WO2022098302A1

WO2022098302A1 - Resin circulation system for homogeneous composite additive manufacturing

Info

Publication number: WO2022098302A1
Application number: PCT/SG2021/050668
Authority: WO
Inventors: Yi Zhang; Aiwu Zhou
Original assignee: Nanyang Technological University
Priority date: 2020-11-05
Filing date: 2021-11-03
Publication date: 2022-05-12
Also published as: CN116490339A

Abstract

A circulating system for vat photopolymerization-based additive manufacturing, a kit for vat photopolymerization-based additive manufacturing, and a vat photopolymerization-based additive manufacturing system are provided. The circulating system for vat photopolymerization-based additive manufacturing includes a pump and a mixing chamber. The pump and the mixing chamber are fluidically coupled together and are configured, in operation, to be fluidically coupled to a vat of a system for the vat photopolymerization-based additive manufacturing via an inlet to the circulating system and an outlet from the circulating system.

Description

RESIN CIRCULATION SYSTEM FOR HOMOGENEOUS COMPOSITE ADDITIVE MANUFACTURING

PRIORITY CLAIM

[0001] This application claims priority from Singapore Patent Application No. 10202011029T filed on 05 November 2020.

TECHNICAL FIELD

[0002] The present invention generally relates to additive manufacturing, and more particularly relates to a resin circulation system for homogeneous composite additive manufacturing.

BACKGROUND OF THE DISCLOSURE

[0003] Additive manufacturing is a process for forming a three-dimensional object which uses data computer-aided-design (CAD) software or 3D object scanners to direct hardware to deposit material, layer upon layer, in precise geometric shapes. The material is supplied as a fine powder which can be various metals, plastics or composite materials. By contrast, when you create an object by traditional means, it is often necessary to remove material through milling, machining, carving, shaping or other means. Although the terms "3D printing" and "rapid prototyping" are applied to additive manufacturing, each process is actually a subset of additive manufacturing.

[0004] Vat polymerization, which includes stereolithography (SLA), diffusion limited aggregation (DLA), two-photon polymerization (2PP) and other similar techniques, is one of the most popular three-dimensional printing technologies. Parts are fabricated layer by layer, and each layer is a cross-section of parts built by curing liquid polymer with a light source. Particles can also be added into the resin to build composites for additional functions. However, it is difficult to distribute particles uniformly in the final parts. Existing solutions use fine nanoparticles, which greatly increases the cost and lacks certain properties of large particles. In addition, even though the particles are nanoscale particles, the particles may still precipitate during the course of printing.

[0005] Fillers-reinforced polymers have become popular in recent years due to their superior mechanical properties. In the polymer composite, the polymers form a matrix to hold the fillers while the fillers provide additional functionalities to the composite. For example, ceramic powder can be used as a filler and can increase the dielectric constant of the polymer. Also, carbon black particles and short carbon fiber can be used as a filled and can make the polymer conductive. In addition, iron oxide (Fe2Os) or neodymium (NdFeB) particles are magnetic materials, and polymers doped with these magnetic particles can respond to external magnetic fields for various actuation methods. Permanently magnetized polymers are possible as well. The most common methods to fabricate composite polymers is casting, where the fillers and liquid polymers are mixed completely before the mixture is cast into a mold. Heat treatment is usually required to accelerate the curing of such mixtures. While casting is simple, casting cannot build complex structures.

[0006] Another possible method to fabricate structures with filler-reinforced polymers is 3D printing. The basic principle is to mix the fillers or particles with raw polymer matrix in the form of powder or resin. For example, different powders may be mixed for sintering /melting in Selective Easer Sintering/ Selective Laser Melting (SLS/SLM), where the polymer binder is sprayed to bind the pre-deposited particles on the platform. [0007] Fillers can also be added to polymer resins for printing by vat polymerization.

A critical issue of this approach is to maintain filler uniformity during the course of printing, whether the fillers are particle or fiber, as the fillers tend to sink quickly in the resin under the effect of gravity. Additional chemicals may be required to maintain a uniform distribution, which may incur additional cost and introduce undesired properties.

