REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63/367,409, filed on June 30, 2022, and entitled SYSTEMS AND METHODS FOR IMPROVING RESISTANCE SPOT WELDING WITH CAST ALUMINUM, the content of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

[0002] This application relates to resistance spot welding, and, more particularly, to control systems and methods for improving aluminum resistance spot welding.

BACKGROUND

[0003] Metal manufacturing can involve welding metal substrates or metal alloy substrates together to form various parts or components of a final product. Various techniques or processes, including, for example, resistance spot welding, can be used to weld the metal substrates. Resistance spot welding can involve positioning metal substrates between electrodes and using the electrodes to apply a compressive force and an electric current to the metal substrates. Heat produced from a resistance of the metal substrates to the electric current, along with the compressive force of the electrodes, can be used to join the metal substrates at the interface, forming local cohesive zones known as weld nuggets. However, certain metals may be difficult to weld with traditional welding techniques, and it may be difficult to weld together two different types of metal substrates. For example, traditional resistance spot welding of cast aluminum to an aluminum sheet may suffer from inside cracks (causing strength and fatigue problems), limited penetration of the sheet (causing strength problems), welding expulsion, and bad tip life of the electrodes, among other problems.

SUMMARY

[0004] The terms “invention,” “the invention,” “this invention” and “the present invention” used in this patent are intended to refer broadly to all of the subject matter of this patent and the patent claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. Embodiments of the invention covered by this patent are defined by the claims below, not this summary. This summary is a high-level overview of various embodiments of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, noris it intended to be usedin isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this patent, any or all drawings, and each claim.

[0005] According to certain embodiments, a method for joining metal substrates includes providing a first electrode and a second electrode where at least one characteristic of the first electrode is different from the second electrode. The method includes applying a compressive force to at least two overlapping metal substrates using the first electrode and the second electrode. In certain embodiments, at least one metal substrate of the at least two metal substrates includes aluminum or an aluminum alloy. The method includes, over a first time period, applying an electric current at a first level and ramping up the electric current from the first level to a second level greater than the first level, and, after the first time period, applying the electric current at the second level for a second time period. In various embodiments, the method includes, after the second time period, ramping down the electric current from the second level over a third time period. A rate of ramping down the electric current is less than a rate of the ramping up of the electric current over the first time period.

[0006] According to some embodiments, a method for joining metal substrates includes providing a first electrode and a second electrode where at least one characteristic of the first electrode is different from the second electrode. The method includes applying a compressive force to at least two overlapping metal substrates using the first electrode and the second electrode. In certain embodiments, at least one metal substrate of the at least two metal substrates comprises aluminum or an aluminum alloy. The method includes, over a first time period, applying an electric current at a first level and ramping up the electric current from the first level to a second level greater than the first level. The method also includes, after the first time period, applying the electric current at a third level for a second time period, and, after the second time period, ramping down the electric current from the third level over a third time period. [0007] Accordingto various embodiments, a method for joining metal substrates includes providing a first electrode and a second electrode, where at least one characteristic of the first electrode is different from the second electrode. The method includes applying a compressive force to at least two overlapping metal substrates using the first electrode and the second electrode. In some embodiments, at least one metal substrate of the at least two metal substrates comprises aluminum or an aluminum alloy. The method includes applying an electric current by: over a first time period, ramping up the electric current at a ramp-up rate; over a second time period after the first time period, applying the electric current at a welding level; and over a third time period after the second time period, ramping down the electric current at a ramp-down rate. In some embodiments, the ramp-down rate is less than the ramp- up rate.

[0008] An improved weld may be formed by the methods described herein. In some embodiments, the weld is formed in the at least two metal substrates where a first metal substrate of the at least two metal substrates is an aluminum sheet and a second metal substrate of the at least two metal substrates is a cast aluminum.

[0009] Various implementations described in the present disclosure can include additional systems, methods, features, and advantages, which cannot necessarily be expressly disclosed herein but will be apparent to one of ordinary skill in the art upon examination of the following detailed description and accompanying drawings. It is intended that all such systems, methods, features, and advantages be included within the present disclosure and protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The features and components of the following figures are illustrated to emphasizethe general principles of the present disclosure. Corresponding features and components throughout the figures can be designated by matching reference characters for the sake of consistency and clarity.

[0011] FIG. 1 illustrates a resistance spot welding system according to embodiments.

[0012] FIG. 2 illustrates an electrode of the resistance spot welding system of FIG. 1.

[0013] FIG. 3 A illustrates a portion of a stamping tool according to embodiments. [0014] FIG. 3B illustrates an electrode of the resistance spot welding system of FIG. 1 stamped using the stamping tool of FIG. 3 A.

[0015] FIG. 4A illustrates a portion of a stamping tool according to embodiments.

[0016] FIG. 4B illustrates an electrode of the resistance spot welding system of FIG. 1 stamped using the stamping tool of FIG. 4 A.

[0017] FIG. 5 illustrates a resistance spot welding system according to embodiments.

[0018] FIG. 6 is a graph depicting a welding curve schedule according to embodiments.

[0019] FIG. 7 is a graph depicting another welding curve schedule according to embodiments.

[0020] FIG. 8 illustrates a method of joining metal substrates according to embodiments.

