Distortion reduction in directed energy deposition.

Abstract

A curved clamp mold and a system and method for using the curved clamp mold to fabricate objects, particularly titanium and titanium alloy objects, by directed energy deposition are provided. The method includes thermally pre-bending a substrate on which the object is to be fabricated to form a pre-bent substrate, attaching the pre-bent substrate to a fixture using the curved clamp mold as a lower support, pre-heating the substrate, and forming the object on the pre-heated pre-bent substrate using directed energy deposition techniques.

Description

[Technical Field]

[0001] The present invention relates to devices and methods for reducing distortion in metal objects, particularly titanium and titanium alloy objects, produced using directed energy deposition additive manufacturing processes, also known as solid freeform fabrication. [Background technology]

[0002] Structural metal parts, such as those made from titanium or titanium alloys, are made from solid billets by conventional manufacturing methods such as casting, forging, or machining. These techniques have the disadvantages of high material waste, as expensive titanium metal is often machined away, and long lead times for manufacturing the metal parts.

[0003] A manufacturing technique known as directed energy deposition (DED), rapid prototyping, rapid manufacturing, additive manufacturing, formed metal deposition, or additive manufacturing, allows for the creation of fully dense physical objects. Metal DED is an additive manufacturing process that uses focused thermal energy to melt and fuse materials as they are deposited. Additive manufacturing builds up near-net-shape products layer by layer, offering greater manufacturing flexibility and potential cost savings. It is also desirable to match the material properties of traditional bulk forming processes, such as forging, while utilizing the same established metal alloys. DED is used for repair, rapid prototyping, and low- or high-volume part production.

[0004] DED systems include several categories of machines that use one or a combination of DED energy sources, such as laser beam (LB), electron beam (EB), or arc-based energy sources, such as plasma arc (PA), gas tungsten arc (GTA), and gas metal arc (GMA). The metal feed material used in DED systems typically includes metal in the form of powder and / or wire. DED is performed under an inert gas atmosphere (e.g., DED using arc-based or LB systems) or under a vacuum atmosphere (EB systems). These are the main methods employed in practice. However, the use of other energy sources, feed materials, and atmospheres, in any combination, may be used.

[0005] Residual stress can be defined as a self-balancing stress that exists in an elastic body even in the absence of external loads, such as thermal and / or mechanical loads. During DED of metal preforms, significant amounts of welding-induced residual stress can be generated and accumulated due to localized heating and cooling cycles as a heat source melts the metal material, deposits each new metal layer, and remelts the previously solidified metal layer. The incompatible elastic and / or plastic strain fields involved in DED of metals, caused by non-uniform thermal loading near the processing area, inevitably lead to the accumulation of complex thermally induced residual stresses and strains during layer-by-layer fabrication. Thermal expansion and contraction can occur as a result of transient temperature excursions and steep temperature gradients that may exist during DED. The formation and relaxation of residual stresses during DED of metals can result in undesirable plastic deformation in areas adjacent to the processing zone, which can carry over to the as-deposited preform. Trapped residual stresses in as-deposited DED preforms can lead to permanent loss of resistivity in the workpiece. This is because the workpiece self-balances the residual stress field still present in the structure when released from the clamping fixture platform or jig. Residual stress-induced deformation is a significant issue for larger components due to the large temperature differences simultaneously present along the DED build process. Unfavorable distribution of residual stresses in engineered components can lead to unexpected or premature failure, i.e., in areas of high tensile stress prone to fracture and fatigue. Stress-relief heat treatments are commonly used to relieve stresses that remain trapped in the as-deposited preform due to the DED fabrication sequence. However, loss of resistivity remains one of the main concerns in most DED processes.

[0006] Residual stresses during DED of metals typically result from the fact that different regions of the component being fabricated undergo different cycles of thermal expansion and contraction. The resulting thermal stresses can result in a non-uniform distribution of irreversible material deformation. After the material cools, some of this deformation can remain, resulting in an internal, completely self-equilibrating stress field in the workpiece. This self-equilibration can cause metal structures to become geometrically out of tolerance due to distortion and warpage. All forms of DED processes require the supply of large amounts of localized heat to the top of the newly deposited layer (exposed to the heat source), the interface between the newly deposited layer and the previous layer, and / or the substrate to achieve a properly fused interface.

[0007] DED manufacturing processes typically use a highly concentrated heat source to generate rapid heating. The generated heat can cause thermal expansion of the material, gradually reducing its yield strength. The heat generated by the heat source is used to melt powder and / or wire feed material and form a weld pool in a portion of the workpiece. This locally applied energy causes the weld area to rapidly increase in temperature and melt locally relative to the surrounding area, which remains relatively cool throughout. Because the molten material does not support a load, the stress below the heat source is close to zero. In areas some distance from the energy application area, i.e., in the build layer immediately adjacent to and below the weld pool, the material expands as a result of heating, but is constrained by the adjacent and cooler material below, inducing an elastic compressive strain. As a result, the stress in the area adjacent to the heat source is compressive. Because the temperature in the area adjacent to the heat source is high and the material's yield strength is low, the stress in this area can be as high as the material's yield temperature at the corresponding temperature. As the thermal energy source moves away from the energy application area, the heated molten material cools and contracts as a solid. However, the contraction of the metal is mechanically constrained by adjacent and underlying layers of material. As cooling continues, the residual stresses within the object are dispersed, typically resulting in high tensile stresses in the top layer, where the material is prevented from contracting, and balancing compressive stresses in the lower layers. Depending on the application, the tensile stresses generated in the top layer can approach the yield strength of the material. If the strain and compressive loads that the metal structural member experiences to balance the compressive forces exceed a critical buckling load, buckling of the metal structural member can occur.

[0008] Due to the layer-by-layer nature of the DED process, the differential heating and cooling loads imposed by each successive layer result in spatially competing material expansion and contraction, ultimately leading to the accumulation of residual stresses in the object being fabricated. A hot layer of molten material is deposited on top of a preceding, cooler layer of the object being built. As a result, as heat from the heat source moves across the workpiece, there are large localized temperature gradients and significant contraction, which can introduce residual stresses into the workpiece caused by incompatible strain fields. Longitudinal and lateral contraction that occurs during solidification of layer upon layer can amplify the accumulation of residual stresses within the as-deposited preform. Stresses can be a function of the material's tensile modulus, coefficient of thermal expansion, and rate of contraction upon cooling. If stresses resulting from these incompatible strains remain in the finished article and are not relieved, the residual stresses can combine and react to generate internal forces that result in undesirable distortions of the object, such as bending, buckling, and rotation. Residual stresses that can form during conventional additive manufacturing processes can be large enough to cause significant distortion, misalignment, tearing, or stress-induced crack formation in the additively manufactured object (see Figures 1A-1H).

[0009] Modeling methods to measure or predict stress induction in molded parts are known in the art (see, for example, U.S. Patent No. 6,249,999 (Sidhu et al., 2017) and U.S. Patent No. 6,249,999 (Nguyen et al., 2018)). Prior art developed to address these shortcomings has met with limited success. For example, post-weld high-pressure mechanical rolling has been used to plastically deform the interconnect material before the formation of subsequent layers (see, for example, U.S. Patent No. 6,249,999 (Colegrove et al., 2012)). Peening processes, such as those taught in U.S. Patent No. 6,249,999 (Sidhu et al., 2015), have been taught to be useful for reducing strain on each metal layer deposited during the building of an additively manufactured part. In these processes, one or more impact processing devices are used to peen or strike a common point on the workpiece to plastically deform at least a portion of the deposited layer after its temperature has decreased. Each impact processing device may strike the workpiece one or more times and can strike at frequencies up to 20 Hz. Laser peening has also been used to impart residual compressive stresses to workpieces (Patent Document 5, Kramer et al., 2014). These methods are not suitable for complex shaped pieces, relieving residual stresses in areas inaccessible by peening or rolling tools. They can also increase the time and complexity to manufacture the workpiece and therefore may be excessively costly or impractical to use.

[0010] These methods can also result in long wait times between layers, which can negatively impact productivity and limit manufacturing flexibility. Excessive cooling between layer depositions can increase the temperature difference between layers, further exacerbating the development of residual stresses. For methods that physically modify the deposited layers, contamination from tooling is also a concern, as the additive process can trap contaminants between layers in the final product. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] U.S. Patent No. 9,555,475 [Patent Document 2] U.S. Patent No. 9,950,476 [Patent Document 3] UK Patent Application No. 2491472 [Patent Document 4] US Patent Application Publication No. 2017 / 0326681 [Patent Document 5] US Patent Application Publication No. 2014 / 0367894 Summary of the Invention [Problem to be solved by the invention]

[0012] Therefore, there is a need in the art for an economical method of performing directional metal deposition in an additive manufacturing system at a metal deposition rate that results in a metal product with reduced or minimized residual stresses or distortion, or both, than is achieved with conventional additive manufacturing processes. It would be desirable to provide a DED process that reduces the incidence of residual stresses or cracks in DED manufactured articles. It would also be desirable to provide a DED process that reduces the incidence of localized distortion in the article being manufactured as additional metal layers are deposited. [Means for solving the problem]

[0013] Accordingly, embodiments provided herein relate to the production of workpieces with reduced or minimized residual stresses or distortion, or both, using additive manufacturing processes that substantially avoid one or more of the problems due to limitations and disadvantages of the related art. As embodied and broadly described, devices, systems, and methods are provided that reduce or minimize residual stresses or distortion, or both, during metal additive manufacturing to achieve products with improved material quality. DED-manufactured products with such reduced residual stresses or distortion demonstrate improved strength, fatigue resistance, and durability. The provided devices, systems, and methods increase the throughput and yield of DED-formed products and can result in workpieces within specified tolerances.

[0014] Because the methods provided herein can reduce or eliminate residual stresses or distortions, or both, the methods can be used to fabricate medium to large (e.g., up to 3 m) DED molded components that cannot be easily manufactured using conventional additive manufacturing processes. Additionally, the reduction or elimination of large amounts of residual stress, distortion, or a combination thereof, typical in conventional DED metal structures, can produce manufactured metal structures that are geometrically within tolerance and specification.

[0015] Residual stress and distortion can be seen as a significant barrier to mainstream acceptance of DED technology for metals, especially in safety-critical applications. Therefore, the devices, systems, and methods described herein that can minimize residual stress or distortion can open up new markets or lead to wider acceptance of DED manufactured components. The devices, systems, and methods provided herein also enable effective control of residual stress and distortion in DED metal structures, thereby improving material utilization efficiency of both the substrate and the DED material. These material utilization improvements can result in the production of within-tolerance DED manufactured products, as well as reduced waste and rework, significantly reducing DED manufacturing costs.

[0016] A DED manufacturing method is provided that includes pre-bending a metal substrate to form a plastically pre-bent substrate prior to DED of a single-sided metal structure. A DED manufacturing method is also provided that includes pre-bending a metal substrate to form a plastically pre-bent substrate and pre-heating the pre-bent substrate prior to DED of the metal structure. An apparatus is also provided for manufacturing components with reduced residual stress and distortion due to DED. The apparatus can be used with a conventional DED energy source used to melt metal powder and / or wire feed material. The apparatus includes a curved clamp mold as a lower support structure for the plastically pre-bent substrate. A system is also provided that uses a conventional DED energy source modified using CAD-CAM program instructions. When executed, the CAD-CAM program instructions cause the DED process to follow the shape of the underlying curved clamp mold.

[0017] DED manufacturing methods are provided that minimize or prevent distortion in DED-manufactured products. This can improve the efficiency of the manufacturing process, such as by minimizing substrate waste and the amount of deposition material that must be used. In particular, because the highest thermally induced stress field can be introduced in the first deposition layer, with distortion effects particularly visible in the substrate, the methods provided herein can preserve substrate material that is sacrificed or lost in conventional additive manufacturing processes. This method can improve material utilization efficiency for both the substrate and the DED material compared to conventional methods. The methods provided herein can effectively control residual stress and distortion in DED structures, thereby reducing material waste and enabling a buy-to-fly ratio, or BTF ratio, closer to 1. Reducing material waste and reducing or eliminating rework time can significantly reduce manufacturing costs.

[0018] A curved clamp mold is provided. The curved clamp mold includes a first side including two or more cavities separated by one or more reinforcing members and a rim having a flat surface around the periphery of the first side, and a second side opposite the first side, having a curved surface and including knurling or corrugations. The curved clamp mold may include a ceramic coating. The reinforcing member may maintain mold rigidity, provide mold deformation resistance, or both. The curved clamp mold may include or be made of a non-magnetic metal. The curved clamp mold may include or be made of a metal having a melting point of 1350°C or higher. The curved clamp mold may include or be made of a metal that is or includes austenitic stainless steel. The austenitic stainless steel may include carbon, chromium, copper, manganese, molybdenum, nickel, nitrogen, phosphorus, silicon, or a combination of any two or more thereof. The austenitic stainless steel may include at least 18% chromium. The austenitic stainless steel can be a 300 series stainless steel. The austenitic stainless steel can include a 304 stainless steel, a 309 stainless steel, a 310 stainless steel, a 316 stainless steel, a 318 stainless steel, a 321 stainless steel, or a 330 stainless steel.

[0019] A ceramic coating can be applied to any one or more surfaces of the curved clamp mold. The ceramic coating can include zirconium dioxide, zirconium dioxide stabilized by the addition of yttrium oxide, yttrium aluminum oxide, alkaline earth metal silicates, ZrVO, Mg(VO), or combinations thereof. The ceramic coating can include ZrOYO. The ceramic coating can have a thickness of 0.1 mm to about 5 mm. The curved clamp mold can have a nominal mold deflection of about 3 mm to about 35 mm. The curved clamp mold can include a bond coat onto which the ceramic coating is applied. The bond coat can be between the surface of the curved clamp mold and the ceramic coating.

[0020] A directed energy deposition method for manufacturing a metal workpiece is also provided. The method can include pre-bending a substrate of a metallic material using thermal energy by forming a plurality of fusion tracks on a first surface of the substrate using a first fusion tool to produce a pre-bent substrate; and using a curved clamp mold described herein as a lower support structure for supporting the pre-bent substrate while secured in the fixture, and securing the pre-bent substrate and the curved clamp mold supporting the pre-bent substrate to the fixture using a plurality of clamps. After the pre-bent substrate and the curved clamp mold are secured in the fixture, the method can include forming a metal workpiece on the second surface of the substrate by an additive manufacturing process that can: a) deposit a layer of molten material on the second surface of the substrate to form a base material, and deposit a subsequent layer of molten material on the base material to form a workpiece; or b) deposit a layer of metal powder on the second surface of the substrate, melt the metal powder to form a base material, and deposit a subsequent layer of metal powder on the base material, and melt the powder to form a workpiece. The second surface of the substrate is opposite the first surface of the substrate. The method can include preheating the pre-bent substrate to a temperature of about 400°C to about 900°C by applying thermal energy to the second side of the substrate while it is secured in the fixture. Pre-bending the substrate can include inducing a temperature gradient in the substrate. The method can use a melting tool including a heat source selected from a laser beam, an electron beam, a plasma arc, a gas tungsten arc, a gas metal arc, and any combination thereof. During pre-heating of the first surface of the substrate, the region to which the thermal energy is applied can reach a temperature that is the melting point of the metallic material or that is about 5°C to about 50°C below or above the melting point of the metallic material. During pre-bending of the first surface of the substrate, the formation of melt tracks can result in the formation of tensile stress at the centerline of each melt track and the formation of compressive stress in regions away from the centerline of each melt track upon cooling of the substrate. The tensile stress at the centerline of the melt track can be within about 10% of the yield strength of the substrate. The tensile stress at the centerline of the melt track can exceed the magnitude of the yield strength of the substrate.

[0021] The pre-bending step may include directing cooling gas toward the melt track using a gas jet device to accelerate cooling of the melt track. Directing cooling gas toward the melt track can create a temperature gradient in the substrate and impart residual stress to the substrate upon cooling. The gas jet device can direct cooling gas toward the melt track at a rate of about 50 L / min to about 500 L / min. The cooling gas can be applied in a constant flow, intermittently, or in a pulsed flow. The cooling gas can include an inert gas selected from argon, helium, neon, xenon, krypton, and combinations thereof. The cooling gas can be applied at a temperature of 100°C or less. The cooling gas can be applied at a temperature of 25°C or less. The gas jet device can generate a turbulent flow of cooling gas, a laminar flow of cooling gas, or a combination of turbulent and laminar flow of cooling gas. The gas jet device can include multiple nozzles, the nozzles can direct cooling gas away from the heat source of the molten tool, and at least one nozzle can direct cooling gas at the as-solidified metal in the molten track.

[0022] In the methods provided herein, the melt tracks can be generated equidistant from one another. The distance between the melt tracks can be about 10 mm to about 60 mm. The method can include determining a centerline of each wall of the preform formed on the second surface of the substrate and positioning the melt tracks on the first surface of the substrate about 10 mm to about 20 mm away from the centerline of the majority of the walls of the preform or workpiece formed on the second surface of the substrate. The majority of the melt lines can be formed on the first surface at one or more locations other than locations corresponding to one or more areas occupied by one or more walls of the workpiece formed on the second side of the substrate.

[0023] In this method, pre-bending can form a pre-bent substrate with a uniform elastic-plastic bend. Pre-bending of the substrate can be performed while the substrate is clamped to a jig and insulated from the jig. The substrate can be clamped to the jig using multiple clamps. One or more of the clamps can include a thermal barrier coating on each surface that contacts the pre-bent substrate. The thermal barrier coating can include ceramic materials, silicon carbide, silicon nitride, boron carbide, or combinations thereof. The ceramic material can include alumina, zirconia, titanium oxide, alkaline earth metal silicates, aluminum titanate, zirconium dioxide, zirconium dioxide stabilized with the addition of yttrium oxide, yttrium aluminum oxide, ZrV2O7, Mg3(VO4)2, or combinations thereof. The thermal barrier coating can have a thickness of 0.1 mm to 5 mm. The clamps can include a knurled pattern or corrugations on the surface that contacts the pre-bent substrate. The clamps can be tightly tightened to fully contact the pre-bent substrate with the underlying curved clamping mold. Each of the clamps may be tightened to a torque of about 10 N·m to about 100 N·m. The clamps may be positioned so that they coincide with the beginning or end of the wall of the workpiece being created.

[0024] In the methods provided herein, preheating of the pre-bent substrate can be performed using one or more melting tools comprising a DED heat source under conditions that a) form a melt track but do not melt the surface of the pre-bent substrate, or b) form a melt track and melt the surface of the pre-bent substrate at the melt track. The positioning of the melting tool can be at a higher standoff position than the standoff position used to form the workpiece.

[0025] The method includes the steps of preheating a pre-bent substrate having a first short edge and an opposite second short edge and a first long edge and an opposite second long edge by: a) positioning a melting tool including a DED heat source at a first edge of the pre-bent substrate secured in a fixture and within about 10 mm to about 60 mm of the first long edge; b) applying thermal energy form the DED heat source of the melting tool starting at the first short edge across a surface of the pre-bent substrate and across the surface to the opposite second short edge to form a first line of energy application to the surface; c) repositioning the DED heat source of the melting tool at the first short edge and offset from the first line of energy application toward the second long edge by a distance of about 10 mm to about 60 mm; and d) repeating steps b) and c) until the line of energy application is applied across the surface of the pre-bent substrate to a position about 10 mm to about 60 mm from the opposite second long edge. The preheating can increase the temperature of the pre-bent substrate to a temperature of about 350°C to about 650°C.

