Screw system of a machine tool for additive manufacturing, machine tool and method for operating a machine tool

Abstract

Screw system of a machine tool (10) for additive manufacturing, comprising: - a screw housing (2) with a discharge opening (3), - a screw (4) which is received and designed in the screw housing (2) for conveying a material (5) towards the discharge opening (3), and - a drive device (6) which is configured to rotate the worm (4) about a rotation axis (40) and to move the worm (4) along the rotation axis (40), - wherein the screw (4) has a closing needle (7) which is arranged at an axial end of the screw (4) and which is designed to close the discharge opening (3), - wherein the snail shell (2) has a tapered shell region (20), and - wherein the discharge opening (3) is arranged in a tip of the tapered housing area (20), characterized in that the screw (4) has a tapered screw area (70) at one axial end facing the discharge opening (3), wherein the closing needle (7) is arranged at a tip of the tapered screw area (70), and wherein the tapered screw area (70) has a smaller angle (21, 71) between the axis of rotation (40) and a respective lateral surface (22, 72) than the tapered housing area (20).

Description

[0001] The invention relates to a screw system of a machine tool for additive manufacturing, a machine tool for additive manufacturing and a method for operating such a machine tool.

[0002] Machine tools for additive manufacturing, particularly for 3D printing, are known in a wide variety of designs from the state of the art. For example, there are screw-based 3D printers that feature a screw for conveying and / or melting the material to be printed. To ensure the cost-effectiveness of such a machine tool with a screw, the highest possible throughput for material discharge is desirable. Especially with machine tools where the conveying and discharge of the material is carried out solely by the screw, precise material dosing often presents problems.

[0003] DE 10 2020 105 363 A1 discloses an extrusion device for the extrusion-based production of at least one three-dimensional object, comprising at least one extrusion unit which is configured to melt an extrusion material and / or to apply an extrusion material to a substrate, wherein the at least one extrusion unit comprises an extruder chamber, an extruder screw arranged in the extruder chamber, an outlet region via which extrusion material can be discharged onto a substrate by means of the extrusion unit, wherein the outlet region has at least one outlet opening via which extrusion material can be discharged onto a substrate by means of the extrusion unit, wherein the extruder screw can be moved between a closed position, in which it is moved relative to the outlet opening in such a way that an exit of extrusion material from the outlet opening is not possible, and at least one open position,in which it is moved relative to the outlet opening in such a way that an exit of extrusion material from the outlet opening is possible, is movably mounted.,

[0004] US 5,622,216 A discloses a method and apparatus for rapidly producing a fully dense, nearly reticulated metal component from a partially solidified metal slurry. A source of metal alloy slurry is provided and maintained under conditions that maintain the slurry state. The slurry is dispensed through a nozzle and applied to a substrate or to a previously dispensed slurry in a predetermined, controlled manner to produce a component with the desired geometry.

[0005] It is therefore an object of the invention to provide a screw system of a machine tool, a machine tool and a method for operating the machine tool, wherein a high throughput and a high accuracy in the dosing of the material can be achieved.

[0006] This object is achieved by a worm system of a machine tool having the features of claim 1, a machine tool having the features of claim 7, and a method for operating a work time machine having the features of claim 9.

[0007] The screw system according to the invention offers the advantage of reliably metering the material during additive manufacturing of components with particularly high precision. In particular, it allows for very rapid and reliable stopping of the material discharge from the machine tool.

[0008] This is achieved according to the invention by a screw system of a machine tool for additive manufacturing, comprising a screw housing with a discharge opening, a screw, and a drive device. The screw is received in the screw housing and designed to convey a material in the direction of the discharge opening of the screw housing. The drive device is configured to rotate the screw about a rotational axis and additionally to displace the screw, in particular translationally, along the rotational axis. The screw has a closure pin arranged at one axial end of the screw. The closure pin is designed to close the discharge opening.

[0009] The discharge opening thus forms a through-opening through the screw housing through which the material, which is preferably plasticized within the screw housing, i.e. preferably melted into a melt, can be discharged or injected. The shut-off needle of the screw preferably has a geometry corresponding to the discharge opening so that the shut-off needle can completely close the discharge opening. Closing and opening of the discharge opening of the screw housing occurs in particular as a function of an axial position of the screw relative to the screw housing. This means that by moving the screw within the screw housing along the axis of rotation, the shut-off needle opens or closes the discharge opening.

