Patent Application
20240131593
The present inventions relate to laser processing of materials and in particular laser building of materials including laser additive manufacturing processes using laser beams having wavelengths from about 350 nm to about 700 nm.
Infrared red (IR) based (e.g., having wavelengths greater than 700 nm, and in particular wavelengths greater than 1,000 nm) additive manufacturing systems suffer from, among other things, two short comings, which limit both the build volume and the build speed. In these IR systems the build volume is limited by the finite size of the scanning systems and the spot that can be created for a given focal length collimator and f-theta lens. For example, in such prior IR systems, when using a 14 mm focal length collimator and a 500 mm F-theta focal length lens the spot size is on the order of 350 Jim for a diffraction limited IR laser beam. This gives an addressable foot print on the raw build material, e.g., a powder bed, of approximately 85 mm×85 mm, which in turn creates or establishes the finite limitation on the build volume for that given resolution (e.g., spot size). The second limitation on the build speed for IR laser systems is the absorption of the laser beam by the materials. While originally, most raw build materials had a modest to low reflectivity for wavelengths in the infrared spectrum, as additivity manufacturing started to use metals, such as gold, silver, platinum, copper and aluminum and alloys thereof, which materials have high and very high IR reflectivity, problems were encountered with using these high reflective IR types of build materials in IR additive manufacturing. As a consequence, the coupling of the infrared laser energy into the raw build materials, e.g., powder bed or particles, is limited with a significant portion of the energy being reflected away, backward or deeper into the raw build material. These limitations are in a way further tied or linked together, compounding the problems and deficiencies of IR additive systems. Thus, the finite penetration depth of the Infrared laser light determines the optimum layer thickness and as a consequence, limits the resolution of the process. Thus, IR laser systems, because of their reflectivity to the typical raw build material have limited layer thicknesses and thus limited resolution.
As used herein, unless expressly stated otherwise, “UV”, “ultra violet”, “UV spectrum”, and “UV portion of the spectrum” and similar terms, should be given their broadest meaning, and would include light in the wavelengths of 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”, “visible spectrum”, and “visible portion of the spectrum” and similar terms, should be given their broadest meaning, and would include light in the wavelengths of from about 380 nm to about 750 nm, and 400 nm to 700 nm.
As used herein, unless expressly stated otherwise, the terms “blue laser beams”, “blue lasers” and “blue” should be given their broadest meaning, and in general refer to systems that provide laser beams, laser beams, laser sources, e.g., lasers and diodes lasers, that provide, e.g., propagate, a laser beam, or light having a wavelength from 400 nm (nanometer) to 500 nm, and about 400 nm to about 500 nm. Blue lasers include wavelengths of 450 nm, of about 450 nm, of 460 nm, of about 460 nm. Blue lasers can have bandwidths of from about 10 pm (picometer) 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 “green laser beams”, “green lasers” and “green” should be given their broadest meaning, and in general refer to systems that provide laser beams, laser beams, laser sources, e.g., lasers and diodes lasers, that provide, e.g., propagate, a laser beam, or light having a wavelength from 500 nm to 575 nm, about 500 nm to about 575 nm. Green lasers include wavelengths of 515 nm, of about 515 nm, of 532 nm, about 532 nm, of 550 nm, and of about 550 nm. Green lasers can have bandwidths of from about 10 μm to 10 nm, about 5 nm, about 10 nm and about 20 nm, as well as greater and smaller values.
Generally, the term “about” and the symbol “—” as used herein, unless specified otherwise, is meant to encompass the larger of: a variance or range of ±10%; and the experimental or instrument error associated with obtaining the stated value.
As used herein, unless stated otherwise, room temperature is 25° C. And, standard ambient temperature and pressure is 25° C. and 1 atmosphere. Unless expressly stated otherwise all tests, test results, physical properties, and values that are temperature dependent, pressure dependent, or both, are provided at standard ambient temperature and pressure, this would include viscosities.
As used herein unless specified otherwise, the recitation of ranges of values herein is 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 a range is incorporated into the specification as if it were individually recited herein.
Typically, a method employed today in additive manufacturing is the use of an infrared laser and a galvanometer to scan the laser beam across the surface of a powder bed in a predetermined pattern. The IR laser beam is of sufficient intensity to create a keyhole welding process that melts and fuses the liquified powder to the lower layer or substrate. This approach has several limitations that determines the speed of the process. For example, a single laser beam is used to scan the surface and the build rate is limited by the maximum scanning speed of the galvanometers (7 m/sec). Manufactures strongly embrace IR technology, and typically believe that it is the only viable wavelength, thus they are working, but with limited success, to overcome this limitation by integrating two or more IR laser/galvanometers into a system, where the two can work in conjunction to build a single part or they can work independently to build parts in parallel. These efforts are aimed at improving the throughput of the additive manufacturing systems, but have been focused solely on IR and have been of limited success, not meeting the long felt need for improved additive manufacturing.
An example of another limitation in IR processing is the finite volume that can be addressed by the IR laser/galvanometer system. In a stationary 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 infrared laser. For example, with a 500 mm F-theta lens the IR laser creates a spot size on the order of 50 μm or a diffraction limited infrared laser. If the laser beam is operating at 100 Watts optical power, then the intensity of the beam is greater than the intensity required to initiate a keyhole welding mode. The keyhole welding mode creates a plume of vaporized material that must be removed out of the path of the laser beam by a cross jet otherwise the laser beam is scattered and absorbed by the vaporized metal. In addition, because the keyhole mode of welding relies on creating a hole in the liquid metal surface that is maintained by the vapor pressure of the vaporized metal, material other than vaporized metal can be ejected from the keyhole. This material is referred to as spatter and results in molten materials being deposited elsewhere on the build plane that can lead to defects in the final part. While the manufactures of additive manufacturing systems have had some limited success in developing rapid prototyping machines, they have failed to meet the long felt need, and achieve the requirements needed to produce commercial or actual parts in volume. To accomplish this a breakthrough in the method of patterning the parts, which prior to the present inventions the art has not achieved.
In general, a problem and failing with IR processing and systems is the requirement or need to fuse the powder in a keyhole welding mode. This can be typically because of the use of a single beam to process the powder. If the laser beam is operating at 100 Watts optical power, then the intensity of the beam is greater than the intensity required to initiate a keyhole welding mode. The keyhole welding mode creates a plume of vaporized material that must be removed out of the path of the laser beam by a cross jet otherwise the laser beam is scattered and absorbed by the vaporized metal. In addition, because the keyhole mode of welding relies on creating a hole in the liquid metal surface that is maintained by the vapor pressure of the vaporized metal, material such as the vaporized metal can be ejected from the keyhole. This material is referred to as spatter and results in molten materials being deposited elsewhere on the build plane that can lead to defects in the final part.
Recent work by Lawrence Livermore National Laboratories using an Optically Activated Light Valve (OALV) has been attempted to address these IR limitations. The OALV is a high-power spatial light modulator that is used to create a light pattern using high power lasers. While the pattern on the OALV is created with a blue LED or laser source from a projector, the output power from the four laser diode arrays are transmitted through the spatial light modulator and used to heat the image to the melting point and a Q-switched IR laser is required to initiate a keyhole weld. The IR laser is used in the keyhole mode to initiate the weld, especially when fusing copper or aluminum materials, and is generally required for these materials. This keyhole weld process typically creates spatter, porosity in the part, as well as high surface roughness. Thus, the OALV systems as do typical IR systems does not eliminate the adverse effects of keyhole initiation of the building process. While it would be better to completely avoid the keyhole welding step, the art has failed to overcome this problem and has not provided this solution. This failure has primarily occurred because at the IR wavelengths the absorption properties of many metals are so low that a high peak power laser is necessary to initiate the process. Since the OALV is only transparent in the IR region of the spectrum, it is not feasible to build, or use this type of system using a visible laser source as the high energy light source. The cost of the components in this system are very high especially the OALV which is a custom unit.
Prior metal based additive manufacturing machines are very limited in that they are either based on a binder being sprayed into a powder bed followed by a consolidation step at high temperatures, or a high-power single mode laser beam scanned over the powder bed by a galvanometer system at high speeds. Both of these systems have significant fallings that the art has been unable to overcome. The first system is capable of high volume manufacturing of parts with loose tolerances due to the shrinkage of the parts during the consolidation process. The second process is limited in build speed by the scan speeds of the galvanometer limiting the maximum power level laser that can be used and consequently, the build rate. Builders of scanning based additive manufacturing systems have worked to overcome this limitation by building machines with multiple scan heads and laser systems, which has not provided an adequate solution to these problems. This does indeed increase the throughput, but the scaling law is linear, in other words a system with two laser scanners can only build twice as many parts as a system with one scanner or build a single part twice as fast. Thus, there is a need for a high throughput, laser-based metal additive manufacturing system that does not suffer from the limitations of the currently available systems.
