Patent Publication Number: US-2021187855-A1

Title: Additive manufacturing system and method using robotic arms

Description:
FIELD OF THE DISCLOSURE 
     Embodiments of the present disclosure generally relate to additive manufacturing of three-dimensional build parts. 
     BACKGROUND 
     Additive manufacturing refers to any process for manufacturing a three-dimensional build part in which successive layers of material are deposited under computerized control. The deposited layers fuse to pre-existing portions of the build part by applying heat, a laser beam, or the like. The size and shape of the build part can be based on a three-dimensional computer model or another electronic data source. Additive manufacturing can be used to fabricate objects that have complex structures and shapes. Additive manufacturing techniques for fabricating metal build parts can allow greater design freedom and yield more precise and repeatable finished products than conventional metal manufacturing techniques, such as die-casting, extruding, milling, and the like. Relative to conventional metal manufacturing techniques, such as milling, additive manufacturing techniques also may produce less material waste. 
     Build parts that are designed to include certain features, such as voids (e.g., channels, cavities, and the like) and projecting appendages, often require the formation of supports during the build process to mechanically support the construction of the appendages and voids. The supports are removed from the build part after the additive manufacturing build process, and the removal process can be costly, difficult, time intensive, and/or labor intensive. For example, the supports may need to be cut and grinded away from the surfaces of the build part, which can be especially difficult to do in certain hard-to-reach areas such as internal cavities. The task of removing the supports post-build reduces manufacturing efficiency and increases production costs. Furthermore, residual material from the supports left intact on the build part may degrade the quality of the finished product. 
     SUMMARY OF THE DISCLOSURE 
     In one or more embodiments of the present disclosure, an additive manufacturing system is provided that includes a first robotic arm and a print head with a nozzle. The first robotic arm is configured to hold a build part during a build process. The print head is configured to deposit source material layer by layer during the build process to construct the build part. The first robotic arm is configured to reorient the build part relative to the print head during the build process to modify an angle of a surface layer of the build part relative to the print head. 
     In one or more embodiments of the present disclosure, a method for additive manufacturing using robotic arms is provided that includes controlling a first robotic arm to hold a build part suspended above a floor. The method includes depositing source material layer by layer on the build part from a nozzle of a print head to construct the build part during a build process. The method also includes controlling the first robotic arm to move the build part relative to the print head and the floor during the build process to modify an angle of a surface layer of the build part relative to the print head and the floor. 
     In one or more embodiments of the present disclosure, an additive manufacturing system is provided that includes a first robotic arm and a second robotic arm. The first robotic arm is mechanically coupled to a first print head. The first print head is configured to deposit source material layer by layer on a build part during a build process to construct the build part. The second robotic arm is mechanically coupled to a second print head. The second print head is also configured to deposit the source material layer by layer on the build part during the build process to construct the build part. The first robotic arm moves the first print head relative to the build part during the build process, and the second robotic arm moves the second print head relative to the build part during the build process. The first and second print heads concurrently deposit the source material on the build part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like numerals represent like parts throughout the drawings, wherein: 
         FIG. 1  is a perspective view of an additive manufacturing system according to an embodiment of the present disclosure; 
         FIG. 2  illustrates a close-up view of a print head according to an embodiment of the additive manufacturing system; 
         FIG. 3  illustrates an initial stage of an additive manufacturing process using the additive manufacturing system shown in  FIG. 1  according to an embodiment; 
         FIG. 4  illustrates a first intermediate stage of the additive manufacturing process with a build part held in a first orientation; 
         FIG. 5  illustrates a second intermediate stage of the additive manufacturing process with the build part held in a second orientation; 
         FIG. 6  illustrates a third intermediate stage of the additive manufacturing process with the build part held in the second orientation; 
         FIG. 7  illustrates a final stage of the additive manufacturing process in which finishing tasks are performed on the build part; 
         FIG. 8  is a block diagram showing a control unit of the additive manufacturing system shown in  FIG. 1  according to an embodiment; 
         FIG. 9  illustrates the additive manufacturing system according to an embodiment in which first and second robotic arms concurrently move during the build process; 
         FIG. 10  illustrates the additive manufacturing system forming non-planar layers of the build part according to an embodiment; 
         FIG. 11  illustrates the additive manufacturing system according to another embodiment in which the additive manufacturing system includes at least three robotic arms; and 
         FIG. 12  is a flow chart of a method for additive manufacturing using robotic arms to modify an orientation of the build part during the build process according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE DISCLOSURE 
     The foregoing summary, as well as the following detailed description of certain embodiments will be better understood when read in conjunction with the appended drawings. As used herein, an element or step recited in the singular and preceded by the word “a” or “an” should be understood as not necessarily excluding the plural of the elements or steps. Further, references to “one embodiment” are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising” or “having” an element or a plurality of elements having a particular property may include additional elements not having that property. 
     In consideration of the cost, time, and labor of performing finishing treatments after the build process to grind away extraneous material, such as supports, to polish various surfaces, and the like, there are advantages in techniques for additively manufacturing build parts with less support material and improved surface quality. Reducing the amount of support material formed and improving the surface quality of the build part can eliminate or at least expedite post-build finishing treatments. 
     Embodiments of the present disclosure provide a system (e.g., an additive manufacturing system) and method for performing additive manufacturing using robots. In one or more embodiments, multiple robots are utilized. The robots perform different tasks for additively manufacturing a build part, such as holding and manipulating the build part that is being constructed, holding and manipulating a print head that fuses source material to the build part, and holding and manipulating a finishing instrument (e.g., a grinder, polishing wheel, and the like). The robots can move with coordinated movements along multiple (e.g., six) degrees of freedom relative to a stationary reference, such as the floor or ground. The movements can be based on a designated movement path within a build plan. The embodiments described herein can utilize only a single robot, two robots, three robots, or more to perform the various additive manufacturing tasks to construct the build part. For example, it is possible for one robot to perform multiple different tasks, as described herein. 
