WO2016164729A1 - Frittage laser en ligne d'encres métalliques - Google Patents

Frittage laser en ligne d'encres métalliques Download PDF

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Publication number
WO2016164729A1
WO2016164729A1 PCT/US2016/026651 US2016026651W WO2016164729A1 WO 2016164729 A1 WO2016164729 A1 WO 2016164729A1 US 2016026651 W US2016026651 W US 2016026651W WO 2016164729 A1 WO2016164729 A1 WO 2016164729A1
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WO
WIPO (PCT)
Prior art keywords
filament
nozzle
substrate
laser
focal area
Prior art date
Application number
PCT/US2016/026651
Other languages
English (en)
Inventor
Jennifer A. Lewis
Mark A. SKYLAR-SCOTT
Suman GUNASEKARAN
Original Assignee
President And Fellows Of Harvard College
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Application filed by President And Fellows Of Harvard College filed Critical President And Fellows Of Harvard College
Publication of WO2016164729A1 publication Critical patent/WO2016164729A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/34—Laser welding for purposes other than joining
    • B23K26/342—Build-up welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/10—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material
    • B22F1/103—Metallic powder containing lubricating or binding agents; Metallic powder containing organic material containing an organic binding agent comprising a mixture of, or obtained by reaction of, two or more components other than a solvent or a lubricating agent
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/22—Driving means
    • B22F12/224—Driving means for motion along a direction within the plane of a layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/22—Driving means
    • B22F12/226—Driving means for rotary motion
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/30—Platforms or substrates
    • B22F12/37—Rotatable
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/38—Housings, e.g. machine housings
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/90—Means for process control, e.g. cameras or sensors
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
    • B23K26/14—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor
    • B23K26/146—Working by laser beam, e.g. welding, cutting or boring using a fluid stream, e.g. a jet of gas, in conjunction with the laser beam; Nozzles therefor the fluid stream containing a liquid
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y10/00—Processes of additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y30/00—Apparatus for additive manufacturing; Details thereof or accessories therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F1/00—Metallic powder; Treatment of metallic powder, e.g. to facilitate working or to improve properties
    • B22F1/05—Metallic powder characterised by the size or surface area of the particles
    • B22F1/054—Nanosized particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
    • B22F10/30—Process control
    • B22F10/36—Process control of energy beam parameters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
    • B22F12/00—Apparatus or devices specially adapted for additive manufacturing; Auxiliary means for additive manufacturing; Combinations of additive manufacturing apparatus or devices with other processing apparatus or devices
    • B22F12/40—Radiation means
    • B22F12/41—Radiation means characterised by the type, e.g. laser or electron beam
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/60—Aspects relating to the preparation, properties or mechanical treatment of green bodies or pre-forms
    • C04B2235/602—Making the green bodies or pre-forms by moulding
    • C04B2235/6021—Extrusion moulding
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/60—Aspects relating to the preparation, properties or mechanical treatment of green bodies or pre-forms
    • C04B2235/602—Making the green bodies or pre-forms by moulding
    • C04B2235/6026—Computer aided shaping, e.g. rapid prototyping
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
    • C04B2235/65—Aspects relating to heat treatments of ceramic bodies such as green ceramics or pre-sintered ceramics, e.g. burning, sintering or melting processes
    • C04B2235/66—Specific sintering techniques, e.g. centrifugal sintering
    • C04B2235/665—Local sintering, e.g. laser sintering
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the present disclosure generally relates to three-dimensional (3D) printing technology. Specifically, the present disclosure relates to inline laser sintering of metallic filaments deposited by 3D printing.
  • FIG. 1 is a schematic diagram illustrating a 3D printer for inline laser sintering of metallic inks according to exemplary embodiments of the present application
  • FIG. 2 is a schematic diagram illustrating an exemplary
  • FIG. 3 is a flowchart illustrating a method for inline laser sintering of metallic inks
  • Fig. 4 illustrates an example of focusing a laser beam over a filament of an ink
  • Fig. 5 illustrates another example of focusing the laser beam over the filament of the ink
  • Fig. 6 illustrates an example of focusing the laser beam over the filament of the ink
  • Fig. 7 illustrates a relationship between a linear motion of a laser beam and a rotational motion of a substrate
  • Figs. 8a and 8b illustrate effects of sintering laser frequency to material properties of sintered silver filaments
  • Figs. 9a and 9b illustrate effects of the sintering laser power to the material properties of the sintered silver filaments
  • FIGs. 10a and 10b illustrate an actual laser direct ink writing apparatus
  • FIGs. 1 1 a - 1 1 i illustrate basic settings of the laser direct ink writing apparatus in an example experiment and experimental results thereof;
  • Figs. 12a - 12c illustrate a method of printing curvilinear structure using a rotating state
  • Figs. 13a and 13b Illustrate effects of pulse repetition rates on microstructure of a printed filaments
  • Figs. 14a - 14i illustrate electrical conductivity and nanostructure of laser-annealed silver wires
  • Figs. 15a and 15b illustrate effects of different pulse repetition rates on annealed silver microstructure.
  • the present disclosure describes an apparatus for 3D printing that allows a printed filament to undergo localized laser heating during deposition.
  • a printed filament may undergo localized laser heating during deposition.
  • silver or other metallic inks may be sintered inline during 3D printing.
  • a sintered conductive filament having a distinct grain structure and/or lower thermal and/or electrical resistivity than achievable with conventional 3D printing may be obtained.
  • Fig. 1 is a schematic diagram illustrating a 3D printer 100 for inline laser sintering of metallic inks.
  • the 3D printer 100 may include a controller 102, a laser generator 104, a waveform generator 108, a light guide 120, a printing nozzle 140 ("the nozzle"), an actuator 150, and a substrate 160.
  • the laser generator 104 may be any type of laser generator that meets the power and wavelength requirements of the present disclosure.
