Patent Publication Number: US-2022228646-A1

Title: Swing Gear Assembly and Method for Manufacturing the Same

Description:
TECHNICAL FIELD 
     This patent disclosure relates generally to a swing gear assembly to provide a rotatable interface between a rotatable upper structure and a lower base of a large scale or heavy machine, and more particular the disclosure relates to a method of manufacturing gear segments from which the swing gear assembly can be assembled. 
     BACKGROUND 
     Large scale and heavy machines like dragline excavators, rope shovels, and rotary cargo container cranes are used in operations like mining, material excavation, and cargo transportation. These machines may include an extended truss assembly from which a work implement can be suspended. For example, a dragline excavator can include a dragline bucket suspended several meters forward of the machine. The dragline bucket can be lowered to the excavation surface and drawn toward the machine via wire ropes or chains so that excavation material is deposited into the dragline bucket. The machines can perform a swing-and-dump maneuver that swings the truss assembly with respect to a vertical axis of the machine to deposit the excavated material or, in the case of a rotary cargo container crane, the cargo container. 
     To enable the swing-and-dump maneuver, the machine can have a swing assembly including in particular a swing gear assembly that functions as the interface between and joins an upper structure of the machine from which the truss assembly is suspended to a lower base on which the machine is supported on the work surface. The swing gear assembly may include an internal gear ring or an external gear ring that meshes with and can be driven by a round pinon to rotate the upper structure. In the example of these large machines like dragline excavators where the truss assembly may extend a hundred meters or more and the bucket may hold several tons of material, it will be appreciated that the swing gear assembly can be several meters in diameter and can be made from high strength materials like steel or iron. Moreover, because of their size, many types of these heavy machines are configured to be built onsite from components that must be transported to the needed location. Accordingly, to facilitate manufacture and transportation of the swing gear assembly, it may be configured as a segmented gear assembly in which the intermeshing gears are assembled from a plurality of individual gear segments in the form of partial angular arcs that can be combined to provide the entire circular circumference of the swing gear assembly. 
     The present disclosure is directed to gear segments and methods of producing gear segments as described above for forming a swing gear assembly for a large scale or heavy duty machine like a dragline excavator. 
     SUMMARY 
     The disclosure describes, in one aspect, a method of producing a gear set for a large scale or heavy machine. The method involves forging a metal block from raw material that has the shape of a rectangular prism including a first lengthwise face and a second lengthwise face and an upper face and a lower face. The metal block is bisected into a first intermediate blank and a second intermediate blank by a diagonal cut disposed between the upper face and the lower face. A plurality of arranged teeth is milled into the first lengthwise face of the first intermediate blank to produce one of an internal toothed segment and an external toothed segment. Similarly, a plurality of arranged teeth is milled into the second lengthwise face of the second intermediate blank to produce one of an internal toothed segment and an external toothed segment. 
     In another aspect, the disclosure describes a gear set including a gear ring with a plurality of teeth. The gear ring may include a first toothed segment having a plurality of gear teeth disposed into a first lengthwise face of a first intermediate blank from which one of the plurality of the toothed segments is machined. The gear ring may also include a second toothed segment having a plurality of gear teeth disposed into a second lengthwise face of a second intermediate blank from which the one of the plurality of the toothed segments is machined. The first intermediate blank and the second intermediate blank are commonly bisected from a metal block. 
     In another aspect, the disclosure describes a gear ring assembled from a plurality of gear segments. Each gear segment includes an upper face and a lower face parallel to and spaced apart from the upper face. Each gear segment further includes a lengthwise face extending between the upper face and the lower face with a plurality of teeth disposed therein. Each gear segment further includes a lengthwise edge parallel to and spaced apart from the lengthwise face and extending partially between the upper face and the lower face. The plurality of teeth is selected from the group comprising internal teeth concavely disposed in the lengthwise face and a plurality of external teeth convexly disposed in the lengthwise face. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevational view of a dragline excavator for excavating earthen materials that includes a rotatable upper structure supported on a lower base joined by a swing gear assembly. 
