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Friction stirring-welding methodRelated Patent Categories: Metal Fusion Bonding, Process, Using Dynamic Frictional Energy (i.e., Friction Welding)Friction stirring-welding method description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060138197, Friction stirring-welding method. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] The present invention relates to a friction stir welding method and a friction stir welding apparatus. DESCRIPTION OF RELATED ART [0002] A conventional technology for welding of a lap joint by means of the friction stir welding technique includes a method of using a welding tool having a flat-shaped tip end surface, or a welding tool having a recess on a tip end surface, and pressing the welding tool into one of members to cause friction stir on the one of the members to make use of plastic flow produced thereby to weld the same to the other of the members (see, for example, JP-A-2001-314981). [0003] In welding of a lap joint by means of friction stir welding, it is important to remove a surface oxide film on a lapped surface to activate a boundary interface. Therefore, it is necessary to heighten pressure of plastic flow. [0004] It is an object of the invention to provide a friction stir welding method for a lap joint, by which a welded part can be made higher in strength than that in the related art. Also, it is an object of the invention to provide a friction stir welding method capable of welding different metals. [0005] In the case where welding tools are pressed into both of an upper plate and a lower plate in lap welding by means of friction stir welding, there is caused an unfavorable problem in terms of outward appearance that a large hole is formed in a welded part to reach the lower plate. Also, in case of lap welding of materials, such as aluminum and nickel, which are considerably different in melting point from each other, there is caused a problem that the both are considerably different in deformation resistance from each other and cavity flaw is generated, since aluminum has the melting point of 660.degree. C. while nickel has the melting point of 1455.degree. C., and welding tools are pressed into both metals of aluminum and nickel. The invention provides a welding method that dissolves the problem. BRIEF SUMMARY OF THE INVENTION [0006] There are two kinds of mechanisms of welding in the invention. [0007] A first mechanism of welding resides in a method of pressing a welding tool only into one of members while rotating the welding tool, causing plastic flow of that member, which is discharged to an outer periphery of the pressed welding tool, so that welding boundary surfaces are activated by such discharge to achieve welding. A shape of the welding tool and characteristics of plastic flow are important for welding. [0008] The invention with respect to the first mechanism of welding obtains favorable results by the use of a welding tool having a small diameter projected part at a tip end of a large diameter shoulder. Desirably, the projected part has a smooth curved surface like a semispherical shape, if possible. Since the projected part can raise pressure in a region of plastic flow, the action of activating welding boundary surfaces increases. For an increase in pressure of plastic flow, it is also effective to provide a semispherical recess around the semispherical projected part to make these regularities contribute to an increase in contact area of the welding tool and a welding member. Also, it is desirable to round an outer peripheral surface of a tip end of the shoulder. Furthermore, since the use of a welding tool having a tip end of a certain radius of curvature also enables an increase in pressure of plastic flow, the action of activating welding boundary surfaces increases. When the action of activating welding boundary surfaces increases, a welding area increases and the welding strength increases. [0009] A second mechanism of welding resides in a method of making a contact angle between a welding tool and a surface of an upper plate an acute angle to perform welding in case of pressing a welding tool only into one of members while rotating the welding tool. In this case, since little metal undergoing plastic flow is discharged, it is possible to make pressure of plastic flow very high. Therefore, the action of activating welding boundary surfaces increases. Such plastic flow is generated mainly in a direction, in which the welding tool rotates. [0010] In the invention with respect to the second mechanism, a contact angle is made an acute angle by pressing of a welding tool having a semispherical shaped tip end only into one of members and causing friction stir to achieve welding. Thereby, since plastic flow is increased in internal pressure, the action of activating welding boundary surfaces increases. [0011] When lapped surfaces of welding members are coated with soft metal, surface oxide films on welding boundary surfaces can be made easy to remove. In the case where welding members are made of carbon steel, such method is very effective. Nickel, zinc, and copper are especially effective as soft metal. [0012] By providing a trapezoidal member on a surface of that member, into which a welding tool is pressed, or working the member to make the same trapezoidal in shape, it is possible to prevent reduction in welding strength even when an indentation is produced due to pressing of the welding tool. [0013] Also, a distance between a welding tool and lapped surfaces can be made short by performing welding in a state wherein a groove is provided on a lapped surface of one of members, and a projected part is provided on a lapped surface of the other of the members, the projected part being fitted into the groove. This method is suited to the case where thick plates are to be welded together. [0014] The invention is applicable to spot welding, in which a welding tool is pressed and pulled out intact and this procedure is repeated. [0015] The invention enables moving a welding tool while performing pressing to achieve continuous welding. [0016] With the friction stir welding method by means of a welding tool according to the invention, it is possible to positively generate plastic flow on welding boundary surfaces of a lap joint to remove and discharge a surface oxide film to activate the boundary surfaces. Thereby, welding with a high welding strength becomes possible. Also, welding of different metals is enabled. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS [0017] FIG. 1 is a cross sectional view showing a first embodiment; [0018] FIG. 2 is a perspective view in the course of welding in the first embodiment; [0019] FIG. 3 is a cross sectional view showing a direction of welding in the course of welding in the first embodiment; [0020] FIG. 4 is a cross sectional view showing a welded part after welding in the first embodiment; Continue reading about Friction stirring-welding method... Full patent description for Friction stirring-welding method Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Friction stirring-welding method patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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