Friction stir welding method for lap weld of dissimilar materials

Abstract

The invention provides a dissimilar material lap weld joint friction stir welding method which comprises the following steps: S1, an earlier-stage preparation stage: coaxially mounting a milling cutter in the tail end of a stirring tool, fixing an upper workpiece above a lower workpiece to form a to-be-welded workpiece, adjusting the inclination angle of the stirring tool to a set value, and welding the to-be-welded workpiece; adjusting the press-in amount of the stirring tool to a set value; s2, in the inserting stage, the stirring tool rotates according to the set rotating speed and moves in the welding direction according to the set rotating speed; s3, in the welding stage, the stirring tool rotates according to the set rotating speed, the press-in amount is kept constant, and the temperature of a weld joint area is kept constant in the welding process; and S4, welding is finished. The milling tool is installed at the tail end of the stirring tool, milling and welding of the lap joint interface are synchronously machined, the assembling difficulty of the stirring tool and the center of the welding seam is lowered, the lap joint interface pre-machining procedure is eliminated, the effective connecting area is enlarged, and the manufacturing efficiency and the welding quality are improved.

Description

Technical Field

[0001] The present invention relates to the field of friction stir welding, and in particular, to a friction stir welding method for lap joints of dissimilar materials. Background Art

[0002] As a common form of welded joint, lap joints widely exist in various welded structures. At present, in the friction stir welding of lap joints, the stirring pin mainly passes through the upper workpiece, and the lap interface between the upper workpiece and the lower workpiece is subjected to rotational forging at the end of the stirring pin, and metallurgical connection is generated under the thermo-mechanical coupling effect to form a dense weld.

[0003] The prior art mainly improves the mechanical properties of the weld by increasing the mechanical connection strength of the lap interface. The US patent with the application number US16564872 and the patent name "Method and apparatus for joining two different materials" discloses a welding method and apparatus for the lap interface of dissimilar materials. A groove is pre-machined in the lower workpiece of the lap interface, and the material of the upper workpiece is extruded into the lower groove by a stirring tool to form a mechanical connection and generate a metallurgical connection by friction with the lower metal. However, this apparatus requires pre-machining a groove in the lower workpiece, which increases the machining process, and the manufacturing efficiency and process adaptability are poor; the groove is in the middle area between the upper workpiece and the lower workpiece and is not easy to observe, resulting in great difficulty in centering the stirring tool with the weld, and it is very easy to cause the deviation of the stirring tool from the center of the groove, resulting in the damage of the groove structure. At the same time, since the material in the upper weld area is extruded and transferred into the lower groove, the thickness of the upper material is reduced, reducing the overall strength of the lap joint.

[0004] The strength of traditional lap joints mainly comes from the metallurgical connection generated by the dynamically recrystallized structure of the materials at the lap interface. However, it is difficult to control the microstructure and properties of this interface, and the improvement of the weld strength is limited. Especially for the welding of dissimilar materials, intermetallic compounds are easily generated at the lap interface, seriously reducing the mechanical properties of the lap joint.

[0005] Therefore, it is necessary to provide a friction stir welding method for lap joints of dissimilar materials, which can realize the synchronous machining of milling and welding of the lap interface, reduce the assembly difficulty of the stirring tool and the weld center, eliminate the pre-machining process of the lap interface, and improve the manufacturing efficiency and welding quality. Summary of the Invention

[0006] Aiming at the defects in the prior art, the purpose of the present invention is to provide a friction stir welding method for lap joints of dissimilar materials.

[0007] According to a friction stir welding method for lap joints of dissimilar materials provided by the present invention, the method includes the following steps:

[0008] Step S1, preliminary preparation stage: coaxially install the milling cutter inside the end of the stirring tool, and the milling end of the milling cutter extends below the lower end face of the stirring tool. Fix the upper workpiece above the lower workpiece to form the workpiece to be welded. Move the stirring tool to the outside of the weld of the workpiece to be welded, adjust the inclination angle of the stirring tool to the set value, and adjust the penetration amount of the stirring tool to the set value;

[0009] Step S2, penetration stage: the stirring tool rotates at the set speed and moves along the welding direction at the set speed. The stirring tool stirs and frictions with the upper workpiece, and the milling cutter mills the lower workpiece surface. During the penetration process, adjust the moving speed of the stirring tool until the stirring tool completely penetrates into the weld;

[0010] Step S3, welding stage: the stirring tool rotates at the set speed, keeps the penetration amount constant, and moves along the welding direction at the set speed to start welding. During the welding process, adjust the moving speed of the stirring tool to keep the temperature of the weld area constant;

[0011] Step S4, after the stirring tool moves to the end point of the set position, leave the workpiece and the welding is completed.

