Patent Publication Number: US-2022226921-A1

Title: Contact tip contact arrangement for metal welding

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/206,149, titled “CONTACT TIP CONTACT ARRANGEMENT FOR METAL WELDING”, filed Jul. 8, 2016, the subject matter of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a contact tip suited for electrically connecting and guiding a welding wire in metal inert gas welding (MIG-welding). 
     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 manufacturing, additive fabrication, additive manufacturing or 3D printing. This technique employs computer aided design software (CAD) 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. 
     Taminger and Hafley (“ Electron Beam Freeform Fabrication for Cost Effective Near - Net Shape Manufacturing ”, NATO/RTOAVT-139 Specialists&#39; Meeting on Cost Effective Manufacture via Net Shape Processing (Amsterdam, the Netherlands, 2006) (NATO). pp 9-25) discloses 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 melting a metal wire into a 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. The electron beam technology has a disadvantage of being dependent upon a high vacuum of 10 −1  Pa or less in the deposition chamber. 
     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 simpler and less costly process equipment. One such method is known as gas tungsten arc welding (GTAW, also denoted as TIG) 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. 
     Abbott et al. (WO 2006/133034, 2006) discloses 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 is disclosed. The electric arc can be provided by gas metal arc welding 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 metal wire guided by and exiting out of a wire guide. The metal of the metal wire 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 metal wire is supplied by an electric arc along with laser irradiation. Welding by melting a metal wire 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). 
     One essential parameter in MIG-welding is to position the tip/end-section of the metal wire above the deposition point with great accuracy and also to ensure a stable and satisfactory electric contact with the consumable wire to enable having control with the melting rate and thus the deposition rate of the metal wire onto the workpiece/substrate. One solution to this problem is described by Westberg (U.S. Pat. No. 2,179,108, 1939). Westberg discloses an apertured copper nozzle from which a metal wire, in the form of a straightened out metallic wire being fed from a wire supply, is made to pass through at a controlled velocity. Both the copper nozzle and the workpiece are electrically connected to an electric power supply setting up an electric potential between them. When the metallic wire passes through the copper nozzle it comes into contact with the nozzle and is thus electrically connected to the electric power supply. When the tip (the end section) of the metallic wire reaches a certain distance above the deposition/welding area, the electric potential creates an electric arc extending from the tip of the metallic wire and down to the deposition/welding area. The electric arc melts the tip of the incoming metallic wire and thus deposits molten metallic material onto the deposition/welding area. 
     In order to ensure safe passage of the metal wire/metallic wire through the aperture/guiding channel of the copper nozzle it is necessary to have a somewhat larger diameter of the aperture than the metal wire. The relatively low mechanical contact between the copper nozzle and the metal wire has resulted in problems with inadequate electric contact between the metal wire and the wire guide, which has given problems with instable electric arcs and electric discharges/spark formations inside the aperture which has locally melted/torn off pieces of the metal wire and led to blockages of the aperture. These problems are taught to be solved in Westberg by having the end section of copper nozzle nearest the deposition are being shaped into a semi-cylinder by removing about half of the cylinder wall to enable pressing the metal wire down onto the semi-cylindrical guide channel by a spring loaded roller wheel and thus increase the electric contact area between the copper nozzle and metal wire. A similar solution is disclosed in Zigliotto (EP 1108491, 2001), which discloses a contact tip for MIG welding torches, comprising a body having connection means for fastening the body to a welding torch, and an axial hole for feeding the wire, the contact tip being provided with a V-shaped notch which extends from the outer wall to the axis, the axial hole leading to the bottom of the notch. The bottom of the notch is inclined and it deviates towards the axis adjacent to the nozzle. The contact tip of Zigliotto is provided with pressing means fitting inside the notch to press the welding wire against the notch bottom and walls, the pressing means consisting of a spring fitting into the notch and resting on the welding wire, the spring having means for coupling with the tip body. 
     Another solution of the same problem is known from Bednarz et al. (WO 2003/039800, 2003), which discloses a contact tip, suitable for electric arc welding using a metal wire, having a body that defines a bore through which the electrode is able to pass to enable electric current from a welding power supply to be transferred from the body to the electrode. In part of the length of the bore between an inlet end and an outlet end, the body has at least one region a primary contact region at which the body is adapted to enable primary electrical contact with the electrode. Along a remainder of the length of the bore, the body is adapted such that any secondary contact between the body and the electrode along the remainder part does not substantially short circuit the primary electrical contact in the primary contact region of the bore. In some embodiments in Bednarz et al., the part of the bore/guiding channel downstream of the body/electric contact being pressed onto the metal wire, may have a larger diameter to alleviate the passage of the metal wire. This downstream section of the guiding channel may also be electrically insulated from the main body of the contact tip by inserting an electrically insulating cylindrical material having a center bore. 
     According to the experience of the inventors, there are problems with clogging of the guidance channel due to spark erosion (unintended electric discharges) between the contact tip and metal wire which may form molten pearls of metal wire material inside the guidance channel which may clog the channel or lead to deviations in the positioning of the metal wire. There also 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. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide a contact tip assembly for MIG-welding that significantly alleviates the problems related to spark erosion inside the guidance channel of the guide of the contact tip. Another objective of the invention is to provide a method for rapid layered manufacture of metal objects, particularly of objects containing Al, Cr, Cu, Fe, Hf, Sn, Mn, Mo, Ni, Nb, Si, Ta, Ti, V, W, or Zr, or composites or alloys thereof. Exemplary metal objects include titanium or a titanium alloy. 
     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 problem with clogging of the guide channel due to sparking or other causes can be significantly alleviated by electrically insulating the guide from the metal wire and employing a separate electric contact to supply the electric current to the metal wire. In the systems, devices and methods provided herein, a consumable contact tip is separate and apart from the guide, and the metal wire is brought into contact with the contact tip after the metal wire has passed through an end portion of the guide. 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. 
