CROSS-REFERENCE TO PROVISIONAL APPLICATION

[0001] This application claims priority from U.S. Provisional Patent Application No.

60/687,448 filed June 6, 2005, the entire disclosure of which is incorporated herein by reference.

GOVERNMENT RIGHTS STATEMENT

[0002] This invention was made with Government support under Agreement No. DAAD

19-02-9-0003, awarded by the Army Research Laboratory. The Government has certain rights in the invention.

TECHNICAL FIELD OF THE INVENTION

[0003] This invention relates to the application of a hybrid laser/arc process to Direct

Metal Deposition for the purposes of making complex, three-dimensional shapes directly from metal powder or wire.

BACKGROUND OF THE INVENTION

[0004] The use of direct metal deposition (DMD) has been examined as a method to reduce manufacturing costs of complex, three-dimensional parts and parts made from expensive starting materials. The goal is to achieve near net shapes in high-cost materials thereby reducing the amount of waste material and time generated during machining. DMD has great potential for aerospace applications where the volume of parts is low, and the added value to the parts is high. [0005] A DMD process has been developed that permits high deposition rates for complex shapes using a high-power (18 kW) CO ₂ laser and powdered metal. The process is accomplished in a chamber under and argon and moisture atmosphere.

[0006] While the laser DMD process produces acceptable product, the operational cost for the CO ₂ laser limits the applications based on the economics of the process. Because laser power is a low-efficiency means of melting the powder, the operational cost is high. More efficient methods of melting metal would include the use of arc or electron beam techniques.

Each of these processes has issues with implementing into the DMD process. As an example, gas metal arc techniques, similar to gas metal arc welding (GMAW), can be used to deposit metal materials but only produce acceptable depositions at slow speed/high heat input conditions.

[0007] The difference between DMD and welding, is that welding joins two substrates, while DMD builds up metal layers on a substrate. For example in GMAW ₅ metal fills the joint between two substrates to join them together. Whereas, in a DMD process using a GMAW power supply and torch, metal is deposited on a substrate to build a three-dimensional structure on the substrate, not to join two substrates together.

[0008] Titanium's high specific strength and modulus, excellent corrosion resistance, high-temperature performance, and biocompatibility make it attractive to many different industries (aerospace, defense, petrochemical, medical). However, the reactive nature of Ti and its molten characteristics make it very difficult to form DMD products. Gas metal arc techniques have several disadvantages that severely limit their application to depositing Ti. These drawbacks include instabilities in metal transfer, excessive spatter, poor control of the deposited layer shape, and high heat input that causes distortion of thin sections during deposition. Also, an increase in productivity is not possible because of wandering of the cathode spot that occurs during deposition.

[0009] The combination of GMAW or gas tungsten arc welding (GTAW) and laser beam welding (LBW), called hybrid welding, has been extensively investigated. However, the combination of gas metal arc and laser beam DMD techniques have not been previously suggested.

SUMMARY OF THE INVENTION

[0010] There exists a need in this art for an economical method of performing direct metal deposition. There further exists a need in this art for a method of increasing throughput and yield of direct metal deposition formed products. A need further exists in this art for a direct metal deposition formed distortion-free products with smooth, well-defined deposition boundaries. In addition, a need exists in this art for a hybrid laser/gas metal arc direct metal deposition technique that minimizes spatter and provides a stabilized arc.

[0011] These and other needs are met by embodiments of the present invention, which provide a direct metal deposition process using a laser/arc hybrid process to manufacture complex, three-dimensional shapes comprising the steps of providing a substrate and depositing a first molten metal layer on the substrate from a metal feedstock using laser radiation and an electric arc.

[0012] These and other needs are further met by embodiments of the present invention, which provide a direct metal deposition process comprising the steps of providing a substrate and depositing a metal from a metal feedstock onto the substrate. An electric arc is generated between the metal feedstock and the substrate and the arc is exposed to laser radiation to form a molten metal pool on the substrate. The molten metal pool is cooled to form a first solid metal layer on the substrate.

[0013] These and other needs are further met by embodiments of the present invention, which provide a direct metal deposition process comprising the steps of providing a substrate and depositing a metal from a metal feedstock on a surface of the substrate. An electric arc is generated between the metal feedstock and the substrate as the arc is simultaneously exposed to laser radiation to form molten metal on the surface of the substrate. A gas is flowed over the metal while the electric arc is generated and the arc is exposed to the laser radiation. The metal is continuously fed to the surface of the substrate and the substrate is moved in relation to a source of the laser radiation and a source of the electric arc while the electric arc is generated and the arc is exposed to the laser radiation. The deposited metal is cooled to form a solid metal layer fixedly attached to the substrate.

