Additive manufacturing system using pulsed laser for 2D printing

Abstract

The present disclosure relates to an additive manufacturing system for two-dimensional printing using a pulsed-modulated laser. An additive manufacturing method is disclosed. The method can include providing a powder bed and directing a sequence of shaped laser beam pulses composed of one or more pulses and having a flux greater than 20 kW / cm<supgt;2< / supgt; at a defined two-dimensional region of the powder bed. This minimizes adverse laser plasma effects during the process of melting and fusing the powder within the defined two-dimensional region.

Description

[0001] This application is a divisional application of an application filed on December 19, 2019, with application number 201980084795.X, and invention name “Additive manufacturing system for two-dimensional printing using pulse-modulated laser”.

[0002] Cross-references to related patent applications

[0003] The present disclosure is a part of a non-provisional patent application claiming the benefit of priority to U.S. Patent Application No. 62 / 781,996, filed on December 19, 2018, which is incorporated by reference in its entirety. Technical Field

[0004] The present disclosure relates generally to additive manufacturing, and more particularly to powder bed fusion additive manufacturing using high throughput lasers with controllable pulse shape and timing for two-dimensional printing. background

[0005] Traditional component machining typically relies on removing material through drilling, cutting or grinding to form a part. In contrast, additive manufacturing, also known as three-dimensional (3D) printing, typically involves the sequential layer-by-layer addition of material to build a part.

[0006] In a high throughput embodiment, a high flux laser beam can be used to melt two-dimensional regions or "tiles" from a layer of metal or other material powder. However, higher peak powers in the optical train equate to an increased risk of laser damage to the optics.

[0007] Another problem with standard high-flux pulse trains for powders is related to the generation of plasma and its rapid volume expansion. As the plasma maintains its volume and expands its volume, shock waves are generated, which push a large amount of powder around the printing (or laser irradiation) area away into the surrounding area. In practice, this chain reaction of laser beam irradiation, plasma generation, plasma maintenance and expansion, shock wave propagation, and powder movement degrades the quality of the printing process.

[0008] This is particularly a problem for additive manufacturing systems based on high-power powder bed fusion. Typical conventional powder bed fusion additive manufacturing systems currently available use a single laser beam with a power of approximately 300W to 1000W and a focused beam diameter of 50 micrometers (50um) to 100um. This corresponds to only about a few MW / cm 2 Laser power flux (for example, a 1000W circular laser beam with a focus diameter of 100um has [1000W / (π*(0.005cm)^2)] = 12.74MW / cm 2Flux), which is enough to melt the metal powder and boil it, but not to the energy density that could possibly generate and sustain a plasma. In addition, due to the small melt volume, any plasma-induced effects are small. Typically, droplets of metal spurts are seen in the printing process of conventional systems, but there is little or no plasma-induced shock wave to push the powder around the print area (plasma-induced shock waves pushing the powder around the print area causes the "Halo effect" that seriously and negatively affects the printing process).

[0009] When using a high power flux laser beam to rapidly melt and solidify the powder layer within the print area, improved processes and systems are needed to prevent unacceptable halo effects. In some cases, useful laser beam power fluxes for 2D powder bed fusion based additive manufacturing systems can range from tens to hundreds of kW / cm 2 Even to GW / cm 2 Unfortunately, in an argon environment, these levels of laser power flux are typically sufficient to generate and sustain a plasma that pushes away powder particles during fabrication to form an unacceptable halo.

[0010] Fortunately, damage to optics and unwanted plasma generation can be reduced or mitigated through proper pulse shaping and timing of high-flux lasers.

[0011] Overview

[0012] In one embodiment of the additive manufacturing method, a powder bed of metal, ceramic, polymer or other material is provided. A pulse comprising one or more pulses having a power of greater than 20 kW / cm is directed at a defined two-dimensional region or "tile" of the powder bed. 2A shaped laser beam pulse train of a flux. The energy is sufficient to melt and fuse the powder within a defined two-dimensional area. System parameters, laser parameters, optical parameters, and powder material parameters are set in some cases so that less than 10% of the powder particles by weight are ejected into an area outside the defined two-dimensional area, in other cases, less than 20% of the powder particles by weight are ejected into an area outside the defined two-dimensional area, in other cases, less than 40% of the powder particles by weight are ejected into an area outside the defined two-dimensional area, in other cases, less than 80% of the powder particles by weight are ejected into an area outside the defined two-dimensional area, in other cases, less than 90% of the powder particles by weight are ejected into an area outside the defined two-dimensional area, in other cases, less than 95% of the powder particles by weight are ejected into an area outside the defined two-dimensional area, and in other cases, less than 99% of the powder particles by weight are ejected into an area outside the defined two-dimensional area.

[0013] In some embodiments, the shaped laser beam pulse sequence is provided by a system including an arbitrary pulsed laser source, at least one preamplifier, and at least one power amplifier. The laser flux can be set at 200 kW / cm 2 Up to 10GW / cm 2 and the defined two-dimensional area of ​​the powder bed was chosen to be between 0.000025 cm 2 Up to 1,000cm 2 In some embodiments, the thickness of the powder layer on the powder bed is between at least one of the range of 1 μm-2000 μm, the range of 25 μm-250 μm, and the range of 50 μm-100 μm. 2 When the pulsed laser intensity is greater than 20 kW / cm, the diameter of the powder used is less than 100,000 um, and in the selected embodiment, the diameter of the powder used is less than 100,000 um. 2 The pulse intensity is 1000 μm and the diameter of the powder used is less than 500 μm.

[0014] In another embodiment, dynamic adjustment of the system can be achieved by providing a calibration step, which includes adjusting at least one of the laser beam energy, pulse width, or area of ​​the defined two-dimensional area in response to the detection area of ​​the halo formed by the preliminary halo test. The pulse shape, number of pulses, or pulse peak power can also be adjusted according to time in response to the detection area of ​​the halo formed by the preliminary halo test. Typically, the radius of the halo is set to exceed the defined two-dimensional area by more than 50 microns. In other embodiments, the radius of the halo is set to exceed the defined two-dimensional area by more than 10 microns. In other embodiments, the radius of the halo is set to exceed the defined two-dimensional area by more than 1 micron.

