WO2021225586A1

WO2021225586A1 - A continuous flow, high throughput, automated additive manufacturing system

Info

Publication number: WO2021225586A1
Application number: PCT/US2020/031535
Authority: WO
Inventors: Vineet Janak PADIA
Original assignee: Wavelet Systems, Llc
Priority date: 2020-05-05
Filing date: 2020-05-05
Publication date: 2021-11-11

Abstract

This invention detailed in this document relates to the manufacturing of three-dimensional objects with the automated removal of additively manufactured parts.

Description

A CONTINUOUS FLOW, HIGH THROUGHPUT, AUTOMATED ADDITIVE MANUFACTURING

SYSTEM

BACKGROUND

The current methodology of additive manufacturing follows the given procedure to create a suitable part. Any failures within this process can lead to failed parts and/or increased manufacturing costs.

The part is designed in a Computer Aided Drawing (CAD) environment, where the user defines the geometric embodiment of the part to fit the user’s design needs. From the environment, the data file is exported to a manufacturing file format, which includes details about the 3- dimensional data of the object. This data is fed into a Computer-Aided Manufacturing (CAM) program that allows the operator to determine manufacturing settings of the part, such as infill, material, part orientation, support settings. The CAM relies upon a Slicer to generate the slices and generates appropriate toolpaths of the extruder. At this point, the machine instructions are sent to the 3d printer for subsequent execution. Upon successful printing, the part often needs manual post-processing, such as removing the part from the build platform or removing supports.

Once the part is fully printed, the part is inspected, usually by a human operator to determine if the part meets the acceptance criteria. If not, the part may be reprinted, and settings are adjusted to tune the machine. This process requires detailed knowledge of the printer and human attention.

There are a few limiting factors preventing additive manufacturing from being cost-effective at a larger scale. Currently, parts cannot be manufactured sequentially. In an effort to produce more parts between human intervention, 3-dimensional printers become very large so that parts can be nested into a single build volume. Batch production with large volume printers is inefficient since any failure is likely to affect the other parts. Larger print volumes are subject to uneven thermal gradients can cause delamination failures due to thermal contraction.

Robotics arms with grippers attempt to replace the human operator but are expensive and present other problems such as gripping the objects without damage. Conveyor belt systems have not been successful because the platform is flexible. The constant heating and cooling of the belt often cause the belt to stretch and wear, which causes adhesion issues over time. Other separation mechanisms, such as actuated arms with blades, often damage parts and separate the objects in unconventional ways. SUMMARY OF THE INVENTION

The present disclosure generally relates to a stage and associated process for use in a 3- dimensional printer, shown in Figure 1. The system that can actively cool the printing platen below ambient temperature to easily separate the 3-dimensional object and progress on to the subsequent printing operation.

The interface between the part and the build plate is considered a restricted connection, due to the adhesion of the object onto the printing surface. Any change in temperature from the original steady-state temperature of the printing platen will cause mechanical stress across the contact area of the object. By quickly lowering the temperature of the platen to a sub-ambient temperature, a sufficiently high shear stress is generated and easily separates the recently completed object. In one aspect, this invention details cooling systems for the platen with thermoelectric cooling elements, liquid cooling, and refrigeration.

The second aspect of the invention relates the actuators and end-effectors to provide the remaining stress to remove the part and transport the object to a storage container. This can be accomplished by a mechanical arm, linear or rotary, and operated under electric, pneumatic, or hydraulic actuation. It is possible that the motion system of the extruder could be used to move the part to the container as well.

Given the capability of automatically removing an object from the printing surface, inspection and automatic parameter tuning functionalities can be added. An imaging device within the build chamber can image the part and send the data to a computing unit. The computing unit can process the image to recover data about the most recently printed layer. By comparing the ideal toolpath to the processed image, a measure of quality is extracted and recorded. Over the course of the print, if the running quality level is too low, the printer can abort the print, make parameter adjustments, and reprint the part.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure 1 outlines a fused-filament additive manufacturing apparatus, with a two-dimensional motion platform that translates the extruder 15 in an XY plane. The extruder 15 is able to selectively deposit thermoplastic onto a platen 13 through electronic control of the filament feed-rate. By incrementing the Z-axis actuator and selectively depositing material in the XY plane in successive layers, the apparatus fabricates a three-dimensional object. The camera 24 images the object 17 within the apparatus and provides data to the processing unit to assess the running quality of the printed layers. The stage 16 is capable of releasing the completed printed object 17 and moving it to a storage location that is located outside of the body of the printer. An automated queue is provided to dictate the next object fabricated by the apparatus.