[0008] Thus, only specific combinations of resin and particles can be chosen, and there is no common solution.

[0009] There is, therefore, a need for systems and methods for homogeneous composite additive manufacturing which overcome the drawbacks of the prior art and provide means to fabricate arbitrary structures of filler-reinforced composite polymers. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the disclosure.

SUMMARY

[0010] According to at least one aspect of the present embodiments, a circulating system for vat photopolymerization-based additive manufacturing is provided. The circulating system includes a pump and a mixing chamber. The pump and the mixing chamber are fluidically coupled together and are configured, in operation, to be fluidically coupled to a vat of a system for the vat photopolymerization-based additive manufacturing via an inlet to the circulating system and an outlet from the circulating system.

[0011] According to another aspect of the present embodiments, a kit for vat photopolymerization-based additive manufacturing is provided. The kit includes a circulating system and a composite polymer fluid for use in the circulating system for the vat photopolymerization-based additive manufacturing. The circulating system includes a pump and a mixing chamber. The pump and the mixing chamber are fluidically coupled together and are configured, in operation, to be fluidically coupled to a vat of a system for the vat photopolymerization-based additive manufacturing. The composite polymer fluid includes resin and particles having a low absorption at a wavelength of a light source used for the vat photopolymerization-based additive manufacturing.

[0012] According to a further aspect of the present embodiments, a vat photopolymerization-based additive manufacturing system is provided. The vat photopolymerization-based additive manufacturing system includes a vat photopolymerization three-dimensional printing system, a circulating system, and a composite polymer fluid for use in the vat photopolymerization-based additive manufacturing system. The vat photopolymerization three-dimensional printing system includes a resin tray and a curing light source. The circulating system includes a pump and a mixing chamber, the pump and the mixing chamber fluidically coupled together and both fluidically coupled to the resin tray. The composite polymer fluid includes resin and particles having a low absorption at a wavelength of the curing light source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to illustrate various embodiments and to explain various principles and advantages in accordance with present embodiments.

[0014] FIG. 1, comprising FIGs. 1A, IB and 1C, depicts a schematic illustration of a circulating system and its parts in accordance with present embodiments, wherein FIG. 1A depicts a schematic illustration of the circulating system, FIG. IB depicts a perspective view of input and output manifolds, and FIG. 1C depicts a perspective view of a mixing chamber.

[0015] FIG. 2, comprising FIGs. 2A and 2B, depicts perspective views of a resin tank with manifolds attached to the resin tank in accordance with the present embodiments for flowing material through the resin tank, wherein FIG. 2 A depicts a perspective view of the resin tank showing the inlet manifold and FIG. 2B depicts a perspective view of the resin tank showing the outlet manifold.

[0016] FIG. 3, comprising FIGs. 3 A and 3B, depicts perspective views of resin tanks with inlet and outlet manifolds in accordance with the present embodiments, wherein FIG. 3 A depicts the resin vat of FIGs. 2A and 2B and FIG. 3B depicts a miniaturized resin vat with printing stage.

[0017] And FIG. 4, comprising FIGs. 4A and 4B, depicts images of three-dimensional (3D) parts printed with and without the circulating system in accordance with the present embodiments, wherein FIG. 4A depicts an image of a 3D part printed with the circulating system in accordance with the present embodiments and FIG. 4B depicts an image of a 3D part printed without the circulating system.

[0018] Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been depicted to scale. DETAILED DESCRIPTION

[0019] The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description. It is the intent of present embodiments to present methods and systems that fabricate structures of filler- reinforced composite polymers based on vat polymerization with recirculating resins.

[0020] Those skilled in the art will readily understand that the methods and systems in accordance with the present embodiments are compatible with any existing vat polymerization machine and provide additional functionalities for composite materials used in the composite polymers. The methods and systems in accordance with the present embodiments enable large particles to be used for printing uniform parts and various types of particles can be used in the printing processes and, advantageously, enable provision of additional functionalities for the composite.

