阅读说明：本技术 均匀金属微滴喷射3d打印孔洞缺陷的抑制方法 (Method for inhibiting hole defects in uniform metal droplet jetting 3D printing ) 是由 伊浩 刘蒙霖 曹华军 齐乐华 邓巍巍 渠达 于 2021-01-19 设计创作，主要内容包括：发明提供均匀金属微滴喷射3D打印孔洞缺陷的抑制方法。该方法包括打印初始化、打印原材料供给、启动感应加热器、启动加热板、启动按需式均匀金属微滴发生器、金属微滴沉积等步骤。本方法提出采用电场诱导作用来抑制均匀金属微滴喷射打印制件内部孔洞缺陷的新思路,利用电场触发金属微滴底部生成泰勒锥,使得金属微滴底部中心区域与沉积基体间预先接触,在根本上抑制微滴碰撞过程中的卷气行为,并利用电场导向吸引作用促进金属微滴对沉积凝固层表面空隙区域的流动填充,实现打印制件内部孔洞缺陷的有效抑制,有望突破均匀金属微滴喷射打印制件致密度难以进一步提升的技术瓶颈。(The invention provides a method for inhibiting hole defects in uniform metal droplet jetting 3D printing. The method comprises the steps of printing initialization, printing raw material supply, starting an induction heater, starting a heating plate, starting an on-demand uniform metal droplet generator, metal droplet deposition and the like. The method provides a new idea of inhibiting the internal hole defects of the uniform metal droplet jet printing workpiece by adopting an electric field induction effect, the electric field is used for triggering the bottom of the metal droplet to generate a Taylor cone, so that the central area of the bottom of the metal droplet is in contact with a deposition matrix in advance, the air entrainment behavior in the droplet collision process is fundamentally inhibited, the electric field guiding attraction effect is used for promoting the flow filling of the metal droplet on the surface gap area of a deposition solidified layer, the internal hole defects of the printing workpiece are effectively inhibited, and the technical bottleneck that the density of the uniform metal droplet jet printing workpiece is difficult to further improve is hopefully broken through.)

1. The method for inhibiting the hole defects in the 3D printing of the uniform metal droplet ejection is characterized by comprising the following steps of:

1) selecting metal or alloy as a printing raw material, and treating oxide skin and impurities on the surface of the printing raw material;

2) feeding the treated printing stock material to an on-demand uniform metal droplet generator; wherein the on-demand uniform metal droplet generator (1) is arranged in a low oxygen low water environment (11); an induction heater (2) is arranged on the outer wall of the on-demand uniform metal droplet generator (1); the bottom of the on-demand uniform metal droplet generator (1) is provided with a nozzle (3); the on-demand uniform metal droplet generator (1) is arranged above a deposition substrate; the on-demand uniform metal droplet generator (1) is grounded;

3) starting the induction heater (2); the induction heater (2) generates heat to heat the printing raw materials, and the printing raw materials are melted into molten liquid metal or alloy;

4) printing initialization; moving the three-dimensional workbench (10) to a printing position, and adjusting the distance between the deposition substrate (7) and the nozzle (3) to a set distance; wherein the three-dimensional table (10) is grounded; an insulating plate (9), a heating plate (8) and a deposition substrate (7) are sequentially laid on the upper surface of the three-dimensional workbench (10) from bottom to top; the deposition substrate (7) is connected with the positive electrode of the high-voltage direct-current power supply I; the three-dimensional workbench (10) is provided with an X-direction moving axis, a Y-direction moving axis and a Z-direction moving axis, and realizes the motion in three directions of XYZ; the deposition substrate (7), the heating plate (8), the insulating plate (9) and the three-dimensional workbench (10) are all arranged in a low-oxygen low-water environment (11);

5) starting a heating plate (8) to carry out preheating treatment on the deposition substrate (7);

6) starting the uniform metal droplet generator (1) according to the requirement, and exciting molten metal or alloy raw materials to extrude out of the nozzle (3) to form a liquid flow;

7) under the induction of the charging electrode (4), negative charges are gathered on the liquid flow; when the length of the liquid flow reaches a certain threshold value, the liquid flow is broken to form negatively charged metal droplets (5); wherein the whole charging electrode (4) is of an annular sheet structure; the charging electrode (4) is provided with a hole for the charged metal droplet (5) to pass through; the charging electrode (4) is arranged between the nozzle (3) and the deposition substrate (7); the charging electrode (4) is communicated with the positive electrode of the periodic high-voltage pulse power supply; the periodic high-voltage pulse power supply intermittently powers up the charging electrode (4);

8) the charged metal droplets (5) with negative charges fly to the electrified deposition substrate (7) through holes on the charging electrode (4); an electric field is gradually formed between the negatively charged metal droplets (5) and the deposition substrate (7); the electric field strength increases as the distance between the two decreases; under the induction of an electric field, the charges are redistributed inside the charged metal droplets (5), and negative charges are gathered at the bottom of the droplets, so that Maxwell stress is increased; when the electric field strength reaches a certain level, the charge level of the charged metal droplets (5) rises above a critical charge level, the charged metal droplets (5) overcome the surface tension and the pressure of the surrounding gas under the action of Maxwell stress to deform, and a Taylor cone (13) is generated at the bottom of the charged metal droplets (5);

9) depositing negatively charged droplets (5) of charged metal onto a deposition substrate (7); the Taylor cone (13) at the bottom of the negatively charged metal droplet (5) is firstly contacted with the surface of the deposition substrate (7), and the environmental gas in the droplet deposition area is discharged out in a following flowing spreading process;

10) according to a digital model of a formed part, repeatedly controlling an on-demand uniform metal droplet generator (1) to generate charged metal droplets (5), and controlling the coordination and matching between the printing deposition of the charged metal droplets (5) and the motion of a three-dimensional workbench (10) to realize the dropwise printing of a first deposition layer;

11) after the former deposition layer is formed, the Z-axis direction of the three-dimensional workbench (10) descends by a deposition layer height; depositing a new printing deposition substrate with the deposited solidified layer (14); -depositing droplets (5) of electrically charged metal on the deposited solidified layer (14); wherein newly incident charged metal droplets (5) and the deposited solidified layer (14) undergo microdomain remelting to form a remelted region (15); the guiding attraction effect of the electric field promotes the flowing filling of the charged metal droplets (5), and further promotes the complete filling of the charged metal droplets (5) to the tiny gaps (16) on the surface of the solidified layer (14);

12) repeating the step 11), realizing the drop-by-drop layer-by-layer printing until the forming is finished, and finally forming a formed part (6);

13) and (3) shutting down the whole printing and deposition system, taking the formed part (6) out of the low-oxygen and low-water environment (11), and tempering the formed part (6).