         FIG. 2  is a perspective view of the swing gear assembly made from a plurality of external toothed segments or internal toothed segments. 
         FIG. 3  is a perspective view of a forged metal block in the shape of a rectangular prism from which the plurality of external toothed segments and internal toothed segments can be manufactured. 
         FIG. 4  is a side elevational view of the metal block illustrating various cuts that may be machined into the metal block to produce a first intermediate blank and a second intermediate blank. 
         FIG. 5  is a perspective view of an internal toothed segment having a plurality of concavely arranged teeth manufactured from the first and/or second intermediate blank. 
         FIG. 6  is a perspective view of an external toothed gear segment having a plurality of convexly arranged teeth manufactured from the first and/or second intermediate blank. 
         FIG. 7  is a schematic representation of the manufacturing steps for the production of external and internal toothed segments from a metal block in accordance with the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure relates to a swing gear assembly for rotatably joining an upper structure to a lower base on large scale or heavy machines used for earthwork operations, large scale construction operations, or cargo handling. Referring to  FIG. 1 , wherein like reference numbers refer to like elements, there is illustrated an example of a heavy machine in the embodiment of a dragline excavator  100  used in earthwork operations such as material excavation and surface mining. Aspects of the disclosure, however, are applicable to other large scale or heavy machines such as rope shovels, cranes, and other types of excavators. The illustrated embodiment of the dragline excavator  100  includes an upper structure  102  that is supported on and rotatable with respect to a lower base  104 . The upper structure  102 , which may also be referred to as a house or cabin, internally accommodates the motors or engines and the hoist and drag mechanisms for powering the operations of the dragline excavator  100  and which may include an operator&#39;s cab  106  located at front of the upper structure from where an operator can observe and control operation of the dragline excavator. The lower base  104  supports the upper structure  102  and contacts the work surface  108  or excavation surface. 
     Joined to and extending from the upper structure  102  can be a frame or truss assembly  110  which includes the truss components and rigging that support and maneuver a dragline bucket  112 . The dragline bucket  112  may be suspended from a boom  114  that extends upward and outward from the front of the upper structure  102  and can be maneuvered by various ropes, cables, or chains. For example, the dragline bucket  112  can be raised and lowered with respect to the work surface  108  by a hoist line  116  that extends along the boom  114  through a sheave  118  at the distal end of the boom and connects to a hoist coupler  120  on the dragline bucket  112 . The dragline bucket  112  can also be drawn horizontally over the excavation surface by a drag line  122 . In operation, for example, to remove overburden that may be located over the material of interest such as coal or other minerals, the dragline bucket  112  is lowered and penetrates into the work surface  108  via the hoist line  116  and drawn toward the upper structure  102  by the drag line  122  thereby gathering material in the bucket. The hoist line  116  and drag line  122  can be retracted and payed out by appropriate drums located in the upper structure  102  and which the lines are wound around. To support the boom  114  during movement of the dragline bucket  112 , the truss assembly  110  can also include a vertical brace  124  that extends upwardly from the upper structure  102 . 
     By way of example, the length of the boom  114  can be a hundred meters or more and the capacity of the bucket  112  can be a hundred tons or more of material. The loads on the hoist line  116  and drag line  122  are significant and can be on the order of hundreds of thousands of foot-pounds of tensile stress. The hoist and drag lines  116 ,  122  can be made from high strength steels wires twisted into a helix and can have diameters on the order of twelve or more centimeters. Accordingly, to counterbalance hoisting and maneuvering of the dragline bucket  112  when loaded, the upper structure  102  that accommodates the hoist and drag machinery can weigh several hundred tons. Correspondingly, the length of the upper structure  102  can be thirty meters or greater and can have a correspondingly large width. 
