Abstract:
A technique is taught for making a lap penetration weldment including a weld bead joining a first component to a second component, the first component overlying the second component, the weld bead penetrating through the first component and into the second component, the first component including a short overlapping portion between a centerline of the weld bead and an edge of the first component. Prior to forming the weld bead, the method includes applying to the short overlapping portion of the first component at least one normal force directed toward the second component, and applying to the short overlapping portion at least one tangential force directed toward the weld bead, the tangential force(s) preventing formation of cracks along a boundary of the weld bead, a fusion zone of the weld bead, or a heat affected zone of the weldment.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is closely related to copending U.S. Patent Application Gas Metal Buried Arc Welding of Lap-Penetration Joints, Ser. No. 10/438,675, filed on May 15, 2003, the teachings of which are fully incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to fusion welding of lap joints and, more particularly, it relates to fusion welded lap penetration joints having reduced discontinuities.  
       BACKGROUND OF THE INVENTION  
       [0003]     It is known to make fusion welded lap penetration joints in metal plates or sheets by means of several processes. These include gas metal buried arc welding (GMBA), laser beam, laser/gas metal arc, and plasma arc.  
         [0004]      FIG. 1  illustrates a prior art lap penetration joint  10  made by one of the fusion welding processes cited above. A first component  12  having thickness  13  overlies a second component  14  having thickness  15 . A fusion weld bead  16 , penetrating through the first component  12  and into second component  14  joins component  12  to component  14 . A short overlapping portion of component  12  is denoted  18 . The edge of the short overlapping portion  18  is denoted  20  and the centerline of the fusion weld bead  16  is denoted  17 . It has been found that a critical minimum applies to the edge distance  22  between the edge  20  of the short overlapping portion  18  and the centerline  17  of weld bead  16 . If the edge distance  22  is less than the critical minimum, discontinuities tend to form in or close to the weld bead  16 . This minimum is referred to in the art as the critical edge distance. The critical edge distance depends on the alloy compositions and on the thicknesses of the components being welded. For 1.5 mm 6061-T6 aluminum alloy being welded to 3 mm 6061-T6 aluminum alloy, the critical edge distance is about 32 mm (1.25″).  
         [0005]     It is often the case that a lap penetration joint is required at a location close to an edge of the sheet or plate being joined.  FIG. 2  shows a defective weldment  31  often resulting from prior art practices. In  FIG. 2 , a first component  32  having a short overlapping portion  34  overlies a second component  14 . The thickness of first component  32  is denoted  13  and the thickness of the second component  14  is denoted  15 . The distance  38  between the edge  36  of short overlapping portion  34  of first component  32  and the centerline  17  of the weld bead  16  is less than the critical edge distance.  
         [0006]      FIG. 2  shows a discontinuity  26  in the weld bead  16 , but close to its boundary, and another discontinuity  27  at the boundary of the weld bead  16 . Discontinuities such as  26  and  27  tend to form at the intersection  23  of the interface  29  between the overlapping portion  34  of first component  32  and the second component  14  and the boundary of the weld bead  16 . Although less common, discontinuities (not shown) may also form in the heat affected zone  25 , usually in the first component  32 .  
         [0007]     These weld discontinuities are caused by a combination of the following factors. One factor is due to the fact that heat tends to be localized in the short overlapping portion  34  because heat cannot be sufficiently conducted away from the weld site. This is in contrast to the short overlapping portion  18  shown in  FIG. 1 , which has an edge distance  22  equal to or exceeding the critical edge distance, and for which heat is sufficiently conducted away. The short-overlapping portion  34  rises to a higher temperature and remains at the higher temperature for a longer time than the short overlapping portion  18  shown in  FIG. 1 .  
         [0008]     Also, due to its lesser width, the short overlapping portion  34  is more flexible and compliant and is more subject to distortion than the cooler short overlapping portion  18 . Upon solidification of the weld bead  16 , the short overlapping portion  34  moves and distorts more than the short overlapping portion  18 , which has an edge distance exceeding the critical edge distance. As the short overlapping portion  34  distorts, generally by bending away from the underlying second component  14 , it introduces intense stresses between the overlapping parts,  34  and  14 , and the adjoining weld bead  16 . This stress, in combination with the stress-intensifying interfacial junction  23 , leads to the formation of these discontinuities, which develop by tearing softened, and/or partly solidified weld metal.  
         [0009]     In order to avoid these problems, it is conventional practice to avoid designs in which the component which is penetrated by a weld bead such as weld bead  16  would have an overlapping portion which is shorter than the critical edge distance for the alloys and thickness of the components being joined. The requirement that the overlapping portion have a certain minimum dimension generally adds weight to the final product produced by the welding process because the overlapping portion typically has no mechanical function except to prevent discontinuities during welding. Such unnecessary weight is particularly undesirable for automobiles, trucks, and aerospace applications and marine products. Also, the unnecessary metal adds to the cost of the product.  