[0021] The systems in accordance with the present embodiments present a plug-and- play resin circulating system compatible with most existing vat polymerization 3D printers. The recirculation system advantageously keeps the resin-particle and/or resinfibre mixture running to maintain uniformity. Notably, large and dense particles can be used to print the parts while no additional chemicals are required to adjust the density and viscosity of the resin.

[0022] Referring to FIG. 1A, a schematic illustration 100 depicts a circulating system for vat photopolymerization-based additive manufacturing in accordance with the present embodiments which includes a peristaltic pump 102 and a mixing chamber 104. The peristaltic pump 102 and the mixing chamber 104 are fluidically coupled together and, during operation, are configured to couple to a vat of the system for vat photopolymerization-based additive manufacturing, such as a resin tray 112, by an inlet to the circulating system and an outlet from the circulating system, such as manifolds 106, 108, respectively. The peristaltic pump 102 is used to recirculate the mixture in the circulating system and through the resin tray 112 in the direction of arrows 114a, 114b, 114c, 114d. From the pump 102, the mixture flows 114a to the mixing chamber 104 and then flows 114b to the outlet manifold 106 from the circulating system into the resin tray 112. After flowing 114c through the resin tray 112, the mixture re-enters the circulating system through the inlet manifold 108 and then flows 114d back to the pump 102. Those skilled in the art will realize that the placement of the pump 102 and the mixing chamber 104 can be in any order (i.e., either before or after one another) so long as they are fluidically coupled.

[0023] Referring to FIG. IB, bifurcating channels 130a, 130b, 130c, 130d of the manifolds 106, 108 ensure uniform flow rate through all nozzles, so that the flow speed is steady when passing through the resin tray of the printing area. An example of the enclosed mixing chamber 104 is depicted in a perspective view 150 in FIG. 1C. The mixing chamber 104 is attached to a rocker arm 152 such that the mixing chamber 104 can rotate freely at one end of the rocker arm 152. A motor 154 makes the mixing chamber move in a circular motion to generate a strong vortex in the mixing chamber 104 to mix the incoming resin and particles thoroughly. The continuous recirculation and mixing ensure that the particles do not sink to the bottom of the resin tray 112 and that the particle/resin mixture is homogenous.

[0024] If the flow rate within the circulating system is too low, particles may precipitate. And, if the flow rate is too high, the resin may flush away the layer that is being printed. Therefore, in accordance with the present embodiments, the flow rate within the circulating system is carefully controlled by a control device (not shown) coupled to the pump 102. Alternatively, the pump 102 may be periodically turned on and off. For example, the pump may be turned on to keep the particles and resins well mixed when as the printing stage lifts (or lowers) and turned off when the layer is being printed.

[0025] In accordance with the present embodiments, a primer layer with no added fillers may be printed on the stage to promote the adhesion of the filler-reinforced material to the stage for upside-down vat polymerization.

[0026] Various particles can be added into the resin for printing as long as the particles should have a low absorption at the wavelength range of the light source. Spectrum analysis and sinking speed evaluation of the mixtures are necessary for vat-based polymerization by this method. In addition, an ideal magnetic particle for magnetic particles in accordance with the present embodiments has a composition of SrFenOig, which has a low absorption at 405nm as compared to other commonly used magnetic particles such as iron (II, III) oxide (FC3O4 and neodymium magnet (NdFeB).

[0027] In accordance with the present embodiments, the recirculating system can be integrated into any vat photopolymerization 3D printing system without any system modifications. Users just need to select manifolds 106, 108 having dimensions corresponding to the resin tray 112 such that the manifolds 106, 108 fit into the resin tray 112. Referring to FIGs. 2A and 2B, perspective views 200, 250 illustrate that the length and nozzles of the manifolds 106, 108 can be designed according to a size of the resin tray 112.

