3D printer with center demolding function and 3D printing method

Abstract

According to the 3D printer with the center demolding function, a guide rod hole is formed in a printing platform, an internal thread piece is rotationally installed at the top of the printing platform, and a demolding rod is screwed into an internal thread hole of the internal thread piece and can downwards penetrate through the guide rod hole; the driving device is installed on the printing platform and used for driving the internal thread part to rotate, and the demolding rod can only move up and down relative to the printing platform and cannot rotate; a demolding hole is formed in the mold, and the demolding rod can move downwards and abut against the release film of the material groove after penetrating through the demolding hole so as to push the release film downwards. The invention further discloses a 3D printing method. After printing of one curing layer is completed, the printing platform is lifted upwards, so that the release film and the model are stripped from outside to inside, the demolding rod moves downwards synchronously and pushes the release film, the release film and the model are stripped from inside to outside, the release film is stripped from inside to outside at the same time, and the stripping speed of the release film is increased.

Description

Technical Field

[0001] The invention relates to a 3D printer with central demolding and a 3D printing method. Background Art

[0002] DLP, LCD / LED and other 3D printers project a surface imaging light beam formed according to the sliced ​​cross-sectional pattern of the three-dimensional model onto the photosensitive resin printing material to achieve single-layer curing, and then solidify and stack the layers to form a three-dimensional model; during the printing process, it is necessary to frequently lift the unfinished model upward to separate the model from the release film and allow the photosensitive resin to enter between the model and the release film to continue printing the next cured layer. When the printing platform is lifted upward, a sealing area is formed between the release film and the cured layer, resulting in the need to overcome the low-pressure area between the release film and the cured layer during the peeling process of the cured layer and the release film, 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 created. The inclined peeling method is to tilt the material trough while lifting the printing platform upward, so that a peeling gap is generated on one side of the solidified layer of the release film. As the peeling gap gradually expands, the release film and the solidified layer are eventually completely peeled off.

[0004] 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 liquid volume of the material tank. At the same time, due to the inclination, the photosensitive resin will shake greatly, which will expand the contact area between the photosensitive resin and the air, making it easy for air to mix into the photosensitive resin, affecting the printing quality of the product model.

[0005] 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 the light-curing 3D printing technology. Summary of the invention

[0006] In order to increase the peeling speed of the solidified layer and the release film during model printing and improve the printing efficiency, the present application first discloses a 3D printer with central film release, which includes a workbench, a transmission mechanism is installed on the workbench, a printing platform is detachably installed on the transmission mechanism, and 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, the guide rod hole extends in the vertical direction and passes through the upper and lower sides of the printing platform, an internal threaded part is rotatably installed on the top of the printing platform, and the demolding rod is screwed into the internal threaded hole of the internal threaded part and can pass through the guide rod hole downward; a driving device for driving the internal threaded part to rotate is also installed on the printing platform, a limiting portion is provided on the demolding rod, and a limiting portion is provided in the guide rod hole, driven by the driving device, the internal threaded part can rotate around the demolding rod, and under the joint action of the limiting portion and the limiting portion, the demolding rod can only move up and down relative to the printing platform but cannot rotate;

[0008] 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 guide rod hole, and the demolding hole penetrates at least one solidified layer downwardly; when a solidified layer penetrated by the demolding hole is completed, the printing platform is moved upward, and the driving device is synchronously started to move the demolding rod downward, and after passing through the demolding hole, it is pressed against the release film of the material trough, and the release film is pushed downward, so that the release film is peeled off from the solidified layer along the lower end edge of the demolding hole; when the release film and the solidified layer are completely peeled off, the driving device can drive the demolding rod to move upward, and make the lower end of the demolding rod leave the release film.

[0009] During the model printing process, after the printing of a solidified layer is completed, the printing platform is lifted upward by the transmission mechanism, and the demolding rod is simultaneously moved downward by the driving device and pressed against the release film, so that the release film is peeled off from the model from the lower edge of the demolding hole, forming an inner peeling opening between the release film and the solidified layer, and at the same time, the release film is peeled off from the outer edge of the model, and after the outer peeling is formed, as the model is lifted, the inner peeling opening continues to expand and expand outward, and 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 is completely peeled off from the solidified layer. 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.

