Melting Extrusion Device, 3D Printer, 3D Printer Control Method and Application

Abstract

The present invention discloses a melt extrusion device, a 3D printer, a 3D printer control method and an application. The melt extrusion device is used for melting and extruding raw materials of a 3D printer. The melt extrusion device includes a screw assembly and a nozzle assembly connected to the screw assembly. The screw assembly includes a housing and at least two screws arranged in the housing. The threads of adjacent screws mesh with each other. The raw materials are evenly mixed and melted by the co-rotation of the screws, and the melted raw materials are extruded through the nozzle assembly. The present invention adopts at least two screws meshing and rotating in the same direction. The raw materials are gradually melted under the rotation and shear of the screws. The shear rate and shear stress of the melt are relatively large at the meshing position, and good backmixing occurs, greatly improving the distribution and mixing ability of various raw materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of 3D printing, and more specifically, relates to a melt extrusion device, a 3D printer, a 3D printer control method and applications. Background Art

[0002] In recent years, 3D printing technology has developed rapidly. According to different forming methods, it can be mainly divided into fused deposition modeling (FDM), selective laser melting (SLM), laser cladding forming (LENS), selective laser sintering (SLS), stereolithography apparatus (SLA), three-dimensional printing (3DP), etc. Among them, the FDM technology has been the most widely used because of its low cost, simple principle and small equipment volume. At present, the FDM technology mainly uses thermoplastic polymer filaments such as PLA and ABS as raw materials. The feeding mechanism feeds them into a high-temperature melting cavity at 200-240 °C, and finally the nozzle sprays them at specific positions of the hot bed device, so as to stack layer by layer to form a three-dimensional object. However, this technology still has the following problems:

[0003] First, the most widely used consumable on the market is uniform filaments, which have undergone a hot forming process of wire drawing before printing, so their mechanical strength has decreased. During printing, the filaments are prone to oxidation and breakage, clogging the nozzle, etc. Once such problems occur in a certain layer, the entire printing process will be wasted, resulting in waste of materials and time;

[0004] Second, once the filaments are drawn into wires, their material compositions are permanently fixed, and the material compositions of the printed models in each area are also uniform. It is impossible to customize the composition ratios of the materials point by point, line by line, and layer by layer according to personal needs, that is, it is impossible to form functional components such as composite materials and heterogeneous gradient materials, which limits the application prospects of this technology.

[0005] In response to the above problems, some publicly disclosed patents have improved the traditional FDM technology. For example, patents CN201410469682.0, CN201810973383.9, CN201810407488.8, CN201910562463.X, etc. have designed new extrusion mechanisms, changing the traditional wire feeding into pellet feeding, melting and extruding the pellets in the form of a single screw, which can achieve the layer-by-layer stacking forming of polymers. However, the mixing ability of the single screw is not strong, the melt extruded through the nozzle contains more bubbles, the density is not high, the extrusion direction is arbitrarily distorted and uncontrollable, and the material ratio control of each point cannot be achieved during the forming process, that is, composite and heterogeneous gradient functional materials cannot be formed. At the same time, the above patents do not give the design scheme of the whole machine. If the screw moves along the XYZ three axes, due to its heavy weight and large inertia, the whole machine will vibrate, and the forming process is unstable or even cannot be formed; Patent CN201910178883.8 mentions using a rotary vane valve to control the feeding ratio of two or more kinds of pellets, and the extrusion system also adopts the above-mentioned single screw rotation melting. In theory, it can overcome the above problems one and two, but the control accuracy of the vane valve is limited, and the single screw still has the above disadvantages; Patent CN201510449256.5 uses a rotary disk nozzle switching and screw feeding method to achieve the composite printing of multiple materials, but the applicable materials are slurries with a certain fluidity, which are not universal for polymer materials, etc., and the multi-nozzle switching process is complex and the forming efficiency is low.

[0006] Therefore, a melting and extrusion device and a 3D printer adaptable to polymers and multiple materials are needed, which can meet the control of the material composition ratio point by point, line by line, and layer by layer. Summary of the Invention

[0007] In view of the above defects or improvement requirements of the prior art, the present invention provides a melting and extrusion device, a 3D printer, a 3D printer control method and applications, aiming to real-time control the material composition ratio point by point, line by line, and layer by layer during the printing process, and realize the integrated forming of complex structures and functions such as composite materials and heterogeneous gradient materials, thereby solving the technical problems in the prior art that the melt extruded contains more bubbles, the density is not high, the extrusion direction is arbitrarily distorted and uncontrollable, and the control of the material composition ratio point by point, line by line, and layer by layer cannot be satisfied.

[0008] To achieve the above object, according to one aspect of the present invention, there is provided a melting and extrusion device for melting and extruding raw materials of a 3D printer, characterized in that the melting and extrusion device includes a screw assembly and a nozzle assembly connected to the screw assembly. The screw assembly includes a housing and at least two screws arranged in the housing. The threads of adjacent screws mesh with each other, and the raw materials are evenly mixed and melted by the co-rotation of the screws, and the melted raw materials are extruded through the nozzle assembly.

[0009] Preferably, the screw is an equal-diameter and gradually-varying screw. Along the direction from the raw material entering to leaving the housing, the depth of the screw thread groove gradually decreases; the length-diameter ratio of the screw is 10 to 16, and the depth of the screw thread ridge of an adjacent screw entering the thread groove of another screw is 0.6 to 1.7 times the minimum thread groove depth.

