Electrodes with curved contours for joining workpieces with curved surfaces

Abstract

A welding electrode for use in resistance spot welding an assembly of metal workpieces having curved surfaces and closed or open cross sections is disclosed. The welding electrode has a body, a welding surface at one end of the body, and a curvature of a curved contour forming the welding surface. When the welding surface is pressed against the workpiece during resistance spot welding, the curvature abuts the periphery of the curved surface of the metal workpiece. When the electrode contacts the curved surface of the workpiece, it has an optimal contact area, which improves pressure and current distribution and improves the spot welding process.

Description

[Technical field]

[0001] The technical field of the present invention relates to welding electrodes for forming electric resistance spot welds between one or more sheet metal layers having a curved surface and another metal workpiece having a curved surface and a closed or open cross section. More specifically, the technical field of the present invention relates to welding electrodes for forming high quality weld nuggets between workpieces having curved surfaces and controlling the welding current path around or through a closed cross section via axially aligned opposing welding electrodes having contoured surface curvatures that match or nearly match the surface curvatures of the contacting workpieces. [Background technology]

[0002] Resistance spot welding is a technique that uses heat generated from resistance to electric current to create a joint (weld) between metal surfaces that contact each other. Resistance spot welding uses a pair of electrodes to focus electric current at a controlled spot and hold the workpieces together while applying force. Typically, the workpieces include thin metal sheets that melt under applied pressure and current and form a molten nugget at the interface between the sheets within the limits of the applied pressure and current. Re-solidification of the molten area creates a weld that joins the two materials together.

[0003] Resistance spot welding is commonly employed in automated assembly line applications due to the efficiency and economic benefits of the process. Resistance spot welding is the primary joining process used in the automotive industry to assemble large components and car bodies. Resistance spot welding is also a common method employed in the manufacture of household appliances, furniture, and the like. The efficiency of resistance spot welding is due to the fact that it melts material in a localized area and does not impart excessive heat to the surrounding material, thereby creating multiple weld spots in a short period of time. Traditionally, resistance spot welding is only applied on flat metal sheets stacked together by a force applied by opposing axially aligned electrodes contacting the outer surfaces of the sheets to be joined, thereby controlling melting and resolidification between the sheets. For the sake of simplicity, flat sheets / surfaces as referred to in this application refer to any sheet or surface that is flat or has a sufficiently large radius such that the sheet / surface is "flat" in effect and in function.

[0004] Resistance spot welding can be used to join materials without direct contact on both exterior surfaces of the sheets being joined, such as welding sheet metal parts to closed section parts such as hydroformed or extruded parts. Resistance spot welding can be done by utilizing a large grounded backing plate or block on the part with a closed section to act as one of the two electrodes in a conventional RSW process, or by methods that utilize two electrodes on the same side of the same material (e.g., U.S. Pat. No. 1,018,911). Both of these processes require flat surfaces for the electrodes and / or backing plate, which requires specialized equipment compared to conventional resistance spot welding, which has opposing electrodes axially aligned with one another.

[0005] Resistance spot welding of curved sheet metal to a metal part having a circular closed cross section using conventional resistance spot welding processes and electrodes with contact areas that are convexly curved or flat results in irregular weld shapes. For surfaces having a cylindrical shape, the linear contact formed between the electrode and the curved surface of the part results in a weld that is elongated and oval shaped rather than a traditional circular shape. In certain applications, welds of this shape may not meet commonly adopted quality specifications and there is concern that performance may be compromised due to lack of symmetry in the joint. Also, the linear contact area results in higher localized stresses that may damage the closed cross section workpiece. This can result in reduced performance and / or functionality of the part.

[0006] Usually, other welding processes such as metal inert gas welding, tungsten inert gas welding, or bump welding are required to thermally join metal components with complex joint shapes. These methods tend to have smaller geometric application limitations than resistance spot welding. However, in various applications, these processes are not as economical as resistance spot welding and have a lower reproducibility, which increases the possibility of quality problems. Therefore, there is a need to propose and improve a method and device for resistance spot welding thin sheets with curved surfaces to curved closed or open cross-section parts that is economically feasible and provides good quality. Summary of the Invention [Means for solving the problem]

[0007] The present invention provides a spot welding electrode with a purpose-built curved welding surface.

