WO2017050592A1

WO2017050592A1 - Printhead for 3d printing of metals

Info

Publication number: WO2017050592A1
Application number: PCT/EP2016/071289
Authority: WO
Inventors: Peter Voehringer; Sebastian Herbster; Udo Riegler; Robert Giezendanner-Thoben; Weidong Qi
Original assignee: Robert Bosch Gmbh
Priority date: 2015-09-24
Filing date: 2016-09-09
Publication date: 2017-03-30
Also published as: DE102015218375A1

Abstract

The invention relates to a printhead (1) for a 3D printer, comprising a reservoir (2) for a metal (3), wherein the reservoir (2) comprises an outlet opening (2e) for the output of drops (3c) of a liquid phase (3b) of the metal (3), wherein the reservoir (2) is delimited by a moveably mounted die (4), such that, by moving the die (4) in the direction of the liquid phase (3b) of the metal (3), the liquid phase (3b) of the metal (3) can be caused to pass through the outlet opening (2e). The invention also relates to a method for operating a print head (1).

Description

Description Title:

Printhead for 3D printing of metals

The invention relates to a printhead for a 3D printer suitable for printing metals and to methods of operation.

State of the art

A 3D printer for a thermoplastic material obtains a solid phase of this material as a starting material, generates a liquid phase therefrom, and selectively deposits this liquid phase at the locations associated with the object to be formed. Such a 3D printer includes a printhead into which the source material is melted. Furthermore, means are provided for generating a relative movement between the print head and the work surface on which the object is to be formed. In this case, either only the print head, only the work surface or both the print head and the work surface can be moved.

The printhead has a first mode of operation in which liquid material exits therefrom and a second mode of operation in which no liquid material exits therefrom. The second operating state is assumed, for example, when a different position is approached on the work surface and no material is to be deposited on the way there. For example, between the two operating states of the print head

be switched by the propulsion of the solid starting material is switched on or off.

Compared to thermoplastics metals have a much higher melting point and at the same time in the liquid state a significant lower viscosity. One research approach to solving the problem of adding liquid metal to the object at defined locations is pneumatic drop-on-demand technology. This technique is described, for example, in (Han-Song Zuo, He-jun Li, Le-juaqi, Jun Luo, Song-yi Zhong, Hai-peng Li, "Effect on Wetting Behavior on-demand technique ", Journal of Materials Processing Technology 214, 2566-2575 (2014).) The metallic starting material is melted by induction heating in a reservoir having an open nozzle at its lower end, around a drop of liquid metal to drive out of this nozzle, the reservoir is supplied by supplying an inert gas with a pressure pulse.

Disclosure of the invention

Within the scope of the invention, a print head for a 3D printer has been developed. This printhead includes a reservoir for a metal. The reservoir has an exit opening for the ejection of drops of a liquid phase of the metal.

According to the invention, the reservoir is supported by a displaceable

Stamp limited, so that by a displacement of the punch in the direction of the liquid phase of the metal, the liquid phase of the metal can be excited to pass through the outlet opening.

It has been recognized that the printhead in this way is structurally much simpler and cheaper to build than a printhead associated with the

pneumatic drop-on-demand technology works. The printhead is also much easier to miniaturize. The smaller the reservoir for the liquid phase of the metal, the less heating power is available for the

Producing the liquid phase of the metal required and the less heat gives the printhead to the environment.

By compared to the pneumatic drop-on-demand technology much more compact dimensions of the printhead according to the invention

For example, be retrofitted into an existing 3D printer, the originally intended for the processing of thermoplastic materials. In particular, such a 3D printer can be used by replacing or changing the printhead either for thermoplastic or for metallic materials.

The operation of the printhead is principally position-independent. Insofar as the liquid phase of the metal is forced by its gravitational pressure in the direction of the outlet opening, such a dimensioning of the dimensions of the

Reservoirs make sense that the atmospheric pressure from outside the

Reservoirs the gravitational pressure counteracts and at least sufficient to compensate for this. In particular, this atmospheric pressure should not be neutralized by the part of the reservoir which houses the liquid phase of the metal being in communication with the atmosphere.

The liquid phase of the metal exits the discharge opening at the exact moment when the total effective pressure from within the reservoir on the liquid phase of the metal is greater than the counterpressure acting outside the discharge opening. There are essentially two sources for the pressure acting on the liquid phase of the metal within the reservoir: On the one hand, pressure can be introduced via the supply of the metal in solid or liquid form. For example, when a solid phase of the metal is introduced into the print head with a mechanical force and fused in the print head, the mechanical force is translated directly to a pressure in the liquid phase of the metal. On the other hand, this can be modulated by the displacement of the stamp, a second pressure component. This modulation can be very fast, so that in rapid succession, a plurality of drops of the liquid phase of the metal can be generated.

