Patent Application
20160346865
The technical field of this disclosure relates generally to resistance spot welding and, more particularly, to resistance spot welding procedures for workpiece stack-ups of different combinations of steel and aluminum workpieces that demand different welding electrodes.
Resistance spot welding is a process used in a number of industries to join together two or more metal workpieces. The automotive industry, for instance, often uses resistance spot welding to join together metal workpieces during the manufacture of a vehicle door, hood, trunk lid, or lift gate, among other vehicle components. Multiple resistance spot welding events are typically performed along a periphery of the metal workpieces or at some other location. While spot welding has been practiced to join together certain similarly-composed metal workpieces—such as steel-to-steel and aluminum-to-aluminum—the desire to incorporate lighter weight materials into a vehicle body structure has created interest in joining steel workpieces to aluminum or aluminum alloy (referred to collectively as “aluminum” for brevity) workpieces by resistance spot welding. Moreover, the ability to resistance spot weld workpiece stack-ups containing different workpiece combinations (e.g., aluminum/aluminum, steel/steel, and aluminum/steel) in an efficient and effective manner would increase production flexibility and reduce manufacturing costs.
Resistance spot welding, in general, relies on the resistance to the flow of electrical current through superposed contacting metal workpieces and across their faying interface to generate heat. To carry out a resistance spot welding process, a set of opposed welding electrodes is clamped at aligned spots on opposite sides of the workpiece stack-up, which typically includes two or three metal workpieces arranged in a lapped configuration, at a weld site. An electrical current is then passed through the metal workpieces from one welding electrode to the other. Resistance to the flow of the electrical current generates heat within the metal workpieces and at their faying interface(s). When the workpiece stack-up includes a steel workpiece and an aluminum workpiece, for instance, the heat generated at the faying interface initiates and grows a molten aluminum alloy weld pool that penetrates into the aluminum workpieces from the faying interface. The molten aluminum alloy weld pool wets the adjacent faying surface of the steel workpiece and, upon cessation of the current flow, solidifies into a weld joint that bonds the workpieces together. When, on the other hand, the workpiece stack-up includes adjacent aluminum workpieces or adjacent steel workpieces, the heat generated at the faying interface initiates and grows a molten aluminum weld pool or a molten steel weld pool, respectively, that penetrates into each workpiece. Upon cessation of the electrical current, the molten weld pool solidify into a weld nugget that fuses the two workpieces together.
Different welding electrodes are oftentimes used depending on whether the welding electrodes will be brought into pressed contact with a steel workpiece or an aluminum workpiece during a resistance spot welding event. Welding electrodes designed for use with steel workpieces typically have a weld face with a diameter of 5 mm to 10 mm and a radius of curvature of 40 mm to flat. Welding electrodes designed for aluminum workpieces, on the other hand, typically have a weld face with a diameter of 6 mm to 20 mm and a radius of curvature of 12 mm to 300 mm. The two classes of welding electrodes may also be composed of different materials. One solution to spot weld adjacent aluminum workpieces or adjacent steel workpieces is via use of dedicated and distinct weld guns—one with welding electrodes for steel, and one with welding electrodes for aluminum—which could be interchanged as needed amid a resistance spot welding process that encounters different stack-ups. Or, as an alternative, a dressing step could be carried out to alter the weld face geometry of a single welding electrode each time the workpiece it would be contacting was changed from steel to aluminum or vice versa. These measures are unsuitable in some cases since they may add cost and time to the overall spot welding process, may occupy floor space that is oftentimes limited in a manufacturing setting, and may pose yet other issues.
A method of resistance spot welding workpiece stack-ups of different combinations of steel workpieces and aluminum or aluminum alloy (“aluminum” for brevity) workpieces is disclosed. The method involves the use of a welding gun arm with a rotatable carrier that supports at least two welding electrodes. The carrier promptly exchanges the welding electrodes via rotation, as needed, as steel and aluminum workpiece combinations are made available for resistance spot welding. Any one of a steel-to-steel workpiece stack-up, an aluminum-to-aluminum workpiece stack-up, or steel-to-aluminum workpiece stack-up can be resistance spot welded together at any time on a single welding operation line with use of the carrier. The carrier may be equipped on only one of the two weld gun arms that together perform resistance spot welding, or it may be equipped on both weld gun arms.