[0010] The material is conveyed toward the discharge opening primarily by rotating the screw around its axis of rotation. Alternatively or additionally, the material can be conveyed toward the discharge opening by moving the screw along its axis of rotation. For example, moving the screw can assist the conveying of the material.

[0011] The screw system is characterized by a particularly simple and cost-effective design, which allows for continuous discharge of the material. The option of closing the discharge opening using the shut-off needle enables immediate and complete interruption of material discharge. This enables highly dynamic closure of the discharge opening in the conveying direction of the material. In particular, closure is possible solely using the screw's shut-off needle, meaning that no additional elements are required for closing the discharge opening. The shut-off needle and the discharge opening thus form a needle-type shut-off system. This not only enables rapid interruption and release of the material feed, but also enables particularly precise metering of the material flow discharged from the discharge opening.The highly dynamic and precise interruption and metering of the material flow offers the additional advantage of enabling the production of particularly high-quality components. In particular, this allows for the achievement of particularly good surface quality. Furthermore, changes in wall thickness, such as discontinuities in wall thickness and perforations in the component, can be created easily and with exceptional precision thanks to the rapid ability to adjust the material discharge.

[0012] The subclaims contain preferred developments of the invention.

[0013] The discharge opening is preferably cylindrical. In particular, the discharge opening is thus designed in the form of a cylindrical through-bore through the screw housing. The cylindrical discharge opening preferably extends along the axis of rotation, i.e., a central axis of the discharge opening is in particular coaxial with the axis of rotation of the screw. A discharge opening with a cylindrical geometry can be manufactured particularly easily and cost-effectively and offers a reliable and precisely adjustable closure option for interrupting the discharge of the material from the screw housing. In particular, a cylindrical discharge opening offers the further advantage that the material discharge can already be completely closed at an inner edge of the discharge opening facing the interior of the screw housing.In this case, a residual volume of material may be located within the cylindrical discharge opening, which can be discharged from the discharge opening, for example, upon further axial displacement of the screw in the discharge direction. This allows, for example, small volumes of material to be metered with particular precision. For example, this can be used to create point-like areas or parts of the component being manufactured.

[0014] Particularly preferably, the ratio of an axial length of the discharge opening to a diameter of the discharge opening is at least 0.2 and at most 10. Preferably, the ratio is at least 0.5 and at most 2. In particular, the diameter of the discharge opening is predetermined by a predefined material flow rate. The axial length can be adjusted, for example, to achieve a desired residual volume within the cylindrical discharge opening. Depending on the axial length, the residual volume of material within the cylindrical discharge opening can be adjusted.

[0015] The shut-off needle is preferably cylindrical. In particular, with a cylindrical discharge opening, an outer diameter of the shut-off needle corresponds to an inner diameter of the discharge opening. More preferably, an axial length of the shut-off needle is equal to an axial length of the cylindrical discharge opening. This means that the shut-off needle can completely fill an internal volume of the discharge opening. In addition to a particularly precise and reliable option for closing the discharge opening, the cylindrical shut-off needle offers the advantage that, when the residual volume within the discharge opening is used, particularly precise dosing of the residual volume to be dispensed is possible. In this case, the shut-off needle acts as a stamp or piston, which can expel the residual volume of material from the discharge opening in a precisely dosed manner.

[0016] According to the invention, the screw housing has a tapered housing section, in particular a conical one. The discharge opening is arranged in a tip of the tapered housing section, which is located in particular at an axial end of the screw housing. This allows for a particularly aerodynamic design of the screw housing to be provided, allowing the material to be conveyed and discharged precisely and without great energy expenditure.

[0017] According to the invention, the screw has a tapered, in particular conically, screw section at an axial end facing the discharge opening. The shut-off needle is arranged at a tip of the tapered screw section. In addition, an angle between a circumferential surface of the tapered screw section and the rotation axis is smaller than an angle between a circumferential surface of the tapered housing section and the rotation axis. This means that an outer side of the screw section is more acute than an inner side of the screw housing. This ensures that the discharge opening can be closed exclusively by means of the shut-off needle, since it prevents, in particular, the screw section from contacting the housing section before the discharge opening is closed by the shut-off needle.