[0028] The XYZ Nobel 1.0A, manufactured by XYZ printing of Taiwan, is an example of a 3D printing system that builds parts upside-down, i.e., the platform descends into the resin tray to start printing and, after completing a layer, the platform ascends one-layer height for printing a next layer. As shown in the perspective views 200 250, the manifolds 106, 108 are designed to be hung at two opposite sides of the resin tray 112. The perspective view 200 (FIG. 2A) depicts the resin tank 112 showing the inlet manifold 108 to the recirculating system with the bifurcating channels 130a, 130b, 130c, 130d designed to pick up the resin/particle mixture from the floor of the resin tray 112. The perspective view 250 (FIG. 2B) depicts the resin tank 112 rotated 180° showing the outlet manifold 106 from the recirculating system with the bifurcating channels 130a, 130b, 130c, 130d designed to eject the resin/particle mixture near the floor of the resin tray 112.

[0029] The system in accordance with the present embodiments can be designed to operate in both continuous mode or period mode. In the continuous mode, the pump 102 is turned on all the time to keep the resin/particle mixture homogenized. The continuous mode is easy to control, but it may affect the curing process if the flow rate is too high.

[0030] In accordance with a variation of the present embodiments, an automated control system may be designed to pump the particles/resin mixture through the circulating system in a periodic mode. While the platform ascends, the tray tilts a bit for a while to level the resin in the printing area. When a position sensor detects the tilting, a first control device coupled to the 3D printing system and coupled to the control device of the circulating system (i.e., a second control device) sends a command to immediately start the pump 102 pumping and pause the printing, so that the resin/particle mixture can be homogenized in accordance with the present embodiments. The first control device and the second control device are electrically coupled together or may be the same control device. After homogenization, the control device(s) stops the pump 102 and resumes the printing (i.e., the tray returns to the original position to start printing). [0031] Particles to be mixed with the light-curing resins for vat photopolymerization in accordance with the present embodiments should have minimal interference with a light source. In the case of magnetic particles, SrFenOw particles are preferred due to their high light transmittance in suspension. When SrFenOig (3- 12pm) particles were added into the resin, a particle content from 0% to 50% was successfully printed.

[0032] Referring to FIGs. 3 A and 3B, perspective views 300, 350 depict resin vats 112, 312 in accordance with the present embodiments. The perspective view 300 depicts the resin vat 112 with the inlet manifold 106 and the outlet manifold 108 and a printing stage 305. The perspective view 350 depicts a miniaturized resin vat 312 with an integrated inlet manifold 306 and an integrated outlet 308 and a matching printing stage 310. A piece of transparent acrylic sheet 330 is glued to the mini resin vat 312 as a detachable bottom. One layer of poly dimethylsiloxane (PDMS) (not shown) is coated on the bottom of the mini resin vat 312 to facilitate the peeling off of the cured resin during printing. An adapter320 is designed to fit the mini resin vat 312 to the printer. The mini vat 312 is well suited for material development and the printing of small parts, as ~100g of composite resin is enough to fill the entire mini resin vat 312. The small size also ensures more uniform flow during circulation, which leads to better homogeneity of printed parts.

[0033] A comparison of three-dimensional parts 410, 460 printed with and without circulating system is shown in FIGs. 4A and 4B, wherein an image 400 depicts the part 410 printed with the circulating system in accordance with the present embodiments and the image 450 depicts the part 460 printed without the circulating system. The part 410 is a column (4mmx20mm) which was printed in 33 minutes with a particle content of 16.7%. The part 460 is a column where clear layer of particles can be seen, and nearly no particles exist in a top part 465 of the column. The part 410 has a totally black colour indicating a uniform distribution of particles and confirming that the circulating system works well.

[0034] The part 460 was printed by first calibrating a height of the building platform and then printing a pre-deposited layer (20*20*0.2mm³). The pre-deposited layer is kept on the building platform while it is cleaned. Then, the height of the building platform is calibrated again. The mixture in accordance with the present embodiments is then loaded into the circulating system and the pump is started. The STL file for printing is then loaded and the part 460 is printed.

