US20180200962A1 - Additive manufacturing using a dynamically grown build envelope - Google Patents

Abstract

The present disclosure generally relates to additive manufacturing systems and methods on a large-scale format. One aspect involves a build unit that can be moved around in three dimensions by a positioning system, building separate portions of a large object. The build unit has an energy directing device that directs, e.g., laser or e-beam irradiation onto a powder layer. In the case of laser irradiation, the build volume may have a gasflow device that provides laminar gas flow to a laminar flow zone above the layer of powder. This allows for efficient removal of the smoke, condensates, and other impurities produced by irradiating the powder (the “gas plume”) without excessively disturbing the powder layer. The build unit may also have a recoater that allows it to selectively deposit particular quantities of powder in specific locations over a work surface to build large, high quality, high precision objects.

Description

CROSS REFERENCE TO RELATED APPLICATIONS
• Reference is made to the following related applications filed concurrently, the entirety of which are incorporated herein by reference:
• U.S. patent application Number [ ], titled “Additive Manufacturing Using a Mobile Build Volume,” with attorney docket number 037216.00059, and filed Jan. 13, 2017.
• U.S. patent application Number [ ], titled “Additive Manufacturing Using a Mobile Scan Area,” with attorney docket number 037216.00060, and filed Jan. 13, 2017.
• U.S. patent application Number [ ], titled “Additive Manufacturing Using a Selective Recoater,” with attorney docket number 037216.00062, and filed Jan. 13, 2017.
• U.S. patent application Number [ ], titled “Large Scale Additive Machine,” with attorney docket number 037216.00071, and filed Jan. 13, 2017.
INTRODUCTION
• The present disclosure generally relates to methods and systems adapted to perform additive manufacturing (“AM”) processes, for example by direct melt laser manufacturing (“DMLM”), on a larger scale format.
BACKGROUND
• A description of a typical laser powder bed fusion process is provided in German Patent No. DE 19649865, which is incorporated herein by reference in its entirety. AM processes generally involve the buildup of one or more materials to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods. Though “additive manufacturing” is an industry standard term (ASTM F2792), AM encompasses various manufacturing and prototyping techniques known under a variety of names, including freeform fabrication, 3D printing, rapid prototyping/tooling, etc. AM techniques are capable of fabricating complex components from a wide variety of materials. Generally, a freestanding object can be fabricated from a computer aided design (CAD) model. A particular type of AM process uses an irradiation emission directing device that directs an energy beam, for example, an electron beam or a laser beam, to sinter or melt a powder material, creating a solid three-dimensional object in which particles of the powder material are bonded together. Different material systems, for example, engineering plastics, thermoplastic elastomers, metals, and ceramics are in use. Laser sintering or melting is a notable AM process for rapid fabrication of functional prototypes and tools. Applications include direct manufacturing of complex workpieces, patterns for investment casting, metal molds for injection molding and die casting, and molds and cores for sand casting. Fabrication of prototype objects to enhance communication and testing of concepts during the design cycle are other common usages of AM processes.
• Selective laser sintering, direct laser sintering, selective laser melting, and direct laser melting are common industry terms used to refer to producing three-dimensional (3D) objects by using a laser beam to sinter or melt a fine powder. For example, U.S. Pat. No. 4,863,538 and U.S. Pat. No. 5,460,758, which are incorporated herein by reference, describe conventional laser sintering techniques. More accurately, sintering entails fusing (agglomerating) particles of a powder at a temperature below the melting point of the powder material, whereas melting entails fully melting particles of a powder to form a solid homogeneous mass. The physical processes associated with laser sintering or laser melting include heat transfer to a powder material and then either sintering or melting the powder material. Although the laser sintering and melting processes can be applied to a broad range of powder materials, the scientific and technical aspects of the production route, for example, sintering or melting rate and the effects of processing parameters on the microstructural evolution during the layer manufacturing process have not been well understood. This method of fabrication is accompanied by multiple modes of heat, mass and momentum transfer, and chemical reactions that make the process very complex.
• FIG. 1 is schematic diagram showing a cross-sectional view of an exemplary conventional system100 for direct metal laser sintering (“DMLS”) or direct metal laser melting (DMLM). The apparatus100 builds objects, for example, thepart122, in a layer-by-layer manner by sintering or melting a powder material (not shown) using anenergy beam136 generated by asource120, which can be, for example, a laser for producing a laser beam, or a filament that emits electrons when a current flows through it. The powder to be melted by the energy beam is supplied byreservoir126 and spread evenly over apowder bed112 using arecoater arm116 travelling indirection134 to maintain the powder at alevel118 and remove excess powder material extending above thepowder level118 to wastecontainer128. Theenergy beam136 sinters or melts a cross sectional layer of the object being built under control of an irradiation emission directing device, such as agalvo scanner132. Thegalvo scanner132 may comprise, for example, a plurality of movable mirrors or scanning lenses. The speed at which the laser is scanned is a critical controllable process parameter, impacting how long the laser power is applied to a particular spot. Typical laser scan speeds are on the order of 10 to 100 millimeters per second. Thebuild platform114 is lowered and another layer of powder is spread over the powder bed and object being built, followed by successive melting/sintering of the powder by thelaser120. The powder layer is typically, for example, 10 to 100 microns. The process is repeated until thepart122 is completely built up from the melted/sintered powder material.
• Thelaser120 may be controlled by a computer system including a processor and a memory. The computer system may determine a scan pattern for each layer andcontrol laser120 to irradiate the powder material according to the scan pattern. After fabrication of thepart122 is complete, various post-processing procedures may be applied to thepart122. Post processing procedures include removal of excess powder by, for example, blowing or vacuuming. Other post processing procedures include a stress release process. Additionally, thermal and chemical post processing procedures can be used to finish thepart122.
• FIG. 2 shows a side view of anobject201 built in aconventional powder bed202, which could be for example a powder bed as illustrated byelement112 ofFIG. 1. Then as thebuild platform114 is lowered and successive layers of powder are built up, theobject201 is formed in thebed202. Thewalls203 of thepowder bed202 define the amount of powder needed to make a part. The weight of the powder within the build environment is one limitation on the size of parts being built in this type of apparatus. The amount of powder needed to make a large part may exceed the limits of thebuild platform114 or make it difficult to control the lowering of the build platform by precise steps which is needed to make highly uniform additive layers in the object being built.