[0026] Forming a metal workpiece may include providing a metal feed material in the form of a wire, heating and melting the wire using a single melting tool so that molten metal material is deposited on areas of a substrate to form a base material, and moving the base material relative to the position of the melting tool in a predetermined pattern such that successive deposits of molten metal material on the base material solidify and form a three-dimensional object.

[0027] Forming a metal workpiece may include: a) providing a metal feed material in the form of a wire; b) heating at least a portion of a surface of a substrate using a first melting tool to form a preheated area on the substrate; c) heating and melting the wire using a second melting tool such that molten metal material is deposited on the preheated area to form a base material; d) moving the base material relative to the positions of the first melting tool and the second melting tool in a predetermined pattern; e) heating at least a portion of a surface of the base material using the first melting tool to form a preheated area on the base material and depositing molten metal material produced by the second melting tool that melts the metal material on the preheated area on the base material; and f) repeating steps d) and e) such that successive deposits of molten metal material on the preheated area on the base material solidify and form the three-dimensional object.

[0028] The method can include using a gas jet device to direct a cooling gas toward a surface of the as-solidified material adjacent a liquid-solid boundary of the molten metallic material, or any combination thereof, and moving the base material relative to the position of the melting tool and the gas jet device in a predetermined pattern such that successive deposits of the molten metallic material solidify and form the three-dimensional object. The first melting tool can include a PTA torch, a laser device, a coaxial powder feed nozzle laser system, an electron beam device, or any combination thereof, and the second melting tool can include a PTA torch, a laser device, a coaxial powder feed nozzle laser system, an electron beam device, or any combination thereof. The first melting tool can include a first PTA torch, and the second melting tool can include a second PTA torch. The first melting tool can include a laser device, and the second melting tool can include a PTA torch. The first melting tool can include a PTA torch, and the second melting tool can include a laser device. The first melting tool can include a coaxial powder feed nozzle laser system, and the second melting tool can include a laser device. The first melting tool can include a coaxial powder feed nozzle laser system, and the second melting tool can include a PTA torch. The first melting tool can include a PTA torch, and the second melting tool can include an electron beam device. The first melting tool can include an electron beam device, and the second melting tool can include a PTA torch. The first melting tool can include an electron beam device, and the second melting tool can include a laser device. The first melting tool can include a laser device, and the second melting tool can include an electron beam device. If the second melting tool includes a PTA torch, the PTA torch can be electrically connected to a DC power source such that an electrode of the PTA torch serves as the cathode and the metallic material can be the consumable electrode serving as the anode.

[0029] In the methods provided herein, all steps of the method, including each of the steps of pre-bending the substrate, pre-heating the pre-bent substrate, and forming the metal workpiece, can be performed in a sealed chamber containing an inert atmosphere, which can include argon, neon, xenon, krypton, helium, or combinations thereof.

[0030] Also provided is a system for directed energy deposition that includes a jig for securing a pre-bent substrate, a curved clamp mold as described herein positioned between the jig and when the pre-bent substrate is secured to the jig, an insulating clamp for securing the pre-bent substrate to the jig, one or more melting tools including a DED heat source for melting a metal source into a molten metal material that is deposited on a surface of a workpiece, a gas jet device for directing cooling gas to impinge on the as-solidified material adjacent the liquid-solid boundary of the liquid melt pool, or any combination thereof, a supply of the cooling gas, and an actuator for positioning and moving the workpiece relative to the melting tool and the jet device.

[0031] Additional features and advantages of the embodiments described herein will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the illustrative embodiments will be realized and attained by the structure particularly pointed out in the written description and claims hereof, as well as the appended drawings.

[0032] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

[0033] The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. [Brief explanation of the drawings]

[0034] [Figure 1A] Photograph of a workpiece manufactured using conventional DED additive manufacturing without stress relief. [Figure 1B] The mismatch is indicated (arrows point to the mismatch location). [Figure 1C] The mismatch is indicated (arrows point to the mismatch location). [Figure 1D] Shows a crack in the workpiece (arrow points to the crack). [Figure 1E] Shows a crack in the workpiece (arrow points to the crack). [Figure 1F] Shows a crack in the workpiece (arrow points to the crack). [Figure 1G] Shows tearing of the workpiece (arrow points to tear). [Figure 1H] Shows tearing of the workpiece (arrow points to tear). [Figure 2A] 10A and 10B are side views of a curved clamp mold illustrating an embodiment in which the ridges have a wavy surface with an exemplary cross-sectional shape that is a frustum-shaped shape, particularly a truncated pyramidal shape. [Figure 2B] 1 is a side view of the same curved clamp mold showing the ceramic coating by dashed lines (exaggerated in the illustration) on the curved surface that will come into contact with the DED substrate (plate). This illustration also shows the nominal mold deflection hmold. [Figure 2C] 1 shows an exemplary cross-sectional shape that is a frustum, particularly a truncated pyramidal shape (enlarged view). [Figure 3A] FIG. 10 is a top view of the same curved clamp mold. [Figure 3B] FIG. 10 is an isometric view of the same curved clamp mold. [Figure 4]1 is a bottom view of a curved clamp mold having four triangular cavities separated by X-shaped stiffeners and a peripheral rim. The peripheral rim and X-shaped stiffeners share a common plane. When the curved clamp mold is placed on a fixture or welding table, only the peripheral rim and stiffeners contact the fixture platform, such as the fixture or welding table. [Figure 5] 1 illustrates an exemplary rapid cooling gas jet device. [Figure 6] 1 shows melt tracks created on a first or backside of a substrate to pre-bend the substrate, and a DED back wall of the workpiece formed on a second or frontside of the substrate. [Figure 7A] 1 illustrates an exemplary heating path that can be used to move a DED energy source to form a melt track on the backside or top surface of a first side of a substrate to pre-bend the substrate toward the heat source. [Figure 7B] Schematically illustrates the relative position of the thermally induced pre-bending fusion track created by the heating path on the backside or first side of the substrate relative to the superimposed (dashed grey line) DED workpiece fabricated on the opposite frontside or second side of the substrate. [Figure 8A] 4 illustrates the uniform longitudinal bow imparted to a substrate when heated to induce melt tracks to pre-bend the substrate, in which the pre-bent substrate rests on a fixture 400. [Figure 8B] The substrate is shown upside down. For the substrate depicted, the maximum nominal substrate deflection 410 perpendicular to the plane of the plate was approximately 15 mm. In the figure, the pre-bent substrate rests on a jig 400. [Figure 9A] 1 is a bottom view of an exemplary insulated high strength steel clamp showing an exemplary substrate, depicting an exemplary surface that can be coated with a ceramic coating to minimize heat flow by conduction between the insulated high strength steel clamp and the pre-bent substrate when the clamp is used to attach the plastic pre-bent substrate and the fixture. [Figure 9B]1 is a side view of an exemplary insulated high strength steel clamp showing an exemplary substrate depicting an exemplary surface that can be coated with a ceramic coating to minimize heat flow by conduction between the insulated high strength steel clamp and the pre-bent substrate when the clamp is used to attach the plastic pre-bent substrate and the fixture. [Figure 9C] 1 is a perspective overhead three-dimensional view of an exemplary insulated high-strength steel clamp showing an exemplary substrate. The substrate depicts an exemplary surface that can be coated with a ceramic coating to minimize heat flow by conduction between the insulated high-strength steel clamp and the pre-bent substrate when the clamp is used to attach the pre-bent substrate and the fixture. [Figure 10] 6 shows an exemplary clamping arrangement for attaching a pre-bent substrate to a fixture using insulating or wave clamps. This figure illustrates that the clamps can be positioned so that the centerline of the clamp (or clamping body, as shown in the solid outline around some of the clamps when several clamps are used in combination) coincides with the centerline of the DED wall start / end locations whenever possible. These substrate clamping constraints can substantially reduce deformation effects resulting primarily from longitudinal residual stresses. Non-optimal clamping can result in localized deformation or buckling due to the lack of clamping constraints. For illustrative purposes, a non-optimal clamping arrangement 650 is shown in the dashed box in the figure. Only one clamp is used, off-center, to axially constrain the upward movement of the base plate. This is a non-optimal clamping arrangement because the centerline of the clamp / clamping body does not coincide with the centerline of the DED wall start / end locations. [Figure 11] The relative positions of the black preheating paths on the front side of the substrate prior to DED deposition are shown schematically, along with the superimposition of the shape of the workpiece to be formed. The exemplary embodiment shows the application of low energy density by a heat source across the surface of the pre-bent substrate in the y-direction and from short edge to short edge in the x-direction. The figure shows solid and dashed black lines representing the tool paths and preheating sequence of two fusion tools running parallel, for example. [Figure 12A]1 shows a schematic diagram of a conventional directed energy deposition configuration in which the substrate is separated from the fixture using, for example, a sheet of alumina insulation or other substrate support mechanism, and the workpiece is fabricated in a layer-by-layer fashion. This configuration minimizes heat flow from the DED substrate to the fixture and prevents extraction of heat generated by the DED process. [Figure 12B] 1 illustrates an exemplary configuration for directed energy deposition using a curved clamp mold provided herein. The curved clamp mold serves as a lower support structure for the pre-bent substrate when the pre-bent substrate is attached to a fixture. The curved clamp mold has a thermal barrier coating layer on top of the curved surface to thermally isolate the curved clamp mold from the plastically pre-bent substrate. The workpiece is manufactured in a layer-by-layer manner. [Figure 13A] Figure 1 shows the deformation caused by DED deposition forming a workpiece on a first substrate having a thickness of 9.5 mm that had not undergone any type of stress relief. Distortion is evident at the short edges of the substrate, causing the substrate to bow upward compared to the flat contour of the substrate before deposition. [Figure 13B] 1 shows the deformation induced by DED deposition on a second substrate of 12.7 mm thickness that has not undergone any type of stress relief. [Figure 13C] 1 shows a third substrate, 9.5 mm thick, that was used for forming the object by undergoing thermal pre-bending, pre-heating and DED treatments. [Figure 14A] 1 illustrates non-optimal settings of individual clamps, with dashed circles indicating areas of non-uniform pressure and heat transfer distribution. [Figure 14B] FIG. 10 shows the setup of an individual clamp, showing evenly distributed pressure on the clamp / baseplate contact area, ensuring uniform pressure and heat transfer distribution. DETAILED DESCRIPTION OF THE INVENTION

[0035] Reference will now be made in detail to one embodiment of the present invention, an example of which is illustrated in the accompanying drawings.

[0036] A.Definition Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs. All patents, patent applications, published applications and publications, websites and other published materials referenced throughout this disclosure are incorporated herein by reference in their entirety unless otherwise noted. In the event that there are multiple definitions for terms herein, those in this section shall prevail.

[0037] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0038] As used herein, ranges and amounts can be expressed as "about" a particular value or range. "About" includes the exact amount. Thus, "about 5%" means "about 5%" as well as "5%." "About" means within typical experimental error for the intended use or purpose.

[0039] As used herein, "optional" or "optionally" means that the subsequently described event or circumstance may or may not occur, and that the description includes cases where the event or circumstance occurs and cases where it does not occur. For example, an optional component in a system means that the component may or may not be present in the system.

[0040] As used herein, "combination" refers to any association between two items or between more than two items. The association may be spatial or may refer to the use of two or more items for a common purpose.

[0041] As used herein, the terms "comprise," "include," and "contain" are synonymous and are inclusive or open-ended, and each term indicates that additional, unrecited elements or method steps may optionally be included.

[0042] As used herein, "and / or" means "either or both" of the elements so conjoined, i.e., elements that are present conjunctively in some cases and disjunctively in other cases. Multiple elements listed with "and / or" should be construed in the same manner, i.e., "one or more" of the elements so conjoined. Other elements other than the elements specifically identified by the "and / or" clause may optionally be present, whether related to those elements specifically identified or not. Thus, as a non-limiting example, a reference to "A and / or B," when used in conjunction with open-ended language such as "comprising," can refer in one embodiment to A only (optionally including elements other than B), in another embodiment to B only (optionally including elements other than A), in yet another embodiment to both A and B (optionally including other elements), etc.

[0043] "Additive manufacturing," as used herein, also known as "additive fabrication," "additive layer manufacturing," "solid freeform fabrication," "shape metal deposition," and "additive manufacturing," refers to an additive process that effects the layer-by-layer fabrication of an object. The process can employ 3D model data, a metal feedstock source such as wire or powder, a heat source (such as a plasma arc, laser, or electron beam) to melt the metal source, or a combination thereof.

[0044] As used herein, "additive manufacturing system" refers to a system used for additive manufacturing.

[0045] "Directed energy deposition" or "DED" as used herein refers to an additive manufacturing process that uses a heat source to fuse materials, particularly metals, by melting them as they are being deposited.

[0046] The terms "plasma transferred arc torch" or "PTA torch," as used interchangeably herein, refer to any device capable of heating and exciting a stream of inert gas into a plasma by an electric arc discharge, and then moving the stream of plasma gas containing the electric arc out an orifice (such as a constricting nozzle) to form a highly collimated arc column of ionized plasma gas that exits the nozzle orifice at high velocity and transfers the intense heat of the arc to a target area, such as a metal wire or substrate.

[0047] The term "metallic material" as used herein refers to any known or contemplated metal or metal alloy that can be employed in a directed energy deposition process to form a three-dimensional object. Examples of suitable materials include, but are not limited to, titanium and titanium alloys, such as Ti-6Al-4V alloy.

[0048] As used herein, a "heat source" refers to a part of a device that can transfer thermal energy therefrom to a metallic material, such as a metal wire or metal powder, or to a substrate or base material, or any combination thereof. Exemplary heat sources include a plasma arc, a laser beam, and an electron beam.

[0049] As used herein, a "melting tool" refers to a device that generates a heat source for preheating or melting a portion of a surface of a metallic material or workpiece, or both, in a DED additive manufacturing process. Examples include a PTA torch that generates an electric arc plasma as a heat source, a laser device that generates a laser beam as a heat source, and an electron beam device that generates an electron beam as a heat source.

[0050] As used herein, the term "base material" refers to the target material onto which molten metal is deposited to form a workpiece. This becomes the substrate when the first layer of metallic material is deposited. Once one or more layers of metallic material are deposited on the substrate, the base material becomes the top layer of the deposited metallic material upon which new layers of metallic material are deposited.

[0051] As used herein, the term "workpiece" refers to a metal object or body being fabricated using directed energy deposition.

[0052] The terms "computer-aided design model" or "CAD model," as used interchangeably herein, refer to any known or conceivable virtual three-dimensional representation of an object to be formed. This virtual three-dimensional representation can be employed in a DED system to coordinate the position and movement of a substrate and to operate a DED heat source and a metal material source, such as a metal powder feeder or metal wire feeder, such that a physical object is built by fusing successive deposits of metal material onto the substrate in a pattern that will build the physical object according to the virtual three-dimensional model of the object. This can be obtained, for example, by first dividing the virtual three-dimensional model into a set of virtual parallel layers, and then dividing each of the parallel layers into a set of virtual quasi-one-dimensional slices, thereby creating a virtual vectorized layered model of the three-dimensional model. A controller can then be operated to deposit and fuse a series of quasi-one-dimensional slices of metal feedstock material onto the substrate in a pattern according to a first layer of the virtual vectorized layered model of the object to form the physical object.

[0053] The sequence is then repeated for a second layer of the object by depositing and fusing a succession of quasi-one-dimensional slices of weldable material onto the previously deposited layer in a pattern according to the second layer of the virtual vectorized layer model of the object. The repetition continues the deposition and fusing process layer-by-layer for each successive layer of the virtual vectorized layer model of the object until the entire object is formed. However, the present invention is not bound by any specific CAD model and / or computer software that drives the controller of the arrangement according to the present invention. The present invention is not bound by any specific type of controller. Any known or conceivable controller (e.g., CAD model, computer software, computer hardware, and actuator) capable of building a metal three-dimensional object by directed energy deposition can be used.

[0054] As used herein, a "cooling gas" is a gas directed toward an as-solidified surface, such as toward a melt track, to directly influence and accelerate the cooling and solidification of the as-solidified metal. The temperature of the gas can be any temperature that cools the surface with which it interacts. The temperature can be less than 100°C, or less than 50°C, or less than 30°C, or less than 25°C, or less than 10°C, or less than 5°C, or less than 0°C, or in the range of about -10°C to about 100°C, or about -5°C to about 90°C, or about 0°C to about 80°C. The temperature can be about 25°C or less.

[0055] As used herein, "residual stress" is stress that exists in a structure even when all external loads are removed due to non-uniformity of residual strains. Residual stresses are typically self-balancing.

[0056] As used herein, "jig" refers to a device used to hold or secure the workpiece, mold, and clamp in place during deposition. For example, a jig can include a tray, pedestal, or platform on which a substrate or other portion of a workpiece can be secured during a DED process.

[0057] As used herein, a "preform" is a workpiece produced by an additive manufacturing process. A preform can be an intermediate or semi-finished part of a final finished part. A preform can have a near-net shape relative to the final finished part and may require some further processing, even if minimal. For example, a preform may require final finish machining to a high resistance configuration.

[0058] As used herein, "Buy-to-Fly Ratio" or "BTF Ratio" refers to the weight ratio of the weight of raw material used to fabricate a component to the weight of the finished product. This ratio may depend on how closely the initial, as-deposited DED preform shape resembles the shape of the finished component. The more material that needs to be removed from the DED preform to fabricate the final component, the higher the BTF ratio.

[0059] As used herein, "length" or "longitudinal direction" with respect to a substrate refers to the direction along the largest of the substrate's three dimensions.

[0060] As used herein, "width" or "width direction" with respect to a substrate refers to the direction along the second largest of the three dimensions of the substrate, typically measured from one short side to the other short side.

[0061] As used herein, "thickness" or "thickness direction" with respect to a substrate refers to the direction along the shortest of the three dimensions of the substrate.

[0062] As used herein, "high strength steel" refers to steel having a tensile strength of 300 MPa or greater.

[0063] As used herein, "high strength low alloy steel" refers to steel having a tensile strength of 370 MPa or greater.

[0064] As used herein, "ultra-high strength steel" refers to steel having a tensile strength of 780 MPa or greater.

[0065] As used herein, a "warm forming temperature" is a temperature below the recrystallization temperature of a material that maximizes the malleability of the metal without allowing recrystallization, grain growth, or metallurgical fracture. Warm forming temperatures can range from about 200°C to about 850°C, depending on the material.

[0066] As used herein, a "hot forming temperature" is a temperature above the recrystallization temperature of a material. Hot forming temperatures can range from about 600°C to about 2000°C, depending on the material.

[0067] As used herein, "backside of substrate" refers to the side of the substrate that faces away from the deposition apparatus during DED fabrication. For example, the backside of the substrate can face the fixture during deposition. The backside of the substrate is the side opposite the side on which deposition occurs.

[0068] As used herein, "front side of a substrate" refers to the side of a substrate that faces a deposition apparatus. For example, the front side of a substrate can be the side on which molten material is deposited during DED. The front side of a substrate can be the side on which a workpiece is formed by DED. The front side of a substrate is the opposite side of the back side of a substrate.

[0069] As used herein, a "void" refers to any unfilled space or void within a mass that does not form a pore through the mass. A void can be a hollowed-out or cut-out space or a space created by adding additional material.

[0070] As used herein, the "nominal mold deflection" or "h" of a curved clamp mold mold (Arrow) is the difference between the maximum height of the arcuate surface measured at the center of the arcuate surface and the top surface of the edge of the curved clamp mold.

