Patent Publication Number: US-2013240490-A1

Title: Welding method

Description:
TECHNICAL FIELD 
     The present disclosure relates to a welding method and more particularly to a tack welding method complementary to a hybrid laser arc welding process. 
     BACKGROUND 
     Hybrid laser arc welding and laser beam welding for joining work pieces is known. Hybrid laser arc welding combines laser beam welding and arc welding, typically gas metal arc welding. U.S. Pat. No. 7,312,417 relates to a laser beam welding process which ensures maintaining a maximal gap width between the sheets and makes possible a maximal utilization of the achievable welding speed. The sheets, prior to welding, are first spot welded, wherein they are clamped only during this spot welding in order to ensure the maintenance of a maximum gap width. However, for narrow groove weld geometries (i.e. the width of the gap is approximately ½ the depth or less), tack welds may not penetrate fully to the root of the weld joint, causing the work pieces to buckle when a final seam weld is applied. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect of the present disclosure, a method of forming a tack weld is provided. The method provides a recess on an edge of a first piece. The edge of the first piece is configured to cooperate with a second piece. The method positions the first piece relative to the second piece so as to provide a gap between the first piece and the second piece. Subsequently, the method provides a tack weld within the recess of the first piece. The recess is configured to accommodate placing the tack weld at a root of the gap. 
     Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of an exemplary set up of a first work piece and a second work piece, according to an embodiment of the present disclosure; 
         FIG. 2  is a top view of the exemplary set up shown in  FIG. 1 ; 
         FIG. 3  is a side view of the exemplary setup of the first and second work piece shown in  FIG. 1  joined by a tack weld; 
         FIG. 4  is a side view of the exemplary setup of  FIG. 3  including a backing material; and 
         FIG. 5  shows a schematic process of forming the tack weld. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is an exemplary setup  100  including a first piece  102  and a second piece  104 , according to one embodiment of the disclosure. As shown in  FIGS. 1 and 2 , the first piece  102  may be configured as a plate and second piece  104  may be configured to include a rail section  106 . The rail section  106  may include a support section  108  configured to cooperate with the first piece  102  and a sloping edge section  110 . The first piece  102  may be configured to include a generally vertical edge  112  proximate to and facing sloping edge section  110 . The configuration of the sloping edge section  110  and the vertical edge  112  forming what is commonly called a J-groove weld joint  114 . It should be understood that the setup  100  may represent a rail assembly for an engine end frame of a medium wheel loader, a channel assembly for a motor grader, track roller frame, and the like. 
     A weld joint  114  may be defined as the gap between the first piece  102  and the second piece  104 . The configuration of the first piece  102  relative to the second piece  104  may define a width W and a depth D for the weld joint  114 , as shown in  FIG. 1 . Narrow groove weld joints may be defined as having a width W that is approximately ½ the depth D or less. In one embodiment, the weld joint  114  may be a narrow J-groove joint, as shown in the accompanied figures. The dimensions of the weld joint  114  may vary. However, in one exemplary embodiment, the weld joint  114  may have a depth of 8 mm and a top opening width of 3 mm to 4 mm. 
     It should be understood that the weld joint  114  described herein may have a relatively smaller weld joint size as compared to that typically used for gas metal arc welding. The weld joint  114  may be relatively narrow such that it may be utilized for hybrid laser arc welding or laser beam welding of the first and second pieces  102 ,  104 . Moreover, the weld joint  114  described herein is merely on an exemplary basis. Although the present disclosure is being described herein primarily with respect to J-groove weld joints, it should be apparent that the present disclosure may be applied to other weld geometries, such as single bevel joint with backing material, and the like, which also lie within the scope of the disclosure. 
     As shown in  FIG. 2 , a recess  202  may be provided on the vertical edge  112  of the first piece  102 . In one embodiment, the recess  202  may be configured to have an arcuate shape. In another embodiment, a plurality of recesses  202  may be provided on the first piece  102 . Parameters related to the recess  202  such as size and distance between two consecutive recesses  202  may vary. For example, a recess  202  provided on a plate having a thickness (weld depth) of 8 mm may be configured with a concave semi-circular shape having a radius of 5 mm. The size of the recess  202  may be based on factors like thickness or other dimensions of the first piece  102 . 
