Patent Publication Number: US-2021178665-A1

Title: Interlace scanning strategies and uses thereof

Description:
PRIORITY INFORMATION 
     The present applicant claims priority to U.S. Provisional Patent Application Ser. No. 62/584,553 titled “Interlace Scanning Strategies and Uses Thereof” filed on Nov. 10, 2017, the disclosure of which is incorporated by reference herein. 
    
    
     FIELD 
     The disclosure relates to an improved method and apparatus for interlace scanning for use in additive manufacturing. 
     BACKGROUND 
     Additive manufacturing (AM) techniques may include electron beam freeform fabrication, laser metal deposition (LIVID), laser wire metal deposition (LMD-w), gas metal arc-welding, laser engineered net shaping (LENS), laser sintering (SLS), direct metal laser sintering (DMLS), electron beam melting (EBM), powder-fed directed-energy deposition (DED), and three dimensional printing (3DP), as examples. 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 (ISO/ASTM52900), 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. As an example, a particular type of AM process uses an energy beam, for example, an electron beam or electromagnetic radiation such as a laser beam, to sinter or melt a powder material and/or wire-stock, creating a solid three-dimensional object in which a material is bonded together. 
     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. Nos. 4,863,538 and 5,460,758 describe conventional laser sintering techniques. More specifically, 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. Electron beam melting (EBM) utilizes a focused electron beam to melt powder. These processes involve melting layers of powder successively to build an object in a metal powder. 
     AM techniques, examples of which are discussed above and throughout the disclosure, may be characterized by using a laser or an energy source to generate heat in the powder to at least partially melt the material. Accordingly, high concentrations of heat are generated in the fine powder over a short period of time. The high temperature gradients within the powder during buildup of the component may have a significant impact on the microstructure of the completed component. Rapid heating and solidification may cause high thermal stress and cause localized non-equilibrium phases throughout the solidified material. Further, since the orientation of the grains in a completed AM component may be controlled by the direction of heat conduction in the material, the scanning strategy of the laser in an AM apparatus and technique becomes an important method of controlling microstructure of the AM built component. Controlling the scanning strategy in an AM apparatus is further crucial for developing a component free of material defects, examples of defects may include lack of fusion porosity and/or boiling porosity. 
       FIG. 1  is schematic diagram showing a cross-sectional view of an exemplary conventional system  110  for direct metal laser sintering (DMLS) or direct metal laser melting (DMLM). The apparatus  110  builds objects, for example, the part  122 , in a layer-by-layer manner (e.g., layers L1, L2, and L3, which are exaggerated in scale for illustration purposes) by sintering or melting a powder material (not shown) using an energy beam  136  generated by a source such as a laser  120 . The powder to be melted by the energy beam is supplied by reservoir  126  and spread evenly over a build plate  114  using a recoater arm  116  travelling in direction  134  to maintain the powder at a level  118  and remove excess powder material extending above the powder level  118  to waste container  128 . The energy beam  136  sinters or melts a cross sectional layer (e.g., layer L1) of the object being built under control of the galvo scanner  132 . The build plate  114  is lowered and another layer (e.g., layer L2) of powder is spread over the build plate and object being built, followed by successive melting/sintering of the powder by the laser  120 . The process is repeated until the part  122  is completely built up from the melted/sintered powder material. The laser  120  may be controlled by a computer system including a processor and a memory. The computer system may determine a scan pattern for each layer and control laser  120  to irradiate the powder material according to the scan pattern. After fabrication of the part  122  is complete, various post-processing procedures may be applied to the part  122 . Post processing procedures include removal of excess powder, for example, by blowing or vacuuming, machining, sanding or media blasting. Further, conventional post processing may involve removal of the part  122  from the build platform/substrate through machining, for example. Other post processing procedures include a stress release process. Additionally, thermal and chemical post processing procedures can be used to finish the part  122 . 
     The abovementioned AM processes is controlled by a computer executing a control program. For example, the apparatus  110  includes a processor (e.g., a microprocessor) executing firmware, an operating system, or other software that provides an interface between the apparatus  110  and an operator. The computer receives, as input, a three dimensional model of the object to be formed. For example, the three dimensional model is generated using a computer aided design (CAD) program. The computer analyzes the model and proposes a tool path for each object within the model. The operator may define or adjust various parameters of the scan pattern such as power, speed, and spacing, but generally does not program the tool path directly. One having ordinary skill in the art would fully appreciate the abovementioned control program may be applicable to any of the abovementioned AM processes. Further, the abovementioned computer control may be applicable to any subtractive manufacturing or any pre or post processing techniques employed in any post processing or hybrid process. 
     The above additive manufacturing techniques may be used to form a component from stainless steel, aluminum, titanium, cobalt chrome, among other metal materials or any alloy. For example, the above alloys may include materials with trade names, Haynes 188®, Haynes 625®, Super Alloy Inconel 625TM, Chronin® 625, Altemp® 625, Nickelvac® 625, Nicrofer® 6020, Inconel 188, and any other material having material properties attractive for the formation of components using the abovementioned techniques. 
     In the abovementioned example, a laser and/or energy source is generally controlled to form a series of solidification lines (hereinafter interchangeably referred to as hatch lines, solidification lines and raster lines) in a layer of powder based on a pattern. A pattern may be selected to decrease build time, to improve or control the material properties of the solidified material, to reduce stresses in the completed material, and/or to reduce wear on the laser, galvanometer scanner, and/or electron-beam. Various scanning strategies have been contemplated in the past, and include, for example, chessboard patterns and/or stripe patterns. 