  • the laser generator may be an 805 nm diode laser generator configured to generate an infrared laser beam 1 10 near 805 nm. Emission of the laser beam 1 10 may be controlled by a waveform generator 108, which is electrically connected with the laser generator 104. Further, the waveform generator 108 may be in electronic communication with and under the control of the controller 102. During operation, the controller 102 may be able to control the waveform generator 108 to input a
  • the predetermined laser actuation signal may be any form.
  • the laser actuation signal may include periodic impulses at a predetermined frequency, a predetermined impulse duration, and predetermined amplitude.
  • the predetermined frequency, duration and amplitude may be constants or may vary with respect of time and space.
  • the laser generator 104 may emit laser impulses with the predetermined amplitude at the predetermined frequency.
  • the laser actuation signal may also be a sinusoidal signal, a periodic triangular signal, or a signal with constant input amplitude.
  • the laser generator 104 may be optically connected to the light guide 120.
  • the laser generator 104 may be connected to the light guide 120 via an optical fiber 106, so that the emitted laser beam 1 10 may be directed into the light guide 120.
  • the light guide 120 may include a housing 122 having a light path therein.
  • the light path may include a fiber optic collimator 136, a first mirror 130, a second mirror 132, a first lens 124, a second lens 126, and a third lens (objective lens) 128, which are all mounted on the housing 122.
  • the fiber optic collimator 136 may be connected to the optical fiber 106 to introduce the laser beam 1 10 from the optical fiber 106 into the light path.
  • the optical fiber may be multi-mode fiber (or single mode fiber).
  • the laser beam Upon exiting the multimode fiber optic, the laser beam has a uniform, top-hat intensity distribution. The narrower the beam, the greater the dispersion, i.e., the smaller the diameter the quicker the laser beam expands when traveling through space.
  • the fiber optic collimator 136 first may actively expand the diameter of the laser beam 1 10 to reduce the rate of diameter expansion. Then the laser beam 1 10 may pass through the first lens 124 and the second lens 126 to further adjust the diameter for filling the back aperture of the third lens (objective lens) 128.
  • the first mirror 130 and the second mirror 132 may be placed between the first lens 124 and the second lens 126 to reflect the laser beam 1 10.
  • the length and direction of the light path between the first lens 124 and the second lens 126 may be adjusted so that when the laser beam passes through the second lens 126, the laser beam is a collimated beam with a proper diameter towards the correct direction.
  • the third lens 128 may focus the laser beam 1 10 at a focal area A.
  • the focal area may be directly below the light guide 120 at a distance I.
  • the first lens 124, the second lens 126, and the third lens 128 are convex achromatic doublet lenses.
  • the first lens 124, the second lens 126, and the third lens 128 may also be designed as a combination of other types of lenses to expand the laser beam 1 10 from the optical fiber 106 and then focus the laser beam 1 10 to the focal area A.
  • the light guide 120 may be configured to select a mode of the laser beam 110 or shape of a cross section of the laser beam 110.
  • the light guide 120 may select and/or shape the laser beam 110 to have an annular cross section ("annular laser beam").
  • the annular beam may be formed by use of a light-filtering annular slit (not shown) placed in a conjugate image plane, through the use of a conical lens and spherical lens (not shown) in the light path, through use of a phase spatial light modulator (not shown) in the light path, use of a hollow optical fiber or a fiber that selects only a high-order mode (such as LP 0 , n where n>5) as the optical fiber 106.
  • a light-filtering annular slit placed in a conjugate image plane
  • a conical lens and spherical lens not shown
  • a phase spatial light modulator not shown
  • the light guide 120 may also include an observer 134 mounted on the housing 122 to observe a small area around the focal area A.
  • the second mirror 132 may be a semi-transparent mirror, such as a pellicle mirror, or a wavelength-selective dichroic mirror that reflects infrared light while transmitting visible light
  • the observer 134 may be a camera above the semi-transparent or dichroic mirror 132 to take pictures or videos over the small area around the focal area A.
  • the nozzle 140 may include a chamber 146 to hold an ink.
  • the chamber 144 may be of a cylindrical or prismatic shape such as a syringe.
  • the nozzle 140 may include an outlet 142 at one end of the chamber 146.
  • the size of the outlet 142 may vary depending on needs. For example, in an exemplary embodiment the outlet 142 may have a diameter of 10 microns.
  • the nozzle 140 may be in communication with the controller 102 and may be actuated by the controller 102. For example, the controller 102 may increase a pressure to the chamber 146 through a gas conduit 148. Consequently, the nozzle 140 may be able to extrude a filament 146 of the ink through the outlet 142.
  • the nozzle 140 may be able to extrude the filament 146 at a predetermined flow rate.
  • the controller 102 may control a pressure actuator, or a fixed flow actuator such as a syringe pump to control the filament 146 flow rate.
  • Typical flow rates used may range from 10 "18 cm 3 /s to 10 "8 cm 3 /s.
  • the extruded filament 146 comprising the ink 144 may be deposited on a substrate 160.
  • the outlet 142 of the nozzle 120 may be positioned substantially and/or sufficiently close to the focal area A, so that the filament 146 may pass through the focal area A when being extruded from the outlet 142.
  • the outlet 142 may be placed within the focal area A.
  • the outlet 142 may be placed at a distance d away from the focal area.
  • the infrared laser beam 1 10 may heat the filament 146 to a temperature equal to or higher than a sintering temperature of the ink.
  • the infrared laser beam 1 10 may also heat the filament 146 to an annealing temperature high enough to solidify the ink but lower than the sintering temperature. The power of the infrared laser, or the
  • temperature the ink is heated by the laser may be determined by specific characteristics of the heated ink. For example, when the laser heats a silver ink filament into a silver wire, conductivity of the silver wire may depend on the temperature of the silver ink filament being heated. A sintered silver ink filament may have higher conductivity than an annealed silver ink filament. Accordingly, depending on the requirement of
  • the power of the laser may be adjusted to sinter the silver wires, which results in a higher conductivity to the silver wire, or simply raise the temperature to an annealing temperature, which results a lower conductivity to the silver wire. Consequently, when the filament 146 passes through the focal area A, or when the focal area A passes through the filament 146, the filament 146 may be selectively heated to form a sintered filament of the corresponding metal, alloy or ceramic. Prior to sintering, the particles of the ink may be weakly bonded by van der Waals, electrostatic, or dipole forces. After sintering, adjacent particles in the filament may be strongly bonded or fused together.
