JP2008110374A - Friction stir welding method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a friction stir welding method and a friction stir welding apparatus capable of promoting the solid state diffusion of a material to be welded by a simple means, reducing occurrence of residual stresses, and obtaining a sound and consistent weld part. <P>SOLUTION: In the friction stir welding method, a rotary tool arranged on one side of a workpiece is pressed against a welding part of the workpiece, and rotated to weld the workpiece by the plastic flow based on the friction heat generated between the rotary tool and the workpiece, an ultrasonic impact element is arranged on the other side of the workpiece to add the ultrasonic impact generated by the ultrasonic impact element to an area after welding of the workpiece. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a friction stir welding method and apparatus capable of obtaining a stable joint without defects even when joining materials having a relatively high melting point.

  In recent years, the friction stir welding shown in Patent Document 1 has been invented as a new solid-phase joining method, and its use is progressing in joining aluminum alloy panels and the like. As shown in FIG. 1, this friction stir welding uses a rotary tool 1 having a projection (probe) 2 at its tip and made of a material that is substantially harder than the workpiece 3, while rotating the rotary tool 1. The probe 2 at the tip is pushed into the abutting portion 4 of the workpiece 3 which is a joining portion, and the material softened by the frictional heat generated between the shoulder portion 5 of the rotating tool and the workpiece is stirred (plastic fluidized) and joined. Unlike melt welding such as arc welding, this is a joining method that utilizes solid phase diffusion, so that the metal structure of the joint 6 becomes a fine structure and has excellent mechanical properties.

However, in this friction stir welding, the joint performance of a metal material having a relatively low melting point such as an aluminum alloy can be obtained as expected, but it is different from a different material having a melting point higher than that of aluminum, such as the joining of an aluminum alloy and a steel material. In addition, the melting point is higher than that of aluminum such as steel materials and Ni-base alloys, and solid-phase diffusion may not occur sufficiently in the bonding of high-strength metal materials. There is a problem that the joint performance cannot be obtained.
Further, in the joining of high-strength metal materials having a high melting point, there is a problem that the joining temperature becomes high and the temperature difference between the heat-affected portions becomes large, and tensile residual stress is generated in the joined portion and the heat-affected portion.

  For such a problem, for example, Patent Document 2 proposes a technique for promoting solid phase diffusion by opening a through hole in a rotary tool and preheating a joint portion through a through hole with a laser. This technique cannot solve the problem of residual stress.

  Further, Patent Document 3 discloses a technique for changing the residual stress of the joint portion and a portion adjacent thereto to a compressive residual stress by burnishing the surface of the joint portion subjected to friction stir welding and the surface adjacent to the joint portion. Although proposed, this technique cannot solve the problem in the case of joining a high-strength metal material having a high melting point.

Japanese Patent No. 2712838 JP 2005-288499 A JP 2005-508256 A Japanese Patent Laying-Open No. 2005-321086 JP 2004-167363 A

  Therefore, in the friction stir welding, the present invention can promote solid-phase diffusion of the materials to be joined by simple means and can reduce the occurrence of residual stress. Even when joining materials having a relatively high melting point, the present invention is more sound. It is an object of the present invention to provide a friction stir welding method and apparatus capable of obtaining a stable joint portion.

  In recent years, an ultrasonic impact treatment (also referred to as an ultrasonic impact treatment) as shown in Patent Document 4 as a new ultrasonic utilization technology has been used to modify the physical state of metallic materials, such as the application of compressive residual stress. However, the present inventor has paid attention to the effect of ultrasonic impact on the material, and this technique is used as a means for promoting solid phase diffusion of the material to be joined in friction stir welding and further reducing residual stress. The present invention was reached with the idea of applying.

The present invention based on the above idea solves the above problems by the following means.
(1) A rotating tool arranged on one side of the workpiece is pressed against the joint of the workpiece and rotated, so that it is processed by plastic flow based on frictional heat generated between the rotating tool and the workpiece. In the friction stir welding method for joining workpieces, an ultrasonic striker is disposed on the other side of the workpiece, and ultrasonic strike by the ultrasonic striker is added to the joining region after joining the workpieces. Friction stir welding method.

