JP2009233697A - Friction stir welding method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a friction stir welding method that can provide sufficient joining strength even in joining metallic members having melting points different from each other. <P>SOLUTION: For the purpose of joining materials having melting points different from each other, the friction stir welding method uses a rotary tool X comprising a columnar tool body 10 and a probe 20 which has smaller diameter than the tool body 10, is formed coaxially with the tool body 10 in a projecting manner from one end of and the tool body 10 is rotatable integrally with the tool body 10. In the method, a first material A having a prescribed melting point and a second material B having a melting point lower than that of the first material A are abutted on each other, the surface height H2 of the second material B is set higher than the surface height H1 of the first material A, the rotary tool X is rotated while the probe 20 is imbedded in the second material B with respect to the abutting part R of the first and second materials A, B and a part of the lower face of the tool body 10 is in contact with the surface of the second material B, thus softening or solidifying the second material B and joining it to the first material A. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention provides a rotation provided with a cylindrical tool body, and a probe that is formed at one end of the tool body so as to have a smaller diameter than the tool body and coaxial with the tool body, and that rotates integrally with the tool body. The present invention relates to a friction stir welding method for joining materials having different melting points using a tool.

  As a method for joining metal members, there is a friction stir welding method using friction heat. In this method, for example, a probe protrudingly formed at the tip of a rotary tool is brought into contact with a portion where an aluminum material and a dissimilar metal member are abutted, and the metal member is softened by frictional heat. As a result, the metal having the lower melting point softens and then solidifies, and is bonded to the metal having the higher melting point, thereby joining the two metal members.

  Patent Document 1 describes a technique for joining a bat body of an aluminum alloy bat and a grip end using a friction stir welding method. Here, it is described that a joint having a good appearance and a stable quality can be obtained by bringing the probe of the rotary tool into contact with the grip end surface and performing friction stir welding.

JP 2007-275396 A

  In the metal material described in Patent Document 1, the metal member of the bat body is a 7000 series aluminum alloy, and the metal member of the grip end is a 5000 series / 6000 series aluminum alloy, or an Al-Cu series or Al-Mg series alloy. Aluminum alloy. Since both metal members have relatively similar melting points, both metal members are likely to be softened when the joining process is performed by the friction stir welding method.

On the other hand, in the friction stir welding method, metal members having greatly different melting points may be joined.
For example, when metal members having different melting points are joined together by friction stir welding, the probe that rotates at a high speed causes the low melting point of the metal member having a low melting point (low melting point metal member) to soften at the abutting portion of both metal members. It is buried on the metal member side. The probe moves in the joining direction along the side surface of the metal member having a high melting point (high melting point metal member), and at this time, the side surface of the high melting point metal member is cut while moving so that a new surface is formed. At that time, the lower surface of the tool main body holding the probe presses the joining surface, and the softened low melting point metal member plastically flows on the new surface. When the low melting point metal member is cured, the low melting point metal member is bonded to the new surface. In this way, the high melting point metal member and the low melting point metal member are joined.

  At the time of friction welding, the softened low melting point metal easily flows around the probe due to the rotation of the probe. For example, if sufficient pressing weight cannot be added to the joining surface, there may be a case where a smooth joining surface cannot be obtained due to a difference in surface height between the two metal members after the low melting point metal member is cured. As a result, the mechanical properties of the joint are low, such as insufficient joint strength between the two metal members.

  Accordingly, an object of the present invention is to provide a friction stir welding method capable of obtaining sufficient bonding strength even when metal members having different melting points are bonded to each other.

  In order to achieve the above object, the first characteristic configuration of the friction stir welding method according to the present invention includes a cylindrical tool body, a tool body having a diameter smaller than that of the tool body, and the tool body so as to join materials having different melting points. A first tool having a predetermined melting point and lower than the first material, using a rotary tool provided with a probe that is coaxially formed and protruded at one end of the tool body and rotates integrally with the tool body. A second material having a melting point is abutted, and the surface height of the second material is set to be higher than the surface height of the first material, and the rotary tool is moved between the first material and the second material. The probe is buried in the second material with respect to the butting portion and rotated while a part of the lower surface of the tool main body is in contact with the surface of the second material to soften and solidify the second material. The first material There is a point to join in.

  As in this configuration, by setting the surface height of the second material to be higher than the surface height of the first material, the lower surface of the tool main body reliably comes into contact with the softened second material. At this time, since the surface of the first material and the lower surface of the tool body do not immediately interfere with each other, the second material can also be reliably pressed.

