WO2019076992A1

WO2019076992A1 - System and method for producing three-dimensional structures using a supporting positive pressure

Info

Publication number: WO2019076992A1
Application number: PCT/EP2018/078440
Authority: WO
Inventors: Björn Timo KLETZ
Original assignee: Deutsches Zentrum für Luft- und Raumfahrt e.V.
Priority date: 2017-10-18
Filing date: 2018-10-17
Publication date: 2019-04-25
Also published as: DE102017124353A1

Abstract

The invention relates to a system (100) for producing three-dimensional structures which have two or more different materials, comprising a 3D printhead (10) which has a first material feed (11) for supplying a semi-continuous fiber material (31) and at least one second material feed (12) for supplying a thermoplastic matrix material (41), said feeds opening into a common mixing chamber of the printhead (10), wherein the mixing chamber of the 3D printhead (10) is designed to control the temperature of the matrix material (41) supplied to the mixing chamber and to form a material mixture from the fiber material (31) and the matrix material (41), and the mixing chamber is in communicative connection with an outlet (13) of the 3D printhead (10), said outlet being designed to discharge the formed material mixture in order to produce the three-dimensional structure. The system (100) has a first material supply device (30), which is designed to supply the semi-continuous fiber material (31) to the first material feed (11) of the 3D printhead (10), and at least one second material supply device (40), which is designed to supply the thermoplastic matrix material (41) to the second material feed (12) of the 3D printhead (10). The invention is characterized in that the first material feed (11) has an inlet (14) through which the semi-continuous fiber material (31) is supplied to the first material feed (11), and a pressure source (34) is provided, said inlet (14) of the first material feed (11) interacting with the pressure source (34) in order to generate a positive pressure at the inlet of the first material feed (11) such that the thermoplastic matrix material (41) is prevented from exiting the inlet (14) of the first material feed (11).

Description

Plant and method for producing three-dimensional structures by supporting overpressure

The invention relates to a plant for producing three-dimensional structures comprising two or more different materials. The invention also relates to a method for producing such a three-dimensional structure by means of the installation according to the invention.

Generative methods can be used to produce components of almost any shape using a suitable material. 3D printing by means of a 3D printer represents a very well-known representative of additive manufacturing processes. In this process, a fusible material, for example a thermoplastic, is printed in layers by means of a 3D printer, resulting in a three-dimensional component at the end of the process or a three-dimensional structure.

The rigidity and strength of a component or structure produced on this basis depend significantly on the corresponding material properties of the fusible material used. Especially with regard to the lightweight construction, it is often desirable that the components are made of fiber composites in order to obtain a high weight-specific strength and rigidity. However, fiber composites have anisotropic material properties, so that strength and rigidity are direction-dependent and thus dependent on the fiber orientation. Therefore, multiple layers of fiber material are often arranged with different fiber orientations, so as to at least partially replicate the homogeneous material properties of, for example, metals. Such, in particular as required integration of fiber material in the 3D Printing would have the decisive advantage that components and structures can be produced whose load paths are adapted to exact conditions without unnecessarily requiring fiber material. From Hauke Prüß, Thomas Vietor: "New design freedom through 3D-printed fiber-plastic composites", Forum for Rapid Technology, issue 12/2015, a 3D printhead is known to which a quasiendlosen fiber material is fed centrally The printing head is fed to a plastic material by means of two feed channels, with the fiber material and plastic material opening in a common mixing chamber, whereby the fiber material passing through is wetted by the plastic material and the resulting material mixture is dispensed, allowing almost any structure with integrated load paths to be developed.

The disadvantage of this known 3D print head lies in the fact that the supply of the thermoplastic material into the mixing chamber creates a pressure within the mixing chamber which also causes the melted thermoplastic material to rise into the feed channel of the fiber material and thus counteract Conveying direction of the quasi-filamentary fiber material is pressed. In the worst case, this can lead to the thermoplastic at the point of entry at which the fiber material is introduced into the 3D print head into the feed channel provided for this purpose, and thus an undesired leakage occurs at the 3D print head. However, there is also the risk that, due to the rising of the molten thermoplastic within the feed channel, it cools and then solidifies again within the feed channel for the fiber material, which finally leads to a delivery interruption of the fiber material and thus to the termination of the process.

It is therefore an object of the present invention to provide an improved system and an improved method for producing three-dimensional structures with the aid of such a 3D print head, without the risk that thermoplastic material will emerge from the 3D print head or that the thermoplastic material will adhere to it Make solidified inside the printhead where it is then comes to a process interruption for lack of further promotion of the fiber material.

The object is achieved with the system according to claim 1 and the method according to claim 8 according to the invention.