[0014] This invention addresses the needs for an improved, economical method of performing direct metal deposition. This invention further addresses the need for a method of increasing throughput and yield of distortion-free direct metal deposition formed parts with smooth, well-defined deposition boundaries. In addition, this invention addresses the need for a hybrid laser/gas metal arc direct metal deposition technique that minimizes spatter and provides a stabilized arc.

[0015] The foregoing and other features, aspects, and advantages of the present invention will become apparent in the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIG. 1 illustrates a hybrid laser/gas metal arc direct metal deposition according to an embodiment of the present invention.

[0017] FIG. 2 illustrates a hybrid laser/gas metal arc direct metal deposition with multiple arcs according to an embodiment of the present invention.

[0018] FIG. 3 illustrates a hybrid laser/gas metal arc direct metal deposition with multiple lasers according to an embodiment of the present invention.

[0019] FIG. 4 illustrates a hybrid laser/gas metal arc direct metal deposition with multiple feedstocks according to an embodiment of the present invention.

[0020] FIG. 5 illustrates a an embodiment of the present invention wherein multiple layers are deposited.

[0021] FIG. 6 illustrates a deposited structure formed by an omni-directional deposition process.

[0022] FIG. 7 is a cross-sectional view of a deposited metal on a substrate formed by the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0023] In certain embodiments of the present invention, the process uses a laser, a

GMAW welder and a multi-axis, computer numerically controlled (CNC) positioning system to create three dimensional shapes directly in metal. Conventional laser DMD processes use a high energy density laser beam and a CNC-controlled positioning system to fuse metal powder or metal wire into complex three-dimensional shapes. The process of the present invention adds an electric arc to the process. The arc is coincident with the laser beam and is used in conjunction with the laser to melt the feedstock material and locally melt the substrate or previously deposited material to which the feedstock is being added. In certain embodiments of the present invention, an electrode is used to generate the arc between the metal feedstock and the substrate. In certain embodiments of the present invention, metal feedstock, such as wire, is used as a consumable electrode.

[0024] In certain embodiments of the present invention, an arc is established between a tungsten electrode and the substrate and the heat of the arc along with the laser radiation is used to melt incoming feedstock and a portion of the substrate. In such as a gas tungsten arc process,

a non-consumable tungsten electrode is used in place of a consumable electrode. In certain embodiments of the present invention, a plasma arc process can be used with laser radiation to melt incoming feedstock.

[0025] An embodiment 10 of a hybrid laser/gas metal arc DMD process according to the present invention is schematically illustrated in Fig. 1. A layer of metal 24 is deposited on a substrate 12. A metal wire feedstock/GMAW electrode 14 supplies the metal to the substrate 12. An electric arc 20 is generated between the metal wire feedstock/GMAW electrode 14 and the substrate 12 Laser radiation 18 is directed from a laser radiation source 16 to the electric arc 20. A molten pool of metal 22 is formed by the laser radiation 18 and the electric arc 20. The metal feedstock 14 is transferred across the arc 20 into the molten metal pool 22. The metal wire feedstock/GMAW electrode 14 is supported by a wire guide 26, which can also function as a gas nozzle for flowing gas across the molten metal 22, in addition to supporting the wire 14. During the deposition process the substrate is translated in the X direction relative to the source of laser radiation 16 and the arc 20.

[0026] In certain embodiments of the present invention the metal is exposed to laser radiation simultaneously with the generation of the arc. In certain embodiments of the present invention, metal is continuously fed to the substrate during a period of time that the arc is generated and the arc is exposed to laser radiation. In certain embodiments of the present invention, the substrate is moved in relation to a source of the laser radiation and a source of the arc during the period of time that the arc is generated and the arc is exposed to laser radiation. [0027] The DMD process of the present invention differs from the hybrid welding process in that it deposits metal to build up three-dimensional shapes on a substrate directly from feedstock material, rather than joining two substrates together. Whereas in the hybrid welding process, metal is deposited in the joint between two metal substrates, to join the metal substrates together. DMD processes of the present invention produce complex, three dimensional shapes, unlike cladding processes, which form a substantially fiat layer on a substrate. [0028] According to certain embodiments of the present invention, multiple laser radiation sources and arcs can be used. FIG. 2 illustrates an embodiment of the present invention 30 that uses a plurality of metal wire feedstock/GMAW electrodes 14. An embodiment of the present invention 40 using multiple laser radiation sources 16 is illustrated in FIG. 3. In certain embodiments of the present invention 50, multiple feedstocks can be employed, as shown in

