3D printing system with mixing device

Abstract

A three-dimensional (3D) printing system (2) is configured to fabricate a three-dimensional 3D article (4) in a layer-by-layer manner. The 3D printing system includes a resin container (6), a tank agitation subsystem (12), a fabrication subsystem (33), and a controller (34). The resin container (6) is configured to contain a photocurable resin (8) and has a lower region within a distance H from a lower surface (10) of the resin container. The agitation subsystem includes (a) a grating (14) disposed within the lower region of the resin container, and (b) an agitation movement mechanism (16) coupled to the grating (14). The fabrication subsystem (33) is configured to form the 3D article (4) by layer-by-layer selective curing of the photocurable resin (8). The controller (36) is configured to operate the agitation movement mechanism (16) to vibrate the grating (14) along a lateral Y-axis to remix filler particles in the photocurable resin (8).

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This non-provisional patent application claims priority to U.S. Provisional Patent Application No. 63 / 215,160, filed June 25, 2021, by Andrew Enslow et al., entitled "3D Printing System with Agitation Device," which is incorporated herein by reference under 35 U.S.C. 119(e). [Technical Field]

[0002] The present disclosure relates to an apparatus and method for the digital fabrication of three-dimensional (3D) articles by layer-by-layer solidification of liquid photocurable build materials. More particularly, the present disclosure relates to a 3D printing system having an apparatus for reducing settling of particulate or fibrous fillers in photocurable build materials. [Background technology]

[0003] 3D printing systems are widely used for product prototyping and manufacturing. One type of 3D printing system utilizes a process called stereolithography. A typical stereolithography system utilizes a resin container, an imaging system, and a build plate within a liquid photocurable resin held by the resin container. Three-dimensional (3D) articles are fabricated layer-by-layer by selectively imaging and solidifying layers of the photocurable resin onto the build plate. Summary of the Invention [Problem to be solved by the invention]

[0004] Photocurable resins with fillers can present particular challenges: the fillers can settle over time, which can lead to variations in the amount of filler present in the resin and can cause defects. [Means for solving the problem]

[0005] In one aspect of the present disclosure, a three-dimensional (3D) printing system is configured to fabricate a three-dimensional 3D article layer-by-layer. In a fabrication mode, the 3D printing system forms a vertical stack of multiple layers by selectively polymerizing individual layers. The 3D printing system includes a resin container, a tank agitation subsystem, a fabrication subsystem, and a controller. The resin container is configured to contain a photocurable resin and has a lower region within a distance H from a bottom surface of the resin container. The agitation subsystem includes (a) a grate disposed within the lower region of the resin container and (b) an agitation movement mechanism coupled to the grate. The fabrication subsystem is configured to form a 3D article by selectively curing the photocurable resin layer-by-layer. The controller is configured to operate the agitation movement mechanism to vibrate the grate along a lateral Y-axis to remix filler particles within the photocurable resin. When the controller operates the fabrication subsystem, no portion of the fabrication subsystem enters the lower region of the resin container. This agitation subsystem includes a grid that generally matches the geometry of the lower sub-region, thereby very efficiently remixing the filler particulates while minimizing unmixed pockets.

[0006] In one implementation, the grid includes a plurality of slats spaced or aligned along a transverse Y-axis and having planes that define an oblique angle with respect to the Y-axis. The oblique angle can be in the range of 30 to 80 degrees. To maximize remixing efficiency, the oblique angle is greater than 45 degrees.

[0007] In another implementation, the grid includes a plurality of slats spaced or aligned along a transverse Y-axis, each slat having a compound bend geometry. The compound bend geometry includes a bend between two planes, including an upper plane and a lower plane. The upper plane defines an upper angle with respect to the Y-axis. The lower plane defines a lower angle with respect to the Y-axis. The lower angle is greater than the upper angle to improve mixing efficiency. The compound geometry improves the bending strength of the slats.

[0008] In yet another implementation, the grating includes a plurality of slats spaced or arranged along a transverse Y-axis, with the slat spacing along the Y-axis equal to S. The grating vibrates with an amplitude along the Y-axis equal to A. A may be at least 125% of S, and may be approximately equal to 150% of S.

