CN111284004B

CN111284004B - 3D printing device and method for integrally manufacturing functional gradient material and structure

Info

Publication number: CN111284004B
Application number: CN202010102009.9A
Authority: CN
Inventors: 兰红波; 齐田宇; 杨建军; 许权; 张源值; 周龙健
Original assignee: Qingdao University of Technology
Current assignee: Qingdao University of Technology
Priority date: 2020-02-19
Filing date: 2020-02-19
Publication date: 2022-06-24
Anticipated expiration: 2040-02-19
Also published as: CN111284004A

Abstract

The invention discloses a 3D printing device and a printing method for integrally manufacturing a functional gradient material and a structure, wherein the 3D printing device comprises: a three-dimensional moving support; the printing nozzle is arranged on the three-dimensional moving support and comprises a stepping motor, a stirring paddle, a shell and a nozzle, wherein the stepping motor is arranged at the end part of the shell, one end of the stirring paddle is connected with an output shaft of the stepping motor through a coupler, the other end of the stirring paddle extends into a mixing chamber in the shell, and the output shaft of the stepping motor and the shell are arranged in a sealing manner; the nozzle and the stepping motor are oppositely arranged at the other end of the shell, and a material flow passage between the nozzle and the mixing chamber is provided with a control valve; the side wall of the mixing chamber is provided with a printing material I inlet and a printing material II inlet which are respectively connected with a printing material I feeding pump and a printing material II feeding pump; an air path I opening and an air path II opening are arranged on the side wall of the shell between the mixing chamber and the stepping motor and are respectively connected with an air source and a vacuum pump.

Description

3D printing device and method for integrally manufacturing functional gradient material and structure

Technical Field

The invention belongs to the technical field of additive manufacturing and functional gradient material/structure manufacturing, and particularly relates to a 3D printing device and a printing method for integrally manufacturing a functional gradient material and a structure.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

The Functional Gradient Material (FGM) is a heterogeneous composite Material in which, during the preparation of the Material, advanced composite technology is adopted to make microscopic elements (including Material components and microstructure) of the Material present continuous (or quasi-continuous) Gradient changes in a certain specific direction, so that the macroscopic properties of the Material also present continuous (or quasi-continuous) Gradient changes in the same direction. The functional gradient material is characterized in that a middle transition layer with gradient change is added in the traditional composite material according to the material content ratio, so that the physical properties of the material are in a gradual change form, and the defects of stress concentration, cracking, peeling and the like generated in the use process of the traditional composite material due to too large physical property difference are avoided or relieved. In addition, the functional gradient material has very good designability, and the volume content of each component material or the spatial distribution of the microstructure is changed in a targeted manner, so that the internal stress distribution of the structure is optimized, and the requirements of different parts on the service performance of the material, such as variable rigidity, variable dielectric constant and the like, are met. As a brand new advanced material, the material not only solves the problem of interface stress of the composite material, but also maintains the composite property of the material. Due to the excellent physical and chemical properties, the functional gradient material is currently applied to the fields of aerospace, biological medicine, nuclear engineering, energy, electromagnetism, optics, sexual electronics, wearable equipment, soft robots and the like, and has a wide application prospect.

According to the different material components contained in the functional gradient material, the functional gradient material is divided into: (1) inorganic functionally gradient materials, mainly including metal/ceramic, metal/nonmetal, metal/metal and ceramic/nonmetal, etc.; (2) the polymer functionally gradient material mainly comprises a high polymer/high polymer, a high polymer/ceramic, a high polymer/metal, a high polymer/inorganic filler and the like, but at present, research and development of the polymer functionally gradient material mainly focuses on two main categories of the high polymer/high polymer and the high polymer/inorganic filler. The polymer functionally graded material (PGM) mainly refers to a generic name of functionally graded materials with a base material being a high molecular material, and compared with inorganic functionally graded materials, the polymer functionally graded material has wider engineering application.

To the knowledge of the inventor, the existing main preparation methods of the functionally graded material are as follows: chemical vapor deposition, physical vapor deposition, plasma spraying, self-propagating high-temperature synthesis, powder metallurgy, centrifugal molding, slip casting, chemical vapor infiltration, and electrowinning. However, these conventional preparation methods can only be used for forming some functionally graded materials with simpler structures, and cannot realize the forming of complex structural members, especially the integrated manufacturing of complex three-dimensional functionally graded materials and structures, and the forming process in the prior art is complex, the efficiency is low, and the cost is high. The additive manufacturing technology (3D printing) appearing in recent years provides a brand-new technical solution for manufacturing the functional gradient material and the functional gradient structural member, and particularly provides an ideal forming method for the functional gradient material and the complex three-dimensional structure by the multi-material and multi-scale 3D printing technology.

According to the difference of the 3D printing raw materials of the functional gradient structure, the method for manufacturing the functional gradient material/structure based on 3D printing is divided into three categories: (1) the raw materials are all liquid (liquid), namely liquid and liquid mixed 3D printing with different volume fractions (or mass fractions); (2) one raw material is liquid (liquid), the other is solid (powder or granular solid, and can be dissolved in the first liquid raw material), namely, liquid and solid mixed 3D printing with different volume fractions (or mass fractions); (3) raw materials are all solid (solid, powder, granular, wire-shaped and the like), namely solid and solid mixed 3D printing with different volume fractions (or mass fractions).

