Friction element joining method

Abstract

It is an object of the invention to provide a friction element engagement method. The present invention is a friction element joining method for joining a plate group by pressing an element provided with a tip angle into the plate group in which two or more metal plates are stacked while rotating the element, the friction element joining method having an oxide film removal step in which the lower surface of the element is removed even when the lower surface of the element is in contact with the oxide film on the upper surface of the lowermost metal plate of the plate group. In the oxide film removal step, an element in which the elevation angle of the element tip angle satisfies a prescribed conditional expression in accordance with the element diameter, the pressure, the rotational speed, and the tensile strength of the lowermost metal plate is used.

Description

Technical Field

[0001] The present invention relates to a friction element joining method for joining a stack of at least two metal plates by joining friction elements. Background Art

[0002] In recent years' automotive industry, for the purpose of achieving both reduction of environmental load based on vehicle body lightweighting and safety, the adoption of high-strength steel sheets called ultra-high-strength steel has been promoted, and it is expected to develop steel sheets with higher strength and high workability in the future. However, along with the increase in strength and workability of steel sheets, a problem has arisen in fusion joining such as resistance spot welding due to the reduction in joint strength caused by embrittlement of the solidification structure. For this reason, joining techniques that can join two or more steel sheets including high-strength steel sheets in a non-fusion manner have attracted attention.

[0003] As a non-fusion joining technique, for example, the application of FEW (Friction Element Welding) that joins by pressing an element into a stack of plates while rotating the element at high speed has been studied as described in Reference 1. As an element used in this friction element joining (FEW), for example, the structure disclosed in Patent Document 1 has been proposed.

[0004] [Reference 1]

[0005] 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 collocated with the JSME / ASME 2017 6th International Conference on Materials and Processing, June 4 - 8, 2017 Los Angeles, California, USA)

[0006] A component is disclosed in Patent Document 1, in which the front end of the mandrel portion of the component (corresponding to the "connecting element" in Document 1) is a substantially flat end face, and a pin-shaped centering portion protrudes from the center of the flat end face. By configuring the component in this way, each connection process is performed by aiming at the connection portion using the pin-shaped centering portion. Thereby, the applied frictional energy can be concentrated at the respective positions of the components to be inserted.

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-527804

[0008] In Patent Document 1, only the shape of the pin at the front end of the mandrel portion of the component is disclosed. However, in actual joining of the components, it is necessary to set the shape of the component corresponding to the joining conditions, but this is not disclosed in Patent Document 1.

[0009] In addition, if an oxide remains on the upper surface of the lower plate that forms a joint with the component, the oxide will mix into the joint, and a sound joint will not be formed, resulting in a problem of reduced joint strength. For this reason, when joining components, it is required to remove the oxide (specifically, the oxide film) on the upper surface of the lower plate that forms a joint with the component.

[0010] Regarding this problem, it is considered to apply the component having the shape described in Patent Document 1. However, in the component of Patent Document 1, the contact area between the pin-shaped centering portion at the lower part of the component and the plate-like member becomes narrow, so it is known that there is a problem that the time required to remove the oxide on the surface of the plate-like member (that is, the upper surface of the lower member) caused by the contact between the centering portion and the plate-like member becomes long.

[0011] Here, the above-mentioned "lower plate that forms a joint with the component" refers to a metal plate that undergoes frictional element joining with the front end (i.e., the lower part of the component) of the component, and is the lowermost metal plate among the metal plates constituting the plate group. The above-mentioned "upper surface of the lower plate" refers to the metal plate surface of the lower plate on the mating surface side with the metal plate disposed above the lower plate. Summary of the Invention

[0012] The present invention has been completed to solve the above problems, and an object thereof is to provide a friction element joining method that can remove the oxide on the upper surface of the lower plate that forms a joint with the component in a short time and obtain a sound joint state when performing friction element joining on a plate group composed of two or more metal plates.

[0013] In the present invention, dedicated research has been conducted to achieve the above problems in the friction element joining method. The friction element joining method refers to a joining method in which a component is pressed into a plate group in which two or more metal plates are overlapped while the component is rotated at high speed to perform friction element joining of the plate group.

[0014] In the process of removing the oxide (oxide film) on the upper surface of the lower plate in the friction element joining method, the inventors conducted experiments using various elements with different tip shapes. As a result, it was found that in order to achieve the above problems, it is effective to appropriately vary the elevation angle (hereinafter, also referred to as "tip elevation angle") of the element provided with a tip angle according to the element diameter (hereinafter, also referred to as "diameter of the element").