2. The method of suppressing uniform metal droplet ejection 3D printing hole defects according to claim 1, wherein: the induced charge quantity is adjusted by adjusting the pulse width and the frequency of the high-voltage pulse power supply.

3. The method of suppressing uniform metal droplet ejection 3D printing hole defects according to claim 1, wherein: the voltage of the high-voltage direct-current power supply I is continuously adjustable within the range of 0-1000V; the voltage of the periodic high-voltage pulse power supply is continuously adjustable within the range of 500-5000V.

4. The method for inhibiting the hole defects in the 3D printing of the uniform metal droplet ejection is characterized by comprising the following steps of:

1) selecting metal or alloy as a printing raw material, and treating oxide skin and impurities on the surface of the printing raw material;

2) feeding the treated printing stock material to an on-demand uniform metal droplet generator; wherein the on-demand uniform metal droplet generator (1) is arranged in a low oxygen low water environment (11); an induction heater (2) is arranged on the outer wall of the on-demand uniform metal droplet generator (1); the bottom of the on-demand uniform metal droplet generator (1) is provided with a nozzle (3); the on-demand uniform metal droplet generator (1) is arranged above a deposition substrate; the on-demand uniform metal droplet generator (1) is grounded;

3) starting the induction heater (2); the induction heater (2) generates heat to heat the printing raw materials, and the printing raw materials are melted into molten liquid metal or alloy;

4) printing initialization; moving the three-dimensional workbench (10) to a printing position, and adjusting the distance between the deposition substrate (7) and the nozzle (3) to a set distance; wherein the three-dimensional table (10) is grounded; an insulating plate (9), a heating plate (8) and a deposition substrate (7) are sequentially laid on the upper surface of the three-dimensional workbench (10) from bottom to top; the deposition substrate (7) is connected with the positive electrode of the high-voltage direct-current power supply I; the three-dimensional workbench (10) is provided with an X-direction moving axis, a Y-direction moving axis and a Z-direction moving axis, and realizes the motion in three directions of XYZ; the deposition substrate (7), the heating plate (8), the insulating plate (9) and the three-dimensional workbench (10) are all arranged in a low-oxygen low-water environment (11);

5) starting a heating plate (8) to carry out preheating treatment on the deposition substrate (7);

6) starting the uniform metal droplet generator (1) according to the requirement, and exciting molten metal or alloy raw materials to extrude out of the nozzle (3) to form a liquid flow;

7) under the induction of the charging electrode (4), negative charges are gathered on the liquid flow; when the length of the liquid flow reaches a certain threshold value, the liquid flow is broken to form negatively charged metal droplets (5); wherein the charging electrode (4) is arranged between the nozzle (3) and the deposition substrate (7); an electric field shielding plate is arranged below the charging electrode (4); the charging electrode (4) and the electric field shielding plate are both of annular sheet structures; holes for the charged metal droplets (5) to pass through are arranged on the charging electrode (4) and the electric field shielding plate; the outer diameter of the electric field shielding plate is larger than that of the charging electrode (4), and the inner diameter of the electric field shielding plate is smaller than that of the charging electrode (4); the charging electrode (4) is connected with the positive electrode of the high-voltage direct-current power supply II; the electric field shielding plate is subjected to grounding treatment;

8) the charged metal droplets (5) with negative charges fly to the electrified deposition substrate (7) through holes on the charging electrode (4); an electric field is gradually formed between the negatively charged metal droplets (5) and the deposition substrate (7); the electric field strength increases as the distance between the two decreases; under the induction of an electric field, the charges are redistributed inside the charged metal droplets (5), and negative charges are gathered at the bottom of the droplets, so that Maxwell stress is increased; when the electric field strength reaches a certain level, the charge level of the charged metal droplets (5) rises above a critical charge level, the charged metal droplets (5) overcome the surface tension and the pressure of the surrounding gas under the action of Maxwell stress to deform, and a Taylor cone (13) is generated at the bottom of the charged metal droplets (5);

9) depositing negatively charged droplets (5) of charged metal onto a deposition substrate (7); the Taylor cone (13) at the bottom of the negatively charged metal droplet (5) is firstly contacted with the surface of the deposition substrate (7), and the environmental gas in the droplet deposition area is discharged out in a following flowing spreading process;

10) according to a digital model of a formed part, repeatedly controlling an on-demand uniform metal droplet generator (1) to generate charged metal droplets (5), and controlling the coordination and matching between the printing deposition of the charged metal droplets (5) and the motion of a three-dimensional workbench (10) to realize the dropwise printing of a first deposition layer;

11) after the former deposition layer is formed, the Z-axis direction of the three-dimensional workbench (10) descends by a deposition layer height; depositing a new printing deposition substrate with the deposited solidified layer (14); -depositing droplets (5) of electrically charged metal on the deposited solidified layer (14); wherein newly incident charged metal droplets (5) and the deposited solidified layer (14) undergo microdomain remelting to form a remelted region (15); the guiding attraction effect of the electric field promotes the flowing filling of the charged metal droplets (5), and further promotes the complete filling of the charged metal droplets (5) to the tiny gaps (16) on the surface of the solidified layer (14);

12) repeating the step 11), realizing the drop-by-drop layer-by-layer printing until the forming is finished, and finally forming a formed part (6);

13) and (3) shutting down the whole printing and deposition system, taking the formed part (6) out of the low-oxygen and low-water environment (11), and tempering the formed part (6).

5. The method of suppressing uniform metal droplet ejection 3D printing hole defects according to claim 4, wherein: the voltage of the high-voltage direct-current power supply I is continuously adjustable within the range of 0-1000V; and the voltage of the high-voltage direct-current power supply II is continuously adjustable within the range of 500-5000V.