This is especially true in a particularly advantageous embodiment of the invention, in which a piezoelectric actuator is provided for displacement of the punch. Such an actuator reacts very quickly to an electrical control with a change in length. He can exert a large force of up to several 100 Newton. The maximum stroke is typically in the order of 50 μηι. As a piezoelectric actuator, for example, a common actuator in diesel injection systems can be misappropriated. Advantageously, the stamp is made of a thermally insulating material having a thermal conductivity of 3 W / (mK) or less. This material may in particular be a ceramic. The liquid phase of the metal has

Temperatures of typically 600 to 1000 ° C, one of which,

For example, piezoelectric actuator is shielded as a rule. For example, if the stamp is 7 mm thick, it cools down to 125 ° C over an air-cooled length of 5 cm. Active cooling along the punch can shorten that length.

In a particularly advantageous embodiment of the invention, the reservoir is tubular with two ends. At its first end, the reservoir for supplying the metal is formed. At its second end it is closed by the stamp. The exit opening is then between the first end and the second end. An internal pressure in the liquid phase of the metal in the reservoir, which expels drops of the liquid phase of the metal from the outlet opening, can then be particularly easily by the

Interaction of the pressures are generated, which are exercised by the supply of the metal on the one hand and by the stamp on the other hand. If a solid phase of the metal is supplied, then a mechanical force can be exerted on this solid phase, which is translated into an internal pressure; If, however, the liquid phase of the metal is supplied at the first end of the reservoir, then a gravitational pressure prevailing in this supply can provide an internal pressure in the reservoir.

Alternatively, in another particularly advantageous embodiment of the invention, in which the reservoir is also tubular with two ends and is formed at its first end for supplying the metal, the reservoir may be formed at its second end as an outlet opening. The reservoir is then no longer closed at this end by the stamp. Instead, the reservoir in this embodiment, in its lateral surface on an additional opening through which the punch is guided. If the printhead is oriented in operation so that the second end of the reservoir at the same time represents the lowest point of the reservoir, the tendency of the. By the

Outlet opening passing through the liquid phase of the metal amplified finally to be released from the reservoir. The tendency to instead wet the outer wall of the reservoir is reduced.

In a further particularly advantageous embodiment of the invention that is

Reservoir formed at its first end for supplying a solid phase of the metal. In addition, a heater effective for the solid phase of the metal is provided to produce the liquid phase of the metal. The liquid phase of the metal is then first formed within the reservoir. It is enclosed between the punch and the supplied solid phase of the metal, so that the internal pressure can be optimally generated by the interaction of the feed with the stamp.

In a further particularly advantageous embodiment of the invention, the heater is an induction heater with at least two mutually separately controllable circuits. In this way, the metal can be gradually heated between the place where it enters the printhead and the place where it enters the liquid phase. In particular, it can be liquefied only shortly before the region of the reservoir in which the outlet opening is arranged. As a result, only a small part of the reservoir is stressed by the contact with the liquid phase of the metal. In addition, compared to a sudden heating of the metal, the temperature gradient in the inner wall of the reservoir can be reduced. Such a temperature gradient can be particularly strong in a ceramic reservoir strong mechanical

Create tensions through which the reservoir can eventually break.

In a further particularly advantageous embodiment of the invention, the inner diameter of the reservoir increases monotonically between its first end and its second end. In particular, this inner diameter in the region in which the punch is movable into the liquid phase of the metal by at least a factor of 5, so for example of wire diameter 1 mm on punch diameter 5 mm, be greater than at the first end of the reservoir. As a result, the punch can have a larger diameter and displace more volume of the liquid phase of the metal per unit stroke. The more volume the punch can displace, the bigger it is Total volume of drops, the total per unit time from the

Outlet opening can be ejected.

At the first end of the reservoir, the solid phase of the metal may for example be supplied in the form of a wire. The diameter of the wire may for example be in the range between 1 mm and 5 mm. The wire is there preferably close to the inner circumference of the reservoir with a game of typically 50 μηι or less. The stamp, however, may for example have a diameter between 7 mm and 12 mm. For example, if the punch has a diameter of 8 mm, it displaces a volume of 2.5 mm ³ at a stroke of 50 μm. For example, if it is desired to expel drops of the liquid phase of the metal with a diameter of 190 μm, then each of these drops has a volume of 0.029 mm ³ . A single stroke of the punch of 50 μηι can then release up to 86 of these drops.

The essential function of the stamper is to effect the ejection of drops from the liquid phase of the metal by modulating the pressure in the reservoir. The source of material for these drops is still the feeder. To release a continuous stream of drops, the

Ingress mass flow into the reservoir, from which immediately, for example, the feed rate of the solid phase of the metal is derived, the

Exit mass flow by released from the outlet opening drops plus the leakage between the outer periphery of the punch and the inner circumference of the reservoir correspond.