     The one or more robots of the additive manufacturing system and method described herein are configured to reorient the build part relative to the print head at least once during the build process to modify an angle of a surface layer of the build part relative to the print head. The build process refers to the stage during which the print head deposits material layer by layer to gradually increase the size of the build part by aggregation of layers. The surface layer refers to the most recent layer deposited on the build part. By using robots to reorient the build part relative to the print head during the build process, several benefits can be achieved including eliminating or at least reducing the amount of supports needed. For example, the build part can be reoriented to construct an appendage of the build part at an angle that does not require the formation of associated support material. Reducing the amount of support material can increase the efficiency of the additive manufacturing process and reduce costs by reducing the time and material used during the build process and avoiding or at least reducing post-build finishing tasks to remove support material from the build part. Another benefit of using robots to reorient the build part and/or the print head during the build process is that, by changing the angle of application at which the source material is fused to the build part, the surface quality of the build part can be improved. For example, some angles of application may result in worse surface quality of the build part than other angles of application depending on various factors. Selectively reorienting during the build process to achieve preferred angles of application can increase manufacturing efficiency and reduce costs by eliminating or at least expediting post-build surface finishing treatments, such as polishing or sanding. 
       FIG. 1  is a perspective view of an additive manufacturing system  100  according to an embodiment of the present disclosure. The additive manufacturing system  100  is configured to perform an additive manufacturing build process to construct a build part  102 . The additive manufacturing system  100  can include one or more robots. A first robotic arm  104  and a second robotic arm  106  are shown in  FIG. 1  and represent discrete robots. The first robotic arm  104  holds the build part  102 . For example, the first robotic arm  104  may carry the build part  102  suspended above a floor  108  or ground if located outdoor. The build part  102  may be partially completed in  FIG. 1 . The second robotic arm  106  holds a print head  110 . The print head  110  includes a nozzle  112  for depositing source material on the build part  102  at controlled locations during the build process. For example, the nozzle  112  is configured to deposit source material layer by layer during the build process to construct the build part  102 . The first robotic arm  104  is configured to reorient the build part  102  relative to the print head  110  during the build process to modify an angle of a surface layer  128  of the build part  102  relative to the print head  110 . 
     In an embodiment, both the first robotic arm  104  and the second robotic arm  106  are independently configurable to move along multiple (e.g., six) degrees of freedom relative to each other (and to the floor  108 ). Both robotic arms  104 ,  106  have a similar construction in  FIG. 1 , including a base section  114  disposed on the floor  108 , an intermediate elongated member  116 , a distal elongated member  118 , and an end  120 . The intermediate elongated member  116  is mechanically coupled between the base section  114  and the distal elongated member  118 . The end  120  is mechanically coupled to the distal elongated member  118 . The various components  114 ,  116 ,  118 ,  120  are rotatable relative to each other at respective joints  122  to provide the multiple degrees of freedom. The movements of robotic arms  104 ,  106  can be motivated by motors and mechanical linkages, including gears, which enable the movements to be precise and repeatable. The movements of the robotic arms  104 ,  106  can be coordinated with each other such that the movement of the second robotic arm  106  can be based, at least in part, on the movement of the first robotic arm  104 , or vice-versa. Furthermore, the movements of the robotic arms  104 ,  106  are based on a build plan that designates instructions for additively manufacturing the build part  102  according to a selected design of the build part  102 . The build plan may be generated in consideration of the ability to reorient the build part  102  during the build process. 
     According to the embodiments described herein, the first robotic arm  104  is controlled to reorient the build part  102  relative to the second robotic arm  106  and the print head  110  thereon during the build process. For example, the orientation of the build part  102  shown in  FIG. 1  can represent a first orientation. The build part  102  that is shown in  FIG. 1  has a main body  124  and an appendage  126  that projects from the main body  124 . The main body  124  and the appendage  126  optionally may be cylindrical and hollow. The appendage  126  is oriented about a central axis that is perpendicular to a central axis of the main body  124 . In  FIG. 1 , the nozzle  112  of the print head  110  is located proximate to a surface layer  128  of the appendage  126  for depositing source material onto the appendage  126  to grow the appendage  126 . In the first orientation shown in  FIG. 1 , the surface layer  128  and additional layers stacked thereon are oriented parallel to the floor  108  (e.g., perpendicular to a direction of gravitational force). The first orientation allows for constructing the appendage  126  without the formation of support material. For example, the source material is applied in annular layers parallel to the floor  108 , so gravity-induced flow of the deposited material is negligible. No part of the appendage  126  is overhanging when in the first orientation. 
     After the appendage  126 , or a section thereof, is completed, the first robotic arm  104  reorients the build part  102  relative to the second robotic arm  106 , which modifies the angle of the surface layer  128  of the appendage  126  relative to the print head  110 . The first robotic arm  104  translates, tilts, and/or rotates the build part  102  to a second orientation, which is not shown in  FIG. 1 . The second robotic arm  106  optionally may also reposition. In the second orientation of the build part  102 , the nozzle  112  of the print head  110  deposits additional layers of source material on the build part  102 . The additional layers may be deposited on the main body  124  or the appendage  126  of the build part  102 . In a non-limiting example, the print head  110  may begin constructing another appendage that projects from the main body  124  at a different location and/or different angle than the appendage  126 . The second orientation can be selected to avoid the formation of support material while constructing the second appendage. The additional layers of source material deposited on the build part  102  while the build part  102  is in the second orientation can be parallel to each other and transverse to the layers of the source material that form the appendage  126 , as shown and described in more detail herein. 
     In one or more embodiments, the build part  102  is secured on a surface  130  of a plate  132  that is planar. The first robotic arm  104  indirectly holds the build part  102  via the plate  132  and reorients the build part  102  by reorienting the plate  132 . The end  120  of the first robotic arm  104  is mechanically coupled to the plate  132 . The end  120  may be bolted or clamped to the plate  132  or may grasp the plate  132 . The end  120  can engage a back surface  134  of the plate  132  opposite the surface  130  on which the build part  102  is located, as shown in  FIG. 1 . Optionally, the end  120  can extend around an edge of the plate  132 . The build part  102  can be secured to the surface  130  of the plate  132  via a welded connection, an adhesive, or the like. In an alternative embodiment, the first robotic arm  104  may hold the build part  102  directly without having the plate  132 , which may be particularly useful for additively manufacturing features in situ onto a pre-formed object. For example, the first robotic arm  104  can be controlled to pick up and hold a pre-formed object, such as a pipe, and the second robotic arm  106  and print head  110  can be controlled to weld additional features onto the pipe while the pipe is held by the first robotic arm  104 . 