[0009] In further implementations, the vibration has a frequency of at least 100 cycles per minute or in the range of 100-200 cycles per minute. Other frequency ranges are possible depending on the rheological properties of the photocurable resin.

[0010] In a further implementation, the lattice is represented by the equation: Y(t)=A * cos(ω * The grating is vibrated along the transverse Y-axis according to a frequency (t + δ). In this equation, t is time in seconds, and Y(t) is the position of the grating along the transverse Y-axis. A is the amplitude of vibration. The term "cos" is a cosine function with arguments in parentheses. The term ω is an angular frequency equal to 2πν. The term ν is the oscillation frequency, which may correspond to or be equal to the motor rotation frequency. The term δ is a constant determined by the initial rotational position of the grating within the range of vibration along the Y-axis. The value of A can be greater than the spacing S between the grating slats. In one exemplary embodiment, A is at least 125% of the slat spacing S, or about 1.5 times S. In a particular exemplary embodiment, S is about 40 millimeters, and A is about 60 millimeters. In an exemplary embodiment, ν is at least about 100 revolutions per minute (RPM) or in the range of 150-200 RPM.

[0011] In another implementation, the lattice includes a pair of elongated bars extending along the Y-axis. A plurality of slats are fixedly attached between the pair of elongated bars. The fixed attachment can be achieved using welding or screws. Alternatively, the lattice with integral elongated bars and slats can be formed using 3D printing.

[0012] In yet another implementation, the grid includes a pair of elongated bars extending along the Y axis. The slats are rotatably mounted between the pair of elongated bars. Each slat can include a pin extending from the end of the slat into the elongated bar along the X axis. The slats rotate individually around the pin, thus rotating around an axis parallel to the X axis. The slats can also include tabs or other features that limit rotation to optimize the angular orientation of the slats. Other variations are possible, such as slats that rotate around an axis oblique to the Y axis. [Brief explanation of the drawings]

[0013] [Figure 1] Schematic of a three-dimensional (3D) printing system for manufacturing or creating 3D articles. [Figure 2] Isometric view of part of a 3D printing system [Figure 3A] Isometric view of the tank agitation subsystem in isolation [Figure 3B] Side view of the tank agitation subsystem in isolation [Figure 4] Isometric view of part of a 3D printing system [Figure 5A] FIG. 1 is an end view of a first embodiment of a slat forming part of a grille; [Figure 5B] FIG. 10 is an end view of a second embodiment of a slat forming part of a lattice; DETAILED DESCRIPTION OF THE INVENTION

[0014] FIG. 1 is a schematic diagram of a three-dimensional (3D) printing system 2 for manufacturing a 3D article 4. In describing the system 2, mutually orthogonal axes X, Y, and Z are utilized, alternatively referred to as the X-, Y-, and Z-axes. Axes X and Y are generally horizontal horizontal axes. The Z-axis is a vertical axis generally aligned with a gravity reference. The term "generally" means that the direction or magnitude is not necessarily precise, but is by design. Thus, the term "generally horizontal" means horizontal (perpendicular to the gravity vector) within design and manufacturing tolerances. The term "generally aligned" means aligned within design and manufacturing tolerances.

[0015] The 3D printing system 2 includes a resin container 6 for containing a photocurable resin 8. In the illustrated embodiment, the photocurable resin 8 includes, among other things, a monomer, a catalyst, and a filler. The catalyst allows the resin 8 to solidify and harden through the application of radiation, such as blue, violet, or ultraviolet radiation, typically having a wavelength less than 450 nm (nanometers). The filler typically includes insoluble fibers or particulates having a density greater than the bulk density of the resin. The purpose of the filler may be to enhance the mechanical, thermal, and / or visual properties of the 3D article 4. Over time, the filler tends to settle downward, and the filler content of the photocurable resin increases in the -Z direction toward the bottom surface 10 of the resin container 6. Eventually, the particles clump together and become impossible to remix.

