FIELD OF THE INVENTION

The present relates to a method and arrangement for manufacturing objects by solid freeform fabrication, especially titanium and titanium alloy objects.

BACKGROUND OF THE INVENTION

Structured metal parts made of titanium or titanium alloys are conventionally made by casting, forging or machining from a billet. These techniques have a disadvantage of high material use of the expensive titanium metal and large lead times in the fabrication.

Fully dense physical objects may be made by a manufacturing technology known as rapid prototyping, rapid manufacturing, layered manufacturing, solid freeform fabrication (SFFF), additive fabrication, additive manufacturing and 3D printing. This technique employs computer aided design (CAD) software to first construct a virtual model of the object which is to be made, and then transform the virtual model into thin parallel slices or layers, usually horizontally oriented. The physical object may then be made by laying down successive layers of raw material in the form of liquid, paste, powder or other layerable, spreadable or fluid form, such as melted metal, e.g., from a melted welding wire, or preformed as sheet material resembling the shape of the virtual layers until the entire object is formed. The layers can be fused together to form a solid dense object.

Solid freeform fabrication is a flexible technique allowing creation of objects of almost any shape at relatively fast production rates, typically varying from some hours to several days for each object. The technique is thus suited for formation of prototypes and small production series, and can be scaled-up for large volume production.

The technique of layered manufacturing may be expanded to include deposition of pieces of the construction material, that is, each structural layer of the virtual model of the object is divided into a set of pieces which when laid side by side form the layer. This allows forming metallic objects by welding a wire onto a substrate in successive stripes forming each layer according to the virtual layered model of the object, and repeating the process for each layer until the entire physical object is formed. The accuracy of the welding technique is usually too coarse to allow directly forming the object with acceptable dimensions. The formed object will thus usually be considered a green object or pre-form which needs to be machined to acceptable dimensional accuracy.

Electron beam freeform manufacturing is known in the art (e.g., see Taminger et al. (“Characterization of2219Aluminum Produced by Electron Beam Freeform Fabrication,” Presented at the 13thSolid Freeform Fabrication Symposium, Aug. 5-7, 2002, Austin, Tex.; In proceedings, University of Texas at Austin (2002); Taminger et al. (“Electron Beam Freeform Fabrication: A Rapid Metal Deposition Process,” Proceedings of the 3rdAnnual Automotive Composites Conference, Sep. 9-10, 2003, Troy, Mich., Society of Plastics Engineers (2003); and Taminger and Hafley (“Electron Beam Freeform Fabrication for Cost Effective Near Net Shape Manufacturing”, NATO/RTOAVT-139 Specialists' Meeting on Cost Effective Manufacture via Net Shape Processing (Amsterdam, the Netherlands, 2006) (NATO). pp. 9-25)). Taminger and Hafley (2006) describes a method and device for manufacturing structural metal parts directly from computer aided design data combined with electron beam freeform fabrication (EBF). The structural part is built by welding on successive layers of a metallic welding wire which is welded by the heat energy provided by the electron beam. The EBF process involves feeding a metal wire onto a preheated area or molten pool made and sustained by a focused electron beam in a high vacuum environment. The positioning of the electron beam and welding wire is obtained by having the electron beam gun and the actuator supporting the substrate movably hinged along one or more axis (X, Y, Z, and rotation) and regulate the position of the electron beam gun and the support substrate by a four axis motion control system. The process is claimed to be nearly 100% efficient in material use and 95% effective in power consumption. The method may be employed both for bulk metal deposition and finer detailed depositions, and the method is claimed to obtain significant effect on lead time reduction and lower material and machining costs as compared to the conventional approach of machining the metal parts.

It is known to use a plasma arc to provide the heat for welding metallic materials. This method may be employed at atmospheric or higher pressures, and thus allow the use of simpler and less costly process equipment. One such method is known as gas tungsten arc welding (GTAW, also denoted as tungsten inert gas (TIG) welding) where a plasma transferred arc is formed between a non-consumable tungsten electrode and the welding area. The plasma arc is usually protected by a gas being fed through the plasma torch forming a protective cover around the arc. TIG welding may include feeding a metal wire or metal powder into the melting pool or the plasma arc as a filler material.

It is known (e.g., see Adams, U.S. Pat. Pub. No. 2010/0193480) to use a TIG-welding torch to build objects by solid freeform fabrication (SFFF), where successive layers of metallic feedstock material with low ductility are applied onto a substrate. A plasma stream is created by energizing a flowing gas using an arc electrode, the arc electrode having a variable magnitude current supplied thereto. The plasma stream is directed to a predetermined targeted region to preheat the predetermined targeted region prior to deposition. The current is adjusted and the feedstock material, such as a metal wire, is introduced into the plasma stream to deposit molten feedstock in the predetermined targeted region. The current is adjusted and the molten feedstock is slowly cooled at an elevated temperature, typically above the brittle to ductile transition temperature of the feedstock material, in a cooling phase to minimize the occurrence of material stresses.

