ELEMENT, FRICTION ELEMENT WELDING METHOD, AND METHOD FOR PRODUCING A FRICTION ELEMENT WELDED JOINT.
Patent Information
- Authority / Receiving Office
- MX · MX
- Patent Type
- Patents
- Current Assignee / Owner
- JFE STEEL CORP
- Filing Date
- 2023-01-26
- Publication Date
- 2026-05-19
Smart Images
Figure MX433857B0
Abstract
Description
The present invention relates to a friction element joint referred to as a FEW (friction element weld). More particularly, the invention relates to a friction element weld for two or more stacked metal sheets, such as steel sheets (e.g., ordinary steel sheets, high-tensile-strength steel sheets, etc.) and light metal sheets (e.g., aluminum sheets, aluminum alloy sheets, copper sheets, etc.), and also to a method of friction element welding using the element and a method for producing a welded friction element joint. BACKGROUND OF THE INVENTION In recent years, studies have been conducted in various fields to address environmental problems such as global warming. In the automotive industry, techniques have been developed to reduce fuel consumption (i.e., improve fuel economy) and thus reduce CO2 emissions. One technique used in practice also incorporates an electric motor (i.e., a hybrid technology). Another technique uses high-strength steel sheets, known as ultra-high-tensile-strength steel sheets, to reduce the amount of steel used, thereby decreasing the vehicle body's weight and increasing the safety of the driver and passengers. Another technique being studied to further reduce vehicle body weight involves using a lightweight metal (such as an aluminum alloy or copper sheets) for the vehicle body. To mass-produce such vehicle bodies on a production line, a technique is needed to firmly bond the lightweight metal material to a steel frame used as the vehicle's chassis. Steel sheets have been conventionally used for vehicle bodies, and general-purpose fusion welding methods (such as arc welding and resistance spot welding) have been widely employed. However, conventional fusion welding methods cannot be used to join steel sheet and light metal sheet as described above. For example, when a fusion welding method is used to join a high-strength steel sheet and an aluminum alloy sheet, an intermetallic compound of Fe and Al forms, causing significant weld embrittlement. Accordingly, a technique for joining a steel sheet and a light metal sheet without fusion has been studied. Non-patent literature1 describes a representative example of such a technique that uses a metallic joining element (hereafter referred to as an element) to perform friction element welding. In this technique, the metal sheets are stacked to form a sheet pile, and the element is rotated at high speed into the sheet pile under pressure (hereafter referred to as being pressed into the sheet pile) to join the metal sheets together. Patent literature 1 describes an element that can be preferentially used for friction element welding. This element includes a mandrel having a non-circular polygonal outer shape with a plurality of rounded corner regions, and the force applied during the joining process aids and facilitates the unloading of a plastically deformed portion of a top sheet into a stack of sheets. An element described in patent literature 2 includes a circular column mandrel, a circular collar projecting outward from the circumference of an upper end portion of the mandrel, and a circular tapered pin projecting from the lower end surface of the mandrel. With the element in patent literature 2, when the element is pressed into a stack of laminations, the pin's apex first makes contact with the stack of laminations, and the pin, held in this position, rotates at high speed, so that the frictional heat generated can be concentrated at a prescribed position. These conventional techniques, i.e., the friction element welding technique described in non-patent literature 1 and the friction element welding techniques using the elements described in patent literature 1 and patent literature 2, are effective when the lowest of two or more stacked metal sheets used as a sheet stack (this sheet referred to hereafter as the bottom sheet) is a steel sheet, the highest metal sheet (the metal sheet disposed on the side on which the element pin is to be made contact) (this sheet is hereafter referred to as a top sheet) is a light metal sheet, and an intermediate metal sheet held between the top and bottom sheets is also a light metal sheet. However, when friction element welding is performed using conventional techniques on a sheet stack where both the bottom and top sheets are steel, the position of the mandrel's central axis tends to fluctuate considerably as the element rotates at high speed with the mandrel in contact with the top sheet to generate frictional heat. This heat is not concentrated in a prescribed position on the top sheet but is dispersed. Consequently, while