[0008] The shape of the welding electrodes is designed to form spot welds in one or more sheet metal layers having a curved surface and in another metal workpiece having a curved surface and a closed or open cross section. These electrode pairs, which may have the same or different geometries and / or curvatures, can be used on robotic, mobile, or stationary equipment with the electrodes arranged in axial alignment and positioned opposite one another. The electrodes are typically used in combination with a power source and weld controller, which can provide DC welding, AC welding, or any other combination and / or method of applying current to the workpiece at a controlled level and duration.

[0009] The resistance spot welding electrode of the present invention is made from, for example, but not limited to, a copper-based alloy having suitable physical and electrical properties to meet the physical force and electrical demands required to form a resistance spot weld. The electrode comprises a section that is attached to the welder for current delivery, either by integrating a shank into the electrode design or by having a portion sized to fit a separate shank portion. The portion of the electrode that is attached to or connected to the shank constitutes the electrode body. The electrode body is usually cylindrical in shape and is the portion that extends from the welding shank. The end of the electrode body opposite the shank is the electrode welding surface. Typically, the welding surface consists of a circular contact surface of a truncated cone, truncated dome, or flattened cylinder, the contact surface usually consisting of a convex dome. The welding surface is the portion of the electrode that abuts against the workpiece during the resistance welding process. According to the present invention, the contacting welding surface is configured to have a curvature portion that contours the workpiece to form a spot weld, achieving the above-mentioned objectives in the present invention.

[0010] The shape of the curved contour of the weld surface of the electrode can be applied to any conventional spot welding electrode shape and size as encompassed by the present invention. The contour is applied or maintained using a machining tool, which also includes cutting features to form or maintain the desired electrode geometry, including, but not limited to, a truncated cone, a dome, a truncated dome, and / or a flat cylinder. The welding setup includes one or more welding electrodes having a weld surface in the shape of the curved contour. The welding electrodes may or may not have the electrode geometry and / or the curved contour of the weld surface or the features described above in common. The curved contour of the weld surface will typically be similar to the curvature of the parts being welded.

[0011] An embodiment of the present invention is a spot welding electrode that produces improved weld geometries when welding a curved sheet metal workpiece to another metal workpiece having a curved surface and a closed or open cross section. When using a spot welding electrode, the contact between the electrode and the workpiece may be a single point or line. This relatively small contact area may make the workpiece more prone to deformation, resulting in reduced performance or functionality. The contact area also limits the possible size and shape of the weld nugget formed, resulting in an elliptical shape as opposed to the standard circular weld nugget formed in a spot welding process between flat sheet metal workpieces. However, while some resistance spot welding applications are suitable for utilizing the above workpieces and using standard spot welding electrodes, certain applications require specific quality and design criteria to be met. Thus, a better performing resistance spot welding electrode for welding a curved sheet metal workpiece to another metal workpiece having a curved surface and a closed or open cross section is desired. A welding surface with a curved contour allows the electrode to have a larger contact area with the workpiece. The increased contact area creates a more evenly distributed pressure profile on the workpiece, reducing the occurrence of workpiece denting, and provides current flow and distribution that, when combined with the improved pressure profile, promotes more uniform and more circular weld nugget formation. In certain scenarios, when spot welding two dissimilar materials, due to differences in thermal and electrical properties between the materials being joined, a thin intermetallic compound may form between the materials instead of a weld nugget. Also, certain scenarios are envisioned where the welding electrode contacts the workpiece on only one side. In these cases, the joint may be formed by surface melting. However, for brevity and ease of explanation, the joint formation in this patent is described in terms of a weld / nugget with opposing electrodes, although the patent and embodiments herein also apply to joining methods that do not form a traditional weld nugget.

