阅读说明：本技术 用于由液态材料增材制造三维工件的方法和设备 (Method and apparatus for additive manufacturing of three-dimensional workpieces from liquid material ) 是由 E·迈尔 R·布莱赫尔 P·弗林格 B·施魏策尔 于 2019-09-27 设计创作，主要内容包括：本发明涉及一种用于由液态材料(1)增材制造三维工件的方法,其中,液态材料(1)被供应给排挤室(2)并且借助压力脉冲经由喷射孔(4)以液滴形状被排出,所述压力脉冲借助限界排挤室(2)的可往复运动的活塞(3)产生。根据本发明,为了优化限界所述排挤室(2)和/或喷射孔(4)的至少一个表面(5,6)的润湿特性,在时间上受限地借助为此被置于振动中的活塞(3)将声波耦入所述液态材料(1)中。本发明还涉及一种用于执行根据本发明的方法的设备。(The invention relates to a method for additive manufacturing of a three-dimensional workpiece from a liquid material (1), wherein the liquid material (1) is supplied to a displacement chamber (2) and is discharged in the form of droplets via a spray opening (4) by means of pressure pulses, which are generated by means of a piston (3) that delimits the displacement chamber (2) and can be moved back and forth. According to the invention, sound waves are coupled into the liquid material (1) in a time-limited manner by means of a piston (3) which is set in vibration for this purpose, in order to optimize the wetting behavior of at least one surface (5,6) bounding the displacement chamber (2) and/or the injection openings (4). The invention also relates to a device for carrying out the method according to the invention.)

1. A method for additive manufacturing of a three-dimensional workpiece from a liquid material (1), wherein the liquid material (1) is supplied to a displacement chamber (2) and is expelled in the shape of droplets via an injection orifice (4) by means of pressure pulses, which are generated by means of a reciprocally movable piston (3) delimiting the displacement chamber (2),

characterized in that, in order to optimize the wetting behavior of at least one surface (5,6) bounding the displacement chamber (2) and/or the injection openings (4), sound waves are coupled into the liquid material (1) in a time-limited manner by means of a piston (3) which is set in vibration for this purpose.

2. Method according to claim 1, characterized in that the sound waves are coupled in by means of the piston (3) before generating a pressure pulse for discharging the liquid material (1).

3. Method according to claim 1 or 2, characterized in that the sound waves are coupled in over a time period of ≦ 10s, preferably ≦ 5s, further preferably ≦ 1 s.

4. Method according to any of the preceding claims, characterized in that the piston (3) is set in vibration with a frequency > 1kHz, preferably > 4kHz, further preferably > 20 kHz.

5. Method according to any of the preceding claims, characterized in that the piston (3) is put into vibration and/or reciprocated by means of an actuator, for example by means of a magnetostrictive, piezoceramic and/or magnetic actuator.

6. Method according to one of the preceding claims, characterized in that, by the coupling in of sound waves, gas bubbles are generated in the liquid material (1), which gas bubbles cause implosions in the region of at least one surface (5,6) bounding the displacement chamber (2) and/or the injection orifices (4), and in that the surface (5,6) is smoothed by the implosion of gas bubbles.

7. An apparatus for carrying out the method according to one of the preceding claims, comprising a displacement chamber (2) which can be filled with a liquid material (1) and which is bounded on one side by a reciprocally movable piston (3) and on the other side by a ceramic body (7) having injection orifices (4), wherein the ceramic body (7) has at least one surface (5,6) which bounds the displacement chamber (2) and/or the injection orifices (4) and which has a wettability which is temporarily modified.

8. The apparatus according to claim 7, characterized in that the injection holes (4) have a diameter (D) of 500 μm or less, preferably 300 μm or less, further preferably 100 μm or less.

9. The device according to claim 7 or 8, characterized in that the piston (3) is operatively connected with an actuator, for example a magnetostrictive, piezoceramic and/or magnetic actuator, such that the piston (3) can be put into vibration and/or reciprocated by means of the actuator.

Technical Field

The invention relates to a method for the additive manufacturing of a three-dimensional workpiece from a liquid, in particular liquefied, material according to the preamble of claim 1. The invention also relates to a device for carrying out the method.

