Patent Publication Number: US-2020283910-A1

Title: Material deposition to form a sheet structure

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of U.S. application Ser. No. 15/388,172, filed Dec. 22, 2016 for “MATERIAL DEPOSITION TO FORM A SHEET STRUCTURE”, which is hereby incorporated by reference herein. 
    
    
     FIELD 
     The present disclosure is directed to a system and a method for creation of a sheet structure using a cold-spray deposition technique. 
     BACKGROUND 
     Gas turbine engines include multiple components, a portion of which are formed as sheet structures. These sheet structures are currently hot or cold formed using dies. The dies include a relatively durable material that is capable of withstanding the temperature, pressure, and other loads applied to the die via the selected forming operation. The material used in the dies may be relatively expensive. Furthermore, formation of dies is a relatively time-consuming and expensive process. The lead time and expense of forming the dies increases as the complexity, such as complex contours and size, of the desired part increases. 
     SUMMARY 
     Disclosed herein is a method for forming a sheet structure. The method includes providing a tool having a formation surface corresponding to a shape of the sheet structure. The method also includes depositing at least one layer of material on the formation surface using a cold-spray deposition technique. The method also includes removing the at least one layer of material from the formation surface to create the sheet structure. 
     In any of the foregoing embodiments, the sheet structure has a thickness between 5 thousandths of an inch (0.127 millimeters) and 1 inch (25.4 millimeters). 
     Any of the foregoing embodiments may also include forming the tool via additive manufacturing. 
     Any of the foregoing embodiments may also include preparing a model of the tool using a computer, and controlling a robot to form the tool based on the model of the tool. 
     Any of the foregoing embodiments may also include forming an interface coating on the formation surface via electroplating, such that depositing the at least one layer of material includes depositing the at least one layer of material on the interface coating. 
     In any of the foregoing embodiments, removing the at least one layer of material from the formation surface includes removing the at least one layer via at least one of applying physical force to the at least one layer of material in a direction away from the formation surface, applying a releasing agent between the at least one layer of material and the formation surface, increasing a temperature of the tool, or etching the at least one layer of material from the formation surface using an acid or other chemically reactive material. 
     Any of the foregoing embodiments may also include removing a portion of the formation surface of the tool to form a recess in the formation surface, wherein depositing the at least one layer of material on the formation surface further includes depositing a greater amount of material in the recess on the formation surface such that the sheet structure has a greater thickness at a location corresponding to the recess. 
     Also described is a system for forming a sheet structure. The system includes a tool having a formation surface corresponding to a desired shape of the sheet structure. The system also includes a cold-spray gun configured to output a gas including particles of a material towards the formation surface at a velocity sufficiently great to cause the particles of the material to bond together. The system also includes a means for separating the material from the formation surface to create the sheet structure. 
     In any of the foregoing embodiments the sheet structure has a thickness between 5 thousandths of an inch (0.127 millimeters) and 1 inch (25.4 millimeters). 
     Any of the foregoing embodiments may also include a computer configured to generate a model of the tool. 
     Any of the foregoing embodiments may also include a robot configured to create the tool based on the model of the tool. 
     Any of the foregoing embodiments may also include an additive manufacturing machine, wherein the robot is configured to form the tool using the additive manufacturing machine. 
     Any of the foregoing embodiments may also include an electroplating machine configured to form an interface coating on the formation surface via electroplating, such that the particles of the material contact the interface coating on the formation surface. 
     In any of the foregoing embodiments, the means for separating the material from the formation surface includes at least one of a mechanical tool usable to pry the material from the formation surface, a releasing agent configured to be applied between the material and the formation surface to separate the material from the formation surface, a heater configured to heat the formation surface to a sufficient temperature to separate the material from the formation surface, or an acid or other chemically reactive material configured to be applied to at least one of the material or the formation surface to etch the material from the formation surface. 