[0012] It will be appreciated by those skilled in the art from the above disclosure and the detailed figures and description of the preferred embodiments below that the present invention provides a significant improvement in the art of systems and methods for resistance spot welding of one or more sheet metal workpieces with curved surfaces to another metal workpiece with a curved surface and a closed or open cross-section. [Brief description of the drawings]

[0013] The figures included below are intended to illustrate certain aspects of the present disclosure and are not to be construed as exclusive embodiments of the present disclosure. The subject matter protected by the present disclosure may adopt modifications, changes, combinations, and / or equivalents in embodiments and functions without departing from the technical scope of the present disclosure.

[0014] [Figure 1A] FIG. 1A is a schematic side view of a welder in a conventional welding operation utilizing standard spot welding electrodes to join a curved workpiece to a circular closed cross-section workpiece. [Figure 1B] FIG. 1B is a top view of a curved workpiece and a circular closed cross-section workpiece illustrating the contact area and pressure area during welding in the system shown in FIG. 1A. [Figure 1C] FIG. 1C is a diagram of the current paths for DC welding in the system shown in FIG. 1A. [Figure 2A] FIG. 2A is an isometric schematic diagram of an exemplary transverse cross-section of a weld between a curved workpiece and a circular closed cross-section workpiece made using the system shown in FIG. 1A. [Figure 2B] FIG. 2B is an isometric schematic diagram of an exemplary longitudinal cross-section of a weld between a curved workpiece and a circular closed cross-section workpiece made using the system shown in FIG. 1A. [Figure 3A] FIG. 3A is an isometric view of an exemplary contoured electrode made with a flat or large radius spot welding electrode. [Figure 3B] FIG. 3B is a top view of an exemplary contoured electrode made from a flat or large radius spot welding electrode. [Figure 4A] FIG. 4A is an isometric view of an exemplary contoured electrode made from a domed or chamfered / truncated spot welding electrode having a large chamfer angle. [Figure 4B]FIG. 4B is a top view of an exemplary contoured electrode made from a domed or chamfered / truncated spot welding electrode having a large chamfer angle. [Figure 5A] FIG. 5A is an isometric view of an exemplary contoured electrode made from a domed or chamfered / truncated spot welding electrode having a small chamfer angle. [Figure 5B] FIG. 5B is a top view of an exemplary contoured electrode made from a domed or chamfered / truncated spot welding electrode having a small chamfer angle. [Figure 6A] FIG. 6A is a schematic side view of a welder in a welding operation according to an embodiment of the present invention when joining a curved workpiece to a circular closed cross-section workpiece utilizing a spot welding electrode having a curved profile. [Figure 6B] FIG. 6B is a top view of a curved workpiece and a circular closed cross-section workpiece illustrating the contact area and pressure area during welding in the system shown in FIG. 6A. [Figure 6C] FIG. 6C is a diagram of the current paths for DC welding in the system shown in FIG. 6A. [Figure 6D] FIG. 6D is a diagram of a current path for DC welding utilizing a spot welding electrode having a curved profile to join a curved workpiece to a circular open cross-section workpiece. [Figure 7A] FIG. 7A is an isometric schematic diagram of an exemplary transverse cross section for welding between a curved workpiece and a circular closed cross section workpiece produced using the system illustrated in FIG. 6A. [Figure 7B] FIG. 7B is an isometric schematic diagram of an exemplary longitudinal cross-section of a weld between a curved workpiece and a circular closed cross-section workpiece made using the system shown in FIG. 6A. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The present disclosure relates to resistance spot welding apparatus and methods of use, and more particularly to a resistance spot welding electrode design that includes a welding surface having a curved contoured curvature for improving weld quality.

