Efficient bulk unfused powder removal system and method

An additive manufacturing system for producing a three-dimensional article includes a print engine, a post-fabrication powder removal apparatus, a transport mechanism, and a controller. The post fabrication removal apparatus includes a rotary frame defining an internal receptacle cavity, a plurality of clamps coupled to a corresponding plurality of actuators, a clamping plate coupled to a lift apparatus, and an agitation device mounted to the clamping plate. The controller is configured to perform the following steps: (1) Operate the transport mechanism to transport the build box to the internal receptacle cavity. (2) Operate the plurality of actuators to engage the build box with the plurality of clamps to secure the build box to the rotary frame. (3) Operate the rotary frame to rotate the build box until unfused powder begins to exit the build box. (4) Operate the agitation device to facilitate pouring of the unfused powder from the build box.

FIELD OF THE INVENTION

The present disclosure concerns an apparatus and method for a layer-by-layer manufacture of three dimensional (3D) articles by selectively fusing or binding powder materials. More particularly, the present disclosure concerns a de-powdering system for efficiently removing unfused or unbound powder from build boxes that are generally too large and heavy for manual handling and lifting when filled with material.

BACKGROUND

Three dimensional (3D) printing systems are in rapidly increasing use for purposes such as prototyping and manufacturing high value and/or customized articles. One type of three dimensional printer utilizes a layer-by-layer process to form a three dimensional article of manufacture from powdered materials. Each layer of powdered material is selectively fused using an energy beam such as a laser, electron, or particle beam or combined with a binder matrix. There is a desire to have large capacity systems that can fabricate physically large articles. One challenge with such systems is an efficient and safe method for a removal of unfused or unbound powder after fabrication is complete.

SUMMARY

In a first aspect of the disclosure, an additive manufacturing system for producing a three-dimensional (3D) article includes at least a print engine, a post-fabrication powder removal apparatus, a transport mechanism, and a controller. The post fabrication removal apparatus includes a rotary frame defining an internal receptacle cavity, a plurality of clamps coupled to a corresponding plurality of actuators, a clamping plate coupled to a lift apparatus, and an agitation device mounted to the clamping plate. The controller is configured to perform the following steps: (1) Operate the transport mechanism to transport the build box to the internal receptacle cavity. (2) Operate the plurality of actuators to engage the build box with the plurality of clamps to secure the build box to the rotary frame. (3) Operate the rotary frame to rotate the build box until unfused powder begins to exit the build box. (4) Operate the agitation device to facilitate pouring of the unfused powder from the build box.

The disclosed system enables efficient and fully automated bulk removal of unfused powder from the 3D article. Operation of the clamps assures a very smooth rotation of the build box. Proper clamping is particularly important for a large metal powder build box due to an enormous weight of the 3D article and unfused powder. Having the agitation device mounted directly to the clamping plate maximizes a percentage of agitation energy that is transferred through the build plate to facilitate removal of powder with the least agitation energy.

In one implementation, the print engine is configured to melt and fuse layers of the powder material using an energy beam. The energy beam can be a laser, an electron beam, or a particle beam.

In another implementation, the transport mechanism transports the build box from the print engine to a cooling station. Step (1) includes transporting the build box from the cooling station to the internal receptacle cavity of the rotary frame.

In yet another implementation, the plurality of clamps includes an upper clamp and at least one lateral clamp for clamping the build box along vertical and lateral axes during step (2). The lateral clamps can include lateral clamps that engage from opposing lateral directions. Providing clamping along multiple axes is advantageous when supporting and rotating a very heavy build box.

In a further implementation, before step (4), the lift apparatus moves the clamp plate into clamping engagement with the build plate and then moves again to extract the build plate from the powder bin. This provides a vibration isolation between the build plate and the powder bin during operation of the agitation device. Wire ropes can provide vibration isolation between the build plate and the rotary frame. The vibration isolation reduces a requirement for a vibratory power level. The vibration isolation and reduced vibratory power level reduce NVH (noise, vibration, and harshness) which is advantageous for various reasons. This reduces vibratory damage to structural components of the manufacturing system including the build box, the rotary frame, and other components of the powder removal apparatus. This also reduces vibratory energy transfer to other components of the manufacturing system such as to the print engine. The powder deposition and beam system are both sensitive to vibrations.

