Titanium alloy component single-sided entry double-layer weld one-time forming electron beam welding method

Abstract

The application provides a one-time forming electron beam welding method for a titanium alloy component with single-sided incidence and double-layer welds, which comprises the following steps: a closed cavity structure titanium alloy component is formed by a plurality of mutually shielded multi-layer thin plates through single-direction electron beam incidence; the focusing current of the electron beam is adjusted; the converging effect of the electromagnetic coil is changed to change the focus position, and then the electron beam keyhole depth and size are changed; the keyhole is adjusted to be an energy channel through which the electron beam passes; the electron beam energy can pass through the first layer of welds to reach the second layer of welds; the controllable linear energy is provided by combining the acceleration voltage, the welding current and the welding speed to ensure that the remaining energy that penetrates reaches the second layer of welds to complete the welding of the second layer of welds again; the low-frequency scanning is combined with the electron beam movement to drive the first layer of molten pool metal to flow and fill the rear channel, and the front channel is opened, so that the channel is dynamically smooth and stable, and the electron beam keyhole effect behavior is adjusted.

Description

Technical Field

[0001] This invention relates to the field of electron beam welding, specifically to a method for single-sided incident electron beam welding of double-layer weld seams in one step for irregularly shaped multi-layer thin plate titanium alloy parts. Background Technology

[0002] Due to functional, strength, and weight considerations, many aerospace products contain multi-layered, thin-plate, enclosed-cavity, box-shaped titanium alloy parts. These parts suffer from poor processability due to their small space, deep cavities, and multiple diagonal ribs. Traditional processing methods involve machining multiple parts separately and then connecting them using corner bolts. However, this significantly increases the added weight of the parts, and the strength cannot compare to that of welded components. To achieve overall weight reduction and improved performance of the integrated structure, a monolithic structural design is adopted. The process involves machining the internal cavity dimensions, then electron beam welding, followed by localized machining of the weld seams and external shape. This solution undoubtedly solves the problem of the inability to machine the internal structure. However, due to the mutual obstruction of the multiple weld seams, electron beam welding also faces beam current accessibility issues, making it difficult to weld the middle layer of weld seams within the parts.

[0003] Currently, electron beam welding of this type of irregularly shaped, multi-layered, thin-plate titanium alloy parts generally employs a layer-by-layer welding method. At most, double-layer welds can be achieved through incident radiation from two directions. However, in multi-layered structures (three or four layers), the intermediate layer weld joints are blocked, preventing the electron beam from reaching them and thus hindering welding. Regardless of whether the direction is forward or reverse, the electron beam cannot reach the intermediate weld due to obstruction by the preceding welds. Furthermore, if the outer welds are completed first, it will impose significant stress on the intermediate structure, causing deformation and affecting the pre-welding state of the intermediate weld joint gap and misalignment. Therefore, how to solve the problem of electron beam accessibility in the blocked intermediate weld bead; how to ensure that the first weld layer is formed simultaneously with the second weld layer; and how to control the state of the second weld layer during the formation of the first weld layer to prevent excessive stress are all technical challenges that need to be addressed when using electron beam welding for these parts. Summary of the Invention

[0004] The purpose of this invention is to address the aforementioned problems in electron beam welding of irregularly shaped multilayer thin plate structures, such as the accessibility of the electron beam current in the middle of the weld bead being blocked, ensuring the formation of the first layer weld while the second layer weld is formed (i.e., ensuring the formation of the two layers weld on all four sides), and reducing the stress influence on the state of the second layer weld while the first layer weld is formed. The invention proposes an electron beam welding method for forming a single-sided incident double-layer weld in one step for electron beam welding of titanium alloy components with irregularly shaped multilayer thin plate structures.

[0005] This invention utilizes the concentrated energy of electron beams to create a channel in the first weld layer by unilateral electron beam incidence, allowing the electron beam to pass through and reach the second weld layer for welding. The channel is then quickly closed to reshape the first weld layer, thus achieving a welding method for a double-layer structure with unilateral incidence and one-time forming.

[0006] The technical means employed in this invention are as follows:

[0007] This electron beam welding method for single-sided incident double-layer welds on titanium alloy components is innovatively optimized based on the forming characteristics of the electron beam's "keyhole effect." By adjusting the keyhole depth, the keyhole in the weld pool is deepened and penetrated when welding thin plates, forming a small energy channel. The electron beam can pass through this channel to reach the second weld layer, thus solving the problem of electron beam accessibility. Enlarging and deepening the "keyhole" in the weld pool is usually achieved by adjusting the line energy. However, excessive line energy increases residual stress after welding, leading to severe component deformation and significant spatter, resulting in metal loss. Simultaneously, the channel cannot be too large to prevent the first weld layer from being actually "welded through," so excessive line energy should be avoided. This method innovatively increases the penetration capability of the electron beam by deepening the focal point, ensuring minimal overall stress on the component while using the lowest possible line energy.

