A stir pin and welding method for friction stir welding capable of realizing lap interface interlocking

Abstract

This invention provides a stirring pin and method for friction stir welding that enables interlocking at lap joints. The method includes a first stirring pin fixed below a shoulder and a second stirring pin fixed below the first stirring pin. The first stirring pin is a tapered shape, wider at the top and narrower at the bottom, while the second stirring pin is a tapered shape, narrower at the top and wider at the bottom. Both the first and second stirring pins have threads on their tapered surfaces, with the threads of the first and second stirring pins rotating in opposite directions. During friction stir lap welding, by controlling a suitable downward pressure, the stirring pins cause the material on the upper plate of the lap joint to migrate downwards under the action of the upper tapered thread, while the lower eccentric tapered thread drives the material on the lower plate to move obliquely upwards, forming an interlocking structure. Compared to the hook-like defects of conventional lap joints, the stirring pin of this invention enables interlocking at the lap joint, increases the effective lap area, and significantly improves the strength of the lap joint.

Description

Technical Field

[0001] This invention belongs to the field of friction stir welding technology, and particularly relates to a stirring pin and welding method for friction stir welding that can achieve interlocking of lap joint interfaces. Background Technology

[0002] Friction stir welding (FSW), invented by the Welding Institute in the UK in 1991, is a solid-state joining technique with advantages such as low welding temperature and minimal deformation, suitable for joining similar or dissimilar metals. The connection between aircraft fuselage skin and stringers, as well as the connection of railway train body structures, primarily uses lap joints. However, when using FSW to weld lap joints of similar or dissimilar metals, hook-shaped defects can form on the advancing side of the joint interface, while "cold lap" defects can occur on the returning side. These two interface defects reduce the effective lap thickness and effective lap width, resulting in a decrease in the effective bonding area of ​​the lap joint interface and weakening the load-bearing capacity of the lap joint. Therefore, when using FSW to weld lap joint structures, it is necessary to avoid hook-shaped defects and "cold lap" defects at the lap joint interface.

[0003] A search of existing patents revealed that invention patent application number 201510427740.8 discloses a friction stir welding lap welding method for eliminating hook defects on the advancing side, which uses an inverted "T"-shaped workpiece to eliminate hook defects on the advancing side. While this method can eliminate hook defects on the advancing side, it cannot solve the problem of "cold lap" defects on the returning side. Invention patent application number 201910915501.5 discloses a friction stir welding stirring head that improves material flow behavior. It reduces hook defects at the lap interface by setting mirror-symmetrically distributed concave textures on the surface of the stirring pin. This method involves setting mirror-symmetrically distributed concave textures on the surface of the stirring pin, but when the stirring pin rotates at high speed, the effect of these concave textures in driving material flow is greatly reduced, resulting in a relatively flat interface morphology and failing to achieve mechanical interlocking.

[0004] In their previous research (Xu et al. An innovative joint interface design for reducing intermetallic compounds and improving joint strength of thick platefriction stir welded Al / Mg joints[J]. Journal of Magnesium and Alloys. 2022[2022-06-15]. https: / / doi.org / 10.1016 / j.jma.2022.01.007.), the inventors discovered that mechanically interlocked interfaces can increase the load-bearing area and improve the tensile strength of the joint. In summary, by controlling the morphology of the lap joint interface during friction stir welding, hook-like defects and cold lap defects can be avoided, potentially leading to reliable connections in lap joints. Summary of the Invention

[0005] The purpose of this invention is to provide a stirring pin and welding method for friction stir welding that can achieve interlocking of the lap joint interface. The welding method using the stirring pin of this invention can not only eliminate defects at the lap joint interface, but also achieve interlocking of the interface, enhance the load-bearing capacity of the lap joint, and improve the mechanical properties of the joint.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A stirring pin for friction stir welding that enables interlocking of overlapping interfaces is characterized in that it includes a first stirring pin fixed below a shoulder and a second stirring pin fixed below the first stirring pin; the first stirring pin is a tapered shape that is wider at the top and narrower at the bottom, and the second stirring pin is a tapered shape that is narrower at the top and wider at the bottom; both the first and second stirring pins are provided with threads on their tapered surfaces, and the threads of the first and second stirring pins are rotated in opposite directions.

[0008] Furthermore, the center line of the first stirring needle is coaxial with the rotating main shaft of the shoulder, while the center line of the second stirring needle is eccentrically set with respect to the rotating main shaft.