FIG. 4. The additional feedstock 52 can either be an additional metal wire or a metal powder. The additional metal feedstock 52 can be supported by a wire guide 54 or a powder dispenser 54 depending on whether the metal feedstock 52 is a wire or powder. In certain embodiments of the present invention, multiple wire feeds 52 using wires of differing compositions can be used to create an alloy different from the substrate 12 or any of the other feedstock 14 materials. [0029] The process of the present invention is applicable to a wide range of metals including titanium, titanium alloys, iron, iron alloys, nickel, nickel alloys, rhenium, rhenium alloys, tantalum, tantalum alloys, cobalt, cobalt alloys, aluminum, aluminum alloys, and mixtures thereof. In certain embodiments of the present invention, the metals are Ti alloys, such as TiAlV alloys; or iron alloys, such as steel and stainless steel.

[0030] In certain embodiments of the present invention, a titanium alloy deposit, such as

Ti-6A1-4V, can be formed in the melt pool by using a Ti wire feedstock, and both Al and V wire or powder feedstocks. The powders, if used, can be mixed prior to deposition or in the melt pool.

[0031] Generally, the metal feedstock is the same type of metal as the substrate.

However, in certain embodiments of the present invention, a different metal or alloy than the substrate can be used as the metal feedstock. In addition, in other embodiments of the present invention, different layers in a multilayer deposition can be formed from different metals or different alloys.

[0032] The diameter of the metal wire feedstock, according to certain embodiments of the present invention, can range from about 0.030 inches to about 0.094 inches. In certain embodiments of the present invention, a metal wire feedstock with a diameter of about 0.063 inches is used.

[0033] Metal powder can be used in conjunction with the feedstock wire as a supplemental material, as illustrated in FIG. 4, in certain embodiments of the present invention. The powder can be of the same composition as the substrate, the wire, or may be a different composition than either the substrate and/or the wire. In certain embodiments of the present invention, the powder can contain non-metallic additives, such as inoculants to reduce grain size; silica; ceramics, such as alumina, for wear-resistance applications, and ceramics conventionally used in forming blade tips; or anything else that enhances a property of the alloy. In addition, to ceramic inoculants, high temperature metals can also be used as inoculants. In certain

embodiments of the present invention, the particle size of the metal powder feedstock ranges from - 35 mesh sieve to + 325 mesh sieve.

[0034] The process of the present invention can be performed in vacuum, in an inert-gas chamber or in atmosphere with localized gas shielding. The gases in the inert-gas chamber or in the localized shielding can be of high-purity to minimize contamination or can contain additives which react with or are absorbed by the molten pool in order to create a desired effect. In certain embodiments of the present invention, oxygen is added to the gas when depositing titanium alloys, resulting in an alloy with a higher oxygen content than there would have been without the oxygen additive to the gas. The effect of the higher oxygen level on the material is an alloy with increased tensile strength. In certain embodiments of the present invention, nitrogen, carbon dioxide, or carbon monoxide can be added to the shielding gas. Like oxygen, the addition of nitrogen, carbon dioxide, and carbon monoxide raise the interstitial content of the deposited titanium and increase its strength.

[0035] The parameters of the process can be varied such that the material fuses to a required density. For most aerospace applications, the requirement is full density in metals. Since the geometry of the features of a part vary, the energy requirements to ensure full density will change accordingly. For example, thick sections on a part require a higher heat input than thinner sections on the same part. Processing parameters can be varied, in certain embodiments of the present invention, in order to maintain geometry requirements, such as a level build or a change in cross section. For example, a thin wall on a part requires less material per unit length than a thicker wall on the same part.

[0036] The present invention can be performed using a GMAW power supply coupled with a laser. In certain embodiments, either or both of the arc and the laser radiation may be continuous or pulsed. In certain embodiments of the present invention, the laser can be a Nd:YAG, CO ₂ , or a Yb-doped fiber laser.

[0037] In certain embodiments of the present invention, the substrate is positioned on a moving platform, such as a 4-axis CNC motion-controlled table. In certain embodiments of the present invention, the laser radiation is oriented substantially normal to the substrate surface and the GMAW electrode is oriented at an acute angle to the substrate surface, as shown in Figure 1. In certain embodiments of the present invention, the GMAW electrode is oriented at an angle of about 50° to about 90° to the substrate. In certain embodiments of the present invention, the wire

- o -

guard includes a gas nozzle to supply a shielding gas. In certain embodiments of the present invention, the shielding gas is an inert gas, such as argon or helium.

