WO2019151998A1

WO2019151998A1 - Fracture detection in additive manufacturing

Info

Publication number: WO2019151998A1
Application number: PCT/US2018/016084
Authority: WO
Inventors: Arthur H. Barnes; William Winters; Daniel Fredrickson
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2018-01-31
Filing date: 2018-01-31
Publication date: 2019-08-08

Abstract

Disclosed herein is a technology that involves an additive- manufacturing apparatus that includes a high-temperature thermic source to produce infrared (IR) to heat and fuse build material in a build chamber. The build chamber holds and handles build material during an additive- manufacturing operation. A separation barrier separates the build chamber from the thermic source. The separation barrier has a window with an IR- transmissive plate therein that permits IR to pass therethrough from the thermic source to the build chamber. The IR-transmissive plate has an electrically conductive trace on its perimeter. The apparatus has a fracture- detection system coupled to the trace. That fracture-detection system measures the electrical resistance of the trace and detects whether the electrical resistance is indicative of an open circuit for the trace.

Description

FRACTURE DETECTION IN ADDITIVE MANUFACTURING

BACKGROUND

[0001] Additive Manufacturing (AM) is a term that describes a type of three- dimensional (3D) printing technologies that build 3D objects by adding layer- upon-layer of material. AM is also called additive fabrication, additive processes, additive techniques, additive layer manufacturing, layer manufacturing, and freeform fabrication.

[0002] Unlike subtractive manufacturing that starts with a solid block of material and then cut away the excess to create a finished part, additive manufacturing builds up a 3D object layer by layer from a geometry described in a 3D design model. In some of the AM approaches, a heat source may be involved in melting and fusing build material for form each successive layer of the 3D object.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] Fig. 1 is a simplified illustration of the relevant portions of an example additive manufacture system in accordance with the technology described herein.

[0004] Fig. 2 illustrates examples IR-transmissive plates in accordance with the technology described herein with one plate being unfractured and one plate being fractured.

[0005] Fig. 3 is a flowchart illustrating an example method in accordance with the technology described herein.

[0006] The Detailed Description references the accompanying figures. In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The same numbers are used throughout the drawings to reference like features and components.

DETAILED DESCRIPTION

[0007] With an example additive manufacturing operation, a high- temperature heat source is used to apply energy to build material to produce a three-dimensional (3D) object. In some instances, the heat source produces infrared (IR) that is used fuse or bind build material. With this example, the heat source is separated from the build material by a window of IR-transmissive material.

[0008] There is a real risk of that glass might crack. If so, the cracked glass can lead the production of defective parts. In extreme cases, the cracked glass could start a chain of events that may escalate to a catastrophic failure.

[0009] The technology described herein involves a glass-fracture detection system for an additive manufacturing operation. That system may include a thin film of electrically conductive material around the perimeter of the glass through which the electrical resistance is measured. A low measured resistance indicates that the glass is intact. An open or high measured resistance indicates a fracture has occurred. If so, safety measures may be activated.

[0010] Fig. 1 is a simplified illustration of the relevant portions of an example additive manufacture system 100 in accordance with the technology described herein. The example additive manufacture system 100 includes a thermic chamber 110, a build chamber 120, a separation barrier 130 between the chambers, and a fracture-detection system 170.

[0011] The thermic chamber 110 includes a high-temperature thermic source 112, a thermic controller 114, and a ventilation system 150 for the thermic chamber. The thermic source 112 may generate heat at temperatures that may exceed 2500°K. The thermic source 112 produces a significant portion of its spectral emission in the near and mid-IR region to effectively warm and melt build material in the build chamber. The near and mid-IR region include 780nm to 10,000nm.

[0012] While described as a singular, the thermic source 112 may include multiple smaller sources. The thermic source 112 is commonly encased in a housing that is cooled by liquid (e.g., water) or forced air convection to meet regulatory, industry, and/or governmental safety standards relating to airborne powder in oxygen-rich environments. Examples of such standards include the European Union’s (EU) ATEX (Atmospheres EXplosibles) directives.

[0013] Indeed, as depicted, the thermic-chamber ventilation system 150 circulates air through the thermic chamber 110. The thermic-chamber ventilation system 150 includes air conveyers 152 (such as fans and blowers) that moves air 154 into and about the thermic chamber 110. The air conveyers 152 are shown inside of the thermic chamber 110 for illustration purposes. In many implementations, the air conveyers 152 are actually outside the thermic chamber 110 itself.

