DE102016224047A1 - Printhead for 3D printing of metals - Google Patents

Abstract

The invention relates to a print head (1) for a 3D printer, in particular a metal printer, comprising a housing (3), a device (28) for supplying a metal (14), a piston (5), a reservoir (7, 27). with an outlet opening (10) and an actuator device (12) for displacing the piston (5).
It is characterized in that the reservoir (7, 27) has a melting region (20) and a displacement chamber (21) for a liquid phase (8) of the metal (14), the melting region (20) being exposed to an inert atmosphere ( 22) is adjacent and with the displacement chamber (21) connected such that the liquid phase (8) of the metal (14) for passage through the outlet opening (10) can be excited by the displacement of the piston (5).
Furthermore, the invention relates to a method for operating a printhead (1).

Description

The invention relates to a printhead for a 3D printer suitable for printing metals and to a method of operating the printhead.

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, it is possible to switch between the two operating states of the print head by switching on or off the propulsion of the solid starting material.

Compared to thermoplastics metals have a much higher melting point and at the same time in the liquid state a much 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 used for example in ( Han-song Zuo, He-jun Li, Le-juaqi, Jun Luo, Song-yi Zhong, Hai-peng Li, "Effect on wetting behavior on the basis of pneumatic drop-on-demand technique", Journal of Materials Processing Technology 214, 2566-2575 (2014)) explained. The metallic starting material is melted by induction heating in a reservoir having an open nozzle at its lower end. To drive a drop of liquid metal from this nozzle, the reservoir is acted upon by supplying an inert gas with a pressure pulse generated by a solenoid valve.

A disadvantage of this solution is the formation of droplets by a pressure pulse on the gas, since the compressibility of the gas only partially allows a high clock frequency of the drive, whereby the build-up rate of a workpiece for industrial use is not acceptable.

One approach without pneumatic drop-on-demand technology is in the writing not yet published at the time of this application DE 102015218375 described.

It shows a printhead comprising a reservoir for a metal without the use of a gas atmosphere, which is driven by a piezoelectric actuator. The metal is inductively heated and continuously changes from the solid phase to the liquid phase.

A disadvantage of this solution is the lack of separation of the solid from the liquid phase of the metal.

• • der Gewährleistung eines dauerhaften Betriebs,
• • der Reproduzierbarkeit der Tropfen, bzw. des Aufbaus des Bauteils,
• • der Energieeffizienz bezüglich der Erschmelzung und der Bauteilerstellung,
• • dem Einhalten von geringen Nebenzeiten z.B. zur Inbetriebnahme und beim Abschalten und
• • dem Austausch von Verschleißteilen.

Currently, no 3D metal printers are known that meet industrial requirements, such as

• • the guarantee of a permanent operation,
• • the reproducibility of the drops, or the structure of the component,
• The energy efficiency with regard to melting and component production,
• • compliance with low non-productive times, eg for commissioning and when switching off and
• • the replacement of wearing parts.

Disclosure of the invention

The object of the invention is to provide a printhead which can be used industrially, permits a high clock frequency and, in the event of interruption of the printing process, a separation of the solid from the liquid phase of the metal.

The object is achieved by the print head according to the invention having the features of claim 1 and the method according to the invention for operating the print head according to claim 12.

The print head according to the invention for a 3D printer, in particular a metal printer, comprises a housing, a device for supplying a metal, a piston, a reservoir with an outlet opening and an actuator device for displacing the piston, the reservoir having a melting region and a displacement chamber for a liquid Phase of the metal, wherein the melting region adjacent to an inert atmosphere and is connected to the displacer such that the displacement of the piston liquid phase of the metal can be excited to pass through the outlet opening.

The device for supplying the metal advantageously ensures easy feeding of the material, whereby material can be replenished as needed and the print head can be used industrially, for example. In addition, for example, after emptying of the reservoir, another suitable material can be supplied.

