Patent Publication Number: US-2018036827-A1

Title: Method for welding together two components, preferably of an exhaust system of an internal combustion engine, by resistance welding

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 U.S.C. §119 of German Application DE 10 2016 114 556.4 filed Aug. 5, 2016, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention pertains to a method for welding together two components, preferably of an exhaust system of an internal combustion engine, by resistance welding. 
     BACKGROUND OF THE INVENTION 
     A method with which a bushing can be fixed to a wall of an exhaust system component by resistance welding is known from a subsequently published German patent application DE 10 2015 216 013. The exhaust system component may be, for example, a catalytic converter, to the housing of which a bushing is to be fixed by welding for receiving a measuring probe, for example, a temperature sensor. 
     An opening, through which access can be gained to the interior of the housing, is provided in the wall. A surface, which provides a welding area of the bushing, can be brought into contact with a wall area of the housing, which wall area is bent outwardly, surrounds the opening and provides a welding area of the housing, is provided on the bushing, wherein said surface can be fixed to the wall area by resistance welding. A longitudinal axis of the bushing may be bent at an angle in relation to a plane in which the surface providing the welding area is located, i.e., it may not be oriented at right angles thereto, so that a measuring probe to be fixed to the bushing can be fixed in a correspondingly sloped position on the housing. The slope of the measuring probe in relation to the housing is determined by the angle between the longitudinal axis of the bushing and the plane in which the surface providing the welding area of the bushing is located. 
     In an alternative embodiment, the surface providing the welding area of the bushing has a conical or frustoconical configuration, so that a part of the bushing that has this surface and provides the welding area of the bushing at least slightly protrudes into and is inserted into the opening when the frustoconical surface provided thereon is in contact with the area of the housing wall, which area is bent outwardly. A longitudinal axis of the bushing is oriented parallel to an axis of the opening provided in the wall of the housing in this embodiment. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a method for welding together two components, preferably of an exhaust system of an internal combustion engine, by resistance welding, in which there is a greater freedom in positioning the two components to be welded together in relation to one another. 
     This object is accomplished according to the present invention by a method for welding together two components, preferably of an exhaust system of an internal combustion engine, by resistance welding, comprising the actions of a) providing a first component with an insertion opening, wherein the insertion opening is surrounded by an insertion opening edge providing a welding area of the first component, b) providing a second component with an insertion area to be inserted into the insertion opening of the first component, wherein a surface of the insertion area (insertion area surface) provides a welding area of the second component, c) inserting the insertion area into the insertion opening such that surface of the insertion area is in contact with the first component essentially along the entire insertion opening edge, and d) applying an electrical voltage to the two components for the resistance welding of the first component to the second component. The surface of the insertion area is curved about two axes, which are not parallel to one another, or is curved about an axis that is parallel to the surface of the insertion area, and/or an insertion surface of the insertion opening edge is not located in one plane. 
     It is made possible by the embodiment in space of the areas of the two components, which are to be welded together, that these can be arranged in different positions in relation to one another, but there is a contact between the two components essentially along the entire insertion opening edge, so that the electrical current leading to the melting of the components can flow in this contact area during the resistance welding, and sufficient heating and hence melting and welding together of the two components can also be achieved in areas in which contact is interrupted, in which a small intermediate space is present between the welding areas of the two components. 
     It should be pointed out in this connection that the two components are in contact with one another in their welding areas essentially along the entire insertion opening edge when the two components are in contact with one another over at least half and preferably at least 80% of the length of the insertion opening edge. 
     It is proposed in one embodiment that is especially advantageous in respect to the selectable positioning of the two components in relation to one another that the surface of the insertion area be spherical in at least some areas or have the shape of ellipsoid or of a rotation ellipsoid. It is possible now to move the two components towards one another and to bring them into the desired position in the manner of a ball joint connection in relation to one another, but a contact between the two components is nevertheless maintained or set over an essential part of the overall length of the insertion opening edge. 
     Provisions may be made in an alternative embodiment for the surface of the insertion area to be, in at least some areas, a cylindrical surface, preferably a regular cylindrical surface. This also makes it possible to weld together the components in relation to one another and to position them in positions pivoted differently in relation to one another. 
