Pull-up DLP type 3D printer and 3D printing method

Abstract

The invention provides a pull-up DLP type 3D printer which comprises a workbench and an air source, a transmission mechanism is installed on the workbench, a printing platform is installed on the transmission mechanism, an air guide hole is formed in the printing platform, and the air source communicates with the air guide hole; a demolding hole communicated with the air guide hole is formed in the model, and the demolding hole at least downwards penetrates through one curing layer; and after the curing layer penetrated by one demolding hole is completed, compressed gas in the gas source can enter the demolding hole through the gas guide hole, so that the release film is gradually stripped from the curing layer from inside to outside. The invention further provides a 3D printing method. In the model printing process, after printing of one curing layer is completed, compressed air in the air source enters the demolding hole through the air guide hole, and the release film and the model are stripped from inside to outside; and meanwhile, the printing platform lifts the model upwards, so that the release film and the model are stripped from outside to inside, an inside and outside bidirectional stripping mode is formed, and the stripping speed and the printing speed of the release film are improved.

Description

Technical Field

[0001] The invention relates to a top-pull DLP type 3D printer and a 3D printing method. Background Art

[0002] When the top-pull light-curing 3D printer is working, multiple cured layers are stacked together to form a product model. In order to reduce the bonding force between the cured layer and the bottom of the material trough so that the cured layer and the bottom of the material trough can be peeled off smoothly, a release film is usually required to be set on the bottom of the material trough. However, during the rising process of the printing platform, since the cured layer and the release film are in a sealed state, the cured layer needs to overcome the low-pressure area generated between the release film and the cured layer during the peeling process, making it difficult for the cured layer and the release film to be peeled off.

[0003] Therefore, in order to facilitate the peeling between the solidified layer and the release film, an inclined peeling method was developed. The inclined peeling method is to tilt the material tank while lifting the printing platform upward, so that a peeling gap is generated on the side of the solidified layer of the release film. As the peeling gap gradually expands, the release film and the solidified layer are finally completely peeled off. Although the inclined peeling method can speed up the peeling of the solidified layer and the release film, the photosensitive resin is easy to overflow from the material tank in the inclined state. To avoid the overflow of the photosensitive resin, it is necessary to increase the depth of the material tank or reduce the amount of liquid in the material tank.

[0004] Therefore, how to speed up the peeling of the solidified layer and the release film to improve printing efficiency is still a problem that needs to be further improved in light-curing 3D printing technology. Summary of the invention

[0005] In order to solve the problem of low efficiency in peeling off the solidified layer and the release film in the prior art and to improve the 3D printing efficiency, the present application proposes a top-pull DLP type 3D printer, which includes a workbench and an air source. A transmission mechanism is installed on the workbench, and the transmission mechanism has a ball screw extending in the vertical direction and a connecting arm engaged with the ball screw. The free end of the connecting arm forms a working end, and a printing platform is detachably installed on the working end. The lower surface of the printing platform forms a working surface, and the connecting arm can drive the printing platform to reciprocate in the vertical direction; an air guide hole is provided on the printing platform, and the air guide hole runs through the upper and lower sides of the printing platform, and the upper end of the air guide hole forms an air inlet, and the lower end of the air guide hole forms an air outlet;

[0006] The air supply pipe of the air source is connected to the air inlet, and a control valve is installed on the air supply pipe. The model is bonded to the printing platform, and a demolding hole is formed in the model. The upper end of the demolding hole is connected to the air outlet, and the demolding hole penetrates at least one solidified layer downward. There is compressed gas in the air source. After a solidified layer penetrated by the demolding hole is completed, the compressed gas in the air source can enter the demolding hole through the air guide hole, so that the release film is gradually peeled off from the solidified layer from the inside to the outside. Preferably, the air guide hole extends in the vertical direction.