     One attempt at controlling the stresses within the material of the built AM component involves the rotation of stripe regions containing a plurality of adjoining parallel vectors, as solidification lines, that run perpendicular to solidification lines forming the boundaries of the stripe region for each layer during an AM build process. Parallel solidification lines, bounded by and perpendicular to a stripe, are rotated for each layer of the AM build. One example of controlling the scanning strategy in an AM apparatus is disclosed in U.S. Pat. No. 8,034,279 B2 to Dimter et al., titled “Method and Device for Manufacturing a Three-dimensional Object,” which is hereby incorporated by reference in its entirety. 
       FIGS. 2 and 3  represent the abovementioned rotating stripe strategy (e.g., identified generally by scan lines  210  of a laser). The laser is scanned across the surface of a powder to form a series of solidification lines  213 A,  213 B. The series of solidification lines form a layer of the build and are bound by solidification lines in the form of stripes  211 A and  211 B that are perpendicular to the solidification lines  213 A and  213 B forming the boundaries of each stripe region. The stripe regions bounded by solidification lines  211 A and  211 B form a portion of a larger surface of the layer to be built. In forming a part, a bulk of the part cross section is divided into numerous stripe regions (regions between two solidified stripes containing transverse solidification lines). A stripe orientation is rotated for each layer formed during the AM build process as shown in  FIGS. 2 and 3 . A first layer may be formed with a series of parallel solidification lines  213 A, in a stripe region, formed substantially perpendicular to and bounded by solidified stripes  211 A. In a subsequent layer formed over the first layer, the stripes  211 B are rotated as shown in  FIG. 3 . By creating a stripe boundary for the solidified lines  213 A and  213 B through a set of solidified stripes  211 B that are rotated with respect to the previous layer, solidification lines  213 B, which are be formed perpendicular to and are bounded by stripes  211 B are also be rotated with respect the solidification lines  213 A of the previous layer. 
     Using the abovementioned rotating stripe strategy, the need exists to further create variance in each layer. By employing the various embodiments disclosed, build efficiency can be further increased by preventing unnecessary jumps of the energy source, preventing unnecessary on/off transitions of the laser, and/or improving control and/or efficiency of heat buildup within the layer. Further the microstructure of the part can be altered by controlling the pattern of stripe regions and solidification lines within the stripe region. 
     However, in a large scale AM apparatus using a mobile or plurality of mobile build units and/or a mobile build platform as discussed below, the abovementioned strategies may be employed. However, when forming a scan region which borders another scan region, there exists a further need to control the energy density and metallurgy of the completed component while still maintaining efficiency. 
     BRIEF DESCRIPTION 
     Aspects and advantages will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one aspect, a method for additive manufacturing is disclosed. The method comprises: forming an at least partially solidified portion within a first scan region, wherein the solidified portion within the first scan region is formed by irradiating a build material along a first irradiation path. A second portion of a build material may be irradiated along a second irradiation path, wherein the second scan region is offset with respect to the first scan region thereby defining an offset region. The offset region is at least partially solidified by the first irradiation path and the second irradiation path and a reference line intersects the first and second irradiation path within the offset region, wherein the reference line is substantially parallel to a side of the first scan region. 
     A first at least partially solidified region may be formed within a second scan region that is spaced with respect to the first scan region, wherein the solidified portion within the second scan region is formed by irradiating a build material along a second irradiation path, wherein the space between the first scan region and the second scan region is at least partially solidified when a first irradiation path and the second irradiation path cross an imaginary line and/or reference line (depicted by a light dashed line down the centerline of  FIGS. 8A and 8B ) within the space between the first scan region and the second scan region. The imaginary line and/or reference line is substantially parallel with a boundary of the first scan region and the second scan region. 
     In one aspect, a method for forming an object is disclosed, the method comprising: forming a partially solidified portion within a first scan region, wherein the solidified portion within the first scan region is formed by irradiating a build material along a first irradiation path within a first stripe region. The method further comprises: forming a partially solidified portion within a second scan zone within a scan region that is spaced with respect to the first scan region, wherein the solidified portion within the second scan region is formed by irradiating a build material along a second irradiation path within a second stripe region. At least one boundary of the first stripe region within the space between the first scan region and the second scan region is shaped so as to interlock with at least one boundary of the second stripe region. 
     In another aspect, a non-transitory computer readable medium storing a program configured to cause a computer to execute an additive manufacturing method is disclosed. The additive manufacturing method may include forming an at least partially solidified portion within a first scan region, wherein the solidified portion within the first scan region is formed by irradiating a build material along a first irradiation path. The method may further include forming an at least partially solidified portion within a second scan region that is spaced with respect to the first scan region, wherein the solidified portion within the second scan region is formed by irradiating a build material along a second irradiation path. The space between the first scan region and the second scan region may be at least partially solidified by irradiating a build material by interlocking the first irradiation path with the second irradiation path. 