     The additive manufacturing system  100  in  FIG. 1  can perform various additive manufacturing techniques. Suitable additive manufacturing processes can include, for example, material extrusion, directed energy deposition, or material jetting. Material extrusion involves extruding source material through a nozzle in tracks or beads that are deposited on the build part. Examples of material extrusion can include fused filament fabrication and fused deposition modeling. Directed energy deposition involves feeding a powder or wire source material into a melt pool that is generated on the surface of the build part, and the source material adheres to the underlying layers by using an energy source such as a laser or electron beam. Material jetting can involve depositing droplets of material layer by layer, such as a photocurable resin or a thermally molten material, and then actively or passively solidifying the material. 
       FIG. 2  illustrates a close-up view of the print head  110  according to an embodiment of the additive manufacturing system  100 . The nozzle  112  is shown in cross-section to show an internal channel  202  through the nozzle  112 . The source material  204  can be a filament or bead of material. The material may include or represent a polymer, a metal, or a ceramic. The source material  204  is supplied from a dispenser which may be coupled to or within the second robotic arm  106  shown in  FIG. 1 . The print head  110  may include feed rollers  206  that engage the source material  204  and rotate to urge the source material  204  towards a tip  208  of the nozzle  112 . The nozzle  112  includes a heating block  210  proximate to the tip  208 . The heating block  210  is configured to increase the temperature of the source material  204  within the channel  202  to reduce the viscosity of the source material  204 . The channel  202  may taper towards the tip  208  such that the tip  208  defines a narrow opening  212  for depositing the source material  204 . The source material  204  can be deposited as heated bead  214  which fuses or bonds to the preceding layer (e.g., the surface layer  128 ) of the build part  102 . Upon cooling and solidifying, the bead  214  forms a new layer of the build part  102 . 
       FIGS. 3-7  illustrate different stages of an additive manufacturing process according to an embodiment using the additive manufacturing system  100  shown in  FIG. 1 .  FIG. 3  illustrates an initial stage of the additive manufacturing process. During the initial stage, the first robotic arm  104  moves or maintains the plate  132  in a first orientation suspended above the floor or ground. The first robotic arm  104  is able to rotate the plate  132  about a vertical axis  302 , a lateral axis  304 , and a longitudinal or depth axis  306 . The axes  302 ,  304 ,  306  are mutually-perpendicular. The vertical axis  302  may be parallel to a direction of gravity (e.g., gravitational force). In the illustrated first orientation, the surface  130  of the plate  132  may be parallel to the floor and perpendicular to the vertical axis  302 . The first orientation may be designated by the build plan, as described in more detail with reference to  FIG. 8 . The first robotic arm  104  is also able to translate the plate  132  along the vertical axis  302 , and the lateral axis  304 , and the longitudinal axis  306 , providing six degrees of freedom. 
       FIG. 4  illustrates a first intermediate stage of the additive manufacturing process with the build part  102  held in the first orientation. While the plate  132  is in the first orientation, the second robotic arm  106  controls the print head  110  to begin depositing source material (e.g., the source material  204  shown in  FIG. 2 ) layer by layer to construct the build part  102  on the plate  132 . The initial layers of source material may automatically bond to the plate  132  (e.g., as a weld), or an adhesive can be applied to the surface  130  prior to depositing the source material.  FIG. 4  shows that the print head  110  has constructed a first section  314  or segment of the build part  102  on the surface  130  of the plate  132 . The first section  314  may represent a main body of the build part. The print head  110  deposits the source material layer  312  by layer  312  in a stack to define the first section  314 . The layers  312  are parallel to each other. In the illustrated embodiment, the layers  312  are also parallel to the surface  130  of the plate  132  and perpendicular to the vertical axis  302  (shown in  FIG. 3 ), or within a designated tolerance range (e.g., 2 degrees, 5 degrees, 10 degrees, or the like) of perpendicular. With each successive addition of material to define another layer  312 , the build part  102  grows taller in the vertical direction extending away from the plate  132 . The surface layer  128  of the build part  102  defines an angle  316  relative to the print head  110 . Specifically, the angle  316  is defined by a longitudinal axis  318  of the print head  110  along which the source material is emitted. The angle  316  is a right angle in the illustrated embodiment. The path of the print head  110  and other settings of the second robotic arm  106  for constructing the first section  314  of the build part  102  may be designated by the build plan. 
       FIG. 5  illustrates a second intermediate stage of the additive manufacturing process with the build part  102  held in a second orientation. After the first section  314  of the build part  102  is completed, according to the build plan, the first robotic arm  104  reorients the build part  102  relative to the second robotic arm  106  and the floor to move from the first orientation to the second orientation. In the illustrated embodiment, the first robotic arm  104  may tilt or rotate the plate  132  (and the build part  102  thereon) about the longitudinal axis  306  (shown in  FIG. 3 ) from the first orientation to achieve the second orientation. Optionally, the first robotic arm  104  may also rotate the plate  132  about the vertical axis  302  and/or the lateral axis  304  to achieve the second orientation. The second orientation may be designated by the build plan. Transitioning the build part  102  from the first orientation to the second orientation modifies the angle  316  of the surface layer  128  of the build part  102  relative to the print head  110 . For example, the surface layer  128  of the first section  314  in the first orientation shown in  FIG. 4  is perpendicular to the vertical axis  302 , but the same surface layer  128  is oblique (e.g., not perpendicular or parallel) to the (longitudinal axis  318  of the) print head  110  in the second orientation shown in  FIG. 5 . The build part  102  is secured to the surface  130  of the plate  132 , so the build part  102  remains fixed in position on the plate  132  even if the second orientation would cause an unsecured build part  102  to fall off the plate  132 . 