[0010] Specifically, the demolding rod includes a hollow rod and a demolding head. The hollow rod includes a main body extending in the vertical direction and a neck formed at the lower end of the main body. The demolding head is fixed at the lower end of the neck. The neck has an air hole extending in the radial direction. One end of the center hole of the hollow rod passes through the top surface of the main body. The other end of the center hole of the hollow rod is connected to the air hole. The lower end of the demolding head is a closed end. The maximum outer diameter of the demolding rod is 1-2 mm smaller than the inner diameter of the demolding hole, and the outer diameter of the demolding head is not larger than the root diameter of the thread of the external thread of the demolding rod. This design allows external air to enter the demolding hole through the center hole and the air hole of the hollow rod, avoiding the demolding hole from causing a vacuum state, so that the demolding rod will not generate negative pressure when pushing the release film downward, so as to smoothly complete the peeling from the inner side of the demolding hole to the model. The maximum outer diameter of the demolding rod is smaller than the inner diameter of the demolding hole, which can prevent the demolding rod from scratching the inner wall of the demolding hole, forming resin particles that fall into the material tank and affect normal printing. The outer diameter of the demolding head is not larger than the bottom diameter of the external thread of the demolding rod so that the demolding rod can be installed in the internal threaded part from top to bottom.

[0011] Furthermore, in order to prevent the stripping head from damaging the release film, the lower end of the stripping head is in the form of an arc surface protruding downward.

[0012] Specifically, the driving 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, and the output shaft of the solid shaft servo motor is connected to the internal threaded part.

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

[0014] The above two structural forms of the driving device can both meet the driving requirements for the film stripping rod, and can be selected according to the specific structural formation and usage habits of the equipment.

[0015] Secondly, the present application also discloses a 3D printing method, which is performed using any of the above-mentioned 3D printers. The enhanced 3D printing method comprises the following steps:

[0016] (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;

[0017] (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 guide rod hole upward; and the demolding hole penetrates downwardly through the lower end surface of the solidified layer located at the lowermost side;

[0018] After each solidified layer is printed, the printing platform is lifted upwards, and the driving device is started at the same time, so that the demolding rod moves downwards and presses against the release film, so that the release film is peeled off outwards along the lower edge of the demolding hole, and at the same time, the release film is peeled off inwards along the outer edge of the model until the solidified layer and the release film are completely peeled off, and the driving device is reversed to move the demolding rod upwards and leave the release film;

[0019] Continue printing the solidified layer until NM solidified layers are printed;

[0020] During the printing interval between two adjacent solidified layers, the driving device stops working;

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

[0022] 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 transmission mechanism is used to lift the printing platform upward, and the driving device is used to simultaneously move the demolding rod downward and press against the release film, so that the release film is peeled off from the model from the lower edge of the demolding hole, and an inner peeling opening is formed between the release film and the solidified layer. At the same time, the release film is peeled off from the outer edge of the model, and after the outer peeling is formed, as the model is lifted, the inner peeling opening continues to expand and expand outward, and 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.

[0023] When printing the last M solidified layers, different processing methods are used according to different needs. When the guide rod hole penetrates the solidified layer at the bottom of the model and does not affect the appearance and use function of the model, the internal and external bidirectional peeling method can be continued to complete the peeling of the release film and the last M solidified layers. However, when the guide rod hole penetrates the solidified layer at the bottom of the model and has 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 guide rod hole does not enter the last M solidified layers downward, and the last M solidified layers are used to complete the sealing of the guide rod hole. After the model is printed, the model is removed from the printing platform, the photosensitive resin retained in the guide rod hole is poured out from the hole located on the starting surface, and the guide rod hole is cleaned.

[0024] Specifically, in the process of peeling the release film from the solidified layer, the photosensitive resin in the demolding hole can flow downward smoothly, and the demolding hole is linear and extends in the vertical direction.

[0025] Furthermore, the set diameter of the hole forming area is greater than or equal to 10 mm of the inner diameter of the film stripping hole. This design makes the wall thickness of the film stripping hole at least 5 mm, so that the film stripping hole area has a higher strength.

[0026] 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.

[0027] 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

[0028] Figure 1 It is a structural schematic diagram of an embodiment of a 3D printer in the present invention.

[0029] Figure 2 yes Figure 1 FIG. 2 is a diagram showing the connection structure between the first driving device and the first internal threaded part and the printing platform.

[0030] Figure 3 yes Figure 2 Center AA view.

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

[0032] Figure 5 yes Figure 3 A partial enlarged view in the middle BB direction.

[0033] Figure 6 It is a structural schematic diagram of the film stripping rod.

[0034] Figure 7 This is a state diagram of the 3D printer when it is working.

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

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

[0037] Fig.10 It is a structural schematic diagram of another embodiment of the 3D printer in the present invention.