     These and other features, aspects and advantages will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain certain principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended FIGS., in which: 
         FIG. 1  is a side view diagram of a conventional additive manufacturing technique used to form at least part of a component; 
         FIG. 2  is a top view depicting a conventional hatch and stripe pattern used to form at least a part of a component; 
         FIG. 3  is a top view depicting a conventional hatch and stripe pattern used to form at least a part of a component; 
         FIG. 4  is a perspective view, depicting example layers of component build during an AM process; 
         FIG. 5  is a top view depicting a hatch and stripe pattern used to form each layer of the component depicted in  FIG. 4 ; 
         FIG. 6  is a side view cross section of a build unit in accordance with one aspect of the disclosure; 
         FIG. 7  is a side view cross section of a build unit and part of the rotating build platform of an additive manufacturing apparatus in accordance with one aspect of the disclosure; 
         FIG. 8A  is a top view showing an example of a region between two adjacent scan zones in accordance with one aspect of the disclosure; 
         FIG. 8B  is a magnified view of  FIG. 8A  showing an example of a region between two adjacent scan zones in accordance with one aspect of the disclosure; 
         FIG. 9A  is a top view showing an example of a region between two adjacent scan zones in accordance with one aspect of the disclosure; 
         FIG. 9B  is a magnified view of  FIG. 9A  showing an example of a region between two adjacent scan zones in accordance with one aspect of the disclosure; 
         FIG. 10  is a top view depicting example orientations of the build unit and scan zones in accordance with one aspect of the disclosure; and 
         FIG. 11  is a top view depicting example orientations of a build unit and scan zones in accordance with one aspect of the disclosure. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention. 
     DETAILED DESCRIPTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     When using any of the abovementioned AM techniques to form a part by at least partially melting a powder, a scan of the laser across the powder material, in a raster scan fashion is used to create hatch scans (hereinafter referred to interchangeably as hatch scans, rasters, scan lines, or solidification lines). During an AM build, the abovementioned solidification lines are used to form the bulk of a part cross section. Contour scans, may further be used to outline the edges of the part cross section. During a raster scan process, the energy source or laser is turned on, increased in power and/or focused in regions where a solid portion of the AM build is desired, and switched off, defocused, pulsed, and/or decreased in power where melt formation of the object&#39;s cross section in that layer are not desired. During a raster scan process, at least partially melting of powder and formation of solidification is repeated along adjacent solidification lines, for example, to form a single melted and fused cross section of the object to be built, while the contour scans create a discrete border or edge of the part. In the example AM apparatus using a powder bed, once the melt formation of one cross section of the object being built is completed, the apparatus coats the completed cross-sectional surface with an additional layer of powder. The process is repeated until the object is complete. 
     It is noted that while a build material is referenced as a powder throughout the specification, any build material may be used to form each layer (e.g, a foil and/or thin sheet of build material). Further, while the terms solidification, melting, and partially solidifying are used throughout the specification, it is noted that the disclosure is intended to be applicable to any type of densification of a build material. For example, the disclosure thought may be applicable to a binder jetting of build material. Binder jetting involves successively depositing layers of additive powder in a similar manner as described above. However, instead of using an energy source to generate an energy beam to selectively melt or fuse the additive powders, binder jetting involves selectively depositing a liquid binding agent onto each layer of powder. For example, the liquid binding agent may be a photo-curable polymer or another liquid bonding agent. Other suitable additive manufacturing methods and variants are intended to be within the scope of the present subject matter. 
     For the above reasons, the laser and/or energy source is controlled to form a series of solidification lines in a layer of powder using a pattern for at least the following reasons; to decrease build time, to control the heat buildup within the powder and/or to increase the efficiency of the build, to improve and/or control the material properties of the solidified material, to reduce stresses in the completed material, and/or to reduce wear on the laser and/or galvanometer scanner. 
     As shown in  FIGS. 4 and 5 , a built AM component includes a plurality of layers  215 ,  216 ,  217 . One example of the abovementioned strategy is shown, for example, a first layer  217  may be divided by software into several stripe regions bounded by, stripes  257  and  277  formed as solidification lines. The stripes  257  and  277  may form a boundary for individually formed parallel adjoining vectors or solidification lines  267 . The surface of the part includes a plurality of stripes covering the surface to be built. As shown in  FIG. 5 , each stripe region is bounded by solidified stripes  257  and  277  in layer  217  form a boundary for a series of parallel solidified lines  267 . The parallel solidification lines  267  are perpendicular to the solidified stripe boundaries  257  and  277 . The stripes are oriented at a first angle in layer  217  with the perpendicular solidification lines  267  being formed substantially perpendicular to the stripes  257  and  277 . The stripe region bound by solidified stripes  256  and  257  on a second layer  216  are angled with respect to the solidified stripe boundaries  257  and  277  on previous layer  217 . Accordingly, solidification lines  266  that run perpendicular to solidified stripes  256  and  276  are also be angled with respect to the solidification lines  267  on previous layer  217 . As the build progresses, a next layer having stripes  265  and  275  on a third layer  215  are angled with respect to stripes  257  and  277  on layer  217 ; and stripes  256  and  276  on layer  216 . 
     Additional details for scan strategies that can be used in accordance with the present invention may be found in U.S. patent application Ser. No. 15/451,108, titled “Triangle Hatch Pattern for Additive Manufacturing,” with attorney docket number 037216.00070, and filed Mar. 7, 2017; U.S. patent application Ser. No. 15/451,043, titled “Leg Elimination Strategy for Hatch Pattern,” with attorney docket number 037216.00078, and filed Mar. 6, 2017; U.S. patent application Ser. No. 15/459,941, titled “Constantly Varying Hatch for Additive Manufacturing,” with attorney docket number 037216.00077, and filed Mar. 15, 2017, the disclosures of which are incorporated herein by reference. 