[0007] During the model printing process, after the printing of a solidified layer is completed, the compressed gas in the gas source enters the demolding hole through the air guide hole, pushing the release film downward, so that the release film begins to peel off from the edge of the demolding hole, forming an inner peeling opening between the release film and the solidified layer. As the compressed gas is continuously injected, the inner peeling opening continues to expand and expand outward; at the same time, the transmission mechanism lifts the model upward through the printing platform, so that the release film can be peeled off synchronously along the outer edge of the solidified layer, and an outer peeling opening is formed between the release film and the solidified layer. As the model is lifted, the outer peeling opening continues to expand and expand inward, forming an inner and outer bidirectional peeling method, until the outer peeling opening and the inner peeling opening are connected to each other, so that the release film and the solidified layer are completely peeled off. Since the release film can be peeled off from both the inner and outer directions at the same time, the peeling speed of the release film is increased, thereby increasing the printing speed.

[0008] Specifically, the printing platform includes a main body and a model plate detachably mounted at the lower end of the main body, the lower surface of the model plate is formed as a working surface, and the model is bonded to the working surface; the air guide hole includes an upper air hole arranged in the main body and a lower air hole arranged in the model plate, an air guide tube is sealedly inserted into the lower air hole through the upper air hole from top to bottom, the air supply pipe is connected to the air guide tube, and the upper end of the demolding hole is connected to the lower air hole.

[0009] The air guide tube can pass through the gap between the main body and the model plate to prevent the compressed gas from leaking out from the gap between the main body and the model plate when flowing through the air guide hole, thereby affecting the peeling efficiency of the release film. The air guide tube is preferably screwed onto the printing platform in a threaded manner.

[0010] Furthermore, the lower air hole is a stepped hole, the large hole of which faces upward, and the lower end of the air guide tube is sealed against the stepped surface of the stepped hole. The stepped hole is used to prevent the air guide tube from extending downward from the air guide hole due to misoperation. When the air guide tube extends downward from the air guide hole, the distance between the printing platform and the release film is relatively narrow in the initial stage of printing, which makes it easy for the air guide tube to press against the release film, causing damage to the release film or directly puncturing the release film, resulting in waste of the release film.

[0011] Furthermore, the control valve is provided with an opening controller. By means of the opening controller, the opening of the control valve can be gradually increased so that the compressed gas in the gas source can slowly enter the demolding hole, thereby preventing the damage or destruction of the model caused by a large amount of compressed air suddenly entering the demolding hole. In specific work, different models need to be tested to determine the appropriate and safe air intake speed.

[0012] Specifically, one end of the connecting arm away from the ball screw has two clamping arms arranged at intervals in the horizontal direction. The two clamping arms extend in a direction away from the ball screw and are parallel to each other. A platform accommodating cavity is formed between the two clamping arms. The platform accommodating cavity has an opening facing away from the ball screw. Corresponding to each clamping arm, a clamping groove is respectively provided on two opposite sides of the printing platform. The printing platform is inserted into the platform accommodating cavity, and each clamping arm is inserted into the corresponding clamping groove. Each clamping arm is fixed to the printing platform by bolts.

[0013] In this design, the printing platform is mounted on the connecting arm using a clamping arm, thereby leaving the top of the printing platform free so that the air guide hole can pass upward through the top of the printing platform to facilitate the connection of the air supply pipe.

[0014] Secondly, the present application also discloses a 3D printing method, characterized in that it is carried out using any of the above-mentioned top-pull DLP type 3D printers, and the 3D printing method comprises the following steps:

[0015] (1) After the 3D modeling of the model to be printed is completed, a cylindrical hole-forming area with a set diameter is calculated, and the hole-forming area can at least extend to an outer end surface of the model to be printed, and the outer end surface is used as the starting surface when the model is printed; the model to be printed is composed of N solidified layers, and the hole-forming area extends downward from the starting surface by NM solidified layers, where N>M;

[0016] (2) Printing the model to be printed with the outer end surface as the starting surface, and forming a demolding hole in the hole forming area during the printing process of the solidified layer of the model, wherein the demolding hole is connected to the air guide hole upward; and the demolding hole penetrates downward through the lower end surface of the solidified layer located at the lowermost side;

[0017] After each solidified layer is printed, the printing platform is lifted up and the control valve is opened at the same time to send the gas in the gas source into the air guide hole and then into the demolding hole, so that the release film is peeled off along the edge of the demolding hole until the solidified layer and the release film are completely peeled off, and then the control valve is closed;

[0018] Continue printing the solidified layer until NM solidified layers are printed;

[0019] During the printing interval between two adjacent curing layers, the control valve remains closed;

[0020] (3) Complete the printing of the last M solidified layers.

