Rotating vat apparatus and method for facilitating continuous liquid interface printing resin reflow

Abstract

The application discloses a rotating liquid tank device and method for promoting continuous liquid interface printing resin backflow, the device comprises a passive transmission mechanism and an active transmission mechanism, the outer circumferential surface of the passive transmission mechanism is fixed with a meshing rack, and the active transmission mechanism meshes with the meshing rack to drive the passive transmission mechanism to rotate. The method comprises the following steps: pouring resin slurry into a groove, stopping when a printing platform is lowered above a oxygen permeable membrane, driving the passive transmission mechanism to rotate by the active transmission mechanism, driving the backflow resin to flow in a flow shear zone between a printed object and the oxygen permeable membrane, diluting the resin in the area, reducing the viscosity, and promoting the resin backflow in the printing process. The application significantly reduces the viscosity of the resin in the printing process, has large-format and large-size printing forming capacity, and overcomes the defects that the traditional continuous liquid interface printing can only print a small format.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of light-cured 3D printing, in particular to a rotating liquid tank device and method for promoting resin backflow in continuous liquid interface printing process. BACKGROUND

[0002] Light-cured 3D printing technology has the advantages of high forming precision and fast forming speed compared with other 3D printing methods, and is widely used in the fields of biological medicine, ceramic manufacturing, dentistry, etc. The traditional digital light processing (DLP) light-cured printing technology needs to go through the repetitive steps of sinking, curing and lifting for each layer. This intermittent and discrete printing method not only affects the printing efficiency, but also causes obvious "step effect" on the surface of the product due to the layer-by-layer accumulation, which seriously affects the surface finish. In recent years, the continuous liquid interface printing technology (CLIP) further innovates light-cured 3D printing. This technology mainly relies on the oxygen-permeable membrane at the bottom of the liquid tank to realize the penetration of oxygen, and the light-cured polymerization reaction is inhibited by oxygen, so a layer of flowing area that will not be cured, also known as dead zone, is formed above the oxygen-permeable membrane. Based on the above principle, the continuous liquid interface printing technology can realize the continuous lifting of the printing platform and the continuous exposure of the light source. Therefore, not only is the printing speed greatly improved, but the continuous forming principle also fundamentally eliminates the "step effect" and improves the surface finish of the product.

[0003] However, an important problem faced by the continuous liquid interface printing technology is the timely filling and backflow of the resin slurry. During the continuous lifting of the printing platform, the resin below the printed object needs to backflow in time to fill the gap left for the next time of curing. The resin slurry used for light-cured 3D printing has non-Newtonian fluid characteristics and high viscosity, and in the continuous liquid interface printing process, the resin slurry often fails to backflow completely within a limited time due to the large printing area or high resin viscosity. Due to the continuous printing method, the time for resin backflow is greatly shortened. Therefore, often due to incomplete filling of the resin, there are printing defects such as voids in the center of the printed object. However, the time for the resin to backflow to the center point is not only related to the design size of the printed object, but also has a great relationship with the viscosity of the printing resin. The higher the viscosity, the slower the backflow speed. Therefore, the existing continuous liquid interface printing technology is difficult to be used for high-viscosity resin slurry and large-size area printing process, and is often used for low-viscosity resin, hollow structure, small area printing forming, which seriously limits the application of the technology. SUMMARY

[0004] In order to solve the above problems, the application discloses a rotating liquid tank device and method for promoting continuous liquid interface printing resin reflux. By utilizing the shear thinning characteristics of resin slurry non-Newtonian fluid, the rotation of the liquid tank is used to generate shear force in the reflux gap between the bottom of the printed object and the oxygen permeable membrane by the rotation of the liquid tank body, so as to form a flow shear zone. Due to the effect of shear force on the resin in the reflux gap, the viscosity of the resin is reduced, the reflux efficiency is further improved, and the resin has the ability to print high-viscosity resin and large-format objects.