[0016] The embodiments described herein describe improvements in resistance spot welding electrode designs useful for producing spot welds on any weldable workpiece. A first embodiment of the present invention provides a spot welding electrode having a welding surface with a curved contour that is effective for producing quality welds on curved metal workpieces having closed or open cross sections. The electrode consists of a portion attached to or integral with the electrode shank at one end, followed by the body of the electrode, and a welding surface with a curved contour surface at the opposite end of the shank. The electrode body may be configured in a number of shapes, but is typically cylindrical. The welding surface with a curved contour can be created on any known welding surface geometry, including, but not limited to, a truncated cone, a truncated dome, or a flat cylinder with or without a convex radius. The curvature of the curved contour is determined to match or nearly match the curvature of the workpiece to be welded.

[0017] In embodiments disclosed herein, methods are described that use electrodes having curved contour curvatures for the production of spot welds between curved weldable workpieces and curved weldable workpieces having closed or open cross sections with improved weld geometry. Such methods include using robotic or non-robotic welding equipment to deliver a predetermined amount of electrical energy (current) for a predetermined time and at a predetermined pressure.

[0018] The disclosed embodiments provide a welding electrode surface having a curved contour curvature that aids in the formation of spot welds with improved geometry by controlling the current distribution and pressure through the surface contact area. The curved contour curvature achieves a larger, more circular contact area with the curved workpiece. The increased contact area allows the electrode to contact the workpiece more easily. The contact pressure is reduced. The lower pressure reduces the deformation of the workpiece during the welding process. The increased area also creates a larger pressure zone where the weld nugget can form and grow before reaching the ejection limit. The larger pressure zone symbiotically creates a larger contact area, which allows for better current distribution at the electrode tip, and allows for the formation of a sufficiently large and regular weld nugget. In some cases, better current distribution and heat flow can also be achieved by applying the force or current on one side. Workpiece considerations that affect the formation of an optimal weld surface with a curved contour curvature include, but are not limited to, workpiece geometry, workpiece quantity, material grade, material thickness, material coating, and workpiece function / application.

[0019] In contrast to conventional spot welding tools and methods, the curved contoured tip can be used on any resistance spot welding equipment with interchangeable welding electrodes, so that the embodiments of the present disclosure can be used on existing conventional spot welding equipment. Furthermore, the embodiments of the present disclosure improve weld geometry compared to conventional spot welding electrodes that create non-circular welds and, in some cases, dents into curved closed or open cross-section workpieces that compromise performance and function, and that may not be acceptable under the welding standards applicable to the project, since non-circular welds may have anisotropic properties, leading to unpredictable and non-uniform performance. Furthermore, the embodiments of the present disclosure form nuggets that meet the strength and internal quality requirements of a given project.

[0020] FIG. 1A shows an exemplary conventional welding operation using a conventional electrode 4 and electrode 10 to form a spot weld at a weld location 6 between a curved sheet metal workpiece 7 and a curved closed cross-section workpiece 8. The welding apparatus consists of an upper welding gun arm 1 having an electrode holder 2 that holds a standard electrode 4 with an electrode shank 3. Cooling of the electrode by water cooling or any other cooling method or agent is often performed and may or may not be utilized in these embodiments, but is not shown in the methods and equipment described herein. The upper welding gun arm 1 is attached to a welding machine (not shown), which may be various types of robotic or non-robotic welding equipment, including any type of welding equipment capable of providing the necessary welding pressure and current for the desired application. The welding machine may be servo-driven, pneumatically driven, or any other type of welding machine capable of implementing similar techniques. The current through the welding machine may be direct current (DC), alternating current (AC), or any other combination and / or method of applying current to the workpiece. Similar to the upper welding gun assembly, a lower welding gun arm 13 is also attached to the welding apparatus. The lower welding gun arm 13 also has an electrode holder 12 that holds a lower electrode 10 with a shank 11 .