     Referring to  FIGS. 1A through 7B , provided is a contact tip assembly  100 , which includes a guide  120  having a longitudinal center axis A-A′, a first end  140 , and an opposite second end  150 , and a center bore  130  extending and running along the longitudinal center axis of the guide  120  from its first end  140  to its second end  150 . The contact tip assembly  100  also can include an electrically insulating lining  160  that is inside of the center bore  130  and that extends at least from the first end  140  to the second end  150  of the guide  120 . The electrically insulating lining  160  includes a guide channel  170  having an inlet opening  145  at the first end  140  and an outlet opening  155  at the second end  150  and running through the linear electrically insulating lining  160  along the longitudinal center axis A-A′, and the electrically insulating lining  160  guides a metal wire  180  being passed through the linear cylindrical guide channel  170  from the inlet opening  145  towards and further out of the outlet opening  155 . The contact tip assembly  100  also includes an electric contact unit  200  containing a contact tip  215  in electric contact with an electric energy source. The electric contact unit  200  can be positioned within a cut out section  115  that exposes the metal wire  180  to the contact tip  215  of the electric contact unit  200 , as illustrated in  FIG. 1A . The electric contact unit  200  can be positioned at a distance away from the outlet opening  155 , as illustrated in  FIGS. 2, 3, 4A and 5 . The assembly can include a contact element pressing assembly  210  for pressing the contact tip  215  of the electric contact element  200  onto the metal wire  180 , as illustrated in  FIGS. 1A, 2 and 3 . The assembly can include a wire pressing assembly  190  for pressing the metal wire  180  into contact with the contact tip  215  of the electric contact element  200 , as illustrated in  FIGS. 4A and 5 . The assembly can include a wire pressing assembly  190  and a contact element pressing assembly  210  (not shown in the figures). 
     The contact tip assembly can include a bottom opening  125  in the bottom of the guide  120 , as illustrated in  FIGS. 1B and 4B . The bottom opening  125  allows dust or pieces of wire to exit the guide  120  prior to coming near the forming piece. The bottom opening  125  can extend to the second end  150  to form a channel. The guide  120  can be made of or include Al, Cr, Cu, Fe, Hf, Sn, Mn, Mo, Ni, Nb, Si, Ta, Ti, V, W, or Zr, or composites or alloys or combinations thereof An exemplary guide  120  can be made of or include titanium or a titanium alloy. 
     The contact tip  215  can be made of or include Cu or a Cu alloy or a Cu composite. In some embodiments, the contact tip  215  includes a Cu/W composite. 
     When a guide  120  includes an electrically insulating lining  160  that forms the guide channel  170 , a coating  165  can be included on the surface of the electrically insulating lining  160 , as illustrated in  FIGS. 6A-7B . The coating  165  faces the metal wire  180  as the metal wire  180  passes through the guide channel  170 . The contact tip assembly provided herein also can include an insulating tip  195  on the surface of the wire pressing assembly  190  that comes into contact with the metal wire  180 . An exemplary embodiment is illustrated in  FIGS. 4A and 4B . 
     An exemplary system that contains the contact tip assembly provided herein is illustrated in  FIG. 12 . The electric contact unit  200  can include an electrical connection  230  that connects the contact tip  215  to a power source and an insulator connector  240  that connects the contact tip  215  to a contact tip support  220 . The contact tip assembly also can include a cut-out section  115  that exposes the metal wire  180  to the contact tip  215  of the electric contact unit  200 . 
     As shown in  FIG. 12 , the contact tip assembly provided herein also can include a support element  300  to which the guide  120  and the electric contact unit can be connected for support; a metal wire deliver source  400 ; and a frame  500  to which the support element  300  can be fastened. A thermally insulating material  310  can be present between all connections.  FIG. 12  shows a thermally insulating material  310  between the support element  300  and the guide  120 , and between the support element  300  and the frame  500 . The contact tip assembly generally is positioned so that after the metal wire  180  passes through the guide  120  the metal wire  180  is positioned in a plasma arc of a plasma transfer arc (PTA) torch above a deposition point of a workpiece. In the contact tip assembly provided herein, the contact tip  215  can be isolated spatially from the PTA torch. 
     Also are provided are methods for providing an electric current to a metal wire during manufacturing of a three-dimensional object of a metallic material by solid freeform fabrication, the methods including feeding a metal wire through a guide; providing a contact tip that is separate and apart from the guide; and contacting the metal wire with the contact tip after the metal wire has passed through an end portion of the guide. 
     Also provided are methods for manufacturing a three-dimensional object of a metallic material by solid freeform fabrication. The methods include depositing successive deposits of a metallic material onto a base material, where each successive deposit is obtained by feeding a metal wire through a guide into an electric contact unit configured to contact the metal wire with a contact tip past the end of the guide; using a PAW torch to heat and melt the wire such that molten metallic material drips onto the preheated area of the base material; and moving the base material and/or the PAW torch in a predetermined pattern such that the successive deposits of molten metallic material solidifies and forms the three-dimensional object. Optionally, a second PAW torch can be used to preheat the base material at the position at which the metallic material is to be deposited. In some embodiments, at least a portion of the base material is melted during preheating to make the base material more receptive. Preheating promotes fusion between the base material and the melted metallic material by deepening the melt-in in the base material. In some embodiments, sufficient heat is applied during preheating to form a molten pool in the base material where the metallic material is to be deposited. The metal wire can be in the form of any wire. The metal wire can be or contain Al, Cr, Cu, Fe, Hf, Sn, Mn, Mo, Ni, Nb, Si, Ta, Ti, V, W, or Zr, or composites or alloys thereof. In some embodiments, the metal wire is a wire that contains Ti or a Ti alloy. 
     Also provided are systems for manufacturing a three-dimensional object of a metallic material by solid freeform fabrication. The systems can include a guide for guiding a metal wire into position above a base material; a contact tip arranged to contact the metal wire past an end of the guide; a welding torch to melt the wire onto a base material; and a computer model of the object to be formed to define a deposition profile such that a physical object is built by fusing successive deposits of the melted wire onto the base material. metal wire. The systems can further include an actuator tray that moves the base material relative to at least the welding torch. The systems can also include an actuator arm that moves the welding torch. In addition, a second welding torch can also be used to preheat the base material at a location over which the wire is melted. The second welding torch can also be moved by an actuator. 
     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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. For clarity, the figures are not to scale and some components are omitted. 
       In the drawings: 
         FIG. 1A  is a schematic drawing showing a side sectional view of an embodiment of the guide  120  of the contact tip assembly  100  showing the location of a cut out section  115  in the top portion of the guide  120  that can accommodate a portion of the electric contact element  200 . In the embodiment shown, the cut out section  115  does not extend to the end of the guide  120 , resulting in a distal extension  110  of the top section.  FIG. 1B  is a schematic drawing showing a bottom view of an embodiment of the guide  120  of the contact tip assembly  100  showing a bottom opening  125  that allows dust or pieces of wire to exit the guide  120  prior to coming near the forming piece. 
         FIG. 2  is a schematic drawing showing a side sectional view of an embodiment of the guide  120  of the contact tip assembly  100  showing the location of a cut out section  115  in the top portion of the guide  120  that can accommodate a portion of the electric contact element  200 . In the embodiment shown, the cut out section  115  extends to the end of the guide  120 . 
