Metal powder fusion manufacturing with improved quality

A method of manufacturing a three-dimensional article is provided for a system including a powder handling module containing stored metal powder. The stored metal powder includes used metal powder that was previously part of the metal powder loaded into a print engine during a previous fabrication process. The method includes (1) loading a volume of the metal powder into an agitation device, (2) operating the agitation device until an avalanche angle of the metal powder is modified to within a specified range to provide a volume of usable metal powder, (3) loading the usable metal powder into a three-dimensional print engine, and (4) operating the print engine to fabricate a the three-dimensional article. This process improves coating quality within the print engine. Improving coating quality improves dimensional accuracy of the three-dimensional article along with reducing defects resulting from coating artifacts.

FIELD OF THE INVENTION

The present disclosure concerns a method of manufacturing three-dimensional metal articles using a layer-by-layer fusion of metal powder. More particularly, the present disclosure concerns a way of providing a more dimensionally accurate and defect-free way of forming metal powder layers.

BACKGROUND

Three dimensional (3D) printing systems are in rapidly increasing use for purposes such as prototyping and manufacturing. One type of three dimensional printer utilizes a layer-by-layer fusion process to form a three dimensional article of manufacture from metal powder. For each layer, a metal powder layer is formed proximate to a build plane and an energy beam such as a laser or electron beam is use to selectively fuse the layer. Once challenge with these systems are defects formed during the formation of the metal powder layers.

SUMMARY

In an aspect of the invention, a method of manufacturing a three-dimensional article is provided for a system including a powder handling module containing stored metal powder. The stored metal powder includes used metal powder that was previously part of the metal powder loaded into a print engine during a previous fabrication process. The method includes (1) loading a volume of the stored powder into an agitation device, (2) operating the agitation device until an avalanche angle of the metal powder is modified to within a specified range to provide a volume of usable metal powder, (3) loading the usable metal powder into a three-dimensional print engine, and (4) operating the print engine to fabricate the three-dimensional article. It is desirable to reduce the avalanche angle of the powder which in turn improves powder coating uniformity. Improved powder coating uniformity reduces surface defects and improves dimensional accuracy for the three-dimensional article.

In one implementation the powder handling module includes a recovered powder silo, a sieve, and a powder storage silo. The method further includes transporting used metal powder into the recovered powder silo, passing the used metal powder through the sieve to provide used and sieved metal powder, and then transporting the used and sieved metal powder into a powder storage silo. The powder storage silo then contains stored metal powder that includes the used and sieved metal powder along with metal powder that was previously in the powder storage silo. The stored metal powder can be a mixture of used and sieved metal powder and new and unused metal powder from a powder supplier.

In another implementation, the powder handling module transports powder by along a tube by entraining the metal powder in a moving inert gas. The powder handling module can include an inert gas source and a vacuum for generating motion of the inert gas for entrainment. This gas entrainment transportation can adversely increase the avalanche angle.

In yet another implementation, the agitation device includes one or more of a stirring device, an ultrasonic transducer, and a motorized vibratory device. Thus, agitation is generic for one or more of stirring or vibrating. The duration of operation is defined as a time during which the metal powder is agitated. The duration time is for one hour or more. The duration time can be equal to or greater than 3 hours, 6 hours, 9 hours, 12 hours, 18 hours, 20 hours, 24 hours, 30 hours, and 40 hours. The duration time depends upon a batch size being agitated and upon a degree to which modifying and controlling the avalanche angle is desired. A longer duration and lower intensity agitation has been found to provide a reduced and consistent avalanche angle.

In a further implementation, the specified range of the avalanche angle is within an overall range of zero to fifty degrees. The avalanche angle can be determined before, during, or after the agitation. Determination can be accomplished by directly measuring the avalanche angle or indirectly by measuring an angle of repose.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG.1is a schematic diagram depicting an embodiment of a three-dimensional printing system2for manufacturing three-dimensional articles from metal powder. This diagram is intended to depict the movement of metal powder between components of system2.

System2includes a print engine4that forms the three-dimensional articles through selective fusion of layers of the metal powder. The print engine4includes a removable powder module (RPM)6. After the print engine4is operated to form a three-dimensional article, the RPM6then contains a three-dimensional article that is surrounded by used or unfused metal powder. The term “used” metal powder is defined as metal powder that resides in and around a three-dimensional article during and after fabrication of the three-dimensional article.