The object separation system Figure 3 is composed of two main subunits, a printing surface 31 and thermal regulation system 33.

During the printing operation, the printing surface is heated to the glass transition temperature of the printing material. The printed material, often a thermoplastic, has a high Coefficient of Thermal Expansion (CTE). This invention implements a printing surface with a low CTE, yet with high thermal conductivity. Upon finishing the print, the rapid cooling of the printed surface causes a rapid contraction of the plastic relative to the printing surface. This high thermal stress at the adhered surface of the printed part can cause a full separation or drastically reduce the force required to separate the part. The printing surface is ideally thermally conductive such that the cooling system can quickly transfer the heat away from the interface to prevent stress relaxation in the printed object.

Figure 11 details a multi-layered printing stage where the top layer 111 is thermally conductive and has a low thermal expansion. Such materials include carbon fiber, alumina, silicon, aluminum nitride. A heat spreader 112 is thermally bonded underneath the top layer to distribute the heat evenly across the stage. The heat spreader 112 is composed of thin copper or aluminum. 113 is thermally bonded to the heat spreader and represents the thermal regulation systems in Figures 2, 3, 4, and 5.

In Figure 11, a combination of materials is used to attain high thermal conductivity and low CTE at low cost by using materials used in printed circuit board production. 102 is a composite material composed of woven fiberglass cloth with an epoxy resin binder. 101 and 103 are thin layers of copper foil laminated to each side.101 provides thermal conductivity across the printed surface and experiences minimal thermal distortion due to the retention of the glass-composite substrate 102. Thermal conductivity is enhanced between 101 and 103 with electrochemically plated holes filled with a thermally conductive material such as copper or solder. The heat from the platen converges to the holes, flows along the length of the plated cylindrical surface and filler material, and then is transferred to the environment by the cooling system.

An aspect of this invention entails a cooling system to remove heat from the printing platen. This can be achieved with ThermoElectric Coolers (TECs) TECs provide several benefits over other refrigeration techniques, including compact size, no moving parts, quiet operation, and precise temperature control. Since the printing platen needs to be heated in the fabrication of the object, the reversal of polarity 13, 24 of the TEC element will generate heat by Joule heating and facilitate adhesion at the beginning of a print. TECs can be arranged in a matrix along the bottom area of the platen. In order to dissipate heat that is both transported and generated by the TEC, a heat sink must be used. Also, fans can be placed underneath or adjacent to the fans to facilitate convective heat transfer.

In the other embodiments, as shown in Figure 4, the cooling system is a vapor-compression cycle. In this cycle, a circulating refrigerant enters the compressor 41 as a vapor. The vapor is compressed at constant entropy and exits the compressor 41 as a vapor at a higher temperature, but still below the vapor pressure at that temperature. The vapor travels through the condenser 45, which cools the vapor until it starts condensing, and then condenses the vapor into a liquid by removing additional heat at constant pressure and temperature. The liquid refrigerant goes through the expansion valve 46, where its pressure decreases, resulting in a mixture of liquid and vapor at a lower temperature and pressure. The cold liquid-vapor mixture then travels through the platen heat exchanger 42, 43, and is completely vaporized by cooling the warm printing platen. The resulting refrigerant vapor returns to the compressor 41 inlet to complete the thermodynamic cycle.

In the other embodiments, as shown in Figure 5, a liquid is circulated through a reservoir tank 55, located outside of the printing volume, through a serpentine channel 53 heat exchanger 52, which is thermally bonded to the platen 54. This reservoir 55 can be kept at room temperature and can be pumped into the heat exchanger 52 that is thermally bonded to the printing surface. The radiator 56 is placed outside the build volume and releases the heat into the environment.

In all cooling system embodiments, temperature sensors 21 are thermally bonded to the underside of the printing platen to measure the temperature profile across the surface.