[0021] When the 3D printing method in the present application is used to print the model of a 3D product, during the printing process of the first NM solidified layers, after each solidified layer is printed, the compressed gas in the gas source is introduced into the demolding hole through the air guide hole. Under the push of the compressed gas, the release film begins to peel off from the edge of the demolding hole, and an inner peeling opening is formed between the release film and the solidified layer. As the compressed gas is continuously introduced, the inner peeling opening continues to expand and expand outward; at the same time, the transmission mechanism lifts the model upward through the printing platform, so that the release film begins to peel off along the outer edge of the solidified layer synchronously, and an outer peeling opening is formed between the release film and the solidified layer. As the model is lifted, the outer peeling opening continues to expand and expand inward, forming an internal and external bidirectional peeling method, until the outer peeling opening and the inner peeling opening are connected to each other, so that the release film and the solidified layer are completely peeled off. Since the release film can be peeled off from both the internal and external directions at the same time, the peeling speed of the release film is increased, thereby increasing the printing speed.

[0022] When printing the last M solidified layers, different processing methods are used according to different needs. When the air holes penetrate downward through the solidified layer at the bottom of the model, it does not affect the appearance and use function of the model, and the internal and external bidirectional peeling method can continue to be used to complete the peeling of the release film and the last M solidified layers. However, when the air holes penetrate downward through the solidified layer at the bottom of the model, it will have an adverse effect on the appearance or use function of the model. It is recommended to still use the traditional method to complete the peeling of the release film and the last M solidified layers, that is, the air holes do not enter the last M solidified layers downward, and the last M solidified layers are used to complete the sealing of the air holes. After the model is printed, the model is removed from the printing platform, and the photosensitive resin retained in the air holes is poured out from the hole located on the starting surface, and the air holes are cleaned.

[0023] Specifically, the film stripping hole is in a straight line shape, and the angle between the film stripping hole and the vertical direction is 0-20°. When the angle between the film stripping hole and the vertical direction is 0°, the film stripping hole extends in the vertical direction. In the specific printing process of the model, the inclination angle of the film stripping hole can be set according to the shape of the model, but the angle between the film stripping hole and the vertical direction is as close to 0° as possible, so that the photosensitive resin in the film stripping hole can flow out of the film stripping hole smoothly under the push of the compressed gas.

[0024] Furthermore, in order to avoid cracks or ruptures in the mold due to the pressure of the compressed gas, the diameter of the hole-forming area is set to be ≥10mm larger than the inner diameter of the demolding hole. This design makes the wall thickness of the demolding hole at least 5mm, so that the demolding hole area has a higher strength and can withstand the pressure of the compressed gas in the demolding hole during the peeling process of the release film.

[0025] Specifically, the inner diameter of the demolding hole is 5-20mm. During the printing process, the photosensitive resin will enter the demolding hole. The inner diameter of the demolding hole should not be too small. If the inner diameter of the demolding hole is too small, it will not only increase the resistance of the photosensitive resin when it flows out of the demolding hole, but also cause the photosensitive resin to solidify in the demolding hole, thereby blocking the demolding hole. The inner diameter of the demolding hole should not be too large. If the demolding hole is too large, it is easy to cause insufficient strength of the model and affect the quality of the product.

[0026] Furthermore, the total thickness of the M solidified layers is 1-5 mm, and the demolding hole does not penetrate the M solidified layers. The M solidified layers at the bottom are used to form a closed layer, which is used to close the lower end of the demolding hole to ensure the integrity of the model appearance. When printing the last M solidified layers, the release film and the solidified layer are still peeled off in a traditional way, and the release film and the solidified layer are peeled off only by the rise of the printing platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of an embodiment of a 3D printer in the present application.

