JP4286962B2 - Friction stir welding method - Google Patents

Description

[0001]
The present invention relates to a friction stir welding method in which workpieces are joined and integrated by relatively advancing the tip of a friction stir welding tool along a joining line between the workpieces while rotating in an embedded state.
[0002]
[Prior art]
In recent years, a friction stir welding method has appeared as a new joining means that replaces welding and brazing of metal materials. This joining method is, for example, as disclosed in Japanese Patent Publication No. 7-505090, when a probe made of a material harder than the workpiece (rod-like object) is slidably contacted with the workpiece, Because the workpiece material is plastically fluidized by the frictional heat and pressure generated at the sliding contact part, the probe is embedded in the workpiece and can be moved through the workpiece in this embedded state. It is a thing that makes use of.
[0003]
For example, as shown in FIG. 1, when a metal plate (1) (1) is abutted and joined as a workpiece, a protruding probe (21) is attached to the tip of a cylindrical portion (20) as a friction stir welding tool (2). ), Press the tool (2) against the starting end of the joining line (L) while rotating the tool (2) at a high speed to embed the probe (21), and follow the joining line (L) as indicated by the arrow. To move. As a result, the material of the metal plate (1) (1) is plastically flowed by the frictional heat and pressure on the front side of the traveling probe (21), and gradually moves to the rear side of the probe (21) while being stirred and kneaded. Since this rear side loses frictional heat and rapidly cools and solidifies, the two metal plates (1) and (1) are joined in a state where the raw metal is agitated and kneaded and is completely integrated.
[0004]
In this case, the temperature at which the metal material plastically flows is considerably lower than the melting point, and joining is in the category of solid-phase joining, so the amount of heat input to the workpiece is small throughout the joining process, and no stress is generated due to solidification shrinkage. There is an advantage that deformation and cracking due to thermal strain in the vicinity of the joint are unlikely to occur. In addition, instead of moving the friction stir welding tool (2) side as shown in FIG. 1, the workpiece may be joined by a machining head arranged at a fixed position while moving the workpiece side.
[0005]
Conventionally, in such friction stir welding, depending on the material and thickness of workpieces to be joined, the specifications of the friction stir welding tool, the rotational speed of the tool, the joining speed, the penetration depth of the tool, etc. The machining conditions were selected to be optimum, and the joining was performed while maintaining these machining conditions constant from the start to the end of the joining.
[0006]
[Problems to be solved by the invention]
However, in the conventional friction stir welding method, when workpieces that accumulate heat more easily than their form and material are to be joined, the amount of heat input to the joining portion gradually increases with the progress of joining, so the start of joining There is a problem in that there is a difference in bonding quality between the part and the end part. In particular, as shown in FIG. 2, when the workpiece (W) such as a pipe material or a bar material having a small diameter φ of 60 mm or less is friction stir welded along the circumferential direction, the difference in the joining quality is particularly remarkable. Since it appears, it is a big problem in practical use. Further, in the conventional friction stir welding method, it takes time to embed the tip of the tool in the work and start feeding on the tool side or work side for joining, and there is a problem that the machining efficiency is poor. It was.
[0007]
In view of the above-described circumstances, an object of the present invention is to provide a friction stir welding method capable of obtaining a uniform joining quality from a joining start site to an end site and achieving a high working efficiency.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the friction stir welding method according to claim 1 of the present invention is characterized in that the amount of heat input to the workpiece from the joining start part to the end part is controlled to be substantially constant. That is, by uniformizing the amount of heat input to the workpiece, the variation in the joining state due to the joining site due to the change in the heat input situation is suppressed, and the difference in the friction stir structure due to the hardening of the plastic fluidized material is reduced. Even joint quality can be obtained from the start to the end of the joint. Particularly, it is suitable for a case where a workpiece (W) such as a small-diameter pipe material or bar material having a diameter φ of 60 mm or less is friction stir welded along the circumferential direction. However, it is not limited to this.
[0009]
Thus, as means for controlling the amount of heat input to the workpiece as described above, the invention according to claim 2 changes the rotational speed of the friction stir welding tool, the invention according to claim 3 changes the welding speed, and the invention according to claim 4. Then, heating or cooling of the work from outside is used, and in the invention of claim 5, heating or cooling on the friction stir welding tool side is used.
[0010]
Moreover, in invention of Claim 6, in the friction stir welding method in any one of the said Claims 1-5, the temperature of the junction part of the workpiece | work in joining or its vicinity is measured, Based on this measured value, it is in joining The amount of heat input to the workpiece is controlled. In this case, the amount of heat input to the workpiece is controlled by directly feeding back from the temperature measurement value during joining, so the amount of heat input from the start to the end of the joining can be equalized by correcting the amount of heat input according to the joining situation. .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
In the friction stir welding method of the present invention, the heat input to the workpiece from the start part to the end part of the joint is controlled to be substantially constant. In the friction stir welding, the main factors involved in the heat input are as follows: a) friction stir The shape of the joining tool, b) the number of rotations of the tool, c) the joining speed, and d) the penetration depth of the tool (contact area between the tool and the workpiece). Thus, a) the shape of the friction stir welding tool and d) the penetration depth of the tool are determined by the thickness and form of the joining portion of the workpieces to be joined, but b) the rotational speed of the tool and c) the joining speed. Can be used as a control factor of heat input.
[0012]
That is, when the heat input is insufficient, the amount of heat input can be increased by increasing the number of rotations of the tool or decreasing the joining speed. On the contrary, when the heat input is excessive, the amount of heat input can be reduced by lowering the rotation speed of the tool or increasing the joining speed. However, in order to enable friction stir welding, there is an allowable range of the ratio between the rotational speed of the tool and the welding speed. Therefore, both are changed within this allowable range to control the heat input.
[0013]
In order to change the rotation speed of the tool, the rotation of the main shaft in the friction stir welding machine may be controlled. In order to change the joining speed, the moving speed of the spindle is controlled in the joining method in which the tool side is moved, and the moving speed of the workpiece is controlled in the joining method in which the workpiece side is moved.
[0014]
Moreover, in this invention, the method of heating or cooling a workpiece | work and the method of heating or cooling the friction stir welding tool side are also employable as a control means of the heat input amount to a workpiece | work. Thus, heater heating, hot air blowing, etc. can be used for heating the work, and methods for promoting exhaust heat by heat exchange by contacting a low temperature fluid can be applied for cooling the work. A cooling mechanism can be used.
