JP2007268605A - Friction stir welding apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a friction stir welding apparatus capable of enhancing the durability of a welding tool, shortening the welding time of a workpiece by the high-speed rotation of the welding tool, and enhancing the welding strength of a welded part. <P>SOLUTION: In the friction stir welding apparatus 1, a welding tool 4 is pressed in a rotating manner against a part 3 to be welded of a workpiece 2 consisting of a steel material, the welding tool is recessed in a portion softened by the friction heat, and the part to be welded of the workpiece is subjected to the solid-phase welding while stirring the softened portion. A film consisting of a material of low chemical reactivity to the workpiece is formed at least on an area of the welding tool in contact with the workpiece, and an inert gas feed means 6 for feeding an inert gas is included in the part to be welded in which the welding tool is recessed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a friction stir welding apparatus that can be suitably implemented to join workpieces made of steel materials such as general structural steel materials, architectural structural steel materials, and automobile steel plates.

A typical prior art is described in US Pat. In this prior art, in a joining tool in which a pin portion that comes into contact with an object to be joined is integrally formed on the central axis of a base material made of a heat-resistant alloy, an outer peripheral portion including the pin portion is made of silicon nitride (Si _By covering with a film made of a ₃ N ₄ ) -based ceramic, a decrease in hardness in a high temperature region is suppressed, and a decrease in strength against friction with a workpiece to be steel material is suppressed.

  In such a conventional technique, a steel material specified as SS400 in the JIS standard is targeted as an object to be joined, and the base material of the joining tool is mainly composed of at least one of Fe, Ni, Co, and W. Made of heat resistant alloy.

JP 2004-82144 A

  In the prior art described in Patent Document 1, since a steel material having a higher melting point than that of an aluminum alloy or the like is joined by friction stirring, a joining tool having a film formed of silicon nitride or the like is used. In such a welding tool, heat generated by friction with the workpieces causes chemical decomposition of the materials constituting the welding tool and diffusion of constituent elements into the workpieces, such as the shoulder portion and the pin portion of the welding tool. The part that generates a stirring driving force in contact with the object to be bonded is significantly worn.

  As a base material for the joining tool, the standard generated energy at 1000 ° C. of a cemented carbide, for example, tungsten carbide, is relatively large at −10 kcal / g · atom. It is stable.

  Moreover, it is easy to produce the solid solution of tungsten in steel. Since the wear of the joining tool caused by these phenomena impairs the formation of the friction stir zone, the joining strength is lowered, and the life of the expensive joining tool is exhausted with a slight use, so that there is a problem that the economy is poor.

  Furthermore, in the friction stir welding of steel materials, the rotational speed of the welding tool is often 250 to 1500 rpm, and when the rotational speed is higher than 1500 rpm, the frictional heating value increases, so that the workpiece is heated early, Although the welding time can be shortened and the joint strength can be improved, the wear of the joining tool is accelerated, and considering the life of the expensive joining tool, there is a limit to increasing the rotation speed, and the shortening of the joining time and the joining strength There is a problem that improvement is limited.

  An object of the present invention is to provide a friction stir welding apparatus capable of improving the durability of a joining tool, shortening the joining time of objects to be joined by high-speed rotation of the joining tool, and improving the joining strength of the joined parts. It is to be.

The present invention is to press a welding tool against a part to be joined made of a steel material while rotating it, immerse it in a softened part by frictional heat, and stir the softened part to be joined. A friction stir welding apparatus for solid-phase joining parts,
A film made of a material having low chemical reactivity with respect to the object to be bonded is formed in at least a region of the bonding tool that comes into contact with the object to be bonded.
The friction stir welding apparatus includes an inert gas supply means for supplying an inert gas to a bonded portion into which the welding tool is immersed.

In the invention, it is preferable that the coating is made of aluminum oxide.
Furthermore, the present invention is characterized in that the coating has a base layer made of titanium carbide and a surface layer made of titanium nitride covering the surface of the base layer.

