Large-volume volumetric additive manufacturing

Abstract

A volumetric additive manufacturing system includes a vial of photopolymer resin material, a light source, and a cooling unit. The light source is configured to discharge light into the vial of photopolymer resin material and thereby solidify pre-selected portions of the photopolymer resin material. The cooling unit is configured to regulate heat generated during solidification of the photopolymer resin material upon exposure to the light from the light source. The cooling unit includes a vat of surround fluid in which the vial of photopolymer resin material is placed.

Description

LARGE- VOLUME VOLUMETRIC ADDITIVE MANUFACTURINGPRIORITY CLAIM

[0001] This application claims priority to U.S. Provisional Application No. 63 / 662,946 filed 21 lune 2024 and U.S. Provisional Application No. 63 / 694,611 filed 13 September 2024, each of which are expressly incorporated by reference herein.BACKGROUND

[0002] Volumetric Additive Manufacturing (VAM) offers speed in creating three- dimensional (3D) geometries. Computed Axial Lithography (CAL), a form of VAM, is a vat photopolymerization process that solidifies a 3D geometry within a preexisting volume of resin in one photo-exposure operation. In CAL, a light source exposes a rotating volume of resin with a computationally optimized projection set inducing gelation wherever the cumulative light dose exceeds a critical energy threshold. This process leads to fast printing times, shape fidelity, isotropic material properties, and printable geometries otherwise rendered difficult with other printing techniques. In addition, this process avoids layer-induced artifacts found in traditional 3D printing techniques. These benefits are largely enabled by the reduced degrees of freedom required to create the 3D geometry: one rotational degree of freedom verses three translational degrees of freedom used in traditional techniques.

[0003] Most research efforts have sought to increase the resolution of CAL printing to create smaller print sizes. Currently, CAL has been used in applications such as microfluidics and optics due to its ability to print fine and supportless architectures with smooth surfaces and bioprinting of living tissue because of its low light intensity, fast print times, and its flexibility to print within yield stress fluids that can suspend cells.

[0004] While there have been many efforts to increase print resolution of CAL, scaling its print volume to larger scales has not been addressed with emphasis. Increasing the printable volume would greatly expand the application space of CAL and VAM. Accordingly, an improved volumetric additive manufacturing system is desirable.SUMMARY

[0005] According to the present disclosure, a volumetric additive manufacturing system is described. The volumetric additive manufacturing system is configured to optically print a three-dimensional (3D) item. The volumetric additive manufacturing system includes a vial of photopolymer resin material, a light source, and a cooling unit. The light source is configured to discharge light into the vial of photopolymer resin material and thereby solidify pre-selected portions of the photopolymer resin material to create the 3D item.

[0006] The cooling unit is configured to regulate heat generated during solidification of the photopolymer resin material upon exposure to the light from the light source. In some embodiments, the cooling unit includes a vat of surround fluid in which the vial of photopolymer resin material is placed. In some embodiments, the surround fluid has a refractive index substantially matched with a refractive index of the photopolymer resin material.

[0007] In some embodiments, the cooling unit further includes an active cooling element configured to withdraw heat from the surround fluid and / or the photopolymer resin material during solidification of the photopolymer resin material. The active cooling element may include a cooling plate, a set of cooling plates, a cooling pipe, a recirculating pipe, a thermally regulated rod, or any combination thereof.

[0008] Additional features of the present disclosure will become apparent to those skilled in the art upon consideration of illustrative embodiments exemplifying the best mode of carrying out the disclosure as presently perceived.BRIEF DESCRIPTIONS OF THE DRAWINGS

[0009] The detailed description particularly refers to the accompanying figures in which:

[0010] Fig. 1 is a diagrammatic view of a volumetric additive manufacturing (VAM) system for use in producing a three-dimensional (3D) item, the VAM system includes a vial of photopolymer resin material, a light source that discharges light into the vial of photopolymer resin material to solidify pre-selected portions thereof, and acooling unit having a vat of surround fluid that the vial of photopolymer resin material is positioned in to regulate heat generated during solidification of the photopolymer resin material;

[0011] Fig. 2 is a perspective view of the VAM system of Fig. 1 showing that the VAM system further includes a lens located between the light source and the vial of photopolymer resin material;

[0012] Fig. 3 is an enlarged view of the vial of photopolymer resin material positioned in the vat of surround fluid of Fig. 2, the surround fluid having a refractive index substantially matched with a refractive index of the photopolymer resin material so that the light passes through the surround fluid to the photopolymer resin material;

[0013] Fig. 4 is a perspective view of the vial of photopolymer resin material positioned in the vat of surround fluid showing that the cooling unit of Fig. 1 further includes a cooling pipe that extends into the vat of surround fluid that is configured to carry secondary cooling fluid through the surround fluid and actively remove heat therefrom;

[0014] Fig. 5 is a top view of the vial of photopolymer resin material positioned in the vat of surround fluid of Fig. 4;

[0015] Fig. 6 is a perspective view of the vial of photopolymer resin material positioned in the vat of surround fluid showing that the cooling unit of Fig. 1 further includes a cooling pipe that extends into the vat of surround fluid along three side walls of the vat;

[0016] Fig. 7 is a top view of the vial of photopolymer resin material positioned in the vat of surround fluid of Fig. 6;

[0017] Fig. 8 is a perspective view of the vial of photopolymer resin material positioned in the vat of surround fluid showing that the cooling unit of Fig. 1 further includes a recirculating pipe that extends into the vat of surround fluid and is configured to circulate surround fluid out of the vat for cooling before being returned to the vat;

[0018] Fig. 9 is a top view of the vial of photopolymer resin material positioned in the vat of surround fluid of Fig. 8;

[0019] Fig. 10 is a perspective view of the vial of photopolymer resin material positioned in the vat of surround fluid showing that the cooling unit of Fig. 1 further includes a cooling plate arranged underneath the vat of surround fluid;

[0020] Fig. 11 is a perspective view of the vial of photopolymer resin material positioned in the vat of surround fluid showing that the cooling unit of Fig. 1 further includes a set of cooling plates in contact with four walls of the vat of surround fluid;

[0021] Fig. 12 is a perspective view of the vial of photopolymer resin material positioned in the vat of surround fluid showing that the cooling unit of Fig. 1 further includes at least one thermally regulated rod that extends into the vial of photopolymer resin material;

[0022] Fig. 13 is a perspective view of the vial of photopolymer resin material positioned in the vat of surround fluid showing that the cooling unit of Fig. 1 further includes a cooling pipe that extends into the vial of photopolymer resin material that is configured to carry secondary cooling fluid through the photopolymer resin material and actively remove heat therefrom;

[0023] Fig. 14 is a perspective view of the vial of photopolymer resin material of Fig. 1 showing that the vial is formed to include an inlet port and an outlet port that directs excess photopolymer resin material out of the vial after solidification of the photopolymer resin material;

[0024] Fig. 15 is a perspective view of the vial of photopolymer resin material of Fig. 1 showing that the vial includes a preexisting insert for overprinting, the preexisting insert held in position within the vial via a ferromagnetic element on the bottom of the vial;

[0025] Fig. 16 is a perspective view of an autoloading system included in the VAM system of Fig. 1, the autoloading system configured to move a plurality of vials so that each vial is sequentially exposed to the light from the light source;

[0026] Fig. 17 is an experimental setup showing three thermocouples suspended in the vial of photopolymer resin material during exposure to the light;

[0027] Fig. 18 is a temperature profile from the experimental setup of Fig. 17 showing results from printing the 3D item with room temperature immersion oil as the surround fluid and cooled immersion oil as the surround fluid;

[0028] Fig. 19 is a representative plot of the heat flow and temperature output from a differential scanning calorimetry run with BPA / PEGDA photopolymer resin material at 18 mM;

[0029] Fig. 20 is a graph showing the corrected heat flow plot from Fig. 19;

[0030] Fig. 21 is a graph showing negative peak area during photopolymerization;

[0031] Fig. 22 is a graph showing negative peak height during photopolymerization;

[0032] Fig. 23 is a graph showing time to peak during photopolymerization;

[0033] Fig. 24 is a cross-sectional view of the experimental setup of Fig. 17;

[0034] Fig. 25 is a graph showing a comparison of a simulation model versus the experimental results for heat flow during the printing process of the 3D item;

[0035] Fig. 26 is a graph showing temperature-dependent variations of resin viscosity and Rayleigh number;

[0036] Fig. 27 is a simplified depiction showing the convection flow in immersion oil surround fluid during the printing process;

[0037] Fig. 28 is a graph showing intensity of the light source according to wavelength;

[0038] Fig. 29 is a graph showing specific heat capacity of the photopolymer resin material as a function of temperature in the range of 250 K to 450 K;

[0039] Fig. 30 is a graph showing the power output of the light source at different pixel values;

[0040] Fig. 31 is a graph showing the power output of the light source as a function of current;

[0041] Fig. 32 is a graph showing the relative intensity output of the light source;

[0042] Fig. 33 is a diagrammatic view of a user interface used to control the VAM system;

[0043] Fig. 34 is another diagrammatic view of the user interface used to control the VAM system; and

[0044] Fig. 35 is an exemplary 3D item produced using the VAM system of Fig. 1.DETAILED DESCRIPTION

[0045] The present disclosure relates to a volumetric additive manufacturing (VAM) system 10 for producing a three-dimensional (3D) item 12. The VAM system 10 includes a vial of photopolymer resin material 14, a light source 16, and a cooling unit 18. The vial of photopolymer resin material 14 holds the photopolymer resin material for solidification therein. The light source 16 discharges light 17 into the vial of photopolymer resin material 14 to solidify pre-selected portions of the photopolymer resin material. The light source 16 cycles through a projection set to discharge the light 17 into the vial 14 while the vial 14 is rotating thereby inducing gelation where the cumulative light dose exceeds a non-linear threshold value. The cooling unit 18 regulates heat generated during solidification of the photopolymer resin material upon exposure to the light 17 from the light source 16.