Additive manufacturing methods include, inter alia, 3D printing, in which a liquid or solid material is built layer by layer into a three-dimensional workpiece. In particular, therefore, methods and devices for 3D printing are currently proposed, in which, however, only liquid or liquefied materials are to be used.

Background

For example, from published german patent application DE 102016224047 a1, a printing head for A3D printing machine, in particular a metal printing machine, is known, which printing head has a reservoir for accommodating metal, which reservoir is formed in a housing. The reservoir comprises a melting region for the molten or liquefied metal and an extrusion chamber, wherein the melting region and the extrusion chamber are connected in such a way that the liquefied metal is forced through the discharge opening by the movement of the piston. Here, the liquefied metal is discharged in the form of droplets.

The 3D printing method using the above type of print head is also referred to as a "drop on demand" method. Here, the reproducibility of the droplet formation is a particular challenge.

Liquid or liquefied metals have a relatively high surface tension. Furthermore, if the liquid metal is in contact with a surface that is difficult to wet, for example a rough surface, there is little surface friction or surface adhesion. With regard to the liquid column consisting of liquid metal formed within the discharge opening of the print head, this effect may result in that the velocity profile of the liquid column is no longer axisymmetric and the drops consisting of liquid metal formed at the ends of the discharge opening are deflected uncontrollably.

Disclosure of Invention

The object on which the invention is based is therefore to specify a method for the additive manufacturing of three-dimensional workpieces from liquid, in particular liquefied, material, which enables a controlled droplet output and thus a high degree of reproducibility of the droplet formation.

To solve this object, a method having the features of claim 1 and a device having the features of claim 7 are proposed. Advantageous embodiments of the invention emerge from the dependent claims.

In the proposed method for additive manufacturing of a three-dimensional workpiece from a liquid material, the liquid material is supplied to a displacement chamber and is discharged in the form of droplets by means of pressure pulses via a discharge orifice. In this case, the pressure pulses are generated by a piston which delimits the displacement chamber and can be moved back and forth. According to the invention, sound waves are coupled into the liquid material in a time-limited manner, to be precise by means of a piston which is set into vibration for this purpose, in order to optimize the wetting behavior of at least one surface which delimits the displacement chamber and/or the injection openings.

The acoustic waves press the liquid material into existing cavities of the surface, so that these cavities are filled with the liquid material. As a result, the contact surface between the liquid material and the surface increases and the surface friction or surface adhesion increases. The problems mentioned at the outset of undesired deflection of the droplets or uncontrolled droplet discharge when the liquid material is discharged from the spray orifice can be avoided or at least significantly reduced in this way.

The advantages of the proposed method emerge particularly clearly when using liquid materials with a large surface tension. The proposed method is therefore preferably applied to the additive manufacturing of three-dimensional workpieces from liquid or liquefied metal. The liquid metal may be, for example, aluminum or an aluminum alloy.

The advantages are particularly evident, furthermore, when at least one surface bounding the displacement chamber and/or the injection openings is comparatively rough. This is the case, for example, when the body forming the injection hole is made of porous ceramic. The body proves to be particularly liquid-phobic, in particular of phobic metals or phobic aluminium. The wettability of the surface of the body can be improved by means of the method according to the invention.

Advantageously, the wettability of the surface is improved only locally to a limited extent, in particular preferentially in the region of the injection openings and/or in the region located upstream of the injection openings, in order to achieve an axisymmetric through-flow of the pipe in these regions. Preferably, a through-flow of the tube with a parabolic linear velocity profile is achieved. Conversely, the small wettability of the surface in the flow direction behind the spray orifice plays a role as an advantage, since it promotes a rapid and reliable drop-off of the liquid droplets. The surface located downstream of the spray openings in the flow direction therefore preferably has the property of repelling liquids, in particular of repelling metals or of repelling aluminum. Since the sound waves coupled in by means of the piston propagate only in the displacement chamber and in the injection openings, the surfaces are also modified in the method according to the invention only with regard to the wettability of the surfaces bounding the displacement chamber or the injection openings.

Preferably, the sound waves are coupled in by means of the piston before the generation of the pressure pulse for discharging the liquid material, for example during an initialization process before the start of the actual printing process. It is merely necessary to ensure that liquid material is present in the displacement chamber. Preferably, the displacement chamber has been completely filled with liquid material. By coupling in the sound waves during the initialization process, it is ensured that the sound waves do not impair the actual printing process.