     Also described is a sheet structure for use in an aircraft. The sheet structure is prepared by a method that includes providing a tool having a formation surface corresponding to a shape of the sheet structure. The method also includes depositing at least one layer of material on the formation surface using a cold-spray deposition technique. The method also includes removing the at least one layer of material from the formation surface to create the sheet structure. 
     In any of the foregoing embodiments, the sheet structure has a thickness between 5 thousandths of an inch (0.127 millimeters) and 1 inch (25.4 millimeters). 
     In any of the foregoing embodiments, the steps further include forming the tool via additive manufacturing, preparing a model of the tool using a computer, and controlling a robot to form the tool based on the model of the tool. 
     In any of the foregoing embodiments, the steps further include forming an interface coating on the formation surface via electroplating, such that depositing the at least one layer of material includes depositing the at least one layer of material on the interface coating. 
     In any of the foregoing embodiments, removing the at least one layer of material from the formation surface includes removing the at least one layer via at least one of applying physical force to the at least one layer of material in a direction away from the formation surface, applying a releasing agent between the at least one layer of material and the formation surface, increasing a temperature of the tool, or etching the at least one layer of material from the formation surface using an acid or other chemically reactive material. 
     In any of the foregoing embodiments, the steps further include removing a portion of the formation surface of the tool to form a recess in the formation surface, wherein depositing the at least one layer of material on the formation surface further includes depositing a greater amount of material in the recess on the formation surface such that the sheet structure has a greater thickness at a location corresponding to the recess. 
     The foregoing features and elements may be combined in various combinations without exclusivity, unless expressly indicated otherwise. These features and elements as well as the operation thereof will become more apparent in light of the following description and the accompanying drawings. It should be understood, however, the following description and drawings are intended to be exemplary in nature and non-limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various features will become apparent to those skilled in the art from the following detailed description of the disclosed, non-limiting, embodiments. The drawings that accompany the detailed description can be briefly described as follows: 
         FIG. 1  is a schematic cross-section of a gas turbine engine, in accordance with various embodiments; 
         FIG. 2  is a flowchart illustrating a method for forming a sheet structure usable in the gas turbine engine of  FIG. 1  using a cold-spray deposition technique, in accordance with various embodiments; 
         FIG. 3  is a block diagram illustrating a system for forming a sheet structure using a cold-spray deposition technique, in accordance with various embodiments; 
         FIG. 4A  is a drawing of a tool used for forming a sheet structure using a cold-spray deposition technique, in accordance with various embodiments; 
         FIG. 4B  is a drawing of the tool of  FIG. 4A  having an interface coating for receiving a cold-spray deposit, in accordance with various embodiments; 
         FIG. 4C  is a drawing of a sheet structure using the tool and interface coating of  FIG. 4B , in accordance with various embodiments; 
         FIG. 5A  is a drawing of a tool having a recess in a formation surface for forming a sheet structure with a feature having a greater thickness relative to other portions of the sheet structure, in accordance with various embodiments; 
         FIG. 5B  is a drawing of the sheet structure with the feature formed using the tool of  FIG. 5A , in accordance with various embodiments; 
         FIG. 6  is a drawing of multiple portions of the sheet structure of  FIG. 5B  having ribs of various shapes, in accordance with various embodiments; 
         FIG. 7A  is a drawing of a portion of an exhaust duct of an aircraft, in accordance with various embodiments; 
         FIG. 7B  is a drawing of two duct segments of the exhaust duct of  FIG. 7A  formed using a cold-spray deposition technique and having flanges for coupling purposes, in accordance with various embodiments; and 
         FIG. 7C  is a drawing of one of the duct segments of  FIG. 7B  illustrating features of the duct segment and the corresponding flange, in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     All ranges and ratio limits disclosed herein may be combined. It is to be understood that unless specifically stated otherwise, references to “a,” “an,” and/or “the” may include one or more than one and that reference to an item in the singular may also include the item in the plural. 