According to the published research results and information at home and abroad, 3D printing technology and process for manufacturing functionally graded materials/structural members have been proposed mainly including: directed energy deposition (LENS), laser cladding, Fused Deposition Modeling (FDM), polymer jetting (Polyjet), powder bed melting, etc., however, after the research of the inventors, the existing 3D printing techniques have found many defects and shortcomings in the manufacture of functionally graded materials/structures: (1) the materials of the components are not mixed uniformly. None of these prior art techniques provide a dedicated compounding unit (especially active material mixing) resulting in non-uniform compounding which results in failure to produce a truly high performance functionally graded material/structure. For example, the existing LENS, laser cladding, FDM and other technologies mostly adopt an integrated nozzle/print head structure, and uniform mixing of multiple materials cannot be achieved in the integrated nozzle, and especially, LENS and laser cladding materials are mixed in a molten pool after injection deposition of each component material, so that the mixing effect is worse. The multi-nozzle structure adopted by the polymer spraying process is also the mixing of a plurality of materials after deposition and before solidification, and the complete and uniform mixing of the multi-component materials cannot be realized. The powder bed melting process restricts the uniform mixing of materials (especially the feeding mode for spreading powder) and has the problem of serious material waste; (2) the existing various 3D printing technologies can not realize the manufacture of continuous functional gradient materials/structural members, can only realize the manufacture of quasi-continuous functional gradient materials/structural members, and can not prepare the functional gradient materials/structural members in the true sense; (3) the processing precision is low, all the existing processes can not realize the manufacture of a micro-scale functional gradient structure, the minimum feature resolution is difficult to realize below 100 micrometers, and particularly, no technology can realize the manufacture of a high-resolution feature structure below 20 micrometers; (4) the existing technologies are difficult to realize the manufacture of functionally graded materials or structural members based on microstructure change due to the limitation of forming precision, and the manufacture of functionally graded materials or functionally graded structures is mostly realized by adjusting the component proportion of the materials; (5) the integrated manufacture of the functional gradient material and the three-dimensional structure cannot be realized, and the integrated manufacture of the simple two-dimensional or 2.5-dimensional structure is mostly realized; (6) the manufacture of a complex three-dimensional functional gradient structural part is difficult to realize; (7) the production efficiency is low, the manufacturing process stability is poor, for example, LENS, laser cladding, FDM, etc., because the material proportion is constantly changed in the printing process, the printing process parameters (laser power, heating temperature of a nozzle, etc.) must be correspondingly adjusted, so that the whole printing process has poor process stability and low printing efficiency; particularly, an integrated printing head structure is adopted, the material mixing and printing functions are integrated, strict sequence and synchronization relation must be ensured for feeding, material mixing and printing, otherwise, required functional gradient materials and forming structures are difficult to print successfully, and the improvement of the processing efficiency is greatly limited; (8) the kinds and shapes of the printable materials are limited, and the printable materials need to be processed in advance into desired shapes and sizes. For example, materials suitable for the current LENS and laser cladding processes are basically powder materials and wire materials, and the shapes and the geometric dimensions of the powder materials and the wire materials are also strictly limited; FDM is suitable for the material to be wire material at present, and the geometric dimension of the FDM is also limited more strictly; polymer jetting is currently only suitable for very low viscosity photosensitive resin materials; powder bed melting is suitably a powdery material, the geometry and dimensions of which are more severely limited; (9) each manufacturing technology also has stricter limits on suitable forming materials, the LENS, laser cladding and powder bed melting technology is mainly used for manufacturing metal-based functionally gradient materials and structures, the FDM is mainly used for manufacturing thermoplastic-based functionally gradient materials/structures, and the Polyjet is mainly used for manufacturing light-cured resin-based functionally gradient materials/structures; (10) the equipment and the process are complex, and the production cost is high.

The invention patent (application publication No. CN109732905A, 3D printer and working method for integrally manufacturing functional gradient material and forming structure) discloses a 3D printer and working method for integrally manufacturing functional gradient material and forming structure, which are mainly suitable for realizing the integral manufacturing of functional gradient material and forming structure by mixing and printing powder/granular solid and powder/granular solid, wherein the raw materials are all solid. However, the mixing of liquid and solid powders has the following problems: (1) in the mixing process, the powder is easy to agglomerate and difficult to disperse, which is a common problem of the existing solid-liquid mixing; (2) if the viscosity of the liquid is too high, air is brought in during the mixing process, bubbles are easy to appear, and the solid powder is difficult to be uniformly mixed in the liquid; (3) the solid-liquid mixed materials with different proportions realize the actions of feeding, mixing, extruding and the like in the printing process, the time consumption of the whole process is short, and the response speed is required to be high. For example, for a PDMS-based functionally gradient material, PDMS has a high viscosity, solid nanoparticles are difficult to mix uniformly in a PDMS liquid, bubbles are easy to occur during mixing, the solid nanoparticles are not uniformly distributed, and the generated bubbles seriously affect the quality of a 3D printed product. For the field of flexible electronics, various single-material flexible substrates widely used at present cannot meet the requirements of practical engineering applications more and more.

Disclosure of Invention

In order to solve the technical problems in the prior art, the invention aims to provide a 3D printing device and a printing method which are manufactured by integrating a functional gradient material and a structure. The 3D printing method can realize uniform mixing of liquid (matrix) and powdery solid (reinforcing phase), and can effectively remove bubbles generated in the mixing process of the liquid and the powdery solid so as to ensure the quality of 3D printed products. In particular, the integrated manufacture of continuous gradient materials and complex structures can be realized.

In order to solve the technical problems, the technical scheme of the invention is as follows:

functional gradient material and structure integration manufacturing's 3D printing device includes:

a three-dimensional moving support;

the printing nozzle is arranged on the three-dimensional moving support and comprises a stepping motor, a stirring paddle, a shell and a nozzle, wherein the stepping motor is arranged at the end part of the shell, one end of the stirring paddle is connected with an output shaft of the stepping motor through a coupler, the other end of the stirring paddle extends into a mixing chamber in the shell, and the output shaft of the stepping motor and the shell are arranged in a sealing manner;

the nozzle and the stepping motor are oppositely arranged at the other end of the shell, and a material flow passage between the nozzle and the mixing chamber is provided with a control valve;

the side wall of the mixing chamber is provided with a printing material I inlet and a printing material II inlet which are respectively connected with a printing material I feeding pump and a printing material II feeding pump;

an air path I opening and an air path II opening are arranged on the side wall of the shell between the mixing chamber and the stepping motor and are respectively connected with an air source (positive pressure) and a vacuum pump (negative pressure);

the stirring paddle comprises a stirring rod and a plurality of blades, the blades are uniformly distributed in a plurality of rows in the circumferential direction of the stirring rod, each row is arranged along the axial direction of the stirring rod and distributed in the whole length direction of the stirring rod, and two adjacent rows of blades are arranged in a staggered manner; the stirring rod penetrates through the whole height direction of the mixing chamber;

and the high-voltage power supply is connected with the conductive nozzle of the printing nozzle.