     The first and/or second robotic arms  104 ,  106  may coordinate movements with each other to avoid collisions and enable depositing material at hard-to-access locations. For example, as the first robotic arm  104  tilts the plate  132  to achieve the orientation shown in  FIG. 5 , the second robotic arm  106  may be configured to translate and/or rotate the print head  110  to avoid a collision between the print head  110  and the left upper corner  133  of the build part  102 . The collision avoidance is enhanced by the maneuverability of the robotic arms  104 ,  106  that allows for both translation and rotation in three-dimensions. Conventional 3-axis additive manufacturing apparatuses may not be able to avoid collisions between the print head and the build part when reorienting, which can damage the build part and/or substantially interfere with or impede the build process. Although only two robotic arms  104 ,  106  are shown in the illustrated embodiment, the coordinated movement for collision avoidance during reorientation can be utilized with more than two robots, such as three or four robotic arms working together to additively form a part. For example, the additive manufacturing system  100  can include the first robotic arm  104  that holds the build part  102 , the second robotic arm  106  that holds the print head  110 , a third robotic arm that holds another print head, and a fourth robotic arm that holds another print head or a finishing tool. The second, third and fourth robotic arms can concurrently operate to form the build part  102  that is held by the first robotic arm without collisions between the robotic arms or the components held by the robotic arms. 
       FIG. 6  illustrates a third intermediate stage of the additive manufacturing process with the build part  102  held in the second orientation. While the build part  102  is in the second orientation, the print head  110  is configured to deposit additional layers of the source material on the build part  102 . For example, the second robotic arm  106  controls the print head  110  to deposit additional source material for constructing another section of the build part  102 . In  FIG. 6 , the print head  110  deposits additional layers  320  to form a second section  322  that projects from a side  324  of the first section  314 . The second section  322  can represent an appendage of the build part  102 . The additional layers  320  are parallel to one another. The layers  320  are transverse to the surface  130  of the plate  132  and the layers  312  (shown in  FIG. 4 ) of the first section  314 , including the surface layer  128 . In an embodiment, the layers  320  may be perpendicular to the vertical axis  302 , or within a designated tolerance range (e.g., 2 degrees, 5 degrees, 10 degrees, or the like) of perpendicular. With each successive addition of material to define another layer  320 , the second section  322  grows taller in the vertical direction extending away from the first section  314 . The second robotic arm  106  may control the print head  110  to have a different angular orientation in  FIG. 6  relative to the orientation in  FIG. 5 . Changing the orientation of the print head  110  during the build process is optional and may be performed to avoid collision with the build part  102 , the plate  132 , and/or the first robotic arm  104 . Alternatively, the orientation of the print head  110  can be changed based on desired surface characteristics of the build part  102 . For example, the deposited material may solidify differently when deposited at different angles. 
     In the illustrated embodiment shown in  FIGS. 4 and 6 , the print head  110  deposits the source material to construct the first section  314  of the build part  102  while the plate  132  and build part  102  are in the first orientation, and deposits the source material to construct the second section  322  (or appendage) of the build part  102  while the plate  132  and build part  102  are in the second orientation. Constructing the second section  322  at a different orientation than the first section  314  allows avoiding the formation of support material associated with the second section  322 , without compromising build quality. For example, in the second orientation, a downskin surface  328  of the second section  322  is no greater than a threshold angle relative to the vertical axis  302 . The vertical axis  302  is parallel to a gravitational force direction  329 . The downskin surface  328  faces at least partially towards the plate  132 . The threshold angle is associated with requiring support material underneath overhanging features. In non-limiting examples, the threshold angle can be 40 degrees, 45 degrees, 50 degrees, or the like. As shown in  FIG. 6 , an angle  330  defined between the vertical axis  302  (parallel to the gravitational force direction) and a tangent line  332  extending from the downskin surface  328  is less than a designated threshold angle. For this reason, the second robotic arm  106  controls the print head  110  to deposit source material to form the second section  322  without depositing additional source material to form supports underneath the downskin surface  328 . For comparison purposes, if the appendage that is the second section  322  is formed with the plate  132  and the build part  102  in the first orientation as shown in  FIGS. 3 and 4 , the angle  330  would exceed the threshold angle so supports would be needed underneath the downskin surface  328  to achieve designated build quality. As described above, the formation of supports undesirably extend the duration of the build process and require post-build tasks to extract the support material from the build part  102 . 
     The second robotic arm  106  can move the print head  110  relative to the build part  102  and the first robotic arm  104  during the build process to modify an angle of the print head  110  relative to the build part  102 . For example, the second robotic arm  106  can manipulate the print head  110  to modify an angle of application at which the source material is deposited on the surface layer  326  of the second section  322 . The angle of application may be selected based on material properties of the source material. Furthermore, the second robotic arm  106  may move the print head  110  relative to the build part  102  based on the design of the build part  102 . For relatively complex shapes, the second robotic arm  106  can manipulate the print head  110  to access hard-to-reach areas of the build part  102  and/or to avoid colliding with projecting portions of the build part  102 . 
     Optionally, after constructing the second section  322  of the build part  102 , the first robotic arm  104  may once again reorient the build part  102  prior to the deposition of additional source material to form another section of the build part  102 . For example, the first robotic arm  104  may move the plate  132  back to the first orientation or to a third orientation that is different from the first and second orientations. 