[0071] It should also be understood that, unless expressly indicated to the contrary, in any method claimed herein that includes more than one step or action, the order of the method steps or actions is not necessarily limited to the order in which the method steps or actions are recited.

[0072] B. Curved clamping mold Conventional DED of metals to produce preforms can introduce residual stresses into the preform. Residual stresses during DED of metals typically result from the fact that different regions of the component being manufactured experience different cycles of thermal expansion and contraction. The resulting thermal stresses can cause uneven distribution of irreversible material deformation. Some of this deformation can remain even after the material cools, resulting in an internal, completely self-equilibrating stress field in the workpiece. If unrelieved, the stresses can promote numerous manufacturing defects. As shown in Figures 1A-1H, a workpiece manufactured using conventional DED additive manufacturing without stress relief (Figure 1A) can exhibit misalignments (Figures 1B and 1C), cracks (Figures 1D, 1E, and 1F), and tears (Figures 1G and 1H). An apparatus is provided that includes a curved clamp mold as a lower support structure for a pre-bent substrate to produce single-sided metal components that are free of residual stresses and distortion-free or have reduced residual stresses or distortion due to DED. The apparatus can be used with conventional DED heat sources used to melt metal powder or metal feedstock, or a combination thereof. The curved clamp mold includes a first side including a peripheral rim having a flat or planar surface, cavities or recesses forming one or more void regions, and one or more reinforcing members. The planar perimeter and the reinforcing members share a common plane. Only the peripheral rim and the reinforcing members contact the fixture or clamping platform. The curved clamp mold also includes a second side opposite the first side, as shown in Figures 2A and 8B. The second side has a curved surface.

[0073] In use, a first side of the clamp mold can face the welding fixture. A curved side of the clamp mold can be positioned against the pre-bent substrate, facing away from the fixture and toward the pre-bent substrate. The planar surfaces of the peripheral rim and the reinforcing members of the curved clamp mold can rest flat on the fixture surface. One or more clamps can be used to secure the pre-bent substrate to the fixture, thereby pressing the pre-bent substrate against the fixture. Thus, the force required to secure the pre-bent substrate to the fixture is between the clamps and the fixture, with the curved clamp mold acting as support between the substrate and the fixture. In an embodiment, the pre-bent substrate is pressed axially downward.

[0074] Due to the contact between the curved mold and the pre-bent substrate, some compressive stress may be felt on the curved mold. The curved clamp mold may be made from a stiff material that is resistant to twisting and deformation to help maintain its shape. Additionally, the curved clamp mold may be made from a material that is resistant to thermal shock, corrosion, and is non-magnetic.

[0075] The curved clamp mold can act as a support structure for the pre-bent DED substrate, positioned between the pre-bent DED substrate and the jig. An exemplary arrangement can include the jig as the bottom surface, on which the curved clamp mold is positioned. The curved clamp mold is positioned so that its first surface faces the jig. The planar surface of the peripheral rim and the reinforcing member on the first side of the curved clamp mold can rest flat on the jig surface. The backside (first side) of the pre-bent substrate, on which the melt track may be present, is positioned so that it faces the side (second side) of the curved clamp mold (facing away from the jig). In this configuration, the backside of the pre-bent substrate faces downward toward the curved surface of the curved clamp mold and the jig. One or more clamps can secure the pre-bent substrate to the jig with the curved clamp mold between the pre-bent substrate and the jig. The force exerted by the clamps on the pre-bent substrate can force the pre-bent substrate into full contact with the curved second side of the curved clamp mold, straightening the pre-bent substrate to conform to the curvature of the second side of the curved clamp mold. Two or more clamps around at least a portion of the periphery of the DED substrate can uniformly press the pre-bent substrate downward toward the fixture, securing the pre-bent substrate to the fixture.

[0076] The curved clamp mold can help mitigate or eliminate deformations, such as welding-induced buckling strains, caused by elastic instabilities generated by compressive residual stresses when the critical buckling stress of the substrate is exceeded. With insulation, which may be on the second surface of the curved clamp mold or on the cavity in the first surface of the curved clamp mold, or a combination thereof, the curved clamp mold can minimize the development of local temperature gradients and resulting deformation patterns that can induce large localized stains. The curved clamp mold can maintain a consistent contact surface with the pre-bent substrate to optimize thermal and mechanical homogeneity across the pre-bent substrate.

[0077] The dimensions of the substrate are selected to accommodate one or more workpieces to be built on the substrate. Typically, the only limitation on the size of the curved clamp mold relative to the substrate is that it must be possible to position the curved clamp mold between the substrate and the jig and clamp the substrate to the jig. The curved clamp mold can be designed to be the same size as the substrate. The curved clamp mold can be designed to be 0.5% to 10% larger than the substrate, as long as the substrate can be clamped to the jig.

[0078] When the substrate is clamped to the fixture with the curved clamping mold between the substrate and the fixture, the curved clamping mold can be designed to be 0.05% to 2.5% smaller than the substrate, as long as the substrate does not come into contact with the fixture. Generally, this is not desirable if the curved clamping mold is much smaller than the substrate, as this can affect manufacturing consistency. Temperature conditions outside the mold / substrate interface area can be different, resulting in different heat transfer conditions, especially in areas that are not in contact with each other, which can result in different residual stress distributions.

[0079] The curved clamp mold is thicker in the center than at the edges. As a result, the curved surface has a maximum height near the center of the curved surface. In the embodiments provided herein, the height of the curved clamp mold measured at or near the center of the curved clamp mold can be in the range of about 3 mm to about 60 mm, or about 12 mm to about 50 mm, or about 15 mm to about 45 mm. The height of the curved clamp mold measured at or near the outer edge of the curved clamp mold can be in the range of about 0.5 mm to about 55 mm, or about 3 mm to about 45 mm, or about 10 mm to about 40 mm. The thickness profile of the curved clamp mold when viewed from the side has a maximum height at the center of the curved clamp mold. The height gradually is reduced toward the outer edges from the curved surface. The height difference across the cross section of the curved clamp mold results in a concave downward curvature on the top surface of the curved clamp mold. In cross section when viewed from the side, the shape of the curved fastening device may resemble the upper half of an ellipse with the minor axis much smaller than the major axis. The ellipse may have an eccentricity that is close to but less than 1 (an eccentricity of 1 is a flat surface).

[0080] The thickness of the curved clamping mold can be designed to mimic or provide the same or similar thermal insulation properties as those achieved with sheets of ceramic insulation conventionally used in DED processes. For example, in conventional DED processes, one or more sheets or plates of alumina (Al2O3) insulation are used to thermally isolate the substrate from a clamping fixture platform, such as a jig. The use of conventional insulation sheets contributes to a more uniform temperature distribution during the DED process while reducing the potential risk of thermal damage to the fixture. The thickness of the sheets or plates can vary. However, conventionally used sheets can be approximately 3 mm to 3.5 mm thick. Multiple ceramic insulation sheets can be used in conventional DED processes. For example, some conventional processes use approximately four sheets or plates of ceramic insulation to provide an approximately 12 mm layer of insulation. Conventionally, more or fewer ceramic insulation sheets may be used. These alumina insulation plates can be cut to size. However, doing so can release alumina particles that can cause respiratory tract or eye irritation. Alumina insulation sheets also tend to be hygroscopic and may initially release water vapor during the high temperatures of the DED process, which can lead to undesirable fluctuations in the deposition environment during processing. Ceramic insulation sheets traditionally used between the substrate and the fixture are also brittle and prone to breakage, and must be discarded after use, thus becoming consumables that increase the cost of DED manufacturing.

[0081] The curved clamp mold can be used in combination with a conventional ceramic insulation plate. The curved clamp mold can replace the old ceramic insulation plate and provide similar insulation while maintaining the same height. This requires only minimal changes to the melting tool setup that provides the heat source or the CAD-CAM path plan that defines the part to be produced by DED. As mentioned above, there are no physical limitations on the thickness of the curved clamp mold other than machine-dependent motion constraints. For example, the height stroke of the DED system can dictate the thickness of the curved clamp mold used. Based on the system's height stroke, the thickness of the curved clamp mold can be selected to maximize heat flow reduction at the mold / fixture interface while allowing sufficient clearance for workpiece production.

[0082] The curved clamp mold can be constructed from any metal with sufficient strength and heat resistance to be used under typical DED processing conditions. The curved clamp mold can be constructed from a corrosion-resistant metal. The curved clamp mold can be constructed from a heat-resistant metal. The curved clamp mold can be constructed from a non-magnetic metal. The curved clamp mold can be constructed from a metal with a melting point of 1350°C or higher. In some configurations, the curved clamp mold contains austenitic stainless steel. The austenitic stainless steel can contain carbon, chromium, copper, manganese, molybdenum, nickel, nitrogen, phosphorus, silicon, or combinations thereof. The austenitic stainless steel can contain at least 18% chromium. The curved clamp mold can be constructed from 300 series stainless steel. The curved clamp mold can be constructed from stainless steel series 304, 309, 310, 316, 318, 321, or 330. The curved clamp mold can be constructed from grade AISI 330 stainless steel. The curved clamping mold can be made from a non-magnetic metal to avoid the unbalanced magnetic field conditions surrounding the welding arc in arc-based DED systems, which can lead to many processing issues, such as magnetic arc blow.

[0083] To minimize or prevent thermal energy transfer from the substrate to the top surface of the curved clamp mold during the DED process, the curved clamp mold can include a ceramic coating. For example, as shown in FIG. 2B , the surface of the curved clamp mold facing the DED substrate (the second curved surface, including the knurling or corrugations) can be ceramic coated. The ceramic coating can be applied directly to the curved surface, or the ceramic coating can be applied to a bond coat applied directly to the second curved surface. The ceramic coating can be applied directly to the first flat surface on the opposite side of the mold, or the ceramic coating can be applied to a bond coat applied directly to the first flat surface. The ceramic coating can provide thermal insulation to minimize or prevent thermal contact between the curved clamp mold and the pre-bent substrate.

[0084] The ceramic coating can be applied using any process, including chemical or electrochemical deposition such as atmospheric plasma spraying, magnetron sputtering, electrophoretic deposition, or physical vapor deposition such as electron beam physical vapor deposition. Any high temperature ceramic coating known in the art can be used (see, for example, U.S. Pat. Nos. 4,321,310 (Ulion et al., 1982), 5,789,330 (Kondo et al., 1998), 5,304,519 (Jackson et al., 1994), 6,387,539 (Subramanian, 2002), and 6,998,064 (Gadow et al., 2006)). Exemplary types of ceramic coatings include zirconium dioxide, zirconium dioxide stabilized by the addition of yttrium oxide, yttrium aluminum oxide, alkaline earth metal silicates, ZrVO, Mg(VO), and combinations thereof. For curved clamping molds, coatings can be made with zirconium dioxide stabilized by the addition of yttrium oxide, such as commercially available Metcro™ 22xx and 23xx powders (available from Oerlikon Metco, Frankfurt, Germany), including Metcro™ 222A, 231A, 233A, 233B, 233C, and 234A, or plasma-sprayed ZrOYO. Coatings can include multiple layers of different types of ceramics or multiple layers of one type of ceramic.

[0085] The ceramic coating used in the curved clamp mold can be selected to be less hygroscopic than conventional alumina insulation. The ceramic coating used in the curved clamp mold can be selected to be non-hygroscopic compared to conventional alumina insulation. By replacing conventional ceramic insulation sheets with curved clamp molds, the process chamber atmosphere can be significantly more stable because less or no water vapor is released into the chamber from the ceramic coating of the curved clamp mold during DED processing compared to the amount of water vapor released from conventional alumina ceramic plates.

[0086] The curved clamping mold can include a bond coat. A bond coat is a coating of a material that can increase adhesion between a substrate and a ceramic coating. A bond coat can provide corrosion resistance to the substrate to which it is applied. A bond coat can be used alone or in combination with a ceramic coating. A bond coat can include chromium and aluminum. A bond coat can include MCrAlY, where M is a metal selected from the group consisting of Co, Ni, Fe, Cr, Co, and Ni / Co combinations. In some applications, the bond coat includes MCrAlY, where M is Ni, Co, or a combination thereof. Exemplary bond coat materials include Amdry™ powder products, such as Amdry™ 962, 9621, 9624, 9625, 963, and 964 (available from Oerlikon Metco, Frankfurt, Germany). The bond coat can be present at a thickness of approximately 1 to 250 μm. An exemplary embodiment is shown schematically in FIG. 2C. The ridges 120 are coated with a bond coat 155. The bond coat 155 is then coated with a ceramic coating 150.

[0087] The thickness of the ceramic coating applied to the curved clamp mold can vary depending on the type of ceramic used and its ability to support both mechanical and thermal loads. In some configurations, the overall thickness of the ceramic coating can be from about 0.1 mm to about 5 mm, or from about 0.25 mm to about 4 mm, or from about 0.3 mm to about 3 mm. Each deposited layer can be thinner than the total amount of ceramic coating applied. However, overall, all of the applied layers of ceramic can form a ceramic coating that is at least 0.1 mm, or at least 0.25 mm, or at least 0.5 mm, or at least 0.75 mm, or at least 1 mm, or at least 1.25 mm, or at least 1.5 mm, or at least 2.0 mm, or at least 2.5 mm, or at least 3.0 mm, or at least 3.5 mm, or at least 4.0 mm, or at least 4.5 mm. The ceramic coating can have a thickness of 0.1 mm, or 0.25 mm, or 0.5 mm, or 0.75 mm, or 1 mm, or 1.25 mm, or 1.5 mm, or 2.0 mm, or 2.5 mm, or 3.0 mm, or 3.5 mm, or 4.0 mm, or 4.5 mm, or 5 mm. The ceramic coating layer can help reduce heat transfer from the pre-bent substrate to the curved clamp mold, thereby reducing heat loss from the pre-bent substrate during DED.

[0088] To further minimize or prevent thermal communication between the curved clamp mold and the pre-bent substrate, the curved surface of the curved clamp mold can be physically modified. A knurled surface can be cut into the curved surface of the curved clamp mold before applying the ceramic coating layer. A wavy surface including a combination of ridges and valleys can be cut into the curved surface of the curved clamp mold before applying the ceramic coating layer. A wavy surface including a combination of ridges and valleys can be cut into the curved surface of the curved clamp mold before applying the ceramic coating layer, where the surface of one or more ridges has a knurled surface. Exemplary embodiments are shown in FIGS. 2A, 2B, 3A, and 3B. The embodiment shown in FIG. 2A shows a curved clamp mold 100 including a top surface 110 that is wavy and includes a combination of ridges 120 and valleys 130, and a bottom surface having a flat or planar rim 140. The curved clamp mold can include an edge 115 on each side, as shown in FIG. 2B. Edges 115 on each side of the mold can help support and / or limit downward movement of the short edges of the plate (substrate) during clamping.

[0089] In the embodiments provided herein, the curved surface of the curved clamp mold includes knurling. The knurled surface on the curved surface of the curved clamp mold can create a linear pattern, a diagonal pattern, a diamond pattern, or a combination thereof on the surface. The diamond knurling can be performed to create a male or female knurling pattern. A male diamond pattern creates raised points. A female diamond pattern creates diamond-shaped indentations. The knurling can result in pillars with straight sides, each substantially perpendicular to the arc of curvature of the curved clamp mold. The pillars can have a planar top surface. The pillars can have a curved top surface. The pillars can have a cross section that is square, rectangular, circular, oval, rhomboid, trapezoidal, triangular, pentagonal, hexagonal, heptagonal, nonagonal, decagonal, frustum-shaped, truncated pyramidal, or any combination thereof. The pillars can be separated from each other by a space. The gap between the pillars can be substantially constant.

[0090] In the embodiments provided herein, the curved surface of the curved clamp mold can include corrugations or be wavy. The curved surface of the mold can be wavy to include alternating ridges and grooves. The corrugations can extend from one long edge of the curved clamp mold to the other long edge. The corrugations can extend from one short edge of the curved clamp mold to the other long edge (see, for example, Figures 3A and 3B). The corrugations result in multiple columns that are perpendicular to the arc of curvature of the curved clamp mold. The periphery of the mold at the curved surface can be contoured with a metallic material and is not coated with a ceramic coating or bond coat.

[0091] The ridges can be pillars with planar top surfaces. The ridges can be pillars with curved top surfaces. The grooves can have planar or curved or U-shaped bottom surfaces. The grooves can include rounded corners to protect against stress concentrations and crack propagation. The ridges can each have a taper that increases their cross-section along their longitudinal axis. In cross-section, the ridges can have a trapezoidal shape. In cross-section, the ridges can have an isosceles trapezoidal shape, where the longer base of the trapezoid forms the base of the ridge and the shorter base of the trapezoid forms the apex of the ridge. In cross-section, the ridges can have the shape of a convex isosceles trapezoid. In cross-section, the ridges can have the shape of a frustum of a regular polygonal pyramid. Exemplary ridges are shown in Figures 2A, 2B, 2C, and 3B.

[0092] Bumps with a frustum-type cross-section, particularly a pyramidal-type cross-section, can transfer stress from the top to the base while avoiding stress deformation of the bumps due to pressure applied to the curved surface of the curved clamp mold when the pre-bent substrate is attached to the jig. Bumps with a frustum-type cross-section can withstand applied loads, forces, and moments that may be applied during the DED process. Forces and moments acting on the plateau (top flat surface) of the bump can be transferred to the base of the bump and ultimately to the backside of the curved clamp mold. When the ridges have a frustum-type cross-section, they can transfer applied loads to a larger surface at the base. The knurled surfaces or valleys between the ridges form a gap between the curved surface of the curved clamp mold and the pre-bent substrate when the curved clamp mold contacts the pre-bent substrate. The gap can be filled with the DED chamber atmosphere or a noble gas, such as argon, which can act as an insulator. Argon gas is a very effective insulator. Solid / gas / solid interfaces have significantly lower electrical conductivity. Therefore, these specific interfaces between the pre-bent substrate, argon gas, and the curved clamp mold effectively function as thermal barriers. Therefore, the gap can also help minimize the average heat transfer rate between the pre-bent substrate and the curved clamp mold. The knurled surface or the combination of ridges and valleys on the curved surface of the curved clamp mold also minimizes the actual contact area between the pre-bent substrate and the curved clamp mold, further reducing heat transfer, thereby retaining most of the heat in the pre-bent substrate and avoiding heat transfer to the fixture or welding table. Therefore, a curved clamp mold including a knurled or wavy surface on the curved surface and a ceramic coating on the curved surface effectively reduces conductive heat transfer from the pre-bent substrate to the curved clamp mold. During the deposition of the first layer, the temperature gradient across the thickness of the pre-bent substrate can be substantially reduced, thereby reducing welding-induced residual stresses that occur during DED of the metal preform. Additionally, titanium and titanium alloys, such as Ti-6Al-4V, have a high yield stress and a relatively low modulus of elasticity, so these metals exhibit a high degree of springback at room temperature.Reducing conductive heat transfer from the pre-bent substrate to the curved clamping mold can facilitate heat accumulation in the substrate during the DED process, thus minimizing the degree of springback.

