DEVICE FOR THE ADDITIVE MANUFACTURE OF THREE-DIMENSIONAL WORKPIECES, AND METHOD FOR OPERATING A DEVICE FOR THE ADDITIVE MANUFACTURE OF THREE-DIMENSIONAL WORKPIECES

Abstract

The invention relates to a device (100) for the additive manufacture of three-dimensional workpieces, in particular a 3D metal printer, comprising a print head (1) and a device (40) for generating an inert atmosphere (22) within the print head (1) by means of a gas (55), in particular inert gas, wherein the print head (1) comprises a housing (3), a device (28) for feeding a metal (14), a piston (5), a reservoir (7) with an outlet opening (10) and an actuator device (12) for displacing the piston (5), wherein the reservoir (7) has a melt region (20) and a displacement body chamber (21) for a liquid phase (8) of the metal (14), wherein the melt region (20) adjoins the inert atmosphere (22) and is connected to the displacement body chamber (21) such that, as a result of the displacement of the piston (5), the liquid phase (8) of the metal (14) can be caused to pass through the outlet opening (10). The invention is distinguished by the fact that the device (40) for generating the inert atmosphere (22) is arranged outside the print head (1), wherein said device comprises an accumulator (41), at least one means (42, 43) for pressure control, and a gas line (50, 51, 52). The invention furthermore relates to methods for operating the device (100).

Claims

1. An apparatus (100) for additive manufacture of three-dimensional workpieces, the apparatus comprising a printhead (1) and an apparatus (40) for generating an inert atmosphere (22) within the printhead (1) by means of a gas (55), wherein the printhead (1) comprises a housing (3), an apparatus (28) for supply of a metal (14), a piston (5), a reservoir (7) having an exit orifice (10) and an actuator apparatus (12) for moving the piston (5), wherein the reservoir (7) has a melt region (20) and a displacement chamber (21) for a liquid phase (8) of the metal (14), wherein the melt region (20) adjoins the inert atmosphere (22) and is connected to the displacement chamber (21) in such a way that the movement of the piston (5) can induce the liquid phase (8) of the metal (14) to pass through the exit orifice (10), characterized in that the apparatus (40) for generating the inert atmosphere (22) is disposed outside the printhead (1) and comprises a storage means (41), at least one means (42, 43) of pressure control, and a gas conduit (50, 51, 52).

2. The apparatus (100) as claimed in claim 1, characterized in that the gas conduit (50, 51, 52) of the apparatus (40) for generating the inert atmosphere (22) is connected to the reservoir (7) via a conduit (53), wherein the conduit (53) is disposed within an insulation plate (26) of the printhead (1).

3. The apparatus (100) as claimed in claim 1, characterized in that the inert atmosphere (22) has a higher pressure (P.sub.i) within the reservoir (7) than an ambient pressure (P.sub.a) outside the printhead (1), wherein the pressure (P.sub.i) is controllable by the at least one means (42, 43) of pressure control.

4. The apparatus (100) as claimed in claim 1, characterized in that the means (42, 43) of pressure control are formed from a pressure control valve (42) and/or a controllable throttle (43).

5. A method of operating an apparatus (100) for additive manufacture as claimed in claim 3, during a printing operation for production of a workpiece by emitting individual droplets (15), characterized in that the pressure (P.sub.i) of the inert atmosphere (22) is controlled by the means (42, 43) of pressure control in such a way that the pressure (P.sub.i) is above the ambient pressure (P.sub.a) and below a limiting pressure that causes emission of droplets (15) through the exit orifice (10).

6. A method of operating an apparatus (100) for additive manufacture of three-dimensional workpieces as claimed in claim 3, during an operation of filling a workpiece, characterized in that the pressure (P.sub.i) of the inert atmosphere (22) is controlled by the means (42, 43) of pressure control in such a way that the pressure (P.sub.i) is above the ambient pressure (P.sub.a) and above a limiting pressure that causes emission of droplets (15) through the exit orifice (10), such that the liquid phase (8) of the metal (14) is emitted through the exit orifice (10) by virtue of the pressure exerted by the inert atmosphere (22).

7. A method of operating an apparatus (100) for additive manufacture of three-dimensional workpieces as claimed in claim 3, during a printing operation for production of a workpiece by emission of individual droplets (15) and filling, characterized in that the production of the workpiece by emission of individual droplets (15) is accomplished such that the pressure (P.sub.i) of the inert atmosphere (22) is controlled by the means (42, 43) of pressure control in such a way that the pressure (P.sub.i) is above the ambient pressure (P.sub.a) and below a limiting pressure that causes emission of droplets (15) through the exit orifice (10) and the filling of the workpiece is accomplished such that the pressure (P.sub.i) of the inert atmosphere (22) is controlled by the means (42, 43) of pressure control in such a way that the pressure (P.sub.i) is above the ambient pressure (P.sub.a) and above the limiting pressure that causes emission of droplets (15) through the exit orifice (10), such that the liquid phase (8) of the metal (14) is emitted through the exit orifice (10) by virtue of the pressure exerted by the inert atmosphere (22).