6. The method for suppressing void defects in uniform metal droplet ejection 3D printing according to claim 1 or 4, wherein: in the step 1), removing oxide skin and impurities on the surface of the printing raw material by adopting a method combining surface mechanical grinding and acid-base corrosion.

7. The method of suppressing uniform metal droplet ejection 3D printing hole defects according to claim 1 or 4, wherein: the inner diameter of the nozzle (3) is 1-1000 mu m. An inert gas glove box is adopted in the low-oxygen and low-water environment (11); the oxygen and water vapor contents in the box body are both below 5 PPM.

8. The method of suppressing uniform metal droplet ejection 3D printing hole defects according to claim 1 or 4, wherein: the deposition substrate (7) is made of a metal material.

9. The method of suppressing uniform metal droplet ejection 3D printing hole defects according to claim 1 or 4, wherein: the deposition substrate (7) is made of non-metal materials; the surface of the deposition substrate (7) is coated with a metal plating layer.

10. The method of suppressing uniform metal droplet ejection 3D printing hole defects according to claim 1 or 4, wherein: a thermocouple (12) measures the temperature of the on-demand uniform metal droplet generator and the deposition substrate (7) in real time.

Technical Field

The invention relates to the technical field of uniform metal droplet jetting 3D printing, in particular to a method for inhibiting hole defects in uniform metal droplet jetting 3D printing.

Background

The additive manufacturing technology based on uniform metal droplet ejection is a new technology different from the traditional metal 3D printing, and is characterized in that parameters such as pulse pressure, vibration waveform and the like are controlled to enable molten metal to be ejected to form uniform droplets of micron-submillimeter scales, then the three-dimensional motion of a deposition substrate is accurately controlled to be matched with the droplets ejected according to needs, point-by-point, line-by-line and layer-by-layer printing of the metal droplets is realized according to a preset scanning track, and finally a target three-dimensional structure is formed. The uniform metal droplet jetting 3D printing technology has the advantages of high ink-jet printing resolution, fine atomized spraying deposition crystal grains and the like, does not need special raw materials and special expensive equipment, and has unique advantages in the aspect of rapid manufacturing of micro complex parts, functional devices and the like. However, the uniform metal droplet ejection 3D printing technology uses discrete metal droplets as a manufacturing unit, and the continuous deposition process of the metal droplets is usually accompanied by phenomena such as gas entrapment and incomplete flow filling, so that the printed parts have many fine hole defects inside, which usually cause stress concentration and trigger crack initiation in the service process of the parts, and finally cause failure of the parts, thereby severely restricting the practical application of the technology.

In the prior art, the density of a metal droplet jet printing part is improved by optimizing and controlling process parameters such as the scanning step distance in/between uniform metal droplet layers, the temperature of a deposited substrate and the like. However, the method is mainly based on the rule of influence of process parameters on the macroscopic density of a printed part, and the detailed forming process of the hole defects in the technology and potential influence factors thereof are not considered yet.

In the process of uniform metal droplet jet printing, the behavior of liquid droplet collision air entrainment is the physical essence of liquid droplet collision dynamics, and under the combined action of local rapid solidification of metal droplets and high resistance caused by a strong melt Marangoni-driven flow, air bubbles entrapped at the bottom of the metal droplets are difficult to discharge under the drive of buoyancy, so that the defect of an air hole formed by air entrainment is difficult to effectively inhibit by optimizing and controlling process parameters; secondly, the surface of a deposited layer formed by continuously accumulating a plurality of metal droplets usually forms a 'shell' -shaped uneven characteristic morphology spontaneously, when molten metal liquid flows and fills in gaps on the surface of the deposited layer, due to the balance among capillary action force of the metal liquid, surface tension and reverse resistance of gas in a filling area, the flowing and filling process usually has an infiltration limit, namely, the tiny gaps in the interface area of the deposited layer are difficult to be completely filled by relying on the spreading and flowing of the metal droplets only.

Based on the above characteristics, the hole defect inside the uniform metal droplet ejection 3D printing part has been a conventional defect which is difficult to be eradicated.

Disclosure of Invention

The invention aims to provide a method for inhibiting the defects of uniform metal droplet jetting 3D printing holes so as to solve the problems in the prior art.

The technical scheme adopted for achieving the aim of the invention is that the method for inhibiting the uniform metal droplet jetting 3D printing hole defects comprises the following steps:

1) selecting metal or alloy as a printing raw material, and treating oxide skin and impurities on the surface of the printing raw material.

2) The treated printing stock material is fed to a uniform metal droplet generator on demand. Wherein the on-demand uniform metal droplet generator is disposed in a low oxygen, low water environment. An induction heater is arranged on the outer wall of the on-demand uniform metal droplet generator. The bottom of the on-demand uniform metal droplet generator is provided with a nozzle. The on-demand uniform metal droplet generator is disposed above a deposition substrate. The on-demand uniform metal droplet generator is grounded.

3) The induction heater is activated. The induction heater generates heat to heat the printing raw materials, and the printing raw materials are melted into molten liquid metal or alloy.

4) And (5) printing initialization. And moving the three-dimensional workbench to a printing position, and adjusting the distance between the deposition substrate and the nozzle to a set distance. And the three-dimensional workbench is grounded. And an insulating plate, a heating plate and a deposition substrate are sequentially laid on the upper surface of the three-dimensional workbench from bottom to top. And the deposition substrate is connected with the anode of a high-voltage direct current power supply I. The three-dimensional workbench is provided with an X-direction moving axis, a Y-direction moving axis and a Z-direction moving axis, and movement in three directions of XYZ is realized. The deposition substrate, the heating plate, the insulating plate and the three-dimensional workbench are all arranged in a low-oxygen and low-water environment.

5) And starting the heating plate to perform preheating treatment on the deposition substrate.

6) The on-demand uniform metal droplet generator is activated to initiate extrusion of molten metal or alloy starting material at the nozzle to form a stream.

