KR102747524B1 - Additive manufacturing system with addressable laser array and real-time feedback control for each source - Google Patents

Abstract

An assembly is provided for combining a group of laser sources into a combined laser beam. A blue diode laser array is further provided for combining laser beams from blue laser diode assemblies. Laser processing operations and applications using the combined blue laser beam from the laser diode array and modules are provided.

Description

Additive manufacturing system with addressable laser array and real-time feedback control for each source

This application claims the benefit of and priority under 35 U.S.C. §119(e)(1) to U.S. Provisional Application Serial No. 62/726,234, filed September 1, 2018, the entire disclosure of which is incorporated by reference herein.

The present invention relates to an array assembly for combining laser beams, and more particularly to an array assembly capable of providing high brightness laser beams for use in systems and applications in the fields of fabrication, manufacturing, entertainment, graphics, imaging, analysis, monitoring, assembly, dentistry and medicine.

Many lasers, particularly semiconductor lasers such as laser diodes, provide laser beams having highly desirable wavelengths and beam qualities, including brightness. These lasers can have wavelengths in the visible range, UV range, IR range, and combinations thereof, as well as higher or lower wavelengths. In addition to semiconductor lasers, the technology of other laser sources (e.g., fiber lasers) is rapidly evolving, with new laser sources continually being developed and offering both existing and new laser wavelengths. While having desirable beam qualities, many of these lasers have lower laser power than is desirable or necessary for certain applications. This low power therefore prevents these laser sources from providing greater utility and commercial applications.

Additionally, previous efforts to combine these types of lasers have generally been inadequate due to, among other reasons, difficulties in beam alignment, difficulty in maintaining beam alignment during application, loss of beam quality, special placement of the laser source, size considerations, and power management.

Infrared (IR)-based (e.g., wavelengths greater than 700 nm, and especially greater than 1,000 nm) additive manufacturing systems using a galvanometer scanner suffer from two drawbacks, above all else: limiting build volume and build speed. In these IR laser systems, the build volume is limited by the finite size of the scanning system and the spot that can be produced for a given focal length collimator and f-theta lens. For example, when using a collimator with a focal length of 140 mm and a lens with a F-θ focal length of 500 mm, the spot size for a 1 μm laser is about 40 μm for a near-diffraction limited single mode laser. This provides an addressable footprint in the powder layer of about 175 mm x 175 mm, which is a limitation on the part size that can be built. A second limitation on the build speed of IR laser systems is the absorption of the laser beam by the powder material. Most raw materials have moderate to high reflectivity for wavelengths in the infrared spectrum. As a result, the coupling of infrared laser energy into the powder layer is limited by the fact that a significant portion of the energy is reflected into the powder layer or back or deeper. These limitations are further compounded or interconnected, further exacerbating the problems and defects of IR additive systems. The finite penetration depth of IR thus determines the optimal layer thickness and consequently limits the resolution and speed of the process. These and other defects of IR-based fabrication and build systems and processes have not been adequately addressed. Thus, a long-held need for improvements in additive fabrication systems and processes has not been met.

As used herein, unless explicitly stated otherwise, the terms "blue laser beam", "blue laser" and "blue" are to be given their broadest meaning and generally refer to a laser beam, or a system providing light, for example a propagating laser beam, laser beams, laser sources, for example lasers and diode lasers, having a wavelength of from about 400 nm to about 500 nm and generally from about 400 nm to about 500 nm. Blue lasers include wavelengths of 450 nm, about 450 nm, 460 nm and about 460 nm. Blue lasers can have bandwidths of from about 10 pm to about 10 nm, about 5 nm, about 10 nm and about 20 nm as well as greater and smaller values.

As used herein, unless expressly stated otherwise, the terms “UV,” “ultraviolet,” “UV spectrum,” “UV portion of the spectrum” and similar terms are to be accorded their broadest meaning and include light with wavelengths from about 10 nm to about 400 nm and from 10 nm to 400 nm.

As used herein, unless expressly stated otherwise, the terms “visible light”, “visible spectrum”, “visible portion of the spectrum” and similar terms are to be accorded their broadest meaning and shall include light with wavelengths from about 380 nm to about 750 nm and from 400 nm to 700 nm.

As used herein, unless expressly stated otherwise, the terms "green laser beam", "green laser" and "green" are to be given their broadest meaning and generally refer to a laser beam, or a system providing light, e.g., a propagating laser beam, laser beams, laser sources, e.g., lasers and diode lasers, having a wavelength of from about 500 nm to 700 nm, such as from about 500 nm to about 700 nm. Green lasers include wavelengths of 515 nm, about 515 nm, 532 nm, about 532 nm, 550 nm and about 550 nm. Green lasers can have bandwidths of about 10 pm to 10 nm, about 5 nm, about 10 nm and about 20 nm as well as greater and smaller values.

In general, as used herein, the term "about" and the symbol "~", unless otherwise specified, are meant to include a deviation or range of plus or minus 10%, experimental or instrumental error associated with obtaining the stated value, and preferably whichever is greater.

As used herein, unless otherwise stated, room temperature is 25 °C. And standard ambient temperature and pressure are 25 °C and 1 atm. Unless otherwise explicitly stated, all tests, test results, physical properties, and values which are temperature dependent, pressure dependent, or both are provided at standard ambient temperature and pressure, which may include viscosity.

Unless otherwise specified, references to ranges of values in this specification, as used herein, are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value within the range is incorporated into the specification as if it were individually recited herein.

Typically, the method used in additive manufacturing uses an infrared laser and a galvanometer to scan a laser beam across the surface of a powder layer in a predetermined pattern. The IR laser beam is powerful enough to melt the liquefied powder and create a keyhole welding process that fuses it to the underlying layer or substrate. This approach has several limitations that determine the speed of the process. For example, a single laser beam is used to scan the surface, and the build speed is limited by the maximum scan speed of the galvanometer (7 m/s). Manufacturers have embraced IR technology strongly, typically believing that this is the only viable wavelength, and have therefore worked to overcome these limitations by incorporating two or more IR lasers/galvanometers into a system, which can be operated together to build a single part, or independently to build parts in parallel. These efforts are aimed at improving the throughput of additive manufacturing systems, but have met with limited success, focusing solely on IR and failing to meet the long-standing need for improved additive manufacturing.

Another limitation of IR processing is the finite volume that can be addressed by the IR laser/galvanometer system. In a fixed head system, the build volume is defined by the focal length of the f-theta lens, the scanning angle of the galvanometer, the wavelength of the IR laser, and the beam quality of the IR laser. For example, an IR laser using a 500 mm F-theta lens produces a spot size of the order of 40 to 50 μm for a diffraction limited IR laser. When the laser beam is operating at 100 W optical power, the intensity of the beam is greater than that required to initiate a keyhole welding mode. The keyhole welding mode creates a plume of vaporized material that must be removed from the path of the laser beam by the cross jet, or else the laser beam is scattered and absorbed by the vaporized metal. In addition, since the keyhole mode of welding relies on creating a hole in the liquid metal surface maintained by the vapor pressure of the vaporized metal, material other than the vaporized metal can be ejected from the keyhole. These materials are referred to as spatter and cause molten material to be deposited elsewhere on the build plane, which can cause defects in the final part. While additive manufacturing system manufacturers have had some limited success in developing rapid prototyping machines, they have failed to meet the long-held need and achieve the requirements for mass production of commercial or practical parts. To achieve this, a breakthrough in part patterning methods that had not been achieved prior to the present invention has not been achieved.

In general, the problem and failure of IR processing and systems is the requirement or need to fuse the powder in keyhole welding mode. This may be because a single beam is typically used to process the powder. When the laser beam is operating at 100 watts of optical power, the intensity of the beam is greater than that required to initiate keyhole welding mode. The keyhole welding mode creates a plume of vaporized material that must be removed from the path of the laser beam by the cross jet, or else the laser beam is scattered and absorbed by the vaporized metal. Additionally, since the keyhole mode of welding relies on creating a hole in the liquid metal surface maintained by the vapor pressure of the vaporized metal, material such as the vaporized metal may be ejected from the keyhole. This material is referred to as spatter and causes molten material to be deposited elsewhere on the build plane, which can cause defects in the final part.

Recent research at Lawrence Livermore National Laboratories using optically activated light valves (OALVs) has attempted to address these IR limitations. An OALV is a high-power spatial light modulator that uses a high-power laser to generate a light pattern. While the pattern of an OALV is generated by a blue LED or laser source in a projector, the output power of an array of four laser diodes is transmitted through the spatial light modulator and used to heat the image to its melting point, which requires an IR laser to initiate the keyhole weld. The IR laser is used in keyhole mode to initiate the weld, particularly when fusing copper or aluminum materials. This keyhole welding process can produce spatter, porosity in the part, and high surface roughness, which is typically required for these materials. Thus, like typical IR systems, the OALV system does not eliminate the detrimental effects of keyhole initiation in the build process. It would be better to completely avoid the keyhole welding step, but this has failed to overcome these issues and has not provided a solution. These failures are mainly due to the fact that the absorption properties of many metals are so low at IR wavelengths that high peak power lasers are required to initiate the process. Since OALVs are transparent only in the IR region of the spectrum, it is impossible to build or use these types of systems using visible laser sources as the high energy light source. The component costs of such systems are very high, especially when the OALV is a custom component.