[0021] FIG. 9 illustrates a weld formed via resistance spot welding according to embodiments

[0022] FIG. 10 illustrates a weld formed via resistance spot welding according to embodiments

[0023] FIG. 11 illustrates a weld formed via resistance spot welding according to embodiments

DETAILED DESCRIPTION

[0024] Described herein are methods and systems for joining two or more metal substrates together by resistance spot welding. According to systems and methods described herein, during a welding technique, a compressive force and an electric current can be applied to the metal substrates via at least two electrodes. In certain embodiments, at least one characteristic of a first electrode of the at least two electrodes may be different from that of a second electrode of the at least two electrodes. In some embodiments, the at least one characteristic may include, but is not limited to, a topography of an electrode tip and/or a tip radius of the electrode tip.

[0025] Applying the compressive force and the electrical current may include controlling an amount of current pursuant to a welding curve provided herein while applying an amount of the compressive force to the metal substrates. Controlling the amount of current pursuant to the welding curves described herein along with the asymmetrical electrodes may reduce expulsion during a ramping up of the current and reduce crack sensitivity during a ramping down of the current.

[0026] The systems and methods provided herein may be useful when one or both of the metal substrates are aluminum or an aluminum alloy. The systems and methods described herein may be particularly useful for joining cast aluminum with aluminum sheet. As nonlimiting examples, the systems and methods described herein may produce welds in metal substrates that include a cast aluminum being joined with an aluminum sheet having an improved penetration in the aluminum sheet. In some non-limiting examples, welds formed according to the methods described herein may be approximately centered between the cast aluminum and the aluminum sheets. In a non-limiting example, a weld formed according to the methods and systems described herein may penetrate more than about 10% the thickness of the aluminum sheet, such as about 20% of the thickness of the aluminum sheet, such as about 30% of the thickness of the aluminum sheet, such as about 40% of the thickness of the aluminum sheet, such as about 50% penetration of the thickness of the aluminum sheet, or more. Optionally, the penetration maybe less than about 100% the thickness of the aluminum sheet, such as optionally less than about 90% of the thickness of the aluminum sheet. In various embodiments, at least one metal substrate may be a cast aluminum or cast aluminum alloy. Various other benefits and advantages may be realized with the systems and methods provided herein, and the aforementioned advantages should not be considered limiting.

[0027] FIG. 1 illustrates a system 100 for resistance spot welding at least a first metal substrate 102 with at least a second metal substrate 104. In certain embodiments, the system 100 may be utilized to join a plurality of metal substrates. In some examples, one or more of the metal substrates may be aluminum or an aluminum alloy. In certain cases, aluminum or aluminum alloys in the Ixxx series, 2xxx series, 3xxx series, 4xxx series, 5xxx series, 6xxx series, 7xxx series, 8xxx series and/or any other aluminum or aluminum alloy materials may be utilized as one or more of the metal substrates.

[0028] By way of non-limiting examples, exemplary Ixxx alloys for use in the methods and products described herein can include AA1100, AA1100A, AA1200, AA1200A, AA1300, AA1110, AA1120, AA1230, AA1230A, AA1235, AA1435, AA1145, AA1345, AA1445, AA1150, AA1350, AA1350A, AA1450, AA1370, AA1275, AA1185, AA1285, AA1385, AA1188, AA1190, AA1290, AA1193, AA1198, or AA1199. [0029] Non-limiting exemplary 2xxx series alloys for use in the methods and products described herein can include AA2001, A2002, AA2004, AA2005, AA2006, AA2007, AA2007A, AA2007B, AA2008, AA2009, AA2010, AA2011, AA2011A, AA2111, AA2111A, AA2111B, AA2012, AA2013, AA2014, AA2014A, AA2214, AA2015, AA2016, AA2017, AA2017 A, AA2117, AA2018, AA2218, AA2618, AA2618 A, AA2219, AA2319, AA2419, AA2519, AA2021, AA2022, AA2023, AA2024, AA2024A, AA2124, AA2224, AA2224A, AA2324, AA2424, AA2524, AA2624, AA2724, AA2824, AA2025, AA2026, AA2027, AA2028, AA2028A, AA2028B, AA2028C, AA2029, AA2030, AA2031, AA2032, AA2034, AA2036, AA2037, AA2038, AA2039, AA2139, AA2040, AA2041, AA2044, AA2045, AA2050, AA2055, AA2056, AA2060, AA2065, AA2070, AA2076, AA2090, AA2091, AA2094, AA2095, AA2195, AA2295, AA2196, AA2296, AA2097, AA2197, AA2297, AA2397, AA2098, AA2198, AA2099, or AA2199.

[0030] Non-limiting exemplary 3xxx series alloys for use in the methods and products described herein can include AA3002, AA3102, AA3003, AA3103, AA3103A, AA3103B, AA3203, AA3403, AA3004, AA3004A, AA3104, AA3204, AA3304, AA3005, AA3005A, AA3105, AA3105A, AA3105B, AA3007, AA3107, AA3207, AA3207A, AA3307, AA3009, AA3010, AA3110, AA3011, AA3012, AA3012A, AA3013, AA3014, AA3015, AA3016, AA3017, AA3019, AA3020, AA3021, AA3025, AA3026, AA3030, AA3130, or AA3065.

[0031] Non-limiting exemplary 4xxx series alloys for use in the methods and products described herein can include AA4004, AA4104, AA4006, AA4007, AA4008, AA4009, AA4010, AA4013, AA4014, AA4015, AA4015A, AA4115, AA4016, AA4017, AA4018, AA4019, AA4020, AA4021, AA4026, AA4032, AA4043, AA4043A, AA4143, AA4343, AA4643, AA4943, AA4044, AA4045, AA4145, AA4145A, AA4046, AA4047, AA4047A, or AA4147.