(2) The workpiece is joined by moving the rotary tool while rotating along the joining portion, and the ultrasonic hitting by the ultrasonic striker is applied to the joining area after joining the workpiece. The friction stir welding method according to (1), wherein the friction stir welding method is added in synchronization with the movement.
(3) Applying ultrasonic striking under the conditions that the frequency of the ultrasonic striker is 1 to 70 kHz, the output of the ultrasonic wave is 100 to 10000 W, and the pressing force of the ultrasonic striker on the workpiece is 5 to 500 N. The friction stir welding method according to (1) or (2), characterized in that it is characterized in that

(4) A rotating tool arranged on one side of the workpiece is pressed against the joint of the workpiece and rotated, thereby processing by plastic flow based on frictional heat generated between the rotating tool and the workpiece. In the friction stir welding apparatus for joining objects, an ultrasonic striking apparatus for adding ultrasonic striking to a joining region after joining the work pieces is disposed on the other side of the work pieces.
(5) The rotating tool is arranged so as to move along the joining portion, and the ultrasonic striking device is arranged so as to move in synchronization with the rotating tool. Friction stir welding device.

According to the present invention, it is possible to promote solid-phase diffusion of the material to be joined and reduce the occurrence of residual stress by a simple means of adding ultrasonic hitting to the joining region after joining the workpieces. Therefore, the above problem in the case of joining materials having a higher melting point can be solved.
Moreover, in the joining of materials having a relatively low melting point such as an aluminum alloy, it is possible to obtain a joint having a higher joint performance such as an improvement in joint strength.

  Hereinafter, an embodiment of the friction stir welding method and apparatus of the present invention will be described in detail with reference to FIGS.

  In the present invention, ultrasonic hitting is used as a means for promoting solid phase diffusion of materials to be joined in friction stir welding. In the present invention, for example, an ultrasonic impact treatment apparatus disclosed in Patent Document 5 can be used. An example is shown in FIG.

  In FIG. 2, reference numeral 7 denotes an ultrasonic striking treatment device, which is a magnetostrictive or piezoelectric transducer 8 that transmits ultrasonic waves, and a wave that guides the ultrasonic waves generated by the transducer 8 to the tip and amplifies the vibration. It comprises a guide 9 and a head 10 attached to the tip of the wave guide 9 on the side facing the workpiece 3.

  The head 10 is provided with one or a plurality of holes 11 at the tip thereof, and a rod-shaped striking pin 12 serving as an ultrasonic striking element is inserted into the hole, and when the transducer 8 transmits ultrasonic waves, The ultrasonic wave is transmitted to the wave guide 9 connected thereto, reaches the head 10 from the tip of the wave guide 9, and vibrates the striking pin 12. By this vibration, the tip of the hitting pin hits the workpiece 3 with an ultrasonic hit, whereby an ultrasonic hitting process is performed.

In the present invention, such an ultrasonic impact treatment device 7 is disposed on the side opposite to the side on which the rotary tool 1 is disposed with respect to the workpiece 3 to be joined as shown in FIG. It is made to move in synchronization with the movement of 1.
As shown in FIG. 3, the position where the ultrasonic hitting processing device 7 is disposed is a position corresponding to the region of the bonded portion after the bonding that follows the position facing the rotary tool 1.

  Further, a support 13 that moves together with the ultrasonic hitting processing device 7 is arranged before and after the ultrasonic hitting processing device 7 so that the workpiece 3 is not deformed by the load of the rotary tool 1 and processed from the side opposite to the rotary tool. The object 3 is supported. The support 13 is a roller and is attached to the moving table 14 together with the ultrasonic hitting device 7 so that it can move in synchronization with the movement of the rotary tool 1.

  And the workpiece 3 is fixed on the surface plate (not shown) arrange | positioned on either side across the space which can move an ultrasonic impact processing apparatus, and the probe 2 of the rotary tool 1 is the workpiece which is a joining location. 3 and is moved while rotating the rotary tool 1 along the joining line of the butted portion, and the impact pin 12 of the ultrasonic impact treatment device 7 disposed on the opposite side of the workpiece from the rotational tool 1. Then, the joining area | region after joining of the workpiece 3 is ultrasonically hit.