[0012] Preferably, in the step S1, the overlapping surface of the upper workpiece and the lower workpiece is a plane.

[0013] Preferably, in the step S1, the stirring tool inclines to the side away from the workpiece to be welded, and an included angle is formed between the axis of the stirring tool and the vertical direction, and the range of the included angle is 1.0 - 1.5°, and the range of the penetration amount of the stirring tool is 0.2 - 0.3 mm.

[0014] Preferably, in the step S1, the installation diameter of the milling cutter is not greater than one-half of the diameter of the end of the stirring tool and not less than one-third of the diameter of the end of the stirring tool, and the milling cutter extends 1.2 - 1.8 mm beyond the end face of the stirring tool after installation.

[0015] Preferably, in the step S2, when the shoulder of the stirring tool contacts the upper workpiece, the moving speed is reduced to 60% of the set speed;

[0016] When the stirring pin of the stirring tool contacts the upper workpiece, the moving speed is reduced to 40% of the set speed;

[0017] When the milling cutter contacts the lower workpiece, the moving speed is reduced to 30% of the set speed;

[0018] When the stirring pin of the stirring tool completely enters the upper workpiece, the moving speed is increased to 50% of the set speed;

[0019] When the shoulder of the stirring tool completely enters the upper workpiece, the moving speed is increased to 80% of the set speed;

[0020] When the stirring tool moves a distance of two shoulder diameters on the upper workpiece, the moving speed is increased to the set speed and enters the welding stage.

[0021] Preferably, in the step S2, the rotation speed range of the stirring tool is 400 - 600 r / min, and the moving speed range of the stirring tool along the welding direction is 80 - 100 mm / min.

[0022] Preferably, in the step S3, during the welding process, the adjustment range of the moving speed of the stirring tool is not greater than 30% of the set speed.

[0023] Preferably, in the step S3, during the welding process, the distance range between the lower end face of the stirring tool and the upper surface of the lower workpiece is 0.5 - 0.8 mm.

[0024] Preferably, in the step S4, the stirring tool stays for 10 - 15 seconds before leaving the workpiece.

[0025] Preferably, the upper workpiece and the lower workpiece are dissimilar materials, and the weldability of the upper workpiece is better than that of the lower workpiece.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. By installing the milling cutter at the end of the stirring tool, the present invention realizes the synchronous processing of milling and welding of the lap joint interface, reduces the assembly difficulty of the stirring tool and the weld center, eliminates the pre - processing process of the lap joint interface, expands the effective connection area, and improves the manufacturing efficiency and welding quality.

[0028] 2. The present invention forms a groove through the milling tool, and the center of the groove is naturally aligned with the stirring tool, without the need for additional adjustment of the alignment degree between the stirring tool and the weld center, greatly reducing the assembly difficulty.

[0029] 3. By adopting a weld mode with a constant heat input during the welding process, the present invention realizes the precise control of the intermetallic compound at the lap joint interface, which helps to optimize the overall performance of the weld; by making both the bottom surface and the side surface of the milling cutter contact the lower workpiece, a metallurgical connection interface can be generated under the action of friction extrusion, expanding the area of the metallurgical connection region, and significantly improving the weld strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] By reading the detailed description of the non - restrictive embodiments with reference to the following drawings, other features, objects, and advantages of the present invention will become more apparent:

[0031] Figure 1 It is a side view showing the penetration stage during friction stir welding of the lap weld mainly embodied in the present invention;

[0032] Figure 2 This is a schematic cross-sectional view mainly showing the friction stir welding of lap joints in the present invention;

[0033] Figure 3 This is a schematic cross-sectional view of the lap joint after welding mainly showing the present invention.

[0034] As shown in the figure:

[0035] Stirring tool 1, upper workpiece 2, lower workpiece 3

[0036] Milling cutter 4, curved weld 5 Specific implementation manner

[0037] The present invention will be described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several changes and improvements can still be made. These all belong to the protection scope of the present invention.