[0035] Thus, it can be seen that the present embodiments provide a circulating system which can be integrated into any vat polymerization machine easily with only minor modification. In accordance with the present embodiments, the modification is mostly only to fit in the manifold, while the key parameters of the machine such as laser intensity or scanning speed can be kept unchanged. In accordance with the present embodiments, various particles of different sizes are possible and will be printed out uniformly. The flow speed and direction of the circulating system can be adjusted to accommodate different machines, particles, or resins. Accordingly, the circulating system in accordance with the present embodiments provides an easy, cheap, and flexible way of fabricating composite polymers. Therefore, those skilled in the art will realize that the circulating system in accordance with the present embodiments is compatible with any existing vat polymerization machine, advantageously enables large particles to be used for printing uniform parts such that various types of particles (e.g., large particles, dense particles, magnetic particles) can be printed, thereby providing additional functionalities for the composite.

[0036] While exemplary embodiments have been presented in the foregoing detailed description of the present embodiments, it should be appreciated that a vast number of variations exist. It should further be appreciated that the exemplary embodiments are only examples, and are not intended to limit the scope, applicability, operation, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing exemplary embodiments of the invention, it being understood that various changes may be made in the function and arrangement of steps and method of operation described in the exemplary embodiments without departing from the scope of the invention as set forth in the appended claims.

Claims

CLAIMS What is claimed is:

1. A circulating system for vat photopolymerization-based additive manufacturing, the circulating system comprising: a pump; and a mixing chamber, wherein the pump and the mixing chamber are fluidically coupled together and are configured, in operation, to be fluidically coupled to a vat of a system for the vat photopolymerization-based additive manufacturing via an inlet to the circulating system and an outlet from the circulating system.

2. The circulating system in accordance with Claim 1 further comprising: an inlet manifold; and an outlet manifold, wherein the inlet manifold and the outlet manifold are fluidically coupled to the pump and the mixing chamber, and wherein, in operation, the inlet manifold is configured to provide the inlet to the circulating system from the vat and the outlet manifold is configured to provide the outlet from the circulating system to the vat.

3. The circulating system in accordance with Claim 1 wherein the vat of the system for the vat photopolymerization-based additive manufacturing includes an integrated inlet manifold and an integrated outlet manifold, and wherein the circulating system is configured, in operation, to be fluidically coupled to the vat of the system for the vat photopolymerization-based additive manufacturing by connecting the inlet to the circulating system to the integrated inlet manifold of the vat and connecting the outlet from the circulating system to the integrated outlet manifold of the vat.

4. The circulating system in accordance with any of the preceding claims wherein the pump comprises a peristaltic pump.

5. The circulating system in accordance with Claim 2 wherein the inlet manifold comprises a plurality of bifurcating channels.

6. The circulating system in accordance with either Claim 2 or claim 5 wherein the outlet manifold comprises a plurality of bifurcating channels.

7. The circulating system in accordance with any of the preceding claims further comprising: a mixing motor; and a rocker arm, wherein the rocker arm couples the mixing chamber to the mixing motor.

8. The circulating system in accordance with Claim 7 wherein the mixing chamber rotates freely at a first end of the rocker arm and the mixer motor is coupled to a second end of the rocker arm opposite the first end, and wherein, in operation, the mixer motor is configured to move the mixing chamber in a circular motion to create a fluid vortex in the mixing chamber.

9. The circulating system in accordance with any of the preceding claims further comprising a control device coupled to the pump to control a fluid flow rate generated by the pump.

10. The circulating system in accordance with Claim 9 wherein the control device in operation is configured to control the pump to periodically turn on and turn off.

11. The circulating system in accordance with Claim 10 wherein the control device is configured to control the pump to turn off when a layer is being printed by the vat photopolymerization-based additive manufacturing system.

12. A kit for vat photopolymerization-based additive manufacturing, the kit comprising: a circulating system comprising: a pump; and a mixing chamber, wherein the pump and the mixing chamber are fluidically coupled together and are configured, in operation, to be fluidically coupled to a vat of a system for the vat photopolymerization-based additive manufacturing; and a composite polymer fluid for use in the circulating system for the vat photopolymerization-based additive manufacturing, the composite polymer fluid comprising: resin; and particles having a low absorption at a wavelength of a light source used for the vat photopolymerization-based additive manufacturing.