• In conventional powder bed systems, such as shown inFIG. 1, theenergy beam136 must scan a relatively large angle θ₁when building a part large enough to occupy most of thepowder bed118. This is because the angle θ₁must increase as the cross-sectional area of the object increases. In general, when making these larger parts, the angle θ₁becomes large at the periphery of the part. The energy density at the point of contact between the laser and powder bed then varies over the part. These differences in energy density affect the melt pool at large angles relative to that obtained when the laser is normal to the powder bed. These melt pool differences may result in defects and loss of fidelity in these regions of the part being built. These defects may result in inferior surface finishes on the desired part.
• Another problem that arises with prior art methods and systems involves cooling the layer of powdered material and removing smoke, condensates, and other impurities produced by irradiating the powder (sometimes called the “gas plume”), which can contaminate the object and obscure the line of sight of the energy beam. It is also important to cool and solidify the layer quickly to avoid formation of deformations or other defects. For large objects, i.e. objects with a largest dimension in the xy plane (for conventional powder bed systems, the plane of the powder bed) of 400 to 450 mm, it is very difficult to provide consistent laminar gas flow and efficient removal of unwanted gasses, particulates, condensates, and other undesirable impurities and contaminants.
• Another problem that arises in the prior art systems and methods is the need to finely control the quantity and location of powder deposited to avoid wasting powder, while also avoiding contact of the powder with undesirable materials. Prior art methods and systems deposit powder using blowing, sliding, or auger mechanisms. These mechanisms utilize multiple moving parts that may malfunction, or may be made of materials that are not suited to contact with the powder due to concerns with contamination.
• For example, EP 2191922 and EP 2202016 to Cersten et al. discuss a powder application apparatus that dispenses powder using rotating conveyor shafts with recesses for holding separate, discrete amounts of powder. Such an apparatus is more prone to failure, because the rotating conveyor shafts must be in motion as long as powder is being deposited.
• Other attempts to overcome the limitations of conventional powder bed systems have failed to address the problems associated with scale-up of these machines. In some cases, attempts to provide large format systems have introduced additional problems and challenges in creating laser fused parts from powder. Prior systems failed to provide uniform layer-wise powder distribution, effective management of the gas plume, and good control of the laser energy density over the part being produced.
• For example, the concept of moving a laser within a build area was explored in U.S.
• Application Publication No. 2004/0094728 to Herzog et al., the present inventors have noted this disclosure does not address how powder might be distributed onto the part being built. These techniques imply more traditional laser powder deposition where powder is injected into a laser beam and melted onto the object being built. Because there is no discussion of how to achieve uniform layers or powder over the part being built, the dimensional accuracy of such systems are very limited. Moreover, because the build environment is large, achieving a suitable gas environment near the laser melt pool would be difficult.
• In another example, the concept of a large format system whereby powder is deposited using a hopper is explored in U.S. patent application Publication No. 2013/0101746 to Keremes et al. Material30 is deposited onto a part40 being built using amaterial applicator28. Retaining walls42 are utilized to allow material30 to build up as the part40 is made. The system utilizes a laser18 placed in a stationary position near the top of the build chamber. As the part40 grows in size, the angle of the laser beam20 increases, particularly at the peripheral regions of the part. In addition, because material30 is deposited onto the part40, the thickness of the material30 deposited onto the part40 is difficult to control precisely.
• International Application No. WO 2014/199149 titled “Additive Manufacturing Apparatus and Method” to McMurtry et al. (“McMurtry”) discusses utilizing multiple polygonal mirrors with a localized gasflow device to build separate portions of an object in a single dimension, i.e. along a line, and lowering the build platform to provide another layer of powder. For large objects, it is difficult to build a platform that can both stably hold sufficient powder, and also be lowered by the precise layer thickness required.
• There remains a need for a large format powder manufacturing system that overcomes the above-mentioned problems.
SUMMARY OF THE INVENTION
• The present invention relates to an additive manufacturing apparatus. In an embodiment, the apparatus comprises a build unit with a powder dispenser and a recoater blade, an irradiation emission directing device, and a positioning system, the positioning system adapted to move the build unit in at least three dimensions which may be, for example, x, y, and z coordinates, during operation. The build unit may also be rotated in the x-y plane. Advantageously, according to an embodiment of the present invention the positioning system can move the build unit within a volume that is at least ten times larger than the cube of the width of the recoater blade. The build unit may also move the build unit around an xy area that is at least ten times larger than the square of the recoater blade width. The irradiation emission directing device may be adapted to direct laser irradiation or e-beam irradiation. For instance, the irradiation emission directing device could be an optical mirror or lens, or it could be an electromagnetic coil.
• The build unit may further comprise a laminar gasflow zone within a gasflow device adapted to provide substantially laminar gas flow over a work surface. The gasflow device may also be adapted to provide a reduced oxygen environment over the work surface. During operation, if the gasflow device provides gas flow over the work surface, then the irradiation emission directing device is adapted to direct laser irradiation from a laser source. The laser source may be within the build unit or outside the build unit. If the laser source is within the build unit, for instance in the case that a fiber optic cable extends from the laser to the build unit, the fiber optic cable transports the laser irradiation from the laser to the irradiation emission directing device (which is within the build unit), then the build unit may further comprise a second positioning system attached to the laser source, the second positioning system adapted to move the laser source within the build unit, independent of the motion of the build unit.
• The present invention also relates to a method for fabricating an object. In an embodiment, the method comprises (a) moving a build unit to deposit a first layer of powder over at least a first portion of a first build area, the build unit comprising a powder dispenser and a recoater blade, (b) irradiating at least part of the first layer of powder within the first build area to form a first fused layer, (c) moving the build unit upward in a direction substantially normal to the first layer of powder, then (d) repeating to form the object. After step (b), but before step (c), the method may further comprise at least the steps of (a′) moving the build unit to deposit a second layer of powder, the second layer of powder abutting the first layer of powder; and (b′) irradiating at least part of the second layer of powder to form a second fused layer. The irradiation may be laser irradiation or e-beam irradiation. When there is a gasflow device providing substantially laminar gas flow to a laminar gasflow zone over a work surface, then the irradiation is laser irradiation.