[0015] In one embodiment, the laser temporal pulse width is between 20 nanoseconds and 100 microseconds. A laser pulse train with a pulse number greater than or equal to one (1) may be used, and the laser pulse peak power may be adjusted over time.

[0016] In another embodiment, a laser system for two-dimensional printing includes a laser pulse signal source and one or more preamplifier modules to receive a laser beam and direct it to an optical isolation device. One or more amplifier modules can be positioned to receive a laser beam from the optical isolation device and direct the laser beam to a defined two-dimensional region of a powder bed. The laser pulse signal source can provide at least one of a square wave, a ramp, or a pulse train, and the optical isolation device can include at least one of a Pockels cell, a Faraday rotator, a Faraday isolator, an acousto-optic reflector, or a volume Bragg grating.

[0017] In another embodiment, the laser control method includes the step of directing a laser pulse signal source to a preamplifier module and an optical modulator or an isolator to provide a first laser beam. The first laser beam can be directed to the amplifier module to provide a laser beam including one or more pulses and having a power greater than 20 kW / cm 2 A shaped laser beam pulse sequence with a flux of 200 kW / cm 2 Up to 10GW / cm 2 The laser pulse width can be set in the range of 20 nanoseconds to 100 microseconds. A laser pulse sequence with a pulse number greater than one (1) can be used, and the laser pulse peak power can be adjusted according to time. 2 Up to 1,000cm 2 A shaped laser beam pulse sequence is guided at the two-dimensional region between.

[0018] In one embodiment, a shaped laser beam pulse sequence may be directed at an additive manufacturing station. For example, a shaped laser beam pulse sequence may be directed at a defined two-dimensional region of an additive manufacturing powder bed to melt and fuse metal or other powder within the defined two-dimensional region.

[0019] In one embodiment, a method of additive manufacturing includes providing an enclosure surrounding a powder bed, and the enclosure having an atmosphere including at least 50% inert gas, optionally at a pressure greater than atmospheric pressure. A pressure greater than 20 kW / cm2 may be directed at a defined two-dimensional region of the powder bed. 2 A laser beam of a certain flux is used to melt and fuse the powder within a defined two-dimensional area.

[0020] In one embodiment, the additive manufacturing method includes providing an enclosure surrounding a powder bed, the enclosure having an atmosphere including at least 50% inert gas, optionally at a pressure below atmospheric pressure. A pressure greater than 20 kW / cm2 may be directed at a defined two-dimensional region of the powder bed. 2 A laser beam of a certain flux is used to melt and fuse the powder within a defined two-dimensional area.

[0021] In one embodiment, the atmosphere may contain at least one of the following: Ar, He, Ne, Kr, Xe, CO2, N2, O2, SF6, CH4, CO, N2O, C2H2, C2H4, C2H6, C3H6, C3H8, i-C4H10, C4H10, 1-C4H8, cic-2, C4H7, 1,3-C4H6, 1,2-C4H6 , C5H12, n-C5H12, i-C5H12, n-C6H14, C2H3Cl, C7H16, C8H18, C10H22, C11H24, C12H26, C13H28, C14H30, C15H32, C16H34, C6H6, C6H5-CH3, C8H10, C2H5OH, CH3OH and iC4H8.

[0022] This application also includes the following aspects:

[0023] 1) An additive manufacturing method, the method comprising:

[0024] Provide a powder bed;

[0025] Directing a pulse comprising one or more pulses having a power of greater than 20 kW / cm at a defined two-dimensional region of the powder bed 2 A shaped laser beam pulse sequence with a flux of

[0026] The powder is melted and fused within the defined two-dimensional region.

[0027] 2) The method according to 1), wherein less than 10% by weight of the powder particles are sprayed into an area outside the defined two-dimensional area.

[0028] 3) The method according to 1), wherein the shaped laser beam pulse sequence is provided by a system comprising an arbitrary pulsed laser source, at least one preamplifier and at least one power amplifier.

[0029] 4) The method according to 1), wherein, at the powder bed, the flux is 20 kW / cm 2 Up to 10GW / cm 2 between.

[0030] 5) The method according to 1), wherein the defined two-dimensional area of ​​the powder bed is within 0.000025 cm 2 Up to 1,000cm 2 between.

[0031] 6) According to the method of 1), the thickness of the powder bed is between at least one of the range of 1 μm-2000 μm, the range of 25 μm-250 μm and the range of 50 μm-100 μm.

[0032] 7) The method according to 1) further includes a calibration step, wherein the calibration step includes adjusting at least one of the laser beam energy, pulse width or the area of ​​the defined two-dimensional region in response to the detection area of ​​the halo formed by the preliminary halo test.

[0033] 8) The method according to 1) further includes a calibration step, wherein the calibration step includes adjusting at least one of the pulse shape, the number of pulses or the pulse peak power according to time in response to the detection area of ​​the halo formed by the preliminary halo test.

[0034] 9) The method according to 1) further comprises the step of detecting a halo area formed by a preliminary halo test, wherein the detected halo radius is set to exceed the defined two-dimensional area by more than 50 microns.

[0035] 10) The method according to 1), wherein less than 10 GW / cm 2 The pulsed laser intensity is 100,000 μm in diameter.

[0036] 11) The method according to 1), wherein a power of more than 20 kW / cm 2 The pulse intensity is 1000 μm and the diameter of the powder used is less than 500 μm.

[0037] 12) The method according to 1), wherein the laser temporal pulse width is between 20 nanoseconds and 100 microseconds.

[0038] 13) The method according to 1), wherein a laser pulse sequence having a pulse number greater than 1 is used.

[0039] 14) The method according to 1), wherein the laser pulse peak power is adjusted according to time.

[0040] 15) A laser system for two-dimensional printing, comprising:

[0041] Laser pulse signal source;

[0042] one or more preamplifier modules for receiving the laser beam and directing the laser beam to the optical isolation device; and

[0043] One or more amplifier modules for receiving the laser beam from the optical isolation device and directing the laser beam to a defined two-dimensional region of the powder bed.

[0044] 16) The laser system according to 15), wherein the laser pulse signal source is capable of providing at least one of a square wave, a ramp, an arbitrary predetermined pulse shape, or a pulse sequence.