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13. The kit for the vat photopolymerization-based additive manufacturing in accordance with Claim 12 wherein the particles comprise magnetic particles.

14. The kit for the vat photopolymerization-based additive manufacturing in accordance with Claim 13 wherein the magnetic particles comprise one or more of SrFenOig, FcsCU, and NdFeB.

15. The kit for the vat photopolymerization-based additive manufacturing in accordance with any of Claims 12 to 14 wherein the circulating system further comprises a mixing motor coupled to the mixing chamber and configured in operation to move the mixing chamber in a circular motion to create a fluid vortex in the mixing chamber to maintain a homogenous mixture of the resin and the particles in the composite polymer fluid.

16. The kit for the vat photopolymerization-based additive manufacturing in accordance with Claim 15 wherein the circulating system further comprises a rocker arm coupled between the mixing chamber and the mixing motor, wherein the mixing chamber is configured to rotate freely at a first end of the rocker arm and the mixer motor is coupled to a second end of the rocker arm opposite the first end, and wherein, in operation, the mixer motor creates the fluid vortex in the mixing chamber by moving the rocker arm to move the mixing chamber in a circular motion.

17. A vat photopolymerization-based additive manufacturing system comprising:

-16- a vat photopolymerization three-dimensional printing system comprising: a resin tray; and a curing light source; a circulating system comprising: a pump fluidically; and a mixing chamber, wherein the pump and the mixing chamber are fluidically coupled together and are both fluidically coupled to the resin tray; and a composite polymer fluid for use in the vat photopolymerization-based additive manufacturing system, the composite polymer fluid comprising: resin; and particles having a low absorption at a wavelength of the curing light source.

18, The vat photopolymerization-based additive manufacturing system in accordance with Claim 17 wherein the circulating system further comprises: an inlet manifold; and an outlet manifold, wherein the inlet manifold and the outlet manifold are fluidically coupled to the pump, the mixing chamber and the resin tray, and wherein, in operation, the inlet manifold is configured to provide a fluid inlet to the resin tray from the circulating system and the outlet manifold is configured to provide a fluid outlet from the circulating system to the resin tray.

19. The vat photopolymerization-based additive manufacturing system in accordance with Claim 17 wherein the resin tray includes an integrated inlet manifold and an integrated outlet manifold, the circulating system connected to the integrated inlet manifold and the integrated outlet manifold and

-17- wherein, in operation, the integrated inlet manifold is configured to provide a fluid inlet to the resin tray from the circulating system and the integrated outlet manifold is configured to provide a fluid outlet from the circulating system to the resin tray.

20. The vat photopolymerization— based additive manufacturing system in accordance with any of Claims 17 to 19 wherein the particles comprise magnetic particles.

21. The vat photopolymerization-based additive manufacturing system in accordance with any of Claims 17 to 19 wherein the vat photopolymerization three- dimensional printing system further comprises: a printing stage; and a first control device, wherein the first control device is coupled to the printing stage and the curing light source to control three-dimensional printing by the vat photopolymerization three-dimensional printing system, and wherein the first control device is configured in operation to print a primer layer as a pre-deposited layer on the printing stage before three-dimensional printing by the vat photopolymerization three- dimensional printing system.

22. The vat photopolymerization-based additive manufacturing system in accordance with Claim 21 wherein the circulating system further comprises a second control device coupled to the pump and configured in operation to control fluid flow within the circulating system and the resin tray of the vat photopolymerization threedimensional printing system.

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23. The vat photopolymerization-based additive manufacturing system in accordance with Claim 22 wherein the first control device and the second control device are one of coupled together or the same control device.

24. The vat photopolymerization-based additive manufacturing system in accordance with Claim 23 wherein the second control device is configured in operation to control the pump to periodically turn off when the first control device is controlling the vat photopolymerization three-dimensional printing system is printing a layer.

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