Binder Jetting 3D Printing Equipment and Printing Method for Low-Mobility Powders

Abstract

The present invention discloses a binder jetting 3D printing device and a printing method for low-fluidity powder, relating to the technical field of 3D printing. The printing method includes: controlling the powder forming module to reach the initial position; the powder forming module includes a powder dropping module and a powder spreading module that move synchronously; adding powder to the powder dropping module through the powder replenishing module; moving the powder forming module to the powder spreading starting position, and controlling the powder to be scattered from the powder replenishing receiving plate of the powder dropping module onto the vibrating plate; controlling the vibration of the vibrating plate to transfer the powder in front of the powder spreading module and level and compact it; completing the powder spreading of a single layer; repeating to complete the laying of the bottom powder layer; repeating on the bottom powder layer to complete the laying of the sliced layer, controlling the inkjet module to move following the powder forming module, and jetting the binder on each sliced layer to obtain a 3D printed product through curing. The present invention adopts a cooperative scheme of layer-by-layer powder supply, independent powder spreading, and independent compaction to ensure high density and high uniformity of the printing area of low-fluidity powder.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing, and in particular to a binder jetting 3D printing device and a printing method for low-fluidity powder. Background Art

[0002] Binder Jetting (BJ, also commonly known as 3DP) is an additive manufacturing technology based on inkjet technology and a 3D printing technology based on a powder bed. It selectively sprays a binder on a powder bed and bonds the powder particles layer by layer to build a three-dimensional solid product. Using fine powder with poor fluidity as printing powder can reduce the surface roughness of the printed part, improve the dimensional accuracy and surface quality of the product, and provide better support in the powder bed to avoid damage caused by the shear force introduced during the powder laying process. From the perspective of post-processing, it can prepare products with uniform structure and fine grains, improve their mechanical properties and service life, and at the same time obtain higher sintering activity during the sintering process, achieve densification at a lower temperature, and reduce sintering energy consumption. However, fine powders with poor fluidity have small particle sizes and large specific surface areas. During the conveying process, they are easily adsorbed on the surfaces of conveying pipes, screws, valves, filters and other devices due to van der Waals forces and electrostatic forces, resulting in uneven and discontinuous powder supply, and even blockage of the conveying device. Secondly, fine powders will also adhere to the surface of the powder spreading roller, changing the effective cross-sectional area and surface roughness of the powder spreading roller, resulting in a deviation between the actual powder spreading thickness and the set value. Moreover, fine powders are prone to form powder agglomerates of different sizes during the powder spreading process, and cannot be effectively dispersed under the push of the powder spreading roller, resulting in large deviations in the uniformity of powder density in different areas. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a binder jet 3D printing device and a printing method for low-fluidity powder, which can improve the printing accuracy of low-fluidity powder and the uniformity of powder density in the entire format, thereby improving the consistency of printed products.

[0004] In order to solve the above problems, the present invention discloses a binder jet 3D printing method for low-fluidity powder, comprising the following steps:

[0005] (1) controlling the movement of the powder forming module so that it reaches an initial position; wherein the powder forming module comprises a powder dropping module and a powder spreading module, and the powder dropping module and the powder spreading module move synchronously;

[0006] (2) adding a preset amount of powder to the powder dropping module through the powder replenishing module, wherein the powder dropping module includes a powder replenishing receiving plate and a vibration plate;

[0007] (3) Move the powder forming module to the starting position for powder spreading, and make the powder fall onto the vibrating plate by controlling the powder replenishing receiving plate;

[0008] (4) By controlling the vibration of the vibrating plate, transfer the powder to a preset area in front of the powder spreading module, and then level and compact the powder layer by layer through the powder spreading module;

[0009] (5) Move the powder forming module to the initial position to complete the powder spreading of a single layer;

[0010] (6) Repeat steps (1) to (5) until the laying of the bottom powder layer is completed;

[0011] (7) Repeat steps (1) to (5) on the bottom powder layer to complete the laying of the sliced layer. Control the inkjet module to move following the powder forming module, spray the binder in the preset area of each sliced layer and cure the powder until the printing of the model is completed to obtain a 3D printed product.

[0012] As an improvement of the above technical solution, the powder forming module further includes a bracket, the powder falling module includes a powder replenishing receiving plate and a vibrating plate, and the powder spreading module includes a powder spreading roller and a compaction roller; the powder replenishing receiving plate, the vibrating plate, the powder spreading roller and the compaction roller are all fixed on the bracket, the vibrating plate is arranged in front of the powder spreading roller, and the compaction roller is arranged behind the powder spreading roller; there is a preset distance between the vibrating plate and the powder spreading roller to form a preset area for powder transfer.

[0013] As an improvement of the above technical solution, the powder spreading roller is used to level the powder scattered by the powder falling module to obtain a powder spreading layer, and the ratio of the density of the powder spreading layer to the loose density of the powder is (0.8 - 1.2):1;

[0014] The compaction roller is used to compact the powder spreading layer to obtain a compacted powder layer, and the ratio of the density of the compacted powder layer to the tapped density of the powder is (0.8 - 1.2):1.

[0015] As an improvement of the above technical solution, the ratio of the thickness of the bottom powder layer to the thickness of each compacted powder layer is (20 - 40):1;

[0016] The ratio of the thickness of each compacted powder layer to the D50 of the powder is (2 - 10):1, and / or, the ratio of the thickness of each compacted powder layer to the D90 of the powder is (1.5 - 10):1.

[0017] As an improvement of the above technical solution, the D50 of the powder is 10μm - 100μm, and / or, the D90 of the powder is 10μm - 100μm;

[0018] The angle of repose of the powder is 35° to 60°.

[0019] As an improvement to the above technical solution, the bottom of the vibration plate is higher than the bottom of the powder spreading roller, and the height difference between the vibration plate and the powder spreading roller is 0.5 mm to 5 mm;

[0020] The rotation directions of the compaction roller and the powder spreading roller are opposite, and the surface roughness of the compaction roller is less than that of the powder spreading roller; the bottom of the powder spreading roller is higher than the bottom of the compaction roller, and the height difference between the powder spreading roller and the compaction roller is 0.01 mm to 1 mm;

[0021] Both the powder replenishment receiving plate and the vibration plate can rotate relative to the bracket; the vibration frequency of the vibration plate is 0.1 Hz to 100 Hz;

[0022] During the process of the powder replenishment module adding powder to the powder dropping module, the powder replenishment receiving plate is in a horizontal position; during the powder spreading process, the powder replenishment receiving plate has an angle with the horizontal direction so that the powder on the powder replenishment receiving plate spills onto the vibration plate.

[0023] As an improvement to the above technical solution, the diameter of the compaction roller is 25 mm to 120 mm, the surface roughness is Ra0.25 to Ra 3.2, the diameter of the powder spreading roller is 25 mm to 120 mm, and the surface roughness is Ra 1.6 to Ra 100.