[0028] Figure 2 yes Figure 1 Center AA view.

[0029] Figure 3 It is a schematic diagram of the structure of the connecting arm.

[0030] Figure 4 This is a state diagram of the 3D printer when it is working.

[0031] Figure 5 This is a diagram showing the state when the release film and the cured layer are partially peeled off.

[0032] Figure 6 This is a diagram showing the state when the release film and the cured layer are completely peeled off. DETAILED DESCRIPTION

[0033] Example 1

[0034] See also Figure 1-Figure 3A top-pull DLP 3D printer includes a workbench 11 and an air source 40. A transmission mechanism is installed on the workbench 11, and the transmission mechanism adopts existing mature technology. The transmission mechanism includes a vertical pole 12 fixed on the workbench 11 and a ball screw 13 rotatably installed on one side of the vertical pole. The ball screw 13 extends in the vertical direction, and one end of a connecting arm 14 is engaged with the ball screw through a screw hole. The connecting arm 14 extends in the horizontal direction, and the printing platform 20 is detachably mounted on the end of the connecting arm 14 away from the ball screw. A servo motor 15 is installed at the lower end of the ball screw. The servo motor is fixedly mounted on the vertical pole. The servo motor can drive the ball screw to rotate, so that the connecting arm can drive the printing platform to reciprocate in the vertical direction.

[0035] A liquid crystal screen 191 is fixedly mounted on the top plate 111 of the workbench 11, and an irradiation unit 19 is fixedly mounted in the inner cavity 112 of the workbench 11. The irradiation unit 19 is fixedly mounted on the bottom plate 113 of the workbench and is located below the liquid crystal screen 191. The material tank 17 is fixedly mounted on the top plate of the workbench and is located above the liquid crystal screen. The irradiation unit provides a shaped light beam for curing the photosensitive resin in the material tank 17. The irradiation unit 19 can be a digital light source processing (DLP) projection device or other types of projection devices (such as LCOS, LCD), but is not limited thereto.

[0036] The material trough 17 specifically includes a trough wall 171 extending in the vertical direction and a release film 174 sealingly arranged at the bottom of the trough wall. A material trough flange 175 is arranged on the outer side of the bottom of the trough wall. Bolts pass through the material trough flange 175 and are screwed onto the workbench to detachably fix the material trough on the workbench.

[0037] In this embodiment, the printing platform 20 includes a main body 21 and a model plate 23. A platform flange 22 is provided on the lower side of the main body 21. The model plate 23 is detachably mounted on the platform flange 22 by bolts. The lower surface of the model plate 23 forms a working surface 231.

[0038] In this embodiment, two clamping arms 141 are arranged at intervals in the horizontal direction at one end of the connecting arm 14 away from the ball screw. The two clamping arms 141 extend in a direction away from the ball screw and are parallel to each other. A platform accommodating cavity 142 is formed between the two clamping arms. The platform accommodating cavity has an opening facing away from the ball screw. Corresponding to each clamping arm 141, a clamping groove 25 is respectively provided on the opposite sides of the main body. The printing platform 20 is inserted into the platform accommodating cavity 142, and each clamping arm 141 is inserted into the corresponding clamping groove 25. The first bolt 16 passes through the clamping arm and is screwed into the first screw hole 251 located in the clamping groove, so that the clamping arm is detachably fixed to the printing platform. To avoid shaking, each clamping arm is fixed to the printing platform by two first bolts.

[0039] An air guide hole is provided on the printing platform. In the present embodiment, the air guide hole comprises an upper air hole 211 arranged in the main body and a lower air hole 232 arranged in the model plate. The upper air hole 211 and the lower air hole 232 both extend in the vertical direction and are coaxially arranged. The upper air hole 211 and the lower air hole 232 are connected up and down, and the upper air hole 211 penetrates the upper end surface of the main body upward, and the lower air hole 232 penetrates the lower end surface of the model plate downward, that is, the upper air hole 211 and the lower air hole 232 together constitute the air guide hole, and the air guide hole penetrates the upper and lower sides of the printing platform, the upper end of the air guide hole forms an air inlet, and the lower end of the air guide hole forms an air outlet.