[0046] Traditionally, VAM is used to produce 3D items on a millimeter to centimeter size scale in a timeframe of seconds to minutes. Scaling the size of 3D items printed via VAM is generally difficult for many reasons. First, heat is generated during the exothermic polymerization process of the photopolymer resin material as a function of the heat of reaction, the concentration of photoinitiator (PI) dissolved in the photopolymer resin material, and the absorbed dose rate. This heat is negligible on a small scale or when printing fine features, but in a large volume of photopolymer resin material when printing larger items, the photopolymer resin material temperature is increased substantially. This increased temperature speeds up the diffusion of radicals, monomers, and dissolved molecular oxygen acting as an inhibiting species. Additionally,temperature affects the reaction kinetics which, in combination with increased diffusion, can lead to undesired polymerization and dark-curing.

[0047] Second, the absorbance of the photopolymer resin material, which is largely a function of the species of PI and the concentration of PI, becomes more significant when increasing the diameter of the vial to allow for printing of a larger 3D item. Beer-lambert absorption limits the penetration depth into the photopolymer resin material. If the absorbance of the photopolymer resin material is too high, light will attenuate quickly and some voxels (3D pixels) will not receive enough light energy to cross the gelation threshold. If the absorbance of the photopolymer resin material is too low, the dose rate is decreased resulting in long gelation times, part sedimentation, and partially gelled seeds that focus the light like a waveguide and lead to striations on the print surface.

[0048] Thus, the VAM system 10 of the present disclosure includes the cooling unit 18 that regulates the heat produced during printing and reduces the impact of the heat generation on undesired polymerization. Further, the VAM system 10 of the present disclosure controls the absorption of the photopolymer resin material via the selection of the PI and the concentration of the PI in the photopolymer resin material. If the concentration of the PI is too low, the degree of crosslinking will be limited, the printing process may take a long time, and the 3D item may be tacky after post-processing. Therefore, using a low absorbing PI, such as Irgacure 907 that weakly absorbs at 405 nm, which is the peak emission wavelength of the light source 16, is beneficial.

[0049] The vial of photopolymer resin material 14 is illustratively coupled to a rotation fixture 20, as shown in Fig. 1. The rotation fixture 20 rotates the vial of photopolymer resin material 14 while the light 17 is directed into the vial of photopolymer resin material 14 about a rotation axis A. The rotation axis A extends through a center point of the vial 14. In exemplary embodiments, the vial of photopolymer resin material 14 has one degree of freedom during printing - rotation. In other words, the vial of photopolymer resin material 14 does not translate or move linearly during the printing process. The vial 14 may be any size, and the size of the vial14 depends on the desired size of the 3D item 12. For example, the vial 14 may have an inner diameter of about 1.5 centimeters to about 15 centimeters. In some embodiments, the vial 14 is made from borosilicate glass.

[0050] The light source 16 discharges the light 17 into the vial of photopolymer resin material 14 to solidify pre-selected portions of the photopolymer resin material, as suggested in Fig. 1. The shape of the light 17 determines the pre-selected portions of the photopolymer resin material that will solidify. The light 17 is delivered to the vial 14 as a set of two-dimensional (2D) images. Because the vial 14 is rotating about the rotation axis A, each image projection propagates through the photopolymer resin material at a different angle. The superposition of exposures from multiple angles results in a 3D energy dose sufficient to solidify the photopolymer resin material in the desired geometry. In some embodiments, the VAM system 10 further includes a lens 22 located between the light source 16 and the vial of photopolymer resin material 14, as shown in Figs. 1 and 2. The lens 22 collimates the light 17 so that parallel rays of the light 17 are delivered to the vial 14.

[0051] As the photopolymer resin material polymerizes upon exposure to the light 17, the photopolymer resin material generates heat. The theoretical enthalpy of reaction for the photopolymer resin material (e.g., diacrylate) is -172.4 kilojoules per mole. When a cylinder having a diameter of 30 millimeters and a height of 50 millimeters is polymerized within 4 minutes, approximately 16,452 joules of heat is generated with about 69 joules transferred to the VAM system per second. Considering the heat capacity of the photopolymer resin material, an estimated temperature increase of about 0.77 Kelvin per second is expected, resulting in a total temperature rise of about 184 °C by the end of the printing process if the system is perfectly insulated. Thus, the cooling unit 18 helps to regulate heat generated during solidification of the photopolymer resin material so that the photopolymer resin material does not experience this temperature rise.

[0052] The cooling unit 18 regulates heat generated during solidification of the photopolymer resin material upon exposure to the light 17 from the light source 16. In some embodiments, the cooling unit 18 includes a vat of surround fluid 24, as shown inFig. 1 and 3. The vial of photopolymer resin material 14 is placed in the vat of surround fluid 24 during the printing process so that the surround fluid absorbs heat generated by the photopolymer resin material during printing. In this way, the vat of surround fluid 24 acts as a passive cooling source to limit the negative impacts of heat generation in large- scale VAM printing.

[0053] In some embodiments, the cooling unit 18 includes the vial of photopolymer resin material 14. In such an embodiment, the vial of photopolymer resin material 14 is cooled or chilled prior to the printing process. In this way, cooling via the vat of surround fluid 24 is not necessary and / or an amount of cooling provided by the vat of surround fluid 24 may decrease as the vial of photopolymer resin material 14 performs at least a portion of the cooling during the print process.

[0054] In illustrative embodiments, the surround fluid has a first temperature, and the photopolymer resin material has a second temperature that is greater than the first temperature. In this way, the surround fluid absorbs heat generated by the photopolymer resin material. In some embodiments, the first temperature may be about 276 Kelvin.

[0055] In some embodiments, the surround fluid has the first temperature prior to the start of the printing process. The vial of photopolymer resin material 14 may then be placed in the vat of surround fluid 24, and the printing process may begin. As heat is generated by the photopolymer resin material upon exposure to the light 17 (i.e., the photopolymer resin material has the second temperature greater than the first temperature), the surround fluid absorbs heat generated by the photopolymer resin material. Thus, at the end of the printing process, the surround fluid may have a third temperature that is greater than the first temperature due to absorption of heat.

[0056] The vat 24 may be a five-sided cube, as shown in FIG. 3. In this way, the vat 24 may be open on a top side thereof to allow for easy insertion and removal of the vial 14 from the vat 24. Between printing different 3D items 12, the surround fluid may be cooled or the surround fluid may be replaced with cooled surround fluid. In some embodiments, the vat 24 is made from borosilicate glass.

[0057] The surround fluid has a refractive index substantially matched with a refractive index of the photopolymer resin material so that the light 17 passes through the surround fluid to the photopolymer resin material during printing. Substantially matched may mean that the two refractive indices have a percent difference of up to 2%.Substantially matched may mean that the two refractive indices have a percent difference of up to 1.5%. Substantially matched may mean that the two refractive indices have a percent difference of up to 1.3%. Substantially matched may mean that the two refractive indices have a percent difference of up to 1.2%. Substantially matched may mean that the two refractive indices have a percent difference of up to 1.18%. Substantially matched may mean that the two refractive indices differ by a value of up to 0.2. Substantially matched may mean that the two refractive indices differ by a value of up to 0.1.Substantially matched may mean that the two refractive indices differ by a value of up to 0.05. Substantially matched may mean that the two refractive indices differ by a value of up to 0.025. Substantially matched may mean that the two refractive indices differ by a value of up to 0.02. Substantially matched may mean that the two refractive indices differ by a value of up to 0.018.

[0058] In some embodiments, the surround fluid is substantially the same as the photopolymer resin material. In some embodiments, the surround fluid is different than the photopolymer resin material.

[0059] In some embodiments, the cooling unit 18 further includes an active cooling element 26, as shown in Fig. 1. In some embodiments, the vat of surround fluid 24 and the active cooling element 26 may cooperate to regulate heat generated during solidification of the photopolymer resin material. The active cooling element 26 withdraws heat from the surround fluid and / or the photopolymer resin material during solidification of the photopolymer resin material.

[0060] In some embodiments, as shown in Figs. 4 and 5, the active cooling element 26 illustratively is a cooling pipe 28 that extends into the vat of surround fluid 24 and is configured to carry secondary cooling fluid 30 through the surround fluid to actively remove heat therefrom. In this way, as the surround fluid absorbs heat generatedby the photopolymer resin material, the secondary cooling fluid 30 removes the absorbed heat from the surround fluid. The cooling pipe 28 stabilizes the surround fluid temperature at or around the first temperature (i.e., 276 Kelvin).