In a yet further implementation, during steps 1) and (2) the rotary frame is in a rotative home position of zero degrees at which an open top of the build box faces upward. During step (3) the rotary frame is rotated about 180 degrees from the home position about a central axis.

In another implementation, the rotary frame rotates back and forth along a central axis to further facilitate unfused powder removal during step (4).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG.1is a schematic block diagram of an embodiment of an additive manufacturing (AM) system2for producing a three-dimensional (3D) article100(FIG.8H). System2includes a plurality of components at least including a print engine4, a cooling station6, a bulk powder removal apparatus or station8, a fine powder removal apparatus or station10, a transport apparatus12, a gas handling system14, and a controller16. The various components4-14can individually have separate “lower level” controllers for controlling their internal functions. In some embodiments, a controller can function as a central controller.

In the following description, controller16will be considered to include all controllers that may reside externally or within the components4-14. Controller16can be internal to AM system2, external to AM system2, or include portions that are both internal and external to AM system2.

The transport apparatus12is for transporting a build box18through the various components4-10in a sequence that includes fabricating, cooling, and de-powdering a 3D article being manufactured. The gas handling system14is for controlling an environment for components4-10. In one embodiment, the gas handling system is configured to evacuate components4-10and then to backfill them with a non-oxidizing gas such as argon or nitrogen in order to maintain the build box18within a non-oxidizing environment.

Controller16includes a processor coupled to a non-transient or non-volatile information storage device which stores software instructions. When executed by the processor, the software instructions operate any or all portions of the system2. In an illustrative embodiment, fabrication, cooling, de-powdering, and other functions can be performed in a fully automated way by controller16.

Controller16is configured to perform steps such as (1) operate gas handling system14to evacuate and backfill components4-10, (2) operate print engine4to fabricate a 3D article100in build box18, (3) operate transport apparatus12to transport build box18(which now contains the 3D article and unfused powder) to the cooling station6, (4) after an appropriate cooling time, operate transport apparatus to transport build box18to build powder removal station8, (5) operate bulk powder removal apparatus8to remove most of the unfused powder from the build box18, and (6) operate transport apparatus12to transport the build box18to the fine powder removal station10. At the fine powder removal station10, residual unfused powder is removed either automatically or manually. All the while, controller16operates the gas handling system14to maintain the non-oxidizing gaseous environment within the components4-10as required.

AM system2can have other components such as an inspection station or a station for facilitating unloading of the 3D article100from the build box18. The additional components can be manually operated or under control of controller16.

FIG.2is a schematic diagram of an embodiment of a 3D print engine4. In describingFIG.2and for subsequent figures, mutually orthogonal axes X, Y and Z can be used. Axes X and Y are lateral axes that are generally horizontal. Axis Z is a vertical axis that is generally aligned with a gravitational reference. By “generally” it is intended to be so by design but may vary due to manufacturing or other tolerances.

The build box18includes a powder bin20containing a build plate22. Build plate22has an upper surface24and is mechanically coupled to a vertical positioning system26. The build box18is configured to contain dispensed metal powder (not shown). The build box18is contained within chamber28surrounded by housing30.

A metal powder dispenser32is configured to dispense layers of metal powder upon the upper surface24of the build plate22or on previously dispensed layers of metal. In the illustrated embodiment, a second powder dispenser34is configured to dispense an additional powder such as another metal or a support material. Powder dispensers32and34are configured to receive powder from powder supplies36and38respectively.

Print engine4includes a beam system40configured to generate a beam42for selectively fusing layers of dispensed metal powder. In an illustrative embodiment, the beam system40includes a plurality of high power lasers for generating radiation beams individually having an optical power layer of at least 100 watts, at least 500 watts, or about 1000 watts or more. The beam system40can include optics for individually steering the radiation beams across a build plane that is coincident with an upper surface of a layer of metal powder. In alternative embodiments, the beam system40can generate electron beams, particle beams, or a hybrid mixture of different beam types.

