Fused material print head

Abstract

A print head for a fused printing machine comprises a body (1) for mounting on the machine, an extrusion screw (2) rotatably mounted in a sleeve (3), a nozzle orifice (61) at one end of the sleeve (3) for receiving a nozzle (4) through which molten material is extracted, drive means (5) for rotating the extrusion screw (2) in an extrusion direction, and distribution means (6) for closing or opening the nozzle orifice (61) between a closed position and an open position, respectively. The head includes control means (7) for directing the distribution means (6) to the closed position by reversing the direction of rotation of the extrusion screw (2). Figure for the abbreviation: Fig. 2

Description

Title of the invention: Fused material printing head technical field

[0001] The invention relates to the volumetric printing of parts made of molten material such as thermoplastic material. It relates more particularly to a print head comprising an extrusion screw. Previous technique

[0002] Various three-dimensional additive manufacturing techniques have emerged recently. Among these techniques, fused filament fabrication (FFF) is particularly noteworthy. Thermoplastic material is first prepared in the form of a filament, for example, with a diameter of one to two millimeters. This filament is then fed into a print head that includes a heating chamber into which the filament is pushed. The filament melts, and the molten material is extruded through a nozzle moving relative to a build platform on which the part is constructed.

[0003] Although this manufacturing process has found its field of application, it remains limited in terms of productivity, that is to say in terms of the volume of material that can be deposited per unit of time.

[0004] In document EP 3 081 364 A1, a print head was proposed for this type of application in which an extrusion screw prepares the molten material. To control the material output according to the printing process, it is proposed to provide a control rod for the nozzle opening. This rod is axially movable, passing through the screw along its axis. The axial mobility of the rod allows the molten material passage from an extrusion chamber, in which the extrusion screw is mounted to rotate towards the nozzle, to be opened or closed, and then onto the part being manufactured.

[0005] This technique requires a specific control device to obtain the movement of the rod. Description of the invention

[0006] The invention aims to provide a print head equipped with an extrusion screw enabling the passage of molten material on command with a simplification of the means for obtaining this command.

[0007] With its objectives in mind, the invention relates to a print head for a fused printing machine, the print head comprising a body for mounting on the machine, an extrusion screw rotatably mounted in a sleeve, and a nozzle orifice at one end of the sleeve for receiving a nozzle. in which a molten material is extracted, drive means for driving the screw in rotation in an extrusion direction and distribution means for closing or opening the nozzle orifice between respectively a closed position and an open position, the head being characterized in that it includes control means for directing the distribution means towards the closed position by reversing the direction of rotation of the screw.

[0008] Current control devices for filament-fused printers generally do not include direct means for closing the nozzle. The method used is a reversal of the filament's movement to release the pressure within the melting chamber. Indeed, it is the filament's movement that determines the pressure inside the melting chamber. Therefore, when the printer's control system determines that the molten material output must be stopped, it commands a slight retraction of the filament by reversing its movement. With the means of the invention, the print head can be directly controlled using the same principle of reversing the movement at the moment when the molten material output is to be stopped. This achieves nozzle closure without modifying the printer's control device.

[0009] According to a first embodiment, the sleeve is pivotally mounted on the body around the axis of the screw. The control means include a freewheel device between the screw and the sleeve configured to allow rotation of the screw in the extrusion direction and to link the rotation of the screw and the sleeve in the opposite direction to the extrusion direction. The nozzle orifice is provided in a bearing fixed relative to the body. The distribution means are controlled by the relative pivoting of the sleeve and the bearing. By connecting the screw drive motor to the output device of the printer control, the screw is driven when it needs to supply molten material, but it reverses when it is desired to stop. By this reverse movement, the freewheel device is used to drive the sleeve and thus control the closure of the nozzle orifice.In the normal direction of screw drive, the freewheeling mechanism allows this rotation. Therefore, a specific control device is not required for this type of print head.

[0010] According to one design feature, the sleeve has a control orifice that is aligned with the nozzle orifice when the distribution means are in the open position and offset from the nozzle orifice when the distribution means are in the closed position. Pivoting the sleeve relative to the nozzle allows the control orifice to be positioned either opposite or beside the nozzle orifice, thus determining the possibility of the molten material flowing to the nozzle.