       FIG. 6  shows an example of one embodiment of a large-scale AM apparatus according to the present invention. The apparatus comprises a positioning system (not shown), a build unit  400  comprising an irradiation emission directing device  401 , a laminar gas flow zone  404 , and a build plate beneath an object being built  415 . The maximum build area is defined by the positioning system (not shown), instead of by a powder bed as with conventional systems, and the build area for a particular build can be confined to a build envelope  414  that may be dynamically built up along with the object. In general, the positioning system used in the present invention may be any multidimensional positioning system such as a gantry system, a delta robot, cable robot, robot arm, etc. The irradiation emission directing device  401  may be independently moved inside of the build unit  400  by a second positioning system (not shown). The atmospheric environment outside the build unit, i.e. the “build environment,” or “containment zone,” may be controlled such that the oxygen content is reduced relative to typical ambient air, and so that the environment is at reduced pressure. In some embodiments, the recoater used is a selective recoater. One embodiment of a selective recoater  411  is illustrated in  FIG. 6 . 
     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  403  providing substantially laminar gas flow zone. An electron-beam may also be used in instead of the laser or in combination with the laser. 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 is incorporated herein by reference. 
     The gasflow device  403  may provide gas to a pressurized outlet portion  403 A and a vacuum inlet portion  403 B which may provide gas flow to a gasflow zone  404 , and a recoater  405 . Above the gasflow zone  404  there is an enclosure  418  which may contain an inert environment  419 . The recoater  405  may include a hopper  406  comprising a back plate  407  and a front plate  408 . The recoater  405  also has at least one actuating element  409 , at least one gate plate  410 , a recoater blade  411 , an actuator  412 , and a recoater arm  413 . The recoater is mounted to a mounting plate  420 .  FIG. 6  also shows a build envelope  414  that may be built by, for example, additive manufacturing or Mig/Tig welding, an object being formed  415 , and powder  416  contained in the hopper  405  used to form the object  415 . In this particular example, the actuator  412  activates the actuating element  409  to pull the gate plate  410  away from the front plate  408 . In an embodiment, the actuator  412  may be, for example, a pneumatic actuator, and the actuating element  409  may be a bidirectional valve. In an embodiment, the actuator  412  may be, for example, a voice coil, and the actuating element  409  may be a spring. There is also a hopper gap  417  between the front plate  408  and the back plate  407  that allows powder to flow when a corresponding gate plate is pulled away from the powder gate by an actuating element. The powder  416 , the back plate  407 , the front plate  408 , and the gate plate  410  may all be the same material. Alternatively, the back plate  407 , the front plate  408 , and the gate plate  410  may all be the same material, and that material may be one that is compatible with any desired material, such as cobalt-chrome for example. In this particular illustration of one embodiment of the present invention, the gas flow in the gasflow zone  404  flows in the x direction, but could also flow in any desired direction with respect to the build unit. The recoater blade  411  has a width in the x direction. The direction of the irradiation emission beam when ⊖2 is approximately 0 defines the z direction in this view. The gas flow in the gasflow zone  404  may be substantially laminar. The irradiation emission directing device  401  may be independently movable by a second positioning system (not shown). This illustration shows the gate plate  410  in the closed position. 
     Further it is noted that while the abovementioned selective powder recoating mechanism  405  only includes a single powder dispenser, the powder recoating mechanism may include multiple compartments containing multiple different material powders are also possible. Similarly, the abovementioned apparatus may include plurality of recoater mechanisms. 
     When the gate plate  410  in the open position, powder in the hopper is deposited to make fresh powder layer  416 B, which is smoothed over by the recoater blade  411  to make a substantially even powder layer. 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. 7  shows a side view of a manufacturing apparatus  300  including details of the build unit  302 , which is pictured on the far side of the build platform. The mobile build unit  302  includes an irradiation beam directing mechanism  506 , a gas-flow mechanism (e.g., similar to gasflow device  403 ) with a gas inlet and gas outlet (not shown) providing gas flow to a gas flow zone in direction  538 , and a powder recoating mechanism  504 . In this example, the flow direction is substantially along the X direction. Above the gas flow zone  538 , there may be an enclosure  540  that contains an inert environment  542 . The powder recoating mechanism  504 , which is mounted on a recoater plate  544 , has a powder dispenser  512  that includes a back plate  546  and a front plate  548 . The powder recoating mechanism  504  also includes at least one actuating element  552 , at least one gate plate  516 , a recoater blade  550 , an actuator  518  and a recoater arm  508 . In this embodiment, the actuator  518  activates the actuating element  552  to pull the gate plate  516  away from the front plate  548 , as shown in  FIG. 7 . There is also a gap  564  between the front plate  548  and the gate plate  516  that allows the powder to flow onto the rotating build platform  310  when the gate plate  516  is pulled away from the front plate  548  by the actuating element  552 . The rotating build platform  310  may be rotatably controlled by a motor  316 . 
       FIG. 7  shows a build unit  302  with the gate plate  516  at an open position. The powder  515  in the powder dispenser  512  is deposited to make a fresh layer of powder  554 , which is smoothed over a portion of the top surface (i.e. build or work surface) of the rotating build platform  310  by the recoater blade  510  to make a substantially even powder layer  556  which is then irradiated by the irradiation beam  558  to a fused layer that is part of the printed object  330 . In some embodiments, the substantially even powder layer  556  may be irradiated at the same time as the build unit  302  is moving, which allows for a continuous operation of the build unit  302  and hence, a more time-efficient production of the printed or grown object  330 . The object being built  330  on the rotating build platform  310  is shown in a powder bed  314  constrained by an outer build wall  324  and an inner build wall  326 . In this particular illustration of one embodiment of the present invention, the gas flow in the gasflow zone  538  flows in the x direction, but could also flow in any desired direction with respect to the build unit. 