[0010] Preferably, the screw assembly further includes a heating assembly arranged on the outer wall of the housing and a cooling assembly arranged facing the heating assembly.

[0011] Preferably, the screw includes a feeding section, a compression section, and a metering section. The heating assembly includes three heating coils, and these three heating coils are arranged on the outer wall of the housing corresponding to the feeding section, the compression section, and the metering section respectively. Heat dissipation fins are arranged between these three heating coils; the cooling assembly includes three cooling fans arranged facing the three heating coils.

[0012] Preferably, the screw assembly further includes a power assembly for driving the at least two screws to rotate in the same direction and in the same phase; the power assembly includes an input motor, a transmission shaft connected to the input motor, a driving gear arranged on the transmission shaft, and a transmission gear fixed on the screw, and the driving gear meshes with the transmission gear.

[0013] According to another aspect of the present invention, a 3D printer is provided, including a feeding and mixing device, a melting and extruding device as described above, a hot bed device, a motion device, and a frame for supporting and fixing the above devices;

[0014] Wherein, the feeding and mixing device is connected to the melting and extruding device, and the feeding and mixing device can provide at least two mixed raw materials for the melting and extruding device; the hot bed device is arranged below the nozzle assembly, and the motion device is used to drive the hot bed device to move in the X-axis, Y-axis, and Z-axis directions.

[0015] Preferably, the feeding and mixing device includes at least two feeding components and a mixing component communicated with the at least two feeding components;

[0016] The feeding component includes a raw material barrel, a rotating dial arranged at the bottom of the raw material barrel, and a stepping motor connected to the rotating dial; the outer ring of the rotating dial is a tooth comb structure, and a feeding hole is opened at a position corresponding to the tooth comb structure at the bottom of the raw material barrel, and the feeding hole is communicated with the mixing component; there is a semi-circular inclined surface arranged above the feeding hole in the raw material barrel, and by controlling the rotation of the rotating dial (12) through the stepping motor, the amount of raw material in the raw material barrel entering the mixing component is controlled;

[0017] The mixing component includes a mixing funnel and a discharging screw connected to the mixing funnel; the discharging screw is used to mix the raw materials entering the mixing funnel and then feed them into the melting and extruding device.

[0018] Preferably, the feeding assembly further includes a weight sensor disposed at the bottom of the raw material barrel and a laser pair sensor disposed at the outlet of the mixing funnel; a transparent window is installed on the side wall of the raw material barrel.

[0019] Preferably, the motion device includes an X-axis motion structure, a Y-axis motion structure, and a Z-axis motion structure; the hot bed device is fixedly connected to the Y-axis motion structure, the X-axis motion structure and the Y-axis motion structure are used to drive the hot bed device to perform horizontal motion, and the Z-axis motion structure is used to drive the hot bed device to perform vertical motion;

[0020] The printer further includes a CCD camera and a laser leveling sensor disposed on the hot bed device.

[0021] According to another aspect of the present invention, there is provided a control method for a 3D printer as described above, the method including:

[0022] Controlling the rotating dials in at least two feeding assemblies to rotate at different rotating speeds through a stepper motor to provide at least two raw materials with different mixing ratios for the extrusion device in real time;

[0023] Making the input motor in the melting and extrusion device rotate, driving at least two screws to rotate in the same direction and in the same phase, turning on the heating assembly, making the raw materials mix evenly and melt, extruding the molten raw materials onto the hot bed device through the nozzle assembly, and at the same time driving the hot bed device to move in the X-axis, Y-axis, and Z-axis directions through the motion device to complete printing;

[0024] During the printing process, receiving the photo information obtained by the CCD camera, comparing it with the CAD size of this layer of the three-dimensional model to obtain a size deviation, and when the size deviation exceeds the set threshold, sending a prompt correction information or stopping printing.

[0025] According to still another aspect of the present invention, there is provided an application of a 3D printer as described above, which is applied to 3D printing of granular polymer materials.

[0026] Generally speaking, compared with the prior art by the above technical solutions conceived by the present invention, at least the following beneficial effects can be achieved.

[0027] (1) In the melting and extrusion device provided by the present invention, at least two screws rotate in the same direction and mesh with each other. The raw materials (especially polymer granular materials) are gradually melted under the rotation and shear of the screws. At the meshing part, the shear rate and shear stress of the melt are large, and good backmixing is generated, greatly improving the distribution and mixing ability of multiple raw materials. Moreover, at least two screws can rotate and melt to convey multiple raw material particles, avoiding the complex process of preparing traditional filaments, expanding the range of available materials to a certain extent, and reducing the production cost.

[0028] (2) The 3D printer provided by the present invention can, through the feeding and mixing device, real-time control the material composition ratio point by point, line by line, and layer by layer during the printing process, achieving the purpose of integrally forming complex structure-functional materials such as composite materials and heterogeneous gradient materials.

[0029] (3) In the 3D printer provided by the present invention, the melting and extrusion device is fixed on the frame without spatial movement, while the hot bed device is fixed on the slider of the Y-axis module and can perform three-dimensional spatial movement in the XYZ directions to undertake the layer-by-layer stacking and forming of the three-dimensional model. This avoids the problem of poor printing quality caused by the heavy and unstable screw-type melting and extrusion device.