     To traverse and maneuver the dragline excavator  100  over the work surface  108 , the lower base  104  can include appropriate propulsion devices  126  such as continuous tracks formed from a band of linked track plates that can translate with respect to the lower base  104 , thereby moving the upper structure  102  over the work surface  108 . In other embodiments, the propulsion devices  126  can be a walker or crawler unit wherein support feet or shoes can be eccentrically lifted and lowered with respect to the work surface  108  and thereby move the upper structure  102  forward or rearward over the work surface  108 . Although the embodiment of a dragline excavator  100  described herein is a type of mobile machine, aspects of the disclosure may also relate to large scale or heavy stationary or fixed machines, such as cargo cranes and the like. 
     One step in an excavation operation is a swing and dump operation. In this step, the upper structure  102  is pivoted with respect to the work surface  108  to move the dragline bucket  112  from the location where it has excavated material to a location where the dragline excavator  100  deposits the material for removal from the excavation site. For example, the material may be deposited on an in-site conveyor or a haul truck. To enable the dragline excavator  100  to conduct the swing and dump operation, the upper structure  102  is located on a swing platform  128  that is rotatably joined to the lower base  104  by a swing assembly  130  so that the upper structure  102  is rotatable relative to the lower base  104  about a vertical axis line  132 . The swing assembly  130  can include a roller bearing  134  that carries the load of the upper structure  102  while enabling relative rotational motion between the upper structure  102  and the lower base  104  with respect to the axis line  132 . Due to the size and weight of the upper structure  102 , it will be appreciated that the swing assembly  130  supports a significant load, possibly on the order of several hundred tons. 
     To drive rotation of the upper structure  102  with respect to the lower base  104 , the swing assembly  130  can be made from components of a gear set  136  on which the swing platform  128  is mounted and that can be operatively associated with a motor accommodated in the upper structure  102 . Referring to  FIG. 2 , the gear set  136  can include an internal gear ring  140  and/or an external gear ring  142 . In accordance with the disclosure, the internal and external gear rings  140 ,  142  can be produced together by a common manufacturing operation and one or the other of the internal or external gear rings can be used in the swing assembly  130  on the dragline excavator  100  or similar machine. For reference, the internal gear ring  140  and the external gear ring are concentrically aligned around the axis line  132  that corresponds to the axis of rotation of the swing assembly  130  when installed on the dragline excavator. When assembled, either the internal gear ring  140  or the external gear ring  142  is fixed to the lower base  104  and can mesh with one or more pinions extending from the upper structure  102  and driven by an electric motor or other power source. The upper structure  102  therefore rotates around the axis line  132  so that the upper structure  102  swings with respect to the lower base  104 . 
     The internal gear ring  140  can be shaped as an annular ring and includes a plurality of radially inward directed internal teeth  144  and the external gear ring  142  can also be shaped as an annular ring and includes a plurality of radially outward directed external teeth  146 . The internal gear ring  140  and the external gear ring  142  can be spur gears wherein the internal teeth  144  and the external teeth  146  extend over the height of the ring-shaped internal gear ring  140  and external gear ring  142  respectively so as to be parallel with the axis line  132 . Further, the internal teeth  144  are circumferentially disposed about and spaced apart along the inner circular periphery of the internal gear ring  140  and the external teeth are circumferential disposed about and spaced apart along the outer circular periphery of the external gear ring  142 . In the illustrated embodiment, the internal teeth  144  and the external teeth  146  can have an involute profile to facilitate intermeshing and sliding contact with respect to the gear teeth on a round pinion that drives rotation of the swing gear assembly  130 . In other possible embodiments, however, the gear teeth may have other configurations such as helical. 
     Because of the size of the upper structure  102  including the truss assembly  110 , it should be appreciated that the gear set  136  should have a correspondingly large size. For example, the pitch diameter  148  of the internal and external gear rings  140 ,  142 , which is indicated schematically by the arrow and which may represent the diametrical dimension extending between the approximate midpoints within the depth of engagement between diametrically opposite inner and external teeth  144 ,  146 , can be on the order of twelve meters or more. 
