WO2023242577A1

WO2023242577A1 - Additive manufacturing apparatus and methods

Info

Publication number: WO2023242577A1
Application number: PCT/GB2023/051564
Authority: WO
Inventors: Nathaniel PETRE
Original assignee: Distributive Additive Manufacturing Ltd
Priority date: 2022-06-15
Filing date: 2023-06-15
Publication date: 2023-12-21
Also published as: GB202208829D0

Abstract

A method of additive manufacturing of a 3D object including sequentially forming a plurality of layers configured to form the object by extruding a plastics material from a nozzle of a movable extruder and selectively admitting a pressurised gas into the plastics material upstream of the nozzle so that the density of the plastics material forming layers is controllably varied.

Description

ADDITIVE MANUFACTURING APPARATUS AND METHODS Field of the Invention The invention relates to additive manufacturing in the form of three-dimensional (3D) printing apparatus and methodology. Background to the Invention 3D printing is a manufacturing process for making three-dimensional objects of various shapes. The three-dimensional objects may be manufactured based on a design model, where the design model is formed via a computer, a drawing or obtaining coordinates representative of an object to be manufactured, for example, by scanning a sample or prototype of the object. 3D printing has been used to manufacture products in a wide variety of technical fields. For example, the automotive, aerospace and consumer goods industries use 3D printing to create prototypes of parts and actual products.3D printing has also found application in the manufacture of medical products. For example, 3D printing has been used in the production of dental implants, prosthetics and drug delivery devices that can be used for direct treatment. 3D printing may efficiently form objects that may be difficult to make via traditional methods. Typically, layers of a material are laid adjacent to one another in sequence to build up an entire three-dimensional object formed in the shape of the design model. For example, a plastics material may be extruded from an extruder head to form an object by depositing successive layers of the plastics material one upon another. The plastics material extruded by the extruder head has a density that is constant. Summary of the Invention The invention provides a method of additive manufacturing of a 3D object as specified in claim 1. The invention also includes an additive manufacturing apparatus extruder as specified in claim 9. Brief Description of the Drawings

In order that the invention may be well understood, some embodiments thereof, which are given by way of example only, will now be described with reference to the drawings in which:

Figure l is a schematic representation of an additive manufacturing apparatus; and

Figure 2 is a perspective view of an embodiment of an extruder for an additive manufacturing apparatus according to Figure 1.

Detailed Description

Referring to Figure 1, an additive manufacturing apparatus (3D printing apparatus) 10 suitable for 3D printing objects of manufacture comprises a filament supplier 12, an extruder 14, an extruder transporter 16 and a table 18.

The extruder transporter 16 may comprise a generally U-shaped frame 20 and a cross member 22 mounted on the U-shaped frame. The extruder 14 is carried by the cross member 22 and the filament supplier 12 is mounted on a transverse portion of the U- shaped frame 20 for supplying plastics material to the extruder. The extruder transporter 16 is provided with drive units DX, DY, DZ to provide the extrader 14 with three controllable components of movement in an X-Y-Z coordinate system. Thus, the extrader transporter 16 is provided with a first drive unit DX to move the U-shaped frame 20 back and forth along the table 18 to provide movement in the X direction (which in the illustrated example is perpendicular to the plane of the drawing sheet), a second drive unit DY to move the extrader 14 back and forth along the cross member 22 to provide movement in the Y direction and a third drive unit DZ to move the cross member 22 up and down the upright portions of the U-shaped frame 20 to provide movement in the Z direction. Suitable drive units for providing these components of movement will be well known to those skilled in the art and will not, therefore, be described in further detail herein.

The filament supplier 12 comprises a structure 24 on which a reel, or spool, 26 carrying a plastics filament 28 is mounted. Suitable filament suppliers for 3D printing apparatus will be well known to those skilled in the art and so the filament supplier 12 will not be described in further detail herein. The filament supplier 12 supplies plastics filament 28 from the spool 26 to the extruder 14.