     The detailed description of various embodiments herein makes reference to the accompanying drawings, which show various embodiments by way of illustration. While these various embodiments are described in sufficient detail to enable those skilled in the art to practice the disclosure, it should be understood that other embodiments may be realized and that logical, chemical, and mechanical changes may be made without departing from the spirit and scope of the disclosure. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. For example, the steps recited in any of the method or process descriptions may be executed in any order and are not necessarily limited to the order presented. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected, or the like may include permanent, removable, temporary, partial, full, and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced contact or minimal contact. Cross hatching lines may be used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     As used herein, “aft” refers to the direction associated with the exhaust (e.g., the back end) of a gas turbine engine. As used herein, “forward” refers to the direction associated with the intake (e.g., the front end) of a gas turbine engine. 
     As used herein, “radially outward” refers to the direction generally away from the axis of rotation of a turbine engine. As used herein, “radially inward” refers to the direction generally towards the axis of rotation of a turbine engine. 
     In various embodiments and with reference to  FIG. 1 , a gas turbine engine  20  is provided. The gas turbine engine  20  may be a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26  and a turbine section  28 . Alternative engines may include, for example, an augmentor section among other systems or features. In operation, the fan section  22  can drive coolant (e.g., air) along a bypass flow path B while the compressor section  24  can drive coolant along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . Although depicted as a two-spool turbofan gas turbine engine  20  herein, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including turbojet, turboprop, turboshaft, or power generation turbines, with or without geared fan, geared compressor or three-spool architectures. 
     The gas turbine engine  20  may generally comprise a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A-A′ relative to an engine static structure  36  or engine case via several bearing systems  38 ,  38 - 1 , and  38 - 2 . It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, including for example, the bearing system  38 , the bearing system  38 - 1 , and the bearing system  38 - 2 . 
     The low speed spool  30  may generally comprise an inner shaft  40  that interconnects a fan  42 , a low pressure compressor  44  and a low pressure turbine  46 . The inner shaft  40  may be connected to the fan  42  through a geared architecture  48  that can drive the fan  42  at a lower speed than the low speed spool  30 . The geared architecture  48  may comprise a gear assembly  60  enclosed within a gear housing  62 . The gear assembly  60  couples the inner shaft  40  to a rotating fan structure. The high speed spool  32  may comprise an outer shaft  50  that interconnects a high pressure compressor  52  and high pressure turbine  54 . A combustor  56  may be located between high pressure compressor  52  and high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  may be located generally between the high pressure turbine  54  and the low pressure turbine  46 . Mid-turbine frame  57  may support one or more bearing systems  38  in the turbine section  28 . The inner shaft  40  and the outer shaft  50  may be concentric and rotate via bearing systems  38  about the engine central longitudinal axis A-A′, which is collinear with their longitudinal axes. As used herein, a “high pressure” compressor or turbine experiences a higher pressure than a corresponding “low pressure” compressor or turbine. 
     The airflow of core flow path C may be compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded over the high pressure turbine  54  and the low pressure turbine  46 . The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. 
     The gas turbine engine  20  may be, for example, a high-bypass ratio geared engine. In various embodiments, the bypass ratio of the gas turbine engine  20  may be greater than about six (6). In various embodiments, the bypass ratio of the gas turbine engine  20  may be greater than ten (10). In various embodiments, the geared architecture  48  may be an epicyclic gear train, such as a star gear system (sun gear in meshing engagement with a plurality of star gears supported by a carrier and in meshing engagement with a ring gear) or other gear system. The geared architecture  48  may have a gear reduction ratio of greater than about 2.3 and the low pressure turbine  46  may have a pressure ratio that is greater than about five (5). In various embodiments, the bypass ratio of the gas turbine engine  20  is greater than about ten (10:1). In various embodiments, the diameter of the fan  42  may be significantly larger than that of the low pressure compressor  44 , and the low pressure turbine  46  may have a pressure ratio that is greater than about five (5:1). The low pressure turbine  46  pressure ratio may be measured prior to the inlet of the low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. It should be understood, however, that the above parameters are exemplary of various embodiments of a suitable geared architecture engine and that the present disclosure contemplates other gas turbine engines including direct drive turbofans. A gas turbine engine may comprise an industrial gas turbine (IGT) or a geared engine, such as a geared turbofan, or non-geared engine, such as a turbofan, a turboshaft, or may comprise any gas turbine engine as desired. 