Conventional metal-based additive manufacturing machines are very limited in that they are based on either a binder sprayed onto a powder layer followed by a high temperature consolidation step or a high power single mode laser beam scanned over the powder layer at high speed by a galvanometer system. Both of these systems have significant drawbacks that the technology has been unable to overcome. The first system can produce parts with loose tolerances in large quantities due to shrinkage of the part during the consolidation process. The second process is limited in build speed by the galvanometer scan speed, which limits the maximum power level laser that can be used, and consequently the build speed. Builders of scan-based additive manufacturing systems have attempted to overcome these limitations by building machines with multiple scan heads and laser systems, which have not provided an adequate solution to these problems. This does indeed increase throughput, but the scaling law is linear. That is, a system with two laser scanners can build twice as many parts or build a single part twice as fast as a system using a single scanner. Therefore, there is a need for a high throughput laser-based additive manufacturing system for metal that does not suffer from the limitations of currently available systems.

The Background section of the present invention is intended to introduce various aspects of the present technology that may be related to embodiments of the present invention. Accordingly, the discussion set forth in this section provides a framework for better understanding the present invention and should not be considered an admission of prior art.

There has been a long-standing and unmet need for, among other things, assemblies and systems for combining multiple laser beam sources into a single or multiple laser beams while maintaining and improving desired beam qualities such as brightness and power. The present invention addresses these needs by, among other things, providing articles of manufacture, devices and processes as taught and disclosed herein.

An embodiment of the present invention is an additive manufacturing system (FIGS. 1, 2, 3) based on a 1-D or 2-D array of laser beams capable of directly fusion of powders in a parallel manner with step-by-step repeatability using a precision gantry system. The speed can be increased by adding a 1-D or 2-D secondary laser beam to preheat and control cooling (FIG. 4). This secondary laser can also be an addressable laser beam array to provide a preheat pattern that matches the pattern being built.

Another element of an embodiment of the present invention is the use of a real-time temperature monitoring camera, such as a thermal imaging camera. The camera can be used to monitor the temperature of the powder layer in real time as it transitions from a solid to a liquid, and the image of the camera can be correlated to the laser pattern to be applied, and the power levels of the individual laser beams can be adjusted according to predetermined requirements to provide adequate fusion and cooling of the printed part. This closed loop temperature control not only minimizes porosity in the manufactured part, but also provides additional benefits such as optimizing surface roughness and minimizing residual stresses within the part.

In an embodiment of the present invention, a means is included to compact the powder layer to minimize porosity of the powder layer, as well as to deposit the powder in real time in any direction during the printing process. The primary mechanism for melting and fusing the powder is a galvo scanned system using conduction mode welding and keyhole mode welding. This approach minimizes spatter and the requirement to protect windows and optics of the manufactured part.

In an embodiment, the present invention includes a sealed enclosure for forming an oxygen-free environment and a recirculation system for the gas that continuously cleans the gas mixture used. Filtration of the gas mixture is necessary because of airborne dust and welding fumes that, if not removed from the environment, can affect image quality and consequently the quality of the parts being built.

In an embodiment, the present invention includes a microprocessing system that performs pre-build analysis, slices the part, and performs an optimal build strategy. As each portion of the part pattern is printed, the gantry system can be instructed to move to the next adjacent part in the pattern, or to move to a random random location if the build strategy calls for random printing of the part pattern to minimize residual stress in the part.

In an embodiment, the present invention would also not require a weld monitor other than a simple visible camera to observe the weld puddle as it propagates. Because of the keyhole-less weld mode, the weld puddle is very stable even when welding copper and aluminum, something that would not be possible with an IR laser source. An IR laser source would have to rely on a weld monitor, such as an Optical Coherent Tomography (OCT) scanner, to get an accurate representation of the keyhole and how the part build progresses due to the instability of the keyhole mode. Since the conduction mode of welding the powder to the substrate is a very stable weld mode, there is no spatter, the welded powder is very uniform in thickness and shape, and the part density is 100% due to the lack of vaporization of the material during the welding process.

Accordingly, laser systems, additive manufacturing systems, processes and laser systems having one or more of the above features are provided. Additive manufacturing systems, processes and laser systems having one or more of the above features are further provided in combination with the following laser systems and methods.

Accordingly, a laser system for performing a laser operation is provided, the system comprising: a plurality of laser diode assemblies; and means for spatially combining the individual blue laser beams to produce a combined laser beam having a single spot in the far-field that can be coupled to an optical fiber for delivery to a target material; each laser diode assembly having a plurality of laser diodes capable of generating an individual blue laser beam along a laser beam path; and the means for spatially combining the individual blue laser beams is optically associated with each of the laser diodes and in the laser beam path.

Also provided are methods and systems having one or more of the following features: having at least three laser diode assemblies; each laser diode assembly having at least one laser diode; the laser diode assemblies are capable of propagating a laser beam having a total power of at least about 2 watts and a beam parameter characteristic of less than 20 mm mrad; the beam parameter characteristic of less than 15 mm mrad; the beam parameter characteristic of less than 10 mm mrad; a means for spatially combining generates a combined laser beam having N times the power density of the individual laser beams; where N is the number of laser diodes in the laser diode assembly; the means for spatially combining increases the power of the laser beam while preserving the brightness of the combined laser beam; the combined laser beam has a power that is at least 50 times the power of the individual laser beams and the beam parameter product of the combined laser beam is less than or equal to N times the beam parameter product of the individual laser beams; the beam parameter product of the combined laser beam is less than or equal to 1.5*N times the beam parameter product of the individual laser beams; The beam parameter product of the combined laser beam is less than or equal to 1*N times the beam parameter product of the individual laser beams; the means for spatially combining increases the power density of the composite laser beam while preserving the brightness of the individual laser beams; the combined laser beam has a power density that is at least 100 times the power of the individual laser beams and the beam parameter product of the combined laser beam is less than or equal to 2*N times the beam parameter product of the individual laser beams; the beam parameter product of the combined laser beam is less than or equal to 1.5*N times the beam parameter product of the individual laser beams; the beam parameter product of the combined laser beam is less than or equal to 1*N times the beam parameter product of the individual laser beams; the optical fiber is solarization resistant; the means for spatially combining has an optical assembly selected from the group consisting of alignment plane parallel plates and wedges for correcting at least one of a position error or a pointing error of the laser diode; The means for spatially combining has a polarizing beam combiner capable of increasing the effective brightness of the combined laser beam across the individual laser beams; the laser diode assembly defines individual laser beam paths having a space between each path, whereby the individual laser beams have a space between each of the paths; the means for spatially combining has a collimator for collimating the individual laser beams on the fast axis of the laser diodes, a periodic mirror for combining the collimated laser beams, the periodic mirror being configured to reflect a first laser beam from a first diode of the laser diode assembly and to transmit a second laser beam from a second diode of the laser diode assembly such that the space between the individual laser beams is filled in the fast direction; the means for spatially combining has a mirror patterned on a glass substrate; the glass substrate is sufficiently thick to shift the vertical position of the laser beams from the laser diodes to fill the voids between the laser diodes; and has a stepped heat sink.

Also provided is a laser system for providing a high brightness, high power laser beam, the system comprising: a plurality of laser diode assemblies; and means for spatially combining blue laser beams to produce a combined laser beam having a final brightness and forming a single spot in the far field that can be coupled to an optical fiber; wherein each laser diode assembly has a plurality of laser diodes capable of producing a blue laser beam having an initial brightness; and wherein each of the laser diodes is locked to a different wavelength by an external cavity to substantially increase the brightness of the combined laser beam, the final brightness of the combined laser beam being substantially equal to the initial brightness of a laser beam from a single laser diode.

Also provided are methods and systems having one or more of the following features: wherein each of the laser diodes is locked to a single wavelength using an external cavity based on a grating, and wherein each of the laser diode assemblies is combined into a combined beam using a combining means selected from the group consisting of narrowly spaced optical filters and gratings; a Raman convertor is used to pump the Raman converter, such as an optical fiber having a GeO ₂ doped central core with an outer core larger than the central core containing the blue pump light and an outer core that produces a higher brightness source; the Raman converter has a P ₂ O ₅ doped core that produces a higher brightness source and an outer core larger than the central core to contain the blue pump light; the Raman converter is an optical fiber having a graded index core for producing a higher brightness source and an outer core larger than the central core containing the blue pump light; the Raman converter is a graded index GeO ₂ doped core and an outer stepped index core; The Raman converter is used to pump the Raman converter fiber which is a graded index _P2O5 doped core and _an outer step index core; the Raman converter is used to pump the Raman converter fiber which is a graded index _GeO2 doped core; the Raman converter is a graded index _P2O5 doped core and _an outer step index core; the Raman converter is a diamond for generating a higher brightness laser source; the Raman converter is a KGW for generating a higher brightness laser source; the Raman converter is _YVO4 for generating a higher brightness laser source; the Raman converter is Ba( _NO3 ) ₂ for generating a higher brightness laser source; the Raman converter is a high pressure gas for generating a high brightness laser source.

