A center demolding 3D printer and 3D printing method

Abstract

The application discloses a center demolding 3D printer, a guide rod hole is formed in a printing platform, a female screw part is rotatably arranged on the top of the printing platform, a demolding rod is screwed in a female screw hole of the female screw part and can pass through the guide rod hole downwards, a driving device is arranged on the printing platform and is used for driving the female screw part to rotate, the demolding rod can only move up and down relative to the printing platform and cannot rotate, a demolding hole is formed in a model, the demolding rod can move downwards and press on a release film of a material groove after passing through the demolding hole, and the release film is pushed downwards. The application further discloses a 3D printing method. After printing of a solidified layer is completed, the printing platform is lifted upwards, the release film is peeled off from the model from outside to inside, the demolding rod is moved downwards and pushes the release film at the same time, the release film is peeled off from the model from inside to outside, and the release film is peeled off from two directions of inside and outside at the same time, so that the peeling speed of the release film is improved.

Description

Technical Field

[0001] This invention relates to a center-demolding 3D printer and a 3D printing method. Background Technology

[0002] 3D printing technologies such as DLP and LCD / LED project a surface imaging beam, formed by the cross-sectional pattern of a 3D model, onto a photosensitive resin printing material to achieve single-layer curing. These layers are then stacked to form a 3D model. During printing, unfinished models need to be frequently lifted to detach from the release liner and allow photosensitive resin to enter between the model and the release liner to continue printing the next cured layer. When the printing platform is lifted, a sealed area forms between the release liner and the cured layer. This creates a low-pressure zone between the release liner and the cured layer during the peeling process, making it difficult to separate the cured layer from the release liner.

[0003] Therefore, in order to facilitate the peeling between the curing layer and the release film, the tilting peeling method was developed. The tilting peeling method involves tilting the material tank while raising the printing platform, so that the release film creates a peeling gap from one side of the curing layer. As the peeling gap gradually expands, the release film is eventually completely peeled off from the curing layer.

[0004] While the tilting peeling method can accelerate the separation of the cured layer from the release film, the photosensitive resin is prone to overflowing from the trough when tilted. To avoid this overflow, the depth of the trough needs to be increased or the liquid volume reduced. In addition, the tilting also causes the photosensitive resin to shake significantly, increasing the contact area between the photosensitive resin and air, which makes it easier for air to mix into the photosensitive resin and affect the printing quality of the product model.

[0005] Therefore, how to accelerate the peeling of the cured layer from the release film to improve printing efficiency remains an issue that needs further improvement in photopolymer 3D printing technology. Summary of the Invention

[0006] To improve the peeling speed of the cured layer and release film during model printing and increase printing efficiency, this application first discloses a center-release 3D printer, which includes a worktable, a transmission mechanism installed on the worktable, and a printing platform detachably installed on the transmission mechanism. The transmission mechanism can drive the printing platform to reciprocate in the vertical direction.

[0007] A guide rod hole is provided on the printing platform, extending vertically and passing through the upper and lower sides of the printing platform. An internally threaded component is rotatably mounted on the top of the printing platform. The demolding rod is screwed into the internally threaded hole of the internally threaded component and can pass downward through the guide rod hole. A drive device for driving the internally threaded component to rotate is also installed on the printing platform. The demolding rod has a limiting part and a limiting part in the guide rod hole. Under the drive of the drive device, the internally threaded component can rotate around the demolding rod. Under the combined action of the limiting part and the limiting part, the demolding rod can only move up and down relative to the printing platform and cannot rotate.

[0008] The model is bonded to the printing platform, and a release hole is formed inside the model. The upper end of the release hole is connected to the guide rod hole, and the release hole penetrates at least one cured layer downwards. After the cured layer through which the release hole has been completed, the printing platform is moved upwards, and the drive device is activated simultaneously to move the release rod downwards. After passing through the release hole, the rod presses against the release film in the material tank, pushing the release film downwards and peeling it off from the cured layer along the lower edge of the release hole. After the release film and the cured layer have been completely peeled off, the drive device can drive the release rod upwards and move the lower end of the release rod away from the release film.

