Ultrasonic rapid cooling multi-external field composite stir friction welding device, welding method and application

Abstract

The invention belongs to the technical field of stir friction welding, and discloses an ultrasonic rapid cooling multi-external field composite stir friction welding device, a welding method and an application thereof, comprising a welding machine head, a stirring head, an ultrasonic auxiliary system and a local rapid cooling auxiliary system; wherein the stirring head is installed on the welding machine head; the ultrasonic auxiliary system comprises an ultrasonic generator, a wire and a vibration device connected in sequence, an ultrasonic tool head of the vibration device extends toward the stirring head, and is located upstream of the stirring head travel path, and during welding, the ultrasonic tool head is brought into contact with the weld and a set pressure is applied to the weld; the local rapid cooling auxiliary system comprises a cooling medium storage, a pump, a second delivery pipe, a nozzle and a protective cover connected in sequence, the nozzle extends toward the stirring head, and is located downstream of the stirring head travel path, and during welding, the nozzle is set toward the weld.

Description

Technical Field

[0001] The invention belongs to the technical field of friction stir welding, and in particular relates to an ultrasonic rapid cooling multi-external field composite friction stir welding device, a welding method and an application thereof. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] As a solid-phase connection technology, friction stir welding has been widely used in aerospace, rail transportation, shipbuilding and other fields due to its advantages such as high degree of automation and high joint quality. However, conventional FSW mainly relies on the friction between the stirring head and the workpiece and the heat generated by the plastic deformation of the material to soften the material in the welding area to form a connection. There are problems such as large welding load, easy wear and fracture of the stirring head, large residual stress in the weld, and narrow process window, which seriously restrict the application of FSW.

[0004] Based on the above problems of conventional FSW, researchers have conducted a lot of exploration in the modification of FSW process. Some studies have assisted stir friction welding by applying heat source. Although applying heat source can soften metal and reduce welding load, it will cause overheating of the workpiece, resulting in the growth of precipitation phase in the weld or too thick IMCs layer, which will reduce the structure and performance of the joint. Some studies have assisted stir friction welding by ultrasound, but the use of ultrasonic external field alone cannot reduce overheating in the shoulder area, which can easily cause joint weakening, especially in the welding process of dissimilar materials, the overheating problem of weld surface is more prominent. Some studies have performed stir friction welding by joint modification. Although it can optimize the flow of plastic materials and improve temperature distribution during welding, it increases the complexity of the process, reduces welding efficiency, and there is also the problem of easy wear of the stirring head.

[0005] In addition, due to the structural characteristics of the stirring head itself, the heat generated by the shoulder of the stirring head is the main source of heat in the conventional stir friction welding process, while the stirring needle generates less heat, which causes uneven temperature distribution inside the weld, and there is a temperature gradient along the thickness direction of the plate, and the temperature gradient increases with the increase of plate thickness. In order to avoid defects at the bottom of the weld and ensure that the plastic material is fully softened and flows, it is usually necessary to use a larger heat input parameter. Therefore, overheating is prone to occur on the upper surface of the workpiece, resulting in coarse grains, dissolution of precipitated phases, and excessively thick IMCs layers, which reduces the organization and performance of the joint. For this reason, some studies have used underwater welding or added liquid nitrogen to the weld surface for cooling, but the cooling method alone is prone to insufficient heat at the bottom of the weld, resulting in holes and unwelded defects at the root of the weld.

[0006] However, due to the inherent properties of the heat generation characteristics of stir friction welding and its welding temperature field. At present, it is still difficult for a single external field assisted stir friction welding to simultaneously reduce the overheating of the material in the upper weld area affected by the shaft shoulder, and to improve the softening and plastic flow ability of the material in the lower weld area affected by the stirring needle, so as to achieve the purpose of coordinated regulation of the thermal coupling process of the upper and lower welds. The above problems seriously limit the further improvement of joint performance, especially in the welding of dissimilar materials and metals that are sensitive to heat and deformation (such as magnesium alloys). The problem of weakened joint performance is more prominent. Summary of the invention

[0007] The purpose of the present invention is to overcome the deficiencies of the above-mentioned prior art and to provide an ultrasonic rapid cooling multi-external field composite stir friction welding device, a welding method and an application thereof.

[0008] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0009] In a first aspect, the present invention provides an ultrasonic quenching multi-external field composite stir friction welding device, comprising a welding machine head, a stirring head, an ultrasonic auxiliary system and a local quenching auxiliary system;

[0010] Among them, the stirring head is installed on the welding machine head;

[0011] The ultrasonic auxiliary system includes an ultrasonic generator, a wire and a vibration device connected in sequence, the vibration device includes an ultrasonic transducer, a horn, a vibration transmission rod and an ultrasonic tool head connected and installed in sequence, the vibration device is installed on the welding machine head, the ultrasonic tool head extends toward the stirring head and is located in front of the stirring head travel path, when welding, the ultrasonic tool head is brought into contact with the workpiece and a set pressure is applied to the workpiece;

[0012] The local rapid cooling auxiliary system includes a cooling medium storage, a conveying device, a second conveying pipe and a nozzle connected in sequence. The nozzle extends toward the stirring head and is located behind the stirring head's travel path. During welding, the nozzle is set toward the weld.

[0013] As a kind of mechanical energy, ultrasonic vibration has the advantages of high frequency and easy transmission. Applying ultrasonic vibration to the weld to assist stir friction welding can soften the weld metal, reduce the rheological stress of the plastic material, improve its plastic fluidity, and optimize the structure and performance of the joint. In addition, applying ultrasonic vibration can reduce the load of the welding process, reduce the wear of the stirring head, expand the welding process window, and improve the welding efficiency.

[0014] However, ultrasonic-assisted friction stir welding cannot solve the problems of overheating on the workpiece surface and large temperature gradient inside the weld. In addition, the existing ultrasonic-assisted friction stir welding is applicable to a small number of materials and scenarios, which is not conducive to rapid industrialization.

