Patent Application
20160339519
The embodiments relate generally to additive manufacturing processes, and in particular to in-process monitoring of powder bed additive manufacturing.
Additive manufacturing (AM) is a workpiece manufacturing process by which a workpiece is manufactured one layer at a time. AM has certain advantages over traditional manufacturing techniques, including less wasted material and reduced labor costs.
There are several different types of AM processes, including, for example, powder bed processes, material deposition processes, and three-dimensional (3D) printing processes. Powder bed processes involve a heating apparatus, such as a laser or electron beam, that fuses a powder, such as stainless steel, cobalt-chrome alloys, or titanium alloys, for example, in accordance with a slice plot one layer at a time to form a workpiece.
AM has some disadvantages. AM may take substantially longer to generate a workpiece than conventional forging, stamping, or molding techniques. It may take hours to generate a single workpiece. Further, because of the need for specialized and relatively expensive AM tools, such as a powder bed, AM may not be suitable for mass production of workpieces. Moreover, AM does not always result in perfect workpieces. In the context of powder bed AM, a few potentially problematic areas are the powder itself, the recoater arm used to recoat the workpiece with an additional layer of powder, the heating apparatus, and the heating apparatus scanning mechanism.
Another disadvantage of AM is that it is difficult or impractical to inspect the workpiece prior to completion. Thus, after a workpiece is completed, the workpiece may be inspected only to determine that shortly after the AM process began, the scanning mechanism was incorrectly aligned, resulting in a misshaped workpiece that must be discarded. This results in material waste and perhaps worse, a substantial reduction in manufacturing throughput.
It may also be very difficult or impossible to properly inspect a workpiece after the workpiece has been completely manufactured, due to the geometry of the part, the thickness of the portions of the workpiece, or other reasons. Thus, a workpiece may have a latent defect that is not detected in a post-manufacturing process and may be installed on a machine only to subsequently fail due to an inability to properly inspect the workpiece.
The embodiments relate to in-process powder bed additive manufacturing (AM). Generally, multiple eddy current sensor arrays are utilized during the AM process such that various aspects of the AM process are continually monitored while the workpiece is being manufactured. The eddy current sensor arrays may include one or more of a defect detection eddy current sensor array, a workpiece edge detection eddy current sensor array, and a powder condition eddy current sensor array. Each eddy current sensor array generates signals as the eddy current sensor array is moved with respect to the powder bed. The signals are continually processed and analyzed, and, if it is determined that a quality problem exists, such as a quality of the powder in the powder bed, a quality of a material layer of the workpiece, or a quality of an edge location of an edge of the workpiece, the AM process may be modified in real-time to correct the problem, an alert may be provided to an operator, and/or the AM process may be halted.
In one embodiment, a powder bed sensing system is provided. The powder bed sensing system includes a defect detection eddy current sensor array that is configured to be movably coupled with respect to a powder bed and that generates a first plurality of sensor signals while moving over a workpiece in the powder bed. The powder bed sensing system also includes a workpiece edge detection eddy current sensor array that is configured to be movably coupled with respect to the powder bed and that generates a second plurality of sensor signals while moving over the workpiece in the powder bed. The powder bed sensing system also includes a controller that is coupled to the defect detection eddy current sensor array and the workpiece edge detection eddy current sensor array. The controller is configured to determine, based on the first plurality of sensor signals, a workpiece material layer quality of a current material layer of the workpiece. The controller is further configured to determine, based on the second plurality of sensor signals, a workpiece edge location quality of the current material layer of the workpiece. The controller initiates an action based on at least one of the workpiece material layer quality and the workpiece edge location quality.
In one embodiment, the action includes initiating the addition of a next material layer.
In one embodiment, the action includes generating an alert and presenting the alert on a display device.
In one embodiment, the action includes adjusting a path of a heating apparatus on a next material layer cycle.
In one embodiment, adjusting the path of the heating apparatus on the next material layer cycle includes altering slice data that identifies locations in the powder bed of a next material layer.
In one embodiment, the action includes adjusting an operating parameter of a heating apparatus, such as a power level of a laser or a scan rate of the laser.
In one embodiment, the powder bed sensing system includes a powder condition eddy current sensor array that is configured to be movably coupled with respect to the powder bed and that generates a third plurality of sensor signals while moving over the powder bed. The controller is further configured to determine, based on the third plurality of sensor signals, a powder quality of powder in the powder bed.
In one embodiment, the powder quality indicates a powder defect, and an alert is generated that identifies the powder defect.
In one embodiment, the defect comprises an inconsistent density of the powder or a void in the powder.
In one embodiment, the controller is configured to determine, based on the first plurality of sensor signals, that the workpiece material layer quality of the current material layer of the workpiece is defective. The workpiece material location of a defect is determined based on the first plurality of sensor signals. A representation of the current material layer and an indication of a location on the current material layer of the defect are presented on a display device.
Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.
The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure.
The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.