[0061] The cooling pipe 28 extends into the vat of surround fluid 24 at a location opposite the light source 16 along a back wall of the vat of surround fluid 24, as shown in Fig. 5. In this way, the cooling pipe 28 does not block the light 17 from reaching the vial of photopolymer resin material 14. The secondary cooling fluid 30 circulates through the cooling pipe 28 to withdraw heat from the surround fluid so that the surround fluid maintains a relatively low temperature (i.e., the first temperature). The cooling pipe 28 may be coupled to a pump to pump the secondary cooling fluid 30 through the cooling pipe 28. The cooling pipe 28 may also be coupled to a heat exchanger to withdraw heat from the secondary cooling fluid 30 after the secondary cooling fluid 30 passes through the vat of surround fluid 24 so that the secondary cooling fluid 30 may be recirculated through the cooling pipe 28.

[0062] In some embodiments, as shown in Figs. 6 and 7, the cooling pipe 28 extends into the vat of surround fluid 24 along three side walls thereof. The cooling pipe 28 does not extend along a front wall of the vat of surround fluid 24 closest to the light source 16. In this way, the cooling pipe 28 does not block the light 17 from reaching the vial of photopolymer resin material 14.

[0063] In some embodiments, as shown in Figs. 8 and 9, the active cooling element 26 illustratively is a recirculating pipe 32 that extends into the vat of surround fluid 24 and is configured to circulate surround fluid out of the vat 24 for cooling before being returned to the vat 24. As the surround fluid absorbs heat generated by the photopolymer resin material, the relatively warmer surround fluid is removed from the vat 24, relatively cooler surround fluid is directed into the vat 24, and the relatively warmer surround fluid is cooled before being returned to the vat 24.

[0064] The recirculating pipe 32 extends into the vat of surround fluid 24 at a location opposite the light source 16 along the back wall of the vat of surround fluid 24, as shown in Fig. 9. In this way, the recirculating pipe 32 does not block the light 17 fromreaching the vial of photopolymer resin material 14. The surround fluid circulates through the recirculating pipe 32 to replace the relatively warmer surround fluid with relatively cooler surround fluid so that the surround fluid maintains a relatively low temperature (i.e., the first temperature). The recirculating pipe 32 may be coupled to a pump to pump the surround fluid through the recirculating pipe 32. The recirculating pipe 32 may also be coupled to a heat exchanger to withdraw heat from the surround fluid after the surround fluid has been removed from the vat 24 so that the surround fluid may be cooled and recirculated. In some embodiments, a flow speed of about 80 milliliters per second is used to stabilize the surround fluid temperature at or around the first temperature (i.e., 276 Kelvin) and minimize air bubbles.

[0065] In some embodiments, as shown in Fig. 10, the active cooling element 26 illustratively is a cooling plate 34 that is in contact with the vat of surround fluid 24 to withdraw heat from the surround fluid. In this way, as the surround fluid absorbs heat generated by the photopolymer resin material, the cooling plate 34 removes the absorbed heat from the surround fluid. The cooling plate 34 stabilizes the surround fluid temperature at or around the first temperature (i.e., 276 Kelvin).

[0066] In some embodiments, the vat 24 is supported on the cooling plate 34 such that the cooling plate 34 is located underneath the vat 24, as shown in Fig. 10. The cooling plate 34 does not block the light 17 from reaching the vial of photopolymer resin material 14. In some embodiments, the cooling plate 34 includes thermoelectric materials 35 and an electrical energy source 37 configured to pass electrical current through the thermoelectric materials 35 to cool the cooling plate 34.

[0067] In some embodiments, as shown in Fig. 11, the active cooling element 26 illustratively is a set of cooling plates 36 that are in contact with the vat of surround fluid 24 to withdraw heat from the surround fluid. As the surround fluid absorbs heat generated by the photopolymer resin material, the set of cooling plates 36 removes the absorbed heat from the surround fluid. The set of cooling plates 36 stabilizes the surround fluid temperature at or around the first temperature (i.e., 276 Kelvin).

[0068] In some embodiments, the set of cooling plates 36 is located on two sides of the vat 24, three sides of the vat 24, or four sides of the vat 24. The set of cooling plates 36 is not located on a side of the vat 24 closest to the light source 16. In this way, the set of cooling plates 36 does not block the light 17 from reaching the vial of photopolymer resin material 14. In some embodiments, the set of cooling plates 36 includes thermoelectric materials 39 and an electrical energy source 41 configured to pass electrical current through the thermoelectric materials 39 to cool the set of cooling plates 36.

[0069] In some embodiments, as shown in Fig. 12, the active cooling element 26 illustratively is at least one thermally regulated rod 38 that extends into the vial of photopolymer resin material 14 and is configured to actively remove heat therefrom. In this way, as the photopolymer resin material generates heat, the at least one thermally regulated rod 38 actively removes the generated heat.

[0070] The at least one thermally regulated rod 38 is optically transparent. The at least one thermally regulated rod 38 has a refractive index substantially matched with a refractive index of the photopolymer resin material so that the light 17 passes through the at least one thermally regulated rod 38 to the photopolymer resin material during printing. The at least one thermally regulated rod 38 withdraws heat from the photopolymer resin material so that the photopolymer resin material maintains its temperature. The at least one thermally regulated rod 38 is coupled to a heat sink 40 to withdraw heat from the at least one thermally regulated rod 38.

[0071] In some embodiments, the at least one thermally regulated rod 38 includes more than one thermally regulated rod 38. In some embodiments, the at least one thermally regulated rod 38 is formed of silica, index-matched polymers, indium tin oxide, metal, or any other suitable material. In some embodiments, the photopolymer resin material may be filled with sub-scattering nanoparticles of thermally conductive material.

[0072] In some embodiments, as shown in Fig. 13, the active cooling element 26 illustratively is a cooling pipe 42 that extends into the vial of photopolymer resin material 14 and is configured to carry secondary cooling fluid 44 through the photopolymer resinmaterial and actively remove heat therefrom. As the photopolymer resin material generates heat, the secondary cooling fluid 44 actively removes the generated heat.

[0073] The secondary cooling fluid 44 circulates through the cooling pipe 42 to withdraw heat from the photopolymer resin material so that the photopolymer resin material maintains its temperature. The cooling pipe 42 may be coupled to a pump to pump the secondary cooling fluid 44 through the cooling pipe 42. The cooling pipe 42 may also be coupled to a heat exchanger to withdraw heat from the secondary cooling fluid 44 after the secondary cooling fluid 44 passes through the vial of photopolymer resin material 14 so that the secondary cooling fluid 44 may be cooled and recirculated. The cooling pipe 42 and / or the secondary cooling fluid 44 are optically transparent. The cooling pipe 42 and / or the secondary cooling fluid 44 have a refractive index substantially matched with a refractive index of the photopolymer resin material so that the light 17 passes through the cooling pipe 42 and / or the secondary cooling fluid 44 to the photopolymer resin material during printing.

[0074] Any combination of the active cooling elements 26 (i.e., the cooling pipe 28, the recirculating pipe 32, the cooling plate 34, the set of cooling plates 36, the at least one thermally regulated rod 38, the cooling pipe 42) may be used in the VAM system 10 with one another. In some embodiments, the VAM system 10 only includes the vat of surround fluid 24 as a passive cooling element. In some embodiments, the VAM system 10 only includes the vat of surround fluid 24 and the pre-cooled vial of photopolymer resin material 14 as passive cooling elements. In some embodiments, the VAM system 10 only includes the pre-cooled vial of photopolymer resin material 14 as a passive cooling element. In other words, in some embodiments, the active cooling element 26 is omitted. In some embodiments, the VAM system 10 includes the vat of surround fluid 24 as a passive cooling element and any one of or any combination of the active cooling elements 26.

[0075] In some embodiments, the cooling unit 18 further includes at least one sensor 46 and / or a controller 48, as shown in Fig. 1. The at least one sensor 46 is in communication with the controller 48. In illustrative embodiments, the at least one sensor46 is a temperature sensor. In some embodiments, the at least one sensor 46 is a noncontact temperature sensor that is spaced apart from the photopolymer resin material and / or the surround fluid. In some embodiments, the at least one sensor 46 is a thermal camera, such as an infrared camera. The at least one sensor 46 may be spaced apart from the vat of surround fluid 24 such that the at least one sensor 46 is located outside of the vat of surround fluid 24. In some embodiments, the at least one sensor 46 is a contact temperature sensor. In some embodiments, the at least one sensor 46 is a thermometer.

[0076] The at least one sensor 46 is fluidly connected to the vat of surround fluid 24 and / or the vial of photopolymer resin material 14 to provide feedback to the controller 48 on the temperature of the photopolymer resin material and / or the surround fluid, which is used as inputs for operation of the cooling unit 18. For example, the at least one sensor 46 may sense, measure, or detect a temperature of the surround fluid and / or the photopolymer resin material during the printing process.

