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JP-7856465-B2 - Friction stir welding method, friction stir welding joining tool, and method for manufacturing friction stir welded joints

JP7856465B2JP 7856465 B2JP7856465 B2JP 7856465B2JP-7856465-B2

Inventors

  • 鈴木 励一
  • 下田 陽一朗
  • 奥田 真三樹

Assignees

  • 株式会社神戸製鋼所

Dates

Publication Date
20260511
Application Date
20220330

Claims (20)

  1. A friction stir welding method for joining a first member made of a metal material and a second member made of a different material from the first member and having at least one through hole, using a joining auxiliary member made of the same material as the first member, A stacking step in which the first member, the second member, and the joining auxiliary member are stacked in the order such that the through hole of the second member is covered by the first member and the joining auxiliary member, The process includes a friction stir welding step in which a rotating joining tool is used to push at least one of the first member and the joining auxiliary member into the through hole, thereby forming a friction stir joint between the first member and the joining auxiliary member, The joining tool comprises a rotating shoulder portion and a joining pin formed coaxially with the shoulder portion on the tip surface of the shoulder portion, which rotates together with the shoulder portion. The area between the tip surface of the shoulder portion and the side surface of the connecting pin is rounded, The area between the side surface of the connecting pin and the tip surface of the connecting pin is rounded. A friction stir welding method wherein the radius of curvature of the R-processing between the tip surface of the shoulder portion and the side surface of the joining pin is 20% or more and 200% or less of the plate thickness of the joining auxiliary member .
  2. The friction stir welding method according to claim 1, wherein the radius of curvature of the R-processing between the side surface of the joining pin and the tip surface of the joining pin is 10% or more and 50% or less of the hole diameter of the through hole of the second member.
  3. The friction stir welding method according to claim 1 or 2, wherein at least one of the first member and the joining auxiliary member is formed by punching and has a protrusion that can be inserted into the through hole corresponding to the through hole of the second member.
  4. The friction stir welding method according to any one of claims 1 to 3 , wherein the first member is made of a hollow material with a closed or open cross-section.
  5. The hollow material has an outer surface on which the second member is superimposed, and an inner surface which is the surface opposite to the outer surface. The friction stir welding method according to claim 4, wherein a backing plate is provided in the region of the inner surface corresponding to the region in which the friction stir welding portion is formed, the backing plate is inserted into the void surrounded by the inner surface and is used to suppress deformation of the hollow material.
  6. In at least the friction stir welding process, the backing plate is in contact with the region of the inner surface corresponding to the region where the friction stir welding portion is formed. The friction stir welding method according to claim 5 , further comprising a removal step of removing the backing plate after the friction stir welding step.
  7. The friction stir welding method according to claim 6 , wherein the backing plate is inserted together with the backing plate into the void surrounded by the inner surface and is pressed by an expandable non-metallic tube that contains a fluid inside.
  8. The joining auxiliary member is formed integrally with the first member such that it has a space between the first member and the joining auxiliary member that allows the second member to be interposed between them. The friction stir welding method according to any one of claims 4 to 7, wherein the overlapping step is performed by interposing the second member between the first member and the joining auxiliary member.
  9. A friction stir welding method according to any one of claims 4 to 8, wherein a 7000 series aluminum alloy is used as the material for the first member and the joining auxiliary member.
  10. The second member consists of a hollow material with a closed or open cross-section. The hollow material has an outer surface on which the first member is superimposed, and an inner surface which is the surface opposite to the outer surface. A friction stir welding method according to any one of claims 1 to 3, wherein a backing plate is provided in the region of the inner surface corresponding to the region in which the friction stir welding portion is formed, the backing plate is inserted into the void surrounded by the inner surface, and is used to suppress deformation of the hollow material.
  11. In at least the friction stir welding process, the backing plate is in contact with the region of the inner surface corresponding to the region where the friction stir welding portion is formed. The friction stir welding method according to claim 10, further comprising a removal step of removing the backing plate after the friction stir welding step.
  12. The friction stir welding method according to claim 11, wherein the backing plate is inserted together with the backing plate into the void surrounded by the inner surface and is pressed by an expandable non-metallic tube that contains a fluid.
  13. The second member consists of a hollow material with a closed or open cross-section. The hollow material has an outer surface on which the first member is superimposed, and an inner surface which is the surface opposite to the outer surface. A friction stir welding method according to any one of claims 1 to 3, wherein an expandable non-metallic tube for containing a fluid is provided in a region of the inner surface corresponding to the region where the friction stir welding portion is formed, the tube being inserted into the void surrounded by the inner surface and for suppressing deformation of the hollow material.
  14. The second member consists of a hollow material with a closed or open cross-section. The hollow material has an outer surface on which the first member is superimposed, and an inner surface which is the surface opposite to the outer surface. A friction stir welding method according to any one of claims 1 to 3, wherein a holding portion capable of holding the joining auxiliary member is located within the void surrounded by the inner surface.
  15. The friction stir welding method according to any one of claims 1 to 14 , wherein a plurality of friction stir-welded portions are formed in the friction stir welding step.
  16. The friction stir welding method according to claim 15 , wherein the plurality of friction stir welds are formed simultaneously.
  17. The through-hole of the second member is a linearly formed groove-shaped through-hole, The friction stir welding method according to any one of claims 1 to 16, wherein the joining tool rotates and moves linearly along the groove-shaped through hole to push at least one of the first member and the joining auxiliary member into the through hole, thereby forming the friction stir joint between the first member and the joining auxiliary member .
  18. The through hole of the second member has a size that allows for the formation of the friction stir joint and the non-jointed portion other than the friction stir joint within its interior. The friction stir joining method according to any one of claims 1 to 17, wherein the joining tool rotates and moves linearly around the through hole, connecting its starting and ending points, to push at least one of the first member and the joining auxiliary member into a portion of the through hole, thereby forming the friction stir joint between the first member and the joining auxiliary member, and creating an airtight or watertight space surrounded by the non- jointed portion.
  19. The second member has a chamfered surface between the surface facing the first member and the joining auxiliary member that is pressed in by the joining tool, and the inner surface of the through hole. A friction stir welding method according to any one of claims 1 to 18 .
  20. A friction stir welding tool used in the friction stir welding method according to any one of claims 1 to 19 , It has a rotating shoulder portion and a connecting pin formed coaxially with the shoulder portion on the tip surface of the shoulder portion, which rotates together with the shoulder portion. The area between the tip surface of the shoulder portion and the side surface of the connecting pin is rounded, The area between the side surface of the connecting pin and the tip surface of the connecting pin is rounded. A joining tool for friction stir welding , wherein the radius of curvature of the R-processing between the tip surface of the shoulder portion and the side surface of the joining pin is 20% or more and 200% or less of the plate thickness of the joining auxiliary member .