Any flowcharts discussed herein are necessarily discussed in some sequence for purposes of illustration, but unless otherwise explicitly indicated, the embodiments are not limited to any particular sequence of steps. The use herein of ordinals in conjunction with an element is solely for distinguishing what might otherwise be similar or identical labels, such as “first plurality of sensor signals” and “second plurality of sensor signals,” and does not imply a priority, a type, an importance, or other attribute, unless otherwise stated herein. The term “about” used herein in conjunction with a numeric value means any value that is within a range of ten percent greater than or ten percent less than the numeric value.
The embodiments relate to in-process powder bed additive manufacturing (AM). Generally, multiple eddy current sensor arrays are utilized during the AM process such that various aspects of the AM process are continually monitored while a workpiece is being manufactured. The eddy current sensor arrays may include one or more of a defect detection eddy current sensor array, a workpiece edge detection eddy current sensor array, and a powder condition eddy current sensor array. Each eddy current sensor array generates signals as the eddy current sensor array is moved with respect to the powder bed. The signals are continually processed and analyzed, and, if it is determined that a quality problem exists, such as a quality of the powder in the powder bed, a quality of a material layer of the workpiece, or a quality of an edge location of an edge of the workpiece, the AM process may be modified in real-time to correct the problem, an alert may be provided to an operator, and/or the AM process may be halted.
A recoater arm 18 is movably coupled with respect to a back rail 20. During the AM process, the first platform 12 is raised a predetermined distance, such as 1/1000 of an inch. The recoater arm 18 moves from a start position 22 in a direction 24 across the powder bed 10 to an end position 26 to move a thin layer of the powder 16 over a second platform 28. The recoater arm 18 may then be returned to the start position 22 or remain at the end position 26, depending on the particular design of the powder bed 10. A heating apparatus 30 heats the thin layer of the powder 16 in accordance with a workpiece data file, sometimes referred to herein as slice data, that identifies, for each material layer of the workpiece 14, the precise location of the respective material layer. In one embodiment, the heating apparatus 30 comprises a laser that is configured to emit a laser beam 32 toward the powder 16 in accordance with the workpiece data file.
The laser beam 32 is scanned at a scan rate in accordance with the workpiece data file to fuse the thin layer of powder 16 and thereby form an additional material layer on the workpiece 14. If the recoater arm 18 was not previously returned to the start position 22, the recoater arm 18 is returned to the start position 22 at this time. The second platform 28 lowers a predetermined distance based on a thickness of a fused material layer of the workpiece 14, and the first platform 12 is raised a predetermined distance, and another AM cycle is initiated. In this manner, the workpiece 14 is iteratively built up layer by layer.
After the AM process is completed, the workpiece 14 may be inspected. If the workpiece 14 fails inspection, it may be necessary to discard the workpiece 14 and generate a new workpiece 14, resulting in reduced throughput, material wastage, and time.
The DDECSA 36, in one embodiment, comprises a plurality of differential probes 48, each differential probe 48 comprising a plurality of coils. In some embodiments, each differential probe 48 may comprise two coils, wound in opposition to one another. The DDECSA 36 may comprise any desired resolution of differential probes 48, such as four differential probes 48 per inch, more than four differential probes 48 per inch, or fewer than four differential probes 48 per inch. As the DDECSA 36 moves over the workpiece 14, the DDECSA 36 generates a first plurality of sensor signals. The first plurality of sensor signals may be continuously communicated to the controller 38 as the DDECSA 36 moves over the workpiece 14. In one embodiment, the first plurality of sensor signals comprises a plurality of differential signals that identify differences between the coils in the plurality of differential probes 48. Based on the first plurality of sensor signals, the controller 38 is configured to determine a workpiece material layer quality of a current material layer of the workpiece 14. The phrase “current material layer” is used herein to refer to the most recent material layer formed on the workpiece 14. The workpiece material layer quality may indicate that no defect has been detected or may indicate that a defect has been detected.
The powder bed sensing system 34 also includes a workpiece edge detection eddy current sensor array (WEDECSA) 50 that is movably coupled with respect to the powder bed 10. In one embodiment, the WEDECSA 50 also comprises a plurality of differential probes 52, each differential probe 52 comprising a plurality of coils. In some embodiments, each differential probe 52 may comprise two coils, wound in opposition to one another. As the WEDECSA 50 moves over the workpiece 14, the WEDECSA 50 generates a second plurality of sensor signals. The second plurality of sensor signals is communicated to the controller 38. Based on the second plurality of sensor signals, the controller 38 is configured to determine a workpiece edge location quality of the current material layer of the workpiece 14. The workpiece edge location quality relates to the accuracy of the edges of the current material layer of the workpiece 14 with respect to the slice data 44 and/or a previous material layer of the workpiece 14. Thus, the workpiece edge location quality may indicate that the actual edge locations of the current material layer are within predetermined tolerances of the edge locations as specified by the slice data 44 or within predetermined tolerances of a previous material layer. Alternatively, the workpiece edge location quality may indicate that the actual edge locations of the current material layer are outside of the predetermined tolerances of the edge locations as specified by the slice data 44 or outside of the predetermined tolerances of a previous material layer.