In a further particularly advantageous embodiment of the invention, the outlet opening is arranged at the end of a discharge pipe, into which the reservoir opens. In this case, the exit angle of the liquid phase of the metal from the discharge pipe is advantageously dimensioned such that the liquid phase of the metal emerging from the discharge pipe does not come into contact with the outer wall of the reservoir. In this way it is avoided that the outer wall is contaminated with the metal, which may be difficult to remove after cooling. At a given internal pressure in the reservoir, which acts on the liquid phase of the metal, depending on the diameter of the exit orifice, internal pressure and surface tension and viscosity of the liquid phase of the metal, the free energy decimation determines whether droplets or a continuous liquid stream will form , Therefore, with a given geometric configuration and for a given metal, it is generally not possible to produce any drop sizes, but only drop sizes in certain ranges or only certain discrete drop sizes.

The invention also relates to a method for operating a printhead according to the invention. In this method, during a monotonous movement of the punch toward the liquid phase of the metal, a plurality of drops of the liquid phase of the metal are emitted from the exit opening, as the position of the punch along an axis directed into the liquid phase of the metal serves as a staircase function Time t is progressing. This is the optimal interaction between the component of the internal pressure in the liquid phase of the metal in the reservoir, which is introduced by the supply of the metal, and the modulation by the stamp.

The invention also relates to a further method for operating a printhead according to the invention. In this method, the metal between the first end of the reservoir and the outlet opening

melted. The specific heat output per unit length of the tubular reservoir is in this case monotonically increased between the first end of the reservoir and the region in which the liquid phase of the metal is formed. On the one hand, this process control has a particularly gentle effect on the material of the reservoir, which may be a ceramic in particular. On the other hand, this process can be in a particularly simple way to the strong

to adapt different behaviors when using different metals

Show melting. Different metals require different amounts of energy in different temperature ranges for further heating per Kelvin, because the heat capacities and melting points

Different metals usually distinguish and because in different metals at certain temperatures take place structural changes that cost energy. Advantageously, at most the 25% of the inner volume of the reservoir closest to the plunger is coated with the liquid phase of the metal. The smaller this proportion, the less energy is required for the provision of the liquid phase and the less the material of the reservoir is stressed by the contact with the liquid phase of the metal.

Further measures improving the invention will be described in more detail below together with the description of the preferred embodiments of the invention with reference to figures.

embodiments

It shows:

Figure 1 embodiment of the printhead according to the invention with

tubular reservoir that is closed at its second end 2b by the punch 4.

Figure 2 embodiment of the printhead according to the invention with

tubular reservoir 2, which has in its lateral surface 2i an additional opening 2j, through which the punch 4 is guided.

FIG. 1 shows a first exemplary embodiment of the invention

Printhead 1. The printhead 1 has a tubular reservoir 2 for the metal 3 having a first end 2a and a second end 2b. The reservoir 2 has an outer wall 2g. At the first end 2a of the reservoir 2, a solid phase 3a of the metal 3 is supplied from left to right, which is illustrated by the arrow. In the sub-area 2c of the reservoir 2, a heater 6 is installed on the lateral surface 2i of the reservoir 2, which comprises four independently controllable circuits 6a, 6b, 6c and 6d, via which the metal 3 can be heated by induction coils. In this case, the heating powers introduced by the four circuits 6a, 6b, 6c and 6d are the same

dimensioned such that the solid phase 3a of the metal 3 only in the region in which the fourth circuit 6d heats the metal 3, in the liquid phase 3b passes. In the transition from the region 2c of the reservoir 2, in which the heater 6 is installed, in the region 2d, which opens into the discharge pipe 2f, the inner diameter of the reservoir 2 increases significantly. This has the purpose that with a stroke of the punch 4, the area 2d and thus the second end

2b of the reservoir 2 closes, as much volume of the liquid phase 3d of the metal 3 is to be displaced. The punch 4 consists of a first part 4a, which comes directly in contact with the liquid phase 3b of the metal 3, and an air-cooled extension 4b, along which the temperature decays from the part 4a to a value that is suitable for the piezoelectric

Actuator 5 at the right end of the extension 4b is compatible. The punch 4 is displaced by the piezoelectric actuator 5 along the axis 2h pointing into the liquid phase 3b of the metal 3. This is indicated by the double arrow. This axis 2h runs in the direction of the x-coordinate. For this, the y-coordinate axis runs vertically in the plane of the drawing.