The controller16can be configured to operate the print engine4to fabricate a 3D article: (1) operate the vertical positioning system26to position an upper surface24of build plate26or of a previously deposited layer of powder at one powder layer thickness below a build plane, (2) operate dispenser32to dispense a layer of metal powder on the upper surface24, (3) operate the beam system to selectively fuse the just-dispensed layer of metal powder, and then repeat steps 1-3 to finish fabrication of the 3D article. The controller can also operate powder dispenser34and other components of print engine4as part of the fabrication.

FIGS.3A and3Bare isometric views of an embodiment of a build box18which includes build plate22within powder bin20. Powder bin20includes an open end44with upper clamp receivers46that extend from an end of powder bin20along the Y-axis. Powder bin20also has a pair of rails48with rollers50for transport within system2. Rails48and rollers50extend along axis Y which is a direction of transport through the system2. Y is a lateral transport direction and X is a transverse lateral direction. Four lateral clamp receivers52are at opposing ends (with respect to the Y-axis) of the powder bin20and face outwardly with respect to the X-axis.

FIG.4is an isometric view of a portion of the build box18to put emphasis on latches54for securing the build plate22to the powder bin20. The powder bin20includes four lower latches54that secure and provide a lower limit for the build plate22during the fabrication and cooling processes. The lower latches54individually have an upper surface56for engaging the build plate22. The lower latches54individually are rotatively mounted about a hinge58having an axis of rotation parallel to the Y axis.

FIG.5is an isometric view of a rotary frame60which is rotatively mounted within the bulk powder removal apparatus8. Rotary frame60is configured to be rotated about a central axis62for up to a complete 360 degree rotation. The central axis62is parallel to Y and is at an approximate center of a circular cross-section of the rotary frame60. Rotary frame60defines an internal receptacle cavity64for receiving the build box18. The build box18is received into the internal receptacle cavity64along the Y axis. The orientation of the rotary frame60illustrated inFIG.5is a rotative “home” position for rotary frame60. A rotation angle such as 90 degrees or 180 degrees refers to a clockwise rotation about central axis62from the home position.

Rotary frame60includes an upper clamp66for engaging and clamping the open end44and upper clamp receivers46of the powder bin20. Coupled between the upper clamp66and rotary frame60are actuators68for raising and lowering the upper clamp66along the vertical axis Z. Upper clamp66has an open top70to allow powder to exit at a rotation angles of about 180 degrees.

FIG.6is a cutaway isometric view of the rotary frame60. The axes X, Y, and Z have the same orientation forFIGS.5and6. Rotary frame60includes four lateral clamps72configured to extend and retract along the X-axis to engage and disengage the four lateral clamp receivers52of the powder bin20. Coupled between the lateral clamps72and the rotary frame60are actuators74for extending and retracting the lateral clamp receivers52along the X-axis.

Rotary frame60includes a clamping plate76configured to engage, clamp, and displace the build plate22. Coupled between the clamping plate76and the rotary frame60is a lift apparatus78(seeFIG.8B,8Ifor more views) for moving the clamping plate76into engagement with the build plate22and for extracting the build plate22from the powder bin20. The clamping plate76includes one or more pneumatic chucks77for gripping portion(s) of the build plate22.

FIG.7is a flowchart of an embodiment of a method80for removing bulk powder from the build box18using the bulk powder removal apparatus8. Prior to method80: (1) Print engine4fabricated a 3D article100onto the upper surface24of build plate22; unfused powder surrounds the 3D article above the upper surface and within the powder bin20. (2) The transport apparatus transported the build box18to the cooling station and time has elapsed for the contents of the build box18to cool.

According to82, the transport apparatus12transfers the build box18to the internal receptacle cavity64of the rotary frame60(direction of motion indicated by block arrow83along Y-axis).FIG.8Ais a side cutaway YZ-view andFIG.8Bis a side cutaway XZ-view of the rotary frame60containing the build box18before any of the clamps (66,72,76) have engaged portions of the build box18. Thus, clamps (66,72,76) are in their retracted state.