[0015] That is, after the element penetrates the upper plate of the plate group, the tip of the high-speed rotating element abuts against the upper surface of the lower plate of the plate group. If the oxide film existing on the upper surface of the lower plate is smoothly discharged using the tip of the element, the process of removing the oxide film (here, referred to as "oxide film removal process on the upper surface of the lower plate") can be shortened. The larger the element diameter, the larger the area of the oxide film that needs to be discharged. At this time, by using an element whose tip elevation angle is set within an appropriate range according to the element diameter, the pressing force and rotational speed in the oxide film removal process, and the tensile strength of the joined material (i.e., the metal plate constituting the plate group), the contact area between the lower part of the element and the upper surface of the lower plate can be appropriately ensured. It was clarified that appropriately managing the tip shape of the element according to the joining conditions in this way is effective for shortening the oxide film removal process on the upper surface of the lower plate.

[0016] In addition, although it will be described later, the above-mentioned "tip elevation angle of the element" refers to Figure 2 the elevation angle (θ) shown in Figure 2 and the above-mentioned "element diameter" refers to

[0017] The present invention has been completed based on such an insight, and the following is the gist.

[0018] [1] A friction element joining method in which an element provided with a tip angle is rotated and pressed into a plate group in which two or more metal plates are overlapped to join the above plate group, wherein,

[0019] it has an oxide film removal process, that is, before the process of starting joining by frictional heat generation, the lower part of the above element is brought into contact with the upper surface of the lowermost metal plate arranged in the lowermost layer of the above plate group to remove the oxide film,

[0020] In the above oxide film removal process,

[0021] when the element diameter is set to D (mm), the tip elevation angle of the element is set to θ (°), the pressing force is set to P (kN), the rotational speed is set to R (rpm), and the tensile strength of the above lowermost metal plate is set to TS (MPa),

[0022] when 5.0 > D ≥ 3.0, use the above element whose above elevation angle satisfies formula (1),

[0023] When 7.0 > D ≥ 5.0, use the above-described element with the elevation angle satisfying formula (2).

[0024] When D ≥ 7.0, use the above-described element with the elevation angle satisfying formula (3).

[0025] (-0.016×D + 0.13)×(P×R / TS) ≤ θ ≤ 60 - D…(1)

[0026] (-0.004×D + 0.071)×(P×R / TS) ≤ θ ≤ 60 - D…(2)

[0027] (-0.0004×D + 0.045)×(P×R / TS) ≤ θ ≤ 60 - D…(3)

[0028] [2] According to the friction element joining method described in [1], wherein

[0029] the rotational speed in the above-described oxide film removal process is 500 rpm or more.

[0030] [3] According to the friction element joining method described in [1] or [2], wherein

[0031] the pressing force in the above-described oxide film removal process is 1 kN or more.

[0032] [4] According to the friction element joining method described in any one of [1] to [3], wherein

[0033] the above-described metal plate is a steel plate, and the tensile strength of the steel plate is 590 MPa or more.

[0034] [5] According to the friction element joining method described in [1] or [2], wherein

[0035] the front end of the above-described element is a conical shape formed by one cone.

[0036] According to the present invention, by appropriately specifying the elevation angle (θ) of the front end of the element according to the element diameter (D) and the joining conditions in the oxide film removal process, it is possible to appropriately ensure the contact area between the lower part of the element and the upper surface of the lower plate. As a result, it is possible to shorten the oxide film removal process on the surface of the metal plate to be joined (i.e., the upper surface of the lower plate) without being affected by the composition of the metal plate (the material to be joined), etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a schematic diagram showing an example of a state in which a plate group composed of two metal plates is joined by the friction element joining method of the present invention.

[0038] Figure 2It is a cross-sectional view showing an example of the element shape used in the friction element joining method of the present invention.

[0039] Figure 3 It is a schematic diagram showing an example of the joining state using an existing element. Detailed Description of the Invention

[0040] Hereinafter, the present invention will be described. In addition, the present invention is not limited to this embodiment.

[0041] First, refer to Figure 1 and Figure 2 to describe the friction element joining method as an embodiment of the present invention. Figure 1 It is a cross-sectional view showing an example of the state in which a plate group composed of two metal plates is joined by the friction element joining method of the present invention. Figure 2 It is a cross-sectional view showing an example of the element shape provided with a front end angle used in the friction element joining method of the present invention.

[0042] In the friction element joining method of the present invention (hereinafter, there are also cases where it is referred to as "joining method"), while rotating the element provided with a front end angle, it is pressed into a plate group in which two or more metal plates are overlapped to join the plate group (refer to Figure 1 , 2 ). This joining is a friction joining using frictional heat generation. The above-mentioned "plate group in which two or more metal plates are overlapped" means a plate group in which two or more metal plates are laminated.

[0043] In addition, in the following description, the case of joining friction elements by overlapping two metal plates will be described, but the present invention can also be applied to the case of joining by overlapping three or more metal plates, and the same effect can be obtained.

[0044] The joining method of the present invention has an oxide film removal process, that is, at least before the process of starting the joining using frictional heat generation, the lower part of the element is brought into contact with the oxide film on the upper surface of the lowermost metal plate (hereinafter, referred to as "lower plate") arranged at the lowermost side in the plate group to remove the oxide film.