[0038] As Figures 1-3 shown, a friction stir welding method for dissimilar material lap joints provided by the present invention includes the following steps:

[0039] Step S1, in the preliminary preparation stage, the milling cutter 4 is rigidly coaxially installed inside the end of the stirring tool 1, and the milling cutter 4 extends beyond the end face of the stirring tool 1, that is, the milling end of the milling cutter 4 extends below the lower end face of the stirring tool 1. The upper workpiece 2 is fixed above the lower workpiece 3 to form a workpiece to be welded. The stirring tool 1 is moved to the outside of the weld of the workpiece to be welded, and the inclination angle of the stirring tool 1 is adjusted to a set value, and the penetration amount of the stirring tool 1 is adjusted to a set value;

[0040] Step S2, in the penetration stage, the stirring tool 1 rotates at a set speed and moves along the welding direction at a set speed. The stirring tool 1 stirs and frictions with the upper workpiece 2, and the milling cutter 4 mills the surface of the lower workpiece 3. During the penetration process, the moving speed of the stirring tool 1 is adjusted until the stirring tool 1 completely penetrates into the weld;

[0041] Step S3, in the welding stage, a formal welding is carried out by using a welding mode with a constant heat input. The stirring tool 1 rotates at a set speed, keeps the penetration amount constant, and moves along the welding direction at a set speed to start welding. During the welding process, the moving speed of the stirring tool 1 is adjusted to keep the temperature of the weld area constant;

[0042] Step S4, after the stirring tool 1 moves to the end point of the set position, the stirring tool 1 is pulled out of the workpiece, and the welding is completed.

[0043] The friction stir welding method for dissimilar material lap joints of the present application realizes the synchronous machining of milling and welding of the lap interface by installing the milling cutter 4 at the end of the stirring tool 1, reduces the assembly difficulty between the stirring tool 1 and the weld center, eliminates the pre-machining process of the lap interface, expands the effective connection area, and improves the manufacturing efficiency and welding quality.

[0044] In step S1, the lap surface of the upper workpiece 2 and the lower workpiece 3 is a plane.

[0045] In step S1, the stirring tool 1 inclines towards the side away from the workpiece to be welded, and an angle A is formed between the axis of the stirring tool 1 and the vertical direction. The range of the angle A is 1.0 - 1.5°, and the penetration amount of the stirring tool 1 ranges from 0.2 - 0.3 mm.

[0046] In step S1, the milling cutter 4 is installed inside the stirring pin at the end of the stirring tool 1. The installation diameter of the milling cutter 4 is not greater than one - half of the diameter of the end of the stirring tool 1 and not less than one - third of the diameter of the end of the stirring tool 1. After the milling cutter 4 is installed, it extends beyond the end face of the stirring tool 1 by 1.2 - 1.8 mm.

[0047] In step S2, when the shoulder of the stirring tool 1 contacts the upper workpiece 2, the moving speed is reduced to 60% of the set speed; when the stirring pin of the stirring tool 1 contacts the upper workpiece 2, the moving speed is reduced to 40% of the set speed; when the milling cutter 4 contacts the lower workpiece 3, the moving speed is reduced to 30% of the set speed; when the stirring pin of the stirring tool 1 completely enters the upper workpiece 2, the moving speed is increased to 50% of the set speed; when the shoulder of the stirring tool 1 completely enters the upper workpiece 2, the moving speed is increased to 80% of the set speed; when the stirring tool 1 moves a distance of two shoulder diameters in the upper workpiece 2, the moving speed is increased to the set speed and enters the welding stage.

[0048] In step S2, the rotational speed range of the stirring tool 1 is 400 - 600 r / min, and the moving speed range of the stirring tool 1 along the welding direction is 80 - 100 mm / min.

[0049] In step S3, during the welding process, the adjustment range of the moving speed of the stirring tool 1 is not greater than 30% of the set speed.

[0050] In step S3, during the welding process, the distance range between the lower end face of the stirring tool 1 and the upper surface of the lower workpiece 3 is 0.5 - 0.8 mm.

[0051] In step S4, the stirring tool 1 stays for 10 - 15 seconds before leaving the workpiece.