The melting range is advantageously adjacent to an inert atmosphere. This ensures that the pressure on the melt is almost constant, so that it has no effect on the print quality. Furthermore, the inert atmosphere ensures that no unwanted chemical reaction takes place in the reservoir. For example, the inert atmosphere may be formed of nitrogen or other inert gas.

The reservoir advantageously has the melting region for melting the metal, which adjoins the inert atmosphere and additionally the displacement chamber. This makes it possible to spatially separate the melting process from the displacement or printing process, thereby improving the reproducibility of the droplets or a component. In this case, the liquid phase of the metal present in the displacement chamber can be excited by the displacement of the piston to pass through the outlet opening in an advantageous manner. The piston is advantageously located directly on the melt, whereby the accuracy of printing continues to increase because the melt is almost incompressible. The melt or liquid phase of the metal passes either via gravity pressure or via a combination of the gravitational pressure and the atmospheric pressure of the inert gas from the melting region into the displacer space. The outlet corresponds to a nozzle and is interchangeable depending on the construction of the reservoir.

In a development, the actuator device is a piezoelectric actuator.

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 on the order of 50-80 μm. An actuation concept by means of piezoelectric actuator advantageously allows a very accurate reproducibility of the drops. In addition, the size of the drops is flexibly adjustable with a constant nozzle diameter. With the piezoelectric actuator are very high frequencies (up to, for example 1000Hz), whereby a very high build-up rate of the desired 3D structure is possible. In addition, an automation of the whole structure is given.

In one development, the piston is designed in several parts, wherein it comprises at least one piston rod made of a metallic material and a punch made of ceramic.

The multi-part design of the piston makes it possible in an advantageous manner to correspond to the different temperature zones in the print head and the respective functional requirements. The piston position is preferably formed from a high temperature resistant metallic material and transmits the strokes of the actuator device on the stamp. This is advantageously formed of a ceramic, which is preferably a melt-media-resistant and temperature-resistant ceramic. This constructive design of the piston allows for suitable temperature management and permanent operation of the printhead. The material used for the ceramic stamp allows printing materials that can have melting temperatures of over 1000 ° C.

In a further development of the piston without actuation of the actuator device by a spring in an initial position is reset. In this case, the spring is arranged in such an advantageous manner between the housing and the piston, that the piston without actuation of the actuator device by the spring in the starting position is reset.

In one development, the housing is designed in several parts, wherein it comprises at least one cooling flange, an insulating plate and the reservoir.

The housing is advantageously designed in several parts, whereby a suitable temperature management and by the use of different materials a permanent operation is ensured. Due to the multi-part design is also given a modular design that allows a needs-based replacement of the components. In addition, the printhead is designed by the multi-part housing such that the different functions are also performed by different components.

In a further development, the cooling flange has a recess for receiving the actuator device and cooling channels for cooling the cooling flange.

The cooling channels provide advantageously for a suitable temperature management in the cooling flange and in the housing whereby the actuator device is protected on the one hand from the outgoing of the melt temperature and on the other hand is cooled by heating during operation of the actuator. The Cooling through the cooling channels thus ensures a suitable temperature and permanent operation of the print head. The temperature management ensures a reduced energy input.

In a further development of the cooling flange is advantageously formed of a metallic material. The metallic material is chosen so that it satisfies the mechanical and thermal stresses of the print head.

In a further development, the insulating plate is advantageously formed from a heat-insulating material and is designed such that it reduces a heat transfer from the reservoir to the cooling flange. The use of the insulating plate allows for suitable temperature management and permanent operation of the printhead. Furthermore, the insulation reduces the energy input and simplifies the temperature control of the printhead. The insulating plate is formed of, for example, a low thermal conductivity ceramic such as zirconia. It can also be used porous ceramics or silicate ceramics, for example.

In one development, the reservoir is designed as a crucible, outside of the crucible, an inductor and within the crucible, a sensor, in particular a temperature sensor are arranged.

