Hybrid manufacturing system

Abstract

A hybrid manufacturing system includes a tool positioning system, a worktable for supporting a workpiece, a tool head coupled to the tool positioning system and movable relative to the worktable with the positioning system. A directed energy deposition (DED) tool is coupled to the tool head. A friction stir welding (FSW) tool is coupled to the tool head and a subtractive machining tool is also coupled to the tool head. The system provides the ability to produce a workpiece by DED additive manufacturing and process the workpiece as layers are deposited with friction stir welding and milling all in the same machine.

Description

HYBRID MANUFACTURING SYSTEMCROSS REFERENCE TO RELATED APPLICATION

[0001] The present application claims the benefit of U.S. Provisional Application No. 63 / 549,744, filed February 5, 2024, which is incorporated herein by reference in its entirety.FIELD

[0002] The present disclosure pertains to hybrid manufacturing systems including one or more additive manufacturing tools, one or more solid-state joining process tools, and one or more subtractive machining tools that can act on a workpiece.ACKNOWLEDGEMENT OF GOVERNMENT SUPPORT

[0003] This invention was made with government support under Grant No. W9124P-18-9-0001 awarded by the Army Contracting Command-Redstone Arsenal. The government has certain rights in the invention.BACKGROUND

[0004] Wire-based directed energy deposition (DED) additive manufacturing techniques can be useful for manufacturing large parts, as well as for joining dissimilar materials together. However, DED processes can create undesirable anisotropic properties in metals such as relatively large, columnar grain structures along deposition paths that adversely affect the mechanical properties of the resulting part. Addressing these issues with other processes and tools during manufacturing often requires moving the part between different machines. This is time-consuming and sacrifices dimensional accuracy due to thermal expansion and contraction that occurs during transfers between machines. Accordingly, a need exists for improved hybrid manufacturing systems.SUMMARY

[0005] Certain examples of the disclosure pertain to hybrid manufacturing systems that combine additive manufacturing, friction stir welding, and milling functionality into a single machine. In one representative example, a hybrid manufacturing system comprises a tool positioning system, a worktable for supporting a workpiece, a tool head coupled to the tool positioning system and movable relative to the worktable with the positioning system, a directed energy deposition (DED) tool coupled to the tool head, a friction stir welding (FSW) tool coupled to the tool head, and a subtractive machining tool coupled to the tool head.

[0006] In any or all of the examples described herein, the subtractive machining tool is a milling tool.

[0007] In any or all of the examples described herein, the FSW tool comprises a spindle coupled to the tool head, and the milling tool is coupled to the spindle of the FSW tool.

[0008] In any or all of the examples described herein, the milling tool is mounted to the FSW tool coaxially with the FSW tool.

[0009] In any or all of the examples described herein, the FSW tool comprises a cylindrical body having an outer planar surface, and a set screw extends through the milling tool and engages the outer planar surface of the cylindrical body to secure the milling tool to the FSW tool.

[0010] In any or all of the examples described herein, the outer planar surface is inclined radially inwardly toward a longitudinal axis of the FSW tool in a direction from a distal tip of the FSW tool toward the spindle.

[0011] In any or all of the examples described herein, the FSW tool and the subtractive machining tool are spaced apart from the DED tool by a specified distance and configured to follow the DED tool along a workpiece during operation.

[0012] In any or all of the examples described herein, the DED tool is a wire arc additive manufacturing (WAAM) tool comprising a torch and a wire supply.

[0013] In any or all of the examples described herein, the tool positioning system comprises an X- axis stage, a Y-axis stage, and a Z-axis stage; the X-axis stage is coupled to and movable with the Y-axis stage; and a plurality of reinforcement members extend between the X-axis stage and the Y-axis stage and are configured to reduce vibration of the X-axis stage and the Y-axis stage during operation.

[0014] In any or all of the examples described herein, the reinforcement members include plates and angle bars.

[0015] In any or all of the examples described herein, the subtractive machining tool is removably attachable to the friction stir welding tool, or the subtractive machining tool and the friction stir welding tool are a unitary body.

[0016] In another representative example, a method comprises processing a workpiece with the hybrid manufacturing system of any one of the examples described herein.

[0017] In another representative example, a hybrid manufacturing system comprises a tool positioning system; a worktable for supporting a workpiece; a directed energy deposition (DED)tool coupled to the tool positioning system; a friction stir welding (FSW) tool coupled to the tool positioning system; and a milling tool coupled to the FSW tool.

[0018] In another representative example, a friction stir welding tool comprises a cylindrical body having a proximal end and a distal end; a pin located at the distal end; and a milling tool on the body of the friction stir welding tool and configured to rotate together with the body of the friction stir welding tool.

[0019] The foregoing and other objects, features, and advantages of the disclosed technology will become apparent from the following detailed description, which proceeds with reference to the accompanying figures.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIGS. 1 A-1D are perspective views of a hybrid manufacturing system according to the examples described herein.

[0021] FIG. 2 is a perspective view of a representative example of a rotating tool assembly of the hybrid manufacturing system of FIGS. 1A-1D.

[0022] FIG. 3 A is a perspective view of the rotating tool assembly.

[0023] FIGS 3B is a cross-sectional view of a friction stir welding tool and milling tool assembly, according to a representative example.

[0024] FIG. 3C is a magnified view of the distal end of the friction stir welding tool of FIG. 3B.

[0025] FIGS. 4A-4C are perspective views of the friction stir welding tool and the milling tool assembly of FIGS. 3A-3C.

[0026] FIG. 4D is a cross-sectional view a friction stir welding tool and milling tool assembly illustrating an angled flat surface on the friction stir welding tool.

[0027] FIG. 5 is a perspective view of the hybrid manufacturing system of FIGS. 1 A-1D illustrating a distance between a welding torch and a spindle of the rotating tools.

[0028] FIGS. 6A-6F illustrate fabrication of sample workpieces using the hybrid manufacturing systems described herein.

[0029] FIGS. 7 A and 7B illustrate the direction of rotation of the friction stir welding tool and a cross-section of a workpiece created using the hybrid manufacturing systems described herein.

[0030] FIGS. 8 A and 8B are electron backscatter diffraction (EBSD) images of deposited material and the nugget zone, respectively, of a workpiece processed with the systems described herein.

[0031] FIG. 9A is a cross-section through a workpiece processed with the systems described herein perpendicular to the weld direction.

[0032] FIG. 9B is a graph illustrating a horizontal profile of Vickers hardness of a workpiece processed with the systems described herein.

[0033] FIG. 10 is a chart illustrating comparative mechanical properties of a workpiece processed with friction stir processing and “as-deposited” without friction stir processing.

[0034] FIG. 11 illustrates another example of a hybrid manufacturing system including a wire-arc directed energy deposition tool and a friction stir welding tool spaced apart by a specified distance.

[0035] FIGS. 12A-12B illustrate workpieces produced by wire-arc directed energy deposition processed with and without the hybrid manufacturing system.

[0036] FIGS. 13A-13D are perspective and cross-sectional views of another example of a hybrid manufacturing system and combined friction stir welding and milling tools.

[0037] FIGS. 14A-14F illustrate fabrication of sample workpieces using the hybrid manufacturing systems described herein.

[0038] FIG.15 illustrates workpieces produced by wire-arc directed energy deposition processed with and without the hybrid manufacturing system.

[0039] FIGS. 16A and 16B are optical and scanning electron microscope images of the transverse sectional area perpendicular to weld tracks of a block produced by wire directed energy deposition.

[0040] FIGS. 16C and 16D are optical and scanning electron microscope images of the transverse sectional area perpendicular to weld tracks of a block produced by a hybrid directed energy deposition and friction stir processing and milling process described herein.

[0041] FIGS. 17A-17B are electron backscatter diffraction images and grain size distribution plots for a sample workpiece produced using wire-arc directed energy deposition.

[0042] FIGS. 17C-17E are electron backscatter diffraction images and grain size distribution plots for a sample workpiece produced using the systems and methods described herein.

[0043] FIGS. 18A-18C are kemal average misorientation maps of a friction stir processing nugget core.

[0044] FIGS. 18D-18F are pole figures of the nugget core.

[0045] FIG. 19A is a cross-section through a sample workpiece processed with the systems and methods described herein perpendicular to the welding direction.

[0046] FIGS. 19B and 19C are graphs of the Vickers hardness of the sample of FIG. 19A in the horizontal and vertical directions, respectively.

[0047] FIG. 20A is a graph of stress and strain of samples produced by hybrid DED and FSP with milling as described herein, and samples produced by DED only.

[0048] FIG. 20B is a chart showing mechanical properties of samples produced by hybrid DED and FSP with milling as described herein, and samples produced by DED only.

[0049] FIGS. 21A and 21B are perspective views illustrating a frame of a hybrid manufacturing system prior to reinforcement.

[0050] FIGS. 22A-22C are additional perspective views showing reinforcement members installed on the frame of a hybrid manufacturing system as described herein.DETAILED DESCRIPTION

[0051] Explanation of Terms

[0052] For purposes of this description, certain aspects, advantages, and novel features of the embodiments of this disclosure are described herein. The disclosed methods, apparatus, and systems should not be construed as being limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The methods, apparatus, and systems are not limited to any specific aspect or feature or combination thereof, nor do the disclosed embodiments require that any one or more specific advantages be present or problems be solved.