[0008] By adjusting the energy of the focusing coil using the focusing current, the electron beam's focus is set to an ultra-low focus (a low focus refers to a focus position located below the workpiece surface but not exceeding the workpiece thickness; an ultra-low focus refers to a low focus position that extends beyond the workpiece thickness). This increases the electron beam's penetration capability, deepening the "keyhole" to penetrate the entire molten pool. The ideal focus position is midway between the first and second weld layers. A focus too high will cause the energy of the upper focus in the second layer to be more dispersed, failing to meet the line energy requirements for the second weld layer's formation; a focus too low will cause the molten pool channel of the first weld layer to further expand, increasing the pressure of the liquid metal filling, resulting in insufficient or incomplete filling and affecting the formation of the first weld layer. The focusing current calculation formula is:

[0009]

[0010] In the formula: J1 and J2 are the focusing currents of the first and second weld surfaces, respectively, and J is the focusing current of the focal point at the desired position.

[0011] Based on this focus, the linear energy required for welding is calculated using the following formula:

[0012]

[0013] In the formula: q is the line energy of electron beam welding, U is the accelerating voltage of the electron beam, I is the welding current of the electron beam, and v is the electron beam welding speed.

[0014] Since higher accelerating voltages are beneficial for improving the penetration ability of the electron beam, at the maximum accelerating voltage, the line energy mainly depends on the welding current density.

[0015] Furthermore, the linear energy requirement of this type of part is assessed by step testing. The required current can be determined between the linear energy of the sum of the thicknesses at the two weld seam locations, calculated using the following formula:

[0016] I1≤I≤I2(3)

[0017] In the formula: I1 is the welding current at the first weld position where the sum of the thicknesses of the two layers is welded at the surface focus, I2 is the welding current at the second weld position where the sum of the thicknesses of the two layers is welded at the surface focus, and I is the welding current of the required electron beam.

[0018] Furthermore, after determining the linear energy, the aperture angle α is defined as the angle formed by the two outermost boundary asymptotes of the electron beam current. The formula for calculating the aperture angle is:

[0019]

[0020] In the formula: d1 is the diameter of the energy channel of the electron beam in the first weld layer, d2 is the diameter of the beam spot on the upper surface of the second weld layer, and H is the distance between the first weld layer and the second weld layer.

[0021] Furthermore, the relationship between the diameters of the spots formed on the upper surfaces of the first and second weld layers is determined by the aperture angle α, thereby determining the energy relationship between the first and second weld layers. The formula is:

[0022]

[0023] Furthermore, the welding speed is adjusted to a higher speed (above 1000 mm / min). With the rapid movement of the electron beam, the liquid metal fills the channel backward under the action of hydrostatic pressure and metal vapor reaction force, taking advantage of the excellent thermal fluidity, light weight, and high liquid surface tension of titanium alloy.

[0024] Furthermore, the faster movement of the laser spot increases the backward flow of the molten pool while shortening the time the energy channel needs to be maintained in a fixed position. Since the shorter the time the energy channel is open, the shorter the time the surrounding liquid metal needs to maintain a high temperature to ensure the channel is subsequently filled, and the less gravitational pressure the surrounding liquid metal has to withstand. Therefore, rapid welding effectively reduces the channel recovery pressure, creating favorable conditions for sufficient liquid metal filling of the first weld layer, allowing the first weld layer to reform.

[0025] Furthermore, by transferring liquid metal, the channel also moves accordingly. Although the time the energy channel spends in a fixed position is shortened, as long as the channel remains open when the electron beam passes through, it will not affect the energy input during the welding of the second weld layer, thus achieving dynamic stability of the channel. The molten pool in the channel also moves with the electron beam, with metal continuously flowing and filling, better sealing the first weld layer. The welding speed of titanium alloy thin plates is determined based on the thickness and specific weldability of the material, but should be above 1000 mm / min.

[0026] Furthermore, low-frequency circular wave electromagnetic scanning oscillations are employed, with the scanning amplitude equal to half the channel diameter, as shown in the formula:

[0027]

[0028] In the formula: d1 is the diameter of the electron beam energy channel in the first weld layer, V x and V y These represent the electromagnetic scanning amplitudes in the x and y directions, respectively.