Also provided is a laser system for performing a laser operation, the system comprising a plurality of laser diode assemblies, each of the plurality of laser diodes capable of generating a blue laser beam along a laser beam path; and means for spatially combining the blue laser beams to create a combined laser beam having a single point in the far field that can be optically coupled to a Raman converter, pumping the Raman converter, and increasing the brightness of the combined laser beam.

Also provided is a method of providing a combined laser beam, the method comprising an array of Raman converter lasers generating blue laser beams at individual different wavelengths and combining the laser beams to produce a higher power source while maintaining the spatial brightness of the original source.

Also provided is a laser system for performing a laser operation, the system having a plurality of laser diode assemblies, each of which has a plurality of laser diodes capable of generating a blue laser beam along a laser beam path; a beam collimating and combining optical devices along the laser beam path; and an optical fiber for receiving the combined laser beam.

Also provided are methods and systems having one or more of the following features: wherein the optical fiber is in optical communication with the rare-earth doped fiber, whereby the combined laser beam can pump the rare-earth doped fiber to produce a higher brightness laser source; and wherein the optical fiber is in optical communication with the outer core of the brightness converter, whereby the combined laser beam can pump the outer core of the brightness converter to produce a higher ratio of brightness enhancement.

Also provided is a Raman fiber having a dual core, one of which is a high-brightness central core; and a means for suppressing a second-order Raman signal in the high-brightness central core, wherein the means is selected from the group consisting of a filter, a fiber Bragg grating, a difference in V number for first- and second-order Raman signals, a difference in round-trip gain for first- and second-order Raman signals due to a length of the fiber or a cavity mirror, and a difference in micro-bend loss.

Also provided is a second harmonic generating system, the system having a first wavelength Raman converter that generates light in a nonlinear crystal at half wavelength of the first wavelength; and an external resonant double crystal configured to prevent the half wavelength light from propagating through the optical fiber.

Furthermore, methods and systems are provided having one or more of the following features: wherein the first wavelength is about 460 nm; the external resonant doubling crystal is KTP; and the Raman converter has a non-circular outer core configured to improve Raman conversion efficiency.

Also provided is a third harmonic generating system, the system having a first wavelength Raman converter for generating light at a second wavelength lower than the first wavelength; and an external resonant double crystal configured to prevent the lower wavelength light from propagating through the optical fiber.

Additionally, a fourth harmonic generation system is provided, the system having a Raman converter generating light at 57.5 nm using an external resonant double crystal configured to prevent light at a wavelength of 57.5 nm from propagating through the optical fiber.

Also provided is a second harmonic generation system, which emits light at 473 nm when pumped by a blue laser diode array at 450 nm, having a rare-earth doped brightness converter with thulium that generates light at half the wavelength of the source laser or 236.5 nm using an external resonant double crystal but which does not allow short-wavelength light to propagate through an optical fiber.

Also provided is a third harmonic generating system having a rare earth doped brightness converter having thulium lasing at 473 nm when pumped by a blue laser diode array at 450 nm to produce light at 118.25 nm, which uses an external resonance but does not allow short wavelength light to propagate through the optical fiber.

Also provided is a third harmonic generation system having a rare-earth doped brightness converter having thulium lasing at 473 nm when pumped by a blue laser diode array at 450 nm to produce light at 59.1 nm, which uses an external resonance but does not allow short-wavelength light to propagate through the optical fiber.

Also provided is a laser system for performing a laser operation, the system having at least three laser diode assemblies; each of the at least ten laser diodes, each of the at least ten laser diodes capable of generating a blue laser beam along a laser beam path having at least about 2 watts of power and a beam parameter product of less than 8 mm-mrad, wherein each of the laser beam paths is essentially parallel such that a space is defined between the laser beams traveling along the laser beam paths; the system having means for spatially combining and preserving the brightness of the blue laser beams positioned along all of the at least thirty laser beam paths, the means for spatially combining and preserving having a collimating optic about a first axis of the laser beam, an array of vertical prisms about a second axis of the laser beam, and a telescope; and the means for spatially combining and preserving fills the space between the laser beams with laser energy to provide a combined laser beam at a power of at least about 600 watts and a beam parameter product of less than 44 mm-mrad.

Also provided is an addressable array laser processing system, the addressable array laser processing system having at least three laser systems of the presently described type, each configured to couple each of the combined laser beams to a single optical fiber, such that each of the at least three combined laser beams can be transmitted along the coupled optical fiber, the three or more optical fibers being optically associated with a laser head; and a control system having a program having a predetermined sequence for delivering each of the combined laser beams at predetermined locations on a target material.

Also provided are methods and systems for an addressable array having one or more of the following features: wherein a target material having powder in a part is imaged onto a powder layer by individually turning a laser beam on and off from a laser head in a predetermined sequence to melt and fuse the powder; wherein the fibers of the laser head are arranged in an arrangement selected from the group consisting of linear, non-linear, circular, diamond, square, triangular, and hexagonal; wherein the fibers of the laser head are arranged in an arrangement selected from the group consisting of 2x5, 5x2, 4x5, at least 5x at least 5, 10x5, 5x10, and 3x4; the target material comprises a powder layer, an x-y motion system capable of transporting the laser head across the powder layer to melt and fuse the powder layer, and a powder delivery system capable of moving behind the laser source to provide a new layer of powder behind the fused layer; and a z-motion system capable of transporting the laser head to increase and decrease the height of the laser head above the surface of the powder layer; A bi-directional powder placement device capable of placing powder directly behind a transmitted laser beam as it moves in the positive x direction or the negative x direction; having a powder supply system coaxial with the plurality of laser beam paths; having a gravity feed powder system; having a powder supply system, wherein the powder is entrained in an inert gas stream; having a powder supply system transverse to N laser beams, where N > 1 and the powder is placed by gravity ahead of the laser beams; having a powder supply system transverse to N laser beams, where N > 1 and the powder is entrained in an inert gas stream intersecting the laser beams.

Also provided is a method of providing a combined blue laser beam having high brightness, the method comprising the steps of operating a plurality of Raman converted lasers to provide a plurality of individual blue laser beams and combining the individual blue laser beams to produce a higher power source while preserving the spatial brightness of the source sources; wherein the plurality of individual laser beams have different wavelengths.

Furthermore, a method of laser processing a target material is provided, the method comprising: having at least three laser systems of the presently described system type for generating three individual combined laser beams into three individual optical fibers; transmitting each of the combined laser beams along the optical fibers to a laser head; and having an addressable array laser processing system for directing the three individual combined laser beams from the laser head in a predetermined sequence at predetermined locations on the target material.

FIG. 1 is a perspective view of an embodiment of a 3-D printer based on a fiber array according to the present invention.
FIG. 2a is a perspective view of an embodiment of a fiber-based printer head according to the present invention.
Figure 2b is a perspective view of the fiber-based printer head of Figure 2a from another perspective.
FIG. 3 is a schematic graphical drawing of an embodiment of an optical bundle and beam path according to the present invention.
FIG. 4a is a perspective view of an embodiment of a 1-D bundle connector output for a fiber bundle for a 1-D patterning system according to the present invention.
FIG. 4b is a perspective view of an embodiment of a fiber combiner according to the present invention.
FIG. 5a is a schematic diagram of an embodiment of a 3-D printer head having a secondary laser heat source and a primary 1-D patterning system according to the present invention.
FIG. 5b is a perspective view of an embodiment of a superimposed image of a secondary laser pattern and a multi-spot primary image according to the present invention.
FIG. 6A is a schematic diagram of an embodiment of a 3-D printer head having a secondary laser heat source and a primary 1-D patterning system according to the present invention.
FIG. 6b is a perspective view of an embodiment of a superimposed image of a secondary laser pattern and a multi-spot primary image according to the present invention.
FIG. 7a is a schematic diagram of an embodiment of a printer head having a one-dimensional primary multi-spot image and a secondary heating image based on a laser diode array for the primary image according to the present invention.
FIG. 7b is a perspective view of an embodiment of a superimposed image of a secondary laser pattern and a multi-spot primary image according to the present invention.
FIGS. 8A to 8F are plan views of various embodiments of a fiber bundle image configuration (e.g., a laser beam pattern or a laser beam forming a laser pattern) on a powder layer according to the present invention, with arrows indicating the direction of movement of the pattern in the layer.
FIGS. 9A to 9F are plan views of various embodiments of a fiber bundle image configuration (e.g., a laser beam pattern or a laser beam forming a laser pattern) on a powder layer, wherein a first laser beam image is related to a second laser beam image according to the present invention, and arrows indicate the direction of movement of the two patterns in the layer (the first image spot is represented as a solid spot and the second image spot is represented as an outline spot).
FIGS. 10A to 10F are plan views of various embodiments of a fiber bundle image configuration (e.g., a laser beam pattern or a laser beam forming a laser pattern) on a powder layer, wherein a first laser beam image is related to a second laser beam image and the second laser beam has different timing characteristics to generate second images of different shapes according to the present invention, and arrows indicate the direction of movement of the two patterns on the layer (the first image spots are represented as solid spots and the second image spots are represented as outline spots).
FIG. 11 is a schematic plan view of image mapping on a powder layer in a thermal imaging camera according to the present invention.
FIG. 12 is a schematic diagram of an embodiment of a control system and closed loop control process according to the present invention.
FIG. 13 is an image and spectrum of a blue Raman converted laser beam according to the present invention.

