METHOD AND DEVICE FOR THE ADDITIVE MANUFACTURING OF A THREE-DIMENSIONAL WORKPIECE FROM A LIQUID MATERIAL

Abstract

The invention relates to a method for the additive manufacturing of a three-dimensional workpiece from a liquid material (1), in which method the liquid material (1) is fed to a displacement chamber (2) and discharged in drop form via a jet hole (4) by means of a pressure pulse which is generated with the aid of a reciprocating piston (3) delimiting the displacement chamber (2). According to the invention, in order to optimise the wetting properties of at least one surface (5, 6) which delimits the displacement chamber (2) and/or the jet hole (4), sound waves are coupled into the liquid material (1) for a limited period of time with the aid of the piston (3) which is caused to vibrate for this purpose. The invention also relates to a device for carrying out the method according to the invention.

Claims

1. A method for the additive manufacturing of a three-dimensional workpiece from a liquid material (1), the method comprising feeding the liquid material (1) to a displacement chamber (2), discharging the liquid material in droplet form via a spray hole (4) by means of a pressure pulse, which is created using a piston (3) which delimits the displacement chamber (2) and can be moved back and forth, and to optimize the wetting properties of at least one surface (5, 6) delimiting the displacement chamber (2) and/or the spray hole (4), coupling soundwaves into the liquid material (1) in a time-restricted manner by setting the piston (3) in vibration.

2. The method as claimed in claim 1, characterized in that the soundwaves are coupled in prior to the creation of a pressure pulse for discharging the liquid material (1) using the piston (3).

3. The method as claimed in claim 1, characterized in that the soundwaves are coupled in over a period of time of ≤10 s.

4. The method as claimed in claim 1, characterized in that the piston (3) is set in vibration at a frequency of >1 kHz.

5. The method as claimed in claim 1, characterized in that the piston (3) is set in vibration and/or moved back and forth using an actuator.

6. The method as claimed in claim 1, characterized in that, by coupling in soundwaves, gas bubbles are created in the liquid material (1), the gas bubbles are made to implode in the region of the at least one surface (5, 6) delimiting the displacement chamber (2) and/or the spray hole (4), and the surface (5, 6) is smoothed by the imploding gas bubbles.

7. A device for carrying out the method as claimed in claim 1, comprising a displacement chamber (2), which can be filled with a liquid material (1) and is delimited on one side by a piston (3) which can be moved back and forth and on the other side by a ceramic body (7) with a spray hole (4), wherein the ceramic body (7) has at least one surface (5, 6) which delimits the displacement chamber (2) and/or the spray hole (4) and has a temporally modifiable wettability.

8. The device as claimed in claim 7, characterized in that the spray hole (4) has a diameter (D) of ≤500 μm.

9. The device as claimed in claim 7, characterized in that the piston (3) is operatively connected to an actuator with the result that the piston (3) can be set in vibration and/or moved back and forth using the actuator.

10. The device as claimed in claim 7, characterized in that the spray hole (4) has a diameter (D) of ≤300 μm.

11. The device as claimed in claim 7, characterized in that the spray hole (4) has a diameter (D) of ≤100 μm.

12. The device as claimed in claim 7, characterized in that the piston (3) is operatively connected to a magnetostrictive, piezoceramic and/or magnetic actuator, with the result that the piston (3) can be set in vibration and/or moved back and forth using the actuator.

13. The method as claimed in claim 1, characterized in that the soundwaves are coupled in over a period of time of ≤5 s.

14. The method as claimed in claim 1, characterized in that the soundwaves are coupled in over a period of time of ≤1 s.

15. The method as claimed in claim 1, characterized in that the piston (3) is set in vibration at a frequency of ≥4 kHz.

16. The method as claimed in claim 1, characterized in that the piston (3) is set in vibration at a frequency of ≥20 kHz.

17. The method as claimed in claim 1, characterized in that the piston (3) is set in vibration and/or moved back and forth using a magnetostrictive, piezoceramic and/or magnetic actuator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The invention is explained in more detail below with reference to the appended drawings, in which:

[0026] FIG. 1 shows a sectional view of a device according to the invention for the additive manufacturing of a three-dimensional workpiece from a liquid material,

[0027] FIG. 2 shows a schematic longitudinal section through the spray hole of the device of FIG. 1,

[0028] FIG. 3 shows a further schematic longitudinal section through the spray hole of the device of FIG. 1,

[0029] FIG. 4 shows an enlarged sectional illustration in the region of contact of the liquid material with the ceramic body forming the spray hole,

[0030] FIG. 5 shows a second enlarged sectional illustration in the region of contact of the liquid material with the ceramic body forming the spray hole, and

[0031] FIG. 6 shows a third enlarged sectional illustration in the region of contact of the liquid material with the ceramic body forming the spray hole.