[0015] On the basis of ultrasonic assisted friction stir welding, a local quenching system is added, which can not only soften the metal through the effect of ultrasonic mechanical vibration and reduce the load of the welding process, but also use the effect of low temperature quenching to solve the problem of overheating on the upper surface of the workpiece and large temperature gradient inside the weld. Through ultrasonic quenching and multiple external fields, the welding thermal coupling process is coordinated and regulated, so as to avoid overheating of the upper part of the weld and promote the flow of materials in the lower part of the weld to avoid welding defects, thus achieving high-quality welding of materials.

[0016] In some embodiments, the ultrasonic-assisted system also includes a pneumatic device, which includes an air compressor, a second delivery pipe and a cylinder connected in sequence, the shell of the cylinder is fixedly installed, the piston of the cylinder is connected to a vibration device, and the vibration device is installed on a first fixed plate through a slide rail.

[0017] The air compressor of the pneumatic device is connected to the cylinder through a delivery pipe. The cylinder applies force to the vibration device to control the lifting and lowering of the vibration device to better adjust the relative position relationship between the ultrasonic tool head and the weld and stirring head, thereby better softening the weld metal, reducing the rheological stress of the plastic material, and improving its plastic fluidity.

[0018] Preferably, a pressure regulating valve is provided on the cylinder. Since the ultrasonic vibration energy will decay along the plate thickness direction, it is necessary to flexibly adjust the output power of the ultrasonic vibration and the contact pressure between the ultrasonic tool head and the substrate according to different plate thicknesses and different materials. By adjusting the pressure in the cylinder through the pressure regulating valve, the contact pressure between the ultrasonic tool head and the workpiece can be better adjusted.

[0019] In some embodiments, the ultrasound-assisted system further comprises an adjustment device, wherein the adjustment device comprises a first fixing plate, a second fixing plate and a third fixing plate connected in sequence;

[0020] The first fixing plate and the lower part of the second fixing plate form a revolving pair, and the upper part of the first fixing plate and the second fixing plate are connected by a curved U-shaped groove, which is used to control the rotation of the vibration device to better adjust the relative angle between the ultrasonic tool head and the stirring head axial direction;

[0021] The second fixing plate is connected to the third fixing plate through a horizontal U-shaped groove, which is used to control the horizontal displacement of the vibration device, so that the ultrasonic tool head can be applied at different positions;

[0022] The third fixing plate is connected to the welding machine head through a vertical U-shaped groove, which is used to control the vertical displacement of the vibration device to better adjust the depth of the ultrasonic head acting on the substrate.

[0023] Preferably, the ultrasonic tool head is a spherical tool head, a flat tool head or a rolling bearing tool head.

[0024] Spherical tool heads are mainly used for the same or different welding of narrow welds of light alloys such as magnesium alloys and aluminum alloys. Because the area of ​​the spherical tool head acting on the workpiece is small, it is suitable for narrow welds. The contact between the spherical tool head and the workpiece is in the form of sliding friction, and the resistance during the movement is relatively large, which is suitable for light alloys such as magnesium alloys and aluminum alloys.

[0025] The flat tool head is mainly used for wide welds of thin plates of light alloys such as magnesium alloys and aluminum alloys; because the flat tool head acts on a large area on the workpiece, it is suitable for wide welds; similar to the spherical tool head, there is also sliding friction between the spherical tool head and the workpiece, which is suitable for light alloys such as magnesium alloys and aluminum alloys. The difference is that the flat tool head has a wide range of ultrasonic action, but the area acting on the weld is large, resulting in greater resistance during the movement process, limiting the contact pressure between the flat ultrasonic tool head and the workpiece, so it is only suitable for welding thin plates.

[0026] Compared with spherical and flat ultrasonic tool heads, the contact between the rolling bearing tool head and the workpiece is rolling friction, with small resistance during movement, and can be used for the same or different welding of high-hardness alloys such as titanium alloy and steel.

[0027] In some embodiments, a protective cover is provided on the nozzle, a gas chamber is provided on the side wall of the protective cover, and an air inlet is provided on one side of the gas chamber;

[0028] The protective cover is provided with air holes on one side of the nozzle, and the air holes are distributed at least on two sides of the nozzle.

[0029] Since the cooling medium is easy to diverge and splash, it causes waste of cooling medium and is not conducive to the precise cooling of the weld. Therefore, a protective cover is used to cover the nozzle. In the process of using quenching liquid to cool the weld, protective gas is sprayed at the same time to limit the cooling medium, avoid splashing everywhere, and reduce waste of cooling medium.

[0030] Preferably, the air holes on both sides of the nozzle are arranged linearly and parallel to the weld.

[0031] Preferably, the protective cover is provided with air holes downstream of the nozzle, and the air holes are arranged in an arc shape. The air holes arranged in an arc shape spray out protective gas to form a gas barrier, which can effectively prevent the quenching liquid from splashing behind the nozzle.

[0032] Preferably, the protective cover is provided with air holes located upstream of the nozzle, and the air holes are arranged linearly and arranged perpendicular to the weld.

[0033] The gas barrier formed by the gas ejected from this part of the pores can effectively prevent the quenching medium from sputtering toward the stirring head, thereby avoiding the adverse effects of the quenching medium on stirring welding.

[0034] Preferably, the diameter of the pores is 3-6 mm, and the distance between adjacent pores is 2-4 mm.

[0035] The protective cover is provided with a nozzle sleeve hole, and the nozzle is installed in the nozzle sleeve hole. The diameter of the nozzle sleeve hole is set to be larger than the outer diameter of the nozzle, so that the protective cover and the nozzle can rotate relatively when they are in fixed contact, and the relative position between the protective cover and the nozzle can be adjusted within a certain range.

[0036] In some embodiments, a universal bamboo tube is connected between the second delivery pipe and the nozzle. The angle of the universal bamboo tube is adjustable so as to accurately align the nozzle with the weld and cool the weld in time after welding.

[0037] Preferably, a temperature controller and a flow control valve are connected between the second delivery pipe and the universal bamboo tube to regulate the temperature and flow of the cooling medium.