[0015]
For heating on the tool side, for example, as shown in FIG. 3 (a), a jacket (3) surrounding the cylindrical portion (20) of the friction stir welding tool (2) is provided, and a heater is provided inside the jacket (3). (4) is installed, or a method of circulating a heating fluid in the same jacket (3) as shown in FIG. In addition, for cooling on the tool side, a low-temperature fluid is circulated in the jacket (3) in the same figure (b), or a coolant distribution method is used inside the tool by the center-through method used in cutting tools. it can.
[0016]
In order to control the amount of heat input to the workpiece from the start part to the end part of the joint with these control means, the control index is set off-line and the on-line feedback method is used to promptly input the heat. There is a method of correcting the amount of heat.
[0017]
In the former off-line method, the joining state of the sample that was actually subjected to friction stir welding was examined by structure observation, etc., and the optimum heat input conditions for each part that appropriately separated from the starting part to the ending part of the joining were trial and error. The heat input control at the time of joining may be performed by the control means described above based on the heat input conditions obtained and found.
[0018]
In the latter on-line method, as shown in FIG. 4, the temperature measurement unit continuously measures the temperature of the bonded portion of the workpiece (W) being bonded or the vicinity thereof, and this measured value is input to the control unit one by one. The controller calculates a required heat input / output amount from the difference between the reference temperature set in advance and the measured value, and outputs a drive signal for adjusting the heat input to the drive unit of the control means. The heat input to the workpiece (W) being joined is corrected by the operation of the part. Instead of such automatic control, the drive unit of the control means is artificially adjusted based on the measured value of the temperature to correct the heat input to the workpiece (W) being joined. Good. For the above temperature measurement, a non-contact type temperature measurement device using a sensor or the like for measuring thermal radiation is suitable, but a contact type temperature measurement device can also be used.
[0019]
Thus, if the heat input to the workpiece in friction stir welding is made uniform, fluctuations in the joining state due to the joining site due to changes in the heat input situation can be suppressed, so there is a difference in the friction stir structure due to hardening of the plastic fluidized material. As a result, the joint quality is uniform from the beginning to the end of the joining, and particularly good results can be obtained in the circumferential joining of small-diameter pipes and rods.
[0020]
On the other hand, when adopting a method that controls the amount of heat input to the workpiece by changing the rotation speed of the friction stir welding tool, it is necessary to bond the tip (probe) of the tool to the workpiece and after the implantation. When the feed on the tool side or the workpiece side is started, the embedding speed and the joining start speed are increased by increasing the number of rotations of the tool. Therefore, the machining efficiency is improved by shortening this time. In addition, if a method of changing the rotation speed or joining speed of the tool is used to control the amount of heat input to the workpiece, a special external device for heating and cooling is unnecessary, which is advantageous in terms of equipment cost. .
[0021]
【Example】
A pipe having a diameter of 50 mm and a thickness of 4.0 mm made of 6063-T5 aluminum material is used as a welding target, and a friction stir welding tool having a probe diameter of 4 mm is used. The rotation speed of the tool is 1300 rpm at the welding start site. The temperature at the joining portion was constantly maintained at about 480 ° C., and friction stir welding was performed along the circumferential direction of the pipe. And when the structure | tissue of the junction part of the obtained joining goods was investigated, it has a homogeneous friction stirring structure | tissue over the whole joining part, and it was confirmed that there is no difference in the quality by a joining part.
[0022]
[Comparative example]
Using the same pipe and friction stir welding tool as in the above example, the number of rotations of the tool was kept constant at 1100 rpm from the start part to the end part of the joint, and friction stir welding along the circumferential direction of the pipe was performed. The temperature of the site changed from 460 ° C. at the start site to 490 ° C. at the end site. And when the structure | tissue of the junction part of the obtained bonded article was investigated, it turned out that there is a big difference in a friction stir structure | tissue in the joining start part and completion | finish part, and joining quality is non-uniform | heterogenous.
[0023]
【The invention's effect】
According to the first aspect of the present invention, in the friction stir welding, the amount of heat input to the workpiece from the start part to the end part of the joint is controlled to be substantially constant. A bonding quality is obtained, and a method suitable for the circumferential bonding of small diameter pipe materials and bar materials is provided.
[0024]
According to the invention of claim 2, in the friction stir welding method described above, the amount of heat input to the workpiece is controlled by a change in the rotational speed of the friction stir welding tool, so that the heat input is controlled by heating or cooling. This eliminates the need for a special external device, and is advantageous in terms of equipment cost. In addition, when the tip of the tool is embedded in the workpiece, or when feeding on the tool side or workpiece side is started after the insertion. The processing efficiency can be improved by increasing the speed.
[0025]
According to the invention of claim 3, in the above friction stir welding method, since the heat input to the workpiece is controlled by the change in the joining speed, the control of the heat input is exceptional as in the case of heating or cooling. This eliminates the need for an external device and is advantageous in terms of equipment cost.
[0026]
According to the fourth and fifth aspects of the present invention, in the friction stir welding method described above, the amount of heat input to the work from the start part to the end part of the work is controlled to be substantially constant by heating or cooling the work or the friction stir welding tool. it can.
[0027]
According to the invention of claim 6, in the friction stir welding method described above, the amount of heat input to the workpiece is controlled by directly feeding back from the measured value of the temperature at or near the bonded portion of the workpiece being joined. The amount of heat input from the start to the end of welding can be equalized by correcting the amount of heat input in response to the joining situation.
[Brief description of the drawings]
FIG. 1 is a perspective view showing joining of metal plates by friction stir welding.
FIG. 2 is a longitudinal side view showing joining of pipe materials by friction stir welding.
FIG. 3 exemplifies a means for controlling the amount of heat input to a workpiece in the friction stir welding method of the present invention. FIG. 3A is a schematic longitudinal side view of a heating type friction stir welding tool using a heater. The figure is a schematic longitudinal side view of the tool for heating or cooling with a fluid.
FIG. 4 is a schematic view illustrating a means for controlling the amount of heat input to the workpiece in the friction stir welding method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Metal plate 2 ... Friction stir welding tool 20 ... Cylindrical part 21 ... Probe (tip part)
3 ... Jacket 4 ... Heater W ... Work