[0009] During the model printing process, after the printing of one cured layer is completed, the printing platform is lifted upwards using a transmission mechanism. Simultaneously, the release rod moves downwards using a drive device and presses against the release film, causing the release film to peel off from the model starting from the lower edge of the release hole. An inner peeling opening is formed between the release film and the cured layer. At the same time, the release film peels off from the outer edge of the model, forming an outer peeling opening. As the model is lifted, the inner peeling opening continues to expand outwards, while the outer peeling opening continues to expand inwards, forming a bidirectional peeling method until the outer and inner peeling openings connect, completely separating the release film from the cured layer. Because the release film can be peeled off from both inside and outside directions simultaneously, the peeling speed of the release film is increased, thereby increasing the printing speed.

[0010] Specifically, the release rod includes a hollow rod and a release head. The hollow rod includes a body extending vertically and a neck formed at the lower end of the body. The release head is fixed to the lower end of the neck. A vent hole extending radially is present in the neck. One end of the central hole of the hollow rod penetrates the top surface of the body, and the other end of the central hole connects to the vent hole. The lower end of the release head is a closed end. The maximum outer diameter of the release rod is 1-2 mm smaller than the inner diameter of the release hole, and the outer diameter of the release head is not greater than the root diameter of the thread of the external thread of the release rod. This design allows external air to enter the release hole through the central hole and the vent hole of the hollow rod, preventing a vacuum state in the release hole. This ensures that no negative pressure is generated when the release rod pushes the release film downwards, thus smoothly peeling it from the mold inside the release hole. The maximum outer diameter of the stripping rod is smaller than the inner diameter of the stripping hole. This prevents the stripping rod from scratching the inner wall of the stripping hole, forming resin particles that fall into the material trough and affect normal printing. The outer diameter of the stripping head is not larger than the root diameter of the external thread of the stripping rod so that the stripping rod can be installed in the internal threaded part from top to bottom.

[0011] Furthermore, to avoid damage to the release film caused by the stripping head, the lower end of the stripping head is a downward-protruding arc surface.

[0012] Specifically, the drive device is a solid shaft servo motor, which is fixedly mounted on the upper side of the printing platform and located on one side of the internal threaded part. The output shaft of the solid shaft servo motor is connected to the internal threaded part.

[0013] Alternatively, the drive device is a hollow shaft torque motor, which includes a stator and a mover rotatably disposed within the stator. The stator is fixedly mounted on the top of the printing platform, and an internal threaded component is fixed to the mover. The hollow shaft torque motor is a servo motor.

[0014] Both of the above-mentioned structural forms of the drive device can meet the driving requirements of the demolding rod, and the choice can be made according to the specific structure of the equipment and usage habits.

[0015] Secondly, this application also discloses a 3D printing method, which uses the 3D printer described in any of the above claims, and the enhanced 3D printing method includes the following steps:

[0016] (1) After the 3D model of the model to be printed is completed, a cylindrical hole area with a set diameter is calculated. The hole area can extend to at least one outer end face of the model to be printed. The outer end face is used as the starting face when printing the model. The model to be printed consists of N curing layers. The hole area extends downward from the starting face by NM curing layers, where N>M.

[0017] (2) Print the model to be printed with the outer end face as the starting face. During the printing process of the curing layer of the model, a demolding hole is formed in the hole forming area. The demolding hole is connected to the guide rod hole upward; the demolding hole penetrates the lower end face of the curing layer located at the bottom.

[0018] After each cured layer is printed, the printing platform is lifted upwards, and the drive device is activated to move the release rod downwards and press it against the release film, causing the release film to peel outwards along the lower edge of the release hole, while simultaneously peeling inwards along the outer edge of the model, until the cured layer is completely separated from the release film. Then, the drive device is reversed to move the release rod upwards and away from the release film.

[0019] Continue printing the cured layers until NM cured layers have been printed;

[0020] The drive unit pauses operation during the printing interval between two adjacent curing layers.

[0021] (3) Complete the printing of the last M curing layers.