the top sheet does not soften easily, the mandrel deforms, preventing a portion of the metal sheet extruded by the pressed element from being discharged. In this case, the element's mandrel does not easily penetrate the top sheet, and therefore the sheets in the stack do not bond together effectively. List of appointments Patent literature PTL1: Publication of Unexamined Japanese Patent Application (Translation of PCT Application) No. 2013-534994 PTL2: Publication of Unexamined Japanese Patent Application (Translation of PCT Application) No. 2013-527804 Non-patent literature NPL1: Jamie D. Skovron, Brandt J Ruszkiewicz, and Laine Mears, “INVESTIGATION OF THE CLEANING AND WELDING STEPS FROM THE FRICTION ELEMENT WELDING PROCESS, (ASME 2017 12th International Manufacturing Science and Engineering Conference co-located with the JSME / ASME 2017 6th International Conference on Materials and Processing, June 4-8, 2017 Los Angeles, California, USA) noLLnn / pznz / e / Yi / u BRIEF DESCRIPTION OF THE INVENTION Technical problem It is an objective of the present invention to solve the problem in conventional techniques and to provide an element used for performing friction element welding on a sheet stack of two steel sheets including a steel sheet disposed as a lower sheet and a steel sheet disposed as an upper sheet or a sheet stack of three or more metal sheets including a lower sheet (i.e., a steel sheet), an upper sheet (i.e., a steel sheet), and at least one metal sheet (i.e., a steel sheet or a light metal sheet) held between the lower and upper sheets, thereby joining the sheets together and providing a method of friction element welding using the element and a method for producing a welded friction element joint using the element. Another objective of the invention is to provide an element that can be applied without any problem to the friction element welding of a sheet stack of two metal sheets including a steel sheet disposed as a lower sheet and a light metal sheet disposed as a top sheet or a sheet stack of three or more metal sheets including a lower sheet (i.e., a light metal sheet), an upper sheet (i.e., a steel sheet), and at least one steel sheet held between the lower and upper sheets, and to provide a method of friction element welding when using the element and a method for producing a welded friction element joint when using the element. Solution to the problem When a suitable technique is developed for friction element welding of a lap stack of two steel sheets, where both the lower and upper sheets are steel, this technique can be readily applied to friction element welding of a lap stack comprising a steel sheet as the lower sheet and a sheet of a lighter metal softer than steel as the upper sheet. In view of this, the present inventors have conducted studies on a technique for performing friction element welding on a lap stack of two steel sheets. The top sheet in the stack of two steel sheets is the steel sheet with which the mandrel of the element makes contact before the mandrel is pressed into the stack. Specifically, the top sheet is a hard steel sheet. To weld the friction element through the top sheet, it is necessary to rotate the element at high speed while preventing the contact position between the mandrel and the top sheet from fluctuating, so that the frictional heat is concentrated at a prescribed position. Accordingly, the inventors have conducted several experiments in which the mandrel is brought into contact with a prescribed position on the top sheet and held in this position while the element rotates at high speed. The inventors then found it effective to place a conical body on the lower end surface of the mandrel. Specifically, as the tip of the high-speed rotating conical body makes contact with the upper sheet and the conical body gradually enters the upper sheet, the steel sheet is extruded. In this case, the amount of extruded steel sheet corresponds to the volume of the conical body pressed into the upper sheet. When the extruded portion of the metal sheet can be gently discharged, the conical body continues to enter the upper sheet with the position of the conical body's tip maintained in a prescribed position. Therefore, when the element can continue rotating at high speed (i.e., the mandrel can continue rotating at high speed) without positional fluctuations, the frictional heat generated concentrates at the prescribed position, and this position softens, readily allowing plastic flow. Thus, when the softened, flowable metal (i.e., the metal in the plastically deformed upper sheet) can be smoothly discharged, the mandrel can penetrate and pierce the upper sheet. Specifically, it has been found that, by arrangement, on the lower end surface of the mandrel, a conical body having a vertex with its angle (hereafter referred to as a “vertical angle”) set within an appropriate range in order to