  According to the present invention, the object to be joined is intended for a steel material. In order to prevent degradation of the film due to oxidation of the film, an inert gas is supplied to the bonded part of the object to be bonded, and the object to be bonded is rotated while rotating the bonding tool on which the film is formed. The pressed portion is pressed into a portion softened by frictional heat, the softened portion is stirred, and the bonded portion of the object to be bonded is solid-phase bonded.

  Since the film of the bonding tool is formed at least in a region in contact with the object to be bonded and is made of a material having low chemical reactivity with the object to be bonded, the affinity for the object to be bonded is weak, and it is thermally stable. In addition, wear due to a chemical reaction between the workpiece and the welding tool can be prevented, and the life of the welding tool can be extended. Further, the bonded portion is shielded from the atmosphere by an inert gas supplied from an inert gas supply means, and deterioration, damage, peeling, and the like of the bonding tool due to a chemical reaction such as oxidation and nitridation of the film are prevented.

  Further, since the surface of the joining tool is covered with a film to prevent a chemical reaction to the object to be joined, it becomes possible to increase the rotation speed of the joining tool, and shorten the joining time of the object to be joined. The efficiency of the joining work can be improved. Furthermore, by enabling high-speed rotation of the welding tool, the amount of frictional heat generated by contact with the workpiece is increased, and the agitation area of the workpiece is expanded, so that the bonding strength between the workpieces is improved. Is done.

  The film may be formed of aluminum oxide, or has a two-layer structure of a base layer made of titanium carbide and a surface layer made of titanium nitride covering the surface of the base layer, and the base layer is configured to improve the adhesion strength of the surface layer. May be. By forming such a one-layer film made of aluminum oxide or a two-layer film on which a base layer and a surface layer are formed on the base material of the bonding tool, a bonding tool with higher hardness can be realized. While suppressing the progress of wear of the tool film, it is possible to prevent solid solution due to diffusion of the film into the object to be bonded, and to improve the bonding strength of the bonded part of the object to be bonded.

  According to the present invention, since the welded portion is friction-stirred in an inert gas atmosphere using a welding tool having a film formed thereon, the wear of the welding tool can be reduced and the durability can be improved. The joint strength of the joint can be improved.

  FIG. 1 is a front view showing a friction stir welding apparatus 1 according to an embodiment of the present invention, and FIG. 2 is a partial enlarged cross-sectional view showing a state in which a welding tool 4 is immersed in a workpiece 2. The friction stir welding apparatus 1 presses the welding tool 4 while rotating the welding tool 4 against the workpiece 3 of the workpiece 2 made of a steel material, immerses the softened portion by frictional heat, and stirs the softened portion. The apparatus main body 5 which solid-phase-bonds the to-be-joined part 3 of the to-be-joined object 2 and the inert gas supply means 6 which supplies an inert gas toward the said joining tool 4 are included.

  The apparatus main body 5 is provided, for example, on the wrist 9 of the robot arm 8 of the articulated robot 7 and is used for spot-joining the part to be joined 3 of the article 2 with the axis L1 substantially vertical. The to-be-joined object 2 is a body of an automobile, a structure of a railway vehicle, or the like, and includes two steel plates 2a and 2b to be joined to each other. A case will be described in which such a workpiece 2 is spot-welded by friction stir welding (abbreviated as FSW) by the friction stir welding apparatus 1 of the present embodiment.

  In this embodiment, the steel material is also referred to as a steel material, and is classified into cast iron, carbon steel, alloy steel, and the like from the composition, and from use, classified into pig iron for casting, rolled steel, cast steel, forged steel, and the like. However, an aluminum alloy having a melting point lower than that of the steel material is not excluded as the article to be joined 2, and the friction stir welding apparatus 1 of the present embodiment can perform the friction stir welding. is there.

  The apparatus body 5 is housed in a base body 12 on which a wrist 9 of the articulated robot 7 is detachably attached by a plurality of bolts, a base body 12 on which the mounting body 11 is fixed on one side, and a base body 12. The lift drive source 13 to be moved, the rotational drive source 14 accommodated in the base 12, the lift 15 attached to the base 12 so as to be liftable along the axis L <b> 1, and the lower end of the lift 15 projectingly provided. Tool holder 16, agitating rod 17 projecting from the lower end of the tool holder 16, the joining tool 4 detachably attached to the agitating rod 17, and an upper end fixed to the one side of the base 12. A bending arm 19 bent in a substantially L shape from a lower part to a lower part of the base 12, a cradle 20 attached to the lower end of the bending arm 19, a cradle 20, and a joining tool 4. It includes a rod-shaped support 21 for supporting the objects to be bonded 2 below, the articulated robot 7, lift driving source 13, and a robot controller 22 for controlling the operation of the rotary driving source 14 and inert gas supply means 6.