[0045] For example, as all the processes of the joining method, it is preferably provided with an upper plate entering process of the element, an oxide film removal process on the upper surface of the lower plate, a plastic deformation process caused by frictional heat generation between the lower part of the element and the upper surface of the lower plate, and a crimping process. In the following description, these processes will be described.

[0046] Here, the above-mentioned "upper plate" refers to the uppermost metal plate among the metal plates (materials to be joined) that make up the plate group. The upper plate and the lower plate can be plate-like components. In addition, the element has a mandrel portion and a collar portion, and a front end angle is provided in the region of the front end of the mandrel portion (i.e., the front end of the element) (refer to Figure 2 ).

[0047] 〔Upper plate insertion process〕

[0048] Although not shown in the figure, first, the plate group is placed on the support table of the joining device in such a way that the overlapping metal plates (i.e., the plate group) face the element mounted on the joining device. Next, the upper plate insertion process starts. In this process, the rotation speed of the element is controlled by the control unit of the joining device. The element rotates and contacts the upper plate, and then the control unit applies a pressing force to press the element into the upper plate. As a result, the upper plate of the plate-like component is plasticized due to frictional heat, the mandrel portion of the element enters the upper plate, and then the element penetrates the upper plate. Furthermore, the lower part of the element contacts the upper surface of the lower plate.

[0049] In addition, from the viewpoint of applying the joining method of the present invention to the joining of metal plates including ultra-high strength steel described later, it is preferable that the pressing force in this process is 3 to 6 kN and the rotation speed is 3000 to 7000 rpm. If the pressing force is less than 3 kN, there is a concern that the entry into the upper plate cannot be promoted. On the other hand, if the pressing force exceeds 6 kN, there is a concern that the load on the joining device becomes large because the element enters the upper plate in a state of insufficient heating. If the rotation speed is less than 3000 rpm, there is a concern that plastic deformation is hindered due to insufficient heating. On the other hand, if the rotation speed exceeds 7000 rpm, there is a concern that the element is deformed due to excessive heating.

[0050] Next, the subsequent oxide film removal process is carried out.

[0051] 〔Oxide film removal process〕

[0052] In the oxide film removal process, the oxide film existing on the upper surface of the lower plate is discharged by bringing the rotating front end of the element (i.e., the lower part of the element) into contact with the upper surface of the lower plate. The element rotates through the control unit of the joining device, and thus the oxide film removal process on the upper surface of the lower plate starts. In this oxide film removal process, when the control unit of the joining device senses that the pressing position of the element has reached a specified depth (i.e., the specified pressing depth), it is determined that the removal of the oxide film is completed and this process ends.

[0053] Here, the above-mentioned "pressing depth" refers to the depth (i.e., the distance in the plate thickness direction) (mm) that the element enters in the plate thickness direction of the lower plate with the position where the front end of the element contacts the upper surface of the lower plate set as 0 mm as the reference.

[0054] The above-mentioned "prescribed press-in depth" refers to the depth in the plate thickness direction (press-in depth) at a position where the area of the contact portion of the component with the lower plate becomes equal to or greater than the cross-sectional area of the mandrel portion of the component, and is set in consideration of the deformation of the component caused by the pressure during press-in.

[0055] In the following embodiments, the "prescribed press-in depth" is set to 0.8 mm based on the results of preliminary tests. This prescribed press-in depth is pre-stored in the storage unit of the bonding device as the "press-in depth setting value". In the control unit, the press-in depth setting value stored in the storage unit is compared with the measured actual press-in depth value obtained by measurement, thereby detecting whether the prescribed press-in depth has been reached. Then, when it is detected that the prescribed press-in depth has been reached, it is determined that the removal of the oxide film has been completed. In addition, as a method for measuring the above-mentioned "actual press-in depth value", for example, there is a method of detecting the position of the cylinder for applying the pressing force using an optical sensor.

[0056] As described above, if an oxide remains on the upper surface of the lower plate where the joint portion with the component is formed, the oxide will mix into the joint portion. Therefore, in the present invention, it is important to prevent the oxide from mixing into the joint portion by removing the oxide film on the upper surface of the lower plate remaining after the oxide film removal process so that it becomes below a prescribed amount. Thereby, a sound joint portion can be formed, and the joint strength can also be improved.

[0057] In order to obtain such an effect, it is also important to appropriately define the relationship between the welding conditions and the component shape (specifically, the component diameter and the elevation angle of the component tip) in the oxide film removal process on the upper surface of the lower plate. As the above-mentioned welding conditions, at least the pressing force, the rotation speed, and the tensile strength of the metal plate can be cited. Thereby, it is possible to shorten the required time (t) (unit: second) from the start to the completion of the oxide film removal. In addition, since the detailed content will be described later, the description here is omitted.

[0058] Next, the subsequent plastic deformation process is performed.