         FIG. 3  is a schematic drawing showing a side sectional view of an embodiment of the guide  120  of the contact tip assembly  100  showing the location of a cut out section  115  in the top portion of the guide  120  that can accommodate a portion of the electric contact element  200 . In the embodiment shown, the cut out section  115  extends to the end of the guide  120 , and the electrically insulating lining  160  extends past the guide  120 . 
         FIG. 4A  is a schematic drawing showing a side sectional view of an embodiment of the guide  120  of the contact tip assembly  100  containing a wire pressing assembly  190  below the metal wire  180  and positioned under the electric contact element  200 . In the embodiment shown, the cut out section  115  extends to the end of the guide  120 , and the electrically insulating lining  160  extends past the guide  120 .  FIG. 4B  is a schematic drawing showing a bottom view of an embodiment of the guide  120  of the contact tip assembly  100  showing a bottom opening  125  that allows dust or pieces of wire to exit the guide  120  prior to coming near the forming piece. In the embodiment depicted, the bottom opening  125  extends to the second end  150  of the guide  120 . 
         FIG. 5  is a schematic drawing showing a side sectional view of an embodiment of the guide  120  of the contact tip assembly  100  containing a wire pressing assembly  190  below the metal wire  180  and positioned under the electric contact element  200 . In the embodiment shown, the electrically insulating lining  160  extends past the guide  120 . 
         FIGS. 6A and 6B  are schematic drawings showing a cross-sectional frontal view of embodiments of the guide  120  of the contact tip assembly  100 . In  FIG. 6A , the cross-section of the electrically insulating lining  160  and the guide  120  are circular. In  FIG. 6B , the cross-section of the electrically insulating lining  160  is square and the guide  120  is circular.  FIGS. 6A and 6B  show the position of optional coating  165  on the electrically insulating lining  160 . 
         FIGS. 7A and 7B  are schematic drawings showing a cross-sectional frontal view of embodiments of the guide  120  of the contact tip assembly  100 . In  FIG. 7A , the cross-section of the electrically insulating lining  160  and the guide  120  are square. In  FIG. 7B , the cross-section of the electrically insulating lining  160  is circular and the guide  120  is square.  FIGS. 7A and 7B  show the position of optional coating  165  on the electrically insulating lining  160 . 
         FIG. 8  is a drawing showing a side view of an embodiment of the guide  120  of the contact tip assembly  100 . 
         FIG. 9  is a drawing showing a top view of an embodiment of the guide  120  of the contact tip assembly  100 . 
         FIG. 10  is a drawing showing a bottom view of an embodiment of the guide  120  of the contact tip assembly  100 . 
         FIG. 11  is a drawing showing a front view of an embodiment of the guide  120  of the contact tip assembly  100 . 
         FIG. 12  is a drawing showing a side view of an embodiment of a system that includes the contact tip assembly  100  provided herein. 
     
    
    
     DETAILED DESCRIPTION 
     A. Definitions 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art to which the inventions belong. All patents, patent applications, published applications and publications, websites and other published materials referred to throughout the entire disclosure herein, unless noted otherwise, are incorporated by reference in their entirety. In the event that there are a plurality of definitions for terms herein, those in this section prevail. Where reference is made to a URL or other such identifier or address, it is understood that such identifiers can change and particular information on the internet can come and go, but equivalent information can be found by searching the internet. Reference thereto evidences the availability and public dissemination of such information. 
     As used here, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. 
     As used herein, the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments. 
     As used herein, ranges and amounts can be expressed as “about” a particular value or range. “About” also includes the exact amount. Hence “about 5 percent” means “about 5 percent” and also “5 percent.” “About” means within typical experimental error for the application or purpose intended. 
     As used herein, “optional” or “optionally” means that the subsequently described event or circumstance does or does not occur, and that the description includes instances where the event or circumstance occurs and instances where it does not. For example, an optional component in a system means that the component may be present or may not be present in the system. 
     As used herein, a “combination” refers to any association between two items or among more than two items. The association can be spatial or refer to the use of the two or more items for a common purpose. 
     The term “plasma transferred arc torch” or “PTA torch” as used interchangeably herein refers to any device able to heat and excite a stream of inert gas to plasma by an electric arc discharge and then transfer the flow of plasma gas including the electric arc out through an orifice (such as a nozzle) to form a constricted plume that extends out of the orifice and transfers the intense heat of the arc to a target region. The electrode and target region can be electrically connected to a power source such that the electrode of the PTA torch becomes the cathode and the target region becomes the anode. This will ensure that the plasma plume including electric arc is delivering a highly concentrated heat flow to a small surface area of the target region with excellent control of the areal extension and magnitude of the heat flux being supplied from the PTA torch. A plasma transferred arc torch has the advantage of providing stable and consistent arcs with little wandering and good tolerance for length deviations between the cathode and anode. Thus, the PTA torch is suitable both for forming heating the base material, e.g., to melt at least a portion thereof or to form a molten pool in the base material, as well as to heat and melt the metallic wire feed. The PTA torch may advantageously have an electrode containing tungsten and a nozzle containing copper. However, the invention is not tied to any specific choice or type of PTA torch. Any known or conceivable device able to function as a PTA torch providing a stable heat source for melting the metal electrode wire can be used. As used herein, a “Plasma Arc Welding torch” or “PAW torch” refers to a welding torch that can be used in plasma arc welding. The torch is designed so that a gas can be heated to a high temperature to form plasma and becomes electrically conductive, the plasma then transfers an electric arc to a workpiece, and the intense heat of the arc can melt metal and/or fuse two pieces of metal together. A PAW torch can include a nozzle for constricting the arc thereby increasing the power density of the arc. The plasma gas typically is argon. Plasma gas can be fed along an electrode and ionized and accelerated in the vicinity of a cathode. The arc can be directed towards the workpiece and is more stable than a free burning arc (such as in a TIG torch). The PAW torch also typically has an outer nozzle for providing a shielding gas. The shielding gas can be argon, helium or combinations thereof, and the shielding gas assists minimizing oxidation of the molten metal. Current typical up to 400 A, voltage typical 25-35 V (up to app. 14 kW). PAW torches include plasma transferred arc torches. 
     The term “metallic material” as used herein refers to any known or conceivable metal or metal alloy which may be formed into a wire and employed in a solid freeform fabrication process to form a three-dimensional object. Examples of suitable materials include, but are not limited to, titanium and titanium alloys such as i.e. Ti-6Al-4V alloys, nickel and nickel alloys and other metals or metal alloys. 