[0032] Non-limiting exemplary 5xxx series alloys for use in the methods and products described herein can include AA5182, AA5183, AA5005, AA5005A, AA5205, AA5305, AA5505, AA5605, AA5006, AA5106, AA5010, AA5110, AA5110A, AA5210, AA5310, AA5016, AA5017, AA5018, AA5018A, AA5019, AA5019A, AA5119, AA5119A, AA5021, AA5022, AA5023, AA5024, AA5026, AA5027, AA5028, AA5040, AA5140, AA5041, AA5042, AA5043, AA5049, AA5149, AA5249, AA5349, AA5449, AA5449A, AA5050, AA5050A, AA5050C, AA5150, AA5051, AA5051A, AA5151, AA5251, AA5251A, AA5351 , AA5451 , AA5052, AA5252, AA5352, AA5154, AA5154A, AA5154B, AA5154C, AA5254, AA5354, AA5454, AA5554, AA5654, AA5654A, AA5754, AA5854, AA5954, AA5056, AA5356, AA5356A, AA5456, AA5456A, AA5456B, AA5556, AA5556A, AA5556B, AA5556C, AA5257, AA5457, AA5557, AA5657, AA5058, AA5059, AA5070, AA5180, AA5180A, AA5082, AA5182, AA5083, AA5183, AA5183A, AA5283, AA5283A, AA5283B, AA5383, AA5483, AA5086, AA5186, AA5087, AA5187, or AA5088.

[0033] Non-limiting exemplary 6xxx series alloys for use in the methods and products described herein can include AA6101, AA6101A, AA6101B, AA6201, AA6201A, AA6401, AA6501, AA6002, AA6003, AA6103, AA6005, AA6005A, AA6005B, AA6005C, AA6105, AA6205, AA6305, AA6006, AA6106, AA6206, AA6306, AA6008, AA6009, AA6010, AA6 110, AA6110 A, AA6011 , AA6111 , AA6012, AA6012 A, AA6013 , AA6113, AA6014, AA6015, AA6016, AA6016A, AA6116, AA6018, AA6019, AA6020, AA6021, AA6022, AA6023, AA6024, AA6025, AA6026, AA6027, AA6028, AA6031, AA6032, AA6033, AA6040, AA6041, AA6042, AA6043, AA6151, AA6351, AA6351A, AA6451, AA6951, AA6053, AA6055, AA6056, AA6156, AA6060, AA6160, AA6260, AA6360, AA6460, AA6460B, AA6560, AA6660, AA6061, AA6061A, AA6261, AA6361, AA6162, AA6262, AA6262A, AA6063, AA6063 A, AA6463, AA6463 A, AA6763, A6963, AA6064, AA6064A, AA6065, AA6066, AA6068, AA6069, AA6070, AA6081, AA6181, AA6181A, AA6082, AA6082A, AA6182, AA6091, or AA6092.

[0034] Non-limiting exemplary 7xxx series alloys for use in the methods and products described herein can include AA7011, AA7019, AA7020, AA7021, AA7039, AA7072, AA7075, AA7085, AA7108, AA7108A, AA7015, AA7017, AA7018, AA7019A, AA7024, AA7025, AA7028, AA7030, AA7031, AA7033, AA7035, AA7035A, AA7046, AA7046A, AA7003, AA7004, AA7005, AA7009, AA7010, AA7011, AA7012, AA7014, AA7016, AA7116, AA7122, AA7023, AA7026, AA7029, AA7129, AA7229, AA7032, AA7033, AA7034, AA7036, AA7136, AA7037, AA7040, AA7140, AA7041, AA7049, AA7049A, AA7149,7204, AA7249, AA7349, AA7449, AA7050, AA7050A, AA7150, AA7250, AA7055, AA7155, AA7255, AA7056, AA7060, AA7064, AA7065, AA7068, AA7168, AA7175, AA7475, AA7076, AA7178, AA7278, AA7278A, AA7081, AA7181, AA7185, AA7090, AA7093, AA7095, or AA7099.

[0035] Non-limiting exemplary 8xxx series alloys for use in the methods and products described herein can include AA8005, AA8006, AA8007, AA8008, AA8010, AA8011, AA8011A, AA8111, AA8211, AA8112, AA8014, AA8015, AA8016, AA8017, AA8018, AA8019, AA8021, AA8021A, AA8021B, AA8022, AA8023, AA8024, AA8025, AA8026,

AA8030, AA8130, AA8040, AA8050, AA8150, AA8076, AA8076A, AA8176, AA8077, AA8177, AA8079, AA8090, AA8091, or AA8093.

[0036] The composition of one metal substrate (e.g., the first metal substrate 102) need not be the same as the composition of another metal substrate (e.g., the second metal substrate 104), although it may be. Each of the metal substrates 102, 104 may have various sizes or thicknesses as desired, and the size or thickness of one metal substrate need not be the same as another metal substrate (although it may be). As illustrated in FIG. 1, the metal substrates 102, 104 may be arranged relative to each other such that the metal substrates 102, 104 overlap and have outermost opposite sides or surfaces 110, 112.