7) Under the induction of the charging electrode, negative charges are accumulated on the liquid flow. When the length of the stream reaches a certain threshold, the stream breaks to form negatively charged metal droplets. Wherein, the whole charging electrode is of an annular sheet structure. And the charging electrode is provided with a hole for the charged metal micro-droplet to pass through. The charging electrode is disposed between the nozzle and the deposition substrate. And the charging electrode is communicated with the positive electrode of the periodic high-voltage pulse power supply. The periodic high-voltage pulse power supply intermittently energizes the charging electrode.

8) The negatively charged metal droplets fly through the holes in the charging electrode toward the energized deposition substrate. An electric field is developed between the negatively charged metal droplets and the deposition substrate. The electric field strength increases as the distance between the two decreases. Under the induction of an electric field, the charge is redistributed inside the charged metal droplet and negative charges accumulate at the bottom of the droplet, thereby increasing the maxwell stress. When the electric field strength reaches a certain level, the charge level of the charged metal droplets rises above a critical charge level, the charged metal droplets overcome the surface tension and the ambient gas pressure under the action of Maxwell stress to deform, and a Taylor cone is generated at the bottom of the charged metal droplets.

9) Negatively charged droplets of charged metal are deposited onto a deposition substrate. The taylor cone at the bottom of the negatively charged metal droplet makes initial contact with the deposition substrate surface and ambient gas in the droplet deposition area is subsequently vented during the subsequent flow spreading process.

10) And repeatedly controlling an on-demand uniform metal droplet generator to generate charged metal droplets according to a digital model of a formed workpiece, and controlling the coordination and matching between the printing deposition of the charged metal droplets and the motion of a three-dimensional workbench to realize the dropwise printing of the first deposition layer.

11) And after the last deposition layer is formed, the Z-axis direction of the three-dimensional workbench descends by a deposition layer height. The deposited solidified layer will serve as a new print deposition matrix. Droplets of charged metal are deposited on the deposited solidified layer. Wherein newly incident charged metal droplets and the deposited solidified layer undergo microdomain remelting to form a remelted region. The guiding attraction of the electric field promotes the flow filling of the charged metal droplets, and thus promotes the complete filling of the charged metal droplets into the micro-voids on the surface of the solidified layer.

12) And step 11) is repeated, and the printing layer by layer is gradually dropped until the forming is finished, and finally the formed part is formed.

13) And (4) closing the whole printing and deposition system, taking the formed part out of the low-oxygen and low-water environment, and tempering the formed part.

Further, the induced charge amount is adjusted by adjusting the pulse width and frequency of the high-voltage pulse power supply.

Further, the voltage of the high-voltage direct-current power supply I is continuously adjustable within the range of 0-1000V. The voltage of the periodic high-voltage pulse power supply is continuously adjustable within the range of 500-5000V.

The invention also provides a method for inhibiting the hole defects of the uniform metal droplet jetting 3D printing, which comprises the following steps:

1) selecting metal or alloy as a printing raw material, and treating oxide skin and impurities on the surface of the printing raw material.

2) The treated printing stock material is fed to a uniform metal droplet generator on demand. Wherein the on-demand uniform metal droplet generator is disposed in a low oxygen, low water environment. An induction heater is arranged on the outer wall of the on-demand uniform metal droplet generator. The bottom of the on-demand uniform metal droplet generator is provided with a nozzle. The on-demand uniform metal droplet generator is disposed above a deposition substrate. The on-demand uniform metal droplet generator is grounded.

3) The induction heater is activated. The induction heater generates heat to heat the printing raw materials, and the printing raw materials are melted into molten liquid metal or alloy.

4) And (5) printing initialization. And moving the three-dimensional workbench to a printing position, and adjusting the distance between the deposition substrate and the nozzle to a set distance. And the three-dimensional workbench is grounded. And an insulating plate, a heating plate and a deposition substrate are sequentially laid on the upper surface of the three-dimensional workbench from bottom to top. And the deposition substrate is connected with the anode of a high-voltage direct current power supply I. The three-dimensional workbench is provided with an X-direction moving axis, a Y-direction moving axis and a Z-direction moving axis, and movement in three directions of XYZ is realized. The deposition substrate, the heating plate, the insulating plate and the three-dimensional workbench are all arranged in a low-oxygen and low-water environment.

5) And starting the heating plate to perform preheating treatment on the deposition substrate.

6) The on-demand uniform metal droplet generator is activated to initiate extrusion of molten metal or alloy starting material at the nozzle to form a stream.

7) Under the induction of the charging electrode, negative charges are accumulated on the liquid flow. When the length of the stream reaches a certain threshold, the stream breaks to form negatively charged metal droplets. Wherein the charging electrode is disposed between the nozzle and the deposition substrate. And an electric field shielding plate is arranged below the charging electrode. The charging electrode and the electric field shielding plate are both of annular sheet structures. And holes for the charged metal droplets to pass through are arranged on the charging electrode and the electric field shielding plate. The outer diameter of the electric field shielding plate is larger than the outer diameter of the charging electrode, and the inner diameter of the electric field shielding plate is smaller than the inner diameter of the charging electrode. And the charging electrode is connected with the positive electrode of the high-voltage direct-current power supply II. And the electric field shielding plate is grounded.

8) The negatively charged metal droplets fly through the holes in the charging electrode toward the energized deposition substrate. An electric field is developed between the negatively charged metal droplets and the deposition substrate. The electric field strength increases as the distance between the two decreases. Under the induction of an electric field, the charge is redistributed inside the charged metal droplet and negative charges accumulate at the bottom of the droplet, thereby increasing the maxwell stress. When the electric field strength reaches a certain level, the charge level of the charged metal droplets rises above a critical charge level, the charged metal droplets overcome the surface tension and the ambient gas pressure under the action of Maxwell stress to deform, and a Taylor cone is generated at the bottom of the charged metal droplets.

9) Negatively charged droplets of charged metal are deposited onto a deposition substrate. The taylor cone at the bottom of the negatively charged metal droplet makes initial contact with the deposition substrate surface and ambient gas in the droplet deposition area is subsequently vented during the subsequent flow spreading process.

10) And repeatedly controlling an on-demand uniform metal droplet generator to generate charged metal droplets according to a digital model of a formed workpiece, and controlling the coordination and matching between the printing deposition of the charged metal droplets and the motion of a three-dimensional workbench to realize the dropwise printing of the first deposition layer.