     The recess  202  may be configured to accommodate reception of a tack weld  302 . In one embodiment, as shown in  FIGS. 3 and 4 , the recess  202  is provided on the first piece  102  such that the recess  202  may increase space for accommodation of the tack weld  302  at a root  116  of the weld joint  114 . 
     As shown in the  FIGS. 3 and 4 , the tack weld  302  may be provided in the recess  202  of the first piece  102  and in contact with the second piece  104 . The tack weld  302  may be positioned at the root  116  of the weld joint  114 . A person of ordinary skill in the art will appreciate that the tack weld  302  may be provided by any known method such as, for example, gas metal arc welding. 
     In another embodiment of the present disclosure, as shown in  FIG. 4 , a backing material  402  may be placed within the weld joint  114  when making the tack weld  302 . The backing material  402  may include a piece of ceramic, copper, or other suitable material. The backing material  402  may include at least one sharp edge  404 . The shape, size and dimensions of the backing material  402  may vary. The backing material  402  may be configured to form a straight edge on the tack weld  302 . 
     In one embodiment, a hybrid laser arc welding method may be used to join the first piece  102  and the second piece  104 . After providing the tack weld  302  in the recess  202  of the first piece  102 , and the second piece  104  a laser beam may be directed at the root  116 , melting a portion of the first and second pieces  102 ,  104  forming a molten pool. A welding electrode may be placed in the weld joint  114  formed by the first and second pieces  102 ,  104  to deposit welding material within the weld joint  114  by an arc welding method. The welding material combines with the molten pool, thereby forming a seam between the first and second pieces. The welding electrode may be a solid, metal core or flux core welding electrode. The laser beam may be a sharp focus or de-focused laser beam. Depending on the size of the weld joint  114 , a center of the laser beam may be aligned to a center of the weld joint  114  or with some offset. It should be noted that, for the exemplary embodiment, the laser beam to electrode distance may vary between 0 to 8 mm. 
     The hybrid laser arc welding may involve using a gas metal arc welding torch and the laser beam. In an exemplary setup, the laser beam may lead and the gas metal arc welding torch may trail in the hybrid laser arc welding process. Moreover, in one embodiment, the gas metal arc welding torch may be positioned substantially perpendicular with respect to a welding direction, while the laser beam may be oriented obliquely with respect to the welding direction. Conversely, in another embodiment, the gas metal arc welding torch may be oriented obliquely with respect to the welding direction, while the laser beam may be substantially perpendicular to the welding direction. 
     The process of forming the tack welding geometry will be described in detail in connection with  FIG. 5 . 
     INDUSTRIAL APPLICABILITY 
     Gas metal arc welding is a known welding technique used to join large structural work pieces. Gas metal arc welding has a low energy density, resulting in a high tolerance for joint variability. 
     If using a gas metal arc welding process, a relatively larger root opening would be required at a joint formed between the first and second pieces  102 ,  104 , in order for the gas metal arc weld to reach a root end of the joint. Hence, in such situations, the larger joint size would have facilitated in providing the tack weld  302  at the root end of the joint formed between the first and second mating surfaces  102 ,  104 . 
     Another welding technique used is laser beam welding, which makes use of concentrated energy from the laser beam to produce joints with large penetration and very low distortion. However, laser beam welding has relatively lesser tolerance for joint variability. 
     Hybrid laser arc welding is a welding process that merges the high penetration and welding speed of laser beam welding with a gap-bridging ability of the gas metal arc welding. Hybrid laser arc welding involves combining gas metal arc welding and laser beam welding to form a welding process which is performed simultaneously in one process zone. It may be understood that depending on the kind of arc, laser beam process used, and other process parameters, the gas metal arc welding process and the laser beam welding process may influence each other in different ways. 
     Hybrid laser arc welding may hence have an improved weld penetration depth and welding speed compared to any of the gas metal arc welding or laser beam welding processes alone. In hybrid laser arc welding, the size of the weld joint  114  may be reduced compared to a joint configured for a gas metal arc welding process and thus allowing the weld size to become smaller. Hybrid laser arc welding may also result in less distortion due to reduced heat input, less filler material required due to a relatively smaller weld size, as well as minimized joint preparation due to elimination of beveling requirements. Also, time required for joint completion may be reduced. 