     To facilitate manufacturing of the internal and external gear rings  140 ,  142 , and to facilitate transportation in the case where the dragline excavator is assembled onsite, the swing assembly  130  can be a segmented gear assembly in which the internal gear ring  140  and the external gear ring  142  are assembled from a plurality of arcuate gear segments including an internal toothed segment  150  and an external toothed segment  152 . The arcuate-shaped internal toothed segments  150  can correspond to partial arcs that, when assembled together, complete the circumference of the internal gear ring  140 . Likewise, the arcuate-shaped external toothed segments  152  can correspond to partial arcs that, when assembled together, complete the circumference of the external gear ring  142 . The internal toothed segment  150  and the external toothed segment  152  can have various angular extensions, for example, 90° so that the internal gear ring  140  and the external gear ring  142  are made up of four identical internal toothed segments  150  and external toothed segments  152  respectively. However, other angular extensions are contemplated such that the internal gear ring  140  and the external gear ring  142  are made up of any suitable number of internal or external toothed segments  150 ,  152 . 
     To manufacture the internal toothed segment  150  and/or the external toothed segment  152 , multiple segments may be produced from the same metal block via specific cuts and machining steps. For example, referring to  FIG. 3 , there is illustrated an exemplary metal block  160  that can be shaped as a rectangular cuboid or rectangular prism from which the segments can be formed. As a rectangular prism, the metal block  160  has a three-dimensional geometry and can include six quadrilateral faces with adjacent faces intersecting at right angles and arranged perpendicular to each other. The quadrilateral faces can be designated as a first lengthwise face  162  and a parallel second lengthwise face  164  that can correspond to the forward and rearward faces of the metal block  160 , a first end face  166  and a parallel second end face  168  that correspond to opposite lengthwise ends of the metal block  160  and define the width of the metal block between the first and second lengthwise faces  162 ,  164 , and an upper face  170  and a parallel lower face  172  that define the vertical height of the metal block  160 . To produce internal and external toothed segments suitably sized for a dragline excavator, the metal block  160  may have a length on the order of two meters or more, a width between the first and second lengthwise faces  162 ,  164  of one meter or more, and a height between the upper face  170  and the lower face  172  of thirty centimeters or more. 
     To provide sufficient strength characteristics to the internal and external toothed segments, the metal block  160  can be made from a suitable metal such as steel or iron. In an embodiment, the metal block  160  can be produced by a metalworking process and in particular formed from a forging process in which an initial quantity of metal produced as a casting or extruded ingot is compressed into the shape of the rectangular prism illustrated in  FIG. 3 . During the forging process, the metal is shaped by applied compressive forces, for example, by repeated strikes from a forging hammer or press and dies. The forging process plastically deforms the metal into the desired shape and can impart desirable strength characteristics and microstructural properties to the metal block  160 . To improve formability where the metal block  160  is made from steel or iron, the forging process may be hot forging process where the initial casting or ingot is heated to a highly elevated temperature. After the metal block  160  has been forged, it may be subjected to additional heat treating processes to impart desirable characteristics such as to improve machinability and strength. In addition to the forging process, in other embodiments of the disclosure, other metal forming processes can be used to form the metal block  160  including, for example, casting and extrusion. 
     Once the metal block  160  has been forged or otherwise shaped into the rectangular prism, the metal block is processed through additional machining steps to produce a first intermediate blank  174  and a second intermediate blank  176 . Referring to  FIGS. 3 and 4 , the first intermediate blank  174  and the second intermediate blank  176  can be identical in shape and size and can be formed by cutting the metal block  160  lengthwise between the upper face  170  and the lower face  172 . Because the cutting process results in dividing the metal block  160  into first and second intermediate blanks  174 ,  176  of equal and congruent shape, size, and mass, it may be referred to as “bisecting” the metal block. 
     The metal block  160  can be cut  178  on a diagonal slant with respect to the first and second end faces  166 ,  168  to bisect the metal block into the first and second intermediate blanks  174 ,  176 . However, rather than making the diagonal cut  178  between the intersection of the first lengthwise face  162  and the upper face  170  and the intersection of the second lengthwise face  164  and the lower face  172 , the diagonal cut  178  can be offset rearward of the first lengthwise face  162  and offset forward of the second lengthwise face  164 . Accordingly, the diagonal cut  178  passes though the upper face  170  and the lower face  172 . 