11) And after the last deposition layer is formed, the Z-axis direction of the three-dimensional workbench descends by a deposition layer height. The deposited solidified layer will serve as a new print deposition matrix. Droplets of charged metal are deposited on the deposited solidified layer. Wherein newly incident charged metal droplets and the deposited solidified layer undergo microdomain remelting to form a remelted region. The guiding attraction of the electric field promotes the flow filling of the charged metal droplets, and thus promotes the complete filling of the charged metal droplets into the micro-voids on the surface of the solidified layer.

12) And step 11) is repeated, and the printing layer by layer is gradually dropped until the forming is finished, and finally the formed part is formed.

13) And (4) closing the whole printing and deposition system, taking the formed part out of the low-oxygen and low-water environment, and tempering the formed part.

Further, the voltage of the high-voltage direct-current power supply I is continuously adjustable within the range of 0-1000V. And the voltage of the high-voltage direct-current power supply II is continuously adjustable within the range of 500-5000V.

Further, in the step 1), removing oxide skin and impurities on the surface of the printing raw material by adopting a method combining surface mechanical grinding and acid-base corrosion.

Further, the inner diameter of the nozzle is 1-1000 μm. The low oxygen and low water environment adopts an inert gas glove box. The oxygen and water vapor contents in the box body are both below 5 PPM.

Further, the deposition substrate is a metal material.

Further, the deposition substrate is a non-metallic material. The surface of the deposition substrate is coated with a metal plating layer.

Further, the thermocouple measures the temperature of the on-demand uniform metal droplet generator and the deposition substrate in real time.

The technical effects of the invention are undoubted: the novel idea of inhibiting the internal hole defects of the uniform metal droplet jet printing part by adopting the electric field induction effect is provided, the electric field is utilized to trigger the bottom of the metal droplet to generate a Taylor cone, so that the central area of the bottom of the metal droplet is in contact with a deposition matrix in advance, the gas entrainment behavior in the droplet collision process is fundamentally inhibited, the electric field guiding attraction effect is utilized to promote the flow filling of the metal droplet to the surface gap area of a deposition solidified layer, the internal hole defects of the printing part are effectively inhibited, the technical bottleneck that the density of the uniform metal droplet jet printing part is difficult to further improve is expected to be broken through, and the foundation is laid for promoting the application of the uniform metal droplet jet 3D printing technology in the fields of high-performance micro structural parts, high-reliability.

Drawings

Fig. 1 is a schematic structural diagram of a uniform metal droplet ejection 3D printing device in embodiment 1;

FIG. 2 is a schematic diagram showing the topography evolution of a charged metal droplet deposition process on a horizontal substrate surface;

FIG. 3 is a schematic diagram of the filling of metal droplets on the surface of a deposited solidified layer in the prior art;

FIG. 4 is a schematic diagram of a flow filling process of charged metal droplets on the surface of a deposited solidified layer.

In the figure: an on-demand uniform metal droplet generator 1, an induction heater 2, a nozzle 3, a charging electrode 4, a charged metal droplet 5, a shaped article 6, a deposition substrate 7, a heating plate 8, an insulating plate 9, a three-dimensional stage 10, a low oxygen and low water environment 11, a thermocouple 12, a taylor cone 13, a deposited solidified layer 14, a re-melted zone 15, a micro-void 16.

Detailed Description

The present invention is further illustrated by the following examples, but it should not be construed that the scope of the above-described subject matter is limited to the following examples. Various substitutions and alterations can be made without departing from the technical idea of the invention and the scope of the invention is covered by the present invention according to the common technical knowledge and the conventional means in the field.

Example 1:

the method for inhibiting the hole defects in the 3D printing of the uniform metal droplet ejection is characterized by comprising the following steps of:

1) selecting metal or alloy as a printing raw material, and treating oxide skin and impurities on the surface of the printing raw material. And removing oxide skin and impurities on the surface of the printing raw material by adopting a method combining surface mechanical grinding and acid-base corrosion.

2) The treated printing stock material is fed to a uniform metal droplet generator on demand. Therein, referring to fig. 1, the on-demand uniform metal droplet generator 1 is disposed in a low oxygen, low water environment 11. An induction heater 2 is arranged on the outer wall of the on-demand uniform metal droplet generator 1. The bottom of the on-demand uniform metal droplet generator 1 is provided with a nozzle 3. The inner diameter of the nozzle 3 can be selected within the range of 1-1000 μm. The on-demand uniform metal droplet generator 1 is arranged above a deposition substrate. The on-demand uniform metal droplet generator 1 is grounded.

3) The induction heater 2 is activated. The induction heater 2 generates heat to heat the printing raw materials, and the printing raw materials are melted into molten liquid metal or alloy.

4) And (5) printing initialization. The three-dimensional table 10 is moved to the printing position, and the deposition substrate 7 is adjusted to a set distance from the nozzle 3. The deposition distance between the nozzle 3 and the deposition substrate 7 is adjusted according to actual requirements. Wherein the three-dimensional table 10 is grounded. And an insulating plate 9, a heating plate 8 and a deposition substrate 7 are sequentially paved on the upper surface of the three-dimensional workbench 10 from bottom to top. The deposition substrate 7 is connected with the positive electrode of the high-voltage direct current power supply I. The magnitude of the voltage of the high voltage dc power supply I affects the strength of the electric field between the charged metal droplets 5 and the energized deposition substrate 7. The voltage of the high-voltage direct-current power supply I is continuously adjustable within the range of 0-1000V. In actual production, the voltage of the high-voltage direct-current power supply I is determined according to actual process conditions, and the purpose of inducing the bottom of the charged metal droplet 5 to generate the Taylor cone is achieved. The insulating plate 9 effectively insulates the deposition substrate 7 from the three-dimensional stage 10. The three-dimensional table 10 has an X-direction movement axis, a Y-direction movement axis, and a Z-direction movement axis, and realizes movements in three XYZ directions. The deposition substrate 7, the heating plate 8, the insulating plate 9, and the three-dimensional stage 10 are all disposed in a low-oxygen and low-water environment 11.