[0030] (4) In the present invention, the screw is strictly limited to an equal-diameter and gradually-varying screw, and the length-diameter ratio ranges from 10 to 16. Compared with a screw with a small length-diameter ratio, the material stays in the barrel for a longer time, which is beneficial to material mixing and plasticization, increases the melt pressure, and eliminates backflow and leakage phenomena.

[0031] (5) In the 3D printer provided by the present invention, the feeding and mixing device controls the feeding amounts of multiple raw materials by adjusting the rotation speed of the rotating dial, enabling real-time regulation of different raw materials for precise mixing in any ratio. Moreover, the setting of the semi-circular inclined surface can effectively prevent the leakage of raw materials when the rotating dial is not in use. A transparent window is installed on the side wall of the raw material barrel, allowing the remaining material amount in the raw material barrel to be observed without opening the barrel.

[0032] (6) In the present invention, a weight sensor is equipped under each raw material barrel; it can monitor the feeding weights of two or more granular materials. The laser opposed sensor is connected to the outlet of the mixing funnel to monitor whether the granular materials are output in a timely manner, thereby precisely controlling the feeding of raw materials.

[0033] (7) In the present invention, the three heating coils of the melting and extrusion device are arranged corresponding to the feeding section, compression section, and metering section, and the three heating coils can be set to different heating temperatures to rapidly heat solid materials to the viscous flow state in the feeding section, enabling the materials to fully discharge gas when entering the compression section; ensuring the melt fluidity in the compression section and ensuring good formability of the materials after extrusion from the nozzle in the metering section. At the same time, the setting of the cooling fan and heat sink can lower the temperature to protect the adjacent components.

[0034] (8) The control method of the screw-type multi-material 3D printer in the present invention can use a CCD camera to monitor the printing quality of each layer and issue a prompt in a timely manner when printing quality problems occur.

[0035] (9) The 3D printer disclosed by the present invention has wide applicability to most polymer materials, and has no special requirements for the state of the material itself. It can form granular and powdery materials, etc., overcoming the disadvantages of uncontrollable material layer by layer, point by point, and line by line in traditional wire melting forming, few available material types, and high production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is a schematic structural diagram of a screw-type multi-material 3D printer provided by an embodiment of the present invention;

[0037] Figure 2 is a cross-sectional view of a feeding and mixing device in the structure of a screw-type multi-material 3D printer provided by an embodiment of the present invention;

[0038] Figure 3 is a bottom view of a feeding and mixing device in the structure of a screw-type multi-material 3D printer provided by an embodiment of the present invention;

[0039] Figure 4 is a top view of a feeding and mixing device in the structure of a screw-type multi-material 3D printer provided by an embodiment of the present invention;

[0040] Figure 5 is a schematic structural diagram of a melting and extrusion device in the structure of a screw-type multi-material 3D printer provided by an embodiment of the present invention;

[0041] Figure 6 is a cross-sectional view of a melting and extrusion device in the structure of a screw-type multi-material 3D printer provided by an embodiment of the present invention;

[0042] Figure 7 is a schematic structural diagram of a motion device and a hot bed device in the structure of a screw-type multi-material 3D printer provided by an embodiment of the present invention.

[0043] In all the drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0044] 1 - feeding and mixing device; 1A - feeding assembly; 1B - mixing assembly; 11 - rotating dial cover; 12 - rotating dial; 13 - rotating dial fixing ring; 14 - coupling; 15 - motor fixing plate; 16 - stepping motor; 17 - mixing funnel; 18 - laser pair sensor; 19 - mixing screw; 110 - mixing joint; 111 - raw material barrel; 112 - mixing bottom plate; 113 - mixing stepping motor; 114 - mixing screw bearing seat; 115 - mixing screw barrel; 116 - weight sensor; 117 - inclined plane; 118 - transparent window;

[0045] 2 - Melting and Extrusion Device; 2A - Screw Assembly; 2B - Nozzle Assembly; 2C - Screw; 21 - Input Motor; 22 - Motor Fixed Bending Part; 23 - Motor Shaft Gear; 24 - Transmission Box Input Large Gear; 224 - First Large Gear Inside the Transmission Box; 227 - Second Large Gear Inside the Transmission Box; 25 - Upper Transmission Box; 26 - Middle Transmission Box; 27 - Lower Transmission Box; 28 - Nozzle Support Plate; 29 - Feeding Cylinder; 210 - Feeding Heat Insulation Plate; 211 - Screw Barrel; 212, 214, 215 - Heating Coils; 213 - Heat Sink; 216 - Heat Insulation Sponge; 217 - Heating Nozzle; 218 - Nozzle Fixed Bending Part; 219 - Cooling Fan; 220 - Transmission Box Cover; 221 - Angular Contact Ball Bearing; 222, 223, 228, 229 - Positioning Sleeves; 225 - First Small Gear Inside the Transmission Box; 226 - Second Small Gear Inside the Transmission Box; 230 - O - Ring Seal; 231 - Flange Gasket; 232 - Right Screw; 233 - Left Screw; 234 - Baffle Plate; 235 - Confluence Core; 236 - Bearing End Cover; 237 - Transmission Shaft;

[0046] 3 - Hot Bed Device; 31 - MK3 Aluminum Substrate Hot Bed; 32 - Hot Bed Heat Insulation Cotton; 33 - Hot Bed Support Plate; 34 - Laser Leveling Sensor; 35 - Heating Coil; 36 - Leveling Nut.