The extruder 14 comprises a filament feeder 30, a heatsink 32 and an extruder head 34. The filament feeder 30 comprises a motor 36, a relatively small gear 38 mounted on the motor output shaft 40, a relatively larger gear 42 mounted on a filament driver shaft 44, a filament driver wheel 46 mounted on the filament driver shaft 44 and a rotatable bearing wheel 48. The filament 28 passes from the filament supplier 12 into a gap between the filament driver wheel 46 and the bearing wheel 48. The filament driver wheel 46 and bearing wheel 48 engage opposite sides of the filament 28. When the motor 36 is energised, the filament driver wheel 46 is rotated by the filament driver shaft 44 so as to apply a drive force to the filament 28, which causes it to be drawn from the spool 26 and fed through the gap between the filament drive wheel 46 and the bearing wheel 48 and on into the extruder head 34 via the heat sink 32. The filament driver wheel 46 may be provided with suitable surface formations (not shown) to allow it to grip the filament 28. Additionally, or alternatively, one or both of the filament driver wheel 46 or the bearing wheel 48 may have a filament contacting surface made of a relatively high friction material to grip the filament 28.

The heatsink 32 is disposed downstream of the filament feeder 30 to provide a heat break between the filament feeder 30 and the extruder head 34. The heatsink 32 comprises a guide passage 50 through which the filament 28 is guided as it travels from the filament feeder 30 to the extruder head 34. The heatsink 32 may be provided with one or more coolant pipes, or passages, 52 through which a piped coolant supply can be conducted through, or around, the heatsink to allow the coolant, typically water, to conduct heat away from the heatsink 32. Additionally, or alternatively, in other embodiments the heatsink 32 may be cooled by a cooling airflow provided by a cooling fan that may be fitted to the heat sink.

The extruder head 34 is disposed downstream of the heat sink 32 and comprises a body 54 that defines a through-passage 56 having an upstream end that, in use, receives, or is an inlet for, the filament 28 that is fed into the extruder head by the filament feeder 30. The downstream end of the through-passage 56 is relatively narrower than the upstream end so that the downstream, or free, end of the extruder head 34 is configured as a nozzle 58 through which softened plastics material is extruded onto the table 18, The body 54 may be a one-piece component or comprise multiple components joined or connected to one another.

The extruder head 34 further comprises one or more heaters 60, 62. The one or more heaters 60, 62 may be wrapped around the body 54 or otherwise connected with the body 54 to enable heat transfer from the one or more heaters 60, 62 into the body 54. The one or more heaters 60, 62 are operable to supply heat into the body 54 to soften the filament 28. The one or more heaters 60 are preferably electric heaters. One or more temperature sensors 64 may be provided on the body 54 to provide signals indicative of the temperature of the body 54 to allow control of the temperature of the filament 28 passing through the extruder head 34. Any suitable temperature sensor, for example a thermistor, may be used.

The extruder head 34 further comprises a gas port. 68 through which gas from a pressurised gas supply unit 70 may be supplied into the through-passage 56 of the extruder head. The gas port 68 is disposed between the upstream end of the body 54 and the one or more heaters 60, 62. The gas supply unit 70 comprises a pressurised gas source 72 and an admittance valve 74. The pressurised gas source 72 may comprise a discrete gas tank or bottle containing a suitable gas, such as air, an inert gas, nitrogen or oxygen free nitrogen (OFN) Alternatively, the pressurised gas source may be a piped factory supply.

A control unit, or controller, 80 controls the operation of the 3D printing apparatus 10. The control unit 80 preferably communicates with a data processor 82, which transmits digital data pertaining to fabrication instructions based on computer object data representative of a design model. The data processor 82 may be a personal computer, a server or any other suitable computing device that may be used to transmit digital data to the controller, typically via a wared or wireless connection. The digital data may, for example, comprise a CAD configuration represented on a computer readable medium in the form of a Standard Tessellation Language (STL) format or the like. Typically, the control unit 80 is configured to output signals to the respective drive units DX, DY, DZ of the extruder transporter 16 to cause a desired movement of the extruder 14 in the X-Y-Z directions and to the motor 36 to cause the filament 28 to be fed into the extruder head 34 at a desired feed rate. The control unit 80 is also preferably configured to output signals to the one or more heaters 60, 62 to cause the heating of the filament 28 in the through-passage 56 to a desired temperature. The control unit 80 preferably receives signals from the one or more temperature sensors 64 to provide feedback for adjusting the output of the heater or heaters 60, 62 to maintain a desired temperature in the through-passage 56. Although not essential, a typical operating temperature would be in the range 230 - 250°C. As described in more detail below, the control unit 80 preferably controls the operation of the admittance valve 74 so that a desired volume flow rate of gas from the gas source 72 is able to flow into the through-passage 56 via the gas port 68.