[0029] The low-frequency rotating vortex of molten metal under the action of electromagnetic force prevents the liquid metal from converging towards the center of the energy channel when the electron beam is not moving. This not only further stabilizes the energy channel, but also moves the electromagnetically rotating vortex when the electron beam moves. The addition of electromagnetic stirring also increases the metal filling force, allowing the liquid metal to better fill the previous channel and improve the formation of the first layer of weld.

[0030] Furthermore, by using the converging effect of the electromagnetic coil, the selection of a more distant focal point controls the electron beam to prevent excessive divergence after passing through the first weld layer. Simultaneously, the accelerating voltage, welding current, and welding speed are controlled to increase the energy density to a level greater than 10. 7 W / cm 2 This ensures that the remaining energy transmitted through the energy channel of the first weld layer reaches the second weld layer and provides sufficient energy for the thermal conduction and fusion of the second weld layer, enabling the welding of the second weld layer. In other words, the first weld layer is an overpenetration weld, while the second layer transforms into an approximately thermally conductive weld.

[0031] Furthermore, the focal point is located between the two weld layers. The first weld layer uses lower focal point welding, and the second weld layer uses upper focal point welding. Through optimized settings of focusing current and line energy, the second weld layer is essentially decoked, ensuring the formation of both the upper and lower surfaces.

[0032] Furthermore, due to the extremely fast propagation speed of the electron beam in the vacuum chamber, and the existence of the energy channel, the second layer of weld is welded and formed first. At the same time, as the electron beam moves, the first layer of weld immediately recovers its shape. Moreover, the electron beam weld is relatively narrow and the stress is relatively small. This makes it possible for the two layers of weld to have almost no mutual influence on each other's pre-welding state during the formation of the weld.

[0033] Furthermore, the first layer of weld may have undercut defects due to the opening of the keyhole channel and a small amount of metal spatter. After the welding is completed, a low-energy decoking repair weld is used to repair it.

[0034] Compared with the prior art, the present invention has the following advantages:

[0035] 1. Applicable to electron beam welding of all titanium alloy multilayer thin plates, enabling pre-machining of irregularly shaped, deep-cavity, and mutually shielding multilayer thin plate structures followed by net-size electron beam welding of the weld seams, solving the accessibility problem of closed structures in such parts. Achieving a single overall welding process eliminates the need for subsequent rework, effectively simplifying the process, reducing production costs, and offering significant advantages in weight reduction for such parts, thus demonstrating broad application prospects.

[0036] 2. It can achieve unidirectional incident electron beam, complete the welding of two layers of weld seams in one go, and achieve single-sided welding with four-sided forming. If combined with changing the incident direction of the electron beam, it can achieve electron beam welding of four layers with shielding structure, thus improving welding processing efficiency.

[0037] 3. Due to the use of electron beam welding with minimal deformation and one-time forming, precise control of the part dimensions during the welding process is achieved. Furthermore, pre-welding finishing of the parts can be completed, reducing the complexity of part processing. Attached Figure Description

[0038] Figure 1 Schematic diagram of electron beam focusing for double-layer weld seam welding.

[0039] Figure 2 Schematic diagram of the electron beam welding line energy step test process.

[0040] Figure 3 A schematic diagram of the electron beam welding process for the first layer of weld.

[0041] In the figure: 1 First layer weld; 2 Second layer weld; 3 Electron beam current; 4 First layer weld pool; 5 First layer weld pool energy channel; 6 Electron beam current focus. Detailed Implementation

[0042] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0043] The electron beam welding method for single-sided incident double-layer weld formation of titanium alloy components with irregular multi-layer thin plate structures comprises the following steps:

[0044] Based on the target part to be welded, the working distance is selected. Combined with the distance between the first weld layer 1 and the second weld layer 2, the energy of the focusing coil is adjusted to control the focusing current. The surface focal points of the first weld layer 1 and the second weld layer 2 are determined through a step test, thereby determining the corresponding focusing current. The selected focal point is located in the middle of the distance between the first and second weld layers. According to formula (1), the required focusing current range is obtained, and the position of the electron beam current focus 6 is set, such as... Figure 1 As shown.

[0045] Based on the step test, the linear energy of the sample obtained by summing the surface focal weld thickness at the first weld layer 1 position and the linear energy of the sample obtained by summing the surface focal weld thickness at the first weld layer 2 position are used. Using formulas (2) and (3), the highest accelerating voltage is selected, and the required welding current is determined, such as... Figure 2 As shown.