smoothly extrude the flowable metal generated by the plastic flow of the upper sheet, the stack of two steel sheets can be joined by friction element welding. When the element of the present invention is used to perform friction element welding on a stack of two metal sheets, including a steel sheet as the lower sheet and a light metal sheet as the upper sheet, the conical body gradually enters the upper sheet with its central axis held in a prescribed position due to the softness of the upper sheet. Furthermore, the frictional heat generated by the mandrel concentrates at the prescribed position, softening it and facilitating plastic flow. Additionally, the conical body positioned on the lower end surface of the mandrel allows the flowable metal (hereafter referred to as "flowing metal") to extrude smoothly, thus preventing defective welds. This effect is significantly enhanced when two conical bodies with different vertical angles are combined. The present invention has been made based on the previous findings. Specifically, the element of the invention is an element for performing friction element welding on a sheet stack of two or more stacked metal sheets by pressing the element into the sheet stack while the element rotates, the element including: a circular column mandrel for inserting the sheet stack; a circular disc-shaped collar disposed in an upper end portion of the mandrel;and a first conical body extending from a lower end surface of the mandrel, wherein the collar diameter is greater than the mandrel diameter, wherein a portion of the outer circumference of the collar has a downward slope or curved shape, wherein a central axis of the first conical body coincides with a central axis of the mandrel, wherein the element further includes a second conical body disposed in contact with the lower side of the first conical body, wherein a bottom surface of the second conical body is smaller in diameter than a bottom surface of the first conical body, wherein a central axis of the second conical body coincides with the central axis of the mandrel, and wherein a vertical angle β(°) of the second conical body and a vertical angle a(°) of the first conical body satisfy the following relation:; β < oc. Preferably, in the element of the invention, the vertical angle <x(°) del primer cuerpo noLLnn / pznz / e / Yi / u cónico satisface 140 < a < 180, and the vertical angle β(°) of the second conical body satisfies < β< 140. Preferably, a distance L (mm) from a lower end of the outer circumference portion of the collar to a vertex of the second conical body in a direction parallel to the central axis of the mandrel satisfies the following relationship: (Ttotal - Tfondo) + 0 02 mm < L < (Ttotal - Tfondo) + 4 mm where Ttotal (mm) is a total thickness of the sheet stack, and Tfondo (mm) is a thickness of a lower sheet in the sheet stack. Preferably, the stack of sheets to which the present invention applies is a stack of sheets comprising a lower sheet formed from a steel sheet and an upper sheet formed from a light metal, or a stack of sheets comprising a lower sheet and an upper sheet formed from respective steel sheets. Preferably, an outer surface of the first conical body and an outer surface of the second conical body each have a coating film formed from a wear-resistant material. The friction element welding method of the invention is a friction element welding method that includes joining a stack of two or more stacked metal sheets by pressing an element into the stack of sheets while the element rotates, wherein the element used is the element described above. The method of producing the welded friction element joint of the invention is a method for producing a welded friction element joint, the method including joining a stack of two or more stacked metal sheets by pressing an element into the stack of sheets while the element rotates, wherein the element used is the element described above. Advantageous effects of the invention According to the present invention, friction element welding can be performed on a sheet stack of two stacked steel sheets (i.e., a sheet stack in which the bottom and top sheets are both steel sheets). Furthermore, friction element welding can also be performed on a sheet stack of three or more stacked steel sheets or a sheet stack in which at least one sheet of light metal is held between two steel sheets used as the bottom and top sheets, so that industrially significant effects can be achieved. On the other hand, the present invention can be stably applied without any problem to the friction element welding of a stack of sheets of two metal sheets including a steel sheet arranged as the lower sheet and a light metal sheet arranged as the upper sheet or a stack of sheets of three or more metal sheets including at least one steel sheet held between the lower sheet (i.e., a steel sheet) and the upper sheet (i.e., a light metal