     In various embodiments, the low pressure compressor  44 , the high pressure compressor  52 , the low pressure turbine  46 , and the high pressure turbine  54  may comprise one or more stages or sets of rotating blades and one or more stages or sets of stationary vanes axially interspersed with the associated blade stages but non-rotating about engine central longitudinal axis A-A′. The compressor and turbine sections  24 ,  28  may be referred to as rotor systems. Within the rotor systems of the gas turbine engine  20  are multiple rotor disks, which may include one or more cover plates or minidisks. Minidisks may be configured to receive balancing weights or inserts for balancing the rotor systems. 
     Various components of gas turbine engine  20  may include one or more sheet structures. A sheet structure may include a relatively flat structure having a fairly broad surface relative to its thickness. For example, a sheet structure may have a thickness between 10 thousandths of an inch (0.0.254 millimeters) and 0.5 inches (12.7 millimeters), or between 15 thousandths of an inch (0.0.381 millimeters) and 250 thousandths of an inch (6.35 millimeters). 
     Conventional processes for manufacturing such sheet structures are relatively expensive and time-consuming. Referring to  FIG. 2 , a method  200  for forming a sheet structure using a cold-spray process is shown. Formation of a sheet structure using the method  200  may be less expensive and less time-consuming than conventional processes. In various embodiments, the method  200  may be used to form sheet structures having a relatively large size. For example, the method  200  may be used to form sheet structures having a surface area of at least 1 inch squared (1 in. 2 , 2.54 centimeters squared (cm 2 )), 10 in. 2  (25.4 cm 2 ), 36 in. 2  (91.44 cm 2 ), or 100 in. 2  (254 cm 2 ). 
     In block  202 , a computer is used to create a model of a tool. A computer may include a processor, a memory, and input device, and an output device. A computer may include one or more computers having processors and one or more tangible, non-transitory memories and be capable of implementing logic. The processor(s) can be a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a graphical processing unit (GPU), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. The memory may be any non-transitory memory capable of storing data. For example, the memory may store instructions to be executed by the processor, may store modeling software, may store a model of a component, or the like. The input device may include, for example, a mouse, a keyboard, a microphone, or the like. The output device may include, for example, a display, a speaker, an input/output port, or the like. 
     The tool may include a formation surface on which a material of the sheet structure is deposited. In that regard, the tool may be modeled such that the formation surface corresponds to a desired shape of the sheet structure. The tool may be modeled using any three-dimensional modeling software such as SolidWorks™, available from Dassault Systèmes of Velizy-Villacoublay, France. 
     The tool may include any material having sufficient yield strength to resist the formation in response to receiving spray from a cold-spray gun. As will be described below, a cold-spray deposition technique delivers material at a relatively low temperature. Accordingly, the tool may include materials having a relatively low thermal resistance, which may result in lower cost of the tools. For example, the tool may include a metal, a plastic, or another compound material such as nylon, polymers, high-temperature resins, aluminum, low melt alloys, or the like. A low melt alloy may include any metallic alloy that has a melting temperature of 450 degrees Fahrenheit (450 degrees F., 233 degrees Celsius (C)) or below. For example, a low melt alloy may include one or more of bismuth, lead, tin, cadmium, indium, and the like. Selection of a material for the tool may be based considering the cost of the material of the tool and a durability of the tool. 
     In block  204 , a robot is controlled to form the tool based on the computer-generated model. The tool may be formed using additive manufacturing, such as stereolithography. In that regard, the robot may be an additive manufacturing device, such as a 3-D printer, connected to the computer. The computer may be electrically coupled to the additive manufacturing device such that the device forms the tool based on the model. In various embodiments, the robot may include a machine separate from the additive manufacturing device and may independently control the additive manufacturing device based on the computer-generated model. In various embodiments, a user may receive the model from the computer and may manually provide information corresponding to the model to an additive manufacturing device. 