     It is proposed in a procedure that is especially advantageous in terms of easy embodiment and also the efficient performance of the welding operation that the insertion opening be provided in action a) by preparing an essentially cylindrical recess in the first component, or/and by inserting the insertion area into the insertion opening in action c) such that the surface of the insertion area is in contact with an insertion surface of the insertion opening edge. 
     As an alternative, provisions may be made, especially for providing a very stable welded connection, for the insertion opening to be provided in action a) with an edge surface of the insertion opening edge, which edge surface is adapted to the shape of the surface of the insertion area, or/and for the insertion area to be inserted into the insertion opening in action c) such that the surface of the insertion area is in contact with an edge surface of the insertion opening edge. 
     The insertion opening may be provided, for example, by removing material, preferably by drilling, cutting, or milling. As an alternative, the insertion opening may be provided by providing a preferably cylindrical attachment on the first component, preferably by shaping of the first component. Such an attachment may be provided, for example, by the shaping of a wall area of the first component, which wall area surrounds an opening, or by attaching a separate component providing the attachment, for example, by welding. 
     Provisions may be made in one embodiment that is especially advantageous in terms of providing a freedom in position the two components in relation to one another for an insertion surface of the insertion opening edge to be located essentially in one plane. 
     The first component may have a tubular configuration with an essentially cylindrical outer circumferential contour in an alternative embodiment, wherein an insertion surface of the insertion opening edge is located essentially on a cylindrical surface. It should be pointed out here that the tabularly configured component may be configured with different cross-sectional geometries, for example, with a circular, oval or elliptical geometry, but with an essentially cylindrical contour, i.e., with a contour that does not consequently change essentially in the direction of a longitudinal axis of the tube. 
     It is proposed, especially if the second component is a bushing for receiving a measuring probe or the like, that the second component extend in the direction of a longitudinal axis of the component and have the insertion area in an end area. This does not necessarily mean that the second component has a larger dimension in this extension direction than, e.g., the diameter of the second component. The longitudinal axis of the second component is, in the sense of the present invention, a reference line expressing a certain extent of symmetry. 
     To make it possible to position, for example, a measuring probe in a sloped position in relation to a housing of a catalytic converter, it is proposed that the second component be inserted into the insertion opening in action c) such that the longitudinal axis of the component is not parallel to an axis of the insertion opening. 
     A precise positioning of the two components to be welded together can be achieved in the method according to the present invention without compromising the quality of the resistance-welded connection to be established by the welding area of the first component or/and the welding area of the second component are provided essentially without projections, i.e., the projection-like elevations generally provided in resistance projection welding. 
     The present invention will be described in detail below with reference to the attached figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a sectional view of two components to be welded together, which are in contact with resistance welding electrodes; 
         FIG. 2  is a perspective view showing the device according to  FIG. 1 ; 
         FIG. 3  is a sectional view of two components to be welded in flat contact; 
         FIG. 4  is a sectional view of two components to be welded together in linear contact; 
         FIG. 5  is a lateral view of a tubular component configured with an insertion opening; 
         FIG. 6  is a component to be welded to the component according to  FIG. 5 ; 
         FIG. 7  is a lateral view of a component with an elliptical cross section; 
         FIG. 8  is a sectional view showing the component of  FIG. 7 , cut along a line VIII-VIII in  FIG. 7 ; and 
         FIG. 9  is a view of a component with an insertion opening, which component is to be welded to the component of  FIG. 7 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings,  FIG. 1  shows two components  10 ,  12  to be welded together by resistance welding with the respective welding electrodes  14 ,  16  that are in contact with them. The first component  10  in  FIG. 1  is an essentially plate-like or flat component. The first component  10  may be, for example, a housing or an area of a housing of an exhaust gas treatment device, e.g., a catalytic converter. The second component  12  is a connection piece, which is to be fixed to the housing or the first component  10  in the example shown in  FIG. 1 . The second component  12  configured as a connection piece has an opening  18 , which is configured, for example, with an internal thread and into which a measuring probe or the like can be screwed. The welding electrode  16  can be inserted into the opening  18  with a complementarily shaped attachment during the resistance welding operation. 