The present invention relates to laser processing of materials, and particularly to laser building of materials, including laser additive manufacturing processes using laser beams having a wavelength of about 350 nm to 700 nm.

1-D Patterning System

FIG. 1 is a perspective view of a 3-D (three-dimensional) additive manufacturing device or printer device (100). The printer device (100) has a fiber configuration entering a print head which is a 1-D (one-dimensional) fiber configuration. Such a 1-D system has incoming fibers arranged in a linear manner as illustrated in FIGS. 2A and 2B, for example, and has a light path and optical device as illustrated in FIG. 3, for example.

Accordingly, FIGS. 1 to 3 are examples of 3-D printers using a 1-D patterning system, where 1-D represents a configuration of fiber bundles that provide and fire a laser beam used to build a 3-D object.

First, referring to FIG. 1, but in the context of FIGS. 2A, 2B and 3, the system (100) comprises an xy gantry system (101) that moves a printer head (200) in the x and y directions. The gantry system is mounted on a base (112) which may be made of granite or metal or other material that is preferably heavy and stable. The base may be vibration insulated from the rest of the system using rubber or air supports underneath it to prevent vibrations from being transmitted from the base to the powder layer (110) and the printer head (200). The entire system (100) may be enclosed in a hermetic environment (not shown in the drawings) to provide an inert atmosphere for powder processing. The inert atmosphere may be argon, nitrogen, helium or another inert gas other than oxygen. The inert atmosphere can be at reduced, atmospheric or elevated pressure and most can be flow through (at the flow and outlet ports), flow in (i.e., makeup gas is introduced but not out), or non-flow (input and output are closed after charging with the inert gas). A preferred embodiment is argon as well as an argon-CO ₂ mixture to facilitate the flow of the molten powder by destroying their surface tension. The gantry stage carries the printer head (200) and the fiber array bundle is delivered to the printer head (200) by a QBH style connector (102). Directly beneath the printer head is a powder bed (110) where the image transmitted by the fiber bundle or array is reimaged as an image (103) in the powder bed (110). The powder is spread by a bidirectional powder diffuser (108) which rides on a pair of linear rails (109) for precise movement. The powder spreader can be moved by the y-motion of the Y translation stage (106) of the gantry system (101) or by a separate motor integrated into the powder spreader assembly. Powder is loaded into the powder spreader at the edges of the base (112) at both the front and rear, and the powder is gravity fed into the powder bed. The powder spreader includes rollers (107) that rotate in the opposite direction of the motion to spread and compact the powder bed. By compacting the powder bed, porosity of the final part can be minimized. Outputs and sensor readings are routed through a flexible cable tray (105) on the side of the gantry as the gantry moves in the y-direction.

The gantry system (101) has a Y translation stage (106) for moving the print head (220) in the y direction; and a Z translation stage (111) for moving the print head (220) in the x direction. The system (100) has a powder layer elevator (104) (for moving the part down as it is built so that the next layer can be deposited on the part).

A preferred embodiment of the printer head (200) is illustrated in FIGS. 2A and 2B. While FIGS. 2A and 2B are perspective views of the same embodiment, it should be understood that, when viewed from another perspective, the print head may typically cover or have a front plate, which is not shown in the drawings. The fiber bundles are arranged in a row, preferably in a straight line, of two, three, four, five, six, two to ten, and combinations thereof, as well as more. The fiber bundles are delivered through a QBH connector (201). The QBH connector (201) is held in place by a collet (202) mounted in a case (203) of the print head (200). The optical system comprises a collimating optic (204) and a focusing optic (205). These two optics may be replaced by a single imaging optic. A laser beam is emitted from the surface of the fiber (210) and the laser beam travels along the laser beam path to the lens (204), lens (205) and then out the window (209) to form an image (103). In addition to the optical system, the printer head (200) may also accommodate a thermal imaging camera or pyrometer camera (207) for monitoring the temperature of the molten pool through an aperture or window (208) for multiple spot images (103) on the powder layer.

Referring to FIG. 4, a schematic diagram of an embodiment of a 1-D optical system (300) and ray tracing of its laser beam path is illustrated. This 1-D optical system may be used, for example, in a print head (200). A fiber bundle (301) has five optical fibers (301a, 301b, 301c, 301d, 301e) arranged in a straight line and provides an output laser beam along a beam path having a ray path (305), the output of which may be collimated by a lens (302), which may be a plano-convex lens, a plano-convex aspheric lens, a pair of lenses, a triplet lens or a similar type of optical device. A collimated beam from an array bundle having a ray path (307) is focused by a focusing lens (303), which may be a plano-convex lens, a plano-convex aspheric lens, a pair of lenses, a triplet lens or a similar type of optical device, into an image (304) having a series of spots (304a, 304b, 304c, 304d, 304e). The size of the fibers is indicated by a scale (320) and the sizes of the image and spots are indicated by a scale (321). The curves of the plano-convex lens and the plano-aspheric lens face each other to minimize spherical aberration of the system. The ray tracing illustrated in FIG. 3 is for two fused silica plano-aspheric lenses. The spot is in the focal plane or Fourier transform plane and due to small aberrations of the system the image is slightly spread resulting in a superposition of individual fiber images (i.e. spots (304a, 304b, 304c, 304d, 304e)) which constitute image (304). The system may also use a single imaging lens wherein the firing face of the fiber source (301) would be positioned at least 2f away from the imaging optics and the image plane would be at least 2f away from the same optics. This approach requires a substantially larger lens than the preferred embodiment which uses a collimating lens and a focusing lens to reimage the fiber bundle. A thermal imaging camera or pyrometer camera preferably monitors the temperature of the melt pool for each individual spot of the multiple spot images on the powder layer.

In embodiments of the 1-D patterning system, the 1-D lines of the emitters, e.g., fiber faces, can be 2, 3, 4, ... n, depending on the physical size of the fiber and the QBH connectors. In embodiments, there is a single fiber. In embodiments, there are 2 to 15, 2 to 10, 5 to 50, 2 to 1,000, 5 to 500, 100 to 2,000, more than 10, more than 20, more than 50, and combinations and variations thereof, and larger and smaller numbers of fibers, for example, arranged side by side. Thus, for example, fibers having a diameter of 200 μm (e.g., having a core diameter of about 10 to about 185 μm) can be used and their beam and beam image are re-imaged onto the powder layer to provide an output for melting and fusing the powder into the base material.

Referring to FIG. 4, a perspective view of an embodiment of a QBH style bundle connector output (700) is illustrated. The connector output (700) has five laser beam emitters and five fibers (701) arranged in a straight line to provide their images, for example, circular spots. The connector output (700) has a mechanical QBH input (702) that accepts the five fibers. This input (702) can be connected to, for example, a printer head, or a combination assembly of the type illustrated in FIG. 4B. The connector output (700) has a protective cover (703) that covers the fibers and has a break sensor.

An example of an embodiment of a fiber bundle combiner is illustrated in FIG. 4b. In this case, the combiner (806) is a free-space combiner having input fibers (801, 802, 803, 804, 805) that are collimated before being combined and refocused into an output fiber bundle (807) and then transmitted by the fibers to, for example, an output connector, a printer head. The fiber bundle receives power from each individual fiber (801, 802, 803, 804, 805) and is reimaged onto a powder layer. The power from each optical fiber can be about 2 Watts (W), 10 W, 100 W, about 150 W, about 500 W, about 1 kW, about 2 kW, about 1 W to about 2 kW, about 2 W to about 150 W, about 250 W to about 1 kW or several kW, and combinations and variations thereof, depending on, for example, how fast the gantry system can scan and the size of the fiber bundle image.

Examples of various embodiments of 1-D fiber bundle configurations and 1-D laser image patterns (e.g., multi-spot images) that can be generated by the printer head are illustrated in FIGS. 8A, 8B, 8C, 8D, 8E, and 8F. The direction of movement of the patterns in the powder layer is indicated by the arrows. These laser patterns can be used with any embodiments of the additive manufacturing system, printer head, and method according to the present invention.

The spots of the multi-spot image can be circular, elliptical, square, rectangular and other shapes; they can be joined, adjacent, overlapping or partially overlapping; they can be linear, rectilinear, curved, zigzag, patterns forming larger areas, for example square or rectangular; combinations and variations of these and other configurations and arrangements. These laser patterns can be used with any of the embodiments of the additive manufacturing system, printer head and method according to the present invention.

The parts are printed by scanning a 1-D image of the fiber bundle across a powder layer. The 1-D image of the high-power fiber output is swept in the y-axis by a gantry system and stepped over in the x-axis to repeat the pattern. The step over can be adjacent to the track printer alone or can be varied arbitrarily depending on the stress pattern desired in the final part. After printing, a powder layer elevator positioned beneath the powder layer drops a predetermined amount of powder layer (e.g., about 40 μm, about 50 μm, about 60 μm, about 35 μm to about 65 μm, and combinations thereof and greater and lesser distances), a powder spreader evenly spreads the powder metal layer, and a roller compacts the powder layer to reduce porosity of the powder. After the powder layer is prepared for the next layer, the next layer is printed with the 1-D image of the fiber bundle scanned across its surface.