Description

This invention relates to a friction stir welding method, a welding tool for friction stir welding, and a friction stir welding joint. Lightweighting automobiles, trains, and other transport vehicles is an ongoing need, as it is expected to improve fuel efficiency and the resulting reduction in CO2 emissions, as well as enhance maneuverability. One way to achieve this is through material substitution, where some steel is replaced with lightweight materials such as aluminum alloys or CFRP (Carbon Fiber Reinforced Plastics). However, this requires dissimilar material joining at the boundaries between components. Dissimilar material joining methods can be broadly classified into (1) welding, (2) mechanical fastening, and (3) adhesive bonding. In the case of welding, for example, when iron and aluminum melt and mix, a brittle intermetallic compound is formed, making it difficult to obtain high strength. Therefore, mechanical fastening and adhesive bonding are more commonly used. However, adhesives exhibit significant anisotropy in strength and are prone to degradation over time, making them unreliable for applications requiring high strength. Therefore, adhesives are generally not used alone but in combination with other methods. Mechanical fastening, on the other hand, is highly reliable and has a proven track record as a method for joining dissimilar materials. Specifically, it often involves the use of steel consumable components (rivets) such as bolts and nuts, SPR (self-piercing rivets), FDS (flow-drill screws), and blind rivets. However, due to various disadvantages such as (a) high cost of consumables, (b) the need to drill through holes in some cases, (c) poor construction efficiency, (d) inability to apply when one of the materials to be joined is hollow, and (e) limitation to point joining rather than linear joining, it has not been able to satisfy all needs. Therefore, there is still a strong desire for the emergence of a dissimilar material joining method that offers (I) fewer limitations in shape and material applicability, (II) low cost, (III) high efficiency, (IV) the possibility of linear joining, and (V) high strength and reliability. Friction stir welding (FSW) is known as a candidate that satisfies a relatively large number of the above conditions (I) to (V). This joining method involves rotating a stirring pin made of a high-strength material such as steel and pressing it into the joint of a soft material such as aluminum, causing a portion of the base materials to be joined to plastically flow and eliminating the interface, thereby joining them. Because this joining method is suitable for soft base materials, it has been industrially used to join aluminum materials together. However, recent advances in the development of high-strength stirring pins have made it possible to use this method for joining steel materials as well. Furthermore, recently, friction stir welding has attracted attention not only for joining metals of the same type, but also for joining dissimilar metals such as aluminum and iron, or between metals and non-metals such as metals and resins. FSW (Friction Spot Joining) is broadly classified into two types: one that uses a rotating stirring pin to move in a planar direction to form a linear joint, and another that uses a rotating stirring pin to move only vertically to form a point-like joint (generally referred to more narrowly as FSJ (Friction Spot Joining) or FSSW (Friction Stir Spot Welding)). The former typically uses large, gantry-type equipment, while the latter typically uses equipment equipped with articulated robots; these two types represent significantly different forms of practical equipment. It has been reported that dissimilar material joining of aluminum and steel is possible by selecting optimal conditions using these FSW devices. For example, Patent Document 1 describes a friction stir welding method in which a steel material having a through hole is sandwiched between a first and second aluminum workpiece and laminated. The material of the second workpiece, which has undergone plastic flow by passing a stirring pin of a friction stir welding tool through the through hole, is joined to the inner wall of the through hole and integrally friction stir-welded with the material of the first workpiece. Furthermore, Patent Document 2 proposes a dissimilar material joining method for joining a metal member to be joined and a resin member to be joined using a joining metal member. The dissimilar material joining method described in Patent Document 2 involves preparing a resin member to be joined, a metal member to be joined, and a joining metal member, all having through holes. The metal member to be joined, the resin member to be joined, and the joining metal member are then stacked so that the through holes are covered by both the metal member and the joining metal member. Finally, a rotating joining tool is used to push the joining metal member into the throug