The advantageous arrangement of the inductor outside the crucible allows fast startup of the printhead and temperatures of up to over 1000 ° C are possible, whereby many printing materials can be used for printing. With the temperature sensor arranged advantageously within the crucible, the inductor can be controlled via a regulating and control system such that the use of energy via temperature control is made possible efficiently. The temperature of the melt can be kept as efficient and gentle to the material in an optimal range, whereby a permanent operation of the print head is made possible.

The temperature sensor is arranged in the crucible so that it can detect the temperature of the melt. In a preferred embodiment, the temperature sensor measures the temperature of the melt and additionally the temperature of the gas atmosphere, or of the inert gas atmosphere, wherein the temperature sensor is formed with one or more temperature sensors.

In a further development, the outlet opening of the reservoir is designed for the ejection of drops of the liquid phase of the metal.

Advantageously, the outlet opening is designed in the form of a nozzle, whereby a desired metering of the liquid phase of the metal is possible. The outlet opening can be firmly integrated into the reservoir, or the crucible, or advantageously be formed in a separate insert for the crucible. As a result, an exchange of the nozzle, for example, with clogged opening, or an application of different nozzle geometries for different applications of the print head is possible.

In a further development, the device for supplying the metal advantageously opens into the reservoir and is arranged in the cooling flange and the insulating plate.

As a result, an easy-to-use material supply and a flexible choice of material is possible, whereby no special wire or special powder are necessary. Furthermore, a change of the alloy is possible within a printing process, whereby a smooth transition from one alloy to another is possible. In addition, combined materials are possible, for example with a solids content such as short carbon fibers, due to the advantageously performed material supply. An automation of the printhead is given.

The inventive method for operating the print head is advantageously characterized in that the metal is supplied by the device for supplying the metal in solid phase through the inert atmosphere in the melting region of the reservoir and melted in the melting region in the liquid phase of the metal , wherein the liquid phase of the metal is conducted from the melting region into the displacement chamber of the reservoir and is emitted as a drop by a working stroke of the piston through the outlet opening.

This sequence makes it possible to separate the melting process spatially from the Verdrängervorgang or printing, whereby the reproducibility of the drops, or a component is improved. In this case, the liquid phase of the metal present in the displacement chamber is advantageously excited by the working stroke of the piston through the outlet opening, wherein the piston rests directly on the melt, whereby the accuracy of the printing increases further, since the melt is almost incompressible.

In a further development of the method, the working stroke of the piston is advantageously produced by an actuation of the piezoelectric actuator and a return stroke to an initial position of the piston without actuation of the piezoelectric actuator is generated by the spring.

The working stroke of the piston by the actuator and the return stroke of the piston to its initial position by the spring allow a reproducible clocking of the printing process with equal strokes, each emitting an equal amount of material in droplet form from the outlet opening, so that reproducible results are achieved.

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

list of figures

• 1 Ein Ausführungsbeispiel des erfindungsgemäßen Druckkopfes.

It shows:

• 1 An embodiment of the print head according to the invention.

embodiment

The figure shows an embodiment of the printhead according to the invention 1 for a 3D printer, especially metal printers.

The printhead 1 includes a housing 3 , a device 28 for supplying a metal 14 in solid phase, a piston 5 , a reservoir 7 . 27 with an outlet opening 10 and an actuator device 12 for displacement of the piston. The reservoir 7 . 27 has a melting range 20 and a liquid phase displacer 21 8th of the metal 14 on, with the melting range 20 in an inert atmosphere 22 adjoins and with the displacement room 21 is connected such that by the displacement of the piston 5 the liquid phase 8th of the metal 14 to pass through the outlet opening 10 is excitable. The liquid phase 8th of the metal 14 is also called melt 8th referred to and the inert atmosphere 22 is by introducing an inert gas 22 in the reservoir 7 , 27 made. The introduction of the inert gas 22 preferably takes place over a cold area of the printhead 1 in the reservoir 7 . 27 instead of.