[0024] As an improvement to the above technical solution, the preset path of the inkjet module movement is: moving along the Y direction, spraying the binder in the preset area and curing and bonding the powder, and then, moving a certain distance along the X direction and moving in the reverse direction along the Y direction, spraying the binder in the preset area and curing and bonding the powder, and realizing the inkjet printing of each layer of sliced layer in segments;

[0025] The moving speed of the inkjet module in the X direction is 100 mm / s to 400 mm / s, and the moving speed in the Y direction is 100 mm / s to 600 mm / s.

[0026] As an improvement to the above technical solution, during the powder spreading process, the moving speed of the powder forming module in the X direction is 50 mm / s to 400 mm / s;

[0027] The no-load stroke speed of the powder forming module moving from the initial position to the powder spreading starting position is 250 mm / s to 500 mm / s;

[0028] The powder replenishing module is provided with a powder outlet vibrator and a powder replenishing belt. The powder for replenishment in the powder replenishing module flows out under the action of the powder outlet vibrator. Through the rotation of the powder replenishing belt and the movement of the powder replenishing module in the Y direction, a preset amount of powder is evenly scattered on the powder replenishing receiving plate. The preset amount of powder added to the powder falling module by the powder replenishing module each time is 1 to 2 times the amount of powder required for each layer of powder spreading.

[0029] Correspondingly, the present invention also discloses a binder jetting 3D printing device for low-fluidity powder, which is used to execute the above-mentioned binder jetting 3D printing method for low-fluidity powder, and includes a powder replenishing module, a powder forming module, an inkjet module and a platform module;

[0030] The platform module includes a printing platform, and the printing platform is provided with a lifting mechanism, and the lifting mechanism is connected to the printing platform for driving the printing platform to lift in the Z direction;

[0031] The powder forming module and the inkjet module are arranged above the platform module along the X direction; the powder forming module includes a powder falling module and a powder spreading module that move synchronously; the powder falling module includes a powder replenishing receiving plate and a vibrating plate for vibrating and scattering the powder; the powder spreading module includes a powder spreading roller and a compaction roller for leveling and compacting the powder scattered by the powder falling module; the inkjet module is used to jet the binder in a preset area of the sliced layer;

[0032] The powder replenishing module is arranged on one side of the platform module and is higher than the powder falling module for replenishing powder to the powder falling module.

[0033] Implementing the present invention has the following beneficial effects:

[0034] 1. For the binder jetting 3D printing method for low-fluidity powder provided by the present invention, before spreading powder for each layer, powder is replenished layer by layer through the powder falling module, which can effectively avoid the cumulative error caused by excessive adhesion and agglomeration of low-fluidity powder on the powder falling module and the powder spreading module, and improve the printing accuracy; at the same time, it avoids the dependence on precise control of the amount of powder for replenishment and reduces the difficulty of powder replenishment.

[0035] 2. For the binder jetting 3D printing method for low-fluidity powder provided by the present invention, by controlling the amplitude and vibration frequency of the vibrating plate arranged at the powder outlet of the powder falling module, secondary destruction is formed on the agglomeration and adhesion of the powder. On the one hand, the fluidity of the low-fluidity powder can be improved, and on the other hand, the uniformity of powder falling can be improved; at the same time, the powder in the powder falling module accumulates between the powder spreading module and the powder falling module as the powder falling module moves, and a large amount of powder that has not participated in powder spreading can be restricted on the vibrating plate, avoiding the damage to the printing area caused by an excessive powder pile in front of the powder spreading module.

[0036] 3. The following movement mode of the powder spreading roller and the compaction roller can continuously and timely compact the powder sufficiently to obtain a high packing density, effectively improve the powder density uniformity within the entire width, and greatly improve the product consistency. At the same time, the independent working mode of the powder spreading roller and the compaction roller can endow them with different roughnesses to complete different powder sweeping and compaction functions. Therefore, each roller can be designed with a larger diameter to resist deformation, which is more suitable for the requirements of large-format industrial equipment. Description of the Drawings

[0037] Figure 1 is a schematic structural diagram of a binder jetting 3D printing device for low-fluidity powder provided by the present invention;

[0038] Figure 2 is Figure 1 an enlarged view of part A of

[0039] Figure 3 is a schematic top view structural diagram of a binder jetting 3D printing device for low-fluidity powder provided by the present invention;

[0040] Figure 4 is a schematic working diagram of the powder replenishing link in the bottom powder layer laying of a binder jetting 3D printing device for low-fluidity powder provided by the present invention;

[0041] Figure 5 is a schematic working diagram of the powder dropping preparation link in the bottom powder layer laying of a binder jetting 3D printing device for low-fluidity powder provided by the present invention;

[0042] Figure 6 is a schematic working diagram of the powder dropping and spreading link in the bottom powder layer laying of a binder jetting 3D printing device for low-fluidity powder provided by the present invention;

[0043] Figure 7 is a schematic working diagram of the completion of the bottom powder layer laying of a binder jetting 3D printing device for low-fluidity powder provided by the present invention;

[0044] Figure 8 is a schematic working diagram of the powder dropping, spreading and inkjetting links in the printing stage of a binder jetting 3D printing device for low-fluidity powder provided by the present invention;

[0045] Figure 9 is a schematic working diagram of the powder replenishing link in the printing stage of a binder jetting 3D printing device for low-fluidity powder provided by the present invention;

[0046] Figure 10 is a schematic movement control logic diagram of a binder jetting 3D printing device for low-fluidity powder provided by the present invention;

[0047] Figure 11It is a schematic flow chart of laying a bottom powder layer by the binder jetting 3D printing method for low-fluidity powder provided by the present invention;

[0048] Figure 12 It is a schematic flow chart of inkjet printing by the binder jetting 3D printing method for low-fluidity powder provided by the present invention. Specific embodiments

[0049] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below.

[0050] The present invention provides a binder jetting 3D printing device for low-fluidity powder, as Figures 1 to 3 shown, which includes a platform module 10, an inkjet module 20, a powder forming module, printing powder 50 and a powder replenishing module 60, wherein the powder forming module includes a powder spreading module 30 and a powder dropping module 40 that move synchronously.

[0051] Specifically, the platform module 10 includes a base 11 and a printing platform 12. The printing platform 12 is provided with a lifting mechanism, and the lifting mechanism is connected to the bottom of the printing platform 12 for driving the printing platform 12 to move up and down along the Z direction. One side of the printing platform is the starting position for powder spreading, and the other side is the initial position. In one embodiment, the platform module 10 further includes a surplus powder collecting device, and the surplus powder collecting device includes a surplus powder collecting box 13 and a surplus powder recycling suction pipe 14. The surplus powder collecting box 13 and the surplus powder recycling suction pipe 14 are arranged on one side of the printing platform 12 away from the starting position for powder spreading, and are used for recycling the surplus powder 56 remaining after powder spreading.

[0052] The powder forming module and the inkjet module 20 are arranged front and back along the X direction on the powder spreading track 15 above the platform module 10. It can be understood that the front and back are defined according to the movement direction of the modules during the powder spreading process. The side pointed by the movement direction from the starting position for powder spreading to the initial position is the front, and the opposite direction is the back. The powder forming module includes a powder spreading module 30 and a powder dropping module 40. The powder spreading module 30 and the powder dropping module 40 move synchronously along the X direction. The powder dropping module 40 is used for dropping powder onto the printing platform 12, and the powder spreading module 30 is used for leveling the powder dropped onto the printing platform 12 by the powder dropping module 40.