8. A method of operating an apparatus (100) for additive manufacture as claimed in claim 3, during a printing operation for emission of a filament, characterized in that the pressure (P.sub.i) of the inert atmosphere (22) is controlled by the means (42, 43) of pressure control in such a way that the pressure (P.sub.i) is above the ambient pressure (P.sub.a) and above a limiting pressure that causes emission of droplets (15) through the exit orifice (10).

9. A method of operating an apparatus (100) for additive manufacture of three-dimensional workpieces as claimed in claim 3, during an operation of emptying the printhead (1), characterized in that the pressure (P.sub.i) of the inert atmosphere (22) is controlled by the means (42, 43) of pressure control in such a way that the pressure (P.sub.i) is above the ambient pressure (P.sub.a) and above the limiting pressure that causes emission of droplets (15) through the exit orifice (10), such that the liquid phase (8) of the metal (14) is emitted through the exit orifice (10) by virtue of the pressure exerted by the inert atmosphere (22), and the reservoir (7) and the displacement chamber (21) are purged by the gas (55).

10. (canceled)

11. The apparatus (100) as claimed in claim 1, characterized in that the apparatus (100) is a 3D metal printer.

12. The apparatus (100) as claimed in claim 1, characterized in that the gas (55) is an inert gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The FIGURE shows:

[0031] FIG. 1 a working example of the apparatus of the invention.

DETAILED DESCRIPTION

[0032] The FIGURE shows a working example of an apparatus 100 for additive manufacture of three-dimensional workpieces, especially a 3D metal printer.

[0033] The apparatus 100 comprises a printhead 1 and an apparatus 40 for generation of an inert atmosphere 22 within the printhead 1 by means of a gas 55, especially inert gas. The printhead 1 comprises a housing 3, an apparatus 28 for supply of a metal 14 in solid phase, a piston 5, a reservoir 7, 27 with an exit orifice 10, and an actuator apparatus 12 for movement of the piston. The reservoir 7, 27 has a melt region 20 and a displacement chamber 21 for a liquid phase 8 of the metal 14, with the melt region 20 adjoining the inert atmosphere 22 and connected to the displacement chamber 21 in such a way that the movement of the piston 5 can induce the liquid phase 8 of the metal 14 to pass through the exit orifice 10. The liquid phase 8 of the metal 14 is also referred to as melt 8, and the inert atmosphere 22 is formed by introduction of the inert gas 55 into the reservoir 7, 27. Introduction of the inert gas 55 preferably takes place via a cold region of the printhead 1 into the reservoir 7, 27.

[0034] The housing 3 is in multipart form, comprising at least a cooling flange 25, the insulation plate 26, and the reservoir 7, 27.

[0035] The apparatus 40 for generation of the inert atmosphere 22 is disposed outside the printhead 1, comprising a storage means 41, especially pressurized storage means for the gas 55, at least one means 42, 43 of pressure control, and a gas conduit 50, 51, 52. The means 42, 43 of pressure control, in the embodiment shown, are formed from an electrical pressure control valve 41 and an electrically controllable throttle 42. It is also possible to use either solely the electrical pressure control valve 42 or solely the electrically controllable throttle 43 for control of the pressure of the inert atmosphere 22 in the reservoir 7, or within the printhead.

[0036] Moreover, the gas conduit 50, 51, 52 of the apparatus 40 for generation of the inert atmosphere 22 is connected to the reservoir 7 via a conduit 53, with the conduit 53 disposed within the insulation plate 26 of the printhead 1. By means of connection adapters (not shown), the apparatus 40 for generation of the inert atmosphere 22 may be connected to the conduit 53 of the printhead 1 by means of the gas conduit 50, 51, 52 disposed outside the printhead 1. The conduit 53 within the insulation plate 26 is preferably designed as a passage hole.

[0037] The piston 5 has a multipart design, comprising at least one piston rod 17 made of a metallic material and a die 18 made of ceramic. The piston rod 17, proceeding from the actuator device 12, projects through the cooling flange 25 and the insulation plate 26 into the reservoir 7, 27, where it merges into the die 18.