[0077] The controller 48 is in communication with the light source 16, the rotation fixture 20, and the cooling unit 18 to control operation of the VAM system 10, as shown in Fig. 1. The controller 48 selectively controls the light source 16, the rotation fixture 20, and / or the cooling unit 18 to print the 3D item 12. The controller 48 receives inputs (i.e., detected temperature data) from the at least one sensor 46 regarding the temperature of the photopolymer resin material and / or the surround fluid. Based, at least in part, on the inputs, the controller 48 modifies operating parameters of the light source 16, operating parameters of the rotation fixture 20, and / or operating parameters of the active cooling element 26. For example, based on the inputs (i.e., detected temperature data), the controller 48 may determine the amount of cooling, if any, needed by the surround fluid via the active cooling element 26. The controller 48 may then control operation of the active cooling element 26 based on this determination. The controller 48 may compare the detected temperature data of the surround fluid to an optimal temperature of the surround fluid (i.e., the first temperature) in the determination of the amount of cooling that is needed.

[0078] For example, based on the determination of the amount of cooling that is needed, the controller 48 may modify a flow rate of the secondary cooling fluid 30 passing through the cooling pipe 28, a temperature of the secondary cooling fluid 30 passing through the cooling pipe 28, a flow rate of the surround fluid passing through the recirculating pipe 32, a temperature of the surround fluid passing through the recirculating pipe 32, a temperature of the cooling plate 34, a temperature of the set of cooling plates 36, a temperature of the at least one thermally regulated rod 38, a flow rate of the secondary cooling fluid 44 passing through the cooling pipe 42, and / or a temperature of the secondary cooling fluid 44 passing through the cooling pipe 42.

[0079] The amount of heating generation by the photopolymer resin material, and thus, the amount of cooling needed, is dependent on the geometry of the 3D item 12, the type of photopolymer resin material, the type of PI, the concentration of the PI, the type of surround fluid, the time needed for the printing process, etc. Thus, the controller 48 uses real time feedback to optimize the printing process.

[0080] The geometry of the 3D item 12 exerts a strong influence on the kinetics of heat dissipation during the printing process. Large, solid items, like The Thinker (see Fig. 35), release significant heat (about 18,898 joules and about 32,656 joules from 75 millimeter and 90 millimeter models, respectively) due to their large volumes, with most heat captured inside. On the other hand, large but thin and porous items, like lattice structures, have small true volumes compared to the enveloped volumes, leading to less heat generation and more efficient heat dissipation owing to larger surface area to volume ratios and more passages for uncured liquid photopolymer resin material.

[0081] The controller 48 includes a memory 50, a microprocessor 52, and a user interface 54, as shown in Fig. 1. The memory 50 has instructions stored therein for performing the printing process and operating the light source 16, the rotation fixture 20, and the cooling unit 18. The microprocessor 52 executes the instructions stored in the memory 50. A user can interact with the user interface 54 to input print parameters and to observe the printing process. An exemplary user interface 54 is shown in Fig. 33. The user interface 54 allows the user to select the projection images, the rotation speed of therotation fixture 20, the number of rotations of the rotation fixture 20, and other parameters. A display button on the user interface 54 may allow the user to project a single image onto the vial 14 for vial alignment purposes prior to the printing process. As shown in Fig. 34, the user may track progression of the printing process on the user interface 54 during the printing process.

[0082] In some embodiments, as shown in Fig. 14, the vial 14 is formed to include an inlet port 56 and an outlet port 58. The inlet port 56 and the outlet port 58 are formed in a bottom surface of the vial 14. During the printing process, the inlet port 56 and the outlet port 58 are closed such that the photopolymer resin material remains separate from the surround fluid. The inlet port 56 is fluidly connected to a first valve 60 and a first conduit 62. The outlet port 58 is fluidly connected to a second valve 64 and a second conduit 66.

[0083] After the printing process is complete (i.e., after the light 17 is no longer being directed toward the vial 14), the vial 14 may be removed from the vat 24. Once removed from the vat 24, the second valve 64 opens so that excess photopolymer resin material in the vial 14 exits the vial 14 through the outlet port 58 to pass through the second conduit 66. In this way, excess photopolymer resin material is drained from the vial 14 while the 3D item 12 is located within the vial 14. After the vial 14 is drained, the first valve 60 opens so that a fluid is directed into the vial 14 through the first conduit 62 and the inlet port 56 while the 3D item 12 is located within the vial 14. The fluid may be a cleaning solution or air. The inlet port 56 and the outlet port 58 allow the 3D item 12 to solidify in a confined environment thereby maintaining resin purity and preventing contamination. During the printing process (i.e., while the vial 14 is being rotated in the vat 24), the inlet port 56 and the outlet port 58 are disconnected from the conduits 62, 66.

[0084] In some embodiments, the VAM system 10 may be used for overprinting or overmolding. In overprinting or overmolding, the 3D item 12 is printed around a preexisting insert 68. During the printing process, it is important for the preexisting insert 68 to remain stationary relative to the photopolymer resin material and to remain aligned along the rotation axis A of the vial 14. The preexisting insert 68 is coupled to a pluglocated within the lip of the vial 14. In some embodiments, the preexisting insert 68 is aligned along the rotation axis A via ferromagnetic elements 70, 72. For example, one ferromagnetic element 70 is coupled to a bottom end of the preexisting insert 68, and another ferromagnetic element 72 is coupled to a bottom surface of the vial 14. The attraction between the ferromagnetic elements 70, 72 maintains the position of the preexisting insert 68 within the vial 14 during the printing process. The ferromagnetic element 70 may comprise a ball bearing. The ferromagnetic element 72 may comprise a neodymium magnet.

[0085] The ferromagnetic elements 70, 72 may be omitted when using preexisting inserts 68 that are denser than the photopolymer resin material. If the preexisting insert 68 is positively buoyant, the preexisting insert 68 may float within the photopolymer resin material and tilt off the rotation axis A. Thus, the magnetic alignment between the ferromagnetic elements 70, 72 maintains the position of the preexisting insert 68 along the rotation axis A.

[0086] In some embodiments, the VAM system 10 includes an autoloading system 74, as shown in Fig. 16. The autoloading system 74 may translate linearly and rotate. A plurality of vials 14 is coupled to the autoloading system 74, as shown in Fig. 16.

[0087] To being the printing process, the autoloading system 74 translates linearly toward the rotation fixture 20 to a load position to couple a first of the plurality of vials 14 to the rotation fixture 20, as shown in Fig. 16. Once coupled to the rotation fixture 20, the autoloading system 74 translates linearly away from the rotation fixture 20 to a print position. The rotation fixture 20 then moves downwardly so that the first of the plurality of vials 14 is positioned in the vat 24 located underneath the rotation fixture 20. The printing process may then be completed with the first of the plurality of vials 14 by directing the light 17 into the first of the plurality of vials 14. Once the printing process is completed with the first of the plurality of vials 14 (i.e., the light 17 is no longer being directed into the first of the plurality of vials 14), the rotation fixture 20 moves upwardly so that the first of the plurality of vials 14 is removed from the vat 24 and the autoloadingsystem 74 moves linearly to the load position to decouple the first of the plurality of vials 14 from the rotation fixture 20.

[0088] Then, the autoloading system 74 rotates so that a second of the plurality of vials 14 may be used in the printing process. After rotation, the autoloading system 74 translates linearly toward the rotation fixture 20 to the load position to couple the second of the plurality of vials 14 to the rotation fixture 20. Once coupled to the rotation fixture 20, the autoloading system 74 translates linearly away from the rotation fixture 20 to the print position. The rotation fixture 20 then moves downwardly so that the second of the plurality of vials 14 is positioned in the vat 24 located underneath the rotation fixture 20. The printing process may then be completed with the second of the plurality of vials 14 by directing the light 17 into the second of the plurality of vials 14. While the printing process is being completed with the second of the plurality of vials 14, the inlet port 56 and the outlet port 58 of the first of the plurality of vials 14 may be connected to the first conduit 62 and the second conduit 66, respectively. The excess photopolymer resin material may then be removed from the first of the plurality of vials 14 and the 3D item 12 contained therein cleaned via the fluid.

[0089] The above described process may continue until each of the plurality of vials 14 coupled to the autoloading system 74 includes the 3D item 12 therein. In this way, each of the plurality of vials 14 is sequentially exposed to the light 17 from the light source 16 for the printing process. The autoloading system 74 enables zero-downtime, continuous production, minimizes handling of the item 12, maintains resin integrity, and allows for automated production workflow. In some embodiments, the autoloading system 74 includes a back plate 76 that blocks the light 17 from reaching the other vials 14 while the light 17 is being directed to the vial 14 coupled to the rotation fixture 20.

[0090] In some embodiments, the photopolymer resin material comprises a 3: 1 weight ratio of Bisphenol A glycerolate diacrylate (BP A) to Poly(ethylene glycol) diacrylate (PEGDA, 250 Da). In some embodiments, the PI included in the photopolymer resin material is 45 mM 2-Methyl-l-[4-(methylthio)phenyl]-2-morpholinopropanone-l (Irgacure 907), lithium phenyl-2,4,6-trimethylbenzoyl phosphinate (LAP),phenylbis(2,4,6-trimethylbenzoyl) phosphine oxide (Irgacure 819), camphorquinone and ethyl 4-dimenthylamino benzoate (CQ and EDAB), 2,4,6-trimethylbenzoyldiphenyl phosphine oxide (TPO), ethyl phenyl(2,4,6-trimethylbenzoyl)phosphinate (TPO-L), or any other suitable PI. In some embodiments, the surround fluid is immersion oil.