[0053] Although the operations of some of the disclosed embodiments are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed methods can be used in conjunction with other methods.

[0054] As used in this disclosure and in the claims, the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the terms “coupled” and “associated” generally mean electrically, electromagnetically, and / or physically (e.g., mechanically or chemically) coupled or linked anddoes not exclude the presence of intermediate elements between the coupled or associated items absent specific contrary language.

[0055] In some examples, values, procedures, or apparatus may be referred to as “lowest,” “best,” “minimum,” or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many alternatives can be made, and such selections need not be better, smaller, or otherwise preferable to other selections.

[0056] In the description, certain terms may be used such as “up,” “down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” and the like. These terms are used, where applicable, to provide some clarity of description when dealing with relative relationships. But these terms are not intended to imply absolute relationships, positions, and / or orientations. For example, with respect to an object, an “upper” surface can become a “lower” surface simply by turning the object over. Nevertheless, it is still the same object.

[0057] Unless otherwise indicated, all numbers expressing angles, dimensions, quantities of components, forces, moments, percentages, times, and so forth, as used in the specification or claims are to be understood as being modified by the term “about.” Accordingly, unless otherwise indicated, implicitly or explicitly, the numerical parameters set forth are approximations that can depend on the desired properties sought and / or limits of detection under test conditions / methods familiar to those of ordinary skill in the art. When directly and explicitly distinguishing embodiments from discussed prior art, the embodiment numbers are not approximates unless the word “about” is recited.

[0058] Although there are alternatives for various components, dimensions, parameters, operating conditions, etc., set forth herein, that does not mean that those alternatives are necessarily equivalent and / or perform equally well. Nor does it mean that the alternatives are listed in a preferred order unless stated otherwise.

[0059] As used herein, values and / or relationships modified by the term “substantially” mean ± 10% of the stated value and / or relationship. “Substantially perpendicular” means an angle of 80° to 100° relative to a reference. “Substantially parallel” means an angle of ± 10° relative to a reference.

[0060] Overview of the Disclosed Technology

[0061] The hybrid manufacturing systems described herein can include any of a variety of tools such as directed energy deposition (DED) additive manufacturing tools, solid state joining process tools, and / or subtractive machining tools. In some examples the various tools can be part of thesame machine and in the same hood or chamber. In some examples, any or all of the tools can be coupled to a common positioning system.

[0062] In some examples, the DED additive manufacturing tools can include tools comprising an energy source such as a torch, a laser, an ion beam, etc., and a consumable material source such as powder or a wire. The consumable materials can include metals and polymers. Example DED additive manufacturing process tools include wire arc additive manufacturing (WAAM) systems (also referred to as “wire-arc DED”), laser metal deposition systems, selective powder deposition systems, etc.

[0063] In some examples, the solid-state joining process tools can include friction stir welding (FSW) tools in which a non-consumable tool bit mixes material from two workpieces along an interface to join the workpieces together without melting the material(s).

[0064] In some examples, the subtractive machining tools can include milling tools, lathes, etc. Any of the tools described herein can be combined in any combination in the hybrid manufacturing systems described herein.

[0065] The hybrid manufacturing systems described herein can include a DED additive manufacturing tool such as a WAAM system, a FSW tool, and a milling tool located in the same process chamber and configured to act sequentially or simultaneously on a workpiece without the need to transfer the workpiece from one process chamber or machine to another. The various tools can be coupled to a tool positioning system that positions each tool relative to the workpiece according to the process to be performed on the workpiece. The workpiece can be mounted to a worktable or other support. In certain examples, the worktable can be movable independently of the tool positioning system to position the workpiece relative to the various tools.

[0066] In certain examples the FSW tool can be positioned at a specified distance from the WAAM tool. In some examples the FSW tool and the WAAM tool can be aligned along an axis of a direction of travel (e.g., of the tool positioning system and / or of the worktable) such that the FSW tool moves along the workpiece in the path of the WAAM tool. In some examples, this allows the FSW tool to take advantage of residual heat in the workpiece from the WAAM process, which can reduce the time needed for a friction stir weld and can facilitate the welding of dissimilar materials.

[0067] In certain examples, the FSW tool and the milling tool can be coupled to a common drive system. For example, the FSW tool (or the milling tool) can comprise a motor and a spindle, and the milling tool can be coupled to the FSW tool and can co-rotate with the FSW tool. For example, the milling tool can be secured to a shaft of the FSW tool such that the pin of the FSW tool extendsbeyond the milling tool along an axis of the FSW tool (and / or of the spindle). The FSW tool can act on the workpiece in a first orientation (e.g., with the workpiece positioned beneath the FSW tool) and the milling tool can act on the workpiece in a second orientation (e.g., with the workpiece and / or the milling tool rotated 90° relative to the first position such that the milling inserts (also referred to as “teeth”) of the milling tool contact the workpiece.

[0068] Example 1 : Hybrid Manufacturing System

[0069] FIG. 1 A illustrates an example of a hybrid manufacturing system 100 including a housing 102 defining a process chamber 104. Referring to FIGS. 1B-1D, the system 100 can include a tool positioning system 106 configured as an X / Y / Z frame including a plurality of actuators and guides for moving a tool head (also referred to as a “tool mount”) 108 within the process chamber 104. In some examples the tool positioning system 106 can move the tool head 108 along the x-axis, the y- axis, and the z-axis shown in FIGS. 1 A-1D, and / or can provide for rotation about any of the axes for as many as six degrees of freedom. The system 100 can also include a worktable 110 coupled to a worktable positioning system 112 located beneath the tool positioning system 106. The worktable positioning system 112 can be configured to translate and / or rotate the worktable 110, and a workpiece positioned on the worktable, about any of the x-, y-, and / or z-axes.

[0070] Referring to FIGS. 2, 3A-3C, and 5, in certain examples the tool head 108 includes a DED system such as a WAAM system 114 including a welding torch 116, a consumable wire supply 117 (FIG. 5), and a tube 118 (FIG. 3 A) configured to extract welding fumes from the chamber. The tool head 108 can further comprise a FSW tool 120 and a milling tool 122, collectively referred to as “rotating tools.” In the illustrated example the FSW tool 120 and the milling tool 122 can be incorporated into a rotating tool assembly 124 shown in FIG. 2 and FIGS. 3A-3C. The rotating tool assembly 124 can include a motor 126 and a spindle 128. In the illustrated example the motor 126 and spindle 128 are not coaxial and thus are coupled by a timing pulley and belt indicated generally at 130 that drives the spindle 128. However, in other examples the motor 126 and spindle 128 can be coaxially aligned and the system need not include a belt or other linkage. Further details regarding how the rotating tool assembly 124 is coupled to the tool head 108 are provided in the following examples.

[0071] FIGS. 3A-3C show the rotating tool assembly 124 coupled to the tool head 108 in the process chamber 104. In the particular implementation shown, the tool head 108 is coupled to the linear actuators of the x-axis frame 132 of the tool positioning system 106, although other configurations are possible.

[0072] FIGS. 3B-3C show the combined FSW tool 120 and the milling tool 122 in greater detail. In the illustrated example, the milling tool 122 can be positioned coaxially around the cylindrical body of the FSW tool 120 and secured to the FSW tool 120. FIG. 4A illustrates the milling tool 122 separate from the FSW tool 120. The cylindrical body of the FSW tool 120 can comprise a proximal end configured to be received in the spindle (or chuck) and a distal end comprising a pin 138. The body of the FSW tool 120 can comprise a flat, angled surface 134 (also referred to as an “outer planar surface”). The angled surface 134 can be angled with a radially inward slope toward the central longitudinal axis 136 of the FSW tool 120 moving in a direction from the pin 138 upwardly along the positive z-axis in FIG. 4A toward the spindle 128. The milling tool 122 can comprise an inner bore 140 with a diameter sized to fit around the body of the FSW tool 120. The milling tool 122 can also comprise a set screw 142 (e.g., a cup point screw). FIGS. 4B-4C illustrate assembly of the milling tool 122 onto the FSW tool 120. The set screw 142 can be positioned over and tightened against the flat, angled surface 134 of the FSW tool 120. The slope of the angled surface 134 radially inwardly toward the longitudinal axis 136 can aid in preventing loosening of the set screw 142 during milling operations. The outer profile of the angled surface 134 can be seen in the cross-sectional view of the assembled FSW tool 120 and milling tool 122 in FIG. 4C. In other examples, the FSW tool and the milling tool can be a unitary body in which the blades / teeth 141 of the milling tool are formed as part of the FSW tool body.

[0073] Referring to FIGS. 3B and 4C, the pin 138 of the FSW tool 120 can extend beyond (e.g., below) the lower (e.g., distal) edge of the milling tool 122. Thus, the pin 138 can be brought into contact with workpiece(s) to be friction stir welded without contacting the milling tool 122 to the workpiece.