The control unit 80 may be configured such that once the manufacturing data is loaded, it can operate without further user intervention. However, in some embodiments, the control unit 80 may receive additional input provided by an operator. Such additional information, may be input using the data processor 82 or via an optional user interface 86 that communicates with the control unit 80. The user interface 86 can be of any type known in the art, such as, but not limited to, a keyboard, a touch screen or the like. For example, the user interface 86 may be configured to allow a user to supply the control unit 80 with information relating to the plastics filament type or specific related data, for example, colour, characteristic distortion, transition temperature or viscosity. As described in more detail below, the data processor 82 or user interface 86 may be used to input parameters and commands relating to the supply of pressurised gas into the through-passage 56 via the gas port 68.

The admittance valve 74 may be electrically, hydraulically or pneumatically actuated in response to control signals received from the control unit 80. The admittance valve 74 may be a simple on/off valve such as a solenoid valve, in which case, the gas supply into the gas port 68 can be varied between zero and a set amount. A simple/on off admittance valve 74 may be used in combination with a manually adjustable valve (not shown), so that the set amount can be varied by manual adjustment. The manually adjustable valve may be a needle valve. In some embodiments, the admittance valve 74 may be a servo valve or other controllable valve that can be continuously selectively opened and closed between an open and closed condition in response to control signals provided by the control unit 80. A controllable admittance valve 74 may be controlled to provide a continuously variable gas throughput between zero throughput corresponding to a closed condition of the valve and a maximum throughput corresponding to a fully open condition of the valve.

In the illustrated embodiment, the extruder head 34 has one gas port 68. It will be understood that this is not essential and that two or more gas ports may be provided. For example, an additional gas port disposed generally opposite the gas port 68 shown in Figures 1 and 2 may assist in obtaining a more even distribution of gas through the plastics filament 28 as it moves through the through-passage 56. Alternatively, multiple gas ports in different horizontal (as viewed in Figure 1) planes may be provided. In embodiments in which multiple gas ports are provided, they may be connected with the admittance valve 74 via a manifold arrangement so that only one admittance valve 74 and pressurised gas source 72 is needed. Alternatively, multiple gas ports may be provided with respective admittance valves, which may be used to control the supply of pressurised gas from a common or multiple gas sources. The gas port, or ports, may comprise a generally circular hole, or holes, as shown in Figure 2 or any other suitably shaped hole or holes. For example, the gas port, or ports, may comprise a slot extending partially around the circumference of the body 54.

In the illustrated embodiment, the gas port 68 extends transverse to the through-passage 56 and extends from a side of the extruder head body 54 to the through-passage perpendicular to the longitudinal axis of the through-passage. It is to be understood that this is not essential. For example, a transversely extending from a side of the extruder head body to the through-passage may be inclined with respect to the through-passage. Furthermore, in some embodiments, a gas port may extend from an end of the extruder head body 54 to the through-passage 56. Thus, a gas port may have an inlet end disposed at the same end of the extruder head body 54 as the inlet end of the through- passage 56. There may be multiple gas ports extending from the end of the extruder head body. In some embodiments, there may be one or more gas ports extending from an end of the extruder head body in combination with one or more gas ports extending from a side of the extruder head body. A gas port extending from the same end of the extruder head body as the through-passage may be configured such that the pressurised gas is contact with the filament for a longer time than a transversely extending gas port, which may result in greater gas absorption by the filament. It will be understood that the combination of controller 80, data processor 82 and user interface 86 is given purely by way of example. For example, the controller and data processor may be combined in a single device. Alternatively, there may be multiple controllers connected with a master controller, or the data processor may function as a master controller. The one or more controllers may take any suitable known form. Suitable controllers for an extruding 3D printing apparatus will be well known to those skilled in the art and so will not be described in further detail herein.

