Automated tube sheet joint solid phase joining method based on friction stir plug welding

Abstract

This invention discloses an automated solid-state joining method for tube-plate joints based on friction stir plug welding, comprising a stirring head and materials to be welded. The materials to be welded include a hollow tube with several flashes and a tube-plate. The method includes the following steps: first, the hollow tube is upset to form flashes; then, an annular groove is formed along the upper edge of the tube-plate hole; the tube segment of the hollow tube is inserted into the tube-plate hole with an interference fit; finally, the tube segment and the tube-plate are pressed together by high-speed rotation of the stirring head to form a welded joint. The flash width of the hollow tube is less than or equal to the width of the annular groove of the tube-plate, and the flash depth of the hollow tube is less than or equal to the depth of the annular groove of the tube-plate. The outer diameter of the hollow tube segment is less than or equal to the inner diameter of the tube-plate. To enable the stirring head to compress the hollow tube and combine it with the tube-plate, the inner diameter of the hollow tube is less than or equal to the median diameter of the stirring pin, the shoulder diameter of the stirring head is greater than or equal to the outer diameter of the annular groove of the tube-plate, and the shoulder diameter of the stirring head is greater than or equal to twice the median diameter of the stirring pin. This invention enables automated production of tube-plate joints and has advantages such as excellent mechanical properties, low welding heat input, and small residual stress and deformation after welding.

Description

Technical Field

[0001] This invention relates to metal plastic processing and friction welding technology, specifically to an automated solid-state connection method for tube sheet joints based on friction stir plug welding. Background Technology

[0002] Stainless steel heat exchanger tubes have advantages such as high heat exchange efficiency and high oxidation resistance, and are widely used in many fields such as food processing, medical equipment, heating systems, air conditioning, and boilers. Among them, the welding quality of the tube sheet joints in heat exchanger tubes is the most critical link. However, stainless steel tube sheet joints still have defects such as low joint pull-out strength, poor corrosion resistance, and poor airtightness, and are difficult to automate production, which restricts their use in pressure equipment.

[0003] Compared with traditional tungsten inert gas welding (TIG) for tube-to-sheet joints, friction stir plug welding produces aesthetically pleasing welds with superior joint mechanical properties and virtually no post-weld deformation. Furthermore, it eliminates the need for filler wire and gas shielding, produces no arc light or dust pollution, and boasts extremely high forming efficiency.

[0004] Friction stir plug welding is a novel solid-state processing method that organically combines friction stir welding and traditional plug welding, enabling efficient and automated welding of tube-to-sheet joints. Traditional friction stir welding of tube-to-sheet structures requires the stirring head to be inserted at an angle to form a fillet weld, but this structure is weaker than a butt weld and suffers from mutual interference between tube bundles, making it impractical. For example, patent CN105414740-B discloses a solid-state diffusion connection method for tube-to-sheet structures that integrates expansion welding, changing the original fillet weld structure into a butt weld structure. However, under the enormous upsetting pressure of friction stir welding, the hollow tubes and tube-to-sheet undergo longitudinal displacement, making it difficult to guarantee the required extension of the upper end of the tube beyond the upper surface k of the tube-to-sheet, thus compromising welding quality. Summary of the Invention

[0005] Purpose of the Invention: The purpose of this invention is to address the shortcomings of existing technologies and provide an automated solid-state connection method for tube sheet joints based on friction stir plug welding. On one hand, the tube section is flush with the tube sheet surface, and the tube sheet has an annular groove and steps. On the other hand, welding is achieved by utilizing the shoulder of the stirring head and the sidewall extrusion of the stirring pin. This invention innovatively proposes a friction stir plug welding method, which can realize automated production of tube sheet joints. It has advantages such as excellent mechanical properties, low welding heat input, and small residual stress and deformation after welding. It can provide a new method and new ideas for the efficient and high-quality production of heat exchanger tube sheet joints.