[0053] In one embodiment, the powder molding module includes a bracket, a powder feeding module 40, and a powder spreading module 30. The powder feeding module 40 includes a powder replenishment receiving plate 41 and a vibrating plate 44. The powder spreading module 30 includes a powder spreading roller 35 and a compaction roller 34. The powder replenishment receiving plate 41, the vibrating plate 44, the powder spreading roller 35, and the compaction roller 34 are all fixed on the bracket. The vibrating plate 44 is disposed in front of the powder spreading roller 35, and the compaction roller 34 is disposed behind the powder spreading roller 35. A preset distance exists between the vibrating plate 44 and the powder spreading roller 34, forming a preset area for powder transfer. It can be understood that the vibrating plate 44, the powder spreading roller 35, and the compaction roller 34 are arranged in sequence from front to back to achieve synchronous powder feeding, powder spreading, and compaction.

[0054] Specifically, the bracket includes a powder feeding mounting seat 46 for fixing the powder feeding module 40 and a powder spreading mounting seat 31 for fixing the powder spreading module 30. The powder replenishment receiving plate 41, an eccentric wheel 42, a connecting rod 43, the vibrating plate 44, and a powder baffle 45 are mounted on the powder feeding mounting seat 46. One end of the powder replenishment receiving plate 41 is connected to the powder feeding mounting seat 46. The powder replenishment receiving plate 41 can rotate counterclockwise. When the powder replenishment receiving plate 41 rotates to the horizontal position, it is used to receive the falling powder 52. When the powder replenishment receiving plate 41 rotates to form an angle with the horizontal direction, a powder feeding channel is reserved, and the falling powder 52 spills onto the vibrating plate 44. The vibrating plate 44 is disposed below the powder replenishment receiving plate 41. One end of the vibrating plate 44 is hinged to the powder feeding mounting seat 46. The driving mechanism 48 is fixed to the powder feeding mounting seat 46. The eccentric wheel 42 is connected to the main shaft 49 of the driving mechanism 48. One end of the connecting rod 43 is sleeved on the eccentric wheel 42, and the other end is hinged to the lower surface of the vibrating plate 44. The connecting rod 43 drives the vibrating plate 44 to vibrate back and forth along the vibration direction 47 under the drive of the eccentric wheel 42. The amplitude and vibration frequency of the vibrating plate 44 are adjusted by the eccentricity and rotation speed of the eccentric wheel 42. The powder baffle 45 is disposed on the side of the powder spreading module 30 close to the powder feeding module 40.

[0055] The powder spreading mounting seat 31 is provided with a powder spreading roller bracket 33 and a compaction roller bracket 32. The powder spreading roller 35 is disposed on the powder spreading roller bracket 33, and the compaction roller 34 is disposed on the compaction roller bracket 32. The powder spreading roller 35 and the compaction roller 34 are arranged front and back along the X direction. The compaction roller rotation direction 36 and the powder spreading roller rotation direction 37 are opposite. The powder spreading roller 35 is used to level the powder scattered by the powder feeding module 40 to obtain a powder spreading layer 53, and the compaction roller 34 is used to compact the powder spreading layer 53 to obtain a compacted powder layer 54. The vibrating plate 44, the powder baffle 45, and the powder spreading roller 35 form a triangular area for carrying the falling powder 52.

[0056] The inkjet module 20 includes an integrated slide rail 21, an inkjet scanning rail 22, an inkjet head integrated mechanism 23, and an inkjet head 24. The setting direction of the inkjet scanning rail 22 is perpendicular to the setting direction of the powder spreading rail 15. The inkjet head integrated mechanism 23 scans along the inkjet scanning rail 22 in the Y direction and sprays out the binder 25 in a preset area for bonding. Then, after the inkjet module 20 moves a certain distance along the X direction, the inkjet head integrated mechanism 23 moves in the opposite direction along the inkjet scanning rail 22, and this combined action is repeated until inkjet printing is completed on the entire working plane.

[0057] The powder replenishing module 60 includes a temporary powder bin 61, a powder replenishing rail 62, an outlet vibrator 63, a powder replenishing belt 64, and a belt drive shaft 65. The powder replenishing module 60 is provided on one side of the platform module 10 away from the powder spreading starting position and moves along the Y direction. The powder replenishing module 60 is higher than the powder falling module 40 and is used to carry the replenishing powder 51 and replenish the powder falling module 40. The outlet vibrator 63 vibrates at a high frequency, forcing the low-fluidity replenishing powder 51 to obtain a certain fluidity, and it flows out from the temporary powder bin 61 of the powder replenishing module 60 along the movement direction 66 of the powder replenishing belt 64 driven by the powder replenishing belt 64, and finally a certain amount of uniform powder is filled on the powder replenishing receiving plate 41.

[0058] The present invention also provides a binder jetting 3D printing method for low-fluidity powders, including the following steps:

[0059] S1. Control the movement of the powder forming module to make it reach the initial position; wherein, the powder forming module includes a powder falling module and a powder spreading module, and the powder falling module and the powder spreading module move synchronously.

[0060] Specifically, when the powder forming module reaches the initial position, the powder falling module is located below the powder replenishing module.

[0061] S2. Add a preset amount of powder to the powder falling module through the powder replenishing module. The powder falling module includes a powder replenishing receiving plate and a vibrating plate.

[0062] Specifically, with the movement of the powder replenishing module along the Y direction, the powder in the powder replenishing module flows out under the action of the outlet vibrator, and through the rotation of the powder replenishing belt, a preset amount of powder is evenly scattered on the powder replenishing receiving plate located at the horizontal position. In one embodiment, the preset amount of powder added to the powder falling module by the powder replenishing module each time is 1 to 2 times the powder amount required for each powder spreading. By controlling the added amount of the replenishing powder each time, excessive powder accumulation in the powder falling module causing agglomeration is avoided, the laying error of each layer of powder is reduced, and the printing accuracy is improved.

[0063] It can be understood that the added amount of the replenishing powder can be adjusted by the working frequency and amplitude of the vibrator, or can also be adjusted by the rotation speed and friction of the powder replenishing belt.

[0064] S3. Move the powder forming module to the starting position of powder spreading, and control the powder replenishment receiving plate to make the powder fall onto the vibrating plate.

[0065] Specifically, after the powder forming module returns to the starting position of powder spreading, the powder replenishment receiving plate flips to make the powder fall onto the vibrating plate. At the same time, the printing platform moves downward a certain distance along the Z direction, leaving a powder spreading space for one layer of powder. The moving speed of the printing platform in the Z direction is 5 mm / s to 30 mm / s.

[0066] S4. Control the vibration of the vibrating plate to transfer the powder to a preset area in front of the powder spreading module, and then level and compact the powder in sequence through the powder spreading module.