sheet), and the effect of preventing the presence of defective welding is obtained. BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a cross-sectional view that schematically illustrates an example of the element of the invention. FIGS. 2A and 2B are cross-sectional views that schematically illustrate examples of a sheet stack to be joined using the element shown in FIG. 1. FIG. 2A shows a sheet stack of two stacked metal sheets, FIG. 2B shows a sheet stack of three stacked metal sheets. FIGS. 3A and 3B are cross-sectional views that schematically illustrate examples of a stack of sheets to be joined using the element shown in FIG. 1. FIG. 3A shows an example before the element is pressed into the stack of sheets, FIG. 3B shows an example after the element has been pressed into the stack of sheets. DETAILED DESCRIPTION OF THE INVENTION Description of the modalities With reference first to FIG. 1, the element of the invention will be described. FIG. 1 is a cross-sectional view that schematically illustrates an example of the element of the invention. As shown in FIG. 1, element 1 of the invention includes: a circular column mandrel 2 for inserting a stack of laminations when the stack of laminations is subjected to welding of the friction element; a circular disc-shaped collar 3 disposed in a first end portion of the mandrel 2 (hereafter referred to as an upper end portion); and a first conical body 4 having a conical shape and extending from a second end surface of the mandrel 2 (hereafter referred to as a lower end surface). The diameter of collar 3 is larger than the diameter of mandrel 2. Therefore, a portion of the outer circumference of collar 3 is arranged so that it protrudes from the circumference of the upper end portion of mandrel 2. In addition, the portion of the outer circumference of collar 3 is formed so that it slopes or curves downwards. The first conical body 4 extends from the lower end surface of the mandrel 2, and the center axis of the first conical body 4 (i.e., the center of its bottom surface) coincides with the center axis of the mandrel 2. Therefore, the lower end surface of the mandrel 2 is not exposed around the bottom surface of the first conical body 4. Specifically, the diameter of the bottom surface of the first conical body 4 is the same as the diameter of the lower end surface of the mandrel 2. A second conical body 5 is arranged in contact with the lower side of the first conical body 4. The central axis of the second conical body 5 (i.e., the center of its bottom surface) coincides with the central axis of the first conical body 4. The bottom surface of the second conical body 5 is smaller in diameter than the bottom surface of the first conical body 4. Specifically, the diameter D2 (mm) of the bottom surface of the second conical body 5 and the diameter D1 (mm) of the bottom surface of the first conical body 4 must satisfy the following relationship: D2 < D1. In other words, the inclined side surface of the first conical body 4 is exposed around the bottom surface of the second conical body 5. In this case, as the second conical body 5 enters the sheet pile, the flowing metal extruded by the second conical body 5 is gently discharged onto the surface of the sheet pile (i.e., the side surface of mandrel 2) along the inclined side surface of the first conical body 4. The diameter D2 of the bottom surface of the second conical body 5 is preferably (D1 90%) (mm) or less and more preferably (D1 50%) (mm) or less. When the diameter D2 of the bottom surface of the second conical body 5 and the diameter D1 of the bottom surface of the first conical body 4 satisfy D2 > D1, the inclined side surface of the first conical body 4 is not exposed around the bottom surface of the second conical body 5, and therefore the flowing metal is not discharged smoothly. In the present invention, it is only necessary to obtain the effect described above of the discharge of the flowing metal, and the lower limit of the diameter D2 of the bottom surface of the second conical body 5 is not particularly specified. From the point of view of facilitating penetration into lamellar materials, the diameter D2 of the bottom surface of the second conical body 5 is preferably (D1 ≤ 10%) (mm) or more, and even more preferably (D1 ≤ 20%) (mm) or more. It is necessary that the vertical angle β(°) of the second conical body 5 and the vertical angle a(°) of the first conical body 4 satisfy the following relationship: β < a. When this relationship is satisfied, the central axis of the second conical body 5 can be held stably in a prescribed position when element 1 is pressed into the sheet pile, and the flowing extruded metal can be discharged smoothly. If the vertical angle α(°) of the first conical body 4 is excessively small, the distance from the bottom surface of the first conical body 4 to the apex of the second conical body 5 is large. In this