     In block  206 , an interface coating may be applied to the formation surface of the tool. The interface coating may include, for example, a metal formed on the formation surface using electroplating. The interface material may include, for example, an epoxy or low melt alloy. In that regard, the interface coating may provide various benefits such as erosion protection of the tool, thermal protection of the tool, generation of a desired surface finish or feature, facilitation of separation of the sheet structure from the tool, and increased rigidity and resistance to deformation resulting from contact with relatively high-velocity spray from a cold-spray gun. In that regard, the formation surface of the tool may include one or both of the interface material or the material of the tool. 
     In various embodiments, it may be desirable to form one or more features, such as ribs, in the sheet structure that have great thickness relative to other portions of the sheet structure. In order to form the feature, a portion of the formation surface may be removed to form one or more recess in the formation surface in block  208 . In response to the sheet structure material being cold-sprayed onto the formation surface, additional material may collect in the recess such that the corresponding part of the sheet structure has a greater thickness at the location corresponding to the recess. In various embodiments, the tool may be formed to have the recess such that removal of a portion of the formation surface is optional. 
     In block  210 , at least one layer of material may be cold-sprayed onto the formation surface (or the interface coating) using a cold-spray deposition technique that utilizes a cold-spray gun. A cold-spray deposition technique is based on direct additive deposition of fine metallic particles that are accelerated to supersonic speeds using inert gas and a cold-spray gun. Inert gas may include at least one of an inert gas, air, or a less reactive gas, such as nitrogen. The cold-spray gun outputs a gas that includes the metallic particles and the inert gas. The output gas is directed towards the formation surface. The kinetic energy used in the process enables bonding of the metallic particles to each other on the formation surface of the tool, allowing the metallic particles to bind together to form the sheet structure. In various embodiments, the inert gas may be heated to a temperature that is between 400 degrees F. (204.4 degrees C.) and 1000 degrees F. (537.8 degrees C.). The temperature of the inert gas may, however, remain significantly below the melting point of the material of the metallic particles. In this context, significantly may refer to 5 percent (5%), or 15%, or 25%. 
     In various embodiments, it may be desirable for the sheet structure to have a greater relative thickness at particular locations. In that regard, the cold-spray gun may be used to apply more of the metallic particles to the particular locations to increase the thickness at the particular locations. 
     In various embodiments, the cold-spray gun may be controlled by at least one of a computer or a robot. In that regard, the computer or robot may be programmed to spray a predetermined amount of the metallic particles at each location of the sheet structure. The predetermined amount of the metallic particles sprayed at each location may result in each location of the sheet structure achieving the desired thickness. 
     Using a computer, and an electromechanical control system that is controlled by the computer, to control the cold-spray gun may result in a relatively accurate deposition of the metallic particles. The computer (or a user) may control such deposition factors as rate of discharge of the metallic particles, a distance from the tool from which the cold-spray gun is used, and the rate of movement of the cold-spray gun relative to the tool to adjust the thickness of the sheet structure. 
     A cold-spray gun outputs a relatively narrow plume of the output gas. This relatively narrow plume results in an ability to precisely position the metallic particles where desired. 
     The metallic particles used to form the sheet structure may include various metals and corresponding alloys such as, for example, titanium, nickel, aluminum and titanium aluminide alloys, cobalt alloys, or the like. 