[0093] The knurling pattern or corrugations on the curved surface of the curved clamp mold can have a ceramic coating layer thereon, as described above. An exemplary embodiment showing a curved clamp mold 100 including a ceramic coating 150 is shown in FIG. 2B. The ceramic is typically applied to the surface of the curved clamp mold to form a ceramic coating. Therefore, the ceramic coating can also be present in the valleys of the knurling pattern or the valleys of the corrugations. The thickness of the ceramic coating alone is limited by the application limitations of the mold and the ability of the ceramic thickness to support the pre-bent substrate and the axially downward clamping force without damaging the ceramic coating when the substrate is clamped into the fixture. Due to limitations in coating technology, it can be more difficult to achieve a thicker layer of ceramic while maintaining the ceramic layer's ability to support the pre-bent substrate without damaging the ceramic coating when the support is clamped into the fixture. The exact support strength of the ceramic and its thermal conductivity can be determined by the ceramic's plasticity. For example, a 2 mm coating of a zirconium dioxide-based ceramic stabilized by the addition of yttrium oxide can provide excellent thermal isolation along with good mechanical support of the substrate without damaging the ceramic coating when the substrate is clamped into a fixture.

[0094] The curved clamp mold can serve as a shape-return structure. In embodiments, the curved clamp mold can serve as a support / shape-return structure. The curved clamp mold can be positioned between the pre-bent substrate and the jig when the pre-bent substrate is secured in the jig. The pre-bent substrate can be clamped in the jig to fully contact the curved upper surface of the curved clamp mold, such as contacting approximately 95% to 100% of the curved upper surface. Once the DED fabrication process is complete, a self-balanced stress state is achieved that allows upward recovery (springback) of the substrate and the DED structures shaped on the substrate after the clamps holding the substrate to the jig are released. The substrate straightens after being released from the clamps.

[0095] Nominal mold deflection h of curved clamping mold mold The arcuate shape is the difference between the maximum height of the center of the curved surface of the curved clamping mold and the upper surface of the edge of the curved clamping mold, as shown in FIG. 2B. In FIG. 2B, the difference between the maximum height 180 of the curved surface and the edge 115 of the curved clamping mold is h mold The mold length ratio L r is the new x dimension of the mold, L i is the ratio of the original mold length L0 to the expected maximum mold deflection h Lr is the nominal mold deflection h mold and the formula L r =L i / L0 Mold length ratio L calculated according to r is approximately proportional to the product of h Lr ≒h mold ×L r 2 is.

[0096] Therefore, for a curved clamping mold with xy dimensions of 635 mm x 190 mm (L x W), the predicted maximum mold deflection h Lr is approximately 3.8 mm. A longer mold, such as a curved clamp mold with xy dimensions of 1905 mm x 635 mm, would require a mold length ratio (Lr =1905 / 635=3) and 3.8 x 3 2 The maximum mold deflection is approximately 34.2 mm. The nominal mold deflection can be from about 3 mm to about 35 mm. Thus, the amount of mold deflection can depend on the mold characteristics. The longer the curved clamp mold needs to be to accommodate a longer substrate, the higher / larger the deflection of the curved clamp mold needs to be.

[0097] The curved clamp mold can also be designed so that the underside of the mold contains cavities or depressions while still maintaining the mold's rigidity and deformation resistance. An exemplary design is shown in Figure 4. Segments of non-magnetic metal on the bottom surface of the curved clamp mold can be machined away to create two or more cavities or depressions. The cavities or depressions can be separated from each other by unmilled areas of metal, which can act as reinforcing members. Unmilled areas of metal can also be present around the periphery of the bottom surface of the mold to form a rim. This design reduces the amount of material required to manufacture the mold while still maintaining the physical stability of the curved clamp mold. Reducing the overall bulk requirement for material used to form the mold can reduce the mold's weight while maintaining the mold's structural rigidity. As an alternative to milling metal to achieve the desired cavities and reinforcing members, a cast mold can be used to fabricate the curved clamp mold by casting it to include these attributes, minimizing the amount of material that needs to be removed to achieve the desired final design. Additionally, additional reinforcement members can be added, such as by attaching a separately provided reinforcement member to the bottom surface of the curved clamp mold. The reinforcement member can be attached by any suitable method. Exemplary methods include welding, screws, bolts, adhesives, or a combination thereof.

[0098] The cavities can have any shape. The cavities can be four triangular cavities separated by molding material to form X-shaped stiffening members that separate the cavities from one another. An exemplary embodiment is shown in FIG. 4. In the illustrated configuration, the substrate is machined to create triangular cavities 160, 162, 164, and 166 while leaving material to form X-shaped stiffening member 170 and flat circumferential rim 140. The outer surfaces of flat circumferential rim 140 and X-shaped stiffening member 170 are coplanar and can lie flat on the fixture surface when secured in a fixture. The cavities can be four square or rectangular cavities separated by molding material to form H-shaped stiffening members that separate the cavities from one another. The cavity can be any shape selected from the group consisting of a square, rectangle, circle, oval, ellipse, trapezoid, parallelogram, pentagon, hexagon, heptagon, star, cross, multi-pointed star, intersecting geometric shapes, polygon, geometric shapes, irregular shapes, regular shapes, symmetric shapes, asymmetric shapes, and combinations thereof.

[0099] In addition to the cost savings achieved by reducing the amount of non-magnetic metal required for fabrication, the cavity + stiffener + rim design offers several functional advantages. One advantage is that only the unmilled portion of the mold's bottom surface comes into contact with the high-strength steel fixture. This reduces conductive heat transfer from the clamping mold to the fixture while maintaining the rigidity of the clamping mold. This reduced heat transfer also contributes to heat retention in the pre-bent substrate, minimizing losses to the fixture.

[0100] Additionally, the cavity on the bottom surface of the curved clamp mold can hold atmosphere or argon gas. Argon can be effectively used as an insulator under the majority of the mold due to the presence of the cavity and the peripheral rim. Argon is a very effective insulator. Any heat flow from the curved clamp mold to the underlying steel fixture will occur only at the solid / solid interface due to conductive heat transfer as a result of the temperature gradient. Because solid / gas / solid interfaces have fairly low thermal conductivity, the cavity on the bottom surface of the curved clamp mold can effectively act as a thermal barrier (e.g., an air or inert gas gap) between the curved clamp mold and the fixture. An air or inert gas gap can be utilized at the interface between the base plate and the clamp mold and / or between the clamp mold and the fixture to help reduce heat transfer from the base plate to the fixture. Therefore, the curved clamp mold can help retain more heat in the pre-bent substrate, further reducing non-uniform temperature gradients and reducing thermal stress in the pre-bent substrate.

[0101] The curved clamp mold can exhibit high durability. After repeated use, the curved clamp clamp can experience some thermal stress that can accumulate and result in some small degree of mold bowing (such as 0.05 mm to approximately 0.5 mm of edge lift after repeated use). The degree of bowing observed in the curved clamp mold after repeated use is not expected to significantly alter the strain relief effect induced in the DED preform. Different object designs may require the use of different sized curved clamp molds to accommodate different sized substrates. Similar curved clamp molds can be used to manufacture objects with similar geometries and / or substrate sizes. For example, objects with similar geometries and / or substrate sizes can be grouped into families, and the same curved clamp mold design can be used within the same object family.

[0102] The exemplary curved clamp molds provided herein can be freestanding. They can be separate and distinct from the fixture. In exemplary embodiments, the curved clamp mold can lie flat on the fixture. The exemplary clamp mold can include a rim with a flat or planar surface around its periphery. The mold curvature can be empirically determined based on data collected from initial trials using ceramic plates. Ceramic plates were cut to various sizes and then used to generate various current curvatures and test their ability to minimize distortion in preforms prepared on the curved mold. Modeling was then used to confirm that the curvatures used experimentally provided close to the desired end result, i.e., distortion-free preforms. In cross section when viewed from the side, the shape of the curved clamping device can resemble the upper half of an ellipse, with the minor axis of orbit much smaller than the major axis of orbit. The ellipse can have an eccentricity close to but less than 1 (an eccentricity of 1 is a flat surface).

[0103] The curved clamp molds provided herein can make fixture redesigns easier, i.e., lighter, cheaper, and more versatile. Current fixtures are over-designed to accommodate the expected reaction forces and stresses that occur when clamping a substrate directly into the fixture and during DED. The curved clamp molds can reduce these expected forces and stresses. The curved clamp molds provided herein can also allow for changes in clamping arrangements compared to traditional clamping arrangements. In some applications, when a curved clamp mold is used, the entire periphery of the substrate can be clamped into the fixture.

[0104] C. Directed Energy Deposition Methods Provided herein is a method of directed energy deposition that alleviates or reduces distortion in objects, particularly titanium and titanium alloy objects, fabricated using directed energy deposition. The method includes thermally pre-bending a substrate on which the object is to be fabricated, attaching the pre-bent substrate to a curved clamp mold provided herein, pre-heating the substrate prior to DED deposition, and fabricating the object by layer-by-layer deposition of metal. Pre-bending the substrate includes inducing a steep through-thickness temperature gradient in the substrate.

[0105] In a thermally induced pre-bending step, a heat source can be used to apply thermal energy at a high energy density to a first or backside surface of the substrate. The thermal energy can be applied to a defined portion of the backside of the substrate to induce a large temperature gradient across the substrate. The large temperature gradient can introduce a high residual stress field within the substrate. The application of thermal energy can subsequently reduce the temperature of the surface to which the thermal energy is applied. In an embodiment, a gas jet device can be used to apply cooling gas. The application of cooling gas can increase the cooling rate, thereby further increasing the stress imparted to the substrate. For example, the heat source can include the electric arc of a plasma torch, such as a PTA torch. The gas jet device can be attached to a support relative to the plasma torch, as shown in FIG. 5. In FIG. 5, a gas jet device 200 is attached to a support 230, and a nozzle 210 of the gas jet device 200 can apply cooling gas to an area heated by a PTA torch 250.

[0106] In contrast, in the preheating step, thermal energy is applied uniformly to the surface of the substrate to minimize temperature gradients along the x, y, and z directions. The thermal energy is applied as uniformly as possible to the front side of the substrate by the heating device. Any heating device or method that provides uniform heating can be used for preheating. For example, direct heating using a heater positioned to apply heat across the surface of the substrate can be used. The heating device can be or include an infrared heater, an induction heater, a resistance heater, or a combination thereof. Exemplary heaters include a conductor-in-conduit heat source, a heater strip, a resistance heating strip, an infrared heater, a positive thermal coefficient ceramic heater, a thick-film ceramic heater, a resistance wire or resistance ribbon heating device, an infrared heater, and an induction heater. Preheating can also be achieved using one or more melting tools to apply thermal energy to the surface of the substrate. The melting tools can be used alone or in combination with an infrared heater, an induction heater, a resistance heater, or a combination thereof. The melting tool can include an electric arc plasma, a laser beam, or an electron beam as a heat source, and multiple melting tools containing the same or different heat sources can be used. The heated area can be maximized by using a lower energy density and applying more thermal energy to a larger area. Multiple heat sources can be used in tandem, series, or parallel to generate multiple "lines" of thermal energy applied to the front surface of the substrate, resulting in more uniform heating of the substrate. This allows for a more uniform temperature increase of the substrate using low energy density heating, resulting in little or minimal temperature gradients, especially across the thickness. Applying thermal energy using one or more melting tools during a preheat dry run (application of heat without adding molten metal) can effectively remove any residual contaminants from the surface of the substrate, such as any contaminants left by any ultrasonic / hand wipe cleaning procedures. Preheating is performed until the target temperature of the substrate is reached.

[0107] In some applications, the target temperature achieved by the preheating process is approximately ±25°C of the DED process temperature, such as the DED deposition temperature, or the DED process temperature. In some applications, the target temperature is within ±25°C of the plastic deformation temperature of the substrate. In some applications, preheating is performed until the substrate has a temperature of approximately 400-900°C. In some applications, preheating is performed until the substrate has a temperature of approximately 500-850°C. Other authors have reported that warm forming can be performed at 200-300°C to help reduce flow stress and also minimize springback in titanium. In some applications, preheating is performed until the substrate has a temperature of approximately 595-815°C.

[0108] The curved clamp mold can act as a support for the pre-bent substrate as it is clamped into the fixture. Among other benefits, the curved clamp mold provides a more consistent and repeatable final residual stress distribution, helping to minimize distortion of the workpiece during and after fabrication.

[0109] DED can be performed after (and while) the substrate is preheated to reduce the generation of temperature gradients during the DED process, especially in the thickness direction (z-direction). Optimally, no stresses are introduced into the fabricated object. However, the DED process is actually a welding process, and typically results in the accumulation of welding-induced residual stresses and deformations during fabrication. Reducing these residual stresses and deformations results in objects exhibiting improved dimensional accuracy and superior mechanical properties. The steps of the method are described in further detail below.

[0110] 1. Pre-bending the board In the methods provided herein, the substrate can be pre-bent before deposition. Pre-bending the substrate can be a separate process from the DED process. In the methods provided herein, thermal energy can be applied to a first side of the substrate to plastically deform the substrate, thus permanently and uniformly pre-bending the substrate. In embodiments, when thermal energy is applied across the surface of the first side of the substrate, one or more autogenous melt tracks or weld lines can be formed. This is significantly different from mechanical pre-bending using mechanical stress, which physically restrains the substrate using a clamp. Mechanical pre-bending can be used to bend the substrate. However, mechanical stress typically does not involve localized melting of planned segments of the substrate surface and is not sufficient to induce the desired uniform plastic deformation within the substrate. Mechanical force introduces a stress redistribution pattern different from that induced by applying localized heat after the substrate is released from the clamp. For example, when a substrate pre-bent with mechanical force is released, the substrate springs back to a state much higher than that achieved by thermal pre-bending.

[0111] In embodiments, the substrate can have a first side and an opposite second side. The first side can be the side that faces the fixture during DED fabrication. The second side can be the side on which the workpiece is formed by DED. For pre-bending, the substrate can be clamped in the fixture with the first side facing upward and the backside facing downward toward the fixture.

[0112] Pre-bending of the substrate can be performed while the substrate is in a flat state. Pre-bending of the substrate can be performed while the substrate is rigidly connected to a fixture using multiple clamps. Pre-bending of the substrate can be performed while the substrate is thermally isolated from the fixture. The substrate can be thermally isolated from the fixture by including one or more sheets of alumina insulation material having the same dimensions as the substrate. In an embodiment, four sheets of alumina insulation material can be used. Other materials that can thermally isolate the substrate from the fixture can be used. A device can be used that has similar thermophysical properties to a curved clamping mold, but in a flat form instead of a curved form, such as a wavy surface including a series of ridges and valleys with a ceramic coating that provides thermal insulation. The use of such a device can eliminate the need for alumina insulation sheets or other sheets of insulation material.

[0113] The substrate can be clamped to the fixture using clamps along all four edges of the substrate and around the entire perimeter of the substrate. In some applications, the substrate can be clamped to the fixture using clamps only along the two opposing longest edges of the substrate. This configuration allows a heat source, such as an electric arc plasma, laser, electron beam device, or any combination thereof, to reach the very edge of the substrate in the length direction. This clamping arrangement allows energy to be delivered edge-to-edge, creating a stress field all the way to the edge of the substrate. This can help balance any subsequent residual stresses introduced during DED fabrication in this particular region.

[0114] It has been found that applying intense thermal energy up to the edge or to within about 5 mm of the edge can minimize or prevent twisting of the substrate. As the distance from the edge to the end of the application of intense thermal energy increases, twisting also increases. The thermal stresses generated when the DED heat source is applied up to 10 mm from the edge are significantly different from those achieved when the heat source is applied up to the edge or only up to 20 mm from the edge. It has been found that substrate thickness makes little difference when considering the distance from the edge that can be tolerated without stress formation becoming a concern. Thicker substrates may require higher arc energy (or heat input) to be supplied during pre-bending, thereby achieving wider and deeper fusion profiles. This can be achieved, for example, by reducing the traverse speed, increasing the amount of thermal energy applied, or a combination of both. Taller DED preforms may also experience less distortion compared to shorter builds. This means that shorter builds allow for a larger mold radius of curvature.

[0115] Clamps can be used to attach the substrate to the fixture, and a consistent clamping force can be applied to all clamps. This can be achieved by torque-controlling the bolts connecting the clamps to the fixture. During the pre-bending stage, a force of 10 to 20 Newton meters (N·m), such as 15 N·m, can be used to tighten the bolts connecting the clamps to the fixture. The thicker the substrate, the higher the torque that can be used.

[0116] The DED heat source generates thermal energy to sufficiently melt planned segments of the substrate's surface in a predetermined order, location, or both, forming an autogenous melt line on the substrate surface. A gas jet device can be used to direct cooling gas at the melt track, causing it to cool rapidly. Heating or heating / cooling thermal cycles can induce controlled formation and development of residual stresses in the substrate. As a result, a uniform thermally induced pre-bending of the substrate can be achieved or controlled to a predetermined level as needed.

[0117] The DED heat source can be configured to provide sufficient thermal energy to induce a melt track on the DED substrate at a relatively high rate. Gas jet devices, if used, can deliver high volumes of cooling gas, such as 100 L / min to 200 L / min, to impart rapid heating / cooling cycles on the substrate surface. For example, using a plasma transferred arc system and a substrate thickness of 9.5 mm to 10 mm, a current of 190 amps, a voltage of 25.5 V, and a traverse speed of 10 mm / s can be used to generate a melt track that is approximately 3 mm wide and up to 1 mm deep. This can correspond to an arc energy delivery of approximately 485 J / mm. The energy and traverse speed can be adjusted for thicker substrates. An exemplary embodiment is shown in FIG. 6. In the illustrated embodiment, a substrate 300 having a first side 310 is shown having melt tracks 350 and 360 on the first side 310 with a space 355 between the melt tracks 350 and 355, and a DED back wall of a preform 330 on a second side 320 of the substrate 300.

[0118] The rapidly applied high temperature, along with the cooling gas from the gas jet device that promotes a fast cooling rate, can create very steep temperature gradients around the molten track and towards the substrate (along the x, y, and z directions), achieving a high stress state that approaches the material yield strength of the substrate material.

[0119] Any gas jet device configured to deliver cooling gas to the molten surface of the substrate to rapidly cool the molten surface can be used. For Ti or Ti alloy materials, an inert gas can be used as the cooling gas. The inert gas can be argon, helium, krypton, xenon, or a combination thereof. The gas jet device can include a pipe, tube, or other conduit, or combination thereof, capable of transporting the cooling gas from a gas supply to the application area. The gas jet device can include a first end attached to the gas supply and a second end. The second end can be positioned to direct the cooling gas exiting the second end toward a desired location on the substrate so that the cooling gas strikes the substrate surface specifically in the region of the molten metal in the melt track. Multiple gas jet devices can be utilized to enhance or accelerate the cooling of the melt track. The second end of the gas jet device can include one or more nozzles that can be adjustably positioned to direct the cooling gas toward the target location. While the effect of the cooling gas impinging on the surface of the substrate can be greatest near the direct impingement of the cooling gas, surrounding areas of the substrate can also be beneficially affected, reducing the temperature near the cooling gas. A pulsed gas flow can be used to provide the cooling gas. A fully turbulent gas flow can be used to improve cooling efficiency. Cooling gas jet devices are known in the art (see, for example, U.S. Pat. Nos. 4,090,697 (Perrine, 1978), 6,390,115 (Rohwer et al., 2002), and 7,381,364 (Yamashita, 2008)). An exemplary gas jet device is described in U.S. Patent Application Publication No. 16 / 019,460, filed June 26, 2018.

[0120] The pipes, tubes, or conduits of the gas jet device can be any material having channels extending therethrough that are compatible with the conditions expected to exist during DED deposition. The gas supply can be any source of cooled gas, such as a compressor or a container of high-pressure gas, in fluid communication with the gas jet device. Methods of supplying pressurized gas to gas conduits are known in the art.