[0045] 17) The laser system according to 15), wherein the optical isolation device can include at least one of a Pockels cell, a Faraday rotator, a Faraday isolator, an acousto-optic reflector or a volume Bragg grating.

[0046] 18) A laser control method comprising the following steps:

[0047] directing a laser pulse signal source to a preamplifier module and an optical modulator or an isolator to provide a first laser beam; and

[0048] The first laser beam is directed to an amplifier module to provide a laser beam comprising one or more pulses and having a power greater than 20 kW / cm at the point of use. 2 A shaped laser beam pulse sequence with a flux of .

[0049] 19) The method according to 18), wherein at the point of use, the flux is 20 kW / cm 2 Up to 10GW / cm 2 between.

[0050] 20) The method according to 18), wherein the laser time pulse width is between 20 nanoseconds and 100 microseconds.

[0051] 21) The method according to 18), wherein a laser pulse sequence with a pulse number greater than 1 is used.

[0052] 22) The method according to 18), wherein the laser pulse peak power is adjusted according to time.

[0053] 23) The method according to 18), wherein the size is 0.000025 cm 2 Up to 1,000cm 2 The shaped laser beam pulse sequence is directed at a two-dimensional region between.

[0054] 24) Method according to 18), wherein the sequence of shaped laser beam pulses is directed at a point of use in an additive manufacturing station.

[0055] 25) The method according to 18), wherein the sequence of shaped laser beam pulses is directed at a defined two-dimensional area of ​​an AM powder bed to melt and fuse the powder within the defined two-dimensional area.

[0056] 26) An additive manufacturing method, the method comprising:

[0057] An enclosure is provided surrounding the powder bed, and the enclosure has an atmosphere comprising at least one of the following: He, Ar, Ne, Kr, Xe, CO2, N2, O2, SF6, CH4, CO, N2O, C2H2, C2H4, C2H6, C3H6, C3H8, i-C4H10, C4H10, 1-C4H8, cic-2, C4H7, 1,3-C4H6, 1, 2-C4H6, C5H12, n-C5H12, i-C5H12, n-C6H14, C2H3Cl, C7H16, C8H18, C10H22, C11H24, C12H26, C13H28, C14H30, C15H32, C16H34, C6H6, C6H5-CH3, C8H10, C2H5OH, CH3OH and iC4H8;

[0058] Directing a pulse comprising one or more pulses having a power of greater than 20 kW / cm at a defined two-dimensional region of the powder bed 2 A shaped laser beam pulse sequence with a flux of

[0059] The powder is melted and fused within the defined two-dimensional region.

[0060] 27) The method according to 26), wherein the atmosphere is at least 1% helium by volume.

[0061] 28) The method according to 26), wherein the atmosphere in the housing is maintained at an absolute pressure between 0 bar and 100 bar.

[0062] 29) The method according to 26), wherein the atmosphere in the enclosure is maintained at a temperature between 20 degrees Kelvin and 5000 degrees Kelvin. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Non-limiting and non-exhaustive embodiments of the present disclosure are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various figures unless otherwise specified.

[0064] Figure 1A The powder layer before responding to the laser is shown;

[0065] Figure 1B Powder motion in response to laser-induced plasma is shown;

[0066] Figure 1C Powder movement in response to any pulse that prevents plasma formation is shown;

[0067] Figure 2 An apparatus for two-dimensional additive manufacturing with reduced plasma formation at high laser flux levels is shown.

[0068] Figure 3A-3C An example pulse of a high flux laser is shown; and

[0069] Figure 4 The modules of a system for providing a suitable pulse sequence are shown. Detailed Description

[0070] In the following description, reference is made to the accompanying drawings which form a part of the specification and in which are shown by way of illustration specific exemplary embodiments in which the present disclosure may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the concepts disclosed herein, and it is understood that the various disclosed embodiments may be modified and other embodiments may be utilized without departing from the scope of the present disclosure. Therefore, the following detailed description is not to be considered in a limiting sense.

[0071] An additive manufacturing system having one or more energy sources (including one or more laser beams or electron beams in one embodiment) is positioned to emit one or more energy beams. A beam shaping optical device can receive one or more energy beams from an energy source and form a single beam. An energy patterning unit receives or generates a single beam and transmits a two-dimensional pattern to the beam, and can reject unused energy that is not in the pattern. An image relay receives the two-dimensional patterned beam and focuses it as a two-dimensional image to a desired position on a highly fixed or movable building platform (e.g., a powder bed). In some embodiments, some or all of any rejected energy from the energy patterning unit is reused.

[0072] In some embodiments, multiple beams from a laser array are combined using a beam homogenizer. The combined beam can be directed to an energy patterning unit that includes a transmissive or reflective pixel addressable light valve. In one embodiment, the pixel addressable light valve includes a liquid crystal module with a polarizing element and a light projection unit that provides a two-dimensional input pattern. The two-dimensional image focused by the image relay can be sequentially directed to multiple locations on the powder bed to build a 3D structure.

[0073] The energy source produces photons (light), electrons, ions or other suitable energy beams or fluxes that can be guided, shaped and patterned. A variety of energy sources can be used in combination. The energy source can include a laser, an incandescent lamp, concentrated solar energy, other light sources, an electron beam or an ion beam. Possible laser types include, but are not limited to: a gas laser, a chemical laser, a dye laser, a metal vapor laser, a solid-state laser (e.g., an optical fiber), a semiconductor (e.g., a diode) laser, a free electron laser, a pneumatic laser, a "Nickel-like" Samarium Laser, a Raman laser or a nuclear pump laser.

[0074] The gas laser may include a laser such as a helium-neon laser, an argon laser, a krypton laser, a xenon ion laser, a nitrogen laser, a carbon dioxide laser, a carbon monoxide laser, or an excimer laser.

[0075] The chemical laser may include a laser such as a hydrogen fluoride laser, a deuterium fluoride laser, a COIL (chemical oxygen iodine laser), or an Agil (all gas phase iodine laser).