     In block  212 , the at least one layer of material (corresponding to the sheet structure) may be removed from the formation surface. This sheet structure may be removed in a variety of manners. In various embodiments, the sheet structure may be physically manipulated away from the formation surface by applying a force to the sheet structure in a direction away from the formation surface. In various embodiments, this physical manipulation may be performed by a user grasping a portion of the sheet structure, may be performed by a user using a tool, such as a crowbar, to separate the sheet structure from the tool, or the like. In various embodiments, the tool may be constructed such that introduction of pressurized fluid causes flexure of the tool (potentially including the formation surface), thus facilitating release of the sheet structure. In various embodiments, water or another fluid may be introduced between the formation surface and the sheet structure via capillary action or other means. In that regard, the fluid may be frozen (and thus expand), exerting a separating force/pressure to facilitate release of the sheet structure. 
     In various embodiments, a releasing agent may be applied between the sheet structure and the tool to facilitate release of the sheet structure from the formation surface. The release agent may include, for example, Boron Nitride (i.e., a hexagonal boron nitride). The release agent may be applied between the sheet structure and the formation surface or between the formation surface and the interface coating prior to cold-spray deposition of the metallic particles or after cold-spray deposition of the metallic particles. The properties of the release agent may result in a weaker bond between the sheet structure and the tool, allowing the sheet structure to be removed from the tool with relative ease. In various embodiments, the release agent may be used and the sheet structure may still be physically manipulated away from the formation surface. 
     In various embodiments, the combination of the tool and the sheet structure may be heated to such a temperature that the sheet structure does not deform yet the tool, or interface coating, deforms or de-bonds from the sheet structure, facilitating release of the sheet structure. In various embodiments, the interface coating may include an adhesive having a melting point above that of the temperature of the cold-spray gas and below that of the sheet structure. In that regard, the sheet structure and the interface coating may be heated to the melting point of the interface coating, facilitating release of the sheet structure. The interface coating may then be reapplied to the tool prior to a new sheet structure being formed on the tool. 
     In various embodiments, the sheet structure may be etched from the tool. For example, an acid such as a Bronsted-Lowry acid or another etching agent or chemically reactive material may be applied to the tool, thereby etching the tool away from the sheet structure. 
     In various embodiments, additional operations may be performed on the sheet structure to complete the part after separation from the tool. For example, the additional operations may include machining of interfaces, welding of the part to additional parts, forming an integral portion of the sheet structure using a cold-spray deposition technique with a different tool, or the like. 
     Turning now to  FIG. 3 , a system  300  for implementing the method  200  of  FIG. 2  is shown. The system  300  includes a computer  302  in communication with an additive manufacturing machine  304  and a robot  306 . In various embodiments, the robot  306  may not be present in the system  300 . In various embodiments, the tool may be made using a machine different from the additive manufacturing machine  304 . 
     A user may create a model of a tool using the computer  302 . In various embodiments, the model may be received by the robot  306  and/or the additive manufacturing machine  304  which may, in turn, form a tool  308 . In various embodiments, a user may provide the model to the robot  306  and/or the additive manufacturing machine  304 . In various embodiments, a user may manually control the additive manufacturing machine  304  to create the tool  308 . 
     The tool  308  may then be provided to an electroplating machine  310  or another device, which may apply an interface coating  312  on the tool  308 . In various embodiments, the electroplating machine  310  may not be present in the system  300  such that no interface coating is applied. In various embodiments, the interface coating  312  may be applied via brushing, spraying, or another device. In various embodiments, the electroplating machine  310  may be controlled by the computer  302  or by another computer or robot to form the interface coating  312 . 
     After the interface coating  312  is applied to the tool  308 , the combined tool  308  and interface coating  312  may be subjected to spray from a cold-spray gun  314 . The cold-spray gun  314  may direct a gas with metallic particles  316  towards the tool  308  and the interface coating  312 . The gas with metallic particles  316  may hit the interface coating  312  and may begin to form one or more layer of material  318  on the interface coating  312 . In various embodiments, the cold-spray gun  314  may be controlled by the computer  302  and/or by a robot  315 . In various embodiments, the cold-spray gun  314  may be controlled by a separate computer or may be independently controlled. 