The housing 3 is designed in several parts, wherein there is at least one cooling flange 25, an insulating plate 26 and the reservoir 7 . 27 includes.

The piston 5 is designed in several parts, wherein it has at least one piston rod 17 made of a metallic material and a stamp 18 made of ceramic. The piston rod 17 protrudes from the actuator device 12 through the cooling flange 25 and the insulating plate 26 into the reservoir 7 . 27 into where they are in the stamp 18 passes.

The cooling flange 25 has a recess 30 for receiving the actuator device 12 acting as a piezoelectric actuator 12 is trained on. The piezoelectric actuator 12 is in the recess during operation 30 fixed so that it is a working stroke on the piston when a voltage is applied 5 , especially on the piston rod 17 of the piston. The piston rod 17 transfers the working stroke to the stamp 18 so that this is the liquid phase 8 of the metal 14 to pass through the outlet opening 10 stimulates. The piston 5 is without actuation of the actuator 12 by a spring 13 in a starting position recoverable, wherein the spring 13 in the recess 30 of the cooling flange 25 between a paragraph 24 and the actor 12 is arranged. The feather 13 is designed as a plate spring.

Furthermore, the cooling flange 25 cooling channels 31 for cooling on. The cooling channels 31 are between the cooling flange 25 and the insulating plate 26 arranged and are flushed with a cooling medium. This serves as cooling against the heating by the melt 8th and for cooling the actuator 12 operational. The cooling flange 25 is formed of a metallic material.

The on the cooling flange 25 on the side of the cooling channels 31 adjacent insulating plate 26 is formed of a heat-insulating material and formed so that it transfers heat from the reservoir 7 . 27 to the cooling flange 25 reduced.

The device 28 for feeding the metal 14 flows into the reservoir 7 . 27 and is in the cooling flange 25 and the insulating plate 26 arranged. The device 28 protrudes through the cooling flange 25 and the insulating plate 26 through and the metal 14 , or the material to be printed 14 is from the outside through the device 28 fed. Pre-metered pieces of material or pellets can preferably be used. At the transition of the insulating plate 26 to the reservoir 7 . 27 there is an opening 29 through which the material 14 in the reservoir 7 . 27 arrives. The opening 29 is through a device 32 closed, so that these preferably only when feeding the material 14 is open, reducing the escape of energy, or gas from the inert atmosphere 22 is reduced.

The reservoir 7 . 27 is as a melting pot 27 formed outside of the crucible 27 an inductor 35 and within the crucible, a sensor 36, in particular a temperature sensor, are arranged. Between the crucible 27 and the inductor 35 , or the inductor coil 35 Optionally, an unillustrated isolator may be located.

The metal 14 arrives in a solid phase 14 in the melting area 20 of the crucible and is through the inductor 35 heated until it is in a liquid phase 8th passes. Upon reaching a desired process temperature of the melt 8th , the through the temperature sensor 36 is determined, the printhead 1 start operation. The liquid phase 8th , or the melt 8th passes through gravity pressure of the melt 8th or by a combination of gravitational pressure and atmospheric pressure of the inert gas 22 on the stamp 18 over in the displacement room 21 , The Stamp 28 of the piston 5 is with a print page 19 in the melt 8th , or of melt 8th surrounded and at the connection side to the piston rod 17 in the inert atmosphere 22 , or from the inert atmosphere 22 surround. The piston rod 17 does not come with the melt due to the process 8th in touch.

The ceramics of the stamp 18 is advantageously very good temperature-conductive to the by the inductor 35 generated heat well in the displacement 21 to be able to transfer.