     Because of the substantial size of the metal block  160 , an appropriate cutting process can be used such as, for example, a band saw or circular blade saw supported on a frame or table that may include rollers or slides to maneuver the metal block with respect to the blade. Other suitable cutting methods include but are not limited to electric discharge machining, laser cutting, and plasma cutting. 
     In an embodiment, to guide and facilitate the cutting process used to form the diagonal cut  178 , one or more guide grooves can be formed in the appropriate faces of the metal block  160 . For example, these may include a pair of lengthwise grooves  180  extending across the upper and lower faces  170 ,  172 , respectively, between the first and second end faces  166 ,  168  and parallel to the first and second lengthwise faces  162 ,  164 . In addition, a pair of diagonal grooves  182  can be formed in the first and second end faces  166 ,  168 , respectively, and that extends between the upper and lower faces  170 ,  172 . The lengthwise grooves  180  and diagonal grooves  182  delineate and can guide the diagonal cut  178  to be made through the metal block  160 . 
     As a result of the diagonal cut  178  to bisect the metal block  160  into the first and second intermediate blanks  174 ,  176 , the intermediate blanks respectively include a first slanted face  184  and a second slanted face  186 . The first and second slanted faces  184 ,  186  made by the diagonal cut  178  extend at an inclined angle between the upper and lower faces  170 ,  172 . Because of the angled orientation of the first and second slanted faces  184 ,  186 , a substantial portion of the upper face  170  remains as part of the first intermediate blank  174  and a substantial portion of the lower face  172  remains part of the second intermediate blank  176 . The resulting first and second intermediate blanks  174 ,  176  can be shaped as trapezoidal cuboids or prisms in that the remaining portions of the upper face  170  and the lower face  172  are parallel and the remaining portions of the first and second end faces  166 ,  168  are parallel but the first and second lengthwise faces  162 ,  164  are nonparallel with respect to the respective first and second slanted faces  184 ,  186 . 
     To reduce weight of the finished internal and external toothed segments, excess material can be removed from the first and second intermediate blanks  174 ,  176 . For example, referring to  FIG. 4 , triangular cuts  188  can be made into the metal block  160  at locations parallel to where the diagonal cuts  178  intersects the upper and lower faces  170 ,  172 . The triangular cuts  188  can extend the length of the metal block  160  with respect to the first and second lengthwise faces  162 ,  164 . The triangular cuts  188  can result in the removal of triangular-shaped wedges  190  of metal from the metal block  160  proximate both the upper face  170  and the lower face  172 . The triangular-shaped wedges  190  may become waste or scape metal for recycling. 
     Because of the triangular cuts  188  and removal of the triangular-shaped wedges  190 , the cross-section of the first and second intermediate blanks  174 ,  176  can be that of a five-sided polygon in that each includes a lengthwise edge  192  formed by the triangular cut  188 . The lengthwise edges  192  can be parallel to the first and second lengthwise faces  162 ,  164  and can extend the length of the metal block  160  between the first and second end faces  166 ,  168 . Any suitable cutting technique can be used to form the triangular cut  188  including, for example, torch-cutting using a fuel and oxygen. 
     Additional machining and metalworking processes can be performed on the first and second intermediate blanks  174 ,  176  to form the finished parts corresponding to the internal and external toothed segments  150 ,  152  illustrated in  FIGS. 5 and 6 . By forming the finished internal and external toothed segments  150 ,  152  from the intermediate blanks  174 ,  176 , the finished segments are unitary, integral parts of sufficient strength and rigidity for the intended application. 