[0005] The technical scheme adopted by the application is:

[0006] One kind is a rotating liquid tank device for promoting resin reflux in continuous liquid interface printing process:

[0007] The device comprises a passive transmission mechanism and an active transmission mechanism, and the passive transmission mechanism and the active transmission mechanism form a rotating liquid tank overall structure, the passive transmission mechanism is in a circular structure, and an annular meshing rack is fixed on the outer circumferential surface of the passive transmission mechanism, the active transmission mechanism is arranged beside the passive transmission mechanism, and the meshing rack drives the passive transmission mechanism to rotate.

[0008] The passive transmission mechanism comprises a liquid storage tank body, a circular groove is formed in the top surface of the liquid storage tank body, the groove is circular to facilitate transmission, and the flow state of the fluid in the liquid tank is more stable, thereby reducing energy loss, an annular meshing rack is fixedly installed on the outer wall of the liquid storage tank body, the meshing rack and the liquid storage tank body are an integral structure, and the integral structure can be integrally machined by CNC or machined in two parts and then combined by welding, and the meshing rack is connected to the active transmission mechanism.

[0009] The active transmission mechanism comprises a driving motor, a shaft coupling and a main transmission component, the driving motor and the main transmission component are horizontally arranged, the driving motor is connected to a power supply, the output end of the driving motor is connected to the main transmission component through the shaft coupling, the main transmission component meshes with the meshing rack, and the driving motor transmits power to the main transmission component through the shaft coupling, so that the liquid storage tank body with the meshing rack is rotated under the driving of the main transmission component.

[0010] A support bearing is fixedly sleeved on the bottom of the liquid storage tank body, the liquid storage tank body is in interference fit with the support bearing, and the support bearing plays a role of fixing the liquid storage tank body, and the meshing rack is located above the support bearing by about 10mm.

[0011] The circular groove bottom of the liquid storage tank body is provided with a transparent oxygen permeable film, and the circular groove bottom generates a solidification dead zone with a thickness of about 100 μm. The groove above the oxygen permeable film is provided with a resin filling area to be filled with a non-Newtonian fluid backflow resin. The upper part of the liquid storage tank body is provided with a circular printing platform which is lifted along the vertical direction. The diameter of the printing platform is greater than 120 mm and less than the inner diameter of the liquid storage tank body, so that the printing device has a large-size printing capacity. The printing platform is below the printing object, and the printing layer thickness is set to 10 μm. A gap is left between the printing object and the oxygen permeable film to form a flow shear zone for the backflow resin. Through the rotation of the liquid storage tank body, a flow shear zone with a thickness of about 110 μm is maintained between the printing object and the oxygen permeable film. Under the action of rotational shear, the resin filling area above the oxygen permeable film accelerates the filling of the non-Newtonian fluid backflow resin.

[0012] The liquid storage tank body and the printing platform are designed in a circular structure, and the rotation is realized by means of meshing rack and supporting bearing. The rotation movement is realized without the need of a central support shaft, which avoids the interference between the central shaft and the bottom ultraviolet light source. In addition, the flow of the liquid in the circular liquid storage tank body is more stable during rotation, and no turbulence is generated, which avoids the loss of flow energy and the damage to the shear flow field.

[0013] The transmission mode of the main transmission component and the meshing rack is worm gear transmission, which can also be chain transmission or gear transmission. The worm gear transmission has a large transmission ratio, and the meshing surface between the worm gear and the gear is relatively large, so that the relative sliding speed is low. The structure of the worm gear transmission is relatively compact, which can reduce the occupied space of the printer.

[0014] The material of the oxygen permeable film is polytetrafluoroethylene film material, which has good light and oxygen permeability.

[0015] II. A method for promoting continuous liquid interface printing by rotating the liquid tank body device:

[0016] 1) Pour the resin slurry into the groove of the liquid storage tank body. When the printing platform is lowered to a distance of 110 μm above the oxygen permeable film, stop. The driving transmission mechanism drives the driven transmission mechanism to rotate.

[0017] 2) The driven transmission mechanism rotates to drive the backflow resin to flow in the flow shear zone between the printing object and the oxygen permeable film. At this time, the printing platform moves upward along the vertical direction to start printing.