[0037] In one non-limiting example, one or more of the metal substrates (e.g., the second metal substrate 104) may be a cast aluminum formed by a casting method such as die casting mold casting, or sand casting, among other casting techniques, and the other metal substrate (e.g., the first metal substrate 102) may be an aluminum sheet. The surface of the cast aluminum may have various finishes and/or qualities as desired. As non-limiting example, the surface of the cast aluminum may be provided as-cast, acid-etched, mechanically brushed, laser-cleaned, and/or otherwise as desired. For discussion purposes, the first metal substrate 102 will be referred to as a sheet substrate 102 and the second metal substrate 104 will be referred to as a cast substrate 104; however, in other embodiments, the arrangement of the cast substrate 104 and sheet substrate 102 may be reversed and/or otherwise arranged as desired.

[0038] The resistance spot welding system 100 includes electrodes 106A-B. While two electrodes 106A-B are illustrated, any number of electrodes may be utilized with the system 100 as desired. The electrodes 106A-B may be any suitable type of electrodes for supplying a desired conductivity during welding, and may include, but are not limited to, copper electrodes, steel electrodes, and/or tungsten electrodes. For discussion purposes, the electrode 106A will be referred to as the sheet-side electrode 106A for contacting the sheet substrate 102 and the electrode 106B will be referred to as the cast-side electrode 106B for contacting the cast substrate 104; however, as previously mentioned, the electrodes 106A-B may be provided in various arrangements as desired.

[0039] In certain embodiments, the electrodes 106A-B are communicatively coupled with a weld controller 114 for controlling one or more welding parameters, including, but not limited to, the welding duration and the welding current, during resistance spot welding. In one non-limiting example, the weld controller 114 may be a middle frequency direct current controller, although in other embodiments, the weld controller 114 may be various other suitable devices or mechanisms as desired. In various aspects, the weld controller 114 may control one or more welding parameters based on a characteristic of the metal substrates 102, 104 to be joined and/or other characteristics of the resistance spot welding system 100. For example, the weld controller 114 may control the welding duration and/or the welding current based at least in part on a composition of the metal substrates 102, 104, a thickness or size of the metal substrates 102, 104, a size of the electrodes 106A-B, a characteristic of the electrodes 106A-B, and/or other characteristics as desired. In certain embodiments, the weld controller 114 controls the resistance spot welding system 100 pursuant to a welding curve schedule 600 and/or a welding curve schedule 700, as discussed in detail below. As discussed in detail below, the welding current provided for the welding duration and pursuant to the welding curve schedule 600 and/or the welding curve schedule 700 produces the weld nugget 108 having a minimum weld size to join the metal substrates 102, 104, or a weld nugget that meets size and mechanical requirements for the joint. Minimum weld size is defined as 4- t, where t is the thickness of the governing metal thickness. In a stack of two metal substrates, the governing metal thickness is generally the thinnest substrate.

[0040] In various embodiments, at least one characteristic of the sheet-side electrode 106A is different from the cast-side electrode 106B, and the electrodes 106 A-B may be considered asymmetrical where the different characteristic of one of the electrodes 106A-B is a weldpositioning characteristic. Asymmetrical electrodes may provide improved control of electrical current flow orientation and/or local current density during welding cycles, which may improve formation and positioning of the weld nugget 108 at the interface of the metal substrateS 102, 104. In embodiments where the metal substrates 102, 104 include the cast substrate 104 and the sheet substrate 102, the asymmetrical electrodes 106A-B may improve penetration of the weld nugget 108 in the aluminum sheet, optionally forming the weld nugget 108 approximately centered between the cast aluminum and the aluminum sheet. The at least one characteristic may be other features of the electrodes 106 A-B as desired suitable for controlling an electric current flow orientation and/or local current density during a welding cycle.

[0041] In the embodiment illustrated in FIG. 1, the at least one characteristic of the electrodes is a surface topography of a tip 116 of each electrode 106 A-B - the sheet-side electrode 106A is stamped to have surface features 124 on the tip 116, and the cast-side electrode 106B is unstamped. Referring to FIG. 2, in some embodiments, a stamping tool 218 having a textured surface 220 may be utilized to stamp or otherwise impart a topography on the sheet-side electrode 106A. The textured surface 220 may have various patterns, shapes, etc. as desired and suitable for controlling the application of electrical current during the welding cycle. FIG. 3 A illustrates a non-limiting example of a stamping tool 318 having pyramid-shaped ribs 322 forming a textured surface 320. The stamping tool 318 may form corresponding pyramid-shaped recesses 324 on a tip 316 of an electrode 306 as illustrated in FIG. 3B. FIG. 4 A illustrates a non-limiting example of a stamping tool 418 having elongated ribs 422 forming a textured surface 420 and compared to the ribs 322. As illustrated in FIG. 4B, an electrode 406 stamped with the stamping tool 418 may have corresponding elongated recesses 424 formed on its tip 416. As mentioned, in embodiments with the cast substrate 104 and the sheet substrate 102, the sheet-side electrode 106A with the textured tip 116 may be arranged to contact the sheet substrate 102, which may facilitate centering and/or penetration of a weld within the aluminum sheet. Various other textures and/or patterns of textures may be used as desired. In some embodiments, when the sheet-side electrode 106 A includes a textured/stampedtip, the other electrode 106B may be un stamp ed/untextured or may have a different texture than the sheet-side electrode 106 A.