[0021] During the spot welding operation of FIG. 1A, the welding electrode 4 held by the upper welding gun arm 1 contacts the outer (upper) surface of the curved workpiece 7 by contact area 5, and the welding electrode 10 held by the lower welding gun arm 13 contacts the outer (lower) surface of the curved closed cross-section workpiece 8 by contact area 9. The welding device appropriately applies a force L between the electrodes 4, 10 based on a predetermined pressure schedule to press the workpieces 7, 8 together and form an area where the weld nugget 6 is formed. FIG. 1B is a top view of the welding process shown in FIG. 1A. The geometry of the upper electrode 4 and the curved workpiece 7 creates a narrow contact point 5, which creates a small elliptical pressure envelope 14 inside which the weld nugget 6 is formed so as to be contained without ejection. Current passes between the electrode 4 and the opposing electrode 10, both axially aligned, through the workpieces 7, 8 at the contact points 5, 9, and through the location of the weld nugget 6. FIG. 1C shows an example of the current path 15 described above. The current I is shown as a direct current flow, with the top electrode 4 being negative and the bottom electrode 10 being positive. Although positive polarity, the embodiment may be applied to any current type or polarity of welding equipment. The geometry of the electrodes 4, 10 and workpieces 7, 8 creates narrow contact points 5, 9, A focused current density is achieved at the contact area 5, 9. A predetermined amount of current is applied in the welding operation, causing an appropriate amount of resistive heating at the weld nugget location 6, which melts the metal in the current path. The welding current is stopped after a predetermined time, and the weld nugget 6 is rapidly cooled by diffusing heat to other portions of the workpieces 7, 8 and the electrode 4, 10, with or without the aid of a cooled electrode, by water or any other coolant or method. The molten area resolidifies, forming a joint between the workpieces. After the welding process, the electrode or workpiece can be moved, and a subsequent weld can be formed at the adjacent weld site.

[0022] 2A and 2B show schematic diagrams of an example of a cross-sectional result resulting from the welding operation shown in FIG. 1A. FIGS. 2A and 2B show isometric schematic cross-sections in both the transverse and longitudinal cross-sectional directions. The limited contact area 5 between the top electrode 4 and the curved workpiece 7 results in significant indentation in the curved workpiece 16, which may also result in indentation in the interior of the curved closed cross-sectional workpiece 8. The indentation 17 in the interior may prevent the intended function of the part, such as threading of a bolt, and / or may result in reduced functionality due to impaired structure. This indentation occurs in part due to the narrow contact point shown in FIG. 1B. Furthermore, the minimal contact area and concentrated current flow inherent in the geometry of this welding operation, particularly in the shape of an ellipse, results in a weld nugget 6 that is notably narrow in the transverse direction in FIG. 2A and long in the longitudinal direction in FIG. 2B. These dimensions and lack of uniformity may result in the weld not meeting common quality standards for certain applications and may also result in reduced and / or anisotropic performance. As described above and shown in the figures, the weld surface has a large effect on the pressure profile and current distribution during the welding process, both of which affect the dimensions and quality of the weld nugget and workpiece assembly.

[0023] In a first embodiment of the present invention, an electrode geometry is provided that is appropriately designed for welding curved workpieces to curved surfaces having closed or open cross sections. This geometry allows for the production of good quality welds across workpiece geometries, workpiece quantities, material grades, material thicknesses, and material coatings by utilizing a contoured weld surface that matches or nearly matches the curvature of the workpieces being welded. The electrode shares some features with conventional electrodes used to spot weld steel or aluminum, but offers the novel feature of a curved contoured weld surface not previously used.

[0024] The novel electrode surface geometry is designed with a curved contour curvature in a number of possible electrode body designs. Now referring to Figs. 3-5, the curved contour weld surface is designed to meet the requirements of several applications. First, it is preferable that the electrode does not dent the workpiece excessively. Excessive denting or metal thinning can weaken the weld and excessive denting into a workpiece with a closed or open cross section can impair the function of the part, such as damaging the threads of a bolt. Other requirements include that the electrode can promote nugget growth to form a nugget of regular shape that is large enough to meet normally accepted quality specifications. There are established dimensional standards for spot welding for certain applications that require welds with specific sizes and shapes to achieve adequate strength. Welds that are smaller than normal or have irregular shapes cannot meet performance requirements in all directions. A further advantage provided by the present invention is that improved workpiece alignment can be achieved compared to standard electrodes. Having multiple electrodes for a workpiece with similar curved contour curvature helps to keep all parts in series to facilitate forming a proper quality weld in the correct location. The curved contour electrode design of the present invention meets the above requirements.