[0018] The step 1) is specifically: the driving motor transmits power to the main transmission component through the shaft coupling. The main transmission component and the meshing rack worm gear transmission drive the liquid storage tank body to rotate. The rotation speed and shear rate of the liquid storage tank body can be adjusted by controlling the rotation speed of the driving motor.

[0019] The step 2) is specifically: the rotating movement of the liquid tank body pulls the flowing resin in the flow shear zone, the flowing resin generates fluid shear force and reduces the viscosity of the flowing resin, the fluid shear force is uniformly distributed, the flowing resin flows stably, and the center of the circular groove of the liquid tank body is taken as the center, the printing process is controlled by the shear rate at different radial positions of the circular groove, the shear rate of the fluid shear force at different radial positions of the circular groove is different at the same rotating speed, and the farther from the center, the higher the shear rate.

[0020] When actually starting printing, the single-layer thickness of the set model slice is 10 mu m, the resin slurry is poured into the liquid tank body, the printing platform is lowered in the vertical direction, and stops when reaching a distance of about 110 mu m above the oxygen permeable membrane. The driving motor transmits power to the main transmission component through the shaft coupling, and under the driving of the main transmission component, the liquid tank body with the meshing rack is rotated. The rotating speed of the liquid tank body and the shear rate thereof can be adjusted by controlling the rotating speed of the driving motor. The slit liquid film formed between the printed object and the oxygen permeable membrane generates fluid shear force under the action of the liquid tank rotation, so that the viscosity of the resin slurry in the slit liquid film is reduced, and the backflow speed of the resin in the printing process is promoted.

[0021] During printing, the resin slurry flows in the slit under the action of shear, and the flow speed of the resin slurry is seriously affected by the viscosity of the liquid itself. Therefore, under the same printing size, the backflow filling time of the resin slurry after shear thinning is greatly shortened, the efficiency of resin flow is improved, and printing defects caused by insufficient backflow filling are avoided.

[0022] The beneficial effects of the present application are:

[0023] 1. The shear thinning property of the non-Newtonian fluid is utilized, the rotating liquid tank body drives the shear action of the thin layer flowing area between the oxygen permeable membrane and the printed object, so that the viscosity of the resin in the area is significantly reduced, the efficiency of resin backflow filling and overall printing is improved, and the ability to print high-viscosity resin is further obtained.

[0024] 2. The circular structure of the liquid tank body and the printing platform ensures the feasibility and stability of power transmission; at the same time, during the rotation of the liquid tank, the liquid resin moves under the action of shear force, the circular structure is used to avoid turbulence and prevent the printed object from being damaged, and the transmission of fluid shear energy is also facilitated.

[0025] 3. The rotating liquid tank structure not only improves the resin backflow efficiency and avoids printing defects, but also has large-format and large-size printing forming capability, overcoming the disadvantage of traditional continuous liquid interface printing that can only print small formats. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 : Rotating liquid tank structure overall schematic diagram.

[0027] Figure 2 : Schematic diagram of the cross section of the rotating liquid tank structure.

[0028] Figure 3 : Shear thinning diagram of non-Newtonian fluid-resin slurry.

[0029] Figure 4 : Schematic diagram of the internal shear force distribution of the rotating liquid tank.

[0030] Figure 5 : Schematic diagram of promoting resin backflow filling.

[0031] In the figure: 1. The overall structure of the rotating liquid tank body, 2. The driving mechanism, 3. The driven transmission mechanism, 4. The liquid storage tank body, 5. The meshing rack, 6. The support bearing, 7. The oxygen-permeable membrane, 8. The printing platform, 9. The printed object, 10. The driving motor, 11. The coupling, 12. The main transmission part, 13. The backflow resin, 14. The area to be filled with resin. DETAILED DESCRIPTION

[0032] The technical solutions of the present application will be described and explained in detail below through specific examples. The described examples are only preferred embodiments of the present application, not all examples. On the basis of this embodiment, the remaining examples without any creative improvements belong to the protection scope of this embodiment.