[0047] 4 - Motion Device; 41 - Y - Axis Motion Slide Block; 42 - Y - Axis Motion Module; 43 - X - Axis Motion Slide Block; 44 - X - Axis Motion Module; 45 - Z - Axis Motion Slide Block; 46 - Z - Axis Motion Module;

[0048] 5 - CCD Camera;

[0049] 6 - Frame; 61 - Bottom Plate; 62 - Nylon Floor Feet; 63 - Touch Screen; 64 - Touch Screen Fixed Plate. Detailed Embodiment

[0050] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0051] An embodiment of the present invention provides a melt extrusion device for melt extruding raw materials of a 3D printer. The melt extrusion device 2 includes a screw assembly 2A and a nozzle assembly 2B connected to the screw assembly 2A. The screw assembly 2A includes a housing and at least two screws 2C arranged in the housing. The threads of adjacent screws 2C mesh with each other. The raw materials are evenly mixed and melted by the co-rotation of the screws 2C, and the melted raw materials are extruded through the nozzle assembly 2B. In a feasible manner of an embodiment of the present invention, the screw 2C is an equal-diameter gradually-varying screw. Along the direction from the entry of the raw materials to the exit of the housing, the depth of the screw groove of the screw 2C gradually decreases; the length-diameter ratio of the screw 2C is 10-16, and the depth of the screw edge of one screw 2C entering the screw groove of another screw 2C is 0.6-1.7 times the minimum screw groove depth. The equal-diameter gradually-varying screw adopted in this embodiment has a relatively large length-diameter ratio. Compared with a screw with a small length-diameter ratio, the residence time of the material in the barrel is long, which is beneficial to the mixing and plasticization of the material, improves the melt pressure, and eliminates the phenomena of backflow and leakage. The left and right hand directions of the screw are both acceptable and have no influence on the performance of the finally extruded melt. Due to the co-rotation and meshing assembly method, the axial rotation phases of the screws need to be kept consistent, otherwise it cannot work. The depth of the screw edge of one screw entering the screw groove of another screw is within the range of 0.6-1.7 times the minimum screw groove depth. Exemplarily, for this embodiment, it is approximately equal to 0.5-1.4 mm.

[0052] See Figure 5 and Figure 6 , in the embodiment of the present invention, two screws 2C in the screw assembly 2A are taken as an example for illustration. It can be understood that the number of screws 2C can also be, for example, 3, 4, 5, etc. For example, it can be three parallel and co-rotating screws, with two meshing regions (a twin-screw has one meshing region). Therefore, the meshing and dispersion effect is increased by more than one time, the plasticization effect is good, and the dispersion is more uniform. The more the number of screws 2C, the better the meshing and dispersion effect, but the weight of the screw assembly 2A will also increase accordingly.

[0053] The screw assembly 2A further includes a heating assembly arranged on the outer wall of the housing and a cooling assembly arranged facing the heating assembly. The screw 2C includes a feeding section, a compression section, and a metering section. The screw is successively the feeding section, the compression section, and the metering section along the feeding direction. The length of each section depends on the type of the material. The applicable material of this printer is an amorphous polymer. The length ratio of the feeding section accounts for 10%-25% of the total working length of the screw, the compression section accounts for 50%-65% of the total working length of the screw, and the length ratio of the metering section accounts for 20%-30% of the total working length of the screw. The total working length of the screw = (12-16) × the outer diameter of the screw. In this embodiment, the diameter of the screw is selected as 13 mm, and the range of 10-20 mm is acceptable.

[0054] The heating assembly includes three heating coils 212, 214, 215, which are disposed on the outer wall of the housing corresponding to the feeding section, the compression section, and the metering section respectively. Heat sinks 213 are provided between the three heating coils 212, 214, 215; the cooling assembly includes three cooling fans 219 facing the three heating coils. The screw assembly 2A further includes a power assembly for driving the at least two screws 2C to rotate in the same direction and in the same phase; the power assembly includes an input motor 21, a transmission shaft 237 connected to the input motor, a driving gear disposed on the transmission shaft 237, and a transmission gear fixed on the screw 2C, and the driving gear meshes with the transmission gear.

[0055] More specifically, the melt extrusion device 2 includes the following components: an input motor 21; a motor fixing bend 22; a motor shaft gear 23; a transmission box input large gear 24; a first large gear 224 inside the transmission box; a second large gear 227 inside the transmission box; an upper transmission box 25; a middle transmission box 26; a lower transmission box 27; a nozzle support plate 28; a feeding cylinder 29; a feeding heat insulation plate 210; a screw barrel 211; heating coils 212, 214, 215; heat sinks 213; heat insulation sponges 216; a heating nozzle 217; a nozzle fixing bend 218; cooling fans 219; a transmission box gland 220; angular contact ball bearings 221; positioning sleeves 222, 223, 228, 229; a first small gear 225 inside the transmission box; a second small gear 226 inside the transmission box; an O-ring 230; a flange gasket 231; a right screw 232; a left screw 233; a baffle plate 234; a confluence core 235; a bearing end gland 236; a transmission shaft 237.