It is furthermore preferred that the sound waves are coupled in over a time period of ≦ 10s, preferably ≦ 5s, further preferably ≦ 1 s. The coupling in of the acoustic waves therefore results in a virtually insignificant delay of the actual printing process, so that the method steps have substantially no effect on the efficiency of the method.

In this case, the piston is preferably set into vibration with a frequency of > 1kHz, i.e. at a frequency which is too high for the actual printing process. This ensures that no premature uncontrolled discharge of the liquid material from the injection opening is caused. Since the injection openings are normally not closed by the closing element.

Preferably, the piston is set in vibration with a frequency of 4kHz or more, more preferably 20kHz or more, i.e. in high frequency vibration. The high-frequency oscillation of the piston can generate sound waves, in particular ultrasonic waves, which result in the existing cavities being completely filled with liquid material.

Preferably, the piston is set in vibration by means of an actuator, for example by means of a magnetostrictive, piezoceramic and/or magnetic actuator. In this case, in particular, an actuator can be used, by means of which the piston is moved back and forth in order to generate the pressure pulses required for discharging the liquid material. In this way, actuators can be saved.

In a further embodiment of the invention, it is proposed that the gas bubbles are generated in the liquid material by coupling in of sound waves. The gas bubble can cause an implosion in the region of at least one surface bounding the displacement chamber and/or the injection opening, so that the surface is smoothed by the implosion of the gas bubble. This means that the original rough surface is purposefully smoothed by cavitation, wherein the smoothing or smoothing results in a desired increase in the contact surface between the liquid material and the surface. Since all cavities cannot be eliminated in this way, the advantage of filling the surface cavities with a liquid material is used as a supplement to the cavitation. Since both effects can be achieved by the coupling in of sound waves, both effects can be utilized simultaneously.

The device proposed for solving the object described at the outset furthermore comprises a displacement chamber which can be filled with the liquid material and which is bounded on one side by a piston which can be moved back and forth and on the other side by a ceramic body having an injection opening. The ceramic body has at least one surface which delimits the displacement chamber and/or the injection opening and which has a temporarily modified wettability. The temporarily modified wettability is achieved by using a device for performing the method according to the invention. The effects or advantages described above in connection with the method then occur.

The proposed device is therefore preferably used for carrying out the method according to the invention.

Since the injection opening is formed in the ceramic body, it is delimited by at least one rougher surface. By coupling in the sound waves by the method according to the invention, the wettability of the surface can be improved such that a tube flow with an axisymmetric velocity profile is present in the injection openings. I.e. deflection of the liquid column in the free beam, i.e. after the outlet of the injection hole, is avoided. The falling line of the droplets formed in this case therefore corresponds to the injection orifice axis.

Preferably, the spray orifices of the apparatus have a diameter D.ltoreq.500. mu.m, preferably.ltoreq.300. mu.m, further preferably.ltoreq.100. mu.m. Thus, the injection hole may also be referred to as a capillary. However, the forces occurring in the capillary tube, which could lead to an uncontrolled outflow of the liquid material from the injection opening, are not formed, so that the injection opening does not have to be closed. The relatively small diameter of the ejection orifice results in a small droplet diameter which enables very precise manufacture of three-dimensional workpieces.

Furthermore, the piston is preferably operatively connected to an actuator, for example a magnetostrictive, piezoceramic and/or magnetic actuator, so that the piston can be set into oscillation and/or moved back and forth by means of the actuator. Preferably, the same actuator is used for oscillation excitation and for the reciprocating movement of the piston, so that actuators can be saved.

Drawings

The invention is explained in detail below with reference to the drawings. The figures show:

figure 1 is a cross-sectional view of an apparatus for additive manufacturing of a three-dimensional workpiece from a liquid material according to the invention,

figure 2 is a schematic longitudinal section of the injection orifice of the device of figure 1,

figure 3 another schematic longitudinal section of the injection orifice of the device of figure 1,

FIG. 4 is an enlarged cross-sectional view of the liquid material in the area of contact with the ceramic body forming the injection orifice,

FIG. 5 is a second enlarged cross-sectional view of the liquid material in contact with the ceramic body forming the injection orifice, an

FIG. 6 is a third enlarged cross-sectional view of the liquid material in contact with the ceramic body forming the injection orifice.