The fiber optic system can also be replaced with individual laser diodes, but this is not a desirable embodiment because of the size of the print head and the complex electronics required to drive the individual laser diodes. The individual laser diodes can be part of an addressable laser diode array bar, in which case the individual laser diodes are part of a continuous bar assembly with individual current drive capability. This is a good alternative to the fiber approach, which is limited in power per emitter.

1D with secondary laser Patterning System

In embodiments, an additional or second laser beam is added to the print head to provide a means for preheating, cooling control and temperature control of the printed image. The second laser beam may also be referred to as a heating beam; the primary laser beam used to melt and fuse the powder to form the object may be referred to as a build laser and a build laser beam.

An embodiment of a print head having primary and secondary laser beams is illustrated in FIG. 5A, wherein a fiber bundle providing the primary laser beam and generating a primary image (409) (which may be a multi-spot image) on a powder layer is delivered by a QBH connector (401) and mounted to the print head (400) by a collet (402). An optical system for the beam path and beam delivery for the primary image (409) comprises a lens (405) for collimating the output of the fiber bundle. The collimated output is focused onto the power layer as the primary image (409) by a focusing lens (406). This optical system is similar to the previous description wherein the lenses may be plano-convex, plano-convex aspheric, doublet or triplet lenses. The secondary laser beam is introduced into the print head (400) via an optical fiber delivered by a QBH connector (403), which is mounted to the print head together with a collet (404). A lens (407) is used to collimate the output of the fibers. The lens (407) may be a plano-convex, plano-convex aspheric, doublet or triplet lens. The doublet or triplet lens must have an air gap since most cements will not withstand high power levels. The collimated beam is converted and focused into a powder layer by a lens or micro lens system (408), which shapes the beam into a secondary image and redirects it to be superimposed with the primary image (409). Examples of these superimposed images are shown in FIG. 5B . The superimposed image (450) may be a primary multi-spot image (451) having primary spots (411 , 412 , 413 , 414 , 415) propagating from the primary fibers of the primary fiber bundle. The primary spots are combined with a secondary image (410) of the secondary converted laser beam. Preferably, the secondary image heats a volume of powder (420). In this embodiment, the secondary laser beam is positioned so as to deposit most of its energy directly in front of the 1-D pattern (451) which translates in the "y" direction as indicated by arrow (416). Both the primary (451) and secondary (410) patterns move in the same direction (416) at the same speed. This secondary beam pattern preheats the powder and assists in the image of the fiber bundles to melt the powder and fuse it to the substrate, and after fusion provides some heat to anneal the material, thereby reducing internal stresses within the printed part. The remainder of the system functions as described in the previous section, except that a thermal imaging camera or pyrometer array is incorporated into the system to provide feedback to the laser system to maintain the powder directly in front of the primary fiber bundle image (451) at a predetermined temperature, preferably just below the melting point of the powder. During the fusion process, the feedback signal from the thermal imaging camera or pyrometer array is used to control the power of the secondary laser, the individual lasers in the fiber bundle that generate the image (451), and both to generate a predetermined powder temperature within the image of the fiber bundle. The predetermined powder temperature used in the system is empirically determined initially in the system and is used as a guideline for all builds to minimize surface roughness, part porosity, and part size. The secondary laser source can be 50 Watts, 100 Watts, 150 Watts, 500 Watts, 1,000 Watts, about 50 Watts to about 2 kW, about 250 Watts to about 1 kW, and several kW, all values within these ranges depending on, for example, the scan speed of the print head and the area of the fiber array pattern being used.

Referring to FIGS. 6A and 6B , a perspective view of a laser head (500) is shown providing a combined image (509) of a secondary (552) and primary image (551) in which a secondary fiber bundle laser source provides an addressable heat pattern on a powder layer. FIG. 6 illustrates the use of a secondary fiber bundle attached to a printer head (500) with a collet (504) with the fiber bundle attached by a connector (503). The primary fiber bundle is attached to the printer head (500) by a connector (501) and a collet (502) and has a collimating lens (505) and a Fourier transform focusing lens (506). A lens (507) collimates the fiber bundle and a beam transformation system (508) generates n images of the secondary fiber bundles that can be individually controlled to form images (552), in this embodiment having images (516, 517, 518, 519, 520) corresponding to powder volumes of the powder layer being heated. By controlling the timing at which each of the secondary laser sources is turned on and off, the preheating and cooling characteristics of each corresponding volume for the images (516-520) can be varied. In the embodiment of FIG. 5b, the two outer fibers providing the outer secondary images (516, 520) are turned on and off simultaneously to preheat the outer edges of the pattern. The two inner fibers providing images (517, 519) are turned on slightly later to allow the heat build-up from the outer fibers to permeate into the inner region because less energy is required in the inner region due to the heating of the two outer fibers. The central secondary fiber image (518) requires less energy, so the source is turned on later at a lower power level and turned off later to provide heat to anneal either a region corresponding to a laser spot (513) or the entire region corresponding to a laser spot (511 to 515), forming a primary multi-spot image (551), depending on the thermal conductivity of the material and the design of the part. Each secondary fiber can deliver power ranging from about 30 watts, 100 watts, 150 watts, about 50 watts to about 2 kW, about 250 watts to about 1 kW and several-kilowatt watts and all values therein, depending on, for example, the scan speed of the print head and the size of the heated pattern.

Referring to FIGS. 7A and 7B , a perspective view of a laser printing head (600) providing a primary multi-spot laser beam image (608) having spots (610, 611, 612, 613, 614) and a secondary laser beam image (609) overlapping the image (608) and heating a volume (651) of power is depicted. The primary laser source is a diode array (601) (which can provide a 1D pattern or a 2D pattern) and the primary laser beam path leaves the array (601) and enters a first beam transformation optic (604) and then a second beam transformation optic (605) to form the image (608) which is a 1D pattern on the surface of a powder layer. The secondary laser has a fiber or fiber bundle connected to the printer head (600) by a connector (603) and a collet (603). The secondary laser beam path travels from the fiber or fiber bundle to a collimating lens (606) and then to a beam transforming optics device (607) to shape the secondary laser beam image (609) and superimpose it with the primary laser beam image (608). The direction of travel of the laser beam and their respective images on the powder layer are indicated by arrows (615).

In the embodiments of FIGS. 7A and 7B, an addressable laser diode array source generates an addressable heat pattern in the powder layer. Each emitter from the addressable laser diode array source (601) may be 3 watts, 10 watts, or more, as limited by the diode array technology. Since the individual power levels of the laser diodes by themselves are insufficient to melt many metallic materials, a secondary heat source or laser source provided by a fiber or fiber bundle to the connector (602) is a requirement of any design utilizing an addressable laser diode array. A heated powder layer or a secondary laser source may be used, wherein the secondary laser source provides an image (609) to preheat a volume of powder (651) to just below its melting point and uses the image from the laser diode array (608) to melt the powder and fuse it to the material below. The secondary laser source may be a single fiber, a fiber bundle, connected to the printer head (600) by the connector (602) and the collet (603), or the secondary laser source may be another laser diode array that is collimated and re-imaged to form a single image (609) or a series of images, such as that shown in the embodiment of FIG. 6a. A preferred embodiment for the laser diode array is a blue laser diode source because of its improved absorption over an IR laser diode source. The 1-D pattern that can be used in a direct laser diode array source is most likely the embodiments of FIGS. 8b and 8d where the spacing between the diodes should be considered in any design, but the image converting optics can be used to generate any of the images of the embodiments of FIGS. 8a-8f.

One or more or all of the primary laser beams forming the primary laser beam pattern can be completely within the area of the secondary laser pattern, partially within the area of the secondary laser pattern, completely outside the area of the secondary laser beam, and combinations and variations thereof. In embodiments, the primary and secondary laser beam patterns can move in the same direction at the same speed, in the same direction at different speeds (e.g., the primary is faster or the secondary is faster), and in different directions at the same or different speeds, and combinations and variations thereof. The primary and secondary laser beams can also be moved in predetermined independent patterns to build a particular type of item or to provide a particular type of functionality to a built item.

The primary laser beam pattern can have one, two, three, four or more, and ten or more laser beams. The secondary laser beam pattern can be a single beam, multiple laser beams, or multiple overlapping laser beams, and combinations and variations thereof.

The primary laser beam cross-section can be circular, elliptical, square or other shaped. The primary laser beam pattern can be arranged linearly in a square configuration, a rectangular configuration, a circular configuration, an elliptical configuration, a parabolic configuration (convex or concave with respect to the motion of the pattern), an arch (convex or concave with respect to the motion of the pattern), an arrow or "V" configuration, a diamond configuration, as well as other geometric patterns and configurations and combinations and variations thereof.

In embodiments, the secondary pattern can range from 1 to N sources arranged in a 1D or 2D pattern, such as high intensity visible light, UV or IR lamps imaged through a spatial light modulator, or high power lasers imaged through a spatial light modulator or a laser array. The secondary laser array can be a laser diode array or a fiber array coupled to a separate laser system.