This Background of the Invention section is intended to introduce various aspects of the art, which may be associated with embodiments of the present inventions. Thus, the forgoing discussion in this section provides a framework for better understanding the present inventions, and is not to be viewed as an admission of prior art.
The present inventions solve these and other problems with IR additive manufacturing systems and process, and address these and other long felt needs, as well as future needs as additive manufacturing process and systems achieve greater prevalence. The present inventions, among other things, solve these problems and needs by providing the articles of manufacture, devices and processes taught, and disclosed herein.
Thus, there is provided an additive manufacturing system for forming metal objects from metal powders, the system having: a laser source to provide a laser beam along a laser beam path; an homogenizer;
a digital micro-mirror device (DMD); optics to configure the laser beam and direct the laser beam path to a target location having a device for holding a surface layer of a metal powder; wherein the laser beam path optically associates the laser source to the homogenizer, the homogenizer to the DMD, the DMD to the optics, and the optics to the target location; whereby the laser beam is directed onto the DMD, wherein the DMD is configured to create a 2-D final pattern that is reflected from the DMD along the laser beam path to create a 2-D final image pattern on the surface; wherein the 2-D final pattern has a wavelength and a power density; whereby the 2-D final image pattern is configured to weld the metal powder; wherein the homogenizer is configured to shape and homogenize the laser beam into a titled spot on the DMD; the titled spot on the DMD defining an image having a pitch and a yaw; and, wherein, the pitch and the yaw of the image is within 12 degrees of an illumination cone angle for the DMD.
Moreover, there is provided these systems and processes having one or more of the following features: wherein the image has dimensions defining image dimensions and the DMD has dimensions defining DMD dimensions and the image dimensions and the DMD dimensions are the same; wherein the pitch and yaw of the image are within about 5 degrees of the illumination cone angle for the DMD; wherein the pitch and yaw of the image are within about 1 degree of the illumination cone angle for the DMD; wherein the spot is rectangular and the image is rectangular; wherein the DMD is configured to comprise an On-State mirror configuration and an Off-State mirror configuration for any given 2-D final image pattern; whereby in either the On-State mirror configuration or the Off-State mirror configuration, the DMD provides a heating laser beam along a heating laser beam path to create a heating image pattern on the surface; wherein the laser beam has a total power, and a fraction of the total power is used to form the heating laser beam; whereby the system is configured to simultaneously provide both the 2-D final image pattern and the heating image pattern on the surface; further having an attenuator on the heating laser beam path prior to the surface; further having a diffuser on the heating laser beam path prior to the surface; wherein the heating laser beam conditioning optics comprise a diffuser; wherein the heating laser beam conditioning optics comprise a diffuser; wherein the On-State provides the 2-D final image pattern; wherein the Off-State provides the 2-D final image pattern; wherein the On-State provides the heating image pattern; wherein the Off-State provides the heating image pattern; wherein the homogenizer has a micro-lens homogenizer; wherein the homogenizer has a homogenizing optical fiber; and, wherein the homogenizer has a diffractive element.
Yet further there is provided an additive manufacturing system for forming metal objects from metal powders, the system having: a laser source to provide a laser beam along a laser beam path; an homogenizer; a digital micro-mirror device (DMD); optics to configure the laser beam and direct the laser beam path to a target location having a device for holding a surface layer of a metal powder; wherein the laser beam path optically associates the laser source to the homogenizer, the homogenizer to the DMD, the DMD to the optics, and the optics to the surface; whereby the laser beam is directed onto the DMD, wherein the DMD is configured to create a 2-D final pattern that is reflected from the DMD along the laser beam path to create a 2-D final image pattern on to the surface; wherein the 2-D final pattern has a wavelength and a power density; whereby the 2-D final image pattern is configured to weld the metal powder; wherein the DMD has a plurality of micro-mirrors, wherein the homogenizer is configured to shape and homogenize the laser beam into a plurality of titled spots on the DMD, wherein the titled spots on the DMD defining a plurality of images having a pitch and a yaw; and, wherein the pitch and yaw of each of the plurality of images is within 12 degrees of a micro-mirror cone angle for each of the plurality of micro-mirrors.
In addition, there is provided these systems and processes having one or more of the following features: wherein the pitch and yaw of each of the plurality of images is with about 5 degrees of the micro-mirror cone angle for each of the plurality of micro-mirrors; wherein the pitch and yaw of each of the plurality of images is within about 1 degree of the micro-mirror cone angle for each of the plurality of micro-mirrors; wherein each of the images has dimensions defining image dimensions and the each of the micro-mirrors has dimensions defining micro-mirror dimensions; and, the image dimensions and the micro-mirror dimensions are the same; wherein the spots are rectangular and the images are rectangular; wherein the DMD is configured to comprise an On-State mirror configurations and an Off-State mirror configurations for any given 2-D final image pattern; wherein the system is configured whereby in either the On-State mirror configurations or the Off-State mirror configurations, the DMD provides a heating laser beam along a heating laser beam path to create a heating image pattern on the surface; wherein the laser beam has a total power, and a fraction of the total power is used to form the heating laser beam; whereby the system is configured to simultaneously provide both the 2-D final image pattern and the heating image pattern on the surface; further having an attenuator on the heating laser beam path prior to the surface; further having a diffuser on the heating laser beam path prior to the surface; wherein the On-State provides the 2-D final image pattern; wherein the Off-State provides the 2-D final image pattern; wherein the On-State provides the heating image pattern; wherein the Off-State provides the heating image pattern; wherein the homogenizer has a micro-lens homogenizer; wherein the homogenizer has a homogenizing optical fiber; and, wherein the homogenizer has a diffractive element.
Furthermore, there is provided an additive manufacturing system for forming metal objects from metal powders, the system having: a laser source to provide a laser beam along a laser beam path; a digital micro-mirror device (DMD); optics to configure the laser beam and direct the laser beam path to a target location having a device for holding a surface layer of a metal powder; wherein the laser beam path optically associates the laser source to the DMD, the DMD to the optics, and the optics to the surface; whereby the laser beam is directed onto the DMD, wherein the DMD is configured to create a 2-D final pattern that is reflected from the DMD along the laser beam path to create a 2-D final image pattern on the surface; wherein the 2-D final pattern has a wavelength and a power density; whereby the 2-D final image pattern is configured to weld the metal powder; and, wherein the DMD is configured to comprise an On-State mirror configuration and an Off-State mirror configuration for any given 2-D final image pattern; wherein the system is configured whereby in either the On-State mirror configurations or the Off-State mirror configurations, the DMD provides a heating laser beam along a heating laser beam path to create a heating image pattern on the surface.
Additionally, there is provided these systems and processes having one or more of the following features: wherein the laser beam has a total power, and a fraction of the total power is used to form the heating laser beam; whereby the system is configured to simultaneously provide both the 2-D final image pattern and the heating image pattern on the surface; further having an attenuator on the heating laser beam path prior to the surface; further having a diffuser on the heating laser beam path prior to the surface; wherein the heating laser beam conditioning optics comprise a diffuser; wherein the heating laser beam conditioning optics comprise a diffuser; and, wherein the On-State provides the 2-D final image pattern; wherein the Off-State provides the 2-D final image pattern.
Yet further, there is provided these systems and processes having one or more of the following features: wherein the laser beam has a blue wavelength; wherein the laser beam has a wavelength less than 600 nm; wherein the laser provides a laser beam having a wavelength selected from the group consisting of blue wavelengths and green wavelengths; wherein the laser has a power from about 1 kW to about 20 kW; and the pattern on the powder metal layer has a peak power density of from about 2 kW/cm2 to about 5 kW/cm2; wherein the laser has a bandwidth selected from the group consisting of about 5 nm, about 10 nm and about 20 nm; wherein the laser beam has a wavelength selected from the group consisting of about 450 nm, about 460 nm, about 515 nm, about 532 nm and about 550 nm; wherein the laser source has a power of about 150 W to about 20 kW; wherein the system has a resolution of about 0.5 μm to about 10 μm; wherein the metal powder has copper; wherein the metal powder has aluminum; and wherein the metal powder has titanium.
Moreover, there is provided the method of building a metal part from a metal powder using any of these systems.
In addition, there is provided the method of forming an image on a bed of a starting material as a part of an additive manufacturing process, the method having, using a micro-lens array to shape and homogenize a laser beam output of a fiber into a tilted rectangular spot on a digital micro-mirror device (DMD), thereby forming an image of a tilted rectangle with dimensions matching the DMD at an angle within about 5 degrees of an illumination cone angle of the DMD in both pitch and yaw.