[0074] Referring to FIG. 5, in some examples the WAAM tool 114 and the FSW tool 120 can be spaced apart by a specified distance L. The specified distance L can be selected to facilitate cooling and / or hardening of the metal material deposited on the workpiece by the WAAM tool 114, while allowing the FSW tool to take advantage of residual heat in the workpiece during friction stir welding. In some examples the WAAM tool 114 and the FSW tool 120 can be arranged with the WAAM tool 114 in a leading position and the FSW tool 120 in a following position such that during operation the FSW tool 120 follows in the path of the WAAM tool 114 on the workpiece in a simultaneous DED additive manufacturing and solid-state joining process. In the illustrated example the WAAM tool 114 and the FSW tool 120 are at the same height (e.g., along the z-axis), but can also be positioned at different heights and / or can be movable independently along the z- axis).

[0075] In use, the WAAM tool 114 can be used to process a workpiece and / or the WAAM tool 114 can be used to build a workpiece. The workpiece can then be repositioned using the worktable positioning system 112 and milled using the milling tool 122. The workpiece can then be processed with the FSW tool 120, for example by moving the workpiece and / or the FSW tool 120 along the path of the WAAM tool 114 between sequential material layers deposited by the WAAM tool. The FSW tool 120 can also be used to process the workpiece after additive manufacturing with the WAAM tool 114, such as by following the WAAM tool 114 across the workpiece (e.g., between layers deposited by the WAAM tool) at the specified distance / ., as illustrated in FIG. 11. The milling tool 122 can be used, for example, between layers deposited by the WAAM tool 114 (e.g., to improve joining between subsequently deposited layers) and / or to remove unneeded material and / or to shape the workpiece to final specified dimensions.

[0076] Further details of the systems and methods described herein are given in the additional examples below.

[0077] Example 2: Hybrid Manufacturing System with WAAM Tool and Combined FSW and Milling Tool

[0078] Wire-based Directed Energy Deposition (DED) technology is attractive in industry due to high productivity and large part production capability. Meanwhile, Friction Stir Processing (FSP) (also referred to as “friction stir welding” and “FSW”) is a solid-state joining process that can modify microstructure, weld lightweight alloys, minimize distortion or fabricate components. Additionally, wire-based DED printed parts need machining process to get the desired dimensional accuracy. This work proposes an integrated system that integrates wire-arc DED, FSP, and milling process together into a standalone system. The design and implementation of the system are discussed in detail, followed by demonstration of the system on an aluminum alloy. The result shows that the material processed by the system can refine the grain size from 78 pm to 1.8 pm, increase the microhardness, and enhance mechanical properties after utilizing the FSP and milling operations on top of the wire-arc DED process.

[0079] Introduction

[0080] Recently, wire-based Directed Energy Deposition (DED) has become an increasingly attractive manufacturing method for large part fabrication. It is a metal additive manufacturing (AM) method that uses welding to deposit metal in a layer-by-layer manner. Its key advantages include inexpensive feedstock and machines, ability to print fully dense large metallic components with geometric complexity, high deposition productivity, and high buy-to-fly ratio. However, wire- DED processed component has some typical issues, namely, geometrical inaccuracy andmicrostructural anomaly. The geometrical inaccuracy refers to deviation of the printed part from the geometric shape as modeled in CAD. The deviation can typically be observed on top surface of the printed part such as wrapping, waviness, and unevenness between the start and end of a deposition path. Regarding microstructure anomaly, columnar grain structure is prevalent in wire- DED processed parts, where large grains are observed to be elongated parallel or sub-parallel to the build direction due to very large thermal gradient during solidification and repeated thermal cycling. The presence of columnar grains leads to anisotropy in mechanical properties and also facilitates microcracking in wire-DED parts.

[0081] In order to improve geometric accuracy, machining techniques are often applied to machine parts to the correct dimensional accuracy. The merging of machining techniques into DED processes is referred to as hybrid additive manufacturing. Meanwhile, to alter the grain structure from columnar to equiaxed, some solutions were reported such as process plan design that accounts for thermal distribution and cycling, controlling over the process parameters resulting grain morphology evolution, using ultrasound, single point incremental forming, and rolling. Also, the use of friction stir process (FSP) as an AM method or in a hybrid AM process has been proposed recently to produce parts with equiaxed grains. Conventional FSP involves moving a rotating nonconsumable tool along the gap between two workpieces that need to be joined together. The FSP causes frictional heating that facilitates the material to undergo intense plastic deformation at elevated temperatures, which result in generation of fine equiaxed grains via recrystallization and stronger and more uniform mechanical properties. This underlying mechanism allows the FSP to join materials without the creation of a heat affected zone, and it is thus considered a solid-state welding process.

[0082] Employing FSP as a standalone AM method was also proposed to enhance the microstructure and mechanical properties of printed parts. As a sheet lamination AM method, the Friction Stir Additive Manufacturing (FSAM) method was proposed by placing a metal plate on top of a build and using the friction stir tool to weld the plate selectively onto the build in a layer-by- layer manner to manufacture part. Another standalone AM method proposed is called Friction Surfacing Additive Manufacturing (FSAM), in which a consumable rod material or feedstock through a hollow stirring tool is used in the process by rotating the consumable tool at high speed on top of the build surface to plasticize and deposit the material as the tool is moving forward.

[0083] The hybrid wire-DED / FSP / milling approach has been recently proposed to build higher performing metallic materials. Some existing systems used two robot arms to respectively perform wire-arc DED and milling of a thin wall on one stage; after printing and milling, the part wasdismounted and moved to other stage for FSP conducted by a standalone FSP machine. Another study introduced the idea that employs the milling process after wire-arc DED of a thin wall and employed a roller to support the machined part during FSP. The laser-based powder DED employing the FSP conducted by a CNC machine was investigated. In addition, another existing system applied FSP and milling to the 205A aluminum printed part, where two thin walls were printed and joined by FSP and milled to size. In all these hybrid wire-DED / FSP / milling research works, the component being built must be switched among three different systems that perform the processing steps of printing, machining, and FSP separately in each layer. Switching among different systems between layers leads to inaccurate geometry of the part after finishing due to the asynchronous coordinate systems. Additionally, this becomes very time consuming due to disassembling and fixturing.

[0084] To overcome these issues, the systems and methods described herein provide a design that integrates all the three processes together, namely wire-arc DED, FSP, and milling, inside a single machine so that these processes can be performed synchronously to modify the microstructure of the wire-arc DED-processed material and improve the performance of the wire-arc DED process.

[0085] Experiment

[0086] Figure la shows a schematic of the 5-axis GEFERTEC Arc605 machine that will be used in this work to demonstrate the development of the proposed integrated wire-DED / FSP / milling system. As shown in the figure, the machine is divided into X / Y / Z linear movement systems and A / B rotational table. FIGS. 1B-1D show details of the linear structure. On the X-frame 132, the X mounting platform 133 that mounts the welding torch is driven by a motor and moved on the linear rail. The Y system 135 moves the X stage that makes the welding torch travel in the y-direction. The height of the welding torch is controlled by the Z gantry 137 that carries both the X / Y stations. The welding torch of the GEFERTEC system is a Fronius TRANSPULS® Synergic 4000 CMT R power source.

[0087] One design consideration for implementing FSP is the substantial axial force, travel force, and torque compared with the milling tool. Axial force is one of the process parameters that produces friction and heat between the tool and the workpiece. Meanwhile, travel force is a consequence of the material resistance to the tool traveling along the stirred line. This force is mainly affected by the travel speed where an increase in speed will increase the force generation. Moreover, the torque is a result of friction between the stirring tool and the base material and directly relates to the heat input into the system. Hence higher friction and larger contact region can produce a higher torque.

[0088] The installation of the FSP and milling tools on the gantry structure of the GEFERTEC machine encounters some issues that need to be resolved. First, they are matched with the existing wire-DED machine structure. The target of this study is building an integrated system such that the welding torch, friction stir tool, and milling tool are in close proximity at a fixed distance with each other. Thus, the additional units can be jigged on the X mounting platform. Second, the axial force generated during FSP produces an opposite force along the Z axis. The force could overload the linear carriage and damage the gantry structure as a result. Third, the integrated system must be strong enough to overcome the travel force caused by FSP. The travel force depends on the height of the friction stir tool and travel speed. Therefore, an appropriate dimension for the FSP tool and suitable process parameter can be selected for preventing damage to the wire-DED machine. Additionally, the distance between the manufacturing surface and the X mounting platform can be minimized to prevent bending of the frame during FSP. Fourth, the FSP causes a high torque due to the friction between the stirring tool and workpiece, and thus a driven motor with sufficient power can be selected to rotate the FSP tool as well as the milling tool. Since higher power motor is typically heavier, FSP motor should not exceed the load bearing capacity of the DED machine. Finally, the FSP system can be designed to be easy to be jigged, dismounted, and maintained.