[0025] As mentioned above, the curved contour curvature portion can be applied to a number of electrode body designs. Figures 3A-5B show several exemplary electrode geometries encompassed by embodiments of the present invention. Possible applications of the designs and embodiments of the present invention include, but are not limited to, the designs shown in Figures 3A-5B. Figures 3A and 3B show isometric and plan views of exemplary curved contour curvature portions applied to flat or nearly flat electrodes. The electrode body 20 terminates in a flat surface 18, which may have a convex curvature portion, which is another common electrode geometry. The curved contour welding surface 19 is configured to achieve an electrode design with a significantly larger contact area. The illustrated contour welding surface 19 is located at the center of the electrode, but may be applied at any position and / or angle. The illustrated contour welding surface is in the form of a linear concave groove perpendicular to the longitudinal axis 31 of the electrode body 20, but any other suitable geometric shape may alternatively be utilized. Furthermore, the orientation of the recessed groove may be perpendicular or non-perpendicular to the longitudinal axis of the electrode body, so long as the area of ​​the recessed groove adequately contacts the curved surface of the workpieces being joined in the welding process. The radius of the curved contoured welding surface 19 is determined to match or nearly match the curvature of the weld workpieces that the electrode is contacting so as to increase the contact area. Figures 4A and 4B show an isometric and top view of an exemplary curved contour on an electrode with a steeply truncated cone geometry. The electrode body 20 terminates in the curved contoured welding surface 19 with a steeply sloping chamfer 21 to reduce the electrode contact area. The larger the welding surface, the higher the power required to produce a weld nugget, and when welding a curved workpiece to a curved workpiece with a closed or open cross section, a too large welding surface may result in a toroidal weld nugget, which is undesirable because it may not meet many commonly accepted quality specifications and may lead to poor performance. 5A and 5B show isometric and plan views of an exemplary curved profile for an electrode having a gently frusto-conical geometry.The electrode body 20 terminates in a welding surface 19 having a curved contour and a gentle chamfer 22 to further reduce the electrode contact area, as required by the application, to achieve the desired weld. A number of different electrode shapes can be used in any configuration to achieve a suitable weld on the workpiece.

[0026] FIG. 6A shows an exemplary welding operation using the curved contour electrode 23 and electrode 26 of the present invention to form a spot weld at a weld location 6 between a curved sheet metal workpiece 7 and a curved closed cross-section workpiece 8. The figure includes electrodes of different geometric shapes, as an example, for the purpose of showing the combinations that can be utilized to achieve a desired weld. The welding apparatus consists of an upper welding gun arm 1 having an electrode holder 2 that holds an electrode 23 with a frusto-conical contour with an electrode shank 3. Electrode cooling with water or any other agent or method, as is commonly used, may or may not be utilized in these embodiments. However, these methods and equipment are not shown. The upper welding gun arm 1 is attached to a welding apparatus (not shown), which may be various types of robotic or non-robotic welding apparatus, including any type of welder capable of providing the welding pressure and current required for the desired application. Similar to the upper welding gun assembly, the lower welding gun arm 13 is also attached to the welding apparatus. The lower welding gun arm 13 also includes an electrode holder 12 that holds a flat cylindrical electrode with a contour 26 with a shank 11.