case, when element 1 is pressed into the stack of sheets, it may be difficult to maintain element 1 such that the centerline of the second conical body 5 coincides with the centerline of the first conical body 4 (i.e., the centerline of mandrel 2). If the vertical angle α(°) is excessively large, the effect of smoothly discharging the metal may not be achieved. It is therefore preferable that the vertical angle α(°) satisfy 140 < a < 180. If the vertical angle β(°) of the second conical body 5 is excessively small, the second conical body 5 can be easily damaged when element 1 is pressed into the stack of sheets, causing the position of the central axis of the second conical body 5 to fluctuate easily. If the vertical angle β(°) is excessively large, the flowing metal may not discharge smoothly. It is therefore preferable that the vertical angle β(°) be < β < 140. When the element 1 described above is used to perform friction element welding, the efficiency of the friction element welding can be increased by increasing the wear resistance of the first conical body 4 and the second conical body 5. It is therefore preferable that a coating film of a wear-resistant material be formed on the outer surface of each of the first conical body 4 and the second conical body 5. No particular limitation is imposed on the wear-resistant material, provided that the operational advantage described above is obtained. Examples of wear-resistant materials include WC, TiN, and other ceramics. A heat-resistant coating and a hardening treatment such as nitriding may also be used. noLLnn / pznz / e / Yi / u With reference to Figures 1, 2A, and 2B below, the relationship between the sheet stack and the element will be described. Figure 2A is a cross-sectional view of a sheet stack of two stacked metal sheets, and Figure 2B is a cross-sectional view of a sheet stack of three stacked metal sheets. The stack of sheets 6 shown in FIG. 2A comprises two stacked metal sheets, including an upper sheet 7 and a lower sheet 8. The stack of sheets 6 shown in FIG. 2B comprises a total of three metal sheets, including an upper sheet 7, a lower sheet 8, and a metal sheet held between them. The present invention is also applicable to a stack of sheets (not shown) comprising a total of four or more metal sheets, including an upper sheet 7, a lower sheet 8, and two or more metal sheets held between them. To perform friction element welding on the sheet stack 6 shown in FIG. 2A or 2B using the element 1 shown in FIG. 1, it is necessary that the mandrel 2 passes through the upper sheet 7 and reaches the lower sheet 8. Therefore, a preferred interval of the distance L (mm) from the lower end of the outer circumference portion of the collar 3 to the vertex of the second tapered body 5 is specified as follows. The distance L is the length in a direction parallel to the center axis of the mandrel 2. Let the total thickness of the stack of sheets 6 be Ttotal (mm), and the thickness of the bottom sheet 8 be Tbackground (mm). Then, when the distance L in element 1 is set such that If Ttotal - Tbackground < distance L, element 1 can be pressed into the upper sheet 7 from above, such that the second conical body 5 reaches the lower sheet 8, thereby performing friction element welding. However, during the pressing of element 1 into the stack of sheets, the first conical body 4, the second conical body 5, and the mandrel 2 soften due to frictional heat. This causes plastic flow, and the flowing metal is discharged on the side surface of the mandrel 2. Therefore, if the distance Les is excessively small (e.g., Ttotal - Tbackground = distance L), a problem arises where element 1 cannot reach the lower sheet 8.If the distance L is excessively large, a problem may arise where, when element 1 is pressed into the lamination stack, mandrel 2 is likely to deform (e.g., bend, twist, or wavy) above the top lamination 7 (before mandrel 2 enters the top lamination 7), so that mandrel 2 cannot be pressed into the lamination stack. It is therefore preferable that the distance L satisfy the following relationship: (Ttotal - Tbackground) + 0.02 mm < distance L < (Ttotal - Tbackground) + 4 mm. The length added to (Ttotal - Tbackground) is not limited as long as the overall interface state is satisfactory, and the length is 0.02 mm or more. The length is preferably 0.2 mm or more, and preferably 0.5 mm or more. Specifically, the distance L is preferably equal to or greater than ((Ttotal - Tbackground) + 0.2 mm), and preferably equal to or greater than ((Ttotal - Tbackground) + 0.5 mm). The upper limit of the length added to (Ttotal - Tbackground) is preferably 2 mm or less, and preferably 1.5 mm or less. Specifically, the distance Les is preferably equal to or less than ((Ttotal - Tbackground) + 2 mm), and preferably equal to or less than ((Ttotal - Tbackground) + 1.5 mm). noLLnn / pznz / e / Yi / u With reference to Figures 