[0038] Fig.11 yes Fig.10 Schematic diagram of the connection structure between the second driving device and the first internal threaded part and the printing platform. DETAILED DESCRIPTION

[0039] Example 1

[0040] See also Figure 1-Figure 6 A 3D printer with center demolding includes a workbench 11, on which a transmission mechanism is installed. 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 a printing platform 20 is detachably installed at one end of the connecting arm 14 away from the ball screw. A servo motor is installed at the lower end of the ball screw. The servo motor is fixedly installed 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.

[0041] The material trough 17 is fixedly installed on the workbench. The material trough 17 includes a trough wall 171 extending in the vertical direction and a release film 174 arranged at the bottom of the trough wall 171. 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 on the workbench to detachably fix the material trough on the workbench.

[0042] An ultraviolet light system is installed in the workbench, which includes a liquid crystal screen fixed on the top plate of the workbench, and a material trough is arranged above the liquid crystal screen. The ultraviolet light system is not shown in the attached drawings. 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 mounted 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, 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.

[0045] A guide rod hole 26 is provided on the printing platform, and the guide rod hole includes an upper guide rod hole 27 provided in the main body and a lower guide rod hole 28 provided in the model plate, and the upper guide rod hole and the lower guide rod hole are through holes and are coaxially arranged. The upper guide rod hole 27 penetrates the upper surface of the main body upward, and the lower guide rod hole 28 penetrates the lower surface of the model plate 23 downward. That is, the guide rod hole extends in the vertical direction and penetrates the upper and lower sides of the printing platform.

[0046] A first internal threaded member 81 is rotatably mounted on the top of the printing platform, and the stripping rod 40 is screwed into the internal threaded hole of the first internal threaded member and can pass downward through the guide rod hole 26. A first driving device for driving the first internal threaded member 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 arranged in the stator 71, a hollow shaft 86 is fixed on the mover 75, and a first internal threaded member is fixed on 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, wherein 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, and the upper flange 711 and the lower flange 712 are integrally formed on the stator 71, and a winding 74 is arranged on the inner side of the stator. The lower end cover 73 is detachably mounted on the upper surface of the main body by bolts, so that the stator is fixedly mounted on the top of the printing platform, and thus the hollow shaft torque motor 70 is mounted 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 upper abutting flange 721 protruding inwardly, and the lower surface of the upper abutting flange 721 is a step surface facing downward. The upper abutting flange 721 is pressed 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 is pressed 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, and the lower step portion has a step surface facing downward, and the lower step portion 77 is formed by the outer peripheral surface of the hollow shaft 86 being recessed radially inward; the lower end cover has a lower abutting flange 731 protruding inward, and the upper surface of the lower abutting flange 731 is a step surface facing upward, and the lower abutting flange 731 abuts against the lower side of the outer ring of the lower angular contact bearing 79 through its upper surface, and the lower step portion 77 abuts 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 through the lower angular contact bearing. The structure of the hollow shaft torque motor can be completed by using existing mature technology, and no further description is given.

[0050] The first internal threaded member is lined in the inner cavity of the hollow shaft 86. A flange 811 is provided at the top of the first internal threaded member 81. The flange 811 is formed by protruding radially outward from the outer circumference of the first internal threaded member 81. The top of the hollow shaft is fixed to the flange 811 by bolts. In order to ensure the connection stability between the first internal threaded member and the hollow shaft, a key 85 is provided between the first internal threaded member and the hollow shaft. The hollow shaft, the first internal threaded member and the guide rod hole are coaxially arranged.

[0051] See also Figure 6 In this embodiment, the demolding rod 40 includes a hollow rod 401 and a demolding head 44. The hollow rod 401 includes a body 41 extending in the vertical direction and a neck portion 42 formed at the lower end of the body. The demolding head is fixed at the lower end of the neck portion. The neck portion 42 has a vent hole 43 extending in the radial direction. The vent hole passes through the rod wall of the hollow rod. One end of the center hole 46 of the hollow rod passes through the top surface of the body upward. The other end of the center hole 46 of the hollow rod is connected to the vent hole. The lower end of the demolding head is a closed end, and the lower end of the demolding head presents a circular arc surface 45 protruding downward. The outer peripheral surface of the body has an external thread that can be engaged with the internal thread of the first internal threaded member. The outer diameter of the demolding 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 demolding head is equal to the root diameter of the thread of the external thread of the body. That is, the outer diameter of the demolding head is not greater than the root diameter of the thread of the external thread of the demolding rod.

[0052] In this embodiment, the demolding rod 40 is made of stainless steel. It is understandable that in other embodiments, the demolding rod can also be made of metal or alloy materials such as copper and aluminum.