  • the sintered filament may exhibit improved electrical conductivity as well as increased physical stiffness, yield strength, resilience, and toughness.
  • the filament is considered sintered when it is completely sintered, or partially sintered, or when either some polymer binder has been burnt out or some particles have coalesced.
  • An unsintered portion of the filament may extend a distance d between the focal area A and the outlet of the nozzle.
  • the distance d may be made sufficiently small so that the viscosity and/or surface tension of the unsintered portion of the filament are able to sustain its shape prior to sintering or reaching the substrate.
  • the nozzle may first be moved to extrude a supported portion of the filament 146 that is deposited directly on the substrate 160. Then, to form the unsupported portion of the structure, the nozzle may be moved in a direction away from the substrate while continuing to extrude the filament. If the rheological properties of the ink and the distance d are properly chosen, the unsintered portion of the filament can sustain its shape without collapse and/or buckle and/or deformation prior to sintering and/or reaching the substrate.
  • the nozzle 140 may be mounted on an actuator 150, which is controlled by the controller 102.
  • the actuator 150 may be any type of mechanical structure that can provide linear and/or rotational motion to the nozzle 140.
  • the actuator 130 may be a carriage rail structure typically used in inkjet printers.
  • the nozzle 140 may be mechanically mounted on a carriage rail 152, or on an air bearing.
  • a carriage motor 154 may be configured to drive a belt or a thread to move the nozzle 140 along the x, y, z direction, or rotate around the z axis in Fig. 1 .
  • the 3D printer may be able to move relative to the underlying substrate 160 at a controlled and predetermined speed to deposit the ink 144 that flows out of the outlet 142 in a predetermined pattern and at a predetermined print speed on the substrate 160.
  • the light guide 120 and the substrate 160 may also be respectively mounted on the actuator 150 and may move together with or independently from the nozzle 140.
  • FIG. 2 is a schematic diagram illustrating an exemplary
  • the electronic controller 102 may be a specially designed electronic device for controlling the 3D printer 100 or may be a computer implementing special applications for controlling the 3D printer 100.
  • the controller may be configured for wired or wireless communication with the 3D printer 100.
  • the controller 102 may vary widely in configuration or capabilities, but it may include one or more central processing units 222 and memory 232, at least one medium 230 (such as one or more transitory and/or non-transitory mass storage devices) for storing application programs 242 or data 244 that may control components of the 3D printer 100.
  • the processing units 222 may execute the application programs 242 or data 244 to perform the controlling methods disclosed in the present disclosure.
  • the controller 102 may further include one or more power supplies 226, one or more wired or wireless network interfaces 250, one or more input/output interfaces 258, and/or one or more operating systems 241 , such as Windows ServerTM, Mac OS XTM, UnixTM, LinuxTM,
  • a controller 102 may include, as examples, industrial programmable motor controllers with or without a graphical user interface, dedicated rack-mounted servers, desktop computers, laptop computers, set top boxes, mobile computational devices such as smart phones, integrated devices combining various features, such as two or more features of the foregoing devices, or the like.
  • Fig. 3 is a flowchart illustrating a method for inline laser sintering of metallic inks.
  • the method may be implemented using the 3D printer 100.
  • the method may be implemented as a set of instructions stored in the storage medium 230 and may be executed by the processor 222 of the controller 102.
  • the method may include the following operations:
  • the filament 146 of an ink 144 may be deposited on an underlying substrate 160.
  • the substrate 160 may be a hard substrate, such as a piece of glass, a silicon wafer.
  • the substrate may be a soft and/or flexible substrate, such as a polymer surface.
  • the ink 144 may be a ceramic ink and/or a metallic ink
  • the ink may be a silver ink, with a sintering temperature of 150-600°C.
  • the 3D printer 100 may extrude the filament 146 at a predetermined speed.
  • the laser beam may be an infrared laser beam capable of heating the filament 146 to a temperature equal to or higher than the sintering temperature of the ink. Consequently, the portion of the filament passing through the focal area may be heated. When the temperature of the portion is higher than the sintering temperature, sintering may occur such that the portion of the filament contains fused metal or ceramic particles.
  • step 306 may further include selecting a wavelength of the laser beam so that the polymer substrate is transparent or substantially transparent to the laser beam (i.e., the laser beam is not substantially absorbed by the polymer substrate).
  • the properly selected wavelength may prevent overheating or ablating of the polymer, and ensure that the laser energy is predominantly absorbed by the silver filament.
  • PET has low absorptivity at a laser wavelength of 808 nm.
  • the 3D printer may select an 808 nm laser as the sintering laser. Consequently, the PET substrate may not be heated or may just be slightly heated, whereas the silver filament may absorb the energy from the laser beam and be sintered.
  • the 3D printer may position the focal area A of the laser beam 110 over the outlet 142 and may move the light guide 120, as shown in Fig. 4. Because the laser beam 110 is always focused on the outlet 142, the filament 146 may be heated by the laser beam 110 immediately when it flows out of the outlet 142. Because the filament 146 is extruded out of the outlet 142 at the predetermined speed, the filament 146 may only be heated by the laser beam for a limited period of time. This limited period of time may include the time when a portion of the filament is in the focal area A. It may also include a short period of time after the portion of the filament moves out of the focal area when the portion is continued to be continues being heated due to heat transferred from the focal area A.
  • the heat from the laser beam 110 may cause physical or chemical effect on the portion of the filament 146.
  • the laser beam 110 may be tuned to a power strong enough to raise the portion of filament 146 within the focal area A to or above the sintering temperature before and/or after the portion of the filament passes through the focal area A, thereby sintering the filament 146.
  • the controller 102 of the 3D printer 100 may select to output an annular laser beam from the laser generator 104.
