Abstract:
Methods and apparatus for welding a component to fill a groove therein. The method entails simultaneously projecting an electric arc and at least first and second laser beams into the groove. The electric arc melts and deposits a filler material in the groove while the first and second laser beams are projected onto opposite first and second walls, respectively, of the groove. The axis of each of the first and second laser beams is oriented at an acute angle relative to the respective wall thereof.

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to welding processes, equipment and materials. More particularly, this invention relates to a welding method and apparatus adapted for filling a groove in an article. 
     It is often economically beneficial to repair components that have suffered cracks rather than replace them. One such repair technique has been referred to as narrow groove welding. Typically, this technique may require preparation of the component prior to welding. For example, the component may be machined to remove the crack and the region immediately surrounding the cracked, with the result that the component is separated into two or more pieces. Thereafter, a weld buildup technique, for example, a cladding technique, may be used to apply material to the machined surfaces of the component to achieve flat surfaces that can be more readily welded. 
     Narrow groove welding has become an important technique in the manufacture and repair of thick-walled components, due in part to advantageous features such as high welding speed and weld quality. Methods for performing narrow groove welding have included gas tungsten arc welding (GTAW) techniques (also known as tungsten inert gas (TIG) welding), laser welding, plasma transferred arc (PTA) welding processes and hybrid laser arc welding (HLAW), which can be performed at room and elevated temperatures. For narrow groove welding, these welding techniques use a filler material, typically a ductile filler or a filler whose chemistry closely matches that of the base metal being welded. 
     The most frequent defect in narrow groove welding is incomplete fusion of the filler material into the walls of the narrow groove. In order to limit the effects of this defect, it is important to maintain uniform and sufficient penetration at both groove walls. Several different approaches have been adopted in attempts to minimize the incomplete wall fusion in narrow groove welding processes. For example, an arc weaving technique has been used wherein a side to side movement along the seam is performed. As a particular example, if a gas metal arc welding technique is used, the electrode may be oscillated by adopting a wire bending technique in which the bending direction is periodically changed. Alternatively, a wire rotating technique can be used that involves rotating an eccentric contact tip. These techniques are effective for penetration at both groove walls. However, wire bending techniques generally require complex systems, the number of oscillations is limited, and the wear resistance of the contact tip is often low. In the case of wire rotating techniques, the minimum root opening is often limited by the need to rotate the whole welding head, and the rotation of the eccentric contact tip may cause the welding head to vibrate, especially in deep groove welding of articles with relatively thick cross-sections. 
     Additional issues can arise if the component being welded is composed of a highly alloyed metal. Such alloys often have inherently poor weldability and therefore require longer welding operation times in order to achieve fusion with the weld walls. Further, many of these alloys must be preheated prior to welding. For example, CrMoV-base steels, such as those used for components of steam turbine engines, often require a preheat temperature of about 350° F. (about 175° C.) or more. These elevated temperatures may create an environment that is unsuitable for manual welding, in which case narrow groove welding is preferably performed by an automated welding system. 
     In view of the above, it can be appreciated that there are certain problems, shortcomings or disadvantages associated with prior art narrow groove welding techniques, and it would be desirable if an improved welding technique were developed that was capable of filling a groove in an article to yield a weldment with improved wall fusion. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention provides a method and apparatus suitable for filling a groove in an article, and capable of yielding a weldment characterized by improved wall fusion. 
     According to a first aspect of the invention, a method is provided that involves welding a component to fill a groove by simultaneously projecting an electric arc and at least first and second laser beams into the groove. The electric arc melts and deposits a filler material in the groove while the first and second laser beams are projected onto opposite first and second walls, respectively, of the groove. The axis of each of the first and second laser beams is oriented at an angle of sixty degrees or less relative to the respective wall thereof. 