[0042] As another non-limiting example, FIG. 5 illustrates a resistance spot welding system 500 that is substantially similar to the resistance spot welding system 100 except that the sheet-side electrode 506A and the cast-side electrode 506B have tips 516 with different tip radiuses. The electrodes 506A-B may have various tip radiuses as desired. In one nonlimiting example, the tip radius of the sheet-side electrode 506A may be about half the tip radius of the cast-side electrode 506B, although it need not be in other embodiments. As a non-limiting example, the sheet-side electrode 506A may have a tip radius of less than or equal to about 100 mm, such as about 75 mm. In some embodiments, the sheet-side electrode 506A may have a tip radius from about 25 mm to about 75 mm. As another non-limiting example, the cast-side electrode 506B may have a tip radius of greater than or equal to about 100 mm, such as about 150 mm. In some embodiments, the cast-side elctrode 506B may have a radius from about 100 to about 150 mm.

[0043] In other non-limiting examples, the tip radius of one electrode may be from about 100 mm to about 150 mm, inclusive, and the tip radius of another electrode may be from about 20 mm to about 75 mm, inclusive. In non-limiting embodiments where one of the metal substrates 102, 104 is cast aluminum and the other is aluminum sheet, the electrode with the smaller tip radius (e.g., sheet-side electrode 506A with a tip radius from about 20 mm to about 75 mm) may be arranged to contact the aluminum sheet and the electrode with the large tip radius (e.g., cast-side electrode 506B with a tip radius from about 100 mm to about 150 mm) may be arranged to contact the cast aluminum, which may facilitate centering and/or penetration of a weld within the aluminum sheet.

[0044] In another non-limiting example, each electrode 106A-B has a diameter, and the diameter of the electrodes 106A-B may be the same, although it need not be in other embodiments. As non-limiting examples, the diameters of each tip may be from about 12 mm to about 20 mm, such as about 12 mm, about 13 mm, about 14 mm, about 15 mm, about 16 mm, about 17 mm, about 18 mm, about 19 mm, and/or about 20 mm.

[0045] In some embodiments, in addition to varying one or more characteristics of the electrodes 106A-B, the characteristics of the surfaces 110, 112 optionally may be controlled and optionally varied to be asymmetrical. As non-limiting examples, the surface 112 of the cast substrate 104 may be an as-cast surface (e.g., no pre-treatement), be an acid-etched surface, be an acid etched and TiZr pre-treatment surface, be a laser cleaned surface (e.g., Gauss laser cleaned surface, continuous wave laser cleaned surface, etc.), combinations thereof, and/or have other surface characteristics has desired.

[0046] Optionally, an adhesive may be provided between the sheet substrate 102 and the cast substrate 104. In other embodiments, the adhesive may be omitted.

[0047] In certain embodiments, a plurality of characteristics may differ between one electrode and the other electrode (and optionally between the surfaces 110, 112). As an example, one electrode (e.g., the sheet-side electrode 106A) may be stamped and have a reduced tip radius and the other electrode (e.g., the cast-side electrode 106B) may be unstamped and have a larger tip radius, or the stamped electrode may have a larger tip radius while the unstamped electrode may have a reduced tip radius. As yet another example, one electrode may be stamped with a first topography and a first tip radius and the other electrode may be stamped with a second topography and a second tip radius. As yet a further example, both electrodes may have a same tip radius, and one electrode is stamped while the other electrode is unstamped. Various other combinations of topography, radii, and/or other characteristics or combinations of characteristics may be utilized as desired. [0048] FIG. 6 illustrates a welding curve schedule 600 according to various embodiments. The welding curve schedule 600 includes both a compressive force 602 and an electric current 604 that is applied to the metal substrates 102, 104 to form a weld such as the weld nugget 108. In certain embodiments, the welding curve schedule 600 may improve positioning and/or formation of the weld nugget 108, particularly when one of the metal substrates 102, 104 is an aluminum sheet and the other is a cast aluminum. The welding curve schedule 600 will be discussed in conjunction with the resistance spot welding system 100 where the electrodes 106 A-B are asymmetrical due to the topography imprinted on the sheetside electrode 106A. However, the welding curve schedule 600 may be used in any welding or system consistent with the embodiments described herein.

[0049] As depicted in FIG. 6, the compressive force 602 and the electric current 604 are applied to the two or more metal substrates 102, 104 via the electrodes 106A-B. In various embodiments, and as previously discussed, the metal substrates 102, 104 may be metal alloys, and optionally one of the metal substrates (e.g., the metal substrate 102) is an aluminum sheet and the other one of the metal substrates (e.g., the metal substrate 104) is a cast aluminum. In certain embodiments, the metal substrates 102, 104 are arranged such that the sheet substrate 102 will be contacted and compressed by the sheet-side electrode 106A with the weld-positioning characteristic (e.g., the surface features 124 in FIG. 1 , the reduced tip radius in FIG. 5, etc.).

[0050] In certain embodiments, the compressive force 602 is applied prior to the application of the electric current 604 and maintained during the application of the electric current 604. In some embodiments, a constant compressive force 602 is applied for the duration of the application of the electric current 604. In various embodiments, the constant compressive force 602 may reduce potential welding fluctuation. Various compressive forces 602 may be applied as desired. As one non-limiting example, the compressive force may be from greater than 0 kN to about 10 kN, such as from about 4 kN to about 8 kN, such as from about 5 kN to about 7 kN, such as about 6 kN and/or such as about 6.5 kN. In other embodiments, the compressive force 602 maybe other compressive forces as desired. The compressive force 602 may be applied for a force duration having a force start time 606 and a force end time 608. The period between the force start time 606 and the force endtime 608 may be any span or duration of time as desired. [0051] The electric current 604 may correspond to various amounts of electric current, energy, or heat and may be applied in various levels a discussed in detail below. In certain examples, the levels of electric current 604 may be between 0 kA and about 65 kA, such as from greater than 0 kA to about 55 kA, such as from greater than 0 kA to about 45 kA, such as from greater than 0 kA to about 40 kA, such as greater than 0 kA to about 35 kA. However, in other embodiments, the electrical current 604 may be applied at different levels as desired.