  • the annular laser beam may have an annular cross section where the power of the laser beam 110 becomes weaker towards the center of the focal area.
  • the outlet 142 of the nozzle 140 may be placed at the center of the annular laser beam 110.
  • the laser power at the center of the focal area A may be tuned low enough that the outlet 142 is not overly heated.
  • the laser may be pulsed such that the time-averaged heat transfer to the silver is reduced, while the maximum temperature reached by the filament during a laser pulse remains high enough for sintering to occur.
  • the print speed and/or extrusion rate may be increased, increasing the convection of heat away from the nozzle, preventing upstream heat diffusion from sintering the nozzle.
  • the nozzle may be heat sinked either passively or actively, by a high thermal conductivity material to limit the temperature of the silver at the nozzle.
  • the 3D printer 100 may linearly move the light guide 120 and the nozzle 140 together when printing the filament 146 along the predetermined path, regardless of whether the predetermined path is a straight line or curved line.
  • the silver When printing on flexible substrates such as a polymeric substrate, and when the wavelength of the laser beam is properly selected to prevent overheating or ablating the polymer, the silver may be heated by the laser beam and the hot silver may generate a localized heat-affected zone (HAZ) in the underlying substrate.
  • the silver may be heated hot enough so that the temperature of the HAZ is high enough to melt the polymeric substrate. Consequently, the laser beam may weld the HAZ with the heated silver filament, thereby providing excellent adhesion properties between the silver filament and the substrate.
  • the 3D printer may select an 808 nm laser as the sintering laser.
  • the PET substrate may not be heated or may just be slightly heated.
  • the silver filament may absorb the energy from the laser beam and be sintered.
  • the laser-heated silver filament may generate a localized heat-affected zone (HAZ) in the underlying PET substrate.
  • the sintering temperature of silver may be 150-600 °C, which overlaps with the melting temperature of PET. Accordingly, the
  • temperature of the HAZ may be high enough to effectively weld the silver to the PET, yielding a mechanical robust connection therebetween.
  • the post sintering may be conducted after the 3D printer finishes printing a 3D structure comprising one or more of the filaments.
  • the 3D printer may include a conveying belt or a robot to send the printed 3D structure to a furnace to anneal the 3D structure.
  • the 3D printer may also include a second laser that to carry out the post sintering by heats the portion of the filament again, after the portion of the filament moves out of the focal area.
  • the annealing may be conducted after the 3D printer finishes printing a 3D structure comprising one or more of the filaments.
  • the 3D printer may include a conveying belt or a robot to send the printed 3D structure to a furnace to anneal the 3D structure.
  • the 3D printer may also include a second laser that to carry out the post sintering by heats the portion of the filament again, after the portion of the filament moves out of the focal area.
  • the annealing may be conducted after the 3D printer finishes printing a 3D structure comprising one
  • the temperature may be higher than 300 °C (such as 500 °C).
  • the annealing may improve density and bending cyclability of the 3D structure.
  • Fig. 5 illustrates another example of focusing a laser beam 100 over the filament 146.
  • the focal area A may be positioned over a portion of the filament at a distance d away from the outlet 142.
  • the 3D printer 100 may move the nozzle 140 to print the filament 146 along a
  • the predetermined path is an L-shaped line.
  • the nozzle 140 may turn left in order to print an L-shaped the filament (shown by the arrow in Fig. 5). If the 3D printer 100 linearly moves the light guide 120 and the nozzle 140 together, the laser beam 110 may turn left together with the nozzle 140. But because the laser focal area A is distance d away from the outlet 142, by turning left together with the outlet 142 the focal area A may move out of the filament 146.
  • the controller 102 may control the 3D printer 100 to linearly move the nozzle 140 and the light guide 120independently, so that the focal area A of the laser beam 110 moves along the extruded filament 146 rather than linearly moving together with the outlet 142.
  • the distance d may be selected to be greater than the diameter of the focal area A, so that the outlet 142 may be outside the focal area A, thereby avoiding being overheated. Meanwhile, the distance d may be sufficiently small that the unsintered portion of the filament 146 between the outlet 142 and the focal area A can maintain its shape and/or integrity prior to sintering and/or being deposited on the substrate.
  • the ink may be a silver ink
  • the laser beam 110 may be focused on the focal area A at distance d away from the outlet 142. As the nozzle 140 moves and the focal area A follows, the laser beam 110 may sinter the silver filament that passes through the focal area into a conductive silver wire.
  • the distance d may be short enough so that when the filament 146 is extruded from the outlet 142, it maintains its shape until it is fully sintered by the laser beam 110, yet far enough such that the material is not sintered inside the nozzle.
  • Fig. 6 illustrates another example of focusing a laser beam 100 over the filament 146. Similar to Fig. 5, the focal area A may be positioned over a portion of the filament 146 at a distance d away from the outlet 142. The distance d may be selected to be greater than the diameter of the focal area A, so that the outlet 142 may be outside the focal area A, thereby avoiding being overheated. Meanwhile, the distance d may be sufficiently small enough, so that the unsintered portion of the filament 146 between the outlet 142 and the focal area A may maintain sustain itself without collapse.
  • the 3D printer 100 may keep the nozzle 140 and the light guide 120 stationary with respective each other, while linearly moving the nozzle 140 and the light guide 120 and rotating the substrate 160 as needed, so that the nozzle 140 may move along the predetermined path relative to the substrate and the focal area A of the laser beam 1 10 may move along the extruded filament 146 on the substrate 160.
  • the predetermined path is an L-shaped line on the substrate 160.
  • the outlet 142 may first move a straight line over the substrate 160.
  • the focal area A of the laser beam 1 10 may also linearly move together with the outlet 142 at the distance d away, so that the focal area maintains on the straight line of filament 146 and the light guide 120 maintains stationary with respect to the nozzle 140.
  • both the nozzle 140 and the light guide 120 may maintain a linear motion and maintain stationary with respect to each other, and the substrate 160 may rotate for ⁇ degree around a rotation center.