       FIG. 7  illustrates a final stage of the additive manufacturing process in which finishing tasks are performed on the build part  102 . The finishing tasks may be performed after the build part  102  is fully constructed. Optionally, at least some finishing tasks may be performed prior to completing the build process before the build part  102  is fully constructed. The finishing tasks can include grinding, sanding, polishing, buffering, cleaning, and/or the like. In  FIG. 7 , the second robotic arm  106  is mechanically coupled to a finishing instrument  340 , and the second robotic arm  106  moves the finishing instrument  340  relative to the build part  102  to one or more of grind, sand, buff, polish, or clean the build part  102 . For example, the finishing instrument  340  can include a buffing wheel (or polishing wheel)  342  that spins and engages surfaces of the build part  102  to smooth the surfaces. Another finishing instrument could include or represent a grinder that has a grinding element, a sander with sandpaper, a cleaner that applies and removes a cleaning solution, or the like. The second robotic arm  106  can be controlled to move the finishing instrument  340  relative to the build part  102  along a path (e.g., a finishing path) that is designated in the build plan. The first robotic arm  104  holds the plate  132  and the build part  102  in the first orientation in  FIG. 7 . Optionally, the first robotic arm  104  may be controlled to reorient the plate  132  and the build part  102  during the finishing tasks, similar to how the first robotic arm  104  reorients the build part  102  during the build process. Reorienting the build part  102  can enable the finishing instrument  340  to access hard-to-reach portions of the build part  102 , such as narrow gaps, voids, and the like. 
     In a non-limiting example, the second robotic arm  106  may be configured to make quick-change substitutions of the devices held by the second robotic arm  106 . For example, upon completing the build process, the second robotic arm  106  may move away from the build part  102 , disconnect the print head  110  from the end  120  of the second robotic arm  106 , and connect the finishing instrument  340  to the end  120  before returning to the build part  102  to perform a finishing task. In another example, the second robotic arm  106  may be configured to be mechanically and operably coupled to multiple end effectors at the same time, such as the print head  110  and the finishing instrument  340 . The second robotic arm  106  can position the print head  110  in an active position of the robotic arm  106  when constructing the build part  102  and then rotate the end  120  to move the finishing instrument  340  into the active position for performing a finishing task. 
     In an alternative embodiment, the finishing instrument  340  may be separate and discrete from the second robotic arm  106 . The finishing instrument  340  can be mechanically connected to a third robotic arm to perform the finishing task or tasks described above. Optionally, the third robotic arm may be controlled to move the finishing instrument  340  to perform a finishing task, such as polishing surfaces of the build part  102 , concurrent with the second robotic arm  106  controlling the print head  110  to deposit additional layers of material on the build part  102  in a location spaced apart from the finishing instrument  340 . By commencing the finishing tasks prior to completing the build process, the speed and efficiency of the additive manufacturing process can be increased relative to performing the build and finishing operations sequentially (e.g., waiting until the build part  102  is fully constructed prior to starting the finishing tasks). Commencing the finishing tasks prior to completing the build process also allows access to finish areas that may otherwise be obstructed by future additive features in the build sequence. For example, the finishing instrument  340  can smooth the inner surface of a cavity before subsequent layers of the build part are deposited which restrict access to the cavity. 
       FIG. 8  is a block diagram showing a control unit  402  or controller of the additive manufacturing system  100  shown in  FIG. 1  according to an embodiment. The control unit  402  may be disposed on a computing device that is discrete from the first robotic arm  104  and the second robotic arm  106 , such as a computer, a workstation, or the like. Alternatively, the control unit  402  may be an integral component of the first robotic arm  104  or the second robotic arm  106 . The control unit  402  may dictate the operations of the first and second robotic arms  104 ,  106  during the additive manufacturing process. For example, the operations may be defined in a build plan  404 . The build plan  404  may designate a movement path for the first robotic arm  104  to move and orient the build part  102  and a deposition path for the second robotic arm  106  to move and control the print head  110  to deposit the source material on the build part  102 . For example, the movement path may instruct the first robotic arm  104  how to manipulate the build part  102  to achieve the first orientation, the second orientation, and any additional orientations relative to the second robotic arm  106  and the floor  108 . The deposition path may instruct the second robotic arm  106  to locate, orient, and move the print head  110  to deposit the source material layer by layer. The build plan  404  is associated with a specific design of the build part  102 , such that implementing the movement path, the deposition path, and other settings prescribed in the build plan  404  produce the build part  102  having the specific design. 
     The control unit  402  represents hardware circuitry that includes and/or is connected with one or more processors  406  (e.g., one or more microprocessors, integrated circuits, microcontrollers, field programmable gate arrays, etc.) that perform operations described in connection with the control unit  402 . The one or more processors  406  may operate based on programmed instructions. The one or more processors  406 , which may include a single processor or multiple processors, are referred to herein in the plural form “processors” without limiting the scope to requiring multiple processors  406 . The processors  406  can generate the build plan  404 . The control unit  402  also includes a tangible and non-transitory computer-readable storage medium (e.g., memory)  408 . The memory  408  may store the programmed instructions (i.e., software) that dictate the operations of the processors  406 . For example, the memory  408  can store the build plan  404  that is generated by the processors  406  and can store additional build plans. The memory  408  may also store a part design file  410  of the build part  102 . The part design file  410  may be a computer-aided design (CAD) file or another data file that describes the physical characteristics of the build part  102 , such as the shape, size, and/or composition of the build part  102 . The build plan  404  may be generated based on the design file  410 . 
     In one or more embodiments, the control unit  402  receives a selection of a design for the build part. For example, the control unit  402  may be communicatively connected to an input device  412  from through which the design is selected. The input device  412  may include a touchpad, a touchscreen, a keyboard, a mouse, physical buttons, a joystick, or the like. The input device  412  enables an operator to provide commands to the additive manufacturing system  100 . In a non-limiting example, the operator can use the input device  412  to select the design file  410 , to initiate the build process, and/or to select or adjust additional settings and parameters. The processors  406  may be operably connected to the input device  412  via a wired or wireless communication pathway. 
     The processors  406  may generate the build plan  404  based on the selected design. For example, the processors  406  may access the design file  410  from the memory  408  and analyze the design file  410 . The analysis may include determining whether the design includes voids, projecting features, and/or the like, that would typically require the formation of support material during the build process. For example, for a candidate or proposed position of the build part on the plate  132 , the processors  406  may calculate the relative angles between downskin surfaces of projecting features and a vertical axis that is parallel to the force of gravity. The processors  406  can compare the relative angles to a designated threshold (such as, for example, 45 degrees), and determine that support material would be required if a relative angle exceeds the designated threshold. 