[0038] In a second aspect, the present invention provides an ultrasonic quenching multi-external field composite stir friction welding method, comprising the following steps: cleaning, clamping and fixing the workpiece to be welded;

[0039] When the stirring head starts to press down for welding, the ultrasonic auxiliary system and the local rapid cooling system are turned on, and ultrasonic energy is applied to the weld metal in front of the stirring head to promote the softening of the weld metal; cooling medium is sprayed on the welding surface behind the stirring head to perform rapid cooling treatment on it. When welding is completed, the ultrasonic auxiliary system and the local rapid cooling system are turned off;

[0040] The power of the ultrasonic generator is 100-2000W, the frequency is 10-50kHz, and the amplitude is 10-80μm.

[0041] In some embodiments, the axial distance between the ultrasonic tool head and the stirring head is 10-30 mm.

[0042] Preferably, the angle between the ultrasonic tool head and the workpiece plane is 30°-60°.

[0043] Preferably, the contact pressure between the ultrasonic tool head and the workpiece is 0.1-3 MPa.

[0044] In some embodiments, the cooling medium is a gas cooling medium and a liquid cooling medium.

[0045] Preferably, the liquid cooling medium is liquid nitrogen or an ethanol solution or a mixed solution of water and ethanol; the gas cooling medium is nitrogen, argon, helium or air, and supersonic airflow is used for gas cooling.

[0046] Preferably, the nozzle for spraying the cooling medium is an atomizing nozzle or a gradually converging and diverging nozzle. The atomizing nozzle is installed and used when the cooling medium is liquid, and the gradually converging and diverging nozzle is installed and used when the cooling medium is gas.

[0047] Select different cooling media to match different materials and application scenarios, select corresponding nozzle types to match different cooling media, and adjust the relative position of the nozzle center to the axis of the mixing head and the workpiece.

[0048] The type of cooling medium depends on different materials and application scenarios. The selection rules are as follows:

[0049] Liquid nitrogen cooling: suitable for thick plate welding; liquid nitrogen can quickly cool the weld surface and has a fast cooling speed, but if the temperature of liquid nitrogen is too low, the temperature of the joint will be too low, which is not conducive to the flow of plastic materials and causes defects such as holes inside the weld. Therefore, liquid nitrogen is not suitable for thin plate welding; and in conventional FSW welding of thick plates, the required stirring head size is large, that is, the shoulder diameter is large and the stirring needle is long, which makes the temperature of the upper surface of the workpiece too high, while the bottom temperature of the stirring needle is low, resulting in a large temperature gradient inside the weld along the plate thickness direction. Therefore, it is necessary to quickly reduce the temperature of the weld surface and reduce the temperature gradient inside the weld to ensure the uniformity of the joint structure and performance.

[0050] Ethanol solution or a mixed solution of ethanol and water: suitable for welding of thin plates; using distilled water can avoid introducing impurities into the weld, and adding a certain proportion of alcohol can not only lower the freezing point of the coolant to ensure that the distilled water does not freeze at the required temperature, but also achieve continuous cooling by absorbing heat through alcohol volatilization after the coolant is deposited on the weld surface. However, the use of mixed liquid cooling requires advance proportioning, complex operation and high cost; and when FSW welding thin plates, the upper surface of the workpiece is prone to overheating, resulting in coarse grains, dissolution of precipitated phases and excessively thick IMCs layers, which reduces the structure and performance of the joint.

[0051] Gas cooling (supersonic airflow): also suitable for welding thin plates; compared with mixed liquid cooling, gas cooling has low cost, clean and safe welding process, no need to clean up after welding, and simple operation, but the cooling time on the weld surface is short, and the cooling effect is slightly inferior to that of mixed liquid cooling.

[0052] In a third aspect, the present invention provides an application of the ultrasonic quenching multi-external field composite stir friction welding device or the ultrasonic quenching multi-external field composite stir friction welding method in stir friction solid phase additive manufacturing.

[0053] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0054] The present invention couples two external fields, ultrasound and rapid cooling, to give full play to their respective advantages. On the one hand, ultrasound can promote the softening of weld metal, reduce the rheological stress of plastic materials, improve their plastic fluidity, and optimize the structure and performance of the joint. At the same time, ultrasound can reduce the load of the welding process, reduce the wear of the stirring head, expand the welding process window, and improve the welding efficiency. On the other hand, coupling the rapid cooling external field can reduce the overheating of the upper surface of the workpiece, avoid the problems of coarse grains, dissolution of precipitated phases and excessive thickness of the IMCs layer, and further improve the performance of the joint. At the same time, the temperature gradient in the thickness direction of the plate is reduced, the temperature distribution inside the weld is regulated, and the uniformity of the structure and performance of the joint is regulated. In addition, it can also avoid the occurrence of strong texture in the joints of difficult-to-deform metals (such as magnesium alloys), resulting in reduced joint performance.

[0055] The tool head and the amplitude transformer of the ultrasonic assisted system of the present invention are connected by a threaded connection, and different types of ultrasonic tool heads can be flexibly replaced. The vibration device and the welding machine head are connected by an adjustment device, and the relative position of the ultrasonic tool head can be flexibly adjusted. It can be applied to different materials and application scenarios and has strong applicability.

[0056] The local rapid cooling auxiliary system of the present invention facilitates replacement of different types of cooling media and nozzles, can be applied to different materials and application scenarios, and has strong applicability; in addition, a protective cover in the shape of a weld is installed on the nozzle, which can accurately cool the weld.

[0057] The invention is easy to operate, does not require large-scale transformation of existing friction stir welding equipment, is conducive to technology upgrading and equipment replacement, and is easy to quickly industrialize and apply.

[0058] The device and process of the present invention are suitable for the same or different welding of magnesium alloys, aluminum alloys, titanium alloys, steels and composite materials.