[0009] Furthermore, the eccentricity d between the centerline of the second stirring needle and the rotating spindle is 2-3 mm.

[0010] Furthermore, the end diameter D2 of the first stirring needle is larger than the root diameter D3 of the second stirring needle, so that a stepped shoulder is formed between the first stirring needle and the second stirring needle.

[0011] Furthermore, at least one notch is provided at the lower edge of the second stirring needle, and the notch is evenly distributed around the circumference of the second stirring needle.

[0012] The friction stir welding method based on the interlocking of the lap joint interface of the stirring pin is characterized in that...

[0013] Step 1: Grind the upper and lower plates to be welded with a wire brush, then clean them with acetone, and fix the upper and lower plates to be welded to obtain a lap joint.

[0014] Step 2: Weld along the center line of the lap joint using the stirring needle, with a pressure of 0.1~0.3mm, a stirring head rotation speed of 300~1000rpm, and a welding speed of 30~100mm / min.

[0015] Furthermore, the shoulder diameter D of the stirring pin is 3 to 5 times the thickness of the upper plate to be welded, the root diameter D1 of the first stirring pin is 1.5 to 2.5 times the thickness of the upper plate to be welded, the end diameter D2 of the first stirring pin is 2 to 3 times the thickness of the lower plate to be welded, the root diameter D3 of the second stirring pin is 4 mm shorter than the end diameter D2 of the first stirring pin, and the end diameter D4 of the second stirring pin is equal to the end diameter D2 of the first stirring pin.

[0016] Furthermore, the length L1 of the first stirring pin used is 2mm shorter than the thickness T1 of the upper plate to be welded, and the length L2 of the second stirring pin is 1 / 2 of the thickness T2 of the lower plate to be welded.

[0017] Furthermore, the thread direction of the first and second stirring pins is related to the rotation direction of the stirring head; when the stirring head rotates clockwise, the thread direction of the first stirring pin is left-handed and the thread direction of the second stirring pin is right-handed; when the stirring head rotates counterclockwise, the thread direction of the first stirring pin is right-handed and the thread direction of the second stirring pin is left-handed.

[0018] Furthermore, the lap material is a weld of the same metal, such as aluminum alloy, magnesium alloy, titanium alloy, or copper alloy, or a weld between dissimilar metals, such as aluminum alloy / magnesium alloy, aluminum alloy / titanium alloy, or aluminum alloy / copper alloy.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] This invention controls the "vertical cross" flow of materials at the interface by designing the morphology and structure of the first and second stirring pins. Under the action of the first stirring pin, the metal at the interface flows downwards. The second stirring pin, with its eccentric structure and tapered thread, not only allows the material to migrate laterally over a distance greater than the diameter of the first stirring pin's end, but also enables it to migrate upwards under the action of the thread, ultimately forming an interlocking structure spontaneously near the interface. This invention eliminates the need for special structural design of the welded plates, achieving interlocking at the interface while also eliminating hook-like and overlap defects. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the friction stir lap welding of the present invention;

[0022] Figure 2 This is a schematic diagram showing the shape and outline of the stirring head for friction stir lap welding according to the present invention.

[0023] Figure 3 This is a schematic diagram of the planar notch at the end of the second stirring pin of the stirring head for friction stir lap welding according to the present invention;

[0024] Figure 4 This is a numerical simulation diagram of material flow near the stirring needle in Embodiment 2 of the present invention.

[0025] In the figure: 1- Friction stir lap weld upper plate, 2- Friction stir lap weld lower plate, where T1 is the thickness of the upper plate of the workpiece to be welded, T2 is the thickness of the lower plate of the workpiece to be welded, 3- Shoulder, 4- First stirring pin, 5- Second stirring pin, 6- Notch, where D is the diameter of the shoulder, D1 is the root diameter of the first stirring pin, D2 is the end diameter of the first stirring pin, L1 is the length of the first stirring pin, D3 is the root diameter of the second stirring pin, D4 is the end diameter of the second stirring pin, L2 is the length of the second stirring pin, and d is the eccentricity between the first and second stirring pins. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] In friction stir welding with interlocking lap joints, the interfaces of the upper and lower plates being welded overlap, such as... Figure 1 The purpose of this invention is to provide a stirring pin and welding method for friction stir welding that enables interlocking at the lap joint interface, thereby solving the problems existing in the prior art. By promoting the "up-down cross" flow of material near the lap joint interface, interlocking is achieved at the lap joint interface, avoiding hook-shaped defects and cold lap defects. To make the above-mentioned objectives, features, and advantages of this invention more apparent and understandable, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Figure 2The diagram shows a friction stir welding needle for interlocking lap joints, as described in this invention. It includes a first stirring needle fixed below a shoulder and a second stirring needle fixed below the first stirring needle. The first stirring needle is tapered (wider at the top, narrower at the bottom), and the second stirring needle is tapered (narrower at the top, wider at the bottom). Both the first and second stirring needles have threads on their tapered surfaces, with the threads of the first and second stirring needles rotating in opposite directions. The centerline of the first stirring needle is coaxial with the rotating shaft of the shoulder, while the centerline of the second stirring needle is eccentrically positioned with an eccentricity d of 2-3 mm from the rotating shaft. The end diameter D2 of the first stirring needle is larger than the root diameter D3 of the second stirring needle, forming a stepped shoulder between the two stirring needles.