[0022] When printing a 3D product model using the 3D printing method described in this application, during the printing of the first NM cured layers, after each cured layer is printed, the printing platform is lifted upwards using a transmission mechanism. Simultaneously, a drive device moves the release rod downwards and presses it against the release film, causing the release film to peel off from the model starting from the lower edge of the release hole. An inner peeling opening is formed between the release film and the cured layer. At the same time, the release film peels off from the outer edge of the model, forming an outer peeling opening. As the model is lifted, the inner peeling opening continues to expand outwards, and the outer peeling opening continues to expand inwards, forming a bidirectional peeling method until the outer and inner peeling openings connect, completely separating the release film from the cured layer. Because the release film can be peeled off from both inside and outside directions simultaneously, the peeling speed of the release film is increased, thereby increasing the printing speed.

[0023] During the printing of the final M cured layers, different processing methods are used depending on the needs. When the guide rod hole penetrates the cured layer located at the bottom of the model without affecting the model's appearance or function, a bidirectional peeling method can be used to complete the separation of the release film from the final M cured layers. However, when the guide rod hole penetrates the cured layer located at the bottom of the model and would adversely affect the model's appearance or function, it is recommended to use the traditional method to complete the separation of the release film from the final M cured layers. That is, the guide rod hole should not penetrate into the final M cured layers, and the final M cured layers should be used to seal the guide rod hole. After the model is printed, remove the model from the printing platform, pour out the photosensitive resin remaining in the guide rod hole through the opening on the starting surface, and clean the guide rod hole.

[0024] Specifically, in order to ensure that the photosensitive resin in the release pores can flow smoothly downwards during the peeling process between the release film and the cured layer, the release pores are straight and extend in the vertical direction.

[0025] Furthermore, the diameter of the perforated area is set to be ≥10mm larger than the inner diameter of the demolding hole. This design ensures that the wall thickness of the demolding hole is at least 5mm, resulting in high strength in the demolding hole area.

[0026] Specifically, the inner diameter of the stripping hole is 5-20mm. During the printing process, photosensitive resin enters the stripping hole. The inner diameter of the stripping hole should not be too small. If the inner diameter is too small, it will not only increase the resistance when the photosensitive resin flows out of the stripping hole, but also cause the photosensitive resin to solidify inside the stripping hole, thus clogging it. The inner diameter of the stripping hole should also not be too large. If the stripping hole is too large, it will easily lead to insufficient strength of the model, affecting the quality of the product.

[0027] Furthermore, the total thickness of the M cured layers is 1-5mm, and the release hole does not penetrate through these M cured layers. The bottom M cured layers form a sealing layer to seal the lower end of the release hole, ensuring the integrity of the model's appearance. When printing the last M cured layers, the release film is still peeled off from the cured layers using the traditional method, relying solely on the rise of the printing platform to complete the peeling. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of one embodiment of the 3D printer in this invention.

[0029] Figure 2 yes Figure 1 A diagram showing the connection structure between the first driving device and the first internal threaded component and the printing platform.

[0030] Figure 3 yes Figure 2 A view from the center AA direction.

[0031] Figure 4 This is a schematic diagram of the connecting arm.

[0032] Figure 5 yes Figure 3 A magnified view of a section in the BB direction.

[0033] Figure 6 This is a schematic diagram of the demolding rod.

[0034] Figure 7 This is a diagram showing the state of a 3D printer in operation.

[0035] Figure 8 This is a diagram showing the state when the release film and the cured layer have partially separated.

[0036] Figure 9 This is a diagram showing the state when the release film and the cured layer are completely separated.

[0037] Figure 10 This is a schematic diagram of another embodiment of the 3D printer in this invention.