Still further, there is provided these systems and methods in which the DMD may be operated with the image to be printed sent to the Off-State mirrors and the non-signal light sent to the On-State mirror such that the image is inverted and the Off-State beam forms an image on the workpiece rather than the On-State.
Moreover, there is provided these systems and methods in which a power in a pre-heater beam may be measured or inferred from a number of pixels in each state and a variable attenuator may be inserted used to maintain constant power on the powder bed pre-heat.
Additionally, there is provided these systems and these systems and methods in which an entrance pupil of the optics receiving the laser beam from the DMD has a size configured to accommodate multiple orders of a diffraction generated by the DMD.
Moreover, there is provided these systems and methods in which the DMD generates a chromatic chirp to the image due to the spacing of mirrors acting as a 2D grating thereby creating a grating dispersion; wherein the system has a 2D grating configured to compensate for the grating dispersion of the DMD.
Additionally, there is provided 3-D systems using a spatial light modulator, an array of spatial light modulators and both to form an energy pattern on a powder bed to either directly fuse a plastic or nylon material or to simply control the temperature of the zone to just below the melt point of the region where the primary laser is about to be scanned. It is theorized that the reason for considering this approach is to improve the energy efficiency of the system. At present either a radiant heater, a zone radiant heat or a build plate temperature control system is used to pre-heat the entire bead to be processed. By reducing the size of the region to be pre-heated, the overall energy consumption of the system can be reduced.
Further, embodiments of the present inventions are based on using a Digital Micro-Mirror Device (DMD) spatial light modulator, an array of DMD devices and both assumes that the power density must be limited to 100 W/cm2 or less when operating in a continuous mode which is sufficient to melt and flow plastics but insufficient to melt and fuse metals.
There is provided an additive manufacturing system for metals that uses a laser and a spatial light modulator, an array of spatial light modulators and both to form an energy pattern on a powder metal layer that is fused to the layer below, a gantry system to step and repeat the image across the powder bed, a motion control system, an elevator to displace the part down as each layer is fused, and a powder distribution system that can both spread the powder and compact it before fusing, and an air tight build chamber.
Moreover, there is provided these lasers, systems and methods having one or more of the following features: a laser in the wavelength range of 300-400 nm; a laser in the wavelength range of 400-500 nm; a laser in the wavelength range of 500-600 nm; a laser in the wavelength range of 600-800 nm; an infrared laser in the range of 800 nm-2000 nm; the laser is homogenized by a light pipe, micro-lens homogenizer, a diffractive element; a homogenizing optical fiber and combinations and variations of these; the laser is time shared between multiple print heads or multiple printer systems; the spatial light modulator is a Digital Micro-Mirror Device (DMD) array which is an array of micro-mirrors; the spatial light modulator is any of a class of spatial light modulator capable of handling multi-W to multi-kW power levels; the DMD is air cooled; the DMD is water cooled; the DMD is water cooled by a water cooler such as a micro-channel cooler; the DMD is cooled by a Peltier cooler; the DMD is cooled by forced air over the front or back or both of the DMD; includes zonal radiant heaters for maintaining the build chamber temperature; includes a heated build plate; includes a pyrometer or a FLIR camera to monitor or control the build plate temperature; includes a thermocouple or RTD embedded in the build plate to monitor or control the temperature of the build plate; includes software for determining the optimum build strategy; includes a separate secondary laser for heating the powder bed only where the pattern will be illuminated; uses an inert atmosphere for the part build; uses an inert atmosphere for keeping the optics in the system clean; and wherein the laser-spatial modulator combination creates and image on the powder bed that has a multi-kW/cm2 power density which is required for fusing metals.
Moreover, there is provided an additive manufacturing system for metals that uses a laser and a spatial light modulator, an array of spatial light modulators, and both to form an energy pattern on a powder metal layer that is fused to the layer below, by for example, using a conduction mode welding process with the aid of a second laser to pre-heat the powder bed, a gantry system to step and repeat the image across the powder bed, to continuously print the image by scrolling the image across the DMD synchronized with the movement of the head, the bed and both to provide a time, and preferably a greater amount of time to melt the powder, a motion control system an elevator to displace the part down as each layer is fused, and a powder distribution system that can both spread the powder and compact it before fusing, and an air tight build chamber.
Further, there is provided these systems and methods having the feature of the build plate include any number of metal materials, including aluminum, anodized aluminum, titanium, steel, stainless steel, nickel, copper, combinations of these, as well as, any other material which may be the same material as the powder or different.
Still further, there is provided these lasers, systems and methods having one or more of the following features: wherein the laser is approximately a 450 nm blue laser; wherein the laser is in the wavelength range of 300-400 nm; wherein the laser is in the wavelength range of 400-500 nm; wherein the laser is in the wavelength range of 500-600 nm; wherein the laser is in the wavelength range of 600-800 nm; wherein the laser is an infrared laser in the range of 800 nm-2000 nm; wherein the laser is homogenized by either a light pipe, micro-lens homogenizer, diffractive element or a homogenizing optical fiber; wherein the laser can be time shared between multiple print heads or multiple printer systems; wherein there is a secondary laser; wherein the secondary laser is a 450 nm blue laser; wherein the second laser is in the wavelength range of 300-400 nm; wherein the secondary laser is in the wavelength range of 400-500 nm; wherein the secondary laser is in the wavelength range of 500-600 nm; wherein the secondary laser is in the wavelength range of 600-800 nm; wherein the secondary laser is an infrared laser in the range of 800 nm-2000 nm; is homogenized by either a light pipe, micro-lens homogenizer, diffractive optical element, or a homogenizing optical fiber; wherein the secondary laser is time shared between multiple print heads or multiple printer systems; wherein the system has a spatial light modulator; wherein the spatial light modulator is a Digital Micro-Mirror Device (DMD); wherein the spatial light modulator is any of a class of spatial light modulator capable of handling multi-Watts to multi-kW power levels; wherein the system includes zonal radiant heaters for maintain the build chamber temperature; wherein the system includes a heated build plate; wherein the system includes a pyrometer or a FLIR camera to monitor or control the build plate temperature; wherein the system includes a thermocouple or RTD embedded in the build plate to monitor or control the temperature of the build plate; wherein the system includes software for determining the optimum build strategy; wherein the system uses an inert atmosphere for the part build; wherein the system uses an inert atmosphere for keeping the optics in the system clean; wherein the system includes a laser-spatial modulator combination that creates and image on the powder bed that has a multi-Watt to multi-kWatt power density.
Moreover, there is provided these lasers, systems and methods having one or more of the following features: having a second laser, wherein in the second laser is used for preheat in the system and creates and region overlapping the image of the spatial-filter laser system on the powder bed that has a multi-Watt to multi-kWatt power density; and, wherein laser system has a powder bed that has a multi-Watt to multi-kWatt power density.
Yet further, there is provided an additive manufacturing system for metals that uses a laser and a spatial light modulator to form a pattern on a powder metal layer that is fused to the layer below, a gantry system to step and repeat the image across the powder bed, a motion control system, an elevator to displace the part down as each layer is fused, and a powder distribution system that can both spread the powder and compact it before fusing, and an air tight build chamber.
Additionally, there is provided these systems, subsystems and methods having one or more of the following features: wherein the laser is in the wavelength of a 450 nm blue laser; wherein the laser has a wavelength range of 300-400 nm; wherein the laser has a wavelength range of 400-500 nm; wherein the laser has a wavelength range of 500-600 nm; wherein the laser has a wavelength range of 600-800 nm; wherein the laser is an infrared laser in the range of 800 nm-2,000 nm; wherein the laser is homogenized by either a light pipe, micro-lens homogenizer, diffractive element, or a homogenizing optical fiber; wherein the laser is time shared between multiple print heads or multiple printer systems; wherein the spatial light modulator is a Digital Micro-Mirror Device (DMD) array which is an array of micro-mirrors; wherein the spatial light modulator is any of a class of spatial light modulator capable of handling multi-W to multi-kW power levels; wherein the DMD is air cooled; wherein the DMD is water cooled by a water heat exchanger such as a micro-channel cooler; wherein the laser is the DMD is cooled by a Peltier cooler; wherein the DMD is cooled by forced air over the front or back or both of the DMD; wherein the system includes zonal radiant heaters for maintain the build chamber temperature; wherein the system includes a heated build plate; wherein the system includes a pyrometer or a FLIR camera to monitor or control the build plate temperature; wherein the system includes a thermocouple or RTD embedded in the build plate to monitor or control the temperature of the build plate; wherein the system includes software for determining the optimum build strategy; wherein the system of claim 1 that includes a separate secondary laser for heating the powder bed only where the pattern will be illuminated; wherein the system uses an inert atmosphere for the part build; wherein the system uses an inert atmosphere for keeping the optics in the system clean; and wherein the laser-spatial modulator combination of the system creates and image on the powder bed that has a multi-kW power density.