[0059] The device and process of the present invention can also be used for friction stir solid phase additive manufacturing of the same or different laminated structures of magnesium alloys, magnesium alloys, aluminum alloys, titanium alloys, steels and composite materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0061] Figure 1 It is a structural diagram of an ultrasonic rapid cooling multi-external field composite friction stir welding device according to an embodiment of the present invention;

[0062] Figure 2 This is a flow chart of the ultrasonic rapid cooling multi-external field composite friction stir welding method according to an embodiment of the present invention;

[0063] Figure 3Schematic diagram of the structure of the ultrasonic adjustment device according to an embodiment of the present invention, wherein a is the second fixing plate, and b is the third fixing plate;

[0064] Figure 4 Schematic diagrams of structures of different types of ultrasonic tool heads according to embodiments of the present invention, wherein a is a spherical tool head, b is a flat tool head, and c is a rolling bearing tool head;

[0065] Figure 5 A schematic diagram of the structure of a protective cover according to an embodiment of the present invention;

[0066] Figure 6 Schematic diagram of different types of nozzles according to an embodiment of the present invention, wherein a is an atomizing nozzle and b is a gradually converging and diverging nozzle.

[0067] Figure 7 It is a diagram showing the application effect of Example 4 of the present invention in the double-sided welding of aluminum-copper dissimilar metal medium and thick plates, wherein a is the weld surface under the multiple external field conditions without “ultrasound + rapid cooling”, b is the weld surface under the multiple external field conditions with the addition of “ultrasound + rapid cooling”, c is the weld cross-section under the multiple external field conditions without “ultrasound + rapid cooling”, d is the weld cross-section under the multiple external field conditions with the addition of “ultrasound + rapid cooling”, and e is a comparison of joint performance under and without the application of “ultrasound + rapid cooling” multiple external field conditions.

[0068] Among them, 1-air compressor; 2-first delivery pipe; 3-cylinder; 4-air pressure regulating valve; 5-first fixed plate; 6-second fixed plate; 6-1 curved U-shaped groove, 6-2 threaded hole, 6-3 through hole; 7-third fixed plate; 7-1 is a horizontal U-shaped groove; 7-2 is a vertical U-shaped groove; 8-ultrasonic tool head; 8-1-spherical tool head; 8-2-plane tool head; 8-3-rolling bearing tool head; 9-vibration transmission rod; 10-amplifier; 11-ultrasonic transducer; 12-conducting wire; 13-ultrasonic generator; 14-welding machine head; 15-fourth fixed plate; 16-flow control valve; 17-delivery device; 18-second delivery pipe; 19-cooling medium storage; 20-temperature controller; 21-universal bamboo tube;

[0069] 22-protective cover; 22-1-nozzle sleeve hole; 22-2-protective air hole; 22-3-air inlet hole;

[0070] 23-nozzle; 23-1-atomizing nozzle; 23-2-gradually converging and expanding nozzle;

[0071] 24-stirring head; 25-base. DETAILED DESCRIPTION

[0072] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0073] The present invention will be further described below in conjunction with the embodiments.

[0074] Example 1

[0075] This embodiment provides an "ultrasound + rapid cooling" multi-external field composite stir friction welding device, such as Figure 1 As shown, it includes an ultrasonic assisted system and a local rapid cooling system, which couples the two external fields of ultrasound and rapid cooling to give full play to their respective advantages, which not only promotes the softening and flow of the material below the weld, but also avoids overheating of the material above the weld, effectively improving the structure and performance of the joint.

[0076] The ultrasonic assisted system includes a pneumatic device, an adjusting device, and a vibration device. The pneumatic device includes an air compressor 1, a first delivery pipe 2, a cylinder 3, and an air pressure regulating valve 4. The adjusting device includes a first fixed plate 5, a second fixed plate 6, and a third fixed plate 7. The vibration device includes an ultrasonic tool head 8, a vibration transmission rod 9, a horn 10, an ultrasonic transducer 11, a wire 12, and an ultrasonic generator 13.

[0077] The ultrasonic generator 13 determines the output power of the ultrasonic vibration, the pneumatic device can flexibly control the lifting and lowering of the vibration device, and the contact pressure between the ultrasonic tool head and the workpiece can be adjusted according to different plate thicknesses through the air pressure regulating valve 4; since the ultrasonic vibration energy will decay along the plate thickness direction, it is necessary to flexibly adjust the output power of the ultrasonic vibration and the contact pressure between the ultrasonic tool head 8 and the substrate 25 according to different plate thicknesses and different materials; when the plate thickness is larger or the substrate is harder, a higher output power and contact pressure are required, and when the plate thickness is smaller or the substrate is softer, a lower output power and contact pressure are required.

[0078] The adjustment device can flexibly adjust the relative position of the vibration device to match different application scenarios. The lower parts of the first fixed plate 5 and the second fixed plate 6 form a rotating pair through the through hole 6-3, and the upper parts of the first fixed plate 5 and the second fixed plate 6 are connected through the U-shaped groove 6-1 to flexibly adjust the angle of the vibration device relative to the stirring head 24; the second fixed plate 6 and the third fixed plate 7 are connected through the threaded hole 6-2 and the horizontal U-shaped groove 7-1 to flexibly adjust the horizontal displacement of the vibration device; the third fixed plate 7 and the welding machine head 14 are connected through the vertical U-shaped groove 7-2 to flexibly adjust the vertical displacement of the vibration device.

[0079] The ultrasonic tool head 8 is in direct contact with the workpiece, and can be replaced by different types including: a spherical tool head 8-1, a flat tool head 8-2, a rolling bearing tool head 8-3, such as Figure 4 As shown, the selection rules are as follows:

[0080] (1) The spherical tool head 8-1 is mainly used for the same or different welding of narrow welds of light alloys such as magnesium alloys and aluminum alloys. Since the area of ​​the spherical tool head acting on the workpiece is small, it is suitable for narrow welds. The contact between the spherical tool head and the workpiece is in the form of sliding friction, and the resistance during the movement is relatively large, which is suitable for light alloys such as magnesium alloys and aluminum alloys.