Upon actuation of the piezoelectric actuator 12 exercises the pressure side 19 of the stamp 18 a pressure on the melt 8th in the displacement room 21 in the direction of the outlet opening 10 and provides for a discharge of a drop 15 through the outlet 10 of the reservoir 7 . 27 , or of the displacement chamber 21 , The outlet opening 10 is for the ejection of drops 15 the liquid phase 8th of the metal 14 formed, wherein the outlet opening 10 the shape of a nozzle 10 and firmly with the crucible 27 may be connected, or as shown in the embodiment, a replaceable insert 11 which allows the use of different nozzle geometries.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102015218375 [0007]

Cited non-patent literature

• Han-song Zuo, He-jun Li, Le-juaqi, Jun Luo, Song-yi Zhong, Hai-peng Li, "Effect on wetting behavior on the basis of pneumatic drop-on-demand technique", Journal of Materials Processing Technology 214, 2566-2575 (2014)) [0005]

Claims (13)

Printhead (1) for a 3D printer, in particular metal printer, comprising a housing (3), a device (28) for supplying a metal (14), a piston (5), a reservoir (7, 27) with an outlet opening ( 10) and an actuator device (12) for displacing the piston (5), characterized in that the reservoir (7, 27) has a melting region (20) and a displacement chamber (21) for a liquid phase (8) of the metal (14) in that the melting region (20) adjoins an inert atmosphere (22) and is connected to the displacement chamber (21) such that the displacement of the piston (5) causes the liquid phase (8) of the metal (14) to pass through Outlet opening (10) can be excited. Printhead (1) to Claim 1 , characterized in that the actuator device (12) is a piezoelectric actuator. Printhead (1) according to one of the preceding claims, characterized in that the piston (5) is designed in several parts, wherein it comprises at least one piston rod (17) made of a metallic material and a punch (18) made of ceramic. Printhead (1) according to one of the preceding claims, characterized in that the piston (5) can be reset to a starting position by a spring (13) without actuation of the actuator device (12). Printhead (1) according to one of the preceding claims, characterized in that the housing (3) is designed in several parts, wherein it comprises at least one cooling flange (25), an insulating plate (26) and the reservoir (7, 27). Printhead (1) to Claim 5 , characterized in that the cooling flange (25) has a recess (30) for receiving the actuator device (12) and cooling channels (31) for cooling the cooling flange (25). Print head (1) after one Claims 5 or 6 , characterized in that the cooling flange (25) is formed of a metallic material. Printhead (1) after one of Claims 5 to 7 , characterized in that the insulating plate (26) is formed of a heat-insulating material and is formed so as to reduce a heat transfer from the reservoir (7, 27) to the cooling flange (25). Printhead (1) after one of Claims 5 to 8th , characterized in that the reservoir (7, 27) is formed as a crucible, outside of the crucible, an inductor (35) and within the crucible, a sensor (36), in particular a temperature sensor, are arranged. Printhead (1) to Claim 9 , characterized in that the outlet opening (10) of the reservoir (7) for the ejection of drops (15) of the liquid phase (8) of the metal (14) is formed. Printhead (1) according to one of the preceding claims, characterized in that the device (28) for feeding the metal (14) into the reservoir (7, 27) opens and in the cooling flange (25) and the insulating plate (26) is arranged , Method for operating a printhead (1) according to one of Claims 1 to 11 characterized in that the metal (14) is fed through the device (28) for feeding the metal (14) in solid phase through the inert atmosphere (22) into the melt area (20) of the reservoir (7, 27) and in the Melting region (20) is melted into the liquid phase (8) of the metal (14), wherein the liquid phase (8) of the metal (14) from the melting region (20) in the displacement chamber (21) of the reservoir (7, 27) out is emitted and by a working stroke of the piston (5) through the outlet opening (10) as a drop (15). Method for operating a printhead (1) after Claim 12 , characterized in that the working stroke of the piston (5) by an actuation of the piezoelectric actuator (12) is generated and a return stroke to an initial position of the piston (5) without actuation of the piezoelectric actuator (12) by the spring (13) is generated ,

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