     The term “base material” as used herein refers to the target material upon which metallic material is to be deposited. This will be the holding substrate when depositing the first layer of metallic material. When one or more layers of metallic material have been deposited onto the holding substrate, the base material will be the upper layer of deposited metallic material that is to have deposited a new layer of metallic material. 
     The term “holding substrate” as used herein refers to the target substrate that is first loaded into the chambers upon which additional material, the same or different from that of the holding substrate, is deposited using the technique of SFFF of solid free form fabrication to form a workpiece. In exemplary embodiments, the holding substrate is a flat sheet. In alternative embodiments, the holding substrate may be a forged part. In alternative embodiments, the holding substrate may be an object upon which additional material is to be deposited. In exemplary embodiments, the holding substrate can become part of the workpiece. The material for the holding substrate can be a metal or a metal alloy. In exemplary embodiments, the holding substrate is made of the same metal as the wire feed material. 
     As used herein, the term “workpiece” refers to a metal body being produced using solid free form fabrication. 
     The term “computer assisted design model” or “CAD-model” as used interchangeably herein refers to any known or conceivable virtual three-dimensional representation of the object that is to be formed which may be employed in the control system of the arrangement according to the second aspect of the invention: to regulate the position and movement of the holding substrate and to operate the welding torch with integrated wire feeder such that a physical object is built by fusing successive deposits of the metallic material onto the holding substrate in a pattern which results in building a physical object according to the virtual three-dimensional model of the object. This may for instance be obtained by forming a virtual vectorized layered model of the three-dimensional object by first dividing the virtual three-dimensional model into a set of virtual parallel horizontal layers and then dividing each of the parallel layers into a set of virtual quasi one-dimensional pieces. Then, the physical object may be formed by engaging the control system to deposit and fuse a series of quasi one-dimensional pieces of the metallic material feed onto the supporting substrate in a pattern according to the first layer of the virtual vectorized layered model of the object. Then, repeating the sequence for the second layer of the object by depositing and fusing a series of quasi one-dimensional pieces of the weldable material onto the previous deposited layer in a pattern according to the second layer of the virtual vectorized layered model of the object. The deposition continues based on the repetition of the deposition and fusing process layer by layer for each successive layer of the virtual vectorized layered model of the object until the entire object is formed. 
     However, the invention is not tied to any specific CAD-model and/or computer software for running the control system of the arrangement according to the invention, and nor is the invention tied to any specific type of control system. Any known or conceivable control system (CAD-model, computer-aid manufacturing (CAM) system or software, computer software, computer hardware and actuators etc.) able to build metallic three-dimensional objects by solid freeform fabrication may be employed. In exemplary embodiments, the control system can be adjusted to separately operate a first PAW torch to preheat the base material and a second PAW torch to melt the feed wire of metallic material onto the preheated area of the base material. The first PAW torch can preheat the base material so that it is receptive to molten drops of melted metal wire, i.e. melted metallic material, at the position at which the melted metallic material is to be deposited. In some embodiments, the preheating does not melt the base material. In alternative embodiments, at least a portion of the base material is melted by the first PAW to make the base material more receptive. In some embodiments, sufficient heat is applied by the first PAW torch to form a molten pool in the base material at the position at which the metallic material is to be deposited. 
     Positioning of the base material and any one or more PAW torches can be accomplished using one or more actuators. In exemplary embodiments, the base material can be repositioned or moved using an actuator tray over which the base material is resting. The actuator tray can move the base material in any direction. In exemplary embodiments the actuator tray can be set on a track or rail system and able to move the base material in any desired direction. Alternatively, the actuator tray may be operated using a mechanical or robotic arm. The actuator may also be operated using hydraulics. Similarly, the one or more PAW torches may be moved using one or more actuators. For example, each of the one or more PAW torch may be attached to an independently controlled actuator arm, such as a robotic or mechanical arm. Use of other types of mechanisms for the actuator arm can also be implemented, such as for example rail or track systems. The actuators may also be operated using hydraulics. In exemplary embodiments in which two or more PAW torches are used, each PAW torch can be moved independently. In alternative embodiment using two or more PAW torches, the position of two or more PAW torches can be fixed relative to each other and one or more actuator arms move the two or more PAW torches simultaneously. In exemplary embodiments, the actuator tray is the only actuator used, keeping the one or more PAW torches at a fixed position during deposition. In alternative embodiments, the actuator tray moves the base material only within two direction in one plane, while one or more actuator arms move the one or more PAW torches in only one direction, for example perpendicularly to the plane in which the actuator tray moves. The opposite may also be true, where the one or more actuator arms move the one or more PAW torches in two directions within a plane while and the actuator tray moves the base material along a single direction. In alternative embodiments, the base material is maintained in a fixed position during deposition, and one or more actuator arms are used to move the one or more PAW torches. In yet an alternative embodiment, an actuator tray and one or more actuator arms are all used to move the base material and the one or more PAW torches. 
     B. Contact Tip Assembly 
     Provided are systems and methods for manufacture of near net shape metal bodies using solid free form fabrication, the systems and methods utilizing a contact tip assembly that significantly alleviates the problems related to spark erosion inside the guide channel of the guide. Build up within the guide channel caused by sparking can result in random electrical connection and physical movement within the guide channel and can result in depositions within the guide channel that can interfere with or prevent movement of the metal wire through the guide. The inventors have determined that the problem with clogging of the guide channel due to sparking or other causes or deflection of the metal wire due to deformities in the guide channel due to build-up caused by sparking can be significantly alleviated by electrically insulating the guide from the metal wire, and using a separate electric contact to supply the electric current to the metal wire. In the systems, devices and methods provided herein, a consumable contact tip is separate and apart from the guide, and the metal wire is brought into contact with the contact tip after the metal wire has passed through an end portion of the guide. 
     The contact tip assembly provided herein includes a guide, a metal wire delivery source the provides the metal wire to the guide, and an electric contact element that electrically connects the wire to the electric power supply. The guide is electrically insulated from the metal wire, and a separate electric contact unit supplies the electric current to the metal wire via a contact tip of the electric contact unit. The guide can be of any material compatible with plasma arc welding. In some embodiments, the guide is or contains titanium or 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 contact tip is or contains copper or a copper alloy. The copper alloy can contain any of copper ASTM Classes II through X. The copper alloy can include copper in combination with any one of Ag, Al, Be, Bo, Cr, In, Mg, Ni, Sn, Sr, W, Zn or Zr, or combinations thereof. For example, the contact tip can include a sintered composition of W and Cu, or an alloy of Cu and W. In exemplary embodiments, the contact tip may have a curved or semi-curved surface where it contacts the wire. The curved, or semi-curved surface can be sized appropriately to accommodate the wire to be contacted. For example, for a wire having a diameter of about 1.6 mm, the contact tip may have a curved or concave surface having a diameter of about 1.8 mm. Also, the surface area of the contact tip can be large enough to help avoid overheating caused by the current transfer. In exemplary embodiments, the width or thickness of the contact tip can range from about 1 mm to about 10 mm. 