[0056] Among them, the input motor 21 is fixed on the motor fixing bend 22, and the motor shaft gear 23 is fixed on the transmission shaft 237 of the motor 21; the housing is composed of the feeding cylinder 29 and the screw barrel 211. The upper transmission box 25, the middle transmission box 26, and the lower transmission box 27 are assembled into a transmission box body by screws. The transmission shaft 237 is fixedly connected with the transmission box input large gear 24, the first large gear 224 inside the transmission box, and the second large gear 227 inside the transmission box. The left screw 233 and the right screw 232 are respectively fixedly connected with the first small gear 225 inside the transmission box and the second small gear 226 inside the transmission box; the transmission box input large gear 24 meshes with the motor shaft gear 23, the first large gear 224 inside the transmission box meshes with the first small gear 225 inside the transmission box, and the second large gear 227 inside the transmission box meshes with the second small gear 226 inside the transmission box, so that the input motor 21 drives the left and right screws to rotate in the same direction and in the same phase.

[0057] In a feasible manner of an embodiment of the present invention, a positioning sleeve 223, 228 and an angular contact ball bearing 221 are mounted on the left screw rod 233, and a positioning sleeve 222, 229 and an angular contact ball bearing 221 are mounted on the right screw rod 232, all of which are coaxially interference-fitted. The lower transmission box 27 is fixed to the nozzle fixing bending member 218 and is fixedly connected to the motor fixing bending member 22 and the nozzle support plate 28 by screws. A bearing end gland 236 is provided at the lower end of the box body, and a transmission box gland 220 is provided at the upper end to prevent axial displacement of the screw rod. An O-ring 230 is provided in the feed cylinder 29, and a heat insulation plate 210 is provided at the feed port. The heat insulation plate 210 is fixedly connected to the above-mentioned mixing joint 110. The feed cylinder 29 is fixedly connected to the screw barrel 211 by screws, and a flange gasket 231 is provided at the connection. Heat dissipation fins 213 and heating coils 212, 214, 215 are installed on the outer wall of the screw barrel 211. These heating coils are mica heating coils. A cooling fan 219 is installed on the nozzle fixing bending member 218 for cooling, and the temperature control of the twin screws is achieved through electronic components.

[0058] For the heating coils 212, 214, 215, the heating temperature has different parameter values for different materials, and there are also differences in the temperature settings of the three heating coils. The set temperature of the heating coil 212 provided at the feeding section is about 20 - 30°C above the viscous flow temperature of the material, and it is necessary to quickly heat the solid material to the viscous flow state so that the material can fully discharge gas when entering the compression section; the set temperature of the heating coil 214 provided at the compression section is within ±10°C of the viscous flow temperature of the material to ensure the melt fluidity; the temperature of the heating coil 215 provided at the metering section is relatively low, about 20 - 50°C above the glass transition temperature, to ensure good formability of the material after extrusion from the nozzle.

[0059] In addition, the screw barrel 211 and the confluence core 235 are fixedly connected by screws, and a baffle 234 and a flange gasket 231 are provided at the connection. The outer wall of the confluence core 235 is coated with heat insulation sponge 216. A threaded hole is opened at the head of the confluence core 235, which is matched with the external thread at the tail of the heating nozzle 217. Raw tape is stuck at the threaded engagement part to prevent fluid leakage. A thermocouple and a thermistor are provided on the heating nozzle 217. The molten body is converted from rotational motion to linear motion through the baffle 234 and finally converges and merges through the confluence core 235 and is ejected from the heating nozzle 217.

[0060] It should be noted that in the melt extrusion device 2, the input motor 21 outputs axial rotation. Through the meshing kinematic pair of the motor shaft gear 23 and the input large gear 24 of the transmission box, the rotational motion is transmitted to the transmission shaft 237. The transmission shaft 237 drives the left screw 233 through the meshing kinematic pair of the first large gear 224 and the first small gear 225 in the transmission box, and drives the right screw 232 through the meshing kinematic pair of the second large gear 227 and the second small gear 226 in the transmission box. Since the transmission ratios of the two sets of kinematic pairs are the same, the rotational speeds of the left and right screws are the same, and the angular velocity output by the input motor 21 is the angular velocity of the left screw 233 and the right screw 232.

[0061] In the actual use process, the working speed of the input motor 21 in the embodiment of the present invention needs to be determined according to the molecular chain length and structure of the raw material particles. For polymer materials with long and complex molecular chains, such as TPE, PA, etc., a relatively small rotational speed of 5 - 12 revolutions per minute is required to generate a large shear force, promote the effective displacement of the molecular chain center of gravity, partially offset the disordered movement of the chain segments, facilitate the release of physical entanglement, and make the material have better fluidity; for polymer materials with short and simple molecular chains, such as PC, PCL, etc., a relatively large rotational speed of 10 - 20 revolutions per minute is used to accelerate the working speed of the 3D printer.