[0033] As shown in Figure 1 , Figure 2 , the rotating liquid tank body device of the present application includes a driven transmission mechanism 3 and a driving mechanism 2. The driven transmission mechanism 3 and the driving mechanism 2 form the overall structure of the rotating liquid tank body 1. The driven transmission mechanism 3 is in a circular structure. An annular meshing rack 5 is fixed on the outer circumferential surface of the driven transmission mechanism 3. The driving mechanism 2 is arranged beside the driven transmission mechanism 3, and the meshing rack 5 drives the rotating movement of the driven transmission mechanism 3.

[0034] The driven transmission mechanism 3 includes a liquid storage tank body 4. A circular groove is formed on the top surface of the liquid storage tank body 4. The circular groove is beneficial for transmission and the flow state of the fluid in the liquid tank is more stable, reducing energy loss. An annular meshing rack 5 is fixedly installed on the outer wall of the liquid storage tank body 4. The meshing rack 5 and the liquid storage tank body 4 are in an integrated structure, which can be integrally processed by CNC or separately processed and then combined by welding. Both are made of stainless steel. The height of the liquid storage tank body 4 is designed to be 60 mm, and the diameter is 150 mm. The tooth surface width of the meshing rack 5 is designed to be 13 mm to avoid vibration during transmission. The meshing rack 5 is connected to the driving mechanism 2.

[0035] The main drive mechanism 2 comprises a driving motor 10, a shaft coupling 11 and a main drive component 12; the driving motor 10 and the main drive component 12 are horizontally arranged, the driving motor 10 is connected with a power supply, the output end of the driving motor 10 is connected with the main drive component 12 through the shaft coupling 11, the main drive component 12 meshes with the meshing rack 5, the driving motor 10 transmits power to the main drive component 12 through the shaft coupling 11, and under the driving of the main drive component 12, the liquid storage tank body 4 with the meshing rack 5 rotates.

[0036] The bottom of the liquid storage tank body 4 is fixedly sleeved with a supporting bearing 6, the liquid storage tank body 4 is in interference fit with the supporting bearing 6, and the supporting bearing 6 plays a role in fixing the liquid storage tank body 4; the meshing rack 5 is located at about 10 mm above the supporting bearing 6.

[0037] The bottom of the circular groove of the liquid storage tank body 4 is provided with a transparent oxygen-permeable film 7, and the oxygen-permeable film 7 is used for preventing free radical polymerization by oxygen permeation, so as to generate a solidified dead zone with a thickness of about 100 μm, that is, a resin flow renewal area; a to-be-resin-filled area 14 is arranged in the groove above the oxygen-permeable film 7, the to-be-resin-filled area 14 is filled with a backflow resin 13 of a non-Newtonian fluid, and a circular printing platform 8 that can ascend and descend along a vertical direction is arranged above the liquid storage tank body 4; the diameter of the printing platform 8 is greater than 120 mm and less than the inner diameter of the liquid storage tank body 4, so that the printing platform 8 has a large-format printing capability; since the printing platform 8 needs to continuously ascend along the vertical direction, the time left for resin slurry backflow filling is short, and the printing platform 8 is only suitable for low-viscosity resin slurry or small-size format printing, and does not have a large-size format printing capability. The backflow resin area is sheared and thinned to realize rapid backflow, the size of the printing platform 8 is designed to be large enough, so as to meet the demand of large-format printing forming. A printed object 9 is arranged below the printing platform 8, the printing platform 8 is made of an aluminum alloy material through CNC processing, and the surface of the printing platform 8 is ground to ensure that the printing platform 8 and the printed object 9 have good adhesion. The liquid storage tank body 4 with the meshing rack 5 is embedded in the supporting bearing 6 below, and is in interference fit with the inner wall of the bearing, so as to ensure the stability of transmission. The printing layer thickness is set to 10 μm, a gap is left between the printed object 9 and the oxygen-permeable film 7 to form a flow shear area for the backflow resin 13, the printed object 9 and the oxygen-permeable film 7 keep a flow shear area with a thickness of about 110 μm through the rotation of the liquid storage tank body 4, and under the action of rotation shear, the to-be-resin-filled area 14 above the oxygen-permeable film 7 accelerates the filling of the backflow resin 13 of the non-Newtonian fluid.