     According to a second aspect of the invention, a method is provided that involves welding a component to fill grooves therein, by simultaneously projecting a first electric arc and at least first and second laser beams into a first groove on a first side of the component and simultaneously projecting a second electric arc and at least third and fourth laser beams into a second groove on a second side of the component. The first and second electric arcs melt and deposit a filler material in the first and second grooves, respectively, while the first and second laser beams are projected onto opposite first and second walls, respectively, of the first groove and the third and fourth laser beams are projected onto opposite third and fourth walls, respectively, of the second groove. The axis of each of the first, second, third and fourth laser beams is oriented at an angle of sixty degrees or less relative to the respective wall) thereof. 
     According to a third aspect of the invention, an apparatus is provided that includes an arc welding apparatus adapted to generate an electric arc for melting and depositing a filler material onto a surface and at least one laser beam generator adapted to generate at least first and second laser beams and project the first and second laser beams onto opposite first and second walls, respectively, of the groove. The at least one laser beam generator is adapted to project the first and second laser beams so that each axis thereof is oriented at an angle of sixty degrees or less relative to the respective wall thereof. 
     A technical effect of the invention is the ability to fill a groove in an article to yield a weldment with improved wall fusion. 
     Other aspects and advantages of this invention will be better appreciated from the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1 ,  2  and  3  are plan views that schematically represent profiles of narrow groove joint geometries that can be welded with a welding technique and apparatus in accordance with certain embodiments of the present invention. 
         FIG. 4  represents a side view that schematically shows an operational arrangement for a hybrid laser arc welding technique of the prior art. 
         FIG. 5  schematically represents a side view of a component and schematically shows a hybrid welding operation being performed within a groove of the component in accordance with an embodiment of the present invention. 
         FIGS. 6 and 7  schematically represent end and plan views, respectively, of the welding operation of  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 ,  2  and  3  represent various nonlimiting configurations of components  10  in which a narrow groove  12  is present and is to be filled using a narrow groove welding technique, for example, to join portions  14  and  16  of the component  10  together to yield a unitary article. The portions  14  and  16  may be products of a step in the original manufacturing or repair of the components  10 . Furthermore, the portions  14  and  16  can be formed of the same or different materials. While the invention is not limited to the welding of any particular material, highly alloyed metal alloys are of particular interest, for example, nonlimiting examples of which include CrMoV-base steels of types used for components of steam turbine engines. 
     Each groove  12  is represented in  FIGS. 1 through 3  as defining flat opposing surfaces or walls  18 . The walls  18  may or may not be parallel to each other, allowing for a wide variety of joint geometries, including but not limited to those represented in  FIGS. 1 through 3 . Each groove  12  also defines a root face  20 , at which the portions  14  and  16  of the component  10  contact each other. The walls  18  of the grooves  12  and the surfaces of the portions  14  and  16  that define the root faces  20  can be produced to have the configurations of the types shown in  FIGS. 1 ,  2  and  3  through the use of conventional machining techniques. In any event, for the purpose of carrying out a narrow groove welding technique, each groove  12  is relatively narrow, for example, having a maximum width of less than 20 mm and preferably in a range of about 10 to about 18 mm, which minimizes the joint volume (the volume defined between the walls  18 ) that must be filled by welding to join the portions  14  and  16  of each component  10 . The maximum depth of the groove  12  is only limited by the capabilities of the welding device. In practice, the methods hereinafter described have successfully welded grooves  12  with a depth of up to about four inches. 