[0027] During the spot welding operation of FIG. 6A, a welding electrode 23 held by the upper welding gun arm 1 abuts the outer (upper) surface of the curved workpiece 7 at contact area 24, and a welding electrode 26 held by the lower welding gun arm 13 abuts the outer (lower) surface of the curved closed cross-section workpiece 8 at contact area 25. The welding equipment appropriately applies a force L between the electrodes 23, 26 according to a predetermined pressure schedule to press the workpieces 7, 8 together and form the area where the weld nugget 6 is formed. FIG. 6B is a top view of the welding process shown in FIG. 6A. Top The geometry of the electrode 23 and the curved workpiece 7 creates a contact area 24 that is mostly circular, resulting in a large, more circular pressure envelope 27 within which the weld nugget 6 is formed and contained, without ejection. Current passes between the electrode 23 and the opposing electrode 26, which are axially aligned with one another, through the workpieces 7, 8 at the contact points 24, 25, and through the location of the weld nugget 6. FIG. 6C shows an exemplary current path 28 described above. The current I is shown as a direct current flow, with the upper electrode 23 being negative and the lower electrode 26 being positive, but this embodiment applies to any current type and / or welding device polarity. The geometry of the electrodes 23, 26 and the workpieces 7, 8 creates a large contact area 24, 25, resulting in a more distributed current density in the contact area 24, 25. A predetermined amount of current is applied in the welding operation, and an appropriate amount of resistive heating occurs at the weld nugget location 6, which melts the metal in the current path. The welding current is stopped after a predetermined time and the weld nugget 6 is rapidly cooled by diffusing heat to the remaining workpieces 7, 8 and electrodes 23, 26, with or without the aid of a water-cooled electrode. Resolidification of the molten area is what forms the joint between the workpieces. After the welding process, the electrode or workpiece may be moved and a subsequent weld can be formed at the adjacent weld site. FIG. 6D shows an exemplary current path 30 used in the above described welding situation performed on a curved workpiece having an open cross section 29.

[0028] 7A and 7B are schematic diagrams showing exemplary cross-sectional results obtained by the welding operation shown in FIG. 6A. FIG. 7A and 7B show isometric schematic cross-sections in both the transverse and longitudinal cross-sectional directions. The increased contact area 24 between the top electrode 23 and the curved workpiece 7, compared to the conventional electrode of FIG. 1A and FIG. 2B, results in little or no denting of the curved workpiece, and no denting of the interior of the curved, closed or open cross-sectional workpiece 8. Thus, there is no degradation in performance and functionality due to the use of an electrode with a curved profile. The lack of denting is due in part to the situation shown in FIG. 6B. The increased contact area and improved current flow inherent in the geometry of this welding operation results in the formation of a weld nugget 6 that grows equally in all directions, has a more circular weld shape, and improves nugget symmetry between the transverse direction shown in FIG. 7A and the longitudinal direction shown in FIG. 7B. The geometry of the weld formed is similar to that of a weld formed in a standard resistance spot welding process between two flat metal sheets. Such weld uniformity results in isotropic and predictable mechanical properties of the joint.

[0029] As stated above, the electrode design of the present disclosure provides significant advantages over conventional electrode designs when used to weld curved workpieces to curved workpieces having closed or open cross sections. However, there are certain design considerations that should be taken into account in order to maximize the benefits of the present invention. First, the welding surface of the curved profile of the electrode needs to be large enough to achieve a good quality weld. If the welding surface is too small, the nugget size may be insufficient because the pressure envelope is too small for the nugget to grow without ejection, and / or dents may occur in the curved workpiece and / or the curved workpiece having a closed or open cross section. Also, if the welding surface is too large, significantly more power may be required to create a proper weld, and toroidal welds and other problems may occur. Similarly, the radius of the curvature of the curved profile needs to be properly determined for the application. If the curvature is too small, the possibility of dents occurring in the workpiece may increase, or the welding equipment may not function properly due to too small a contact area. Also, if the curvature is too great, the contact area will be reduced, which can create a situation similar to that when using conventional electrodes. As with all commonly used spot welding electrodes, the electrodes of the present invention can show signs of wear and, in some cases, can develop geometries that are no longer acceptable for the application. When this occurs, the electrode may need to be replaced or redressed in an electrode tip dressing process. Coating or Material surface conditions, such as oil, can further affect electrode wear and / or electrode effectiveness.