DETAILED DESCRIPTION

[0032] What can be derived from FIG. 1 by way of example is a preferred embodiment of a device according to the invention for the additive manufacturing of a three-dimensional workpiece from a liquid, in particular liquefied material. The device is suitable in particular for carrying out the method according to the invention. The device illustrated is a 3D printer or a printhead of a 3D printer in the present case.

[0033] Constituent parts of the device are a housing 10 and a piston 3 which is received in the housing 10 such that it can move back and forth and delimits a displacement chamber 2 formed in the housing 10. The displacement chamber 2 is filled with a liquid material 1, in particular with a liquid or liquefied metal, for example with an aluminum melt, during operation of the device. The movements back and forth of the piston 3 make it possible to create pressure pulses which lead to the liquid material 1 being discharged via a spray hole 4. The spray hole 4 is formed in a ceramic body 7 which has a first surface 5 facing the displacement chamber 2 and a second surface 8 facing a substrate chamber 9. The spray hole 4 is delimited by a surface 6 of the ceramic body 7. The ceramic body 7, which has a plate-like form in the present case, is connected to the housing 10 via a clamping sleeve 11.

[0034] The spray hole 4 formed in the ceramic body 7 has a diameter D of smaller than 500 μm on the substrate-chamber side. That is to say that a considerable pressure pulse is required to press the liquid material 1 through the narrow spray hole 4. The pressure pulse is created using the piston 3, which is connected to an actuator (not illustrated) for this purpose.

[0035] When the liquid material 1 exits the spray hole 4, discrete droplets form, which separate at the surface 8 of the ceramic body 7 and move in freefall toward a workpiece carrier. The fall line in freefall corresponds here ideally to the longitudinal axis of the spray hole 4 in order to allow precise positioning of the droplets on the workpiece carrier. The three-dimensional workpiece to be manufactured is thus built up droplet by droplet on the workpiece carrier.

[0036] Since the ceramic body 7 is comparatively porous for manufacturing reasons, the surfaces 5, 6 and 8 have a low wettability in relation to the liquid material 1, with the result that the contact surface area 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 has proven to be an advantage since the low wettability is conducive to a fast and uniform separation of the droplets. In the case of the surfaces 5 and 6, the low wettability has proven to be a disadvantage, however, since at the same time the surface friction or adhesion of the liquid material 1 decreases at these surfaces 5, 6.

[0037] This can lead, as illustrated by way of example in FIGS. 2 and 3, to the velocity profile (indicated by arrows) of a liquid column of liquid material 1 located in the spray hole 4 not being axially symmetrical, with the result that the liquid column exiting the spray hole 4 and/or the droplets forming in that case are deflected (see FIG. 3). The freefall line of the droplets in that case no longer corresponds to the longitudinal axis of the spray hole 4, with the result that a precise placement of the droplets is no longer possible.

[0038] In order to prevent this, in the proposed method, before the start of the actual manufacturing process an initialization is carried out, in which the piston 3 is induced into high-frequency vibrations for a short time using the actuator. The high-frequency vibrations have the effect that the liquid material 1 is pressed into cavities 12 of the surfaces 5, 6 of the ceramic body 7, with the result that said cavities fill completely with liquid material 1 (see FIG. 5). In this way, the contact surface area between the liquid material 1 and the ceramic body 7 is enlarged and the surface friction or adhesion of the liquid material 1 in the region of the spray hole 4 is thus increased, with the result that the risk of deflection of the droplets when they exit the spray hole 4 is considerably reduced.

[0039] Furthermore, the inducement into vibrations of the piston 3 makes it possible to create gas bubbles in the liquid material 1 that implode at the surfaces 5, 6 of the ceramic body 7 and, in the course of cavitation erosion, lead to a smoothing of the rough surfaces 5, 6 (see FIG. 6). This smoothing or leveling of the surfaces 5, 6 likewise contributes to an improvement in the wettability of the surfaces 5, 6.

[0040] In the present case, a region with an enlarged diameter D′ is arranged upstream of the spray hole 4 of the device illustrated in FIG. 1, into which region the displacement chamber 2 extends. The region arranged upstream is accordingly delimited by a surface 5, the wettability of which is likewise improved by using the method according to the invention.