  • the combination of the linear motion and rotational motion may result in a left turn of the outlet 142 with respect to the substrate 142 while at the same time the motion of the focal area A may follows the printed L-shaped filament 146.
  • the controller 102 may determine the linear motion of the laser beam 1 10 and/or the nozzle 140 and the rotational motion of the substrate 160 based on a relationship shown in Fig. 7.
  • S(x, y) may be a predetermined path traced on or above a substrate and may be a function of two coordinates x, y that define a plan where the substrate 160 locates.
  • the predetermined path S(x, y) may have a positive or negative curvature ⁇
  • r is the vector between 0 and A.
  • the 3D printer gantry may move the nozzle and laser beam at velocity v xy and the rotary stage may rotate with angular velocity ⁇ such that
  • the controller 102 may be able to select a pair of nozzle and laser velocity v xy and substrate angular velocity ⁇ in order for the printed features to follow the predetermined path
  • ⁇ is a relative angular velocity of the substrate 160 with respect to the laboratory frame around a rotation center O
  • v xy is the relative linear velocity of the laser beam 1 10 with respect to the laboratory, and may be generated by the linear translation of the 3D printer x- and y-axes. Therefore, the same equation may apply to any scenario where the laser beam 1 10 (or the outlet 142) has a relative linear velocity and a relative angular velocity with respect to the substrate 160.
  • the predetermined path S(x, y) is a function with respect to the x-y plan.
  • the 3D printer may determine a pair of 3D nozzle and laser velocity and substrate angular velocity to print a 3D predetermined path, using the same principle of the 2D model.
  • the predetermined path may be a 3D function S(x, y, z) in the x-y-z space.
  • the curvature ⁇ may be out of the plane of the substrate.
  • the printer may determine the needed translational motion of the nozzle and laser velocity along x-y plane, y-z plane, and z-x plan.
  • the 3D printer may also determine the needed angular speed of the substrate along x-axis, y-axis, and z-axis, so that the combination motion
  • the substrate 160 may be stationary during printing, and the nozzle 140 and the light guide 120 may be moved linearly together and rotated together around an axis, such that the outlet 142 prints the filament 146 on or above the substrate 160 along the predetermined path, and the focal area A moves along the filament 146.
  • the nozzle 140 and the light guide 120 may be rotated together around an axis, and the substrate 160 may be moved linearly, so that the outlet 142 prints the filament 146 on the substrate 160 along the predetermined path and the focal area A moves along the filament 146.
  • the nozzle 140 and the light guide 120 may remain stationary, and the substrate 160 may be moved linearly and rotated around an axis, so that the outlet 142 prints the filament 146 on the substrate 160 along the predetermined path and the focal area A moves along the filament 146.
  • the laser beam 110 may be a waveform laser with predetermined amplitude and frequency.
  • the controller 102 may control the waveform generator 108 to generate a waveform actuation signal at the predetermined frequency. Accordingly, when the waveform generator 108 actuates the laser generator 104, the emitted laser beam 1 10 may have waveform amplitude at the
  • the laser beam 1 10 may have any amplitude of any waveform.
  • the laser beam 1 10 may be pulsed laser beam comprising laser pulses.
  • the power of the laser beam 1 10 may be 0.1 mJ/pulse, 1 mJ/pulse, 5mJ/pulse, 20mJ/pulse, or 200mJ/pulse.
  • the frequency may be any number.
  • the frequency may be 5 Hz, 20 Hz, 200, or 1000 Hz.
  • An example composition for the silver ink in its unsintered state is a colloidal silver nanoparticle solution, stabilized with chains of linear poly(acrylic acid), in a solution of diethanolamine, water, and ethanol.
  • Fig. 8A illustrates effects of the laser beam pulse frequency on the density and microstructure of sintered silver filaments.
  • the silver filament may be sintered by the laser beam through burnout of a polymeric binder and/or polymerization.
  • the silver filament may be a conductive electrode of a micro scale electronic device, such as an electrode of integrated circuit on a silicon chip.
  • the scale bar in Fig. 8A is 5 ⁇ .
  • the sintered silver filament exhibits a denser structure when sintered at a higher laser frequency and a more porous structure when sintered at a lower laser frequency.
  • Fig. 8B is a chart of resistivity of the sintered silver filament versus sintering frequency of the laser. It shows that the resistivity of the silver filament generally decreases when the sintering frequency increases.
  • Fig. 9A illustrates effects of the laser beam pulse power on the nanostructure of sintered silver filaments.
  • the scale bar in the top pictures of Fig. 8A is 100 nm, and the scale bar in the bottom pictures of Fig. 8A is 5 pm.
  • the sintered silver filament exhibits a different nanostructure when sintered at different laser pulse powers.
  • Fig. 8B is a chart of resistivity of the sintered silver filament versus pulse power of the laser. It shows that the resistivity of the silver filament dramatically decreases when the pulse frequency increases.
  • the controller 102 of the 3D printer may be able to select the power and frequency of the laser beam 110. For example, when a printed structure requires lower resistivity and higher mechanical strength, the controller 102 may select the laser beam 110 to be higher than 200 Hz and 200 mJ/pulse.
  • the controller may also dynamically vary the laser power, pulse frequency, or pulse duration settings during printing to spatially pattern electrical and/or mechanical properties. For example, a temporary reduction in laser power during printing can produce a length of filament with a higher electrical resistivity, thus producing a 3D printed electrical resistor.
  • DIW direct ink writing
  • Fig. 10 illustrate an actual Laser-DIW apparatus, wherein Fig. 10a is a photograph showing the Laser-DIW printhead that combines a laser microscope and silver ink extrusion system, both mounted on a 3- axis printer, and the substrate on top of a rotating stage; and Fig. 10b is a photograph of the housing of the objective lens and nozzle above a silicon wafer substrate.
  • an 808 nm diode laser (Shanghai-Laser & Optics Century Co. Ltd.) is coupled via an SMA connector to a 200 ⁇ multimode optical fiber.