[0067] As the powder forming module moves along the X direction, the vibrating plate starts to vibrate to improve the fluidity of the low-fluidity powder and transfer the powder to a preset area in front of the powder spreading module. With the vibration of the vibrating plate, the low-fluidity powder agglomerated under the action of gravity regains better fluidity. At this time, the fluidity of the powder is not sufficient to allow it to flow out completely, but it will gradually slide down with the movement of the powder spreading module and the vibration of the vibrating plate. To avoid the phenomenon of powder shortage or powder accumulation during the powder spreading process, it is necessary to appropriately adjust the amplitude and / or vibration frequency of the vibrating plate. It should be noted that although the vibrating plate provides powder fluidity exceeding the minimum requirement, the powder will only flow to a limited area under the spatial limitation of the vibrating plate and the powder bed. This feature avoids the formation of an excessive powder pile in the advancing direction of the powder spreading roller due to the change in powder fluidity, thus largely avoiding the powder pushing problem caused by an excessive powder pile.

[0068] In a preferred embodiment, adjust the amplitude and vibration frequency of the vibrating plate so that the powder in the powder dropping module accumulates between the powder spreading module and the powder dropping module, control the powder accumulation in front of the powder spreading module, and avoid horizontal powder pushing and vertical crushing of the printed area. Among them, the amplitude and vibration frequency of the vibrating plate are adjusted by the eccentricity and rotation speed of the eccentric wheel. To avoid the phenomenon of powder shortage or powder accumulation during the powder spreading process, the vibration frequency of the vibrating plate is 0.1 Hz to 100 Hz, exemplarily 1 Hz, 5 Hz, 10 Hz, 30 Hz or 60 Hz, but not limited thereto. More preferably, the vibration frequency of the vibrating plate is 5 Hz to 20 Hz. The eccentricity of the eccentric wheel is 0.1 mm to 5 mm, exemplarily 0.4 mm, 0.8 mm, 1 mm, 2 mm or 4 mm, but not limited thereto. More preferably, the eccentricity of the eccentric wheel is 0.4 mm to 1 mm, and the specific setting is related to the powder fluidity and the size of the powder outlet of the vibrating plate.

[0069] While the powder dropping module completes the powder dropping, the powder spreading module flattens and compacts the powder. In one embodiment, the powder spreading speed of the powder forming module along the X direction is 50mm / s~400mm / s, and the idle stroke speed of the powder forming module after powder replenishment is 250mm / s~500mm / s. Correspondingly, the rotation speeds of the compaction roller and the powder spreading roller, as well as the vibration frequency of the vibration plate need to be changed proportionally.

[0070] In the powder spreading module, the powder spreading roller and the compacting roller are arranged front and back along the X direction, and the rotation direction of the compacting roller is opposite to that of the powder spreading roller. The powder spreading roller and the compacting roller can be independently driven by a split design, and the rotation speed and direction of both can be adjusted independently. It can be understood that the powder spreading roller is used to sweep the powder scattered by the powder falling module to obtain a powder spreading layer, and the compacting roller is used to compact the powder spreading layer to obtain a compacted powder layer. Therefore, the compacting roller is closer to the powder layer than the powder spreading roller. In one embodiment, the bottom of the powder spreading roller is higher than the bottom of the compacting roller, and the height difference is 0.01mm~1mm, and exemplarily 0.05mm, 0.1mm, 0.4mm, 0.6mm or 0.8mm, but not limited to this, which is specifically related to the compactability of the powder.

[0071] In a preferred embodiment, the diameter of the compacting roller is 25 mm to 120 mm, and the surface roughness is Ra 0.05 to Ra 3.2; the diameter of the powder spreading roller is 25 mm to 120 mm, and the surface roughness is Ra 1.6 to Ra 100; the surface of the powder spreading roller has higher visible lines or bumps; the powder spreading roller rotates counterclockwise, and the compacting roller rotates clockwise. It is understandable that the compacting roller should have a smooth surface, and the powder spreading roller should have a rough surface. The powder spreading roller with a high roughness surface generates a greater shear force when rotating counterclockwise, rolling away excess powder forward to avoid excessive downward pressure. The slightly smooth compacting roller, which is installed slightly lower than the powder spreading roller, rotates clockwise. The smooth compacting roller generates a greater downward pressure when rotating clockwise, compacting the loose powder. While compacting the powder, it avoids the horizontal shear force and horizontal displacement of the powder under high compaction, thereby avoiding problems such as pushing powder in all directions.

[0072] In one embodiment, the ratio of the density of the powder layer to the loose density of the powder is 1:(0.8~1.2), and the ratio of the density of the compacted powder layer to the tapped density of the powder is 1:(0.8~1.2), which is specifically related to the compactability of the powder. This can weaken the adhesion and mixing of the falling powder, reduce the shear force and downward pressure of the powder layer, and ensure that the powder that is not involved in the printing or the bonding area of ​​the old powder layer has sufficient support strength to avoid powder push damage.

[0073] In one embodiment, to avoid excessive powder accumulation in front of the powder spreading module, the bottom of the vibrating plate is higher than the bottom of the powder spreading roller by a height difference of 0.5 mm to 5 mm, exemplary values being 0.8 mm, 1 mm, 2 mm, 3 mm or 4 mm, but not limited thereto.

[0074] In a preferred embodiment, to achieve a uniform powder spreading density, the ratio of the thickness of the bottom powder layer to the thickness of each compacted powder layer is (20 - 40):1, that is, the compacted powder layer is laid 20 - 40 times layer by layer to form the bottom powder layer; the ratio of the thickness of each compacted powder layer to the D50 of the powder is (2 - 10):1, and / or the ratio of the thickness of each compacted powder layer to the D90 of the powder is (1.5 - 10):1.

[0075] Optionally, the D50 of the powder is 10 μm to 100 μm, the D90 is 10 μm to 100 μm, and the angle of repose of the powder itself or the powder mixed with additives is 35° to 60°. By controlling the performance parameters of the powder, the powder has a certain fluidity and can overcome the formation of internal powder arches. Among them, the angle of repose of the powder can be adjusted by the content of additive liquid in the powder, the particle size of the powder, the moisture content, and the sphericity of the powder.

[0076] S5. Move the powder forming module to the initial position to complete the powder spreading of a single layer.

[0077] In a preferred embodiment, as the powder forming module moves to the initial position, the remaining powder that has not participated in powder spreading near the powder spreading roller falls into the remaining powder collection device, avoiding cumulative errors in the next powder replenishment and spreading processes. Moreover, the recovery of the remaining powder can also avoid relying on the precise control of the powder replenishment amount, reducing the difficulty of powder replenishment. Specifically, the negative pressure of the remaining powder recovery suction pipe is -0.4 MPa to -0.6 MPa.

[0078] S6. Repeat S1 - S5 until the laying of the bottom powder layer is completed.

[0079] The bottom powder layer is a powder layer of a certain thickness formed on the printing platform. The laying of the bottom powder layer can not only prevent the printed part from adhering to the printing platform but also stabilize the density of each compacted powder layer through multi-layer powder spreading. More importantly, the compacted bottom powder layer can provide sufficient support for the first inkjet area, avoiding the problem of powder pushing caused by the loose state of natural powder accumulation.