[0089] Based on the considerations above, a customized system that equips the FSP and milling tools is designed as shown in FIG. 2. The motor, timing pulley and belt, and spindle are arranged in a Z-shaped structure. The spindle is assembled onto the double 160x80 aluminum extrusion which is designed to be sufficiently strong and lightweight. The aluminum extrusion is linked to the linear units through Plate 1. Moreover, Plate 1 is connected to Plate 2 welded to the hooks by the M16 screws. The slot of the hooks is fit in the X mounting platform as shown in FIGS. 1 A-1D. The FSP / milling system is fabricated separately, assembled, and mounted onto the wire-DED machine gantry in the following order: (i) The hooks are mounted onto the X-mounting platform, (ii) two angle steel frames are fit into the X-frame and locked by four Ml 6 screws through the holes that are coaxial with four existing holes on the X-fame, and (iii) the M12 screws connect the FSP / milling system onto the gantry structure next to the welding torch of the wire-DED machine.

[0090] The integrated wire-DED / FSP / milling system after installation is shown in FIG. 3A. The spindle BT30 and driven asynchronous motor are mounted next to the welding torch at a horizontal distance of 25 cm apart. The manufacturing follows the processing steps in the sequence of wire- DED, milling, FSP, milling, and these steps repeat in the next print layer. Consequently, the friction stir tool and milling tool need to be switched repeatedly, which would not only interrupt the process continuity and cost more time, but also reduces manufactured accuracy because of the tool handling. In order to overcome this issue, a unique design solution is introduced herein bymodifying a surface milling tool BAP400R 63-22-4T to fit with the FSP tool (see FIG. 3B). This solution essentially combines the FSP tool and machining tool into one tool, resulting in time saving and manufacturing consistency and accuracy. FIG. 3C shows the dimensions of the friction head which has a concave shoulder and threaded pin. The FSP installed in this integrated system can be applied without any tilt angle.

[0091] A 1.2 mm diameter ER5183 aluminum alloy wire is used as the base material deposited on the 6061 -aluminum substrate of size 150x70x60mm. Chemical compositions of the 5183 aluminum alloy are indicated in Table 1. The surface of the substrate is milled and cleaned with acetone before printing to eliminate any residual oxide and grease. The deposition is conducted at 1000 mm / min of welding torch speed, 8 m / min of wire feed speed, and 15 1 / min of a high-purity argon (99.99%) as shielding gas. The distance between the tip of the welding torch and the substrate is 15 mm.

[0092] Three layers are deposited in an area of 140 mm long and 40 mm width (FIG. 6 A). After deposition, the top surface is milled of the built part to create a uniform 10 mm thickness (FIG. 6B). The FSP is performed as shown at FIG. 6C. The friction stir tool rotates in a counterclockwise direction at 900 rpm and the travel speed is 20 mm / min. After FSP, the milling process is applied again to remove the stirred flash (FIG. 6D) before wire EDM cutting.Table 1: Chemical composition of the 5183 aluminum alloys used in the current study (wt. %)

[0093] A tensile bar and a small cube are extracted from the block longitudinally along the center of the friction stirred line using the Mitsubishi MV2400S - Advanced Type 3 EDM system. A schematic diagram of the sample is illustrated in FIG. 6E, while the dimensions of the tensile bar is shown in FIG. 6F.

[0094] One side of cross-section surface of the cube is polished and electro etched to reveal the melt pool of the deposited material and weld zone of the FSP. The other side was mirror polished and chemical etched to observe grain structure by EBSD. The other cube was mirror polished and measured microhardness by AMH55 LECO micro indentation hardness testing system.

[0095] Results and Discussion

[0096] Weld appearance can be an important characteristic of a high-quality friction stirred weld. FIGS. 7A-7B indicate the weld appearance including surface appearance and transverse cross section perpendicular to weld line. FIG. 7A shows the surface morphology of the friction stirred weld that is formed beneath the tool shoulder. It has a clean appearance with uniform width and no obvious surface defects. These features of the stirred surface may be because of large contact surface between the friction tool shoulder and the deposited material which causes more frictional heat. The higher generated heat and better mixing of the material through the stirring may be the reason for the smooth appearance.

[0097] FIG. 7B illustrates the macroscopic appearance of the cross-section of the FSP on the deposited wire-arc DED material. It reveals clearly between the stirred zone and melt pool of wirearc DED material. It is apparent that the stirred interior itself exhibits a high degree of continuity and no voids. Heating generated during FSP and intense plastic deformation can result in generation of a recrystallized fine-grained microstructure within stirred zone. This area is usually known as the nugget zone or weld nugget illustrated by the dashed white line. The nugget zone widens near the top surface where it experiences extreme deformation and frictional heating by contact with the friction tool shoulder during processing. In some examples formation of the nugget zone can depend on the friction process parameters and thermal conductivity of the deposited material. The explanation was because of the process of friction heating due to the rotation of the tool and the forward movement extrudes the material around to the retreating side of the tool. It also reveals the heat affected zone indicated by the darker color between the nugget zone and the deposited material and bounded by the solid-white line.

[0098] FIGS. 8A-8B indicate the EBSD grain structure at position of the as-built material (FIG. 8A) and nugget zone (FIG. 8B). The region of deposited material shows a typical columnar structure that follows the thermal gradient of the melt pool. It has a relatively coarse grain structure of which the average grain size is 71 pm. Meanwhile, the microstructure in the nugget region is different from the parent material. Grain size of the nugget zone is 1.8 pm, which is drastically smaller than the deposited material. FSP generates mechanical and thermal processes that include material flow with the stirring tool rotation, heating and cooling steps. The plastic deformation and thermal exposure during friction stir processing induce the occurrence of dynamic recrystallization (DRX) in the nugget zone. There are some major grain evolution mechanisms including continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX). The former one is the formation of new grains by the gradual misorientation increase of the subgrains.The latter mechanism includes nucleation and growth of strain-free grains, where the new grain in the nugget zone were smaller than the original subgrains.

[0099] Horizontal profile of Vickers hardness in the weld are indicated in FIGS. 9A-9B. The positions of profile indicated in FIG. 9A. There is considerable hardening in the nugget region compared to the deposited material. The stirred region had an average hardness of about 113 Hv which is much higher than that of the deposited material that is about 87 Hv. There is no significant variation in the horizontal hardness profile of nugget region. Following the Hall-Petch relationship, the increase in hardness in the nugget region is caused by the fine recrystallized grain structure. FIG. 9B additionally indicates the heat affected zone where the profile is inclined.

[0100] The Young’s modulus, yield strength and ultimate tensile strength of the tensile samples extracted from the deposition are shown in FIG. 10. The Young’s modulus of the as-deposited with FSP is 52.3 GPa, which is higher than the printed part without FSP at 46.9 GPa. A similar trend is observed in the yield strength where the FSP increases from a value of 155 MPa to 226 MPa. The ultimate strength of the printed part conducted by FSP is 350 MPa which is higher than the as- deposited without FSP at 308 MPa. Moreover, the elongation of the wire-DED part with FSP is 10.6% higher than the one without FSP at 6.8%.

[0101] With FSP, the wire-arc DED processed aluminum 5183 shows vastly different microstructure with refinement of the grain size from 78 pm to 1.8 pm, which is caused by the transformation of the grain morphology from fully columnar to fully equiaxed. More importantly, the Young’s modulus, yield strength, and ultimate strength are significantly enhanced. The high strength of the printed part with FSP is most likely related to grain boundary strengthening. According to the Hall-Petch relationship, the reduction in the grain size results in an increase in the strength of the material. The extent of the strengthening is estimated by:

[0102] where <J0and is the constant of the natural resistance of the Al lattice to dislocation motion, and KHau-petch= 140 (Pa / pm1 / 2). According to the formula, finer grains lead to higher strength.

[0103] An integrated system combining wire-based DED, FSP, and subtractive milling has been successfully developed and employed to build Al 5183. The microhardness, microstructural properties, and mechanical properties are investigated. The microstructure of the wire-arc DED deposited material has a typical columnar grain structure due to thermal gradient. FSP can refine grain size to equiaxed grains drastically. Compared to the as-built counterpart, the microhardness of part employed the FSP was increased by 114 Hv. The result of mechanical properties of the samplewith FSP show that Young’s modulus, yield strength, and ultimate strength and elongation are all higher than the as-deposited part.

[0104] Wire-based DED can be similar to welding, and thus large residual stress and distortion is a common issue. Using a localized high-intensity energy source to melt metal wire, the temperature of the material around the melting zone rises rapidly compared to the surrounding material which causes larger thermal gradients around the deposition. The hot material expansion is restricted by the surrounding cold material, which develops compressive stresses in the region. During cooling, the hot material shrinks and is restricted by surrounding material, resulting in tensile stresses in the part. Additionally, in the case of multiple-layer processing, heat accumulation is progressively developed, and a large amount of heat is accumulated at the end of the built part. Moreover, the substrate can undergo many heating and cooling cycles during the deposition process. This non- uniform variation of temperature can result in thermal imbalance leading to thermal stress in the substrate. When the component is ungripped, some of the stresses are relieved and result in distortion and some are retained in the component and are known as residual stresses. While the residual stress in the printed part affects the component performance, the distortion of the substrate leads to dimensional inaccuracy.