[0016] System 2 includes a tank agitation subsystem 12 that further includes a grate 14 coupled to an agitation movement mechanism 16. In the illustrated embodiment, grate 14 covers a generally rectangular lateral area and is confined to a lower region of vessel 6 that is within height H of bottom surface 10. The generally rectangular grate 14 is sized and configured to efficiently agitate photocurable resin 8 within vessel 6. In operation, agitation movement mechanism 16 is configured to move grate 14 in an oscillatory (reciprocating) motion having an amplitude A and a frequency v. In the exemplary embodiment, the oscillatory motion is sinusoidal.

[0017] System 2 includes a build plate 18 having an upper surface 20 on which the 3D article 4 is formed. A build plate support structure 22 supports the build plate 18. A vertical movement mechanism 24 is operable to vertically position the build plate support structure 22, and thereby the build plate 18. In one embodiment, the vertical movement mechanism 24 includes a stationary motor coupled to a lead screw. The build plate support structure 22 includes a threaded bearing that receives the lead screw. As the motor rotates the lead screw, the build plate support structure 22 is translated up and down.

[0018] System 2 includes a material coating subsystem 26 configured to apply a thin layer of resin to the top surface 20 of build plate 18 or 3D article 4. In one embodiment, material coating subsystem 26 includes a rubber wiper that translates along the lateral Y-axis. Material coating subsystem 26 can include a lateral movement mechanism, such as a lead screw (which can operate similarly to the vertical movement mechanism) or a motor-driven belt, that provides movement and positioning of the wiper along Y.

[0019] System 2 includes an imaging subsystem 28 for selectively curing a layer of photocurable resin 8 in a build plane 30. In the illustrated embodiment, imaging system 28 generates a radiation beam 32 that scans along build plane 30. Imaging system 28 includes a laser that generates radiation beam 32 and a pair of galvanometer mirrors for scanning the radiation beam across build plane 30 along X and Y. Build plate 18, build plate support structure 22, vertical translation mechanism 24, material coating subsystem 26, and imaging subsystem 28 are collectively referred to as a fabrication subsystem 33.

[0020] The controller 34 includes a processor 36 coupled to a non-volatile or non-transitory information storage device 38. The processor 36 may alternatively be referred to as a processing unit (PU) or a central processing unit (CPU), as known in the art of computing technology. The non-transitory information storage device 38 may include one or more of flash memory and other mass storage devices, such as a magnetic disk drive, both of which are known in the art of computing technology.

[0021] The storage device 38 stores the software instructions. The controller 34 is configured to operate the tank agitation subsystem 12 and the fabrication system 33 (although perhaps not both simultaneously) when the processor 36 executes the software instructions. In one embodiment, the controller operates the tank agitation subsystem 12 (vibrating the grating 14) when the fabrication subsystem 33 is idle (not operating to fabricate the 3D article 4; perhaps except for the vertical movement mechanism 24). The controller operates the fabrication subsystem 33 when the tank agitation subsystem 12 is idle (possibly except for the vertical movement mechanism 24). In a further embodiment, the tank agitation subsystem 12 can include the vertical movement mechanism 24.

[0022] In one embodiment, controller 34 operates tank agitation subsystem 12 in the following manner: (a) controller 34 operates agitation movement mechanism 16 to vibrate grating 14 along the Y-axis with amplitude A and periodicity T or frequency v; (b) controller 34 operates vertical movement mechanism 24 to raise and lower build plate 18 within photocurable resin 8 simultaneously with (a). Material coating subsystem 26 and imaging subsystem 28 are inactive while tank agitation subsystem 12 is operating.

[0023] In one embodiment, the controller 34 operates the fabrication subsystem 33 in the following manner: (a) the controller 34 operates the vertical movement mechanism to position the top surface 20 (of the build plate 18 or a previously imaged portion of the 3D article 4) proximate to the build plane 30, (b) the controller 34 operates the coating subsystem 26 to form a new layer of photocurable resin on the top surface 20, (c) the controller operates the imaging subsystem 28 to selectively cure and solidify the new layer of photocurable resin, and repeats (a)-(c) to complete the fabrication of the 3D article 4. During fabrication, the plate support structure 22 does not enter the lower region of the resin reservoir 6.