[0038] The cooling flange 25 has a recess 30 to accommodate the actuator device 12 in the form of a piezoelectric actuator 12. During operation, the piezoelectric actuator 12 is fixed in the recess 30 in such a way that, on application of a voltage, it exerts a working stroke on the piston 5, specifically on the piston rod 17 of the piston. The piston rod 17 transmits the working stroke to the piston 18, such that it induces the liquid phase 8 of the metal 14 to pass through the exit orifice 10. Without actuation of the actuator 12, the piston 5 can be reset to a starting position by a spring 13, with the spring 13 disposed in the recess 30 of the cooling flange 25 between a shoulder 24 and the actuator 12. The spring 13 takes the form of a cup spring.

[0039] In addition, the cooling flange 25 has cooling channels 31 for cooling. The cooling channels 31 are disposed between the cooling flange 25 and the insulation plate 26, and a cooling medium flows through them. This serves as cooling against the heating by the melt 8 and for cooling of the actuator 12 in operation. The cooling flange 25 is formed from a metallic material.

[0040] The insulation plate 26 adjoining the cooling flange 25 on the side of the cooling channels 31 is formed from a heat-insulating material and is designed in such a way that it reduces heat transfer from the reservoir 7, 27 to the cooling flange 25.

[0041] The apparatus 28 for supply of the metal 14 opens into the reservoir 7, 27 and is disposed in the cooling flange 25 and the insulation plate 26. The apparatus 28 projects through the cooling flange 25 and the insulation plate 26, and the metal 14, or the material 14 to be printed, is suppliable through the apparatus 28 from the outside. It is possible with preference to use pre-dosed pieces of material, or pellets. At the transition of the insulation plate 26 to the reservoir 7, 27, there is an orifice 29 through which the material 14 enters the reservoir 7, 27. The opening 29 is closable by an apparatus 32, such that it is preferably open only when the material 14 is being supplied, which reduces the escape of energy, or gas, from the inert atmosphere 22.

[0042] The reservoir 7, 27 takes the form of a melt crucible 27, with an inductor 35 disposed outside the melt crucible 27 and a sensor 36, especially a temperature sensor, within the melt crucible. There may optionally be an insulator (not shown) between the melt crucible 27 and the inductor 35, or the inductor coil 35.

[0043] The metal 14 reaches the melting region 20 of the melt crucible in a solid phase 14 and is heated by the inductor 35 until it is converted to a liquid phase 8. On attainment of a desired process temperature of the melt 8, which is ascertained by the temperature sensor 36, the printhead 1 can commence operation. The liquid phase 8, or the melt 8, under gravity of the melt 8 or through a combination of gravity and atmospheric pressure of the inert gas 22, moves past the die 18 into the displacement chamber 21. The die 18 of the piston 5 is surrounded by a pressure side 19 in the melt 8, or by melt 8, and, on the connection side to the piston rod 17, surrounded in the inert atmosphere 22, or by the inert atmosphere 22. The piston rod 17 does not come into contact with the melt 8 by virtue of the process.

[0044] The ceramic of the die 18 advantageously has very good thermal conductivity, in order to be able to efficiently transfer the heat generated by the inductor 35 into the displacement chamber 21.

[0045] On actuation of the piezoelectric actuator 12, the pressure side 19 of the die 18 exerts a pressure on the melt 8 in the displacement chamber 21 in the direction of the exit orifice 10, and ensures expulsion of a droplet 15 through the exit orifice 10 of the reservoir 7, 27, or of the displacement chamber 21. The exit orifice 10 is designed for the expulsion of droplets 15 of the liquid phase 8 of the metal 14, the exit orifice 10 having the form of a nozzle 10 and being connectable in a fixed manner to the melt crucible 27, or, as shown in the working example, having an exchangeable insert 11 that permits the use of different nozzle geometries.

[0046] The inert atmosphere 22 within the reservoir 7 during operation is at a higher pressure P.sub.i than an ambient pressure P.sub.a outside the printhead 1, the pressure P.sub.i being controllable by the at least one means 42, 43 of pressure control.

[0047] The invention also covers methods of operating the apparatus 100 for additive manufacture.

[0048] In a first method, especially during a printing operation for production of a workpiece by emission of individual droplets 15, the pressure P.sub.i of the inert atmosphere 22 is controlled, or adjusted, by the means 42, 43 of pressure control in such a way that the pressure P.sub.i is above the ambient pressure P.sub.a and below a limiting pressure that causes, or would cause, emission of droplets 15 through the exit orifice 10. The higher pressure P.sub.i of the inert atmosphere 22 relative to the ambient pressure P.sub.a offers pressure assistance for the piston 5. The pressure P.sub.i here is below a limiting pressure that would cause expulsion of droplets 15 from the exit orifice 10 of the printhead 1 without the piston 5 performing a stroke, or a pressure pulse, on the melt 8. The pressure P.sub.i of the inert atmosphere 22 to be established by the means 42, 43 of pressure control is dependent, for example, on the metal 14 to be processed and the resulting viscosity of the melt 8. And also on the size of the exit orifice 10.