According to claim 1, a plant for producing three-dimensional structures is proposed, which have two or more different materials. The system in this case has a 3D print head, which has a first material supply for feeding a quasiendlosen fiber material and at least a second material supply for supplying a thermoplastic matrix material, which open in a common mixing chamber of the print head, wherein the mixing chamber of the 3D print head for tempering the the matrix material supplied to the mixing chamber and for forming a material mixture of the fiber material and the matrix material is formed. The mixing chamber communicates with an outlet of the SD print head so that the material mixture formed in the mixing chamber can be output for printing the three-dimensional structure. In this case, the first material feed, with which the fiber material is supplied to the mixing chamber of the 3D print head, preferably has a feed channel which is arranged axially relative to the outlet of the 3D print head, so that the fiber material can be in particular ribbon or thread-like , is guided from the first material supply through the mixing chamber to the outlet. In addition, the system has a first material supply device, which is designed to provide the quasi-filamentary fiber material to the first material supply of the 3D print head, and at least one second material supply device, which is designed to provide the thermoplastic matrix material to the second material supply of the 3D print head , Thus, during the fabrication of the three-dimensional structure, both the thermoplastic matrix material and the quasi-non-fibrous material may be continuously fed to the 3D print head to form the material mixture in the mixing chamber and then output for printing the structure. According to the invention, it is now provided that the first material feed has an input on the 3D print head, through which the quasi-filamentary fiber material is fed to the first material feed and thus to the 3D print head. Furthermore, the system has a pressure source for generating an overpressure by means of a pressure medium, wherein the input of the first material supply according to the invention with the pressure source cooperates such that at the input an overpressure is applied or generated, so that an exit of the thermoplastic matrix material at the entrance the first material supply is prevented. Because the continuous pushing of thermoplastic matrix material into the mixing chamber an overpressure is generated in the mixing chamber, which acts not only in the direction of the outlet of the 3D print head, but also against the conveying direction of the quasi-filament fiber material in the direction of input of the first material supply, wherein by applying An overpressure at the entrance of the first material feed prevents leakage of the thermoplastic matrix material at this point. In any case, it can thereby be achieved that the thermoplastic matrix material optionally solidifies due to a temperature gradient within the feed channel of the first material feed and thus prevents or damages conveying of the matrix material.

This makes it possible to reliably supply both a fiber material and a thermoplastic matrix material to a 3D print head, without fear of damage to the fiber materials or contaminants of the 3D print head.

In an advantageous embodiment, it is provided that the first material supply device, which provides the quasi-filamentary material on the first material supply to the 3D print head, has a pressure vessel for storing the quasi-filamentary fiber material and has a pressure-tight fiber guide, the pressure-tight on the pressure vessel on the one hand and pressure-tight on the first material supply of the 3D print head, that is connected to the input of the first material supply, on the other hand. The stored in the pressure vessels quasi-filament fiber material is now passed through the pressure-tight fiber guide through to the entrance of the first material supply of the 3D print head, from where it then through the feed channel is conveyed to the mixing can and through the mixing cans to the outlet of the 3D printhead.

In this case, a pressure source, for example by providing a pressure connection to the pressure vessel, is provided, with which an internal pressure can be generated in the interior of the pressure vessel and the pressure-tight fiber guide, which acts until the input of the first material feed on the 3D print head, so that thereby generates an overpressure at the inlet of the first material supply and prevents leakage of the thermoplastic matrix material at the entrance of the first material supply.

In an advantageous embodiment, a control unit is provided, which is designed to control the pressure source such that the generated overpressure varies, i. is variable in terms of its strength. This can be reacted to changing boundary conditions during the manufacturing process by changing the internal pressure. The varying of the overpressure can, for example, also be achieved by a variation of the internal pressure in the pressure vessel or pressure-tight fiber guide. In an advantageous embodiment, it is conceivable that the control unit for controlling the pressure source is designed such that the generated overpressure is set as a function of the printing speed of the 3D print head. Thus, it is conceivable that when the printing speed of the SD print head is increased, the overpressure is also increased in order to take account of the pressure prevailing in the mixing chamber due to the increased printing speed. Because by increasing the printing speed and the material output per time must be increased, whereby more matrix material per time must be introduced into the mixing chamber. Therefore, it is also advantageous if the control unit for driving the

Pressure source is designed such that the generated overpressure is adjusted in dependence on a material feed rate of the quasi-filamentous fiber material and / or the thermoplastic matrix material. In a further advantageous embodiment, the first material supply of the 3D print head has a sensor system which is designed to detect a filling level of the thermoplastic matrix material in the first material supply, wherein a control unit is provided, which is designed to drive the pressure source such that the generated Overpressure is set as a function of the detected filling level. This makes it possible to respond to the changing pressures within the mixing head finely graduated by adjusting the internal pressure within the pressure vessel and the pressure-tight fiber guide.