[0076] Metal vapor lasers may include lasers such as helium cadmium (HeCd) metal vapor lasers, helium mercury (HeHg) metal vapor lasers, helium selenium (HeSe) metal vapor lasers, helium silver (HeAg) metal vapor lasers, strontium vapor lasers, neon copper (NeCu) metal vapor lasers, copper vapor lasers, gold vapor lasers, or manganese (Mn / MnCl2) vapor lasers. Rubidium or other alkali metal vapor lasers may also be used. Solid-state lasers may include lasers such as ruby ​​lasers, Nd:YAG lasers, NdCrYAG lasers, Er:YAG lasers, neodymium YLF (Nd:YLF) solid-state lasers, neodymium-doped yttrium vanadate (Nd:YVO4) lasers, neodymium-doped calcium borate yttrium oxide Nd:YCa4O(BO3) lasers. 3Or abbreviated as Nd:YCOB, neodymium glass (Nd:glass) laser, titanium sapphire (Ti:sapphire) laser, thulium YAG (Tm:YAG) laser, ytterbium YAG (Yb:YAG) laser, Yb2O3 (glass or ceramic) laser, ytterbium-doped glass laser (rod, plate / chip and fiber), holmium YAG (Ho:YAG) laser, chromium ZnSe (Cr:ZnSe) laser, cerium-doped lithium strontium (or calcium) aluminum fluoride (Ce:LiSAF, Ce:LiCAF), promethium-doped 147 phosphate glass (147Pm +3 :glass) solid-state lasers, chromium-doped chrysoberyl (alexandrite) lasers, erbium-doped and erbium-ytterbium co-doped glass lasers, trivalent uranium-doped calcium fluoride (U:CaF2) solid-state lasers, divalent samarium-doped calcium fluoride (Sm:CaF2) lasers, or F-centered lasers.

[0077] Semiconductor lasers may include laser medium types such as GaN, InGaN, AlGaInP, AlGaAs, InGaAsP, GaInP, InGaAs, InGaAsO, GaInAsSb, lead salts, vertical cavity surface emitting lasers (VCSELs), quantum cascade lasers, hybrid silicon lasers, or combinations thereof.

[0078] For example, in one embodiment, a single Nd:YAG q-switched laser can be used in combination with multiple semiconductor lasers. In another embodiment, an electron beam can be used in combination with an array of ultraviolet semiconductor lasers. In other embodiments, a two-dimensional array of lasers can be used. In some embodiments with multiple energy sources, pre-patterning of the energy beam can be accomplished by selectively activating and deactivating the energy sources.

[0079] The laser beams may be shaped by a variety of imaging optics to combine, focus, diverge, reflect, refract, homogenize, adjust intensity, adjust frequency, or otherwise shape and direct one or more laser beams received from a laser beam source toward an energy patterning unit. In one embodiment, a wavelength selective mirror (e.g., a dichroic mirror) or a diffractive element may be used to combine multiple beams each having a different wavelength of light. In other embodiments, a polygonal mirror, a microlens, and a refractive or diffractive optical element may be used to homogenize or combine multiple beams.

[0080] Energy patterning can include static or dynamic energy patterning elements. For example, photons, electrons or ion beams can be blocked by a mask having fixed or movable elements. In order to increase the flexibility and ease of image patterning, pixel addressable masks, image generation or transmission can be used. In some embodiments, the energy patterning unit includes an addressable light valve to provide patterning alone or in combination with other patterning mechanisms. The light valve can be transmissive, reflective or use a combination of transmissive and reflective elements. The pattern can be dynamically modified using electrical addressing or optical addressing. In one embodiment, a transmissive optically addressed light valve is used to rotate the polarization of light passing through the valve, wherein the optically addressed pixels form a pattern defined by a light projection source. In another embodiment, a reflective optically addressed light valve includes a write beam for modifying the polarization of a read beam. In yet another embodiment, the electronic patterning device receives an address pattern from an electrical or photon stimulation source and generates a patterned emission of electrons.

[0081] The rejected energy processing unit can be used to distribute, redirect, or utilize energy that is not patterned and passes through the energy pattern image repeater. In one embodiment, the rejected energy processing unit may include a passive or active cooling element that removes heat from the energy patterning unit. In other embodiments, the rejected energy processing unit may include a "beam dump" to absorb any beam energy that is not used to define the energy pattern and convert it into heat. In other embodiments, the rejected beam energy can be recovered using beam shaping optics. Alternatively or additionally, the rejected beam energy can be directed to an article processing unit for heating or further patterning. In some embodiments, the rejected beam energy can be directed to an additional energy patterning system or article processing unit.

[0082] The image relay receives a patterned image (usually a two-dimensional image) from the energy patterning unit and directs it to the article processing unit. In a manner similar to the beam shaping optical device, the image relay may include optical devices for combining, focusing, diverging, reflecting, refracting, adjusting intensity, adjusting frequency, or otherwise shaping and directing the patterned image.

[0083] The article handling unit may include a walled chamber and a bed, and a material dispenser for distributing materials. The material dispenser may distribute, remove, mix, provide a gradual change or change in material type or particle size, or adjust the layer thickness of the material. The material may include metals, ceramics, glass, polymer powders, other fusible materials that can undergo a thermally induced phase change from solid to liquid and back to solid, or a combination thereof. The material may also include a composite of a fusible material and an infusible material, wherein the imaging relay system may selectively target either or both components to melt the fusible component while either ignoring the infusible material or subjecting it to evaporation / destruction / combustion or other destruction processes. In certain embodiments, slurries, sprays, coatings, wires, strips, or sheets may be used. Unwanted materials may be removed for disposable use or recycling by using a blower, a vacuum system, sweeping, vibrating, shaking, tilting, or flipping the bed.

[0084] In addition to material handling components, an article handling unit may include components for holding and supporting 3D structures, mechanisms for heating or cooling the chamber, auxiliary or supporting optics, and sensors and controls for monitoring or adjusting material or environmental conditions. Article handling units may fully or partially support a vacuum or inert gas atmosphere to reduce unwanted chemical interactions and mitigate the risk of fire or explosion (particularly for reactive metals).

[0085] The control processor may be connected to control any component of the additive manufacturing system. The control processor may be connected to various sensors, actuators, heating or cooling systems, monitors and controllers to coordinate operations. A variety of sensors (including imagers, light intensity monitors, thermal, pressure or gas sensors) may be used to provide information for control or monitoring. The control processor may be a single central controller, or alternatively may include one or more independent control systems. The controller processor is provided with an interface that allows manufacturing instructions to be input. The use of a variety of sensors allows various feedback control mechanisms, which improves quality, manufacturing throughput and energy efficiency.