[0014] Fig. 1 shows a particular example airflow and arrangement of air conveyers 152. However, a particular implementation may have different arrangements. Air may be pulled into and/or pushed out of the thermic chamber 110. Air may flow in different patterns than as shown in Fig. 1. Regardless, the ventilation system 150 generates airflow in such a manner as to keep the temperature of the thermic source 112 within a specified operational and safe range. Also, the airflow keeps the thermic chamber and reflectors in a safe range.

[0015] The thermic controller 114 is a directable component that provides electricity to the thermic source 112. Using this electricity, the thermic source 112 produces heat. The thermic controller 114 is shown inside of the thermic chamber 110 for illustration purposes. In many implementations, the thermic controller 114 is outside the thermic chamber 110 itself.

[0016] The build chamber 120 includes a build bed 122, build-material supply 124, and a ventilation system 160 for the build chamber. The build chamber 120 is designed to hold and handle build material during an additive-manufacturing operation. During that additive-manufacturing operation, a 3D object 126 is built on the build bed 122. That build bed 122 and its related components may handle the 3D object 126 as it is being built. The build material from which the 3D object is being constructed layer by layer is supplied by a build-material supply 124. The build chamber 120 may be described as an enclosure of the build bed 122.

[0017] The build material may be a powder, liquid, or sheet material for building the 3D object 126 layer by layer. The particular details of how the build- material supply 124 actually supplies the build material to the build bed 122 for the additive manufacturing operation vary according to necessities and the design of the build material and the additive manufacturing system.

[0018] The additive manufacturing system 100, as depicted, employs a powdered build material. More particularly, the build material is a polymer. However, the build material may be composed of other types or combinations of types of materials in other implementations. Examples of such materials include (but are not limited to) polymer, metal, ceramic, nylon, polyamide, alumide, acrylonitrile butadiene styrene (ABS), resin, steel, nitinol, gold, silver, wax, titanium, ceramic, gypsum, filaments, polylactic acid (PLA), polyvinyl alcohol (PVA), high-density polyethylene (HDPE), glass, wood filament, metal filament, carbon fiber, or polyethylene terephthalate (PETT).

[0019] Indeed, as depicted, the build-chamber ventilation system 160 circulates air through the build chamber 120. The build-chamber ventilation system 160 includes air conveyers 162 (such as fans and blowers) that moves air 164 into and about the build chamber 120.

[0020] Fig. 1 shows a particular example airflow and arrangement of air conveyers 162. However, a particular implementation may have different arrangements. Air may be pulled into and/or pushed out of the build chamber 120. Air may flow in different patterns than as shown in Fig. 1. Regardless, the ventilation system 160 generates airflow in such a manner as to keep the build chamber 120 (and its components) within a specified operational and safe range. [0021] As its name implies, the separation barrier 130 physically separates the thermic chamber 110 from the build chamber 120. This physical separation prevents physical material in one chamber from physically interacting with the material in the other chamber. For example, the loose airborne particles of the powdered build material in the build chamber 120 cannot enter the thermic chamber 110. In particular, the airborne powdered build material should not interact with the high-temperature thermic source 112.

[0022] Without this physical separation, the powdered build material may migrate into the thermic chamber 110 and contaminate, gum-up, and/or interfere with the operation of the components of the thermic chamber 110. More particularly, the combination of the powdered build material, oxygen from the ventilation systems, and the high-temperature thermic source 112 is a recipe for fire.

[0023] Although it is physically separated from the build chamber 120, the thermic source 112 provides the heat to melt and fuse the 3D object 126 being built. More particularly, the thermic source 112 generates IR radiation 116 to convey is thermal energy. In some instances, the source may produce ultraviolet (UV) radiation to cure the build material.

[0024] The separation barrier 130 includes an opening or window 134 with an IR-transmissive plate 132 therein. A window seal 136 seals the IR-transmissive plate 132 into the window 134, thereby maintaining the air-sealed separation between the two chambers.

[0025] As its name implied, the IR-transmissive plate 132 allow for IR radiation to pass through. The IR-transmissive plate 132 may allow other forms of electromagnetic or light radiation to pass through, but the IR radiation is of particular relevance. Examples of material from which the IR-transmissive plate may be constructed include (but are not limited to) glass, quartz, fused silica, sapphire, IR transmisive plastics/polymers, Arsenic Trisulfate, Barium Fluoride, Cadmium Telluride, Calcium Fluoride, Fused Silica, Gallium Arsenide, Germanium, IR Polymer (Opaque), IR Polymer (Transparent), Lead Fluoride, Lithium Fluoride, Magnesium Fluoride, Magnesium Oxide, Sodium Chloride, Silicon, Thallium Bromo Iodide, Zinc Selenide, and Zinc Sulfide.