[0011] According to an improvement, the control means include limiting means for restricting the pivoting movement of the sleeve relative to the body between the closed and open positions. These limiting means allow for precise determination of the sleeve position that controls the closing or opening and aligns the control orifice and the nozzle orifice. For example, the limiting means restrict the movement to an angle between 15 and 20°.

[0012] According to an improvement, the control means further comprise elastic return means from the closed position to the open position. From the closed position, when the screw is rotated, the freewheel releases the sleeve, and the elastic return means return the sleeve to the open position.

[0013] According to one design feature, the print head includes a hopper for receiving granular material at the end of the screw opposite the nozzle orifice. The hopper thus supplies the extrusion screw with granular material so that the screw can melt this material and pressurize it before delivering it through the nozzle.

[0014] According to one design feature, the print head includes at least one heating element arranged around the jacket to melt the material to be injected. The jacket is thus heated so that the material pushed by the extrusion screw is melted, in addition to the energy supplied directly by the screw. Brief description of the figures

[0015] The invention will be better understood and other features and advantages will become apparent upon reading the following description, the description referring to the accompanying drawings, among which: • [Fig.1] is a longitudinal cross-sectional view of a print head according to an embodiment of the invention; • [Fig.2] is a perspective and cross-sectional view of the head of [Fig.1]; • Fig. 3 is a cross-sectional view of the distribution means. open position; • [Fig.4] is a view similar to [Fig.3] in the shutter position. Detailed description

[0016] A print head for a fused printing machine according to an embodiment of the invention is shown in Figures 1 to 4. The print head is intended to be part of a three-dimensional printing machine, not shown, in which the print head deposits a bead of molten thermoplastic material first onto a support plate, then onto The part being built. The machine controls the relative movements between the print head and the build plate, which determines the geometry of the part. The machine also controls the supply or cessation of the molten material flow.

[0017] The head comprises a body 1 for mounting on the machine, an extrusion screw 2 rotatably mounted in a sleeve 3, a nozzle orifice 61 at one end of the sleeve 3 for receiving a nozzle 4 through which molten material is extracted, drive means 5 for rotating the extrusion screw 2 in an extrusion direction, and distribution means 6 for closing or opening the nozzle orifice 61 between a closed position and an open position, respectively. The drive means 5 comprise an electric motor having a stator 50 fixed to and housed within the body 1, and a rotor 51 rotatably mounted coaxially with the stator 50. The rotor 51 is further connected to the extrusion screw 2, which extends coaxially beyond the rotor 51.

[0018] The head further includes control means 7 for controlling the distribution means 6 towards the closing position by reversing the direction of rotation of the extrusion screw 2.

[0019] For this purpose, the sleeve 3 is pivotally mounted on the body 1 around the axis of the extrusion screw 2, being housed in a cup 10 extending from the body 1. The sleeve 3 is retained in the cup 10 by a pin 81 screwed radially onto the sleeve 3 and passing through a slot 80 in the cup 10. A ball bearing 70 is interposed between the extrusion screw 2 and the sleeve 3 near the motor 5. The control means 7 comprise, beside the ball bearing 70, a freewheel device 71 between the extrusion screw 2 and the sleeve 3 configured to allow the rotation of the extrusion screw 2 in the direction of extrusion and to link the rotation of the extrusion screw 2 and the sleeve 3 in the opposite direction to the direction of extrusion.

[0020] The sleeve 3 further comprises, successively from the cup 10, a first heating zone 31 at the level of the ball bearing 70 and the freewheel device 71, a hopper 33, a second heating zone 32, a heating zone 34, and terminates in a cylindrical guide surface 35. The cylindrical guide surface 35 receives a bearing 9 which is fixed relative to the body 1 by means of a support (not shown). The bearing 9 has the nozzle orifice 61.

[0021] The distribution means 6 are controlled by the relative pivoting of the sleeve 3 and the bearing 9. The sleeve 3 has a control orifice 60 which is aligned with the nozzle orifice 61 when the distribution means 6 are in the open position and which is offset from the nozzle orifice 61 when the distribution means 6 are in the closed position.