  When the rotary tool rotates while a part of the lower surface of the tool body is in contact with the surface of the second material, the softened second material is pressed by the lower surface of the tool body. As a result, the softened second material is strongly pressed against the butted surface of the first material that is still solid, and a joint having sufficient strength can be obtained.

  According to a second characteristic configuration of the friction stir welding method according to the present invention, the rotation axis of the tool body is inclined so that the probe precedes the surface of the first material and the second material in the joining direction. When viewed from the side, a region of 75% or more and less than 100% from the rear side of the lower surface of the tool main body is brought into contact with the second material for bonding.

  Like this structure, the pressing force with respect to the softened 2nd material can be heightened by inclining the rotating shaft center of a tool main body to the state which a probe precedes. At that time, by making the rear region of the lower surface of the tool main body contact the second material, the advancing tool main body does not hit the second material, and the softened second material is surely pressed. can do. As a result of providing the advancing angle in the tool body in this way, the second material is strongly pressed against the first material, and a stronger joint can be obtained.

  The third characteristic configuration of the friction stir welding method according to the present invention is that the inclination angle of the tool body is set to 0 to 5 degrees.

The inclination angle of the rotation axis is appropriately set according to the difference in surface height between the two materials, the flow characteristics of the material used, and the like. For example, when the difference in surface height between the two materials is large, it is necessary to bring the rear edge of the lower surface of the tool close to the surface of the first material that has not been softened, so the inclination angle is set large. Further, when joining a material having high fluidity in a softened state, the inclination angle is set to be slightly smaller in order to prevent the softened material from scattering to the front side in the traveling direction of the tool body.
By setting the inclination angle of the tool main body to 0 to 5 degrees as in this configuration, it is possible to apply an appropriate pressing force to the second material and to join while preventing the softened material from scattering.

Embodiments of the present invention will be described below with reference to the drawings.
In the friction stir welding method, for example, a probe that is a rotating tool is brought into contact with a portion where metal members are brought into contact with each other in a state of high-speed rotation to generate frictional heat, and the metal member is softened by the frictional heat and joined. .
The friction stir welding method in this specification is used particularly when materials having different melting points are joined together. The material can be used, for example, for joining a body portion and a top plate portion of a piston for an internal combustion engine.

  In the friction stir welding method of the present invention, as shown in FIGS. 1 to 3, the first material A having a predetermined melting point and the second material B having a melting point lower than the first material A are abutted, The surface height H2 of the second material B is set to be higher than the surface height H1 of the first material A. The rotary tool X is rotated while being offset toward the second material B side with respect to the abutting portion R of the first material A and the second material B, and the second material B is softened by frictional heat generated by the probe 20. The probe 20 is buried in the second material B, and the rotary tool is moved along the joining direction in a state in which a part 13 of the lower surface of the tool body 10 is in contact with the surface of the second material B. B is softened and solidified and joined to the first material A. Hereinafter, an example in which the high melting point metal member A1 is used as the first material A and the low melting point metal member B1 is used as the second material B will be described.

(Rotation tool)
The rotary tool X includes a cylindrical tool body 10 and a probe 20 that is smaller than the tool body 10 and has a coaxial core with the tool body 10 so as to protrude from one end of the tool body 10 and rotate integrally with the tool body 10. Prepare. The tool body 10 and the probe 20 rotate around the coaxial core Z. Both of these may be configured separately or integrally.
The rotary tool X is connected to a motor drive unit (not shown) in order to rotate the tool body 10 and the probe 20. The motor drive unit is configured such that the rotation direction of the tool body 10 and the probe 20 can be either forward or reverse.

  The probe 20 contacts the refractory metal member A1 while rotating. Thereby, the side surface of the refractory metal member A1 is hit or cut to remove the oxide film present on the side surface, and the side surface is subjected to uneven processing. Thereby, the low melting point metal member B1 is firmly joined to the high melting point metal member A1. The surface shape of the probe 20 may be provided with arbitrary irregularities, or may be configured as a simple cylindrical surface.

  Furthermore, it is preferable that the distal end portion of the probe 20 has a slightly rounded shape rather than a rectangular shape when viewed in a direction perpendicular to the rotation axis. With such a configuration, when the probe 20 comes into contact with the low melting point metal member B1 at the start of joining, the first contact point of the surface of the probe 20 with the low melting point metal member B1 can be obtained near the rotation axis. it can. As a result, the vibration of the rotary tool at the start of joining is reduced, and the operability is greatly improved, such as allowing the probe to enter the exact position of the joint. When the probe 20 rotates at a high speed in this state, the probe 20 is easily buried in the low melting point metal member B1 from the contacted position.