[0062] Another embodiment of the present invention provides a 3D printer, which is a screw - type multi - material 3D printer. Refer to Figure 1 , including a feeding and mixing device 1, the melt extrusion device 2 described above, a hot bed device 3, a motion device 4, and a frame 6 for supporting and fixing the above devices;

[0063] Among them, the feeding and mixing device 1 is connected to the melt extrusion device 2, and the feeding and mixing device 1 can provide at least two kinds of mixed raw materials for the melt extrusion device 2; the hot bed device 3 is arranged below the nozzle assembly 2B, and the motion device 4 is used to drive the hot bed device 3 to move in the X - axis, Y - axis, and Z - axis directions.

[0064] Refer to Figures 2-4 , the feeding and mixing device 1 includes at least two feeding components 1A and a mixing component 1B communicated with the at least two feeding components 1A; the feeding component 1A includes a raw material barrel 111, a rotating dial 12 arranged at the bottom of the raw material barrel 111, and a stepping motor 16 connected to the rotating dial 12; the outer circle of the rotating dial 12 is a tooth comb structure, and the tooth width of the tooth comb structure is the same as the feeding hole. The bottom of the raw material barrel 111 is provided with a feeding hole corresponding to the tooth comb structure, and the feeding hole is communicated with the mixing component 1B; there is a semi - circular inclined surface 117 arranged above the feeding hole in the raw material barrel 111. By controlling the rotation of the rotating dial 12 through the stepping motor 16, the amount of raw material in the raw material barrel 111 entering the mixing component 1B is controlled.

[0065] In this embodiment, two feeding components 1A are taken as an example for illustration. However, it can be understood that the number of feeding components can be adjusted according to the actual situation.

[0066] Further, the rotating dial 12 is arranged within the rotating dial fixing ring 13, coaxially and with a clearance assembled at the bottom of the raw material barrel 111. Both ends of the coupling 14 are respectively connected to the rotating dial gland 11 and the stepping motor 16. The rotation of the rotating dial 12 is controlled by the stepping motor 16 to control the feeding amount of the granular raw material. The raw material barrel 111, the rotating dial gland 11, the mixing bottom plate 112, the motor fixing plate 15, and the stepping motor 16 are sequentially installed and fixed from top to bottom.

[0067] The mixing component 1B includes a mixing funnel 17 and a discharge screw 19 connected to the mixing funnel 17. The discharge screw 19 is used to mix the raw materials entering the mixing funnel 17 and then feed them into the melt extrusion device 2. Among them, the mixing funnel 17 is installed below the mixing bottom plate 112 to receive the raw materials (especially granular raw materials) conveyed by the rotating dial 12. The raw materials flow into the mixing screw barrel 115 through the mixing funnel 113. The mixing stepping motor 113, the mixing screw bearing seat 114, and the mixing screw barrel 115 are sequentially connected. The raw materials are coaxially assembled with the mixing screw barrel 115, and a mixing joint 110 is installed at the discharge end of the screw.

[0068] The feeding component 1A further includes a weight sensor 116 arranged at the bottom of the raw material barrel 111 and a laser pair sensor 18 arranged at the outlet of the mixing funnel 17. A transparent window 118 is installed on the side wall of the raw material barrel 111.

[0069] The raw material particles in the raw material barrel 111 enter the dial tooth gaps (i.e., the tooth comb structure) under the action of gravity. Each tooth gap accommodates a fixed amount of particles. The rotation of the dial drives the movement of the materials in the tooth gaps. During the movement process, the weight sensor 116 monitors the materials passing through per unit time to achieve the online monitoring function. Subsequently, the particles leak out from the small holes at the bottom of the raw material barrel and enter the discharge screw 19 through the mixing funnel 17. The rotation of the discharge screw 19 completes the preliminary mixing and conveying of the raw material particles. For large particle raw materials (particle diameter above 1.5 mm), the dial 12 rotates at a low speed to prevent the ineffective handling of the non-entering particles in the tooth gaps caused by too high a rotation speed. For small particle materials (particle diameter below 1.5 mm), the dial 12 can rotate at a high speed to improve the working efficiency.

[0070] In a feasible manner of the embodiment of the present invention, refer to Figure 7, the motion device 4 includes an X-axis motion structure, a Y-axis motion structure, and a Z-axis motion structure; the hot bed device 3 is fixedly connected to the Y-axis motion structure, and the X-axis motion structure and the Y-axis motion structure are used to drive the hot bed device 3 to perform horizontal motion, and the Z-axis motion structure is used to drive the hot bed device 3 to perform vertical motion; specifically, the X-axis motion structure includes an X-axis motion slider 43 and an X-axis motion module 44, the Y-axis motion structure includes a Y-axis motion slider 41 and a Y-axis motion module 42, and the Z-axis motion structure includes a Z-axis motion slider 45 and a Z-axis motion module 46.

[0071] The X-axis motion module 44, the Y-axis motion module 42, and the Z-axis motion module 46 include a stepper motor, a synchronous belt, a pulley, a linear guide rail, etc. The motion slider is in clearance fit with the linear guide rail and can move linearly along the guide rail; among them, the X-axis motion slider 43 is assembled on the X-axis motion module 44, and the bottom of the X-axis motion module 44 is fixed on the Z-axis motion slider 45; the Y-axis motion slider 41 is assembled on the Y-axis motion module 42, and the Y-axis motion module 42 is installed on the X-axis motion slider 43; the Z-axis motion module 46 is fixed to the bottom plate 61 and the frame 6 by screws, and the Z-axis motion slider 45 is assembled on the Z-axis motion module 46. Through the sliding of the slider on the motion module, the XYZ three-dimensional space motion of the hot bed device is realized; the hot bed support plate 33 is fixed on the Y-axis motion slider 41 and can perform three-directional motion in the X, Y, and Z axes, so that the molten raw material extruded by the melting and extrusion device 2 falls onto the hot bed device 3, thereby realizing the layer-by-layer stacking and forming of the three-dimensional model.