[0059] 〔Plastic Deformation Process〕

[0060] In the plastic deformation process, under the pressing force adjusted by the control unit of the bonding device, the component is pressed into the lower plate while being rotated at high speed. Thereby, the friction bonding process is started. In the friction bonding process, the tip of the component that has entered the lower plate undergoes plastic deformation of the lower plate and the component due to frictional heat generation. The tip of the mandrel portion of the component is connected to the lower plate by friction element bonding, and the material of the upper plate extruded due to plastic deformation comes into contact with the upper part of the component and is pressed by the collar portion.

[0061] In addition, from the perspective of applying the joining method of the present invention to the joining of metal plates including the ultra-high strength steel described later, it is preferable that the pressing force in this process is 3 to 6 kN and the rotational speed is 3000 to 7000 rpm. If the pressing force is less than 3 kN, there is a concern that the entry into the upper plate cannot be promoted. On the other hand, if the pressing force exceeds 6 kN, there is a concern that the load on the joining device becomes large because the element enters the upper plate in a state of insufficient heating. If the rotational speed is less than 3000 rpm, there is a concern that plastic deformation is hindered due to insufficient heating. On the other hand, if the rotational speed exceeds 7000 rpm, there is a concern that the element is deformed due to excessive heating.

[0062] Next, the subsequent crimping process is performed.

[0063] 〔Crimping process〕

[0064] In the crimping process, mechanical joining of the element and two or more metal plates constituting the plate group is achieved. The control unit of the joining device finally applies a pressing force to the element in a state where the rotation of the element has stopped, and crimps the material of the metal plate extruded due to plastic deformation with the element, thereby completing the friction joining process.

[0065] In addition, from the perspective of applying the joining method of the present invention to the joining of metal plates including the ultra-high strength steel described later, it is preferable that the pressing force in this process is 8 to 9 kN. If the pressing force is less than 8 kN, there is a concern that the crimping is insufficient. On the other hand, if the pressing force exceeds 9 kN, there is a concern that the element is deformed.

[0066] Through the above processing, as Figure 1 shown, a sound joining state of the metal plate and the element constituting the plate group can be obtained.

[0067] In addition, in the above joining method, a metal plate provided with a lower hole (for example, a through hole) can also be used as the upper plate. The lower hole can also be formed, for example, by performing pre-hole processing. In this case, the above-described process of the element entering the upper plate is omitted. That is, after the plate group is set on the support table of the joining device in such a manner that the overlapping metal plates (i.e., the plate group) face the element mounted on the joining device, the above-described process of removing the oxide film on the upper surface of the lower plate and subsequent processes are performed.

[0068] Next, the relationship between the joining conditions of the oxide film removal process and the element shape in the present invention will be described in detail.

[0069] As described above, in order to shorten the time required for the oxide film removal process on the upper surface of the lower plate, it is effective to smoothly discharge the oxide film. Therefore, as a result of repeated intensive studies by the present inventors, it has been found that: (a) the elevation angle of the tip of the element is set within an appropriate range according to the element diameter, the pressing force and rotational speed in the oxide film removal process, and the tensile strength of the metal plate (lower plate), and (b) by using an element with the elevation angle of the tip within an appropriate range in the oxide film removal process, the contact area between the lower part of the element and the upper surface of the lower plate can be appropriately ensured.

[0070] It has also been found that: by using this element, the oxide film remaining on the upper surface of the lower plate after the oxide film removal process is removed so as to be below a specified amount, and the mixing of oxides into the joint can be appropriately suppressed.

[0071] Specifically, in the oxide film removal process, when the element diameter is D (mm), the elevation angle of the tip of the element is θ (°), the pressing force in the oxide film removal process is P (kN), the rotational speed in the oxide film removal process is R (rpm), and the tensile strength of the lowermost metal plate (lower plate) is TS (MPa),

[0072] When 5.0 > D ≥ 3.0, an element with an elevation angle satisfying formula (1) is used,

[0073] When 7.0 > D ≥ 5.0, an element with an elevation angle satisfying formula (2) is used,

[0074] When D ≥ 7.0, an element with an elevation angle satisfying formula (3) is used.

[0075] (-0.016 × D + 0.13) × (P × R / TS) ≤ θ ≤ 60 - D…(1)

[0076] (-0.004 × D + 0.071) × (P × R / TS) ≤ θ ≤ 60 - D…(2)

[0077] (-0.0004 × D + 0.045) × (P × R / TS) ≤ θ ≤ 60 - D…(3)

[0078] In the present invention, in the oxide film removal process, it is important to use an element having a shape satisfying the conditional expressions of formulas (1) to (3). The reasons are as follows.