[0105] The distortion can be managed by selecting process parameters such as voltage, current, wire feed rate, and / or travel speed. Heat treatment is one method to reduce residual stress and distortion of the substrate. Substrate preheating or secondary localized preheating can be used to reduce the cooling rate, which can result in smaller thermal gradient and residual stress. Although it is possible to subject a printed part with clamped substrate to heat treatment in a furnace to relieve thermal residual stress, thermal post-processing is costly and time consuming for large parts produced by wire DED processes.

[0106] In order to demonstrate the effect of FSP on residual stress and distortion, two 10-layer wire-arc DED deposition sample builds 202 and 204 that were 175 mm long and 40 mm wide were deposited on respective substrates 206 and 208 that were 300 mm long, 100 mm wide, and 10 mm thick as shown in FIGS. 12A and 12B. The FSP was conducted after every deposited layer on sample 204. The deformations of the builds with and without FSP are shown in FIGS. 12A and 12B. Both substrates were clamped at one end to illustrate the distortion at the other end (see FIG. 12A). FIG. 12B shows that the vertical distortion of the substrate 208 of the build 204 with FSP is 1 mm smaller than the substrate 206 of the build 202 without FSP. This reduction can be explained by the re-heating effect induced by FSP in that the temperature generated by the FSP tool reaches 75%-80% of the material melting point. This temperature relieves the residual stress formed by thewire-arc DED process, resulting in smaller distortion on the substrate 208. Additionally, the side views in FIG. 12A reveal the variation in the height of the two blocks 202 and 204. Comparing the designed experiment in which the layer thickness is 2 mm, the DED deposition with FSP is closer to the desirable dimension than the one without. This experiment demonstrated that FSP can greatly reduce residual stress and distortion and contribute to dimensional accuracy of the final part.

[0107] The hybrid manufacturing systems and methods described herein can provide a number of significant advantages over existing systems. For example, incorporating a DED manufacturing tool, a solid-state joining process tool, and a subtractive machining tool in one machine allows a workpiece to be processed with any of the tools in sequence and / or simultaneously without the need to transfer the workpiece between different machines. This can improve not only efficiency but also dimensional accuracy because the workpiece does not have to be dismounted and remounted in different machines for each process. Friction stir welding materials that have been deposited or joined by DED additive manufacturing can also improve the mechanical properties of the resulting part. For example, a weld produced with WAAM followed by FSW can exhibit sufficiently high strength properties that post-processing heat treatment is not required. This can be particularly advantageous for large parts for which sufficiently large heat treatment furnaces may not be available. Additionally, co-locating a DED additive manufacturing system and FSW tool can facilitate friction stir welding of high temperature materials at a higher rate of speed and more efficiently because the FSW tool can take advantage of the residual heat in the workpiece from the DED process. The systems described herein can also facilitate stronger joints between dissimilar materials by stirring the dissimilar materials at the interface after deposition by wire-arc DED.

[0108] Example 3: Integrated Hybrid Wire- Arc Directed Energy Deposition, Friction Stir Processing, and Milling System for Multi-Track, Multi-Layer Part Manufacturing

[0109] Wire-based Directed Energy Deposition (DED) is a widely-used manufacturing method due to its high productivity and large part fabrication capability. Meanwhile, Friction Stir Processing (FSP) (also referred to herein as “friction stir welding”) is a solid-state joining process that can modify microstructure and weld lightweight alloys. Additionally, wire-based DED printed parts may benefit from machining process to achieve the desired dimensional accuracy. To take advantage of all these three processes, the present application proposes an integrated hybrid system by combining the wire-arc DED, FSP, and milling processes into a standalone system which can fabricate superior materials in a multi-track, multi-layer manner for the first time. The integrated system can improve dimensional accuracy and productivity by processing the workpiece without the need to move it between different systems. It is demonstrated that a 150x40^21 mm3block ofaluminum alloy AA5183 can be fabricated using the hybrid wire-DED / FSP / milling process from wire feedstock. Material characterization shows that the hybrid process is able to refine the grain size by two orders of magnitude to sub-micron scale, while eliminating or substantially eliminating all the pores and microcracks produced by the DED process. These enhancements result in significantly improved mechanical properties including Young’s modulus (15%), yield strength (161%), ultimate strength (33%), and hardness (55%) without compromising ductility.

[0110] Introduction

[0111] Recently, wire-based Directed Energy Deposition (DED) has become an increasingly attractive manufacturing method for large part fabrication. The wire-DED process is a metal Additive Manufacturing (AM) method that uses welding to deposit metal in a layer-by-layer manner. Its advantages include inexpensive feedstock and machines, ability to produce fully dense large metallic components with geometric complexity, high deposition rate, and high buy-to-fly ratio. However, wire-DED processed materials can experience large heat input and slow cooling rate, which can result in large residual stress and warping. Also, the large thermal gradient during solidification and repeated thermal cycling in the process leads to large columnar grains, which elongate parallel or sub-parallel to the build direction. The columnar grains not only lead to anisotropic mechanical behavior but can also facilitate microcracking in wire-DED parts.

[0112] Recent advancements in the hybridization of WAAM with FSP have focused on improving mechanical properties, microstructure and surface quality. The hybrid approach can address the inherent challenges in wire-DED processed materials, such as poor surface finish, porosity, residual stress, and anisotropic mechanical properties. By hybridizing wire-DED and FSP, researchers have demonstrated significant improvements in the final part properties. For instance, some existing systems use two robot arms to respectively perform wire-arc DED and milling of a thin wall on one stage and other stage for FSP conducted by a standalone FSP machine. Laser-based powder DED employing FSP conducted by a CNC machine has also been investigated. In addition, other existing systems applied FSP and milling to a 205A aluminum printed part, where two thin walls were printed and joined by FSP and milled to size. However, multi-layer, multi -track bulk samples have not been realized to date.

[0113] In all the past hybrid wire-DED / FSP / milling research works, the component being built must be switched sequentially among three different systems to perform the independent processing steps (DED, machining, and FSP) separately in each layer. Switching among different systems between layers results in lower dimensional accuracy in the fabricated part. Additionally, switching is time consuming due to disassembling and fixturing and becomes more difficult withbuild height as thermal stress and distortion both increase. Although the concept of developing a system that can fabricate without switching component has been introduced, setting up three robots to perform welding, milling and FSP simultaneously to process a component is quite complicated in terms of implementation and control.

[0114] To address this issue, this work proposes an innovative concept of a hybrid system, where the wire-DED, milling and FSP processes are integrated into one standalone system. In particular, these processes can be performed synchronously and continuously to manufacture parts with enhanced microstructure and mechanical properties. The ability of the proposed hybrid system has been demonstrated by producing a multi-layer, multi -track AA5183 block with much improved microstructure and mechanical properties compared to its DED-processed counterpart.

[0115] Experimental Methods: System Design and Implementation

[0116] FIGS. 13A-13D show a schematic of the 5-axis GEFERTEC Arc605 machine used in this work to demonstrate development of the proposed integrated wire-DED / FSP / milling system. As shown in FIGS. 13A-13D, the machine includes X / Y / Z linear movement systems (also referred to as “stages”) and an A / B rotational table (also referred to as a “worktable”). The welding torch is attached on the X-frame (also referred to as the “X-axis stage”) that is positioned on the Y-frame (also referred to as the “Y-axis stage”). The height of the welding torch is controlled by the Z gantry (also referred to as the “Z-axis stage”) that carries both the X / Y stations.

[0117] The implementation of the hybrid system faces some challenges. First, they are compulsorily matched with the existing wire-DED machine structure. In some examples, the additional units are mounted on the X mounting platform, but could be mounted on the Y platform or the Z gantry. Second, the axial force generated during FSP produces an opposite force along the Z axis. The force could overload the linear carriage and damage the gantry structure as a result. Third, the integrated system must be strong enough to overcome the FSP travel force that depends on the height of the friction stir tool and travel speed. Therefore, selecting an appropriate dimension for the FSP tool and suitable process parameter can help prevent damage to the machine. Additionally, the distance between the manufacturing surface and the X mounting platform can be minimized to help prevent bending of the machine frame during FSP. Fourth, a driven motor power must be sufficient to rotate the FSP tool but should not exceed the load bearing capacity of the DED machine. Finally, the FSP assembly should be designed for the tool to be easily mounted, dismounted, and maintained.

[0118] Based on the considerations above, a customized assembly equipped with the FSP and milling tools is designed and implemented, see FIGS. 13A-13B. The motor, timing pulley and belt,and spindle are arranged in a Z-shaped structure. The spindle is assembled onto the double 160^80 aluminum extrusion which is designed to be strong and lightweight. The aluminum extrusion platform is connected to the linear carriages on Plate 1, which is connected to Plate 2 by Ml 6 screws. The new unit is hooked and fixed onto the X mounting platform.

[0119] The FSP / milling tool assembly is fabricated separately, assembled, and mounted onto the gantry of the machine as shown in FIG. 13B. The tool holder is designed to allow for the milling operation and FSP operation to change quickly. The tool assembly is mounted next to the welding torch at a horizontal distance of 25 cm apart. FIGS. 13C and 13D show the cross-sectional view of the combined milling and FSP tool design with exemplary dimensions. The FSP tool (StirWeld, France) has a spiral shoulder and threaded pin.