The welding electrodes supported on the carrier may be the same or different in construction. For example, one welding electrode may be configured for spot welding steel workpieces, and the other welding electrode may be configured for spot welding aluminum workpieces. As another example, one welding electrode may be configured for spot welding thin gauge steel workpieces, and the other welding electrode may be configured for spot welding thick gauge steel workpieces. Still further, as another example, one welding electrode may be configured for spot welding thin gauge aluminum workpieces, and the other welding electrode may be configured for spot welding thick gauge aluminum workpieces. Another example contemplates that both welding electrodes could be configured for spot welding workpieces of similar materials and similar constructions.
As it exchanges the welding electrodes, the carrier may be indexed to different positions in order to use the welding electrode most suited for the particular workpiece stack-up being resistance spot welded (e.g., steel-to-steel, an aluminum-to-aluminum, or steel-to-aluminum) at that time. The carrier may be indexed to each of its different positions by an indexing feature that may include many designs and constructions including, for example, a protrusion and a recess mated together. For example, a protrusion may extend from the weld gun arm and a recess associated with each of the different positions of the carrier may be located in the carrier. In this example, the protrusion may be received in and mated with one of the recesses to provide an indexing feature that indexes the carrier to one position, and then, after rotation of the carrier, the same protrusion may be received in a mated with another recess to provide another indexing feature that indexes the carrier to another position. Of course, in another example, a recess may be located in the weld gun arm and protrusion associated with each of the different positions of the carrier may extend from the carrier to achieve the same indexing mechanics.
The indexing feature may also participate in the resistance spot welding process. In particular, during a resistance spot welding event, the indexing feature may be involved in passing electrical current between the welding arm and the carrier and, additionally, may bear forces exerted on the carrier. When the indexing feature is a protrusion and a recess mated together, for example, electrical current may be passed between the weld gun arm and the carrier through the mated protrusion/recess in order to facilitate passage of the electrical current through a workpiece stack-up using the welding electrode associated with the indexed position of the carrier. And, during such time that electrical current is being passed through the workpiece stack-up, forces (e.g., from the clamping force imposed on the welding electrodes by the weld gun arms) exerted on the carrier may be borne by the mated protrusion/recess. In one specific instance, the carrier is forced toward the weld gun arm—with the protrusion and the recess mated together to provide an indexing feature—to overcome an oppositely-directed biasing force applied against the carrier.
The methods and assemblies detailed in this description resolve shortcomings encountered when resistance spot welding workpiece stack-ups of different combinations of steel workpieces and aluminum or aluminum alloy (again, referred to collectively as “aluminum”) workpieces. A weld gun arm is described that has a rotatable carrier supporting a pair of welding electrodes. One welding electrode is preferably suited for making contact with a steel workpiece while the other welding electrode is preferably suited for making contact with an aluminum workpiece. The carrier is constructed to promptly exchange the welding electrodes, as needed, as steel and aluminum workpiece combinations become available for resistance spot welding. Workpiece stack-ups comprised of steel-to-steel workpieces, aluminum-to-aluminum workpieces, and steel-to-aluminum workpieces can be resistance spot welded at any time and in any order in a single resistance spot welding operation line more efficiently and flexibly than previously possible. Indeed, interchanging dedicated and distinct weld guns is no longer required, nor is a dressing step needed to alter and repurpose the weld face geometry of a single welding electrode based on the composition of the workpiece it will be pressed against during spot welding (although the welding electrodes supported on the carrier may still be periodically redressed to remove contaminants and to recreate their weld faces).
The first workpiece 14 can be a coated or uncoated steel substrate or a coated or uncoated aluminum substrate, and the second workpiece 16 can likewise be a coated or uncoated steel substrate or a coated or uncoated aluminum substrate. Depending on the compositions of their constituent workpieces, the workpiece stack-up 12 could be made up of all steel workpieces, all aluminum workpieces, or one or more steel workpieces and one or more aluminum workpieces. A steel workpiece includes a steel substrate that can be galvanized (i.e., zinc coated), aluminum coated, or bare (i.e., uncoated). The coated or uncoated steel substrate may be composed of any of a wide variety of steels including a low carbon steel (also referred to as mild steel), an interstitial-free (IF) steel, a high-strength low-alloy (HSLA) steel, or an advanced high strength steel (AHSS) such as dual phase (DP) steel, transformation-induced plasticity (TRIP) steel, twinning-induced plasticity (TWIP) steel, complex-phase (CP) steel, martensitic (MART) steel, hot-formed (HF) steel, and press-hardened (PHS) steel.