[0006] Technical solution: The present invention provides an automated solid-state connection method for tube sheet joints based on friction stir plug welding, comprising a stirring head and materials to be welded, the materials to be welded including hollow tubes with several flashes and tube sheets, comprising the following steps:

[0007] First, the hollow tube (3) is upset to form a flash (6). Then, an annular groove is opened along the upper edge of the tube sheet hole. The tube section of the hollow tube is inserted into the tube sheet hole with an interference fit. Finally, the tube section and the tube sheet are welded together by the high-speed rotation of the stirring head. The flash width f of the hollow tube is less than the annular groove width d of the tube sheet, and the flash depth g of the hollow tube is less than the annular groove depth e of the tube sheet. The outer diameter d1 of the hollow tube section is less than the inner diameter a of the tube sheet, and d1+0.02=a. In order for the stirring head to squeeze the hollow tube to combine with the tube sheet, the inner diameter d2 of the hollow tube is less than the middle diameter D1 of the stirring needle, that is, d2≤D1. The shoulder diameter D2 of the stirring head is greater than the outer diameter a+2d of the annular groove of the tube sheet, and the shoulder diameter D2 of the stirring head is greater than twice the middle diameter D1 of the stirring needle, that is, D2≥(a+2d) and D2≥2D1.

[0008] A step is made at the lower edge of the tube sheet hole. The combined effect of the annular groove and the step can further prevent the hollow tube from moving downward under the huge upsetting force of the friction stir welding spindle. The step width b of the tube sheet is less than or equal to the wall thickness of the heat exchange tube body. The step width of the tube sheet is 0.3 to 6 mm. The step depth of the tube sheet is 1 to 3 mm. The width d and depth e of the annular groove of the tube sheet are related to the wall thickness of the hollow tube, and are respectively 0.5 to 2 mm and 1 to 3 mm.

[0009] Furthermore, the tilt angle of the friction stir plug welding spindle is -0.5° to 0.5°, and the downward pressure is 1 to 3 mm; for hollow tubes with a smaller wall thickness (0.5 to 1.5 mm), the rotation speed is 400 to 1200 rpm, and the loading duration is 10 to 30 s; for hollow tubes with a larger wall thickness (1.5 to 3.0 mm), the rotation speed is 2000 to 6000 rpm, and the loading duration is 20 to 40 s.

[0010] Furthermore, the stirring head is made of PCBN or W-Re alloy.

[0011] Beneficial effects: This invention first sets the hollow tube section flush with the tube sheet surface, ensuring that the high-speed rotation of the stirring head shoulder applies heat to both the hollow tube and the tube sheet simultaneously, and also facilitating rapid assembly. Furthermore, annular grooves and steps are formed in the tube sheet; then, welding is achieved by pressing together the shoulder in the middle of the stirring head and the sidewall of the stirring pin. Compared with existing technologies, this invention has the following advantages:

[0012] (1) The present invention processes an annular groove structure on the upper edge of the tube sheet, which, together with the flash structure formed by the upsetting of the tube section, can ensure that the upsetting force is not too large during the welding process, causing the tube section to shift downwards and out of position. It can also allow the material squeezed out during the friction stir welding process to have sufficient space to flow, and can increase the contact area between the tube section and the tube sheet, thereby improving the welding quality.

[0013] (2) No welding materials are required in the entire solid-phase connection process of the present invention. No smoke or dust is generated during the welding process. The welding efficiency is high and it is an environmentally friendly welding method. Furthermore, the welding process can be fully automated, and the welding efficiency is significantly higher than that of existing methods. A single tube sheet joint can be welded within 40 seconds.

[0014] (3) The present invention changes the tube sheet joint structure from fillet weld to butt weld, and the weld strength is significantly better than the original weld.

[0015] (4) This invention can be applied to tube sheet heat exchanger structures made of stainless steel, and can also be used for welding tube sheet structures made of other materials such as aluminum alloy, magnesium alloy, and titanium alloy. It has the advantages of excellent mechanical properties, low welding heat input, and small residual stress and deformation after welding. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the present invention without steps.

[0017] Figure 2 This is a schematic diagram of the overall structure of the present invention when steps are provided;

[0018] Figure 3 This is a schematic diagram of the friction stir plug welding process for a tube sheet structure in one embodiment of the present invention;

[0019] Figure 4 The following is a diagram of the assembly and post-weld physical sample of the tube sheet welding test piece as an example. Detailed Implementation

[0020] The technical solution of the present invention will be described in detail below, but the scope of protection of the present invention is not limited to the embodiments described.