3A and 3B below, the friction element welding procedure using element 1 will be described. Figures 3A and 3B are cross-sectional views that schematically illustrate examples of the lamination stack 6 to be joined using element 1 (see Figure 2A). Figure 3A shows an example before element 1 is pressed into the lamination stack 6, and Figure 3B shows an example after element 1 has been pressed into the lamination stack 6. In Figures 3A and 3B, the pressing device for pressing element 1 into the lamination stack 6 is omitted. When element 1 is pressed into the stack of laminations 6, the high-speed rotating element 1 moves down from the top side of the upper lamination 7, and the apex of the second conical body 5 makes contact with the upper lamination 7 (see FIG. 3A). At this point, the central axis of the second conical body 5 and the central axis of the first conical body 4 (i.e., the central axis of the mandrel 2) are set to be perpendicular to the upper lamination 7. Then the high-speed rotating element 1 continues moving downward, and the second conical body 5 gradually enters the upper lamination 7 from its apex. In this case, the central axis of the second conical body 5 serves as the axis of rotation for element 1, which is held in a prescribed position. Then the high-speed rotating element 1 continues moving downwards, and the flowing metal is discharged onto the side surface of the mandrel 2 along the side surface of the first conical body 4. Specifically, the flowing metal extruded by the second conical body 5, pressed into the sheet pile, is discharged onto the side surface of the mandrel 2 along the inclined side surface of the first conical body 4. As element 1 continues to move downwards while rotating at high speed, frictional heat is generated between the lower end surface of element 1 and the upper sheet 7, and between the side surface of element 1 and the upper sheet 7, so that the heated upper sheet 7 undergoes plastic flow. The softened portion of the upper sheet 7 is then discharged onto the side surface of mandrel 2. In this way, element 1 can be pressed into the stack of sheets, and mandrel 2 reaches the lower sheet 8, so that plastic flow also occurs on a surface layer portion of the lower sheet 8 (see FIG. 3B). It is inevitable that frictional heat will cause mandrel 2 to soften. Therefore, the moment mandrel 2 reaches the lower sheet 8, the first conical body 4 and the second conical body 5 collapse, and their shapes prior to mandrel 2 being pressed into the sheet stack (see FIG. 1) no longer remain. When the pressure insertion of mandrel 2 stops, the softened upper sheet 7, the softened lower sheet 8, and the softened mandrel 2 fuse and solidify, and a bonding surface 9 forms between the lower sheet 8 and mandrel 2. The portion of the upper sheet 7 that is discharged during the pressing of the mandrel 2 into the sheet stack moves upward along the lateral surface of the mandrel 2. This occurs because the lower sheet 8 is positioned below the mandrel, inhibiting the downward movement of the flowing metal. The discharged portion of the upper sheet 7 moves into a clearance above the mandrel, protrudes into this clearance, is contained by the outer circumference portion of the collar 3, and is thus secured to element 1. Specifically, when the sheet stack 6 of two stacked metal sheets shown in FIG. 2A is subjected to friction element welding using element 1 of the invention, the lower sheet 8 and the mandrel 2 join at the joining surface 9, and the upper sheet 7 is secured to the mandrel 2 and the collar 3 (see FIG. 3B). noLLnn / pznz / e / Yi / u Similarly, when the sheet stack 6 of three stacked metal sheets shown in FIG. 2B is subjected to friction element welding or when an un-illuminated sheet stack of four or more stacked metal sheets is subjected to friction element welding, the bottom sheet 8 and mandrel 2 are joined at the joining surface 9, and the top sheet 7 and the other metal sheets (the metal sheets held between the top sheet 7 and the bottom sheet 8) are fixed to the mandrel 2 and collar 3. When element 1 of the invention is used to perform friction element welding, no particular limitation is imposed on the types of metal sheets stacked to form the sheet stack 6. However, when a steel sheet is arranged as the bottom sheet 8, sufficient frictional heat is generated by the bottom sheet 8 and the mandrel 2, and a firm bond is formed on the bonding surface 9. For example, sheet stack 6 can be a sheet stack of two steel sheets, including one steel sheet arranged as the lower sheet 8 and one steel sheet arranged as the upper sheet 7, or a sheet stack of three or more metal sheets, including at least one metal sheet (a steel sheet or a light metal sheet) held between the lower sheet 8 (i.e., a steel sheet) and the upper sheet 7 (i.e., a steel sheet). On the other hand, sheet stack 6 can be, for example, a sheet stack of two