  As a result, the material is softened by frictional heat generated between the rotary tool and the material, the softened material is stirred by the rotation of the tool, and the workpiece 3 is joined at the butting portion to form a joint. At this time, the solid phase diffusion temperature of the material can be substantially reduced by applying ultrasonic impact to the joint from the side opposite to the side where the rotary tool is disposed.

  As a result, the solid-phase diffusion phenomenon of the material is accelerated, the structure of the joint and the structure of the workpiece adjacent thereto become more uniform, and the occurrence of joint defects is prevented to obtain a joint with stable joint performance. Furthermore, since the compressive residual stress can be applied to the joint by ultrasonic impact, the tensile residual stress generated in the heat affected zone or the like can be reduced and the fatigue resistance performance can be improved. Moreover, joint strength can be improved in the joining of materials having a relatively low melting point such as an aluminum alloy.

As shown in FIG. 3, the position where the ultrasonic hit is applied (the center of the hitting range) is the position facing the rotary tool 1 (the center of the rotary tool and the center of the rotary tool) on the surface opposite to the surface that contacts the rotary tool. It is assumed that the joining portion where the rearward joining has already been performed, that is, the joining region after joining, is the position where the center of the hitting range coincides. In addition, if the distance between the position where the ultrasonic impact is applied and the rotary tool is too large, the effect of the ultrasonic impact on the acceleration of the solid phase diffusion is reduced, but the temperature after bonding is reduced to reduce the tensile residual stress. Since it is effective to apply ultrasonic hitting to the portion, the distance is preferably not more than 5 times the thickness t of the workpiece.
Further, the range for applying the ultrasonic hit is required to be at least the thickness t of the workpiece, but for reducing the residual stress, it is preferable to hit the joined portion and the adjacent portion where stirring is performed. However, it is difficult to hit a very wide range due to the structure of the apparatus, and the range is less than twice the thickness.

  The frequency of the striking pin 12 that is an ultrasonic vibrator is selected from the range of 1 to 70 kHz according to the material of the material to be joined. This is because if the frequency is less than 1 kHz, the solid phase diffusion temperature of the material cannot be substantially lowered, and if the frequency exceeds 70 kHz, the effect is saturated. For the same reason, the output of the ultrasonic wave is selected from the range of 100 to 10000 W, and the pressing force is selected from the range of 5 to 500 N. However, if the pressing force exceeds 500 N, the plastic deformation of the workpiece increases, The dimensional accuracy and appearance of

  The hitting pins 12 can be made as long as one can hit the required range, but in order to hit the joint and its adjacent portion, two or more hitting pins 12 may be arranged in one or more rows. It is advantageous. Further, the shape of the tip may be any of a hemispherical shape, a bowl shape, a bowl shape, etc., but a bowl shape combining a convex and a concave is highly effective.

  The rotary tool used in the present invention does not need a special tool and can use a commonly used tool. However, when a material having a high melting point such as a steel material is joined, a shoulder portion and a probe are included. The tip is preferably made of cemented carbide, sialon ceramics, polycrystalline boron nitride (PCBN), polycrystalline diamond (PCD), or the like.

  In addition, the operating conditions of the rotary tool may be those conventionally used, but in the present invention, as described above, the solid phase diffusion temperature of the material can be substantially lowered, so that However, since the required amount of heat generation can be reduced, the rotational speed, pressing force, and moving speed of the rotating tool can be changed to those with less load.

In the ultrasonic hitting apparatus shown in FIG. 2, the hitting pin 12 is supported by a holder 16 that is detachably attached to the wave guide 3 by an annular metal fitting 15, and the holder can be replaced.
Further, a resin cover 17 can be provided in the middle portion of the wave guide 9 and filled with a porous body 18 for holding a lubricating coolant.

In the above, the case where line joining is performed along the butted portion where the joining portions are linearly continuous has been described, but the present invention can also be applied to point joining.
In point welding, a rotating tool with a probe at the tip is placed at the location where the workpieces are to be overlapped and joined, and the rotating tool is pushed into one workpiece while rotating to rotate as in the case of line welding. The material of the stacked workpieces is softened by using frictional heat generated by the rotational operation of the tool, plastic flow is generated, and the overlapped portions of the workpieces are spot-joined.