  The elevating drive source 13 is constituted by a servo motor and elevating power transmission means for transmitting the rotational force of the servo motor to the elevating body 15 as an upward and downward linear moving force along the axis L1. The lifting power transmission means is realized by a ball screw mechanism or the like. The rotational drive source 14 includes a servo motor and a rotational power transmission means for transmitting the rotational force of the servo motor as the rotation of the stirring rod 17 around the axis L1. The rotational power transmission means is realized by a timing belt and a plurality of pulleys around which the timing belt is wound.

  The robot controller 22 executes a preset operation program in response to a command input from an input device such as a personal computer or a teaching pendant, and the articulated robot 7, the lift drive source 13, the rotation drive source 14. The inert gas supply means 6 is controlled in accordance with predetermined operating conditions, and the workpiece 2 supplied on the support 21 is spot-bonded. The predetermined operating conditions include, for example, the rotational speed of the welding tool 4, the amount of immersion in the welded portion 3, the immersion time, the pressing force, and the inert gas supply means 6 starting and stopping the supply of inert gas. . Such a robot controller 22 is also realized by a computer, and includes a storage device in which the operation program is stored, a main control device, an output device, and the like.

  The inert gas supply means 6 is realized by a pressure vessel filled with, for example, Ar gas, which is an inert gas, and a pressure / flow rate adjusting unit, and the inert gas discharged from the vessel valve of the pressure vessel An inert gas supply source 27 that can flow out at a predetermined flow rate and a secondary pressure by a control signal from the robot controller 22, and the tool holder of the stirring rod 17 are hermetically attached to the lower end of the tool holder 16. 16 and a substantially cylindrical cover body 28 surrounding the joining tool 4, a nipple 29 connected to the cover body 28, and a nipple 29 discharged from an inert gas supply source 27. It has a gas guide pipe 30 for guiding the active gas, and a cylindrical seal member 31 interposed between the tool holder 16 and the cover body 28.

  The cover body 28 includes a cylindrical body 32 having a right cylindrical shape, and a guide portion 33 having a truncated cone shape that is connected to one end of the body 32 in the axial direction and decreases in diameter as the distance from the body 32 increases. The other end portion in the axial direction of the body portion 32 is mounted so as to surround the lower end portion of the tool holding body 16 and is detachably attached to the lower end portion of the tool holding body 16 together with the seal member 31 with a plurality of bolts or the like. It is done.

  Such a cover body 28 may be made of an aluminum alloy, for example, to prevent damage due to adhesion of high-temperature molten metal droplets, or made of general-purpose synthetic resin such as engineering plastic that is easy to replace and lightweight. Furthermore, in order to prevent damage due to fatigue caused by high-speed rotation of the joining tool 4 or the like, it may be made of fiber reinforced plastic (abbreviated as FRP).

  An end surface 34 of the guide portion 33 facing the workpiece 2 is perpendicular to the axis of the body portion 32. In addition, the workpiece 2 is perpendicular to the axis of the support tool 21 while being supported by the support tool 21. The axis of the support 21 is perpendicular to the axis L2 of the joining tool 4. In such a state, the end surface 34 of the guide portion 33 is separated from the upper surface of the workpiece 2 with a slight space ΔL. This interval ΔL is selected to be 1 to 3 mm. The axis of the trunk portion 32 exists on a straight line common to the axis L2 of the welding tool 4.

  An annular space 30 is formed by the cover body 28 between the lower end surface 16a of the tool holder 16 and the upper surface 2c of the workpiece 2 (that is, the upper surface of the upper steel plate 2a). An inert gas is supplied from the nipple 29 to maintain a pressure slightly higher than the atmospheric pressure, and an inert gas atmosphere in which the intrusion of air is prevented is set. Friction stir welding is performed.