         [0010]     There is, therefore, clearly a need for a method of making welded lap penetration joints wherein the overlapping portions have smaller dimensions than the critical edge distances used currently.  
       SUMMARY OF THE INVENTION  
       [0011]     In one aspect, the present invention is a weldment including a first component and a second component, the second component disposed in overlapping relationship with the first component. A fused weld bead joins the first component to the second component, the fused weld bead penetrating through the first component and into the second component. The first component has a short overlapping portion whereby an edge to centerline distance from an edge of the first component to the centerline of the weld bead is less than a critical edge to centerline distance, the critical edge to centerline distance being a distance below which cracking tends to occur near and/or along a boundary of the weld bead, a fusion zone of the bead, or a heat affected zone of the weldment. The weldment is essentially free of discontinuities.  
         [0012]     In another aspect, the present invention is a method of making a lap penetration joint, the lap penetration joint including a weld bead attaching a first component to a second component, the weld bead penetrating through the first component and into the second component, the first component having a short overlapping portion between a centerline of the weld bead and an edge of the first component. The method includes applying to the short overlapping portion of the first component at least one normal force directed toward the second component. The method also includes applying to the short overlapping portion of the first component at least one tangential force, the tangential force(s) being tangential (i.e parallel) to faying surfaces of the first component and the second components, the tangential force(s) being directed toward the weld bead, the tangential force(s) conteracting and preventing formation of cracks along a boundary of the weld bead, a fusion zone of the weld bead, or a heat affected zone of the weldment when the weld bead is made.  
         [0013]     In an additional aspect, the present invention is a weldment including a first component and a second component, the second component disposed in overlapping relationship with the first component. A fused weld bead joins the first component to the second component, the fused weld bead penetrating through the first component and into the second component. The first component includes a short overlapping portion whereby an edge to centerline distance from a first edge of the first component to a centerline of the weld bead is less than a critical edge to centerline distance for the first component, the critical edge to centerline distance for the first component being a distance below which cracking tends to occur close to and/or along a boundary of the weld bead, a fusion zone of the bead, or a heat affected zone of the weldment; the second component also including a short overlapping portion whereby an edge to centerline distance from a second edge of the second component to a centerline of the weld bead is less than a critical edge to centerline distance for the second component. The critical edge to centerline distance for the second component is a distance below which cracking tends to occur close to and/or along the boundary of the weld bead, the fusion zone of the bead, or the heat affected zone of the weldment. The weldment is essentially free of discontinuities.  
         [0014]     In yet another aspect, the present invention is a method of making a lap penetration joint, the lap penetration joint comprising a weld bead attaching a first component to a second component, the weld bead penetrating through the first component and into the second component. The first component includes a short overlapping portion between a centerline of the weld bead and a first edge of the first component, the second component also including a short overlapping portion between the centerline of the weld bead and a second edge of the second component. The method includes applying to the short overlapping portion of the first component at least one first normal force, the at least one first normal force being directed toward the second component, and applying to the short overlapping portion of the first component at least one first tangential force, the at least one first tangential force being tangential to faying surfaces of the first component and the second component, the at least one first tangential force being directed toward the weld bead. The method also includes applying to the short overlapping portion of the second component at least one second normal force, the at least one second normal force being directed toward the first component, and it includes applying to the short overlapping portion of the second component at least one second tangential force, the at least one second tangential force being tangential to faying surfaces of the first component and the second component, the at least one second tangential force being directed toward the weld bead. The method further includes forming the weld bead; the tangential forces counteracting and preventing formation of cracks close to and/or along a boundary of the weld bead, a fusion zone of the weld bead, or a heat affected zone of the weldment.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIG. 1  is a schematic of a prior art fusion welded lap penetration joint having an overlapping portion with an edge distance equal to or exceeding the critical edge distance;  
         [0016]      FIG. 2  is a schematic of a prior art attempt to make a fusion penetration lap weld with an overlapping portion having an edge distance less than the critical edge distance;  
         [0017]      FIG. 3  is an illustration of a setup for making a fusion welded lap joint, the setup applying normal and tangential constraints to a short overlapping portion of the joint to prevent weld discontinuities;  
         [0018]      FIG. 4  is an illustration of a setup for making a fusion welded lap joint, the setup applying one tangential constraint and two normal constraints to a short overlapping portion of the joint to prevent weld discontinuities;  
         [0019]      FIG. 5  is an illustration of a setup for making a fusion welded lap joint, the setup employing a single clamp member to provide both normal and tangential constraints;  
         [0020]      FIG. 6  is an illustration of a setup for making a fusion welded lap joint, the setup applying a tangential constraint and also applying normal constraints on both sides of the weld bead;  
         [0021]      FIG. 7  is an illustration of a fusion welded lap penetration joint according to the present invention, the joint having an overlapping portion with an edge distance less than the critical edge distance;  
         [0022]      FIG. 8  is a schematic illustration showing the path that stress follows from the first component through weld bead  16  to the second component when tension is applied to the weldment;  
         [0023]      FIG. 9  illustrates a setup for making a fusion welded lap joint wherein both the first component and the second component have short overlapping portions, the short overlapping portions lying on opposite sides of the weld bead; and  
         [0024]      FIG. 10  illustrates a setup for making a fusion welded lap joint wherein both the first component and the second component have short overlapping portions, the short overlapping portions lying on the same side of the weld bead. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0025]     Referring now to  FIG. 3 , a setup  40  is shown, in accordance with the present invention. A first component  32  having a short overlapping portion  34  is placed over a second component  14 . The intended site for a weld bead is indicated in phantom as  41 . The edge to weld centerline distance  38  of the short overlapping portion  34  is less than the critical minimum distance for the first component  32  and the second component  14 .  