[0049] The pressure P.sub.i is adjusted such that droplets 15 are expelled only when the piston 5 is moved by the actuator 12.

[0050] In a second method, especially during an operation of filling a workpiece, the pressure P.sub.i of the inert atmosphere 22 is controlled, or adjusted, by the means 42, 43 of pressure control in such a way that the pressure P.sub.i is above the ambient pressure P.sub.a and above the limiting pressure that causes emission of droplets 15 through the exit orifice 10, such that the liquid phase 8 of the metal 14 is emitted through the exit orifice 10 by virtue of the pressure exerted by the inert atmosphere 22.

[0051] The higher pressure P.sub.i of the inert atmosphere relative to the ambient pressure P.sub.a makes it possible for the printhead 1 to generate a continuous expulsion of the liquid phase 8 of the metal 14, or of the melt 8, with the pressure P.sub.i of the inert atmosphere 22 above a limiting pressure for expulsion of droplets 15, in such a way that the liquid phase 8 of the metal 14, or the melt 8, can be forced out of the exit orifice 10 into a cavity of a workpiece. The stroke, or the pressure pulse, of the piston 5 on the melt 8 is interrupted for this operation. During the filling of the workpiece, the piston 15 may be positioned either within or outside the melt 8. This method enables very rapid filling of regions in a workpiece, or in a 3D-printed part, which can reduce the overall print time for a workpiece.

[0052] In a third method, especially during a printing operation for production of a workpiece by emission of individual droplets 15 and filling, the workpiece is produced by emission of individual droplets 15 by employing the first method, and the workpiece, especially a cavity of a workpiece, is filled by employing the second method.

[0053] The methods described above may be combined as desired during a printing operation.

[0054] In a fourth method, especially during a printing operation for emission of a filament, the pressure P.sub.i of the inert atmosphere 22 is controlled, or adjusted, by the means 42, 43 of pressure control such that the pressure P.sub.i is above the ambient pressure P.sub.a and above a limiting pressure that causes emission of droplets 15 through the exit orifice 10.

[0055] The higher pressure P.sub.i of the inert atmosphere 22 relative to the ambient pressure P.sub.a makes it possible for the printhead 1 to produce a filament, with the pressure P.sub.i of the inert atmosphere 22 above a limiting pressure for expulsion of droplets 15, in such a way that the liquid phase 8 of the metal 14, or the melt 8, is forced continuously out of the exit orifice 10 of the printhead 1, such that, after the setting of the melt, a filament, or a strand, is formed from the metal 14. No additional stroke of the piston 5 is necessary for this process. During the production of the filament, this may be positioned either within or outside the melt.

[0056] In a fifth method, especially during an operation of emptying the printhead 1, the pressure P.sub.i of the inert atmosphere 22 is controlled by the means 42, 43 of pressure control in such a way that the pressure P.sub.i is above the ambient pressure P.sub.a and above the limiting pressure that causes emission of droplets 15 through the exit orifice 10, such that the liquid phase 8 of the metal 14 is emitted through the exit orifice 10 by virtue of the pressure exerted by the inert atmosphere 22, with purging of reservoir 7 and the displacement chamber 21 by the gas 55.

[0057] The higher pressure P.sub.i of the inert atmosphere 22 relative to the ambient pressure P.sub.a makes it possible for the melt 8 to be very substantially removed from the printhead 1, with the pressure P.sub.i of the inert atmosphere 22 above a limiting pressure for expulsion of droplets 15, in such a way that the liquid phase 8 of the metal 14, or the melt 8, is forced continuously out of the exit orifice 10. For this purpose, no additional stroke of the piston 5 is necessary. During the emptying operation, this should be positioned outside the melt 8, so that no residues of the liquid phase 8 of the metal 14 adhere to the die 18 of the piston 5.

[0058] The emptying of the printhead 1, or of the reservoir 7 and the displacement chamber 21, takes place in that the melt 8 still present within the printhead 1, preferably at the end of a printing operation, is purged from the printhead 1, or the reservoir 7 and the displacement chamber 21, in that the inert gas 55 is introduced into the printhead with the pressure P.sub.i, or the elevated pressure with respect to the ambient pressure P.sub.a of the printhead 1. As a result, during the cooling and setting of the melt 8, stresses that occur in the components of the printhead 1 that come into contact with the melt 8 are avoided.

[0059] The methods described above may be executed individually or successively in combination for operation of the apparatus 100 for additive manufacture.