[0021] like Figure 1 and Figure 3 As shown, the automated tube sheet joint solid-state joining method based on friction stir plug welding of the present invention includes a stirring head 1 and materials to be welded. The materials to be welded include a hollow tube 3 with several flashes 6 and a tube sheet 4, and include the following steps:

[0022] First, the hollow tube 2 is upset to form a flash 6. Then, an annular groove 7 is opened along the upper edge of the hole in the tube sheet 4. The tube segment of the hollow tube 3 is inserted into the hole in the tube sheet 4 with an interference fit. Finally, the tube segment and the tube sheet 4 are welded together by high-speed rotation and extrusion of the stirring head 1. The width f of the flash 6 of the hollow tube 3 in the tube sheet 4 step 8 is less than or equal to the width d of the annular groove 7 in the tube sheet 4, and the depth g of the flash 6 of the hollow tube 3 is less than or equal to the depth e of the annular groove 7 in the tube sheet 4. The outer diameter d1 of the tube sheet 4 is less than or equal to the inner diameter a of the tube sheet 4, and d1 + 0.02 = a; the stirring head 1 can compress the heat exchange tube body to combine with the tube sheet 4, the inner diameter d2 of the hollow tube 3 is less than or equal to the middle diameter D1 of the stirring needle 2, that is, d2 ≤ D1, the diameter D2 of the shoulder 5 of the stirring head 1 is greater than or equal to the outer diameter a + 2d of the annular groove 7 of the tube sheet 4, and the diameter D2 of the shoulder 5 of the stirring head 1 is greater than or equal to twice the middle diameter D1 of the stirring needle 2, that is, D2 ≥ (a + 2d) and D2 ≥ 2D1.

[0023] like Figure 2 As shown, in this embodiment, a step 8 is also formed at the lower edge of the holes in the tube sheet 4. The width b of the step 8 in the tube sheet 4 is less than or equal to the wall thickness of the heat exchange tube body. Here, the width of the step 8 in the tube sheet 4 is 0.3 to 6 mm; the depth of the step 8 in the tube sheet 4 is 1 to 3 mm; the width d and the depth e of the annular groove 7 in the tube sheet 4 are both related to the wall thickness of the hollow tube 3, and are respectively 0.5 to 2 mm and 1 to 3 mm.

[0024] The solid-state joining method of the present invention utilizes the high-speed rotation and extrusion action of the stirring head 1 to generate heat in the tube wall. Under plastic deformation, the material ultimately forms a reliable connection based on the combined effects of temperature and pressure. Compared with the prior art, its friction stir plug welding produces aesthetically pleasing welds, excellent joint mechanical properties, and almost no deformation after welding. Furthermore, it does not require filler wire or gas protection, eliminates arc light and dust pollution, and has extremely high forming efficiency. In summary, the annular groove 7, step 8, and flash 6 of the tube sheet 4 and the hollow tube 3 in the present invention can effectively avoid the aforementioned problems generated during the friction stir plug welding process.

[0025] Example 1:

[0026] This example uses a hollow tube 3 and a tube sheet 4 made of 316L stainless steel as the research object. The outer diameter d1 of the hollow tube 3 is 12mm, the inner diameter d2 is 8mm, and the wall thickness is 2mm. The diameter D2 of the shoulder 5 of the stirring head 1 is 16mm, and the mean diameter D1 of the stirring needle 2 is 8mm. The solid-phase connection method of the tube sheet 4 joint includes the following steps:

[0027] Step 1:

[0028] according to Figure 1The tube sheet 4 is designed such that several through holes with a diameter of 10mm are drilled on the tube sheet 4 using a drilling machine. Then, a 12mm diameter drill bit is used to drill until the hole stops 1mm from the bottom edge of the tube sheet 4. That is, the inner diameter a of the tube sheet 4 is 12mm, the width b of the step 8 is 1mm, and the depth c of the step 8 is 1mm. Then, a 14mm diameter drill bit is used to drill until the hole stops 1mm deep. That is, the width d of the annular groove 7 is 1mm and the depth e is 1mm.

[0029] Step 2:

[0030] according to Figure 2 The pipe design adopts a partial upsetting process, which increases the outer diameter of the pipe section while keeping the inner diameter unchanged. Then, the upset part is machined on a lathe. After machining, the width f of the flash 6 of the pipe section is 1mm and the depth g of the flash 6 is 1mm.

[0031] Step 3:

[0032] The holes in the tube sheet and the rusted areas on the tube wall were polished using sandpaper no coarser than 400 grit. Then, the oil stains were cleaned sequentially with alcohol and acetone solutions. After cleaning, the tubes were hammered into the holes in the tube sheet, ensuring a tight fit so that the tubes could not rotate within the holes. Finally, the tube sheet structure with the inserted tubes was fixed in a friction stir welding apparatus for welding (see...). Figure 4 (a)).