[0079] The large contact area between the lower part of the element and the upper surface of the lower plate can effectively discharge the oxide film, so the joint strength of the obtained joint is increased. Therefore, it is considered effective to ensure the contact area between the lower part of the element and the upper surface of the lower plate by increasing the element diameter (D) and making the front end of the element closer to flat. On the other hand, in an element with a smaller element diameter (D), if the contact area between the lower part of the element and the upper surface of the lower plate is increased, the thermal influence caused by the heat input to the element becomes larger, and as a result, the joint strength of the obtained joint is reduced. Therefore, in the present invention, the above conditional expression is defined by gradually changing the elevation angle (θ) of the front end of the element according to the element diameter (D) so that the contact area between the lower part of the element and the upper surface of the lower plate becomes optimal.

[0080] Specifically, when the element diameter (D) satisfies 5.0 > D ≥ 3.0, the conditional expression (1) is defined in such a way that the smaller the element diameter (D), the larger the elevation angle (θ) of the front end of the element. When the elevation angle (θ) of the front end of the element does not satisfy the conditional expression (1), the contact area between the lower part of the element and the lower plate surface becomes narrow, and the oxide film removal effect cannot be obtained. In addition, as described above, in an element with a smaller element diameter (D), in order to ensure the contact area, the thermal influence caused by the heat input becomes larger. In addition, if the element diameter is small, the diameter of the joint part becomes small, so there is a possibility that sufficient joint strength cannot be obtained. Therefore, in the present invention, the case where the element diameter (D) is 3.0 mm or more is taken as the object.

[0081] In addition, when the element diameter (D) satisfies 7.0 > D ≥ 5.0, compared with the element diameter (D) of the conditional expression (1), the element diameter (D) of this conditional expression (2) is larger, so the thermal influence is reduced. Therefore, compared with the conditional expression (1), the conditional expression (2) is defined in such a way that the elevation angle (θ) of the front end of the element changes more gently. When the elevation angle (θ) of the front end of the element does not satisfy the conditional expression (2), the contact area between the lower part of the element and the lower plate surface becomes narrow, and the oxide film removal effect cannot be obtained.

[0082] Moreover, when the element diameter (D) satisfies D ≥ 7.0, compared with the conditional expressions (1) and (2), the element diameter (D) of this conditional expression (3) is larger. Therefore, even if the elevation angle (θ) of the front end of the element becomes smaller, the thermal influence can be suppressed and the contact area can be ensured. Therefore, the conditional expression (3) is defined in such a way that the larger the element diameter (D), the smaller the elevation angle (θ) of the front end of the element. When the elevation angle (θ) of the front end of the element does not satisfy the conditional expression (3), the contact area between the lower part of the element and the lower plate surface becomes narrow, and the oxide film removal effect on the joint surface cannot be obtained.

[0083] In addition, the upper limit value of the element diameter (D) to which the conditional expression (3) is applied is not particularly specified, but the element diameter (D) is preferably 9.0 mm or less. The reason is as follows. When the element diameter (D) exceeds 9.0 mm, the torque required for the element to rotate and penetrate increases, so it can be assumed that the required device structure also becomes larger. That is, from the perspective of the automobile assembly process, the practicality is impaired.

[0084] In the oxide film removal process of the present invention, in addition to specifying the above conditional expressions, the following bonding conditions can also be specified for the purpose of further promoting the discharge of the oxide film.

[0085] 〔Rotation speed R〕(Preferred condition)

[0086] In the oxide film removal process, the rotation speed R is preferably 500 rpm or more. This is because when the rotation speed R becomes 500 rpm or more, the plastic deformation caused by frictional heat generation is promoted, and the removal of the oxide film is promoted. The rotation speed R is more preferably 5000 rpm or more. The upper limit of the rotation speed R is not particularly specified, but from the perspective of suppressing the reduction of the element strength due to excessive heat generation, the rotation speed R is preferably 9000 rpm or less, and more preferably 8000 rpm or less.

[0087] 〔Pressing force P〕(Preferred condition)

[0088] In the oxide film removal process, the pressing force P is preferably 1 kN or more. This is because when the pressing force P is 1 kN or more, the plastic deformation of the lower plate is promoted, and the removal of the oxide film is promoted. The pressing force (P) is more preferably 3 kN or more, and further preferably 7 kN or more. The upper limit of the pressing force (P) is not particularly specified, but from the perspective of the element strength, the pressing force (P) is preferably 10 kN or less, and more preferably 9 kN or less.

[0089] In addition, in the present invention, in the oxide film removal process, it is preferable that the required time (t) from the start to the completion of the removal of the oxide film on the upper surface of the lowermost metal plate (the upper surface of the lower plate) is 5 seconds or less. The reason is as follows. When this required time exceeds 5 seconds, the element becomes high temperature due to frictional heat generation, and as a result, the umbrella part of the element is thermally deformed, and sufficient joint strength cannot be obtained. The lower limit of the required time is not particularly specified. From the perspective of shortening the bonding process, the required time is preferably 1 second or less.