  At this time, the inert gas supplied from the nipple 29 into the space 30 is guided to the guide portion 33 whose flow path cross-sectional area is smaller than that of the body portion 32, and the gap between the cover body 28 and the article 2 to be joined is introduced. As a result of leakage at a minute flow rate from the gap of the interval ΔL, the space 30 in the cover body 28, particularly the periphery of the welding tool 4, is always kept filled with the inert gas. The welding tool 4 whose surface is covered with a film is pressed against the workpiece 2 while rotating, and the welded portion 3 is softened by the frictional heat generated between the welding tool 4 and the workpiece 2. The bonded portion 3 is solid-phase bonded by stirring the part, but since the bonded portion 3 is shielded from the atmosphere by an inert gas, the bonding tool 4 by a chemical reaction such as oxidation and nitridation of the film is performed. Deterioration, damage and peeling Etc. can be prevented.

  The supply of the inert gas from the inert gas supply means 6 to the bonding tool 4, and thus the bonded portion 3, is caused by chemical reaction and electrical affinity due to the coating 50 contacting the workpiece 2 at a high temperature. In order to prevent decomposition due to the above, it is attempted to cope with the problem by forming a film having chemical reactivity and affinity with the object 2 to be bonded. However, depending on the type of the film 50, the oxidation resistance temperature may be low. Therefore, it may be carried out with the intention of preventing a decrease in bonding strength due to diffusion of the coating 50 of the bonding tool 4 into the workpiece 2 at a high temperature.

  In the present embodiment, the configuration in which the nipple 29 is provided in the central portion of the axial direction of the body portion 32 of the cover body 28 toward the axis L1 is illustrated, but in another embodiment of the present invention, The nipple 29 may be provided at a plurality of locations, for example, 2 to 3 locations at equal intervals in the circumferential direction toward the axis L2 on the barrel portion 32. The stirring rod 17 and the barrel portion 32 are provided at 1 to 3 locations. It may be provided so as to incline toward each other, and may be provided so that an inert gas is injected toward the bonded portion 3 at 1 to 3 locations. In yet another embodiment of the present invention, a nozzle may be used in place of the nipple 29. By using the nozzle, the inert gas supply direction is given directivity, and friction stirring is performed. Immediately before the start, it may be sprayed from the nozzle toward the part to be joined 3, and the space around the joining tool 4 may be made an inert gas atmosphere in a short time to prevent contact between the high temperature part and the atmosphere.

  FIG. 3 is a perspective view showing a structure for attaching the welding tool 4 to the stirring rod 17, FIG. 3 (1) shows a state where the welding tool 4 is separated from the stirring rod 17, and FIG. Shows a state of being attached to the stirring rod 17. The stirring rod 17 is formed in a columnar shape, and a fitting portion 42 in which an external screw 41 is engraved is formed at a lower end portion 40 thereof. The fitting portion 42 is formed with a fitting recess 43 into which the joining tool 4 is partially fitted. The fitting portion 42 is screwed with a fixture 45 in which an inner screw 44 that is screwed into the outer screw 41 is engraved.

  The outer screw 41 and the inner screw 44 are formed so as to be tightened by rotating the fixing tool 45 in the direction opposite to the rotation direction of the stirring rod 17, and the bonding tool 4 is reverse to the rotation direction from the workpiece 2. The fixing tool 45 is configured not to loosen during joining by receiving the reaction force in the direction. The fitting recess 43 is formed coaxially with the axis L1 of the stirring rod 17 and has a square cross section perpendicular to the axis L1. The fitting recess 43 also rotates around the joint tool 4 fitted into the fitting recess 43. It is preventing.

  The joining tool 4 includes a mounting portion 46, a shoulder portion 47, and a pin portion 48. The shoulder portion 47 is continuous with the mounting portion 46, and the pin portion 48 is continuous with the shoulder portion 47. The shoulder portion 47 and the pin portion 48 are formed in a coaxial columnar shape or conical shape, and the diameter of the pin portion 48 is smaller than that of the shoulder portion 47.

