Patent Application
20180043631
The present disclosure relates to additive manufacturing methods for printing three-dimensional (3D) parts. Additive manufacturing is generally a process in which a three-dimensional (3D) object is manufactured utilizing a computer model of the objects. The basic operation of an additive manufacturing system consists of slicing a three-dimensional computer model into thin cross sections, translating the result into two-dimensional position data, and feeding the data to control equipment which manufacture a three-dimensional structure in a layerwise manner using one or more additive manufacturing techniques. Additive manufacturing entails many different approaches to the method of fabrication, including fused deposition modeling, ink jetting, selective laser sintering, powder/binder jetting, electron-beam melting, electrophotographic imaging, and stereolithographic processes.
In extrusion-based additive manufacturing systems (also referred to as fused deposition modeling), an extruder on a print head extrudes a bead of material as the print head is moved along a tool path to form a single layer of a part. The bead of material has a height, referred to as a layer height, and a width, referred to as a road width. After depositing a layer of material, either the part is lowered or the print head is raised by an amount equal to the layer height, and the next layer of the part is extruded. Typically, both part and support materials are deposited in a like manner, such that a support structure is built underneath overhanging portions, in cavities, or otherwise supporting a part under construction. A host computer generates additional geometry acting as a support structure for the overhanging or free-space segments of the 3D part being formed. The layerwise deposition process is repeated to form a printed part resembling the digital representation.
In an electrophotographic 3D printing process, each slice of the digital representation of the 3D part and its support structure is printed or developed using an electrophotographic engine. The electrophotographic engine generally operates in accordance with 2D electrophotographic printing processes, but with a polymeric toner. The electrophotographic engine typically uses a conductive support drum that is coated with a photoconductive material layer, where latent electrostatic images are formed by electrostatic charging, followed by image-wise exposure of the photoconductive layer by an optical source. The latent electrostatic images are then moved to a developing station where the polymeric toner is applied to charged areas, or alternatively to discharged areas of the photoconductive insulator to form the layer of the polymeric toner representing a slice of the 3D part. The developed layer is transferred to a transfer medium, from which the layer is transfused to previously printed layers with heat and/or pressure to build the 3D part.
There are two competing goals when setting the layer height for an additive manufacturing system. The first is that the part should be manufactured as quickly as possible. This goal leads to the selection of the tallest possible layer height since taller layer heights require fewer total layers and thus fewer printing steps to produce the part. The second goal is to form a part with smooth surfaces that accurately reflect the model of the part being constructed. This goal leads to the selection of the shortest possible layer heights, since shorter layer heights reduce the stair-step appearance of some surfaces and allow the part to be constructed such that the part's dimensions are close to the model's dimensions. As the layer heights increase, the differences between the part's dimensions and the model's dimensions tend to increase and some surfaces on the part start to look jagged.
A method of additive manufacturing prints a part by adding layers to the part. The heights of the layers are determined by determining an orientation of at least one surface of a model of the part and setting a layer height for a layer to be added to the part based on the determined orientation of the at least one surface of the model of the part.
In a further embodiment, an additive manufacturing system includes a processor that receives a model of a part and designates different layer heights for different portions of the part based in part on orientations of surfaces of the model. The AM system prints layers of material at thicknesses based on the layer heights designated by the processor.
In a still further embodiment, an additive manufacturing system includes a processor that receives a model of a part and slices the part to form tool paths with layer heights wherein different tool paths have different layer heights based in part on orientations of surfaces of the model.
In the embodiments described below, parts are manufactured using a set of different layer heights. Before manufacturing the part, a model of the part is sliced to identify a best layer height for different portions of the model. The best layer height for a slice is selected based on how close to vertical the surfaces of the model are that intersect the slice. As noted above, it is better to have shorter layer heights for surfaces that are close to horizontal so as to reduce the stair-step or jagged appearance of the surface and it is better to have taller layer heights for vertical surfaces so as to reduce the print time. In some embodiments, to avoid having a large number of changes in the layer height, the best layer height is determined for multiple contiguous slices to form bands of slices that are assigned the same layer height. In still further embodiments, limits are applied that control how much the layer height can change between successive slices. In additional embodiments, the layer heights of one or more slices are altered to reduce the difference between the height of a key point on the part and the height of the same key point on the model.
Embodiments of the present disclosure may be used with any suitable additive manufacturing system.