[0121] The cooling gas can be supplied to provide a target flow rate of gas impinging on the substrate surface. The gas flow rate can be greater than 50 L / min, or greater than 100 L / min, or greater than 150 L / min, or greater than 200 L / min. The gas flow rate can be between 50 L / min and 500 L / min. The gas flow rate can be between 50 L / min and 250 L / min. The gas flow rate can be between 50 L / min and 100 L / min. The flow rate can be selected for fast cooling and thus the creation of high temperature and stress gradient conditions in the substrate.

[0122] The cooling gas can include an inert gas, such as argon, helium, neon, xenon, krypton, and combinations thereof. The cooling gas can be applied in a constant flow, or intermittently, or in a pulsed flow. The applied cooling gas temperature can be any temperature. The cooling gas temperature can be the ambient temperature of the additive manufacturing process. The cooling gas temperature can be applied at a gas temperature of about 100°C or less. The cooling gas temperature can be about room temperature or less, such as about 25°C or less. The cooling gas temperature can range from about -10°C to about 80°C.

[0123] For a preform or workpiece formed on the second surface of the substrate, the number of DED walls having a centerline parallel to the short edge of the substrate and the number of DED walls having a centerline parallel to the long edge of the substrate can be determined. If the majority of the DED walls of the preform or workpiece have centerlines parallel to the short edge of the substrate, melt tracks can be generated parallel to the short edge of the substrate. Generally, for substrates with a large length-to-width aspect ratio, melt tracks should be generated along their longest axis, i.e., the axis where the greatest effect of distortion is expected. If the majority of the DED walls of the preform or workpiece have centerlines parallel to the long edge of the substrate, melt tracks can be generated preferentially parallel to the long edge of the substrate to counteract the greatest effect of distortion along the longest axis of the substrate.

[0124] The thermally induced pre-bending on the first or backside of the substrate can be applied so that the resulting melt track and the typical distribution of longitudinal and transverse residual stresses caused by welding are positioned about 10 mm to about 20 mm from the centerline of the majority of the DED walls of the preform or workpiece deposited on the second or front side of the substrate. The pre-bending shaping technique applied to the first side of the substrate can be performed so that the resulting melt track is positioned about 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, or 20 mm from the centerline of the DED walls of the workpiece deposited on the second or front side of the substrate parallel to the long edge of the substrate. The melt track can be positioned so that it lies under a minimum area of ​​the DED walls of the workpiece. An exemplary embodiment is shown in FIG. 6.

[0125] Prior knowledge of the shape of the DED workpiece to be deposited on the second side of the substrate can be used to determine the pre-bend heating procedure to be applied to the first side of the substrate. The heating procedure can be designed to minimize the number of melt tracks under the area where the DED workpiece will be built. The final integrated residual stress distribution resulting from the combination of both DED and melt tracks has a low tensile peak at the DED centerline and low balancing compressive stresses away from the DED centerline when compared to the original residual stress profile of DED without the pre-bend melt tracks (i.e., a high tensile peak at the DED centerline and balancing compressive stresses away from the centerline).

[0126] An exemplary embodiment illustrating the application of thermal energy to create a melt track on a substrate is shown in Figure 7A. This figure schematically illustrates an exemplary heating path that can be used to move a DED energy source to form a melt track on the backside or top surface of the first side of the substrate to pre-bend the substrate toward the heat source. The black arrow indicates the direction / path of the DED energy source. ES The circle containing the symbol indicates the sequence X, where X is 1 to 6, across the surface of the first side 310 of the substrate 300. S indicates the start of a path of energy application. E indicates the end of a path resulting in a heating path. In the pattern shown, heating can start at the top edge across the x direction (1 ES ), then the heat source can be moved less than halfway across the substrate in the y direction and heat can be applied from short edge to short edge in the y direction (2 ES This step is ES , 4 ES , 5 ES and 6 ES The first heating pass 370 can be repeated for 1 ES The second heating path 371 corresponds to ES The third heating path 372 corresponds to ES The fourth heating path 373 corresponds to ES The fifth heating path 374 corresponds to ES The sixth heating path 375 corresponds to ES Corresponds to.

[0127] A predetermined DED heating / cooling thermal cycle can induce controlled formation and development of residual stress in the substrate. Application of cooling gas using a gas jet device (not shown) can be used to accelerate cooling. As a result, a uniform thermally induced pre-bending of the substrate can be achieved / controlled to a predetermined level.

[0128] FIG. 7B shows the heat generated by heating paths 370-375 on the backside or first side of the substrate (1 ES ~6 ES 6A shows a schematic representation of the relative position of a thermally induced pre-bend melt track (shown as a ) to a superimposed (grey dashed line) DED workpiece preform 600 fabricated on the opposite front or second side of the substrate. The melt track can result from the application of thermal energy in a heating path.

[0129] The heat source of the melting tool can heat the backside of the substrate, forming melt tracks at predefined locations on the substrate and applying thermal stress to the substrate. This thermal stress can cause the substrate to bend. The substrate can be clamped in a fixture. Therefore, bending of the substrate is not apparent while the substrate is attached to the fixture. When the clamp is removed, the substrate can bow upward away from the fixture, i.e., toward the heat source. A well-defined radius of the bow can define a uniformly deformed pre-bent substrate. After the clamp is removed from the fixture, the resulting uniform elastic-plastic pre-bending effect on the substrate caused by the application of thermal energy is shown in Figure 8A. The resulting substrate 300 bows upward away from the fixture 400, exhibiting the nominal substrate deflection. In Figure 8B, the substrate is flipped upside down. As can be seen in Figure 8B, the pre-bent substrate has a uniform elastic-plastic bend (bow) caused by the application of intense thermal energy and cooling gas, which induces large temperature and stress gradients on the backside of the substrate. Figure 8B shows the nominal substrate deflection 410.

[0130] The thermally induced substrate pre-bending procedure can result in a longitudinal residual stress distribution. Comparison of the residual stress maps of several pre-bent substrates thermally pre-bent as described herein reveals that significant tensile stresses occur at the weld centerline (+σ L , up to 600Mpa), and further away, balanced by compressive stress (-σ L , maximum -300 MPa), a characteristic distribution of residual stresses was demonstrated.

[0131] Nominal board deflection h of the board along the z direction for a board with dimensions of 635 mm x 190 mm x 9.5 mm (L x W x T) sub (bow shape)(h sub =z max -z min ) can be 15 mm after the thermally induced substrate pre-bending is applied. This is a measurement that is also verified by modeling. The substrate length ratio L r is the new x-dimension of the board, L i The ratio of the board length L0 to the board length L0 of 635 mm. Lr is the nominal board deflection h sub and the formula L r =L i / L0 The board length ratio L is calculated according to r is approximately proportional to the product of h Lr ≒h sub ×L r 2 is.

[0132] For example, if the board length ratio is 3 (i.e., L r The relatively long substrate size (=1905 / 635=3) was reduced to 15 × 3 after thermally induced substrate pre-bending was applied. 2 = 135mm. The amount of board deflection may therefore depend on the properties of the board. The longer the board, the higher / larger the deflection required.

[0133] The heat source that provides the thermal energy to create the melt track on the backside of the substrate can be any energy source capable of providing sufficient thermal energy to melt the substrate in the heat application area to form the melt track. Exemplary heat sources that can be used include electric arc plasma, laser beam, electron beam, and any combination thereof. In some configurations, two or more melting tools providing separate heat sources can be used. For example, one melting tool providing a heat source can be used to preheat the substrate, and a second melting tool providing a heat source can be used to melt the preheated substrate to form the melt track. When multiple melting tools providing separate heat sources are used, they can be the same or different from each other. Examples of combinations of multiple melting tools providing DED heat sources include two PTA torches that generate electric arc plasma, two laser devices that generate laser beams, two electron beam devices that generate electron beams, a PTA torch that generates electric arc plasma and a laser heat source that generates a laser beam, a PTA torch that generates electric arc plasma and an electron beam heat source that generates an electron beam, and a laser device that generates an electron beam and an electron beam device that generates an electron beam.

[0134] Sufficient heat can be applied to the substrate surface to heat it so as to melt at least a portion of the substrate in the heat-applied region to form a melt track. The target temperature supplied by the heat source can be the melting temperature of the substrate material, or a temperature 5°C to 50°C higher than the melting temperature of the substrate, or a temperature 10°C to 20°C higher than the melting temperature of the substrate. Localized heating of the substrate can help induce stress in the substrate to create a highly stressed substrate in an elastic-plastic state. When the substrate is unclamped from the fixture, it bows, forming a pre-bent substrate to stabilize or balance the residual stress imparted by the pre-bending step. The highest stress is typically induced at the melt track. The tensile stress peak is located at the centerline of the melt track. The tensile residual stress peak may be close to the yield strength of the material. As the distance from the centerline increases, the residual stress becomes compressive. The amount of upward displacement (i.e., bowing) can be observed to determine whether sufficient stress has been induced. The greater the displacement, the higher the residual stress induced during pre-bending. For most substrates, the maximum tensile residual stress is close to the yield strength of the parent material. The sequence and location of these melt tracks relative to the DED can be modified to achieve the target residual stress redistribution.

[0135] The amount of heating required to induce a target stress and the number of melt tracks generated on the backside of a substrate can be determined experimentally. For example, DED can be used to fabricate an object on a first substrate without pre-bending the first substrate and measure the resulting distortion in that substrate. A second substrate having similar properties to the first substrate can then be pre-bent by forming melt tracks on the backside of the second substrate by an amount necessary to fully or partially compensate for the amount of distortion measured in the first substrate. The amount of heating required to induce a target stress and the number of melt tracks generated on the backside of the substrate can also be determined based on modeling predictions, modeling, calculations, or a combination thereof. Modeling can be used to predict, for example, distortion and residual stress generation in the substrate, and experiments can be used to confirm the modeling predictions. Simulations have also been found to provide very good agreement with experimental data. In some embodiments, in addition to the predetermined placement of melt tracks about 10 mm to about 20 mm from the centerline of the preform, melt tracks can also be generated along the longest substrate length for high aspect ratio parts. Assuming a relatively symmetrical square preform shape is produced on a square substrate, a crisscross pre-bending thermal energy application pattern can be used on the underside of the substrate to induce bending in both the longitudinal and lateral directions, resulting in a clamp mold that can assume a dome shape.

[0136] After forming, the pre-bent substrate can be handled in a consistent manner as would a conventional substrate. For consistency, the pre-bent substrate temperature can be selected. The same temperature can be used to form similar preforms. The temperature of the pre-bent substrate can be room temperature when in use and secured in a jig. The temperature of the pre-bent substrate can be 50°C or higher when in use and secured in a jig. In a typical additive manufacturing process, the number of substrates needed to produce a target number of preforms can be determined, and a sufficient number of pre-bent substrates can be produced one at a time, and then each can be individually secured in a jig at the target temperature, such as room temperature.

[0137] 2. Fixing the pre-bent board to the jig After the pre-bending of the substrate is completed, the pre-bent substrate can be attached to a jig or welding table. The pre-bent substrate can be attached to the jig using, for example, a clamp attached to the jig. A curved clamp mold can be used as a lower support between the pre-bent substrate and the jig. The pre-bent substrate can have the same curvature as the curved clamp mold. The pre-bent substrate can have a curvature different from that of the curved clamp mold. The pre-bent substrate can be positioned so that the backside having the melt track can contact the curved surface of the curved clamp mold. The clamp attached to the jig can apply a force to the pre-bent substrate to elastically deform the pre-bent substrate. The clamp can conform the pre-bent substrate to the curvature of the curved clamp mold. The clamp can be made of high-strength steel, ultra-high-strength steel, or high-strength low-alloy steel.

[0138] As clamping progresses to secure the pre-bent substrate to the fixture, the curvature of the pre-bent substrate can gradually become similar to the curvature of the curved clamp mold. Clamping can cause the curvature of the pre-bent substrate to become equal to the maximum deflection of the curved clamp mold. Sufficient force can be applied by the clamps to ensure that the surface of the pre-bent substrate is in full contact with the curved surface of the curved clamp mold. The thicker the substrate, the greater the resistance. Therefore, the clamps may need to apply more force to overcome the elastic reaction of the pre-bent substrate to conform the pre-bent substrate to the curved clamp mold. The amount of force required by the clamps to attach the pre-bent substrate to the fixture and contact the underlying curved clamp support can be from about 10 Nm to about 120 Nm. For example, for a Ti-6Al-4V substrate having a thickness of about 9.5 mm to 10 mm, the clamps can apply only 40 Nm of torque to attach the pre-bent substrate to the fixture and conform the pre-bent substrate to the curved clamp mold.

[0139] The clamps can be torqued to apply an initial firm clamping force to the substrate, followed by additional torque to apply a final torque to the substrate. The initial firm clamping can be achieved by sequentially tightening the clamps or by tightening clamps positioned opposite each other. The curvature of the pre-bent substrate can gradually become similar to the curvature of the curved clamp mold. When the final torque is applied, the pre-bent substrate can be in full contact with the curved clamp mold. When the final torque is applied, the pre-bent substrate can be in contact with about 95% to about 100% of the curved clamp mold.

[0140] The pre-bent substrate can be coupled to the curved clamp mold to ensure complete contact, such as about 95% to about 100% contact, between the substrate and the curved clamp mold, resulting in consistent thermal and mechanical conditions at the interface between the pre-bent substrate and the curved clamp mold. The curvature of the curved clamp mold allows for significantly less torque to be applied to the substrate through the clamp than would be required to mount the pre-bent substrate flat in the fixture without the curved clamp mold. The mold curvature can be mimicked by a plate interface condition. Complete contact between the substrate and the curved clamp mold can be a good indicator of satisfactory clamping. To achieve satisfactory clamping, (a) a consistent clamping force can be used by applying torque-controlled, firm tightening of the clamp mounting bolts; (b) consistent dimensions can be selected from the clamps; (c) clamping can be applied symmetrically; (d) proper clamp installation can ensure uniform pressure and heat transfer distribution to avoid gaps and non-uniform pressure application; or (e) any combination of (a)-(d). For example, the clamp can be attached to a base plate via countersunk screws that are flush with the top surface of the clamp to ensure uniform pressure and heat transfer distribution between the clamp and base plate. The bottom and side contact faces of the clamp can be configured and arranged to be flush with and in contact with the base plate to ensure uniform pressure and heat transfer distribution. See, for example, Figures 14A and 14B. Dashed circles 544, 545, 546, 547, 548, and 549 in Figure 14A indicate areas of uneven pressure and heat transfer distribution due to the way countersunk screws 510 and bolts 520, adjusted via nuts 525, adjust the clamp 500 to attach the base plate 550 to the fixture surface 530. In the illustrated example, the base plate 550 is insulated from the fixture surface 530 by layers of alumina thermal insulation plates 540-543.

[0141] To avoid uneven pressure and heat transfer distribution, as shown in FIG. 14B, the countersunk head screw 510 can be adjusted so that its tip 515 is flush with the top surface 507 of the clamp 500. This allows for uniform pressure and heat transfer distribution. Boxes 575, 576, 577, and 578 in FIG. 14A illustrate the areas of uniform pressure and heat transfer distribution achieved by the way the countersunk head screw 510 and bolt 520, adjusted via nut 525, adjust the clamp 500 to attach the base plate 550 to the fixture surface 530. The illustrated embodiment shows the clamp's bottom contact facet 505 and side contact facet 507 flush with the top and side surfaces of the base plate, respectively, to ensure uniform pressure and heat transfer distribution.

[0142] When the pre-bent substrate is mounted in a fixture using a curved clamping mold as the lower support, there may be a slight redistribution of longitudinal residual stresses, e.g., +σ at the weld centerline. L The tensile stress peak can increase from about 600 MPa to about 700 MPa, while -σ away from the centerline L The compressive stress may be reduced from about -300 MPa to about -200 MPa.

[0143] The clamping of the pre-bent substrate into the curvature clamp may occur in an elastic mode. The curvature imposed by clamping the substrate into the mold may be fully reversible if the substrate is then released from the curvature clamp mold. This is particularly true for substrates made from metals that have high springback at room temperature. The elastic deformation imposed by the clamp force may be distinguishable from the plastic deformation introduced into the substrate in the pre-bending step.

[0144] Clamps used to secure a substrate to a jig or welding table can typically be made from materials that exhibit high strength and low deformability. Due to its high strength, thermal stability, and deformation resistance, steel can be used as a material for the clamp. Steel typically has a higher thermal conductivity than the substrate. For many substrates, the heat transfer of the steel in the clamp can be orders of magnitude higher than that of the substrate. The difference in heat transfer between the clamp and the substrate can cause the clamp to act as a heat sink. During the DED process, the clamp's direct contact with the substrate as a heat sink can result in rapid thermal energy flow from areas of the substrate adjacent to or near the clamp attachment point to the clamp and from the clamp to the jig or welding table. As a result, high temperature gradients can be induced in the pre-bent substrate during the DED process. These high temperature gradients can impose stresses and strains on the substrate during the deposition process.

[0145] The clamps can be insulated to reduce or prevent the formation of temperature gradients due to the clamps acting as heat sinks. Insulation can reduce or prevent heat transfer from the substrate through the clamps to the fixture. A thermal barrier coating can be applied to all surfaces of the clamps. The thermal barrier coating can be applied to all surfaces of the clamps that may come into contact with the substrate. The thermal barrier coating can be any coating that does not effectively transfer thermal energy. The thermal barrier coating can be made of a ceramic material, silicon carbide, silicon nitride, boron carbide, or any combination thereof. The ceramic material can be or include alumina, zirconia, titanium oxide, alkaline earth metal silicate, aluminum titanate, zirconium dioxide, zirconium dioxide stabilized by the addition of yttrium oxide, yttrium aluminum oxide, ZrV2O7, Mg3(VO4)2, or a combination thereof. Any high-temperature ceramic coating known in the art can be used (see, for example, U.S. Pat. Nos. 4,321,310 (Ulion et al., 1982), 5,789,330 (Kondo et al., 1998), 5,304,519 (Jackson et al., 1994), 6,387,539 (Subramanian, 2002), and 6,998,064 (Gadow et al., 2006)). The clamps can be coated with zirconium dioxide stabilized by the addition of yttrium oxide, such as plasma-sprayed ZrO28Y2O3. The thermal barrier coating can include multiple layers of different types of ceramic, carbide, or nitride, or combinations thereof, or multiple layers of one type of ceramic, carbide, nitride, or combinations thereof.

[0146] Many of these materials are commercially available and can be applied using a variety of techniques known in the art, for example, the thermal barrier coating can be applied using any process including atmospheric plasma spraying, magnetron sputtering, chemical or electrochemical deposition such as electrophoretic deposition, or physical vapor deposition such as electron beam physical vapor deposition, or any combination thereof.