     An exemplary embodiment of a system containing the contact tip assembly provided herein is shown in  FIG. 12 . In the exemplary system depicted in  FIG. 12 , the contact tip assembly includes a guide  120  and an electric contact unit  200  positioned above the guide  120 . The electric contact unit  200  contains a replaceable contact tip  215  (not shown in the figure) and electrical connection  230  for connecting the contact tip  215  with a power source, such as a DC power source. The electric contact unit  200  can include a contact tip pressing assembly  210  that can exert a downward pressure against a contact tip support  220  to press the contact tip  215  into contact with the metal wire  180 . The downward pressure to keep the contact tip  215  into contact with the metal wire  180  can be achieved, for example, by using a spring, hydraulics, pneumatic actuators, mechanized screws or a motorized piston assembly or any combination thereof. When the contact tip support  220  presses the contact tip  215  into contact with the metal wire  180 , an electric circuit with a PTA torch  600  can be completed. 
     The guide  120  and the electric contact unit  200  are shown connected to a support element  300 . The guide  120  and the electric contact unit  200  are thermally isolated from the support element  300  by including a thermally insulating material  310  between the contact points. The support element  300  is shown attached to a frame  500 . It should be understood that support element  300  and frame  500  are simply illustrative. Other supporting structures also can be used. A metal wire delivery source  400 , also electrically insulated, provides a metal wire  180  to one end of the guide  120 . The metal wire  180  passes through the guide  120  and exits the other end of the guide  120 , where it is positioned in the plasma arc above the deposition point of the workpiece. With the exemplary configuration provided herein, there is a single point of contact between the metal wire and the contact tip of the electric contact unit. This allows a stable contact point to be maintained. This also promotes stable resistive preheating of the metal wire wire before coming into contact with the arc and being melted. 
     The guide  120  can be of any shape, as long as it is configured to receive a metal wire  180  and allow the metal wire  180  to pass through the guide  120  without hindrance. An exemplary guide  120  is shown in detail in  FIGS. 8-11 . As depicted in  FIG. 8 , the guide  120  can have a generally cylindrical shape to accommodate a metal wire  180  that is in the form of a wire with a substantially circular cross section. The shape of the outer portion of the guide  120  can have a cross section that is circular, oval, elliptical, or polygonal, for example, square, triangular, rectangular, pentagonal, hexagonal, octagonal, or any combination thereof. In  FIGS. 6A and 6B , the cross-section of the guide  120  is shown as circular. In  FIGS. 7A and 7B , the cross-section of the guide  120  is shown as square. 
     In an exemplary embodiment, the guide  120  can be fluid cooled. For example, the guide can be designed to include an internal path for fluid flow through the guide. The fluid can be any suitable fluid, such as water, a C 1 -C 5  alcohol, a polyalphaolefin, an alkylene glycol, such as ethylene glycol or propylene glycol, or mixtures thereof. In some embodiments, the cooling fluid is water, a mixture of water and propylene glycol, or a mixture of water and ethylene glycol. The cooling fluid can include additives, such as salts, corrosion inhibitors, pH adjusters or combinations thereof. 
     The guide can include projections or protrusions from the outer surface, such as to align the guide, or to allow attachment of the guide to a support or to other elements. As shown in  FIG. 8 , which shows a side view of the guide  120 , the guide  120  can include fastener projections  122  and  124  for connecting the guide  120  to the support element  300  (as shown in  FIG. 12 ). The fastener projections  122  and  124  can be threaded to accommodate a bolt or screw that can be used to attach the guide  120  to the support element  300 . The guide  120  can include a protrusion  127  that can engage with and/or guide the placement of the electric contact unit  200 . 
     As show in  FIG. 8 , the guide  120  can include a cut out section  115  in the upper portion of the guide  120  that can accommodate a portion of the end of the electric contact unit  200 . The cut out section  115  results in the formation of a cut out first wall  111  that contains a cut out entry opening  112 , and a cut out second wall  114  that contain a cut out exit opening  113 . The metal wire  180  enters the cut out section  115  via cut out entry opening  112  and exits the cut out section  115  via cut out exit opening  113 , ultimately exiting the guide  120  via outlet opening  155 . 
       FIG. 9  shows a top view of the guide  120 . As shown in the figure, the guide  120  can include a bottom opening  125  beneath the cut out section  115 . The bottom opening  125  allows any dust or particles of the metal wire  180  to exit the guide  120  prior to coming near the forming piece. The bottom opening  125  can extend to the second end  150  of the guide  120 , as shown in  FIG. 10 . 
       FIG. 11  shows a skewed front view of the guide  120 . This view illustrates an embodiment where the electrically insulating lining  160  extends from the second end  150  of the guide  120 . The metal wire  180  is surrounded by the electrically insulating lining  160  for some distance as it exits the guide  120  via outlet opening  155 . The electrically insulating lining  160  extending from second end  150  does not have to completely surround the metal wire  180 . For example, a portion of the bottom of the electrically insulating lining  160  can be removed. For example, measured from the horizontal diameter of the electrically insulating lining  160 , an arc segment subtending an angle of from about 10° to about 180° can be removed. When the electrically insulating lining  160  has a circular cross section, removal of an arc segment subtending an angle of 180° results in a semi-circular electrically insulating lining  160  covering the upper portion of the metal wire  180 . 
     The guide can be electrically insulated from the metal wire using an electrically insulating lining containing an electrically insulating material suitable for use in the conditions to which the guide would be exposed during welding. The electrically insulating material can be or contain an electrically insulative ceramic. Such ceramics are known in the art and can include the oxides or nitrides of Al, B, Zr, Mg, Y, Ca, Si, Ce, In and Sn and combinations thereof (e.g., see U.S. Pat. No. 6,344,287 (Celik et al., 2002); U.S. Pat. No. 4,540,879 (Haerther et al., 1985); and U.S. Pat. No. 7,892,597 (Hooker et al., 2011)). The electrically insulating material can be or contain aluminum nitride, aluminum oxide, magnesium nitride, magnesium oxide, quartz, silicon nitride, boron nitride, zirconium dioxide and mixtures and combinations thereof. 
     The electrically insulating lining can be configured to be contained within the guide. An exemplary embodiment is shown in  FIG. 4A , where the electrically insulating lining  160  does not extend past the end of the guide  120 . The electrically insulating lining can be configured to extend from one or both ends of the guide. An exemplary embodiment is shown in  FIG. 5 , where the electrically insulating lining  160  extends past the end of the guide  120 . 