[0091] As an example, to prepare the photopolymer resin material, the BPA may be heated to 80 °C before combining the BPA and PEGDA in a 3 : 1 ratio by weight using a planetary mixer (THINKY Corporation ARM-310, Laguna Hills, CA). The Irgacure 907 may be added into the BPA / PEGDA mixture using alternating cycles of the planetary mixer and a sonicator (QSonica, Q500, Newtown, CT) until the photopolymer resin material is transparent and no clumps of PI are present. The prepared photopolymer resin material may be poured into the vial 14, and the vial 14 may be degassed in a vacuum chamber to remove any bubbles. The vial 14 may then sit for about four days away from light while open to the atmosphere so that oxygen can replenish in the photopolymer resin material.

[0092] Refractive indices (RI) of the BPA / PEGDA photopolymer resin material and the immersion oil surround fluid at different working temperatures are shown in Table 1 .TABLE 1.

[0093] Fig. 35 shows a 3D item 12 printed with the VAM system 10 using the surround fluid having the first temperature of 276 Kelvin. An exemplary 3D item 12 is Rodin’s The Thinker having a height of 7.5 centimeters, as shown in Fig. 35. The Thinker was printed in a 62 millimeter diameter vial 14 with 45 millimolar photopolymer resin material. The Rodin’s The Thinker having a height of 7.5 centimeters was also printedwith room temperature surround fluid (298 Kelvin), and the result was an overcured and shapeless blob that could not be cleanly removed from the vial 14. Thus, the cooling unit 18 allows larger 3D items 12 to be printed that would otherwise be difficult or impossible to print.

[0094] As an example, the VAM system 10 can produce 3D items 12 within a 350 cm3build volume with printing speeds of over 23 cm3per minute. The VAM system 10 can resolve 3D items 12 up to 9 centimeters by 7 centimeters by 7 centimeters within minutes while maintaining sub-millimeter resolutions. This is over ten times the largest print and over five times the highest throughput reported with traditional CAL systems. Table 2 shows exemplary volume, print time, and throughput of the VAM system 10 during the printing of two differently sized models of Rodin’s The Thinker. The 90 mm tall The Thinker was printed in a vial 14 having a 81 millimeter diameter with a 25 millimolar photopolymer resin material.TABLE 2.

[0095] As an example, to measure the heat generation during printing, three thermocouples were positioned in the vial 14 in room temperature photopolymer resin material at specific radii, as shown in Fig. 17. The print process produced a solid cylinder with a 15 millimeter radius in the center of the vial 14 and a height of 50 millimeters. The thermocouples were positioned with one thermocouple at r = 0 mm at the center of the vial 14 (Tr=Omm), another thermocouple at r = 15 mm at the edge of the printed cylinder (Tr=15mm), and a third thermocouple at r = 30 mm inside the edge of the vial 14 (Tr=30mm)-

[0096] A solid cylinder was first printed using cooled immersion oil surround fluid at 276 Kelvin. The vial 14 rested in the cooled immersion oil surround fluid for about 60 seconds before and after printing. The solid cylinder was fully resolved (i.e., solidified) after visual inspection in 216 seconds (after 6 rotations at 10° per second). The temperature at the center of the vial 14, Tr=Omm, and at the edge of the printed cylinder, Tr=i5mm, both increased during printing and continued to increase after the exposure to the light 17 had been stopped, reaching a maximum of 390 Kelvin and 325 Kelvin, respectively, as shown in Fig. 18. The temperature at the edge of the vial 14, Tr=30mm, decreased immediately during the 60 second pre-dwell time and continued to slowly decrease during the entire printing and post-dwell time to a minimum of 289 K, as shown in Fig. 18, due to the vat of surround fluid 24 (i.e., the cooling unit 18).

[0097] A solid cylinder was then printed using room temperature immersion oil surround fluid at 298 Kelvin. The same light dose energy was supplied to the photopolymer resin material and all other conditions were maintained. At the onset time, the temperature at the center of the vial 14, Tr=Omm, for both experiments is identical. However, as shown in Fig. 18, the temperature at the center of the vial 14, Tr=Omm, increased faster and reached a higher maximum (400 Kelvin) with the room temperature immersion oil surround fluid. The temperature at the edge of the vial 14, Tr=30mm, continuously decreased in the cooled immersion oil surround fluid case, but Tr=30mmmaintained its temperature until the end of printing in the room temperature immersion oil surround fluid case. As there was no cooling effect, there was no change in Tr=30mmuntil 173 seconds into printing in the room temperature immersion oil surround fluid case when the temperature began to increase. This change indicates that heat generated from the desired region (the cylinder formation region) propagated to the undesired region, whereas the cooled immersion oil surround fluid was able to limit heating to the desired region.

[0098] The temperature at the edge of the printed cylinder, Tr=15mm, exhibited the greatest difference between the two cases, as shown in Fig. 18. With room temperature immersion oil surround fluid, Tr=15mrnbegan to increase earlier than Tr=Ommand reached a maximum of 386 Kelvin. These differences may be attributed to heat generation during printing, which were made more apparent from visible inspection of the vial 14 after printing. For the room temperature immersion oil surround fluid case, an overcured cylinder larger than the desired 30 millimeter diameter was attached to the walls of the vial 14 with additional cured material branching out from the center. The cooled immersion oil surround fluid may have slowed down molecular motions of radicals and inhibitors, as well as the consequent reaction kinetics, resulting in less propagation of reaction into the undesired region thereby preventing overcuring. Further, the convective motion of the photopolymer resin material is also drastically reduced.

[0099] To explore the heat generation during photopolymerization, experiments with differential scanning calorimetry using a light guide attachment were performed. Different concentrations of the PI (Irgacure 907) from 5 millimolar to 80 millimolar with four of those between 32 millimolar and 46 millimolar were tested. Each sample was exposed to 30 mWcm’2intensity light in two different exposure periods for 90 seconds each separated by an isothermal rest with the light off, as shown in Fig. 19. Fig. 19 shows a representative plot of the heat flow and temperature output from a differential scanning calorimetry run with BPA / PEGDA photopolymer resin material at 18 millimolar. The shaded regions represent when the light was turned on. The first exposure measures the reaction heat flow, while the second exposure establishes a baseline heat flow from the light source. The heat flow during the second exposure is subtracted from the first exposure to obtain the corrected reaction heat flow, as shown in Fig. 20.

[0100] The peak area (AP), the peak height (hP), and the time to peak (tP) for each photopolymer resin material was calculated, as shown in Figs. 21-23, respectively. The values of the peak area and peak height are negative because the photopolymer resin material undergoes highly exothermic reactions. The total exothermic energy from each photopolymerization reaction is shown in Fig. 21. The maximum heat flow during photopolymerization is shown in Fig. 22. The time until maximum heat flow after photoexposure began is shown in Fig. 23. Error bars represent one standard deviation. The peak area and the peak height were smallest and the peak time largest with a lower PIconcentration, as shown in Figs. 21-23, due to the longer reaction times. Fewer PI molecules lead to a slower reaction and fewer reaction sites. As the concentration of PI increases, the peak area and the peak height increases while the peak time decreases until about 30 millimolar where the trend disappears and an asymptote is reached. This effect may be due to the competition of the initiation and termination reactions both triggered by the radical initiators.

[0101] A heat flow model was also created using thermodynamic data to track the energy flow for cooling enabled printing processes. For the source term, the heat generation measured with photoDSC was used and values for the thermal properties of the photopolymer resin material, the immersion oil surround fluid, and the vial 14 were used. The thermal diffusivity of the photopolymer resin material with the transient thermal grating method (a = 0.0766 ± 0.0041 mm2s-1) was measured. Values for the respective thermal properties of the immersion oil surround fluid and the vial 14 are shown in Table 3.TABLE 3.

[0102] A MATLAB pdepe solver was created to calculate the temperature as a function of time at different radii based on the diagram shown in Fig. 24, which matches the experimental setup from Fig. 17. The MATLAB pdepe solver takes the thermal properties of the photopolymer resin material, the immersion oil surround fluid, and the glass material of the vial 14 as inputs (Table 3) along with boundary conditions and initial conditions. The solver was set up for ID heat conduction with cylindricalcoordinates matching the schematic shown in Fig. 24. The source term was defined as the heat flow measured from photoDSC for the specific resin formulation. The plot output by the DSC is taken and fit to a piecewise polynomial function. This source term is isolated to the area within the print which is where the resin is polymerized, and thus, generating the heat. The source term also has a time component to it and does not start generating heat until after the inhibition time, during which all the local oxygen is depleted and the polymerization reaction starts.