     In an embodiment, the processors  406  perform automated slicing of the build part design based, at least in part, on the analysis of whether support material would be required to support various features and/or voids of the build part. The automated slicing operation can include partitioning the design into different segments or sections that are to be constructed at different orientations of the build part. For example, voids and features of the design that are determined to require support material are partitioned from other sections of the design that would not require support material when oriented in the candidate or proposed orientation. Referring to  FIG. 6 , during the planning stage, the processors  406  may determine that the second section  322  of the build part  102  would require support material if constructed in the first orientation, so the processors  406  partition the second section  322  from the first section  314  to avoid constructing the second section  322  in the first orientation. The automated slicing can also include automated determination of other orientations of the build part to enable formation of all sections of the build part according to the selected design without requiring support material and while satisfying various other goals or standards (e.g., relating to efficiency and/or quality). For example, the processors  406  can select the second orientation that is shown in  FIGS. 5 and 6  to enable the formation of the second section  322  without using support material. 
     After the automated slicing to partition the design of the build part and determine the orientations at which to form each partitioned section of the build part, the processors  406  may perform automated path planning based on the partitioned sections and the orientations. The automated path planning refers to determining the actual operations of the robotic arms  104 ,  106  to physically construct the build part  102  by constructing different sections at different associated orientations. The automated path planning includes the generation of the movement path for the first robotic arm  104  and the deposition path for the second robotic arm  106 . The paths may include designated coordinates to which the robotic arms should move to at corresponding times. The movement path and the deposition path may incorporate the changes of orientation. For example, the movement path instructs the first robotic arm  104  to reorient the plate  132  and the build part  102  from the first orientation to the second orientation at a time that the second robotic arm  106 , moving along the deposition path, completes the formation of the first section  314  of the build part  102  shown in  FIG. 4 . The movement and depositions paths, as well as parameters, conditions, settings, and/or other operations can be incorporated into the build plan  404 . 
     For the build process, the control unit  402  may communicate the build plan  404  to the first and second robotic arms  104 ,  106  for the robotic arms  104 ,  106  to implement the build plan  404  in coordinated fashion. Alternatively, the control unit  402  may communicate command signals to the robotic arms  104 ,  106 , such that the command signals are based on the build plan  404 . The first and second robotic arms  104 ,  106  may move and operate to implement the command signals and thereby implement the build plan  404 . Optionally, the control unit  402  may be configured to update or modify the build plan  404  during the build process. For example, the control unit  402  may be configured to re-plan the deposition path of the second robotic arm  106  in response to detecting a change in the orientation of the build part. 
       FIG. 9  illustrates the additive manufacturing system  100  according to an embodiment in which the first and second robotic arms  104 ,  106  concurrently move during the build process. For example, the first robotic arm  104  moves the build part  102  concurrent with movement of the print head  110  by the second robotic arm  106 . The first robotic arm  104  can move along the movement path of the build plan while the second robotic arm  106  moves along the deposition path. The print head  110  can continuously deposit material onto the build part  102  as the build part  102  is moved by the first robotic arm  104 . 
     In the illustrated embodiment, the build part  102  has an elongated, curved outer surface  420  extending from a first end  422  to an opposite, second end  424 .  FIG. 9  shows a first arrangement  426  of the components (e.g., the robotic arms  104 ,  106 , build part  102 , and print head  110 ) at a first time during the build process and a second arrangement  428  of the components at a second time during the build process. The illustrated embodiment shows that translating both the build part  102  and the print head  110  enables extending the print envelope (e.g., print coverage) to a size or length greater than the movement capability range of the second robotic arm  106  holding the print head  110 . For example, in the first arrangement  426 , the second robotic arm  106  positions the print head  110  to deposit material on the build part  102  proximate to the first end  422 . During the intervening time between the first arrangement  426  and the second arrangement  428 , the first robotic arm  104  translates the build part  102  relative to the print head  110  and the second robotic arm  106  concurrently translates the print head  110  relative to the build part  102 . For example, the first robotic arm  104  pivots an angle  430  in a first direction  432  which causes the build part  102  to move in an arc. The second robotic arm  106  linearly moves the print head  110  in a second direction  434  for a distance  436  from the first arrangement  426  to the second arrangement  428 . The curved movement of the build part  102  and linear movement of the print head  110  shown in  FIG. 9  are merely for example, such that the build part  102  can be moved linearly and/or the print head  110  can be moved along a curved path in other embodiments. 
     In the second arrangement  428 , the second robotic arm  106  positions the print head  110  to deposit material on the build part  102  proximate to the second end  424 . In the illustrated embodiment, during the time from the first arrangement  426  to the second arrangement  428 , the print head  110  continuously deposits material along the length of the outer surface  420  of the build part  102 . The length of the outer surface  420  between the two locations of the print head  110  shown in  FIG. 9  is longer than the distance  436  moved by the print head  110  and also longer than the distance moved by the build part  102 . Moving the build part  102  and the print head  110  in generally opposite directions during the build process can extend the print envelope without requiring a larger structural footprint. 
       FIG. 10  illustrates the additive manufacturing system  100  forming non-planar layers  440  of the build part  102  according to an embodiment. The build part  102  may have a non-planar, contoured surface. In a non-limiting example, the build part  102  may be an airfoil. Curved surfaces typically include small edges or steps when formed by parallel-stacked planar layers according to conventional additive manufacturing techniques. The edges or steps along the curved surfaces may have to be subsequently grinded to provide an acceptable smoothness of the surface. The quality of the curved surfaces can be improved during the build process by utilizing the additive manufacturing system  100  to deposit the material in non-planar layers, at least at the curved surfaces. Conventional additive manufacturing systems may not be able to build curved surfaces via non-planar layers due to orientation limitations of the hardware, collision issues with the build part due to relatively short extension of the print head nozzle, and/or the like. For example, most additive manufacturing systems only have three axes of motion and are limited to contours that are shallower in depth than the extension length of the nozzle. The robotic arms  104 ,  106  of the additive manufacturing system  100  can have six degrees of freedom, allowing for three-dimensional translation of a given component and rotation of the component about each of three mutually-perpendicular axes. Furthermore, the first and second robotic arms  104 ,  106  can reorient the build part  102  and the print head  110 , respectively, to enable the print head  110  to access areas of the build part  102 , without collision, that would not be achievable using conventional additive manufacturing systems. 