[0052] The electric current 604 may controlled and selectively applied for a current duration having a current start time 610 and a current end time 612. In certain embodiments, the current duration is less than the force duration. In various aspects, the current start time 610 is a predetermined duration or period of time after the force start time 606. In such examples, delaying the current start time 610 to be after the force start time 206 may ensure that the metal substrates are positioned as desired between the electrodes 106A-B.

[0053] As mentioned, within the current duration, the electric current 604 may be applied to various levels and for certain time periods. In some embodiments, during a first time period 614 (or a “ramping up” time period), the electric current 604 is ramped up from a first level 616 to a second level 618 that is greater than the first level 616. In some embodiments, the first level 616 may be 0 kA (e.g., the current is ramped from 0 kA to the welding current used during a second time period 620), although it need not be in other embodiments. In certain aspects, applying the electric current 604 that is ramped up from the first level 616 to the second level of the first time period 614 may avoid or minimize potential explosion, among other benefits.

[0054] After the first time period 614 and during the second time period 620, the electric current 604 is applied at the second level 618. In certain embodiments, applying the electric current 604 at the second level 618 for the second time period 620 may allow for the creation of a weld nugget. In certain embodiments, the second time period 620 optionally may be less than the first time period 614, although it need not be in other examples.

[0055] After the second time period 620, the electric current 604 is ramped down (e.g., decreased) from the second level 618 over a third time period 622 (or a “ramping down” time period). In certain embodiments, ramping down the electric current 604 over the third time period 622 may be at a ramp-down rate that is less than the ramp-up rate during the first time period 614. The third time period 622 may be greater than the first time period 614. In some embodiments, the longer duration and/or the reduced rate of change of the ramp-down rate compared to the first time period 614 may reduce crack sensitivity (e.g., reduce the tendency of cracks or other defects to form in the cured weld nugget), among other benefits, thereby improving the quality of the weld. In some embodiments, over the third time period 622, the electric current 604 is ramped down from the second level 618 to a third level 624. In certain embodiments, the third level 624 maybe 0 kA (e.g., the electric current is ramped down from the second level 618 to 0 kA), although it need not be in other embodiments. In some embodiments and as illustrated in FIG. 2, the third level 624 may be the same as the first level 616; however, in other embodiments the third level 624 maybe less than or greater than the first level 616 as desired.

[0056] The welding curve schedule 600 in FIG. 6 is provided for illustrative purposes only, and the specific values of the levels of the electric current 604, the level of the compressive force 602, and/or the time periods of the electric current 604 should not be considered limiting. As a non-limiting example, FIG. 7 illustrates another example of a welding curve schedule 700 according to embodiments of the disclosure.

[0057] The welding curve schedule 700 is similar to the welding curve schedule 600 and includes the compressive force 602 and the electric current 604. Compared to the welding curve schedule 600, the first time period 614 of the welding curve schedule 700 starts at a first intermediate level 626 that is greater than the first level 616 and less than the second level 618. In addition, compared to the welding curve schedule 600, the rate at which the electric current 604 in the welding curve schedule 700 is ramped up over the first time period 614 is reduced. As such, in the welding curve schedule 700, over the first time period 614, the electric current 604 is ramped up from the first intermediate level 626 to a second intermediate level 628 that is greater than the first intermediate level 626 and less than the second level 618. Similar to the welding curve schedule 600, the welding curve schedule 700 applies the electric current 604 at the second level 618 over the second time period 620 and ramps down the electric current from the second level 618 over the third time period 622.

[0058] In one non-limiting example, the welding curve schedule 700 may be particularly useful when using the resistance spot welding system 500 where the weld-positioning characteristic is the reduced tip radius of the sheet-side electrode 506A for contacting the aluminum sheet as the sheet substrate 102 (rather than the cast aluminum). However, the welding curve schedule 700 is not limited to the resistance spot welding system 500 and may be used with other resistance spot welding systems consistent with the disclosure.

[0059] FIG. 8 illustrates a method of joining at least two metal substrates 102, 104 using a welding curve schedule accordingto various embodiments. While reference will be made to the welding curve schedule 600 illustrated in FIG. 6 and the resistance spot welding system 100 illustrated in FIG. 1, the method may be performed with other welding curve schedules consistent with the disclosure as desired and/or other systems as desired.

[0060] In a block 802, the method include applying the compressive force 602 to the metal substrates 102, 104 using the electrodes 106A-B. In certain embodiments, applying the compressive force brings the metal substrates 102, 104 into contact with one another and/or may position the metal substrates 102, 104 relative to each other. In some embodiments, the metal sub strate 102 is an aluminum sheet and the metal sub strate 104 is a cast aluminum, and block 402 may include positioning the metal substrates 102, 104 and/or the resistance spot welding system 100 such that the sheet-side electrode 106A with the weld-positioning characteristic (e.g., the surface features 124) will contact the aluminum sheet. The method may include performing the steps illustrated in blocks 804, 806, and 808 while applying the clamping force.

[0061] In a block 804, the method includes applying the electric current 604 for the first time period 614. In various embodiments, block 804 includes ramping the electric current 604 from the first level 616 to the second level 618 over the first time period 214. In other embodiments, such as the welding curve schedule 700, block 804 may include ramping up the electric current 604 from the first intermediate level 626 and/or to the second intermediate level 628.