[0038] Figure 11 yes Figure 10 Diagram showing the connection structure between the second drive unit and the first internal threaded component and the printing platform. Detailed Implementation

[0039] Example 1

[0040] Please see Figures 1-6 A center-demolding 3D printer includes a worktable 11 on which a transmission mechanism is mounted. This transmission mechanism utilizes existing mature technology and includes a vertical rod 12 fixed to the worktable 11 and a ball screw 13 rotatably mounted on one side of the vertical rod. The ball screw 13 extends vertically, and one end of a connecting arm 14 is engaged with the ball screw via a screw hole. The connecting arm 14 extends horizontally, and a printing platform 20 is detachably mounted on the end of the connecting arm 14 away from the ball screw. A servo motor is mounted at the lower end of the ball screw and fixed to the vertical rod. The servo motor drives the ball screw to rotate, enabling the connecting arm to reciprocate the printing platform vertically.

[0041] The material trough 17 is fixedly installed on the workbench. The material trough 17 includes a trough wall 171 extending in a vertical direction and a release film 174 disposed at the bottom of the trough wall 171. A material trough flange 175 is provided 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.

[0042] An ultraviolet light system is installed inside the workbench. The ultraviolet light system includes an LCD screen fixed to the top plate of the workbench, and a material trough is arranged above the LCD screen. The ultraviolet light system is not shown in the attached figure. The ultraviolet light system adopts existing mature technology and will not be described in detail.

[0043] 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 installed on the platform flange 22 by bolts. The lower surface of the model plate 23 is formed as a working surface 231.

[0044] In this embodiment, at the end of the connecting arm 14 away from the ball screw, there are two horizontally spaced retaining arms 141. The two retaining arms 141 extend away from the ball screw and are parallel to each other, forming a platform receiving cavity 142 between the two retaining arms. The platform receiving cavity has an opening away from the ball screw. Corresponding to each retaining arm 141, a slot 25 is provided on opposite sides of the main body. The printing platform 20 is inserted into the platform receiving cavity 142, and each retaining arm 141 is inserted into the corresponding slot 25. The first bolt 16 passes through the retaining arm and is screwed into the first screw hole 251 located in the slot, so that the retaining arm is detachably fixed to the printing platform. To avoid shaking, each retaining arm is fixed to the printing platform by two first bolts.

[0045] A guide rod hole 26 is provided on the printing platform. This guide rod hole includes an upper guide rod hole 27 located within the main body and a lower guide rod hole 28 located within the model plate. Both the upper and lower guide rod holes are through holes and are coaxially arranged. The upper guide rod hole 27 extends upwards through the upper surface of the main body, and the lower guide rod hole 28 extends downwards through the lower surface of the model plate 23. That is, the guide rod hole extends vertically and passes through both the upper and lower sides of the printing platform.

[0046] A first internally threaded component 81 is rotatably mounted on top of the printing platform. A demolding rod 40 is screwed into the internally threaded hole of the first internally threaded component and can pass downward through the guide rod hole 26. A first drive device for driving the first internally threaded component to rotate is also mounted on the printing platform.

[0047] In this embodiment, the first driving device is a hollow shaft torque motor 70, which is a servo motor. The hollow shaft torque motor 70 includes a stator 71 and a mover 75 rotatably disposed within the stator 71. A hollow shaft 86 is fixed to the mover 75, and a first internally threaded component is fixed to the hollow shaft 86. An upper end cover 72 and a lower end cover 73 are respectively installed at the upper and lower ends of the stator 71. The upper end cover 72 is bolted to the upper flange 711 at the upper end of the stator 71, and the lower end cover 73 is bolted to the lower flange 712 at the lower end of the stator 71. Both the upper flange 711 and the lower flange 712 are integrally formed on the stator 71. A winding 74 is provided inside the stator. The lower end cover 73 is detachably bolted to the upper surface of the main body, thereby fixing the stator to the top of the printing platform and thus mounting the hollow shaft torque motor 70 on the upper surface of the printing platform.

[0048] In this embodiment, an upper connecting flange 76 is provided on the outer peripheral surface of the hollow shaft 86, and the upper end cover has an inwardly protruding upper abutting flange 721. The lower surface of the upper abutting flange 721 is a downward-facing stepped surface. The upper abutting flange 721 presses against the upper side of the outer ring of the upper angular contact bearing 78 through its lower surface, and the upper connecting flange 76 presses against the lower side of the inner ring of the upper angular contact bearing, so that the upper end cover is rotatably connected to the hollow shaft 86 through the upper angular contact bearing.