In a further advantageous embodiment, the system is adapted to temper the pressure medium used to generate the overpressure, so as to prevent solidification of the thermoplastic matrix material, which is located in the first material supply.

An overpressure in the sense of the present invention refers to a pressure at the inlet of the first material feed which is higher in relation to the ambient pressure around the 3D print head. Incidentally, the invention is also achieved according to the invention with the method according to claim 8 for producing three-dimensional structures. Advantageous embodiments can be found in the corresponding subclaims.

The invention will be explained in more detail by way of example with reference to the attached figures. It shows:

Figure 1 - Schematic representation of the system according to the invention.

FIG. 1 shows the plant 100 according to the invention, which schematically shows the essential elements of the plant 100 in a preferred embodiment. As a result, the system 100 has a 3D print head 10 which is provided for printing a material mixture of at least two materials 31, 41 for producing three-dimensional structures. In this case, a fiber material 31 is fed to the 3D printing head 10 via a first material feed 11, which then opens into a mixing chamber (not shown) located in the 3D printing head 10. Furthermore, a thermoplastic matrix material 41 is supplied to the 3D print head via a second material feed 12, wherein the second material feed in the example of FIG. 1 has three material inputs, which then all together in the

Mixing chamber of the 3D printhead 10 open. The fiber material 31 and the thermoplastic matrix material 41 are then mixed together in the mixing chamber of the SD print head, resulting in a material mixture which is then output via an outlet 13 of the 3D print head for printing the structure.

The thermoplastic matrix material 41 is thereby provided by means of a second material supply device 40, which is only schematically indicated here in the example of FIG. The fibrous material 31 is, on the other hand, provided by means of a first material supply device 30, which in the exemplary embodiment of FIG. 1 has a pressure vessel 42 in which the fibrous material 31 is located and stored. Furthermore, the first material supply device 30 has a pressure-tight fiber guide 33, which is connected pressure-tight on the one hand to the pressure vessel 32 and on the other hand to an input 14 of the first material supply 1 1 of the 3D print head 10. The stored in the pressure vessel 32 fiber material 31 is then guided by the pressure vessel 32 through the pressure-tight fiber guide 33 to the input 14 and thus provided on the first material supply 1 1 then the 3D print head and its mixing chamber. The pressure vessel 32 has a pressure port 34, which constitutes a pressure source in the sense of the present invention. This makes it possible to pressurize the interior of the pressure vessel 32 and the fiber guide 33 with an internal pressure, so that an overpressure is set at the inlet 14 of the first material supply, which is to prevent thermoplastic matrix material from leaving the mixing chamber from the inlet 14 can. Overpressure here means that there is a greater pressure than atmospheric pressure, wherein in the ratio of the internal pressure in the mixing chamber almost pressure identity or pressure equality should prevail in order to prevent a corresponding leakage.

To control the print head 10 and the fiber delivery and the adjustment of the pressure while a control unit 20 is provided, with the help of the control unit 20, the internal pressure in the pressure vessel 32 and the pressure-tight fiber guide 33 can be adjusted accordingly. It is conceivable that the setting of the internal pressure for generating the overpressure at the input 14 in dependence on a printing speed or a Materialzuführgeschwindigkeit. It is also conceivable that the print head within the material supply 1 1 has a sensor system 15 with which the level within the material supply 1 1 can be measured by ascending the thermoplastic matrix material. Thus, it is conceivable that the sensor system 15 is, for example, a proximity switch which signals a corresponding imminent escape of the thermoplastic matrix material from the inlet 14, whereby the control unit 20 then increases the internal pressure in the pressure vessel 32 and the pressure-tight fiber guide 33 to such an extent leakage from the entrance 14 is avoided. LIST OF REFERENCE NUMBERS