In
In the shown embodiment, each consumable assembly 112 includes container portion 114, guide tube 116, and print heads 118, where each print head 118 preferably includes an extruder 120 of the present disclosure. Container portion 114 may retain a spool, coil, or other supply arrangement of a consumable filament, such as discussed in Mannella et al., U.S. Pat. Nos. 28,985,497 and 9,073,263; and in Batchelder et al., U.S. Pat. No. 9,090,428.
Guide tube 116 interconnects container portion 114 and print head 118, where a drive mechanism of print head 118 (and/or of system 110) draws successive segments of the consumable filament from container portion 114, through guide tube 116, to the extruder 120 of the print head 118. In this embodiment, guide tube 116 and print head 118 are subcomponents of consumable assembly 112, and may be interchanged to and from system 110 with each consumable assembly 112. Alternatively, as discussed below, guide tube 116 and/or print head 118 (or parts thereof) may be components of system 110, rather than subcomponents of consumable assemblies 112.
As shown, system 110 includes system housing 126, chamber 128, platen 130, platen gantry 132, head carriage 134, and head gantry 136. System housing 126 is a structural component of system 110 and may include multiple structural sub-components such as support frames, housing walls, and the like. In some embodiments, system housing 126 may include container bays configured to receive container portions 114 of consumable assemblies 112. In alternative embodiments, the container bays may be omitted to reduce the overall footprint of system 110. In these embodiments, container portions 114 may stand adjacent to system housing 126, while providing sufficient ranges of movement for guide tubes 116 and print heads 118.
Chamber 128 is an enclosed environment that contains platen 130 for printing 3D part 122 and support structure 124. Chamber 128 may be heated (e.g., with circulating heated air) to reduce the rate at which the part and support materials solidify after being extruded and deposited (e.g., to reduce distortions and curling). In alternative embodiments, chamber 128 may be omitted and/or replaced with different types of build environments. For example, 3D part 122 and support structure 124 may be built in a build environment that is open to ambient conditions or may be enclosed with alternative structures (e.g., flexible curtains).
Platen 130 is a platform on which 3D part 122 and support structure 124 are printed in a layer-by-layer manner, and is supported by platen gantry 132. In some embodiments, platen 130 may engage and support a build substrate, which may be a tray substrate as disclosed in Dunn et al., U.S. Pat. No. 7,127,309, fabricated from plastic, corrugated cardboard, or other suitable material, and may also include a flexible polymeric film or liner, painter's tape, polyimide tape (e.g., under the trademark KAPTON from E.I. du Pont de Nemours and Company, Wilmington, Del.), or other disposable fabrication for adhering deposited material onto the platen 130 or onto the build substrate. Platen gantry 132 is a gantry assembly configured to move platen 130 along (or substantially along) the vertical z-axis.
Head carriage 134 is a unit configured to receive one or more removable print heads, such as print heads 118, and is supported by head gantry 136. Examples of suitable devices for head carriage 134, and techniques for retaining print heads 118 in head carriage 134, include those disclosed in Swanson et al., U.S. Pat. Nos. 8,403,658 and 8,647,102. In some preferred embodiments, each print head 118 is configured to engage with head carriage 134 to securely retain the print head 118 in a manner that prevents or restricts movement of the print head 118 relative to head carriage 134 in the x-y build plane, but allows the print head 118 to be controllably moved out of the x-y build plane (e.g., servoed, toggled, or otherwise switched in a linear or pivoting manner).
Head gantry 136 is a belt-driven gantry assembly configured to move head carriage 134 (and the retained print heads 118) in (or substantially in) a horizontal x-y plane above chamber 128. Examples of suitable gantry assemblies for head gantry 136 include those disclosed in Comb et al., U.S. Pat. No. 9,108,360, where head gantry 136 may also support deformable baffles (not shown) that define a ceiling for chamber 128. In alternative embodiments, head gantry 136 may utilize any suitable mechanism for moving head carriage 134 (and the retained print heads 118), such as robotic actuators, and the like.
In a further alternative embodiment, platen 130 may be configured to move in the horizontal x-y plane within chamber 128, and head carriage 134 (and print heads 118) may be configured to move along the z-axis. Other similar arrangements may also be used such that one or both of platen 130 and print heads 118 are moveable relative to each other. Platen 130 and head carriage 134 (and print heads 118) may also be oriented along different axes. For example, platen 130 may be oriented vertically and print heads 118 may print 3D part 122 and support structure 124 along the x-axis or the y-axis. In another example, platen 130 and/or head carriage 134 (and print heads 118) may be moved relative to each other in a non-Cartesian coordinate system, such as in a polar coordinate system.