[0147] The thickness of the thermal barrier coating applied to the clamp can vary depending on the type of insulating material used and its ability to support a load without damage due to the application of compressive forces. In some configurations, the thickness of the thermal barrier coating can be 0.1 mm to 5 mm, or 0.25 mm to 4 mm, or 0.3 mm to 3 mm, or 0.4 mm to 2 mm, or 0.5 mm to 1.5 mm. The thermal barrier coating can be at least 0.1 mm, or at least 0.25 mm, or at least 0.5 mm, or at least 0.75 mm, or at least 1 mm, or at least 1.25 mm, or at least 1.5 mm, or at least 2.0 mm, or at least 2.5 mm, or at least 3.0 mm, or at least 3.5 mm, or at least 4.0 mm, or at least 4.5 mm. The thermal barrier coating can have a thickness of 0.1 mm, 0.25 mm, 0.5 mm, 0.75 mm, 1 mm, 1.25 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, or 5 mm. The thermal barrier coating layer can reduce heat transfer from the DED substrate to the fixture, thereby reducing heat loss from the DED substrate. One example of a thermal barrier coating is 0.5 mm to 1.5 mm of ZrO28Y2O3 plasma sprayed onto the contact surfaces of the clamps to help reduce conductive heat transfer from the DED substrate to the clamps. This improves insulation and reduces thermal conductivity.

[0148] To further reduce heat transfer from the substrate through the clamp to the fixture, the surface of the clamp in thermal communication with the substrate can be modified to have a knurled pattern. The knurling on the surface can reduce the amount of surface of the clamp that comes into contact with the substrate. The knurling can reduce the likelihood of heat conduction between the clamp and the substrate. Any knurling pattern known in the art can be used on the surface of the clamp that may come into contact with the substrate. Exemplary knurling patterns include angled patterns such as diagonal patterns, linear patterns, diamond patterns, or any combination thereof. The knurling pattern can also have a thermal barrier coating layer on its surface.

[0149] To reduce heat transfer from the substrate through the clamp to the fixture, the surface of the clamp in thermal communication with the substrate can be modified to have a corrugated surface including a series of ridges and valleys. The corrugated surface can reduce the amount of surface of the clamp in contact with the substrate. The corrugated surface can reduce the likelihood of heat conduction between the clamp and the substrate. Any corrugated pattern known in the art can be used. The corrugations can be in any direction on the surface of the clamp. Exemplary configurations include angled patterns such as diagonal corrugations, linear corrugations parallel to the long edges, linear corrugations parallel to the short edges, or combinations thereof. The corrugated surface can also have a thermal barrier coating layer on its surface.

[0150] Due to limitations in coating technology, thicker layers of thermal barrier coatings capable of withstanding the compressive forces required to secure the pre-bent substrate to the fixture can be more difficult to achieve. The desired compressive strength of the thermal barrier coating can depend on the thermal barrier coating's composition. For example, a 0.5-2.0 mm coating of a zirconium dioxide-based ceramic stabilized with the addition of yttrium oxide has been shown to provide good thermal insulation and good compression resistance without damaging the thermal barrier coating when the substrate is connected to the fixture using clamps.

[0151] Exemplary clamp configurations are shown in Figures 9A, 9B, and 9C. Figure 9A shows a bottom view of clamp 500 with threaded holes 501 for accepting flathead screws and holes 502 for accommodating bolts. Top surface 507 can include ceramic-coated surfaces 509 at the edges that will contact the base plate. Top surface 507 can be wavy. Figure 9B shows a side view of clamp 500, showing the ceramic-coated surfaces 509 of bottom and side contact facets 505, 506 that will contact the base plate. Figure 9C shows a three-dimensional view of clamp 500, showing a perspective overhead view of clamp 500's threaded holes 501 and ceramic-coated bottom and side contact facets 505, 506. Clamps with the same design (e.g., clamps all the same length or width, or the same length and width) can be used. Clamps with different lengths and / or widths can also be used.

[0152] Insulated clamps can be placed around the entire periphery of the pre-bent substrate to ensure full contact, such as about 95% to about 100% contact, between the pre-bent substrate and the curved clamping mold. An exception to using only insulated clamps is when a PTA torch is used as the DED melting tool, providing the electric arc plasma as the heat source. In such a configuration, one or more non-insulated clamps can be used to provide a path for electrical current. For example, in an exemplary configuration, two or three non-insulated clamps can be used to ensure a stable current path from the power source. In such a configuration, one or more non-insulated clamps can be positioned on the short edges of the base plate and one non-insulated clamp can be positioned in the mid-section of the longest base plate dimension. Other configurations can be used.

[0153] To reduce stress and strain in the substrate during metal deposition and object fabrication, clamps can be positioned above the substrate so that their centerlines coincide with the beginning and ending locations of DED strings / walls whenever possible. An exemplary configuration is shown in FIG. 10 . In the illustrated configuration, clamps 500 are positioned around the periphery of preform 600 so that substantially the entire periphery of substrate 300 is clamped to fixture 400, and their centerlines are positioned to coincide with the beginning and ending locations of DED strings / walls of preform 600 whenever possible (shown as clamps 610, 615, 620, 625, and 630). These substrate clamping constraints can substantially reduce deformation effects resulting primarily from longitudinal residual stresses during deposition. Non-optimal clamping can result in localized deformation or buckling due to the lack of clamping constraints, as shown by dashed outline 650.

[0154] Different clamping arrangements can be used during pre-bending and mounting the pre-bent substrate in a fixture for DED processing. Different clamping arrangements can be selected because applying thermal energy to the backside of the substrate during pre-bending using a melting tool providing the DED heat source may require increased access by the heat source to the entire or near-entire length of the substrate to generate uniform deflection along the longest substrate length. Insulating clamps may not be used at the edges to allow the melting tool providing the DED heat source to apply thermal energy to the entire length of the substrate. During object building by metal deposition on the front side of the substrate, insulating clamps can be placed around the periphery of the substrate, particularly at the beginning and end of the DED walls, to help reduce localized deformation resulting from residual stress generation. The clamping configuration can (1) promote symmetry across the plate, (2) utilize clamps with identical geometries when possible, (3) allow desired access to the substrate by the melting tool providing the DED heat source, and (4) meet the torque requirements needed to mount the pre-bent substrate in the fixture.

[0155] The use of a curved clamp mold can significantly improve the manufacturing process. However, it is possible to perform the DED process on the front side of a pre-bent substrate by using a sheet of insulation, such as a sheet or plate of conventional alumina (Al2O3) insulation cut to form a curvature that generally matches the arc of the pre-bent substrate. This requires significantly more work than using the curved clamp mold provided herein. In addition, workpiece-to-workpiece variability can occur due to variations in the thickness of the alumina insulation sheet and the formation of layers of the pre-cut sheet to match the curvature of the pre-bent substrate. The curved clamp mold provided herein can reduce or prevent such part-to-part variability by providing a mold with consistent physical and mechanical properties that can be used multiple times.

[0156] 3. Preheat the board Once the pre-bent substrate is secured in the fixture using the curved clamping mold and insulating clamps, the pre-bent substrate can be pre-heated before the DED process begins. The pre-heating step is intended to treat a majority of the front surface of the substrate with a heat source to uniformly heat the substrate as a whole to the target temperature. Subsequently, a workpiece is built using the DED process while the pre-bent substrate is still hot.

[0157] Contrary to the way energy is applied to the backside of the substrate in the pre-bending step, where a steep temperature gradient and a high cooling rate are selected to induce higher internal tensile and compressive stresses during the pre-heating step, energy is supplied more gently and consistently toward the front side of the substrate. During the pre-heating step, energy can be applied to the front side of the substrate using a heat source under conditions that do not locally melt the substrate surface. During the pre-heating step, energy can be applied to the front side of the substrate using a heat source under conditions that do not form a continuous melt track. Because near-uniform heating is desired, energy from the heat source can be applied at a relatively slow speed from the melting tool providing the heat source. In this case, the melting tool providing the heat source is positioned at a higher standoff distance (further from the substrate) to apply thermal energy at a lower energy density. In addition, because the pre-heating step is intended to heat the substrate before building a workpiece using the DED process, no cooling gas is applied using a gas jet device. As a result, the cooling rate is significantly lower than that which can occur in the pre-bending step.

[0158] This slower heating / cooling cycle during preheating can promote a slow cooling rate and low temperature gradient formation in the substrate along the x, y, and z directions. Energy application during preheating can be performed in a manner that allows for slow residual heat accumulation because heat can be dissipated through the pre-bent substrate volume by conduction. For example, a lower energy density can impart a lower temperature gradient to the substrate. These conditions can generate a "nearly" uniform temperature distribution across the base plate, allowing for slow accumulation of residual heat because heat can be dissipated through the base plate volume by conduction. The pre-bent substrate is thermally isolated from the bending clamp mold, and insulating clamps are used to secure the pre-bent substrate to the fixture. Therefore, residual heat can be more easily retained in the substrate.

[0159] Low energy densities can be sequentially applied to the substrate to generate a near-uniform temperature distribution across the surface and through the thickness of the substrate. To avoid exposing one area to accumulated thermal energy, the application of energy can begin at a first edge of the substrate and continue across the surface of the substrate along the x-direction until it reaches a second, opposite edge of the substrate. The melting tool providing the heat source can then be returned to the first edge and repositioned some distance in the y-direction from the first pass of energy application. Energy is applied along the x-direction. This process is repeated until the temperature of the pre-bent substrate reaches the target temperature. The more uniform the temperature distribution in the substrate, the better the effects of stress and distortion in the substrate are mitigated.

[0160] An exemplary pattern of energy application during preheating is shown in Figure 11. The black arrows indicate the direction / path of the DED energy source. ES The circle containing the symbol indicates the sequence X, where X is 1 to 8, across the surface of the second side 320 of the substrate 300. S indicates the start of a path of energy application. E indicates the end of a path resulting in a heating path. In the pattern shown, heating begins at the bottom edge across the x direction (1 ES The heat source is then moved in the y direction up to a point approximately 1 / 9 of the way from the initial heating path. Heat is applied from short edge to short edge in the y direction (2 ES This procedure continues for 3 minutes until heat is applied across the surface of the substrate 300. ES , 4 ES , 5 ES , 6 ES , 7 ES and 8 ES The first heating pass 700 is repeated for 1 ES The second heating path 705 corresponds to ES The third heating path 710 corresponds to ES The fourth heating path 715 corresponds to ES The fifth heating path 720 corresponds to ES The sixth heating path 725 corresponds to ES The seventh heating path 730 corresponds toES The eighth heating path 735 corresponds to ES . A single energy source or multiple energy sources can be used in the preheating path. The figure shows solid and dashed black lines representing the tool path and preheating sequence of two parallel melting tools. The illustrated embodiment describes heating using a DED energy source. However, other energy sources can be used. Exemplary alternative energy sources include, for example, one or more lasers, one or more induction heaters, or any combination of lasers, DED energy sources, and induction heaters. Additionally, other methods and devices that can enable the base plate to be heated uniformly, such as induction heating, resistance heating, etc., can also be used.

[0161] The direction of preheating can be the same as the actual DED process for forming the preform, such that the temperature and residence time of the region under the DED deposition region can be similar. For example, as shown in Figure 11, the start (S) and end (E) positions of the application of thermal energy for preheating (shown as black arrows and marked with circles, respectively) are in the same direction as the direction of metal deposition during the DED process.

[0162] Any heat source that generates thermal energy can be used to apply the thermal energy application. For example, electric arc-based, laser beam, and electron beam heat sources can be used alone or in combination to achieve the preheating effect. For example, one or more thermal arc welding sources, such as a preheating PTA torch and a melting PTA torch, can be applied laterally across the substrate to heat it. The PTA torches can be positioned to reduce temperature gradient formation and shorten the total preheating time. Other heat sources based on laser energy and electron beam energy can also be used for the same purpose, but with a suitable set of parameters to achieve similar heating of the substrate. The spacing between the application areas of thermal energy for preheating can be determined by the amount of heat supplied by the heat source. The spacing between the application areas of thermal energy for preheating can be determined by the heat distribution supplied by the heat source.

[0163] For example, two PTA thermoelectric arc plasma welding torches can be used simultaneously, crossing sideways, to heat a substrate. The two torches can have a relative (fixed) distance from each other, such as about 20 mm to 40 mm. This configuration allows thermal energy to be applied along the x-direction and across the y-direction so that the heat is supplied and spread as uniformly as possible without overlapping the centerlines of the heat sources. On the other hand, for a fixed substrate width, the amount of preheating can be varied if a more focused heat source, such as laser energy or electron beam energy, is used for this purpose. The laser or electron beam spot can be designed to be larger to provide a wider heating area on the substrate. Other methods and devices, including induction heaters and resistance heaters, can enable the substrate to be heated uniformly.

[0164] Uniform preheating can be achieved using a melting tool that provides a DED heat source. The sequence and parameters used to achieve preheating using a melting tool that provides a DED heat source can be controlled to apply energy to the substrate and generate a lower temperature gradient than that imposed on the substrate during the pre-bending step. Preheating can be performed to uniformly increase the temperature of the substrate. In an exemplary embodiment, preheating can be performed to uniformly increase the temperature of the substrate to a temperature ranging from about 350°C to about 650°C, depending on the substrate material. For example, a Ti-containing substrate can be preheated to a temperature ranging from about 400°C to about 550°C. For some Ti alloys, the substrate can be preheated to a temperature ranging from about 450°C to about 500°C to reduce temperature gradient formation when DED is performed. Preheating can reduce internal stress buildup during the DED process by reducing any local stresses due to heating as the molten metal is deposited to shape the workpiece. Preheating the substrate to an elevated temperature, such as a warm or hot wire forming temperature, can result in near-zero distortion in the preparation of the weld bead on the substrate during DED workpiece formation because the resulting temperature gradient can be significantly smaller than the temperature gradient created through the thickness when the weld is deposited on the substrate at room temperature. The preheating is not intended to significantly alter or melt the substrate surface and can result in the formation of the weld seam without the addition of any metal.

[0165] For preheating, indirect heating can be used, such as heating a pre-bent substrate clamped in a fixture in a furnace to raise the temperature of the substrate. In some applications, this is not feasible or practical. The time required to move the substrate / fixture combination from the furnace into a chamber where the DED process can occur can result in significant loss of residual heat from the substrate, defeating the purpose of the preheating step. The system can be modified to include a furnace. The furnace can be accessed through the deposition chamber to enable use of the furnace to preheat the substrate.

[0166] Direct heating can be used using a heating device positioned to apply heat across the surface of the substrate while it is mounted in the fixture. Any method and heating device that allows the substrate to be uniformly heated prior to deposition can be used. The heating device can be or include an induction heater, a resistance heater, or a combination thereof. Exemplary heaters include conductor-in-conduit heat sources, heater strips, resistance heating strips, infrared heaters, positive thermal coefficient ceramic heaters, thick film ceramic heaters, resistance wire or resistance ribbon heating devices, and induction heaters, as well as heaters that can include any combination thereof.

[0167] 4. DED process to create the workpiece Once the substrate is preheated to a target temperature, a DED process can be performed to form a workpiece on the substrate. During the creation of an object by metal deposition on the front side of the substrate, clamps can be positioned at the beginning and end of the DED walls to help reduce localized deformations that typically result from residual stress generation.

[0168] The pre-bent substrate can be in full contact, such as about 95% to about 100% contact, with the curved clamp mold attached to the fixture via an insulated / non-insulated clamp before preheating. The substrate can be thermally isolated from the fixture by the curved clamp mold. The curved clamp mold can include an insulating ceramic layer on its curved surface that can contact the pre-bent substrate. The pre-bent substrate does not adhere to the curved clamp member. Furthermore, as can be seen from this arrangement, a workpiece can be shaped on the surface of the pre-bent substrate while the pre-bent substrate is fixed in the fixture. The pre-bent substrate can become part of the workpiece. However, no part of the curved clamp mold becomes part of the workpiece.

[0169] The pre-bent substrate has an arcuate shape and is attached to a curved clamp, which also has an arcuate shape. Meanwhile, the inclination of the curvature of the pre-bent substrate, which is fixed to the fixture by the curved clamp member as support between the pre-bent substrate and the fixture, does not affect the overall deposition conditions. The radius of curvature of the curved clamp mold is large enough so that the effects of gravity do not adversely affect the dynamics of the weld pool. Therefore, deposition on the pre-bent substrate in contact with the curved clamp mold can be similar to that achieved when depositing on a substrate in a flat position. The radius of curvature of the curved clamp mold can be selected so that the effects of gravity caused by the inclination do not affect the behavior of the liquid weld pool being deposited or formed on the surface of the pre-bent substrate. In addition, the controller used in the DED process to build the workpiece can adapt the z-coordinate to the curvature of the curved clamp mold to ensure that the DED process can provide consistent energy / processing conditions during the production of the workpiece. CAD-CAM program instructions can be executed such that the melting tool follows the exact shape of the curved clamping mold to provide the DED heat source, ensuring that the overall processing conditions, especially the standoff distance, are not affected.

[0170] The design of a workpiece built by the DED process can be positioned on the front side of the substrate so that the majority of the workpiece wall formed by the deposition of weld metal is between, and preferably equidistant from, adjacent weld tracks on the back side of the substrate. This positioning allows non-uniform plastic deformation and high tensile stresses that can occur in the fusion zone during DED fabrication of the workpiece to occur in the region of high compressive stress imposed by the pre-bending process. Compressive forces that can form as the workpiece weld cools can occur in the region of high tensile stress imposed by the pre-bending process. Therefore, positioning the workpiece wall on the front side of the substrate relative to the fusion tracks on the back side of the substrate can balance the residual stress field and reduce overall distortion in the as-deposited preform.

[0171] An exemplary deposition pattern for forming a preform is shown in Figure 11. As shown, the preform 600 is positioned on the front or second side 320 of the substrate 300 such that the majority of the walls, such as 380, 382, ​​and 384, of the workpiece preform 600 formed by the deposition of molten metal are between, and preferably equidistant from, adjacent preheat passes 700, 705, 710, 715, 720, 725, 730, and 735 on the back or first side 310 of the substrate 300. Exemplary layer-by-layer DED sequence passes are sequentially indicated by boxes S1-S5. Arrows indicate the layer-by-layer DED direction.

[0172] The method for manufacturing a metal workpiece using the DED process provided herein can create a three-dimensional object of a metal material by fusing successive deposits of the metal material on a substrate. Any DED process can be used to shape the workpiece. The DED process can use one or more melting tools to provide an energy source, alone or in combination. Exemplary melting tools that can be used include a PTA torch that provides an electric arc plasma as a heat source, a laser device that provides a laser beam as a heat source, an electron beam device that provides an electron beam as a heat source, and combinations thereof. In some configurations, two or more melting tools that provide a heat source can be used. For example, one melting tool that provides a DED heat source can be used. For example, one melting tool that provides a DED heat source can be used to preheat a substrate, and a second melting tool that provides a DED heat source can be used to melt the metal material to form molten metal that can be deposited on the preheated area. When multiple melting tools that provide a DED heat source are used, they can be the same or different from each other. Exemplary combinations of multiple fusing tools include two PTA torches, two laser beam devices, two electron beam devices, a PTA torch and a laser beam device, a PTA torch and an electron beam device, and a laser beam device and an electron beam device.

[0173] In some methods, a first melting tool can be used to deliver energy to at least a portion of the surface of a base material, e.g., a location where a metal material is to be deposited, for surface heating of the substrate. This differs from a preheating step used to raise the temperature of the entire substrate to a target temperature during the DED process to minimize temperature gradients. In contrast, for surface heating of a base material, whether it be the substrate or a previously deposited metal layer, the first melting tool delivers high-intensity energy to a limited area of ​​the base material, raising the temperature of the base material in the area of ​​energy application to a slightly lower temperature, such as 0.1% to 10% below the melting temperature, or to the melting temperature. Surface heating of the base material can improve the wetting and spreading characteristics of the weld bead. Surface heating of the base material can improve the contact angle of the weld bead. Surface heating of the base material can make the surface more receptive to molten metal being deposited on the heated surface.