[0024] FIG. 2 is an isometric view of a portion of a three-dimensional (3D) printing system 2. Some features have been omitted. The resin container 6 has a generally rectangular cross-section. In the illustrated embodiment, the vertical movement mechanism 24 includes a motor coupled to a vertical lead screw. The lead screw threads into a portion of the build plate support structure 22. Rotation of the motor raises or lowers the build plate support structure 22, depending on the direction of motor rotation.

[0025] 3A and 3B are isometric and side views illustrating an isolated embodiment of the tank agitation subsystem 12. The rectangular grid 14 includes two elongated bars 40 extending along the Y axis that support a plurality of slats 42 therebetween. The slats 42 each have a major axis along the X axis and are aligned along the Y axis. In an alternative embodiment, the slats can each have a major axis that defines an oblique angle with respect to the X and Y axes.

[0026] In a first embodiment, the slats 42 are fixedly attached to the two elongated bars 40. The slats 42 can be welded to the elongated bars 40 or attached to the elongated bars 40 with a number of screws. Alternatively, the combination of the elongated bars 40 and the slats 42 can be 3D printed as one integral unit.

[0027] In a second embodiment, the slats 42 are rotatably mounted to the two elongated bars 40. The rotational mounting of the slats 42 may include pins extending from the ends of the slats 42 into the elongated bars 40 along the X axis. The mounting may also include tabs or other features that limit the rotation of the slats 42 relative to the elongated bars 40 to optimize the effectiveness of the slats 42 in stirring and mixing the photocurable resin 8.

[0028] The agitation movement mechanism 16 includes a motor 44 connected to four support bars 46 by linkages 48. When the motor rotates 360 degrees, the rectangular grating 14 vibrates back and forth along the Y axis with amplitude A. When the motor is rotated at a frequency v, the grating vibrates back and forth sinusoidally along the Y axis with frequency v.

[0029] 4 is an isometric cross-sectional view of a portion of system 2 including vessel 6 in which a portion of tank agitation subsystem 12 is installed. As shown, support bars 46 extend vertically along the inside edge of wall 50 to rectangular grid 14.

[0030] FIG. 5A is an end view of a first embodiment of slats 42 as seen or viewed along the X-axis. Slats 42 are generally planar or parallelepiped in shape. The major axis of slats 42 is along X, and the slat planes define an oblique angle with respect to the transverse Y-axis. In the illustrated embodiment, the angle is approximately 60 degrees. However, the angle with respect to the Y-axis can vary from 30 to 80 degrees, or 30 to 70 degrees, or 30 to 60 degrees. To maximize mixing efficiency, the angle is greater than 45 degrees or in the range of 45 to 80 degrees.

[0031] Figure 5B is similar to Figure 5A, except that slat 42 is a composite slat 42. Slat 42 includes two planar surfaces (52 and 54) separated by a bend 56. Having bend 56 makes slat 42 stiffer, thus allowing for the use of thinner material.

[0032] The two flat surfaces (52 and 54) include an upper flat surface 52 that defines an upper oblique angle relative to the Y axis and a lower flat surface 54 that defines a lower oblique angle relative to the Y axis. In the illustrated embodiment, the lower oblique angle is greater than the upper oblique angle. This upper and lower oblique angle relationship improves the mixing efficiency of the grating 14. In the illustrated embodiment, the upper oblique angle is approximately 45 degrees and the lower oblique angle is approximately 60 degrees.

[0033] The slat spacing is S and the slat height is h. In an exemplary embodiment, the slat height h is about 20 millimeters. Generally, to provide sufficient mixing, the height h is preferably greater than 15 millimeters. Values ​​of h greater than 20 millimeters are better for mixing, but at the expense of the grid 14 occupying a larger volume of the vessel 8.

[0034] The vibration of the grating 14 is along Y and preferably has an amplitude A greater than S to ensure sufficient agitating fluid motion. Preferably, A is at least 125% of S, or about 150% of S. In an exemplary embodiment, the parameters include: h is approximately equal to 20 millimeters, S is approximately equal to 40 millimeters, and A is approximately equal to 60 millimeters.