[0049] A lower step portion 77 is provided at the lower end of the hollow shaft 86. This lower step portion has a downward-facing stepped surface and is formed by a radial inward recess from the outer circumferential surface of the hollow shaft 86. The lower end cover has an inwardly protruding lower abutment flange 731. The upper surface of the lower abutment flange 731 is an upward-facing stepped surface. The lower abutment flange 731 abuts against the lower side of the outer ring of the lower angular contact bearing 79 via its upper surface. The lower step portion 77 presses against the lower side of the inner ring of the lower angular contact bearing, so that the lower end cover is rotatably connected to the hollow shaft 86 via the lower angular contact bearing. The structure of the hollow shaft torque motor can be completed using existing mature technology and will not be described in detail here.

[0050] The first internally threaded component is lined within the cavity of the hollow shaft 86. A flange 811 is provided on the top of the first internally threaded component 81, which is formed by radially protruding outward from the outer circumferential surface of the first internally threaded component 81. The top of the hollow shaft is bolted to the flange 811. To ensure the connection stability between the first internally threaded component and the hollow shaft, a key 85 is provided between the first internally threaded component and the hollow shaft. The hollow shaft, the first internally threaded component, and the guide rod hole are coaxially arranged.

[0051] Please see Figure 6 In this embodiment, the stripping rod 40 includes a hollow rod 401 and a stripping head 44. The hollow rod 401 includes a body 41 extending vertically and a neck 42 formed at the lower end of the body. The stripping head is fixed to the lower end of the neck. The neck 42 has a radially extending vent hole 43 that penetrates the wall of the hollow rod. One end of the central hole 46 of the hollow rod extends upward through the top surface of the body, and the other end of the central hole 46 of the hollow rod communicates with the vent hole. The lower end of the stripping head is a closed end, and the lower end of the stripping head has a downward-protruding arc surface 45. The outer circumferential surface of the body has an external thread that can mesh with the internal thread of the first internal threaded component. The outer diameter of the stripping head is not greater than the root diameter of the thread of the external thread of the body. Specifically, in this embodiment, the outer diameter of the stripping head is equal to the root diameter of the thread of the external thread of the body. That is, the outer diameter of the stripping head is not greater than the root diameter of the thread of the external thread of the stripping rod.

[0052] In this embodiment, the demolding rod 40 is made of stainless steel. It is understood that in other embodiments, the demolding rod may also be made of metals or alloys such as copper and aluminum.

[0053] Please see Figure 5 To simplify the accompanying drawings, Figure 5 The main body 21 section line has been removed. Viewed axially along the guide rod hole 26, the cross-section of the guide rod hole 26 includes a superior arc 261 and a straight segment 262 closing the superior arc 261, such that the guide rod hole 26 is formed by a circular hole with a radially inward protrusion within the circular hole. The area where the straight segment is located forms the protrusion, which serves as a limiting portion of the guide rod hole. A limiting portion is provided on the demolding rod 40. In this embodiment, the limiting portion is a tangential plane 47 formed on one side of the demolding rod 40 that adapts to the aforementioned protrusion.

[0054] The stripping rod 40 is screwed into the internal threaded hole of the first internal threaded component and freely inserted into the guide rod hole 26. When the mover drives the first internal threaded component to rotate around the stripping rod via the hollow shaft, the protrusion can press against the cutting plane, so that the stripping rod can only move up and down relative to the printing platform and cannot rotate.

[0055] Model 30 is bonded to the working surface 231 of the printing platform. A demolding hole 31 is formed in the model. The upper end of the demolding hole is connected to the guide rod hole. The demolding hole penetrates downward through at least one cured layer. After the cured layer penetrated by the demolding hole is completed, the printing platform is moved upward, and the first drive device is started simultaneously to move the demolding rod downward. After passing through the demolding hole, the rod presses against the release film in the material tank and pushes the release film downward, so that the release film peels off from the cured layer along the lower edge of the demolding hole. After the release film and the cured layer are completely peeled off, the first drive device can drive the demolding rod to move upward and make the lower end of the demolding rod leave the release film.