  • the laser is collimated at the outlet of the multimode fiber by a collimating lens (A), and reflected by a 750 nm short- pass dichroic mirror (Edmund Optics Inc.) (C).
  • the dichroic mirror was selected to transmit a small amount ( ⁇ 1 %) of the laser light to enable visualization of the reflected laser spot by the microscope camera (Imaging Developing Systems, GmbH) for alignment purposes (B).
  • the laser power, pulse duration and pulse frequency is modulated by a square wave from a waveform generator (Keysight).
  • the laser beam is expanded 2X via a pair of achromatic doublet lenses (D) before being focused by a 0.16 NA, 15.29 mm focal distance aspheric objective lens (Thorlabs Inc.) (G).
  • the silver ink is loaded into a syringe (F) which is extruded via a high-pressure piston (Nordson EFD) (E), pressurized via a pressure controller (Nordson EFD).
  • EFD high-pressure piston
  • Nedson EFD pressure controller
  • the nozzle may be moved relative to the laser focus by means of a three-axis micrometer (I).
  • the alignment and printing is aided by a side view camera and lens system (Imaging)
  • Developing Systems, GmbH) H. All the systems described above are mounted onto a 3-axis printing stage (Aerotech Inc.).
  • the substrate (J) is mounted on a rotary stage (Aerotech Inc.) (L).
  • An x-y leveling stage (K) lies in between the rotary stage and the substrate to ensure that the substrate x-y plane is aligned parallel to the x-y plane of the 3-axis printer.
  • Fig. 1 1 illustrates the basic settings of the example, i.e., a laser sintered DIW (Laser-DIW).
  • a laser sintered DIW Laser-DIW
  • an 808 nm IR laser is focused to a 100 ⁇ spot adjacent to the aperture of the glass nozzle through which a concentrated silver nanoparticle ink (85 wt% solids) is deposited
  • Fig. 1 1 a Schematic of the Laser-DIW printhead, which consists of the laser microscope, silver ink syringe and nozzle. Fig. 10).
  • the patterned features are rapidly heated by the focused laser to form a mechanically robust, electrically conductive wire.
  • the power of the laser may be adjusted to sinter the silver wires, which results in a higher conductivity to the silver wire, or simply raise the temperature to an annealing temperature, which results a lower conductivity to the silver wire.
  • the laser heating process is referred to as annealing process.
  • the printed silver wires vary in diameter from ⁇ 1 m to 20 ⁇ depending on the nozzle diameter, extrusion pressure, and printing speeds used.
  • the in-line laser annealing process induces a visible change of emissivity (dull to shiny) of the printed wires at the macroscale (Fig. 1 1 b, Side and top views showing the IR laser (the zigzag arrow) focused immediately downstream of the nozzle.
  • the sample To print curvilinear features via Laser-DIW, the sample must be rotated relative to the laser-nozzle axis using a rotary stage, such that the curvilinear wire is always patterned in a direction parallel to the laser- nozzle axis (Fig. 1 1 d, A side-view showing freeform 3D printing of a metal hemispherical spiral. Fig. 1 1 e, A photograph showing the objective lens positioned directly above the nozzle with the 3D metallic structures printed below.).
  • Fig. 12 illustrates a method of printing curvilinear structure using a rotating state
  • Fig. 12a is a 3D spline created in Solidworks and Fig. 12b shows that the 3D spline is uploaded to a custom MATLAB script
  • Fig. 12c is a diagram showing the rotating stage and a curvilinear wire being printed above.
  • a path is first drawn up using Bezier curves (Fig. 12a) and split up into piece-wise linear segments (Fig. 12b). Studying an arbitrary curve to be printed (Fig. 12c), let dS represent a short segment that lies
  • the instantaneous x-y curvature of the wire being printed, K xy is defined by: where ⁇ represents the instantaneous x-y bearing of the wire segment, or equivalently, the current angle of the rotary stage.
  • ⁇ represents the instantaneous x-y bearing of the wire segment, or equivalently, the current angle of the rotary stage.
  • the printer In addition to rotating the stage, the printer must be translated in x, y and z to map both the translation of the point P on the substrate as the stage rotates, and generate the net print velocity v p relative to the motion of P. If r represents the vector connecting the center of rotation of the rotary stage, 0, with point P, then the printer must be translated with velocity v xyz governed by the following equation of motion: where ⁇ denotes the unit vector along the rotation axis of the rotary stage.
  • any arbitrarily shaped piece-wise linear wire with G-code commands [x n , y n , z n ] can be converted into new 4-dimensional commands [x n , y n , z n , ⁇ ⁇ ].
  • a custom script that implements the mathematical conversion necessary for Laser-DIW has been made available at MATLAB Central.
  • the laser must be placed as close to the ink deposition nozzle as possible (Fig. 11 g, Examples of printing
  • the exemplary embodiment uses a simplified one-dimensional heat transfer model to study the temperature distribution along the silver wire during printing at a speed v p , which accounts for the input laser energy (3 ⁇ 4) as well as convective (c/ c ) and radiative (c/ R ) heat loss.
  • the temperature distribution is modeled by the following convection-diffusion equation: k(x,t)
  • the density p, the specific heat capacity c p , and the thermal conductivity k of printed wire are a function of its thermal history.
  • the exemplary embodiment numerically solves this partial differential equation using a finite difference method.
  • the upstream heat transfer is reduced by three key mechanisms. First, using laser flash thermal analysis, the heat- annealed silver features have a 50-fold higher thermal diffusivity compared to the as-printed silver ink (20 mm2s-1 and 0.4 mm2s-1 , respectively). Hence, the laser-annealed regions of the printed silver wires serve as a downstream heat sink, limiting upstream heat transfer to the ink reservoir within the nozzle.
  • the characteristic upstream heating distance at a print speed of 1 mm s-1 is 400 ⁇ . Notably, this printing speed is more than 1000 times higher than meniscus printing.