In use of the additive manufacturing apparatus 10, the filament feeder 30 draws plastics filament 28 from the spool 26 and feeds it into the extruder head 34 via the guide passage 50 of the heat sink 32. As the plastics filament 28 moves through the through- passage 56 it is softened by heat supplied from the one or more heaters 60, 62 allowing it to be extruded through the nozzle 58. As the plastics material is extruded from the nozzle 58, the control unit 80 controls operation of the extruder transporter 16 so that the extruder 14 is moved in the X and Y directions to deposit a layer of plastics material having a desired configuration based on the computer object data representative of the design model. Typically, once deposition of a layer of plastics material is completed, the control unit 80 will cause the extruder transporter 16 to move the extruder 14 away from the table 18 in the Z direction so that subsequent layers of material can be successively deposited on previously deposited layers of material to form a 3D object of manufacture 90.

In an aspect of some embodiments of the invention there is provided a method of additive manufacturing of a 3D object. The method can be executed using an additive manufacturing apparatus, for example the additive manufacturing apparatus 10. The method comprises sequentially forming a plurality of layers, each patterned according to the shape of a cross section of the 3D object. In various embodiments, at least one of the layers is formed with plastics material injected with a pressurised gas so that all or a part of the layer has a density that is less than the density of parts of the layer or other layers formed from the same plastics material without gas injection. It will be understood that by suitable control of the pressurised gas admitted into the extruder head, a 3D object may be formed with layers having different densities. Alternatively, or additionally, the density within each layer may be varied allowing an object to be formed with sections that have a relatively low-density adjacent sections having a relatively higher density.

Any plastics filament suitable for use with known 3D printing apparatus extruders may be used. It has been found that at least some embodiments are particularly effective when used with 99.8% recycled PET, PP or HDPE. It has been found that the higher the percentage of recycled plastics material in the filament, for example 75% or more, the better the material adheres to itself when foamed by the pressurised gas. It is believed this may be a result of a chaotic surface area that attaches well.

Claims

1. A method of additive manufacturing of a 3D object comprising: sequentially forming a plurality of layers configured to form the object by extruding a plastics material from a nozzle of a movable extruder; and selectively admitting a pressurised gas into said plastics material upstream of said nozzle, whereby the density of the plastics material forming said layers is controllably varied.

2. A method as claimed in claim 1, wherein selectively admitting said pressurised gas comprises selectively opening and closing a valve.

3. A method as claimed in claim 2, wherein selectively admitting said pressurised gas comprises selectively varying an open condition of said valve between a partially open condition and a fully open condition.

4. A method as claimed in any one of the preceding claims, wherein said pressurised gas is air, an inert gas, nitrogen or oxygen free nitrogen.

5. A method as claimed in any one of the preceding claims, wherein said plastics material is fed into said extruder as a plastics filament.

6. A method as claimed in any one of the preceding claims, wherein said plastics material comprises at least one of recycled PET, PP or HDPE.

7. A method as claimed in claim 5 or 6, wherein said plastics material comprises at least 75% recycled plastics material.

8. A method as claimed in any one of the preceding claims, wherein said movable extruder comprises an extruder head provided with one or more heaters to supply heat to soften said plastics material and said pressurised gas is admitted into extruder head via a gas port disposed upstream of said one or more heaters.

9. An additive manufacturing apparatus extruder comprising: an extruder head body having a through-passage and a gas port connected with said through-passage, the through-passage having an upstream end into which, in use, a plastics filament is fed and a downstream end from which softened plastics material from said plastics filament is extruded; and a gas supplier unit connected with said gas port, the gas supplier unit comprising an admittance valve to control admittance of a pressurised gas from a pressurised gas source into said through-passage via said gas port.

10. An additive manufacturing apparatus extruder as claimed in claim 9, further comprising at least one heater connected with said extruder head body to heat said plastics filament, wherein said gas port is disposed between said upstream end and the at least one heater.

11. An additive manufacturing apparatus extruder as claimed in claim 9 or 10, wherein said admittance valve comprises an electrically actuable valve.

12. An additive manufacturing apparatus extruder as claimed in claim 9, 10 or 11, wherein said admittance valve is configured to provide a lowermost gas throughput condition and an uppermost gas throughput condition and is selectively controllable to provide continuously variable gas throughput conditions between said lowermost and uppermost gas throughput conditions.