[0040] Since the upper air hole 211 and the lower air hole 232 both extend in the vertical direction and are coaxially arranged, the air guide hole extends in the vertical direction.

[0041] For the convenience of connection, an air guide tube 26 is installed on the printing platform. The air guide tube is specifically a stainless steel tube. The air guide tube is sealedly inserted into the lower air hole from top to bottom through the upper air hole. In order to prevent the air guide tube from extending downward from the air guide hole, in this embodiment, the lower air hole is a step hole, and the large hole of the step hole faces upward, so that the step hole has a step surface facing upward, and the lower end of the air guide tube is sealed against the step surface of the step hole. To ensure the sealing, a rubber sealing ring is provided between the step surface and the air guide tube. While preventing the compressed gas from leaking out from the gap between the body and the model plate when flowing through the air guide hole, it can also reduce or prevent the sensitive resin in the air guide hole from penetrating into the gap between the body and the model plate. Specifically in this embodiment, the upper air hole is a threaded hole, and the liquid guide tube is screwed into the upper air hole.

[0042] The air source 40 is specifically a compressed air storage tank storing compressed air, the exhaust port of the compressed air storage tank is connected to the air guide pipe 26 via an air supply pipe 41, and a control valve 42 is installed on the air supply pipe 41, and an opening controller is installed on the control valve. Specifically in this embodiment, the control valve adopts a diaphragm valve with an opening controller.

[0043] The model 30 is bonded to the working surface 231 of the printing platform, and a demolding hole 31 is formed in the model. The upper end of the demolding hole 31 is connected to the air outlet, and the demolding hole penetrates part of the solidified layer downward. When a solidified layer penetrated by the demolding hole is completed, the gas in the gas source can enter the demolding hole through the air guide hole, so that the release film is gradually peeled off from the solidified layer from the inside to the outside.

[0044] For details about the demolding hole 31, please refer to the relevant content in Example 2 below.

[0045] Example 2

[0046] See also Figure 4-Figure 6This embodiment describes a 3D printing method, which is performed using the top-pull DLP 3D printer in Embodiment 1. The 3D printing method includes the following steps:

[0047] (1) After the 3D modeling of the model to be printed is completed, the cylindrical hole area with a set diameter is calculated. Please also refer to Figure 2 ,exist Figure 2 In the model 30 shown, the model 30 is represented by a dotted line, and the area enclosed by the double-dotted line 91 is the hole forming area. For clear display, the double-dotted line 91 extends upward to the model plate 23, and the double-dotted line 91 extends downward to the bottom of the model 30. For clear display, the model 30 is not provided with a section line.

[0048] In this embodiment, the film stripping hole is in a straight line shape, and the film stripping hole extends in the vertical direction, that is, the angle between the film stripping hole and the vertical direction is 0°. It can be understood that in other embodiments, the film stripping hole can also be set at an angle, and the angle between the film stripping hole and the vertical direction can specifically be 1°, 5°, 8°, 12°, 16° or 20°, and of course, it can also be other angles between 1-20°.

[0049] The set diameter of the hole forming area is 20mm, the demolding hole is a circular hole, and the inner diameter of the demolding hole is 10mm, so that the set diameter of the hole forming area is 10mm larger than the inner diameter of the demolding hole. The hole forming area extends to an outer end face 35 of the model to be printed, and the extension direction of the hole forming area is perpendicular to the outer end face, and the outer end face can be used as the starting face when the model is printed. In this embodiment, the model to be printed is composed of 1000 solidified layers, and the hole forming area extends 990 solidified layers downward from the starting face, that is, N=1000, M=10, NM=990, N>M. The thickness of each solidified layer is 0.1mm.

