Abstract:
Buried arc welding is employed to fuse together a first component, a second component, and a third component or an underlying portion of the second component, the first and second components in butting relationship along a butting joint and the third component or underlying portion of the second component lying beneath the butting joint.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is closely related to U.S. Pat. No. 6,828,526, titled Gas Metal Buried Arc Welding of Lap-Penetration Joints, filed on May 15, 2003, the teachings of which are fully incorporated by reference herein. 
   FIELD OF THE INVENTION 
   The present invention relates to arc welding and, more particularly, it relates to arc welding of integrally backed square butt joints. 
   BACKGROUND OF THE INVENTION 
   It is known to make integrally backed square butt joints by gas metal arc welding. Two or three metal components are joined by this process. When three components are joined, two of them are placed in an abutting relationship along an abutting joint, with the third component lying behind the abutting joint. All three are then fused into a single weldment. When two components are joined, the first component of the two is placed in an abutting relationship with a first portion of the second component along an abutting joint, with a second portion of the second component lying behind the abutting joint. 
   A specific application is to make a bulkhead or deck by butt welding sheets or plates to each other, with stiffening elements, i.e. studs or joists, backing up the butt welded elements, behind the butt welded joints. 
     FIG. 1  shows a prior art arrangement  10  for making such a weldment. A first component  12  and a second component  14  are placed over a third component  16  with a joint gap  18  between the first component  12  and the second component  14 . The components are then secured in that position. A consumable metal electrode  19  is placed over joint gap  18 , electrode  19  being of a composition metallurgically compatible with component  12 , component  14  and component  16 . Typically, electrode  19  has a composition similar to the compositions of component  12 , component  14  and component  16 . 
   An electric potential is applied between electrode  19  and the components  12 ,  14  and  16 . An arc is then initiated between electrode  19  and the components  12 ,  14  and  16 . Molten metal from electrode  19 , is superheated in the arc and is accelerated towards the joint gap  18 , fusing with portions of components  12 ,  14  and  16 . Depending upon the thickness of the joint, multiple passes may be required to build up a plurality of weld beads filling joint gap  18  and thus joining components  12 ,  14  and  16 . A significant expense of this type of welding is that a sufficient quantity of the consumable electrode  19  must be supplied to fill joint gap  18 . In addition, the extra number of weld passes and the associated increase in the amount of weld metal and welding heat input per linear length can lead to extra weld induced distortion of the weldment. 
     FIG. 2  illustrates a prior art arrangement  20  for making an integrally backed square butt joint comprising a first component  12  and a second component  22 , the second component  22  having an abutting portion  24  and an underlying portion  26 ; which underlies first component  12 . As before, a joint gap  18  is provided to facilitate welding of component  12  to component  22 . 
     FIG. 3  illustrates a prior art arrangement  30  for making an integrally backed square butt joint comprising first component  32 , second component  34  and third component  16 , third component  16  underlying first component  32  and second component  34 . Arrangement  30  provides a V-shaped joint gap  38  which facilitates the welding process. 
     FIG. 4  illustrates another prior art arrangement  40  which is for making an integrally backed square butt joint comprising first component  32  and second component  42 . Second component  42  includes an abutting portion  44  and an underlying portion  46 . As before, arrangement  40  provides a V-shaped joint gap  38  which facilitates the welding process. A significant expense of these prior arrangements having a V-shaped joint gap is due to the requirement for joint preparation, by machining or cutting. 
   Also, for all of these prior art arrangements, a sufficient quantity of the consumable electrode  19  and welding power must be supplied to fill the joint gap,  18  or  38 . Also, welding-induced distortion may occur due to the large amount of metal that must be filled into the joint gap,  18  or  38 . Furthermore, a rather wide weld bead results from either of these arrangements. 