[0038] The traditional square liquid tank is not conducive to transmission, therefore, the liquid tank body 4 and the corresponding printing platform 8 are designed as a circular structure, and the rotation driving is realized by means of the annular meshing rack 5 and the support bearing 6 at the bottom end of the liquid tank, so that the rotation movement can be realized without the center support shaft, and the interference between the center shaft and the bottom ultraviolet light source is avoided. In addition, the liquid flow is more stable in the rotating process of the circular liquid tank body 4, and no turbulence is generated, so that the loss of flow energy and the damage to the shear flow field are avoided.

[0039] As shown in the viscosity of the resin slurry and the relationship between the shear rate of the light-cured 3D printing resin slurry is shown in the figure, the viscosity of the resin slurry is significantly affected by the shear rate. In the initial stage of shearing, the viscosity of the resin slurry decreases significantly, and finally tends to be stable, showing obvious non-Newtonian fluid characteristics, and finally the viscosity of the resin slurry is significantly reduced by about 10 times under the influence of shearing. Figure 3

[0040] The transmission mode of the main transmission component 12 and the meshing rack 5 is worm gear transmission, and can also be chain transmission or gear transmission; the worm gear transmission has a large transmission ratio, and the meshing surface between the worm gear and the gear is relatively large, the relative sliding speed is low, the structure of the worm gear transmission is relatively compact, and the occupied space of the printer can be reduced.

[0041] The material of the oxygen-permeable film 7 is polytetrafluoroethylene film material, which has good light and oxygen permeability.

[0042] The continuous liquid interface printing method of the rotating liquid tank body device of the application comprises the following steps:

[0043] 1) Pour the resin slurry into the groove of the liquid tank body 4, lower the printing platform 8 along the vertical direction to stop when it is 110μm above the oxygen-permeable film 7, and drive the passive transmission mechanism 3 to rotate by the driving transmission mechanism 2.

[0044] 2) The passive transmission mechanism 3 rotates to drive the backflow resin 13 to flow in the flow shear zone between the printing object 9 and the oxygen-permeable film 7, and at this time the printing platform 8 moves upward along the vertical direction to start printing.

[0045] Step 1) is specifically: the driving motor 10 transmits power to the main transmission component 12 through the shaft coupling 11, and the main transmission component 12 and the meshing rack 5 are driven to rotate by the worm gear transmission, so that the liquid tank body 4 rotates.

[0046] Step 2) is specifically: the rotating motion of the liquid tank body 4 pulls and tears the flowing resin 13 in the flow shear zone, the flowing resin 13 generates fluid shear force and reduces its own viscosity, and the shear distribution effect of the fluid shear zone between the printing object 9 and the oxygen-permeable film 7 driven by the rotating liquid tank is shown in the figure. Figure 4 ​As shown, the fluid shear force is uniformly distributed, and the resin 13 flows stably. The printing process is controlled by the shear rate at different radial positions of the circular groove, and the shear rate of the fluid shear force at different radial positions of the circular groove is different at the same rotational speed. The farther from the center, the higher the shear rate.

[0047] When the printing actually starts, the single-layer thickness of the model slice is set to 10 μm, the resin slurry is poured into the liquid tank body 4, the printing platform 8 is lowered in the vertical direction, and stops when it reaches a distance of about 110 μm above the oxygen-permeable film 7. The driving motor 10 transmits power to the main transmission component 12 through the shaft coupling 11, and under the drive of the main transmission component 12, the liquid tank body 4 with the meshing rack 5 is rotated. The rotational speed of the liquid tank body 4 and its shear rate can be adjusted by controlling the rotational speed of the driving motor 10. The slit liquid film formed between the printed object 9 and the oxygen-permeable film 7 generates fluid shear force under the action of the liquid tank rotation, which reduces the viscosity of the resin slurry in it, and promotes the backflow speed of the resin in the printing process.