[0053] See also Figure 5 , to simplify the attached figure, Figure 5 The section line of the main body 21 is cancelled. When observed along the axial direction of the guide rod hole 26, the cross section of the guide rod hole 26 includes a major arc 261 and a straight line segment 262 closing the major arc 261, so that the guide rod hole 26 is formed by a circular hole, and a radially inward protrusion is provided in the circular hole, wherein the area where the straight line segment is located is formed as the protrusion, and the protrusion is formed as the limiting part of the guide rod hole. A limiting part is provided on the stripping rod 40. In this embodiment, the limiting part is a tangent plane 47 formed on one side of the stripping rod 40 and capable of adapting to the above-mentioned protrusion.

[0054] The demolding rod 40 is screwed into the internal thread hole of the first internal thread part and freely inserted into the guide rod hole 26. When the mover drives the first internal thread part to rotate around the demolding rod through the hollow shaft, the protrusion can be pressed against the cutting plane, so that the demolding rod can only move up and down relative to the printing platform but cannot rotate.

[0055] The model 30 is bonded to the working surface 231 on the printing platform, and a demolding hole 31 is formed in the model. The upper end of the demolding hole is connected to the guide rod hole, and the demolding hole penetrates at least one solidified layer downward; when a solidified layer penetrated by the demolding hole is completed, the printing platform is moved upward, and the first driving device is synchronously started to move the demolding rod downward, and after passing through the demolding hole, it is pressed against the release film of the material trough, pushing the release film downward, so that the release film is peeled off from the solidified layer along the lower edge of the demolding hole; when the release film and the solidified layer are completely peeled off, the first driving 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 about the demolding hole 31, please refer to the relevant content in Example 3 below.

[0057] Example 2

[0058] See also Fig.10 and Fig.11 This embodiment is basically the same as the first embodiment, and the only difference is the driving device. Fig.10 , Fig.11 In both Figure 1-Figure 6The same reference numerals 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, and the positioning sleeve 64 extends in the vertical direction. A bearing seat 641 is formed at the lower end of the positioning sleeve, and the bearing seat 641 is fixedly installed 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 internal threaded member 66 is rotatably lined in the positioning sleeve 64, and a lower support step surface 661 and an upper support step surface 662 are formed on the outer peripheral surface of the second internal threaded member 66, wherein the lower support step surface 661 faces downward and the upper support step surface faces upward. The outer ring of the first bearing 65 is supported on the bearing seat, and the lower support step surface is supported on 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 cover is pressed against the outer ring of the second bearing. The second internal threaded member is rotatably maintained on the top of the printing platform through the first bearing and the second bearing. Both the first bearing and the second bearing 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, and 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 the solid shaft servo motor, a belt 612 is wrapped around the pulley and the second internal threaded member, a belt groove is provided on the outer circumference of the second internal threaded member, and the belt is clamped in the belt 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 internal threaded member to form a gear combination, and the solid shaft servo motor 61 drives the second internal threaded member to move up and down through the gear combination.

[0062] The demolding rod 40 is screwed into the internal thread hole of the second internal thread part and freely inserted into the guide rod hole 26. When the mover drives the second internal thread part to rotate around the demolding rod through the hollow shaft, the protrusion can be pressed against the cutting plane, so that the demolding rod can only move up and down relative to the printing platform but cannot rotate.

[0063] Example 3

[0064] See also Figure 7-Figure 9 This embodiment describes a 3D printing method. The 3D printing method is performed using the 3D printer in Implementation 1 or Implementation 2. The enhanced 3D printing method includes the following steps:

[0065] (1) After the 3D modeling of the model to be printed is completed, the cylindrical hole area with a set diameter is calculated. Please refer to Figure 3 ,exist Figure 3 In the figure, the model 30 is represented by a dotted line, and the area enclosed by the double-dotted line 91 is the reinforcement 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, no section line is set for the model 30. In this embodiment, the film stripping hole is straight, and the film stripping hole extends in the vertical direction.

[0066] 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.

[0067] 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.

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

[0069] (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 guide rod hole upward and penetrates the lower end surface of the solidified layer located at the lower side downward.

[0070] After each solidified layer is printed, the printing platform is lifted upward, and the driving device is started at the same time, so that the demolding rod moves downward and presses against the release film. As the printing platform is gradually lifted, the demolding rod moves downward synchronously, so that the release film is peeled outward along the lower edge of the demolding hole until the solidified layer and the release film are completely peeled off. The demolding hole is connected to the external atmosphere by the center hole 46 in the demolding rod to eliminate the negative pressure phenomenon caused by atmospheric pressure. When the solidified layer and the release film are completely peeled off, the driving device is reversed to move the demolding rod upward, leaving the release film, and the demolding head retracts into the demolding hole. The driving device refers to the hollow shaft torque motor 70 in Example 1 or the solid shaft servo motor 61 in Example 2.