[0086] Designs, implementations, and methods of operation of laser systems with long pulse agility and scalability are described to reduce damage to optics and minimize the "halo" effect induced by laser plasma in the print bed. Since both effects are proportional to the peak intensity of the laser source, high power laser sources with power fluxes of 20 kilowatts per square centimeter to over 1 gigawatt per square centimeter at the use point (e.g., the print plane) are particularly susceptible to optics damage and laser-induced plasma effects. In some embodiments, the plasma associated with the halo effect can be initiated by the release of vapor / particles formed by material ablated / evaporated from a powder (Fe, Cr, Al, Co, Ti, Si, etc.), particularly from a metal component. Because the laser heats the powder, this release of vapor / particle material from the surface can occur at such a high rate that a sufficient amount of material can enter the gas region above the area being printed, even while the laser is still emitting. The released material has an extremely high absorption rate for the laser light still incident on the tile being printed, so it overheats and produces a plasma that not only produces shock waves and a halo effect, but also begins to reflect and disperse any further incident laser energy. This rejection effect reduces the amount of energy used by the print bed and negatively affects the quality of the printing process within the tile. The high thermal conductivity of the process gas allows the gas to quickly conduct away the heat generated from the laser heating and melting process. Therefore, the high thermal conductivity helps to eliminate the plasma before the plasma volume expansion is maintained, and thus minimizes the mechanical impact of the shock wave that pushes the surrounding powder away. The high thermal conductivity of the process gas also serves to remove heat from the top surface of the powder layer, thus reducing the vertical temperature gradient in the powder layer and allowing the powder layer to be heated and melted more evenly. As a result, the higher conductivity of the ideal process gas causes more heat to be transferred into the base (print plate or previously printed layer below the current layer), and thus brings the temperature of the base closer to the melting point without melting the top of the current powder layer. This creates favorable thermal conditions to bond the powder layer to the substrate or previously printed layer beneath the current layer.

[0087] In some embodiments, an engineered gas is used to form the atmosphere in the enclosure, which serves to mitigate plasma generation and "halo" issues. In some embodiments, an inert gas comprising primarily helium can enhance the incorporation and operation of a powder bed fusion based additive manufacturing process within a controlled temperature and pressure range.

[0088] In addition to designing the gas species, operating conditions (such as temperature) can be used to further enhance the desired thermal conduction or heat transfer coefficient away from the tile surface. For example, in the case of 1 bar of He engineered gas, the thermal conductivity can be increased from about 0.15 to about 0.3 between 0°C and 600°C. Increasing the pressure in turn can also help this process by increasing the heat transfer coefficient and increasing the energy required to move the shock wave. The closed atmosphere temperature can be set between 20 degrees Kelvin (i.e., cryogenic temperature) and 5000 degrees Kelvin. In some embodiments, the atmosphere temperature of the housing can be set between 200 degrees Celsius and 600 degrees Celsius.

[0089] Adjustment of operating conditions, such as pressure, can be used to further enhance additive manufacturing and reduce the halo effect. The atmosphere in the enclosure can be maintained at an absolute pressure between 0 bar and 100 bar. In some embodiments, the pressure of the atmosphere in the enclosure is below atmospheric pressure. In other embodiments, the pressure of the atmosphere in the enclosure is above atmospheric pressure. During the additive manufacturing process, the laser interacts with the powder material and the substrate, and the melted powder material begins to coalesce. This process has the potential to capture air bubble gaps in the material. By sufficiently reducing the gas pressure, these bubbles will begin to shrink and eventually collapse on themselves, which produces a higher density material during the melting process. In some cases, the process may occur at an absolute pressure between 0.5 bar and 1.0 bar, in other cases it may occur at an absolute pressure between 0.25 bar and 1.0 bar, in other cases it may occur at an absolute pressure between 0.1 bar and 1.0 bar, in other cases it may occur at an absolute pressure between 0.01 bar and 1.0 bar, in other cases it may occur at an absolute pressure between 0.001 bar and 1.0 bar, in other cases it may occur at an absolute pressure between 0.0001 bar and 1.0 bar, in other cases it may occur at an absolute pressure between 1E-6 bar and 1.0 bar, in other cases it may occur at an absolute pressure between 1E-6 bar and 1E-3 bar, and in other cases it may occur at an absolute pressure between 1E-10 bar and 1.0 bar.

[0090] In addition, operating conditions (such as high pressure at different temperatures) can be adjusted after or during the additive process to improve part quality. Historically, the hot isostatic pressing (HIP) process has been performed after the part has been made by additive manufacturing, but there are considerable benefits to introducing it during the process. The HIP process can be operated between 500 bar and 1000 bar and at 400°C to 1500°C. However, it is not enough to operate the printing process at high temperature and high pressure alone, because the HIP process is based on compressing low-pressure gas pockets. To do this, the pressure needs to be cycled at different stages of the printing process. The printing process will continue at low pressure, then pause intermittently and increase the pressure at high temperature to expel pores and gas pockets.

[0091] In other embodiments, other derivative or alternative approaches may include circulating and recirculating the engineered process gas in-situ during the process, or introducing an inert process gas environment only locally in the print chamber where the laser beam melting of the metal powder occurs.

[0092] Advantageously, using the described gases and operating conditions, the generation and volume expansion of plasma during the printing process is suppressed or minimized. Powder movement in response to laser beam melting and molten metal and mechanical impacts ("halo") to surrounding metal powder are minimized and have no significant impact on continuing aspects of the additive printing process (e.g., "stitching" adjacent tiles together). Minimized generation and volume expansion of plasma can also minimize the "blocking" or "scattering" effect of the plasma on the laser beam above the print area.

[0093] The high thermal conductivity of He-containing engineered process gases also helps reduce vertical temperature gradients across the depth of the metal powder layer, resulting in more uniform heating and melting conditions. It enables the use of high-power flux lasers to quickly heat, melt, and solidify metal powders for bonding to the substrate.