[0056] For details regarding the demolding hole 31, please refer to the relevant content in Example 3 below.

[0057] Example 2

[0058] Please see Figure 10 and Figure 11 This embodiment is basically the same as Embodiment 1, except that the driving device is different. Figure 10 , Figure 11 Of the two and Figures 1-6The same reference numerals in the accompanying drawings represent the same technical features. In this embodiment, the driving device is referred to as the second driving device, which is a solid shaft servo motor 61. A positioning sleeve 64 is provided on the upper surface of the printing platform. The positioning sleeve 64 extends vertically, and a bearing seat 641 is formed at the lower end of the positioning sleeve. The bearing seat 641 is fixedly mounted on the upper surface of the printing platform by bolts. An end face flange 642 is formed at the upper end of the positioning sleeve, and a bearing cover 63 is fixed to the end face flange by bolts.

[0059] The second internally threaded component 66 is rotatably housed within the positioning sleeve 64. A lower support step surface 661 and an upper support step surface 662 are formed on the outer circumferential surface of the second internally threaded component 66, with the lower support step surface 661 facing downwards and the upper support step surface facing upwards. The outer ring of the first bearing 65 is supported on the bearing housing, and the lower support step surface supports the inner ring of the first bearing. The inner ring of the second bearing 62 is supported on the upper support step surface, and the bearing cap presses against the outer ring of the second bearing. This allows the second internally threaded component to be rotatably held at the top of the printing platform via the first and second bearings. Both the first and second bearings are angular contact bearings.

[0060] The solid shaft servo motor is fixedly mounted on the upper side of the printing platform and located on one side of the internal threaded part. The output shaft of the solid shaft servo motor is connected to the internal threaded part.

[0061] A pulley 611 is fixedly mounted on the output shaft of a solid shaft servo motor. A belt 612 is wrapped around the pulley and a second internally threaded component. A groove is provided on the outer circumferential surface of the second internally threaded component, and the belt is held in the groove. It can be understood that the pulley 611 can also be replaced with a gear, and a meshing gear is provided on the second internally threaded component to form a gear combination. The solid shaft servo motor 61 drives the second internally threaded component to move up and down through the gear combination.

[0062] The stripping rod 40 is screwed into the internal threaded hole of the second internal threaded component and freely inserted into the guide rod hole 26. When the mover drives the second internal threaded component to rotate around the stripping rod via the hollow shaft, the protrusion can press against the cutting plane, so that the stripping rod can only move up and down relative to the printing platform and cannot rotate.

[0063] Example 3

[0064] Please see Figures 7-9 This embodiment describes a 3D printing method using the 3D printer described in Embodiment 1 or Embodiment 2. This enhanced 3D printing method includes the following steps:

[0065] (1) After the 3D model of the model to be printed is completed, calculate the cylindrical hole area with a set diameter. Please refer to [link / reference]. Figure 3 ,exist Figure 3 In the diagram, model 30 is represented by a dashed line, and the area enclosed by the double-dotted line 91 is the reinforced area. For clarity, the double-dotted line 91 extends upwards to model plate 23 and downwards to the bottom of model 30. Similarly, for clarity, no cross-sectional lines are provided on model 30. In this embodiment, the demolding holes are straight lines and extend vertically.

[0066] The diameter of the hole-forming area is set to 20mm, and the release hole is a circular hole with an inner diameter of 10mm, making the set diameter of the hole-forming area 10mm larger than the inner diameter of the release 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, which can serve as the starting face for model printing. In this embodiment, the model to be printed consists of 1000 cured layers, and the hole-forming area extends downward from the starting face by 990 cured layers, i.e., N=1000, M=10, NM=990, N>M. The thickness of each cured layer is 0.1mm.