     When the cut out section is present, the electrically insulating lining can be configured to be contained within the guide and not extend into the cut out section or extend past the end of the guide. An exemplary embodiment is shown in  FIG. 2 , where electrically insulating lining  160  is contained within the guide  120 . In some embodiments when the cut out section is present, the electrically insulating lining can be configured to extend into the cut out section or extend past the end of the guide or both. An exemplary embodiment is shown in  FIG. 3 , where electrically insulating lining  160  extends into cut out section  115  and extends past the end of guide  120 . 
     The electrically insulating lining can contain a central bore through which the metal wire can pass. The central bore typically is of a shape that easily accommodates the metal wire. For example, when the metal wire is a wire having a circular cross section, the electrically insulating lining includes a central bore with a circular cross section. The central bore of the electrically insulating lining generally is of a diameter that is slightly larger than the diameter of the metal wire. This accommodates any variation in the size of the cross-section of the metal wire, such as variation in wire diameter. For example, when the metal wire is a metal wire, the wire diameter can have a certain variation of diameter, and a tolerance in variation can be used to determine the size of the central bore of the electrically insulating lining. For example, the central bore of the electrically insulating lining can be sized to accommodate the diameter of a metal wire in the form of a metal wire plus a variance tolerance of 0.01 mm 
     The diameter of the metal wire, according to certain embodiments of the present invention, can range from about 0.8 mm to about 5 mm. The metal wire can have any practically implementable dimension, e.g., 1.0 mm, 1.6 mm, 2.4 mm, etc. The feed rate and positioning of the metal wire can be controlled and modulated in accord with the effect of the power supply to the PAW torch in order to ensure that the metal wire is being continuously heated and is melted when it reaches the intended position above the preheated area of the base material. 
     When the electrically insulating lining includes an insulative ceramic in the vicinity of the central bore through which the metal wire passes, the insulative ceramic can include a surface treatment to reduce the roughness of the surface of the metal wire insulative ceramic. The surface treatment can help to minimize or eliminate scratching or scoring of the metal wire as it passes through the electrically insulating lining. For example, the surface of the electrically insulating lining can be treated to include a surface glaze that reduces the friction-causing attraction forces between the lining surface and the electrode. Laser glazing treatment can be used to reduce surface pores, cracks or deformations on the surface to reduce friction and produce a smoother insulative ceramic surface. The surface of the electrically insulating lining can be treated to include a diamond-like-carbon coating. A synthetic fluoropolymer, such as polytetrafluoroethylene (PTFE) can be applied to the surface of the electrically insulating lining to reduce friction. The surface treatment can help to minimize the formation of small pieces of metal wire that can form due to interaction of the metal wire with a rough insulative ceramic surface. In each of  FIGS. 6A, 6B, 7A and 7B , an optional coating  165  is shown on the surface of the electrically insulating lining  160  facing center bore  130 . 
     The electrically insulating lining  160  can be of any shape, as long as it is configured to have a center bore  130  that receives a metal wire  180  and allows the metal wire  180  to pass through the electrically insulating lining  160 . The shape of the outer portion of the insulating lining  160  can have a cross section that is circular, oval, elliptical, or polygonal, for example, square, triangular, rectangular, pentagonal, hexagonal, or octagonal. As depicted in  FIGS. 6A and 7B , the electrically insulating lining  160  can have a substantially circular cross section with a center bore  130  that has a circular cross section.  FIGS. 6B and 7A  show an electrically insulating lining  160  that has a square cross section with a center bore  130  that has a circular cross section. 
     The electric contact unit contains a replaceable contact tip that is brought into contact with the metal wire. As discussed earlier, the contact tip may have a curved or semi-curved surface sized to accommodate the wire. Also, the surface area of the contact tip can be large enough to help avoid overheating caused by the current transfer. In exemplary embodiments, the width or thickness of the contact tip can range from about 1 mm to about 10 mm. The contact tip electrically connects the metal wire to a direct current power source. The electrical connection can be made so that a circuit is formed that connects the power source, the electrode of a PTA torch and the metal wire (via the replaceable contact tip). When the metal wire enters the arc of the PTA torch, the plasma plume including electric arc delivers a highly concentrated heat flow to a small surface area of the metal wire. The PTA torch can have an electrode made of tungsten and a nozzle made of copper or copper alloy. However, the invention is not tied to any specific choice or type of PTA torch. Any known or conceivable device able to function as a PTA torch can be used. Also, the invention may be implemented using a PAW torch that is not a PTA torch. 
     In the methods provided, welding by melting a metal wire heated by an electric arc (gas metal arc welding or GMAW), particularly using non-reactive gases to make the arc (metal inert gas welding or MIG-welding) is used in the solid free form fabrication of a metal object. In these methods, a metal wire is made to melt in the plasma produced by torch using an electric arc, and the melting metal wire is deposited onto the workpiece to add to and form the near net shape metal bodies. 
     An electrically insulating material also can be used to isolate the electric contact unit from the arc of a PTA torch. The electrically insulating material can be positioned at the outlet opening of the guide of the metal wire so that it extends some distance from the outlet opening. The length of the electrically insulating material extending from the outlet opening can be 0.1 to 10 mm, or from about 0.5 to 5 mm, or about 1 mm. 
     In some embodiments, the electric contact unit can be positioned within a cut out section of the metal wire guide and the guide can include an electrically insulating material that is positioned at the outlet opening of the guide. An exemplary embodiment is shown in  FIG. 8 , which shows cut out section  115  of guide  120  for receiving the electric contact unit  200 , and electrically insulating material  160  extending past the end of the guide  120 . 
     The electrically insulating material can include any material suitable for use at the temperatures near the plasma arc. The electrically insulating material can be or contain an electrically insulative ceramic. Such ceramics are known in the art and can include the oxides or nitrides of Al, B, Zr, Mg, Y, Ca, Si, Ce, In and Sn and combinations thereof (e.g., see U.S. Pat. No. 6,344,287 (Celik et al., 2002); U.S. Pat. No. 4,540,879 (Haerther et al., 1985); and U.S. Pat. No. 7,892,597 (Hooker et al., 2011)). The electrically insulating material can be or contain aluminum nitride, aluminum oxide, magnesium nitride, magnesium oxide, quartz, silicon nitride, boron nitride, zirconium dioxide and mixtures and combinations thereof. 