[0026] As shown, the thermic source 112 generates the IR radiation 116 that passes through the IR-transmissive plate 132 to the unfused build material on the 3D object 126 on the build bed 122 of the build chamber 120.

[0027] Also depicted is a cross-section of part of an electrically conductive trace 140. The trace 140 is applied to a perimeter of the IR-transmissive plate 132. As depicted, the trace may be attached to the side of the plate 132 facing or inside the build chamber 120. Doing this increases the life of the trace. If the trace 140 was on the other side of the plate 132, then it would be subjected to the intense heat in the thermic chamber 110 and potential damage from periodic cleaning and scraping of the plate.

[0028] As depicted, the trace 140 is on the perimeter of the plate, but inside the perimeter of the window seal 136. In some implementations, the trace 140 may be inside and under the window seal 136 and not exposed to either chamber. In some implementations, the trace may be applied to the outer edge of the plate itself rather than on either side of the plate. In some instances, the trace may be sandwiched inside the plate.

[0029] The fracture-detection system 170 is electrically operatively coupled to the electrically conductive trace 140. That is, the fracture-detection system 170 is coupled to the trace 140 in such a manner to apply a low voltage thereto. Herein, a low voltage is less than five volts. In addition, the fracture-detection system 170 measures the electrical resistance of the electrical circuit formed by the trace 140.

[0030] Because of the stresses of shipping, handling, and installation of the plate and the extreme irradiance levels, optical power, and thermal shock, it is possible that the IR-transmissive plate 132 can fracture due to mechanical stresses created by thermal expansion or thermal shock. If the IR-transmissive plate 132 were to fail, the resulting fracture would also break the thin trace 140 on that plate. A plate fractures can allow the cooling air inside the thermic chamber 110 to escape and potentially disturb the build material in the build chamber 120 leading to defective parts.

[0031] When the plate fractures, the circuit formed by the trace would become an open circuit. Thus, the electrical resistance of that broken trace that the fracture-detection system 170 is monitoring shoots up to very large value. That value may be defined as that being above a defined threshold. The threshold is set to capture the different ways that the resistance of an open circuit may be described, such as infinite, maximum measurable by the limits of the equipment, undefined, or arbitrarily large relative the expected measurement for a closed circuit.

[0032] Fig. 2 illustrates examples IR-transmissive plates in accordance with the technology described herein with one plate being unfractured and one plate being fractured.

[0033] While the IR-transmissive plate 132 is shown in Fig. 1 in cross-section, the IR-transmissive plate 132 is shown in elevation view in Fig. 2. The IR- transmissive plate 132 is a plate or pane of glass and is shown as such in Fig. 2. The IR-transmissive plate 132 is shown in its window 134, but without the window seal for simplicity.

[0034] The electrically conductive trace 140 is shown on the perimeter of the IR-transmissive plate 132. Indeed, the electrical circuit formed by the trace 140 is shown electrically operatively connected to its power source, which is the fracture-detection system 170. In other implementations, the fracture-detection system 170 might not provide the power to the trace 140.

[0035] As depicted, the electrically conductive trace 140 is a thin film of conductive material adhered to the perimeter of the IR-transmissive plate 132. Because the trace 140 forms a circuit, it does not completely encircle the perimeter of the plate. In some instances, the trace may be attached to some other area of the plate. [0036] The trace 140 is thin enough that a fracture of the plate will fracture the trace so as to produce an open circuit in the trace 140. For example, the trace may be thinner than 15 nm.

[0037] Fig. 2 also shows an example of a failed IR-transmissive plate 232. This failed plate 232 is the same plate 132 after a failure has occurred.

[0038] The failed IR-transmissive plate 232 includes a fracture 234 extending from one edge of the plate to the other. The IR-transmissive plate is brittle and/or thin enough that any failure results in a fracture extending across the entire extent of the plate, as shown by fracture 234. For example, the plate may be at least as thin as 1.0mm.

[0039] Because it extends across the plate 232, the fracture 234 causes at least one break in the trace to produce an open-circuit trace 240. Consequently, the fracture-detection system 170 detects an electrical resistance of the trace that is representative of an open circuit (e.g., measured resistance exceeds a defined threshold). In response to that detection, the fracture-detection system 170 sends a fracture-indication signal to a safety system 250.