The inventor finds that a large amount of bubbles are generated in the mixing process of liquid (such as PDMS) and solid powder (such as SiC), and the quality of a 3D printed product is seriously affected if the mixture is directly printed, so that the invention firstly proposes that after the solid-liquid mixture is uniformly mixed, a mixing chamber is vacuumized, and meanwhile, the sealing in the mixing chamber is ensured, so that the mixed material is in a negative pressure state to remove the bubbles in the mixed material, and the quality of the 3D printed product is improved.

The output shaft of the stepping motor and the shell are arranged in a sealing mode, the material flow channel between the nozzle and the mixing chamber is provided with the control valve, and the control valve is in a closed state in the mixing and vacuumizing processes, so that the sealing state can be kept in the mixing chamber.

The design purpose of the invention is used for 3D printing after uniform mixing of liquid with certain viscosity and powdery solid, solid powder is easier to agglomerate and is difficult to disperse in the liquid with certain viscosity, the liquid with certain viscosity and the powdery solid are difficult to uniformly mix by adopting the traditional single-blade or multi-blade stirring paddle, particularly, the mixing dead angle is easy to generate, and under the condition, the performance of the 3D printing structure is inevitably influenced.

The inventor has designed the stirring rake, makes the puddler pass the whole direction of height in compounding room, and the blade distributes in the whole length direction of puddler, and this kind of setting makes the stirring rake can both carry out the stirring of equivalent degree to the material of the whole direction of height in the compounding room, can effectively avoid mixing the appearance at dead angle. Set the blade evenly distributed in the multirow of puddler circumference, the blade staggered distribution of adjacent two rows, when the stirring, the stirring rake is when producing whole stirring effect to the material, still can produce a lot of little local vortex and more obvious local shearing mixing effect when the blade that the phase staggered distributed stirs the material, and then effectively improve the mixed effect of liquid and powdered solid, make it can misce bene in the short time. And the mixing efficiency of two kinds of materials improves and makes printing efficiency and the printing quality that 3D gradient printed improve greatly.

In some embodiments, the part of the blades is rectangular blades, the blades are perpendicular to the tangential direction of the stirring rod and parallel to the axial direction of the stirring rod, and the part of the blades is arranged at a position far away from the free end of the stirring rod.

Further, the blades provided at the free end portions of the stirring rods are shaped like right triangles.

In some embodiments, the mixing chamber comprises a pre-mixing chamber and a secondary mixing chamber which are communicated with each other, the secondary mixing chamber is located below the pre-mixing chamber, the nozzle is located below the secondary mixing chamber, the horizontal cross-sectional area of the secondary mixing chamber is larger than that of the pre-mixing chamber, the printing material I inlet and the printing material II inlet are arranged on the side wall of the pre-mixing chamber, and the ratio of the diameter of the stirring paddle to the diameter of the pre-mixing chamber is 1: 1.2-2.

Because the viscosity of the liquid is relatively high, the solid powder is easy to agglomerate, and the size of the traditional stirring paddle is far smaller than the specification of the mixing chamber, if the liquid and the solid powder are completely injected into the mixing chamber and then stirred and mixed uniformly, the mixing difficulty of the liquid and the solid powder is greatly improved, and too many mixing dead angles are generated. The invention creatively provides that solid powder and liquid are mixed firstly to prepare mixed liquid (printing material II) with the maximum mass percentage of the solid powder, and then the mixed liquid (printing material II) and pure liquid or the mixture of the pure liquid and curing agent (printing material I) are mixed according to a preset program in proportion, the mixing difficulty of the solid powder and the liquid can be reduced to a certain extent by adopting the mode, but the inventor finds out through experiments that even by adopting the mode, the solid powder in the printing material II is agglomerated because the printing material II contains more solid powder and the solid powder is settled to a certain extent in the conveying and storing processes, in addition, the solid powder agglomeration phenomenon still exists in the mixing processes of the printing material I and the printing material II, so the structure in a mixing chamber needs to be improved, to improve the uniformity of mixing of the liquid with the solid powder.

Therefore, the mixing chamber is arranged as a pre-mixing chamber and a secondary mixing chamber, and the important point is that the inlets of the two materials are arranged on the side wall of the pre-mixing chamber, the diameter of the pre-mixing chamber is slightly larger than the diameter of the stirring paddle (note: the diameter of the stirring paddle is the sum of the diameter of the stirring rod and the radial width of the blade), and in the process of injecting the two materials into the pre-mixing chamber, the two materials are quickly pre-mixed under the stirring action of the stirring paddle which rotates quickly, so that the agglomeration of solid powder is avoided. Because the liquid has certain viscosity, a certain time is needed for the liquid to flow downwards through the premixing chamber, and the preliminary mixing can be realized in the premixing process.

The feeding flow rate of the printing material is difficult to accurately control, so that the two materials in the same batch are difficult to uniformly mix on the whole only through the premixing chamber, and when the two materials after premixing enter the secondary mixing chamber to be uniformly mixed on the whole, the batch of materials is favorably homogenized on the whole.

Furthermore, the ratio of the diameter of the stirring paddle to the diameter of the secondary mixing chamber is 1: 3-4.

When the diameter of the secondary mixing chamber is smaller, the two materials are difficult to be mixed in the height direction, when the diameter of the secondary mixing chamber is larger, the two materials are difficult to be mixed in the horizontal direction, and when the diameter of the secondary mixing chamber and the diameter of the stirring paddle are 1:3-4, the two materials are easy to be mixed integrally.

Furthermore, the height of the pre-mixing chamber is 10mm-50mm, and the height of the secondary mixing chamber is 5mm-35 mm.