[0018] Preferably, the drive device is configured to drive the screw hydraulically and / or pneumatically and / or electromagnetically and / or electrically. For example, the drive device can comprise a first drive unit configured to drive the rotation of the screw about the rotation axis and a second drive unit configured to drive the displacement of the screw along the rotation axis.

[0019] Preferably, the screw housing further comprises a mouthpiece, which is formed as a separate part from a base body of the screw housing. At least part of the discharge opening is formed by the mouthpiece. In particular, the mouthpiece is designed to be replaceable, so that, for example, different geometries, such as different axial lengths of the discharge opening, can be provided easily and particularly cost-effectively.

[0020] Furthermore, the invention leads to a machine tool for additive manufacturing, which comprises the described screw system. The machine tool is preferably intended for 3D printing components, in particular made of plastic. The screw system enables particularly cost-effective and energy-saving production of 3D-printed components.

[0021] The machine tool preferably further comprises a heating device configured to heat the screw housing and / or the screw. Heating by means of the heating device can melt the material within the screw housing. Preferably, the melting of the material can be achieved exclusively, or alternatively, only in a supporting manner, by heating by means of the heating device.

[0022] Furthermore, the invention relates to a method for operating the described machine tool. In particular, the method can be regarded as a method for additive manufacturing of components using the machine tool. The method comprises the following steps: - Rotating the screw of the screw system of the machine tool around the rotation axis in order to convey the material within the screw housing towards the discharge opening, and - Moving the screw along its rotation axis to close or open the discharge opening of the screw housing using the screw's shut-off pin. This process thus allows for particularly precise and highly dynamic control of the material discharge from the screw housing, particularly with regard to quickly and precisely interrupting and re-opening the material flow through the discharge opening.

[0023] The method preferably further comprises the step of increasing the volume of material to be discharged by displacing the screw in the direction of the discharge opening, wherein the screw is simultaneously rotated about its axis of rotation. This means that, in addition to conveying the material by means of the rotation of the screw, the axial displacement of the screw in the direction of the discharge opening is used to discharge a particularly large amount of material through the discharge opening in a short time. The screw can preferably further comprise a non-return valve which is designed to prevent backflow of the material, i.e. movement of the material in the axial direction and away from the discharge opening. In this way, for example, material can be effectively injected by axially displacing the screw, similar to an injection molding process.

[0024] Particularly preferably, the method further comprises the step of controlling a material throughput by changing an annular gap between a needle tip of the shut-off needle and an inner wall of the screw housing by axially displacing the screw. The needle tip forms the axial end of the shut-off needle. The annular gap is preferably located between the needle tip and an inner edge of the discharge opening facing the screw. This allows the volume flow of the material to be discharged to be adjusted particularly precisely.

[0025] The method preferably further comprises the step of discharging a residual volume of the material located within the discharge opening. In particular, the residual volume is discharged after an annular gap between a needle tip of the shut-off needle and an inner wall of the discharge opening has been closed. This means that the residual volume of material is located within the discharge opening after a fluid passage from the interior of the screw housing through the discharge opening to the outside has already been completely closed by the valve needle. By further displacing the screw in the axial direction, the shut-off needle can partially or completely press the residual volume of material out of the discharge opening. This makes it possible, for example, to apply dots or very small amounts of material to the component to be manufactured in short pulses.

[0026] More preferably, the method further comprises the steps: - filling a granular or powdery material into the screw housing, and - Plasticizing the material by rotating the screw and / or by heating the screw housing and / or by heating the screw.

[0027] The melting, i.e. plasticization, of the material can thus be achieved either by the rotation of the screw alone or by the introduction of heat or a combination of both.

[0028] Further details, advantages, and features of the present invention will become apparent from the following description of exemplary embodiments with reference to the drawings. Functionally identical components are always identified by the same reference numerals. It shows: Fig. 1 is a schematic sectional view of a machine tool according to a first embodiment of the invention, Fig. 2 a detail of the machine tool of the Fig. 1, Fig. 3 another detail of the machine tool of the Fig. 1, and Fig. 4 Details of a machine tool according to a second embodiment of the invention.