     After the material  318  has been applied to the interface coating  312 , the combined tool  308 , interface coating  312 , and material  318  may be subjected to a separating means  320 . The separating means  320  may include any method or structure used to separate the material  318  from the interface coating  312  as described above with reference to block  212  of  FIG. 2 . The separating means  320  may separate the material  318  from the interface coating  312 . The resulting material  318  may correspond to a sheet structure  322 . 
     Referring now to  FIGS. 4A and 4B , an exemplary tool  400  and sheet structure  401  is shown. The tool  400  has a formation surface  402 . The formation surface  402  has a shape that corresponds to a desired shape of the sheet structure  401 . The tool  400  includes one or more pockets  404  positioned within the tool  400  and having a material that is different from the remaining material of the tool  400 . The pockets  404  may be designed to reduce the likelihood of deformation of the tool  400  due to impact with a relatively high velocity gas from a cold-spray gun  410 . In that regard, the pockets  404  may include a material having a yield strength that is greater than that of the remaining portions of the tool  400 . For example, the pockets  404  may include an epoxy or a low melt alloy. 
     An interface coating  406  may be applied to the formation surface  402  of the tool  400 . The interface coating  406  may provide benefits as described above with reference to  FIG. 2 . 
     A cold-spray gun  410  may deposit metallic particles onto the interface coating  406  to form one or more layer of material  408 . In order to deposit metallic particles onto the interface coating  406 , the cold-spray gun  410  may move relative to the tool  400 . For example, the cold-spray gun  410  may move from a first location  412  to a second location  414 , depositing metallic particles at desired thicknesses along the way. 
     After the desirable amount of material  408  has been applied to the interface coating  406 , the material  408  may be separated from the interface coating  406  in one or more manners as described above with reference to  FIG. 2 . 
     Referring now to  FIGS. 4A, 4B, and 4C , the material  408  that is separated from the interface coating  406  may be the sheet structure  401 . As shown, the sheet structure  401  has a shape that corresponds to the shape of the formation surface  402 . The sheet structure  401  may have a thickness  416  that corresponds to the amount of metallic particles deposited on the interface coating  406 . The cold-spray gun  410  may achieve the desired thickness  416  in one or more of a variety of manners. For example, the desired thickness  416  may be achieved by making a predetermined number of passes over the formation surface  402  with the cold-spray gun  410 , may be achieved by adjusting the rate of flow of gas exiting the cold-spray gun  410 , may be achieved by adjusting the rate at which the cold-spray gun  410  moves relative to the formation surface  402 , or the like. 
     Turning now to  FIGS. 5A and 5B , another tool  500  may include a formation surface  502  on which at least one layer of material  508  is directly deposited to form a sheet structure  501 . Stated differently, the tool  500  may not include an interface coating. The formation surface  502  may have a shape that is similar to the formation surface  402  of  FIG. 4A . However, it may be desirable for the sheet structure  501  to have one or more feature  518  such as a rib. 
     In order to form the feature  518 , a portion  519  of the formation surface  502  may be removed from the tool  500  to form a recess  520 . In various embodiments, a tool that includes an interface coating may be manipulated such that a portion of the interface coating and/or the formation surface  502  is removed from the tool to form the feature on the sheet structure. In various embodiments, the tool  500  may be formed with the recess  520  in place such that the tool  500  may be used without removal of any of the tool  500 . 
     After the portion  519  of the formation surface  502  is removed, a cold-spray gun  510  may deposit metallic particles on the formation surface  502 . In various embodiments, the cold-spray gun  510  may be manipulated across the formation surface  502  to deposit additional material within the recess  520 . In various embodiments, the recess  520  may have particular features that facilitate bonding of the metallic particles within the recess  520 . For example, the recess  520  may have an angle  522  that is greater than 90 degrees. The angle  522  may allow the metallic particles to bond together and entirely fill the recess  520 . 
     In response to the sheet structure  501  being separated from the formation surface  502 , the metal that was deposited in the recess  520  may form the feature  518  such as the rib. In various embodiments, the recess  520  may not be completely filled by the material. In that regard, the sheet structure  501  may have an indentation, or a volume, where the recess  520  is not completely filled. 