In some embodiments, the powder bed sensing system 34 also includes a powder condition eddy current sensor array (PCECSA) 54 that is movably coupled with respect to the powder bed 10. In one embodiment, the PCECSA 54 comprises a plurality of absolute probes 56, each absolute probe 56 comprising a single coil. As the PCECSA 54 moves over the powder 16, the PCECSA 54 generates a third plurality of sensor signals. The third plurality of sensor signals is communicated to the controller 38. Based on the third plurality of sensor signals, the controller 38 is configured to determine a powder quality of the powder 16. The powder quality may indicate that the quality of the powder 16 is suitable for generation of another material layer of the workpiece 14, or the powder quality may indicate that the quality of the powder 16 is unsuitable for the generation of another material layer of the workpiece 14.
Based on the workpiece material layer quality, the workpiece edge location quality, and the powder quality, the controller 38 initiates an action. If the workpiece material layer quality indicates that no defect has been detected, the workpiece edge location quality indicates that the actual edge locations of the current material layer are within predetermined tolerances, and the powder quality indicates that the quality of the powder 16 is suitable for the generation of another material layer, the action may comprise an addition of another material layer to the workpiece 14. Thus, for each AM cycle, the powder bed sensing system 34 is configured to scan the current material layer for defects, the actual locations of the edges of the current material layer for consistency and accuracy, and the powder bed 10 for suitability in generating a subsequent material layer.
As will be discussed in greater detail herein, if the powder bed sensing system 34 determines that there are problems in any of these three areas, the controller 38 may initiate an action, such as alerting an operator to the problem, automatically altering operational characteristics of the heating apparatus 30, and the like. Thus, the powder bed sensing system 34 may improve the quality of the workpiece 14 or may simply raise an alert to an operator that a problem has occurred such that further manufacturing of the workpiece 14 is not recommended.
In other embodiments, depending on the particular defect identified, the controller 38 may determine that the particular defect is below a quality threshold, but that one or more operating parameters of the heating apparatus 30 may be altered such that the particular defect does not occur in subsequent material layers of the workpiece 14. For example, where the heating apparatus 30 comprises a laser, the controller 38 may determine that the particular defect is indicative of a laser beam of insufficient power or a laser beam of excessive power. The controller 38 may adjust a laser power operating parameter of the laser such that a laser beam of greater power, or lesser power, respectively, is utilized for subsequent material layers 64 to prevent the particular defect from further occurring.
Referring again to
In one embodiment, the controller 38 may access the slice data 44 to determine the specified locations of each edge of the workpiece 14. By comparing the edge map to the slice data 44, the controller 38 determines that an actual location 76 of an edge 78 of the workpiece 14 deviates from a specified location 80 by a distance 82. It is common that workpieces manufactured by an AM process may need post-manufacturing processing, and some edge deviation may be acceptable and not compromise the functionality of the workpiece 14. Thus, the controller 38 may compare the distance 82 to the predetermined tolerance and determine that the distance 82 is within the predetermined tolerance and that the workpiece edge location quality is satisfactory.
Alternatively, the controller 38 may compare the distance 82 to a predetermined tolerance and determine that the distance 82 is outside the predetermined tolerance and that the workpiece edge location quality is unsatisfactory. The controller 38 may then initiate an action, such as generating an alert and presenting the alert on the display device 46. Alternatively, or additionally, the controller 38 may determine that the distance 82 is not sufficient to halt the AM process but may adjust the path of the heating apparatus 30 for subsequent material layers 64 to correct for the deviation.
In one embodiment, the controller 38 may adjust the path of the heating apparatus 30 by modifying the slice data 44 to alter the locations of the edges of subsequent material layers 64 of the workpiece 14.
In another embodiment, the controller 38 may maintain a history of edge maps generated by the controller 38 for each material layer 64. The controller 38 may compare an edge map that corresponds to the current material layer 64 to the edge map that corresponds to the previous material layer 64 to determine edge location deviation. In some embodiments, the controller 38 may compare a plurality of edge maps that correspond to a plurality of successive material layers 64 to determine if the edge locations of the successive material layers 64 are drifting in a certain direction or pattern. The controller 38 may then adjust the path of the heating apparatus 30 to halt the drift, thereby preventing a relatively small incremental edge location deviation from becoming a defect that renders the workpiece 14 unusable.
Note that for purposes of illustration, the three sensor arrays, in particular the DDECSA 36, the WEDECSA 50, and the PCECSA 54, have been shown in a particular configuration, but the embodiments are not limited to any particular configuration, and the particular configuration of the three sensor arrays may differ based on the particular system. For example, the WEDECSA 50 may lead the DDECSA 36, rather than trail the DDECSA 36. Moreover, some sensor arrays may operate while moving in one direction with respect to the powder bed 10, and other sensor arrays may operate while moving in the opposite direction.
Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.