     However, in hybrid laser arc welding, the reduced size of the weld joint  114  leads to the tack weld  302  to reside at a top portion of the weld joint  114 , leading to development of a root gap between the first and second pieces  102 ,  104 . The presence of the tack weld  302  at the top portion of the weld joint  114  may also cause a reduction in the penetration of the hybrid laser arc weld and/or laser beam weld, by obstructing a path of the laser beam to reach the root  116  of the weld joint  114 . Further, the tack weld  302  residing at the top portion of the weld joint may also lead to instability of the hybrid laser arc welding process which could result in spatters, welding fumes, porosity, and the like. 
     One solution may include providing the tack weld  302  from behind the first and second mating surfaces  102 ,  104 . However, in some instances providing the tack weld  302  from the reverse side of the weld joint  114  may not be feasible due to accessibility issues based on factors like enclosed structural design, limited groove size, and the like. 
     The present disclosure relates to a tack welding method complementary to a relatively narrow grooved joint size. Referring to  FIG. 5 , initially, at step  502 , the recess  202  is provided on the vertical edge  112  of the first piece  102 . In one embodiment, a plurality of recesses  108  may be provided on the first piece  102 . The recess  202  may be configured to accommodate reception of the tack weld  302 . In another embodiment, the recess  202  may be shaped like an arc, semi-circle, or similar configuration. Parameters related to the recess such as size, shape, dimensions, and the like may vary, without limiting the scope of the disclosure. 
     Subsequently, at step  504 , the first piece  102  may be positioned relative to the second mating surface  104  to define the weld joint  114  between the first and second pieces  102 ,  104 . In one embodiment, the weld joint  114  may be configured as a J-groove joint, a single bevel joint, a flare joint, and the like. It should be understood that the disclosure may be utilized in any application making use of a narrow groove weld joint  114  as disclosed herein. The disclosure may also be utilized in regular grooved joints without any limitation. 
     At step  506 , the tack weld  302  is provided within the recess  202  between the first piece  102  and the second piece  104 . The recess  202  on the vertical edge  112  of the first piece  102  is provided such that the tack weld  302  may be accommodated at the root  116  of the weld joint  114 . It should be understood that the recess  202  provided on the vertical edge  112  of the first piece  102  may increase the space between the first and second pieces  102 ,  104  to accommodate the reception of the tack weld  302  at the root  116  of the weld joint  114 . The tack weld  302  when provided at the root  116  of the weld joint  114  may hold the first and second pieces  102 ,  104  in a tight and strong manner. 
     In one embodiment, as shown in  FIG. 4 , the backing material  402  may be placed in the weld joint  114  when the tack weld  302  is being made. The backing material  402  may be made of ceramic. 
     When the backing material  402  is being used, the recess  202  of the first piece  102  may be initially half-filled or filled such that at least a portion of the recess  202  is provided with the tack weld  302 . The tack welding is provided by suitably placing a welding wire and melting the root  116  of the weld joint  114 . Subsequently, the backing material  402  may be placed in the weld joint  114  such that the sharp edge  404  of the backing material  402  is in contact with the tack weld  302 , causing the straight edge to be formed on the tack weld  302 . Then, a remaining portion of the recess  202  may be fully filled by the tack weld  302 . It may be understood that the tack welding may be provided by any known method. 
     The backing material  402  may be configured to form a straight edge on the tack weld  302 . The straight edge formed on the tack weld  302  may facilitate in subsequent welding of the first and second pieces  102 ,  104  using the laser beam. The formation of the straight edge may result in less metal in the weld joint  114 , facilitating the laser beam to melt the root  116  of the weld joint  114  without a lack of fusion or porosity defect. 
     Thereafter, the first and second pieces  102 ,  104  may be joined together by a known welding method. In one embodiment, hybrid laser arc welding may be used. A person of ordinary skill in the art will appreciate that the first and second pieces  102 ,  104  and the weld joint  114  described above are merely on an exemplary basis. Other applications not described herein also lie within the scope of this disclosure. 
     While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed machines, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.