[0094] Figure 1A A cross section and top section of a powder layer system 100A before responding to a laser are shown. A cross-sectional view 101 taken from a cut plane 107 shows a powder layer 103 resting on a substrate 102, which contains possible tiles to be printed. A top view 104 shows a view of the same set of tiles from above. In this example, there is powder in the area of ​​a tile 106 to be printed. The tile to be printed is surrounded by powder 105 that constitutes a possible tile to be printed in the future.

[0095] Figure 1BA cross section and top section of a powder layer system 100B in response to a laser beam having a flux greater than 20 megawatts per square centimeter and generally ranging between 100 megawatts and 10 gigawatts per square centimeter are shown. At such a power flux level, a large amount of laser-induced plasma is formed at the point of use. A cross-sectional view 101 taken from a cut plane 107 shows a powder layer 103 resting on a substrate 102, which contains possible tiles to be printed. A top view 104 shows a view of the same set of tiles from above. In this example, there is a tile 106 printed with a laser 108. The printed tile is surrounded by powder 105 that constitutes a possible tile to be printed in the future. The vapor generated by the heating of the powder is overheated by the laser 108, forming a gas 109 expansion wave, which pushes the powder previously in a good uniform layer 103 away from the "halo" area 110 next to the printed tile 106. This movement of powder causes further accumulation on nearby tiles 112, which changes their layer thickness. Movement of powder from the "halo" region 111 and accumulation of powder in nearby tiles 112 causes problems with printing future layers.

[0096] Figure 1C The response is shown in an atmosphere containing primarily helium, and using the following Figures 3A-3C A cross section and top section of a powder layer system 100C of a laser beam of various shaped laser pulse sequences described in more detail, the laser beam having a flux greater than 20 megawatts per square centimeter and typically in the range of 100 megawatts to 10 gigawatts per square centimeter. A cross-sectional view 101 taken from a cut plane 107 shows a powder layer 103 resting on a substrate 102, the powder layer 103 containing possible tiles to be printed. A top view 104 shows a view of the same set of tiles from above. In this example, there is a tile 106 printed with a laser 108 in an environment that is primarily helium. The printed tile is surrounded by powder 105 that constitutes a possible future tile to be printed. Because the printing is performed using a shaped laser pulse sequence, the vapor generated by the heating of the powder is not overheated by the laser 108, and the gas expansion wave that may push the powder away from the previously uniform layer 103 is largely or completely eliminated, allowing the powder 105 next to the printed tile 106 to be printed in a future shot. Furthermore, the powder layer 103 is not increased, which prevents problems with future layers.

[0097] In selected embodiments, greater or lesser amounts of helium or other inert gases may be used to provide the atmosphere within the additive manufacturing enclosure. For example, Ar, He, Ne, Kr, Xe, CO2, N2, O2, SF6, CH4, CO, N2O, C2H2, C2H4, C2H6, C3H6, C3H8, i-C4H10, C4H10, 1-C4H8, cic-2, C4H7, 1,3-C4H6, 1,2-C4H6, C5H12, n-C5H12, i-C5H12, n-C6H14, C2H3Cl, C7H16, C8H18, C10H22, C11H24, C12H26, C13H28, C14H30, C15H32, C16H34, C6H6, C6H5-CH3, C8H10, C2H5OH, CH3OH, iC4H8 can be used. In some embodiments, a refrigerant or large inert molecule (including but not limited to sulfur hexafluoride) may be used. A closed atmosphere composition having at least about 1% He by volume (or number density) and a selected percentage of inert / non-reactive gas may be used. In some embodiments, greater than 1% He may be used, while in other embodiments, greater than 10% He may be used, while in other embodiments, greater than 20% He may be used, while in other embodiments, greater than 40% He may be used, while in other embodiments, greater than 80% He may be used, and in other embodiments, 95% or more He may be used. In addition to the composition of the engineered gas, the range of operating temperature and pressure of the engineered gas may be selected to minimize the generation of plasma and improve print quality. Complex molecules and gases with large atomic weights may have benefits associated with greater mass and more force or energy to move. Although the thermal conductivity of larger molecules (such as sulfur hexafluoride) is lower than that of He (similar to Ar), the gas density is much greater and will vent other gases (O2, H2O vapor, N2, etc.) released from the powder during the printing process (wherein the powder is heated to melting temperature and a phase change is induced). These lighter gases will effectively float above the much denser gases and be removed quickly from the process area. Additionally, the more complex molecules have vibrational and rotational energy storage modes that the noble gases do not have. These additional energy modes increase the specific heat of the gas at high temperatures and help reduce the ionization potential of the gas by absorbing more energy from the surrounding metal vapor.Additionally, in the case of SF6 (sulfur hexafluoride), if the primary inert gas molecules are to be decomposed (by plasma decomposition, or by interaction with released radicals such as O, C, H, OH, various combinations, including various combinations of species from powder alloys, etc.), the free radicals formed by the decomposition will help scavenge the released gases (O, O2, H, OH, H2O, Fe, Cr, etc.) during the printing process. Different gases can be used to print different materials by changing the atomic properties, density, or temperature of the gas.

[0098] Figure 2 A system 200 is shown in which an incident laser beam 201 is directed to a powder bed by a reflector 211 to form a printing laser beam 202. An insignificant portion of the beam is transmitted through the reflector 211 to a laser flux sensor 205 to detect the laser flux. A vision system 206 is aimed at a print area 203 on a base substrate 204. The image captured by the vision system 206 is transmitted to a computer processor 207. A controller 208 uses the results of the image processing to generate control signals to adjust the shape, power, and format of the laser pulses. In one embodiment, the amount of helium supplied from a helium tank 209 to a print chamber 210 can also be adjusted, and the print chamber atmosphere temperature is regulated.

[0099] Figure 3A-3C shows a general type of output pulse waveform that can be used to eliminate or minimize the formation of laser plasma and its associated "halo" effect on the printing process. Figure 3A As seen in graph 300A, square pulses may be used where the defined width and amplitude are set below the laser damage threshold requirements for the laser system optics and below the plasma threshold that causes undesirable powder motion and halo formation.