5) The heating plate 8 is activated to perform a preheating process on the deposition substrate 7. It is worth noting that the thermocouple 12 measures the temperature of the on-demand uniform metal droplet generator and the deposition substrate 7 in real time. The thermocouple 12 measures the heating temperature of the metal or alloy and the preheating temperature of the deposition substrate 7 in real time, and then feeds back data to the induction heater 2 and the heating plate 8, thereby realizing closed-loop control of the temperature of the metal or alloy material and the preheating temperature of the substrate.

6) The on-demand homogeneous metal droplet generator 1 is activated to initiate extrusion of molten metal or alloy starting material at the nozzle 3 to form an unbroken stream.

7) Under the induction of the charging electrode 4, negative charges are accumulated on the liquid flow. When the length of the liquid flow reaches a certain threshold value, the liquid flow is broken to form negatively charged metal droplets 5, and the charging process of the charged metal droplets 5 is completed. The actual amount of charge of the charged metal droplets 5 is q and the rayleigh limit of the charged metal droplets 5 is q_R。Where ε is the gas dielectric constant in the deposition atmosphere E. δ is the surface tension of the charged metal droplet 5. R is the radius of the charged metal droplet 5.

Wherein, the whole charging electrode 4 is of an annular sheet structure. The charging electrode 4 is provided with a hole for the charged metal droplet 5 to pass through. The charging electrode 4 is arranged between the nozzle 3 and the deposition substrate 7. The charging electrode 4 is connected with the positive pole of the periodic high-voltage pulse power supply. The induced charge quantity is adjusted by adjusting the pulse width and the frequency of the high-voltage pulse power supply. The voltage of the periodic high-voltage pulse power supply is continuously adjustable within the range of 500-5000V. In actual production, the voltage of the periodic high-voltage pulse power supply is determined according to the droplet size and actual requirements. The periodic high-voltage pulse power supply intermittently energizes the charging electrode 4. The droplets are charged by the charging electrode 4 when the high voltage pulse power supply is turned on. The high-voltage pulse power supply is in a disconnected state in the time period before and after the charged metal droplets 5 are in contact with the deposition substrate 7, so that the influence of an interference electric field on the spreading and deposition of the charged metal droplets 5 is avoided.

8) The negatively charged metal droplets 5 fly through the holes in the charging electrode 4 towards the energized deposition substrate 7. An electric field is gradually formed between the negatively charged metal droplets 5 and the deposition substrate 7. The electric field strength increases as the distance between the two decreases. Under the induction of an electric field, the charge is redistributed inside the charged metal droplet 5 and negative charges accumulate at the bottom of the droplet, thereby increasing the maxwell stress. When the electric field strength reaches a certain level, the charge level of the charged metal droplets 5 rises above the critical charge level, the charged metal droplets 5 deform under the maxwell stress against the surface tension and the ambient gas pressure, and the bottom of the charged metal droplets 5 generates taylor cones 13.

To quantify the charge of the charged metal droplets 5, a dimensionless charge level is defined as Γ ═ q/q_RIn the formula, gammaFor a dimensionless charge level of the charged metal droplets 5 and q the actual amount of charge of the charged metal droplets 5, the amount of charge q of the charged metal droplets 5 can be directly measured by a charge amplifier, q_RThe rayleigh limit of the charged metal droplet 5 (the maximum amount of charge that the charged metal droplet 5 can carry while ensuring that it does not break up). The dimensionless charge level Γ describes the maximum amount of charge that the charged metal droplet 5 can carry before the electrical stress overcomes the surface tension of the charged metal droplet 5, where control of the charged amount of the charged metal droplet 5 can be achieved by adjusting the voltage of a high voltage pulsed power supply in communication with the charging electrode 4. When the charge level of the charged metal droplet 5 rises above a critical level of about 1% rayleigh limit, the maxwell stress overcomes the accumulated gas pressure and surface tension of the charged metal droplet 5, deforming the bottom of the charged metal droplet 5 to produce a taylor cone 13. Wherein the Rayleigh limit isWhere ε is the gas dielectric constant in the deposition environment 11, δ is the surface tension of the charged metal droplet 5, and R is the radius of the charged metal droplet 5. Theoretical critical charge ofDepending only on the capillary number Ca based on the gas viscosity, Ca ═ μ gU/δ, where μ is the viscosity of the charged metal droplet 5 starting material, g is the acceleration of gravity, U is the deposition velocity, and δ is the charged metal droplet 5 surface tension.

9) Referring to fig. 2, the deposition spreading behavior of a single charged metal droplet 5 towards a deposition substrate 7 undergoes collisions, spreading and solidification. The taylor cone 13 at the bottom of the charged metal droplet 5 makes initial contact with the surface of the deposition substrate 7. Driven by inertial forces, the charged metal droplets 5 flow and spread. The ambient gas in the droplet deposition area is discharged with a potential to spread to a maximum diameter.

10) According to the digital model of the formed part, the uniform metal droplet generator 1 on demand is repeatedly controlled to generate the charged metal droplets 5, and the coordination matching between the printing deposition of the charged metal droplets 5 and the movement of the three-dimensional workbench 10 is controlled, so that the first deposition layer is printed dropwise.

11) After the last deposition layer is formed, the Z-axis direction of the three-dimensional table 10 is lowered by one deposition layer height. With the solidified layer 14 already deposited, the substrate will be deposited as a new print. Charged metal droplets 5 are deposited on the deposited solidified layer 14.

The surface of the deposited solidified layer 14 formed by the multiple droplets deposited in succession may not be completely smooth under the action of surface tension. Can be approximately regarded as a continuous arc composition, and a tiny gap 16 exists between adjacent droplets.

Referring to fig. 3, in the conventional uniform metal droplet jet printing process, when molten metal flows and fills into the gaps on the surface of the deposited layer, the infiltration limit exists in the flow filling process due to the effect of reverse resistance. The small arrows in the figure indicate the opposing resistance against further filling of the droplets.

Referring to fig. 4, in this embodiment, when a deposited droplet is brought into contact with an already deposited droplet, the newly incident charged metal droplet 5 and the already deposited solidified layer 14 undergo micro-domain interfusion to form a re-melted region 15. The guiding attraction of the electric field promotes the flow spreading of the charged metal droplets 5, and thus promotes the complete filling of the minute voids 16 on the surface of the solidified layer 14 by the charged metal droplets 5.