   INTRODUCTION TO THE INVENTION 
   The cross referenced patent, Gas Metal Buried Arc Welding of Lap-Penetration Joints, U.S. Pat. No. 6,828,526, teaches that gas metal buried arc welding can advantageously be employed for lap penetration joints. Advantages include the ability to melt through and remove oxides from faying surfaces and the ability to penetrate deeply into a stack of two or more components to be joined. With gas metal buried arc welding, surface oxides are removed and are floated to the surface of the weld as slag. It is believed that higher current densities in combination with more intense electromagnetic forces and higher temperatures in the buried arc, in comparison with conventional arc welding, facilitate inciting through and removal of the surface oxides. 
   In the present invention, the ability of a buried arc to penetrate deeply into one or more workpieces and cut through oxide layers, is employed to make an integrally backed square butt weld without a joint gap such as joint gap  18  or joint gap  38  discussed above. 
   Advantages to the buried arc include a reduction in the amount of consumable metal electrode which is required, consequent reduction in the heat input per linear length and weld induced distortion, increase in productivity due to the smaller number of weld passes needed to weld the thicker sections and also, it has been found that narrower welds can be obtained 
   Accordingly, it is an objective of the present invention to provide a method of making integrally backed square butt joints using a smaller quantity of consumable metal electrode than the prior art. 
   It is another objective of the present invention to provide a method of making integrally backed square butt joints that are comprised of either two or three pieces, whereby the former joint is made of a ledge in the “bottom” part onto which the top part is placed so its edge forms a square butt joint with the square edge of the “bottom” part. In this type of joint, the ledge in the “bottom” part functions as the third part of the integrally backed square butt joint that is made up of three pieces. 
   It is another objective of the present invention to provide a method of making integrally backed square butt joints which is effective in removing oxides from the faying surfaces. 
   A further objective of the present invention is to provide a method of welding integrally backed square butt joints wherein the welding arc penetrates deeply into the components to be joined. 
   Another objective of the present invention is to provide a weldment comprising integrally backed members wherein the weld is narrower than prior art welds. 
   An additional objective of the present invention is to facilitate the operation of machining a bead on a weldment comprising integrally backed square butt welded components, so the bead is flush with the components. 
   Yet another objective of the present invention is to make integrally backed square butt welded structures without requiring high power density based welding processes such as lasers or electron beams. 
   Still another objective of the present invention is to reduce welding-induced distortion of integrally backed square butt welds. 
   SUMMARY OF THE INVENTION 
   In one aspect, the invention is a method of making a weldment comprising a first component, a second component and a third component, the first component in an abutting relationship with the second component along an abutting joint, the third component in underlying relationship with the first component and the second component beneath the abutting joint. The method includes positioning the first component, the second component and the third component so that the first component is in the abutting relationship with the second component and, also, the third component is in the underlying relationship with the first component and the second component. The method further includes positioning a consumable metal electrode near the first component and the second component, applying an electric potential to the electrode and starting an arc, causing the arc to at least partially bury itself in the abutting joint, the arc forming a cavity for itself, whereby a pool of molten metal beneath the cavity penetrates into the third component. The method further includes maintaining the electric potential and current of the electrode at values appropriate for buried arc welding, and feeding the consumable metal electrode to maintain the tip of the electrode at a distance appropriate for buried arc welding. The method further includes moving the electrode along the abutting joint whereby the arc is likewise moved, and whereby the molten metal solidifies behind the arc to form a weld bead joining the first component to the second component and the third component, thus forming the weldment. 
   In another aspect, the present invention is a weldment comprising a first component, a second component and a third component, the first component in an abutting relationship with the second component, the third component in underlying relationship with the first component and the second component beneath the abutting joint, a weld bead made by buried arc welding joining the first component, the second component, and the third component. 