[0080] S7. Repeat S1 - S5 on the bottom powder layer to complete the laying of the sliced layer. Control the inkjet module to move with the powder forming module, spray the binder in the preset area of each sliced layer and cure the powder until the printing of the model is completed to obtain a 3D printed product.

[0081] Specifically, the preset path of the inkjet module movement is as follows: move along the Y direction, spray the binder in the preset area and cure the bonded powder. Subsequently, move a certain distance along the X direction and move in the reverse Y direction, spray the binder in the preset area and cure the bonded powder, and achieve the inkjet printing of each sliced layer in segments.

[0082] In one embodiment, the moving speed of the inkjet module in the X direction is 100 mm / s to 400 mm / s, exemplarily 150 mm / s, 200 mm / s, 250 mm / s, 300 mm / s or 350 mm / s, but not limited thereto. The moving speed in the Y direction is 100 mm / s to 600 mm / s, exemplarily 150 mm / s, 200 mm / s, 300 mm / s, 400 mm / s or 500 mm / s, but not limited thereto. With continuous segmented movement and scanning, the inkjet module will complete the inkjet printing of the entire printing area.

[0083] In one embodiment, according to the components of the binder, the binder can be one or more of two-component binders, multi-component binders, and single-component binders; according to the solvent properties of the binder, the binder can be one or more of water-based binders, oil-based binders, and alcohol-based binders; according to the materials of the binder, the binder can be an organic binder and / or an inorganic binder; according to the excitation source of the binder, the binder can be one or more of dry-curing binders, heat-curing binders, chemically reactive curing binders, and UV-curing binders. Specifically, it can be selected according to the type of powder and the required performance of the printed product.

[0084] Generally speaking, the movement relationship and control logic of all modules are as Figure 10As shown in the figure. In the entire printing system, the motion controller 100 is responsible for receiving printing instructions from the printing software and controlling each sub-motion controller. The main modules in the system perform motion modes such as linear, rotational, or vibrational motions on the set degrees of freedom of motion, which are specifically controlled by each sub-motion controller, including the Z-axis linear motion controller 110, the X-axis linear motion controller 120, the Y-axis linear motion controller 130, the R rotational linear motion controller 140, the W vibrational motion controller 150, and the F flipping motion controller 160. Finally, each module performs motion according to the designed motion mode 170 to complete the printing behavior. Specifically, the platform module 10 makes a lifting motion Z1 in the Z-axis direction, the inkjet module 20 makes a linear reciprocating motion Y1 along the inkjet scanning track 22, and makes a scanning linear motion X1 along the powder spreading track 15 in a segmented manner. The powder spreading module 30 makes a scanning linear motion X2 along the powder spreading track 15, and the powder spreading roller 35 and the compaction roller 34 inside it respectively make reverse rotational motions R1 and R2. The powder dropping module 40 fixed together with the powder spreading module 30 also makes a scanning linear motion X2 along the powder spreading track 15, and the powder replenishment receiving plate 41 inside it makes a flipping motion F1 to control the working position of the dropped powder. The eccentric wheel 42 makes a rotational motion R3 along the axis, and drives the vibrating plate 44 through the connecting rod 43 to improve the fluidity of the powder. The powder replenishment module 60 makes a powder replenishment linear motion Y2 along the powder replenishment track 62, and the powder outlet vibrator 63 inside it makes a high-frequency vibration W1, and cooperates with the rotational motion R4 of the belt drive shaft 65 to drive the powder replenishment belt 64 to take out the powder from the temporary powder bin 61 and drop it onto the powder replenishment receiving plate 41.

[0085] The specific process and operation are as follows.

[0086] Before the inkjet printing starts, powder spreading for the bottom powder layer is required. The main function of this step is to pre-form a certain thickness of powder under the printed part, which can not only prevent the printed part from sticking to the printing platform, but also stabilize the compaction density of each layer of powder through multi-layer powder spreading. More importantly, the compacted bottom powder layer can provide sufficient support for the first inkjet area, avoiding the problem of powder pushing caused by the loose state of natural powder accumulation. The schematic diagram of the process of powder spreading for the bottom powder layer is as Figure 11As shown, the action logic of the specific operation is 301 to 305. First, the powder replenishment waiting step 301 is carried out. The printing platform rises to the top, the powder dropping module moves to directly below the powder replenishment module, the vibrating plate is closed, and the inkjet module returns to the starting position of powder spreading and waits. Then, step 302 is carried out, and the powder replenishment module replenishes an appropriate amount of powder to the powder dropping module. Subsequently, in step 303, the printing platform descends by the height of one layer thickness. Then, in step 304, the powder spreading module and the powder dropping module return to the starting position of powder spreading, start to move horizontally to the right, the vibrating plate is activated to convey the powder to the front of the powder spreading roller, and through the powder sweeping of the powder spreading roller and the compaction of the compaction roller, the powder spreading action of one layer of powder is completed. Finally, in step 305, the action steps of 301 to 304 are repeated to complete the powder spreading of the bottom powder layer. Specifically, it is described in combination with the working schematic diagram.

[0087] First, as Figure 4 shown, the inkjet module 20 moves along the X direction on the powder spreading track 15 to the left side of the platform module 10 to standby. The printing platform 12 moves downward along the Z direction by a certain distance to leave a powder spreading space. The powder spreading module 30 and the powder dropping module 40 are fixed to each other and move along the X direction to the right side of the platform module 10 to prepare for the powder replenishment action. Wait for the powder replenishment receiving plate 41 to rotate to the horizontal position. The belt drive shaft 65 in the powder replenishment module 60 starts to rotate, driving the powder replenishment belt 64 to rotate counterclockwise. The printing powder 50 is carried out of the powder replenishment module 60 along with the movement of the powder replenishment belt 64. At this time, the powder outlet vibrator 63 vibrates at a high frequency, forcing the low-fluidity powder replenishment powder 51 to obtain a certain fluidity and flow out of the temporary powder bin 61 of the powder replenishment module 60. As the powder replenishment module 60 moves along the powder replenishment track 62 in the Y direction at a certain uniform speed, finally, a certain amount of uniform powder dropping powder 52 is filled on the powder replenishment receiving plate 41, and the powder replenishment module 60 stops powder replenishment and returns to the initial position.

[0088] Subsequently, as Figure 5 shown, the printing platform descends by the height of one layer thickness, and then the powder spreading module 30 and the powder dropping module 40 move along the X direction to the left side of the platform module 10 to prepare for powder dropping. At this time, the powder replenishment receiving plate 41 rotates counterclockwise, and the powder dropping powder 52 slides into the triangular area formed by the vibrating plate 44, the powder baffle 45, and the powder spreading roller 35.

[0089] Subsequently, as Figure 6As shown, the powder spreading module 30 and the powder falling module 40 move rightward along the X direction. During the movement, the eccentric wheel 42 drives the connecting rod 43 and the vibrating plate 44 to form a reciprocating vibration along the vibration direction 47. The amplitude and vibration frequency are adjusted by the eccentricity and rotational speed of the eccentric wheel 42. With the assistance of this vibration, the low-fluidity powder 52 that has re-aggregated under the action of gravity regains better fluidity and evenly slides in front of the powder spreading roller 35. Importantly, at this time, the fluidity of the powder is not sufficient for it to flow out completely, and it will gradually slide down as the powder spreading module 30 and the powder falling module 40 move rightward. To avoid powder shortage or powder accumulation during powder spreading, it is necessary to appropriately adjust the amplitude and / or vibration frequency of the vibrating plate 44.