[0052] The upper workpiece 2 and the lower workpiece 3 are dissimilar materials, and the weldability of the upper workpiece 2 is better than that of the lower workpiece 3.

[0053] Taking the friction stir welding of a lap joint between a 5-mm thick aluminum alloy and a titanium alloy as an example, the friction stir welding method for dissimilar material lap joints is described. During welding, the stirring tool 1 rotates at a set speed and moves along the welding direction at a set inclination angle; the stirring tool 1 stirs and frictions in the upper workpiece 2, and the milling cutter 4 mills the surface of the lower workpiece 3; the upper workpiece 2 and the lower workpiece 3 are dissimilar materials, the upper workpiece 2 is an aluminum alloy, and the lower workpiece 3 is a titanium alloy.

[0054] The shoulder diameter of the stirring tool 1 is 26 mm, the end diameter of the stirring tool 1 is 12 mm, and the mounting diameter of the milling cutter 4 is 5 mm; the milling cutter 4 is installed at the end of the stirring tool 1, and after installation, the milling cutter 4 protrudes 1.5 mm beyond the end face of the stirring tool; the stirring tool 1 is moved to the outside of the upper workpiece 2 and the lower workpiece 3, and the initial distance is set to 40 mm; the inclination angle A of the stirring tool 1 is adjusted to 1.2°, the penetration amount of the stirring tool 1 is adjusted to 0.2 mm, and the distance H from the end of the stirring tool 1 to the lower workpiece is 0.6 mm.

[0055] In the plunge stage, the stirring tool 1 rotates at a set speed of 500 r / min and moves along the welding direction at a set speed of 100 mm / min; when the shoulder of the stirring tool 1 contacts the upper workpiece 2, the moving speed is reduced to 60 mm / min; when the stirring pin of the stirring tool 1 contacts the upper workpiece, the moving speed is reduced to 40 mm / min; when the milling cutter 4 contacts the lower workpiece 3, the moving speed is reduced to 30 mm / min; when the stirring pin of the stirring tool 1 completely enters the upper workpiece 2, the moving speed is increased to 50 mm / min; when the shoulder of the stirring tool 1 completely enters the upper workpiece 2, the moving speed is increased to 80 mm / min; when the stirring tool 1 moves a distance of two shoulder diameters, i.e., 52 mm, in the upper workpiece 2, the moving speed is increased to the set speed of 100 mm / min and enters the welding stage.

[0056] In the welding stage, the formal welding is carried out in a welding mode with a constant heat input. The stirring tool 1 rotates at a set speed of 500 r / min and keeps the penetration amount constant at 0.2 mm; the temperature at the end of the stirring tool 1 is collected in real time during the welding process and kept constant, and the set value is 450 °C; when the welding temperature is higher than 450 °C, the moving speed of the stirring tool 1 is increased; when the welding temperature is lower than 450 °C, the moving speed of the stirring tool 1 is decreased; the adjustment range of the moving speed is not more than 130 mm / min.

[0057] In the welding end stage, after the stirring tool 1 moves to the set position end point, the welding is completed to form a curved weld 5, stays for 15 seconds, and the stirring tool 1 is withdrawn from the upper workpiece 3, and the welding ends.

[0058] In this application, synchronous milling is achieved by the milling tool 4 at the end of the stirring pin during the welding process, eliminating the pre-processing procedure for the lap interface of the workpiece before welding, reducing the production cost, and improving the production efficiency.

[0059] In this application, a groove is formed by machining with the milling tool 4, and the center of the groove is naturally aligned with the stirring tool 1, eliminating the need for additional adjustment of the alignment between the stirring tool 1 and the center of the weld seam, thus greatly reducing the assembly difficulty.

[0060] In this application, a weld seam method with a constant heat input is adopted during the welding process, enabling precise control of the intermetallic compound at the lap interface, which helps to optimize the overall performance of the weld seam.

[0061] In this application, both the bottom surface and the side surface of the milling tool 4 are in contact with the lower workpiece 3, and a metallurgical connection interface can be generated under the action of friction and extrusion, expanding the area of the metallurgical connection region and significantly enhancing the weld strength.

[0062] In the description of this application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to this application.

[0063] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. Without conflict, the embodiments of this application and the features in the embodiments can be arbitrarily combined with each other.