Combined with the data processing unit 18, the temperature profile can be analyzed and subsequently used to control the desired heat transfer within the cooling system.

In other embodiments, as shown in Figure 6, a 3-dimensional printing apparatus wherein an end-effector 68 is mechanically coupled to a threaded component 62 that is advanced by a leadscrew 63, and/or the end-effector 68 is mechanically coupled to a belt which is rotated by a drive pulley.

In other embodiments, as shown in Figure 7, the end-effector 76 is mechanically coupled to a rotary actuator 71 for angular movement.

In other embodiments, as shown in Figure 8, the actuators in the x-y-z positioning assembly 81 are used to transport the part to the storage area via a paddle-like surface 85.

The end-effector depicted in Figures 6, 7, 8, and 9 can have a compliant elastomeric material that makes constant contact with the printing surface for the purpose of removing remaining residue on the printing surface.,

The end-effector depicted in Figures 6, 7, 8, and 9 can have a solvent nozzle that dispenses controlled volumes of solvent to dissolve and remove remaining residue on the printing surface for the purpose of promoting adhesion.

The end-effectors depicted in Figures 6, 7, 8, and 9 can be driven by an electric motor, end- effector is driven by a pneumatic actuator, and end-effector is driven by a hydraulic actuator.

With reference now to Figure 6, an embodiment of the part removal system is illustrated. An arm is actuated in a linear motion to move the part from its printed location to the storage container. The arm can be actuated by a motor that is mechanically coupled to a leadscrew, which in turn advances a threaded component in the arm coupling. Linear motion can be achieved by using pneumatic or hydraulic actuation, wherein the actuator is a piston.

Yet another embodiment of the invention is illustrated in Figure 7. In this embodiment, the arm is linear motion to move the part from its printed location to the storage container. The arm can be actuated by a motor, either directly or through a mechanical transmission. Rotary motion can be achieved by using pneumatic or hydraulic rotary actuators. Figure 10 illustrates an embodiment in which a threaded rod or lead screw 38 causes the blade 20 to traverse the printing surface 12 to engage and then remove a printed part. As shown in Figure 11, it is contemplated that the blade 20 may be supported on both sides by guides 40 and 42.

After parts have been released as discussed above, compressed air may be used to remove a part from the printing surface, as shown in Figure 9.

Figure 8 is an embodiment that uses the existing XY motion system of the printer to impart the force to move the printed part. A flat paddle 85 adjacent to the extruder 86 can be used to provide a flat uniform surface to push the separated object 83 into a storage container 82.

BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is an orthogonal view of a three-dimensional printing apparatus with a block diagram representing the various electronic controllers

Figure 2 is the cross-sectional view of a cooling system embodiment with a matrix of thermoelectric cooling devices and temperature sensors

Figure 3 is a side view of the full cooling system embodiment with the element depicted in FIG2

Figure 4 is an orthogonal bottom view combined with a block diagram of a cooling system embodiment implementing vapor-compression cycle

Figure 5 is an orthogonal bottom view combined with a block diagram of a cooling system embodiment implementing a circulated liquid cooling.

Figure 6 is an orthogonal top view of the printing surface along with an arm to transport the printed part into a storage container.

Figure 7 is an orthogonal top view of the printing surface along with an arm to transport the printed part into a storage container.

Figure 8 is an orthogonal top view of the printing surface along with the existing XY gantry and paddle to transport the printed part into a storage container.

Figure 9 is an orthogonal top view of the printing surface and demonstrates the use of compressed air to transport the printed part into a storage container.

Figure 10 is an orthogonal side view of a printing plate embodiment and thermal connection to the cooling system

Figure 11 is an orthogonal side view of another printing plate embodiment and thermal connection to the cooling system

Claims

1. A 3-dimensional object printer comprising one or more component from: a. an x-y-z positioning assembly adapted to three-dimensionally position the extrusion tip within the working volume; b. a controller electrically coupled to each of the build platform, the extruder, and the x-y-z positioning assembly, the controller operable to control the build platform, the extruder, and the x-y-z positioning assembly to fabricate an object in three-dimensions from the build material; c. a platen with a printing surface made from a material that has a high coefficient of thermal expansion and high thermal conductivity; d. a plurality of heating and cooling elements thermally bonded to the platen and controlled by an electronic controller to vary the thermo-spatial profile of the platen; e. a plurality of temperature sensing elements thermally bonded to the platen sensing the thermo-spatial profile of the platen; f. a temperature control device to rapidly cool the platen causing the release of the printed object(s) from the platen; g. an actuator to transport the printed object into a storage container where the force, speed, and position are regulated by an electronic controller; an end-effector to transport the printed object into a storage container where the force, speed, and position are regulated by an electronic controller; and h. An imaging system to assess the quality of the individual printed layers of the printed object.