[0050] It is understood that the inner diameter of the demolding hole can also be 5mm, 7mm or 9mm. When the set diameter of the hole-forming area is larger, the inner diameter of the demolding hole can also be 12mm, 15mm or 20mm. Of course, according to the different sizes of the hole-forming area, the inner diameter of the demolding hole can be flexibly selected between 5-20mm.

[0051] (2) The model to be printed is printed with the outer end surface as the starting surface. During the printing process of the solidified layer of the model, a demolding hole 31 is formed in the hole forming area. The demolding hole 31 is connected to the air guide hole upward and penetrates downward through the lower end surface of the solidified layer located at the lower side.

[0052] After each solidified layer is printed, the printing platform is lifted upwards and the control valve 42 is slowly opened to allow the compressed air in the compressed air tank to enter the air guide hole and then enter the demolding hole 31. The compressed air is used to push the release film downwards so that the release film is peeled off along the edge of the demolding hole until the solidified layer and the release film are completely peeled off. Figure 5 Due to the adhesive force and the adsorption force generated by the vacuum, when the printing platform is lifted upward, the corresponding area of ​​the release film 174 will be lifted upward, so that an outer peeling opening 902 is generated between the outer edge of the solidified layer and the release film. At the same time, the compressed air entering the demolding hole 31 will push the release film downward, so that the release film is peeled off outward along the edge of the demolding hole, and an inner peeling opening 901 is generated between the release film and the solidified layer. The release film can be peeled off from both the inside and outside of the solidified layer, forming an inside-outside bidirectional peeling method.

[0053] See also Figure 6 As the inner peeling opening 901 and the outer peeling opening 902 continue to extend and expand, the inner peeling opening 901 and the outer peeling opening 902 are connected to each other, so that the release film is completely peeled off from the solidified layer. When the solidified layer is completely peeled off from the release film, the control valve is closed.

[0054] Since the release film can be peeled off from both the inside and outside directions, the peeling efficiency is improved, and the lifting height of the printing platform can be reduced when the release film is peeled off, thereby improving the printing efficiency.

[0055] When opening the control valve, it is necessary to use an opening controller to control the opening of the control valve so that the opening of the control valve gradually increases, so that the compressed gas in the gas source can slowly enter the demolding hole, avoiding damage or destruction to the model due to a large amount of compressed air suddenly entering the demolding hole. In a specific embodiment, it is necessary to conduct experiments on the specific model in advance to determine an appropriate and safe air intake speed.

[0056] Continue to print the solidified layer until 990 solidified layers are printed, that is, NM solidified layers are printed. As the printing progresses, the demolding hole is extended as the model is extended. During the printing interval between two adjacent solidified layers, the control valve remains closed.

[0057] (3) The printing of the last 10 solidified layers is completed, that is, the printing of the last M solidified layers is completed.

[0058] In order to maintain the integrity of the model appearance, the M solidified layers at the bottom together form a closed layer 32, which closes the lower end of the demolding hole to maintain the integrity of the model appearance. In this embodiment, the closed layer is composed of the 10 solidified layers at the bottom, that is, the M solidified layers together constitute the closed layer. For details, please refer to Figure 2In this embodiment, the thickness H of the sealing layer is 1 mm. It can be understood that, according to different requirements, the thickness of the sealing layer can also be 2 mm, 3 mm, 4 mm or 5 mm, or other thicknesses between 1-5 mm.

[0059] When printing the last 10 solidified layers, the release film and the solidified layer are still peeled off in a traditional way, relying solely on the rise of the printing platform to complete the peeling of the release film and the solidified layer.

[0060] After the model is printed, the model is removed from the printing platform, the photosensitive resin retained in the air holes is poured out from the opening on the starting surface, and the air holes are cleaned.