[0038] In certain embodiments of the present invention, lasers with a power ranging from about 400 W to about 20 kW can be used to generate the laser radiation. In certain embodiments of the invention the laser spot size ranges from a diameter of about 0.01 inches to about 0.3 inches. There is no known limit on the laser power and laser spot size. As the laser power is increased the laser spot size increases and the rate of metal deposition increases. In certain embodiments of the present invention, about 12 pounds of metal can be deposited per hour. In certain embodiments of the present invention, the amount of metal deposited ranges up to 20 pounds metal per hour. In certain embodiments of the present invention, a greater amount of laser power can be provided for arc stabilization as travel speed increases at the same spot size. [0039] Initiation of the arc occurs when the wire momentarily touches or strikes a metal surface. During arc initiation metal can spatter. Spattering can be reduced by optimizing the arc initiation conditions of the laser/gas metal arc deposition process. To decrease spatter the laser power can be reduced and the travel speed increased. In certain embodiments of the present invention, the GMAW electrode can be oriented substantially vertical to the substrate and the laser radiation can be oriented at an acute angle to the substrate.

[0040] Processes according to the present invention have a wide range of applications. In aerospace applications, parts formed according to the present invention can be used as bulkheads, pylon panels, pylon ribs, splice plates, wing folds, vertical tail spars, and frames. [0041] In certain embodiments of the present invention, substrates up to 10 feet in length and 3 feet wide can be deposited with metal up to 6 inches or greater in depth on both sides of the substrate. Allowing the formation of parts with a thickness of over 12 inches. There is no known limit on the width, length, and thickness of the deposited layer, other than those dictated by the dimensions and capacity of the deposition chamber. The substrate is usually a part of the finished part, but in certain embodiments of the present invention, the substrate can be removed from the deposited metal structure, such as by machining, to produce a self-supported direct metal deposited part.

[0042] Parts formed according to the present invention can be formed on a flat substrate.

Alternatively, the substrates can be castings or forgings, with complex features deposited thereon

using the process of the present invention. The present invention, thus, allows the formation of complex part geometries that cannot be cast or forged.

[0043] The deposited metal layer, according to the present invention, is fixedly adhered to the substrate by forming a metallurgical bond to the substrate surface. In certain embodiments of the present invention, the inventive process, the melt depth of the deposited metal layer ranges from less than about 0.050 inches to about 0.25 inches.

[0044] The thickness of a single deposited layer, according to certain embodiments of the present invention, can range from about 0.050 inches to about 0.25 inches. In certain embodiments of the present invention, each deposited layer ranges from about 0.1 inches to about 0.2 inches thickness. Thus, multiple deposition passes are required to build up the deposited metal layer in applications requiring thicker layers. An embodiment of the present invention 70 illustrating the formation of multiple deposited layers is shown in FIG. 5. Subsequent to the deposition of the first metal layer 72, the substrate 12 is lowered in the Z .direction, relative to the arc and laser sources, and a second metal layer 74 is deposited in the same manner as described herein for forming single layers. To ensure the registration of subsequently deposited layers 74, a CNC positioning system (not shown) is used to move the substrate as required.

[0045] Direct metal deposition processes according to the present invention can be used to fabricate complex shapes. For example a "U" shaped element 60 as illustrated in FIG. 6 (or circular element (not shown)), can be formed without stopping or resetting the position or orientation of the laser radiation source and metal feedstock/metal arc electrode. As shown in FIG. 6, the "U" shaped element includes opposed legs 62, 64 connected by transverse leg 66. Legs of the "U" shaped element are formed by omni-directional deposition, as illustrated by arrows 67, 68, 69.

[0046] A cross-sectional view 80 of a deposited metal 84 on a substrate 82 formed by the present invention is illustrated in FIG. 7. The metal layer 84 is fixedly attached to the surface 88 of the substrate 82, as evidenced by the melt depth 86 into the substrate 82. [0047] In order to eliminate residual stresses and distortion and to optimize mechanical and metallurgical properties, parts formed according to the present invention can be subsequently heat treated, as in prior art direct metal deposition processes.

[0048J The embodiments illustrated in the instant disclosure are for illustrative purposes.

They should not be construed to limit the scope of the claims. As is clear to one of ordinary skill in this art, the instant disclosure encompasses a wide variety of embodiments not specifically illustrated herein.