Patent Application
20190314915
The present disclosure relates generally to joining metal workpieces together and, more particularly, relates to resistance spot welding steel workpieces together that have surface coatings residing on them.
Resistance spot welding is a process employed by a number of industries to join together metal workpieces. The automotive industry, for instance, uses resistance spot welding to join together steel workpieces during the manufacture of structural frame members (e.g., pillar reinforcements, beam reinforcements, and cross-member reinforcements) and during the manufacture of closure members (e.g., doors, hoods, trunk lids, and lift gates), among other uses. Advanced high-strength steels (AHSS) are a family of steel materials that have been introduced more recently for certain automobile members. Surface coatings are often provided on automobile members—whether the members are made of AHSS materials or other steel materials—for protection against exposure to the environment outside of the associated automobile, and for other reasons.
In an embodiment, a method of resistance spot welding a workpiece stack-up includes several steps. The workpiece stack-up includes a first steel workpiece and a second steel workpiece. One step involves providing the first steel workpiece and providing the second steel workpiece. The first steel workpiece has a first surface coating. Another step involves applying a filler metal to a first surface of the first steel workpiece. Another step involves bringing the second steel workpiece to the first steel workpiece. A second surface of the second steel workpiece adjoins the filler metal. Yet another step involves clamping a first welding electrode and a second welding electrode on the first and second steel workpieces at the filler metal. Another step involves passing electrical current between the first and second welding electrodes and through the first and second steel workpieces. The electrical current also passes through the filler metal. And yet another step involves terminating the passage of electrical current in order to establish a weld joint between the first and second steel workpieces.
In an embodiment, the first steel workpiece is composed of an advanced high-strength steel (AHSS) material, and the second steel workpiece is likewise composed of an advanced high-strength steel (AHSS) material.
In an embodiment, the first surface coating is composed of a zinc (Zn) material.
In an embodiment, the first surface coating resides on a first exterior surface of the first steel workpiece. The first exterior surface is situated opposite the first surface to which the filler metal is applied.
In an embodiment, the second steel workpiece has a second surface coating. The second surface coating resides on a second exterior surface of the second steel workpiece. The second exterior surface is situated opposite the second surface to which the filler metal is adjoined.
In an embodiment, the filler metal is composed of a low-carbon steel material.
In an embodiment, the step of applying the filler metal involves coating the first surface of the first steel workpiece with the filler metal by way of thermal spraying.
In an embodiment, the step of applying the filler metal involves layering the filler metal on the first surface of the first steel workpiece by way of additive manufacturing.
In an embodiment, layering the filler metal on the first surface of the first steel workpiece involves 3D printing.
In an embodiment, the established weld joint includes material of the first steel workpiece, further includes material of the second steel workpiece, and also includes material of the filler metal.
In an embodiment, the first welding electrode, the second welding electrode, or both of the first and second welding electrodes, have a weld face with a radius of curvature that ranges between approximately 20 millimeters (mm) and substantially flat.
In an embodiment, the filler metal has a thickness dimension that ranges between approximately 0.05 millimeters (mm) and 2.0 mm.
In an embodiment, a method of resistance spot welding a workpiece stack-up includes several steps. The workpiece stack-up includes a first steel workpiece and a second steel workpiece. One step involves providing the first steel workpiece and providing the second steel workpiece. The first steel workpiece is composed of an advanced high-strength steel (AHSS) material, and the second steel workpiece is likewise composed of an advanced high-strength steel (AHSS) material. The first steel workpiece has a first faying surface, and has a first exterior surface situated opposite the first faying surface. Similarly, the second steel workpiece has a second faying surface, and has a second exterior surface situated opposite the second faying surface. A first surface coating resides on the first exterior surface, and a second surface coating resides on the second exterior surface. Another step involves layering a filler metal on the first faying surface of the first steel workpiece by way of additive manufacturing. Another step involves bringing the second steel workpiece to the first steel workpiece. The second faying surface of the second steel workpiece adjoins the filler metal. Yet another step involves clamping a first welding electrode and a second welding electrode on the first and second steel workpieces at the filler metal. Another step involves passing electrical current between the first and second welding electrodes. And yet another step involves terminating the passage of electrical current in order to establish a weld joint between the first and second steel workpieces.
In an embodiment, the first surface coating is composed of a zinc (Zn) material, and the second surface coating is likewise composed of a zinc (Zn) material.
In an embodiment, the filler metal is composed of a low-carbon steel material.
In an embodiment, the filler metal has a thickness dimension that ranges between approximately 0.05 millimeters (mm) and 2.0 mm.
In an embodiment, layering the filler metal on the first surface of the first steel workpiece involves 3D printing.
In an embodiment, the established weld joint includes material of the first steel workpiece, further includes material of the second steel workpiece, and also includes material of the filler metal.
