hardened 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 heated receptacle of a vessel in the printer where the solid metal is melted and the melted metal fills the receptacle. As used in this document, the term “receptacle” means a cavity within a structure that is configured to hold melted metal. The receptacle is made of non-conductive material around which an electrical wire is wrapped to form a coil. An electrical current is passed through the coil to produce an electromagnetic field that causes the meniscus of the melted metal at a nozzle of the receptacle to separate from the melted metal within the receptacle 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 (MEM) printer.
The melted metal in the receptacle of the vessel in the printer needs to be maintained at a level sufficient to support metal drop ejection operations without exhausting the supply of melted metal in the printer. In one metal drop ejecting printer a blue laser is directed to the surface level of the melted metal in the receptacle and a reflective sensor monitors the reflection of the laser by the surface level to determine the current height of the melted metal in the receptacle. When the sensor output indicates the level of the surface has dropped to a threshold position within the receptacle, the wire-feeding actuator is operated to feed more solid metal into the receptacle.
During the printing process performed by a MEM printer, the metal, which is typically aluminum and alloys, such as magnesium, form oxides as the metal is melted at the inlet to the vessel. These oxides are commonly referred to as “dross.” As used in this document, the term “dross” means a combination of materials in the vessel of a MHD printer that is unsuitable for object formation. These materials include aluminum oxide, magnesium oxide, aluminum trapped by these oxides, and gas bubbles formed during melting of the solid metal. This dross builds up in the vessel during the printing process and the amount of dross produced corresponds to the amount of metal melted in the vessel. Dross builds at the top of the melted metal in the vessel and causes issues during printing.
One issue arising from the production of dross is the adverse impact of dross on the ability of the laser level-sensor to measure the molten metal level in the vessel. The dross is dark and has a rough surface that affects the reflection of the laser and its reception at the reflective sensor. If the level is not accurately monitored, the vessel can empty during the printing process and ruin the metal object. All dross related level-sensing failures lead to a premature shutdown of the printer, removal of the dross, replacement of the vessel nozzle, and restarting of the printer. Because the printer must be shutdown to remove the dross, its time of operation is limited. This time of operation limitation means the amount of metal ejected is also limited so the number and size of the objects produced is sub-optimal. Additionally, the temperature of the melted metal cannot reach the temperatures optimal for metal drop ejection since the higher melted metal temperatures produce more dross. Finding a way to keep the dross from affecting the melted metal level sensing and extending the time for printer production would be beneficial.
A new vessel for a 3D metal object printer keeps dross produced in the vessel from interfering with the sensing of the melted metal level by the laser level sensor. The new vessel includes a wall defining a receptacle within the vessel, the receptacle having a first end and a second end, and a divider within the receptacle to separate a first portion of the receptacle from a second portion, the divider extending a distance from the first end of the receptacle that is less than a distance from the first end to the second end.
A new 3D metal object printer includes the new vessel to keep dross produced in the vessel from interfering with the sensing of the melted metal level by the laser level sensor. The new 3D metal object printer includes an ejector head that defines a receptacle configured to hold molten metal, the receptacle having a first end and a second end, and a divider within the receptacle to separate a first portion of the receptacle from a second portion, the divider extending a distance from the first end of the receptacle that is less than a distance from the first end to the second end.
A new metal insert for filling the new vessel accommodates the divider in the new vessel. The new metal insert includes an elongated portion configured to be received in a first housing of the removable vessel, a slot formed in the elongated portion of the metal insert that is configured to receive a divider within the first housing of the removable vessel, and a bulbous portion configured to be received in a second housing of the removable vessel.
The foregoing aspects and other features of a vessel for a 3D metal object printer that keeps dross produced in the vessel from interfering with the sensing of the melted metal level by the laser level sensor are explained in the following description, taken in connection with the accompanying drawings.
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.
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
A controller 148 operates the switches 152. One switch 152 can be selectively operated by the controller to provide electrical power from source 156 to the heater 160, while another switch 152 can be selectively operated by the controller 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.
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.
Using like reference numbers for like components, a new 3D metal object printer 100′ is shown in
As will be explained below with reference to
The upper housing 204 along with the divider 192 are formed with boron nitride and the lower housing 208 is formed with graphite. In some embodiments the divider 192 and the upper housing are integrally formed while in other embodiments, the divider is placed within the receptacle and attached to the wall or walls forming the receptacle. 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 (
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.