[0174] A second melting tool can be used to heat and melt the metallic material, depositing the molten metallic material on the surface-heated area of ​​the base material heated by the first melting tool. A gas jet device can be used to direct cooling gas across the surface of the liquid weld pool, impinge on the surface of the liquid weld pool, impinge on the surface of the solidified material adjacent the liquid-solid boundary of the liquid weld pool, or any combination thereof. The base material can be moved relative to the positions of the first and second melting tools and the gas jet device in a predetermined pattern such that successive deposits of molten metallic material solidify and form the three-dimensional workpiece. Alternatively, the first and second melting tools and the gas jet device can be moved relative to the position of the base material in a predetermined pattern such that successive deposits of molten metallic material solidify and form the three-dimensional workpiece.

[0175] In the methods provided herein, the cooling gas can be or include an inert gas, such as argon, helium, neon, xenon, krypton, and combinations thereof. The cooling gas can have a flow rate measured at the inlet of about 1 L / min to about 300 L / min. The cooling gas can be applied in a constant flow, intermittently, or in a pulsed flow. The flow of the cooling gas can be adjusted to generate a turbulent flow of the cooling gas near the weld pool. For example, the velocity of the cooling gas through the gas jet device can be increased so that the cooling gas exiting the gas jet device exhibits turbulent flow instead of laminar flow. The cooling gas can be supplied using multiple nozzles on a single gas jet device or multiple gas jet devices to direct a combination of laminar and turbulent flow of the cooling gas near the weld pool.

[0176] The temperature of the applied cooling gas can be any temperature. The cooling gas temperature can be the ambient temperature of the chamber in which the additive manufacturing process is performed. The cooling gas temperature can be about room temperature or below, such as about 25°C or below. The cooling gas can be at a refrigerated temperature, such as from -150°C to about 4°C or from -10°C to about 10°C.

[0177] The number and configuration of nozzles in the gas jet device and / or the number of gas jet devices and their configuration and arrangement can be selected to supply cooling gas along the direction of movement over the length of the workpiece, such as from about 5 mm to about 50 mm, or from about 10 mm to about 40 mm, or from about 15 mm to about 30 mm, a distance at or surrounding the thermal energy impingement region.

[0178] In the methods provided herein, a melting tool providing a DED heat source can be used in combination with a gas jet device to control the weld pool conditions. The gas jet device generates a cooling gas that results in a temperature reduction of about 1200°C to about 600°C or about 1000°C to about 800°C. In some methods where the workpiece is formed from a Ti alloy, a temperature reduction of 1000°C to 800°C can be used.

[0179] The methods provided herein can be implemented in any additive manufacturing system. The methods can be implemented in a system in which an inert gas surrounds only a heat source such as an electric arc plasma, or surrounds a fusion tool including a heat source, or surrounds the fusion tool and workpiece. The methods can be implemented in a system including a sealed chamber filled with an inert gas to provide an inert atmosphere in which the entire process is carried out. The inert atmosphere can be or contain argon, xenon, neon, krypton, helium, or a combination thereof, allowing for inert atmosphere deposition.

[0180] Exemplary differences between a conventional substrate configuration for the DED process and the process provided herein using a curved clamp mold are shown in Figures 12A and 12B. Figure 12A shows the conventional configuration, in which substrate 300 is secured to fixture 400 (via clamps, not shown) but is thermally isolated from fixture 400 by alumina thermal insulation plates 540, 541, 542, and 543 positioned between substrate 300 and fixture 400. Substrate 300, which has not undergone any stress relief treatment, is flat. Metal material is deposited on the top surface of substrate 300 during the DED process to produce preforms 600 and 600'.

[0181] In contrast, FIG. 12B illustrates an exemplary embodiment of a substrate configuration using a curved clamp mold 100 having a knurled or wavy surface (not shown) coated with a ceramic coating 150. In the illustrated configuration, the curved clamp mold 100 can serve as a lower support for the substrate 300 when the substrate 300 is secured to a fixture 400 (via clamps, not shown). The curved clamp mold 100 can thermally isolate the substrate 300 from the fixture 400, thereby eliminating the need for any alumina thermal insulation plates or other substrate support devices conventionally used to thermally isolate the substrate from the fixture. The substrate 300 can then be subjected to the relief process disclosed herein, whereby the substrate 300 is pre-bent. The pre-bent substrate 300 can be clamped to the curved clamp mold 100 using thermal insulation clamps (not shown). The illustrated curves are exaggerated. The radius of curvature of the curved clamp mold 100 is large enough so that the effects of gravity do not adversely affect the weld pool dynamics, so that deposition is similar to that achieved when depositing in a flat position. Metal material is deposited on the top surface of the substrate 300 during the DED process to produce preforms 600 and 600'.

[0182] D. System Also provided is a system for shaping a metal workpiece by a DED process, the system including a fixture to which a pre-bent substrate is secured, a curved clamping mold that can act as a lower support for the pre-bent substrate when the pre-bent substrate is secured in the fixture, an insulating clamp for securing the pre-bent substrate to the fixture, one or more melting tools including a DED energy source for melting a metal source into a molten metal material that can be deposited onto a surface of a base metal (for a first layer, the base metal is the surface of the substrate, and for subsequent layers, the base metal is the surface of a previously deposited metal layer), and a cooling gas source for directing a cooling gas across, onto, or adjacent to a liquid-solid boundary of a liquid weld pool. The system may include a gas jet device that can be directed to impinge on the solidified material; a supply of cooling gas; a system for positioning and moving the base material relative to the melting tool and gas jet device; and a controller that can retrieve a design model, such as a computer-aided design (CAD) model, of the metal workpiece to be formed and employs the design model to adjust the position and movement of the system to position and move the base material and operate the melting tool and gas jet device such that the workpiece is built by melting the metal material on the base material to form successive deposits of the metal material to form the workpiece.

[0183] A single melting tool can be used, or two melting tools can be used. For example, a first preheating torch generates a single preheating electric arc plasma and a second torch generates a double electric arc plasma. Two torches can be used simultaneously in a tandem configuration. The preheating arc can provide thermal energy for surface heating or preconditioning of a substrate at a portion of the substrate surface, such as the location where the metal DED material will be deposited. In addition, the double electric arc plasma can be powered by a separate power source. The double electric arc plasma can be used to resistively heat and melt metal on the heated surface area of ​​the substrate. The double electric plasma arc ensures sufficient fusion between the workpiece substrate and the molten metal generated by the action of the electric arc plasma on the metal, such as a metal wire feed material. For example, the second melting tool can be a torch that generates a double electric arc plasma. One arc burns between the torch's tungsten electrode and the workpiece (PTA), and the other arc burns between the torch's tungsten electrode and the wire feed material (main arc), both using positive polarity. The PTA electric arc plasma can deepen the fusion characteristics of the molten metal into the preheated surface of the base material. This can be controlled independently of the main electric arc plasma. The main electric arc plasma can be established between the torch and the current-carrying wire feed material. Heat generated by the PTA electric arc plasma column traveling to the workpiece and heat generated by the main electric arc plasma circuit can melt the wire feed material. The wire feed material can produce molten metal that can be deposited on the workpiece. Superheat from the molten metal droplets can maintain a weld pool near the surface-heated area of ​​the base material. Surface heating of the base material can enhance fusion and improve the wetting and spreading characteristics of the liquid pool, thereby resulting in better overall DED characteristics. Regarding the deposition profile, surface heating of the substrate can enable a shallower and wider deposition profile. Improved weld bead characteristics can result in a profile with a favorable weld bead contact angle toward the base material.This can promote sufficient fusion to the base material and adjacent weld beads. Improved weld bead and fusion characteristics can result in a manufactured product with improved mechanical integrity.

[0184] Each melting tool can be separately controlled and therefore individually adjusted to create separate fields of temperature and pressure. An advantage of this arrangement can be that the amount of thermal energy applied to the metal feed material melted onto the surface heating region of the base material can be greater than the thermal energy applied to the surface of the base material, avoiding overheating of the base material.

[0185] The DED manufacturing system provided herein can include a PTA torch, a laser device, an electron beam device, or any combination thereof as a melting tool. In some configurations, a first PTA torch electrically connected to a workpiece surface can heat a target deposition area on the workpiece to form a surface-heated area, and a second PTA torch electrically connected to a consumable electrode can heat and melt the consumable electrode, resulting in molten metal droplets that can fall onto the surface-heated area of ​​the target deposition area. In some configurations, the PTA torch can surface-heat a target deposition area on the workpiece to form a surface-heated area, and the laser device can heat and melt a metal wire or metal powder, resulting in molten metal that can be deposited onto the surface-heated area of ​​the target deposition area. In some configurations, the PTA torch can heat a target deposition area on the workpiece to form a surface-heated area, and the electron beam device can heat and melt a metal wire, resulting in molten metal droplets that can fall onto the surface-heated area of ​​the target deposition area.

[0186] In some configurations, a laser device can spot heat a target deposition area on a substrate to form a spot heated area, and a PTA torch electrically connected to a consumable electrode can heat and melt the consumable electrode, resulting in droplets of molten metal that can fall into the spot heated area of ​​the target deposition area. In some configurations, a first laser device can spot heat a target deposition area on a substrate to form a spot heated area, and a second laser device can heat and melt a metal wire or metal powder, resulting in molten metal that can fall onto the spot heated area of ​​the target deposition area. In some configurations, a laser device can spot heat a target deposition area on a substrate to form a spot heated area, and an electron beam device can heat and melt a metal wire, resulting in droplets of molten metal that can fall onto the spot heated area of ​​the target deposition area.

[0187] In some configurations, an electron beam device can spot heat a target deposition area on a workpiece to form a spot heated area, and a PTA torch electrically connected to a consumable electrode can heat and melt the consumable electrode, resulting in droplets of molten metal that can fall onto the spot heated area of ​​the target deposition area. In some configurations, an electron beam device can spot heat a target deposition area on a workpiece to form a preheated area, and a laser device can heat and melt a metal wire or metal powder, resulting in droplets of molten metal that can fall onto the spot heated area of ​​the target deposition area. In some configurations, a first electron beam device can spot heat a target deposition area on a workpiece to form a spot heated area, and a second laser device can heat and melt a metal wire or metal powder, resulting in molten metal that can fall onto the spot heated area of ​​the target deposition area.

[0188] In some configurations, the DED manufacturing system can include a laser device or a PTA torch that can be positioned to direct energy (e.g., laser energy or a plasma transferred arc, respectively) to a target region of the workpiece to form a surface-heated region. The PTA torch or laser device can be positioned to direct energy to an end of a consumable electrode or metal wire positioned above the surface-heated region of the workpiece. The energy can melt the end of the consumable electrode or metal wire to form molten metal droplets that can fall onto the surface-heated region of the workpiece below the end of the consumable electrode or metal wire. A melting tool that directs energy to the target deposition region can deepen the penetration of the molten metal droplets into the workpiece, thereby promoting fusion between the workpiece and the molten metal material being deposited thereon. The melting tool used to melt the consumable electrode or metal wire can also contribute heat energy near the spot-heated region of the target deposition region and can contribute heat energy provided by the melting tool directed at the workpiece. The superheat from the molten metal droplets can help maintain a weld pool near the spot-heated region of the workpiece.

[0189] The consumable electrode or metal wire can be or include Al, Cr, Cu, Fe, Hf, Sn, Mn, Mo, Ni, Nb, Si, Ta, Ti, V, W, or Zr, or a composite or alloy thereof. In some embodiments, the consumable electrode can be a wire containing Ti or a Ti alloy. The consumable electrode or metal wire can be or include a titanium alloy containing Ti in combination with one or a combination of Al, V, Sn, Zr, Mo, Nb, Cr, W, Si, and Mn. For example, exemplary titanium alloys include Ti-6Al-4V, Ti-6Al-6V-2Sn, Ti-6Al-2Sn-4Zr-6Mo, Ti-45Al-2Nb-2Cr, Ti-47Al-2Nb-2Cr, Ti-47Al-2W-0.5Si, Ti-47Al-2Nb-1Mn-0.5W-0.5Mo-0.2Si, and Ti-48Al-2Nb-0.7Cr-0.3Si. The consumable electrode or metal wire can contain aluminum, iron, cobalt, copper, nickel, carbon, titanium, tantalum, tungsten, niobium, gold, silver, palladium, platinum, zirconium, alloys thereof, and combinations thereof. The consumable electrode can include a solid wire electrode, a cored wire electrode, or a strip electrode.

[0190] A typical cross section of the consumable electrode or metal wire is circular. The diameter of the consumable electrode or metal wire can be up to about 10 mm and can range from about 0.8 mm to about 5 mm. The consumable electrode or metal wire can have any practically feasible cross section, such as 1.0 mm, 1.6 mm, and 2.4 mm, or from about 0.5 mm to about 3 mm. The feed rate and positioning of the consumable electrode or metal wire can be controlled and adjusted in harmony with the influence of the power supply to the PTA torch, laser device, electron beam device, or any combination thereof, to ensure that the consumable electrode or metal wire is continuously heated and melts when it reaches its intended location above the preheated area of ​​the workpiece.

[0191] The laser device can generate a laser beam of sufficient energy to transfer thermal energy to the base material to preheat a surface region of the base material or melt a metal wire. Preheating the base material via energy from the laser beam can promote fusion between the base material and the molten metal material by deepening melting characteristics in the base material. In some embodiments, the energy from the laser beam of the laser device can melt at least a portion of the base material. In some embodiments, the laser beam of the laser device can apply sufficient heat to form a molten pool in the base material at a location for depositing a metal material produced by a PTA torch or another laser or electron beam device.

[0192] Examples of suitable laser devices include ytterbium (Yb) lasers, Yb fiber lasers, Yb fiber-coupled diode lasers, Yb:glass lasers, diode-pumped Yb:YAG lasers, neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers, CO lasers, CO lasers, Nd:glass lasers, neodymium-doped yttrium orthovanadate (Nd:YVO) lasers, Cr:ruby lasers, diode lasers, diode-pumped lasers, excimer lasers, gas lasers, semiconductor lasers, solid-state lasers, dye lasers, X-ray lasers, free-electron lasers, ion lasers, gas-mixed lasers, chemical lasers, and combinations thereof. Preferred lasers include Yb lasers, particularly Yb fiber lasers. In many applications, the wavelengths used by Yb fiber lasers may have lower reflectivity compared to other laser wavelengths.

[0193] The PTA torch can be any configuration capable of generating an electric arc plasma to resistively heat and melt a consumable electrode, or establishing an arc using a non-reactive gas (metal inert gas welding or MIG welding), gas metal arc welding (GMAW), or other processes capable of heating a target area on the surface of a workpiece. The consumable electrode can be melted in the plasma generated by the PTA torch using an electric arc. The melted consumable electrode can be deposited in a weld pool on a workpiece to add to and form a near-net-shape metal body. Preheating the workpiece via energy from the PTA torch can promote fusion between the workpiece and the molten metal material by deepening the melting characteristics in the workpiece. In some embodiments, at least a portion of the workpiece can be melted by energy from the PTA torch plasma. In some embodiments, the PTA torch plasma can provide sufficient heat to form a molten liquid on the workpiece at a location where the molten metal material is deposited by a different PTA torch or laser device.

[0194] The combination of thermal pre-bending of the substrate by inducing a melt track, the use of a curved clamping mold, and pre-heating of the substrate prior to forming the workpiece via the DED process enables the formation of near-net-shape metal workpieces that significantly mitigate the problems associated with internal residual stresses and distortions evident in many conventional additively manufactured products, thereby improving manufacturing repeatability, improving dimensional accuracy, and producing workpieces that exhibit increased strength, fatigue resistance, and durability. [Example]

[0195] The following examples are included for illustrative purposes only and are not intended to limit the scope of the embodiments provided herein.

[0196] Example 1 The first test substrate, for which deflection without residual stress relief was measured, was a first base plate substrate made of Ti-6Al-4V, measuring 635 mm x 190 mm x 9.5 mm (L x W x T). This substrate was clamped to a fixture or welding table, and the workpiece was fabricated on top of it by preheating the base metal using a first PTA torch and melting a Ti-6Al-4V wire using a second PTA torch to form molten metal that could be deposited onto the preheated base metal. The deposition rate was 7.5–10 mm / s. Using an inert gas, the cooling gas was directed at a high flow rate to impinge on the as-solidified material adjacent to the liquid-solid boundary of the liquid weld pool. After deposition was completed, the component was cooled, removed from the fixture, and the substrate was inspected for deformation.

[0197] Distortion was evident at the short edges of the substrate. The substrate bowed upward compared to the flat contour of the substrate before deposition. The observed deformation is shown in Figure 13A.

[0198] A second base plate substrate made of Ti-6Al-4V with dimensions (L x W x T) of 635 mm x 190 mm x 12.7 mm was used as the second test substrate. The same workpiece was fabricated using the same conditions as described above. Figure 13B shows the deformation caused by DED deposition on a 12.7 mm thick substrate that had not undergone any type of residual stress relief. This shows upward bowing at the short edges of the substrate, with the left edge bowing upward by approximately 7 mm and the right edge bowing upward by approximately 6.0 mm compared to the flat contour of the substrate before deposition.

[0199] Figure 13C shows a third baseplate substrate, having dimensions (L x W x T) of 635 mm x 190 mm x 9.5 mm, made from Ti-6Al-4V, used to form the object by thermal pre-bending, preheating, and DED processing as described herein. The substrate was securely clamped to the fixture using insulating clamps around the entire length of the substrate's long edges; however, no clamps were used on the substrate's short edges. Between the substrate and the fixture, the substrate was thermally isolated from the fixture using four layers of alumina insulating plates (RS-1200 Keranova) each approximately 3.2 mm thick and having the same dimensions as the substrate.

[0200] A PTA torch was used to provide thermal energy to the first side of the substrate to form melt tracks in the substrate. The final integrated residual stress distribution determined by the combination of DED and the melt tracks has a lower tensile peak at the DED centerline and lower compressive stress balancing away from the DED centerline when compared to the original residual stress profile of DED without the pre-bending melt tracks (i.e., a high tensile peak at the DED centerline and balancing compressive stress further away). The pattern used to form the melt tracks is shown in Figures 7A and 7B. As shown, the PTA torch, acting as the DED heat source, was positioned at one edge of the substrate. The spacing between melt tracks can be predicted based on the shape of the workpiece being fabricated. For example, melt tracks can be formed in areas that are not beneath the walls of the workpiece to be formed in order to minimize the final integrated residual stress distribution in the workpiece. For example, the majority of the melt lines on the first surface can be formed in one or more locations other than those corresponding to one or more areas occupied by one or more walls of the workpiece to be formed on the second side of the substrate. To induce maximum thermal stress in the substrate, a high energy density (e.g., arc energy supplied at approximately 450 J / mm to approximately 550 J / mm) was applied at a speed of 6 to 16 mm / s to rapidly melt a portion of the substrate surface and form an autogenous weld seam. This was then rapidly cooled using a gas jet device that directed a high flow rate of cooling gas at 25°C toward the weld seam. This resulted in a weld track with high tensile stress near the centerline of the weld track and high compressive stress at distances away from the centerline. In an exemplary embodiment, for a substrate thickness of 9.5 to 10 mm, a weld track approximately 3 mm wide and up to 1 mm deep was produced using a single heat source with a current of approximately 150 A to approximately 250 A, a voltage of approximately 20 V to approximately 30 V, and a traverse speed of 6 mm / s to 16 mm / s.