2-D Patterning System

A preferred embodiment uses two-dimensional (2D) fiber bundles or laser arrays as the heat or energy source when printing metal parts. Examples of several 2-D fiber bundles and the laser patterns or multi-spot images they produce are illustrated in FIGS. 8D-8F . FIG. 8F is an image of a square spot formed from an array of square or rectangular optical fibers, or other optical devices shaping the beam to provide these spots. In an embodiment, a variation from the 1-D patterning system and the 2-D patterning system embodiments is the addition of more fiber rows to the printer head (compare FIGS. 8D and 8E ) and a larger addressable area. These 2-D sources can have individual laser power levels of 3 W, 10 W, 20 W, 100 W, 150 W, about 50 W to about 2 kW, about 250 W to about 1 kW, and several kW, depending on the scan speed of the printer system and the size of the printed pattern.

The 2-D patterning system can also be combined with a single secondary laser source, an array of secondary laser sources or a bundle of secondary laser sources and combinations and variations thereof to provide energy for preheating or controlled cooling of the pattern to be printed. In an embodiment, a high power image on a powder layer can be overlaid on a single secondary layer. Referring to FIGS. 9A-9F , plan views of embodiments of composite images of a primary image and a secondary image are illustrated. The direction of travel of the primary and secondary beam patterns is indicated by arrows in each drawing.

Figure 9a illustrates an embodiment of a rectilinear 1-D multi-spot primary image angled with respect to the direction of movement and complete with a circular secondary image.

Figure 9b illustrates an embodiment of a first image, which is a tilted array 1-D image with dead space between each spot compensated for by the tilt angle of the spots, and a single second image provided by a second laser source to preheat the powder prior to fusion. In this embodiment, the second image is adjacent to, but not overlapping with, the first beam pattern.

Figure 9c illustrates an embodiment of a simple linear array primary image overlaid with a rectangular secondary laser image to provide both preheat and post-fusion energy to control temperature through the build sequence.

Figure 9d illustrates an embodiment of a spaced 2-D array pattern overlapped by a single elliptical secondary laser spot to provide the energy required for a given scan rate to bring the temperature of the powder just below the melting temperature and provide a means to anneal the material after welding.

Figure 9e illustrates an embodiment of a 2-D primary image from a high-density fiber array with a single preheat beam image from a secondary laser source adjacent to and in front of the primary image.

Figure 9f illustrates an embodiment of a 2-D primary image from a dense array of adjacent square fibers. In the embodiment, the squares are overlapped to minimize the processing gap. This dense array pattern is overlapped by a secondary laser source for the purpose of preheating the powder, providing additional energy during the melting and bonding steps, and finally providing some temperature control after the melting and fusion steps.

In the embodiments of FIGS. 9A-9F and other embodiments of the secondary laser pattern and image, these secondary laser sources for the secondary image pattern can have powers of, for example, about 2 Watts, about 3 Watts, about 10 Watts, about 20 Watts, about 50 Watts, about 100 Watts, about 150 Watts, about 50 Watts to about 2 kW, about 10 Watts to about 200 W, about 50 Watts to about 500 W, about 250 Watts to about 1 kW and several kW, depending on the scan speed of the print head, the power of the primary laser beam and the size of the area to be heated.

Combining a fiber bundle primary laser source with a fiber bundle secondary source allows for the preheat and cool temperature cycles to be varied while the object is being built. Thus, the preheat and cool process cycles can be varied, for example adapted, to suit the conditions of the build item being built. In this way, information about the properties of the build item, such as temperature, roughness, density, and spectrum of emitted or reflected light, can be used to vary and adjust the secondary fiber laser beam properties, such as on-time and power, thereby "on-the-fly" adjusting the secondary image with respect to both the build of the item and the subsequent build. Figures 10A-10F illustrate different configurations and timing effects that are possible when overlaying an addressable secondary preheat pattern with an addressable laser image pattern. Another advantage of laser preheating is that it is not necessary to heat an entire layer or chamber, which uses significant amounts of energy.

Temperature control system

Prior to the present invention, conventional additive manufacturing systems operated in an open-loop fashion, which did not allow for precise control of the print quality. This was a significant shortcoming of these prior systems, and is what embodiments of the present invention seek to address and improve. In embodiments of the present invention, a feedback loop is used to precisely control the temperature of each 1-D or 2-D pattern, as well as the secondary laser patterns and powder layers through which these patterns are delivered. This feedback loop provides many advantages, including, for example, that the built parts have lower porosity, lower defects, and better surface roughness than an open-loop system can achieve. Since the gantry system moves relatively slowly compared to a galvanometer-based system, it is possible to measure the temperature of the powder layer at every point in the print pattern and to make real-time, much more optimal changes during the print process based on the temperature profile of the article as the power setting of the laser processing that area of the print pattern is adjusted. In embodiments, the temperature profile of the layer is monitored and controlled on a laser spot-by-laser-spot basis, and then the power, timing, and both of the laser spots are adjusted to control the build process of the article. Figure 11 illustrates how an image (1101) of a fiber bundle can be re-imaged (1103) onto a camera sensor array (1102). Software for reading the sensor array can recognize the heated regions and provide an average temperature for each region. If all laser sources are of equal power, the center pixel will read a much higher temperature than the output pixels and power to the inner source can be reduced until a uniform temperature profile is achieved. This allows the powder to melt and fuse within an optimal temperature range. This applies to 1D fiber bundle images as well as 2D fiber bundle images. Once the temperature of the regions is measured, a series of command signals are calculated (1204-1210) to increase and decrease the power to each region until a uniform or predetermined optimal temperature profile is achieved, as shown in Figure 12. Thus, the image (1201) of the array or fiber bundle on the powder layer is imaged to a device for analysis by an image sensor, such as a camera, such as a FLIR camera. This provides a matrix (1202) of temperature profiles on a pixel-by-pixel basis. A processor, e.g., a computer, microprocessor, interpolates and transforms the temperature profile from the matrix (1202) in conjunction with the build program, and adjusts the laser power to meet the build strategy by sending control signals (1204-1210) to the lasers associated with the individual fibers or to the images generated by these lasers. In this way, on-the-fly adjustments of the laser beam and build profile are provided. In addition, real-time feedback signals are provided to the laser source so that if the powder is not melted properly, power to that area can be increased to increase the likelihood of melting it properly. This occurs in areas where there is a large variation in the diameter of the powder, where larger diameter powders require more energy to melt than smaller diameter powders. This is also important to prevent the smaller diameter powders from vaporizing, so that real-time temperature feedback to the laser source can be used to adjust the average area temperature sufficient to melt the larger powder particles but insufficient to vaporize the smaller powder particles.

Examples of systems, processes, configurations and methods of embodiments of the present systems and methods are set forth in Table 1.

Furthermore, general embodiments of the present invention relate to combinations of laser beams, systems for making such combinations, and processes for utilizing the combined beams. In particular, the present invention relates to arrays, assemblies, and devices for combining laser beams from multiple laser beam sources into one or more combined laser beams. These combined laser beams preferably preserve, improve, or preserve and improve various aspects and characteristics of the laser beams from the individual sources.

Embodiments of the present array assemblies and the combined laser beams they provide may find wide application possibilities. Embodiments of the present array assemblies are compact and durable. Embodiments of the present array assemblies may be applied in welding, additive manufacturing including 3D printing; additive manufacturing - milling systems, for example, additive and subtractive manufacturing; astronomy; meteorology; imaging; projection including entertainment; medicine including dentistry, and the like.

Although this disclosure focuses on blue laser diode arrays, it should be understood that these embodiments are only illustrative of the types of array assemblies, systems, processes, and combined laser beams contemplated by the present invention. Accordingly, embodiments of the present invention include array assemblies for combining laser beams from a variety of laser beam sources, such as solid-state lasers, fiber lasers, semiconductor lasers, as well as other types of lasers, and combinations and variations thereof. Embodiments of the present invention include combinations of laser beams across all wavelengths, for example, laser beams having wavelengths ranging from about 380 nm to 800 nm (e.g., visible light), from about 400 nm to about 880 nm, from about 100 nm to 400 nm, from 700 nm to 1 mm, and combinations and variations of specific wavelengths within these various ranges. Embodiments of the present arrays may also find application in microwave coherent radiation (e.g., wavelengths greater than about 1 mm). Embodiments of the present arrays may combine beams from one, two, three, tens, or hundreds of laser sources. These laser beams can range in power from a few milliwatts to several watts or even several kilowatts.

An embodiment of the present invention preferably comprises an array of blue laser diodes configured to generate a high-brightness laser source. Such a high-brightness laser source can be used to directly process a material, i.e., mark, cut, weld, braze, heat treat, or anneal the material. The material to be processed, e.g., a starting material or a target material, can include any material or component or composition, including but not limited to, thin film transistors (TFTs), 3D printing starting materials, metals including gold, silver, platinum, aluminum and copper, plastics, tissues and semiconductor components such as semiconductor wafers. Direct processing can include, for example, removing gold from electronic products, projection displays and laser light shows.

Embodiments of the present high brightness laser source can also be used to pump a Raman laser or an anti-Stokes laser. The Raman medium can be a fiber optic device or a crystal such as diamond, KGW (potassium gadolinium tungstate, KGd( _WO4 ) ₂ ), _YVO4 and Ba( _NO3 ) ₂ . In an embodiment, the high brightness laser source is a blue laser diode source, which is a semiconductor device operating in the wavelength range of 400 nm to 500 nm. The Raman medium is a brightness converter and can enhance the brightness of the blue laser diode source. The brightness enhancement can extend along the wavelength up to any manner that produces a beam having an ^M2 of about 1 and 1.5, i.e., a single mode, diffraction limited source, i.e., a beam parameter product of less than 1, less than 0.7, less than 0.5, less than 0.2 and less than 0.13 mm-mrad.