[0103] The inhibition time for CAL may be defined as= [O2,o] R nit where [O2,o] is the initial concentration of molecular oxygen in the resin and Rinitis the initiation rate of the PI. The initiation rate is equal to (pPabsNA^ hv~^ where (p is the quantum efficiency of the initiator, Pabsis the dose rate during printing, NAis Avogadro’s number, and hv is the energy of one photon of light. For the cylinder printing experiment, the projection set and the rotation speed of the vial 14 resulted in a dose rate of Pabs = 6.75 mW cm-3and the initial concentration of oxygen taken was [O2,o] = 0.0012 M. In this model, it is assumed that the quantum efficiency is 0.3 which is in line with typical Pls. Thus, the source term is active after the inhibition time and the 60 second dwell time.

[0104] The boundary conditions are set such that there is no flux at the rotation axis A and the temperature of the immersion oil is always constant at 276 Kelvin. The initial conditions for the model are the temperature in the vial 14 is equal to 298 Kelvin and the temperature outside of the vial 14 and within the vat 24 is 276 K.

[0105] Once all these parameters are set, MATLAB solves the partial differential equation to determine the temperature as a function of position and time. The model can be easily adjusted to account for different temperatures involved and for different size vials and printed cylinders. This model is limited by being a ID problem looking at the radial direction, and the model does not account for the diffusion and temperature dependent kinetics of the system.

[0106] Fig. 25 shows the comparison of the results from the simulation and the experiment for 45 millimolar BPAGDA / PEGDA photopolymer resin material withcooled immersion oil surround fluid at 276 Kelvin. This simulation provides a spatiotemporal temperature profde of a specific resin voxel in compliance with its distance from the rotation axis A at a given timeframe.

[0107] The onset times for all three temperature profiles show good agreement between experiment and simulation, as shown in Fig. 25. The maximum temperatures achieved for Tr=Ommand Tr=15mmare 2.5% and 1 .0% larger than the experimentally measured results, respectively. The minimum temperature achieved for Tr=30mmis 1.0% below the experimentally measured result. The profile of the temperature curves for the simulation after the onset time do not directly match the experiment. This may be attributed to the heat generation term measured from photoDSC not accounting for diffusion, convection, and dose rate effects that play a large role in CAL. Nevertheless, these results indicate that the model can more accurately match the onset time and peak temperatures of large CAL printing with cooled immersion oil surround fluid.

[0108] Fig. 26 shows temperature-dependent variations of resin viscosity and Rayleigh number. An increase of viscosity occurs upon cooling. Over the temperature range of the VAM system 10 (about 10°C to about 50°C), the viscosity changes by an order of magnitude (about 10 Pa ■ s to about 200 Pa ■ s). The reduction in heat and increase in viscosity both contribute to reduction in convective flow, which may be estimated using flow around a horizontal cylinder (Fig. 27) and the non-dimensional Rayleigh number, Ra = 1.308 X 106~ 3.227 x 107. The coupled viscothermal Rayleigh number varies geometrically with temperature (Fig. 26) with a total reduction of convective flow by an order of magnitude. Fig. 27 is a simplified depiction showing the convection flow in immersion oil surround fluid during the printing experiment.

[0109] Fig. 28 shows the output of an exemplary light source 16. The two largest peaks in the curve occur at 402 nanometers and 434 nanometers. Fig. 29 shows the specific heat capacity of the BPA / PEGDA photopolymer resin material as a function of temperature.

[0110] Fig. 30 shows the power output of an exemplary light source 16 at different pixel values. As expected, the light intensity scales linearly with the pixel value.As shown in Fig. 30, a maximum intensity of 41.2 mWcm’2is achieved. Another way of modifying the output intensity of an exemplary light source 16 is to change the current going to the light source 16, as shown in Fig. 31. Fig. 31 shows a nearly linear trend, which indicates that adjusting the current is another method to scale the intensity of the light source 16 during printing. Fig. 32 shows the relative intensity output of an exemplary light source 16. The full width half max is 13.5 nanometers with a maximum intensity at 405.5 nanometers.

[0111] In some embodiments, the light source 16 may be a 4K Phoenix Light Engine with an Ankaa 76.5 micrometer projection lens (In-Vision, Vienna, Austria). The light source 16 may be attached to a M-401 XY Linear stage (Newport) with a 13 millimeter travel distance. In some embodiments, the lens 22 may be a MgF2 coated 200 millimeter PCX Condenser Lens with a 400 millimeter focal length (Edmund Optics, Barrington, NJ). The lens 22 may be supported with a 3D printed holder. The focal plane may have a maximum image size of 79.0 millimeters by 125.0 millimeters with a pixel size of 49.9 micrometers. The light beam was characterized at the focal plane with specifications shown in Figs. 30 and 32.

[0112] In some embodiments, the vat of surround fluid 24 may be positioned on a 9204-M manual Z linear stage (Newport) with a 2 inch travel distance. In some embodiments, the rotation fixture 20 may be a PRM1\MZ8 rotation stage (Thorlabs, Newton, NJ) with a maximum rotation speed of 25° per second. The rotation fixture 20 may be attached to a manual 400 millimeter travel linear stage oriented vertically. This allows easy raising and lowering of the vial 14 into and out of the vat 24. The rotation fixture 20 may be controlled by a KDC101 Brushed DC Servo Motor Controller (Thorlabs).

[0113] A method of producing the 3D item 12 via volumetric additive manufacturing is provided herein. The method may include filling the vial 14 with photopolymer resin material. The method may include filling the vat 24 with surround fluid. The method may include coupling the vial of photopolymer resin material 14 to the rotation fixture 20. The method may include placing the vial of photopolymer resinmaterial 14 into the vat of surround fluid 24. The method may include rotating the vial of photopolymer resin material 14 while the vial of photopolymer resin material 14 is positioned in the vat of surround fluid 24. The method may include solidifying preselected portions of the photopolymer resin material by discharging the light 17 through the surround fluid and into the vial of photopolymer resin material 14.

[0114] The method may include chilling the vat of surround fluid 24. Chilling the vat of surround fluid 24 may be performed prior to the step of placing the vial of photopolymer resin material 14 into the vat of surround fluid 24. Chilling the vat of surround fluid 24 may be performed during the step of solidifying pre-selected portions of the photopolymer resin material by discharging the light 17 through the surround fluid and into the vial of photopolymer resin material 14. Chilling the vat of surround fluid 24 may be performed prior to the step of placing the vial of photopolymer resin material 14 into the vat of surround fluid 24 and during the step of solidifying pre-selected portions of the photopolymer resin material by discharging the light 17 through the surround fluid and into the vial of photopolymer resin material 14.

[0115] Chilling the vat of surround fluid 24 may be performed by passing electrical current through the thermoelectric materials 35, 39 of the cooling plate 34, 36. Chilling the vat of surround fluid 24 may be performed by circulation of secondary cooling fluid 30 through the surround fluid. Chilling the vat of surround fluid 24 may be performed by circulating surround fluid out of the vat 24, cooling the surround fluid outside the vat 24, and returning the cooled surround fluid to the vat 24.

[0116] The method may include chilling the vial of photopolymer resin material 14. Chilling the vial of photopolymer resin material 14 may be performed during the step of solidifying pre-selected portions of the photopolymer resin material by discharging the light 17 through the surround fluid and into the vial of photopolymer resin material 14.

[0117] Chilling the vial of photopolymer resin material 14 may be performed by circulation of secondary cooling fluid 44 through the photopolymer resin material. Chilling the vial of photopolymer resin material 14 may be performed by cooling the at least one thermally regulated rod 38.

[0118] The method may include, after solidifying pre-selected portions of the photopolymer resin material by discharging the light 17 through the surround fluid and into the vial of photopolymer resin material 14, removing excess photopolymer resin material from the vial 14 via the outlet port 58. The method may include, after solidifying pre-selected portions of the photopolymer resin material by discharging the light 17 through the surround fluid and into the vial of photopolymer resin material 14, directing a fluid into the vial 14 via the inlet port 56.

[0119] The following numbered clauses include embodiments that are contemplated and non-limiting:

[0120] Clause 1. A volumetric additive manufacturing system, the system comprising a vial of photopolymer resin material; a light source configured to discharge light into the vial of photopolymer resin material and thereby solidify pre-selected portions of the photopolymer resin material; and a cooling unit configured to regulate heat generated during solidification of the photopolymer resin material upon exposure to the light from the light source, the cooling unit including a vat of surround fluid in which the vial of photopolymer resin material is placed, wherein the surround fluid has a refractive index substantially matched with the photopolymer resin material.

[0121] Clause 2. The system of clause 1, any other suitable clause, or any other suitable combination of clauses, wherein the surround fluid has a temperature lower than that of the photopolymer resin material.

[0122] Clause 3. The system of clause 1, any other suitable clause, or any other suitable combination of clauses, wherein the surround fluid is substantially the same material as the photopolymer resin material.

[0123] Clause 4. The system of clause 1, any other suitable clause, or any other suitable combination of clauses, wherein the cooling unit includes an active cooling element configured to withdraw heat from the surround fluid and / or the photopolymer resin material during solidification of the photopolymer resin material.

[0124] Clause 5. The system of clause 4, any other suitable clause, or any other suitable combination of clauses, wherein the active cooling element is a cooling plate in contact with the vat of surround fluid.

[0125] Clause 6. The system of clause 5, any other suitable clause, or any other suitable combination of clauses, wherein the vat of surround fluid is supported on the cooling plate.