[0081] (2) The flat tool head 8-2 is mainly used for wide welds of thin plates of light alloys such as magnesium alloys and aluminum alloys. The flat tool head has a large area acting on the workpiece, so it is suitable for wide welds. Similar to the spherical tool head, there is sliding friction between the spherical tool head and the workpiece, so it is suitable for light alloys such as magnesium alloys and aluminum alloys. The difference is that the flat tool head has a wide range of ultrasonic action, but a large area acting on the weld, which results in greater resistance during the movement and limits the contact pressure between the flat ultrasonic tool head and the workpiece. Therefore, it is only suitable for welding thin plates.

[0082] (3) The rolling bearing tool head 8-3 described above: Compared with spherical and flat ultrasonic tool heads, the contact between the rolling bearing tool head and the workpiece is rolling friction, and the resistance is small during the movement, which can be applied to the same or different welding of high-hardness alloys such as titanium alloy and steel.

[0083] The power of the ultrasonic generator is 100-2000W, the frequency is 10-50kHz, the amplitude is 10-80μm, the distance between the ultrasonic tool head and the axis of the stirring head is 10-30mm, the angle formed with the workpiece plane is 30-60°, and the contact pressure with the workpiece is 0.1-3MPa.

[0084] The local rapid cooling auxiliary system includes a fourth fixed plate 15 , a conveying device 17 , a second conveying pipe 18 , a cooling medium storage 19 , a universal bamboo tube 21 , a protective cover 22 , and a nozzle 23 . The conveying device 17 includes a flow control valve 16 and a temperature controller 20 .

[0085] The protective cover 22 is designed to be in the shape of a weld to achieve precise cooling of the weld, and includes a nozzle sleeve hole 22-1, a protective air hole 22-2, and an air inlet hole 22-3. The nozzle sleeve hole 22-1 is used to cover the nozzle 23, and the relative positions of the two can be flexibly adjusted; the protective air holes 22-2 are densely distributed on the protective cover 22 to form a strong protection for the cooling medium and prevent the cooling medium from escaping. The air inlet hole 22-3 is connected to the air compressor 1 to provide gas for the protective cover 22.

[0086] The cooling medium includes: gas, liquid nitrogen or ethanol solution. The type of cooling medium depends on different materials and application scenarios. The selection rules are as follows:

[0087] (1) Liquid nitrogen cooling: Suitable for thick plate welding; liquid nitrogen can quickly cool the weld surface and has a fast cooling speed. However, if the temperature of liquid nitrogen is too low, the temperature of the joint will be too low, which is not conducive to the flow of plastic materials and causes defects such as holes inside the weld. Therefore, liquid nitrogen is not suitable for thin plate welding. In conventional FSW welding of thick plates, the required stirring head size is large, that is, the shoulder diameter is large and the stirring needle is long, which makes the temperature of the upper surface of the workpiece too high, while the bottom temperature of the stirring needle is low, resulting in a large temperature gradient inside the weld along the plate thickness direction. Therefore, it is necessary to quickly reduce the temperature of the weld surface and reduce the temperature gradient inside the weld to ensure the uniformity of the joint structure and performance.

[0088] (2) Mixed solution of ethanol and water: suitable for welding thin plates. Using distilled water can avoid introducing impurities into the weld, while adding a certain proportion of ethanol can not only lower the freezing point of the coolant and ensure that the distilled water does not freeze at the required temperature, but also achieve continuous cooling through ethanol volatilization and heat absorption after the coolant is deposited on the weld surface. However, the use of mixed liquid cooling requires advance proportioning, which is complicated to operate and has high cost. When FSW welding thin plates, in order to avoid defects at the bottom of the weld and ensure that the plastic material is fully softened and flowed, a larger heat input parameter is usually required. Therefore, overheating is prone to occur on the upper surface of the workpiece, resulting in coarse grains, dissolution of the precipitated phase, and excessively thick IMCs layer, which reduces the microstructure and performance of the joint.

[0089] (3) Gas cooling (supersonic airflow): Suitable for thin plate welding or additive manufacturing; compared with mixed liquid cooling, gas cooling has low cost, clean and safe welding process, no need for cleaning after welding, and simple operation. However, the gas is easy to disperse and is greatly affected by the surrounding environment gas. The cooling time on the weld surface is short, and the cooling effect is poor compared with the mixed liquid of distilled water and alcohol.

[0090] The types of nozzles 23 include atomizing nozzles 23-1, gradually converging and expanding nozzles 23-2, such as Figure 6 As shown, the atomizing nozzle is installed and used when the cooling medium is liquid, and the atomized coolant has the advantages of strong cooling capacity and uniform cooling effect. The gradually converging and expanding nozzle is installed and used when the cooling medium is gas. The airflow is continuously accelerated in the nozzle to obtain supersonic airflow, which will cause a sharp drop in temperature, thereby obtaining a low-temperature supersonic airflow. The position of the nozzle determines the degree of cooling, which can be flexibly adjusted through the universal bamboo tube 21 according to the specific application scenario.

[0091] The distance between the center of the nozzle and the axis of the stirring head is 10-30 mm, the angle formed with the axis of the stirring head is 30-60°, and the height from the workpiece is 10-30 mm.

[0092] Example 2

[0093] This embodiment discloses a welding method based on the "ultrasonic + rapid cooling" multi-external field composite friction stir welding device described in Example 1. In this embodiment, the material of the substrate 25 is AZ31B-H24 magnesium alloy, the plate length is 200mm, the width is 70mm, and the thickness is 3mm. In this example, the shaft shoulder of the stirring head 24 used is concave, the diameter is 12mm, the stirring needle morphology is conical with right-handed threads, the needle length is 2.8mm, the root diameter is 4.2mm, the end diameter is 3.2mm, the stirring head speed used is 800rpm, the welding speed is 50mm / min, the downward pressure is 0.1mm, and the stirring head inclination angle is 2.5°.