[0071] See also Figure 8 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, due to the pushing effect of the demolding rod on the release film, 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 directions of the solidified layer, forming an inside-outside bidirectional peeling method.

[0072] See also Fig. 9 As the inner stripping opening 901 and the outer stripping opening 902 continue to extend and expand, the inner stripping opening 901 and the outer stripping opening 902 are connected to each other, so that the release film is completely stripped from the solidified layer. When the solidified layer is completely stripped from the release film, the stripping rod is lifted upward to retract the stripping head into the stripping hole.

[0073] 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.

[0074] 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.

[0075] (3) The printing of the last 10 solidified layers is completed, that is, the printing of the last M solidified layers is completed.

[0076] 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 3In 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.

[0077] 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.

[0078] After the model is printed, the model is removed from the printing platform, the photosensitive resin retained in the guide rod hole is poured out from the hole located on the starting surface, and the guide rod hole is cleaned.

Claims

1. A 3D printer with central demolding, characterized in that: It includes a workbench, on which a transmission mechanism is installed, and a printing platform is detachably installed on the transmission mechanism, and the transmission mechanism can drive the printing platform to reciprocate in a vertical direction; A guide rod hole is provided on the printing platform, the guide rod hole extends in the vertical direction and passes through the upper and lower sides of the printing platform, an internal threaded part is rotatably installed on the top of the printing platform, and the demolding rod is screwed into the internal threaded hole of the internal threaded part and can pass through the guide rod hole downward; a driving device for driving the internal threaded part to rotate is also installed on the printing platform, a limiting portion is provided on the demolding rod, and a limiting portion is provided in the guide rod hole, driven by the driving device, the internal threaded part can rotate around the demolding rod, and under the joint action of the limiting portion and the limiting portion, the demolding rod can only move up and down relative to the printing platform but cannot rotate; 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 guide rod hole, and the demolding hole penetrates at least one solidified layer downward; When a solidified layer is completed through a demolding hole, the printing platform is moved upward, and the driving device is started synchronously to move the demolding rod downward. After passing through the demolding hole, the demolding rod is pressed against the release film of the material trough to push the release film downward so that the release film is peeled off from the solidified layer along the lower edge of the demolding hole. When the release film is peeled off from the solidified layer, the driving device can drive the demolding rod to move upward and make the lower end of the demolding rod leave the release film.

2. The 3D printer according to claim 1, characterized in that: The demolding rod comprises a hollow rod and a demolding head. The hollow rod comprises a main body extending in a vertical direction and a necking portion formed at the lower end of the main body, and the demolding head is fixed at the lower end of the necking portion. The necking portion is provided with an air hole extending in a radial direction, one end of the center hole of the hollow rod passes through the top end surface of the main body, the other end of the center hole of the hollow rod is connected to the air hole, and the lower end of the demolding head is a closed end. The maximum outer diameter of the demolding rod is 1-2 mm smaller than the inner diameter of the demolding hole, and the outer diameter of the demolding head is not larger than the root diameter of the thread of the external thread of the demolding rod.

3. The 3D printer according to claim 2, characterized in that: The lower end of the film stripping head is in the form of an arc surface protruding downward.

4. The 3D printer according to claim 1, characterized in that: The driving 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, and 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 driving device is a hollow shaft torque motor, which includes a stator and a mover rotatably arranged inside the stator. The stator is fixedly mounted on the top of the printing platform, and the internal threaded part is fixed on the mover. The hollow shaft torque motor is a servo motor.

6. A 3D printing method, characterized in that: The enhanced 3D printing method is carried out using the 3D printer according to any one of claims 1 to 5, and 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 guide rod hole upward; and the demolding hole penetrates downwardly 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 upwards, and the driving device is started at the same time, so that the demolding rod moves downwards and presses against the release film, so that the release film is peeled off outwards along the lower edge of the demolding hole, and at the same time, the release film is peeled off inwards along the outer edge of the model until the solidified layer and the release film are completely peeled off, and the driving device is reversed to move the demolding rod upwards and leave the release film; Continue printing the solidified layer until NM solidified layers are printed; During the printing interval between two adjacent solidified layers, the driving device stops working; (3) Complete the printing of the last M solidified layers.

7. The 3D printing method according to claim 6, characterized in that: The demoulding hole is linear and extends in the vertical direction.

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.

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