     As is shown in more detail in  FIG. 3 , the two components  10 ,  12  are connected to one another such that a longitudinal axis A 1  of the second component  12  or connection piece extending, e.g., along in the direction of this axis extends at an acute angle, i.e., not parallel, in relation to an axis A 2  of an insertion opening  20  formed in the first component  10 . An edge area  22  surrounding the insertion opening  20  on the first component  10  forms a welding area  24  of the first component  10 , on which a welding area  30  of the second component  12 , which said welding area  30  is to be provided in the area of a surface  28  of the insertion area, is to be fixed. 
     In the exemplary embodiment shown in  FIGS. 1 through 3 , the second component  12  has an essentially rotationally symmetrical configuration especially in its insertion area  26  or the surface  28  of the insertion area provided there in relation to the longitudinal axis A 1 , and the surface  28  of the insertion area is configured, in particular, in this exemplary embodiment with an essentially convex, spherical shape, which means that the surface of the insertion area is curved about two axes, which are, for example, mutually at right angles to one another. 
     Corresponding to this spherical or curved shape of the surface  28  of the insertion area, the first component  10  may also be curved spherically, but concavely in the area of the insertion opening edge  22  or of an edge surface  32 , which directly encloses the insertion opening  20  and faces same. Thus, there is an essentially flat contact between the surface  28  of the insertion area and the edge surface  32  during the insertion of the insertion area  26  into the insertion opening  20 . The two components  10 ,  12  are thus in connection with one another due to the contact of two surfaces having complementary spherical shapes in the manner of a ball joint, so that, without loss of the mutual contact, the second component  12  can be pivoted in relation to the first component  10 . This makes it possible to position the longitudinal axis A 1  in a sloped manner in relation to the axis A 2  of the insertion opening  20 , but also to arrange it parallel thereto if necessary. There is, in principle, a freedom in selecting the positioning of the second component  12  in relation to the first component  10 . 
     When connecting the components  10 ,  12  to one another by a resistance welding method, the two components  10 ,  12  are arranged in the position intended for the fitting together in relation to one another, e.g., after the two components  10 ,  12  have been brought into contact with the respective welding electrodes  14 ,  16  associated with them, for example, in the manner shown in  FIG. 1 . The surface  28  of the insertion area is ideally in contact with the edge surface  32  over the entire circumference of the insertion opening  20  or of the edge area  22 . Based on possibly unavoidable manufacturing tolerances, there may be areas in which a small gap-like intermediate space is present between the two surfaces  28 ,  32 . 
     To carry out the welding operation, a voltage is applied to the two welding electrodes  14 ,  16 , so that the two components  10 ,  12  melt locally and are thus welded together on their surface areas that are in contact with one another based on the electrical current now flowing and the heating of the two components  10 ,  12 , which now occurs. Since the contact is present between the two components  10 ,  12  essentially over the entire circumference of the insertion opening edge  22 , the components will essentially also be welded together in the area of the surfaces  28 ,  32  that are in contact with one another. Based on the heating of the material of which the two components  10 ,  12  consist, this material is also melted and forms a welded connection even where small gap-like intermediate spaces are present, so that this welded connection is formed such that it extends without interruptions about the axis A 2  of the insertion opening  20  and a gas-tight, stable welded connection is also formed, in particular. The provision of projection-like elevations on at least one of the two components to be welded together, as this is generally the case in so-called resistance projection welding, is not necessary for obtaining an uninterrupted, gas-tight welded connection in the procedure according to the present invention. 
     The insertion opening  20  may be prepared, for example, by a spherical cutter in the first component  10  in the embodiment of the component  10  shown in  FIG. 3 . The radius of curvature of the spherical cutter is duplicated on the edge surface  32  of the insertion opening edge  22  and is selected essentially such that it corresponds to the radius of curvature of the surface  28  of the insertion area. 