       FIG. 10  shows the build process at a first time  442  and a subsequent, second time  444 . The print head  110  is depositing material to form different locations of a common non-planar layer  440  at the first and second times  442 ,  444 . In the illustrated embodiment, the build part  102  is formed of both planar layers  446  and non-planar layers  440 . For example, multiple planar layers  446  may be formed first on the plate  132 . Optionally, the planar layers  446  may be formed while the first robotic arm  104  holds the plate  132  in a fixed orientation relative to the print head  110  and second robotic arm  106 . The non-planar layers  440  are formed on top of the planar layers  446 . In an embodiment, the first robotic arm  104  reorients the build part  102  relative to the print head  110  and second robotic arm  106  during the formation of the non-planar layers  440 . For example, the build part  102  may be reoriented as the print head  110  deposits material onto the build part  102  to provide a desired application angle, such as to maintain the print head  110  oriented normal to the tangent of the surface on which the material is being deposited. 
     At the first time  442  in  FIG. 10 , the first robotic arm  104  holds the plate  132  with a right end  450  of the plate  132  disposed higher than an opposite, left end  452  of the plate  132 . The orientation at the first time  442  allows the print head  110  to deposit material that is approximately (e.g., with 1, 2, 3, or 5 degrees of) normal to a first area  454  of the build part  102  on which the new material is deposited. At the second time  444 , the first robotic arm  104  holds the plate  132  with the right end  450  of the plate  132  disposed lower than the left end  452 . Due to the curve of the build part  102  and the progression of the build process, the print head  110  at the second time  444  deposits material approximately normal to a second area  456  of the build part  102  on which the new material is deposited. In an embodiment, the first and second robotic arms  104 ,  106  operate in tandem such that the second robotic arm  106  moves and/or controls the print head  110  to continuously deposit material while the first robotic arm  104  concurrently reorients the build part  102 . 
       FIG. 11  illustrates the additive manufacturing system  100  according to another embodiment. The additive manufacturing system  100  in  FIG. 11  utilizes three robotic arms  104 ,  106 ,  502  to construct a designated build part  504 . The second robotic arm  106  is coupled to the print head  110 , which is a first print head. A third robotic arm  502  is mechanically coupled to a second print head  506 . Like the first and second robotic arms  104 ,  106 , the third robotic arm  502  is able to manipulate and move the print head  506  in multiple degrees of freedom, such as six degrees of freedom, relative to other components (e.g., the robotic arms  104 ,  106 ). Both print heads  110 ,  506  are controlled to deposit the source material layer by layer on the build part  504  to construct the build part  504 . Optionally, the build plan  404  shown in  FIG. 8  can be generated to include a deposition path that is specific to the third robotic arm  502 . The first and second print heads  110 ,  506  are configured to concurrently deposit the source material on the build part  504 . The print heads  110 ,  506  may concurrently deposit source material along different areas of the build part  504  without interfering with each other. Utilizing multiple print heads  110 ,  506  to form a common build part  504  can drastically reduce the build time. 
       FIG. 12  is a flow chart of a method  600  for additive manufacturing using robotic arms to modify an orientation of the build part during the build process according to an embodiment. In an example, the method  600  is performed by the additive manufacturing system  100  shown in  FIG. 1 , including the control unit  402  shown in  FIG. 8 . Optionally, some operator input can be provided in one or more of the steps. Optionally, the method  600  may include more steps than shown in  FIG. 12 , fewer steps than shown in  FIG. 12 , different steps that are not shown in  FIG. 12 , and/or a different arrangement or order of the steps than shown in  FIG. 12 . 
     The method  600  begins at  602 , at which a first robotic arm is controlled to hold a build part in a first orientation suspended above a floor or ground. The first robotic arm may directly couple to the build part or may directly couple to a plate on which the build part is constructed and/or affixed. At  604 , a source material is deposited layer by layer on the build part in the first orientation via a nozzle of a print head to construct a section (e.g., a first section) of the build part. The initial layer of the build part may be deposited directly on a surface of the plate held by the first robotic arm. The print head may be coupled to a second robotic arm that moves the print head relative to the build part, the first robotic arm, and the floor or ground to deposit the source material onto the build part. The movement of the second robotic arm can modify an angle of the print head relative to the build part. Optionally, a second print head may concurrently deposit the source material onto the build part with the first print head. The second print head may be coupled to a third robotic arm that is controlled to move relative to the first and second robotic arms without physically contacting or otherwise interfering with the first and second robotic arms. Utilizing multiple print heads and multiple robots to construct the build part can significantly reduce the build time. 
     At  606 , the first robotic arm is controlled to move the build part relative to the print head and the floor during the build process to modify an angle of a surface layer of the build part relative to the print head and the floor. In an example, the first robotic arm is controlled to reorient the build part to a second orientation relative to the floor or ground after the section of the build part is constructed. The first robotic arm may tilt the build part about at least one of three mutually-perpendicular axes from the first orientation to the second orientation. 
     At  608 , the source material is deposited layer by layer on the build part in the second orientation to construct another section (e.g., a second section) of the build part. The set of layers of the build part that are deposited when the build part is in the second orientation may be transverse to the set of layers deposited when the build part is in the first orientation. The additional layers are deposited by at least the first print head. The second print head optionally can be controlled to operate in tandem with the first print head. 
     Optionally, after depositing the layers of source material on the build part in the second orientation, the first robotic arm may be controlled to reorient the build part again to a third orientation or back to the first orientation. After the repositioning, the second robotic arm may be controlled to once again use the print head to deposit additional layers of source material on the build part, and this process may repeat until the construction of the build part is completed. 