An aluminum workpiece includes an aluminum substrate that may be coated or bare (i.e., no natural or applied surface coatings). The coated or uncoated aluminum alloy substrate may be composed of aluminum, an aluminum-magnesium alloy, an aluminum-silicon alloy, an aluminum-magnesium-silicon alloy, or an aluminum-zinc alloy. The aluminum substrate, for example, may be composed of a 4xxx, 5xxx, 6xxx, or 7xxx series wrought aluminum alloy sheet layer, or a 4xx.x, 5xx.x, or 7xx.x series aluminum alloy casting, and may further be employed in a variety of tempers including annealed (O), strain hardened (H), and solution heat treated (T). Some more specific kinds of aluminum that can be used as the aluminum alloy substrate include, but are not limited to, 5754 aluminum-magnesium alloy, 6022 aluminum-magnesium-silicon alloy, 7003 aluminum-zinc alloy, and Al-10Si-Mg aluminum die casting alloy. In addition, these and other suitable aluminum materials may be coated with their natural refractory oxide layer(s), zinc, or a conversion coating, and weld-through adhesives or sealers that are normally used in resistance spot welding operations may also be present.
Still referring to
Amid resistance spot welding operations, the weld gun arms 18, 20 press their respective welding electrodes against opposite sides and outer surfaces of the overlaid workpieces 14, 16 at a weld site 22, with accompanying weld faces of the electrodes aligned across and with each other. A faying interface 24 is located between the first and second workpieces 14, 16 at confronting and abutting faying surfaces of the workpieces 14, 16. The faying interface 24 encompasses instances of direct contact between the workpiece faying surfaces, as well as instances of indirect contact where the faying surfaces are not in direct contact but are in close enough proximity to each another—such as when a thin layer of adhesive, sealer, or some other intermediate material is present—that resistance spot welding can still be practiced.
In the embodiment presented by
For an aluminum workpiece, on the other hand, the first welding electrode 26 can possess a weld face geometry with a diameter between 6 mm to 20 mm, or more narrowly between 8 mm to 12 mm, and a radius of curvature between 12 mm to 300 mm, or more narrowly between 20 mm to 150 mm. And, for aluminum, the first welding electrode 26 can be composed of a suitable copper alloy such as C15000, can be composed so that at least its weld face is composed of a refractory-based material such as a tungsten-copper alloy. Still, other features of the first welding electrode 26 may change depending on whether the electrode 26 confronts and is to be pressed against an aluminum or steel workpiece. For instance, for an aluminum workpiece, the weld face of the first welding electrode 26 may have surface features to penetrate oxide layers formed on the outer surface of the aluminum workpiece. Examples include texturing and designs and constructions such as those described in U.S. Pat. Nos. 6,861,609; 8,222,560; 8,274,010; 8,436,269; 8,525,066; and 8,927,894; and in U.S. patent application publication number 2014/0076859.
The second weld gun arm 20 has a different design and construction than the first weld gun arm 18. The second weld gun arm 20 can remain stationary or can move during the welding action. But perhaps most conspicuously, the second weld gun arm 20 carries a pair of welding electrodes instead of just one. The second weld gun arm 20 could have more than two welding electrodes in other embodiments. In
The second and third welding electrodes 28, 30 are not necessarily limited to constructions that can accommodate pressed engagement with steel workpieces and aluminum workpieces, respectively, as shown in
Referring particularly to
The kind of process efficiency and flexibility attributed to the carrier 32 may be regularly called for in a welding operation line involving vehicle components where steel-to-steel, aluminum-to-aluminum, and steel-to-aluminum workpieces are increasingly more common among components of different makeup and materials. Exchanging the second and third welding electrodes 28, 30 through rotation of the carrier 32 can occur faster than interchanging dedicated and distinct weld guns or repeatedly dressing a single welding electrode to alter its weld face geometries to match the composition of the workpiece it will be brought into contact with. The second weld gun arm 20 and its carrier 32, moreover, are considerably less costly than furnishing dedicated and distinct welding machines for resistance spot welding the different workpiece combinations (steel-to-steel, aluminum-to-aluminum, and steel-to-aluminum) that may be contained in the workpiece stack-up 12. Furthermore, having a single weld gun arm with exchangeable welding electrodes frees-up manufacturing floor space that might otherwise be occupied by weld guns meant for aluminum workpieces and weld guns meant for steel workpieces.