     In an alternative embodiment shown in  FIG. 4 , the insertion opening  20  is provided as an essentially cylindrically configured opening in the first component  10 . This insertion opening  20  may be formed, for example, by drilling, cutting, punching or the like. Based on the cylindrical configuration of the insertion opening  20 , i.e., the edge surface  32  is consequently essentially a cylindrical surface, for example, with a circular contour, there is essentially no flat contact between the second component  12 , which is inserted with its insertion area  26  into the insertion opening  20  at least slightly, and the first component  10 . The second component  12  with second component surface  28  of the insertion area is rather in contact with an insertion surface  34  of the edge area  22 . It should be pointed out that the insertion opening  20  has, in principle, two such surfaces, and the insertion surface  34 , which is also shown in  FIG. 4 , is the surface with which the insertion area  26  can come into contact. 
     The insertion area  26  is provided with an, e.g., spherical surface  28  of the insertion area, i.e., with a surface that is curved about two axes that are, for example, at right angles to one another, in the exemplary embodiment shown in  FIG. 4  as well, and the radius of curvature is equal in all surface areas because of the spherical shape. If the insertion opening  20  is provided with a circular contour, there is ideally an essentially linear contact between the surface  28  of the insertion area and the insertion surface  34 , which contact extends about the axis A 2  of the insertion opening  20  without interruptions. However, as is shown on the left-hand side of the insertion opening  20 , a small gap-like intermediate space  36  may develop between the surface  28  of the insertion area and the insertion surface  34  in some circumferential areas, for example, due to manufacturing tolerances. As was already explained above with reference to  FIG. 3 , the material of the two components  10 ,  12  will also be melted in these areas and thus connected to one another by welding based on the short distance and the generally comparatively small circumferential extension of such gap-like intermediate spaces  36  when the voltage necessary for the welding is applied and the welding current flows. 
       FIGS. 5 and 6  show an alternative embodiment of two components  10 ′,  12 ′ to be connected to one another. The component  10 ′ may be, for example, a tube extending in the direction of a longitudinal axis A 3 , i.e., it may have an essentially cylindrical shape, for example, with a round cross-sectional geometry. The insertion opening  20 ′ may be prepared in the first component  10 ′, for example, by means of a solid cylindrical milling cutter. This insertion opening has an axis A 2  extending essentially at right angles to the longitudinal axis A 3  of the first component  10 ′. Thus, the edge area  22 ′ of the opening  20 ′ or the insertion surface  34 ′ as well as the edge surface  32 ′ are not in one plane, unlike in the exemplary embodiment according to  FIGS. 1 through 4 , but, due to the curved configuration of the first component  10 ′, they are likewise curved. In particular, the insertion surface  34 ′ lies on the cylindrical outer circumferential surface  38 ′ of the first component  10 ′. 
     In association with this shape of the edge area  22 ′, which shape extends about the axis A 2  in a ring-like manner and is curved in the direction of the axis A 2  of the insertion opening  20 ′, the second component  12 ′ has a complementarily shaped surface  28 ′ of the insertion area, which is curved, for example, complementarily to the curvature of the edge area  22 ′, for example, it is also curved in a circular manner. The surface  28 ′ of the insertion area is curved in this exemplary embodiment about a single axis A 4 , for example, with an essentially constant radius of curvature, this axis A 4  being parallel to the surface of the insertion area rather than intersecting the surface of the insertion area. 
     The second component  12 ′ can be inserted into the insertion opening  20 ′ with the insertion area  26 ′ thus formed, so that the essentially cylindrical surface  28 ′ of the insertion area, which is curved, for example, in a circular manner, comes into contact with the correspondingly curved edge area  22 ′. Depending on how the insertion opening  20 ′ was prepared, an essentially linear contact develops with the insertion surface  34 ′ or a flat contact develops on the edge surface  32 ′ at least locally. 
     In this embodiment as well, the two components  10 ′,  12 ′ can be positioned by pivoting the second component  12 ′ about the axis A 4  such that an angle will develop, if necessary, between the two axes A 1  and A 2 , i.e., the second component extending essentially in the direction of the longitudinal axis A 1  is not consequently necessarily arranged at right angles to the longitudinal axis A 3  of the first component  10 ′ and thus it must be connected to the first component  10 ′. Consequently, there is a freedom in positioning the second component  12 ′ in relation to the first component  10 ′ in this case as well. 