[0035] The frequency v is at least about 100 revolutions per minute (RPM) or in the range of 150-200 RPM. One revolution is equivalent to moving the grating 14 back and forth along the Y axis by a distance A (amplitude).

[0036] The particular embodiments and applications described above are intended to be illustrative only and do not exclude modifications and variations encompassed by the following claims.

Claims

1. 1. A three-dimensional (3D) printing system for manufacturing a 3D article, comprising: a container configured to contain a photocurable resin and having a lower region within a distance H from a bottom surface of the container; a tank agitation subsystem including a grate disposed within the lower region and an agitation movement mechanism coupled to the grate; a fabrication subsystem configured to form the 3D article by layer-by-layer selective curing of the photocurable resin; and a controller configured to operate the agitation movement mechanism to vibrate the grating along a Y-axis and remix the filler particles within the photocurable resin. A three-dimensional (3D) printing system comprising:

2. The three-dimensional (3D) printing system of claim 1 , wherein the grating includes a plurality of slats spaced along a Y-axis.

3. 3. The three-dimensional (3D) printing system of claim 2, wherein each of the plurality of slats has at least one planar surface that defines an oblique angle with respect to the Y-axis, the oblique angle having a magnitude within a range of 30 to 80 degrees.

4. 3. The three-dimensional (3D) printing system of claim 2, wherein the slats have a defined slat spacing therebetween, and wherein the lattice vibrations along the Y-axis have an amplitude greater than the slat spacing.

5. The three-dimensional (3D) printing system of claim 4 , wherein the amplitude is at least 125% of the slat spacing.

6. 3. The three-dimensional (3D) printing system of claim 2, wherein the slats extend over a vertical height greater than 15 millimeters.

7. The three-dimensional (3D) printing system of claim 2 , wherein each of the slats has a bend between two generally planar surfaces, including an upper planar surface and a lower planar surface.

8. 8. The three-dimensional (3D) printing system of claim 7, wherein the upper plane defines an upper angle with respect to the Y axis and the lower plane defines a lower angle with respect to the Y axis, the lower angle being greater than the upper angle.

9. 10. The three-dimensional (3D) printing system of claim 1, wherein the grating includes a pair of elongated bars extending along the Y-axis and a plurality of slats fixedly mounted between the pair of elongated bars.

10. 10. The three-dimensional (3D) printing system of claim 1, wherein the grating includes a pair of elongated bars extending along a Y-axis and a plurality of slats rotatably mounted between the pair of elongated bars.

11. The three-dimensional (3D) printing system of claim 1 , wherein the vibration has a frequency of at least 100 cycles per minute.

12. 1. A method of operating a 3D printing system, comprising: a container configured to contain a photocurable resin and having a lower region within a distance H from a bottom surface of the container; a tank agitation subsystem including a grate disposed within the lower region and an agitation movement mechanism coupled to the grate; a fabrication subsystem configured to form a 3D article by layer-by-layer curing of the photocurable resin. and activating the agitation mechanism to vibrate the grating along the Y axis to remix the filler particles within the photocurable resin. A method comprising:

13. The method of claim 12, wherein the grid includes a plurality of slats spaced along the Y axis.

14. 14. The method of claim 13, wherein each of the plurality of slats has at least one planar surface that defines an oblique angle with respect to the Y axis, the oblique angle having a magnitude within a range of 30 to 80 degrees.

15. 14. The method of claim 13, wherein the vibration of the grating along the Y-axis has an amplitude greater than the spacing of the slats.

16. 14. The method of claim 13, wherein the slats extend over a vertical height of greater than 15 millimeters.

17. 14. The method of claim 13, wherein each of the slats has a bend between two generally planes including an upper plane and a lower plane.

18. 14. The method of claim 13, wherein an upper portion defines an upper angle relative to the Y axis and a lower portion defines a lower angle relative to the Y axis, the lower angle being greater than the upper angle.

19. 14. The method of claim 13, wherein the slats individually define major axes along axes X perpendicular to the Y axis.

20. 13. The method of claim 12, wherein the vibration has a frequency of at least 100 cycles per minute.

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