[0033] Step 4:

[0034] The parameters that need to be controlled during the welding of the friction stir plug include: the rotational speed (rpm) of the stirring head 1, the loading duration (s), the pressure applied (mm), and the spindle tilt angle (°). In this embodiment, the stirring head 1 is used with a rotational speed of 1200 rpm, a loading duration of 30 s, a pressure applied of 2 mm, and a spindle tilt angle of 0°. After welding, the tube sheet 4 connector is obtained (see...). Figure 4 (b) and conduct organizational performance analysis on it.

[0035] Example 2:

[0036] This example uses a tube and tube sheet 4 made of 316L stainless steel as the research object. The outer diameter d1 of the tube is 12mm, the inner diameter d2 is 10mm, the wall thickness is 1mm, the diameter D2 of the shoulder 5 of the stirring head 1 is 24mm, and the mean diameter D1 of the stirring needle 2 is 11mm. The solid-phase connection method of the tube sheet 4 joint includes the following steps:

[0037] Step 1:

[0038] according to Figure 1The tube sheet 4 is designed such that several through holes with a diameter of 10mm are drilled on the tube sheet 4 using a drilling machine. Then, a 12mm diameter drill bit is used to drill until the hole stops 0.5mm from the bottom edge of the tube sheet 4. That is, the inner diameter a of the tube sheet 4 is 12mm, the width b of the step 8 is 1mm, and the depth c of the step 8 is 0.5mm. Then, a 14mm diameter drill bit is used to drill until the hole stops 0.5mm deep. That is, the width d of the annular groove 7 is 1mm and the depth e is 0.5mm.

[0039] Step 2:

[0040] according to Figure 2 The pipe design adopts a partial upsetting process, which increases the outer diameter of the pipe section while keeping the inner diameter unchanged. Then, the upset part is machined on a lathe. After machining, the width f of the flash 6 of the pipe section is 1mm and the depth g of the flash 6 is 0.5mm.

[0041] Step 3:

[0042] Same as Example 1.

[0043] Step 4:

[0044] The parameters that need to be controlled during friction stir plug welding include: the rotational speed (rpm) of the stirring head 1, the loading duration (s), the pressure applied (mm), and the spindle tilt angle (°). In this embodiment, the stirring head 1 is used with a rotational speed of 800 rpm, a loading duration of 10 s, a pressure applied of 1 mm, and a spindle tilt angle of -0.5°. After welding, the tube sheet 4 joint can be obtained, and its microstructure and properties can be analyzed.

[0045] Example 3:

[0046] This example uses a tube and tube sheet 4 made of 316L stainless steel as the research object. The outer diameter d1 of the tube is 10mm, the inner diameter d2 is 6mm, and the wall thickness is 2mm. The diameter D2 of the shoulder 5 of the stirring head 1 is 14mm, and the mean diameter D1 of the stirring needle 2 is 7mm. The solid-phase connection method of the tube sheet 4 joint includes the following steps:

[0047] Step 1:

[0048] according to Figure 1 The tube sheet 4 is designed such that several through holes with a diameter of 6mm are drilled on the tube sheet 4 using a drilling machine. Then, a 10mm diameter drill bit is used to drill until the hole stops 1.5mm from the bottom edge of the tube sheet 4, which means the inner diameter a is 10mm, the width b of the step 8 of the tube sheet 4 is 2mm, and the depth c of the step 8 is 1.5mm. Then, a 12mm diameter drill bit is used to drill until the hole stops at a depth of 2mm, which means the width d of the annular groove 7 is 1mm and the depth e is 2mm.

[0049] Step 2:

[0050] according to Figure 2 The pipe design adopts a partial upsetting process, which increases the outer diameter of the pipe section while keeping the inner diameter unchanged. Then, the upset part is machined on a lathe. After machining, the width f of the flash 6 of the pipe section is 1mm and the depth g of the flash 6 is 2mm.

[0051] Step 3:

[0052] Same as Example 1.

[0053] Step 4:

[0054] The parameters that need to be controlled during the friction stir plug welding process include: the rotational speed (rpm) of the stirring head 1, the loading duration (s), the pressure applied (mm), and the spindle tilt angle (°). In this embodiment, the stirring head 1 is used with a rotational speed of 4000 rpm, a loading duration of 40 s, a pressure applied of 3 mm, and a spindle tilt angle of 0.5°. After welding, the tube sheet 4 joint can be obtained, and its microstructure and properties can be analyzed.