         [0026]     In accordance with the present invention, a clamp member  42  is positioned to exert a tangential force through pad  44  on the short overlapping portion  34 . A normal force is also applied by the clamp member  46  to location  47  on the short overlapping portion  34 . The clamp member  42  and the clamp member  46  may be portions of screw type clamps, hydraulic clamps, pneumatic clamps, electrically actuated clamps, or any other suitable type of clamps.  
         [0027]     When the invention is practiced, according to this embodiment, the clamp member  42 , the pad  44  and the clamp member  46  are placed in the positions indicated, and the tangential and normal forces are applied. A fusion penetration lap weld is then made at site  41 . After the weld bead has solidified and cooled, the clamps  42  and  46  as well as the pad  44  are removed.  
         [0028]      FIG. 4  illustrates an alternative setup  50 , in accordance with another aspect of the invention. As before, a tangential force is applied by clamp member  42  through pad  44  to the short overlapping portion  34 . Also, the clamp member  46  applies a normal force to the proportionalizing member  52  having first leg  54  and second leg  56 . The first leg  54  applies a first normal force to short overlapping portion  34  at proximal site  55  and second leg  56  applies a second normal force to the distal site  57  on short overlapping portion  34  through pad  44 . Because of the proportionalizing member  52 , the normal force exerted by first leg  54  is proportional to the normal force exerted by the second leg  56 .  
         [0029]     When the invention is practiced, according to this embodiment, the clamp member  42  and the pad  44  are placed in position and the tangential force is applied to short overlapping portion  34 . Also, the proportionalizing member  52  is placed in position and clamp member  46  is placed in position and caused to apply a normal force to proportionalizing member  52 , thus applying proportional normal forces at proximal site  55  and at distal site  57  on the short overlapping portion  34 . A fusion lap penetration weld is then made at site  41 . After the weld bead has solidified and cooled, the clamps  42  and  46  as well as the proportionalizing member  52  and the pad  44  are removed.  
         [0030]      FIG. 5  illustrates another alternative setup  60 , in accordance with another aspect of the invention. In this setup, a clamp member  64  engages a notched pad  62  to exert a tangential force at pressure application site  65  on the end of short overlapping portion  34 . Also, clamp member  64  exerts a normal force at pressure application site  57  on short overlapping portion  34 .  
         [0031]     When the invention is practiced, according to this embodiment, the clamp member  64  and the pad  62  are placed in position, and the tangential and normal forces are applied. A fusion lap penetration weld is then made at site  41 . After the weld bead has solidified and cooled, the clamp  64  and the pad  62  are removed.  
         [0032]      FIG. 6  illustrates a setup  70  in which a tangential force is applied to short overlapping portion  34  by clamp member  42  acting through pad  44 . Also, in this configuration a normal force is applied by clamp member  46  at site  47  on the short overlapping portion  34  and, furthermore, at site  74 , on the opposite side of the intended site  41  of the weld bead  16 , clamp member  72  applies a normal force to the long overlapping portion  35  of first component  32 .  
         [0033]      FIG. 7  illustrates a weldment  30  produced in accordance with the present invention. A first component  32  having a short overlapping portion  34  and a thickness  13  overlies a second component  14  having a thickness  15 . First component  32  is joined to second component  14  by weld bead  16  which penetrates through first component  32  and into second component  14 . The edge distance  38  between the edge  36  of short overlapping portion  34  and the centerline  17  of weld bead  16  is less than the critical edge distance. The weldment  30  is substantially free of discontinuities.  
         [0034]      FIG. 8  shows why it is desirable for the short overlapping portion  34  to be as short as possible.  FIG. 8  shows a tensile force  80  applied to first component  32  and an equal and opposite force  82  applied to the second component  14 . These forces result in tension and tension/shear stresses in the weldment which generally follow path  84  from first component  32  through weld bead  16  and through second component  14 . The short overlapping portion  34  is generally not involved in these stresses. To minimize the weight of the weldment  30 , the short overlapping portion  34  should be as short as possible.  