[0100] Figure 3B A graph 300B is shown having a shaped pulse sequence with Figure 3A The pulses shown in Figure 1 have similar energy content, but are delivered as a series of short pulses whose individual pulse widths and pulse intervals can be adjusted to reduce laser damage and powder motion. 2 Up to 10GW / cm 2At laser flux levels between the outputs, pulse trains are not typically performed using simple oscillators (such as mode-locked oscillators) because such systems have insufficient timing and pulse shape flexibility to operate reliably without optical damage or unintentional plasma generation. Feeding a simple pulse train into an amplifier system will produce a spike-shaped pulse train (i.e., the first pulse will be very high, while the trailing pulses are lower). This is due to gain saturation in the amplifier, where the first pulse entering the saturated amplifier steals the available energy.

[0101] Figure 3C 300C is a graph showing a shaped pulse (or pulse train) that varies the amplitude of the laser peak power over time to improve overall performance while minimizing laser damage and reducing powder movement.

[0102] It should be appreciated that other improvements in system operation resulting from shaped laser pulse operation may include minimizing laser energy requirements and / or adjusting material properties of printed parts.

[0103] In operation, the pulse length can be tailored to reduce the peak intensity below the optical damage threshold for limited-capacity optics.

[0104] The pulse length can be tailored so that the peak intensity at the powder layer is below the plasma formation limit, improving 2D tile printing.

[0105] The range of pulse lengths can be tailored to specific materials with different laser absorption, melting points, and heat of fusion to minimize the creation of laser plasma that would impede effective printing due to “halo” effects.

[0106] As another example of improved operation, 316 stainless steel powder (which has a melting point of 1371 degrees Celsius - 1399 degrees Celsius) can be printed at the print bed with greater than 8 joules per square centimeter and pulse widths greater than 200 nanoseconds in a helium environment at room temperature. Alternatively, aluminum powder (which has a lower melting point of 659 degrees Celsius) requires a lower flux to print, but due to its low density (light weight per powder particle), the halo effect is enhanced. To reduce powder motion, long pulse widths of greater than 200 nanoseconds can be used. As another example, tungsten powder (a very high melting point metal of 3399 degrees Celsius) will minimize plasma formation, but will require a lot of energy to melt. In contrast, fused silica (a potential optical component) has a very high melting point (which would require a lot of laser flux), but has a relatively low density, which would benefit from very long pulse lengths of greater than 500 nanoseconds to avoid severe halo issues.

[0107] The pulse length can be tailored to improve the mechanical properties of the finished printed part by changing the way energy is delivered to the powder and effectively controlling the temperature changes and resulting stresses and / or crystallization properties.

[0108] Figure 4 An example of a high-flux laser system 400 is shown that is capable of generating arbitrary and adaptable pulse waveforms to minimize the possibility of laser damage, reduce or effectively eliminate the "halo" induced by the laser plasma in the powder on the print bed, and adjust the finished material properties of the additively manufactured part. The arbitrary pulse laser source 401 can be composed of an arbitrary waveform generator coupled to a fiber-coupled diode laser source. For efficiency, the laser preamplifier 402 and power amplifier 403 are used in a multipass format, and the stored energy and size are adjustable to match the system requirements. Faraday rotator 404, Faraday isolator and Pockels cell 405 are used to prevent parasitic reflections from damaging the low-energy part of the system and minimize energy losses in the output pulses. The laser relay and imaging system 406 is used to minimize laser spatial modulation and expand the beam as the energy increases, helping to avoid laser damage and allowing efficient energy extraction. The output 407 of the laser system can be directed to the print engine and ultimately to the powder bed.

[0109] The arbitrary pulse laser source 401 comprises a source of pulsed electrical signals, such as an arbitrary waveform generator or an equivalent acting on a continuous laser source (such as a laser diode). In some embodiments, this can also be achieved by a fiber laser or a fiber-emitting laser source, which is then modulated by an acousto-optic or electro-optic modulator. In some embodiments, a high repetition rate pulse source using a Pockels cell can be used to generate a pulse train of arbitrary length.

[0110] Various preamplifier modules 402 are used to provide high gain to the laser signal, while optical modulators and isolators can be distributed throughout the system to reduce or avoid optical damage, improve signal contrast, and prevent damage to the lower energy portions of the system 400. Optical modulators and isolators 404 can include, but are not limited to, Pockels cells, Faraday rotators, Faraday isolators, acousto-optic reflectors, or volume Bragg gratings. The preamplifier modules 402 can be diode-pumped or flashlamp-pumped amplifiers and configured as single-pass and / or multi-pass or cavity-type architectures. It will be appreciated that the term preamplifier is used here to refer to amplifiers that are not thermally limited (i.e., they are smaller) relative to the power amplifiers 403 (which are larger). The power amplifiers will typically be positioned as the final unit in the laser system and are the modules most susceptible to thermal damage (including, but not limited to, thermal fracture or excessive thermal lensing).

[0111] The preamplifier module 402 may include a single pass preamplifier that is useful in systems where energy efficiency is not an overly important concern. For systems that are more energy efficient, a multipass preamplifier may be configured to extract a lot of energy from each preamplifier 402 before entering the next stage. The number of preamplifiers 402 required for a particular system is limited by the system requirements and the storage energy / gain available in each amplifier module. Multipass preamplification may be achieved by angle multiplexing or polarization switching (e.g., using a wave plate or Faraday rotator).

[0112] Alternatively, the preamplifier 402 may include a cavity structure having a regenerative amplifier type configuration. While such a cavity structure may limit the maximum pulse length due to typical mechanical considerations (the length of the cavity), in some embodiments, a "white cell" cavity may be used. A "white cell" is a multi-pass cavity structure in which each pass has a small angular deviation. By providing an entrance and exit path, such a cavity can be designed to have a very large number of passes between the entrance and exit, allowing for large gain and efficient use of the amplifier. An example of a white cell is a confocal cavity, where the beam is injected slightly off-axis and the mirror is tilted so that a ring pattern is produced on the mirror after multiple passes. The number of passes can be varied by adjusting the injection angle and the mirror angle.

[0113] The power amplifier modules 403 are also used to provide sufficient stored energy to meet the system energy requirements while supporting sufficient thermal management to enable operation at the repetition rate required by the system, whether they are diode pumped or flash lamp pumped.