[0090] In addition, in the present invention, in the oxide film removal process, it is preferable that the remaining rate of the oxide film on the upper surface of the lowermost metal plate is less than 20%. The reason is as follows. When the remaining rate of this oxide film is 20% or more, the area of the joint part between the element and the lower plate decreases, and as a result, there is a concern that the joint strength may be reduced. The lower limit of the remaining rate of the oxide film is not particularly specified.

[0091] Here, asFigure 1 , 3 As shown, the "oxide film residual rate" refers to the ratio of the oxide on the upper surface of the metal plate (here, the upper surface of the lower plate) remaining at the interface between the element and the metal plate after the oxide film removal process. In addition, the oxide film residual rate can be measured by the method described in the following examples.

[0092] Next, Figure 2 One embodiment of the element used in the bonding method of the present invention will be described.

[0093] Figure 2 is a longitudinal sectional view taken by cutting in a manner passing through the center of element 1. As Figure 2 shown, element 1 used in the present invention has a mandrel portion 2 and a collar portion 3.

[0094] As Figure 1 shown, element 1 is a tool for joining the friction element of the plate group by pressing it into the plate group in which two or more metal plates are overlapped while rotating element 1.

[0095] The mandrel portion 2 is provided at the axis of element 1, and the portion other than the front end is formed in a cylindrical shape. The diameter (mm) of this cylindrical shape is the element diameter (D). The front end of the mandrel portion (i.e., the front end of the element) is inclined in a manner that the front end portion protrudes and is formed in a conical shape. As Figure 2 shown in the sectional view, the side surface of this conical shape becomes a tapered shape. Specifically, as Figure 2 shown, the straight line passing through the end of the cylindrical shape and the axis of the element becomes a tapered shape. There is no flat area at the front end of the mandrel portion. That is, the cross-section of the cone is a straight line, and there is no flat area parallel to the straight line perpendicular to the axis of the element. This is for the following reason. This is because: if there is a flat area, there will not be a sufficient difference in the pressure for extruding the oxide film between the center of the mandrel portion and the outer peripheral side of the mandrel portion, and thus there is a concern that the discharge effect of the oxide film cannot be obtained sufficiently.

[0096] In the present invention, the angle (i.e., the taper angle) (°) formed by the straight line perpendicular to the axis of element 1 at the position of the protruding front end of the mandrel portion and the side surface of the conical shape (i.e., the tapered surface) is defined as the elevation angle (θ).

[0097] The total length L (mm) of the mandrel portion 2 is a length equal to or less than the total thickness of the metal plates constituting the plate group 6. The total length L of the mandrel portion 2 only needs to be adjusted to a length that can join the front end of the mandrel portion 2 to the lower plate 8. This total length L is preferably 3 to 6 mm.

[0098] The collar portion 3 is provided above the mandrel portion 2, that is, at the head of element 1. As Figure 2As shown, the shape of the collar portion 3 can be formed, for example, into the shape of a wafer or a truss. The shape of the collar portion 3 only needs to be a shape that can suppress the material of the upper plate 7 from being extruded due to plastic flow.

[0099] In addition, Figure 2 The "H" shown represents the distance from the position of the foremost end of the mandrel portion to the position where cutting has been performed in a direction perpendicular to the central axis of the mandrel. In addition, since this H is less than or equal to the overall length L of the mandrel portion 2, H < L is satisfied.

[0100] Specifically, the element shape of the element 1 used in the present invention is formed such that the elevation angle (θ) at the front end is within the numerical range derived from the above conditional expression composed of the element diameter (D), the pressing force P and rotational speed R in the oxide film removal process, and the TS of the metal plate (material to be joined). Thereby, the oxide film on the upper surface of the lower plate is easily discharged from the joint interface, and the oxide film removal process can be shortened. As a result, even if this process is shortened, compared with the joining using the conventional element disclosed in the above Patent Document 1, a sound joint state can be ensured in the joining using the element 1 of the present invention.

[0101] Next, use Figure 1 and Figure 3 to describe the joint state of the joint obtained by the joining method of the present invention.

[0102] Figure 1 shows an example of the state in which a plate group composed of two metal plates is joined using the element 1 provided with a front end angle of the present invention. In Figure 3 In the existing example, an example of the state in which a plate group composed of two metal plates is joined using the existing element 10 is shown. Figure 1 and Figure 3 Both use the above-described joining method of the present invention as the joining method. In addition, Figure 1 and Figure 3 are cross-sectional views in the plate thickness direction cut in a manner passing through the center of the element of the obtained joint.

[0103] As Figure 3 In the existing example shown, when joining using the existing element 10 by the joining method of the present invention, the plate group 6 composed of two metal plates ( Figure 3 The upper plate 7 and lower plate 8 shown in ) becomes a state joined by the element 10. However, as Figure 3 shown, although the upper plate 7 and lower plate 8 are joined by the element 10, there is a gap between the material of the upper plate 7 that has been plastically deformed and extruded during the joining process and the collar portion 3 provided on the upper part of the mandrel.