Additional examples of suitable devices for print heads 118, and the connections between print heads 118, head carriage 134, and head gantry 136 include those disclosed in Crump et al., U.S. Pat. No. 5,503,785; Swanson et al., U.S. Pat. No. 6,004,124; LaBossiere, et al., U.S. Pat. Nos. 7,384,255 and 7,604,470; Batchelder et al., U.S. Pat. Nos. 7,896,209 and 7,897,074; and Comb et al., U.S. Pat. No. 8,153,182. For instance, extruder 120 may optionally be retrofitted into an existing additive manufacturing system.
System 110 also includes controller assembly 138, which is one or more computer-based systems configured to operate the components of system 110. Controller assembly 138 may communicate over communication line(s) 140 with the various components of system 110, such as print heads 118 (including extruder 120), chamber 128 (e.g., with a heating unit for chamber 128), head carriage 134, motors for platen gantry 132 and head gantry 136, and various sensors, calibration devices, display devices, and/or user input devices.
Additionally, controller assembly 138 may also communicate over communication line 142 with external devices, such as computing device 150 over a network connection (e.g., a local area network (LAN) connection, a universal serial bus (USB) connection, or the like). While communication lines 140 and 142 are each illustrated as a single signal line, they may each include one or more electrical, optical, and/or wireless signal lines and intermediate control circuits, where portions of communication line(s) 140 may also be subcomponents of the removable print heads 118.
In some embodiments, computing device 150 and controller assembly 138 are internal to system 110, allowing a user to operate system 110 over a network communication line 142, in the same or similar manner as a two-dimensional printer. Alternatively, computing device 150 may be one or more external computer-based systems (e.g., desktop, laptop, server-based, cloud-based, tablet, mobile media device, and the like) that may communicate with the internal computer-based system(s) of controller assembly 138.
In accordance with one embodiment, computing device 150 provides a set of tool paths with layer heights 152 to controller assembly 138. During a printing operation, controller assembly 138 may direct platen gantry 132 to move platen 130 to a predetermined height within chamber 128 based on the height of the next layer in tool paths 152. Controller assembly 138 may then direct head gantry 136 to move head carriage 134 (and the retained print heads 118) around in the horizontal x-y plane above chamber 128 along the tool path 152 for the layer. Controller assembly 138 may also command print heads 118 to selectively draw successive segments of the consumable filaments from container portions 114 and through guide tubes 116, respectively.
The successive segments of each consumable filament are then melted in the extruder 120 of the respective print head 118 to produce a molten material. Upon exiting extruder 120, the resulting extrudate may be deposited onto platen 130 as a series of roads for printing 3D part 122 or support structure 124 in a layer-by-layer manner. After the print operation is complete, the resulting 3D part 122 and support structure 124 may be removed from chamber 128, and support structure 124 may be removed from 3D part 122. 3D part 122 may then undergo one or more additional post-processing steps, as desired.
In step 300 of
At step 302, a sampling interval or height is selected. The sampling interval is a vertical interval between horizontal sampling planes that are used to sample surfaces of the model to determine a best layer height for the surfaces. Such sampling is discussed further below. In step 302, the sampling interval is selected such that each of the selected usable layer heights is an integer multiple of the sampling interval. For example, in
At step 304, a band height is set such as band height 420 of
At step 306, a maximum change in layer height between layers is set. For example, the maximum layer height can be set to 0.003 inch, meaning that the layer height could change from 0.007 inch to 0.010 inch between successive layers but could not change from 0.007 inch to 0.013 inch or from 0.013 inch to 0.007 inch between successive layers.
Returning to the method of
At step 204, a list of height key points 160 is received. Because extrusion-based additive manufacturing systems build parts from discrete layers, it can be difficult to build the parts to the exact dimensions found in the model. For example, the overall height of the built part may be different from the overall height of the model because the top of the model falls in the middle of a layer rather than at the top of a layer. As a result, the built part will either be slightly larger than the model or slightly smaller than the model. The height key points in list 160 are points in the model that the designer wants the built part to match as much as possible. Thus, the part designer wants the part to be built such that the heights of the key points on the part are as close to the heights of those points on the model as possible. For example, the top of the model can be in the list of key points such that the overall height of the built part is as close as possible to the overall height of the model. By building the part so that the built key points are as close as possible to the model key points, it is possible to construct a “near net” part, which is a part that requires very little post-print processing to achieve the desired size and shape for the part.