   In a further aspect, the invention is a weldment comprising a first component, a second component and a third component, the first component in abutting relationship with the second component, the third component in underlying relationship with the first component and the second component beneath the abutting joint, a narrow weld bead made by buried arc welding joining the first component, the second component, and the third component. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic illustration of a prior art arrangement for forming an integrally backed square butt weld by gas metal arc welding; 
       FIG. 2  is a schematic illustration of a prior art arrangement for forming a two component integrally backed butt joint by gas metal arc welding; 
       FIG. 3  is a schematic illustration of a prior art arrangement for forming an integrally backed square butt joint wherein a V-shaped joint gap is provided to facilitate the welding process; 
       FIG. 4  is a schematic illustration of a prior art arrangement for forming a two component integrally backed butt joint wherein a V-shaped joint gap is provided to facilitate the welding process; 
       FIG. 5  is a schematic illustration of an arrangement, according to the present invention, for forming an integrally backed square butt joint by gas metal arc welding; 
       FIG. 6  is a schematic illustration of an arrangement, according to the present invention, for forming a two component integrally backed butt joint by gas metal arc welding; 
       FIG. 7  is a schematic illustrating a section cut through the weld pool during gas metal buried arc welding of an integrally backed square butt joint; 
       FIG. 8  is a schematic section of the arrangement of  FIG. 4  cut along the plane indicated as  8 - 8  in  FIG. 7 ; 
       FIG. 9  is a schematic section of a weld made according to the present invention, cut along the plane indicated as  9 - 9  in  FIG. 8 ; 
       FIG. 10  is a section similar to  FIG. 9  with the weld bead machined flush with the surfaces of the components being joined; and 
       FIG. 11  is a schematic illustration showing a shielding cup which supplies inert gas to the area being welded. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   For purposes of the description hereinafter, the terms “upper”, “lower”, “level”, “above”, “below”, “beneath” etc and derivatives thereof relate to the invention, as it is oriented in the drawing figures. However, it is to be understood that the invention may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the drawings, and described in the following specification, are simply exemplary embodiments of the invention. Hence, specific dimensions and other physical characteristics related to the embodiments disclosed herein are not to be considered as limiting. 
   Attention is now directed to  FIG. 5  which illustrates an arrangement  50 , according to a presently preferred embodiment of the invention, the arrangement being for butt welding component  12  to component  14  and simultaneously joining these to component  16 , which underlies components  12  and  14 . No joint gap is provided between component  12  and component  14 , as was the case for the prior art arrangements illustrated in  FIGS. 1 and 2 . In the presently preferred embodiment shown in  FIG. 5 , component  12  lies adjacent component  14  to define an abutting joint  17  therebetween. The consumable metal electrode  19  is placed above the abutting joint  17 . 
   After the arrangement shown in  FIG. 5  is established, an arc is initiated, typically by establishing an electric potential (voltage) between the components  12  and  14  being joined and the tip of the consumable metal electrode  19  and by touching it to component  12  and/or component  14 . 
     FIG. 6  illustrates an arrangement  60  for joining a first component  12  to a second component  22 , the second component  22  having an abutting portion  24  and an underlying portion  26 ; underlying portion  26  underlying first component  12 . First component  12  is placed adjacent abutting portion  24  of second component  22  to define an abutting joint  67  therebetween. 
   After the arrangement shown in  FIG. 6  is established, an arc is initiated, typically by impressing an electric potential between the components  12  and  22  being joined and the tip of consumable metal electrode  19  and by touching electrode  19  to component  12  and/or component  22 . 
     FIG. 7  illustrates the welding process for the arrangement shown in  FIG. 5 . The arc  72  forms a cavity  75  for itself and for a molten metal layer  74 . Cavity  75  subsumes the abutting joint  17 , melting portions of the first component  12  and the second component  14 , and it penetrates into the third component  16 , as illustrated in  FIG. 7 . 
   The electric potential and current of the arc are maintained at levels appropriate for buried arc welding, and the elevation of the tip of the consumable metal electrode  19  is maintained at a value appropriate for buried arc welding. The consumable metal electrode  19  is then moved along the abutting joint  17  at a speed appropriate for buried arc welding. 