[0062] In a block 806, the method includes applying the electric current 204 at the second level 618 for the second time period 620. In a block 808, the method includes ramping down the electric current 604 from the second level 618 over the third time period 622.

[0063] FIGS. 9-11 illustrate non-limiting examples ofRSWjoints formed using the welding curve schedule 600 or the welding curve schedule 700.

[0064] FIG. 9 illustrates an RSW joint 901 formed using the welding curve schedule 600 and with one of the electrodes having the topography illustrated in FIG. 3B. In this embodiment, the metal substrate 902 was a 6xxx series aluminum alloy sheet having a thickness of 2.0 mm, and the metal substrate 904 was a cast aluminum having a thickness of 3.0 mm. The electrode with the topography of FIG. 3B was contacted with the metal substrate 902. In this embodiment, the first time period was 40 milliseconds (ms), the second time period was 80 ms, and the second time period was 200 ms. The second level of the electric current was 38 kA. The compressive force applied was 6 kN. As illustrated in FIG. 9, the weld nugget 908 formed at the interface of the substrates 902, 904 had a penetration of about 0.943 mm into the aluminum sheet, which was about 47% the thickness of the aluminum sheet.

[0065] FIG. 10 illustrates an RSW joint 1001 formed using the welding curve schedule 600 and with one of the electrodes having the topography illustrated in FIG. 4B. In this embodiment, the metal substrate 1002 was a 6xxx series aluminum alloy sheet having a thickness of 2.0 mm, and the metal substrate 1004 was a cast aluminum having a thickness of 3.0 mm. The electrode with the topography of FIG. 4B was contacted with the metal substrate 1002. In this embodiment, the first time period was 40 ms, the second time period was 80 ms, and the second time period was 200 ms. The second level of the electric current was 38 kA. The compressive force applied was 6 kN. As illustrated in FIG. 10, the weld nugget 1008 formed at the interface of the substrates 1002, 1004 had a penetration of about 0.873 mm into the aluminum sheet, which was about 43% the thickness of the aluminum sheet.

[0066] FIG. 11 illustrates an RSW joint 1101 formed using the welding curve schedule 700 and with one of the electrodes having the topography illustrated in FIG. 5. In this embodiment, the metal substrate 1102 was a 6xxx series aluminum alloy sheet having a thickness of 2.0 mm, and the metal substrate 1104 was a cast aluminum having a thickness of 3.0 mm. The electrode with the reduced tip radius of FIG. 5 was contacted with the metal substrate 1102. In this embodiment, the first time period was 70 ms, the second time period was 80 ms, and the second time period was 200 ms. The second level of the electric current was 32 kA. The compressive force applied was 6 kN. As illustrated in FIG. 11, the weld nugget 1108 formed at the interface of the substrates 1102, 1104 had an overall thickness of 3.439 mm, which was about 69% the thickness of the overlapping substrates 1102, 1104.

[0067] A collection of exemplary embodiments are provided below, including at least some explicitly enumerated as “Illustrations” providing additional description of a variety of example embodiments in accordance with the concepts described herein. These illustrations are not meant to be mutually exclusive, exhaustive, or restrictive; and the disclosure not limited to these example illustrations but rather encompasses all possible modifications and variations within the scope of the issued claims and their equivalents.

[0068] Illustration 1. A method for joining metal substrates, the method comprising: providing a first electrode and a second electrode, wherein at least one characteristic of the first electrode is different from the second electrode; applying a compressive force to at least two overlapping metal substrates usingthe first electrode and the second electrode, wherein at least one metal substrate of the at least two metal substrates comprises aluminum or an aluminum alloy; over a first time period, applying an electric current at a first level and ramping up the electric current from the first level to a second level greater than the first level; after the first time period, applying the electric current at the second level for a second time period; and after the second time period, ramping down the electric current from the second level over a third time period, wherein a rate of ramping down the electric current is less than a rate of the ramping up of the electric current over the first time period.

[0069] Illustration 2. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein a first metal substrate of the at least two metal substrates comprises a cast aluminum, and wherein a second metal substrate of the at least two metal substrates comprises an aluminum sheet.

[0070] Illustration 3. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the first time period is less than the third time period.

[0071] Illustration 4. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the third time period is greater than the first time period and greater than the second time period.

[0072] Illustration 5. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the at least one characteristic comprises a topography of a tip of the first electrode, and wherein the method comprises stamping the first electrode and imprinting a topography on the tip of the first electrode.

[0073] Illustration 6. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein a first metal substrate of the at least two metal substrates comprises an aluminum sheet, wherein a second metal substrate of the at least two metal substrates comprises a cast aluminum, and applying the compressive force comprises contacting the first electrode with the first metal substrate. [0074] Illustration 7. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the at least one characteristic comprises a tip radius of a tip of the first electrode, and wherein a tip radius of the first electrode is less than a tip radius of the second electrode.

[0075] Illustration 8. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein a first metal substrate of the at least two metal substrates comprises an aluminum sheet, wherein a second metal substrate of the at least two metal substrates comprises a cast aluminum, and applying the compressive force comprises contacting the first electrode with the first metal substrate.