[0067] It is understandable that the inner diameter of the demolding hole can also be 5mm, 7mm, or 9mm. When the set diameter of the pore area is larger, the inner diameter of the demolding hole can also be 12mm, 15mm, or 20mm. Of course, depending on the size of the pore area, the inner diameter of the demolding hole can be flexibly selected between 5-20mm.

[0068] Since the outer diameter of the stripping rod body 41 is the largest, in this embodiment, the outer diameter of the stripping rod body is 8.5 mm, which is 1.5 mm smaller than the inner diameter of the stripping hole. That is, the maximum outer diameter of the stripping rod is 1.5 mm smaller than the inner diameter of the stripping hole. It can be understood that in other embodiments, the maximum outer diameter of the stripping rod can also be 1 mm, 1.2 mm, 1.8 mm, 2 mm smaller than the inner diameter of the stripping hole, or other data between 1 and 2 mm.

[0069] (2) Print the model to be printed with the outer end face as the starting face. During the printing process of the curing layer of the model, a demolding hole 31 is formed in the hole area. The demolding hole 31 is connected to the guide rod hole upward and penetrates the lower end face of the curing layer located at the bottom side downward.

[0070] After each cured layer is printed, the printing platform is raised, and the drive device is activated to move the release rod downwards, pressing it against the release film. As the printing platform gradually rises, the release rod moves downwards synchronously, causing the release film to peel outwards along the lower edge of the release hole until the cured layer is completely separated from the release film. The central hole 46 inside the release rod connects the release hole to the outside atmosphere, eliminating the negative pressure phenomenon caused by atmospheric pressure. After the cured layer is completely separated from the release film, the drive device is reversed, causing the release rod to move upwards, away from the release film, and the release head retracts back into the release hole. The drive device refers to the hollow shaft torque motor 70 in Example 1 or the solid shaft servo motor 61 in Example 2.

[0071] Please see Figure 8 Due to the adhesive force and the adsorption force generated by the vacuum, when the printing platform is lifted upward, it will drive the corresponding area of ​​the release film 174 upward, so that an outer peeling opening 902 is generated between the outer edge of the cured layer and the release film. At the same time, due to the pushing action of the release rod on the release film, the release film is peeled outward along the edge of the release hole, and an inner peeling opening 901 is generated between the release film and the cured layer. The release film can be peeled from both the inside and outside of the cured layer, forming a bidirectional peeling method.

[0072] Please see Figure 9 As the inner peeling port 901 and the outer peeling port 902 continue to extend and expand, they become interconnected, allowing the release film to completely peel off from the cured layer. Once the cured layer and the release film are completely separated, the release rod is lifted upwards, causing the release head to retract back into the release hole.

[0073] Because the release film can be peeled off from both the inside and outside, the peeling efficiency is improved, and the lifting height of the printing platform during release film peeling is reduced, thereby improving printing efficiency.

[0074] Continue printing the cured layers until 990 cured layers have been printed, which is equivalent to printing NM cured layers. As printing progresses, the release holes lengthen with the model. During the interval between printing two adjacent cured layers, the control valve remains closed.

[0075] (3) Complete the printing of the last 10 curing layers, that is, complete the printing of the last M curing layers.

[0076] To maintain the integrity of the model's appearance, the M cured layers at the bottom layer together form a sealing layer 32. This sealing layer seals the lower end of the demolding hole to maintain the integrity of the model's appearance. In this embodiment, the sealing layer is composed of the 10 cured layers at the bottom layer, that is, M cured layers together constitute the sealing layer. Please refer to [link / reference] for details. Figure 3In this embodiment, the thickness H of the sealing layer is 1 mm. It can be understood that, depending on 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 and 5 mm.

[0077] When printing the last 10 cured layers, the release film is still peeled off from the cured layer in the traditional way, relying solely on the rise of the printing platform to complete the peeling of the release film from the cured layer.

[0078] After printing the model, remove the model from the printing platform, pour out the photosensitive resin remaining in the guide rod hole through the opening on the starting surface, and clean the guide rod hole.