10 - 3D printhead

1 1 - first material feed

12 - second material supply

13 - outlet

14 - entrance

15 - sensor system

20 - control unit

30 - first material supply device

31 - fiber material

32 - pressure vessel

33 - pressure-tight fiber guide

34 - Pressure source

40 - second material supply device

41 - thermoplastic matrix material

100 - plant

Claims

claims

1 . Plant (100) for producing three-dimensional structures comprising two or more different materials, comprising a 3D print head (10) having a first material feed (11) for feeding a quasi-filamentary fiber material (31) and at least one second material feed (12 ) for feeding a thermoplastic matrix material (41), which open in a common mixing chamber of the print head (10), wherein the mixing chamber of the SD print head (10) for controlling the temperature of the mixing chamber supplied matrix material (41) and for forming a material mixture of the Formed fiber material (31) and the matrix material (41), wherein the mixing chamber communicates with an outlet (13) of the 3D print head (10), which is adapted to output the material mixture formed to produce the three-dimensional structure, wherein the plant (100) has a first material supply device (30) for providing the quasi-less chamfer is formed to the first material feed (1 1) of the SD print head (10), and at least one second material providing means (40), which for providing the thermoplastic matrix material (41) to the second material supply (12) of the 3D -Printed head (10) is formed, characterized in that the first material supply (1 1) has an input (14) through which the quasi-filamentless fiber material (31) in the first material supply (1 1) is supplied, and a pressure source (34 ), wherein the input (14) of the first material supply (1 1) with the pressure source (34) for generating an overpressure at the input of the first material supply (1 1) cooperates such that an exit of the thermoplastic matrix material (41) at the entrance (14) of the first material supply (1 1) is prevented.

2. Plant (100) according to claim 1, characterized in that the first material supply device (30) has a pressure vessel (32) for supporting the quasi-filamentless fiber material (31) and a pressure-tight fiber guide (33), the pressure-tight manner to the pressure vessel (32 ) is connected on the one hand and pressure-tight to the first material supply (1 1) of the 3D print head (10) on the other hand, so that the quasi-filament fiber material (31) from the pressure vessel (32) through the pressure-tight fiber guide (33) to the first material supply ( 1 1) of the 3D print head (10) can be passed, wherein the pressure source (34) for generating an internal pressure in the interior of the pressure vessel (32) and the pressure-tight fiber guide (33) is formed such that the

Overpressure at the input (14) of the first material supply (1 1) generates and leakage of the thermoplastic matrix material (41) on the first material supply (1 1) is prevented.

Plant (100) according to claim 1 or 2, characterized in that a control unit (20) is provided, which is designed for controlling the pressure source (34) such that the generated overpressure varies.

Plant (100) according to claim 1 or 2, characterized in that a control unit (20) is provided, which is designed to control the pressure source (34) such that the generated overpressure in dependence on a printing speed of the 3D print head (10). is set.

Plant (100) according to any one of the preceding claims, characterized in that a control unit (20) is provided, which is designed for controlling the pressure source (34) such that the overpressure generated in dependence on a Materialzuführgeschwindigkeit of quasi filamentary material (31) and / or the thermoplastic matrix material (41) is adjusted.

Plant (100) according to one of the preceding claims, characterized in that the first material supply (1 1) has a sensor system (15) which is designed to detect a filling level of the thermoplastic matrix material (41) in the first material supply (1 1) wherein a control unit (20) is provided, which is designed for controlling the pressure source (34) such that the generated overpressure is adjusted in dependence on the detected filling level. 7. Plant (100) according to one of the preceding claims, characterized in that the system is designed for tempering the pressure medium used to generate the internal pressure.

8. A method of manufacturing three-dimensional structures comprising two or more different materials, comprising the steps of:

- Providing a system (100) for producing a three-dimensional structure according to one of the preceding steps;

- supplying quasi-filamentous fiber material (31) and thermoplastic matrix material (41) to the 3D printing head (10) of the installation (100); and

- Printing the material mixture of the fiber material (31) and the matrix material (41) to form the three-dimensional structure;

marked by

- Generating an overpressure means of the pressure source (34) at the input (14) of the first material supply (1 1) such that leakage of the thermoplastic matrix material (41) on the first material supply (1 1) is prevented.

9. The method according to claim 8, characterized in that an internal pressure is generated by means of the pressure source (34) in the interior of a pressure vessel (32) and a pressure-tight fiber guide (33) of the first material supply device (30) during printing of the material mixture such that the overpressure at the inlet (14) of the first material supply (1 1) generates and leakage of the thermoplastic matrix material (41) on the first material supply (1 1) is prevented.

10. The method according to claim 8 or 9, characterized in that during the printing of the material mixture of the generated pressure is varied.

1 1. Method according to one of claims 8 to 10, characterized in that the generated overpressure in dependence on a printing speed of the 3D print head (10) by means of a control unit (20) is adjusted.

Method according to one of claims 8 to 1 1, characterized in that the overpressure generated in dependence on a material feed rate of the quasi-filamentous fiber material (31) and / or the thermoplastic matrix material (41) by means of a control unit (20) is adjusted.

Method according to one of claims 8 to 12, characterized in that the overpressure generated in dependence on a detected by a sensor system (15) filling level of the thermoplastic matrix material (41) in the first material supply (1 1) by means of a control unit (20) is adjusted. 14. The method according to any one of claims 8 to 13, characterized in that the pressure medium used to generate the overpressure is tempered.