[0030] The dimensions of the stirring pin are determined by the dimensions of the overlapping materials to be welded. First, the shoulder diameter D of the stirring head, the root diameter D1 of the first stirring pin, the end diameter D2 of the first stirring pin, the root diameter D3 of the second stirring pin, and the end diameter D4 of the second stirring pin are determined based on the thicknesses of the upper and lower plates to be welded. The shoulder diameter D is 3 to 5 times the thickness of the upper plate to be welded, the root diameter D1 of the first stirring pin is 1.5 to 2.5 times the thickness of the upper plate to be welded, the end diameter D2 of the first stirring pin is 2 to 3 times the thickness of the lower plate to be welded, the root diameter D3 of the second stirring pin is 4 mm shorter than the end diameter D2 of the first stirring pin, and the end diameter D4 of the second stirring pin is equal to the end diameter D2 of the first stirring pin.

[0031] The lengths of the first stirring pin, L1, and the second stirring pin, L2 are determined based on the thicknesses of the upper and lower plates to be welded. The length of the first stirring pin, L1, is 2 mm smaller than the thickness T1 of the upper plate to be welded, and the length of the second stirring pin, L2, is half the thickness T2 of the lower plate to be welded.

[0032] Determine the eccentricity and thread direction of the first and second stirring pins. The distance d between the center lines of the first and second stirring pins is 2~3mm. The thread direction of the first stirring pin is opposite to that of the second stirring pin and is related to the rotation direction of the stirring head. For example, when the stirring head rotates clockwise, the thread direction of the first stirring pin is left-handed and the thread direction of the second stirring pin is right-handed.

[0033] To further enhance metal flow near the tip of the second stirring pin, at least one notch 6 is provided at the lower edge of the second stirring pin, such as... Figure 3 As shown. Preferably, three notches 6 are provided, and the three notches 6 are evenly distributed along the circumference of the second stirring pin.

[0034] During welding, the upper and lower plates to be welded are first ground with a wire brush, then cleaned with acetone, and fixed to form a lap joint. The stirring needle is then used to weld along the center line of the lap joint, with a pressure of 0.1~0.3mm, a stirring head rotation speed of 300~1000rpm, and a welding speed of 30~100mm / min. This welding method is suitable for upper and lower plates made of the same or different metals. The thickness of the upper plate and the lower plate is 4~10mm. Example

[0035] This embodiment provides a stirring pin for friction stir welding that enables interlocking of lap joints and a welding method, including the following steps:

[0036] Step 1: The upper and lower plates to be welded are made of 2024 aluminum alloy and 7075 aluminum alloy, respectively, with plate thicknesses of 6mm and 5mm. The shoulder diameter is 24mm, the root diameter of the first stirring pin is 12mm, the tip diameter of the first stirring pin is 10mm, the root diameter of the second stirring pin is 6mm, and the tip diameter of the second stirring pin is 10mm.

[0037] Step 2: Select a stirring needle length of 4mm and a second stirring needle length of 2.5mm.

[0038] Step 3: The distance between the center lines of the first and second stirring pins is 2mm. Rotate the stirring head clockwise, with the first stirring pin having a left-hand thread and the second stirring pin having a right-hand thread.

[0039] Step 4: Grind the upper and lower plates to be welded with a wire brush, then clean them with acetone, and fix the upper and lower plates to be welded to obtain a lap joint.