Yet further there is provided an additive manufacturing system for metals that uses a laser and a spatial light modulator to form a pattern on a powder metal layer that is fused to the layer below with the aid of a second laser to pre-heat the powder bed, a gantry system to step and repeat the image across the powder bed, a motion control system an elevator to displace the part down as each layer is fused, and a powder distribution system that can both spread the powder and compact it before fusing, and an air tight build chamber.
Still further there is provided an additive manufacturing system for metals that uses multiple lasers and multiple spatial light modulators to form a single larger pattern on a powder metal layer that is fused to the layer below, a gantry system to step and repeat the image across the powder bed, a motion control system, an elevator to displace the part down as each layer is fused, and a powder distribution system that can both spread the powder and compact it before fusing, and an air tight build chamber.
Moreover there is provided an additive manufacturing system for metals that uses multiple lasers and multiple spatial light modulators to form a checkboard pattern of images and non-images on a powder metal layer that is fused to the layer below, a gantry system to step and repeat the image across the powder bed, a motion control system, an elevator to displace the part down as each layer is fused, and a powder distribution system that can both spread the powder and compact it before fusing, and an air tight build chamber.
Yet further there is provided a laser spatial-light modulator combination that creates an image and moves the image across the DMD to create a stationary image on the moving gantry system to extend the exposure time for printing the pattern in the material being fused. Still further there is provided an additive manufacturing system for forming metal objects from metal powders, the system having: a laser source to provide a build laser beam along a build laser beam path; a heating means for heating a metal powder; a Digital Micro-Mirror Device (DMD) on the laser beam path, whereby the build laser beam is directed into the DMD, wherein the DMD creates a 2-D image pattern that is reflected from the DMD along the laser beam path to an optical assembly; and, the optical assembly directing the laser beam to the metal powder, whereby the 2-D image pattern is delivered to the metal powder.
Additionally, there is provided these systems, subsystems and methods having one or more of the following features: wherein the heating means is selected from the group consisting of electric heaters, radiant heaters, IR heaters and a laser beam; wherein the heating means is a laser beam having a wave length in the blue wave length range; wherein the metal powder forms a bed of metal powder; wherein the laser beam has a wave length select from the group consisting of blue and green; wherein the laser beam has a wave length selected from the group consisting of about 450 nm, about 460 nm, about 515 nm, about 532 and about 550 nm; wherein the laser source has a power of about 1 kW to about 20 kW; wherein and the 2-D image delivers a peak power density to the metal powder of from about 2 kW/cm2 to about 5 kW/cm2; wherein the DMD has maximum average power density level; and wherein the peak power density level of the 2-D image on the metal powder is at least 500× greater than the maximum average power density level of the DMD; wherein the DMD has maximum average power density level; and wherein the peak power density level of the 2-D image on the metal powder is at least 1,000× greater than the maximum average power density level of the DMD; wherein the heating means is configured to heat the powder to within 200° C. of a melting point of the metal powder; wherein the heating means is configured to heat the powder to within 100° C. of a melting point of the metal powder; wherein the heating means is configured to heat the powder to about 400° C. of a melting point of the metal powder; wherein the heating means is configured to heat the powder to about 600° C. of a melting point of the metal powder; wherein the heating means is configured to heat the powder to about 400° C. of a melting point of the metal powder and maintain the powder at that temperature; wherein the heating means is configured to heat the powder to about 600° C. of a melting point of the metal powder and maintain the powder at that temperature; wherein the heating means is configured to heat the powder to within 200° C. of a melting point of the metal powder and maintain the powder at that temperature; having a second laser source to provide a second build laser beam along a second build laser beam path; a second Digital Micro-Mirror Device (DMD) on the second laser beam path, whereby the second build laser beam is directed into the second DMD, wherein the second DMD creates a second 2-D image pattern that is reflected from the second DMD along the second laser beam path to a second optical assembly; wherein the 2-D image pattern is delivered to a first area of the metal powder, and the second 2-D image pattern is delivered to a second area of the metal powder; wherein the first area and the second area are different; and, wherein the first area and the second area are adjacent.
Additionally, there is provided these systems, subsystems and methods having one or more of the following features: wherein the DMD array is optimized for wavelengths in at least one of the following wavelengths: the blue wavelength range, 400 nm, about 440 nm, 450 nm, and about 450 nm, 460 nm and about 460 nm, the green wavelength range, 515 nm, about 515 nm, 532 nm, about 532 nm, and the red wavelength range of 600 nm to 700 nm.
Additionally, there is provided these systems, subsystems and methods having one or more of the following features: wherein the build laser beam has a wavelength selected from at least one of the following wavelengths: the blue wavelength range, 400 nm, about 440 nm, 450 nm, and about 450 nm, 460 nm and about 460 nm, the green wavelength range, 515 nm, about 515 nm, 532 nm, about 532 nm, and the red wavelength range of 600 nm to 700 nm.
Yet further there is provided an additive manufacturing system for forming metal objects from metal powders, the system having: a laser source to provide a build laser beam along a build laser beam path; a second laser source for providing a heating laser beam; a Digital Micro-Mirror Device (DMD) on the laser beam path, whereby the build laser beam is directed into the DMD, wherein the DMD creates an image that is reflected from the DMD along the laser beam path to an optical assembly; and, the optical assembly directing the laser beam to the metal powder, whereby the image is delivered to the metal powder.
Still further there is provided a laser spatial-light modulator combination that projects a 2-D pattern onto a powder bed with an optimized grey scale in time or in the pattern, such that the heat manipulates the molten puddle into the desired build shape yielding sharper transitions and denser parts.
Additionally, there is provided a system where an additional beam path is created to collect the laser light not directed to the build area. This second beam path is redirected by mirrors or prisms to overlap or be adjacent to the build pattern from the main build laser beam with a spot smaller than; larger than; or the same size as the pattern from the build laser beam. This additional beam may be homogenized by either a light pipe, micro-lens homogenizer, diffractive element, or a homogenizing optical fiber and shaped in a gaussian, super-gaussian, flat-top, annulus, or asymmetric beam. This additional beam provides additional heat to the molten puddle or adjacent to the puddle to increase the printing speed.
In general, the present inventions relate to laser processing of materials, laser processing by matching preselected laser beam wavelengths to the material to be processed to have high or increased levels of absorptivity by the materials, systems configurations that provide for greater speed, efficiency and size of objects that are built, and in particular laser additive manufacture of raw materials into large structures, parts, components and articles with laser beams having high absorptivity by starting raw materials.
An embodiment of the present systems and methods can use any laser wavelengths, but the preferred embodiment is to use a pair of blue lasers to print and fuse the layers of the part in a parallel fashion using a spatial light modulator as the means of defining the pattern on the powder bed that is to be fused. The laser source and the laser beam in embodiments can have wavelengths in the blue wavelength range and preferably can be 450 nm, about 450 nm, 460 nm, about 460 nm and have bandwidths of about 10 μm, about 5 nm, about 10 nm and about 20 nm, and from about 2 nm to about 10 nm, as well as greater and smaller values. The laser source and the laser beam in embodiments can have wavelengths in the green wavelength range and, for example, can be 515 nm, about 515 nm, 532 nm, about 532, nm, 550 nm, about 550 nm and have bandwidths of about 10 μm, about 5 nm, about 10 nm and about 20 nm, and from about 2 nm to about 10 nm, as well as greater and smaller values. Combinations and variations of these various wavelengths can be use in a system.
The print engine for an embodiment of the present systems and methods is based on a Digital Micro-Mirror Device (DMD) array, embodiments of which can be obtained from Texas Instruments (TI), which creates the 2-D energy pattern to be printed. All of the DMD products made by TI are candidates for this process, the DMD used to print the pattern in
In general, a Digital Micromirror Device (DMD), is a device that uses very small mirrors that can be made of aluminum to reflect light to make an image. The DMD may also be referred to as DLP chip. Embodiments of these devices can be a couple of centimeters (cm), from about 1 cm to about 3 cm, from about 1 cm to about 2 cm, a centimeter or less, less than 0.5 cm, less than 0.2 cm, or smaller, for their cross sectional dimension, (e.g., side of square, diameter of a circle, or long side of a rectangle, these devices may also be other shapes), These DMDs can contain from about 100,000 to 4 million, at least about 100,000, at least about 500,000, at least about 1 million, about 2 million, or more, mirrors, with each mirror, measuring about 4 μm or less, about 7.56 μm or less, about 10.8 μm or less, about 10 μm or less, from about 4 μm to about 20 μm and combinations and variations of these and larger and smaller sizes. The mirrors can be laid out in a predetermined pattern, such as matrix, for example, like a photo mosaic, with each mirror representing one pixel.