[0046] By combining the aperture angle α and using formulas (4) and (5), along with parameters such as welding current and welding voltage, the penetration capability of the electron beam is increased, the linear energy of the electron beam is adjusted, and the "keyhole" of the electron beam in the weld pool 4 is deepened, so that the "keyhole" is deepened to penetrate the entire weld pool, forming a weld pool energy channel 5, such as... Figure 3 As shown. The diameter of the energy channel of the electron beam in the first weld layer 1 and the diameter of the beam spot on the upper surface of the second weld layer are calculated, and the focusing current is finely adjusted according to the formation of the energy channel 5 of the weld pool.

[0047] By adjusting the welding speed, under the movement of the high-speed electron beam 3, the liquid metal in the weld pool 4 moves rapidly in the electron beam. Taking advantage of the excellent thermal fluidity, light weight, and high liquid tension of titanium alloy, the liquid metal fills the channels backward under the action of hydrostatic pressure and metal vapor reaction force, continuously replenishing the energy channels 5 of the weld pool, so that the first weld 1 is reshaped.

[0048] The scanning amplitude is calculated using formula (6) based on the low-frequency circular wave electromagnetic scanning oscillation. The low-frequency rotating stirring vortex of the weld pool 4 under the action of electromagnetic force prevents the liquid metal from converging towards the center of the energy channel when the electron beam is not moving. When the electron beam moves, the electromagnetically rotating vortex also moves. The addition of electromagnetic stirring also increases the metal filling power, allowing the liquid metal to better fill the previous channel and improve the formation of the first weld 1.

[0049] By leveraging the converging effect of the electromagnetic coil, the accelerating voltage, welding current, and welding speed are controlled to increase the energy density to a level greater than 10.7 W / cm 2 This ensures that the remaining energy transmitted through the energy channel 5 of the first weld reaches the second weld 2 and provides sufficient energy for the heat conduction and fusion of the second weld, thus enabling the welding of the second weld 2 to be completed.

[0050] The focal point is located between the two weld layers. The first weld layer (1) uses lower focal point welding, and the second weld layer (2) uses upper focal point welding. Through optimized settings of focusing current and line energy, the second weld layer is essentially decoked, ensuring the formation of both the upper and lower surfaces.

[0051] Because the keyhole channel 5 of the first weld pool will not be fully filled during the filling process, and the electron beam 3 will also cause some metal loss during its passage, the surface of the first weld layer 1 will have some undercut and depressions. A modification weld is used to improve the surface quality of the first weld layer 1.

[0052] Example 1: A TA15M titanium alloy part with a closed cavity box structure of 4 layers of thin-walled partitions, each layer has a welding thickness of 2mm and a spacing of 160mm between each layer of thin plates.

[0053] I. Cleaning

[0054] Use a metal brush to polish the weld seam on both sides of the weld seam, within a 25mm radius on each side, until it shows a metallic sheen. Clean the part to be polished with a white cloth dampened with acetone, ensuring it is free of oil.

[0055] II. Parts Installation and Positioning

[0056] The processed workpiece is fixed in the tooling fixture, and the positioning parts ensure that the butt gap of all welds is no more than 0.1mm and the misalignment is no more than 0.2mm.

[0057] TIG welding is used for tack welding at corners and outer edges, while other positions use uniform three-point symmetrical tack welding. TIG welding tack welding is performed using a 2.5mm diameter yttrium tungsten electrode, approximately 80mA current, 2.0mm diameter pure titanium welding wire, and high-purity argon gas protection at 8-10L / min. For 2mm thick butt-welded titanium plates without beveling, the penetration depth can reach over 0.5mm. Besides fixing the relative positions of the parts, manual tack welding also ensures a certain level of strength. It provides some resistance to stress after completing two layers of weld in one direction, preventing deformation of the two layers of weld in the opposite direction due to stress during the previous welding process, which could lead to increased butt gaps and misalignments.

[0058] III. Assembly

[0059] Install the positioned parts into the electron beam vacuum chamber, adjust the working distance between the parts and the electron beam gun, and ensure that the weld surface is horizontal and perpendicular to the incident direction of the electron beam.

[0060] IV. Welding

[0061] The focusing currents of the first and second surface focal points were determined to be 2220mA and 2176mA respectively through step tests. Based on formula (1), the focusing current of 2220mA was selected to match the stability of the energy channel.

