METHOD AND DEVICE FOR THE RAPID MANUFACTURE OF A THREE-DIMENSIONAL WORKPIECE FROM A MOLTEN MATERIAL

Abstract

The invention relates to a method for the rapid manufacture of a three-dimensional workpiece from a molten material (1), in particular a molten metal, in which method the molten material (1) is supplied to a compression chamber (2) and delivered in drop form via an injector hole (4) by means of a pressure pulse which is generated with the aid of a reciprocating piston (3) that delimits the compression chamber (2). According to the invention, the compression chamber (2) is degassed before manufacturing begins and/or during a pause in the manufacturing. In a first step, ultrasonic waves are coupled into the molten material (1) in the compression chamber (2), which generate a force (F.sub.Bjrk) that makes the gas in the molten material (1) sink, and in a second step, after the ultrasonic excitation has ended, the piston (3) is introduced deeper into the compression chamber (2) in order to remove the rising gas via a conduit (5) of the piston (3). The invention also relates to a device for carrying out the method according to the invention.

Claims

1. A method for the generative manufacture of a three-dimensional workpiece from a molten material (1), wherein the molten material (1) is fed to a compression chamber (2) and discharged in drop form via a spray hole (4) by a pressure pulse generated by a reciprocating piston (3) that delimits the compression chamber (2), the method comprising degassing the compression chamber (2) before manufacturing begins and/or during a pause in manufacture, wherein, in a first step, ultrasonic waves are coupled into the molten material (1) present in the compression chamber (2), which generate a force (F.sub.Bjrk) that makes gas in the molten material (1) sink, and, in a second step, after ultrasonic excitation has ended, the piston (3) is moved deeper into the compression chamber (2) in order to discharge the gas, which is then rising, via a guide (5) for the piston (3).

2. The method as claimed in claim 1, characterized in that the ultrasonic waves are coupled into the molten material (1) by the piston (3), which is set into high-frequency oscillation for this purpose.

3. The method as claimed in claim 2, characterized in that the piston (3) is set into oscillation and/or moved backward and forward by means of an actuator (6).

4. The method as claimed in claim 1, characterized in that, before the ultrasonic excitation, the molten material (1) present in a region of the spray hole (4) is cooled down until the molten material falls below the solidus line of the molten material (1).

5. The method as claimed in claim 4, characterized in that the molten material (1) present in the region of the spray hole (4) is cooled down with molecular nitrogen (N.sub.2).

6. A device for carrying out the method as claimed in claim 1, comprising a compression chamber (2) which can be filled with a molten material (1), in particular a molten metal, and which is delimited, on the one hand, by a reciprocating piston (3) and, on the other hand, by a ceramic body (8) with a spray hole (4) for discharging the molten material (1), and further comprising an actuator (6), for example a magnetostrictive, piezoceramic and/or magnetic actuator (6), by means of which the piston (3) can be set into high-frequency oscillation and/or moved backward and forward, wherein the piston (3) has an at least sectionally conically shaped tip (9) for delimiting the compression chamber (2).

7. The device as claimed in claim 6, characterized in that the actuator (6) is capable of high frequency, enabling the piston (3) to be set into high frequency oscillations ≥20 kHz by means of the actuator (6).

8. The device as claimed in claim 6, characterized in that the piston (3) is manufactured from ceramic and/or is connected to the actuator (6) via a one-part or multi-part piston rod (11).

9. The method as claimed in claim 2, characterized in that the piston (3) is set into oscillation and/or moved backward and forward by a magnetostrictive, piezoceramic and/or magnetic actuator (6).

10. The method as claimed in claim 4, characterized in that the molten material (1) present in the region of the spray hole (4) is cooled down with molecular nitrogen (N.sub.2), which is fed to the spray hole (4) from the outside by a lance (7).

11. The method as claimed in claim 1, wherein the compression chamber (2) is degassed before manufacturing begins.

12. The method as claimed in claim 1, wherein the compression chamber (2) is degassed during a pause in manufacture.

13. The method as claimed in claim 1, wherein the compression chamber (2) is degassed before manufacturing begins and during a pause in manufacture.

14. A method for the generative manufacture of a three-dimensional workpiece from a molten metal, wherein the molten material (1) is fed to a compression chamber (2) and discharged in drop form via a spray hole (4) by a pressure pulse generated by a reciprocating piston (3) that delimits the compression chamber (2), the method comprising degassing the compression chamber (2) before manufacturing begins and/or during a pause in manufacture, wherein, in a first step, ultrasonic waves are coupled into the molten material (1) present in the compression chamber (2), which generate a force (F.sub.Bjrk) that makes gas in the molten material (1) sink, and, in a second step, after ultrasonic excitation has ended, the piston (3) is moved deeper into the compression chamber (2) in order to discharge the gas, which is then rising, via a guide (5) for the piston (3).

15. The method as claimed in claim 14, characterized in that the ultrasonic waves are coupled into the molten material (1) by the piston (3), which is set into high-frequency oscillation for this purpose.

16. The method as claimed in claim 15, characterized in that the piston (3) is set into oscillation and/or moved backward and forward by means of an actuator (6.

17. The method as claimed in claim 14, characterized in that, before the ultrasonic excitation, the molten material (1) present in a region of the spray hole (4) is cooled down until the molten material falls below the solidus line of the molten material (1).