In an embodiment the DMD includes; a CMOS DDR. SRAM chip, which is a memory cell that will electrostatically cause the mirror to tilt to the on or off position, depending on its logic value (0 or 1); a heat sink; an optical window, which allows the laser to pass through while protecting the mirrors from dust and debris.
In embodiments the DMD has on its surface several hundred thousand microscopic mirrors, or more, arranged in typically a rectangular array which correspond to the pixels in the image to be formed and displayed. The mirrors can be individually rotated, e.g., ±10-12°, or more or less, to an on or off state. In the on state, the laser from the laser source, e.g., the build laser and build laser beam, is reflected into the lens making the pixel direct the build laser energy into the image on the powder bed. In the off state, the laser beam, e.g., the build laser, is directed elsewhere, e.g., to a beam dump, making the pixel not contribute to the image or the fusing of the powder. It being understood that in embodiments the pre-heat laser beam many also be directed to and reflected or refracted from a DMD device to form a pre-heat image on the powder in the bed.
In an embodiment, which could be theorized as being analogous to greyscales of picture, the mirror is toggled on and off very quickly, and the ratio of on time to off time determines the amount of fusion or bonding of the powder in the powder bed. This provides the capability to control laser power, and power density (e.g., kW/10 cm2), of the laser beam on the powder bed, without changing the power of the output beam from the laser source. In some embodiments more than 500 different powers and power densities, more than 700 different powers and power densities, and more than 100,000 different powers and power densities can be obtained. An alternative method to achieve a grey scale affect is to pixelate the image, dropping out individual pixels that are small in size compared to the thermal diffusion length in the material being processed. This effectively reduces the average power delivered to the image. This grey scale, whether in time or in space can be used to manipulate the melt pool and force it into a preferred shape.
Embodiments of DMDs for use in the present systems, print heads and print engines, can be obtained from TI, these DMDs would include: DLP2010, DLP3000, DLP3010, DLP4500, DLP4710, DLP5500, DLP6500, DLP7000, DLP9000, DLP9000x, DLP9500, with digital controllers; DLPA2000, DLPA3000, DLPA3005, DLPC3430, DLPC3433, DLPC3435, DLPC3438, DLPC3439, DLPC3470, DLPC3478.
Turning to
Turning to
In an embodiment, of the additive manufacturing systems, the first laser beam path is the build laser beam and the build laser beam path, as it is the laser beam that fuses the powder to build an object. The build laser beam can have a wavelength in the blue wavelength range and preferably 440 nm, about 440 nm, 450 nm, and about 450 nm, 460 nm and about 460 nm, in the green wavelength range and, for example, can be 515 nm, about 515 nm, 532 nm, about 532 nm. The build laser beam can have any of the powers, power densities, peak powers and repetition rates set forth in this specification. The second laser beam path and the second laser beam which travels along that path, is a pre-heat laser beam. It does not need to be the same wavelength, and can be anything from 440 nm to 1,100 microns, or it can be the same wavelength as the build laser, it has a lower, similar or higher power density on the powder bed and is used to pre-heat the powder bed, as well as maintain the temperature of the powder bed, to facilitate the build laser's ability to fuse the powder to build an object.
In an embodiment of printer head 230, the second laser input 212 is connected to a laser source for pre-heating the bed of powder. In this manner, the second laser beam path, and its associate optics are for a pre-heating system. Thus, in this embodiment the first beam path and components from connector 201 through window 209 to image 210, as described above, provides a laser beam for fusing the powder bed material together, i.e., a build laser beam, or fusing laser beam; and the second beam path is for providing a pre-heating laser beam.
An embodiment of the present systems and methods can use any laser wavelength, but the preferred embodiment is to use a pair of blue lasers to print and fuse the layers of the part in a parallel fashion using an array of spatial light modulators combined with an array of lasers as a means to define a 2-D energy pattern on the powder bed to be fused. The energy pattern may be contiguous or separate, when separate portions of the part or separate parts are processed in parallel. By combining multiple energy patterning systems together, a higher total power can be delivered to the surface of the powder bed and as a result a larger part can be printed with a single pulse resulting in a substantial improvement in the build rate for the machine. Multiple DMDs are used because of the limitation on the power handling capability of the DMD. An off the shelf DMD system is capable of handling from 25 W/cm2 up to 75 W/cm2 of blue laser light on a continuous basis depending on the backplane temperature and cooling method. The larger the part to be produced, the greater the amount of total power required to completely melt the 2-D pattern across the surface. Since the DMD in embodiments can be the limiting factor for the power delivered, multiple DMDs in parallel can be used to provide the area scaling necessary to achieve the high build rates desired. Furthermore, this print engine can be mounted on a precision gantry system that allows the 2-D image to be stitched together to form a larger 2-D image which is a single layer of the part. Embodiments of the system can include a powder spreader as part of the gantry system or separate from the gantry, and an elevator as part of the build volume. The build volume should have reduced oxygen, and preferably is oxygen free and can be filled, for example, with either an inert gas such as Argon, or a mixture of gases to promote the fusing process such as Argon-CO2. The energy patterned areas can be pre-heated by a secondary laser source or directly heated by electric heaters and radiant heaters to reduce the heat loss from the part during the manufacturing process. The secondary laser or secondary heat source raises the base temperature of the powder bed and reduces the energy requirements for melting the powder by the laser/spatial modulator system, i.e., the fusing or build laser beam or sub-system of the additive manufacturing system. The light from mirrors not directing the beam to the powder bed can also be collected, redirected, and homogenized to preheat the powder bed to reduce the energy required from the laser. In embodiments, the conduction mode welding process is the preferred method for fusing each layer together which eliminates the spatter normally encountered in the keyhole process which is the baseline process for all additive manufacturing scanned laser systems.
2-D Energy Patterning System (for 3-D Build)
A preferred embodiment for this system is a Digital Micro-Mirror Device (DMD) from TI. This array consists of micro-mirrors that tilt when commanded to turn-off or turn-on the transmitted light. Grey scale is accomplished by modulating the position of the mirrors or the power setting of the laser at a high speed during the process to set the amount of energy to be delivered to the surface or by randomly turning mirrors to the off state throughout the image to reduce the average power density in the image. A preferred DMD arrays is one that has been optimized for use with the wavelength of the laser beam, e.g., optimized for wavelengths in the blue wavelength range and preferably 400 nm, about 440 nm, 450 nm, and about 450 nm, 460 nm and about 460 nm optimized for wavelengths in the green wavelength range and, for example, can be 515 nm, about 515 nm, 532 nm, about 532 nm and in the red wavelength range of 600 nm to 700 nm. Typical DMDs for light in the visible wavelengths have a reflectivity of 88% at 450 nm and a diffraction efficiency in excess of 64%. This high transmissivity enables these devices to handle an average power density of 25 W/cm2 or greater depending on the cooling method, and to handle build laser beams in the blue, green and red wavelengths, (visible light). Tests conducted on the DMD with a micro-channel cooler have shown that it is safe to operate the device at power densities of up to 75 W/cm2. DMDs can have operating power densities, e.g., average power density rating, of from about 25 W/cm2 to 160 W/cm2, about 50 W/cm2 to 100 W/cm2, and about 25 W/cm2 to 75 W/cm2, as well as greater and smaller values. The average power density rating is the continuous heat load rating for this device. Because of the high reflectivity, short pulses at low repetition rates can have a substantially higher power density than the continuous power rating of the device. Turning to
Thus, in embodiments of the present system the DMD devices in additive manufacturing systems and methods are subject to, and reflect and direct laser beams to form an image on the powder bed, where the laser beams have a peak power density (kW/cm2) on the powder bed that is 2×, 10×, 100×, 1,500×, from 100× to 1,000× and greater, than the average rated power density for the DMD.