  • operating the laser in a pulsed mode instead of CW allows one to achieve high maximum
  • the laser pulse duration should be sufficiently long such that the characteristic thermal diffusion distance is large compared with the wire diameter:
  • this characteristic length is 40 ⁇ , which is significantly larger than the thickest (-20 ⁇ ) wires being printed.
  • the simulation further predicts that for low PRR, the maximum temperature reached along the wire becomes non-uniform, even when all segments of the wire receive an equal laser exposure. This manifests in low PRR producing macroscopically heterogeneous wires with a non-uniform nanostructure.
  • Fig. 13 shows how the PRR affects the microstructure of the printed filaments. At low PRR, the microstructure is highly porous throughout the thickness of the filament, whereas operating at a high PRR produces filaments that are uniform (Fig. 13a, wire porosity decreases with increasing PRR.).
  • Filaments that are annealed using low PRR exhibit a periodic, heterogeneous microstructure at a spatial frequency that is related to the print velocity and the PRR (Fig. 13b, wires annealed at low PRR exhibit periodic heterogeneity. Scale bars: 10 ⁇ .).
  • heating the wire at a 1 ms pulse duration at 100 Hz generates a silver wire with a uniform nano- and microstructure, as predicted by the more uniform thermal history (Fig. 1 1 i).
  • equation 6 models a worst-case scenario for thermal management, as a substrate would serve as a heat-sink that limits upstream heat transfer. Printing directly onto a substrate would also significantly reduce the maximum annealing temperature, particularly when the wire is annealed by CW laser exposure, as a more uniform through-thickness heating would result in more heat-loss to the substrate.
  • microstructure of printed wires produced by continuous-wave and pulsed laser operation show a similar progression with increasing laser intensity, i.e. they undergo both densification and grain growth as expected during thermal annealing
  • Fig. 14b microstructure of silver wires annealed by continuous wave laser illumination. Numbers indicate peak illumination intensity in kW/cm 2 . Scale bars: 10 ⁇ (i), 100 nm (ii).
  • Fig. 14c microstructure of silver wires annealed by pulsed (1 ms, 100 Hz) laser illumination. Numbers indicate peak illumination intensity in kW/cm 2 . Scale bars: 10 ⁇ (i), 100 nm (ii).).
  • Laser-DIW enables one to create patterned regions of low-to-high resistance simply by modulating the local laser intensity during silver ink printing. For example, when the laser power is modulated to varying degrees during printing, a series of 500 ⁇ silver segments with graded resistivity are created in-line within the same conductive silver wire, as visualized by gradations in the infrared signatures upon passing a constant current along the printed wire (Fig. 14d, a varying laser intensity profile (top) results in corresponding infrared emissions from resistive elements as current is passed through the wire. Each resistor is approximately 500 ⁇ in length.).
  • l-V characteristics of resistors created in this manner are initially linear until a critical current is reached, beyond which Joule-heating from resistive losses results in auto- annealing of the resistors causing a large deviation from Ohmic behavior (Fig. 14e, l-V characteristics of two resistors formed at different laser intensities. Current is stepped up (unfilled) to a certain level, and then stepped down (filled).). If, after the onset of auto-annealing, the current is stepped back down, a new linear characteristic is observed with a lower value of resistance, representing the increased conductivity from auto- annealing. This behavior is characteristic of a write-once read-many (WORM) memory element, or 'anti-fuse'. It is noted that the critical current or potential difference at which the anti-fuse anneals can be programmed via careful choice of laser power.
  • WORM write-once read-many
  • Laser-DIW enables conductive silver wires to be patterned on flexible, low-cost plastic substrates, such as poly (ethylene terephthalate), PET (Fig. 14f, SEM images of various diameter wires laser annealed onto PET films.
  • Middle row oblique views of silver wires;
  • Bottom row magnified images of the interface between the silver (Ag) and PET substrate.).
  • PET is of particular interest for flexible electronic and
  • the laser- heated silver ink generates a localized heat-affected zone (HAZ) in the underlying plastic substrate.
  • HAZ effectively welds the silver to the PET (Fig. 14f, bottom row), yielding mechanical robust electrodes that can withstand a tape peel test.
  • the laser wavelength could be selected to ensure maximal optical transparency. As the laser energy is predominantly absorbed by the silver wire, and not the PET itself, the HAZ width increases with the diameter of the wire (Fig.
  • PET films with printed submicron silver wires with a center-to-center separation distance of 500 ⁇ exhibit exceptional optical transparency (Fig. 14h, an array of silver wires, with submicron widths, are printed onto a transparent PET film across a 1 cm 2 area, using a wire spacing distance of 500 ⁇ . The resulting film, indicated by the white dashed line, remains transparent.).
  • wires annealed at low PRR exhibit periodic heterogeneity. Scale bars: 10 ⁇ .) were minimal ( ⁇ 1 %) throughout the 1 ,000 cycle test.
  • the thick wires due to the presence of microscopic defects and porosity, are not able to withstand the same degree of extension when compared with defect-free thin-film approaches, which can reach a 50% strain.
  • the silver nanoparticle ink is synthesized using a protocol similar to that previously described . Briefly, 0.9 g of a 25% wt/v solution of 50 kDa poly(acrylic acid) (Polysciences Inc., Warrington, PA), in water and 1 .8 g of a 50% wt/v 5 kDa poly(acrylic acid) (Polysciences Inc) are dissolved into 50 g of distilled water in a clean 500 ml Erlenmeyer flask. 40 g of diethanolamine (Sigma Aldrich, St. Louis, Ml) is then added, and the solution is allowed to return to room temperature while stirring at 300 rpm using a 1 -inch stir bar.
  • diethanolamine Sigma Aldrich, St. Louis, Ml
  • the nanoparticles After 5 min of additional stirring, the nanoparticles are allowed to settle under quiescent conditions. The supernatant is decanted away, and the silver nanoparticle sediment is transferred quickly via a spatula into a separate 50 ml conical tube, ensuring that the suspension does not dry. The nanoparticles are then centrifuged at -13,000 g for 20 min into a dense pellet, and the supernatant is discarded. The nanoparticles are then suspended again by adding 15 ml of water followed by vigorous vortexing. The suspension is filtered through a 5 ⁇ syringe filter by splitting the solution into two 50 ml conical tubes and adding 35 ml of ethanol into each tube. The
  • nanoparticles are allowed to settle for 20 min before decanting the supernatant.