     Another embodiment is shown in  FIGS. 7 through 9 . This corresponds in terms of the basic configuration of the two components  10 ,  12  to the embodiment described with reference to  FIGS. 1 through 4 . The first component  10  may consequently have an essentially flat configuration at least in the area of the insertion opening  20 , so that the insertion opening  20  or the edge area  22  thereof is also located in one plane. The second component  12  shown in a lateral view in  FIG. 7  is configured such that it extends, for example, in the direction of the longitudinal axis A 1 . Unlike in the embodiments according to  FIGS. 1 through 4 , the second component  12  is not configured, especially in the second component insertion area  26 , with a surface  28  of the insertion area extending along the longitudinal axis A 1  in a rotationally symmetrical manner. The second component  12  could be configured, for example, with an elliptical cross-sectional geometry, at least in its insertion area  26 . 
     If the second component  12  is cut in a plane E bent at an angle in relation to the longitudinal axis A 1  thereof, a circumferential contour of the cross-sectional surface, which is correspondingly also elliptical and is shown in  FIG. 8 , is obtained in the insertion area  26 . If the second component  12  is arranged with a corresponding slope angle of the longitudinal axis A 1  in relation to the first component  10 , a contact extending essentially completely circularly about the axis of the insertion opening  20 , which axis is at right angles to the drawing plane of  FIG. 9 , can be obtained in the above-described manner between the two components  10 ,  12  if the insertion opening  20  in the first component  10  has a shape complementary to the cross-sectional geometry of the insertion area  26 , which geometry is shown in  FIG. 8 . 
     This means that, according to the present invention, if the geometry of the insertion area  26  is known and the slope angle provided for the second component  12  in relation to the first component  10  is known as well, the shape of the insertion opening  20  can be selected such that the course of the insertion opening edge  22  of the circumferential contour of the second component  12  also corresponds, in second component areas, that come into contact with the first component  10  to the surface  28  of the insertion area. When the resistance welding operation is carried out, a welded connection of the two components  10 ,  12 , which extends uninterruptedly for the entire edge area  22 , can then be obtained in the above-described manner. 
     Since the second component  12  is nevertheless curved about two axes in the area of its surface  28  of the insertion area in this embodiment as well, even though it is curved with a radius of curvature varying over the surface  28  of the insertion area, the second component  12  can be welded in a certain range of variations in relation to the first component  10  in this embodiment as well, without a substantial loss of mutual contact being lost between these two components  10 ,  12 . A gap-like intermediate space may now develop locally between the two components  10 ,  12 , which, unless this gap-like intermediate space exceeds a certain extent in the circumferential direction, will nevertheless be closed due to melting of the two components  10 ,  12  when the welding voltage is applied to the two components  10 ,  12  and when welding current flows. 
     The above explanations show that, due to the fact that in the two components to be connected to one another, the component that has the insertion area with the curved surface of the insertion area has a surface curved about at least one axis in this insertion area, this component will always protrude slightly into the insertion opening of the other component when the contact is established. Due to this mutual meshing, it is possible to perform a pivoting at least in a small range of angles even in case of nonspherical shape of the surfaces that are in contact with one another, and nevertheless to obtain an uninterrupted course of the welded connection area when a resistance welding operation is carried out. 
     This manner of connecting the two components to one another can also be achieved independently from the configuration especially of the first component. As is shown in the different embodiment, this component may have a flat configuration, at least in the area in which the insertion opening is to be provided, so that the insertion edge area or an insertion surface thereof is correspondingly also in one plane. As an alternative, the first component may be curved in this area. The insertion opening on the first component may be prepared, as was mentioned above, for example, by machining, i.e., for example, drilling, milling or cutting. It is also possible, in principle, to prepare this opening by shaping of the first component as an attachment extending, for example, cylindrically in the direction of the axis of the opening. An end face of this attachment may then be configured, for example, with the edge surface geometry shown in  FIG. 3  for the flat contact the surface of the insertion area of the second component. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.