     In carrying out a narrow groove welding technique, the two portions  14  and  16  of each component  10  are preferably initially joined by welding the root face  20  using any suitable welding process. Suitable distances between the surfaces at the root face  12  prior to welding will depend on the penetration capabilities of the welding process used. Once this initial welding step, referred to as a root pass, has been successfully completed to join the two portions  14  and  16  of the component  10  together, filler passes are performed to fill the remaining narrow groove  12  of the component  10  with a suitable filler material. In one embodiment of the present invention, filler passes are preformed using a hybrid laser arc welding (HLAW) process, also known as laser-hybrid welding. HLAW is a process that combines laser beam and arc welding techniques, such that both welding processes simultaneously occur in the same weld pool. As schematically represented in  FIG. 4 , a HLAW process may entail projecting a laser beam  24  perpendicularly onto surfaces  22  of the portions  14  and  16  to be welded, while an electric arc  26  of an arc welding process (for example, gas metal arc welding (GMAW, also known as metal inert gas (MIG) welding) or gas tungsten arc welding (GTAW, also known as tungsten inert gas (TIG) welding) is typically positioned behind (aft) and angled forward toward the focal point of the laser beam  24  on the component  10 . A filler metal is deposited with the electric arc  26 , by which the groove (not shown in  FIG. 4 ) can be filled. Because HLAW techniques can be high energy density processes that result in lower overall heat input as compared to other welding processes, the use of a HLAW process has the capability of improving the quality of a resulting weldment by lowering thermal stresses in the component  10 . 
     The filler metal can be provided in the form of electrodes that are consumed in a GMAW process, or a wire that is fed into the arc  26 . In either case, the filler metal is melted and forms metallic drops that deposit onto the surfaces of the walls  18  within the groove  12 . Various compositions can be used as the filler metal, with preferred materials depending on the compositions of the portions  14  and  16  of the component  10  and the intended application. For example, a ductile filler may be preferred to reduce the tendency for cracking in the resulting weldment, or a filler may be chosen whose chemistry more closely matches the base metal (or metals) of the component portions  14  and  16  to more nearly maintain the desired properties of the component  10 . 
     A common issue when performing a narrow groove welding process is the incomplete fusion of the filler metal into the walls  18  of the groove  12 . This issue may be exacerbated if the component  10  being welded is formed of a highly alloyed metal, nonlimiting examples of which include CrMoV-base steel components of steam turbine engines However, the methods herein described may be used on any other materials, such as, but not limited to, carbon steel, stainless steel, superalloys, low-alloy steel, and others. 
     According to a preferred aspect of the present invention, an HLAW welding system of the type represented in  FIG. 4  can be modified to utilize multiple laser beams  30  and  32 , as schematically represented in  FIGS. 5 ,  6  and  7 , instead of the single laser beam  24  represented in  FIG. 4 . The component  10  represented in  FIGS. 5 ,  6  and  7  is preferably similar in geometry to the joint represented in  FIG. 3 . The electric arc  26  and the filler material applied by the arc  26  can be the same as that described in reference to  FIG. 4 . In the particular embodiment shown in  FIGS. 5 through 7 , two laser beams  30  and  32  are shown, though the use of additional laser beams is also within the scope of the invention. The laser beams  30  and  32  may be generated by separate laser beam generators or, as represented in  FIGS. 5 and 6 , generated by splitting a single laser beam  34  with the use of a suitable laser beam splitter  36 , for example, a prism. As evident from  FIG. 6 , each laser beams  30  and  32  is directed at an acute angle, a, relative to one of the walls  18  of the groove  12 , and defines projections  36  and  38  on the surfaces of the walls  18  adjacent a root face  20  previously formed at the base of the groove  12 . As also seen in  FIG. 6 , the electric arc  26  is projected at an acute angle relative to each of the laser beams  30  and  32 . The angle between the electric arc  26  and the optical axis of each laser beam  30  and  32  will typically be up to about sixty degrees, for example, about ten to about sixty degrees, and more preferably about twenty to about thirty degrees. Good results have been obtained with an angle of about twenty-six degrees between the electric arc  26  and the optical axis of each laser beam  30  and  32 . However, the angle used will depend on the geometry of the particular component  10  being welded. Any angle may be used that is suitable for allowing all of the heating elements work together to provide a common molten metal which is operable to solidify and join surfaces  14  and  16  with a common filler metal. Furthermore, the laser beams  30  and  32  need not necessarily be projected at the same angle as long as each laser beam  30  and  32  impinges its respective wall  18 . Likewise, projections  36  and  38  may be offset from one another along the welding direction by up to about ten millimeters. 