12) And step 11) is repeated, and the printing layer by layer is gradually dropped until the forming is finished, and finally the formed part 6 is formed.

13) The entire printing deposition system is shut down, the shaped article 6 is removed from the low oxygen, low water environment 11, and the shaped article 6 is tempered.

According to the embodiment, by means of the characteristic that the charged liquid drop deforms under the induction of the electric field, the collision deposition behavior of the metal droplet is regulated and controlled, so that a Taylor cone is generated at the bottom of the metal droplet in the process of approaching the substrate, the central area of the bottom of the metal droplet is controlled to be in contact with the substrate in advance, the form and the motion track of a solid-liquid-gas three-phase contact line are changed, the environmental gas in the droplet deposition micro-domain is exhausted, and the gas entrainment behavior of the collision deposition of the metal droplet is fundamentally inhibited. Meanwhile, the spreading and flowing of the molten metal droplets can be promoted by the guiding and attracting action of the electric field, so that the droplets are spread more sufficiently, good filling of a layer interface micro-gap area is facilitated, and the purpose of directly printing and forming a high-densification workpiece is further achieved.

Example 2:

this example applies example 1 to the printing and forming of a high-density block of 7075 aluminum alloy. The main steps of this example are the same as example 1.

In the present embodiment, the nozzle 3 is positioned in focus to the initial deposition position by controlling the coordinated movement of the X-axis and the Y-axis of the three-dimensional stage 10, and the Z-axis of the three-dimensional stage 10 is controlled so that the distance between the nozzle 3 and the deposition substrate 7 is 30 mm.

Cutting 7075 aluminum alloy bar stock supplied by the market to enable the bar stock to be smoothly placed into the on-demand uniform metal droplet generator 1, removing oxide skin and impurities on the surface of the bar stock by adopting a grinding process and an acid-base corrosion combined method, and then placing the bar stock into the on-demand uniform metal droplet generator 1 and sealing the bar stock.

The whole printing working space 11 is deoxidized and dewatered by an inert gas glove box, and the water vapor and oxygen contents of the working environment are kept to be lower than 5 PPM. And starting the induction heater 2 to heat the metal raw material in the on-demand uniform metal droplet generator 1, controlling the heating temperature to 800-850 ℃, and completely melting the 7075 aluminum alloy raw material in the on-demand uniform metal droplet generator 1. The heating plate 8 was turned on to subject the deposition substrate 7 to a preheating treatment at a temperature set to 150 ℃. In actual production, the voltage of the high-voltage direct-current power supply I can be selected within the range of 0-500V, and the voltage of the high-voltage pulse power supply II can be selected within the range of 2000-5000V. In this embodiment, the voltage of the high voltage dc power supply I is 300V. The voltage of the periodic high-voltage pulse power supply is 3000V. The nozzle 3 with the diameter of 350 mu m is adopted to spray the molten 7075 aluminum alloy droplet 5, the process parameters are controlled to ensure that the diameter of the sprayed 7075 aluminum alloy droplet 5 is 500 +/-5 mu m, the 7075 aluminum alloy droplet 5 generated by spraying is charged according to requirements by the charging electrode 4, and the charged droplet 5 flies to the electrified deposition substrate 7 through a circular hole in the center of the charging electrode 4. As the distance between the 7075 aluminum alloy droplet 5 and the energized deposition substrate 7 gradually decreased, generation of the taylor cone 13 at the bottom of the 7075 aluminum alloy droplet 5 and preliminary contact with the deposition substrate 7 was induced, and subsequently, the 7075 aluminum alloy droplet 5 was spread around the generated taylor cone 13 for deposition without involving the ambient gas. Therefore, uniform 7075 aluminum alloy droplets 5 are ejected and printed repeatedly, the three-dimensional workbench 10 is controlled to perform three-dimensional motion according to a preset printing program in the process, when the 7075 aluminum alloy droplets 5 are printed on the surface of a deposited solidified layer 14, a re-melting area 15 is formed in the interface of the printed layer, hole defects are easily generated near a micro gap 16 area on the surface of the solidified layer 14, and the guiding and attracting effects of an electric field can promote the aluminum alloy droplets 5 to flow and fill the gap 16 on the surface of the solidified layer 14, so that the formation of the printed hole defects is inhibited. And (3) after the 7075 aluminum alloy block 6 is printed, deposited and formed layer by drop, line by line and layer, closing the whole printing and depositing system, taking the formed part 6 out of the low-oxygen and low-water environment 11, tempering the formed part, and eliminating thermal stress to obtain the high-density 7075 aluminum alloy block meeting the use requirement.

Example 3:

this example applies example 1 to Sn60Pb40 tin-lead alloy high reliability bump array inkjet forming. The main steps of this example are the same as example 1.

In this embodiment, the material for jet printing is replaced with Sn60Pb40 tin-lead alloy for electronic packaging, the heating temperature of the induction heater 2 is controlled to 350 to 400 ℃, and the preheating temperature is controlled to 50 ℃ when the heating plate 8 performs the preheating treatment on the deposition substrate 7. The bump array is composed of a series of discrete single deposition-state metal droplets, the layer-by-layer printing process is not involved in printing, the deposition positions of the charged metal droplets 5 need to be arranged according to actual requirements, and the deposition substrate 7 needs to be specially selected according to electronic packaging requirements. When the deposition substrate 7 is made of a metal material, the deposition substrate can be directly connected to the positive electrode of the high-voltage direct-current power supply I, and when the deposition substrate 7 is made of a non-metal material, a metal coating needs to be integrally prepared on the surface of the deposition substrate 7 by adopting a surface coating technology in advance and then connected to the positive electrode of the high-voltage direct-current power supply I. In actual production, the voltage of the high-voltage direct-current power supply I can be selected within the range of 0-300V, and the voltage of the high-voltage pulse power supply II can be selected within the range of 500-2000V. In this embodiment, the voltage of the high voltage dc power supply I is 100V. The voltage of the periodic high-voltage pulse power supply is 1100V. In the preparation of the bump array, the size of a single charged metal droplet 5 is generally required to be smaller, so that the small-sized nozzle 3 needs to be replaced for jet printing. In the embodiment, a nozzle 3 with the diameter of 200 μm is adopted to spray molten Sn60Pb40 tin-lead alloy droplets 5, and the process parameters are controlled to ensure that the sprayed Sn60Pb40 tin-lead alloy droplets 5 have the diameter of 300 +/-3 μm. Because the hole defect between each charged metal droplet 5 and the deposition substrate 7 is inhibited by the electric field induction effect, the prepared salient point array is combined with the deposition substrate 7 more compactly, and the requirement of high-reliability electronic packaging is further met.