metal sheets, including one steel sheet arranged as the lower sheet 8 and one light metal sheet arranged as the upper sheet 7, or a sheet stack of three or more metal sheets, including at least one steel sheet held between the lower sheet 8 (i.e., a steel sheet) and the upper sheet 7 (i.e., a light metal sheet). The technique of the present invention is, of course, applicable to a stack of sheets including a steel sheet serving as the lowest metal sheet, a light metal sheet serving as the highest metal sheet, and another light metal sheet serving as an intermediate metal sheet held between the lowest and highest sheets. Element 1 of the invention includes two conical bodies with different vertical angles, allowing the flowing metal to be discharged smoothly. Therefore, friction element welding can be performed without any problems on the sheet stack 6, in which not only the lower sheet 8 is a steel sheet but also the upper sheet 7 is a steel sheet, so that, in the resulting joint, the sheets in the stack 6 are firmly joined. As described above, in the friction element welding method of the invention using the element described above, the element of the invention is pressed into a sheet stack of two or more stacked metal sheets while rotating to thereby join the sheets in the sheet stack. In the method of producing the welded friction element joint of the invention using the element described above, the element of the invention is pressed into a stack of two or more stacked metal sheets while rotating to thereby join the sheets in the stack of sheets. The welding conditions for friction elements in these cases are adjusted appropriately to achieve the effects described above. Preferred welding conditions include an element rotation speed (rpm) of 500 to 9000 rpm and a pressing force (kN) of 3 to 9 kN. When friction element welding is performed using any of these methods, the effects described above can also be achieved. The friction element welding procedure has already been described, and its description will be omitted. EXAMPLES The present invention will be described in more detail below by way of examples. The following examples do not limit the present invention, and any modification that satisfies the substance of the invention is also included within the technical scope of the present invention. The element shown in FIG. 1 was used to perform friction element welding on a stack of sheets, consisting of a total of two stacked steel sheets, as shown in FIG. 3A, including top and bottom sheets. In some sheet stacks, a total of three metal sheets were stacked together. The combinations of top and bottom sheets and combinations of three metal sheets are shown in Table 1. The rotation speed (rpm) of the element and the pressing force (kN) during friction element welding performed on each sheet stack are shown in Table 2. The shapes of the elements used are shown in Table 2. A “heat-resistant oxide coating” shown in Table 2 was used, as exemplified above by the coating film formed from the wear-resistant material.For comparison purposes, elements that include only a conical body were used to perform friction element welding. Table 1 Stack of sheets Bottom sheet Top sheet Between bottom and top sheets Tensile strength Thickness t Metal sheet Tensile strength Thickness t Metal sheet Tensile strength Thickness t Metal sheet a 1470 MPa 1.6 mm Steel sheet 980 MPa 1.0 mm Steel sheet b 1470 MPa 1.6 mm Steel sheet 980 MPa 1.6 mm Steel sheet c 1470 MPa 1.6 mm Steel sheet 1470 MPa 1.0 mm Steel sheet d 1180 MPa 1.6 mm Steel sheet 980 MPa 1.0 mm Steel sheet e 1470 MPa 1.0 mm Steel sheet 980 MPa 1.0 mm Steel sheet f 1470 MPa 1.6 mm Steel sheet 1470 MPa 1.0 mm Steel sheet 980 MPa 1.0 mm Steel sheet g 1470 MPa 1.6 mm Steel sheet 270 MPa 1.0 mm Light metal sheet 980 MPa 1.0 mm Steel sheet £ ai Table 2 Comment on them | Inventive Example | Inventive Example Inventive Example Comparative Example Inventive Example Comparative Example Inventive Example Comparative Example Inventive Example Comparative Example Inventive Example Inventive Example Inventive Example I Inventive Example Inventive Example Inventive Example Inventive Example Vertical angle 120 s 100 < < 100 120 co 120 120 120 120 100 a 160 150 140 140 150 140 170 140 160 140 160 140 130 130 160 160 160 160 160 Joint evaluation General evaluation <c cq o o q co <c a ω resistencia (kn) lo lo 2 oj csi cu s apariencia x x condiciones de soldadura fuerza presión r- 1- r— velocidad rotación (rpm) | 6500 i elemento película recubrimiento tín n!1 tin wc recubierta óxido resistente al calor distancia l (mm) diámetro d2 superficie del fondo segundo cuerpo cónico lp 1.4 lp lp ip <p d1 primer 4.55 5.5 dos cuerpos cónicos satisfacen β<α co pila láminas cu <73 cu _q _£2 "o cd to unión no. cm 03 cdVI EC Two joints (hereafter referred to as "welded friction element joints") were produced for each of the joints shown in Table 2. One