[0029] In the Fig. Figure 1 shows a schematic sectional view of a machine tool 10 according to a first exemplary embodiment of the invention. The machine tool 10 is intended for the additive manufacturing, in particular for 3D printing, of components. The machine tool 10 comprises a screw system 1 with a screw housing 2 and a screw 4 accommodated in the screw housing 2. The screw 4 extends along a rotational axis 40 and is designed to convey a material 5 along a direction of the rotational axis 40 when the screw 4 rotates about the rotational axis 40.

[0030] Material 5 is preferably a plastic. Material 5 can be filled into the screw housing 2 in granulate form via a filling opening 27.

[0031] To drive the rotation of the screw 4 about the rotation axis 40, the screw system 1 also comprises a drive device 6 with a rotary drive 61. The drive device 6 also has a lifting device 62, by means of which the screw 4 can be displaced translationally along the rotation axis 40.

[0032] The machine tool 10 also includes a heating device 8 with a plurality of heating elements 80 surrounding the screw housing 2. This allows the screw housing 2 to be heated to plasticize the material 5 within the screw housing 2.

[0033] The screw housing 2 has a discharge opening 3 at its axial end, through which the plasticized material 5 conveyed by the screw 4 can be discharged in order to produce components. The discharge opening 3 has a cylindrical geometry, as can be seen in particular in the detail of the Fig. 2. An axial length 31 of the discharge opening 3 is approximately 0.5 times a diameter 32 of the discharge opening 3. The discharge opening 3 is located at a tip of a conically tapered housing area 20 of the screw housing 2.

[0034] The screw 4 has a shut-off needle 7 at its axial end. The shut-off needle 7 is located at a tip of a conically tapered screw section 70 of the screw 4. The shut-off needle 7 has a cylindrical geometry corresponding to the geometry of the discharge opening 3. As a result, by displacing the screw 4 in the direction of the discharge opening 3, the shut-off needle 7 can be pushed into the discharge opening 3, thereby closing the discharge opening 3 and thus interrupting the discharge of the material 5. This state is in Fig. 3 shown.

[0035] The shut-off needle 7 and the discharge opening 3 thus form a needle-type shut-off system that enables reliable and highly dynamic stopping of the material discharge from the discharge opening 3. This offers the particular advantage that the material discharge can be stopped directly and immediately at the dosing point, in particular without the need for additional components such as valves or the like, and without the rotation of the screw 4 having to be stopped.

[0036] Furthermore, the axial displacement of the screw 4 offers the advantage that the material throughput, i.e., the volume flow of the material 5 to be discharged, can be controlled easily and precisely. In detail, by axially displacing the screw 4, an annular gap 9 can be created between a needle tip of the shut-off needle 7 and an inner wall of the screw housing 2 (see FIG. Fig. 2) to control the material throughput, for example at a constant rotation speed of the screw 4.

[0037] To achieve the most precise control of the material throughput, the screw 4 and screw housing 2 are coordinated so that the narrowest cross-section for metering the material 5 is always present in the area of ​​the shut-off needle 7. For this purpose, a first angle 71 between a screw shell surface 72 of the conically tapered screw section 70 and the rotation axis 40 is smaller than a second angle 21 between an inner housing shell surface 22 of the conically tapered housing section 20 and the rotation axis 40.

[0038] A further advantage of the needle valve system with valve pin 7 and discharge opening 3 is that the cylindrical configuration of the two elements enables particularly precise dosing of the smallest quantities of material 5. For this purpose, a residual volume of material 5, which is located within the discharge opening 3 immediately after the annular gap 9 has been closed, can be discharged from the discharge opening 4 by further displacement of the screw 4 along the rotation axis 40. This is exemplified by Fig. 4, which shows a second embodiment of the invention. For example, very precise point-like structures can be created on the component to be manufactured in a particularly simple manner, such as in the area A of the Fig. 4, which shows a simplified schematic plan view of an area manufactured by means of the machine tool 10.

[0039] The machine tool 10 of the second embodiment, of which detailed views are shown in the Fig. 4, differs from the machine tool 10 of the first exemplary embodiment in an alternative design of a tip of the screw housing 2. In detail, the screw housing 2 has a mouthpiece 25, which is designed as a separate part from a base body of the screw housing 2. This means that the mouthpiece 25 is designed to be replaceable. At least part of the discharge opening 7 is formed by the mouthpiece 25. As a result, in particular, an axial length 31 of the discharge opening 3 can be easily changed by replacing the mouthpiece 25. For example, different residual volumes of the material 5 can be provided within the discharge opening 3 depending on the intended use. Furthermore, in the event of wear, the outer tip of the screw housing 2 can be easily replaced, whereby precise metering of the material 5 can always be ensured.