     The orientation and power of the laser beams  30  and  32  are intentionally adapted to enable the laser beams  30  and  32  to interact with the groove walls  18  in a manner that ensures fusion between the groove walls  18  and the filler metal deposited with the electric arc  26  during the welding process. The laser beams  30  and  32  are not required to deeply penetrate the groove walls  18 , and therefore may be at lower power levels than are typical used in prior art HLAW welding processes. As nonlimiting examples, the power levels of the laser beams  30  and  32  may be about 2 kW to about 4 kW, preferably about 2.5 kW to about 3.5 kW. Furthermore, the power levels of the laser beams  30  and  32  can be the very same, and in most cases are preferably within about 50 percent of each other. The projection angle (α) at which the optical axis of each laser beam  30  and  32  is oriented relative to the surface of the wall  18  onto which the beam  30  or  32  is projected will typically be greater than zero degrees but less than 60 degrees, for example, about 10 to about 50 degrees, and more preferably about 15 to about 45 degrees. Good results have been obtained with projection angles of about 20 degrees. While the beams  30  and  32  and essentially perpendicular to the surfaces  22  of the component portions  14  and  16  as viewed from the side (perpendicular to the direction that the welding operation progresses through the groove  12 ), it is foreseeable that the beams  30  and  32  could be inclined individually or together toward or opposite the direction that the welding operation progresses through the groove  12   
     The arc welding apparatus that generates the electric arc  26  for the process represented in  FIG. 6  is preferably a GMAW welder, although other types of arc welders may be used. Particular parameters relating to the operation and use of the arc welder and its electric arc  26 , such as fill materials, deposit rates of the fill material, arc welder power levels, etc., will generally be understood by those skilled in the art and therefore will not be discussed in any detail here. 
     In addition to improving fusion between the filler metal and the groove walls  18 , the laser beams  30  and  32  may further be directed in a manner that helps to stabilize the projection  28  of the electric arc  26 , represented in  FIGS. 6 and 7  as being projected onto the root face  20 . The molten pool generated by the electric arc  26  may not be stable in the molten pool, specifically at its projection  28  edges due to its free arc characteristics, which may cause a lack of fusion in narrow groove welding. For this reason, it may be desirable for each of the laser beams  30  and  32  to be spaced from the center of the arc projection  28  by a distance of less than about 10 mm along the welding direction. The laser beams  30  and  32  impinge on the molten pool generated by electric arc  26  which may cause the molten pool to become stable due to a relatively constant temperature gradient being established around the energy-concentrated laser beams  30  and  32 . Directing the laser beams  30  and  32  in this manner eliminates the need for a high power laser commonly used in HLAW devices thereby reducing the overall cost of the welding process. Stabilization of the electric arc projection  28  can be particularly advantageous during high speed welding runs, and may allow for welding speeds of 60 inches per minute (about 150 centimeters per minute) or more, as compared to about 20 inches per minute (about 50 centimeters per minute) or less typical for traditional arc welding process. 
     The above described joint filling processes may be automated with a seam tracking technique, and may be repeated as necessary until the narrow groove  12  of the component  10  is adequately filled. While the welding operation is represented in  FIGS. 5 through 7  as being performed on one side of a component  10 , it is also within the scope of the invention to simultaneously perform welding operations on opposite sides of a component, for example, to weld the grooves  12  of the components  10  represented in  FIGS. 1 and 2 . Such a welding technique can greatly decrease the welding time and further improve the resulting weldment by lowering distortion and residual stresses due to the creation of a symmetric weldment. For this purpose, the welding operations performed on opposite sides of the component can be directly opposite each other, though they may be offset from one another in the direction of the weld path by a distance of up to 50 mm. 
     While the invention has been described in terms of particular embodiments, it is apparent that other forms could be adopted by one skilled in the art. For example, the physical configuration of the HLAW welding system could differ from that described, and materials and processes other than those noted could be used. Therefore, the scope of the invention is to be limited only by the following claims.