     It is noted that while the abovementioned selective powder recoating mechanism  504  only includes a single powder dispenser, the powder recoating mechanism may include multiple compartments containing multiple different material powders are also possible. Further, while a single recoater apparatus is shown, the invention is applicable to an apparatus having a plurality of recoater apparatuses. 
     Additional details for a build units and positioning mechanisms for a single and/or multiple units that can be used in accordance with the present invention may be found in U.S. patent application Ser. No. 15/610,177, titled “Additive Manufacturing Using a Mobile Build Volume,” with attorney docket number 037216.00103, and filed May 31, 2017; U.S. patent application Ser. No. 15/609,965, titled “Apparatus and Method for Continuous Additive Manufacturing,” with attorney docket number 037216.00102, and filed May 31, 2017; U.S. patent application Ser. No. 15/610,113, titled “Method for Real-Time Simultaneous Additive and Subtractive Manufacturing With a Dynamically Grown Build Wall,” with attorney docket number 037216.00108, and filed May 31, 2017; U.S. patent application Ser. No. 15/610,214, titled “Method for Real-Time Simultaneous and Calibrated Additive and Subtractive Manufacturing,” with attorney docket number 037216.00109, and filed May 31, 2017; U.S. patent application Ser. No. 15/609,747, titled “Apparatus and Method for Real-Time Simultaneous Additive and Subtractive Manufacturing with Mechanism to Recover Unused Raw Material,” with attorney docket number 037216.00110, and filed May 31, 2017; U.S. patent application Ser. No. 15/406,444, titled “Additive Manufacturing Using a Dynamically Grown Build Envelope,” with attorney docket number 037216.00061, and filed Jan. 13, 2017; U.S. patent application Ser. No. 15/406,467, titled “Additive Manufacturing Using a Mobile Build Volume,” with attorney docket number 037216.00059, and filed Jan. 13, 2017; U.S. patent application Ser. No. 15/406,454, titled “Additive Manufacturing Using a Mobile Scan Area,” with attorney docket number 037216.00060, and filed Jan. 13, 2017; U.S. patent application Ser. No. 15/406,461, titled “Additive Manufacturing Using a Selective Recoater,” with attorney docket number 037216.00062, and filed Jan. 13, 2017; U.S. patent application Ser. No. 15/406,471, titled “Large Scale Additive Machine,” with attorney docket number 037216.00071, and filed Jan. 13, 2017, the disclosures of which are incorporated herein by reference. 
     As mentioned above, a build unit (e.g., as shown in  FIGS. 6 and 7 ) is used to selectively provide a build material (e.g., powder) and at least partially melt or sinter the build material within a scan region. As the size of the component being manufactured using the AM apparatus increases, portions of the component may require a build unit to move to another scan zone. Further, portions of the build may require two or more scan zones to be connected to form a single larger at least partially solidified layer of the AM build. For example, as shown in  FIGS. 8A and 8B , a first scan zone  801  may be near a second scan zone  803 . The first scan zone  801  may represent a portion of a scan-able region at a first location of the build unit (e.g., build units  302  and/or  400  as shown in  FIGS. 6 and 7 ) and/or may represent a first position of the build platform  310  shown in  FIG. 7  with respect to the build unit  302 , for example. The second scan zone  803  may represent a portion of a scan-able region at a second location of the build unit (e.g., build units  302  and/or  400  as shown in  FIGS. 6 and 7 ) and or may represent a second position of the build platform  310  shown in  FIG. 7  with respect to the build unit  302 , for example. When forming a layer of the AM build by at least partially solidifying a build material in scan zone  801  and/or  803 , excessive heat build-up may occur at offset region  802  between the first scan region  801  and the second scan region  803 . 
     A scan-able region may represent a surface area over which the irradiation source is capable of at least partially fusing a build material at a specific location of the build unit. For example, with reference to  FIG. 6 , a scan-able region may include a surface area of the powder  416 B and/or fused region  415  over which the irradiation source  402  is capable of operating (e.g., capable of fusing and/or sintering the build material) while the build unit  400  is in a single orientation with respect to the build surface  415  and/or  416 B. In other words regions  801  and  803 , may represent a surface that is at least a portion of a total scan-able region while a build unit and/or platform is in a single stationary orientation. 
     As shown in  FIGS. 8A-B , each of the scan regions  801  and/or  803  may be selected by software which divides each layer of a desire AM build into build unit positions and raster-scan regions. Each scan region  801  and/or  803  may include solidification lines  811  and/or  813  which may be bounded by a stripe  810  and/or  820 . As mentioned above each stripe may be a separate solidification line or may simply represent a border for each of the solidification lines  811  and/or  813 . If the stripes  810  and/or  820  are borders an irradiation source may follow a path along a build material to form each solidification line  811  and/or  813  and may be defocused, pulsed, decreased in power, and/or turned off at the stripe  810  and/or  820 . 