Claims

1. A top-pull DLP 3D printer, characterized in that: The invention comprises a workbench and an air source, a transmission mechanism is installed on the workbench, the transmission mechanism has a ball screw extending in a vertical direction and a connecting arm meshed on the ball screw, the free end of the connecting arm forms a working end, a printing platform is detachably installed on the working end, the lower surface of the printing platform forms a working surface, and the connecting arm can drive the printing platform to reciprocate in the vertical direction; an air guide hole is provided on the printing platform, the air guide hole runs through the upper and lower sides of the printing platform, the upper end of the air guide hole forms an air inlet, and the lower end of the air guide hole forms an air outlet; The air supply pipe of the air source is connected to the air inlet, and a control valve is installed on the air supply pipe. The model is bonded to the printing platform, and a demolding hole is formed in the model. The upper end of the demolding hole is connected to the air outlet, and the demolding hole penetrates at least one solidified layer downward. There is compressed gas in the air source. After a solidified layer penetrated by the demolding hole is completed, the compressed gas in the air source can enter the demolding hole through the air guide hole, so that the release film is gradually peeled off from the solidified layer from the inside to the outside.

2. The top-pull DLP 3D printer according to claim 1, characterized in that: The printing platform includes a main body and a model plate detachably mounted on the lower end of the main body, the lower surface of the model plate is formed as a working surface, and the model is bonded to the working surface; the air guide hole includes an upper air hole arranged in the main body and a lower air hole arranged in the model plate, an air guide tube is sealedly inserted into the lower air hole from top to bottom through the upper air hole, the air supply pipe is connected to the air guide tube, and the upper end of the demolding hole is connected to the lower air hole.

3. The top-pull DLP 3D printer according to claim 2, characterized in that: The lower air hole is a stepped hole, the large hole of which faces upward, and the lower end of the air guide pipe is sealed against the stepped surface of the stepped hole.

4. The top-pull DLP 3D printer according to claim 1, characterized in that: The control valve is provided with an opening controller.

5. The top-pull DLP 3D printer according to claim 1, characterized in that: One end of the connecting arm away from the ball screw has two clamping arms arranged at intervals in the horizontal direction. The two clamping arms extend in a direction away from the ball screw and are parallel to each other. A platform accommodating cavity is formed between the two clamping arms. The platform accommodating cavity has an opening facing away from the ball screw. Corresponding to each clamping arm, a clamping groove is respectively provided on two opposite sides of the printing platform. The printing platform is inserted into the platform accommodating cavity, and each clamping arm is inserted into the corresponding clamping groove. Each clamping arm is fixed to the printing platform by bolts.

6. A 3D printing method, characterized in that: The 3D printing method is carried out by using the top-pull DLP type 3D printer according to any one of claims 1 to 5, and the 3D printing method comprises the following steps: (1) After the 3D modeling of the model to be printed is completed, a cylindrical hole-forming area with a set diameter is calculated, and the hole-forming area can at least extend to an outer end surface of the model to be printed, and the outer end surface is used as the starting surface when the model is printed; The model to be printed is composed of N solidified layers, and the hole-forming area extends downward from the starting surface by NM solidified layers, where N>M; (2) Printing the model to be printed with the outer end surface as the starting surface, and forming a demolding hole in the hole forming area during the printing process of the solidified layer of the model, wherein the demolding hole is connected to the air guide hole upward; and the demolding hole penetrates downward through the lower end surface of the solidified layer located at the lowermost side; After each solidified layer is printed, the printing platform is lifted up and the control valve is opened at the same time to send the gas in the gas source into the air guide hole and then into the demolding hole, so that the release film is peeled off along the edge of the demolding hole until the solidified layer and the release film are completely peeled off, and then the control valve is closed; Continue printing the solidified layer until NM solidified layers are printed; During the printing interval between two adjacent curing layers, the control valve remains closed; (3) Complete the printing of the last M solidified layers.

7. The 3D printing method according to claim 6, characterized in that: The film stripping hole is straight, and the angle between the film stripping hole and the vertical direction is 0-20°.

8. The 3D printing method according to claim 6, characterized in that: The set diameter of the hole forming area is ≥10mm larger than the inner diameter of the film stripping hole.

9. The 3D printing method according to claim 6, characterized in that: The inner diameter of the demolding hole is 5-20mm.

10. The 3D printing method according to claim 6, characterized in that: The total thickness of the M solidified layers is 1-5 mm, and the demolding holes do not penetrate the M solidified layers.

Images