[0094] The specific welding process is as follows: Figure 1 and Figure 2 As shown, the following steps are included:

[0095] Step 1: Before welding, grind the surface of the workpiece to be welded to remove the oxide film, and clean it with alcohol to remove surface oil and impurities;

[0096] Step 2: Place the workpiece to be welded on the workbench and then clamp the workpiece to be welded with a fixture;

[0097] Step three, connect the stirring head to the main shaft of the friction stir welding machine, adjust the X-axis, Y-axis and Z-axis coordinates of the welding machine so that the main shaft of the stirring head is located directly above the butt joint surface and the axis of the stirring needle is aligned with the center line of the weld.

[0098] Step 4: adjust the position of the ultrasonic assisted system and select relevant components and parameters. Since the substrate is a thinner magnesium lightweight alloy plate, a lower ultrasonic output power should be selected. The power of the ultrasonic generator is set to 300W, the frequency is 20kHz, the amplitude is 40 microns, the distance between the ultrasonic tool head and the axis of the stirring head is 20mm, and the angle is 45°. Since the plate is thin, the contact pressure between the ultrasonic tool head and the workpiece should be low, which is 0.2MPa. In addition, due to the small shoulder diameter and narrow weld width, the required ultrasonic vibration area is small, so a spherical ultrasonic tool head should be selected.

[0099] Step five, select the components and related parameters of the local rapid cooling auxiliary system, and select a mixture of alcohol and distilled water as the cooling medium. Since the stirring head speed in this embodiment is 800rpm, the welding speed is 50mm / s, the welding heat input is large, and the temperature of the upper surface of the workpiece is large, requiring lower temperature cooling. The degree of gas cooling is insufficient and cannot solve the problem of overheating of the upper surface. However, the workpiece is thin, and the use of liquid nitrogen as the cooling medium will cause the temperature of the joint to be too low, which is not conducive to the performance and organization of the joint. The corresponding matching nozzle is an atomizing nozzle. In order to enhance the cooling intensity, the position of the nozzle is adjusted to be closer to the weld behind the stirring head. The specific distance between the center of the nozzle and the axis of the stirring head is 15mm, and the height from the workpiece is 15mm.

[0100] Step six, set the welding parameters (in this embodiment, the preferred stirring head speed is 800 rpm, the welding speed is 50 mm / s, the downward pressure is 0.1 mm, and the stirring head inclination angle is 2.5°), and start the friction stir welding machine.

[0101] Step seven, as the stirring head is pressed down to the set value (in this embodiment, the stirring needle is set to press into the workpiece 2.9mm), the stirring head begins to move along the specified trajectory, and the "ultrasonic + rapid cooling" multi-external field composite stir friction welding device is started, and the ultrasonic + rapid cooling auxiliary external field is applied at the same time. When the stirring head reaches the specified position and the workpiece is pulled out, the "ultrasonic + rapid cooling" multi-external field composite stir friction welding device is closed, and the welding is completed.

[0102] Example 3

[0103] This embodiment discloses a welding method based on the "ultrasonic + rapid cooling" multi-external field composite stir friction welding device described in Example 1. In this embodiment, the material of the substrate 25 is SS304 stainless steel plate and TC4 titanium alloy plate, the plate length is 200mm, the width is 70mm, and the thickness is 8mm. The shoulder of the stirring head 22 used is concave and has a diameter of 22mm. The stirring needle is cylindrical with a right-handed thread, with a diameter of 7.5mm and a needle length of 7.8mm. The stirring head rotation speed used is 1000rpm, the welding speed is 30mm / s, the downward pressure is 0.2mm, and the stirring head inclination angle is 2.5°.

[0104] The specific welding process includes the following steps:

[0105] Step 1: Before welding, grind the surface of the workpiece to be welded to remove the oxide film, and clean it with alcohol to remove surface oil and impurities;

[0106] Step 2: Place two workpieces to be welded on a workbench and connect them, then clamp the two sets of workpieces to be welded with a fixture;

[0107] Step three, connect the stirring head to the main shaft of the friction stir welding machine, adjust the X-axis, Y-axis and Z-axis coordinates of the welding machine so that the main shaft of the stirring head is located directly above the butt joint surface and the axis of the stirring needle is aligned with the center line of the weld.

[0108] Step 4. Adjust the position of the ultrasonic-assisted system and select related components and parameters. Since the substrate is a thicker steel or titanium high-hardness alloy plate, a higher ultrasonic output power should be selected. The power of the ultrasonic generator is set to 2000W, the frequency is 25kHz, the amplitude is 70μm, the distance between the ultrasonic tool head and the axis of the stirring head is 10mm, and the angle is 60°. Since the substrate material is relatively hard, a rolling bearing ultrasonic tool head should be selected, which has less resistance during the movement and less wear on the tool head. In addition, since the plate is thicker, the contact pressure between the ultrasonic tool head and the workpiece should be higher, 0.6MPa.

[0109] Step five, select the components and related parameters of the local rapid cooling auxiliary system, and select liquid nitrogen as the cooling medium. Since the stirring head used in this embodiment has a rotation speed of 1000rpm and a welding speed of 30mm / s, the welding heat input is large, and the thermal conductivity of the base material is poor, which causes the upper surface of the workpiece to overheat, making the temperature gradient inside the weld larger along the plate thickness direction. Therefore, liquid nitrogen is selected as the cooling medium to quickly reduce the temperature of the weld surface and reduce the temperature gradient inside the weld; the corresponding matching nozzle is an atomizing nozzle; in order to enhance the cooling intensity, the position of the nozzle is adjusted to be closer to the weld behind the stirring head. Specifically, the distance between the center of the nozzle and the axis of the stirring head is 10mm, and the height from the workpiece is 10mm.

[0110] Step 6, setting welding parameters (in this embodiment, the preferred stirring head speed is 1000 rpm, the welding speed is 30 mm / s, the downward pressure is 0.15 mm, and the stirring head inclination angle is 2.5°), and starting the friction stir welding machine;

[0111] Step seven, as the stirring head is pressed down to the set value (in this embodiment, the stirring needle is set to press into the workpiece 7.95mm), the stirring head begins to move along the specified trajectory, and the "ultrasonic + rapid cooling" multi-external field composite stir friction welding device is started, and the ultrasonic + rapid cooling auxiliary external field is applied at the same time. When the stirring head reaches the specified position and the workpiece is pulled out, the "ultrasonic + rapid cooling" multi-external field composite stir friction welding device is closed, and the welding is completed.