In some embodiments, the control valve is a normally closed solenoid valve.

The valve is closed during stirring and vacuumizing bubble removal, so that mixed materials are prevented from entering the nozzle, and liquid backflow is prevented during vacuum bubble removal.

In some embodiments, the printing platform is located below the printing nozzle, and the printing platform is provided with a heating structure. The heating structure can heat the printing platform to heat and solidify the printed structure in time.

In some embodiments, a curing module is also mounted on the three-dimensional moving support. The device is used for timely heating or light curing of the printed structure.

The 3D printing method for integrally manufacturing the functional gradient material and the structure comprises the following steps:

mixing liquid with a curing agent or pure liquid raw materials to prepare a printing material I;

mixing the liquid with the solid powder, or uniformly mixing the printing material I with the solid powder to prepare a printing material II;

preheating a printing platform;

conveying the printing material I and the printing material II to a mixing chamber of a printing nozzle according to a proportion set by a program, rotating a stirring paddle to premix the printing materials in the feeding process, and then integrally mixing the premixed printing materials;

in the material mixing process, a vacuum pump acts to pump negative pressure to a material mixing chamber, bubbles in the mixed material are removed, after a certain time is maintained, a control valve is opened to recover normal pressure, then a certain positive pressure is applied, a high-voltage power supply is turned on, and a three-dimensional moving support moves according to the tracks in the X direction and the Y direction set by a program to print and form the geometric shape of the layer structure;

after printing one layer, the printing nozzle is lifted to the height of the next layer along the Z direction, and the procedures of mixing, bubble removing and printing the next layer are carried out according to the program setting until the whole gradient geometric structure is printed.

And closing the high-voltage power supply, closing the positive pressure, closing the heating of the printing platform, moving the three-dimensional movable support to a printing completion station, and taking down the formed part from the printing platform.

In some embodiments, the printing material II is prepared by first mixing the liquid and the solid powder with stirring, and then placing the mixture into the ultrasonic disperser for uniform mixing.

The ultrasonic disperser is beneficial to improving the dispersion uniformity of the solid powder in the liquid, and the more uniform the solid powder is distributed in the printing material II, the more beneficial the subsequent printing process is.

In some embodiments, the temperature of the printing platform after preheating is 30-180 ℃.

In some embodiments, the pressure after the negative pressure is drawn on the mixing chamber is 0.5-1.5 bar.

In some embodiments, the working range of the positive pressure gas circuit is 30-80 kpa;

negative pressure gas circuit working range: 0.5-1.5bar, working pressure of normal pressure gas circuit: 0 pa.

In some embodiments, the high voltage power supply is configured to be capable of outputting direct current high voltage, outputting alternating current high voltage, outputting pulse high voltage, and setting bias voltage, the set bias voltage range is 0-2KV continuously adjustable, the direct current high voltage is 0-5KV, the output pulse direct current voltage is 0- +/-4 KV continuously adjustable, the output pulse frequency is 0Hz-3000Hz continuously adjustable, and the alternating current high voltage is 0- +/-4 KV.

In some embodiments, the liquid is a thermoset or photocurable material such as PDMS, Ecoflex, SEBS block copolymers, photosensitive resins, hydrogels, and the like.

In some embodiments, the solid powder is SiC, SiO₂、Al₂O₃、TiO₂And a reinforcing phase material or a modifying material such as graphene or carbon nanotubes.

In some embodiments, marking material I and marking material II are mixed in a continuous gradient ratio. The solid content in the matrix is continuously increased from one side to the other side, and the characteristic of continuous functional gradient is presented, so that the rigidity and the thermal conductivity of the printing material are continuously changed.

In some embodiments, marking material I and marking material II are mixed in a discrete gradient ratio (the multilayer structure has the same ratio material). The solid content in the matrix is increased discontinuously from one side to the other side, and the discrete functional gradient characteristic is presented, so that the rigidity and the thermal conductivity of the printing material are changed in a discrete gradient manner.

The amount of printing material per layer must be consistent with the amount of printing material I and printing material II supplied. In the case of discrete gradient materials, the same ratio of the amounts of the multiple layers of printing material must be used in concert with the amounts of the printing material I and printing material II required to print the gradient layers.

The present invention sets two printing modes, extrusion molding and jet molding. The extrusion forming printing efficiency is prior, and the printing precision is considered; the precision printing degree of the jet forming is prior, and the printing efficiency is considered.

The print data file (program) includes at least: geometric information, material information (material ratio of each component).

The printing function gradient structure can be set to have multiple layers with the same material information according to the actual printing requirements (printing efficiency and actual printing requirements or precision requirements and the like).

Based on the working method of the 3D printer, geometric information of each layer of the printing structural part is determined according to model data of the formed structural part, material information and a printing mode are set according to the requirements of material/structure functional gradient, the required component materials are sent into the mixing module by the feeding module according to the proportion required by the component materials, and after the components are fully mixed under the stirring action of the printing nozzle blade, the printing materials are extruded to the tip end of the conductive nozzle under the pressure action of positive pressure of the printing nozzle gas path system I; according to the difference of printing geometric characteristic structures, different printing modes are adopted respectively, and the geometric structure forming is realized by matching with the movement of the three-dimensional workbench.

As a further limitation, the different printing modes are specifically: for a macro structure, the printing material is extruded and deposited on a substrate or a formed structure by directly utilizing the pressure of a positive pressure air path of a printing nozzle air path system I, if the micro-scale feature structure is printed, a high-voltage power supply is started, and the printing material is sprayed and deposited on the substrate or the formed structure by utilizing an electric field to drive a 3D (three-dimensional) spraying and depositing printing process.

By setting two printing modes, the first printing mode (extrusion molding) is directly formed by adopting air pressure extrusion and is used for printing a macro structure and a characteristic structure with low precision requirement, and the mode has higher printing efficiency; the second mode adopts an electric field to drive a jet deposition 3D printing process (jet forming) for printing the micro-nano characteristic structure, particularly realizes the manufacture of a microstructure-based continuous functional gradient material and a structural member by utilizing the mode, and simultaneously requires the manufacture of a material component and a microstructure variation functional gradient material and a structural member, and has very high precision. The two printing modes can simultaneously give consideration to the printing efficiency and the printing precision, and ensure the realization of large-area macro/micro/nano cross-scale 3D printing and the efficient manufacture of large-size high-precision functional gradient structural parts.