• The present invention also relates to an additive manufacturing apparatus comprising a selective recoater. In an embodiment, the apparatus comprises a powder dispenser, e.g. a hopper, the powder dispenser comprising a powder storage area and at least a first and second gate, the first gate operable by a first actuator that allows opening and closing the first gate, the second gate operable by a second actuator that allows opening and closing the second gate, and each gate adapted to control the dispensation of powder from the powder storage area onto a work surface. The powder dispenser may have any number of powder gates, for instance at least ten powder gates, or more preferably at least twenty gates. Advantageously, the powder dispenser and each gate may be made of the same material, for instance cobalt-chrome, which may also be the material of the powder. Each actuator may be, for example, either an electric actuator or a pneumatic actuator. The selective recoater may be part of a build unit adapted to provide a layer of powder over the work surface. The build unit may further comprise an irradiation emission directing device, which may be adapted to direct a laser irradiation, or it may be adapted to direct e-beam irradiation. The build unit may further comprise a gasflow device adapted to provide substantially laminar gas flow over the layer of powder.
• The present invention also relates to a method for fabricating an object using a selective recoater. In an embodiment, the method comprises (a) depositing powder onto a work surface from a powder dispenser, the powder dispenser comprising a powder storage area and at least a first and second gate, the first gate operable by a first actuator that allows opening and closing the first gate, the second gate operable by a second actuator that allows opening and closing the second gate, and each gate adapted to control the dispensation of powder from the powder storage area onto the work surface; (b) irradiating at least part of the first layer of powder to form a first fused layer; and (c) repeating at least steps (a) through (b) to form the object. Each gate may be attached to a spring mounted to the powder dispenser that opposes the force of the actuator. The powder used may be a material suitable for additive manufacturing, such as cobalt-chrome, and each surface of the powder dispenser and gates that comes into contact with the powder may be made from the same material. The method may further comprise a step of opening the first gate while leaving the second gate closed to selectively deposit powder onto the work surface. The method may also involve irradiating at least part of the first layer of powder to form a portion of a build envelope, and opening the first gate to deposit powder within the build envelope while closing the second gate to avoid depositing powder outside the build envelope.
• The present invention also relates to an additive manufacturing apparatus comprising a mobile gasflow device. In an embodiment, the apparatus comprises a laser emission directing device, a build unit comprising a gasflow device adapted to provide substantially laminar gas flow to a laminar gasflow zone within two inches of, and substantially parallel to, a work surface, a positioning system adapted to provide independent movement of the build unit in at least two dimensions that are substantially parallel to the work surface, the laser emission directing device adapted to direct laser irradiation to a build area over the work surface during operation of the apparatus. The positioning system may be adapted to provide independent movement of the build unit in at least three dimensions. The positioning system may also be adapted to allow for rotation of the build unit in two dimensions substantially parallel to the work surface. The gasflow device may be adapted to maintain a laminar gasflow zone, to provide a low oxygen environment around the work surface in a region below the build unit. There may also be a reduced oxygen gas zone above the laminar gasflow zone. Both gas zones may be contained within a containment zone surrounding at least the build unit and positioning system. The laser emission directing device may be within the build unit, and the laser irradiation may be transported from a laser to the laser emission directing device via a fiber-optic cable. The build unit may further comprise a powder delivery unit and a recoater arm.
• The present invention also relates to a method for fabricating an object using a gasflow device with a laminar flow zone. In an embodiment, the method comprises (a) moving a build unit over a build area of a work surface, the build unit comprising a gasflow device around a laminar flow zone over the build area, the gasflow device providing substantially laminar gas flow within two inches of, and substantially parallel to, the work surface, (b) irradiating at least a portion of the build area of the work surface with a laser that passes through the laminar flow zone to form a first fused layer; and (c) repeating at least steps (a) through (b) to form the object. The method may further comprise a step (d) of moving the build unit vertically away from the work surface. Steps (a) and (b) may be repeated after step (d). The build unit may be rotated 90° and moved in a direction perpendicular to the direction of movement in step (a).
• The present invention also relates to an apparatus for making an object from powder using a mobile scan area. In an embodiment, the apparatus comprises a build unit with a powder delivery unit, a recoater arm, a laser emission directing device, and a gasflow device around a laminar flow zone, the gasflow device adapted to provide substantially laminar gas flow within two inches of, and substantially parallel to, a work surface, and a positioning system adapted to provide independent movement of the build unit in at least three dimensions. The apparatus may further comprise a containment zone enclosing the build unit and positioning system. The build unit may be at least partially enclosed to form a low oxygen environment above the build area of the work surface, i.e. around the path of the beam. The laser emission directing device may be positioned within the build unit at a height such that, when the apparatus is in operation, the maximum angle of the laser beam relative to normal within the build area is less than about 15°. A fiber-optic cable may extend from the laser to the build unit, and thus transport laser irradiation from the laser to the laser emission directing device. The laser emission directing device may have a laser positioning unit that allows movement of the laser emission directing device within the build unit, independent of the motion of the build unit. The build unit may further comprise an x-y axis galvo adapted to control the laser beam in x-y, and the laser positioning system may be adapted to move the laser emission directing device in x, y, and/or z. The positioning system may be adapted to allow rotation of the build unit in the two dimensions that are substantially parallel to the work surface.
• The present invention also relates to a method for fabricating an object using a mobile scan area. In an embodiment, the method comprises (a) moving a build unit to deposit a first layer of powder over at least a first portion of a first build area, the build unit comprising a powder delivery unit, a recoater arm, a laser emission directing device, and a gasflow device around a laminar flow zone over a build area of a work surface, the gasflow device providing substantially laminar gas flow within two inches of, and substantially parallel to, the work surface; (b) irradiating at least part of the first layer of powder within the first build area to form a first fused layer; (c) moving the build unit upward in a direction substantially normal to the first layer of powder; and (d) repeating at least steps (a) through (c) to form the object. Steps (a) and (b) may be repeated after step (d). The laser emission directing device may be positioned within the build unit at a height above the build area to provide a maximum angle relative to normal within the build area of less than 15°.