Turning to
In an embodiment, a 6 kW blue laser source (a build laser beam) is operated with a pulse width of 6.5 mseconds and a repetition rate of 3 Hz, this corresponds to a build rate in excess of 75 cc/hr when using copper powder. A homogenizer is used to evenly distribute the laser energy across the DMD. The power density on the DMD is 2.5 kW/cm2 which is 2 cm wide by 1.1 cm high. The DMD has a resolution of 1,920 mirrors by 1,080 mirrors on a 10.8 μm pitch. The reflectivity of the DMD mirrors at this wavelength is approximately 88%, the transmissivity of the device's window is 97%, the diffraction efficiency of the DMD is −62% at this wavelength and the transmissivity of the imaging optic is assumed to be 99%. Using a 2:1 imaging optic, a 10 mm×5.5 mm image is relayed to the powder bed and the estimated losses results in −6 kW/cm2 power density on the powder bed from the laser-spatial light modulator combination which is a factor of 1.6× above the intensity used in the test in
By resolution of the system or method, it is meant that objects built by the system can have their smallest part, or smallest dimension, equal to the stated resolution, e.g., the resolution defines the smallest dimension of an object that can be built. Thus, by resolution of the laser systems, resolution of the method, it is meant that the system and method have the ability to build a part, or have features in that part, that are at the resolution. Thus, by way of example a 75 μm resolution would provide the ability to build parts having their smallest dimension at 75 μm, having their smallest feature at 75 μm, or both. Embodiments of the blue laser 3-D additive manufacturing systems, e.g., 3-D blue laser printers, and embodiments of the blue laser 3-D additive manufacturing methods have resolutions from about 0.5 μm to about 200 μm, and larger, about 0.5 μm to about 100 μm, about 0.5 μm to about 50 μm, less than about 100 μm, less than about 75 μm, less than about 50 μm, less than about 25 urn, less than about 10 μm, and less than about 5 μm. The systems can have both the capability for large resolution, e.g., greater than 200 μm, and very fine resolution of about 0.5 μm to about 10 μm, and 1 μm to about 5 μm. Further, embodiments of the present systems and methods, including the embodiments and examples in the specification, as well as those embodiments having, wavelengths of blue, 440 nm, about 440 nm, 460 nm, green, 515 nm, about 515 nm, 532 nm, about 532 nm, 550 nm, about 550 nm, have resolutions from about 10 μm to about 0.5 μm, less than 10 μm. less than 5 μm, less than 2 μm, from about 3 μm to about 0.9 μm, about 1 μm, and smaller values, as well as the other values in this paragraph.
An embodiment using a 500 Watt blue laser source to heat the copper powder bed through the DMD, can provide a pulse wide of up to 78 msec when pulsed at a 1.5 Hz repetition rate. Under these conditions, the 500 Watt blue laser source would deliver 39 Joules to the copper powder bed which is sufficient energy to go from a 400° C. background bed temperature to melting the copper.
In some embodiments, while the laser-spatial light modulator combination is capable of providing sufficient energy to melt the 50 μm thick powder layer, it may not be sufficient energy to fuse to the layers below. Since a conduction mode weld proceeds through the layers of material in a spherical fashion, the weld is as wide as it is deep. For example, a 50 μm deep weld bead would be at least 50 μm wide. To make certain that the powder layer is fused to the layer beneath it, then the minimum feature size will have to be at least 1.5-2× the depth of the powder layer. This means that a 75-100 μm wide bead is used to fuse the powder layer to the lower layer. Taking the energy required to fuse to the lower solid layers into consideration increases the energy required to melt and fuse the powder from 36 Joules to 86 Joules when going from 400° C. to the melting point of copper. In embodiments, this is not achievable with just the laser-spatial filter combination, so either the bed temperature is raised or a separate source of heat is added. By adding a second laser, preferably without a spatial light modulator, the additional heat is added to raise the temperature of the powder, without melting it. Thus, this second laser, can pre-heat the powder and maintain the temperature of the powder layer and the build object above ambient temperature, for example the powder can be pre-heated to and maintained at temperature of greater than 100° C., greater than 200° C., greater than 300° C., greater than 400° C., from about 300° C. to about 600° C., within 300° C. of the melting point of the powder, within 200° C. of the melting point of the powder, within 100° C. of the melting point of the powder, up to and just below the melting temperature of the powder, and high and lower temperatures.
As used herein, unless expressly stated otherwise, spatial light modulator, laser/spatial light modulator, DMD systems, laser-spatial, and similar such terms, refer to the same general type of system, or subsystem, using micro-mirrors, micro-reflective assemblies, or similar reflective components having micro level or sub-micro level resolutions, to create the laser pattern and images for the build laser beam on the powder bed as well as liquid crystal and other types of crystal based spatial light modulators.
The second laser (e.g., second beam path of
In an embodiment, the laser-spatial light modulator pair is based on a 6,000 Watt blue laser operating at a repetition rate of 1.5 Hz. The pre-heat laser is a 750 Watt laser. The pre-heat laser operates for the same duration as mentioned above (66 msec) to increase the powder bed temperature to within 200° C. of the melt temperature of the material to be melted (e.g. the powder in the powder bed), in this case copper. A pyrometer or FLIR camera is used to monitor the temperature of the powder bed during this pre-heat process and controls the laser power to maintain that temperature until the laser-spatial light modulator image illuminates the powder bed region and fuses the powder to the lower layer. The 6,000 Watt laser is on for 6.5 msec, while the 750 Watt laser may be on for 66 msec or longer. In this embodiment, the chamber temperature is assumed to be at or near room temperature.
In an embodiment, the laser-spatial light modulator pair is based on a 500 Watt blue laser operating at a maximum repetition rate of 1.5 Hz. The pre-heat is a 1,000 Watt laser. The pre-heat laser operates for the same duration as the case above, about 78 msecs. However, the pre-heat laser with the higher power level now operates for only 25 msecs, giving additional time to reposition the pattern. In this embodiment, the chamber is assumed to be at or near room temperature.
The laser printing engine described is mounted on a precision gantry system, such as the embodiment of
The build begins with a Computer Assisted Design file, typically a step file. Software first divides the object into 50 μm slices, less or greater depending on resolution and shape. The surface revealed after the slicing is then divided up into sections that are the same image size as the spatial light modulator. The build strategy is then decided by the software as to which portion of the pattern to expose first, what the exposure levels should be and what support structure if any should be used. The software also determines the optimum on-time for the pre-heat laser as well as the laser-spatial modulator system. The pre-heat time may vary depending on the density of the base material, the melt temperature of the base material, the amount of material in the layer below the layer to be fused and the density of the material in the layer below the layer to be fused. Based on the size of the part, the part complexity and the orientation of the part, radiant heaters may be used to keep the bed, walls or ceiling of the build chamber at an optimum temperature to prevent heat loss at the wrong rate to the build environment. This processing sequence is outlined in
Embodiments of the present inventions have a laser system illuminating a Digital Multi-mirror Device (DMD) which is imaged through an optical system to a workpiece for additive manufacturing. Illumination of a DMD with a coherent laser source will generate both grating dispersion and diffraction due to the small pitch of the DMD, typically about 10 microns. The optical system can correct for dispersion of the laser source by incorporating a grating with opposite dispersion and a 4f optical system to collect and magnify or de-magnify the beam such that the angular magnification matches the dispersion from the DMD. The power in each diffraction order can be adjusted by the angle of incidence of the input beam onto the DMD such that the system is in a blaze or anti-blaze condition or between these conditions. With the power directed into the lowest dispersion orders, the entrance pupil of the optical system is designed such that the lowest five (5), or nine (9) orders of the diffraction are collected by the optical system and imaged onto the workpiece. The laser will pass through a beam homogenizer, set of crossed Powell lenses, a fiber homogonizer, or other beam shaping optic or optics before forming an image on the DMD. The homogeneity of the illumination on the DMD may vary and may be corrected in software by varying the on time for each pixel as a function of the power of the illumination on any given pixel. This may be accomplished by precisely characterizing the beam before the print or by monitoring the illumination of the DMD or the image on the workpiece in real time during the print to account for any changes to the beam or the homogeneity.
A part model consists of an image or sequence of images, along with the instructions on how to slice and execute tool paths for each image slice which is displayed on the DMD. A slice refers to a rectangular image segment that is printed in a single horizontal or vertical linear stage motion. The length or width of a slice is dependent on the size of the DMD region in use. Slices may be displayed as a sequence of images on the DMD as the stage translates. The frames may be offset and modified to account for variations in the printing speed, the DMD to powder bed magnification, mirror pitch, laser pulse duration, processing delays, previous layer thicknesses or geometry. The frames may be repeated for printing parts or portions of parts which require additional power to be delivered to the workpiece.
The DMD will heat during the printing due to absorption on the mirrors, limiting the frame rate due to the requirement for cooling. The DMD may be developed or modified with High Reflection (HR) mirrors to reduce the thermal load on the mirrors. In addition to HR mirrors, a DMD with larger or smaller mirrors or larger, smaller, or different shaped mirror mounts may be utilized or developed to decrease the thermal relaxation time of the DMD. In addition, the DMD will cool more rapidly in one mirror state compared to another. The DMD may be run in a state where between pulses of the laser all mirrors on the DMD are shifted to the state which dissipates heat most efficiently to reduce the amount of time required for cooling down the DMD.