Detailed Description

Fig. 1 shows an exemplary embodiment of a device according to the invention for the additive production of a three-dimensional workpiece from a liquid, in particular liquefied, material. The device is particularly suitable for performing the method according to the invention. The device shown here is currently a 3D printer or a print head of a 3D printer.

The components of the device are a housing 10 and a piston 3 which is received in the housing 10 in a reciprocating manner and which delimits a displacement chamber 2 formed in the housing 10. During operation of the device, the displacement chamber 2 is filled with a liquid material 1, in particular a liquid or liquefied metal, for example an aluminum melt. A pressure pulse can be generated by the reciprocating movement of the piston 3, which pressure pulse causes the liquid material 1 to be discharged through the injection opening 4. The injection openings 4 are formed in a ceramic body 7 which has a first surface 5 facing the displacement chamber 22 and a second surface 8 facing the base chamber 9. The injection holes 4 are delimited by a surface 6 of a ceramic body 7. The ceramic body 7, which is now of plate-like design, is connected to the housing 10 by means of a clamping sleeve 11.

The injection hole 4 formed in the ceramic body 7 has a diameter D of less than 500 μm on the substrate space side. I.e. a significant pressure pulse is required in order to extrude the liquid material 1 through the narrow injection hole 4. The pressure pulses are generated by means of a piston 3, which is connected to an actuator (not shown) for this purpose.

As the liquid material 1 emerges from the outlet opening 4, discrete droplets are formed, which fall off the surface 8 of the ceramic body 7 and, in the case of free fall, move toward the workpiece carrier. The drop line in the case of free fall ideally corresponds to the longitudinal axis of the spray opening 4, in order to be able to achieve precise positioning of the liquid droplet on the workpiece carrier. The three-dimensional workpiece to be produced is thus built up drop by drop on the workpiece carrier.

Since the ceramic body 7 is relatively porous as a result of manufacturing, the surfaces 5,6 and 8 have a low wettability with respect to the liquid material 1, so that the contact surface between the liquid material 1 and the ceramic body 7 is not very large (see fig. 4). In the case of the surface 8 facing the substrate chamber 9, this proves to be advantageous, since the small wettability promotes a rapid and uniform drop-off of the droplets. In the case of the surfaces 5 and 6, however, a small wettability proves to be disadvantageous, since the surface friction or surface adhesion of the liquid material 1 on the surfaces 5,6 is simultaneously reduced.

As is shown by way of example in fig. 2 and 3, this can result in the velocity profile (indicated by the arrows) of the liquid column of liquid material 1 located in the injection openings 4 not being axisymmetric, so that the liquid column or the subsequently formed droplets emerging from the injection openings 4 are deflected (see fig. 3). The free fall line of the drop no longer corresponds to the longitudinal axis of the spray opening 4, so that the drop can no longer be positioned precisely.

In order to prevent this, in the proposed method, an initialization is carried out before the start of the actual production process, at which initialization the piston 3 is excited for a short time by means of the actuator for high-frequency oscillations. The high-frequency vibrations cause the liquid material 1 to be pressed into the cavities 12 of the surfaces 5,6 of the ceramic body 7, so that these cavities are completely filled with the liquid material 1 (see fig. 5). In this way, the contact surface between the liquid material 1 and the ceramic body 7 increases and thus the surface friction or surface adhesion of the liquid material 1 in the region of the spray opening 4 increases, so that the risk of droplets being deflected when discharging from the spray opening 4 is significantly reduced.

Furthermore, by means of the vibration excitation of the piston 3, gas bubbles can be generated in the liquid material 1, which implode on the surfaces 5,6 of the ceramic body 7 and lead to smoothing of the rough surfaces 5,6 by cavitation (see fig. 6). This smoothing or flattening of the surfaces 5,6 also contributes to improving the wettability of the surfaces 5, 6.

Currently, the injection orifice 4 of the device shown in fig. 1 is preceded by a region of increased diameter D' into which the displacement chamber 2 extends. The preceding region is therefore bounded by a surface 5, the wettability of which is also improved by using the method according to the invention.