[0090] As it moves rightward along the X direction, the powder 52 falling from the powder falling module 40 is transferred to the printing platform 12 to form a flat and loose powder layer 53. The powder spreading roller 35 rotates along the powder spreading roller rotation direction 37 to level the powder layer. Subsequently, the powder layer 53 passes through the compaction roller 34 that rotates clockwise along the compaction roller rotation direction 36. Since the height of the compaction roller 34 is slightly lower than that of the powder spreading roller 35, the loose powder is compacted to form a compacted powder layer 54. As the powder spreading module 30 and the powder falling module 40 move rightward, the powder spreading operation for the entire width is gradually completed.

[0091] After that, the powder spreading module 30 and the powder falling module 40 move to the right side of the platform module 10 again to prepare for the powder replenishment operation for the next layer. Repeat Figures 4 to 6 the action steps shown until the powder spreading of the bottom powder layer at the specified height is completed, as shown in Figure 7 At this time, the excess powder forms excess powder 56 when passing through the excess powder collection box 13. Under the negative pressure action of the excess powder recovery suction pipe 14, the excess powder 56 is recycled.

[0092] Then, the inkjet printing process is carried out, and the action logic is as shown in Figure 12 Similar to the powder spreading process of the bottom powder layer, inkjet printing requires powder replenishment, starting point preparation, powder spreading and other steps. However, the difference is that after the powder replenishment operations in steps 401 and 402 are completed, in the printing platform lifting step 403, in addition to descending by the thickness of one powder layer, the printing platform also descends an additional safety distance. In one embodiment, this safety distance is usually 2 to 10 times the thickness of the powder layer. The purpose is to prevent the residual powder on the surfaces of the powder spreading roller and the compaction roller from contacting the inkjet area of the previous compacted powder layer during the process of the powder forming module moving from the initial position to the powder spreading starting position, causing damage to the printed pattern and problems such as binder sticking to the roller. Then, in the powder spreading step 404, the printing platform needs to rise this safety distance before powder spreading can be carried out. Then, after powder spreading, the following inkjet step 405 is required. Finally, in 406, the action steps of 401 to 405 are repeated until the printing of all models is completed, as shown in Figure 8 andFigure 9 As shown

[0093] Since binder jetting bonds powder by selectively jetting binder layer by layer on a powder bed to finally construct a three-dimensional product, after each layer of powder is spread and compacted, the inkjet module moves horizontally in the Y direction, jets binder in a specific area and cures and bonds the powder. Subsequently, the inkjet module moves horizontally a certain distance in the X direction and moves horizontally in the reverse Y direction, jets binder in a specific area and cures and bonds the powder, achieving inkjet printing of each compacted powder layer in segments. As Figure 8 shown, at this time, the powder spreading module 30 and the powder dropping module 40 work normally as Figure 6 usual. The difference is that the inkjet module 20 will move to the left boundary of the printing platform 12 along the X direction. The inkjet head integration mechanism 23 then moves in the Y direction along the inkjet scanning track 22. During this process, the inkjet head 24 jets out binder 25 in the designed area to form a new powder layer bonding area 55. After completing the printing of this area, the inkjet module 20 moves a certain distance to the right along the X direction, and the inkjet head integration mechanism 23 moves in the reverse direction along the inkjet scanning track 22 to complete the inkjet printing of this area. With continuous segmented movement and scanning to the right, the inkjet module 20 will complete the inkjet printing of the entire printing format.

[0094] After completing the powder spreading and inkjet printing of one layer of powder, the system will re-enter the powder replenishment step as Figure 9 shown, similar to Figure 4 shown, the system will repeat the actions of each step of powder replenishment, powder dropping and inkjet printing as Figures 4 to 8 shown. The new powder layer bonding area 55 will bond with the old powder layer bonding area 58, and stack layer by layer to form a three-dimensional printed blank. The new compacted powder layer 54 will also be mixed with the powder 57 that has not participated in printing before and still remain in an unbonded loose powder state, and will be recycled together when the printed blank is taken out later for the next printing.

[0095] The following further illustrates the present invention with specific embodiments:

[0096] Embodiment 1

[0097] This embodiment provides a binder jetting 3D printing method for low-fluidity powder, including the following steps:

[0098] S1. Control the movement of the powder forming module to make it reach the initial position; wherein, the powder forming module includes a powder dropping module and a powder spreading module, and the powder dropping module and the powder spreading module move synchronously.

[0099] The powder is non-spheroidized alumina powder with a D50 of 30 μm and an angle of repose of 45°. The size of the printing platform is 1200 mm × 800 mm × 800 mm, the moving speed in the Z direction is 20 mm / s, the size of the excess powder collection box is 1200 mm × 200 mm × 800 mm, the diameter of the excess powder recovery suction pipe is 50 mm, and the negative pressure is -0.4 MPa.

[0100] S2. Add a preset amount of powder to the powder dropping module through the powder replenishment module. The powder dropping module includes a powder replenishment receiving plate and a vibrating plate.

[0101] In the powder replenishment module, the vibration frequency of the vibrator is 100 Hz, the width of the powder replenishment belt is 300 mm, the diameter of the belt drive shaft is 60 mm, and the rotational speed along the movement direction of the powder replenishment belt is 1 r / s.

[0102] In the powder dropping module, the length of the powder replenishment receiving plate is 1200 mm, the width is 100 mm, the eccentricity of the eccentric wheel is 1 mm, and the vibration frequency of the vibrating plate along the vibration direction is 20 Hz.

[0103] The amount of powder replenishment filled into the powder dropping module each time is 1.5 times the amount of powder required for each powder spreading layer.

[0104] S3. Move the powder forming module to the powder spreading starting position, and control the powder replenishment receiving plate to make the powder fall onto the vibrating plate.

[0105] S4. Control the vibration of the vibrating plate to transfer the powder to a preset area in front of the powder spreading module, and then level and compact the powder in sequence through the powder spreading module.

[0106] In the powder spreading module, the powder spreading speed of the powder spreading module along the X direction is 200 mm / s, and the non-working stroke speed is 500 mm / s. The powder spreading module includes a powder spreading roller and a compaction roller. The diameter of the powder spreading roller is 60 mm, the surface roughness is Ra 25, the diameter of the compaction roller is 60 mm, and the surface roughness is Ra 1.0. The rotation direction of the compaction roller is clockwise, the rotation direction of the powder spreading roller is counterclockwise, and the height difference between the compaction roller and the powder spreading roller is 0.22 mm.

[0107] S5. Move the powder forming module to the initial position to complete the powder spreading of a single layer.

[0108] S6. Repeat S1 - S5 until the bottom powder layer is laid.