[0112] Example 4

[0113] This embodiment discloses a method for double-sided friction stir welding of dissimilar metals based on the "ultrasonic + rapid cooling" multi-external field composite friction stir welding device described in Example 1. In this embodiment, the materials of the substrate 25 are T2 copper alloy and AA6061-T6 aluminum alloy, and the plate length is 200mm, the width is 70mm, and the thickness is 12mm. In this example, the shoulder of the stirring head 22 used is concave, with a diameter of 18mm, and the stirring needle is in the shape of a smooth cylindrical surface, with a needle length of 6mm and a diameter of 8mm.

[0114] The specific welding process is as follows: Figure 1 and Figure 2 As shown, the following steps are included:

[0115] Step 1: Before welding, grind the surface of the workpiece to be welded to remove the oxide film, and clean it with alcohol to remove surface oil and impurities;

[0116] Step 2: Place the workpiece to be welded on the workbench and then clamp the workpiece to be welded with a fixture;

[0117] Step three, connect the stirring head to the main shaft of the friction stir welding machine, adjust the X-axis, Y-axis and Z-axis coordinates of the welding machine so that the main shaft of the stirring head is located directly above the butt joint surface and the axis of the stirring needle is aligned with the center line of the weld.

[0118] Step 4. Adjust the position of the ultrasonic assisted system and select related components and parameters. Set the power of the ultrasonic generator to 400 W, the frequency to 20 kHz, the amplitude to 40 μm, the distance between the ultrasonic tool head and the axis of the stirring head to 20 mm, and the angle to 45°. Since the plate is thin, the contact pressure between the ultrasonic tool head and the workpiece should be as low as 0.3 MPa. Select a spherical ultrasonic tool head as the ultrasonic tool head.

[0119] Step 5, select the components and related parameters of the local rapid cooling auxiliary system, select a mixture of alcohol and distilled water as the cooling medium, and the corresponding matching nozzle is an atomizing nozzle; the distance between the center of the nozzle and the axis of the stirring head is 15mm, and the height from the workpiece is 15mm.

[0120] Step six, set the welding parameters (in this embodiment, the preferred stirring head speed is 800 rpm, the welding speed is 300 mm / min, the downward pressure is 0.2 mm, the stirring head inclination angle is 2.5°, and the stirring head is biased towards the aluminum alloy by 2.7 mm), and start the friction stir welding machine.

[0121] Step seven, as the stirring head is pressed down to the set value (in this embodiment, the stirring needle is set to press into the workpiece 6.2mm), the stirring head begins to move along the specified trajectory, and the "ultrasonic + rapid cooling" multi-external field composite stir friction welding device is started, and the ultrasonic + rapid cooling auxiliary external field is applied at the same time. When the stirring head reaches the specified position and the workpiece is pulled out, the "ultrasonic + rapid cooling" multi-external field composite stir friction welding device is closed, and the welding of the first side weld is completed.

[0122] Step 8, turn the workpiece over and repeat the above steps to weld the second weld on the back side until the welding is completed.

[0123] Example 5

[0124] This embodiment discloses an additive manufacturing method for an "ultrasonic + rapid cooling" multi-external field composite stir friction welding device based on the embodiment 1. In this embodiment, the materials of the substrate and the additive plate are both 2024-T4 aluminum alloy, the length of the substrate is 200 mm, the width is 100 mm, and the thickness is 4 mm. The length of the additive plate is 200 mm, the width is 35 mm, and the thickness is 4 mm. The shoulder of the stirring head used is concave and has a diameter of 20 mm. The shape of the stirring needle is cylindrical with a right-hand thread, a diameter of 8 mm, and a needle length of 5 mm. The rotation speed of the stirring head used is 600 rpm, the welding speed is 120 mm / s, the downward pressure is 0.2 mm, and the inclination angle of the stirring head is 2.5°.

[0125] The specific additive process includes the following steps:

[0126] Step 1: Before welding, grind the joint surface of the additive plate and the substrate to remove the oxide film, and clean it with alcohol to remove surface oil and impurities;

[0127] Step 2, clamping the additive plate on the base plate;

[0128] Step three, connect the stirring head to the main shaft of the friction stir welding machine, adjust the X-axis, Y-axis and Z-axis coordinates of the welding machine so that the main shaft of the stirring head is located above the additive plate and the axis of the stirring needle is aligned with the center line of the additive area.

[0129] Step 4: Adjust the position of the ultrasonic-assisted system and select related components and parameters. Since both the substrate and the additive plate are thinner aluminum alloy plates, a lower ultrasonic output power should be selected. The power of the ultrasonic generator is set to 300W, the frequency is 20kHz, the amplitude is 40μm, the distance between the ultrasonic tool head and the axis of the stirring head is 20mm, and the angle is 45°. Since the plate is thin, the contact pressure between the ultrasonic tool head and the workpiece should be as low as 0.2MPa. In addition, since the shoulder diameter is large, in order to ensure the area of ​​the additive zone, the area required for ultrasonic vibration is large, and a flat ultrasonic tool head should be selected.

[0130] Step five, select the components and related parameters of the local rapid cooling auxiliary system, and use gas as the cooling medium. Since the stirring head speed in this embodiment is 600rpm, the welding speed is 120mm / s, the welding heat input is low, the temperature on the upper surface of the workpiece is low, and the temperature gradient inside the weld is small, the required cooling degree is small, so a low-cost gas is selected as the cooling medium. Compared with liquid cooling, there is no need to clean the additive surface after gas cooling, which facilitates continuous additive and is beneficial to additive efficiency.