  • the nanoparticle suspension in one conical tube is transferred to the other by use of a spatula before compacting the silver nanoparticles by centrifugation at 13,000 g for 20 min.
  • the nanoparticle pellet is then transferred out of the conical tube using a spatula, and placed in a jar to be mixed in a planetary mixer (Thinky Corp., Madison Hills, CA 92653).
  • the ink is then transferred via spatula into a 3 ml syringe (Nordson EFD, East Buffalo, Rl) and centrifuged for 10 min at 4,000 g to remove trapped air.
  • the syringe is then placed into an HP3 high- pressure dispensing adaptor (Nordson EFD), connected to a variable pressure supply (Nordson EFD) and a 2-inch long glass nozzle with either a 10 m or 1 ⁇ inner diameter added to the syringe (World Precision Instruments).
  • HP3 high- pressure dispensing adaptor Nedson EFD
  • variable pressure supply Nedson EFD
  • 2-inch long glass nozzle with either a 10 m or 1 ⁇ inner diameter added to the syringe (World Precision Instruments).
  • the syringe and high pressure adaptor are mounted onto the laser microscope and aligned with the focused laser spot.
  • the focused laser and ink printhead are of the following designs.
  • a 5 W 808 nm CW diode laser (Shanghai Laser & Optics Century Co. Ltd., Shanghai, China) is connected to the laser microscope by means of a 200 ⁇ multimode optical fiber (Thorlabs Inc., Newton, NJ), and collimated via a 0.26 NA, 1 1 .07 mm collimating lens.
  • the collimated beam is magnified 2X by a telescope consisting of a pair of IR anti-reflective achromatic doublet lenses (Thorlabs Inc.), and focused to a 100 ⁇ spot using a 0.16 NA, 12.43 mm working distance aspheric objective lens.
  • the laser focus spot possesses a uniform, top-hat intensity distribution.
  • the laser path includes a short-pass 750 nm dichroic mirror (Edmund Optics) that reflects the IR laser light, and transmits visible light collected by the objective to a CMOS camera (IDS, Obersulm, Germany) that serves as an alignment microscope.
  • the dichroic mirror is selected to enable a small amount of IR light to be transmitted ( ⁇ 1 %) to enable visualization of the substrate-reflected laser light with the top alignment camera.
  • the entire optical setup is mounted on an optical breadboard, which itself is mounted onto an x-y-z translating 3D printing gantry (Aerotech Inc., Pittsburg, PA).
  • the laser diode driver is modulated by a square-wave signal derived from either a waveform generator (Keysight) or a National Instruments NI-6211 , to enable the precise variation of the laser pulse power, frequency and duration.
  • the laser is first focused onto the substrate by observing the laser spot on the alignment camera.
  • x, y, and z micrometers are used to move the silver ink syringe and nozzle relative to the focused laser spot.
  • a separate side camera (Imaging Development Systems) is used to aid this process.
  • the nozzle is typically placed -100 ⁇ away from the laser spot.
  • the silver ink is extruded through the nozzle by applying pressure (typically 150-200 psi), and the printer is translated in x, y, and z.
  • the rotary stage alignment is achieved by the following.
  • a rotary stage is used for mounting the sample to enable the construction of curved lines.
  • the rotary stage is positioned directly underneath the laser microscope.
  • the laser is focused on the top surface of a glass slide colored with a permanent marker.
  • the laser spot ablates the permanent marker, tracing a circle, whose center lies at the center of rotation.
  • the center of rotation is then supplied to a custom
  • MATLAB script that converts a series of x-y-z Gcode commands into a new set of commands in x-y-z, and ⁇ .
  • the conductivity is measured as follows. Four 75 mm electrodes, consisting of gold stripes, are patterned onto a 75 mm x 25 mm glass slide by sputter coating. Next, linear wires are printed perpendicular to the stripes and a four-point probe is used to measure resistance between the center two stripes, separated by 6.35 mm. To calculate electrical resistivity, their cross-sectional areas are measured by image analysis of scanning electron micrographs of cut wires.
  • exemplary embodiments of the present disclosure relate to devices and methods for sintering metallic inks extruded from a 3D printer
  • the devices and methods may also be applied to other applications.
  • the devices and methods may also be used to sinter ceramic inks.
  • the laser beam is an ultraviolet laser
  • the devices and systems may also be used to real-time cure a printed structure made by photosensitive epoxy or acrylate ink.
  • the present disclosure intends to cover the broadest scope of systems and methods in 3D printing field.

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Abstract

La présente invention concerne un dispositif de frittage en ligne d'une encre pendant l'impression 3D. Le dispositif comprend une buse ayant un orifice de sortie pour l'extrusion d'un filament comprenant une encre, où la buse est configurée de façon à se déplacer par rapport à un substrat sous-jacent; un générateur laser pour émettre un faisceau laser; et un guide de lumière en liaison optique avec le générateur laser pour recevoir le faisceau laser du générateur laser et focaliser le faisceau laser sur une zone focale déterminée par un chemin de la buse sur le substrat.
PCT/US2016/026651 2015-04-08 2016-04-08 Frittage laser en ligne d'encres métalliques WO2016164729A1 (fr)

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CN111868004A (zh) * 2018-03-21 2020-10-30 3 D矿物公司 经由液体途径的陶瓷增材制造方法和实施所述方法的设备
CN110744198A (zh) * 2018-07-19 2020-02-04 林肯环球股份有限公司 具有全向构建路径的激光热丝增材沉积头
WO2022140455A1 (fr) * 2020-12-21 2022-06-30 Divergent Technologies, Inc. Éléments thermiques pour le démontage de structures liées par adhérence à base de nœuds

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