Claims (5)

In the friction stir welding method in which the tip part of the friction stir welding tool is relatively advanced while rotating in the embedded state along the workpiece joining line, and the workpieces are joined and integrated, from the start part to the end part of the joint. The friction stir welding method is characterized in that the amount of heat input to the workpiece is controlled to be substantially constant by changing the rotational speed of the friction stir welding tool. In the friction stir welding method in which the tip part of the friction stir welding tool is relatively advanced while rotating in the embedded state along the workpiece joining line, and the workpieces are joined and integrated, from the start part to the end part of the joint. A friction stir welding method characterized in that the amount of heat input to the workpiece is controlled to be substantially constant by changing the joining speed. In the friction stir welding method in which the tip part of the friction stir welding tool is relatively advanced while rotating in the embedded state along the workpiece joining line, and the workpieces are joined and integrated, from the start part to the end part of the joint. friction stir welding method of the heat input to the work provided a jacket surrounding the cylindrical portion of the friction stir welding tool, and controlling the placing heating means or cooling means within the jacket thus substantially constant . The friction stir welding method according to any one of claims 1 to 3 , wherein a temperature of a bonded portion of the workpieces being bonded or a temperature in the vicinity thereof is measured, and an amount of heat input to the workpieces being bonded is controlled based on the measured value. The friction stir welding method according to any one of claims 1 to 4 , wherein the workpiece is a pipe member or a rod member having a diameter of 60 mm or less, and the workpiece is friction stir welded along a circumferential direction.

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