• The present invention also relates to a method for fabricating an object using a recoater blade and a dynamically grown build envelope. In an embodiment, the method comprises (a) moving a recoater blade to form a first layer of powder over at least a portion of a first build area, (b) irradiating at least part of the first layer of powder within the first build area to form a first fused layer, and (c) repeating steps (a) and (b) to form the object, wherein a build envelope retains unfused powder about the object and has a volume that is larger than the cube of the recoater blade width. For instance, it may be ten times larger than the cube of the recoater blade width. The method may further comprise the steps (a′) moving the recoater to form a second layer of powder over at least a portion of a second build area and adjacent the first layer of powder; and (b′) irradiating at least part of the second layer of powder within the second build area to form a second fused layer. Steps (a′) and (b′) may be performed after step (b) but before step (c). The method may further comprise a step (d) of removing the build envelope and unfused powder within an envelope area to reveal the object. The powder material may be cobalt-chrome. The build envelope may be formed from powder fused by irradiation. For example, the build envelope may be formed by laser powder deposition. The second layer of powder may be substantially even with the first layer of powder. The irradiation may be conducted in a reduced oxygen environment, and may be laser irradiation. The irradiation may also be e-beam irradiation. The method may further comprise using a second build unit to build at least a portion of a second object. The method may also comprise using a second build unit to build at least a portion of the build envelope.
• The present invention also relates to a method for fabricating an object using a build unit and a dynamically grown build envelope. In an embodiment, the method comprises (a) moving a build unit to deposit a first layer of powder over at least a first portion of a first build area, the build unit comprising a powder dispenser, a recoater blade, and a directed energy emission directing device; (b) irradiating at least part of the first layer of powder within the first build area to form a first fused layer of the object; and (c) repeating steps (a) and (b) to form the object, wherein a build envelope retains unfused powder. The method may further comprise (a′) moving the recoater to form a second layer of powder over at least a portion of a second build area and abutting the first layer of powder; and (b′) irradiating at least part of the second layer of powder within the second build area to form a second fused layer. Steps (a′) and (b′) may be performed after step (b) but before step (c). The method may further comprise step (d) of removing the build envelope and unfused powder within the envelope area to reveal the object. The powder material may be cobalt-chrome. The build envelope may be formed from powder fused by irradiation. For example, the build envelope may be formed by laser powder deposition. The second layer of powder may be substantially even with the first layer of powder. The irradiation may be conducted in a reduced oxygen environment, and may be laser irradiation. The irradiation may also be from an electron beam.
• In general, any number of build units may be used in parallel, i.e. substantially simultaneously, to build one or more object(s) and/or build envelope(s), all on the same work surface.
BRIEF DESCRIPTION OF THE FIGURES
• FIG. 1 shows an exemplary prior art system for DMLM using a powder bed.
• FIG. 2 shows a conventional powder bed that is moved down as the object is formed.
• FIG. 3 shows a large scale additive manufacturing apparatus according to an embodiment of the invention.
• FIG. 4 shows a side view of a build unit according to an embodiment of the invention.
• FIG. 5 shows a side view of a build unit dispensing powder according to an embodiment of the invention.
• FIG. 6 shows a top view of a build unit according to an embodiment of the invention.
• FIG. 7 shows a top view of a recoater according to an embodiment of the present invention.
• FIG. 8 illustrates a large scale additive manufacturing apparatus with two build units according to an embodiment of the present invention.
• FIGS. 9A-9C illustrate a system and process of building an object according to an embodiment of the invention.
• FIGS. 10A-10D illustrate a system and process of building an object according to an embodiment of the invention.
• FIG. 11 shows an object being built by two build units in accordance with an embodiment of the invention.
• FIG. 12 shows two objects being built by a single build unit according to an embodiment of the invention.
DETAILED DESCRIPTION
• This detailed description and accompanying figures demonstrate some illustrative embodiments of the invention to aid in understanding. The invention is not limited to the embodiments illustrated in the figures, nor is it limited to the particular embodiments described herein.
• The present invention relates to an apparatus that can be used to perform additive manufacturing, as well as methods for utilizing the apparatus to additively manufacture objects. The apparatus includes components that make it particularly useful for making large additively manufactured objects. One aspect of the present invention is a build unit. The build unit may be configured to include several components necessary for making high precision, large scale additively manufactured objects. These components may include, for example, a recoater, a gasflow device with a gasflow zone, and an irradiation emission directing device. An irradiation emission directing device used in an embodiment of the present invention may be, for example, an optical control unit for directing a laser beam. An optical control unit may comprise, for example, optical lenses, deflectors, mirrors, and/or beam splitters. Advantageously, a telecentric lens may be used. Alternatively, the irradiation emission directing device may be an electronic control unit for directing an e-beam. The electronic control unit may comprise, for example, deflector coils, focusing coils, or similar elements. The build unit may be attached to a positioning system (e.g. a gantry, delta robot, cable robot, robot arm, belt drive, etc.) that allows three dimensional movement throughout a build environment, as well as rotation of the build unit in a way that allows coating of a thin powder layer in any direction desired.