     For example, the plurality of internal teeth  144  of the internal toothed segment  150  may be machined into the first and/or second lengthwise faces  162 ,  164  of the first and/or second intermediate blanks  174 ,  176 . Likewise, the external teeth  146  of the external toothed segment  142  can be machined into the first and/or second lengthwise faces  162 ,  164  of the first and/or second intermediate blanks  174 ,  176 . Because the internal toothed segment  150  is only a partial arc of the circumference of the finished outer gear ring, the internal teeth  144  are arranged as a plurality of concavely arranged teeth  194  that curve inward into the internal toothed segment  150 . Similarly, the external teeth  146  are arranged as a plurality of convexly arranged teeth  196  that curve outwardly with respect to the external toothed segment  152 . 
     The internal teeth  144  associated with the plurality of concavely arranged teeth  194  and the external teeth  146  associated with the plurality of convexly arranged teeth  196  can be machine into the first and second lengthwise faces  162 ,  164  of the respective first and second intermediate blanks  174 ,  176  by a suitable machining process. For example, while hobbing with a hob cutting tool is a machining process often used to remove metal from a blank to form gear teeth, because of the size of the first and second intermediate blanks  174 ,  176  and because the finished internal and external toothed segments  150 ,  152  are only a partial arc of some degrees of the complete internal and external gear rings, other metal removing processes like broaching and milling may be used in addition or instead. 
     In an embodiment, to further reduce weight of the finished internal and external toothed segments  150 ,  152  through the removal of excess material, a plurality of pockets  198  can be machined into the first and second intermediate blanks  174 ,  176 . For example, a plurality of recesses or pockets  198  can be machined into the slanted face  184  of the first intermediate blank  174  corresponding to the internal toothed segment  150  generally in the axial direction by a peripheral milling process using a milling cutter. Another plurality of recesses or pockets  198  can be machined into the slanted face  186  of the second intermediate blank  176  corresponding to the external toothed segment  152  generally in an axial direction with a milling cutter. The plurality of pockets  198 , for example, in the illustrated embodiment four pockets, can be linearly spaced along the lengthwise edge  192  generally adjacent to the plurality of concavely arranged or convexly arranged teeth  194 ,  196  and can have similar or dissimilar shapes. 
     Machining of the plurality of pockets  198  may define a plurality of structural supports  200  that are integrally fixed with respect to the finished internal and external toothed segments  150 ,  152  and that linearly separate the plurality of pocket  198  with respect to the lengthwise dimension of the internal and external toothed segments. The structural supports  200  can extend towards and are generally orthogonal or perpendicular with respect to the lengthwise edge  192  and generally have a downward sloping configuration The structural supports  200 , which can be generally orthogonal or perpendicular to the plurality of concavely or convexly arranged teeth  194 ,  196 , can radially brace the teeth as the inner and outer gear rings intermesh with the pinion that drives the swing assembly. The uppermost extension or surface of the plurality of structural supports  200  can correspond to the slanted faces  184 ,  186  created by the diagonal cut  178  described above. Accordingly, the structural supports  200  are inclined downwardly as they extend to the lengthwise edge  192  of the respective internal and external toothed segments  150 ,  152 . The downwardly sloped structural supports  200  can serve to direct or transfer forces or loads applied to the concavely or convexly arranged teeth  194 ,  196  that the structural supports brace to the upper structure or lower base of the dragline excavator. 
     The plurality of pockets  198  can form a corresponding plurality of recessed bearing surfaces  202  into the internal and external toothed segments  150 ,  152  that are generally parallel to the remaining portions of the upper face  170  and the lower face  172 . Disposed into the recessed bearing surfaces  202  can be one or more axial through holes  204  formed, for example, by drilling and adapted to receive threaded fasteners there through to secure the internal and external toothed segments  150 ,  152  to the lower base of the dragline excavator. Locating the axial through holes  204  in the recessed bearing surfaces  202  created by the pockets  198  has an advantage of shortening the length of fasteners used to secure the toothed segments to the lower base of the dragline excavator as appropriate. Washers may be used to spread the load of the fasteners over the recessed bearing surfaces  202 . In addition to the axial through holes  204 , to facilitate lifting and installation of the internal toothed segment  150  and external toothed segment  152 , one or more threaded lifting holes  206  can be disposed at appropriate locations. 