[0030] Thus, the systems and methods of the present disclosure are well adapted to achieve the objects and advantages described herein as well as those inherent therein. The specific embodiments described above are illustrative only, as the contents of the present disclosure may be modified and implemented in equivalent and different manners apparent to those skilled in the art having the benefit of the teachings herein. Moreover, no limitations are intended to the details of construction or design shown herein, other than as set forth in the following claims. Thus, the specific exemplary embodiments disclosed above may be altered, combined or modified, and all such variations are deemed to be within the scope of the present disclosure. The systems and methods illustrated herein may be suitably implemented without any element not specifically disclosed herein and / or any element disclosed herein. Additionally, although components and methods are described in terms "comprising," "containing," or "having" various elements or steps, the components and methods may be "consisting essentially of" or "consisting of" various elements and steps. Additionally, the terms set forth in the claims are to be given their plain and ordinary meaning unless expressly and unambiguously defined by the patentee. Moreover, the indefinite articles used in the claims are defined herein to mean one or more of the elements they refer to. In the event that there may be any conflict herein in the use of a word or term in this specification and in one or more of the patent documents or other documents incorporated herein by reference, the non-conflicting definition here shall control.

[0031] As described herein, the phrase "at least one of" modifying a series of items, along with the terms "and" or "or" separating any of the items, modifies the series as a whole, rather than each member (i.e., each item). The phrase "at least one of" means including at least one of any one of the items in the series, and / or at least one of any combination of the items, and / or at least one of each item. For example, the phrase "at least one of A, B, and C" or "at least one of A, B, or C" means A only, B only, or C only, any combination of A, B, and C, and / or at least one of each of A, B, and C, respectively.

Claims

1. providing an electrode having a body with a welding surface at one end, the welding surface having a curvature of a curved profile, the curvature covering the entire welding surface, the curvature having the same radius as the curvature of one or more workpieces to be welded; contacting the curvature of the welding surface of the electrode with the one or more workpieces to form at least one electric resistance spot weld in the one or more workpieces; A method of using an electrode comprising:

2. The method of claim 1 , wherein the welder is a robotic or stationary welder.

3. 2. The method of claim 1, wherein the electrode has a dome or cone shape between the body and the welding surface having the curvature.

4. The method of claim 1 , wherein the one or more workpieces have curved surfaces.

5. The method of claim 4 , wherein the one or more workpieces have a closed or open cross-section.

6. The method of claim 1 , wherein the curvature portion is a recessed groove.

7. 7. The method of claim 6, wherein the recessed grooves are linear.

8. 8. The method of claim 7, wherein the recessed groove is perpendicular to the longitudinal axis of the body.

9. providing an electrode having a body with a welding surface at one end, the welding surface having a recessed groove therein, the recessed groove forming an entirety of the welding surface, the recessed groove having the same radius as a portion of curvature of one or more workpieces to be welded; contacting the recessed groove on the welding surface of the electrode with the one or more workpieces to form at least one electric resistance spot weld on the one or more workpieces; A method of using an electrode comprising:

10. The method of claim 9, wherein the welder is a robotic or stationary welder.

11. 10. The method of claim 9, wherein the electrode has a dome or cone shape between the body and the welding surface having the recessed groove.

12. The method of claim 9 , wherein the one or more workpieces have curved surfaces.

13. The method of claim 12 , wherein the one or more workpieces have a closed or open cross-section.

14. 10. The method of claim 9, wherein the recessed grooves are straight.

15. The method of claim 10, wherein the recessed groove is perpendicular to a longitudinal axis of the body.

16. 1. An electrode for performing spot welding of one or more curved workpieces, comprising: The electrode has a body with a welding surface at one end; The welding surface has a curvature portion of a curved profile; The curvature covers the entire welding surface, The electrode, wherein the curved portion has the same radius as the curved portion of the one or more curved workpieces.

17. 17. The electrode of claim 16, comprising a dome or cone shape between said body and said welding surface having said curvature.

18. 20. The electrode of claim 17, wherein the curvature portion is a recessed groove.

19. 20. The electrode of claim 18, wherein the recessed grooves are linear.

20. 20. The electrode of claim 19, wherein the recessed groove is perpendicular to a longitudinal axis of the body.

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