[0072] The X, Y, and Z-axis motion modules 44, 42, and 46 adopt a ball screw slider structure, which is internally provided with a precision ball screw and a precision linear guide rail. The slider has high linearity and high position accuracy during motion. The X, Y, and Z-axis sliders 43, 41, and 45 adopt an integral closed sliding frame to prevent external impurities from entering the module and affecting the accuracy of the ball screw.

[0073] The hot bed device 3 includes an MK3 aluminum substrate hot bed device 31, a hot bed insulation cotton 32, a hot bed support plate 33, a laser leveling sensor 34, a heating coil 35, and a leveling nut 36. The overall structure is similar to that of the hot bed of a traditional FDM printer. The MK3 aluminum substrate hot bed device 31, the hot bed insulation cotton 32, and the hot bed support plate 33 are fixedly connected in sequence from top to bottom by screws. The heating coil 35 is located below the MK3 aluminum substrate 31 and can heat up to a maximum temperature of 100 °C; the laser leveling sensor 34 is located above the hot bed device 3. There are four leveling nuts 36, which are respectively located at the four corners below the hot bed support plate 33. By non-contact measurement of the heights of four points of the hot bed device by the leveling sensor 34 and manually adjusting the leveling nuts 36 to make the heights of the four points consistent with the maximum height, the leveling of the hot bed device can be achieved.

[0074] The printer further includes a CCD camera 5 disposed on the hot bed device 3. Two CCD cameras 5 are respectively arranged on both sides above the hot bed device, one on each side, to take real-time photos of the printing surface of each layer, extract the boundary contour curve based on the binocular vision theory and related image processing algorithms, and compare it with the CAD dimension of this layer of the three-dimensional model. If the dimension deviation exceeds the set threshold, the operator will be prompted to make corrections or stop printing, so as to monitor the printing quality of each layer.

[0075] The frame 6 is assembled from 40×40 profiles through T-nuts, screws and angle pieces, and further includes a bottom plate 61, nylon floor feet 62, a touch screen 63, and a touch screen fixing plate 64. As a feasible way, the feeding speed of each feeding component in the feeding and mixing device, the rotation speed of the screw in the melting and extrusion device, the heating temperature of the heating component, the movement of the moving device, the on-line monitoring of the raw material situation through the weight sensor and the laser pair sensor, the process of on-line monitoring the printing quality of each layer, etc. can all be completed by a control system electrically connected to the corresponding components. The control system can be, for example, a single-chip microcomputer, a chip and other components with control functions that can be integrated with the touch screen, or a terminal, etc.

[0076] Another embodiment of the present invention provides a control method for a screw-type multi-material 3D printer. Specifically, the method includes: controlling the rotating dials in at least two feeding components to rotate at different rotating speeds through a stepping motor to provide at least two kinds of mixed raw materials for the extrusion device; rotating the input motor in the melting and extrusion device to drive at least two screws to rotate in the same direction and in the same phase, turning on the heating component to make the raw materials mix evenly and melt, extruding the molten raw materials onto the hot bed device through the nozzle assembly, and at the same time driving the hot bed device to move in the X-axis, Y-axis and Z-axis directions through the moving device to complete printing; during the printing process, receiving the photo information obtained by the CCD camera, comparing it with the CAD dimension of this layer of the three-dimensional model to obtain the dimension deviation, and when the dimension deviation exceeds the set threshold, sending out a prompt correction message or stopping printing.

[0077] More specifically, the entire forming process of 3D printing includes the following steps: S1 Use modeling software such as UG and Pro / E to establish a three-dimensional model and define the material composition ratio of each region. Then, use slicing software to slice the model layer by layer to obtain data information such as the contour of each layer of the model and the material composition of different regions; S2 Import the above data information into the control software / system, and generate drive programs including dial rotation, discharge screw rotation, twin-screw extrusion rotation, hot bed three-axis movement, temperature control, etc. according to the material and path planning data of layer-by-layer slicing; S3 Import the above drive programs into the 3D printer and start forming by stacking point by point, line by line, and layer by layer. During the forming process, control the rotation speed of the rotating dial and the rotation speed of the twin-screw to control the material composition of each point and each layer. After forming each layer, lower the height of a set layer thickness, and then the nozzle deposits the next layer on the already formed layer. Stack layer by layer in this way until the forming of the entire model is completed; S4 Perform post-processing such as support removal and surface polishing on the above-mentioned formed green body to obtain the required composite material and heterogeneous gradient material parts.

[0078] Another embodiment of the present invention provides an application of a screw-type multi-material 3D printer, which is applied to the 3D printing of granular polymer materials. It solves the problems in the prior art that 3D printers are not suitable for the printing of multiple granular polymer materials, the melt extruded by the nozzle contains more bubbles, the density is not high, the extrusion direction is arbitrarily distorted and cannot be controlled, and the material ratio control of each point cannot be achieved during the forming process.