At step 206, a band of 3-D model 158 is selected. In most embodiments, the first band that is selected begins at the bottom of 3-D model 158 and extends upward by the band height amount set at step 200 and stored in layer height parameters 154. The process then continues at step 208 where a best layer height for the band is determined based on the polygons of the 3-D model that are within the band.
In step 500, a bottommost sampling plane in the band is selected and at step 502, all polygons on the model that are intersected by the sampling plane are identified. For example, in
At step 504, one of the polygons intersected by the selected sampling plane is selected and at step 506 the orientation of the surface of the polygon is determined. In one particular embodiment, the orientation is determined by determining an angle between the polygon's outwardly facing normal and a horizontal component of that normal. For example, if polygon 624 is selected at step 504, angle 660 between normal 662 and the horizontal component 664 of normal 662 is determined at step 506. At step 508, the method determines if more polygons intersected by the selected sampling plane need to be processed. If so, the method returns to step 504 to select a new polygon intersected by the sampling plane selected at step 500 and step 506 is repeated for the new polygon.
When an orientation has been determined for each of the polygons intersected by the selected sampling plane at step 508, the process continues at step 510 where a representative orientation is determined from those orientations. In the various embodiments, the representative orientation can be any one of an average of all of the orientations, a segment length-weighted average orientation; a median of all of the orientations, and a largest or smallest orientation, for example. The segment-length weighted orientation weights each orientation by the relative length of the segment formed by the intersection of the sampling plane with the polygon, where the length is relative to total length of all segments formed by the intersection of the sampling plane with the model.
At step 512, a best layer height for the selected sampling plane is determined using the representative orientation. In some embodiments, each of the usable layer heights is associated with a range of representative orientations. For example, a smallest layer height can be assigned to representative orientations where the angle between the normal and the horizontal component of the normal is between 90° and 78°, an intermediate layer height can be assigned to representative orientation where that angle is between 57° and 78° and the largest layer height can be assigned to orientations where that angle is between 0° and 57°.
At step 514, the method determines if there are more sampling planes to be processed in the band. If there are more sampling planes, the process returns to step 500 to select the next sampling plane above the current sampling plane in the band and steps 502-512 are repeated for the next sample.
When a best layer height has been identified for each sampling plane in the band at step 514, a limited-span voting method is used to identify a filtered layer height for each sampling plane at step 516. In the limited-span voting, each sampling plane in the band is selected in turn. For each sampling plane, the layer heights for a number of sampling planes, S, above and below the sampling planes are retrieved. In accordance with one embodiment, the number of sampling planes S is half the number of sampling planes in the band. The layer height that is found most often in this limited span of sampling planes is then assigned as the filtered layer height for the selected sampling plane. If there are fewer than S sampling planes above or below the selected sampling plane, only the existing sampling planes participate in the vote. The limited-span voting of step 516 is not performed in all embodiments.
At step 518, a voting method is used to select the best layer height for the band. In particular, for each layer height, the number of sampling planes that were assigned that layer height at step 516 (or step 512 if step 516 is not performed) is determined and the layer height assigned to the largest number of sampling planes is selected as the best layer height for the band.
Returning to
At step 212, the heights of one or more layers in the band are altered in order to better align a top of a layer with a key point in height key points 160. For example, in
In a second example shown in
After the height of one or more layers have been adjusted at step 212, the process of
At step 216, the process determines if the top of the model has been reached. If the top of the model has not been reached, the process continues at step 218 where the best layer height for the next layer is determined. In accordance with one embodiment, the best layer height for the next layer is determined using the process of
When the top of the model is reached at step 216, the process ends at step 224.
The first band selected by step 206 of the process of
Band 918 spans two surfaces 913 and 920, which have different normals 912 and 922. The angle between normal 912 and horizontal component 914 of normal 912 is in the upper range while the angle between normal 922 and its horizontal component is zero degrees. Based on the voting performed by the different sampling planes across the band, the shortest layer height is identified as the best layer height for band 918 at step 208. However, since the top layer of band 902 is the largest layer height and the difference between the largest layer height and the smallest layer height exceeds the maximum allowed change in layer heights, the layer height for band 918 is set to the intermediate layer height 916 at step 210.