  At this time, in the present invention, an ultrasonic striking device is disposed on the other side of the workpiece where the rotary tool is not disposed, and the ultrasonic transducer is applied to the bonded region after the workpiece is bonded, as in the case of line bonding. Add a blow. Thereby, also in the case of spot welding, solid phase diffusion of the material to be joined can be promoted, and generation of residual stress can be reduced.

Ultrasonic hammering is performed after welding has been completed and rotation of the rotary tool has stopped or after the rotary tool has left the workpiece, but as with wire bonding, acceleration of solid phase diffusion and residual It depends on which effect of stress reduction is prioritized.
The position where the ultrasonic hit is applied is the joining region where the joining is completed and the periphery thereof, but the center position of the impact may be slightly deviated from the center position of the joining region.

  Hereinafter, examples in which the present invention is applied to joining of an aluminum alloy and a steel material will be described. However, the present invention is not limited to the conditions shown in the examples, and the examples are feasibility of the present invention. And an example of a condition for confirming the effect. The present invention is defined only by the matters described in the claims, and various conditions can be adopted within the scope of the matters.

(Example 1)
A sample made of A6061 aluminum alloy or A5083 aluminum alloy was used as the material to be joined, and the friction stir welding was performed without applying ultrasonic impact to the region after joining from the back of the sample.
While evaluating the joining state of the obtained sample, the test piece was cut out from the sample and the tension test was implemented.

For friction stir welding, a rotating tool made of tool steel with a diameter of 6.0 mm is used, the rotational speed of the rotating tool is 1000 rpm and 1500 rpm, the moving speed is 1300, 1900, and 2000 mm / min, and the butt joint is wired. Joined.
In addition, the condition of the ultrasonic hitting process performed on a part of the sample is that the hitting pin is arranged at a distance of 2 to 13 mm rearward from the position just below the probe of the rotating tool with respect to the traveling direction, and the hitting pin is vibrated. The number was 10 kHz and 25 kHz, the ultrasonic output was 1.5 kW and 10 kW, and the pressing force to the workpiece was 6, 80, and 120 N.

R1, 11-13, R2, 21-23, R3, 31-33 of Table 1 show the conditions of friction stir welding and ultrasonic hammering treatment, and Table 2 shows the test results obtained.
In addition, in order to evaluate a joining state, X-ray inspection was implemented after joining, the joining defective location was specified, and the total length (mm) in which the defective location per 1 m exists was measured. Further, the tensile test was performed by collecting a test piece from a region determined to be healthy as a result of the X-ray inspection.

R1, R2, and R3 are the results of performing only friction stir welding. Since the moving speed of the rotary tool is slightly larger than the normal conditions, poor bonding such as poor fusion occurs. As a result, it can be seen that even the tensile test piece collected from the joint sound part has a joint at the fracture position, and sufficient joint strength is not obtained.
On the other hand, in the case of 11-13, 21-23, and 31-33, which are examples of the present invention, since the ultrasonic impact treatment was performed from the back side after the friction stir welding, the residual stress generated during the friction stir welding is reduced. As a result, the fatigue strength of the joint was greatly improved.
In addition, the smaller the distance L between the friction stir welding tool portion and the position where the ultrasonic impact treatment is performed, the more the occurrence of joining defects was suppressed, and as a result, the joint strength was improved. Note that the effect of reducing the residual stress expressed by SR / YP was more remarkable when L was larger than the plate thickness.

(Example 2)
Next, friction stir welding was similarly performed using a sample made of carbon steel or stainless steel. The carbon steel used is JSC590Y steel, JSC270E steel, JSC780Y steel, and the stainless steel is austenitic SUS304.
Friction stir welding uses a rotating tool made of PCBN with a diameter of 4.5 mm and 6.9 mm, and butt joints are line-bonded with the rotational speed of the rotating tool being 800 rpm and the moving speed being 80 mm / min and 30 mm / min. At the same time, a rotating tool made of the same PCBN was used, and the lap joint was point-joined with the rotating tool rotating at 800 and 1500 rpm.