     The contact tip within the electric contact unit contains copper or a copper alloy. Contact tips are commercially available (e.g., from Brouwer Metaal b.v.), and the invention is not limited to any specific type of contact tip. The contact tip can be attached to a cylindrical support within the electric contact unit. In some embodiments, the contact tip is thermally insulated from the cylindrical support by using an intervening thermal insulating material. Any thermal insulating material that can withstand the temperatures to which the contact tip could be exposed are appropriate for use within the electric contact unit. An exemplary thermal insulating material is ceramic, which also can be selected to be electrically insulative, which would minimize or prevent any of the electric current from being transferred from the contact tip to the electric contact unit. Any of the ceramics described above could be used to construct an appropriate fitting for attaching the contact tip to the cylindrical support within the electric contact unit. 
     The contact tip within the electric contact unit is maintained in contact with the metal wire to insure constant current to the metal wire and a completed circuit of containing the power source, metal wire and the target area. In some embodiments, the contact tip is maintained in contact with the metal wire via a contact tip pressing assembly. The contact tip pressing assembly can be part of the electric contact unit, or can be a separate element. As shown schematically in  FIG. 6A , the contact tip pressing assembly  210  can exert a downward pressure against the contact tip support  220  to press the contact tip  215  into contact with the metal wire  180 . The downward pressure to keep the contact tip  215  into contact with the metal wire  180  can be achieved by using, e.g., a spring, hydraulics, mechanized screws or a motorized piston assembly. When a spring is used, the spring can be selected to exert a force of appropriate strength or magnitude so that it is not so strong that the contact tip  215  scratches the metal wire  180  but strong enough to maintain contact between the contact tip  215  and the metal wire  180 . Depending on the configuration chosen, a spring, such as a compression spring, having a spring constant of from about 0.001 to about 10 N/m can be used to force the contact tip  215  down against metal wire  180 . 
     In some embodiments, the contact tip is maintained in contact with the metal wire via a wire pressing assembly. As shown schematically in  FIG. 9 , the wire pressing assembly  190  can exert an upward pressure against the metal wire  180  as is passes over the wire pressing assembly  190  to press the metal wire  180  into contact with the contact tip  215 . The upward pressure to keep the metal wire  180  in contact with the contact tip  215  can be achieved, for example, by using, e.g., a pin, lever or clip, such as an L-shaped clip, attached to a spring, hydraulics, mechanized screws or a motorized piston assembly. The pin or clip contacts the metal wire and pushes the metal wire upwards into contact with the contact tip. The upward force can be provided by a spring, hydraulics, mechanized screws or a motorized piston assembly or combinations thereof. The force to press the metal wire into contact with the contact tip can be selected to be of appropriate strength or magnitude so that it is not so strong that the contact tip  180  or wire pressing assembly  190  scratches the metal wire, e.g., metal wire, but strong enough to maintain continuous contact between the contact tip  215  and the metal wire  180 . Depending on the configuration chosen, a spring, such as a compression spring having a spring constant of from about 0.001 to about 10 N/m can be used, alone or in combination, to force the wire pressing assembly  190  up toward the contact tip  215 . In some embodiments, a combination of a contact tip pressing assembly to press the contact tip downward, and a wire pressing assembly to press the metal wire upward, is used. Alternatively, the contact tip pressing assembly presses upward and the wire pressing assembly presses the metal wire downward. In yet alternative embodiments, the contact tip assembly does not press, and the wire is contacted to the contact tip only by the metal wire pressing assembly. Alternatively, no wire metal pressing assembly is used and the contact tip is pressed against the wire by the contact tip assembly. In yet an alternative embodiment, no pressure is applied to either the metal wire or the contact tip. 
     The wire pressing assembly can include an insulating tip on its surface that interfaces and comes into contact with the metal wire. As shown in  FIG. 4A , an optional insulating tip  195  is shown on the surface of the wire pressing assembly  190  and it is the insulating tip  195  that contacts the metal wire. The insulating tip can be made of any material compatible with the environment and temperature to which the contact tip would be exposed. For example, the insulating tip on the wire pressing assembly can be or contain an electrically insulative ceramic. Exemplary ceramics include the oxides or nitrides of Al, B, Zr, Mg, Y, Ca, Si, Ce, In and Sn and combinations thereof. The electrically insulating material can be or contain aluminum nitride, aluminum oxide, magnesium nitride, magnesium oxide, quartz, silicon nitride, boron nitride, zirconium dioxide and mixtures and combinations thereof. 
     C. Examples 
     The following examples are included for illustrative purposes only and are not intended to limit the scope of the embodiments provided herein. 
     First Example Embodiment 
     The first example embodiment of the contact tip assembly is shown schematically in  FIGS. 1A and 1B . As illustrated in the figure, the contact tip assembly includes a guide  120  having a longitudinal center axis A-A′, a first end  140 , and an opposite second end  150 , and a linear center bore  130  extending and running along the longitudinal center axis of the guide  120  from its first end  140  to its second end  150 . Also present is an electrically insulating lining  160  inside of the center bore  130 , the electrically insulating lining  160  extending at least from the first end  140  to the second end  150  of the guide  120 . The electrically insulating lining  160  includes a guide channel  170  having an inlet opening  145  at the first end  140  and an outlet opening  155  at the second end  150  and running through the linear electrically insulating lining  160  along the longitudinal center axis A-A′. The electrically insulating lining  160  guides a metal wire  180  being passed through the linear cylindrical guide channel  170  from the inlet opening  145  towards and further out of the outlet opening  155  via the center bore  130 . The contact tip assembly also includes an electric contact unit  200  containing a contact tip  215  in electric contact with an electric energy source, where the electric contact unit  200  is located at a distance away from the outlet opening  155 . The contact tip assembly also includes a contact element pressing assembly  210  for pressing a contact tip  215  of the electric contact unit  200  onto the metal wire  180 . As illustrated in  FIG. 1B , the bottom of the guide  120  includes a bottom opening  125  that allows dust or pieces of wire to exit the guide  120  prior to coming near the forming piece. In the example embodiment, the guide  120  is made of Ti-6Al-4V alloy, the contact tip  215  is a W/Cu composite, and the contact tip pressing assembly includes a compression spring. 
     In use, the metal wire  180  is a wire made of Ti-6Al-4V alloy, which is continuously supplied by a wire feeder and enters inlet opening  145  and traverses the guide  120  via the guide channel  170 . The contact tip  215  is connected via an insulator connector  240 , which is ceramic, to a contact tip support  220 , and is pushed down against the metal wire  180  via the force of a compression spring in the contact tip pressing assembly  210 . The metal wire exits the guide  120  via outlet opening  155  and is positioned such that its distal end is located above preheated area at the deposition area on the base material. The metal wire is heated at a melting rate of the distal end such that droplets of molten electrode are continuously being supplied to the preheated area of the base material. In some embodiments, droplets of molten electrode are continuously being supplied to a molten pool on the base material. 