Withers et al. (U.S. Pat. Pub. No. 2006/185473) also describes using a TIG torch in place of the expensive laser traditionally used in a SFFF process with relatively low cost titanium feed material by combining the titanium feed and alloying components in a way that considerably reduces the cost of the raw materials. Withers et al. teaches that an unalloyed commercially pure titanium wire (CP Ti wire) which is lower in cost than alloyed wire can be used, and the CP Ti wire can be combined with powdered alloying components in-situ in the SFFF process by combining the CP Ti wire and the powder alloying components in the melt of the welding torch or other high power energy beam. Wither et al. also teaches that titanium sponge material can be mixed with alloying elements and formed into a wire where it may be used in an SFFF process in combination with a plasma welding torch or other high power energy beam to produce near net shaped titanium components.

Abbott et al. (WO 2006/133034, 2006) describes 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. The electric arc can be provided by gas metal arc welding torch using the metal feedstock as an electrode. Abbott et al. teaches that the use of laser radiation in combination with gas metal arc welding stabilizes the arc and purportedly provides higher processing rates. Abbott et al. utilizes a consumable electrode guided by and exiting out of a wire guide. The metal of the consumable electrode is melted at the end and the molten metal is deposited by positioning the end over the deposition point. The required heat for melting the consumable electrode can be supplied by an electric arc expanding between the tip of the electrode and the workpiece/deposition substrate, and by a laser irradiating the deposition area. Welding by melting a consumable electrode heated by an electric arc is known as gas metal arc welding (GMAW), of which in the case of using non-reactive gases to make the arc is also denoted as metal inert gas welding (MIG-welding).

Titanium metal or titanium alloys heated above 400° C. may be subject to oxidation upon contact with oxygen. It is thus necessary to protect the weld and heated object which is being formed by layered freeform manufacture against oxygen in the ambient atmosphere.

One solution to this problem is taught by Guldberg (WO 2011/019287), which discloses a method for increasing the deposition rate by performing the manufacturing of objects by SFFF, especially titanium and titanium alloy objects, in a reactor chamber which is closed to the ambient atmosphere. By making the deposition chamber sufficiently void of oxygen, the need for employing protective measures to avoid oxidizing the newly welded area by ambient atmospheric oxygen is no longer present, such that the welding process may proceed at a larger velocity since the welded zone may be allowed to have a higher temperature without risking excessive oxidation of the weld. For example, in production of objects of titanium or titanium alloy, there is no longer need for cooling the welded zone to below 400° C. to avoid oxidation.

Another solution for increasing the deposition rate is known from Keicher et al. (U.S. Pat. No. 6,268,584), which discloses a deposition head assembly consisting of the following features: an array of output powder nozzles for creating a converging flow of powder to the deposition region, a central orifice which allows the multiple beams to be focused onto the deposition substrate, and coaxial gas flow for each of the powder nozzles to concentrate the stream of powders from these nozzles in order to provide a longer working distance between the nozzle and the deposition head assembly. The longer working distance is critical to insure that molten metal particulates are not attached to the deposition apparatus during processing. In particular, Keicher et al. describes a manifold system designed into the deposition head assembly that can use more than one laser beam simultaneously for the deposition process. The deposition head assembly also incorporates a means for actively concentrating the powder stream from each orifice to increase material utilization efficiency.

Another solution to the problems associated with the reactive nature of molten Ti is described by Abbott et al. (WO 2006/133034), which describes using a combination of a gas metal arc and laser welding. Gas metal arc techniques have several disadvantages that severely limit their application to depositing Ti. These drawbacks include instabilities in metal transfer, excessive spatter, and 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. The solution to these problems according to Abbott et al. is to a direct metal deposition process that includes 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.

A problem to be addressed is the speed of deposition of material on the base material to form the workpiece. One could increase the temperature of the metal wire to preheat the metal wire so that it melts at a faster rate. However, higher temperatures can result in spray transfer or spatter or an uncontrolled molten metal addition from the melted electrode into the molten metal pool, resulting in poor deposition and lack of control of the shape of the deposited layer. Excessive temperatures of the preheated area or molten pool also can result in distortion of the thin sections during deposition.

Accordingly, there exists a need in this art for an economical method of performing direct metal deposition at an increased rate of metal deposition. There further exists a need in this art for a method of increasing throughput and yield of direct metal deposition formed products.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a device for building metallic objects by SFFF.

Another objective of the invention is to provide a method for rapid layered manufacture of objects in titanium or titanium alloys.

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.