  In addition, the ultrasonic hammering treatment conditions performed on some samples are as follows. In the butt joint, the hammering pin is disposed at a distance of 2 mm and 4 mm backward from the position of the rotary tool from the position just below the probe. The frequency of the pins was 20 kHz and 25 kHz, the output of the ultrasonic waves was 2 kW and 5 kW, and the pressing force against the workpiece was 500 N. In addition, in the point joining of the lap joint, the striking pin is disposed at a distance of 3 mm and 5 mm rearward from the position immediately below the probe of the rotary tool, the striking pin has a frequency of 225 kHz, and an ultrasonic output of 2, 5 The pressure on the workpiece was 70, 150, and 450 N.

R4, 41, R5, 51, R6, 61, R7, 71, R8, 81 in Table 1 show the conditions of friction stir welding and ultrasonic impact treatment, and Table 2 shows the test results obtained.
In addition, when a joining form is a point joining, it is difficult to detect a joining defect with an X-ray. However, in the case of point joining, since the center part of the point joining is recessed in a concave shape if it is carried out soundly, there is no problem if the amount of the indentation reaches a predetermined amount (the height of the probe probe). That is, if the rotary tool is damaged and worn and does not bite into the joint, normal joining cannot be performed. Therefore, it is possible to determine a joint failure by visual observation or by measuring the depth of the concave portion.
Therefore, using the dent amount as a soundness index of the point joint, accepting the joint where the dent amount larger than the plate thickness is secured, rejecting the joint not secured, and the acceptance rate in Table 2 Described.

  R4, R5, R6, R7, and R8, which are comparative examples in which friction stir welding was performed without adding ultrasonic striking treatment, had insufficient joint soundness and were inferior in tensile strength and fatigue strength. It was. Since 41, 51, 61, 71 and 81 of the present invention were subjected to ultrasonic impact treatment from the back side after the friction stir welding, solid phase diffusion during the joining was promoted, and the tensile strength of the joint portion was improved. It was. Moreover, the residual stress generated at the time of joining was reduced, and as a result, the fatigue strength of the joint part was greatly improved.

It is a figure for demonstrating the conventional friction stir welding. It is a figure for demonstrating an ultrasonic hit processing apparatus. It is a figure for demonstrating this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rotating tool 2 Rotating tool probe 3 Work piece 4 Butting part 5 Rotating tool shoulder part 6 Joint part 7 Ultrasonic impact processing apparatus 8 Transducer 9 Wave guide 12 Impact pin (ultrasonic impactor)
13 Support tool 14 Moving table t Thickness of workpiece

Claims (5)

  By pressing and rotating the rotating tool placed on one side of the workpiece against the workpiece joint, the workpiece is joined by plastic flow based on frictional heat generated between the rotating tool and the workpiece. In the friction stir welding method, the ultrasonic stirrer is disposed on the other side of the workpiece, and the ultrasonic striking by the ultrasonic hitter is added to the joining region after joining the workpiece. Method.   The workpiece is joined by moving the rotary tool while being rotated along the joining portion, and the ultrasonic hitting by the ultrasonic striker is synchronized with the movement of the rotary tool in the joining region after joining the workpiece. The friction stir welding method according to claim 1, wherein the friction stir welding method is added.   The ultrasonic striking device is characterized in that the ultrasonic striking force is applied under the conditions of the ultrasonic striking element having a frequency of 1 to 70 kHz, an ultrasonic wave output of 100 to 10,000 W, and a pressing force of the ultrasonic striking member on a workpiece of 5 to 500 N The friction stir welding method according to claim 1 or 2.   By pressing and rotating the rotating tool placed on one side of the workpiece against the workpiece joint, the workpiece is joined by plastic flow based on frictional heat generated between the rotating tool and the workpiece. In the friction stir welding apparatus, the friction stir welding apparatus is characterized in that an ultrasonic striking device for applying ultrasonic striking to the joining region after joining the work pieces is disposed on the other side of the work piece.   5. The friction stir welding apparatus according to claim 4, wherein the rotary tool is arranged to move along a joining portion, and the ultrasonic striking apparatus is arranged to move in synchronization with the rotary tool. .

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