The force exerted in the supply of the solid phase 3a of the metal 3

mechanical force is converted immediately to a pressure in the liquid phase 3b of the metal 3 in the reservoir 2. A second pressure component is introduced by the movement of the punch 4. Especially the modulation of the pressure by the punch 4 causes the liquid phase 3b of the metal 3 in the form of drops 3c to emerge from the outlet opening 2e at the end of the discharge pipe 2f. In this case, the exit angle of the discharge pipe 2f is dimensioned such that the droplets 3c finally leave the discharge pipe and do not come into contact with the outer wall 2g of the reservoir 2.

In the exemplary embodiment shown in FIG. 2, the reservoir 2 is no longer closed by the punch 4 at its second end 2b. Instead, the reservoir 2 opens at this second end 2b in the discharge pipe 2f with the outlet opening 2e. The punch 4 is guided with its extension 4b through the additional opening 2j in the lateral surface 2i of the reservoir 2. The first part 4a of the punch 4 seals the opening 2j against the liquid phase 3b of the metal 3. The punch 4 is displaced during operation of the print head along the axis 2h, which is directed to the liquid phase 3b of the metal 3. In contrast to FIG. 1, this axis 2h now runs in y- Coordinate direction in the plane of the drawing, while the solid as a wire phase 3a of the metal 3 is still oriented along the x-coordinate direction.

If this embodiment of the print head is oriented in operation so that the x-coordinate direction points downward, the second end 2b of FIG

Reservoirs 2 at the same time its lowest point. The opposite to the

Embodiment made in accordance with Figure 1 constructive change then has the effect that the drops 3c of the metal 3 are more likely to finally detach from the reservoir 2.

Claims

claims

1. Printhead (1) for a 3D printer, comprising a reservoir (2) for a metal (3), the reservoir (2) having an outlet opening (2e) for the ejection of drops (3c) of a liquid phase (3b) of the metal (3), characterized in that the reservoir (2) is delimited by a displaceably mounted punch (4) so that displacement of the punch (4) in the direction of the liquid phase (3b) of the metal (3 ) the liquid phase (3b) of the metal (3) can be excited to pass through the outlet opening (2e).

Second print head (1) according to claim 1, characterized in that a piezoelectric actuator (5) for displacement of the punch (4) is provided.

3. printhead (1) according to one of claims 1 to 2, characterized

characterized in that the punch (4) consists of a thermally insulating material having a thermal conductivity of 3 W / (mK) or less.

4. printhead (1) according to one of claims 1 to 3, characterized

characterized in that the reservoir (2) is tubular with two ends (2a, 2b), formed at its first end (2a) for feeding the metal (3) and closed at its second end (2b) by the punch (4) is.

5. Printhead (1) according to any one of claims 1 to 3, characterized in that the reservoir (2) is tubular with two ends (2a, 2b), at its first end (2a) for feeding the metal (3). is formed at its second end as an outlet opening (2e) is formed and in its lateral surface (2i) has an additional opening (2j), through which the punch (4) is guided.

6. printhead (1) according to one of claims 4 to 5, characterized

characterized in that the reservoir (2) is formed at its first end (2a) for supplying a solid phase (3a) of the metal (3), and in that a heater (6) acting on the solid phase (3a) of the metal is used to produce the liquid phase (3b) of the metal (3) is provided.

7. printhead (1) according to claim 6, characterized in that the

Heater (6) is an induction heater with at least two mutually separately controllable circuits (6a, 6b, 6c, 6d).

8. printhead (1) according to one of claims 4 to 7, characterized

characterized in that the inner diameter of the reservoir (2) monotonously increases between its first end (2a) and its second end (2b).

9. Printhead (1) according to claim 8, characterized in that the inner diameter of the reservoir (2) in the region in which the punch (4) in the liquid phase (3b) of the metal (3) is movable by at least one Factor 5 be greater than at the first end of the reservoir (2).

10. printhead (1) according to one of claims 1 to 9, characterized

in that the outlet opening (2e) is arranged at the end of a discharge pipe (2f) into which the reservoir (2) opens.

11. A method for operating a printhead (1) according to any one of claims 1 to 10, characterized in that during a monotonous movement of the punch (4) in the direction of the liquid phase (3b) of the metal (3) a plurality of drops ( 3c) of the liquid phase (3b) of the metal (3) is emitted from the outlet opening (2e) by the position of the punch (4) along an axis (2h) directed into the liquid phase (3b) of the metal (3) Step function of time t is progressing.

12. A method for operating a printhead (1) according to any one of claims 6 to 10, characterized in that the metal (3) between the first end (2a) of the reservoir (2) and the outlet opening (2e) is melted, wherein the specific heat output per unit length of tubular reservoir (2) between the first end (2a) of the reservoir (2) and the region in which the liquid phase (3b) of the metal (3) is formed, is monotonously increased.

13. The method according to claim 12, characterized in that at most the stamp (4) closest to 25% of

Inside volume of the reservoir (2) with the liquid phase (3b) of the metal (3) are occupied.