The invention is based on the realization that the deposition rate may be increased by use of a two gun system, which can include, e.g., a first welding gun for pre-heating the target deposition area on the base material, and a second welding gun for heating and melting a metal wire. Various combinations of first and second welding guns can be used. The first welding gun can include a laser device for pre-heating the target deposition area on the base material, and the second welding gun can include a plasma arc welding (PAW) torch, such as a plasma transferred arc (PTA) torch, for heating and melting a metal wire onto the target deposition area on the base material. The first welding gun can include a PAW torch, such as a PTA torch for pre-heating the target deposition area on the base material, and the second welding gun can include a laser device for heating and melting a metal wire onto the target deposition area on the base material. The first welding gun can include a first laser device for pre-heating the target deposition area on the base material, and the second welding gun can include a second laser device for heating and melting a metal wire onto the target deposition area on the base material. The first welding gun can include a laser device for pre-heating the target deposition area on the base material, and the second welding gun can include a coaxial powder feed nozzle laser system for heating and melting metal powder onto the target deposition area on the base material. The first welding gun can include an electron beam device for pre-heating the target deposition area on the base material, and the second welding gun can include a laser device for heating and melting a metal wire onto the target deposition area on the base material. The first welding gun can include a laser device for pre-heating the target deposition area on the base material, and the second welding gun can include an electron beam device for heating and melting a metal wire onto the target deposition area on the base material. The first welding gun can include a first electron beam device for pre-heating the target deposition area on the base material, and the second welding gun can include second electron beam device for heating and melting a metal wire onto the target deposition area on the base material.

Provided herein are systems for building metallic objects by solid freeform fabrication, the systems including a first welding gun for pre-heating the base material at a position at which the metallic material is to be deposited; a second welding gun to melt a source of metal into droplets of metallic material that are deposited onto the preheated area of the base material; an actuator tray that moves the base material relative to at least the first welding gun, or an actuator arm that moves the first welding gun, or an actuator arm that moves the second welding gun, or any combination of these actuators; and a control system able to read a computer assisted design (CAD) model of the object to be formed and employ a CAD-model to regulate the position and movement of the system for positioning and moving the base material and to operate the welding guns such that a physical object is built by fusing successive deposits of the metallic material onto the base material.

The first welding gun preheats the base material so that it is receptive to molten drops of melted metal wire at the position at which the melted metallic material is to be deposited. In some embodiments, at least a portion of the base material can be melted by the first welding gun to make the base material more receptive. In some embodiments, sufficient heat is applied by the first welding gun to form a preheated area in the base material at the position at which the metallic material is to be deposited. In some embodiments, sufficient heat is applied by the second welding gun to form a molten pool in the base material at the position at which the metallic material is to be deposited. It is noted that although the invention is described in correlation with the use of a metal wire, any conductive structure that can be guided and melted to deposit material can be used, for example any consumable electrode of appropriate size and shape can be used.

The first welding gun can promote fusion between the base material and the melted metallic material by deepening the melt-in in the base material. The first welding gun can help to ensure adequate melt-in by the superheated melted metallic material that the melted metallic material may not be able to achieve by itself.

The system can include a PAW torch, such as a PTA torch, as the first welding gun and a laser device as the second welding gun. In such systems, the PAW torch can be electrically connected to a direct current power source such that the electrode of the PAW torch becomes the cathode and the metal wire becomes the anode.

The second welding gun can also be designed to contribute thermal energy in the preheated area. Also, the first welding gun and second welding guns can be located on the opposite sides of the base material.

Also provided are methods for manufacturing a three-dimensional object of a metallic material by solid freeform fabrication, where the object is made by fusing together successive deposits of the metallic material onto a base material, the methods including using a first welding gun to preheat at least a portion of the surface of the base material, e.g., at the position at which the metallic material is to be deposited; using a second welding gun to heat and melt a metallic material such that molten metallic material is deposited onto the preheated area of the base material, and moving the base material relative to the position of the first and second welding guns in a predetermined pattern such that the successive deposits of molten metallic material solidifies and forms the three-dimensional object.

The methods provided herein can utilize a PAW torch, such as a PTA torch, as the first welding gun and a laser device as the second welding gun. The methods provided herein can utilize a laser device as the first welding gun and a PAW torch as the second welding gun. In such systems, the PAW torch can be electrically connected to a direct current power source such that the electrode of the PAW torch becomes the cathode and the metal wire becomes the anode.

The methods provided herein can utilize a first laser device as the first welding gun, and a second laser device as the second welding gun. The methods provided herein can utilize a laser device as the first welding gun, and a coaxial powder feed nozzle laser system as the second welding gun. The methods provided herein can utilize an electron beam device as the first welding gun, and a laser device as the second welding gun. The methods provided herein can utilize a laser device as the first welding gun, and an electron beam device as the second welding gun. The methods provided herein can utilize an electron beam device as the first welding gun, and a laser device as the second welding gun. The methods provided herein can utilize a first electron beam device as the first welding gun, and a second electron beam device as the second welding gun.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or can be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

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.