[0040] With the additive manufacture system 100 described herein, the thermic chamber is held at a negative air pressure. That is, the additive manufacturing system 100 maintains the air pressure in the thermic chamber 110 at a lower level than the air pressure in the build chamber 120. Said in another way, the build-chamber ventilation system 160 generates air pressure within the build chamber 120 that is greater than the air pressure in the thermic chamber 110 that is generated by the thermic-chamber ventilation system 150.

[0041] Because of the negative air pressure in the thermic chamber, when the plate breaks, the build material powder may be sucked into the thermic chamber. This would directly and simultaneously expose the high-temperature thermic source 112 to combustible powder and oxygen, which is a potentially explosive combination. [0042] The safety system 250 receives the fracture-indication signal. That signal may be in response to a detection that the measured electrical resistance is indicative of an open circuit for the trace. In response to that signal, the safety system 250 deactivates or signals for a deactivation of some portion of the additive manufacture device 100.

[0043] For example, the safety system 250 may signal or initiate one or more of the following:

• the thermic controller 114 to power-down or deactivate the thermic source 112;

• the build-material supply 124 to cut of the supply of build material;

• injection of a fire retardant (not shown) into one or both chambers;

• power cut-off for the entire additive manufacture system 100;

• a safety shutter (not shown) to reimpose a physical barrier between the chambers;

• some other effective safety measure.

[0044] In some implementations, the fracture-detection system 170 and the safety system 250 may be combined into a common system.

[0045] Fig. 3 is a flow diagram illustrating example process 300 in accordance with the technologies described herein. The additive manufacture system 100 (or a portion thereof) discussed above is an example of an apparatus that is suitable implement the example process 300. For simplicity in discussion, the example process 300 is described below as being performed by an additive-manufacturing apparatus.

[0046] At block 310, the additive-manufacturing apparatus performs an additive-manufacturing operation. In that apparatus, the build material is supplied to a build chamber of the additive-manufacturing apparatus and a high- temperature thermic source is engaged to produce infrared (IR) radiation to apply energy to the build material in the build chamber.

[0047] As part of the performance of the additive-manufacturing operation, the additive-manufacturing apparatus may maintain a lower air pressure in a housing of the high-temperature thermic source relative to an air pressure of the build chamber.

[0048] At block 312, the example process 300 continues unless there is some indication to stop. A stop or a fracture-indication signal 330 would be sufficient to cease the example process and proceed to an end at 320. If the example process continues, it continues to block 314.

[0049] At block 314, the additive-manufacturing apparatus applies a low- voltage electrical current to an electrically conductive trace on a perimeter of an IR-transmissive plate of a separation barrier. That separation barrier separates the build chamber from the thermic source. The IR-transmissive plate permits IR to pass therethrough from the thermic source to the build chamber.

[0050] At block 316, the additive-manufacturing apparatus senses the electrical resistance of the trace. That is, the additive-manufacturing apparatus measures, monitors, detects, etc. the electrical resistance of the trace.

[0051] At block 318, the additive-manufacturing apparatus determines whether the sensed electrical resistance is indicative of an open circuit. It may make this determination by the measured resistance exceeding a designated threshold. Alternatively, the resistance changing rapidly may be an indication of an open circuit.

[0052] If the sensed electrical resistance is not indicative of an open circuit (e.g., the resistance is low and/or consistent), then the example process returns to block 316 to continue sensing the resistance of the trace.

[0053] If the sensed electrical resistance is indicative of an open circuit, then the example process returns to block 312 to signal 330 that the example process to end at block 320. This is a ceasing of the performance of the additive manufacturing operation. It may include, for example, a deactivation of the high- temperature thermic source or a terminating the supply of build material to the build chamber.

[0054] In effect, the additive manufacturing operation cannot be resumed or reunited until the broken IR-transmissive plate is replaced with a new or unbroken one and the example process 300 restarted.

[0055] In some implementations, the thermic source 112 may be described as a radiation source that produces electromagnetic radiation, such as IR radiation and ultraviolet (UV) radiation. The UV radiation may cure build materials. These implementations may use a transmissive plate that allow electromagnetic radiation (such as IR and UV) to pass therethrough from the radiation source to the build material in the build chamber.