  A shoulder 11 is provided around the probe 20 and on the lower surface of the tool body. The shoulder portion 11 has a function of pressing the softened low melting point metal member B1. The pressing effect starts to occur from the position where the shoulder portion 11 is in contact with the low melting point metal member B1, and the stronger the lower the shoulder portion 11 is toward the low melting point metal member B1, the more effective the effect is exerted. However, even when the shoulder portion 11 is further lowered, there is a limit until the shoulder portion 11 comes into contact with the refractory metal member A1.

(Specific bonding method)
The joint shape before the joining process of both metal members is a butt joint in which the surface heights of both metal members are different. (FIGS. 1 and 2). In this embodiment, the case where flat plates are joined is shown. In the friction stir welding method of the present invention, the surface height H2 of the low melting point metal member B1 is set higher than the surface height H1 of the high melting point metal member A1. The height difference (step) d between the two metal members is influenced by the thickness of the two metal members, but is about 1.0 to 2.0 mm, for example.

  At the time of joining, the probe 20 is rotated in a state where the lower surface of the probe 20 is in contact with the upper surface of the low melting point metal member B1. The frictional heat between the probe 20 and the low melting point metal member B1 softens the low melting point metal member B1, and the probe 20 is buried in the low melting point metal b (FIGS. 2A and 2B). A new surface 30 appears on the side surface of the refractory metal member A1 due to friction with the buried probe 20. When the softened low melting point metal b is plastically flowed and then cured on the new surface 30 of the high melting point metal member A1, the low melting point metal member B1 is joined to the high melting point metal member A1 on the new surface 30 (FIG. 2C).

  As the height setting range of the probe 20, the position where the height of the probe 20 is the lowest is a position where the probe 20 abuts on the surface of the refractory metal member A1, and the position where the height of the probe 20 is the highest is This is the position where the probe 20 comes into contact with the surface of the low melting point metal member B1 (FIG. 2 (a)). That is, the height of the tool body 10 can be adjusted by the level difference d between the surface height H2 of the low melting point metal member B1 and the surface height H1 of the high melting point metal member A1.

The rotation axis Z of the tool body 10 is inclined so that the probe 20 precedes the joining direction w with respect to the surfaces of the high melting point metal member A1 and the low melting point metal member B1.
The inclination angle α of the rotation axis Z of the tool body 10 is set to, for example, 0 to 10 degrees, preferably about 0 to 5 degrees.
When the advance angle is provided so that the probe 20 precedes the joining direction w as described above, the region located on the rear side in the joining direction w on the lower surface of the tool body 10 is surely formed on the surface of the low melting point metal member B1. Can be contacted.
If the inclination angle α exceeds 10 degrees, when the tool body 10 is moved in the joining direction w, the resistance acting on the lower surface of the tool body 10 becomes excessive, and it becomes impossible to join efficiently.
At this time, the contact area between the shoulder 11 of the tool main body 10 and the low melting point metal member B1 is 75% or more and less than 100% from the rear end of the lower surface of the tool main body 10 when viewed from the side with respect to the joining direction. (FIG. 3).

  As a result of setting in this manner, the low-melting point metal member B1 can positively apply pressure when the tool body 10 advances, and the softened low-melting point metal b is prevented from scattering, and the softened metal is used as the high-melting point metal member A1. Can be pressed against the surface. As a result, the high-melting point metal member A1 and the low-melting point metal member B1 can be reliably bonded to obtain a strong bonded portion.

  Examples of combinations of metal members having different melting points include aluminum alloy and steel (general carbon steel, special steel, alloy steel), magnesium alloy and steel, and the like. In these combinations, the steel may be a titanium alloy.

  In a piston for an internal combustion engine that is an object to be joined, the top surface portion P1 of the piston is a high-melting point metal member A1, and the main body portion P2 is a low-melting point metal member B1, and both these metal members are joined by the friction stir welding method of the present invention. (FIG. 4). The rotary tool X having the form shown in Table 1 was used. The top surface portion P1 is made of AC8A, and the main body portion P2 is made of a metal material made of Ti-6Al-4V.