     Optionally, the method  600  may include, at  610 , performing one or more secondary finishing tasks on the build part after the build part is constructed. One or more finishing tasks may be performed after the build part is fully constructed. Optionally, at least some finishing tasks may be performed prior to completing the build process before the build part is fully constructed. The method may include mechanically coupling a finishing instrument to the second robotic arm, and then controlling the second robotic arm to move the finishing instrument relative to the build part for the finishing instrument to engage the build part. The finishing instrument can represent or include a grinder, a polishing wheel, a buffing wheel, a sander, a cleaning device, or the like. In a non-limiting example, the second robotic arm may be configured to replace the print head with the finishing instrument after the build process is complete. In another embodiment, the finishing instrument is coupled to, and controlled by, another robotic arm (e.g., a third or fourth robotic arm) instead of the second robotic arm that includes the print head. The finishing tasks can represent or include removing build supports from the build part, surface finishing (e.g., grinding, polishing, sanding, cleaning, and/or the like), adding and/or cleaning holes in the build part, removing the base plate, grinding the base plate, and/or the like. 
     Optionally, the method  600  may also include generating a build plan for additively manufacturing the build part. The build plan can be generated by one or more processors of a control unit (or controller). The build plan can be based on an analysis of a design of the build part and a proposed or candidate position of the build part that represents the location and orientation relative to the plate at which the build part is to be constructed. As a result of the analysis, the build plan may select the first and second orientations and all additional orientations of the build part during the build process. The build plan can designate a movement path for the first robotic arm to move the build part during the build process to achieve the various selected orientations at designated times. The build plan can also designate a deposition path for the second robotic arm to move the print head to deposit the source material during the build process. The deposition plan can account for the reorientation of the build part at the designated times. For example, at each of the designated times, the second robotic arm may reorient (e.g., translate and/or rotate) the print head relative to the first robotic arm to get into position for constructing the second section of the build part. 
     The build plan can be generated to achieve certain goals, such as to avoid or at least reduce the amount of support material formed during the build process that will need to be extracted from the build part. For example, the build part design may include a projecting feature or appendage that projects from a main body of the build part. The second orientation may be selected to prevent a downskin surface of the appendage from being oriented greater than a threshold angle relative to vertical (e.g., a gravitational force direction). The threshold angle can be 40 degrees, 45 degrees, 50 degrees, or the like. The threshold angle is associated with requiring support material underneath the downskin surface. By reorienting the build part such that the downskin surface of the appendage is no greater than the threshold angle, the appendage can be constructed while the build part is in the second orientation without forming support material underneath the downskin surface. The appendage can represent the additional section of the build part that is constructed in step  608 . In one or more embodiments, the build plan selects multiple orientations for the build part during the build process to avoid the formation of support material without compromising the quality of the build part. By eliminating or reducing the amount of support material formed, the manufacturing efficiency can be increased and costs reduced by increasing the speed of the build process, reducing material waste, and alleviating post-build finishing tasks. The finishing tasks that may be alleviated include extracting the support material from the build part and smoothing the surfaces of the build part that were formerly attached to the support material, via grinding, sanding, buffing, polishing, or the like. 
     While various spatial and directional terms, such as top, bottom, lower, mid, lateral, horizontal, vertical, front and the like are used to describe embodiments of the present disclosure, it is understood that such terms are merely used with respect to the orientations shown in the drawings. The orientations can be inverted, rotated, or otherwise changed, such that an upper portion is a lower portion, and vice versa, horizontal becomes vertical, and the like. 
     The diagrams of embodiments herein illustrate one or more control or processing units, such as the control unit  402  shown in  FIG. 8 . It is to be understood that the control or processing units represent circuits, circuitry, or portions thereof that are implemented as hardware with associated instructions (e.g., software stored on a tangible and non-transitory computer readable storage medium, such as a computer hard drive, ROM, RAM, or the like) that perform the operations described herein. The hardware can include state machine circuitry hardwired to perform the functions described herein. The hardware can include electronic circuits that include and/or are connected to one or more logic-based devices, such as microprocessors, processors, controllers, or the like. Optionally, the control unit  402 , or the one or more processors  406  thereof, represents processing circuitry such as one or more of a field programmable gate array (FPGA), application specific integrated circuit (ASIC), microprocessor(s), a quantum computing device, and/or the like. The circuits in various embodiments are configured to execute one or more algorithms to perform functions described herein. The one or more algorithms include aspects of embodiments disclosed herein, whether or not expressly identified in a flowchart or a method. 
     As used herein, the term “control unit,” or the like includes any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC), application specific integrated circuits (ASICs), logic circuits, and any other circuit or processor including hardware, software, or a combination thereof capable of executing the functions described herein. Such are exemplary only and are thus not intended to limit in any way the definition and/or meaning of such terms. The control unit  402  shown in  FIG. 8  is configured to execute a set of instructions that are stored in one or more storage elements (such as one or more memories), in order to process data. The set of instructions includes various commands that instruct the control unit  402  (e.g., the processor(s)  406  thereof) as a processing machine to perform specific operations such as the methods and processes of the various embodiments of the subject matter described herein. In an embodiment, the set of instructions is in the form of a software program. The processing of input data by the processing machine is in response to user commands, in response to results of previous processing, or in response to a request made by another processing machine. As used herein, the term “software” includes any computer program stored in memory for execution by a computer, including but not limited to RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. 
     As used herein, a structure, limitation, or element that is “configured to” perform a task or operation is particularly structurally formed, constructed, or adapted in a manner corresponding to the task or operation. For purposes of clarity and the avoidance of doubt, an object that is merely capable of being modified to perform the task or operation is not “configured to” perform the task or operation as used herein. 
     It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the various embodiments of the disclosure without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments of the disclosure, the embodiments are by no means limiting and are example embodiments. Many other embodiments will be apparent to those of ordinary skill in the art upon reviewing the above description. The scope of the various embodiments of the disclosure should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms “including” and “in which” are used as the plain-English equivalents of the respective terms “comprising” and “wherein.” Moreover, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112(f), unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. 
     This written description uses examples to disclose the various embodiments of the disclosure, including the best mode, and also to enable any person skilled in the art to practice the various embodiments of the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the various embodiments of the disclosure is defined by the claims, and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if the examples have structural elements that do not differ from the literal language of the claims, or if the examples include equivalent structural elements with insubstantial differences from the literal language of the claims.