of the welded friction element joints was used to observe the appearance of a cross-section of the joint, and the weld condition of the sheet stack was evaluated. Specifically, a welded friction element joint with the mandrel penetrating through the top sheet and bonded to the bottom sheet (see FIG. 3B) was rated as "good weld" (indicated by the symbol: O), and a welded friction element joint with the mandrel not penetrating through the top sheet and a welded friction element joint with the mandrel not bonded to the bottom sheet were rated as "defective weld" (indicated by the symbol: ). The results of the evaluation are shown in Table 2. The other welded friction element joint, with the weld condition rated as "good weld" (symbol: O) in the previous appearance observation, was used for a tensile test to examine the joint's strength. The joint's strength was measured in accordance with JIS Z 3137. A welded friction element joint with a strength of 6.0 kN or more was rated "excellent (A)," and a welded friction element joint with a strength of 3.0 kN or more and less than 6.0 kN was rated "good (B)." A welded friction element joint with a strength of 2.0 kN or more and less than 3.0 kN was rated "fair (C)." The results are shown in Table 2. A welded friction element joint with the weld condition classified as "defective weld (symbol: -)" in the above appearance observation was not subjected to the tensile test, and "poor (D)" was placed in the evaluation column in Table 2, As can be seen from Table 2, all the joints in the Inventive Examples had a good appearance, and their strength was 2.2 kN or more. List of Reference Signs element mandrel collar first conical body second conical body stack of sheets upper sheet lower sheet bonding surface< / c>
Claims
1. An element for performing friction element welding on a lamination stack of two or more stacked metal laminations by pressing the element into the lamination stack while the element rotates, the element characterized in that it comprises: a circular column mandrel for inserting the lamination stack; a circular disc-shaped collar disposed in an upper end portion of the mandrel;and a first conical body extending from a lower end surface of the mandrel, wherein the collar diameter is greater than the mandrel diameter, wherein a portion of the outer circumference of the collar has a downward slope or curved shape, wherein a central axis of the first conical body coincides with a central axis of the mandrel, wherein the element further comprises a second conical body disposed in contact with a lower side of the first conical body, wherein a bottom surface of the second conical body is smaller in diameter than a bottom surface of the first conical body, wherein a central axis of the second conical body coincides with the central axis of the mandrel, and wherein a vertical angle β(°) of the second conical body and a vertical angle a(°) of the first conical body satisfy the following relation: β < oc.; 2. The element according to claim 1, further characterized in that the vertical angle a(°) of the first conical body satisfies 140 < ex < 180, and wherein the vertical angle β(°) of the second conical body satisfies 90 < β < 140.
3. The element according to claim 1 or 2, further characterized in that a distance L (mm) from a lower end of the outer circumference portion of the collar to a vertex of the second conical body in a direction parallel to the central axis of the mandrel satisfies the following relationship: (Ttotal - Tbackground) + 0.02 mm < L < (Ttotal - Tbackground) + 4 mm where Ttotal (mm) is a total thickness of the lamination stack, and Tbackground (mm) is a thickness of a lower lamination in the lamination stack.
4. The element according to any of claims 1 to 3, further characterized in that a lower sheet in the stack of sheets is a steel sheet, and wherein an upper sheet in the stack of sheets is a light metal.
5. The element in accordance with any of claims 1 to 3, further characterized in that a lower sheet in the sheet stack and an upper sheet in the sheet stack are both steel sheets.
6. The element according to any of claims 1 to 5, further characterized in that an outer surface of the first conical body and an outer surface of the second conical body each have a coating film formed of a wear-resistant material.
7. A friction element welding method characterized in that it comprises joining a stack of two or more stacked metal sheets by pressing an element into the stack of sheets while the element rotates, wherein the element used is the element according to any one of claims 1 to 6.
8. A method for producing a welded friction element joint, the method characterized in that it comprises joining a stack of two or more stacked metal sheets by pressing an element into the stack of sheets while the element rotates, wherein the element used is the element according to any one of claims 1 to 6.