In an embodiment, "n" or "N" (e.g., tens, hundreds or more) laser diode sources may be configured in a fiber optic bundle to enable an addressable light source for marking, melting, welding, ablating, annealing, heat treating, cutting materials and combinations and modifications thereof in several laser operations and procedures.

An embodiment of a laser system has an addressable laser delivery configuration. The system has an addressable laser diode system. The system provides independently addressable laser beams to a plurality of fibers (more or fewer fibers and laser beams are contemplated). The fibers are combined into a fiber bundle contained within a protective tube or cover. The fibers of the fiber bundle are fused together to form a printing head including an optical assembly that focuses the laser beam along a beam path and directs the laser beam to a target material. The printing head and powder hopper thus move in a positive direction with the movement of the printing head. Additional material may be placed over the fused material each time the printing head or hopper passes. Since the printing head is bi-directional and fuses material in both directions as the printing head moves, the powder hopper operates behind the printing head to provide build-up material to be fused in the next pass of the laser printing head.

An "addressable array" means that one or more of the following: the powder; the duration of the shots; the order of the shots; the location of the shots; the power of the beams; the shape of the beam spot as well as the focal length (e.g., the penetration depth in the z direction) can be independently varied, controlled and predetermined or that each laser beam of each fiber can provide a precise and predetermined delivery pattern that can produce a very precise end product (e.g., a build material) from the target material. Embodiments of the addressable array can also have the ability for individual beams and laser stops generated by those beams to perform various predetermined precise laser operations such as annealing, ablation and melting.

The following examples are provided to illustrate various embodiments of the laser arrays, systems, devices, and methods of the present invention. These examples are for illustrative purposes only and are not intended to, and should not be construed as, limiting the scope of the present invention.

Example 1

An array of blue laser diodes spatially combined to create a single spot in the far field that can be coupled to a solar-resistant optical fiber for transmission to a workpiece.

Example 2

An array of blue laser diodes as described in Example 1, which are combined polarized beams to increase the effective brightness of the laser beam.

Example 3

An array of blue laser diodes having a space between each collimated beam in the fast axis of the laser diodes in combination with a periodic plate that reflects the first laser diode(s) and transmits the second laser diode(s) to fill the space between the laser diodes in the fast direction of the first array.

Example 4

Patterned mirror on a glass substrate used to achieve space filling of example 3.

Example 5

A patterned mirror on one side of a glass substrate to achieve space filling of Example 3, wherein the glass substrate has a thickness sufficient to shift the vertical position of each laser diode to fill the void space between the individual laser diodes.

Example 6

Step heat sinks performing space filling of Example 3 and pattern mirrors as described in Example 4.

Example 7

An array of blue laser diodes as described in Example 1, wherein each individual laser is locked to a different wavelength by an external cavity, thereby increasing the brightness of the array to substantially the equivalent brightness of a single laser diode source.

Example 8

An array of blue laser diodes as described in Example 1, wherein individual arrays of laser diodes are locked to a single wavelength using an external cavity based on a grating, and each array of laser diodes is combined into a single beam using narrowly spaced optical filters or gratings.

Example 9

An array of blue laser diodes as described in Example 1 used to pump a Raman converter such as an optical fiber having a pure fused silica core and a fluorinated outer core containing blue pump light to produce a higher brightness source.

Example 10

An array of blue laser diodes as described in Example 1 used to pump a Raman converter such as an optical fiber having a GeO ₂ doped central core with outer cores larger than the central core to contain the outer core and blue pump light to generate a higher brightness source.

Example 11

An array of blue laser diodes as described in Example 1 used to pump a Raman converter such as an optical fiber having _{a P2O5 doped} core and an outer core larger than the central core to contain the blue pump light to generate a higher brightness source.

Example 12

An array of blue laser diodes as described in Example 1 used to pump a Raman converter such as an optical fiber having a graded index core and an outer core larger than the central core to contain blue pump light to produce a higher brightness source.

Example 13

An array of blue laser diodes as described in Example 1 used to pump a Raman converter fiber with a graded index GeO ₂ doped core and an external step index core.

Example 14

An array of blue _laser diodes as described in Example 1 used to pump a Raman converter fiber with graded index _P2O5 doped core and external step-index core.

Example 15

An array of blue laser diodes as described in Example 1 used to pump a Raman converter fiber with a graded index GeO ₂ doped core.

Example 16

An array of blue _laser diodes as described in Example 1 used to pump a Raman converter fiber with graded index _P2O5 doped core and external step-index core.

Example 17

Other embodiments and variations of the embodiment of Example 1 are contemplated. An array of blue laser diodes as described in Example 1 used to pump a Raman converter such as diamond to produce a higher brightness laser source. FIG. 13 illustrates an image (1301) and a spectrum (1302) of a blue Raman converted laser beam from a diamond chip and a wavelength shift from 450 nm to 478 nm. An array of blue laser diodes as described in Example 1 used to pump a Raman converter such as KGW to produce a higher brightness laser source. An array of blue laser diodes as described in Example 1 used to pump a Raman converter such as YVO ₄ to produce a higher brightness laser source. An array of blue laser diodes as described in Example 1 used to pump a Raman converter such as Ba(NO ₃ ) ₂ to produce a higher brightness laser source. An array of blue laser diodes as described in Example 1 used for pumping a high pressure gas Raman converter to produce a higher brightness laser source. An array of blue laser diodes as described in Example 1 used for pumping a rare earth doped crystal to produce a higher brightness laser source. An array of blue laser diodes as described in Example 1 used for pumping a rare earth doped fiber to produce a higher brightness laser source. An array of blue laser diodes as described in Example 1 used for pumping an outer core of a brightness converter to produce a higher brightness enhancement ratio.

Example 18

An array of Raman converted lasers operating at individual wavelengths and combined to produce higher power sources while preserving the spatial brightness of the original sources.

Example 19

Raman fibers and filters having dual cores, fiber Bragg gratings, means for suppressing second-order Raman signals in a high-brightness central core by using differences in V numbers for first- and second-order Raman signals or differences in micro-bend losses.

Example 20

N laser diodes with N > 1 that can be individually turned on and off and imaged onto a powder layer to melt and fuse the powder into unique components.

Example 21

An array of N laser diodes, wherein N ≥ 1 of Example 1, wherein the outputs can be fiber coupled and each fiber can be arranged in a linear or non-linear manner to image or focus onto the powder, thereby creating an addressable array of high power laser beams capable of melting or fusion of the powder layer by layer into a unique shape.

Example 22

An array of one or more laser diodes combined via a Raman converter whose output can be fiber coupled and each fiber arranged in a linear or non-linear manner to form an addressable array of N > 1 high power laser beams that can be imaged or focused onto the powder to melt or fuse the powder layer by layer into a unique shape.

Example 23

An x-y motion system capable of transporting N > 1 blue laser sources across a powder layer while melting and fusing the powder layer with a powder delivery system positioned behind the laser source to provide a new layer of powder behind the fused layer.

Example 24

A z-motion system capable of increasing/decreasing the height of the part/powder layer of Example 20 after a new powder layer is placed.

Example 25

The z-motion system can increase/decrease the height of the part/powder of Example 20 after the powder layer is fused by the laser source.

Example 26

Bidirectional powder placement capability for example 20 where the powder is placed directly behind the laser spot(s) as they move in the positive x-direction or negative x-direction.

Example 27

Bidirectional powder placement capability of Example 20, where the powder is placed directly behind the laser spot(s) as it moves in the positive y direction or negative y direction.

Example 28

Powder supply system coaxial with N laser beam where N > 1.

Example 29

A powder supply system in which powder is gravity fed.

Example 30

A powder supply system in which the powder is entrained in an inert gas flow.

Example 31

A powder supply system crossing an N laser beam where N > 1 and the powder is placed by gravity directly in front of the laser beam.

Example 32

A powder supply system traversing an N laser beam, where N > 1 and the powder is entrained in an inert gas flow intersecting the laser beam.

Example 33

For example, a second harmonic generation system that uses the output of a Raman converter at 460 nm and produces light at half the wavelength of the source laser, or 230 nm, using an external resonant double crystal such as a KTP, but which does not allow short-wavelength light to propagate through the fiber.

Example 34

For example, a third harmonic generation system that uses an external resonant double crystal using the output of a Raman converter at 460 nm, but which does not allow shorter wavelength light to propagate through the optical fiber, to produce light at 115 nm.

Example 35

For example, a fourth harmonic generation system that uses an external resonant double crystal using the output of a Raman converter at 460 nm, but which does not allow shorter wavelength light to propagate through the optical fiber, to produce light at 57.5 nm.

Example 36

A second harmonic generation system that uses an external resonant double crystal to generate light at half the wavelength of the source, or 236.5 nm, using the output of a rare-earth doped brightness converter such as thulium that lasers at 473 nm when pumped by a blue laser diode array at 450 nm, but does not allow short-wavelength light to propagate through the optical fiber.

Example 37

A third harmonic generation system using an external resonant double crystal, using the output of a rare-earth doped brightness converter such as thulium that lasers at 473 nm when pumped by a blue laser diode array at 450 nm, but which produces light at 118.25 nm, which does not allow shorter wavelength light to propagate through the optical fiber.