     In one aspect of the disclosure, the solidification lines of each of the first scan region  801  and the second scan region  803  may be formed so as to interlock within the offset region  802  between each scan region. The solidification lines  811  and  813  may be formed so as to interlock at alternating intervals within offset region  802  between the two scan regions. For simplification, the scan regions  801  and  803  are shown as ending at the line proximal to  801  and  803  in  FIG. 8B , however it is noted that any of the methods of interlocking or forming solidification lines may be applied between any two or more scan regions. For example, a scan region may be formed above and/or below one or both of scan regions  801  and  803  in the Y direction as shown in  FIG. 8A . Further, additional scan regions may be formed alongside each of the scan regions  801  and/or  803  in the X direction, for example. In one aspect, an at least partially solidified portion within a first scan region  801  may be formed. The solidified portion within the first scan region  801  may be formed by irradiating a build material along a first irradiation path  830 ,  811 . A second portion of a build material may be irradiated along a second irradiation path  813 , wherein the second scan region  803  is offset with respect to the first scan region thereby defining an offset region  802 . The offset region  802  is at least partially solidified by the first irradiation path  830 ,  811  and the second irradiation path  813  and a reference line located at  819  intersects the first and second irradiation path within the offset region  802 , wherein the reference line  819  is substantially parallel to a side of the first scan region  801 . 
     As mentioned above, when forming a layer of the AM build by at least partially solidifying a build material in scan zone  801  and/or  802 , excessive heat build-up and/or decreased temperature may occur at various regions of space  802  between the first scan region  801  and the second scan region  803 . In order to compensate for excessive heat build-up in offset region  802 , the process parameters may be adjusted to assure that the layer being built has the desired properties. For example, the solidification lines formed in region  812  may be formed with different process parameters than solidification lines  811  and  813  to compensate for any excessive heat build-up within space  802 . 
     In another aspect the solidification lines  812  may be formed using the altered process parameters and/or the same process parameters in offset region  802  and may be formed in an interlocking configuration such that an at least partially solidified portion is formed within a first scan region  801 , wherein the solidified portion within the first scan region is formed by irradiating a build material along a first irradiation path  811 . A second at least partially solidified portion may be formed within a second scan region  803  that is spaced with respect to the first scan region  801 . The solidified portion within the second scan region  803  may be formed by irradiating a build material along a second irradiation path  813 , wherein the offset region  802  between the first scan region  801  and the second scan region  803  is at least partially solidified when a first irradiation path  811  and the second irradiation path  813  cross a reference line  819  within the offset region  802  between the first scan region  801  and the second scan region  803 , wherein the reference line  819  is substantially parallel with at least one of the boundaries  810  and/or  820  of the first scan region  801  and the second scan region  803  and is spaced equidistantly therebetween. In other words, a first portion  830  of a solidification line  811  within the first scan region  801  may be formed so as to extend either to or slightly past a stripe and/or end of scan region  810 . A subsequently formed and/or parallel portion of a solidification line  832  may be formed so as to pass a stripe and/or end of scan region  810  and pass the first portion  830  of the adjacent portion of the solidification line. The solidification  813  of scan region  803  may be formed so as to interlock with the portions  830  and  832  of solidification lines  811  of scan region  801 . Application of the abovementioned examples allows for the metallurgy and/or energy build up within an offset region  802  to be controlled so as to improve metallurgical properties and/or dimensional accuracy of the completed component. 
     As mentioned above, the process parameters may also be controlled during an AM build process as energy is imparted into the build material. For example, when using a laser, a laser energy imparted into the build material is derived from the laser power, the scan speed, and the scan spacing. The laser power, is energy directed into the built part (e.g., the build material and the component being built) as opposed to the wattage input into the laser. Thus, the laser power may comprise a focus of the laser, a pulse of the laser, and/or wattage of the laser. Scan speed is the velocity at which the laser moves across the build profile. The scan speed may be determined by the velocity at which galvanometer scanner directs the laser, for example. Scan spacing is the spacing between each solidification line formed in the build material. Any of the abovementioned process parameters may be controlled to impart a specific energy into the build material. Thus, while not limited as such, an energy density may be controlled by controlling any one of or a combination of the abovementioned values. 
     Excessive energy densities during a build process could result in warping, dimensional inaccuracies, and/or boiling porosity in the finished component. Energy densities that are too low could result in improper bonding of the completed component. Thus, throughout the build the energy density may be constantly controlled based on an estimated or detected energy density build up and/or decrease in energy density within a region of the build. Any of the abovementioned variables may be altered within a region to assure a consistent build and/or to control the metallurgical properties of the completed layer and/or multiple completed layers. Further description of the possible variation in energy density imparted during the build process is disclosed in U.S. patent application Ser. No. 15/771,808, titled “Scanning Strategy for Perimeter and Region Isolation,” with attorney docket number 037216.00127, and filed Sep. 21, 2017, which is hereby incorporated by reference in its entirety. 