Claims

1. A center-demolding 3D printer, characterized in that, It includes a worktable, on which a transmission mechanism is installed, and a printing platform is detachably mounted on the transmission mechanism, which can drive the printing platform to reciprocate in the vertical direction; A guide rod hole is provided on the printing platform, extending vertically and passing through the upper and lower sides of the printing platform. An internally threaded component is rotatably mounted on the top of the printing platform. The demolding rod is screwed into the internally threaded hole of the internally threaded component and can pass downward through the guide rod hole. A drive device for driving the internally threaded component to rotate is also installed on the printing platform. The demolding rod has a limiting part and a limiting part in the guide rod hole. Under the drive of the drive device, the internally threaded component can rotate around the demolding rod. Under the combined action of the limiting part and the limiting part, the demolding rod can only move up and down relative to the printing platform and cannot rotate. The model is bonded to the printing platform, and a demolding hole is formed inside the model. The upper end of the demolding hole is connected to the guide rod hole, and the demolding hole penetrates at least one cured layer downwards. After the cured layer has passed through a release hole, the printing platform moves upward and the drive device is activated simultaneously, causing the release rod to move downward. After passing through the release hole, the rod presses against the release film in the material tank, pushing the release film downward and peeling it off from the cured layer along the lower edge of the release hole. Once the release film and the cured layer have completely separated, the drive device can move the release rod upward and remove the lower end of the release rod from the release film.

2. The 3D printer according to claim 1, characterized in that, The stripping rod includes a hollow rod and a stripping head. The hollow rod includes a body extending vertically and a neck formed at the lower end of the body. The stripping head is fixed to the lower end of the neck. The neck has a vent hole extending radially. One end of the central hole of the hollow rod penetrates the top surface of the body, and the other end of the central hole of the hollow rod communicates with the vent hole. The lower end of the stripping head is a closed end. The maximum outer diameter of the stripping rod is 1-2 mm smaller than the inner diameter of the stripping hole, and the outer diameter of the stripping head is not greater than the root diameter of the thread of the external thread of the stripping rod.

3. The 3D printer according to claim 2, characterized in that, The lower end of the stripping head has a downward-protruding arc surface.

4. The 3D printer according to claim 1, characterized in that, The drive unit is a solid shaft servo motor, which is fixedly mounted on the upper side of the printing platform and located on one side of the internal threaded part. The output shaft of the solid shaft servo motor is connected to the internal threaded part.

5. The 3D printer according to claim 1, characterized in that, The drive unit is a hollow shaft torque motor, which includes a stator and a mover rotatably disposed within the stator. The stator is fixedly mounted on the top of the printing platform, and an internal threaded component is fixed on the mover. The hollow shaft torque motor is a servo motor.

6. A 3D printing method, characterized in that, The 3D printing method, performed using any one of claims 1-5, comprises the following steps: (1) After the 3D model of the model to be printed is completed, a cylindrical hole area with a set diameter is calculated. The hole area can extend to at least one outer end face of the model to be printed, and the outer end face is used as the starting face when printing the model. The model to be printed consists of N curing layers, and the hole-forming area extends downward from the starting surface by NM curing layers, where N > M; (2) Print the model to be printed with the outer end face as the starting face. During the printing process of the curing layer of the model, a demolding hole is formed in the hole forming area. The demolding hole is connected to the guide rod hole upward; the demolding hole penetrates the lower end face of the curing layer located at the bottom. After each cured layer is printed, the printing platform is lifted upwards, and the drive device is activated to move the release rod downwards and press it against the release film, causing the release film to peel outwards along the lower edge of the release hole, while simultaneously peeling inwards along the outer edge of the model, until the cured layer is completely separated from the release film. Then, the drive device is reversed to move the release rod upwards and away from the release film. Continue printing the cured layers until NM cured layers have been printed; The drive unit pauses operation during the printing interval between two adjacent cured layers. (3) Complete the printing of the last M curing layers.

7. The 3D printing method according to claim 6, characterized in that, The exfoliation pores are straight and extend vertically.

8. The 3D printing method according to claim 6, characterized in that, The diameter of the pore formation area is set to be ≥10mm larger than the inner diameter of the demolding hole.

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

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

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