     Referring now to  FIGS. 5A and 6 , the sheet structure  501  may be formed to have a variety of features by forming recesses  520  in the tool  500 . For example, the sheet structure  501  may have straight ribs  600  extending in one direction or two directions parallel to a surface of the sheet structure  501 . The sheet structure  501  may also be formed to have hexagonal ribs  602 . The sheet structure  501  may also be formed to have iso-grid ribs  604  or circular ribs  606 . 
     Referring now to  FIGS. 7A, 7B, and 7C , the method  200  may be used to form parts for an annular or other non-flat structure, such as a portion of an exhaust duct  700 . The exhaust duct  700  may include a first duct segment  702 , a second duct segment  704 , a third duct segment  706 , and a fourth duct segment  708 . Each of the duct segments  702 ,  704 ,  706 ,  708  may be formed as a sheet structure and may have a curved surface. Each of the duct segments  702 ,  704 ,  706 ,  708  may be coupled together to form the portion of the exhaust duct  700 . 
     In order to fasten each of the duct segments  702 ,  704 ,  706 ,  708  together, the ends of the duct segments  702 ,  704 ,  706 ,  708  may be formed to have a flange that interfaces with a flange of an adjacent duct segment  702 ,  704 ,  706 ,  708 . For example, the fourth duct segment  708  may include a flange  710  designed to interface with a flange  712  of the third duct segment  706 . The flange  710  and the flange  712  may be coupled together via, for example, welding or use of a fastener  714 . 
     In order to provide an effective means of transitioning structural stiffness between relatively thin deposited sheet regions of the fourth duct segment  708  and the flange  710  (which is relatively rigid) of the fourth duct segment  708 , the fourth duct segment  708  may be formed to have an increasing thickness towards the flange  710 . For example, the fourth duct segment  708  has a first thickness  716  and a second thickness  718 . The second thickness  718  may be closer to the flange  710  than the first thickness  716 . The second thickness  718  may be greater than the first thickness  716 . The thickness of the fourth duct segment  708  may increase from the location of the first thickness  716  to the flange  710 . Such tapering can be performed using a known structural practice and may be integrally formed into the fourth duct segment  708  via preferential deposition of material. 
     This increase in thickness may be formed in a variety of manners. In various embodiments, a cold-spray gun may be controlled to deposit the metallic particles at a faster rate as the cold-spray gun approaches the flange  710 , the cold-spray gun may be controlled to make additional passes over the corresponding tool as it approaches the flange  710 , the cold-spray gun may be controlled to reduce its rate of movement relative to the tool as it approaches the flange  710 , or the tool may be designed to have a recess that corresponds to the increasing thickness of the fourth duct segment  708 . 
     In various embodiments, the flange  710  may be formed in a variety of manners. For example, the tool may be designed to have a recess that corresponds to the flange  710 . As another example, the fourth duct segment  708  may be initially formed without the flange  710  and used in conjunction with a separate tool to form the flange  710 . 
     While the disclosure is described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the disclosure. In addition, different modifications may be made to adapt the teachings of the disclosure to particular situations or materials, without departing from the essential scope thereof. The disclosure is thus not limited to the particular examples disclosed herein, but includes all embodiments falling within the scope of the appended claims. 
     Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the disclosure. The scope of the disclosure is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Moreover, where a phrase similar to “at least one of a, b, or c” is used in the claims, it is intended that the phrase be interpreted to mean that a alone may be present in an embodiment, b alone may be present in an embodiment, c alone may be present in an embodiment, or that any combination of the elements a, b and c may be present in a single embodiment; for example, a and b, a and c, b and c, or a and b and c. Different cross-hatching is used throughout the figures to denote different parts but not necessarily to denote the same or different materials. 
     Systems, methods and apparatus are provided herein. In the detailed description herein, references to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments. 
     Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112(f), unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.