• FIG. 3 shows an example of one embodiment of a large-scaleadditive manufacturing apparatus300 according to the present invention. Theapparatus300 comprises apositioning system301, abuild unit302 comprising an irradiation emission directing device303, a laminar gas flow zone307, and a build plate (not shown in this view) beneath an object being built309. The maximum build area is defined by thepositioning system301, instead of by a powder bed as with conventional systems, and the build area for a particular build can be confined to abuild envelope308 that may be dynamically built up along with the object. Thegantry301 has anx crossbeam304 that moves thebuild unit302 in the x direction. There are twoz crossbeams305A and305B that move thebuild unit302 and thex crossbeam304 in the z direction. Thex cross beam304 and thebuild unit302 are attached by a mechanism306 that moves thebuild unit302 in the y direction. In this illustration of one embodiment of the invention, thepositioning system301 is a gantry, but the present invention is not limited to using a gantry. In general, the positioning system used in the present invention may be any multidimensional positioning system such as a delta robot, cable robot, robot arm, etc. The irradiation emission directing device303 may be independently moved inside of thebuild unit302 by a second positioning system (not shown). The atmospheric environment outside the build unit, i.e. the “build environment,” or “containment zone,” is typically controlled such that the oxygen content is reduced relative to typical ambient air, and so that the environment is at reduced pressure.
• There may also be an irradiation source that, in the case of a laser source, originates the photons comprising the laser irradiation that is directed by the irradiation emission directing device. When the irradiation source is a laser source, then the irradiation emission directing device may be, for example, a galvo scanner, and the laser source may be located outside the build environment. Under these circumstances, the laser irradiation may be transported to the irradiation emission directing device by any suitable means, for example, a fiber-optic cable. When the irradiation source is an electron source, then the electron source originates the electrons that comprise the e-beam that is directed by the irradiation emission directing device. When the irradiation source is an electron source, then the irradiation emission directing device may be, for example, a deflecting coil. When a large-scale additive manufacturing apparatus according to an embodiment of the present invention is in operation, if the irradiation emission directing devices directs a laser beam, then generally it is advantageous to include a gasflow device providing substantially laminar gas flow to a gasflow zone as illustrated inFIG. 3, 307 andFIG. 4, 404. If an e-beam is desired, then no gasflow is provided. An e-beam is a well-known source of irradiation. For example, U.S. Pat. No. 7,713,454 to Larsson titled “Arrangement and Method for Producing a Three-Dimensional Product” (“Larsson”) discusses e-beam systems, and that patent is incorporated herein by reference. When the source is an electron source, then it is important to maintain sufficient vacuum in the space through which the e-beam passes. Therefore, for an e-beam, there is no gas flow across the gasflow zone (shown, for example atFIG. 3, 307).
• Another advantage of the present invention is that the maximum angle of the beam may be a relatively small angle θ₂to build a large part, because (as illustrated inFIG. 3) thebuild unit302 can be moved to a new location to build a new part of the object being formed309. When the build unit is stationary, the point on the powder that the energy beam touches when θ₂is 0 defines the center of a circle in the xy plane (the direction of the beam when θ₂is approximately 0 defines the z direction), and the most distant point from the center of the circle where the energy beam touches the powder defines a point on the outer perimeter of the circle. This circle defines the beam's scan area, which may be smaller than the smallest cross sectional area of the object being formed (in the same plane as the beam's scan area). There is no particular upper limit on the size of the object relative to the beam's scan area.
• In some embodiments, the recoater used is a selective recoater. One embodiment is illustrated inFIGS. 4 through 7.
• FIG. 4 shows abuild unit400 comprising an irradiationemission directing device401, agasflow device403 with apressurized outlet portion403A and avacuum inlet portion403B providing gas flow to agasflow zone404, and arecoater405. Above thegasflow zone404 there is anenclosure418 containing aninert environment419. Therecoater405 has ahopper406 comprising aback plate407 and afront plate408. Therecoater405 also has at least oneactuating element409, at least onegate plate410, arecoater blade411, anactuator412, and arecoater arm413. The recoater is mounted to a mountingplate420.FIG. 4 also shows abuild envelope414 that may be built by, for example, additive manufacturing or Mig/Tig welding, an object being formed415, andpowder416 contained in thehopper405 used to form theobject415. In this particular embodiment, theactuator412 activates theactuating element409 to pull thegate plate410 away from thefront plate408. In an embodiment, theactuator412 may be, for example, a pneumatic actuator, and theactuating element409 may be a bidirectional valve. In an embodiment, theactuator412 may be, for example, a voice coil, and theactuating element409 may be a spring. There is also a hopper gap417 between thefront plate408 and theback plate407 that allows powder to flow when a corresponding gate plate is pulled away from the powder gate by an actuating element. Thepowder416, theback plate407, thefront plate408, and thegate plate410 may all be the same material. Alternatively, theback plate407, thefront plate408, and thegate plate410 may all be the same material, and that material may be one that is compatible with the powder material, such as cobalt-chrome. In this particular illustration of one embodiment of the present invention, the gas flow in thegasflow zone404 flows in the y direction, but it does not have to. Therecoater blade411 has a width in the x direction. The direction of the irradiation emission beam when θ₂is approximately 0 defines the z direction in this view. The gas flow in thegasflow zone404 may be substantially laminar. The irradiationemission directing device401 may be independently movable by a second positioning system (not shown). This illustration shows thegate plate410 in the closed position.
• FIG. 5 shows the build unit ofFIG. 4, with thegate plate410 in the open position (as shown by element510) and actuating element509. Powder in the hopper is deposited to makefresh powder layer521, which is smoothed over by therecoater blade511 to make a substantially evenpowder layer522. In some embodiments of the present invention, the substantially even powder layer may be irradiated at the same time that the build unit is moving, which would allow for continuous operation of the build unit and thus faster production of the object.
• FIG. 6 shows a top down view of the build unit ofFIG. 4. For simplicity, the object and the walls are not shown here. Thebuild unit600 has an irradiationemission directing device601, anattachment plate602 attached to thegasflow device603,hopper606, andrecoater arm611. The gasflow device has agas outlet portion603A and agas inlet portion603B. Within thegasflow device603 there is agasflow zone604. Thegasflow device603 provides laminar gas flow within the gasflowzone604. There is also arecoater605 with arecoater arm611, actuatingelements612A,612B, and612C, andgate plates610A,610B, and610C. Therecoater605 also has ahopper606 with aback plate607 andfront plate608. In this particular illustration of one embodiment of the present invention, the hopper is divided into three separate compartments containing threedifferent materials609A,609B, and609C. There are alsogas pipes613A and613B that feed gas out of and into thegasflow device603.
• FIG. 7 shows a top down view of a recoater according to an embodiment of the invention. In this particular illustration the recoater has ahopper700 with only a single compartment containing apowder material701. There are threegate plates702A,702B, and702C that are controlled by three actuatingelements703A,703B, and703C. There is also arecoater arm704 and a wall705. When the recoater passes over a region that is within the wall, such as indicated by707, the correspondinggate plate702C may be held open to deposit powder in thatregion707. When the recoater passes over a region that is outside of the wall, such as the region indicated as708, the correspondinggate plate702C is closed by its correspondingactuating element703C, to avoid depositing powder outside the wall, which could potentially waste the powder. Within the wall705, the recoater is able to deposit discrete lines of powder, such as indicated by706. The recoater blade (not shown in this view) smooths out the powder deposited.