[0104] Here, as the above-mentioned "existing component", a component with a conical shape at the front end of the mandrel part of the component is used. However, the angle is not specified according to the component diameter and bonding conditions as in the present invention.

[0105] The inventors of the present invention believe that this gap is caused by the oxide film removal process on the lower plate surface of the friction element bonding method. Observing the cross-section of the bonding part of the bonding joint where the discharge of the oxide film existing on the upper surface of the lower plate in the oxide film removal process is insufficient, oxides caused by the oxide film on the upper surface of the lower plate remain at the bonding interface between the component 10 and the lower plate 8. As a result, the bonding state is not sound. This is caused by insufficient time of the oxide film removal process and insufficient discharge of the oxide film. In addition, it is considered that the contact area between the component and the upper surface of the lower plate cannot be sufficiently ensured due to inappropriate adjustment of the component shape, and the removal of the oxide film is not promoted.

[0106] In contrast, as Figure 1 shown, when the component 1 of the present invention (refer to Figure 2 ) is bonded by the bonding method of the present invention, the plate group 6 composed of two metal plates ( Figure 1 the upper plate 7 and the lower plate 8 in) becomes a state bonded by the component 1. Specifically, for the plate group 6 composed of two plate-like members (the upper plate 7 and the lower plate 8), the front end of the mandrel 2 is connected to the lower plate 8 by friction element bonding, and the material of the upper plate 7 that is plastically deformed and extruded during the bonding process is pressed by the collar part 3 provided on the upper part of the mandrel. Thus, each metal plate 7, 8 and the component 1 are in a bonded state.

[0107] As Figure 1 shown, observing the cross-section of the bonding part in the component 1 of the present invention, a sound bonding state was confirmed. That is, it can be seen that in the case of using the bonding method of the component 1 with a front end angle of the present invention, different from the case of using the existing component 10 shown in Figure 3 , the residual ratio of oxides after the oxide film removal process can be significantly reduced.

[0108] In addition, in the present invention, a steel plate can be used as the metal plate (material to be bonded) constituting the plate group. In this case, it is only necessary to overlap two or more metal plates including at least one steel plate to form a plate group. For example, an aluminum alloy plate and a steel plate can be overlapped to form a plate group. In addition, for example, steel plates can also be overlapped with each other to form a plate group. In the case of a plate group of an aluminum alloy plate and a steel plate, the aluminum alloy plate can be arranged as either the upper plate or the lower plate.

[0109] As Figure 1As in the example shown, in the present invention, metal plates including ultra-high strength steel can be applied to the upper plate 7 and the lower plate 8. In the present invention, "ultra-high strength steel" refers to a steel plate with a tensile strength (TS) of 980 MPa or more, and "high strength steel" refers to a steel plate with a tensile strength (TS) of 590 MPa or more and less than 980 MPa. In addition, the tensile strength of the lower plate is preferably 590 MPa or more.

[0110] Examples

[0111] Hereinafter, in order to further understand the present invention, examples will be used for description. In addition, the present examples do not limit the present invention, and as long as they satisfy the gist of the present invention, they are all included in the technical scope of the present invention.

[0112] As test specimens, metal plates shown in the upper plate and the lower plate of Table 1 were overlapped to form a plate group. The upper plate of plate group A used an upper plate with Φ7 mm pre-hole processing performed.

[0113] In the present example, only the oxide film removal process in the above-mentioned various processes was performed, and the evaluation described later was carried out. In the oxide film removal process, it was controlled to be carried out with the pressing force and rotation speed shown in Table 2. At this time, as described above, the press-in depth was set to 0.8 mm. In addition, the shape of the element used in the joining used an element with an element diameter (D) and an elevation angle (θ) of the element being the values shown in Table 2. In addition, the front-end removal height was 0. This "front-end removal height" refers to the height of the conical starting point (refer to Figure 2 ).

[0114] The evaluation of shortening the time of the oxide film removal process of the present invention was carried out as follows.

[0115] 〔Evaluation of shortening the time〕

[0116] In the present example, the "time t (seconds) required until the oxide film removal process is completed" in Table 2 represents the required time of the oxide film removal process of the present invention. Specifically, the time required from the start of the removal of the oxide film to the completion of the removal in the oxide film removal process was set as the "required time (t)". For the start of the removal of the oxide film removal process, it was judged as "start" when the front end of the element contacted the upper surface of the lower plate. For the completion of the removal of the oxide film removal process, it was judged as "completed" when the front end of the element reached the above-mentioned press-in depth. In addition, in the present example, the upper limit value of the required time of the oxide film removal process was set to 5 seconds.

[0117] Here, when the required time (t) is 0 seconds or more and less than 2 seconds, the symbol "A" is marked; when the required time (t) is 2 seconds or more and less than 3 seconds, the symbol "B" is marked; when the required time (t) is 3 seconds or more, the symbol "C" is marked. In addition, when the oxide film removal process is not completed within the above upper limit time (within 5 seconds), the symbol "F" is marked. The evaluations "A", "B", and "C" are evaluated as qualified, and "A" represents the best. The evaluation "F" is evaluated as unqualified, and "F" represents the worst. The obtained evaluation results are shown in Table 2.