[0040] Step 5: Use the stirring needle to weld along the center line of the lap joint, with a downward pressure of 0.1 mm, a stirring head rotation speed of 800 rpm, and a welding speed of 60 mm / min to complete the friction stir welding. Example

[0041] This embodiment provides a stirring pin and method for friction stir welding that can achieve interlocking at the lap joint interface, including the following steps:

[0042] Step 1: The upper and lower plates to be welded are selected as 6061 aluminum alloy and AZ31B aluminum alloy, respectively, with plate thicknesses of 5mm and 4mm. The shoulder diameter is 20mm, the root diameter of the first stirring pin is 12mm, the tip diameter of the first stirring pin is 10mm, the root diameter of the second stirring pin is 6mm, and the tip diameter of the second stirring pin is 10mm.

[0043] Step 2: Select a stirring needle length of 3mm and a second stirring needle length of 2mm.

[0044] Step 3: The distance between the center lines of the first and second stirring pins is 2mm. Rotate the stirring head clockwise, with the first stirring pin having a left-hand thread and the second stirring pin having a right-hand thread.

[0045] Step 4: Grind the upper and lower plates to be welded with a wire brush, then clean them with acetone, and fix the upper and lower plates to be welded to obtain a lap joint.

[0046] Step 5: Use the stirring needle to weld along the center line of the lap joint, with a downward pressure of 0.1 mm, a stirring head rotation speed of 900 rpm, and a welding speed of 50 mm / min to complete the friction stir welding.

[0047] The material flow near the stirring needle used in Example 2 was simulated using numerical simulation methods. Figure 4 As can be seen, the metal near the second stirring pin flows toward the end of the first stirring pin, while the metal near the end of the first stirring pin migrates to both sides, forming an interlocking structure at the overlapping interface.

[0048] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A stirring pin for friction stir welding that enables interlocking at lap joints, characterized in that, It includes a first stirring pin fixed below the shoulder of the shaft, and a second stirring pin fixed below the first stirring pin; the first stirring pin is a tapered shape that is "wider at the top and narrower at the bottom", and the second stirring pin is a tapered shape that is "narrower at the top and wider at the bottom". Both the first stirring pin and the second stirring pin are provided with threads on their tapered surfaces, and the threads of the first stirring pin and the second stirring pin are rotated in opposite directions. The center line of the first stirring needle is coaxial with the rotating main shaft of the shoulder, and the center line of the second stirring needle is eccentrically set with respect to the rotating main shaft; The eccentricity d between the center line of the second stirring needle and the rotating main shaft is 2-3 mm; The end diameter D2 of the first stirring needle is larger than the root diameter D3 of the second stirring needle, so that a stepped shoulder is formed between the first stirring needle and the second stirring needle. At least one notch is provided at the lower edge of the second stirring needle, and the notch is evenly distributed around the circumference of the second stirring needle. The shoulder diameter D of the stirring pin used is 3 to 5 times the thickness of the upper plate to be welded, the root diameter D1 of the first stirring pin is 1.5 to 2.5 times the thickness of the upper plate to be welded, the end diameter D2 of the first stirring pin is 2 to 3 times the thickness of the lower plate to be welded, the root diameter D3 of the second stirring pin is 4 mm shorter than the end diameter D2 of the first stirring pin, and the end diameter D4 of the second stirring pin is equal to the end diameter D2 of the first stirring pin. The length L1 of the first stirring pin used is 2mm smaller than the thickness T1 of the upper plate to be welded, and the length L2 of the second stirring pin is 1 / 2 of the thickness T2 of the lower plate to be welded.

2. A friction stir welding method based on the interlocking of the lap joint interface of the stirring pin as described in claim 1, characterized in that, Step 1: Grind the upper and lower plates to be welded with a wire brush, then clean them with acetone, and fix the upper and lower plates to be welded to obtain a lap joint. Step 2: Weld along the center line of the lap joint using the stirring needle, with a downward pressure of 0.1~0.3mm, a stirring head rotation speed of 300~1000rpm, and a welding speed of 30~100mm / min; The thread direction of the first and second stirring pins is related to the rotation direction of the stirring head. When the stirring head rotates clockwise, the thread direction of the first stirring pin is left-handed and the thread direction of the second stirring pin is right-handed. When the stirring head rotates counterclockwise, the thread direction of the first stirring pin is right-handed and the thread direction of the second stirring pin is left-handed.

3. The friction stir welding method for interlocking lap joints according to claim 2, characterized in that, The lap material is a weld of the same metal, such as aluminum alloy, magnesium alloy, titanium alloy or copper alloy, or a weld between dissimilar metals such as aluminum alloy / magnesium alloy, aluminum alloy / titanium alloy or aluminum alloy / copper alloy.

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