     In exemplary embodiments, a plasma transferred arc is formed by a PTA torch that is electrically connected to a DC power source such that the electrode of the PTA torch becomes the cathode and the metal wire becomes the anode. The plasma transferred arc is continuous and directed to heat and melt the distal end of the metal wire. The effect of the DC power source is modulated to maintain a heating and melting rate in accordance with the feeding velocity of the wire such that the formation of the droplets of molten metal wire, in this example Ti-6AL-4V alloy wire, are timed to maintain a continuous drip of molten wire onto the preheated surface of the base material, or into a molten pool on the base material. The effect supplied by the DC power source and the feeding velocity of the wire are constantly monitored and modulated by a control system such that the preheated area of the base material of the molten pool of the base material is supplied with molten wire at a rate providing the intended deposition rate of the Ti-6Al-4V alloy. 
     A control system (such as a computer-aided manufacturing system) can be simultaneously engaged to operate and regulate the engagement of one or more actuators (not shown) that constantly positions and moves the base material and one or more PAW or PTA torches such that the intended deposition spot as given by the CAD-model of the object that is to be formed. The control system can also be engaged to operate any actuator controlling a preheating PAW or PTA torch such that a preheated area of the base material, or a molten pool in the base material, is where the melted metallic material is to be deposited. 
     The control system used in exemplary embodiments of the invention described herein can provide partial or complete automation of the deposition apparatus. The control system can include a computer processor or central processing unit (CPU), CPU display, one or more power supplies, power supply connections, signal modules as inputs and/or outputs, integrated shielding of analog signals, storage devices, circuit boards, memory chips or other storage medium, a non-transitory computer-readable storage medium having a computer-readable program embodied therein, or any combination thereof. The computer-readable program can containing appropriate software for automating any one or combination of systems. Exemplary control modules include, but are not limited to, the SIMATIC-S7-1500 from Siemens AG (Munich, Germany), the IndraMotion MTX system available from Bosch Rexroth AG (Lohr am Main, Germany). And the SIGMATEK C-IPC compact industrial computer system available from SIGMATEK GmbH &amp; Co. KG (Lamprechtshausen, Austria). 
     Second Example Embodiment 
     The second example embodiment of the contact tip assembly is shown schematically in  FIGS. 4A and 4B . As illustrated in the figure, the contact tip assembly includes a guide  120  having a longitudinal center axis A-A′, a first end  140 , and an opposite second end  150 , and a linear center bore  130  extending and running along the longitudinal center axis of the guide  120  from its first end  140  to its second end  150 . Also present is an electrically insulating lining  160  inside of the center bore  130 , the electrically insulating lining  160  extending at least from the first end  140  to the second end  150  of the guide  120 . The electrically insulating lining  160  includes a guide channel  170  having an inlet opening  145  at the first end  140  and an outlet opening  155  at the second end  150  and running through the linear electrically insulating lining  160  along the longitudinal center axis A-A′. The electrically insulating lining  160  guides a metal wire  180  being passed through the linear cylindrical guide channel  170  from the inlet opening  145  towards and further out of the outlet opening  155  via the center bore  130 . The contact tip assembly also includes an electric contact unit  200  containing a contact tip  215  in electric contact with an electric energy source, where the electric contact unit  200  is located at a distance away from the outlet opening  155 . The contact tip assembly also includes a wire pressing assembly  190  for pressing the metal wire  180  into contact with the contact tip  115  of the electric contact unit  200 . In the example embodiment, the wire pressing assembly  190  has an insulating tip  195  that is ceramic. The wire pressing assembly  190  includes a spring that maintains the insulating tip  195  in contact with the metal wire  180 . 
     In use, the metal wire  180  is a wire made of Ti-6Al-4V alloy, which is continuously supplied by a wire feeder and enters inlet opening  145  and traverses the guide  120  via the guide channel  170 . The contact tip  215  is connected via an insulator connector  240 , which is ceramic, to a contact tip support  220 , which is in a fixed position. The metal wire  180  is pushed up against the contact tip  215  via the force of a compression spring in the wire pressing assembly  190 . The metal wire exits the guide  120  via outlet opening  155  and after passing above the wire pressing assembly  190  is positioned such that its distal end is located above the preheated are of the base material at the deposition area on the base material. The metal wire is heated at a melting rate of the distal end such that droplets of molten electrode are continuously being supplied to preheated area on the base material. 
     A plasma transferred arc is formed by a PTA torch that is electrically connected to a DC power source such that the electrode of the PTA torch becomes the cathode and the metal wire becomes the anode. The plasma transferred arc is continuous and directed to heat and melt the distal end of the metal wire. The effect of the DC power source is modulated to maintain a heating and melting rate in accordance with the feeding velocity of the wire such that the formation of the droplets of molten metal wire, in this example Ti-6AL-4V alloy wire, are timed to maintain a continuous drip of molten wire onto the preheated area on the base material. The effect supplied by the DC power source and the feeding velocity of the wire are constantly monitored and modulated by a control system such that the preheated area of the base material is supplied with molten wire at a rate providing the intended deposition rate of the Ti-6Al-4V alloy. The control system is simultaneously engaged to operate and regulate the engagement of an actuator (not shown) that constantly positions and moves the base material such that the preheated area of the base material to receive the molten metal is located at the intended deposition spot as given by the CAD-model of the object that is to be formed. 
     It will be apparent to those skilled in the art that various modifications and variation can be made in the present invention without departing from the 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. 
     REFERENCE SIGNS LIST 
     The following is a listing of the reference numerals used in the description and the accompanying Drawings.
     A-A′ Longitudinal center axis   B-B′ Vertical axis     100  Contact tip assembly     110  Distal extension     111  Cut out first wall     112  Cut out entry opening     113  Cut out exit opening     114  Cut out second wall     115  Cut out Section     120  Guide     122  Fastener projection 1     124  Fastener projection 2     125  Bottom opening     127  Protrusion     130  Center bore     140  First end     145  Inlet opening     150  Second end     155  Outlet opening     160  Electrically insulating lining     165  Coating     170  Guide channel     180  Metal wire     190  Wire pressing assembly     195  Insulating tip     200  Electric contact unit     210  Contact tip pressing assembly     215  Contact tip     220  Contact tip support     230  Electrical connection     240  Optional insulator connector     300  Support element     310  Thermally insulating material     400  Metal wire delivery source     500  Frame     600  PAW torch