The number of mirrors in the state corresponding to the part model will vary depending on the part which is to be printed. In a typical printed geometry, the spatial duty cycle, that is the percentage of mirrors in the state corresponding to the part model, will vary and be less than 100%, typically less than 75%, and often lower. The power incident on the mirrors not in the state corresponding to the part model can be utilized by directing it in a secondary beam, called the pre-heater beam, which is sent through a diffuser and softly focused onto the workpiece. The pre-heater beam may contain a variable amount of power and may incorporate a variable attenuator to reduce the power to a constant level throughout the print. The pre-heater beam will generate a spot on the workpiece which is equal to or larger than the part model and may be used to both pre-heat the powder bed and/or be used to cure the part post printing. The Pre-heater beam may have a variable focus to allow for adjustment of the fluence on the powder bed due to changes in the process parameters, changes in the material properties during the print or changes to the pattern being printed.
In addition, the Pre-heater beam may be the state which is referred to as the ON-STATE by the manufacturer or the OFF-STATE where the other state is the state which corresponds to the part model to be printed. A system may also be designed such that the DMD is tiled, and two images are multiplexed onto the DMD on alternating pixels. In this configuration the ON-STATE will correspond to one of the part model beams while the OFF-STATE will correspond to one of the other part model beams. The pixels for each beam which are not corresponding to the part model will be directed into the FLAT-STATE of the DMD and this beam will be the pre-heat beam. In this configuration the pre-heat beam may be split into two beams and directed to the two separate printing areas for each of the multiplexed images.
The system may be used with either a powder bed or with a blown powder system. The powder that is placed on the bed or blown into the print head may be a single alloy or a blend of metal alloys. In the configuration where a blend of metal alloys is used, the blend may vary throughout the print and the process parameters of the laser and optical system may be varied to account for the different material and optical properties of the alloy(s). Following the printing of the part, the part may be put through a Hot Isostatic Pressing (HIP) process to increase the density of the part. If a HIP process is to be conducted, the process parameters will be adjusted to account for the change in finished part dimensions.
When Illuminated by spatially coherent laser light the DMD will generate a number of diffraction orders with the first order surrounded by 4 additional orders and 45° in each direction. The distance between each of the orders in angular space is given by λ/d where λ is the wavelength of light of the optical system and d is the grating pitch. This invention uses an entrance pupil which subtends the lowest five (5) or nine (9) orders with a full angle of greater than 4.8° or 9.6° for a central wavelength of 450 nm and a standard DMD pitch of 10.8 microns.
The angle of incidence on the DMD affects if the DMD is in a blaze condition or an anti-blaze condition. A blaze condition occurs when the output angle of an order of the grating dispersion for the central wavelength of the laser corresponds to the output angle of the lowest diffraction order due to the tilt of the mirrors. The incident angle is given by θi, and the angle of the various grating dispersion orders are given by the grating equation which can be re-arranged to solve for the grating dispersion order angle as a function of the order number, n as:
The diffraction input angle φi is given by φi=θi+θtilt where θtilt is the tilt of the mirrors in the ON-STATE or the OFF-STATE. The diffraction output angle φr=φi. For the case of a DMD operating at 450 nm with a 10.8 micron mirror pitch in the OFF-STATE configuration there are three input angles which satisfy the blaze conditions between −10° and 40° input angle for the 7+th, +8th and +9th orders at −33.5°, −24.7° and −13.6° respectively. This is shown schematically in
The grating dispersion that is created by illumination of the DMD with a broadband laser source can be compensated by selection of a corresponding grating imaged with magnification through a 4f optical system with a turning mirror. The initial grating dispersion caused by the DMD and compensated by the correction grating are both given by the grating equation shown here:
d(sin(θi)+sin(θn))=nλ
The partial derivative of either the input or the output angle is taken as a function of the wavelength and given by:
15 The partial derivative of either the input or the output gives the angular spread of the beam. The output beam of the DMD is ΔθDMD and the input to the grating is ΔθG. These are written as:
The spot size of a focused beam in the paraxial approximation is given by Ø=f*θe. Where Ø is the focused spot diameter and f is the focal length of the lens. In the preferred embodiment the 4f system is constructed such that the DMD is placed one focal length in front of a lens with focal length of f1 and the grating is placed one focal length behind a second lens with a focal length of f2. The two lenses are separated by a distance of f1+f2 such that they share a focused spot or virtual spot at the Fourier plane.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that a laser part image may be defined on a layer-by-layer basis. Each image is divided into smaller overlapping rectangles, representing the eventual tool path and corresponding patterns to be displayed on the DMD. Further, the frames may be offset from one another by a calculated number of pixels based on the speed of the stage, DMD to powder surface de-magnification, DMD mirror pitch, Laser pulse duration, and/or delays associated with displaying images. In addition, the frames may be repeated when printing coarse geometry or to save on computation times.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that images may be transformed or otherwise processed at any time, including at run time, to influence Laser to powder interactions, leverage collected in-situ data, impart a bias on final build characteristics, or account for existing anomalies in the powder. Image manipulation may also be performed based on other knowledge on the part, environment, or process.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that the DMD state may be cycled during the idle time to dissipate heat more efficiently than resting in the previous image state.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that a DMD with AR coated mirrors may be used or developed to reduce thermal losses in the mirrors.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that a DMD design with different sized mirrors may be used or developed to decrease the thermal relaxation time.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that the images formed on the DMD form a gradient to the laser power by turning off select mirrors at sizes smaller than the minimum particle size. The gradient may be formed by turning off mirrors statically or by alternating on and off pixels between frames while the laser is dwelling in a region.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that a digital gray-scaling of the DMD may be used to homogenize the beam and spot on the workpiece by turning off specific pixels in the image or by reducing the dwell time of specific pixels to reduce the power delivered to the spot for a given region.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that a powder fed onto the bed contains a different mixture of alloys in different regions of the print, and the laser and DMD may be adjusted to account for the different process parameters needed to print the varying metal alloy mixture.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that the system accommodates two or more DMDs per laser head where the DMDs are synchronized, and the beam actively switched between the two such that while one or more DMD(s) are cooling between pulses the laser source is illuminating a subsequent DMD and operating in a CW or quasi-CW mode.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that the pre-heating beam may follow the printed area to additionally cure the printed part following the print.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that the pre-heating beam may have a variable focus to adjust the fluence on the part during or between layers or during and stage of the print.
The various embodiments of additive manufacturing systems and processes, including the Examples and Figures, may also include or be configured such that a HIP (hot isostatic pressing) post-processing may be conducted to improve the quality of the printed parts.
The following examples are provided to illustrate various embodiments of the present laser systems and components of the present inventions. These examples are for illustrative purposes, may be prophetic, and should not be viewed as limiting, and do not otherwise limit the scope of the present inventions.
An embodiment of an additive manufacturing system as generally shown in
An embodiment of the DMD print head as generally shown in
An embodiment of the present invention relates to using multiple DMD within the same imaging aperture or parallel imaging apertures. Turing to
Two additional laser build subsystems of the same configuration as system 941, 942, would be used in this system, but are not shown in the drawing. These additional two systems would provide images for image tiles 950c, 950d. In this embodiment the tile images are preferably adjacent.
For additional laser build subsystems of the same configuration as system 941, 942, would be used in this system, but not shown in the drawing. These four additional systems would provide images for image tiles adjacent to 950a, 950b, 950c and 950d into the paper to create a 2-d tiled image.
This system can have lens configurations that provide either an inverting or non-inverting image.
Each DMD has its own laser source and the image space of each DMD can be tiled used shearing mirrors to create a continuous image space over a much larger area than a single DMD system can achieve. There can be some dead space between each DMD image space which can be minimized with proper positioning of the shearing mirrors. The image space can also be effectively spliced together by adjusting the tilt and position of each shearing mirror.
An embodiment of the present invention relates to using multiple DMD within different imaging apertures to create a parallel build capability. Turning to
Each DMD has its own laser source and the image space of each DMD is tiled on the surface of the powder bed creating a checkboard pattern of images and non-image areas. The build strategy can be to either use each single DMD image space to build an individual part. Or to use each individual DMD image space to build a larger part by building multiple sections in parallel.
A second, third or fourth set of systems extending into the paper or adjacent to the shown systems can be added to expand the addressable image area on the powder bed.
This system can have lens configurations that provide either an inverting or non-inverting image.
An embodiment of the present invention relates to using laser beams having visible laser beams, and in particular having wavelengths from 350 nm to 700 nm, in additive laser manufacturing process, and in an additive laser manufacturing system, to build articles (e.g., structures, devices, components, parts, films, volumetric shapes, etc.) from raw materials, such as starting powders, nanoparticles, particles, pellets, beds, powder beds, spray powders, liquids, suspensions, emulsions and combinations and variations of these and other starting materials known, or later developed, in the laser additive manufacturing arts, including the 3-D printing arts.