[0040] In addition to the above written description of the invention, for its supplementary disclosure, reference is hereby explicitly made to the graphic representation of the invention in the Fig. 1 referred to. List of reference symbols 1 screw system 2 snail shells 3 Discharge opening 4 snail 5 Material 6 Drive device 7 locking needle 8 Heating device 9 Annular gap 10 Machine tool 20 Housing area 21 first angle 22 lateral surface 25 mouthpiece 27 Filling opening 31 axial length 32 diameter 40 Rotation axis 61 rotary drive 62 lifting device 70 snail area 71 second angle 72 lateral surface 80 heating elements

Claims

[1] Screw system of a machine tool (10) for additive manufacturing, comprising: - a screw housing (2) with a discharge opening (3), - a screw (4) which is accommodated in the screw housing (2) and designed to convey a material (5) in the direction of the discharge opening (3), and - a drive device (6) which is arranged to rotate the screw (4) about a rotation axis (40) and to displace the screw (4) along the rotation axis (40), - wherein the screw (4) has a closure needle (7) which is arranged at an axial end of the screw (4) and which is designed to close the discharge opening (3), - wherein the screw housing (2) has a tapered housing area (20), and - wherein the discharge opening (3) is arranged in a tip of the tapered housing area (20), characterized bythat the screw (4) has a tapered screw region (70) at an axial end facing the discharge opening (3), wherein the closure needle (7) is arranged at a tip of the tapered screw region (70), and wherein the tapered screw region (70) has a smaller angle (21, 71) between the axis of rotation (40) and a respective lateral surface (22, 72) than the tapered housing region (20). [2] Screw system according to claim 1, wherein the discharge opening (3) is cylindrical. [3] Screw system according to claim 2, wherein a ratio of an axial length (31) of the discharge opening (3) to a diameter (32) of the discharge opening (3) is at least 0.2 and at most 10, preferably at least 0.5 and at most 2. [4] Screw system according to one of the preceding claims, wherein the closure needle (7) is cylindrical. [5] Screw system according to one of the preceding claims, wherein the screw is driven by means of the drive device (6) hydraulically and / or pneumatically and / or electromagnetically and / or electrically. [6] Screw system according to one of the preceding claims, wherein the screw housing (2) has a mouthpiece (25) which is designed as a separate part from a base body of the screw housing (2), and wherein at least a part of the discharge opening (3) is formed by the mouthpiece (25). [7] Machine tool for additive manufacturing, comprising a screw system (1) according to one of the preceding claims. [8] Machine tool according to claim 7, further comprising a heating device (8) which is arranged to heat the screw housing (2) and / or the screw (4). [9] Method for operating a machine tool (10) according to claim 7 or 8, comprising the steps: - rotating the screw (4) of the screw system (1) of the machine tool (10) around the rotation axis (40) to convey the material (5) in the direction of the discharge opening (3), and - Moving the screw (4) along the rotation axis (40) to close or open the discharge opening (3) of the screw housing (2) by means of the closing needle (7) of the screw (4). [10] The method of claim 9, further comprising the step of: - Increasing the volume of material to be discharged by moving the screw (4) in the direction of the discharge opening (3) while simultaneously rotating the screw (4) around the rotation axis (40). [11] The method of claim 9 or 10, further comprising the step: - Controlling a material throughput by changing an annular gap (9) between a needle tip of the shut-off needle (7) and an inner wall of the screw housing (2) by means of axial displacement of the screw (4). [12] A method according to any one of claims 9 to 11, further comprising the step: - discharging a residual volume of the material (5) which is located within the discharge opening (3), in particular after closing an annular gap (9) between a needle tip of the shut-off needle (7) and an inner wall of the discharge opening (3). [13] Method according to one of claims 9 to 12, further comprising the steps: - filling a granular or powdery material (5) into the screw housing (2), and - Plasticizing the material (5) by rotating the screw (4) and / or by heating the screw housing (2) and / or by heating the screw (4).

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