     The interlocking pattern may also be achieved by forming a first stripe region and a second stripe boundary in an interlocking configuration. With reference to the example shown in  9 A and  9 B, a partially solidified portion may be formed within a first scan region  701 , wherein the solidified portion within the first scan region  701  is formed by irradiating a build material along a first irradiation path  711  bounded by a first stripe  716  within an offset region (shown as  702  in  FIG. 9A ) or within space  712  (as shown in  FIG. 9B ) defined between a border  710  of a first scan region  701  and the border  720  of a second scan region  703 . The first irradiation path may be formed as a series of substantially parallel solidification lines  711 . The stripe boundary  716  may be shaped as a toothed configuration as shown in  FIG. 9B . However, it is noted that the above configuration is only an example and that an interlocking pattern joining each scan region may be formed as a number of interlocking shapes. For example, the stripe boundary may be formed as a series of semicircles, a sinusoidal curve, dovetails, and/or rectangular, square, angled geometries, or any other type of interlocking geometry. Further, a partially solidified portion may be formed within a second scan zone  703  within a scan region that is spaced with respect to the first scan region  701 , wherein the solidified portion within the second scan region is formed by irradiating a build material along a second irradiation path  713  bounded by a second stripe region  703  which may be substantially parallel with and/or overlap the first stripe region  716 . By forming a series of parallel solidification lines  713  bounded by the at least one boundary of the first stripe region  701  region within the space  712  between the first scan region  701  and the second scan region  703 , the solidification lines and each solidified region may be formed so as to interlock with at least one boundary of the second stripe region. 
     As discussed supra, the stripe  716  may be a separate solidification line or may simply represent a border for each of the solidification lines  711  and/or  713 . If the stripes of each scan region  701  and/or  703  are borders, an irradiation source may follow a path along a build material to form each solidification line  711  and/or  713  and may be defocused, pulsed, decreased in power, and/or turned off at the stripe  716 . The second scan region  703  may also be irradiated to form solidification lines  713  at a second energy density. The first energy density and second energy density may be the same or may be varied depending on the determined heat build-up within the layer and/or the desired metallurgical properties of the completed component and/or layer. 
     One example implementation is shown in  FIG. 10 .  FIG. 10  represents a top view of a build unit movement within a build area  900 . The build area  900  may be a powder bed and/or may be an area supplied with powder and/or build material by a build unit. A build unit may first be positioned in a first position and/or orientation represented by  902 A. It is noted that the outline  902 A may represent a scan-able region and/or a build unit outline and is simplified for clarity purposes. Further, it is noted that portion  902 A may be referred to interchangeably as a scan-able region or a build unit and may include a larger or smaller area in relation to a scan zone  901 A. As mentioned above, the scan zone  901 A may be a portion of a scan-able region  902 A which may represent a surface area over which the irradiation source is capable of at least partially fusing a build material at a specific location of the build unit e.g., position  902 A. For example, with reference to  FIG. 6 , a scan-able region may include a surface area of the powder  416 B and/or fused region  415  over which the irradiation source  402  is capable of operating (e.g., capable of fusing and/or sintering the build material) while the build unit  400  is in a single orientation with respect to the build surface  415  and/or  416 B. In other words regions  901 A and  901 B, may represent a surface that is at least a portion of a total scan-able region while a build unit and/or platform is in a single stationary orientation. 
     As shown in  FIG. 10 , first scan zone  901 A may be near a second scan zone  901 B. The first scan zone may represent a portion of a scan-able region  902 A at a first location of the build unit (e.g., build units  302  and/or  400  as shown in  FIGS. 6 and 7 ) and/or may represent a first position of the build platform  310  shown in  FIG. 7  with respect to the build unit  302 , for example. A second scan zone  901 B may represent a portion of a scan-able region  902 A at a second location of the build unit (e.g., build units  302  and/or  400  as shown in  FIGS. 6 and 7 ) and or may represent a second position of the build platform  310  shown in  FIG. 7  with respect to the build unit  302 , for example. The first scan zone may be irradiated to form a series of solidification lines  908 A between each stripe  906 A. It is noted however, that this example is not limiting, for example, the first scan zone  901 A may be formed using any of the abovementioned and incorporated raster scan schemes. Likewise, the second scan zone  902 B may be formed by irradiating the powder along a series of solidification lines  908 B bounded by stripes  906 A. While not shown in  FIG. 10 , the stripe and/or solidification line scheme may be varied when forming the first scan zone  901 A and the second scan zone  901 B. Further, a third scan zone  901 C within a third scan-able region  902 C may be at least partially solidified by irradiating the build material along a series of solidification lines bounded by stripes  906 C. As mentioned above, the stripe and/or solidification line scheme may be varied when forming the first scan zone  901 A and the second scan zone  901 B and the third scan zone  901 C and any combination of solidification line and/or stripe schemes may be used. Further, it is noted that while arrows  909  and  910  show example movements of the build unit, the first, second, and third scan zones may be solidified in any order. When forming a layer of the AM build by at least partially solidifying a build material in scan zone  901 A,  901 B, and/or  901 C, an interlocking stripe scheme, as shown in  FIGS. 9A-B  may be used in space  903 A and/or  903 B between the first, second, and/or third scan regions  901 A-C. Further, any of the abovementioned process parameters may be varied when connecting scan regions  901 A-C. 
     As another example, scan zones  911 A,  911 B, and  911 C may also be formed at three separate positions of the build unit. Similarly to the scenario above, because of the overlap of each scan-able region  912 A-C, portions  913 A and/or  913 B may be formed by the build while the build unit remains stationary after any single or multiple scan zones are formed that border portions  913 A and/or  913 B. It is further noted that portions  903 A-B and/or  913 A-B could be formed by moving the build unit (e.g., along directions  919  and  920 ) to an intermediate position between each of the scan zones  901 A-C and/or  911 A-C as well. When forming a layer of the AM build by at least partially solidifying a build material in scan zone  911 A,  911 B, and/or  911 C, an interlocking solidification path may be used in each of the scan zones  911 A,  911 B, and/or  911 C (e.g., as shown in  FIGS. 8A-B ) the interlocking solidification paths may be used to at least partially solidify space  913 A and/or  913 B between the first, second, and/or third scan regions  911 A-C. Further, any of the abovementioned process parameters may be varied when connecting scan regions  911 A-C. 