Compared with the prior art, the invention has the beneficial effects that:

(1) the invention can realize the integrated manufacture of liquid (liquid) and solid (solid) discrete or continuous functional gradient materials and complex three-dimensional structural parts. The manufacturing of discrete or continuous functionally graded materials and structural members can be realized according to different components and proportions of the materials, and the manufacturing of the continuous functionally graded materials and structural members can also be realized according to the change of the microstructure. The functional gradient structure can be manufactured according to different components and proportions of the material.

(2) The invention adopts an active mixing method and is provided with a special active mixing module, can realize the high-efficiency and uniform mixing of two printing materials with different proportions, and is particularly suitable for printing high-viscosity materials.

(3) The present invention sets two printing modes, extrusion molding and jet molding. The printing efficiency and the printing precision can be simultaneously considered, the integrated manufacturing of the material based on the material microstructure functional gradient material and the forming structure is realized, the realization of large-area macro/micro/nano cross-scale 3D printing is ensured, and the efficient manufacturing of large-size high-precision functional gradient structural parts is realized. The printing precision is high, and the manufacture of the functional gradient material and the structural component of the micro-scale characteristic structure can be realized, in particular the manufacture of the large-area macro/micro/nano cross-scale functional gradient material and the structural component can be realized.

(4) The invention separates the feeding module and the mixing spray head module and respectively sets up special functional modules. The feeding and mixed printing processes are not affected, the printing efficiency and stability are improved, and the multi-material cross-scale complex three-dimensional structure can be manufactured efficiently at low cost.

(5) The automatic printing material feeding device can realize automatic accurate feeding and efficient mixing of printing materials according to quantity. According to the material proportioning requirement, the feeding parameters are set, the printing material is conveyed accurately and quantitatively, and then the active mixing nozzle is used for mixing materials efficiently and uniformly. The material is carried and compounding is efficient to and accurate compounding.

(6) The invention has wide application range, and is particularly suitable for the matrix material being liquid material and the reinforcing phase being solid material; it is also suitable for materials (different concentrations) in which both the matrix material and the reinforcement phase material are liquids.

(7) The invention has the advantages of simple structure, low cost and high efficiency. The method is particularly suitable for manufacturing the base functional gradient materials and structures such as PDMS, hydrogel and the like, and is particularly suitable for the efficient batch manufacturing of PDMS/SiC functional gradient substrates.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are included to illustrate an exemplary embodiment of the invention and not to limit the invention.

Fig. 1 is a schematic structural diagram of a 3D printing apparatus manufactured by integrating a functionally graded material and a molding structure for liquid and solid raw materials according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of the overall structure of a print head according to an embodiment of the present invention;

FIG. 3 is a schematic view of a partial cross-sectional structure of a print head according to an embodiment of the present invention;

FIG. 4 is a schematic view of a compounding stirring rod according to an embodiment of the present invention;

FIG. 5 is a schematic view of a control valve according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of the printing principle of an embodiment of the present invention;

fig. 7 is a flow chart of the 3D printing work flow of the integrated manufacturing of the functionally graded material and the molding structure according to the embodiment of the invention.

Wherein, 1, feed module I, 2, feed module II, 3, gas circuit system I, 4, gas circuit system II, 5, print the shower nozzle, 501, step motor, 502, gas circuit I opening, 503, gas circuit II opening, 504, printing material I import, 505, printing material II import, 506, the mixing chamber, 507, anchor clamps, 508, the control valve, 509, the shaft coupling, 510, the sealing washer, 511, the stirring rake, 512, the electrically conductive nozzle, 6, the Z axle workstation, 7, the X axle workstation, 8, the Y axle workstation, constitute triaxial XYZ motion module jointly, 9, the support, 10, upper portion solidification module, 11, print platform, 12, the bottom plate, 13, the frame, 14, high voltage direct current power supply, 15, control module.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

Example 1

FIG. 1 is a schematic structural diagram of a functionally gradient device for active mixing based on multiple materials according to an embodiment of the present invention, which includes: the device comprises a feeding module I1, a feeding module II2, an air path system I (positive pressure air path) 3, an air path system II (negative pressure air path) 4, a printing spray head module 5, a Z-axis workbench 6, an X-axis workbench 7 and a Y-axis workbench 8, wherein an XYZ three-axis movement module, a support 9, an upper curing module 10, a printing platform 11, a bottom plate 12, a rack 13, a high-voltage direct-current power supply 14 and a control module 15 are jointly formed.

Specifically, the feeding module I1 and the feeding module II2 are respectively connected to the print head module 5, the print head module 5 is fixed on the support 9, and the support 9 is fixed on the Z-axis workbench; the Z-axis workbench 6, the X-axis workbench 7 and the Y-axis workbench 8 jointly form an XYZ three-axis motion module, the XYZ three-axis motion module is arranged on a rack 13, and the rack 13 is fixed on a bottom plate 12; the printing platform 11 is arranged right below the printing nozzle module 5 and is fixed on the bottom plate 12; the upper curing module 10 is fixed on the bracket 9; the air path system I3 is connected with the printing nozzle module 5, and the air path system II4 is connected with the printing nozzle module 5; the high-voltage direct-current power supply 14 is connected with the conductive nozzle of the printing nozzle module 5. The control module 15 controls the functions of the individual modules and the cooperative work of the respective functional modules, etc.

The feeding module 1 and the feeding module 2 adopt precise injection pumps and are connected with the feeding holes of the printing nozzle module 5 through hoses and pipe joints (a printing material I inlet 504 and a printing material II inlet 505).