The unfused metal powder8can then be transported into a powder handling module (PHM)10. In the illustrated embodiment, the PHM10includes a recovered powder silo12, a sieve14, and a powder storage silo16. The PHM also includes a gas handling system18.

The recovered powder silo12is configured to receive the used metal powder from the RPM6. The sieve14is configured to remove fused or agglomerated portions of the used powder. The powder storage silo16receives the used and sieved powder from sieve14as well as new metal powder from new powder supply20that may come directly from a metal powder manufacturer. Thus, the powder storage silo16typically stores both used and sieved powders from previous operations of the print engine4as well as new powder from a new powder supply20. New powder is defined as metal powder from a powder manufacturer that has not yet resided in a three-dimensional print engine4during fabrication of a three-dimensional article.

The gas handling system (GHS)18is used to maintain an inert or non-oxidizing atmosphere within the PHM10. The GHS18can include a source of inert gas such as nitrogen or argon, a vacuum source, controllable valves, sensors, and other features. In the illustrated embodiment, the metal powder (used, sieved, new, mixture) is transported to, from, and within the PHM by entrainment in moving inert gas. The vacuum source along with controllable valves are used to generate a velocity of the inert gas to entrain and transport the metal powder through tubes22. For some embodiments of system2, the transport of the powder can be partly or completely under a force of gravity. For example, transferring of powder between sieve14or to the removable powder module (RPM) can be partly or completely driven by a force of gravity.

As discussed supra, the powder storage silo16stores metal powder from more than one source including new and used metal powder. The stored metal powder may have an increase or variations in an avalanche angle due to effects of operation of the print engine4, recovery from the RPM6, and transport through the tubes22. The increased and/or variability in avalanche angle can adversely affect coating uniformity when the print engine4is operated.

An agitation unit24is configured to receive a volume of the stored metal powder from the powder storage silo16sufficient to at least fill an empty RPM6or to recharge a print engine4. The agitation unit24includes one or more of a stirring device, an ultrasonic device, and a motor-driven vibratory device. The agitation device24operates to reduce an avalanche angle of the metal powder and to reduce an overall range of the avalanche angle.

In an embodiment, the agitation device includes a bucket with a motorized stir bar. The gas handling system18is coupled to the bucket to maintain a non-oxidizing atmosphere in the bucket. The motorized stir bar is configured to stir the powder contained within the bucket.

A controller26is coupled to various portions of system2. Controller26can include a single physical controller or multiple controllers as desired. Controller26includes a processor coupled to an information storage device. The information storage device stores software instructions. When executed by the processor, the software instructions can operate portions of PHM10, new powder supply20, agitation unit24, and other portions of system2. As stated earlier, controller26may actually be a plurality of controllers26that are dedicated to individual portions of system2which can operate either cooperatively or independently.

FIG.2is a schematic diagram of an embodiment of a print engine4. In describing print engine4, a lateral axis X and vertical axis Z can be used. Print engine4includes an outer housing28that encloses a process chamber30. Within the process chamber30is the RPM6.

A lower portion or vessel32of the RPM6contains metal powder34. An upper portion or vessel36of RPM6contains a vertical movement actuator38coupled to a platen40. The vertical movement actuator38is configured to vertically position an upper surface42of platen40.

A powder transport43is coupled between the lower vessel32and a dispensing hopper44. The powder transport43can include one or more motorized augers that rotationally transport the powder from the lower vessel32to the dispensing hopper44. The dispensing hopper44dispenses the powder into a coater46. The coater46is configured to scan in X along a horizontal support48while depositing layers of metal powder34over or above the upper surface42. Besides scanning and depositing metal powder34layers, the coater46periodically moves to a position under the dispensing hopper44to be recharged (refilled) with metal powder34.

Above the chamber30is a beam system50for generating an energy beam52for selectively fusing deposited layers of the metal powder34. The energy beam52can be a laser beam or a particle beam. When beam52is a laser beam, optical beam power levels tend to be at least about 100 watts or more, 500 watts or more, or about 1000 watts for melting layers of metal powder34. The beam system50can be configured to generate a plurality of different energy beams52that operate in parallel to increase productivity of the print engine4.