[0120] Materials and Methods

[0121] A 1.2 mm diameter AA5183 wire was used as the feedstock material deposited on the Al 5083 substrate. The chemical composition of the AA5183 is shown in Table 2. The surface of the 200x 100x 10 mm3substrate was milled and cleaned with acetone before printing to eliminate any residual oxide and grease. A block was built by depositing ten layers with a surface area of 150x40 mm2using wire-DED alone. The deposition was conducted using a Fronius TRANSPULS® Synergic 4000 CMT R power source at 1000 mm / min of welding torch speed, 8 m / min of wire feed speed, and 15 l / min of a high-purity argon (99.99%) as shielding gas. The stick-out length was set to 15 mm. These process parameters have been optimized by the wire-DED machine manufacturer GEFERTEC for processing AA5183 following their standard procedure. A second block was built to the same dimensions using the proposed hybrid DED / FSP / milling process. FIGS. 14A-14D show the four steps of the hybrid process together with a schematic of the thickness reduction in each step. After the DED deposition of a material layer at a track distance of 3 mm (FIG. 14A), the top surface of the built part is milled (FIG. 14B) to create a uniform 2.5 mm thickness to facilitate the FSP step (FIG. 14C). The friction stir tool is set to rotate in a clockwise at 900 rpm with a travel speed of 100 mm / min.

[0122] Table 2: Chemical composition of the AA5183 used in the current study (wt. %)

[0123] The FSP parameters utilized in this work have been recommended by the FSP tool supplier (StirWeld, France) based on their own process optimization procedure. The distance of two adjacent FSP lines in a layer was set to 3 mm and the thickness between two FSP consecutive layers was set to 2 mm. The FSP tool plunge depth, defined as the penetration depth by the tool shoulder into the surface of workpiece, was 0.5 mm. The total penetration of the FSP tool (including the pin length of 3.2 mm) was 3.7 mm, while the layer-overlapping distance was 1.2 mm. The FSP process was applied to the material with no tilt angle. After FSP, the milling process was applied again to smooth the stirred surface by removing the debris (FIG. 14D). The total reduction of bead height after FSP and milling combined was roughly 1 mm. Once the block was fully built by the hybrid process, wire EDM (Mitsubishi MV2400S - Advanced Type 3) was used to extract two tensile bars and a 15x 10x 10 mm3cuboid for microstructure characterization. A schematic diagram of the locations of the specimens is shown in FIG. 14E and the tensile bar dimensions are shown in FIG. 14F.

[0124] The tensile testing was conducted using the MTS880 system at a 0.6 mm / min strain rate. Before microstructure characterization, the surface of the cubic samples was ground using a 1200 grit SiC paper and then polished with diamond and colloidal silica suspensions. Electro etching was then applied to reveal melt pools of the deposited material and nugget zone of the FSP, which were captured by a digital microscope- VHX-7000N. Detailed microstructures of the as-built and hybrid samples were characterized by using the ThermoFisher Apreo HiVac Scanning Electron Microscope (SEM) and Electron Backscatter Diffraction (EBSD). Vickers microhardness was measured by the AMH55 LECO micro indentation hardness testing system under a load of 100 g.

[0125] Results and Discussion: Weld Appearance

[0126] FIG. 15 shows the blocks fabricated by the wire-DED process and the hybrid process, respectively. The block produced by wire-DED (left side of FIG. 15) is approximately 10 mm thicker than the CAD model and has a dome shape at the top instead of a flat surface. This is caused by the higher residual heating and lower cooling rate near the edge, resulting in a lower bead height near the edge compared to the center. On the other hand, applying the milling process to smooth the top surface of each wire-DED deposited layer, the layer height of the hybrid- processed block (right side of FIG. 15) becomes consistent. It is evident that the hybrid system can enhance dimensional accuracy of the final part.

[0127] FIGS. 16A-16D illustrate detailed views of the transverse cross-section perpendicular to weld tracks of the two blocks without FSP (FIGS. 16A and 16B) and with FSP (FIGS. 16C and 16D). The melt pool boundaries of weld tracks and large pores (-100 pm in size) can be observedin FIG. 16A. A close-up view (FIG. 16B) at two melt pool boundaries reveals several microcracks and pores. These microcracks have been observed in wire-arc DED processing of the AA5183 alloy, which was attributed to the combined effects of thermal stress, unfavorable columnar grains, and long solidification intervals. The black dashed curves in FIGS. 16A-16D indicate the melt pool boundaries. The black solid arrows indicate pores, while the black dashed arrows denote the microcracks. The areas of 1 to 5 indicated in FIGS. 16A and 16C are for subsequent EBSD analysis.

[0128] FIG. 16C illustrates the macroscopic appearance of the transverse cross section of the material fabricated by the hybrid process, revealing the distinct FSP track boundaries. It can be observed that the friction stirred zone is fully overlapped with a high degree of continuity and no apparent defects, indicating that the voids and microcracks seen in DED-processed material are all removed. During the FSP process, the shoulder applies a high downward force and a frictional force along the tool rotation direction to generate heat which stays below the melting point. Moreover, the rotating pin stirs the softened material, causing it to flow and close the voids and microcracks under high compressive stress. As shown in FIG. 16D, the appearance of the FSP nugget zone has an onion ring shape often seen in conventional FSP. The nugget pattern is caused by frictional heating from the rotation of the threaded FSP tool and the forward movement which extrudes material around to the retreating side of the tool.

[0129] Microstructure

[0130] FIGS. 17A-17E illustrate the grain structure obtained by EBSD at different locations on the cross section of the DED-processed material (FIGS. 17A-17B) and hybrid-processed material (FIGS. 17C-17E)) corresponding to the areas numbered 1 to 5 in FIGS. 16A-16D, respectively. The center of the melt pool in the DED-processed material (FIG. 17 A) has a typical columnar structure with a mean grain size of 91.6 pm. The grain structure image in FIG. 17B is taken at the intersection of three melt pools (indicated by dashed curves), where columnar grains are observed in the two adjacent melt pools on top and equiaxed grains in the melt pool at the bottom with a mean grain size of 60.6 pm. This is also expected since the thermal gradient is smaller at the top of the melt track compared to the bottom, thus promoting the formation of equiaxed grains. Additionally, FIGS. 17A-17E include electron backscatter diffraction (EBSD) images and grain size distribution plots of the deposited material at a melt pool (FIG. 17A) and melt pools boundaries (FIG. 17B), and FSP regions at the nugget center (FIG. 17C), the boundary between adjacent FSP lines (FIG. 17D) and layers (FIG. 17E). The black-dash curves indicate the melt pool boundaries.The average grain size (AGS) and standard deviation (SD) are marked in the grain size distribution subplot.

[0131] Meanwhile, the microstructure of the hybrid-processed material is drastically different from that of the DED-processed material. The grain structure and size distribution at the nugget center, between adjacent FSP tracks, and between deposited layers are shown in FIGS. 17C, 17D, and 17E, respectively. The mean grain sizes in these locations are respectively 0.58 pm, 0.78 pm, and 0.73 pm, which are two orders of magnitude smaller than those in the DED-processed material and can be attributed to dynamic recrystallization caused by the friction stirring process. The degree of grain refinement and grain size variation are consistent with results obtained by applying FSP to conventional aluminum alloys. The kernel average misorientation (KAM) and pole figure (PF) under the hybrid DED / FSP conditions are illustrated in FIGS. 18A-18F. The KAM measures the average misorientation of a point within a grain relative to its neighboring points, serving as an indicator of dislocation density. It is evident that misorientations primarily occur near the grain boundaries, with values remaining low in the grain interiors (FIGS. 18A-18C).

[0132] The inverse pole figure (IPF) map (FIGS. 17A-17E) and the PF (FIGS. 18D and 18E) show a randomly oriented arrangement of sub-micron grains, separated by large-angle grain boundaries. The precise mechanisms underlying the formation of fine grain structures during FSP is still not fully understood since the process is challenging to analyze in situ and only the final microstructure can be examined. To date, these grain structures have often been attributed to dynamic recrystallization. It has been suggested that the fine grains develop during the stirring action, driven by the rotation of existing sub-grains within the parent structure. This process likely also involves dynamic recovery (DRV) and geometrical dynamic recrystallization (GDRX), owing to the high stacking fault energy of aluminum and its alloys. In the DRV phase, the recovery rate increases with rising dislocation density, leading to the rearrangement of dislocations into low- angle boundaries and the formation of subgrains. At steady state, these equiaxed subgrains are nearly dislocation-free in their interiors and maintain a consistent subgrain size and boundary misorientation. The initiation of GDRX occurs as strain increases during DRV, particularly when the separation of previous boundaries approaches the size of the subgrains. The boundaries can annihilate each other, and the parent grain effectively divide into new grains. The ellipsoidal shape of the grains in the nugget center, would require further investigation into its formation mechanism. The grain size variation with locations leads to hardness variation, which is discussed next.