The Z-axis workbench 6, the X-axis workbench 7 and the Y-axis workbench 8 jointly form an XYZ three-axis motion module, the XYZ three-axis motion module adopts a gantry type high-precision displacement workbench and can adopt a servo motor, a stepping motor or a linear motor and the like. Wherein the working stroke of the X, Y shaft is 200mm, the repeated positioning precision is not less than +/-1 μm, the positioning precision is not less than +/-5 μm, and the highest speed is 500 mm/s. The working stroke of the Z axis is 100mm, the repeated positioning precision is not less than +/-1 mu m, the positioning precision is not less than +/-30 mu m, and the maximum speed is 200 mm/s.

The high-voltage direct-current power supply 14 can output direct-current high voltage. The set direct current high voltage range is 0-4 kV.

The upper curing module 10 is composed of a curing unit and a connecting frame, the curing unit is installed on the connecting frame and forms an included angle with the installation platform, the included angle is adjustable between 0-90 degrees, and the connecting frame is fixed on the support 9. The upper curing module comprises heating curing modules such as far infrared heating and laser heating, or ultraviolet curing modules such as UV curing lamps.

The printing platform 11 has a leveling function and an electric heating function, and can be a circular table or other structural shapes, the heating temperature range of the printing platform 11 is 30-150 ℃, the printing platform 11 can be leveled, a substrate can be placed on the printing platform 11 during printing, and if the surface of an existing object is printed, the object can be fixed on the printing platform 11 for printing.

The gas path system I3 can adopt high-purity nitrogen. Positive working range: 30-80 kpa. Working range of gas circuit system II 4: 0.5-1.5 bar.

The control module 15 realizes integrated control over the XYZ three-axis motion module, the feeding module 1, the feeding module 2, the printing nozzle module 5, the high-voltage direct-current power supply 14, the upper curing module 10, the printing platform 11, the gas circuit system I3, the gas circuit system II4 and the like.

Fig. 2 is a schematic structural diagram of an active mixing showerhead module according to an embodiment of the present invention, which includes: the printing device comprises a stepping motor 501, a gas path I502, a gas path II503, a printing material I inlet 504, a printing material II inlet 505, a mixing chamber 506, a clamp 507, a control valve 508, a coupler 509, a sealing ring 510, a stirring paddle 511 and a conductive nozzle 512, wherein the stepping motor 501 and the stirring paddle 511 are interconnected through the coupler 509, the stirring paddle 511 is installed inside the mixing chamber 506, the mixing chamber 506 is fixed on the clamp 507, a material conveying opening is formed in the side surface of the mixing chamber 506, the printing material I inlet 504 and the printing material II inlet 505 are respectively connected with a feeding module 1 and a feeding module 2 through hoses, materials enter the mixing chamber 506 under the action of the feeding module, stirring and mixing are completed under the action of the stirring paddle 511, the control valve 508 is installed between the bottom end of the mixing chamber 506 and the conductive nozzle 512, the conductive nozzle 512 is a metal nozzle or a nozzle coated with a conductive material, and the inner diameter of the nozzle is 100 mu m, is connected with the positive pole of the high-voltage direct current power supply 14 through a lead.

A schematic diagram of a stirring paddle according to an embodiment of the invention is shown in FIG. 4. The stirring paddle material be duralumin, whole puddler has 8 layers of blade to distribute all around, and every layer has two blades, is 180 between the blade, two blades on upper and lower layer stagger 90. The blades are of uniform length. The mixer is connected with the stepping motor through the coupler, and the mixture is subjected to forces in all directions in the mixing process and is uniformly mixed.

FIG. 5 is a schematic view of a control valve according to an embodiment of the present invention. The control valve is a normally closed solenoid valve, the mixing chamber is connected to the upper surface of the thread, the printing nozzle is connected to the lower surface of the thread, and the valve is closed when the material enters the nozzle for stirring and vacuuming bubble removal, so that the material is prevented from entering the nozzle, and liquid backflow is prevented during vacuum bubble removal. The inside unable vacuum environment that keeps of shower nozzle, liquid will get into the vacuum pump, not only is difficult to realize the bubble removal operation, can cause the damage to the vacuum pump moreover.

A schematic diagram of printing according to an embodiment of the present invention is shown in fig. 6. The conductive nozzle 512 is a stainless steel needle of type 21G (the outer diameter is 810 μm, the inner diameter is 510 μm), and is arranged at the bottom of the control valve 508 and connected with the positive electrode of the high-voltage direct-current power supply 14 through a lead. The conductive nozzle 512 forms a strong electric field with the substrate 1101 placed on the printing platform 11, and drives the material to be jet-deposited on the substrate 1101.

The working flow chart of the embodiment of the invention can be realized by using the device, as shown in fig. 7. The technological process of the integrated manufacture of the functionally graded material and the structure comprises the following steps:

(1) and (5) setting a system. Determining the geometric information of each layer of the printing structural part and generating a printing data file;

(2) performing printing pretreatment, namely finishing preparation work before printing;

(3) printing a functional gradient structure, which mainly comprises 3D printing of conveying materials, mixing materials, conveying extrusion and geometric forming according to the proportion;

(4) after each layer is printed, the Z-axis workbench 6 is lifted by one layer thickness, and then the printing of the next layer structure is finished. Repeating the processes until all the layer structures are printed;

(5) and closing each device and each module, and taking down the printed formed functional gradient structural member.

The printing data file at least comprises the following layers of structures: geometric information, material information (material ratio of each component).

According to the printing function gradient structure, multiple layers with the same material information can be arranged according to the actual printing requirements (printing efficiency, actual printing requirements or precision requirements and the like).

The invention takes a PDMS/SiC functionally graded substrate as an embodiment, realizes a working method for integrally manufacturing a discrete functionally graded material and a structure, and explains the specific process flow steps:

step 1: print data file preparation. According to the structural requirements of a printed matter, the volume ratios of SiC to PDMS from one side (outer surface) to the other side (inner surface) of the functional gradient substrate are respectively determined to be 0%, 10%, 20%, 30%, 40% and 50%, the printing height of each layer is determined to be 0.2mm, and the line spacing is set to be 0.3 mm.