2. An apparatus of Claim 1 wherein the printing surface has a lower coefficient of thermal expansion relative to that of the printed object wherein the material is selected from carbon fiber, alumina, silicon, aluminum nitride, and low carbon steel.

3. An apparatus of Claim 1 wherein the printing surface is thermally conductive to rapidly cool the printed object.

4. An apparatus of Claim 1 wherein the printing platen is composed of a heat spreader that is thermally bonded to the printing surface.

5. An apparatus of Claim 1 wherein the printing platen is composed of a multilayer substrate with plated holes filled with a thermally conductive material.

6. An apparatus of Claim 1 that is comprised of a matrix of thermoelectric coolers and heaters coupled to the controller and configured to provide active cooling and heating to the platen.

7. An apparatus of Claim 1 that is comprised of a vapor-compression refrigeration cycle to cool and heat the build platform.

8. An apparatus of Claim 1 that is comprised of a liquid circulation system to cool and heat the build platform.

9. An apparatus of Claim 1 in which the end-effectors can consist of one or more of: a leadscrew, threaded component, belt, linear actuator, rotary actuator, solvent nozzle, elastomeric wiper, electric motor, pneumatic actuator, and hydraulic actuator.

10. An apparatus of Claim 1 wherein the mechanism is comprised of one or more of the following: a. the end-effector is mechanically coupled to a threaded component that is advanced by a leadscrew; b. the end-effector is mechanically coupled to a belt which is rotated by a drive pulley; c. the end-effector is mechanically coupled to a rotary actuator for angular movement; d. the end-effector has a solvent nozzle, the actuators in the x-y-z positioning assembly are used to transport the part to the storage area; e. the end-effector has a compliant elastomeric wiper that makes constant contact with the printing surface; f. the end-effector is driven by an electric motor; g. a pneumatic actuator drives end-effector; and h. end-effector is driven by a hydraulic actuator.

11. An apparatus of Claim 1 wherein the mechanism is comprised of one or more of the following: a. the end-effector is mechanically coupled to a belt which is rotated by a drive pulley; b. the end-effector has a solvent nozzle, the actuators in the x-y-z positioning assembly are used to transport the part to the storage area; c. the end-effector has a compliant elastomeric wiper that makes constant contact with the printing surface; and d. the end-effector is driven by an electric motor.

12. An apparatus of Claim 1 wherein the mechanism is comprised of one or more of the following: a. the end-effector is mechanically coupled to a threaded component that is advanced by a leadscrew; b. the end-effector has a solvent nozzle, the actuators in the x-y-z positioning assembly are used to transport the part to the storage area; c. the end-effector has a compliant elastomeric wiper that makes constant contact with the printing surface; and d. the end-effector is driven by an electric motor.

13. An apparatus of Claim 1 wherein the mechanism is comprised of one or more of the following: a. the end-effector has a solvent nozzle, the actuators in the x-y-z positioning assembly are used to transport the part to the storage area; b. the end-effector has a compliant elastomeric wiper that makes constant contact with the printing surface; and c. a pneumatic actuator drives end-effector.

14. A method of use of an apparatus of Claim 1 for continuous flow 3-dimensional printing of objects by automatically removing manufactured parts with active thermal regulation and mechanical transport mechanisms, imaging the part while printing for inspection and consequently adjusting parameters based upon the inspection data.

15. A method of use of Claim 14 for continuous flow 3-dimensional printing of objects by automatically removing manufactured parts with active thermal regulation and mechanical transport mechanisms.

16. A method of use of Claim 14 for 3-dimensional printing of objects by imaging the part while printing for inspection and consequently adjusting parameters based upon the inspection data.