[0131] Step 6, set the additive process parameters (in this embodiment, the preferred stirring head speed is 600 rpm, the welding speed is 120 mm / s, the downward pressure is 0.2 mm, and the stirring head inclination angle is 2.5°), and start the friction stir welding machine;

[0132] Step seven, as the stirring head is pressed down to the set value (in this embodiment, the stirring needle is set to press into the workpiece 5.2mm), the stirring head begins to move along the specified trajectory, and the "ultrasonic + rapid cooling" multi-external field composite stir friction welding device is started, and the ultrasonic + rapid cooling auxiliary external field is applied at the same time. When the stirring head reaches the specified position and the workpiece is pulled out, the "ultrasonic + rapid cooling" multi-external field composite stir friction welding device is closed, and the first layer of additive manufacturing is completed.

[0133] Step 8. After the single-layer additive manufacturing is completed, move the stirring head upward and repeat the above steps 1, 2, 3, 5, and 6 to achieve multi-layer additive manufacturing and finally obtain a high-performance additive body.

[0134] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. Ultrasonic rapid cooling multi-external field composite stir friction welding device, characterized in that: Including welding machine head, stirring head, ultrasonic auxiliary system and local quenching auxiliary system; Among them, the stirring head is installed on the welding machine head; The ultrasonic tool head of the ultrasonic auxiliary system extends toward the stirring head and is located in front of the travel path of the stirring head. During welding, the ultrasonic tool head is brought into contact with the workpiece and a set pressure is applied to the workpiece. The nozzle of the local quenching auxiliary system extends toward the stirring head and is located behind the travel path of the stirring head. During welding, the nozzle is set toward the weld. The ultrasonic auxiliary system comprises a pneumatic device, which comprises an air compressor, a first delivery pipe and a cylinder connected in sequence, the shell of the cylinder is fixedly installed, the piston of the cylinder is connected to a vibration device, and the vibration device is installed on a first fixed plate through a slide rail; an air pressure regulating valve is arranged on the cylinder; the ultrasonic tool head is a spherical tool head, a flat tool head or a rolling bearing tool head; The local quenching auxiliary system comprises a cooling medium storage, a conveying device, a second conveying pipe and a nozzle connected in sequence; a universal bamboo tube is connected between the second conveying pipe and the nozzle; a temperature controller and a flow control valve are connected between the second conveying pipe and the universal bamboo tube; The cooling medium is a gas cooling medium and a liquid cooling medium; the liquid cooling medium is liquid nitrogen or a mixed solution of ethanol and water; the gas cooling medium is nitrogen, argon, helium or air, and supersonic airflow is used for gas cooling; the nozzle for spraying the cooling medium is an atomizing nozzle or a gradually converging and expanding nozzle; The nozzle is provided with a protective cover, a gas chamber is provided on the side wall of the protective cover, and an air inlet is provided on one side of the gas chamber; the protective cover is provided with air holes on one side of the nozzle, and the air holes are distributed at least on both sides of the nozzle.

2. The ultrasonic rapid cooling multi-external field composite friction stir welding device according to claim 1, characterized in that: The ultrasonic auxiliary system also includes an ultrasonic generator, a wire and a vibration device connected in sequence. The vibration device includes an ultrasonic transducer, a horn, a vibration transmission rod and an ultrasonic tool head connected and installed in sequence. The vibration device is installed on the welding machine head.

3. The ultrasonic rapid cooling multi-external field composite friction stir welding device according to claim 1, characterized in that: The ultrasound-assisted system further comprises an adjusting device, wherein the adjusting device comprises a first fixing plate, a second fixing plate and a third fixing plate connected in sequence; The first fixing plate and the lower part of the second fixing plate form a revolving pair, and the upper part of the first fixing plate and the second fixing plate are connected through a curved U-shaped groove; The second fixing plate is connected to the third fixing plate via a horizontal U-shaped groove; The third fixing plate is connected to the welding machine head through a vertical U-shaped groove.

4. The ultrasonic rapid cooling multi-external field composite friction stir welding device according to claim 1, characterized in that: The air holes on both sides of the nozzle are arranged linearly and parallel to the weld; the protective cover is provided with air holes located downstream of the nozzle, and these air holes are arranged in an arc shape; the protective cover is provided with air holes located upstream of the nozzle, and these air holes are arranged linearly and perpendicular to the weld.

5. The ultrasonic rapid cooling multi-external field composite friction stir welding device according to claim 4, characterized in that: The diameter of the pores is 3-6 mm, and the distance between adjacent pores is 2-4 mm.

6. An ultrasonic rapid cooling multi-external field composite stir friction welding method, using the ultrasonic rapid cooling multi-external field composite stir friction welding device according to any one of claims 1 to 5, characterized in that: The steps include: cleaning, clamping and fixing the workpiece to be welded; When the stirring head starts to press down for welding, the ultrasonic auxiliary system and the local rapid cooling system are turned on, and ultrasonic energy is applied to the weld metal in front of the stirring head to promote the softening of the weld metal; cooling medium is sprayed on the welding surface behind the stirring head to perform rapid cooling treatment on it. When welding is completed, the ultrasonic auxiliary system and the local rapid cooling system are turned off; The power of the ultrasonic generator is 100-2000W, the frequency is 10-50kHz, and the amplitude is 10-80μm.

7. The ultrasonic rapid cooling multi-external field composite stir friction welding method according to claim 6, characterized in that: The axial distance between the ultrasonic tool head and the stirring head is 10-30 mm.

8. The ultrasonic rapid cooling multi-external field composite stir friction welding method according to claim 6, characterized in that: The angle between the ultrasonic tool head and the axis of the stirring head is 30°-60°.

9. The ultrasonic rapid cooling multi-external field composite stir friction welding method according to claim 6, characterized in that: The contact pressure between the ultrasonic tool head and the workpiece is 0.1-3MPa.

10. Application of the ultrasonic rapid cooling multi-external field composite friction stir welding device according to any one of claims 1 to 5 or the ultrasonic rapid cooling multi-external field composite friction stir welding method according to any one of claims 6 to 9 in friction stir solid phase additive manufacturing.

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