[0133] Microhardness

[0134] FIG. 19A shows a cross section of the hybrid block with horizontal and vertical dashed lines along which microhardness is measured, where the results are shown in FIG. 19B and 19C, respectively. The hybrid-processed material has considerably higher hardness than the DED- processed material. While the mean hardness of the DED-processed material is 90 HV, the hybrid- processed regions along the horizontal line (FIG. 19B) and vertical line (FIG. 19C) and have hardness values of 117-136 HV and 128-148 HV, respectively.

[0135] Along the horizontal line within a FSP track, the hardness attains a maximum value at the center of the track and decreases very slightly toward the boundary, but it decreases sharply as the distance becomes 0.2-0.8 mm away from the boundary (between two adjacent tracks) and finally decreases to a minimum at the boundary. Along the vertical line within a FSP track, the hardness value is at a maximum at about 0.8 mm above the boundary between horizontal layers (e.g., at the nugget center), decreases nearly linearly with slight fluctuations toward the boundary, and drops to a minimum at the boundary. The variations within each FSP track along the horizontal and vertical are generally consistent among the different tracks measured.

[0136] The hardness variation can be explained by the grain size observed in previous sub-section according to the Hall-Petch relationship, which states that finer grains lead to increased hardness. Here the largest measured hardness value is found to be precisely in the nugget center which is where the smallest grain size is observed (FIG. 17C). The hardness value measured at the boundary between horizontal layers is larger than that at the boundary between adjacent FSP tracks, which is also consistent with the measured grain sizes at these two respective locations (FIGS. 17D and 17E).

[0137] Mechanical Properties

[0138] The stress-strain curves of the tensile specimens extracted from the hybrid- and DED- processed walls are shown respectively in FIG. 20A. A comparison of the Young’s modulus, yield strength, and ultimate strength of these tensile specimens is shown in FIG. 20B. It can be observed that the Young’s modulus of the hybrid-processed material is 67.8 GPa, which is 15% larger than the DED-processed one at 58.7 GPa. The hybrid-processed material also improves the yield strength from 158 MPa to 413 MPa (161% increase) and ultimate strength from 318 MPa to 422 MPa (33% increase). Moreover, the elongation also sees a slight increase from 24.4% to 25.4% using the hybrid process when compared with the DED process. As a comparison, AA5083 plate processed by FSP reaches a yield strength of 165 MPa, ultimate strength of 300 MPa, and hardnessof 117 HV. Therefore, the AA5183 produced by the proposed hybrid process can achieve an improvement of 250% in yield strength, 40% in ultimate strength, and 26% in hardness.

[0139] The significant enhancement of mechanical properties can be attributed to the refinement of grain size from 91.6 pm to sub-micron scale using FSP, which represent an increase of two orders of magnitude. The refined grains increase the strength of the hybrid-processed material according to the Hall-Petch relationship, which states that the yield strength is inversely proportional to the square root of the grain size. Finer grains provide more grain boundaries, which serves as obstacles to dislocation movement, enhancing the hybrid material strength. Additionally, the mechanical stirring and heat generated during FSP consolidate the material by eliminating pores and microcracks, which can improve the ductility of the material.

[0140] Comparison with FSAM

[0141] The most similar AM method to the proposed hybrid process is the Friction Stir Additive Manufacturing (FSAM), whose consumable friction stir tool is also used as the feedstock to deposit the material. Compared with FSAM, the proposed hybrid process has both advantages and disadvantages. The hybrid process would take several times longer to produce the same quantity of materials since it involves three different processing steps within one layer of deposition.However, since the feedstock to the hybrid process uses a wire of ~1 mm diameter, which is typically much smaller than the FSAM consumable tool bar diameter (typical 1-2 cm), the hybrid process can potentially produce parts with geometric features which are one order of magnitude finer. Since the FSP tool tip (3 mm diameter) used in the hybrid process is much smaller than the FSAM tool diameter, the grain size produced by the former is expected to be smaller as well. The grain size in AA5083 produced by FSAM is 2-3 pm, which is indeed 3-4 times larger than that produced using the hybrid process. As a result, the yield strength (148-273 MPa), ultimate strength (165-362 MPa), and hardness (86-135 HV) of F SAM-processed AA5083 are also smaller than those produced by the hybrid process.

[0142] Conclusions

[0143] This work proposes a unique integrated system which combines wire-DED, FSP, and subtractive milling. An independent motor and spindle mechanism that drives a combined FSP and milling tool has been designed and installed next to the welding torch in a commercial wire-DED machine. The system was successfully developed and employed to fabricate a 150x20x21 mm3block made of AA5183. Microhardness, microstructural, and mechanical properties of the block are investigated. The systems and methods described herein can provide the following features and advantages. The proposed system can perform wire-arc DED, milling, FSP sequentially, withoutchanging the tools or moving the workpiece, to produce fully dense multi-track, multi-layer bulk samples. The hybrid process is able to completely remove the pores and microcracks generated by the DED process. The hybrid process changes the grain texture from mostly columnar in the DED material to fully equiaxed grains, while also reducing the grain size drastically from 91.6 pm to the sub-micron scale in the hybrid-processed material, representing a two orders of magnitude refinement. The grain refinement and elimination of pores and microcracks leads to significantly improved mechanical properties including Young’s modulus (15%), yield strength (161%), ultimate strength (33%), and hardness (55%) without compromising ductility. Future studies will focus on fabrication of complex parts using the hybrid system, optimization of processing speed, and investigation of microstructure and material properties obtained using different process parameters.

[0144] Example 4: Hybrid Manufacturing System with Reinforcement and Vibration Damping

[0145] FIG. 21 A shows a schematic of the frame, where the X-axis stage (also referred to as the “X-axis mounting platform” and the “X-axis frame”) is coupled to (e.g., on top of) and movable with a Y-axis stage (also referred to as the “Y-axis frame”). The X- and Y-axis stages are leveled (e.g., movable up and down along the Z-axis) by a Z-axis stage or actuator system. The tool head, and thus the FSP unit, the milling too, and the WAAM tool, are mounted on the X mounting platform as shown in FIG. 2 IB. The Z axial force generated during FSP produces an opposite force along the Z-axis direction. The combination of the force and rotational moving of the FSP tool can result in oscillation and vibration of the system, which in some cases can be due to weakness of the joints between the X-axis stage frames and the Y-axis stage linear rails and bearings that is marked by the dashed oval in FIG. 2 IB. In order to make the system more rigid, reinforcement members such as frames, metal plates, and angle bars can be added to support the connection between the X- axis stage frame and the Y-axis stage frame as illustrated in FIG. 22A. In the illustrated example, the metal plate 1 was welded to connect the X-axis stage frame and the Y-axis stage linear moving rail as shown in FIG. 22C to help make the connection sturdier. Moreover, four steel angles (also referred to as “angle bars”) were welded into the X-axis stage frame. The other ends of the frames were welded into the metal Plate 2 that is mounted on additional linear units. The X-axis stage frame, plate 1 and plate 2, and the angle bars create a triangle structure that stabilizes the system during processing. The implementation of the reinforcement is shown in FIGS. 22B and 22C.

[0146] Additionally, in some examples the workpiece can be held stationary on the worktable during building with the WAAM tool, processing with the friction stir welding tool, and / or duringmilling with the milling tool, and the various tools can move around the workpiece as needed during production and processing.

[0147] Additional Examples of the Disclosed Technology

[0148] In view of the above-described implementations of the disclosed subject matter, this application discloses the additional examples enumerated below. It should be noted that one feature of an example in isolation or more than one feature of the example taken in combination, and optionally, in combination with one or more other features of one or more further examples are further examples also falling within the disclosure of this application. Additionally, the dimensions shown in the drawings are merely examples and are not intended to be limiting.

[0149] Example 1. A hybrid manufacturing system, comprising: a tool positioning system; a worktable for supporting a workpiece; a tool head coupled to the tool positioning system and movable relative to the worktable with the positioning system; a directed energy deposition (DED) tool coupled to the tool head; a friction stir welding (FSW) tool coupled to the tool head; and a subtractive machining tool coupled to the tool head.

[0150] Example 2. The hybrid manufacturing system of any example herein, particularly example1, wherein the subtractive machining tool is a milling tool.

[0151] Example 3. The hybrid manufacturing system of any example herein, particularly example2, wherein the FSW tool comprises a spindle coupled to the tool head, and the milling tool is coupled to the spindle of the FSW tool.

[0152] Example 4. The hybrid manufacturing system of any example herein, particularly example3, wherein the milling tool is mounted to the FSW tool coaxially with the FSW tool.

[0153] Example 5. The hybrid manufacturing system of any example herein, particularly example4, wherein the FSW tool comprises a cylindrical body having an outer planar surface, and a set screw extends through the milling tool and engages the outer planar surface of the cylindrical body to secure the milling tool to the FSW tool.

[0154] Example 6. The hybrid manufacturing system of any example herein, particularly example5, wherein the outer planar surface is inclined radially inwardly toward a longitudinal axis of the FSW tool in a direction from a distal tip of the FSW tool toward the spindle.