         [0035]     A weldment such as weldment  30  is preferred for applications wherein flange width and/or weight is critical. These applications include components of automobiles, trucks, trailers, railway vehicles, aerospace or marine products.  
         [0036]      FIG. 9  illustrates a setup  90  for making a fusion welded lap joint wherein both the first component  92  and the second component  94  have short overlapping portions, which lie on opposite sides of the weld bead. First component  92  has thickness  93  and short overlapping portion  98 . Short overlapping portion  98  has an edge to centerline distance  102  from edge  112  of first component  92  to centerline  17 . Edge to centerline distance  102  is smaller than the critical edge to centerline distance for first component  92 .  
         [0037]     Second component  94  has thickness  95  and short overlapping portion  99 . Short overlapping portion  99  has an edge to centerline distance  104  from edge  114  of second component  94  to centerline  17 . Edge to centerline distance  104  is smaller than the critical edge to centerline distance for second component  94 .  
         [0038]     Preferably, remote portion  132  of first component  92  is immobilized, and remote portion  134  of second component  94  is immobilized, by means not shown. Clamp member  46  applies a first normal force to short overlapping portion  98  of first component  92  and, in accordance with the present invention, clamp member  42  applies a first tangential force to short overlapping portion  98  of first component  92 . Likewise, clamp member  126  applies a second normal force to short overlapping portion  99  of second component  94  and, in accordance with the present invention, clamp member  122  applies a second tangential force to short overlapping portion  99  of second component  94   
         [0039]      FIG. 10  illustrates a setup  10  for making a fusion welded lap joint wherein both the first component  92  and the second component  94  have short overlapping portions, which lie on the same side of the weld bead. First component  92  has thickness  93  and short overlapping portion  98 . Short overlapping portion  98  has an edge to centerline distance  102  from edge  112  of first component  92  to centerline  17 . Edge to centerline distance  102  is smaller than the critical edge to centerline distance for first component  92 .  
         [0040]     Second component  94  has thickness  95  and short overlapping portion  99 . Short overlapping portion  99  has an edge to centerline distance  104  from edge  114  of second component  94  to centerline  17 . Edge to centerline distance  102  is smaller than the critical edge to centerline distance for second component  94 .  
         [0041]     Preferably, remote portion  132  of first component  92  is immobilized, and remote portion  134  of second component  94  is immobilized, by means not shown. Clamp member  46  applies a first normal force to short overlapping portion  98  of first component  92  and, in accordance with the present invention, clamp member  42  applies a first tangential force to short overlapping portion  98  of first component  92 . Likewise, clamp member  126  applies a second normal force to short overlapping portion  99  of second component  94  and, in accordance with the present invention, clamp member  122  applies a second tangential force to short overlapping portion  99  of second component  94 .  
         [0042]     After the setup shown in  FIG. 9  or  FIG. 10  is made, a weld bead  16  (not shown in these figures) is formed at the intended site  41  of weld bead  16 .  
         [0043]     As a specific example of this invention, a sheet of 6061-T6 aluminum 2 mm thick was welded to a sheet of 6061-T6 which was three millimeters thick. The 2 mm thick sheet was placed on top and it was this sheet which was penetrated by the gas metal buried arc welding process to yield a weld bead forming a lap penetration joint. The short overlapping portion of the 2 mm thick sheet had an edge distance less than the critical edge distance for this material.  
         [0044]     The technique employed was gas metal buried arc welding. The filler wire was ER5356 and the filler wire diameter was 1.2 mm. The welding current was 307 Amperes and the welding voltage was 19.3 volts. The wire feed rate was 254 mm/sec and the welding speed of travel was 30 mm/sec.  
         [0045]     This technique is recommended for welding components comprised of heat treatable and non-heat treatable alloys (e.g. 5xxx, 2xxx, 6xxx and cast A5xx aluminum alloys) in the form of extrusions, sheet, castings and/or forgings. For example, the first component may be a sheet, plate or casting, and the second component may be an extruded part, a sheet, plate or cast part. The first component may be a 5xxx aluminum sheet, and the second component may be a 6xxx extruded part.  
         [0046]     The weld bead  16  may be made by gas metal arc welding, gas metal buried arc welding, laser beam welding, or hybrid laser/gas metal arc welding. It can also be made by plasma arc welding, or by laser/plasma hybrid welding.  
         [0047]     By employing the techniques of this invention, it is often possible for the edge distance  38  to be as small as one third of the critical edge distance for the components being joined.  
         [0048]     Although the presently preferred embodiments of the invention have been discussed in some detail above, it is to be understood that the invention may be otherwise embodied within the scope of the appended claims.