[0055] Comparative example:

[0056] This example uses a tube and tube sheet 4 made of 316L stainless steel as the research object. The tube has an outer diameter of 12mm, an inner diameter of 10mm, and a wall thickness of 1mm. The solid-state connection method of the tube sheet 4 joint includes the following steps:

[0057] Step 1:

[0058] Several through holes with a diameter of 10 mm were drilled on tube sheet 4 using a drilling machine.

[0059] Step 2:

[0060] Before assembling tube sheet 4, clean it with acetone; the tube wall needs to be polished with a flap wheel for at least 50mm at both ends, and the tube wall thickness should not be reduced. Assemble the tube bundle and protect the welded parts of the tube ends with plastic wrap.

[0061] Step 3:

[0062] The tube sheet joint 4 should be spot welded every 120° using manual tungsten inert gas (TIG) welding. The arc start and end of the root pass must be off-center from the spot welding area. Each joint should be welded in three passes using manual TIG welding, with each pass facing upwards. The first pass should use autofusion welding, while the second and third passes should use filler wire welding. After welding, the tube sheet joint 4 can be obtained, and its microstructure and properties can be analyzed.

[0063] As can be seen from the data and figures of the above embodiments, the present invention can realize the automated production of tube sheet 4-joints, and has the advantages of excellent mechanical properties, low welding heat input, and small residual stress and deformation after welding. It can provide a new method and new ideas for the efficient and high-quality production of heat exchanger tube sheet 4-joints.

Claims

1. An automated solid-state connection method for tube sheet joints based on friction stir plug welding, comprising a stirring head (1) and materials to be welded, the materials to be welded comprising a hollow tube (3) with several flashes (6) and a tube sheet (4), characterized in that, Includes the following steps: First, the hollow tube (3) is upset to form a flash (6). Then, an annular groove (7) is opened along the upper edge of the hole in the tube sheet (4). The tube section of the hollow tube (3) is inserted into the hole in the tube sheet (4) with an interference fit. Finally, the outer wall of the tube section of the hollow tube (3) is formed with the tube sheet (4) by high-speed rotation and extrusion of the shoulder (5) of the stirring head (1) and the side wall of the stirring needle (2). Among them, the width f of the flash (6) of the hollow tube (3) is less than the width d of the annular groove (7) of the tube plate (4), the depth g of the flash (6) of the hollow tube (3) is less than the depth e of the annular groove (7) of the tube plate (4); the outer diameter d1 of the hollow tube (3) is less than the inner diameter a of the tube plate (4), and d1+0.02=a; the inner diameter d2 of the hollow tube (3) is less than the middle diameter D1 of the stirring needle (2), that is, d2≤D1; the diameter D2 of the shoulder (5) of the stirring head (1) is greater than or equal to the outer diameter a+2d of the annular groove (7) of the tube plate (4), and the diameter D2 of the shoulder (5) of the stirring head (1) is greater than or equal to twice the middle diameter D1 of the stirring needle (2), that is, D2≥(a+2d) and D2≥2D1; The tube sheet (4) also has a step (8) at the lower edge of the hole. The width b of the step (8) of the tube sheet (4) is 0.3~6mm. The depth of the step (8) of the tube sheet (4) is 1~3mm. The width d and the depth e of the annular groove (7) of the tube sheet (4) are related to the wall thickness of the hollow tube (3), and are respectively 0.5~2mm and 1~3mm. Furthermore, the width b of the step (8) of the tube sheet (4) is less than or equal to the wall thickness of the hollow tube (3).

2. The automated tube sheet joint solid-state connection method based on friction stir plug welding according to claim 1, wherein the tilt angle of the friction stir plug welding spindle is -0.5° to 0.5°, and the downward pressure is 1 to 3 mm; For hollow tubes (3) with a wall thickness of 0.5~1.5mm, the rotation speed is 400~1200rpm and the loading duration is 10~30s. For hollow tubes (3) with a wall thickness of 1.5~3.0mm, the rotation speed is 2000~6000rpm and the loading duration is 20~40s.

3. The automated tube sheet joint solid-state connection method based on friction stir plug welding according to claim 1, wherein the stirring head (1) is made of PCBN or W-Re alloy.

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