18. The method as claimed in claim 17, characterized in that the molten material (1) present in the region of the spray hole (4) is cooled down with molecular nitrogen (N.sub.2).

19. The method as claimed in claim 15, characterized in that the piston (3) is set into oscillation and/or moved backward and forward by a magnetostrictive, piezoceramic and/or magnetic actuator (6).

20. The method as claimed in claim 17, characterized in that the molten material (1) present in the region of the spray hole (4) is cooled down with molecular nitrogen (N.sub.2), which is fed to the spray hole (4) from the outside by a lance (7).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The invention is explained in greater detail below with reference to the attached drawings. In the drawings:

[0021] FIG. 1 shows a schematic longitudinal section through a device according to invention for the generative manufacture of a three-dimensional workpiece from a molten material,

[0022] FIG. 2 shows an enlarged detail of FIG. 1, and

[0023] FIG. 3 shows a schematic illustration of the forces which act on a gas bubble within a liquid.

DETAILED DESCRIPTION

[0024] FIGS. 1 and 2 show, by way of example, a preferred embodiment of a device according to the invention for the generative manufacture of a three-dimensional workpiece from a molten material 1, in particular from a molten metal. The device is a 3D printer or a print head of a 3D printer.

[0025] Components of the device are a reciprocating piston 3 which delimits a compression chamber 2. The compression chamber 2 is filled with the molten material 1. As a result of the reciprocating movements of the piston 3 (see FIG. 1, arrow in the piston 3), pressure pulses are generated which result in some of the molten material 1 being discharged via a spray hole 4 formed in a ceramic body 8 delimiting the compression chamber 2. The ceramic body 8, which in the present case is plate-shaped, is connected via a clamping sleeve 14 to a hollow-cylindrical housing part 15, which delimits the compression chamber 2 in the radial direction.

[0026] The spray hole 4 formed in the ceramic body 8 has a diameter D which is less than 500 μm. This means that a significant pressure pulse is required to force the molten material 1 through the narrow spray hole 4. The pressure pulse is generated by means of the piston 3, which is connected for this purpose to a piezoceramic actuator 6 via a multi-part piston rod 11. The piston rod 11 and the piston 3 are preloaded against the actuator 6 by means of at least one spring 12.

[0027] As the molten material 1 emerges from the spray hole 4, discrete drops are formed, which separate from the underside of the ceramic body 8 and move in free fall toward a workpiece support (not shown). The line of fall in the free fall ideally corresponds to the longitudinal axis of the spray hole 4 in order to allow the drops to be placed accurately on the workpiece support. The three-dimensional workpiece to be manufactured is thus built up drop by drop on the workpiece support.

[0028] In order to force the molten material 1 out of the compression chamber 2 via the spray hole 4, a sufficiently high pressure or pressure pulse must be built up. This is only possible if there is no highly compressible medium, such as air, in the compression chamber 2. During operation of the device, however, it may happen that air is sucked in from outside via the spray hole 4 and thus gets under the piston 3. This air must be removed before the device is put into operation.

[0029] This means that—in accordance with the method according to the invention—the compression chamber 2 is degassed before the actual manufacture of a three-dimensional workpiece begins. For this purpose, the piston 3 is set into high-frequency oscillation, by means of which ultrasonic waves are coupled into the molten material 1. The molten material 1 transmits the oscillations to the enclosed gas, with the result that this gas sinks as a gas bubble 10 in the molten material 1. The sinking is due to a force F.sub.Bjrk which acts on the gas bubble, more specifically counter to a buoyancy force F.sub.Bou. At the same time, any gas bubbles 10 which adhere to the inner circumferential surface of the housing part 15 are detached and thus likewise sink. If the ultrasonic excitation is then terminated and the piston 3 is moved deeper into the compression chamber 2 (see FIG. 2, arrow in the piston 3), it being possible for the piston stroke to be one to several millimeters, the gas bubbles 10 rise upward as a result of the buoyancy force F.sub.Bou and are discharged from the compression chamber 2 via a guide 5 for the piston 3. The discharge of the gas bubbles 10 is promoted by the conically shaped tip 9 of the piston 3.

[0030] To ensure that no molten material 1 is discharged via the spray hole 4 as the piston 3 is moved into the compression chamber 2, the molten material 1 located in the region of the spray hole 4 is first intensively cooled or frozen. For this purpose, the region of the spray hole 4 is flushed from the outside with molecular nitrogen N.sub.2, it being possible to use a lance 7 for the flushing (see FIG. 1). Once the degassing process has been completed, the frozen molten material 1 is then heated up again and liquefied, making it possible to start the actual manufacture of the three-dimensional workpiece.

[0031] FIG. 3 illustrates, by way of example, the forces which act on a gas bubble 10 enclosed in the liquid during the coupling of ultrasonic waves into a liquid. Initially, a buoyancy force F.sub.Bou acts, and, without ultrasonic excitation, this would lead to the gas bubble 10 rising in the liquid. The buoyancy force F.sub.Bou is counteracted by a force F.sub.D (“drag force”) and a force F.sub.Bjrk (“Bjerknes force”), which together are greater than the buoyancy force F.sub.Bou, causing the gas bubble 10 to sink in the liquid.

[0032] The present invention makes use of this phenomenon, with only the buoyancy force F.sub.Bou being used for the final discharge of the gas bubbles 10 from the compression chamber 2.