[0056] These processes are illustrated as a collection of blocks in a logical flow graph, which represents a sequence of operations that can be implemented in mechanics alone, with hardware, and/or with hardware in combination with firmware or software. In the context of software/firmware, the blocks represent instructions stored on one or more computer-readable storage media that, when executed by one or more processors, perform the recited operations.

[0057] Note that the order in which the processes are described is not intended to be construed as a limitation, and any number of the described process blocks can be combined in any order to implement the processes or an alternate process. Additionally, individual blocks may be deleted from the processes without departing from the spirit and scope of the subject matter described herein.

[0058] The term "machine-readable medium" is non-transitory machine- storage medium, computer-readable storage medium, computer-storage medium, machine-readable storage medium, or the like. For example, machine- readable medium may include, but are not limited to, magnetic storage devices (e.g., hard disk, floppy disk, and magnetic strips), optical disks (e.g., compact disk (CD) and digital versatile disk (DVD)), smart cards, flash memory devices (e.g., thumb drive, stick, key drive, and SD cards), and volatile and non-volatile memory (e.g., random access memory (RAM), read-only memory (ROM)).

Claims

CLAI M S What is claimed is:

1. An additive-manufacturing apparatus comprising:

a high-temperature thermic source to produce infrared (IR) to apply energy to a build material in a build chamber, wherein the build chamber holds and handles build material during an additive-manufacturing operation;

a separation barrier separating the build chamber from the thermic source, the separation barrier having window with an IR-transmissive plate therein that permits IR to pass therethrough from the thermic source to the build chamber; an electrically conductive trace of the IR-transmissive plate;

a fracture-detection system coupled to the trace, the fracture-detection system to measure electrical resistance of the trace and to detect that the measured electrical resistance is indicative of an open circuit for the trace.

2. An apparatus of claim 1 wherein the high-temperature thermic source is encased in a housing that is liquid or air cooled.

3. An apparatus of claim 1 wherein, the build material is powdered.

4. An apparatus of claim 1 wherein the high-temperature thermic source is encased in a housing with lower air pressure relative to an air pressure of the build chamber.

5. An apparatus of claim 1 wherein the electrically conductive trace is a thin film adhered to the perimeter of the IR-transmissive plate.

6. An apparatus of claim 1 further comprising a safety system to respond to the measured electrical resistance being indicative of an open circuit by deactivation of some portion of the apparatus.

7. An apparatus of claim 1 , wherein the IR-transmissive plate is glass.

8. An additive-manufacturing apparatus comprising:

a radiation source to produce electrometric radiation to apply energy to a build material on a build bed, wherein the build bed holds and handles build material during an additive-manufacturing operation;

a separation barrier separating the build bed from the radiation source, the separation barrier includes a transmissive plate that permits electromagnetic radiation to pass therethrough from the radiation source to the build material on the build bed;

an electrically conductive trace of the plate, wherein the trace is thin enough that a fracture of the plate breaks the trace so as to produce an open circuit in the trace;

a fracture-detection system coupled to the trace, the fracture-detection system to apply a low voltage to the trace and to detect that a measured electrical resistance is indicative of an open circuit for the trace.

9. An apparatus of claim 8, wherein the radiation source is a high- temperature thermic source to produce infrared (IR) radiation.

10. An apparatus of claim 8, wherein the electrically conductive trace is a thin film adhered to a perimeter of the transmissive plate.

11. An apparatus of claim 8 further comprising a safety system to respond to the measured electrical resistance being indicative of an open circuit by deactivation of the radiation source.

12. A method comprising:

perform an additive-manufacturing operation of an additive-manufacturing apparatus, wherein build material is supplied to a build chamber of the additive manufacturing apparatus and a radiation source is engaged to produce electromagnetic radiation to apply energy to the build material in the build chamber;

applying an electrical current to an electrically conductive trace on a transmissive plate of a separation barrier that seperates the build chamber from the radiation source, the transmissive plate permits electromagnetic radiation to pass therethrough from the radiation source to the build chamber;

detecting electrical resistance of the trace;

in response to that detection, ceasing the performance of the additive manufacturing operation.

13. A method as recited in claim 12, wherein the radiation source is a high-temperature thermic source to produce infrared (IR) radiation.

14. A method as recited in claim 12, wherein the electrically conductive trace is a thin film adhered to a perimeter of the transmissive plate.

15. A method as recited in claim 12, wherein the ceasing the performance of the additive-manufacturing operation includes terminating a supply of build material to the build chamber.