     In a possible embodiment, to enable the arc-shaped internal gear segments  150  and the external gear segments  152  to be circumferentially aligned in an abutting arrangement and produce a circumferential circles associated with the internal gear ring and the external gear ring respectively, the first and second end faces  166  or  168  may be cut or milled at an angle between the lengthwise faces  162 ,  164  and the lengthwise edge  192 . The first and second end faces  166  or  168  may be milled using an end mill or similar cutting tool. 
     INDUSTRIAL APPLICABILITY 
     Referring to  FIG. 7 , there is illustrated a schematic diagram of a series of metalworking steps and processes that can be conducted to form and finish a plurality of internal toothed segments and external toothed segments that can manufactured together and selected for assembly into a large diameter swing gear assembly. The different steps and processes physically alter the metal material at different stages to produce the finished part. The schematic diagram in  FIG. 7  is exemplary only, and the order of the individual steps and processes may change and particular steps and processes may be omitted or added. In addition to  FIG. 7 , the examples of metalworking and manufacturing processes will be explained with reference to  FIGS. 3-4  illustrating the metal block  160  and  FIGS. 5-6  illustrating the finished internal toothed segment  150  and finished external toothed segment  152 . 
     In an initial forming process  300 , raw metal material such as steel or iron is cast or extruded to form a raw casting or ingot  302 . Casting and extrusion are considered to be types of bulk forming processes as familiar to persons of skill in the art of metalworking. Casting involves heating the metallic raw material, for example, iron ore or steel, to molten liquid that is poured into a mold or cast and cooled until solid. In extrusion, hot metal may be pushed through a die defining a desired cross-sectional shape to produce an ingot. The solid metal assumes the form of the mold, cast or, in the case of extrusion, assume the cross-section of the die, as indicated by the casting or ingot  302  in  FIG. 7 . 
     In a subsequent forging process  304 , the casting or ingot  302  can be formed or worked to produce the metal block  160  in the shape of a rectangular prism. Forging may be considered a type of metal forming process in which the casting or ingot is further shaped by applying compressive forces to cause mechanical deformation. In forging and similar metal forming processes, the shape and physical properties of the metal work piece may be altered by physical deformation without removal of the metal material. The compressive forces may be applied by placing the casting or ingot in a die defining the desired shape and repeatedly striking the part, for example, with a forge press or power hammer. In an embodiment, the forging process  304  may be a hot forging process in which the casting or ingot is heated while being compressed to enable the microstructural grains or crystals of the metal to reform or adapt to the imparted shape. In addition to producing a desired shape, forging improves the strength of the metal through work hardening and alignment of molecules on microstructural scale. By way of example, the metal block  160  produced by the forging process  304  may be sized two or more meters in length by one or more meter in width by thirty centimeters or more in vertical height. 
     In an embodiment, the metal block  160  can undergo a heat treating process  306  in which the metal block is heated to an elevated temperature for a period of time and cooled. Heat treatment is a type of treatment process that alters the microstructural properties of the metal block  160  to improve strength, rearrange or reorder the molecular or atomic structure, or to achieve other physical properties. In an embodiment, the heat treating process  306  can be done to improve machinability of the metal block  160 , for example, an annealing process that softens the metal block. 
     The metal block  160  may thereafter undergo a series of machining steps in which some metal is removed or cut away to product the finished parts. For example, to assist in subsequent machining, a groove forming process  308  can be conducted in which a plurality of guide grooves is cut into the metal block  160 . This may include the lengthwise groove  180  and the diagonal grooves  182  described above. Cutting the guide grooves can be accomplished by an end mill or similar cutting tool. The lengthwise grooves  180  and diagonal grooves  182  may penetrate the respective face of the metal block  160  only by a few centimeters, but can function as an outline or guide for subsequent cutting processes. 