Claims

1. A friction stir welding method for overlapping welds of dissimilar materials, characterized in that: The following steps are involved: Step S1, in the preliminary preparation stage, the milling tool (4) is coaxially installed inside the end of the stirring tool (1), and the milling end of the milling tool (4) extends below the lower end surface of the stirring tool (1), the upper workpiece (2) is fixed above the lower workpiece (3) to form a workpiece to be welded, the stirring tool (1) is moved to the outside of the weld of the workpiece to be welded, the inclination angle of the stirring tool (1) is adjusted to a set value, and the pressing amount of the stirring tool (1) is adjusted to a set value; Step S2, the penetration stage, the stirring tool (1) rotates at a set speed and moves along the welding direction at a set speed, the stirring tool (1) stirs and rubs with the upper workpiece (2), and the milling tool (4) mills the surface of the lower workpiece (3). During the penetration process, the moving speed of the stirring tool (1) is adjusted until the stirring tool (1) is completely penetrated into the weld; Step S3, welding stage, the stirring tool (1) rotates at a set speed, keeps the amount of pressure constant, and moves along the welding direction at a set speed to start welding. During the welding process, the moving speed of the stirring tool (1) is adjusted to keep the temperature of the weld area constant; Step S4, after the stirring tool (1) moves to the set position end point, it leaves the workpiece and the welding ends.

2. The friction stir welding method for overlapping welds of dissimilar materials according to claim 1, characterized in that: In the step S1, the overlapping surfaces of the upper workpiece (2) and the lower workpiece (3) are planes.

3. The friction stir welding method for overlapping welds of dissimilar materials according to claim 1, characterized in that: In step S1, the stirring tool (1) is tilted toward a side away from the workpiece to be welded, an angle is formed between the axis of the stirring tool (1) and the vertical direction, the angle range is 1.0-1.5°, and the pressing amount of the stirring tool (1) is in the range of 0.2-0.3 mm.

4. The friction stir welding method for overlapping welds of dissimilar materials according to claim 1, characterized in that: In step S1, the installation diameter of the milling tool (4) is not greater than half of the diameter of the end of the stirring tool (1) and not less than one third of the diameter of the end of the stirring tool (1). After installation, the milling tool (4) protrudes from the end face of the stirring tool (1) by 1.2-1.8 mm.

5. The friction stir welding method for overlapping welds of dissimilar materials according to claim 1, characterized in that: In the step S2, when the shoulder of the stirring tool (1) contacts the upper workpiece (2), the moving speed is reduced to 60% of the set speed; When the stirring needle of the stirring tool (1) contacts the upper workpiece (2), the moving speed is reduced to 40% of the set speed; When the milling tool (4) contacts the lower workpiece (3), the moving speed is reduced to 30% of the set speed; When the stirring needle of the stirring tool (1) completely enters the upper workpiece (2), the moving speed is increased to 50% of the set speed; When the shoulder of the stirring tool (1) completely enters the upper workpiece (2), the moving speed is increased to 80% of the set speed; When the stirring tool (1) moves a distance of two shaft shoulder diameters on the upper workpiece (2), the moving speed is increased to the set speed and the welding stage is entered.

6. The friction stir welding method for overlapping welds of dissimilar materials according to claim 1, characterized in that: In step S2, the rotation speed of the stirring tool (1) is in the range of 400-600 r / min, and the moving speed of the stirring tool (1) along the welding direction is in the range of 80-100 mm / min.

7. The friction stir welding method for overlapping welds of dissimilar materials as claimed in claim 1, characterized in that: In the step S3, the adjustment range of the moving speed of the stirring tool (1) during the welding process is not greater than 30% of the set speed.

8. The friction stir welding method for overlapping welds of dissimilar materials as claimed in claim 1, characterized in that: In the step S3, during the welding process, the distance between the lower end surface of the stirring tool (1) and the upper surface of the lower workpiece (3) is in the range of 0.5-0.8 mm.

9. The friction stir welding method for overlapping welds of dissimilar materials as claimed in claim 1, characterized in that: In step S4, the stirring tool (1) stays on the workpiece for 10-15 seconds before leaving the workpiece.

10. The friction stir welding method for overlapping welds of dissimilar materials according to claim 1, characterized in that: The upper workpiece (2) and the lower workpiece (3) are made of different materials, and the weldability of the upper workpiece (2) is better than that of the lower workpiece (3).

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