In the embodiment shown in
The first position is shown in
Between the first and second positions, the carrier 32 swivels over an imaginary swivel plane 300, as shown best in
The carrier 32 can have different designs and constructions, which may be dictated by the design and construction of the second weld gun arm 20. In the embodiment illustrated in
In this embodiment, the carrier 32 has a stem 42 and a base 44, and is seated in a cutout 40 of the body 34. In other embodiments, the cutout 40 need not be provided. The stem 42 can be coupled to the body 34 for rotation as the carrier 32 moves, and can be fitted with bearings to assist the rotation. An electrically insulating cover or material such as an adhesive, coating, or jacket could be set around the stem 42 in order to shield the stem and preclude electrical current flow between the body 34 of the second weld gun arm 20 and the stem 42. The base 44 is centered about the stem 42 and can support the second and third welding electrodes 28, 30 near its ends by any type of suitable mounting. The base 44 has a lengthwise extension that generally matches that of the cutout 40, and has a widthwise extension that is narrower than that of the body 34. The lengthwise and widthwise extensions of the base 44, as well as its size and shape, can configure the base 44 appropriately to lack or minimize structures that might interfere with the resistance spot welding procedure. Further, in both the first and second positions, the lengthwise extent of the base 44 can be in general alignment with the lengthwise extent of the body 34 so as to again avoid potential interference with the welding procedure. This alignment is perhaps shown best by the top view of
The first and second welding electrodes 28, 30, the carrier 32, the base 44, and the second gun arm 20 can be arranged at various angles relative to the upper gun arm 18. For instance, although not shown specifically in the Figures, the first and second welding electrodes 28, 30, the carrier 32, the base 44, and the second gun arm 20 can be angled away or tilted from the second workpiece 16 to further distance the welding electrode that is not being used to exchange current from the second workpiece 16 if additional clearance is desired. Such tilting can be accommodated by angling the welding electrodes 28, 30 on the carrier 32—by use of fixed mounting features on the carrier 32 or permanent or temporary adaptors—to counter the tilt of the second gun arm 20 in order to maintain contact between the weld face of whichever welding electrode is being used to exchange current and the second workpiece 16.
The carrier 32 can have yet additional designs and constructions that facilitate its functionality during use. For example, the carrier 32 could be actuated between the first and second positions by a rack-and-pinion assembly, a pneumatic or hydraulic actuator assembly, a servomotor, or some other type of actuation technique. The carrier 32 could have a cooling system meant to keep the carrier and its welding electrodes 28, 30 at an acceptable temperature and avoid overheating amid welding. The cooling system could include external cooling lines 46 and internal cooling lines for circulating coolant through the carrier 32 and to the electrodes 28, 30. The coolant is preferably water but, of course, is not so limited and could be something else.
Depending on how the carrier 32 is actuated, the carrier 32 may be indexed at the first and second positions. The indexing can be carried out at each of the first and second positions by an indexing feature such as a protrusion and a recess mated together. In the embodiment shown best in
The second and third recesses 50, 52 are shaped to receive insertion of the protrusion 48 and, as such, have a complementary rounded shape to that of the protrusion 48. Here, the recesses 50, 52 are depressions set into the bottom surface 54 of the carrier 32, with the second recess 50 being located underneath the second welding electrode 28 and the third recess 52 being located underneath the second welding electrode 30.