  The mounting portion 46 is formed so that it can be gently fitted into the fitting recess 43 of the stirring rod 17. The mounting portion 46 has a substantially rectangular parallelepiped shape with the fitting recess 43 corresponding to a substantially rectangular parallelepiped space, and has a square cross-sectional shape. The pin portion 48 is formed coaxially with the shoulder portion 47 and in the shape of a right cylinder. The diameter and axial dimension of the shoulder portion 47 and the pin portion 48 are determined in advance according to the material of the material to be joined, the joining conditions, the joining strength, the shape of the joining trace, and the like. For example, the diameter of the shoulder portion 47 is set to 10 mm, and the diameter of the pin portion 48 is set to 4 mm.

  In a state where the mounting portion 46 is gently fitted in the fitting recess 43, as shown in FIG. 3 (2), the shoulder portion 47 and the pin portion 48 are arranged coaxially with the axis L1 of the stirring rod 17. . The shoulder portion 47 partially protrudes from the stirring rod 17. Further, the pin part 48 protrudes from the shoulder part 47.

  The fixture 45 is detachably formed on the tip 40 of the stirring rod 17. A through hole 49 is formed in the fixture 23, a part of the shoulder portion 47 of the welding tool 4 and the pin portion 48 protrude from the through hole 36, and the four corners around the shoulder portion 47 of the mounting portion 46 are fixed. The joining tool 4 is attached to the lower end 30 of the stirring rod 17 by being pressed by the tool 23. In the state in which the welding tool 4 is mounted on the stirring rod 17, the mounting portion 46 and the fitting recess 43 are formed in a rectangular parallelepiped shape, so that the bonding tool 4 is large in the direction opposite to the rotation direction from the workpiece 2 during bonding. Even if the reaction force is received, the joining tool 4 is prevented from being angularly displaced around the axis L <b> 1 of the stirring rod 17. Further, since the welding tool 4 is held by the lower end 30 of the stirring rod 17 by the fixing tool 45, when the welding tool 4 is worn out by screwing the fixing tool 45 away from the stirring rod 17, the new tool is used. The welding tool 4 can be exchanged.

Such a joining tool 4 is made of a material mainly composed of silicon nitride (Si ₃ N ₄ ), and the mounting portion 46, the shoulder portion 47 and the pin portion 48 are integrally formed by sintering, and the surfaces thereof are formed. As will be described later, a film 50 is formed. The stirring rod 17 and the fixture 23 are made of tool steel such as SKD-61, for example.

FIG. 4 is an enlarged sectional view of a part of the joining tool 4. Aluminum oxide (Al _2), which is a material having high wear resistance with respect to the workpiece 2, is formed on the entire surface including the shoulder portion 47 and the pin portion 48, which are regions that contact at least the workpiece 2 of the welding tool 4. A film 50 made of O ₃ ) is formed. The substrate 51 on which such a film 50 is formed is made of a cemented carbide containing silicon nitride as a main component, and the film 50 is formed on the surface thereof by a chemical vapor deposition method (Chemical Vapor).
Deposition (abbreviated as CVD), physical vapor deposition (abbreviated as PVD) or thermal spraying. The thickness ΔT of the film 51 is selected from 1 μm to 20 μm, for example.

The aluminum oxide is a titanium-based film (for example, titanium nitride TiNx (x = 0.4 to 1.2), titanium carbide TiCx (x = 0.6 to 2.3), titanium carbonitride Ti (CN), etc.). Compared to, it has excellent thermal stability and has a high hardness of 2000-2400 Hv (kg / mm ² ).

  FIG. 5 is an optical micrograph showing the bonding state of the bonded portion 3 when the two steel plates 2a and 2b are spot-bonded by friction stirring with the bonding tool 4 on which the film 50 is formed. FIG. It is a figure which shows the cross-sectional image of a base material when a friction stirring is carried out with the joining tool 4 in which the membrane | film | coat 50 is not formed, and a friction stirring area | region, FIG.6 (2) shows the state which the silicon nitride has spread | diffused in the friction stirring area | region. It is a figure which shows the elemental analysis image shown. 6 (1) and 6 (2) show the cross-sectional structure of section VI in FIG.