After the layer height has been selected for band 918, the process of
At step 216, the process of
The process then returns to step 216 where the process determines that the top of the model has not been reached and the best layer height for a next layer 946 is determined at step 218. For layer 946, the best layer height is a small layer height 948. Since this layer height is different from the layer height of layer 936, the process returns to step 206 to select band 950, which includes layer 946. The best layer height for band 950 is then identified at step 208 as small layer height 948. Since small layer height 948 differs from layer height 916 of layer 936 by less than the maximum allowed change in layer heights, small layer height 948 is selected as the layer height for band 950 at step 212.
Embodiments of the present invention can be applied in the context of computer systems other than computing device 10. Other appropriate computer systems include handheld devices, multi-processor systems, various consumer electronic devices, mainframe computers, and the like. Those skilled in the art will also appreciate that embodiments can also be applied within computer systems wherein tasks are performed by remote processing devices that are linked through a communications network (e.g., communication utilizing Internet or web-based software systems). For example, program modules may be located in either local or remote memory storage devices or simultaneously in both local and remote memory storage devices. Similarly, any storage of data associated with embodiments of the present invention may be accomplished utilizing either local or remote storage devices, or simultaneously utilizing both local and remote storage devices.
Computing device 10 further includes an optional hard disc drive 24, an optional external memory device 28, and an optional optical disc drive 30. External memory device 28 can include an external disc drive or solid state memory that may be attached to computing device 10 through an interface such as Universal Serial Bus interface 34, which is connected to system bus 16. Optical disc drive 30 can illustratively be utilized for reading data from (or writing data to) optical media, such as a CD-ROM disc 32. Hard disc drive 24 and optical disc drive 30 are connected to the system bus 16 by a hard disc drive interface 32 and an optical disc drive interface 36, respectively. The drives and external memory devices and their associated computer-readable media provide nonvolatile storage media for the computing device 10 on which computer-executable instructions and computer-readable data structures may be stored. Other types of media that are readable by a computer may also be used in the exemplary operation environment.
A number of program modules may be stored in the drives and RAM 20, including an operating system 38, one or more application programs 40, other program modules 42 and program data 44. In particular, application programs 40 can include programs for implementing slicing module 156, for example. Program data 44 may include data such as data in layer height parameters 154, 3-D model 158, height key points 160 and toolpaths with layer heights 152, for example.
Processing unit 12, also referred to as a processor, executes programs in system memory 14 and solid state memory 25 to perform the methods described above.
Input devices including a keyboard 63 and a mouse 65 are optionally connected to system bus 16 through an Input/Output interface 46 that is coupled to system bus 16. Monitor or display 48 is connected to the system bus 16 through a video adapter 50 and provides graphical images to users. Other peripheral output devices (e.g., speakers or printers) could also be included but have not been illustrated. In accordance with some embodiments, monitor 48 comprises a touch screen that both displays input and provides locations on the screen where the user is contacting the screen.
The computing device 10 may operate in a network environment utilizing connections to one or more remote computers, such as a remote computer 52. The remote computer 52 may be a server, a router, a peer device, or other common network node. Remote computer 52 may include many or all of the features and elements described in relation to computing device 10, although only a memory storage device 54 has been illustrated in
The computing device 10 is connected to the LAN 56 through a network interface 60. The computing device 10 is also connected to WAN 58 and includes a modem 62 for establishing communications over the WAN 58. The modem 62, which may be internal or external, is connected to the system bus 16 via the I/O interface 46.
In a networked environment, program modules depicted relative to the computing device 10, or portions thereof, may be stored in the remote memory storage device 54. For example, application programs may be stored utilizing memory storage device 54. In addition, data associated with an application program may illustratively be stored within memory storage device 54. It will be appreciated that the network connections shown in
Suitable 3D printers or additive manufacturing systems for printing 3D parts according to the methods of the embodiments include any suitable additive manufacturing technology or 3D printing system that may benefit from the embodiments, such as those based on extrusion-based techniques, ink jetting, selective laser sintering, powder/binder jetting, electron-beam melting, digital light processing (DLP), stereolithography, direct laser metal sintering, electrophotographic and electrostatographic processes. Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.