[0079] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A 3D printer, characterized in that, It includes a feeding and mixing device (1), a melting and extrusion device (2), a hot bed device (3), a motion device (4), and a frame (6) for supporting and fixing the above devices; Among them, the feeding and mixing device (1) is connected to the melting and extrusion device (2), and the feeding and mixing device (1) can provide at least two kinds of mixed raw materials for the melting and extrusion device (2); the hot bed device (3) is arranged below the nozzle assembly (2B), and the motion device (4) is used to drive the hot bed device (3) to move in the X-axis, Y-axis, and Z-axis directions; The melting and extrusion device (2) includes a screw assembly (2A) and a nozzle assembly (2B) connected to the screw assembly (2A). The screw assembly (2A) includes a housing and at least two screws (2C) arranged in the housing. The threads of adjacent screws (2C) mesh with each other. The raw materials are evenly mixed and melted by the co-rotation of the screws (2C), and the melted raw materials are extruded through the nozzle assembly (2B); The feeding and mixing device (1) includes at least two feeding components (1A) and a mixing component (1B) communicated with the at least two feeding components (1A); The feeding component (1A) includes a raw material barrel (111), a rotating dial (12) arranged at the bottom of the raw material barrel (111), and a stepping motor (16) connected to the rotating dial (12); the outer circle of the rotating dial (12) is a tooth comb structure, and a feeding hole is opened at the position of the bottom of the raw material barrel (111) corresponding to the tooth comb structure. The feeding hole is communicated with the mixing component (1B); there is a semi-circular inclined surface (117) arranged above the feeding hole in the raw material barrel (111). The rotation of the rotating dial (12) is controlled by the stepping motor (16) to control the amount of raw materials in the raw material barrel (111) entering the mixing component (1B); during the forming process, the rotation speed of the rotating dial and the rotation speed of the twin screws are controlled to control the material composition of each point and each layer; The mixing component (1B) includes a mixing funnel (17) and a discharge screw (19) connected to the mixing funnel (17); the discharge screw (19) is used to mix the raw materials entering the mixing funnel (17) and then feed them into the melting and extrusion device (2); The feeding component (1A) also includes a weight sensor (116) arranged at the bottom of the raw material barrel (111) and a laser pair sensor (18) arranged at the outlet of the mixing funnel (17); during the movement, the weight sensor (116) monitors the weight of the materials passing through per unit time, and the laser pair sensor (18) is used to monitor whether the granular materials are output in time, so as to accurately control the feeding of raw materials.

2. The 3D printer according to claim 1, characterized in that, The screw (2C) is an equal-diameter gradually changing screw. Along the direction from the raw materials entering to leaving the housing, the depth of the screw groove of the screw (2C) gradually decreases; the screw assembly (2A) also includes a heating component arranged on the outer wall of the housing and a cooling component arranged facing the heating component.

3. The 3D printer according to claim 2, characterized in that, The screw (2C) includes a feeding section, a compression section, and a metering section. The heating assembly includes three heating coils (212, 214, 215), and the three heating coils (212, 214, 215) are arranged on the outer wall of the housing corresponding to the feeding section, the compression section, and the metering section respectively. Heat sinks (213) are arranged between the three heating coils (212, 214, 215); the cooling assembly includes three cooling fans (219) arranged facing the three heating coils.

4. The 3D printer according to claim 1, characterized in that, The screw assembly (2A) further includes a power assembly for driving the at least two screws (2C) to rotate in the same direction and in the same phase; the power assembly includes an input motor (21), a transmission shaft (237) connected to the input motor, a driving gear arranged on the transmission shaft (237), and a transmission gear fixed on the screw (2C), and the driving gear meshes with the transmission gear.

5. The 3D printer according to claim 1, characterized in that, A transparent window (118) is installed on the side wall of the raw material barrel (111).

6. The 3D printer according to claim 1, characterized in that, The motion device (4) includes an X-axis motion structure, a Y-axis motion structure, and a Z-axis motion structure; the hot bed device (3) is fixedly connected to the Y-axis motion structure, and the X-axis motion structure and the Y-axis motion structure are used to drive the hot bed device (3) to perform horizontal motion, and the Z-axis motion structure is used to drive the hot bed device (3) to perform vertical motion; The printer further includes a CCD camera (5) and a laser leveling sensor (34) arranged on the hot bed device (3).

7. A control method for a 3D printer according to any one of claims 1-6, characterized in that, The method includes: Controlling the rotating dials in at least two feeding assemblies to rotate at different rotating speeds by a stepper motor to provide at least two kinds of mixed raw materials for the extrusion device; Rotating the input motor in the melting and extrusion device to drive the at least two screws to rotate in the same direction and in the same phase, turning on the heating assembly to uniformly mix and melt the raw materials, extruding the molten raw materials onto the hot bed device through the nozzle assembly, and at the same time driving the hot bed device to move in the X-axis, Y-axis, and Z-axis directions by the motion device to complete printing; During the printing process, receiving the photo information obtained by the CCD camera, comparing it with the CAD dimensions of this layer of the three-dimensional model to obtain a dimension deviation, and when the dimension deviation exceeds the set threshold, sending out a prompt correction message or stopping printing.

8. An application of a 3D printer according to any one of claims 1-6, characterized in that, Applied to 3D printing of granular polymer materials.

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