When the two steel plates 2a and 2b are friction stir welded by the joining tool 4 on which the film 50 is not formed, the elements of the joining tool 4 are re-exposed to the recrystallization region by an electron probe micro analyzer (abbreviated as EPMA). As shown by the white dots in FIG. 6A, the mapped analysis results show that the elements of the bonding tool 4 are dispersed by frictional heat when the bonding tool 4 that does not form the film 50 is used.

  FIG. 7 is a graph showing the relationship between the bonding time and the tensile shear strength when the friction stir welding is performed using the bonding tool 4 in which the film 50 is formed on the workpiece 2. As is apparent from the figure, the welding time is 1.0 second to 2 seconds even when the friction stir welding is performed on the workpiece 2 at either 2500 rpm or 3500 rpm. It was confirmed that when the time was changed to 0.0 second, the tensile shear load of the joined article 2 to be joined could be increased, and thus the tensile shear strength was increased. Further, when the rotational speed of the welding tool 4 is changed from 2500 rpm to 3500 rpm, the tensile shear load of the workpiece 2 can be increased. Therefore, by increasing the rotational speed of the welding tool 4, the workpiece 2 It was confirmed that the tensile shear strength was improved.

  FIG. 8 is a diagram showing a difference in the amount of wear of the welding tool 4 depending on the presence or absence of the coating 50 and the presence or absence of an inert gas. The upper part of the figure shows the worn state of the welding tool 4 on which the film 50 is not formed, and the lower part shows the worn state of the bonding tool 4 on which the film 50 is formed. In order to confirm the effect of suppressing wear due to the formation of the coating 50 of the welding tool 4, the number of hit points is increased to 0, 40, and 100, and the rotation speed of the welding tool 4 is 3000 rpm and the pressing force in the atmosphere. The outer appearance of the pin portion 48 when the friction stir for 1.0 second is shown in the upper part. Further, the number of hit points was increased to 0, 40, 100, and 200, and the rotational speed of the welding tool 4 was set to 3000 rpm and the pressing force was 5390 N in Ar gas as an inert gas, and friction stirring was performed for 1.2 seconds. Each appearance of the pin part 48 at the time is shown below. In this measurement experiment, a film made of a silicon nitride base material on which the film 50 is not formed as the bonding tool 4 and a film of titanium carbonitride (TiCN) having a hardness of 3000 Hv and a thickness of 10 μm on the surface of the silicon nitride base material. 50 was used.

  As is clear from the comparison between the external appearances of the pin portions 48 shown in the upper stage and the external appearances of the pin parts 48 shown in the lower stage, the wear resistance of the bonding tool 4 in which the film 50 is formed in an inert gas. Was confirmed to be excellent.

  FIG. 9 is a graph showing the relationship between the number of hit points in friction stir welding and the diameter of the pin portion 48. In the figure, the relationship between the number of striking points and the diameter of the pin portion 48 by friction stir welding using the welding tool 4 on which the film 50 is formed is indicated by the symbol ◆, and friction using the welding tool 4 on which the film 50 is not formed. The relationship between the number of striking points by stir welding and the diameter of the pin portion 48 is indicated by a symbol Δ, and it was confirmed that the wear of the pin portion 48 hardly occurs until the number of striking points is 0 to 200 by forming the film 50. .

  By using the joining tool 4 in which the film 50 is formed in this way, the joining tool 4 can obtain high strength and wear resistance and thermal shock resistance. When the spot welding is repeated, the welding tool 4 is repeatedly heated to a high temperature at the time of joining, and is kept at a low temperature when moving to the next part 3 to be joined, and the temperature change of the joining tool 4 is large. As described above, the bonding tool 4 according to the present embodiment has a thermal shock resistance, and therefore can withstand rapid temperature changes. Even if spot bonding to a plurality of bonded portions 3 is repeated, the bonding tool 4 is used. The required strength can be maintained.

  Further, in the friction stir welding, since the pin portion 48 can be sufficiently immersed in the joined portion 3 and rotated at a high speed, the flow region of the joined portion 3 is increased, and the shoulder portion 27 is further joined by the joined portion 3. 3, by sliding the fluidized part of the joined part 3 around the axis L1, the joining strength is improved, and the wear amount of the joining tool is significantly reduced. Stirring efficiency can be improved.