In this piston P, the top surface portion P1 and the main body portion P2 are overlapped, and the overlapping portion is joined over the periphery of the piston P. As shown in FIG. 4, the overlapping portion of both members is provided with a thick convex portion on the lower surface of the top surface portion P <b> 1, and this convex portion is formed by fitting into a concave portion provided in the main body portion P <b> 2.
At this time, the outer diameter of the main body part P2 is set larger by a predetermined amount than the outer diameter of the top surface part P1. In this state, first, joining is performed to obtain a healthy joint, and then the side surface of the piston P is ground to obtain a piston having a desired size.

  A cooling channel q is provided on the center side of the piston P along the joint portion of the main body portion P2 and the top surface portion P1. This is a structure for circulating the cooling oil when the engine is operated, and particularly for cooling the top surface portion P1. When the main body portion P2 and the top surface portion P1 are brought into contact with each other at the time of joining, a region where the main body portion P2 and the top surface portion P1 abut on the region between the joint portion and the cooling channel q, that is, a region of width r. (FIG. 4B).

The joining performed to the periphery of the piston P in this way is joining according to a cylindrical surface joint, for example, as schematically shown in FIGS. In addition, the ratio of the size of the rotary tool and the object to be joined in these drawings is not necessarily actual.
As shown in FIG. 6, the angle of the tool body 10 is inclined by a predetermined angle β with respect to the normal direction n of the high melting point metal member A1 and the low melting point metal member B1 (FIG. 6). Specifically, it is 0 to 5 degrees.
The joining process of the piston P is performed while the metal members are butted together at the butting portion R and rotated in this state.

  In the present embodiment, the optimum level difference d between the high melting point metal member A1 and the low melting point metal member B1 can be calculated as follows, for example. For example, the diameter φ1 = 12 mm of the tool body 10, the diameter φ2 = 5 mm of the probe 20, and the diameter φ3 = 90 mm of the low melting point metal member B1. The rotary tool X having the form shown in Table 1 was used.

When the rotary tool X is inclined 3 degrees with respect to the normal direction n and the probe 20 presses the low melting point metal member B1, a position where 75% or more of the circumference of the shoulder portion 11 contacts the metal member is set. To do. At this time, the minimum value L _min of the length of the buried region 12 was set to 8 mm (FIG. 7), and the step d was obtained by the following calculation formula.

[Equation 1]
d = L _min · tan 3 = 0.42

  At this time, the diameter φ4 of the refractory metal member A1 is calculated by the following calculation formula.

[Equation 2]
φ4 = φ3-2d = 89.16mm

  The level difference d is appropriately set according to the curvature of both metal members or the size of the probe 20.

Schematic showing a rotary tool and metal member used in the friction stir welding method of the present invention Schematic of rotating tool and metal member during joining process Side view schematic diagram of rotating tool and metal member during joining process Schematic diagram when joining piston for internal combustion engine which is the object to be joined Schematic when joining cylindrical tubes that are objects to be joined Schematic diagram of a side view when joining cylindrical tubes that are joining objects Schematic diagram showing the level difference calculation method

Explanation of symbols

A (A1) 1st material (refractory metal member)
B (B1) Second material (low melting point metal member)
H1 Surface height of the first material H2 Surface height of the second material R Butt portion n Normal direction w Joining direction Z Rotating axis X Rotating tool 10 Tool body 12 Buried region 13 Part of the lower surface of the tool body 20 Probe α Tool body angle

Claims (3)

In order to join materials having different melting points, a cylindrical tool main body, a diameter smaller than that of the tool main body, and coaxially formed with the tool main body so as to protrude from one end of the tool main body and rotate integrally with the tool main body. A rotating tool with a probe,
A first material having a predetermined melting point and a second material having a melting point lower than that of the first material are abutted, and the surface height of the second material is set higher than the surface height of the first material. ,
The probe is embedded in the second material with respect to the abutting portion between the first material and the second material, and a part of the lower surface of the tool body contacts the surface of the second material. A friction stir welding method in which the second material is rotated and softened and solidified to be joined to the first material. Inclining the rotation axis of the tool body to a state in which the probe precedes the surface of the first material and the second material in the joining direction,
2. The friction stir welding method according to claim 1, wherein, in a side view, a region of 75% or more and less than 100% from the rear side of the lower surface of the tool main body is brought into contact with the second material for bonding.   The friction stir welding method according to claim 2, wherein an inclination angle of the tool body is 0 to 5 degrees.

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