According to84, the actuator(s)68are retracted to lower and engage the upper clamp66with the open end44and upper clamp receivers46of the powder bin20.FIG.8Cis a side cutaway through the YZ-plane illustrating step84(direction of motion indicated by block arrows85). The upper clamp66then applies a vertical clamping force upon the build box18.

According to86, the actuators74are expanded inwardly along the X-axis to engage the lateral clamps72with the lateral clamp receivers52.FIG.8Dis an isometric cutaway view illustrating step86. After steps84and86, the build box18is clamped and restrained vertically and laterally.

According to88, the lift apparatus78raises the clamping plate76which engages and clamps the build plate22.FIG.8Eis a side cutaway view with a horizontal cut parallel to the X-plane illustrating step88. The upward motion lifts the build plate22off of lower latches54and the build plate22is clamped with at least one pneumatic chuck77(FIG.6) that is part of the clamping plate76.

According to90, the rotary frame60is rotated 180 degrees while the powder bin20and build plate22are separately clamped to the rotary frame60.FIG.8Fis a side cutaway XZ-view illustrating step90. Because the powder bin20is open at the end opposite to the build plate22, a majority of the unfused powder will then fall vertically downward and into a capturing portion of the bulk powder removal apparatus8below the rotary frame60. Also, in the inverted 180 degree position of the rotary frame60, the latches54rotate inwardly so that the build plate22can be extracted in step92.

According to92, the lift apparatus raises the clamping plate76to extract the build plate22from the powder bin20. This is an important step to provide vibration isolation of the build plate22from the powder bin20.FIG.8Gis a side cutaway XZ-view illustrating step92with lift apparatus78lifting the clamping plate76and extracting the build plate22.

FIG.8His a side schematic cutaway view illustrating isolated parts including the 3D article100with attached unfused powder coupled to the build plate22which is in turn coupled to the clamping plate76. The 3D article100has been fabricated with a clearance102between inside surfaces104of the powder bin20and the 3D article100.

FIG.8Iis an isometric view of the powder bin20, the build plate22, and the clamping plate76.FIGS.8G,8H, and8Iall correspond to step92in which the build plate22has been extracted from the powder bin20and therefore the build plate22is mechanically isolated from the powder bin20. Wire rope isolators106also mechanically couple the clamping plate76to the rotary frame60. Thus, the clamping plate76is vibration isolated from the powder bin20and from the rotary frame60. The wire rope isolators106have a higher stiffness Kcalong the X-axis and a lower stiffness Ka=0.5 Kcalong the Y-axis and a lower stiffness Kb=0.5Kcalong the Z-axis.

Two agitation devices108are mounted to the clamping plate76. In the illustrated embodiment, the agitation devices108individually contain a motor coupled to an eccentric weight. The motor has an axis of rotation aligned with the X-axis. The primary vibratory force direction is along the vertical Z axis (perpendicular to the upper surface24of the build plate). A secondary vibratory force direction is along the Y-axis which is parallel to the upper surface24.

According to94, one or both of the agitation devices108are activated to facilitate and enhance removal of the unfused powder. Because the build plate clamp is vibration isolated from the powder bin20and the rotary frame60, nearly all of the vibratory energy is transmitted and utilized for removing powder with minimal wasted energy that would otherwise vibrate the powder bin20and/or the rotary frame60.

According to96, concurrent with operating the agitation device(s)108, the rotary frame rotates back and forth from the position ofFIG.8G.FIG.8Jillustrates this rocking rotational motion about central axis62(FIG.5). This rocking motion further facilitates and enhances removal of the unfused powder. In an illustrative embodiment, the rocking motion would be about the Y axis for plus and minus 90 degrees from the position ofFIG.8G(or between 90 and 270 degrees from the position ofFIG.8B).

The specific embodiments and applications thereof described above are for illustrative purposes only and do not preclude modifications and variations encompassed by the scope of the following claims.