[0155] Example 7. The hybrid manufacturing system of any example herein, particularly any one of examples 1-6, wherein the FSW tool and the subtractive machining tool are spaced apart from the DED tool by a specified distance and configured to follow the DED tool along a workpiece during operation.

[0156] Example 8. The hybrid manufacturing system of any example herein, particularly any one of examples 1-7, wherein the DED tool is a wire arc additive manufacturing (WAAM) tool comprising a torch and a wire supply.

[0157] Example 9. The hybrid manufacturing system of any example herein, particularly any one of examples 1-8, wherein: the tool positioning system comprises an X-axis stage, a Y-axis stage, and a Z-axis stage; the X-axis stage is coupled to and movable with the Y-axis stage; and a plurality of reinforcement members extend between the X-axis stage and the Y-axis stage and are configured to reduce vibration of the X-axis stage and the Y-axis stage during operation.

[0158] Example 10. The hybrid manufacturing system of any example herein, particularly example 9, wherein the reinforcement members include plates and angle bars.

[0159] Example 11. The hybrid manufacturing system of any example herein, particularly any one of examples 1-10, wherein the subtractive machining tool is removably attachable to the FSW tool, or wherein the subtractive machining tool and the FSW tool are a unitary body.

[0160] Example 12. A method, comprising processing a workpiece with the hybrid manufacturing system of any example herein, particularly any one of examples 1-11.

[0161] Example 13. A hybrid manufacturing system, comprising: a tool positioning system; a worktable for supporting a workpiece; a directed energy deposition (DED) tool coupled to the tool positioning system; a friction stir welding (FSW) tool coupled to the tool positioning system; and a milling tool coupled to the FSW tool.

[0162] Example 14. The hybrid manufacturing system of any example herein, particularly example13, wherein the FSW tool comprises a spindle coupled to the tool head, and the milling tool is coupled to the spindle of the FSW tool.

[0163] Example 15. The hybrid manufacturing system of any example herein, particularly example14, wherein the milling tool is mounted to the FSW tool coaxially with the FSW tool.

[0164] Example 16. The hybrid manufacturing system of any example herein, particularly example15, wherein the FSW tool comprises a cylindrical body having an outer planar surface, and a set screw extends through the milling tool and engages the outer planar surface of the cylindrical body to secure the milling tool to the FSW tool.

[0165] Example 17. The hybrid manufacturing system of any example herein, particularly example16, wherein the outer planar surface is inclined radially inwardly toward a longitudinal axis of the FSW tool in a direction from a distal tip of the FSW tool toward the spindle.

[0166] Example 18. The hybrid manufacturing system of any example herein, particularly any one of examples 13-17, wherein the FSW tool and the subtractive machining tool are spaced apart from the DED tool by a specified distance and configured to follow the DED tool along a workpiece during operation.

[0167] Example 19. The hybrid manufacturing system of any example herein, particularly any one of examples 13-18, wherein the DED tool is a wire arc additive manufacturing (WAAM) tool comprising a torch and a wire supply.

[0168] Example 20. A friction stir welding tool, comprising: a cylindrical body having a proximal end and a distal end; a pin located at the distal end; and a milling tool on the body of the friction stir welding tool and configured to rotate together with the body of the friction stir welding tool.

[0169] Example 21. The friction stir welding tool of any example herein, particularly example 20, wherein the milling tool is mounted to the friction stir welding tool coaxially with the friction stir welding tool.

[0170] Example 22. The friction stir welding tool of any example herein, particularly example 21, wherein the cylindrical body of the friction stir welding tool comprises an outer planar surface, and a set screw extends through the milling tool and engages the outer planar surface of the cylindrical body to secure the milling tool to the friction stir welding tool.

[0171] Example 23. The friction stir welding tool of any example herein, particularly example 22, wherein the outer planar surface is inclined radially inwardly toward a longitudinal axis of the friction stir welding tool in a direction from a distal tip of the friction stir welding tool toward the spindle.

[0172] Example 24. The friction stir welding tool of any example herein, particularly any one of examples 20-23, wherein the milling tool is removably attachable to the friction stir welding tool, or wherein the milling tool and the friction stir welding tool are a unitary body.

[0173] In view of the many possible embodiments to which the principles of the disclosed technology may be applied, it should be recognized that the illustrated embodiments are only examples and should not be taken as limiting the scope of the disclosure. Rather, the scope of the disclosure is at least as broad as the following claims and equivalents of the recited features. We therefore claim all that comes within the scope and spirit of these claims.

Claims

CLAIMS:

1. A hybrid manufacturing system, comprising: a tool positioning system; a worktable for supporting a workpiece; a tool head coupled to the tool positioning system and movable relative to the worktable with the positioning system; a directed energy deposition (DED) tool coupled to the tool head; a friction stir welding (FSW) tool coupled to the tool head; and a subtractive machining tool coupled to the tool head.

2. The hybrid manufacturing system of claim 1, wherein the subtractive machining tool is a milling tool.

3. The hybrid manufacturing system of claim 2, wherein the FSW tool comprises a spindle coupled to the tool head, and the milling tool is coupled to the spindle of the FSW tool.

4. The hybrid manufacturing system of claim 3, wherein the milling tool is mounted to the FSW tool coaxially with the FSW tool.

5. The hybrid manufacturing system of claim 4, wherein the FSW tool comprises a cylindrical body having an outer planar surface, and a set screw extends through the milling tool and engages the outer planar surface of the cylindrical body to secure the milling tool to the FSW tool.

6. The hybrid manufacturing system of claim 5, wherein the outer planar surface is inclined radially inwardly toward a longitudinal axis of the FSW tool in a direction from a distal tip of the FSW tool toward the spindle.

7. The hybrid manufacturing system of any one of claims 1-6, wherein the FSW tool and the subtractive machining tool are spaced apart from the DED tool by a specified distance and configured to follow the DED tool along a workpiece during operation.

8. The hybrid manufacturing system of any one of claims 1-7, wherein the DED tool is a wire arc additive manufacturing (WAAM) tool comprising a torch and a wire supply.

9. The hybrid manufacturing system of any one of claims 1-8, wherein: the tool positioning system comprises an X-axis stage, a Y-axis stage, and a Z-axis stage; the X-axis stage is coupled to and movable with the Y-axis stage; and a plurality of reinforcement members extend between the X-axis stage and the Y-axis stage and are configured to reduce vibration of the X-axis stage and the Y-axis stage during operation.

10. The hybrid manufacturing system of claim 9, wherein the reinforcement members include plates and angle bars.

11. The hybrid manufacturing system of any one of claims 1-10, wherein the subtractive machining tool is removably attachable to the FSW tool, or wherein the subtractive machining tool and the FSW tool are a unitary body.

12. A method, comprising processing a workpiece with the hybrid manufacturing system of any one of claims 1-11.

13. A hybrid manufacturing system, comprising: a tool positioning system; a worktable for supporting a workpiece; a directed energy deposition (DED) tool coupled to the tool positioning system; a friction stir welding (FSW) tool coupled to the tool positioning system; and a milling tool coupled to the FSW tool.

14. The hybrid manufacturing system of claim 13, wherein the FSW tool comprises a spindle coupled to the tool positioning system, and the milling tool is coupled to the spindle of the FSW tool.

15. The hybrid manufacturing system of claim 14, wherein the milling tool is mounted to the FSW tool coaxially with the FSW tool.

16. The hybrid manufacturing system of claim 15, wherein the FSW tool comprises a cylindrical body having an outer planar surface, and a set screw extends through the milling tool and engages the outer planar surface of the cylindrical body to secure the milling tool to the FSW tool.

17. The hybrid manufacturing system of claim 16, wherein the outer planar surface is inclined radially inwardly toward a longitudinal axis of the FSW tool in a direction from a distal tip of the FSW tool toward the spindle.

18. The hybrid manufacturing system of any one of claims 13-17, wherein the FSW tool and the milling tool are spaced apart from the DED tool by a specified distance and configured to follow the DED tool along a workpiece during operation.

19. The hybrid manufacturing system of any one of claims 13-18, wherein the DED tool is a wire arc additive manufacturing (WAAM) tool comprising a torch and a wire supply.

20. A friction stir welding tool, comprising: a cylindrical body having a proximal end and a distal end; a pin located at the distal end; and a milling tool on the body of the friction stir welding tool and configured to rotate together with the body of the friction stir welding tool.

21. The friction stir welding tool of claim 20, wherein the milling tool is mounted to the friction stir welding tool coaxially with the friction stir welding tool.

22. The friction stir welding tool of claim 21, wherein the cylindrical body of the friction stir welding tool comprises an outer planar surface, and a set screw extends through the milling tool and engages the outer planar surface of the cylindrical body to secure the milling tool to the friction stir welding tool.

23. The friction stir welding tool of claim 22, wherein the outer planar surface is inclined radially inwardly toward a longitudinal axis of the friction stir welding tool in a direction from a distal tip of the friction stir welding tool toward a spindle when the friction stir welding tool is coupled to the spindle.

24. The friction stir welding tool of any one of claims 20-23, wherein the milling tool is removably attachable to the friction stir welding tool, or wherein the milling tool and the friction stir welding tool are a unitary body.

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