• Advantageously, a selective recoater according to an embodiment of the present invention allows precise control of powder deposition using powder deposition device (e.g. a hopper) with independently controllable powder gates as illustrated, for example, inFIG. 6, 606, 610A, 610B, and 610C andFIG. 7, 702A, 702B, and 702C. The powder gates are controlled by at least one actuating element which may be, for instance, a bidirectional valve or a spring (as illustrated, for example, inFIG. 4, 409. Each powder gate can be opened and closed for particular periods of time, in particular patterns, to finely control the location and quantity of powder deposition (see, for example,FIG. 6). The hopper may contain dividing walls so that it comprises multiple chambers, each chamber corresponding to a powder gate, and each chamber containing a particular powder material (see, for example,FIG. 6, and 609A, 609B, and 609C). The powder materials in the separate chambers may be the same, or they may be different. Advantageously, each powder gate can be made relatively small so that control over the powder deposition is as fine as possible. Each powder gate has a width that may be, for example, no greater than about 2 inches, or more preferably no greater than about ¼ inch. In general, the smaller the powder gate, the greater the powder deposition resolution, and there is no particular lower limit on the width of the powder gate. The sum of the widths of all powder gates may be smaller than the largest width of the object, and there is no particular upper limit on the width of the object relative to the sum of the widths of the power gates. Advantageously, a simple on/off powder gate mechanism according to an embodiment of the present invention is simpler and thus less prone to malfunctioning. It also advantageously permits the powder to come into contact with fewer parts, which reduces the possibility of contamination. Advantageously, a recoater according to an embodiment of the present invention can be used to build a much larger object. For example, the largest xy cross sectional area of the recoater may be smaller than the smallest cross sectional area of the object, and there is no particular upper limit on the size of the object relative to the recoater. Likewise, the width of the recoater blade may smaller than the smallest width of the object, and there is no particular upper limit on the width of the object relative to the recoater blade. After the powder is deposited, a recoater blade can be passed over the powder to create a substantially even layer of powder with a particular thickness, for example about 50 microns, or preferably about 30 microns, or still more preferably about 20 microns. Another feature of some embodiments of the present invention is a force feedback loop. There can be a sensor on the selective recoater that detects the force on the recoater blade. During the manufacturing process, if there is a time when the expected force on the blade does not substantially match the detected force, then control over the powder gates may be modified to compensate for the difference. For instance, if a thick layer of powder is to be provided, but the blade experiences a relatively low force, this scenario may indicate that the powder gates are clogged and thus dispensing powder at a lower rate than normal. Under these circumstances, the powder gates can be opened for a longer period of time to deposit sufficient powder. On the other hand, if the blade experiences a relatively high force, but the layer of powder provided is relatively thin, this may indicate that the powder gates are not being closed properly, even when the actuators are supposed to close them. Under these circumstances, it may be advantageous to pause the build cycle so that the system can be diagnosed and repaired, so that the build may be continued without comprising part quality. Another feature of some embodiments of the present invention is a camera for monitoring the powder layer thickness. Based on the powder layer thickness, the powder gates can be controlled to add more or less powder.
• In addition, an apparatus according to an embodiment of the present invention may have a controlled low oxygen build environment with two or more gas zones to facilitate a low oxygen environment. The first gas zone is positioned immediately over the work surface. The second gas zone may be positioned above the first gas zone, and may be isolated from the larger build environment by an enclosure. For example, inFIG. 4element404 constitutes the first gas zone,element419 constitutes the second gas zone contained by theenclosure418, and the environment around the entire apparatus is the controlled low oxygen build environment. In the embodiment illustrated inFIG. 4, the first gasflowzone404 is essentially the inner volume of thegasflow device403, i.e. the volume defined by the vertical (xz plane) surfaces of the inlet and outlet portions (403A and403B), and by extending imaginary surfaces from the respective upper and lower edges of the inlet portion to the upper and lower edges of the outlet portion in the xy plane. When the irradiation emission directing device directs a laser beam, then the gasflow device preferably provides substantially laminar gas flow across the first gas zone. This facilitates removal of the effluent plume caused by laser melting. Accordingly, when a layer of powder is irradiated, smoke, condensates, and other impurities flow into the first gasflow zone, and are transferred away from the powder and the object being formed by the laminar gas flow. The smoke, condensates, and other impurities flow into the low-pressure gas outlet portion and are eventually collected in a filter, such as a HEPA filter. By maintaining laminar flow, the aforementioned smoke, condensates and other impurities can be efficiently removed while also rapidly cooling melt pool(s) created by the laser, without disturbing the powder layer, resulting in higher quality parts with improved metallurgical characteristics. In an aspect, the gas flow in the gasflow volume is at about 3 meters per second. The gas may flow in either the x or y direction.
• The oxygen content of the second controlled atmospheric environment is generally approximately equal to the oxygen content of the first controlled atmospheric environment, although it doesn't have to be. The oxygen content of both controlled atmospheric environments is preferably relatively low. For example, it may be 1% or less, or more preferably 0.5% or less, or still more preferably 0.1% or less. The non-oxygen gases may be any suitable gas for the process. For instance, nitrogen obtained by separating ambient air may be a convenient option for some applications. Some applications may use other gases such as helium, neon, or argon. An advantage of the invention is that it is much easier to maintain a low-oxygen environment in the relatively small volume of the first and second controlled atmospheric environments. In prior art systems and methods, the larger environment around the entire apparatus and object must be tightly controlled to have a relatively low oxygen content, for instance 1% or less. This can be time-consuming, expensive, and technically difficult. Thus it is preferable that only relatively smaller volumes require such relatively tight atmospheric control. Therefore, in the present invention, the first and second controlled atmospheric environments may be, for example, 100 times smaller in terms of volume than the build environment. The first gas zone, and likewise the gasflow device, may have a largest xy cross sectional area that is smaller than the smallest xy cross sectional area of the object. There is no particular upper limit on the size of the object relative to the first gas zone and/or the gasflow device. Advantageously, the irradiation emission beam (illustrated, for example, as402 and502) fires through the first and second gas zones, which are relatively low oxygen zones. And when the first gas zone is a laminar gasflow zone with substantially laminar gas flow, the irradiation emission beam is a laser beam with a more clear line of sight to the object, due to the aforementioned efficient removal of smoke, condensates, and other contaminants or impurities.