  FIG. 10 is an enlarged cross-sectional view showing a welding tool 4a according to another embodiment of the present invention. Note that portions corresponding to those of the above-described embodiment are denoted by the same reference numerals. In the bonding tool 4a of the present embodiment, a film 50a having a base layer 53 made of titanium carbide (TiC) and a surface layer 54 made of titanium nitride (TiN) covering the surface of the base layer 53 is formed by, for example, a CVD method. . The titanium carbide has a hardness of 9 or more in terms of Mohs hardness, a melting point of 3400 to 3500 ° C., and is stable up to 400 ° C. against oxygen.

  By forming such a film 50a, it is possible to realize a bonding tool 4a having a higher hardness, while suppressing the progress of wear of the film 50a of the bonding tool 4a, and the application of the film 50a into the article 2 to be bonded. Solid dissolution due to diffusion can be prevented, the bonding strength of the bonded portion 3 of the workpiece 2 can be improved, and the adhesion of the surface layer 54 to the base material can be improved. For example, high-speed rotation of 3000 rpm to 3500 rpm It is possible to prevent damage and peeling of the coating film 50a.

It is a front view which shows the friction stir welding apparatus 1 of one Embodiment of this invention. FIG. 4 is a partial enlarged cross-sectional view showing a state in which the welding tool 4 is immersed in the workpiece 2. FIGS. 3A and 3B are perspective views showing a structure for attaching the welding tool 4 to the stirring rod 17, FIG. 3A shows a state in which the welding tool 4 is separated from the stirring rod 17, and FIG. The state attached to 17 is shown. 3 is an enlarged cross-sectional view of a part of the welding tool 4. FIG. It is an optical microscope photograph which shows the joining state of the to-be-joined part 3 when two steel plates 2a and 2b are spot-joined by friction stirring with the joining tool 4 in which the membrane | film | coat 50 was formed. FIG. 6 (1) is a diagram showing a cross-sectional image of the base material and the friction stir zone when friction stir is performed by the welding tool 4 on which the film 50 is not formed, and FIG. 6 (2) shows that silicon nitride is in the friction stir zone. It is a figure which shows the elemental analysis image which shows the state which has spread | diffused. It is a graph which shows the relationship between joining time and tensile shear strength when carrying out friction stir welding using the joining tool 4 which formed the film | membrane 50 in the to-be-joined object 2. FIG. It is a figure which shows the difference in the abrasion amount of the joining tool 4 by the presence or absence of the film | membrane 50, and the presence or absence of an inert gas. It is a graph which shows the relationship between the number of striking points of friction stir welding, and the diameter of the pin part. It is an expanded sectional view which shows the joining tool 4a of the other form of implementation of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Friction stir welding apparatus 2 To-be-joined object 2a, 2b Steel plate 3 To-be-joined part 4 Joining tool 5 Apparatus main body 6 Inert gas supply means 7 Articulated robot 8 Robot arm L1 Axis 11 Attachment body 12 Base 13 Lift drive source 14 Rotation drive Source 15 Lifting body 16 Tool holder 17 Stirring rod 19 Bending arm 20 Base 21 Supporting tool 22 Robot controller 27 Inert gas supply source 28 Cover body 29 Nipple 30 Gas guide tube

Claims (3)

Rotate the welding tool against the part to be joined made of steel material while rotating it, immerse it in the softened part by frictional heat, and stir the softened part to solidify the part to be joined. A friction stir welding apparatus for joining,
A film made of a material having low chemical reactivity with respect to the object to be bonded is formed in at least a region of the bonding tool that comes into contact with the object to be bonded.
A friction stir welding apparatus comprising an inert gas supply means for supplying an inert gas to a bonded portion into which the welding tool is immersed.   The friction stir welding apparatus according to claim 1, wherein the film is made of aluminum oxide.   2. The friction stir welding apparatus according to claim 1, wherein the coating has a base layer made of titanium carbide and a surface layer made of titanium nitride covering the surface of the base layer.