In an embodiment, a method of resistance spot welding a workpiece stack-up includes several steps. The workpiece stack-up includes a first steel workpiece and a second steel workpiece. One step involves providing the first steel workpiece and providing the second steel workpiece. The first steel workpiece is composed of an advanced high-strength steel (AHSS) material, and the second steel workpiece is likewise composed of an advanced high-strength steel (AHSS) material. The first steel workpiece has a first faying surface, and has a first exterior surface situated opposite the first faying surface. Similarly, the second steel workpiece has a second faying surface, and has a second exterior surface situated opposite the second faying surface. A first surface coating resides on the first exterior surface, and a second surface coating resides on the second exterior surface. The first surface coating is composed of a zinc (Zn) material, and the second surface coating is similarly composed of a zinc (Zn) material. Another step involves layering a filler metal on the first faying surface of the first steel workpiece by way of additive manufacturing. The filler metal is composed of a low-carbon steel material. Another step involves bringing the second steel workpiece to the first steel workpiece. The second faying surface of the second steel workpiece adjoins the filler metal. Yet another step involves clamping a first welding electrode and a second welding electrode on the first and second steel workpieces at the filler metal. Another step involves passing electrical current between the first and second welding electrodes. And yet another step involves terminating the passage of electrical current in order to establish a weld joint between the first and second steel workpieces. The established weld joint includes material of the first steel workpiece, further includes material of the second steel workpiece, and also includes material of the filler metal.
In an embodiment, the filler metal has a thickness dimension that ranges between approximately 0.05 millimeters (mm) and 2.0 mm.
One or more aspects of the disclosure will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:
The methods and assemblies detailed in this description resolve shortcomings encountered when resistance spot welding workpiece stack-ups that include one or more steel workpieces with surface coatings. A filler metal is added to the workpiece stack-ups amid the resistance spot welding process. The addition has been shown to minimize—and in some cases altogether preclude—fracturing and cracking resulting from liquid metal embrittlement (LME) and caused during resistance spot welding procedures. Workpieces of coated advanced high-strength steel (AHSS) materials, in particular, have demonstrated minimization and preclusion of LME fracturing and cracking when subject of the methods and assemblies detailed herein. The resistance spot welding process described below hence effectively joins steel workpieces with an improved joint quality and joint strength. The advancements, it is thought, are due in part to lower localized temperatures accompanying the resistance spot welding process with the addition of the filler material, among other possible rationales. And while the methods and assemblies are described in the context of automotive members, skilled artisans will appreciate that the methods and assemblies are not so limited and can be employed in other contexts such as aerospace, marine, railway, and industrial equipment applications, among others.
Referring now to
In the embodiment presented, the first and second steel workpieces 14, 16 are coated to provide a protective barrier against certain unwanted conditions, such as against corrosion that could result from exposure to the environment outside of the associated automobile. The first steel workpiece 14 has a first surface coating 32 residing on its first exterior surface 24, and the second steel workpiece 16 has a second surface coating 34 residing on its second exterior surface 28 (the surface coatings can be layered so thinly, e.g., 50 μm or less, that a separate and distinct depiction in the FIGS. has not been illustrated). In addition to the first and second exterior surfaces 24, 28, the first and second surface coatings 32, 34 can reside on other surfaces of the first and second steel workpieces 14, 16, including on the first and second faying surfaces 26, 30. The first and second surface coatings 32, 34 can be composed of zinc (galvanized), a zinc-iron alloy (galvanneal), a zinc-nickel alloy, nickel, aluminum, an aluminum-magnesium alloy, an aluminum-zinc alloy, or an aluminum-silicon alloy; still, other compositions are possible in other examples. In other embodiments, only one of the workpieces of a particular workpiece stack-up need have a surface coating; for instance, in this embodiment the second steel workpiece 16 need not have a surface coating, and instead could be a bare steel workpiece lacking a surface coating.
Still referring to
Referring now to
In the automotive industry, as well as other industries, steel workpieces are joined together by resistance spot welding processes. The steel workpieces can be a part of larger automobile member assemblies, or can themselves constitute the automobile members—examples of automobile members include, but are not limited to, structural frame members (e.g., pillar and beam and cross-member reinforcements) and closure members (e.g., doors, hoods, trunk lids, and lift gates). Surface coatings are commonly provided on surfaces of the automobile members, including the surface coatings set forth above, prior to performing the resistance spot welding processes. While productive, drawbacks such as microscopic fracturing and cracking have been observed in certain cases in which resistance spot welding is carried out on steel workpieces with the surface coatings. The drawbacks have been particularly observed in workpieces of coated advanced high-strength steel (AHSS) materials.
Referring now to
The resistance spot welding process set forth herein resolves these drawbacks. In different embodiments, the resistance spot welding process can have more, less, and/or different steps and parameters than those detailed in this description, and the steps can be performed in different orders than described. In the embodiment of
A second step 76 of the resistance spot welding method 72 involves applying a filler metal 78 to a first surface 80 (in this case, the first faying surface 26) of the first steel workpiece 14. The filler metal 78 can be composed of various metal materials depending in part upon the material compositions of the first and second steel workpieces 14, 16 and compatibility therebetween. When the first and second steel workpieces 14, 16 are made of an AHSS steel, for instance, the filler metal 78 can have a composition of a low-carbon steel material. Still, other compositions are possible in other embodiments. The filler metal 78 can be applied to the first surface 80 by way of different application technologies and techniques. In an embodiment, the filler metal 78 is coated on the first surface 80 via a thermal spraying process in which the filler metal 78 is sprayed on the first surface 80 in a molten or semi-molten state. Types of thermal spraying processes that may be suitable in a given embodiment include, but are not limited to, plasma spraying, wire arc spraying, and laser plasma spraying. Still, other types of thermal spraying are possible in other embodiments. Further, the filler metal 78 can be layered on the first surface 80 via an additive manufacturing process. In an embodiment, the filler metal 78 is added to the first surface 80 layer-upon-layer by 3D printing. Still, other types of additive manufacturing processes are possible in other embodiments.