Step 2: and (4) pretreatment before printing. PDMS elastomer and curing agent were mixed as 10: 1 and then the mixture is uniformly mixed and vacuumized to prepare pure PDMS (printing material I). And (3) preparing a variable-component printing liquid, preparing a PDMS/SiC mixed liquid with the SiC content of 50% by using an ultrasonic vibration method, stirring and mixing to uniformly disperse SiC particles in the PDMS solution, and preparing the high-concentration PDMS/SiC mixed liquid (printing material II). Pure PDMS (printing material I) and high-concentration PDMS/SiC mixed liquid (printing material II) are respectively placed in the feeding module 1 and the feeding module 2, the heating temperature of the printing platform 11 is set to 80 ℃, the air path system I3 and the air path system II4 are in a preparation state, the printing spray head module 5 is in a standby state, each motion platform is in an enabling state, and the preparation before the whole printing is completed.

And step 3: printing of a bottom layer structure:

(3-1) feeding, closing the gas circuit system I3 and the gas circuit system II4, and closing the control valve 508. Feeding a set amount of printing material I (pure PDMS) into the active mixing nozzle 5 by means of a feeding module I (syringe pump I);

(3-2) mixing materials, after the printing material I (pure PDMS) is fed, starting an air path system II4 (the negative pressure value is set to be 1bar), vacuumizing to remove air bubbles, and after the air bubbles are completely eliminated, closing the air path system II 4. Opening the air path system I3, opening the control valve 508 and enabling the printing platform to reach the set temperature of 80 ℃;

(3-3) printing, namely, conveying a printing material I to a printing spray head 512 by using the pressure (positive pressure 20kpa) of an air path system I adjusted by a precision pressure reducing valve, starting a high-voltage direct-current power supply 14 by using a stainless steel needle head with the model 21G (the outer diameter is 810 microns and the inner diameter is 510 microns) and adjusting the voltage value to 1500V, and then printing a bottom layer structure (pure PDMS) according to the process parameters set by a printing program.

And 4, step 4: printing a gradient layer structure:

and (4-1) feeding, after the bottom layer structure is printed, lifting the spray head by a corresponding height, and printing a silicon carbide content 10% gradient layer. Closing the gas path system I3 and the gas path system II4, closing the control valve 508, feeding the material into the material mixing chamber 506 of the printing spray head according to the feeding speed and the feeding time of the feeding module I and the feeding module II set in the program, and stopping feeding when the required feeding amount is reached;

(4-2) mixing materials, starting a negative pressure gas circuit 4 (the negative pressure value is set to be 1bar) of a gas circuit system II, setting the rotating speed and the mixing time (the rotating speed is 150rpm, the stirring time is 15s) of a stepping motor 501, vacuumizing to remove bubbles, closing the gas circuit system II4, opening a gas circuit system II 3 after the bubbles are completely eliminated, opening a control valve 508, and printing when the heating temperature of the printing platform 11 reaches 85 ℃;

and (4-3) printing, namely, conveying the uniformly mixed printing material to a printing spray head 512 by using the pressure (positive pressure 24kpa) of an air path system I adjusted by a precision pressure reducing valve, and driving an XYZ three-axis module to move according to the process parameters and the printing path set by the printing program by combining the 1500V direct-current voltage value to finish the printing of a 10% gradient layer.

And 5: after printing one layer, the Z-axis workbench 6 is lifted by 0.2mm, and after printing of the first proportioning is finished, the operations are repeated according to the material information, the geometric information and the printing mode of the second proportioning, so that printing of the second proportioning structure is finished. In the printing process, the temperature of the printing platform 11 is also increased properly along with the increase of the number of layers, and when the printing is carried out to the height of the fourth proportion, the upper curing module 10 is started to cure the top of the structure.

Step 6: the above operations are repeated to complete all printing.

And 7: and (4) post-treatment. After printing is finished, closing the feeding module 1 and the feeding module 2; closing the control valve 508; closing the gas circuit system I3 and the gas circuit system II 4; turning off the high-voltage direct-current power supply 14; the heating function of the printing platform 11 is turned off; closing the upper curing module 10; and closing the printing nozzle mixing functional group, returning the printing nozzle module 5 to the initial printing position of the workbench, and taking down the PDMS/SiC functional gradient substrate after printing.

Example 2

Further, in this embodiment, air circuit system II4 is changed into atmospheric air circuit 4, its working pressure: 0 pa.

The invention uses PDMS/SiO₂The functionally graded substrate is an embodiment, a working method for realizing the integrated manufacture of continuous functionally graded materials and structures is realized, and specific process flow steps are described as follows:

step 1: print data file preparation. Determining the SiO of the functionally graded substrate from one side (outer surface) to the other side (inner surface) according to the structural requirements of the printed matter₂The concentration of the ink is continuously changed from 0% to 50%, the printing height of each layer is determined to be 0.2mm, and the line spacing is set to be 0.3 mm.

Step 2: and (4) pretreatment before printing. PDMS elastomer and curing agent were mixed as 10: 1 and then the mixture is uniformly mixed and vacuumized to prepare pure PDMS (printing material I). Preparing the printing liquid with variable components, and preparing SiO by ultrasonic vibration method₂PDMS/SiO with 50% content₂Mixing the mixed solution with stirring to obtain SiO₂The particles are uniformly dispersed in PDMS solution to prepare high-concentration PDMS/SiO₂Mixed solution (printing material II). Printing materials I (pure PDMS), SiO₂PDMS/SiO with 50% concentration₂The mixed liquid (printing material II) is respectively placed in the feeding module 1 and the feeding module 2, the heating temperature of the printing platform 11 is set to 80 ℃, the printing spray head module 5 is in a standby state, each moving platform is in an enabling state, and the whole preparation before printing is completed.