     FIG. 8  is a section cut along the plane  8 - 8  shown in  FIG. 7 .  FIG. 8  shows the direction of movement  70  of the consumable metal electrode  19 . The consumable metal electrode  19  is moved at a speed appropriate for buried arc welding in the direction of arrow  70 . At this speed, the cavity  75 , the buried arc  72  and the molten metal layer  74  are as shown in  FIGS. 7 and 8 .  FIG. 8  also shows the forward travel angle  71  of the consumable metal electrode  19 . Molten metal layer  74  on the back side of cavity  75  solidifies to form weld bead  78  having surface  80  behind the buried arc  72 . 
     FIG. 9  is a view cut along line  9 - 9  in  FIG. 8 . It shows the weld bead  78  joining the first component  12 , the second component  14  and the third, underlying, component  16 . The surface  80  of weld bead  78  will generally be higher than the surface  13  of component  12  or surface  15  of component  14 . 
     FIG. 10  is a view similar to  FIG. 9 , but  FIG. 10  is the configuration after the weld bead  78  has been trimmed so that machined surface  82  of weld bead  78  is flush with surfaces  13  and  15  of components  12  and  14 , respectively. 
   The process of welding the configuration illustrated in  FIG. 6  for the two component system is similar to the process discussed above for the configuration illustrated in  FIG. 5 , which is for the three component system. 
   Numerical Values for the Presently Preferred Embodiments 
   It has been found that the method described above works well for the component thicknesses and operational parameters which follow. 
   When making a three component integrally backed butt weld, as shown in  FIG. 5 , it has been believed that the first component  12  and the second component  14  should have a thickness of at least about 1 mm and, preferably, no more than about 18 mm. The process has been found to work well when these components have a thickness of about 3.5 mm. The thickness range from 1 to 18 mm also applies to the thickness of the abutting portion  24  of the second component  22  illustrated in  FIG. 6 . The method is recommended for the aluminum alloy 5383-H34. 
   The method is believed to work well when the thickness of the third component  16 , or the underlying portion  26  of second component  22  is from about 3 mm to about 7 mm. The process has been found to work well when the thickness of the third component  16 , is about 4.5 mm. The method worked well when the third component  16  was an extruded stiffener comprised of the aluminum alloy 6061-T6. For these alloys, a consumable metal electrode comprised of aluminum alloy 5356 and 1.6 mm in diameter is recommended. The forward travel angle  27  of the consumable electrode  19 , preferably, should be about 5-15 degrees. 
   The electric potential and current of the arc should be appropriate for buried arc welding. It is believed that the electric potential should be in a range from 17-29 Volts, and that the current should be in a range from 70-600 Amperes. Generally, higher values of electric potential and current should be employed for welding thicker components according to this principle. For the presently preferred thicknesses cited above, an electric potential of about 25.7 Volts and a current of about 326 Amperes has been found to work well. 
   The consumable metal electrode was supplied at about 7.5 meters per minute, and the speed of travel of the electrode was 0.86 meters/minute. 
   For situations wherein the components to be joined are comprised of aluminum alloys, a shielding gas is required.  FIG. 11  shows a shielding cup  84  for supplying a laminar flow of a shielding gas such as argon. Shielding cup  84  has a bottom edge  86  located at a standoff distance  88  from the surface  15  of second component  14 . The standoff distance  58  was about 9.5 mm. 
   The preferred orientation for this process is the “flat down hand” position. For the three component system, the first component  12  and second component  14  are flat with third component  16  beneath the abutting joint  17  between them. For the two component system, first component  12  and second component  22  are flat, with the underlying portion  26  of second component  22  beneath the abutting joint  67 , between first component  12  and the abutting portion  24  of second component  22 . 
   Specific embodiments of the invention has been described above. It is to be understood, of course, that the invention may be otherwise embodied within the scope of the appended claims.