[0118] In addition, the distribution of the oxide film remaining on the upper surface of the lower plate after the oxide film removal process was observed using the lower plate after the oxide film removal process ended by the method shown below. Then, the evaluation was carried out according to the criteria shown below.

[0119] 〔Observation of the distribution of the oxide film〕

[0120] The observation of the distribution of the oxide film was carried out immediately after the oxide film removal process of the present invention was completed. The distribution observation used the lower plate after the oxide film removal process ended. EPMA (Electron Probe Micro Analyzer) was used to observe the distribution of the oxide on the surface of the steel plate (the upper surface of the lower plate) at the interface between the component and the steel plate. The observation area was Figure 1 the range of the remaining oxide measurement represented by the square in. Specifically, the area including the interface between the lower part of the component and the lower plate and corresponding to the plate width direction of the component diameter (D) was used as the above measurement range.

[0121] Five visual fields were appropriately selected equidistantly in the left and right directions centered on the component axis, and the average value of the oxide amounts measured in the above 10 visual fields was obtained. This average value was used as the oxide amount after the oxide film removal process. In addition, the oxide amount on the surface of the lower plate before the oxide film removal process was obtained by observing the cross-section of the lower plate using EPMA. Then, the distribution ratio x (%) of the oxide amount after the above oxide film removal process to the oxide amount on the surface of the lower plate before the oxide film removal process was obtained. This distribution ratio x was used as the above "oxide film remaining rate (%)".

[0122] Here, when the distribution ratio x of the remaining oxide is less than 10%, it is evaluated as symbol "A". When the distribution ratio x is 10% or more and less than 20%, it is evaluated as symbol "B". When the distribution ratio x is 20% or more and less than 30%, it is evaluated as symbol "C". When the distribution ratio x is 30% or more, it is evaluated as symbol "F". The evaluations of "A" and "B" are qualified (sound bonding state), and "A" represents the best. The evaluations of "C" and "F" are unqualified, and "F" represents the worst. In addition, as described above, the "sound bonding state" refers to a bonding state in which the distribution of the remaining oxide is significantly reduced. The obtained evaluation results are shown in Table 2.

[0123] [Table 1]

[0124]

[0125] [Table 2]

[0126]

[0127] For Nos. 2, 4, 8, 10, and 26 shown in Table 2, each conditional expression was applied according to the element diameter (D), but the elevation angle (θ) of the front end of the element used in the bonding did not satisfy each conditional expression. As a result, the contact area between the lower part of the element and the surface of the lower plate became narrow, and the effect of removing the oxide film on the bonding surface could not be obtained.

[0128] Description of Reference Numerals

[0129] 1, 10... elements; 2... mandrel part; 3... collar part; 6... plate group; 7... upper plate; 8... lower plate; 9... interface of the bonding part between the element and the lower plate.

Claims

1. A method for joining friction elements, which presses an element having a front end angle into a stack of two or more overlapping metal plates while rotating the element to join the stack of plates, characterized in that it has an oxide film removal process, that is, before the process of starting the joining using frictional heat generation, the lower part of the element is brought into contact with the upper surface of the lowermost metal plate in the stack of plates to remove the oxide film, in the oxide film removal process, when the diameter of the element is D (mm), the elevation angle of the front end of the element is θ (°), the pressing force is P (kN), the rotational speed is R (rpm), and the tensile strength of the lowermost metal plate is TS (MPa), when 5.0 > D ≥ 3.0, the element with the elevation angle satisfying formula (1) is used, when 7.0 > D ≥ 5.0, the element with the elevation angle satisfying formula (2) is used, when D ≥ 7.0, the element with the elevation angle satisfying formula (3) is used, (-0.016×D + 0.13)×(P×R / TS) ≤ θ ≤ 60 - D…(1) (-0.004×D + 0.071)×(P×R / TS) ≤ θ ≤ 60 - D…(2) (-0.0004×D + 0.045)×(P×R / TS) ≤ θ ≤ 60 - D…(3).

2. The method for joining friction elements according to claim 1, characterized in that the rotational speed in the oxide film removal process is 500 rpm or more.

3. The method for joining friction elements according to claim 1 or 2, characterized in that the pressing force in the oxide film removal process is 1 kN or more.

4. The method for joining friction elements according to claim 1 or 2, characterized in that the metal plate is a steel plate, and the tensile strength of the steel plate is 590 MPa or more.

5. The method for joining friction elements according to claim 3, characterized in that the metal plate is a steel plate, and the tensile strength of the steel plate is 590 MPa or more.

6. The method for joining friction elements according to claim 1 or 2, characterized in that the front end of the element is a conical shape composed of one cone.

Images