[0076] Illustration 9. A method for joining metal substrates, the method comprising: providing a first electrode and a second electrode, wherein at least one characteristic of the first electrode is different from the second electrode; applying a compressive force to at least two overlapping metal substrates using the first electrode and the second electrode, wherein at least one metal substrate of the at least two metal substrates comprises aluminum or an aluminum alloy; over a first time period, applying an electric current at a first level and ramping up the electric current from the first level to a second level greater than the first level; after the first time period, applying the electric current at a third level for a second time period; and after the second time period, ramping down the electric current from the third level over a third time period.

[0077] Illustration 10. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the third level is greater than the second level.

[0078] Illustration 11. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the at least one characteristic comprises a tip radius of a tip of the first electrode, and wherein a tip radius of the first electrode is less than a tip radius of the second electrode.

[0079] Illustration 12. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein a first metal substrate of the at least two metal substrates comprises an aluminum sheet, wherein a second metal substrate of the at least two metal substrates comprises a cast aluminum, and applying the compressive force comprises contacting the first electrode with the first metal substrate. [0080] Illustration 13. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the tip radius of the first electrode is less than 100 mm, and wherein the tip radius of the second electrode is greater than 100 mm.

[0081] Illustration 14. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the third time period is greater than the first time period and greater than the second time period.

[0082] Illustration 15. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein a rate of ramping down the electric current is less than a rate of the ramping up of the electric current over the first time period.

[0083] Illustration 16. A method for joining metal substrates, the method comprising: providing a first electrode and a second electrode, wherein at least one characteristic of the first electrode is different from the second electrode; applying a compressive force to at least two overlapping metal substrates using the first electrode and the second electrode, wherein at least one metal substrate of the at least two metal substrates comprises aluminum or an aluminum alloy; and applying an electric current by: over a first time period, ramping up the electric current at a ramp-up rate; over a second time period after the first time period, applying the electric current at a welding level; and over a third time period after the second time period, ramping down the electric current at a ramp-down rate, wherein the ramp-down rate is less than the ramp-up rate.

[0084] Illustration 17. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the at least one characteristic comprises a topography of a tip of the first electrode, wherein a first metal substrate of the at least two metal substrates comprises an aluminum sheet, wherein a second metal substrate of the at least two metal substrates comprises a cast aluminum, wherein the method comprises stamping the first electrode and imprinting a topography on the tip of the first electrode, and wherein applying the compressive force comprises contacting the first electrode with the first metal substrate.

[0085] Illustration 18. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the at least one characteristic comprises a tip radius of a tip of the first electrode, wherein a tip radius of the first electrode is less than a tip radius of the second electrode, wherein a first metal substrate of the at least two metal substrates comprises an aluminum sheet, wherein a second metal substrate of the at least two metal substrates comprises a cast aluminum, and wherein applying the compressive force comprises contacting the first electrode with the first metal substrate.

[0086] Illustration 19. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the first time period is greater than the second time period.

[0087] Illustration 20. The method of any of the preceding or subsequent illustrations or combination of illustrations, wherein the third time period is greater than the first time period and greater than the second time period.

[0088] Illustration 21 . A weld formed by the method of any of the preceding or subsequent illustrations or combination of illustrations.

[0089] The subject matter of embodiments is described herein with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be usedin conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described. Directional references such as “up,” “down,” “top,” “bottom,” “left,” “right,” “front,” and “back,” among others, are intended to refer to the orientation as illustrated and described in the figure (or figures) to which the components and directions are referencing. Throughout this disclosure, a reference numeral with a letter refers to a specific instance of an element and the reference numeral without an accompanying letter refers to the element generically or collectively. Thus, as an example (not shown in the drawings), device “12A” refers to an instance of a device class, which may be referred to collectively as devices “12” and any one of which may be referred to generically as a device “12”. In the figures and the description, like numerals are intended to represent like elements. As used herein, the meaning of “a,” “an,” and “the” includes singular and plural references unless the context clearly dictates otherwise.

[0090] In this description, reference is made to alloys identified by AA numbers and other related designations, such as “series” or “7xxx.” For an understanding of the number designation system most commonly used in naming and identifying aluminum and its alloys, see “International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys” or “Registration Record of Aluminum Association Alloy Designations and Chemical Compositions Limits for Aluminum Alloys in the Form of Castings and Ingot,” both published by The Aluminum Association.

[0091] As used herein, a sheet generally refers to an aluminum product having a thickness of less than about 4 mm. For example, a sheet may have a thickness of less than about 4 mm, less than about 3 mm, less than about 2 mm, less than about 1 mm, less than about 0.5 mm, or less than about 0.3 mm (e.g., about 0.2 mm).

[0092] As used herein, terms such as “cast metal product,” “cast product,” “cast aluminum alloy product,” and the like are interchangeable and refer to a product produced by methods such as die-casting, mold casting, or sand casting.

[0093] All ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more, e.g. 1 to 6.1 , and ending with a maximum value of 10 or less, e.g., 5.5 to 10. Unless stated otherwise, the expression “up to” when referring to the compositional amount of an element means that element is optional and includes a zero percent composition of that particular element. Unless stated otherwise, all compositional percentages are in weight percent (wt. %).

[0094] The above-described aspects are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the present disclosure. Many variations and modifications can be made to the above-described embodiment(s) without departing substantially from the spirit and principles of the present disclosure. All such modifications and variations are intended to be included herein within the scope of the present disclosure, and all possible claims to individual aspects or combinations of elements or steps are intended to be supported by the present disclosure. Moreover, although specific terms are employed herein, as well as in the claims that follow, they are used only in a generic and descriptive sense, and not for the purposes of limiting the described invention, nor the claims that follow.