[0126] Clause 7. The system of clause 6, any other suitable clause, or any other suitable combination of clauses, wherein the cooling plate surrounds the vat of surround fluid on four sides thereof.

[0127] Clause 8. The system of clause 5, any other suitable clause, or any other suitable combination of clauses, wherein the cooling plate includes thermoelectric materials and an electrical energy source configured to pass electrical current through the thermoelectric materials to cool the cooling plate.

[0128] Clause 9. The system of clause 4, any other suitable clause, or any other suitable combination of clauses, wherein the active cooling element is a cooling pipe that extends into the vat of surround fluid and is configured to carry secondary cooling fluid through the surround fluid and actively remove heat therefrom.

[0129] Clause 10. The system of clause 9, any other suitable clause, or any other suitable combination of clauses, wherein the cooling pipe extends only along a back side of the vat of surround fluid opposite the light source.

[0130] Clause 11. The system of clause 9, any other suitable clause, or any other suitable combination of clauses, wherein the cooling pipe extends along three sides of the vat of surround fluid.

[0131] Clause 12. The system of clause 4, any other suitable clause, or any other suitable combination of clauses, wherein the active cooling element is a recirculating pipe that extends into the vat of surround fluid and is configured to circulate surround fluid out of the vat for cooling before being returned to the vat.

[0132] Clause 13. The system of clause 4, any other suitable clause, or any other suitable combination of clauses, wherein the active cooling element is at least one thermally regulated rod that extends into the vial of photopolymer resin material.

[0133] Clause 14. The system of clause 13, any other suitable clause, or any other suitable combination of clauses, wherein the at least one thermally regulated rod is optically transparent.

[0134] Clause 15. The system of clause 13, any other suitable clause, or any other suitable combination of clauses, wherein the at least one thermally regulated rod has a refractive index substantially matched with the photopolymer resin material.

[0135] Clause 16. The system of clause 4, any other suitable clause, or any other suitable combination of clauses, wherein the active cooling element is a cooling pipe that extends into the vial of photopolymer resin material and is configured to carry secondary cooling fluid through the photopolymer resin material and actively remove heat therefrom.

[0136] Clause 17. The system of clause 16, any other suitable clause, or any other suitable combination of clauses, wherein the cooling pipe has a refractive index substantially matched with the photopolymer resin material.

[0137] Clause 18. The system of clause 4, any other suitable clause, or any other suitable combination of clauses, wherein the cooling unit includes a temperature sensor and a controller in communication with the temperature sensor.

[0138] Clause 19. The system of clause 18, any other suitable clause, or any other suitable combination of clauses, wherein the temperature sensor is configured to measure temperature associated with the photopolymer resin material and / or the surround fluid.

[0139] Clause 20. The system of clause 19, any other suitable clause, or any other suitable combination of clauses, wherein the temperature sensor is a non-contact sensor that is spaced apart from the photopolymer resin material and / or the surround fluid.

[0140] Clause 21. The system of clause 18, any other suitable clause, or any other suitable combination of clauses, wherein the controller is in communication with the lightsource and the controller is configured to modify operating parameters of the light source based, at least in part, on input from the temperature sensor.

[0141] Clause 22. The system of clause 18, any other suitable clause, or any other suitable combination of clauses, wherein the controller is in communication with the active cooling element and the controller is configured to modify operating parameters of the active cooling element based, at least in part, on input from the temperature sensor.

[0142] Clause 23. The system of clause 1, any other suitable clause, or any other suitable combination of clauses, wherein the vial is formed to include an inlet port and an outlet port configured to direct excess photopolymer resin material out of the vial after solidification of the photopolymer resin material.

[0143] Clause 24. The system of clause 23, any other suitable clause, or any other suitable combination of clauses, wherein the inlet port is configured to direct a fluid into the vial after solidification of the photopolymer resin material.

[0144] Clause 25. The system of clause 24, any other suitable clause, or any other suitable combination of clauses, wherein the fluid includes a cleaning solution or air.

[0145] Clause 26. A method of producing an item via volumetric additive manufacturing, the method comprising filling a vial of photopolymer resin material; placing the vial of photopolymer resin material into a vat of surround fluid, wherein the surround fluid has a refractive index substantially matched with the photopolymer resin material; and solidifying pre-selected portions of the photopolymer resin material by discharging light through the surround fluid and into the vial of photopolymer resin material.

[0146] Clause 27. The method of clause 26, any other suitable clause, or any other suitable combination of clauses, further comprising chilling the vat of surround fluid.

[0147] Clause 28. The method of clause 27, any other suitable clause, or any other suitable combination of clauses, wherein chilling the vat of surround fluid is performed prior to the step of placing the vial of photopolymer resin material into the vat of surround fluid.

[0148] Clause 29. The method of clause 27, any other suitable clause, or any other suitable combination of clauses, wherein chilling the vat of surround fluid is performed during the step of solidifying pre-selected portions of the photopolymer resin material by discharging light through the surround fluid and into the vial of photopolymer resin material.

[0149] Clause 30. The method of clause 29, any other suitable clause, or any other suitable combination of clauses, wherein the vat of surround fluid is part of a cooling unit, and the cooling unit includes an active cooling element in contact with the vat of surround fluid.

[0150] Clause 31. The method of clause 30, any other suitable clause, or any other suitable combination of clauses, wherein the active cooling element is a cooling plate in contact with the vat of surround fluid.

[0151] Clause 32. The method of clause 31, any other suitable clause, or any other suitable combination of clauses, wherein the cooling plate includes thermoelectric materials and chilling the vat of surround fluid is performed by passing electrical current through the thermoelectric materials.

[0152] Clause 33. The method of clause 30, any other suitable clause, or any other suitable combination of clauses, wherein the active cooling element is a cooling pipe that extends into the vat of surround fluid and chilling the vat of surround fluid is performed by circulation of secondary cooling fluid through the surround fluid.

[0153] Clause 34. The method of clause 30, any other suitable clause, or any other suitable combination of clauses, wherein the active cooling element is a recirculating pipe that extends into the vat of surround fluid and chilling the vat of surround fluid is performed by circulating surround fluid out of the vat, cooling the surround fluid outside the vat, and returning the cooled surround fluid to the vat.

[0154] Clause 35. The method of clause 30, any other suitable clause, or any other suitable combination of clauses, wherein operating parameters of the light source and / or the cooling unit are modified based, at least in part, on input from a temperature sensor.

[0155] Clause 36. The method of clause 35, any other suitable clause, or any other suitable combination of clauses, wherein the temperature sensor is a non-contact temperature sensor.

[0156] Clause 37. The method of clause 26, any other suitable clause, or any other suitable combination of clauses, further comprising chilling the vial of photopolymer resin material.

[0157] Clause 38. The method of clause 37, any other suitable clause, or any other suitable combination of clauses, wherein chilling the vial of photopolymer resin material is performed during the step of solidifying pre-selected portions of the photopolymer resin material by discharging light through the surround fluid and into the vial of photopolymer resin material.

[0158] Clause 39. The method of clause 38, any other suitable clause, or any other suitable combination of clauses, further comprising providing a cooling unit that includes an active cooling element.

[0159] Clause 40. The method of clause 39, any other suitable clause, or any other suitable combination of clauses, wherein the active cooling element is a cooling pipe that extends into the vial of photopolymer resin material and chilling the vial of photopolymer resin material is performed by circulation of secondary cooling fluid through the photopolymer resin material.

[0160] Clause 41. The method of clause 39, any other suitable clause, or any other suitable combination of clauses, wherein the active cooling element is at least one thermally regulated rod that extends into the vial of photopolymer resin material and chilling the vial of photopolymer resin material is performed by cooling the at least one thermally regulated rod.

[0161] Clause 42. The method of clause 39, any other suitable clause, or any other suitable combination of clauses, wherein operating parameters of the light source and / or the cooling unit are modified based, at least in part, on input from a temperature sensor.

[0162] Clause 43. The method of clause 42, any other suitable clause, or any other suitable combination of clauses, wherein the temperature sensor is a non-contact temperature sensor.

[0163] Clause 44. The method of clause 26, any other suitable clause, or any other suitable combination of clauses, further comprising, after solidifying pre-selected portions of the photopolymer resin material by discharging light through the surround fluid and into the vial of photopolymer resin material, removing excess photopolymer resin material from the vial via an outlet port.

[0164] Clause 45. The method of clause 44, any other suitable clause, or any other suitable combination of clauses, further comprising, after solidifying pre-selected portions of the photopolymer resin material by discharging light through the surround fluid and into the vial of photopolymer resin material, directing a fluid into the vial via an inlet port.

[0165] Clause 46. The method of clause 26, any other suitable clause, or any other suitable combination of clauses, further comprising rotating the vial of photopolymer resin material while the vial of photopolymer resin material is positioned in the vat of surround fluid

[0166] Clause 47. The method of clause 26, any other suitable clause, or any other suitable combination of clauses, further comprising providing the volumetric additive manufacturing system of one of clauses 1-25.