And step 3: printing a gradient structure:

(3-1) feeding, closing the gas circuit system I3, closing the control valve 508, and feeding into the active mixing nozzle mixing chamber according to the feeding speed and feeding time of the feeding module I and the feeding module II set in the program;

(3-2) mixing materials, setting proper rotating speed of a stepping motor 501 and proper mixing time (the rotating speed is 160rpm, the stirring time is 10s), fully mixing two printing materials in a mixing chamber, opening an air path system I3, opening a control valve 508, and printing when the heating temperature of a printing platform 11 reaches 70 ℃;

(3-3) printing, wherein the uniformly mixed printing material is conveyed to a printing spray head 512 by using the pressure (positive pressure 20kpa) of an air path system I3 adjusted by a precision pressure reducing valve, a stainless steel needle head is adopted as the conductive nozzle 512, the type 21G (the outer diameter is 810 microns, and the inner diameter is 510 microns), a high-voltage direct-current power supply 14 is started, the voltage value is adjusted to 1300V, and then the XYZ three-axis module is driven to move according to the process parameters and the printing path set by the printing program to print.

And 4, step 4: when printing one layer, the Z-axis worktable 6 rises by 0.2mm, and the feeding speed of the feeding modules I and II is changed along with the increase of the layer number, so that SiO is enabled₂The concentration of (b) is continuously varied. During printing, the temperature of the printing platform 11 is increased as the number of layers increases, and when the proper height is printed, the upper curing module 10 is opened to cure the top of the structure.

And 5: the above operations are repeated, and all printing is completed.

Step 6: and (5) post-treatment. After printing is finished, closing the feeding module 1 and the feeding module 2; closing the control valve 508; the gas path system I3 and the high-voltage direct-current power supply 14 are closed, and the heating function of the printing platform 11 is closed; closing the upper curing module 10; closing the printing nozzle mixing function group, returning the printing nozzle module 5 to the initial printing position of the workbench, and taking down the PDMS/SiO which is printed₂A functionally graded substrate.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. Functional gradient material and structure integration manufacturing's 3D printing device, its characterized in that: the method comprises the following steps:

a three-dimensional moving support;

the nozzle and the stepping motor are oppositely arranged at the other end of the shell, a material flow passage between the nozzle and the mixing chamber is provided with a control valve, the control valve is a normally closed electromagnetic valve, the upper surface of the control valve is connected with the mixing chamber through threads, and the lower surface of the control valve is connected with the printing nozzle;

an air path I opening and an air path II opening are formed in the side wall of the shell between the mixing chamber and the stepping motor and are respectively connected with an air source and a vacuum pump, and after the solid-liquid mixture is uniformly mixed, the mixing chamber is vacuumized;

the mixing chamber comprises a pre-mixing chamber and a secondary mixing chamber which are communicated with each other, the secondary mixing chamber is positioned below the pre-mixing chamber, the nozzle is positioned below the secondary mixing chamber, the horizontal cross-sectional area of the secondary mixing chamber is larger than that of the pre-mixing chamber, the side wall of the pre-mixing chamber is provided with a printing material I inlet and a printing material II inlet, and the ratio of the diameter of the stirring paddle to the diameter of the pre-mixing chamber is 1: 1.2-2;

the ratio of the diameter of the stirring paddle to the diameter of the secondary mixing chamber is 1: 3-4;

the height of the pre-mixing chamber is 10mm-50mm, and the height of the secondary mixing chamber is 5mm-35 mm;

2. The 3D printing device according to claim 1, wherein: part of the blades are rectangular blades, the blades are vertical to the section direction of the stirring rod and parallel to the axial direction of the stirring rod, and the part of the blades are arranged at positions far away from the free end part of the stirring rod;

the blades provided at the free end of the stirring rod are in the shape of a right triangle.

3. The 3D printing method for integrally manufacturing the functional gradient material and the structure is characterized in that: printing using the functionally graded material of claim 1 integrally manufactured with a structure 3D printing device, comprising the steps of:

uniformly mixing the liquid and the solid powder, or uniformly mixing the printing material I and the solid powder to prepare a printing material II;

preheating a printing platform;

after printing one layer, the printing nozzle is lifted to the height of the next layer along the Z direction, and the processes of material mixing, bubble removing and printing of the next layer are carried out according to the program setting until the whole gradient geometric structure is printed;

4. The 3D printing method according to claim 3, characterized in that: the preparation method of the printing material II comprises the steps of firstly preliminarily stirring and mixing liquid and solid powder, and then putting the mixed material into an ultrasonic disperser for uniformly mixing.

5. The 3D printing method according to claim 3, characterized in that: the temperature of the printing platform after preheating is 30-180 ℃;

the working range of the positive pressure gas circuit is 30-80 kpa;

6. The 3D printing method according to claim 3, characterized in that: the high-voltage power supply is configured to be capable of outputting direct-current high voltage, outputting alternating-current high voltage and outputting pulse high voltage, and is capable of setting bias voltage, wherein the set bias voltage range is 0-2KV continuously adjustable, the direct-current high voltage is 0-5KV, the output pulse direct-current voltage is 0- +/-4 KV continuously adjustable, the output pulse frequency is 0Hz-3000Hz continuously adjustable, and the alternating-current high voltage is 0- +/-4 KV.

7. The 3D printing method according to claim 3, characterized in that: the liquid is PDMS, Ecoflex, SEBS block copolymer, photosensitive resin, hydrogel thermosetting or photo-curing material;

the solid powder is SiC or SiO₂、Al₂O₃、TiO₂Graphene, carbon nanotube reinforcement phase material or modified material.

8. The 3D printing method according to claim 3, wherein: mixing the printing material I and the printing material II in a continuous gradient proportion;

alternatively, the printing material I and the printing material II are mixed in discrete gradient proportions.

9. The 3D printing method according to claim 3, wherein: the different printing modes are specifically: for a macro structure, the printing material is extruded and deposited on a substrate or a formed structure by directly utilizing the pressure of a positive pressure air path of a printing nozzle air path system I, if the micro-scale feature structure is printed, a high-voltage power supply is started, and the printing material is sprayed and deposited on the substrate or the formed structure by utilizing an electric field to drive a 3D (three-dimensional) spraying and depositing printing process.