[0114] The spatial and temporal amplitude of an amplified laser beam is difficult to control. Almost every aspect of a laser amplifier system can negatively affect the laser beam, including: optical aberrations, thermally induced wavefront errors, hardware vibrations, thermal birefringence polarization losses, temperature-dependent gain, interference of the laser pulse with itself, amplified reflections from the internal surfaces of the laser, and many other factors. All of these effects reduce the spatial and / or temporal uniformity of the propagating beam. In general, laser applications require consistency and high brightness. One solution is to try to design all of the above aberrations out of the system to obtain a diffraction-limited beam that can then be focused into a very small spot or imaged to a delivery location. This is a very difficult problem, usually resulting in lower efficiency, and in the case of imaging, imperfect amplitude control is still often produced. Another approach is beam homogenization, which is achieved by essentially generating many beam samples and superimposing them in the near field. This approach increases the divergence of the beam and increases the minimum achievable spot size, but produces the benefit of achieving a nominal flat-top profile beam in the near field or far field as required. The difficulty with this approach is the presence of laser "speckle," which is essentially interference peaks and valleys from all beam samples. This speckle causes problems for the laser system itself, as intensity spikes can damage optics, and also results in non-uniform flux at the point where the laser is used for exposure, cutting, welding, joining, or powder bed fusion additive manufacturing.

[0115] Several methods of combating laser "speckle" by "wiggling" the speckle in time include beam deflectors (acousto-optic, electro-optic, mechanical), RF phase modulators, and wavelength division multiplexing. Additionally, the spatial or temporal coherence of the laser beam itself can be reduced by increasing the spectral bandwidth, increasing the angular content, or even through the brute force of multiple uncorrelated sources (which together can reduce the contrast of the speckle and increase the robustness and effectiveness of the overall laser system).

[0116] Thermal management of power amplifiers can include many embodiments in terms of amplifier geometry (rod, slab, disk), cooling direction (edge ​​cooling, surface cooling), and cooling medium (solid conduction, liquid or gas). In one embodiment, fluid cooling of the slab amplifier transmission surface can provide a scalable method to achieve high average power. One feature of laser systems used for printing is the importance of the consistency and uniformity of the laser across the printer image plane. The fluid can be of any type that is transparent to the laser wavelength. In the case of laser wavelengths between 900nm and 1100nm, fluids such as silicone oil, water, distilled water, noble or inert gases such as helium, or other gases such as H2, N2, O2, or CO2 can be used. Another benefit of the gas cooling method is that the turbulence of the gas can enhance the uniformity of the laser beam (reduce speckle) by moving the "speckle" in time, thereby improving printing performance, and protecting downstream optics from high peak intensities that can cause laser damage.

[0117] The power amplifier module 403 can be configured as a single pass and / or multi-pass or cavity type architecture. The amplifier module can include a single pass amplifier that is available in a system that is not overly concerned about energy efficiency. For a more energy efficient system, a multi-pass amplifier can be configured to extract a lot of energy from each amplifier before entering the next stage. The number of amplifiers required for a particular system is limited by the system requirements and the available storage energy / gain in each amplifier module. Multi-pass pre-amplification can be achieved by angle multiplexing, polarization switching (wave plates, Faraday rotators).

[0118] Alternatively, the power amplifier 403 may include a cavity structure having a regenerative amplifier type configuration. As discussed with respect to the preamplifier module 402, in some embodiments, a white box cavity may be used for the power amplification 403.

[0119] It is understood that laser flux and energy can be scaled in this architecture by adding more preamplifiers and amplifiers with proper thermal management and optical isolation.

[0120] Many modifications and other embodiments of the present invention will occur to those skilled in the art who have benefited from the foregoing description and the teachings presented in the associated drawings. Therefore, it should be understood that the present disclosure is not limited to the specific embodiments disclosed, and modifications and other embodiments are considered to be included within the scope of the appended claims. It should also be understood that other embodiments of the present invention can be implemented without the elements / steps specifically disclosed herein.

Claims

1. A laser system for two-dimensional printing, comprising: Laser pulse signal source; one or more preamplifier modules for receiving a laser beam and directing the laser beam to an optical isolator; and one or more amplifier modules for receiving the laser beam from the optical isolation device and directing the laser beam to a defined two-dimensional region of the powder bed; Wherein, the laser system is dynamically adjusted through a calibration step, and the calibration step includes adjusting at least one of the laser beam energy, pulse width or the area of ​​the defined two-dimensional region in response to the detection area of ​​the halo formed by the preliminary halo test.

2. The laser system according to claim 1, wherein: The laser pulse signal source can provide at least one of any predetermined pulse shape or pulse sequence.

3. The laser system according to claim 1, wherein: The optical isolation device includes at least one of a Pockels cell, a Faraday rotator, a Faraday isolator, an acousto-optic reflector or a volume Bragg grating.

4. The laser system according to claim 1, wherein: The laser pulse signal source can provide at least one of a square wave and a ramp.

5. A laser control method comprising the following steps: directing a laser pulse signal source to a preamplifier module and an optical modulator to provide a first laser beam; and The first laser beam is directed to an amplifier module to provide a laser beam comprising one or more pulses and having a power greater than 20 kW / cm at the point of use. 2 a shaped laser beam pulse sequence of a flux of 1000 nm to 1000 nm, wherein the shaped laser beam pulse sequence is directed at a defined two-dimensional region of an additive manufacturing powder bed to melt and fuse the powder within the defined two-dimensional region; and The method further includes a calibration step, which includes adjusting at least one of the laser beam energy, the pulse width or the area of ​​the defined two-dimensional region in response to the detection area of ​​the halo formed by the preliminary halo test.

6. The method according to claim 5, wherein: At the point of use, the flux is 20 kW / cm 2 Up to 10GW / cm 2 between.

7. The method according to claim 5, wherein: The laser pulse width is between 20 nanoseconds and 100 microseconds.

8. The method according to claim 5, wherein: Utilize a laser pulse train with a pulse number greater than 1.

9. The method according to claim 5, wherein: The peak power of the laser pulse is adjusted as a function of time.

10. The method according to claim 5, wherein: The size is 0.000025cm 2 Up to 1,000cm 2 The shaped laser beam pulse sequence is directed at a two-dimensional region between.

11. The method according to claim 5, wherein: The laser pulse signal source can provide at least one of any predetermined pulse shape or pulse sequence.

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