In an embodiment to build articles from raw materials in laser additive processes, wavelengths are used that have lower reflectivity, high absorptivity, and preferably both for the starting raw material. In particular, in an embodiment laser beam wavelengths are predetermined based upon the starting materials to preferably have absorption of about 10% and more, about 40% and more, about 50% and more, and about 60% and more, and in the range of 10% to 85%, 10% to 50%, about and about 40% to about 50%. In particular, in an embodiment laser beam wavelengths are predetermined based upon the starting materials to preferably have reflectivity's of about 97% and less, about 60% and less, about 30% and less, and in the range of 70% to 20%, in the range of 80% to 30%, and in the range of about 75% to about 25%. In embodiments combinations of both these high absorptions and these low reflectivities can be present. In a preferred embodiment of the systems and processes, the laser beam or beams have wavelengths from about 400 nm to about 500 nm are used to build articles from starting materials made up of gold, copper, brass, silver, aluminum, nickel, alloys of these metals, and other metals, non-metals, materials, and alloys and combinations and variations of these.
In an embodiment the use of blue lasers, e.g., about 380 nm to about 495 nm wavelength, to additive manufacture articles from gold, copper, brass, nickel, nickel plated copper, stainless steel, and other, materials, metals, non-metals and alloys, is preferred. Blue laser beams are highly absorbed by these materials at room temperature, e.g., absorptivities of greater than about 50%. One of several advantages of the present inventions is the ability of a preselected wavelength laser beam, such as the blue laser beam, that is better able to better couple the laser energy into the material during the laser operation, e.g., the additive manufacturing process. By better coupling the laser energy to the material being built into an article, the chance of a runaway process, which typically can occur with the infrared lasers is greatly reduced and preferably eliminated. Better coupling of the laser energy also allows for a lower power laser to be used, which provides capital cost savings or enables multi-laser systems to be cost effective. Better coupling also provides for greater control, higher tolerances and thus greater reproducibility of built articles. These features, which are not found with IR lasers and in IR laser additive manufacturing operations, are important, to among other products, products in the electronics, micro-mechanical systems, medical components, engine components and power storage fields.
In an embodiment a blue laser that operates in a CW mode is used. CW operation can be preferred over a short pulse laser, in many additive manufacturing applications, because of the ability to rapidly modulate the laser output and control the building process in a feedback loop, resulting in a highly repeatable process with optimum mechanical and other physical and esthetic properties, such as reduced surface roughness, improved porosity and improved electrical characteristics.
Preferably, in some embodiments active monitoring of the article being build is used to check the quality of the article and the efficiency of the additive manufacturing process and systems. For example, when the laser is processing a high resolution region of the part being printed, a thermal camera can be used to monitor the average temperature of the surface and a feedback loop can be used to decrease or increase the laser power to improve the weld puddle and ultimately the surface quality of the part. Similarly, when the laser beam is defocused to sweep through a large low resolution region of the part, the feedback loop can command more laser power to keep the average temperature at the optimum processing point, greatly reducing the time to print a part.
Examples of scanners and optics that can be used with the present systems include mirrors mounted on high speed motors, rotating polygon mirrors or high speed galvanometers. A mirror mounted on axis of a high speed motor can create a scanning beam as the mirror is rotated through 360 degrees. The higher the speed of the motor, the faster the scan. The only issue with this approach is that the laser must be turned off once the mirror is no longer reflecting the beam as the back side of the mirror passes by the laser beam entrance aperture. The high speed mirror can be used to scan either the x axis or the y axis, whichever axis is chosen, the mirror which scans the other axis must scan at a slow speed proportional to the time it takes to complete one full scan in the initial axis. It is preferred to use a high speed stepper motor in this axis to enable the mirror to be moved in discrete steps while remaining stationary while the first axis is completing its scan. Similarly, a multi-faceted mirror or polygon mirror can be used to perform the high speed scan function allowing higher scan speeds because the scan is reset to the starting position as the beam transitions across each facet of the mirror. These types of mirrors are currently being used in supermarket scanners to scan a product's bar code as it passes by. The primary axis can also be scanned with a high speed galvanometer type mirror which is a resonant type motor and oscillates at a continuous frequency producing high speed movement of the beam. It is also possible to precisely position galvanometer mirrors to a predetermined position, allow systems based on the first and second axis being a galvanometer driven mirror to draw in a vector mode where any point on the process bed can be rapidly addressed by simultaneously moving both mirrors. It is also feasible to combine mirrors mounted on translation stages in a “flying optic” type design where the beam is delivered through free space to a mirror mounted on a gantry style system and is moved in a two dimensional, raster or vector mode at very high speeds.
Embodiments of the present system do not contain and do not require a scanner to build an object.
Turning to
Turning to
The system is configured so that the DMD has an On-State mirror configuration and an Off-State mirror configuration for any given 2-D final image pattern. In either the On-State mirror configuration or the Off-State mirror configuration (and preferably only one or the other and not both) the DMD provides a heating laser beam 1120a along a heating laser beam path 1120 to create a heating image pattern on the surface 1106b. Preferably the heating laser beam and the heating image pattern is a pre-heating laser beam and pre-heating image pattern, in that this laser beam and pattern pre-heats (e.g., increases the temperature before welding), softens or both the starting material, e.g., the metal powder. The heating laser beam and the heating image pattern may also perform other functions such as annealing or the functions of the secondary laser beam. Preferably the wavelength of the heating laser beam 1120 and the laser beam 1102 are the same.
Heating laser beam conditioning optics 1125 may also be including along heating beam path 1120. The conditioning optics 1125 may have an attenuator, a diffuser, other optical devices and combinations and various of these.
The systems and methods of examples 1-13 where the build laser beam has a wavelength selected from one of the following wave lengths: the blue wavelength range, 400 nm, about 440 nm, 450 nm, and about 450 nm, 460 nm and about 460 nm, the green wavelength range, 515 nm, about 515 nm, 532 nm, about 532 nm, and the red wavelength range of 600 nm to 700 nm. And, were the build laser beam has one or more of the beam properties, e.g., power, power density, repetition rate, etc. set forth in these specifications.
It is noted that there is no requirement to provide or address the theory underlying the novel and groundbreaking processes, materials, performance or other beneficial features and properties that are the subject of, or associated with, embodiments of the present inventions. Nevertheless, various theories are provided in this specification to further advance the art in this area. The theories put forth in this specification, and unless expressly stated otherwise, in no way limit, restrict or narrow the scope of protection to be afforded the claimed inventions. These theories many not be required or practiced to utilize the present inventions. It is further understood that the present inventions may lead to new, and heretofore unknown theories to explain the function-features of embodiments of the methods, articles, materials, devices and system of the present inventions; and such later developed theories shall not limit the scope of protection afforded the present inventions.
It should be understood that the use of headings in this specification is for the purpose of clarity, and is not limiting in any way. Thus, the processes and disclosures described under a heading should be read in context with the entirely of this specification, including the various examples. The use of headings in this specification should not limit the scope of protection afford the present inventions.
The various embodiments of systems, equipment, techniques, methods, activities, and operations set forth in this specification may be used for various other activities and in other fields in addition to those set forth herein. Among others, embodiments of the present inventions can be used with the methods, devices and system of Patent Application Publication Nos. WO 2014/179345, 2016/0067780, 2016/0067827, 2016/0322777, 2017/0343729, 2017/0341180, and 2017/0341144 the entire disclosure of each of which are incorporated herein by reference. Additionally, these embodiments, for example, may be used with: other equipment or activities that may be developed in the future; and with existing equipment or activities which may be modified, in-part, based on the teachings of this specification. Further, the various embodiments set forth in this specification may be used with each other in different and various combinations. Thus, for example, the configurations provided in the various embodiments of this specification may be used with each other. For example, the components of an embodiment having A, A′ and B and the components of an embodiment having A″, C and D can be used with each other in various combination, e.g., A, C, D, and A, A″ C and D, etc., in accordance with the teaching of this Specification. Thus, the scope of protection afforded the present inventions should not be limited to a particular embodiment, configuration or arrangement that is set forth in a particular embodiment, example, or in an embodiment in a particular Figure.
The invention may be embodied in other forms than those specifically disclosed herein without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive.
This application: (i) claims under 35 U.S.C. § 119(e)(1) the benefit of the filing date of, and claims the benefit of priority to, U.S. provisional application Ser. No. 63/342,615 filed May 16, 2022; (ii) is a continuation in part of U.S. patent application Ser. No. 16/550,216 filed Aug. 24, 2019, which claims under 35 U.S.C. § 119(e)(1) the benefit of the filing date of, and claims the benefit of priority to, U.S. provisional application Ser. No. 62/722,198 filed Aug. 24, 2018 and 62/726,233 filed Sep. 1, 2018, the entire disclosure of each of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63342615 | May 2022 | US | |
| 62722198 | Aug 2018 | US | |
| 62726233 | Sep 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16550216 | Aug 2019 | US |
| Child | 18318639 | US |