• One advantage of the present invention is that, in some embodiments, the build plate may be vertically stationary (i.e. in the z direction). This permits the build plate to support as much material as necessary, unlike the prior art methods and systems, which require some mechanism to raise and lower the build plate, thus limiting the amount of material that can be used. Accordingly, the apparatus of the present invention is particularly suited for manufacturing an object within a large (e.g., greater than 1 m³) build envelope. For instance, the build envelope may have a smallest xy cross sectional area greater than 500 mm², or preferably greater than 750 mm², or more preferably greater than 1 m². The size of the build envelope is not particularly limited. For instance, it could have a smallest cross sectional area as large as 100 m². Likewise, the formed object may have a largest xy cross sectional area that is no less than about 500 mm², or preferably no less than about 750 mm², or still more preferably no less than about 1 m². There is no particular upper limit on the size of the object. For example, the object's smallest xy cross sectional area may be as large as 100 m². Because the build envelope retains unfused powder about the object, it can be made in a way that minimizes unfused powder (which can potentially be wasted powder) within a particular build, which is particularly advantageous for large builds. When building large objects within a dynamically grown build envelope, it may be advantageous to build the envelope using a different build unit, or even a different build method altogether, than is used for the object. For example, it may be advantageous to have one build unit that directs an e-beam, and another build unit that directs a laser beam. With respect to the build envelope, precision and quality of the envelope may be relatively unimportant, such that rapid build techniques are advantageously used. In general, the build envelope may be built by any suitable means, for instance by Mig or Tig welding, or by laser powder deposition. If the wall is built by additive manufacturing, then a different irradiation emission directing device can be used to build than wall than is used to build the object. This is advantageous because building the wall may be done more quickly with a particular irradiation emission directing device and method, whereas a slower and more accurate directing device and method may be desired to build the object. For example, the wall may be built from a rapidly built using a different material from the object, which may require a different build method. Ways to tune accuracy vs. speed of a build are well known in the art, and are not recited here.
• For example, as shown inFIG. 8, the systems and methods of the present invention may use two or more build units to build one or more object(s). The number of build units, objects, and their respective sizes are only limited by the physical spatial configuration of the apparatus.FIG. 8 shows a top down view of a large-scaleadditive manufacturing machine800 according to an embodiment of the invention. There are twobuild units802A and802B mounted to apositioning system801. There arez crossbeams803A and803B for moving the build units in the z direction. There arex crossbeams804A and804B for moving the build units in the x direction. Thebuild units802A and802B are attached to thex crossbeams804A and804B by mechanisms805A and805B that move the units in the y direction. The object(s) being formed are not shown in this view. A build envelope (also not shown in this view) can be built using one or both of the build units, including by laser powder deposition. The build envelope could also be built by, e.g., welding. In general, any number of objects and build envelopes can be built simultaneously using the methods and systems of the present invention.
• Advantageously, in some embodiments of the present invention the wall may be built up around the object dynamically, so that its shape follows the shape of the object. A dynamically built chamber wall advantageously results in the chamber wall being built closer to the object, which reduces the size of support structures required, and thus reduces the time required to build the support structures. Further, smaller support structures are more stable and have greater structural integrity, resulting in a more robust process with less failure. In one embodiment, two build envelopes may be built, one concentric within the other, to build objects in the shape of, for example, circles, ovals, and polygons. If the wall is built by welding, then support structures such as buttresses may be advantageously built on the wall as needed, to support overhangs and other outwardly-built features of the object. Therefore, according to an embodiment of the present invention, a dynamically built chamber wall enables object features that would be either impossible or impractical using conventional technology.
• FIGS. 9A-9C illustrate an object built vertically upward from powder, within a dynamically grown build envelope, on a vertically stationary build plate according to one embodiment of the present invention. In this illustration theobject900 is built on a verticallystationary build plate902 using abuild unit901. Since thebuild unit901 may be capable of selectively dispensing powder within thebuild envelope903, the unfused depositedpowder904 is generally entirely within thebuild envelope903, or at least a substantial portion of the unfused depositedpowder904 stays within thebuild envelope903. As shown inFIG. 9C, thebuild unit901 may be moved away from theobject900 to more easily access theobject900. Mobility of the of thebuild unit901 may be enabled by, for instance, a positioning system (not shown in this view).
• FIGS. 10A-10D illustrate a system and process of building anobject1000 and buildenvelope1001 layer by layer on a verticallystationary build plate1002, using abuild unit1003. Theobject1000 has a topmost fusedlayer1004 and thebuild envelope1001 has a topmost fusedlayer1005. There is unfused deposited powder1006. In this particular illustration of one embodiment of the present invention, a first layer of thebuild envelope1001 is built, as shown byelement1007 inFIG. 10B. Then the build unit may provide a fresh layer of powder1008 (FIG. 10C). Then the fresh layer of powder may be irradiated to form a new topmost fused layer of the object1009 (FIG. 10D). Mobility of the of thebuild unit1003 may be enabled by, for instance, a positioning system (not shown in this view).
• FIG. 11 shows an object1100 being built by abuild units1102 and a build envelope1105 being built by abuild unit1101 on a verticallystationary build plate1103. There is unfused depositedpowder1104. Mobility of the of thebuild units1101 and1102 may be enabled by, for instance, a positioning system (not shown in this view).
• FIG. 12 shows twoobjects1200 and1201 being built by asingle build unit1202 on a verticallystationary build plate1203. There is unfused depositedpowder1204 and1205. Mobility of the of thebuild unit1202 may be enabled by, for instance, a positioning system (not shown in this view).