Example 38

A fourth harmonic generation system using an external resonant double crystal, using the output of a rare-earth doped brightness converter such as thulium that lasers at 473 nm when pumped by a blue laser diode array at 450 nm, but which produces light at 59.1 nm, which does not allow shorter wavelength light to propagate through the optical fiber.

Example 39

Any other rare-earth doped fibers and crystals that can be pumped by a high-power 450 nm source to produce visible or near-visible output can be used in Examples 34 to 38.

Yes 40

High-power visible light is fired into the non-circular outer core or clad to pump the inner core of the Raman or rare-earth doped core fiber.

Example 41

Use of polarization-maintaining fibers to enhance the gain of a Raman fiber by aligning the polarization of the pump with that of the Raman generator.

Example 42

An array of blue laser diodes as described in Example 1 used to pump a Raman converter, such as an optical fiber, structured to produce a higher brightness source of a particular polarization.

Example 43

An array of blue laser diodes as described in Example 1 used to pump a Raman converter such as an optical fiber structured to generate a higher brightness source of a particular polarization and to maintain the polarization state of the pump source.

Example 44

An array of blue laser diodes as described in Example 1 used to pump a Raman converter such as an optical fiber to produce a higher brightness source having a non-circular outer core structured to improve Raman conversion efficiency.

Example 45

Embodiments of examples 1 to 44 may also include one or more of the following components or assemblies: a device for flattening the powder at the end of each pass before the laser is scanned over the powder layer; a device for scaling the output power of the laser by combining multiple lower power laser modules through a fiber combiner to produce a higher power output beam; a device for scaling the output power of a blue laser module by combining multiple lower power laser modules through free space to produce a higher power output beam; a device for combining multiple laser modules on a single baseplate with built-in cooling.

It is noted that it is not necessary to provide or address the theory underlying the new and innovative process, material, performance, or other advantageous features and characteristics of the embodiments of the present invention or related thereto. Nevertheless, various theories are provided herein to further advance the art in this field. The theories presented herein do not in any way limit, restrict, or narrow the scope of protection provided to the claimed invention unless expressly stated otherwise. These theories are not required or practiced to utilize the present invention. It is also understood that the present invention may lead to new and heretofore unknown theories to explain the function-features of the embodiments of the methods, articles, materials, devices, and systems of the present invention; and such theories developed later do not limit the scope of protection provided by the present invention.

It should be understood that the use of headings in this specification is for clarity and is not intended to be limiting in any way. Accordingly, the processes and disclosures described under the headings should be read in the context of this specification as a whole, including the various examples. The use of headings in this specification should not limit the scope of protection afforded to the invention.

The various embodiments of the lasers, diodes, arrays, modules, assemblies, activities, and operations described herein can be used in a variety of other activities and fields in addition to those described herein. Among other things, embodiments of the present invention can be used with the methods, devices, and systems of Patent Application Publication Nos. WO 2014/179345, 2016/0067780, 2016/0067827, 2016/0322777, 2017/0343729, 2017/0341180, and 2017/0341144, the entire disclosures of each of which are herein incorporated by reference. Additionally, for example, these embodiments can be used with other equipment or activities that may be developed in the future; and with existing equipment or activities that may be modified in part in accordance with the teachings herein. Furthermore, the various embodiments described herein can be used in different and various combinations with one another. Thus, for example, the configurations provided in the various embodiments of the present disclosure can be used together with each other. For example, the components of the embodiment having A, A' and B and the components of the embodiment having A'', C and D can be used together with each other in various combinations, for example, A, C, D and A, A'', C and D, etc., according to the teachings of the present disclosure. Therefore, the scope of protection provided by the present disclosure should not be limited to the configurations or arrangements described in the specific embodiments, the specific embodiments and examples, or the embodiments of the specific drawings.

The present invention may be embodied in other forms than those specifically disclosed herein without departing from the spirit or essential characteristics of the present invention. The described embodiments are to be considered in all respects as illustrative only and not restrictive.

Claims (87)

An additive manufacturing system for providing multi-spot 1-D images, multi-spot 2-D images, or both, to a powder layer,
A light source in optical communication with a plurality of optical fiber arrays to transmit a multi-spot image, a controller for monitoring each spot of the multi-spot image of the powder layer, and a printer head,
The controller has a program having a predetermined sequence to deliver a light source in optical communication with a plurality of optical fiber arrays at predetermined locations on the target material,
The printer head includes a thermal imaging optical system in optical communication with one end of the optical fiber array, a reimaging optical device, and a thermal imaging camera system;
The optical fiber array is in optical communication with a reimaging optical device,
The reimaging optical device is configured to image a multi-spot image received from the light source onto the surface of the powder layer,
The thermal imaging optical system controls the temperature of the powder layer in the area exposed to the image of the light source by providing a control signal, thereby controlling the multi-spot image formed on the surface of the powder layer.
The multi-spot image formed on the surface of the powder layer has sufficient power density to fuse and build parts from the powder,
The control signal comprises a signal proportional to the temperature of the powder layer, or a signal proportional to the temperature of a melt puddle generated from each spot image among the multi-spot images shaped on the surface of the powder layer.
Additive manufacturing system. In paragraph 1,
The light source comprises a plurality of optical fibers coupling light from a fiber Raman laser array operating in the wavelength range of 300 nm to 500 nm.
Additive manufacturing system. In paragraph 1,
The light source comprises a laser diode array operating in a wavelength range of 360 nm to 550 nm.
Additive manufacturing system. In paragraph 1,
The light source comprises a plurality of optical fibers coupled to laser diodes operating in the wavelength range of 360 nm to 550 nm.
Additive manufacturing system. delete delete In paragraph 1,
A fiber array is a bundle of fibers mounted on a single QBH connector.
Additive manufacturing system. In paragraph 1,
A fiber array is made up of individual fibers mounted independently.
Additive manufacturing system. In paragraph 1,
Includes a high-resolution thermal imaging camera to directly monitor the temperature at each spot during operation and provide feedback signals to a microprocessor that controls power to each spot to control the build quality of the part on a spot-by-spot basis.
Additive manufacturing system. In paragraph 1,
Including an array of pyrometers to directly monitor the temperature at each spot during operation and provide feedback signals to a microprocessor that controls power to each spot to control the build quality of the part on a spot-by-spot basis.
Additive manufacturing system. In paragraph 1,
The printer head is mounted on an xy gantry system to translate a 1-D or 2-D image across the surface of the powder layer.
Additive manufacturing system. In paragraph 1,
Including a gravity fed powder delivery system that operates in both directions;
Additive manufacturing system. In paragraph 1,
Including a rotating wheel moving in the opposite direction to the direction of movement of the hopper to reduce the porosity of the powder layer by compacting and densifying the powder.
Additive manufacturing system. delete delete In paragraph 1,
Including a blue laser source to fuse copper powder,
Additive manufacturing system. In paragraph 1,
Including a blue laser source to fuse gold powder,
Additive manufacturing system. In paragraph 1,
Containing a blue laser source for fusing aluminum powder;
Additive manufacturing system. In paragraph 1,
Contains a blue laser source for fusing all metals and metal alloys.
Additive manufacturing system. delete In paragraph 1,
The reimaging optical device is,
A collimator, which may be a plano-convex lens, a plano-convex aspheric lens, a double or triple lens pair; and
A focusing optical device comprising a plano-convex lens and a plano-convex aspherical lens,
The light source is 1f from the collimating lens and 1f from the focusing lens.
Additive manufacturing system. In paragraph 1,
The reimaging optical device is,
a lens at least 2f away from the light source; and
Comprising a multi-spot image formed on the surface of the powder layer at least 2f away from the lens in the opposite direction,
Additive manufacturing system. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete In paragraph 1,
The additive manufacturing system includes an optical coherence tomography (OCT) system to monitor the building of the parts in real time.
Additive manufacturing system. delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete delete In paragraph 1,
The thermal imaging optical system of the printer head is
A collimator, which may be a plano-convex lens, a plano-convex aspheric lens, a double or triple lens pair; and
A focusing optical device comprising a plano-convex lens and a plano-convex aspherical lens,
The light source is 1f from the collimating lens and 1f from the focusing lens.
Additive manufacturing system. In paragraph 1,
The thermal imaging optical system of the printer head is a reimaging optical device having a light source at least 2f away from the collimating lens and an image at least 2f away from the focusing lens in the opposite direction.
Additive manufacturing system. delete delete delete delete delete In paragraph 1,
Including multiple gantries to print images that are part of the part.
Additive manufacturing system. In paragraph 1,
An optical system comprising multiple gantries and configured to combine multiple image sources to produce a larger continuous image.
Additive manufacturing system. In paragraph 1,
Including multiple gantries to print images in a checkboard fashion, which are fused together by step-by-step repetition of the gap pattern.
Additive manufacturing system. In paragraph 1,
The light source is a number of lasers,
By further including a controller and camera system to monitor each spot of the multi-spot image of the powder layer, thereby providing control signals in real time to the controller for each laser among the plurality of lasers to control melting and fusion of the powder to optimize surface roughness, porosity and stress in the resulting part.
Additive manufacturing system. delete delete