[0048] In the printing process, the backflow process of the resin slurry under the action of shear is as shown in FIG. 6. Figure 5 As shown, the liquid flows in the slit, and its flow speed is seriously affected by the viscosity of the liquid itself. Therefore, under the same printing size, the backflow filling time of the shear-thinning resin slurry is greatly shortened, the efficiency of resin flow is improved, and the printing defects due to insufficient backflow filling are avoided.

Claims

1. A continuous liquid interface printing method for promoting the backflow of resin in a rotating liquid tank device, characterized in that: the rotating liquid tank device comprises a passive transmission mechanism (3) and an active transmission mechanism (2), the passive transmission mechanism (3) is circular in overall structure, and an annular meshing rack (5) is fixed on the outer circumferential surface of the passive transmission mechanism (3); the active transmission mechanism (2) is arranged beside the passive transmission mechanism (3), and the active transmission mechanism (2) meshes with the meshing rack (5) to drive the passive transmission mechanism (3) to rotate; the passive transmission mechanism (3) comprises a liquid storage tank (4); a circular groove is formed in the top surface of the liquid storage tank (4), and an annular meshing rack (5) is fixedly installed on the outer wall of the liquid storage tank (4); the meshing rack (5) is connected with the active transmission mechanism (2); the bottom of the circular groove of the liquid storage tank (4) is provided with a transparent oxygen-permeable film (7), a resin filling area (14) is arranged in the groove above the oxygen-permeable film (7), the resin filling area (14) is filled with a non-Newtonian fluid backflow resin (13), a circular printing platform (8) is arranged above the liquid storage tank (4) and can move up and down along the vertical direction, a printed object (9) is arranged below the printing platform (8), the printing layer thickness is set to 10 μm, and a gap with a thickness of 110 μm is left between the printed object (9) and the oxygen-permeable film (7) to form a flow shear zone; the continuous liquid interface printing method comprises the following steps: 1) pouring resin slurry into the groove of the liquid storage tank (4), stopping when the printing platform (8) is lowered to a distance of 110 μm above the oxygen-permeable film (7) along the vertical direction, and driving the passive transmission mechanism (3) to rotate by the active transmission mechanism (2); 2) the passive transmission mechanism (3) drives the backflow resin (13) to flow in the flow shear zone between the printed object (9) and the oxygen-permeable film (7), and at this time the printing platform (8) moves upward along the vertical direction to start printing; the step 2) is specifically that the rotating motion of the liquid storage tank (4) pulls the backflow resin (13) in the flow shear zone, the backflow resin (13) generates fluid shear force and reduces its own viscosity, the center of the circular groove of the liquid storage tank (4) is taken as the center, the printing process is controlled by the shear rate at different radial positions of the circular groove, and at the same rotating speed, the shear rate of the fluid shear force at different radial positions of the circular groove is different, and the farther from the center, the higher the shear rate.

2. The continuous liquid interface printing method for promoting the backflow of resin in the rotating liquid tank device according to claim 1, characterized in that: the active transmission mechanism (2) comprises a driving motor (10), a shaft coupling (11) and a main transmission component (12); the driving motor (10) and the main transmission component (12) are horizontally arranged, the driving motor (10) is connected with a power supply, the output end of the driving motor (10) is connected with the main transmission component (12) through the shaft coupling (11), and the main transmission component (12) meshes with the meshing rack (5). ​ 3. The method for promoting continuous liquid interface printing according to claim 2, wherein the step 1) is specifically: the driving motor (10) transmits power to the main transmission component (12) through the shaft coupling (11), and the main transmission component (12) and the meshing rack (5) drive the liquid storage tank (4) to rotate through a worm gear transmission.

4. The method for promoting continuous liquid interface printing according to claim 1, wherein the bottom of the liquid storage tank (4) is fixedly sleeved with a support bearing (6), the liquid storage tank (4) is in interference fit with the support bearing (6), and the meshing rack (5) is located above the support bearing (6).

5. The method for promoting continuous liquid interface printing according to claim 3, wherein the transmission mode of the main transmission component (12) and the meshing rack (5) is worm gear transmission. ​ ​ ​

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