A gas handling system54includes a vacuum pump and a supply of inert gas such as nitrogen or argon. In an illustrative embodiment, the process chamber30is shielded from a laser system50.

A controller56is coupled to various portions of the print engine4. Controller56includes a processor coupled to an information storage device. The information storage device stores software instructions. When executed by the processor, the software instructions can operate portions of the print engine4including the RPM6. Operation of the controller56can perform various operations including fabricating a three-dimensional article58in a layer-by-layer manner from powder34.

As such controller56is configured to: (1) Operate the gas handling system54to evacuate chamber30and to backfill chamber30with an inert gas (e.g., nitrogen or argon), (2) operate actuator38to position upper surface42proximate to a build plane60, (3) operate coater46to dispense a layer of powder34on upper surface42defining the build plane60, (4) operate beam system50to selectively melt and thus fuse the layer of powder dispensed to form a layer of article58, (5) repeat (2)-(4) to form additional layers of the three-dimensional article58. In repeating step (2), a top surface of the article58is positioned proximate to the build plane60. During or between steps (2)-(4), the controller56is configured to operate the coater46, dispensing hopper44, and powder transport43as needed to recharge the coater46and maintain a supply of powder34in the dispensing hopper44. After the three-dimensional article58is formed, the controller56can operate portions of the print engine4to allow the RPM6to be unloaded from the chamber30. Controller56can also monitor sensors and operate other portions of print engine4not described.

FIG.3is a flowchart of an embodiment of a method62for operating system2for manufacturing three-dimensional articles58. At least some of the method steps are performed by controller26which can include controller56.

According to64, a removable powder module (RPM)6is loaded into the print engine4. According to66, the print engine4is operated to produce the three-dimensional article58. According to68, used powder is transported from the print engine4to the powder handling module (PHM)10. According to70, the three-dimensional article58is removed from the print engine4.

According to the PHM10embodiment ofFIG.1, step68includes transporting the used powder into recovered powder silo12, passing the powder through sieve14, and transporting the now used and sieved powder into the powder storage silo16which may already include used powder from earlier fabrication processes and new powder from a new powder supply20. The combination of metal powders stored in powder storage silo16can be referred to as “stored metal powder.”

According to72, a batch of the stored metal powder from the PHM is agitated until an avalanche angle for the powder is within a specified range. As part of step72, an angle of repose or avalanche angle can be measured one or more times to find out starting values and to monitor progress.

In some embodiments, the agitation process duration is an hour or more depending upon the type of agitation employed. For some types of agitation, the duration may be 5 hours or more, 10 hours or more, 30 hours or more, or up to 40 hours.

When the agitation includes stirring of the metal powder, the stirring is effective at certain rotation rates below about 80 revolutions per minute (RPM). A stirring rotation rate of about 20 RPM for about 12 hours has been found to be effective. When the agitation includes vibration, a vibration frequency of about 600 Hertz (Hz) for 12 hours has been found to be effective. Agitation in an inert gas appears to be somewhat better than agitation in air.

Less aggressive agitation for longer times have been found to be optimal for the quality of usable metal powder. Stirring between 5 to 15 RPM for 40 hours has produced the best results but at the expensive of a longer cycle time. Tests that have been run are based on a limited range of sample sizes and materials. The optimal time and rotation rate may vary with batch size, specific metal used, and other factors.

The specified range of the avalanche angle is within an overall range of zero to 50 degrees. The specified range is likely to be narrower however based upon a type of coater46and coating process used.

The avalanche angle can be determined by direct measurement or indirectly by measuring an angle of repose. The angle of repose is approximately 2 degrees less than the avalanche angle. Methods of measuring angle of repose and avalanche angle are generally known.

According to step74—after the metal powder has been sufficiently agitated, the resultant agitated powder is loaded into an empty RPM6. Then the RPM6can be loaded into the print engine—looping back to step64.

In an alternative embodiment toFIGS.1-3, the overall system may not have an RPM. Then the metal powder would be directly transferred from the PHM to and from the print engine4. Otherwise, the agitation process (element24ofFIG.1and element72ofFIG.3) would be the same. In some embodiments, vessel32and vessel36can be separate vessels (not part of one module or RPM) and can have various locations within the print engine4.

Thus, 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.