Claims (22)

1. A method for fabricating an object, comprising:

(a) moving a recoater blade to form a first layer of powder over at least a portion of a first build area;

(b) irradiating at least part of the first layer of powder within the first build area to form a first fused layer; and

(c) repeating steps (a) moving and (b) irradiating to form subsequent layers of powder adjacent to the fist fused layer and to irradiate the subsequent layers of powder to form the object, wherein a build envelope retains unfused powder about the object and has an xy cross sectional area which is larger than the square of the recoater blade width measured in the x direction.

2. (canceled)

3. (canceled)

4. The method ofclaim 2, wherein the second layer of powder is substantially even with the first layer of powder.

5. The method ofclaim 1, wherein the step of irradiating is conducted using a laser beam that is directed by a laser irradiation directing device in a reduced oxygen environment.

6. The method ofclaim 1, wherein the step of irradiating is conducted using an e-beam that is directed by an e-beam irradiation directing device.

7. The method ofclaim 1, wherein the build envelope is formed from powder fused by irradiation.

8. The method ofclaim 1, wherein the build envelope is formed by laser powder deposition.

9. The method ofclaim 1, further comprising a step (d) of removing the build envelope and unfused powder to reveal the object.

10. The method ofclaim 5, wherein a fiber-optic cable extends from a laser to the irradiation directing device.

11. A method for fabricating an object comprising:

(a) moving a build unit to deposit a first layer of powder over at least a first portion of a first build area, the build unit comprising a powder dispenser, a recoater blade, and an irradiation emission directing device;

(b) irradiating at least part of the first layer of powder within the first build area to form a first fused layer of the object;

(c) repeating steps (a) and (b) to form the object, wherein a build envelope retains unfused powder.

12. The method ofclaim 11, further comprising:

(a′) moving the recoater to form a second layer of powder over at least a portion of a second build area and abutting the first layer of powder; and

(b′) irradiating at least part of the second layer of powder within the second build area to form a second fused layer.

13. The method ofclaim 12, wherein steps (a′) and (b′) are performed after step (b) but before step (c).

14. The method ofclaim 12, wherein second layer of powder is substantially even with the first layer of powder.

15. The method ofclaim 11, wherein the step of irradiating is conducted using a laser beam that is directed by a laser irradiation directing device in the build unit, and is conducted in a reduced oxygen environment.

16. The method ofclaim 11, wherein the step of irradiating is conducted using an electron beam that is directed by an e-beam irradiation directing device.

17. The method ofclaim 11, wherein the build envelope is formed from powder fused by irradiation.

18. The method ofclaim 11, wherein the build envelope is formed by laser powder deposition.

19. The method ofclaim 11, further comprising step (d) of removing the build envelope and unfused powder within the envelope area to reveal the object.

20. The method ofclaim 15, wherein a fiber-optic cable extends from a laser to the irradiation directing device of the build unit.

21. The method ofclaim 11, comprising using a second build unit to build at least a portion of a second object.

22. The method ofclaim 11, comprising using a second build unit to build at least a portion of the build envelope.

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