[0022] The control means 7 further include limiting means 8 for limiting the pivoting movement of the sleeve 3 relative to the body 1 between the closed position and the open position. These limiting means 8 include the pin 81 which moves within the aperture 80 over an angular portion, on the order of 15 to 20°.

[0023] The control means 7 further include elastic return means from the closed position to the open position, not shown.

[0024] The heating zone 34 of the jacket 3 is surrounded by a heating element 340, for example by an electrical resistance of helical shape.

[0025] In a conventional manner, the nozzle orifice 61 receives an interchangeable nozzle 4, for example by screwing, through which the material exits to be deposited on the part being manufactured.

[0026] The operation of the print head will now be described.

[0027] The print head is mounted on a volumetric printing machine by attaching the body 1 and the bearing 9, with the hopper 33 oriented to hold thermoplastic granules. During operation, the temperature inside the jacket 3 is increased and regulated by the heating element 340. When a bead of material is to be deposited, the motor 5 is energized and drives the extrusion screw 2 in a direction permitted by the freewheel device 71. The return means rotate the jacket 3 to the open position, as shown in [Fig. 3], to a position determined by the limiting means 8. The rotation of the extrusion screw 2 draws granules from the hopper 33 to the nozzle orifice 61, where they melt to form molten material, which is then pressurized by the extrusion screw 2.The molten material can then pass through the control orifice 60 and then the nozzle orifice 61 and be deposited onto the part being formed.

[0028] When the material deposition process needs to be interrupted, the motor 5 is commanded to first reverse its rotation and then stop. By reversing its rotation, the freewheel device 71 engages and couples the sleeve 3 with the extrusion screw 2. The sleeve 3 then pivots towards the closed position against the return means, until the limiting means 8 block the pivoting. The control orifice 60 shifts relative to the nozzle orifice 61, and the material can no longer be extracted.

[0029] To resume the material deposition, it is sufficient to resume the rotation of the extrusion screw 2. The return means put the sleeve 3 back into the open position and the extraction of the material can resume.

[0030] The invention is not limited to the embodiments described above by way of example. Instead of a freewheel, a permanent friction system could be used.

Claims

Demands

1. Print head for a fused printing machine, the print head comprising a body (1) for mounting on the machine, an extrusion screw (2) rotatably mounted in a sleeve (3), a nozzle orifice (61) at one end of the sleeve (3) for receiving a nozzle (4) through which molten material is extracted, drive means (5) for driving the extrusion screw (2) in rotation in an extrusion direction and distribution means (6) for closing or opening the nozzle orifice (61) between respectively a closed position and an open position, the head being characterized in that it comprises control means (7) for controlling the distribution means (6) towards the closed position by reversing the direction of rotation of the extrusion screw (2).

2. Print head according to claim 1, wherein the sleeve (3) is pivotally mounted on the body (1) about the axis of the extrusion screw (2), the control means (7) comprising a freewheel device (71) between the extrusion screw (2) and the sleeve (3) configured to permit the rotation of the extrusion screw (2) in the direction of extrusion and to link the rotation of the extrusion screw (2) and the sleeve (3) in the direction opposite to the direction of extrusion, the nozzle orifice (61) being provided in a bearing (9) fixed relative to the body (1), the distribution means (6) being controlled by the relative pivoting of the sleeve (3) and the bearing (9).

3. Print head according to claim 2, wherein the sleeve (3) has a control orifice (60) which is aligned with the nozzle orifice (61) when the dispensing means (6) are in the open position and which is offset from the nozzle orifice (61) when the dispensing means (6) are in the closed position.

4. Print head according to any one of claims 2 or 3, wherein the control means (7) comprise limiting means (8) for limiting the pivoting travel of the sleeve (3) relative to the body (1) between the closed position and the open position.

5. Print head according to claim 4, wherein the limiting means (8) limit the deflection to an angle between 15 and 20°.

6. Print head according to any one of claims 2 to 5, wherein the control means (7) further comprise elastic return means from the shutter position to the open position.

7. Print head according to any one of the preceding claims, characterized in that it comprises a hopper (33) for receiving granular material at the end of the extrusion screw (2) opposite the nozzle orifice (61).

8. Print head according to any one of the preceding claims, characterized in that it comprises at least one heating element (340) arranged around the jacket (3) to melt the material to be injected.

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