Example 4:

the embodiment provides a method for suppressing a uniform metal droplet ejection 3D printing hole defect, which is characterized by comprising the following steps of:

1) selecting metal or alloy as a printing raw material, and treating oxide skin and impurities on the surface of the printing raw material.

2) The treated printing stock material is fed to a uniform metal droplet generator on demand. Wherein the on-demand uniform metal droplet generator 1 is disposed in a low oxygen, low water environment 11. An induction heater 2 is arranged on the outer wall of the on-demand uniform metal droplet generator 1. The bottom of the on-demand uniform metal droplet generator 1 is provided with a nozzle 3. The on-demand uniform metal droplet generator 1 is arranged above a deposition substrate. The on-demand uniform metal droplet generator 1 is grounded.

3) The induction heater 2 is activated. The induction heater 2 generates heat to heat the printing raw materials, and the printing raw materials are melted into molten liquid metal or alloy.

4) And (5) printing initialization. The three-dimensional table 10 is moved to the printing position, and the deposition substrate 7 is adjusted to a set distance from the nozzle 3. Wherein the three-dimensional table 10 is grounded. And an insulating plate 9, a heating plate 8 and a deposition substrate 7 are sequentially paved on the upper surface of the three-dimensional workbench 10 from bottom to top. The deposition substrate 7 is connected with the positive electrode of the high-voltage direct current power supply I. The voltage of the high-voltage direct-current power supply I is continuously adjustable within the range of 0-1000V. The three-dimensional table 10 has an X-direction movement axis, a Y-direction movement axis, and a Z-direction movement axis, and realizes movements in three XYZ directions. The deposition substrate 7, the heating plate 8, the insulating plate 9, and the three-dimensional stage 10 are all disposed in a low-oxygen and low-water environment 11.

5) The heating plate 8 is activated to perform a preheating process on the deposition substrate 7.

6) The on-demand homogeneous metal droplet generator 1 is activated to initiate extrusion of molten metal or alloy starting material at the nozzle 3 to form a stream.

7) Under the induction of the charging electrode 4, negative charges are accumulated on the liquid flow. When the length of the stream reaches a certain threshold value, the stream breaks to form negatively charged metal droplets 5. Wherein the charging electrode 4 is arranged between the nozzle 3 and the deposition substrate 7. An electric field shielding plate is arranged below the charging electrode 4. The charging electrode 4 and the electric field shielding plate are both of annular sheet structures. The charging electrode 4 and the electric field shielding plate are provided with holes for the charged metal droplets 5 to pass through. The outer diameter of the electric field shielding plate is larger than the outer diameter of the charging electrode 4, and the inner diameter is smaller than the inner diameter of the charging electrode 4. And the charging electrode 4 is connected with the positive electrode of the high-voltage direct-current power supply II. And the voltage of the high-voltage direct-current power supply II is continuously adjustable within the range of 500-5000V. The electric field shielding plate is grounded to shield an interference electric field generated by the charging electrode 4.

8) The negatively charged metal droplets 5 fly through the holes in the charging electrode 4 towards the energized deposition substrate 7. An electric field is gradually formed between the negatively charged metal droplets 5 and the deposition substrate 7. The electric field strength increases as the distance between the two decreases. Under the induction of an electric field, the charge is redistributed inside the charged metal droplet 5 and negative charges accumulate at the bottom of the droplet, thereby increasing the maxwell stress. When the electric field strength reaches a certain level, the charge level of the charged metal droplets 5 rises above the critical charge level, and the charged metal droplets 5 deform under the maxwell stress against the surface tension and the ambient gas pressure, generating taylor cones 13 at the bottoms of the charged metal droplets 5.

9) Negatively charged metal droplets 5 are deposited towards a deposition substrate 7. The taylor cone 13 at the bottom of the negatively charged metal droplet 5 makes initial contact with the surface of the deposition substrate 7 and the ambient gas in the droplet deposition area is subsequently expelled during the subsequent flow spreading process.

10) According to the digital model of the formed part, the uniform metal droplet generator 1 on demand is repeatedly controlled to generate the charged metal droplets 5, and the coordination matching between the printing deposition of the charged metal droplets 5 and the movement of the three-dimensional workbench 10 is controlled, so that the first deposition layer is printed dropwise.

11) After the last deposition layer is formed, the Z-axis direction of the three-dimensional table 10 is lowered by one deposition layer height. With the solidified layer 14 already deposited, the substrate will be deposited as a new print. Charged metal droplets 5 are deposited on the deposited solidified layer 14. Wherein newly incident charged metal droplets 5 undergo microdomain remelting with the deposited solidified layer 14, forming remelted regions 15. The guiding attraction of the electric field promotes the flow filling of the charged metal droplets 5, and thus promotes the complete filling of the minute voids 16 on the surface of the solidified layer 14 by the charged metal droplets 5.

12) And step 11) is repeated, and the printing layer by layer is gradually dropped until the forming is finished, and finally the formed part 6 is formed.

13) The entire printing deposition system is shut down, the shaped article 6 is removed from the low oxygen, low water environment 11, and the shaped article 6 is tempered.

Example 5:

the main steps of this example are the same as example 1 or 4, wherein the uniform metal droplet ejection 3D printing device is placed in an inert gas glove box. The oxygen and water vapor contents in the box body are both below 5 PPM.

Example 6:

the main steps of this embodiment are the same as those of embodiment 1 or 4, wherein the deposition substrate 7 is made of a metal material.

Example 7:

the main steps of this embodiment are the same as those of embodiment 1 or 4, wherein the deposition substrate 7 is made of a non-metal material. The surface of the deposition substrate 7 is coated with a metal plating layer.