In addition to its use in indexing, the indexing feature (comprised in this embodiment by the protrusion 48 and one of the recesses 50, 52) can also be used to pass electrical current during welding, to bear forces exerted during welding, or both. To pass electrical current, the protrusion 48 may be composed of a material exhibiting a suitable electrical conductivity such as the materials set forth above with respect to the carrier 32—e.g., a hard copper alloy material like a beryllium-copper RWMA class 3 alloy—such that electrical current can pass between the protrusion and the body 34 of the second weld gun arm 20 and ultimately through the carrier 32 when an indexing feature is established. For instance, when the carrier 32 is indexed in the first position as shown in
Electrical current is preferably delivered to the carrier 32 only by way of the mated protrusion 48 and recess 50 or 52. Indeed, as described above, the stem 42 of the carrier 32 is electrically insulated and therefore cannot exchange electrical current with the body 34 of the second weld gun arm 20. Moreover, to further isolate the flow of current through an indexing feature only, a gap 56 is present between the bottom surface 54 of the carrier 32 and a confronting surface of the body 34. This gap 56 precludes unwanted physical contact between the carrier 32 and the body 34 and is large enough to prevent electric discharge between the carrier 32 and the body 34 given the current levels employed in during resistance spot welding events. The only physical contact between the carrier 32 and body 34 during resistance spot welding, and thus the only conduit for electrical current flow between the two, is through the protrusion 48 and one of the second or third recesses 50 or 52 depending on the position of the carrier (first or second indexed position).
When the second weld gun arm 20 presses the first or second welding electrode 28, 30 against the second workpiece 16, forces are exerted on the carrier 32. In this embodiment, between the carrier 32 and body 34, those forces are borne by the mated protrusion 48 and recess 50 or 52. The protrusion 48 and recesses 50, 52 are designed and constructed to possess sufficient robustness to bear the exerted forces associated with repetitive spot welding events. The forces are therefore transmitted from the carrier 32 and to the body 34 by way of the mated protrusion 48 and recess 50 or 52.
Furthermore, one or more springs 58 may be provided between the bottom surface 54 of the carrier 32 and the body 34 of the second weld gun arm 20 to assist separating the mated protrusion 48 and the recess 50 or 52 and to bring them to an unmated state. The one or more springs 58 yield to the forces exerted on the carrier 32 when the second or third welding electrodes 28, 30 is clamped against the second workpiece 16 in preparation for and during spot welding, which in turn establishes mating between the protrusion 48 and recess 50 or 52. Conversely, when second or third welding electrodes 28, 30 is not clamped against the second workpiece 16, the one or more springs 58 bias the carrier 32 and body 34 away from each other. The protrusion 48 and recess 50 or 52 are thus more easily brought to the unmated state with the spring(s) 58, and clearance is therefore provided for the carrier 32 to rotate and exchange the first and second welding electrodes 28, 30 when desired.
Having the indexing feature pass electrical current and/or bear forces removes the need for a construction elsewhere in the carrier 32 and the body 34 to fulfill these same functionalities. Previously-known constructions for passing electrical current and enduring forces for similar purposes are more involved than desired in some cases. For instance, cables and laminated shunts are sometimes used for passing electrical current and various structures are used for enduring forces. While the cables, laminated shunts, and structures may still be suitable in some embodiments, the protrusion 48 and recesses 50, 52 are comparatively much simpler.
A first weld gun arm 160 of the assembly 110, however, has a different design and construction than the first weld gun arm 18 of
Lastly, it should be appreciated that the Figures depict the components of the resistance spot welding assembly 10 schematically, and that certain designs and constructions will inevitably be altered in production. For instance, the width, length, and shape of the carrier 32 and its base 44 can be modified. In applications in which the carrier 32 will be manipulated at a deep overlap with the workpiece stack-up 12 for performing a resistance spot weld, the base 44 can be lengthened considerably more than what is shown so that the non-working electrode is spaced away from a terminal edge of the workpiece stack-up 12 and would remain free-of-contact with the workpiece stack-up 12. Alternatively, as shown in
The above description of preferred exemplary embodiments and related examples are merely descriptive in nature; they are not intended to limit the scope of the claims that follow. Each of the terms used in the appended claims should be given its ordinary and customary meaning unless specifically and unambiguously stated otherwise in the specification.