[0201] Upon release from the jig, the pre-bent substrate bowed upward, exhibiting a deflection of approximately 15 mm, similar to that shown in Figure 8A. The pre-bent substrate was then attached to a jig using a curved clamping mold as a lower support and an insulating clamp to attach the pre-bent substrate to the jig. The pre-bent substrate was positioned so that the side with the melt track faced the curved clamping mold. Pre-heating of the pre-bent substrate was achieved using two PTA torches, which delivered a lower energy density to the pre-bent substrate surface by positioning the PTA torches at a higher standoff distance to reduce the risk of creating localized melt tracks that could cause fusion problems at the baseplate contact surface during DED metal deposition. For example, pre-heating was performed using two PTA torches at an arc voltage of 20–30 V, using a current range of 150–250 A. The traverse speed was 6–12 mm / s. For example, the arc energy delivered by the first PTA torch could be 460 J / mm. The arc energy supplied by the second PTA torch can be 430 J / mm. Another important aspect is the fact that the pre-bending track was performed with a higher plasma gas flow compared to that used in pre-heating. A higher plasma gas flow generates a stiffer electric arc, and therefore an electric arc with a higher energy density. Regarding the standoff distance, a 25% to 50% higher standoff distance or a 30% to 40% higher standoff distance can be used during pre-heating compared to that used in pre-bending. No cooling gas was used during the pre-heating process.

[0202] After the substrate temperature reached 450°C to 550°C, DED deposition of the metal forming the object was carried out in a sealed chamber containing an argon inert atmosphere. The DED process used two PTA torches. The first PTA torch directed thermal energy toward a target area of ​​the workpiece to form a preheated region. The second PTA torch directed thermal energy (1) toward the end of a consumable electrode or metal wire positioned above the preheated region of the workpiece, and (2) toward the preheated region. The energy from the second PTA torch melted the end of the consumable electrode or metal wire, forming droplets of molten metal. These droplets fell onto the preheated region of the workpiece directly below the end of the consumable electrode or metal wire. In this process, a gas jet device was used to direct a high flow rate of cooling gas at a temperature of 25°C toward the as-solidified material adjacent to the liquid-solid boundary of the molten metal. Deposition continued until the workpiece was completed. The workpiece was cooled in the deposition chamber to a temperature below 400°C. The workpiece was then removed from the deposition chamber, followed by the pre-bent substrate from the jig. Depending on the speed at which the operator removes the workpiece, the pre-bent substrate can be removed from the jig at temperatures up to 200-300°C. In this example, the pre-bent substrate was removed from the jig at a temperature of approximately 250°C.

[0203] As shown in FIG. 13C, the workpiece exhibited slight upward movement (only about 0.5 mm) at the short edge of the substrate, indicating that the use of the curved clamp mold in combination with pre-bending and pre-heating eliminated a significant amount of the residual stress observed in the test substrate when using the conventional DED process.

[0204] Repeatability was tested using the same substrate and workpiece design under the same conditions as described above. The method demonstrated consistent and repeatable results across all three workpieces produced. The deviation in substrate deformation between the first and second workpieces was approximately 0.5 mm, while the deviation in substrate deformation between the second and third workpieces was approximately 0.1 mm.

[0205] The stress relief heat treatment did not significantly affect the overall dimensions of the workpiece. For example, after stress relief, a very slight upward movement of approximately 0.5 mm occurred at the short edges of the plate. This means that the residual stresses in the as-deposited workpiece are very low as a result of the described stress relief.

[0206] It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

[0207] Below is a list of reference numbers used in this specification and the accompanying drawings. [Explanation of symbols]

[0208] 100 curved clamping mold 105 Knurled or wavy surface 110 Upper surface 115 Edge 120 Ridge 130 Valley 140 flat rim 150 ceramic coating 155 Bond Coat 160 Cavity 162 Cavity 164 Cavity 166 Cavity 170 Reinforcement member 180 Maximum height 200 Gas Jet Device 210 nozzle 230 Support 250 PTA torch 300 boards 310 1st side 320 2nd side 330 Preform DED rear wall 350 Melting Truck 355 Space between melting tracks 360 Melting Truck 370 First pre-bending heating path 371 Second pre-bending heating path 372 Third pre-bending heating path 373 4th pre-bending heating path 374 5th pre-bending heating path 375 6th pre-bending heating path 380 Preform Wall 382 Preformed Wall 384 Preform Wall 400 Jig 410 Nominal Board Deflection 500 clamp 501 screw hole 502 holes 505 Bottom contact facet 506 Side contact facet 507 Upper surface of clamp 509 ceramic coated surface 510 Flat head screw 515 Top of countersunk screw 520 volts 525 Nut 530 Upper surface of jig 540 Alumina Heat Insulation Plate 541 Alumina Heat Insulation Plate 542 Alumina Heat Insulation Plate 543 Alumina Heat Insulation Plate 544 Regions of Uneven Pressure and Heat Transfer Distribution 545 Regions of Uneven Pressure and Heat Transfer Distribution 546 Regions of Uneven Pressure and Heat Transfer Distribution 547 Regions of Uneven Pressure and Heat Transfer Distribution 548 Regions of Uneven Pressure and Heat Transfer Distribution 549 Regions of Uneven Pressure and Heat Transfer Distribution 550 base plate 575 Box showing areas of uneven pressure and heat transfer distribution 576 Box showing areas of uneven pressure and heat transfer distribution 577 Box showing areas of uneven pressure and heat transfer distribution 578 Box showing areas of uneven pressure and heat transfer distribution 600 preforms 600' preform 610 Fastening body 615 Fastening body 620 Fastening body 625 Fastening body 630 Fastening body 650 Non-optimal tightening area 700 First preheating path 705 Second preheating path 710 Third preheating path 715 4th preheating path 720 5th preheating path 725 6th preheating heating path 730 7th preheating path 735 8th Preheating Path

Claims

1. On a first side, two or more cavities separated by one or more reinforcing members, and a rim having a flat surface around the outer peripheral portion of the first side comprising a first side; A second side opposite to the first side, having a curved surface and including a knurl or a corrugation, and a ceramic coating comprising a curved clamping mold.

2. The curved clamping mold according to claim 1, wherein the reinforcing member maintains mold rigidity, provides mold deformation resistance, or both.

3. The curved clamping mold according to claim 1 or 2, further comprising a non-magnetic metal.

4. The curved clamping mold according to any one of claims 1 to 3, further comprising a metal having a melting point of 1350 °C or higher.

5. The curved clamping mold according to claim 3 or 4, wherein the metal includes austenitic stainless steel.

6. The curved clamping mold according to claim 5, wherein the austenitic stainless steel includes carbon, chromium, copper, manganese, molybdenum, nickel, nitrogen, phosphorus, silicon, or any combination of two or more thereof.

7. The curved clamping mold according to claim 5, wherein the austenitic stainless steel includes at least 18% chromium.

8. The curved clamping mold according to claim 5, wherein the austenitic stainless steel is 300 series stainless steel.

9. The curved clamping mold according to claim 5, wherein the austenitic stainless steel includes 304 stainless steel, 309 stainless steel, 310 stainless steel, 316 stainless steel, 318 stainless steel, 321 stainless steel, or 330 stainless steel.

10. The ceramic coating is zirconium dioxide, zirconium dioxide stabilized by the addition of yttrium oxide, yttrium aluminum oxide, alkaline earth metal silicate, ZrV ２ O ７ , Mg ３ (VO ４ ) ２ or a combination thereof, the bending tightening mold according to any one of claims 1 to 9.

11. The ceramic coating is ZrO ２ 8Y ２ O ３ The bending tightening mold according to any one of claims 1 to 10, comprising

12. The curved clamping mold according to any one of claims 1 to 11, wherein the ceramic coating has a thickness of 0.1 mm to about 5 mm.

13. The curved clamping mold according to any one of claims 1 to 12, further comprising a nominal mold deflection of about 3 mm to about 35 mm.

14. The curved clamping mold according to any one of claims 1 to 13, further comprising a bond coat on which the ceramic coating is applied.

15. A directed energy deposition method for manufacturing a metal workpiece, Preparing to bend a substrate made of a metallic material using thermal energy by forming a plurality of molten tracks on a first surface of the substrate using a melting tool, thereby generating a pre-bent substrate; Using the bending clamping mold according to any one of claims 1 to 14 as a lower support structure for supporting the pre-bent substrate, and fixing the pre-bent substrate and the bending clamping mold for supporting the pre-bent substrate to a jig using a plurality of clamps; Forming the metal workpiece on the second surface of the substrate by an additive manufacturing process including melting a metal feed material, depositing a layer of molten metal on the second surface of the substrate to form a base material, and depositing a subsequent layer of molten metal on the base material to form the workpiece; including; The method of directed energy deposition, wherein the second surface of the substrate is on the opposite side of the first surface of the substrate.

16. The method according to claim 15, wherein the metal feed material is a metal in the form of powder, wire or a combination thereof.

17. The method according to claim 15 or 16, further including the step of preheating the pre-bent substrate to a temperature of about 400 °C to about 900 °C by applying thermal energy to the second side of the substrate before forming the metal workpiece while the pre-bent substrate is fixed to the jig.

18. The method according to any one of claims 15 to 17, wherein the step of pre-bending the substrate includes inducing a temperature gradient in the substrate.

19. The method according to any one of claims 15 to 18, wherein the melting tool includes a heat source selected from a laser beam, an electron beam, a plasma arc, a gas tungsten arc, a gas metal arc and any combination thereof.

20. The method according to any one of claims 15 to 19, wherein during the pre-bending of the substrate, the application region of the thermal energy reaches a temperature that is the melting point of the metallic material or a temperature that is about 5 °C to about 50 °C lower or higher than the melting point of the metallic material.

21. The method according to any one of claims 15 to 20, wherein during the pre-bending of the first surface of the substrate, the formation of the molten tracks results in the formation of tensile stress at the center line of each of the molten tracks during cooling of the substrate and the formation of compressive stress in a region away from the center line of each of the molten tracks.

22. The method according to claim 21, wherein the tensile stress at the center line of the molten track is within about 10% of the yield strength of the substrate.

23. The method according to claim 21, wherein the tensile stress at the center line of the molten track exceeds the magnitude of the yield strength of the substrate.

24. The method according to any one of claims 15 to 23, wherein the preliminary bending step further comprises directing a cooling gas towards the molten track using a gas jet device to accelerate cooling of the molten track.

25. The method according to claim 24, wherein directing the cooling gas towards the molten track forms a temperature gradient in the substrate and imparts residual stress to the substrate during cooling.

26. The method according to claim 24 or 25, wherein the gas jet device directs the cooling gas towards the molten track at a rate of about 50 L / min to about 500 L / min.

27. The method according to any one of claims 24 to 26, wherein the cooling gas is applied in a constant flow, or intermittently, or in a pulsed flow.

28. The method according to any one of claims 24 to 26, wherein the cooling gas comprises an inert gas selected from argon, helium, neon, xenon, krypton, and combinations thereof.

29. The method according to any one of claims 24 to 28, wherein the cooling gas is applied at a temperature of 100°C or less.

30. The method according to any one of claims 24 to 29, wherein the cooling gas is applied at a temperature of 25°C or less.

31. The method according to any one of claims 24 to 30, wherein the gas jet device generates a turbulent flow of the cooling gas, a laminar flow of the cooling gas, or a combination of the turbulent and laminar flows of the cooling gas.

32. The method according to any one of claims 24 to 31, wherein the gas jet device includes a plurality of nozzles, the nozzles direct the cooling gas in a direction away from the heat source of the melting tool, and at least one nozzle directs the cooling gas towards the solidified metal of the molten track.

33. The method according to any one of claims 15 to 32, wherein the molten tracks are generated equidistant from each other.

34. The method according to any one of claims 15 to 33, wherein the distance between the molten tracks is about 10 mm to about 60 mm.

35. Determining the centerlines of each wall of the preform formed on the second surface of the substrate; Positioning the molten track on the first surface of the substrate at a distance of about 10 mm to about 20 mm from the centerlines of most of the walls of the preform formed on the second surface of the substrate; The method according to any one of claims 15 to 34, further comprising.

36. Forming most of the molten line on the first surface at one or more locations other than the locations corresponding to one or more regions occupied by one or more walls of the workpiece formed on the second side of the substrate, the method according to any one of claims 15 to 35.

37. The method according to any one of claims 15 to 36, wherein the pre-bending forms a pre-bent substrate having uniform elastoplastic bending.

38. The method according to any one of claims 15 to 37, further comprising pre-bending the substrate while the substrate is clamped to a jig and insulated from the jig.

39. The method according to any one of claims 15 to 38, wherein one or more clamps include a heat insulating coating on each surface in contact with the pre-bent substrate.

40. The method according to claim 39, wherein the heat insulating coating includes a ceramic material, silicon carbide, silicon nitride, boron carbide, or a combination thereof.

41. The ceramic material is alumina, zirconia, titanium oxide, alkaline earth metal silicate, aluminum titanate, zirconium dioxide stabilized by addition of yttrium oxide, yttrium aluminum oxide, ZrV ２ O ７ , Mg ３ (VO ４ ) ２ or a combination thereof, the method according to claim 40.

42. The method according to claim 40 or 41, wherein the thickness of the heat insulating coating is from 0.1 mm to 5 mm.

43. The method according to any one of claims 39 to 42, wherein the clamp includes a knurled pattern or a waveform on the surface in contact with the pre-bent substrate.

44. The method according to any one of claims 39 to 43, further comprising tightly clamping the clamp to bring the pre-bent substrate into complete contact with the underlying curved clamping mold.

45. The method according to claim 44, wherein each of the clamps is tightly clamped with a torque of about 10 N·m to about 100 N·m.

46. The method according to any one of claims 39 to 45, wherein the clamp is positioned such that the clamp coincides with the start or end of the wall of the workpiece being produced.

47. a) forming the molten track without melting the surface of the pre-bent substrate, or b) forming the molten track and melting the surface of the pre-bent substrate in the molten track The method according to claim 15, further comprising preheating the pre-bent substrate using one or more melting tools including a DED heat source under conditions where the molten track is formed and the surface of the pre-bent substrate is melted in the molten track. **Claim 48** The method according to claim 47, further comprising positioning the one or more melting tools at a stand-off position higher than the stand-off position used to form the workpiece. **Claim 49** The pre-bent substrate includes a first short edge and an opposite second short edge, and a first long edge and an opposite second long edge, and further includes a step of preheating before DED deposition for forming a workpiece, and the preheating includes: a) positioning a melting tool including a DED heat source at the first short edge of the pre-bent substrate fixed to the jig and within about 10 mm to about 60 mm of the first long edge; b) applying the thermal energy from the DED heat source of the melting tool starting from the first short edge across the surface of the pre-bent substrate and across the surface to the opposite second short edge to form a first energy application line on the surface; c) repositioning the DED heat source of the melting tool at the first short edge and shifting it by a distance of about 10 mm to about 60 mm from the first energy application line towards the second long edge; d) repeating steps b) and c) until the energy application line is applied across the surface of the pre-bent substrate to a position from about 10 mm to about 60 mm from the opposite second long edge. The method according to claim 48, including the above steps. **Claim 50** The method according to claim 48 or 49, further comprising preheating the pre-bent substrate by applying thermal energy to the front side of the substrate using a heating device before DED deposition for forming a workpiece. **Claim 51** The method according to claim 50, wherein the heating device includes an infrared heater, an induction heater, a resistance heater, or a combination thereof. **Claim 52** The method according to claim 50, wherein the heating device includes an in-conduit conductor heat source, a heater strip, a resistance heating strip, an infrared heater, a positive temperature coefficient ceramic heater, a thick film ceramic heater, a resistance wire heater, a resistance ribbon heating device, an infrared heater, an induction heater, or a combination thereof. **Claim 53** The preheating raises the temperature of the preliminary bending substrate to a temperature of from about 350°C to about 650°C, the method according to any one of claims 47 to 52.

54. The forming of the metal workpiece provides the metal feedstock in the form of a wire, heating and melting the wire using a single melting tool such that a molten metal material is deposited onto an area of the substrate to form a base material, moving the base material relative to the position of the melting tool in a predetermined pattern such that a continuous deposit of molten metal material on the base material solidifies and forms a three-dimensional object comprises the method according to any one of claims 16 to 53.

55. The forming of the metal workpiece a) provides the metal feedstock in the form of a wire; b) heats at least a part of the surface of the substrate using a first melting tool to form a preheated area on the substrate; c) heats and melts the wire using a second melting tool such that a molten metal material is deposited onto the preheated area to form a base material; d) moves the base material relative to the positions of the first and second melting tools in a predetermined pattern; e) heats at least a part of the surface of the base material using the first melting tool to form a preheated area on the base material and deposits the molten metal material produced by the second melting tool that melts the metal material onto the preheated area on the base material; f) repeating steps d) and e) such that a continuous deposit of molten metal material on the preheated area on the base material solidifies and forms a three-dimensional object comprises the method according to any one of claims 16 to 53.

56. using a gas jet device to direct a cooling gas across the surface of the molten metal material, or onto the surface of the molten metal material, or onto the surface of the solidifying material adjacent to the liquid-solid boundary of the molten metal material, or any combination thereof; and moving the base material relative to the positions of the melting tool and the gas jet in a predetermined pattern such that a continuous deposit of molten metal material solidifies and forms the three-dimensional object further comprises the method according to claim 54 or 55.

57. The first melting tool comprises a PTA torch, a laser device, an electron beam device, or any combination thereof, and The second melting tool includes a PTA torch, a laser device, a coaxial powder feeding nozzle laser system, an electron beam device, or any combination thereof, according to the method of claim 54 or 55.

58. The first melting tool includes a first PTA torch, and the second melting tool includes a second PTA torch, or The first melting tool includes a laser device, and the second melting tool includes a PTA torch, or The first melting tool includes a PTA torch, and the second melting tool includes a laser device, or The first melting tool includes a laser device, and the second melting tool includes a coaxial powder feeding nozzle laser system, or The first melting tool includes PTA, and the second melting tool includes a torch coaxial powder feeding nozzle laser system, or The first melting tool includes a PTA torch, and the second melting tool includes an electron beam device, or The first melting tool includes an electron beam device, and the second melting tool includes a PTA torch, or The first melting tool includes an electron beam device, and the second melting tool includes a laser device, or The first melting tool includes a laser device, and the second melting tool includes an electron beam device, according to the method of claim 57.

59. When the second melting tool includes a PTA torch, the PTA torch is electrically connected to a DC power source such that the electrode of the PTA torch is the cathode and the metal material is the consumable electrode that is the anode, according to the method of claim 58.

60. Each of the step of pre-bending the substrate and the step of forming the metal workpiece is performed within a sealed chamber containing an inert atmosphere, according to the method of any one of claims 15 to 59.

61. The inert atmosphere includes argon, neon, xenon, krypton, helium, or a combination thereof, according to the method of claim 60.

62. A jig for fixing the pre-bent substrate, and A bending clamping mold according to any one of claims 1 to 14, positioned between the jig and the pre-bent substrate when the pre-bent substrate is fixed to the jig, and A clamp for fixing the pre-bent substrate to the jig, and One or more melting tools including a DED heat source for melting a metal source to form a metal molten material deposited on the surface of the base material A gas jet device for directing a cooling gas so as to impinge on the solidified material adjacent to the liquid-solid boundary of the liquid melt pool to affect the temperature gradient, a supply unit for the cooling gas, and an actuator for positioning and moving the base material relative to the melting tool and the gas jet device comprising a system for directed energy deposition.

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