[0109] S7. Repeat S1 - S5 on the bottom powder layer to complete the laying of the slice layer. The powder forming module moves horizontally along the X direction, spreads and compacts the powder on the bottom powder layer to form a slice layer with a thickness of 0.2 mm. After each slice layer is formed, an inkjet module sprays the binder on a specific area of this layer and cures the powder. Repeat until a 3D printed product is obtained.

[0110] In the inkjet module, the moving speed of the inkjet module in the X direction is 400 mm / s, the moving speed of the inkjet module in the Y direction is 500 mm / s, the number of inkjet heads is 8, and the binder is epoxy resin.

[0111] Example 2

[0112] This embodiment provides a binder jetting 3D printing method for low-fluidity powder, including the following steps:

[0113] S1. Control the movement of the powder forming module to make it reach the initial position; wherein, the powder forming module includes a powder dropping module and a powder spreading module, and the powder dropping module and the powder spreading module move synchronously.

[0114] The powder is natural quartz sand powder, with D50 being 70 μm and the powder repose angle being 42°. The size of the printing platform is 2500 mm × 1500 mm × 1000 mm, the moving speed in the Z direction is 20 mm / s, the size of the excess powder collection box is 2500 mm × 400 mm × 400 mm, the diameter of the excess powder recovery suction pipe is 80 mm, and the negative pressure is -0.5 MPa.

[0115] S2. Add a preset amount of powder to the powder dropping module through the powder replenishing module, and the powder dropping module includes a powder replenishing receiving plate and a vibrating plate.

[0116] In the powder replenishing module, the vibration frequency of the vibrator is 120 Hz, the width of the powder replenishing belt is 400 mm, the diameter of the belt drive shaft is 50 mm, and the rotational speed along the movement direction of the powder replenishing belt is 2 r / s.

[0117] In the powder dropping module, the length of the powder replenishing receiving plate is 2500 mm, the width is 120 mm, the eccentricity of the eccentric wheel is 3 mm, and the vibration frequency of the vibrating plate along the vibration direction is 10 Hz.

[0118] The amount of powder replenishment filled into the powder dropping module each time is 1.8 times the amount of powder required for each powder spreading layer.

[0119] S3. Move the powder forming module to the powder spreading starting position, and control the powder replenishing receiving plate to make the powder fall onto the vibrating plate.

[0120] S4. Control the vibration of the vibrating plate to transfer the powder to a preset area in front of the powder spreading module, and then level and compact it successively through the powder spreading module.

[0121] In the powder spreading module, the powder spreading speed of the powder spreading module in the X direction is 300 mm / s, and the non-printing speed is 500 mm / s. The powder spreading module includes a powder spreading roller and a compaction roller. The diameter of the powder spreading roller is 60 mm, and the surface roughness is Ra 12.5. The diameter of the compaction roller is 120 mm, and the surface roughness is Ra 0.6. The rotation direction of the compaction roller is clockwise, the rotation direction of the powder spreading roller is counterclockwise, and the height difference between the compaction roller and the powder spreading roller is 0.3 mm.

[0122] S5. Move the powder forming module to the initial position to complete the powder spreading of a single layer.

[0123] S6. Repeat S1 - S5 until the bottom powder layer is laid.

[0124] S7. Repeat S1 - S5 on the bottom powder layer to complete the laying of the slice layer. The powder forming module moves horizontally in the X direction, spreads and compacts the powder on the bottom powder layer to form a slice layer with a thickness of 0.4 mm. After each slice layer is formed, the inkjet module sprays the binder on specific areas of this layer and cures the powder, and repeat until the 3D printed product is obtained.

[0125] In the inkjet module, the moving speed of the inkjet module in the X direction is 400 mm / s, the moving speed of the inkjet module in the Y direction is 600 mm / s, the number of inkjet heads is 12, and the binder is a silicate inorganic binder.

[0126] Example 3

[0127] This example provides a binder jetting 3D printing method for low-fluidity powder, including the following steps:

[0128] S1. Control the movement of the powder forming module to make it reach the initial position; among them, the powder forming module includes a powder dropping module and a powder spreading module, and the powder dropping module and the powder spreading module move synchronously.

[0129] The powder is 316L stainless steel fine powder, D50 is 10 μm, and the powder angle of repose is 46°. The size of the printing platform is 800 mm × 500 mm × 400 mm, the moving speed in the Z direction is 10 mm / s, the size of the excess powder collection box is 800 mm × 100 mm × 300 mm, the diameter of the excess powder recovery suction pipe is 30 mm, and the negative pressure is -0.5 MPa.

[0130] S2. Add a preset amount of powder to the powder dropping module through the powder replenishing module. The powder dropping module includes a powder replenishing receiving plate and a vibrating plate.

[0131] In the powder replenishing module, the vibration frequency of the vibrator is 10 Hz, the width of the powder replenishing belt is 200 mm, the diameter of the belt drive shaft is 30 mm, and the rotational speed along the movement direction of the powder replenishing belt is 3 r / s.

[0132] In the powder-filling module, the length of the powder-supplement receiving plate is 800 mm, the width is 40 mm, the eccentricity of the eccentric wheel is 1 mm, and the vibration frequency of the vibrating plate in the vibration direction is 10 Hz.

[0133] The amount of powder-supplement powder filled into the powder-filling module each time is twice the amount of powder required for each powder-spreading layer.

[0134] S3. Move the powder molding module to the starting position of powder spreading, and control the powder-supplement receiving plate to make the powder fall onto the vibrating plate.

[0135] S4. By controlling the vibration of the vibrating plate, transfer the powder to a preset area in front of the powder-spreading module, and then level and compact it successively through the powder-spreading module.

[0136] In the powder-spreading module, the powder-spreading speed of the powder-spreading module in the X direction is 100 mm / s, and the non-working stroke speed is 300 mm / s. The powder-spreading module includes a powder-spreading roller and a compaction roller. The diameter of the powder-spreading roller is 50 mm, and the surface roughness is Ra 12.5. The diameter of the compaction roller is 50 mm, and the surface roughness is Ra 0.25. The rotation direction of the compaction roller is clockwise, the rotation direction of the powder-spreading roller is counterclockwise, and the height difference between the compaction roller and the powder-spreading roller is 0.05 mm.

[0137] S5. Move the powder molding module to the initial position to complete the powder spreading of a single layer.

[0138] S6. Repeat S1 - S5 until the laying of the bottom powder layer is completed.

[0139] S7. Repeat S1 - S5 on the bottom powder layer to complete the laying of the slice layer. The powder molding module moves horizontally in the X direction, spreads and compacts the powder on the bottom powder layer to form a slice layer with a thickness of 0.1 mm. After each slice layer is formed, the inkjet module sprays the binder on a specific area of this layer and cures the powder, and repeat until the 3D printing product is obtained.

[0140] In the inkjet module, the moving speed of the inkjet module in the X direction is 200 mm / s, the moving speed of the inkjet module in the Y direction is 400 mm / s, the number of inkjet heads is 12, and the binder is a water-based binder.