     It is noted that  FIG. 10  shows a limited number of possible positions for simplicity purposes, it each of the abovementioned examples, the build unit may further progress to any position within the build area  900  to at least partially solidify a region and the same inventive principles may be applied. One having ordinary skill in the art would further appreciate that the abovementioned scan zones could be solidified in any desired order and the examples are not limiting. Further, one having skill in the art would further appreciate that the current invention could be applied to various possible AM build scenarios over each layer being formed. 
     Another example implementation is shown in  FIG. 11 .  FIG. 11  represents a top view of a build unit movement within a mobile build area  1000 , which may be rotatable along directions shown by arrow  1001 . The build area  1000  may be a powder bed and/or may be an area supplied with powder and/or build material by the build unit. A build unit may first be positioned in a first position and/or orientation represented by  1012 A. It is noted that the outline  1012 A may represent a scan-able region and/or a build unit outline and is simplified for clarity purposes. Further, it is noted that portion  1012 A may be referred to interchangeably as a scan-able region or a build unit and may include a larger or smaller area in relation to a scan zone  1012 A. As mentioned above, the scan zone  1012 A may be a portion of a scan-able region  1012 A which may represent a surface area over which the irradiation source is capable of at least partially fusing a build material at a specific location of the build unit e.g., position  1012 A. For example, with reference to  FIG. 7 , a scan-able region may include a surface area of the powder  314  and/or fused region  330  over which the irradiation source  558  is capable of operating (e.g., capable of fusing and/or sintering the build material) while the build unit  302  is in a single orientation with respect to the build surface  300 . In other words regions  1018 A and  1018 B, may represent a surface that is at least a portion of a total scan-able region  1012 A and  1012 B while a build unit and/or platform  1000  is in a single stationary orientation. 
     As shown in  FIG. 11 , first scan zone  1011 A may be near a second scan zone  1011 B. The first scan zone may represent a portion of a scan-able region  1012 A at a first location of the build unit and/or may represent a first position of the build platform  1000  with respect to the build unit, for example. A second scan zone  1011 B may represent a portion of a scan-able region  1012 B at a second location of the build unit and/or platform  1000 . The first scan zone may be irradiated to form a series of solidification lines  1018 A which may be formed across the entire surface of the build zone  1011 A and or may be bounded by a single and/or plurality of stripes  1006 A. It is noted however, that this example is not limiting, for example, the first scan zone  1012 A may be formed using any of the abovementioned and incorporated raster scan schemes. Likewise, the second scan zone  1012 B may be formed by irradiating the powder along a series of solidification lines  1018 B. While not shown in  FIG. 11 , the stripe and/or solidification line scheme may be varied when forming the first scan zone  1012 A and the second scan zone  1012 B. It is noted that while arrows  1019  and  1009  show example movements of the build unit in a radial direction of the build platform  1000 , the first and second scan zones may be solidified in any order. 
     When forming a layer of the AM build by at least partially solidifying a build material in scan zone  1011 A, and/or  1011 B, an the solidification paths  1018 A and  1018 B may be formed as alternately interlocking solidification paths within region  1013  (e.g., as shown in  FIGS. 8A-B ) the interlocking solidification paths may be used to at least partially solidify space  1013  between the first and second scan regions  1011 A-B. Further, any of the abovementioned process parameters may be varied when connecting scan regions  1011 A-B. 
     As another example, scan zones  1001 A and  1001 B may also be formed at two separate positions of the build unit. Similarly to the scenario above, because of the overlap of each scan-able region  1002 A-B, portion  1003  may be formed by the build while the build unit remains stationary after any single or multiple scan zones are formed that border portion  1003 . It is further noted that portions  1013  and/or  1003  could be formed by moving the build unit to an intermediate position between each of the scan zones  1011 A-B and/or  1001 A-B as well. 
     As mentioned above, the stripe and/or solidification line scheme may be varied when forming the first scan zone  1001 A and the second scan zone  1001 B and any combination of solidification line and/or stripe schemes may be used. Further, it is noted that while arrows  1009  and  1019  show example movements of the build unit, the first and second scan zones may be solidified in any order. When forming a layer of the AM build by at least partially solidifying a build material in scan zone  1001 A and  1001 B, an interlocking stripe scheme, as shown in  FIGS. 9A-B  may be used in space  1003  between the first and second scan regions  1001 A-B. Further, any of the abovementioned process parameters may be varied when connecting scan regions  1001 A-B. 
     It is noted that  FIG. 11  shows a limited number of possible positions for simplicity purposes, it each of the abovementioned examples, the build unit may further progress to any position within the build area  1000  to at least partially solidify a region and the same inventive principles may be applied. Further, it is noted that either in combination with the build unit moving or while the build unit is stationary, the build platform  1000  may be moved to move a new scan zone under the build unit. One having ordinary skill in the art would further appreciate that the abovementioned scan zones could be solidified in any desired order and the examples are not limiting. Further, one having skill in the art would further appreciate that the current invention could be applied to various possible AM build scenarios over each layer being formed. 
     This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspect, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application.