Claims

CLAIMS1. A volumetric additive manufacturing system, the system comprising a vial of photopolymer resin material, a light source configured to discharge light into the vial of photopolymer resin material and thereby solidify pre-selected portions of the photopolymer resin material, and a cooling unit configured to regulate heat generated during solidification of the photopolymer resin material upon exposure to the light from the light source, the cooling unit including a vat of surround fluid in which the vial of photopolymer resin material is placed, wherein the surround fluid has a refractive index substantially matched with the photopolymer resin material.

2. The system of claim 1, any other suitable claim, or any other suitable combination of claims, wherein the surround fluid has a temperature lower than that of the photopolymer resin material.

3. The system of claim 1, any other suitable claim, or any other suitable combination of claims, wherein the surround fluid is substantially the same material as the photopolymer resin material.

4. The system of claim 1, any other suitable claim, or any other suitable combination of claims, wherein the cooling unit includes an active cooling element configured to withdraw heat from the surround fluid and / or the photopolymer resin material during solidification of the photopolymer resin material.

5. The system of claim 4, any other suitable claim, or any other suitable combination of claims, wherein the active cooling element is a cooling plate in contact with the vat of surround fluid.

6. The system of claim 5, any other suitable claim, or any other suitable combination of claims, wherein the vat of surround fluid is supported on the cooling plate.

7. The system of claim 6, any other suitable claim, or any other suitable combination of claims, wherein the cooling plate surrounds the vat of surround fluid on four sides thereof.

8. The system of claim 5, any other suitable claim, or any other suitable combination of claims, wherein the cooling plate includes thermoelectric materials and an electrical energy source configured to pass electrical current through the thermoelectric materials to cool the cooling plate.

9. The system of claim 4, any other suitable claim, or any other suitable combination of claims, wherein the active cooling element is a cooling pipe that extends into the vat of surround fluid and is configured to carry secondary cooling fluid through the surround fluid and actively remove heat therefrom.

10. The system of claim 9, any other suitable claim, or any other suitable combination of claims, wherein the cooling pipe extends only along a back side of the vat of surround fluid opposite the light source.

11. The system of claim 9, any other suitable claim, or any other suitable combination of claims, wherein the cooling pipe extends along three sides of the vat of surround fluid.

12. The system of claim 4, any other suitable claim, or any other suitable combination of claims, wherein the active cooling element is a recirculating pipe that extends into the vat of surround fluid and is configured to circulate surround fluid out of the vat for cooling before being returned to the vat.

13. The system of claim 4, any other suitable claim, or any other suitable combination of claims, wherein the active cooling element is at least one thermally regulated rod that extends into the vial of photopolymer resin material.

14. The system of claim 13, any other suitable claim, or any other suitable combination of claims, wherein the at least one thermally regulated rod is optically transparent.

15. The system of claim 13, any other suitable claim, or any other suitable combination of claims, wherein the at least one thermally regulated rod has a refractive index substantially matched with the photopolymer resin material.

16. The system of claim 4, any other suitable claim, or any other suitable combination of claims, wherein the active cooling element is a cooling pipe that extends into the vial of photopolymer resin material and is configured to carry secondary cooling fluid through the photopolymer resin material and actively remove heat therefrom.

17. The system of claim 16, any other suitable claim, or any other suitable combination of claims, wherein the cooling pipe has a refractive index substantially matched with the photopolymer resin material.

18. The system of claim 4, any other suitable claim, or any other suitable combination of claims, wherein the cooling unit includes a temperature sensor and a controller in communication with the temperature sensor.

19. The system of claim 18, any other suitable claim, or any other suitable combination of claims, wherein the temperature sensor is configured to measure temperature associated with the photopolymer resin material and / or the surround fluid.

20. The system of claim 19, any other suitable claim, or any other suitable combination of claims, wherein the temperature sensor is a non-contact sensor that is spaced apart from the photopolymer resin material and / or the surround fluid.

21. The system of claim 18, any other suitable claim, or any other suitable combination of claims, wherein the controller is in communication with the light source and the controller is configured to modify operating parameters of the light source based, at least in part, on input from the temperature sensor.

22. The system of claim 18, any other suitable claim, or any other suitable combination of claims, wherein the controller is in communication with the active cooling element and the controller is configured to modify operating parameters of the active cooling element based, at least in part, on input from the temperature sensor.

23. The system of claim 1, any other suitable claim, or any other suitable combination of claims, wherein the vial is formed to include an inlet port and an outlet port configured to direct excess photopolymer resin material out of the vial after solidification of the photopolymer resin material.

24. The system of claim 23, any other suitable claim, or any other suitable combination of claims, wherein the inlet port is configured to direct a fluid into the vial after solidification of the photopolymer resin material.

25. The system of claim 24, any other suitable claim, or any other suitable combination of claims, wherein the fluid includes a cleaning solution or air.

26. A method of producing an item via volumetric additive manufacturing, the method comprising filling a vial of photopolymer resin material, placing the vial of photopolymer resin material into a vat of surround fluid, wherein the surround fluid has a refractive index substantially matched with the photopolymer resin material, and solidifying pre-selected portions of the photopolymer resin material by discharging light through the surround fluid and into the vial of photopolymer resin material.

27. The method of claim 26, any other suitable claim, or any other suitable combination of claims, further comprising chilling the vat of surround fluid.

28. The method of claim 27, any other suitable claim, or any other suitable combination of claims, wherein chilling the vat of surround fluid is performed prior to the step of placing the vial of photopolymer resin material into the vat of surround fluid.

29. The method of claim 27, any other suitable claim, or any other suitable combination of claims, wherein chilling the vat of surround fluid is performed during the step of solidifying pre-selected portions of the photopolymer resin material by discharging light through the surround fluid and into the vial of photopolymer resin material.

30. The method of claim 29, any other suitable claim, or any other suitable combination of claims, wherein the vat of surround fluid is part of a cooling unit, and the cooling unit includes an active cooling element in contact with the vat of surround fluid.

31. The method of claim 30, any other suitable claim, or any other suitable combination of claims, wherein the active cooling element is a cooling plate in contact with the vat of surround fluid.

32. The method of claim 31, any other suitable claim, or any other suitable combination of claims, wherein the cooling plate includes thermoelectric materials and chilling the vat of surround fluid is performed by passing electrical current through the thermoelectric materials.

33. The method of claim 30, any other suitable claim, or any other suitable combination of claims, wherein the active cooling element is a cooling pipe that extends into the vat of surround fluid and chilling the vat of surround fluid is performed by circulation of secondary cooling fluid through the surround fluid.

34. The method of claim 30, any other suitable claim, or any other suitable combination of claims, wherein the active cooling element is a recirculating pipe that extends into the vat of surround fluid and chilling the vat of surround fluid is performed by circulating surround fluid out of the vat, cooling the surround fluid outside the vat, and returning the cooled surround fluid to the vat.

35. The method of claim 30, any other suitable claim, or any other suitable combination of claims, wherein operating parameters of the light source and / or the cooling unit are modified based, at least in part, on input from a temperature sensor.

36. The method of claim 35, any other suitable claim, or any other suitable combination of claims, wherein the temperature sensor is a non-contact temperature sensor.

37. The method of claim 26, any other suitable claim, or any other suitable combination of claims, further comprising chilling the vial of photopolymer resin material.

38. The method of claim 37, any other suitable claim, or any other suitable combination of claims, wherein chilling the vial of photopolymer resin material is performed during the step of solidifying pre-selected portions of the photopolymer resin material by discharging light through the surround fluid and into the vial of photopolymer resin material.

39. The method of claim 38, any other suitable claim, or any other suitable combination of claims, further comprising providing a cooling unit that includes an active cooling element.

40. The method of claim 39, any other suitable claim, or any other suitable combination of claims, wherein the active cooling element is a cooling pipe that extends into the vial of photopolymer resin material and chilling the vial of photopolymer resin material is performed by circulation of secondary cooling fluid through the photopolymer resin material.

41. The method of claim 39, any other suitable claim, or any other suitable combination of claims, wherein the active cooling element is at least one thermally regulated rod that extends into the vial of photopolymer resin material and chilling the vial of photopolymer resin material is performed by cooling the at least one thermally regulated rod.

42. The method of claim 39, any other suitable claim, or any other suitable combination of claims, wherein operating parameters of the light source and / or the cooling unit are modified based, at least in part, on input from a temperature sensor.

43. The method of claim 42, any other suitable claim, or any other suitable combination of claims, wherein the temperature sensor is a non-contact temperature sensor.

44. The method of claim 26, any other suitable claim, or any other suitable combination of claims, further comprising, after solidifying pre-selected portions of the photopolymer resin material by discharging light through the surround fluid and into the vial of photopolymer resin material, removing excess photopolymer resin material from the vial via an outlet port.

45. The method of claim 44, any other suitable claim, or any other suitable combination of claims, further comprising, after solidifying pre-selected portions of the photopolymer resin material by discharging light through the surround fluid and into the vial of photopolymer resin material, directing a fluid into the vial via an inlet port.

46. The method of claim 26, any other suitable claim, or any other suitable combination of claims, further comprising rotating the vial of photopolymer resin material while the vial of photopolymer resin material is positioned in the vat of surround fluid47. The method of claim 26, any other suitable claim, or any other suitable combination of claims, further comprising providing the volumetric additive manufacturing system of one of claims 1-25.

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