[0141] Examples 1 - 3 are detected, and the detection method is as follows:

[0142] (1) Powder-spreading layer density W p : Take a sample in the powder-spreading layer and calculate the powder-spreading layer density according to the following formula;

[0143]

[0144] Among them, the sampled product is placed on the measuring table, and the weight of the sampled product in the air is measured and recorded as W1; the sampled product after waterproof treatment is placed on the measuring table, and the weight of the sampled product after waterproof treatment in the air is measured and recorded as W2; the sampled product after waterproof treatment is placed in water, and the weight of the sampled product after waterproof treatment in water is measured and recorded as W3.

[0145] (2) Compacted powder layer density W y : Sample from the compacted powder layer and calculate the compacted powder layer density according to the following formula;

[0146]

[0147] Among them, the sampled product is placed on the measuring table, and the weight of the sampled product in the air is measured and recorded as W4; the sampled product after waterproof treatment is placed on the measuring table, and the weight of the sampled product after waterproof treatment in the air is measured and recorded as W5; the sampled product after waterproof treatment is placed in water, and the weight of the sampled product after waterproof treatment in water is measured and recorded as W6.

[0148] (3) Printing efficiency: Calculate the printing efficiency according to the following formula;

[0149]

[0150] (4) Printing space density difference RSD: Sample at different positions on the printing platform (the number of samples is more than 9), calculate the printing density at different positions, and calculate the printing space density difference according to the following formula;

[0151]

[0152] Among them, calculate the standard deviation of the printing density of the sampled products at different positions and record it as W s ; calculate the arithmetic mean of the printing density of the sampled products at different positions and record it as . The calculation of the printing density of the sampled products at different positions is the same as the calculation methods of the powder spreading layer density and the compacted powder layer density.

[0153] The specific test results are as follows:

[0154]

[0155] The above is the preferred embodiment of the invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A binder jet 3D printing method for low-flow powder, characterized in that: The following steps are involved: (1) controlling the movement of the powder forming module to make it reach an initial position; wherein the powder forming module comprises a powder dropping module and a powder spreading module, and the powder dropping module and the powder spreading module move synchronously; (2) adding a preset amount of powder to the powder dropping module through the powder replenishing module, the powder dropping module comprising a powder replenishing receiving plate and a vibration plate; the preset amount is 1 to 2 times the amount of powder required for each layer of powder laying; the repose angle of the powder is 35° to 60°; (3) moving the powder forming module to the powder spreading starting position, and controlling the powder replenishing receiving plate to cause the powder to fall onto the vibration plate; (4) by controlling the vibration of the vibration plate, the powder gradually slides down along with the movement of the powder spreading module and the vibration of the vibration plate, and is transferred to a preset area in front of the powder spreading module, and then is leveled and compacted in sequence by the powder spreading module; the powder spreading module includes a powder spreading roller and a compaction roller, and there is a preset distance between the vibration plate and the powder spreading roller, forming a preset area for powder transfer; The powder forming module also includes a bracket, the powder replenishing receiving plate, the vibration plate, the powder spreading roller and the compaction roller are all fixed on the bracket, the vibration plate is arranged in front of the powder spreading roller, and the compaction roller is arranged behind the powder spreading roller; The bottom of the vibration plate is higher than the bottom of the powder spreading roller, and the height difference is 0.5mm~5mm; The compacting roller and the powder spreading roller rotate in opposite directions, and the surface roughness of the compacting roller is smaller than that of the powder spreading roller; the bottom of the powder spreading roller is higher than the bottom of the compacting roller, and the height difference is 0.01 mm to 1 mm; The powder replenishing receiving plate and the vibration plate can both rotate relative to the bracket; the vibration frequency of the vibration plate is 0.1Hz~100Hz; During the process of the powder replenishing module adding powder to the powder dropping module, the powder replenishing receiving plate is located in a horizontal position; during the powder spreading process, the powder replenishing receiving plate has an angle with the horizontal direction so that the powder on the powder replenishing receiving plate falls to the vibration plate; (5) moving the powder forming module to an initial position to complete the laying of a single layer of powder; (6) Repeat steps (1) to (5) until the base powder layer is laid; (7) Repeat steps (1) to (5) on the base powder layer to complete the laying of the slice layer, control the inkjet module to follow the movement of the powder forming module, spray the binder in the preset area of ​​each slice layer and solidify the powder until the printing of the model is completed to obtain a 3D printed product.

2. The binder jet 3D printing method of low-fluidity powder according to claim 1, characterized in that: The powder spreading roller is used to sweep the powder scattered by the powder falling module to obtain a powder spreading layer, and the ratio of the density of the powder spreading layer to the loose density of the powder is (0.8-1.2):1; The compacting roller is used to compact the powder layer to obtain a compacted powder layer, and the ratio of the density of the compacted powder layer to the tap density of the powder is (0.8~1.2):

1.

3. The binder jet 3D printing method of low-fluidity powder according to claim 2, characterized in that: The ratio of the thickness of the base powder layer to the thickness of each compacted powder layer is (20-40):1; The ratio of the thickness of each compacted powder layer to the D50 of the powder added by the powder replenishing module is (2~10):1, and / or the ratio of the thickness of each compacted powder layer to the D90 of the powder added by the powder replenishing module is (1.5~10):

1.

4. The binder jet 3D printing method of low-fluidity powder according to claim 3, characterized in that: The D50 of the powder is 10 μm to 100 μm, and / or the D90 of the powder is 10 μm to 100 μm.

5. The binder jet 3D printing method of low-fluidity powder according to claim 1, characterized in that: The diameter of the compacting roller is 25 mm to 120 mm, and the surface roughness is Ra 0.25 to Ra 3.2; the diameter of the powder spreading roller is 25 mm to 120 mm, and the surface roughness is Ra 1.6 to Ra 100.

6. The binder jet 3D printing method of low-fluidity powder according to claim 2, characterized in that: The preset path of movement of the inkjet module is: moving along the Y direction, spraying the binder in the preset area and curing the adhesive powder, then moving a certain distance in the X direction and moving in the opposite direction in the Y direction, spraying the binder in the preset area and curing the adhesive powder, and inkjet printing of each slice layer is achieved in sections; The moving speed of the inkjet module in the X direction is 100 mm / s to 400 mm / s, and the moving speed in the Y direction is 100 mm / s to 600 mm / s; The X direction is the direction in which the powder spreading module moves, and the Y direction is the direction of the X direction on the horizontal plane rotated 90° counterclockwise.

7. The binder jet 3D printing method of low-fluidity powder according to claim 6, characterized in that: During the powder spreading process, the moving speed of the powder forming module in the X direction is 50 mm / s to 400 mm / s; The idle travel speed of the powder forming module from the initial position to the powder spreading starting position is 250 mm / s to 500 mm / s; The powder replenishing module is provided with a powder outlet vibrator and a powder replenishing belt. The powder replenishing powder in the powder replenishing module flows out under the action of the powder outlet vibrator. The preset amount of powder is evenly sprinkled on the powder replenishing receiving plate through the rotation of the powder replenishing belt and the movement of the powder replenishing module in the Y direction. The preset amount of powder added by the powder replenishing module to the powder falling module each time is 1 to 2 times the amount of powder required for each layer of powder laying.

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