     To bisect the metal block  160  into the first and second intermediate blanks  174 ,  176  described above, a diagonal cut  178  can be made via a diagonal cutting process  310  in which a cutting tool like a band saw or blade saw is directed lengthwise through the metal block  160 . Alternatively, the diagonal cutting process  310  can be conducted using a laser or a plasma torch or electrical discharge machining. The diagonal cutting process  310  produces the first and second intermediate blanks  174 ,  176  shaped as trapezoidal cuboids or prisms that have six opposing faces in which at least two opposing faces are non-parallel. 
     Another cutting process, in particular, a triangular cutting process  312  to produce the triangular cut  188  described above, can be conducted either before or after the first and second intermediate blanks  174 ,  176  have been separated from the metal block  160 . The triangular cutting process  312  removes the triangular-shaped wedges  190  described above so that the resulting shape of the first and second intermediate blanks has the cross-section of a five-sided polygon. The triangular cutting process  312  can be accomplished with a plasma torch or a fuel-oxygen torch. 
     To produce the finished part from the first and second intermediate blanks  174 ,  176 , further machining and, in particular, milling may be conducted to remove additional metal and produce the final shape. To produce the plurality of concavely arranged internal teeth  194  associated with the internal toothed segment  150 , a gear milling process  314  or gear hobbing process can be conducted. The gear milling process  314  can be conducted by penetrating the lengthwise face  162  of the first intermediate blank  174  with a mill or hob to remove metal and shape the vertically arranged individual teeth. Similarly, the gear milling process  314  can be conducted on the lengthwise face  164  of the second intermediate blank  176  with a mill or hob to shape the plurality of convexly arranged teeth  196  associated with the external toothed segment  152 . In an embodiment, either or both of the first and/or second intermediate blanks  174 ,  176  can be used to produce either or both of the internal toothed segment  150  and/or external toothed segment  152 . 
     To reduce the weight of the internal and external toothed segments  150 ,  152  while producing the structural supports  200 , a recessed milling process  316  can be conducted in which the plurality of pocket  198  are milled into the slanted faces  184 ,  186  of the first and second intermediate blanks  174 ,  176 . The recessed milling process  316  can be conducted using an end mill or similar cutting tool. Because the resulting structural supports  200  are generally oriented orthogonally with respect to the pluralities of concavely and convexly arranged teeth  194 ,  196 , the structural support  200  may brace and support applied loads during meshing of swing gear assembly and the pinion that drives rotation of the swing assembly. 
     To facilitate installation of the internal toothed segment  150  and the external toothed segment  152 , a drilling process  318  an be conducted in which the plurality of axial through holes  204  are drilled with a drill bit into the recessed bearing surfaces  202  formed by the plurality of pockets  198 . Additional metalworking processes can be conducted to produce the finished parts corresponding to the internal toothed segment  150  and external toothed segment  152  such as, for example, further heat treatment such as direct hardening, induction hardening or carburizing to improve strength, wear resistance, etc. 
     A final step may be an assembly process  320  in which the internal toothed segments  150  and external toothed segments  152  are transported and delivered to an excavation site for assembly into the swing assembly  130 . A plurality of internal toothed segments  150  can be arranged and aligned to produce the circumference of the internal gear ring  140  that is concentrically located about the axis line  132  of machine rotation. Similarly, the plurality of external tooth segments  152  can be arranged to produce the circumference of the external gear ring  142  concentrically aligned about the axis line  132  of machine rotation. The internal and external toothed segments  150 ,  152 , can be joined to adjacent segments by, for example, fasteners or welding. One of the assembled internal gear rings  140  or external gear rings  142  can be selected for assembly into the swing assembly of a dragline excavator or similar machine. 
     The disclosure therefore provides a swing gear assembly for large scale or heavy machinery which is assembled from a plurality of external and/or internal toothed segments. The external and internal toothed segments are manufactured via a series of metalworking processes intended to increase efficiency and reduce cost of manufacturing and to provide structural elements that may improve load-transfer ability and strength of the gear segments. These and other possible advantages and features of the disclosure are apparent to a person of skill in the art from the foregoing description and accompanying drawings. 
     It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated. 
     Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. 
     The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. 
     Accordingly, this disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.