In the second step 76 of the resistance spot welding method 72, the filler metal 78 can be applied to the first surface 80 in different patterns and with different thicknesses. In certain embodiments, the filler metal 78 can be configured in an annular pattern, can be configured in a lined pattern, can be configured in a crossed pattern, can be configured in a solidly-filled pattern, and/or can be configured in a dotted pattern. Still, other patterns are possible in other embodiments. Whatever pattern configuration is prepared, the precise thickness dimension of the filler metal 78 applied in this step may be based upon—among other possible influences—lowering the localized temperatures attendant in subsequent steps of the resistance spot welding method 72 at abutment interfaces between the first and second welding electrodes 36, 38 and the first and second steel workpieces 14, 16, as described more below. In the second step 76, a thickness 77 of the filler metal 78 can have a value that ranges between approximately 0.05 mm and 2.0 mm. It has been determined that keeping the thickness value within this range effectively lowers the localized temperatures at the abutment interfaces between the first and second welding electrodes 36, 38 and the first and second steel workpieces 14, 16. Still, other thickness ranges are possible in other embodiments. In the same manner, the precise amount of the filler metal 78 applied in this step may be based upon—among other possible influences—lowering the localized temperatures attendant in subsequent steps of the resistance spot welding method 72 at abutment interfaces between the first and second welding electrodes 36, 38 and the first and second steel workpieces 14, 16.
A third step 82 of the resistance spot welding method 72 involves bringing the second steel workpiece 16 to the first steel workpiece 14 and over the applied filler metal 78. A second surface 84 (in this case, the second faying surface 30) of the second steel workpiece 16 comes into direct abutment with, and adjoins, the filler metal 78. In this step, the first and second steel workpieces 14, 16 overlap and overlie each other with the filler metal 78 sandwiched therebetween. A fourth step 86 of the resistance spot welding method 72 involves clamping the first and second welding electrodes 36, 38 on the first and second steel workpieces 14, 16 at the weld site 18 and over the sandwiched filler metal 78. The first and second welding electrodes 36, 38 make direct contact with the first and second exterior surfaces 24, 28, as depicted in
As described, the resistance spot welding method 72 resolves the drawbacks described above and encountered when joining coated steel workpieces like the first and second steel workpieces 14, 16 with the first and second surface coatings 32, 34. The addition of the filler metal 78 has proven to lower the localized temperatures in the fifth step 88 at the abutment interfaces between weld face surfaces of the first and second welding electrodes 36, 38 and the first and second exterior surfaces 24, 28 of the first and second steel workpieces 14, 16. The localized temperatures generated at these abutment interfaces can be decreased to 1,200° C. in some embodiments. The filler metal 78 raises the number of faying interfaces present in the workpiece stack-up 12 (i.e., a first faying interface is produced between the first faying surface 26 and the confronting and opposed surface of the filler metal 78, and a second faying interface is produced between the second faying surface 30 and the confronting and opposed surface of the filler metal 78) compared to a workpiece stack-up lacking the filler metal 78. The greater number of faying interfaces offers greater electrical resistance amid the fifth step 88 which can increase and may concentrate the localized temperatures thereat, and may more readily initiate and establish a weld joint like the weld joint 90. Further, in at least some embodiments, a minute gap can exist between the filler metal 78 and the respective first and second faying surfaces 26, 30 at the first and second faying interfaces, which again offers greater electrical resistance amid the fifth step 88. In some cases, this means that a weld schedule with a more abbreviated weld current duration can be employed. And the shortened weld time can lessen the heat at the abutment interfaces, and can reduce the propensity of zinc (Zn) diffusing into the grain boundary of the austenite microstructure (if a particular surface coating indeed contains zinc). In a similar way, the addition of the filler metal 78—and hence the addition to the overall thickness of the workpiece stack-up 12—can abate the degree of heat that propagates to the abutment interfaces. With an increased overall thickness, a central point of heat propagation is hence displaced to a central region of the filler metal 78, as opposed to the central point being situated at the first and second faying surfaces 26, 30. Furthermore, because of the lowered localized temperatures at the abutment interfaces, the thermal expansion/contraction tensile stresses experienced at the abutment interfaces may in turn be diminished. As a result, the fracturing and cracking associated with LME and previously observed is minimized or altogether precluded by the resistance spot welding method 72.
The microstructure of
It is to be understood that the foregoing is a description of one or more aspects of the disclosure. The disclosure is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the disclosure or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.
As used in this specification and claims, the terms “e.g.,” “for example,” “for instance,” “such as,” and “like,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.