[0062] Through step tests, combined with formulas (2) and (3), the highest accelerating voltage of 150KV was selected, and the line energy was compared and optimized to obtain a welding current of 24mA suitable for 2mm thick TA15M titanium alloy plates.

[0063] The energy channel is determined by formulas (4) and (5). The electron beam at the lower focus "welds through" the first weld to form an energy channel with a diameter of 1.2 mm, which then reaches the second weld. The welding of the second weld is completed under the action of the remaining energy.

[0064] Adjust the welding speed to 1200 mm / min. Utilize the excellent thermal fluidity, light weight, and high liquid surface tension of titanium alloy. Under the action of hydrostatic pressure and metal vapor reaction force, the liquid metal fills the channel backward.

[0065] Combining formula (6), the scanning amplitude is calculated to be 0.6. The electromagnetic scanning oscillation of the molten pool with a circular wave at a low frequency of 100HZ causes a layer of weld molten pool to form a stirring vortex, so that the liquid metal will not gather towards the center of the energy channel when the electron beam does not move. When the electron beam moves at a speed of 1200mm / min, the electromagnetic rotating vortex also moves and fills the previously formed channel.

[0066] After the weld is formed, the first layer of weld will have undercut and depression of about 0.2mm due to metal loss. A low-energy finishing weld of 2265mA focused current and 15mA welding current is used to improve the surface quality of the first layer of weld 1.

[0067] After completing the welding of these two layers of welds, adjust the position of the parts, reverse the incident direction of the electron beam, and repeat the above process to perform electron beam welding of the two layers of welds on the back.

Claims

1. A method of electron beam welding of a titanium alloy component with one-sided entry of a double-layer weld, characterized in that, The steps are as follows: (1) The energy of the focusing coil is adjusted by focusing current to set the focal point of the electron beam to be super-hypofocal, increase the penetration ability of the electron beam, and deepen the "keyhole" to penetrate the whole molten pool; The selected position of the focusing focal point is in the middle of the distance between the first layer and the second layer of the weld; on the basis of the focal point, the line energy required for welding is adjusted; The calculation formula of the focusing current is: In the formula, J1 and J2 are the focusing currents of the surface focal points of the first layer of the weld and the second layer of the weld respectively, and J is the focusing current of the focal point at the set position; The calculation formula of the line energy of the electron beam is: In the formula, q is the line energy of the electron beam welding, U is the acceleration voltage of the electron beam, I is the welding current of the electron beam, and v is the welding speed of the electron beam; (2) The line energy requirement of the part is evaluated by the step test, and the required current can be determined between the line energy of the sum of the thicknesses at the positions of the two layers of the weld respectively; The calculation formula of the required current is: I1≤I≤I2(3) In the formula, I1 is the welding current of the sum of the thicknesses of the two layers at the position of the first layer of the weld with the surface focal point, I2 is the welding current of the sum of the thicknesses of the two layers at the position of the second layer of the weld with the surface focal point, and I is the required welding current of the electron beam; (3) After the line energy is determined, the included angle formed by the two boundary asymptotes of the outermost side of the electron beam current is the aperture angle α; The calculation formula of the aperture angle α is: In the formula, d1 is the diameter of the energy channel of the electron beam at the first layer of the weld, d2 is the diameter of the beam current spot on the surface of the second layer of the weld, and H is the distance between the first layer of the weld and the second layer of the weld; (4) The diameter relationship of the spot formed on the surface of the first layer of the weld and the second layer of the weld is determined through the aperture angle α, and then the energy relationship of the first layer of the weld and the second layer of the weld is determined; The energy relationship formula of the first layer of the weld and the second layer of the weld is: (5) The welding speed is adjusted, and the welding is carried out at a higher speed. Under the rapid movement of the electron beam current, the liquid heat flow of titanium alloy has good fluidity, the specific gravity is relatively light, and the liquid tension is large. Under the action of the hydrostatic pressure and the metal vapor reaction force, the liquid metal fills the channel backward; (6) The rapid movement of the spot increases the backward flowability of the molten pool while shortening the time required to maintain the energy channel at a fixed position. The shorter the time of opening the energy channel, the shorter the time required to maintain the high temperature of the surrounding liquid metal to ensure that the channel is subsequently filled, and the smaller the gravity pressure that the surrounding liquid metal needs to bear. Therefore, fast welding effectively reduces the channel recovery pressure, creates favorable conditions for the first layer of the weld to be filled with sufficient liquid metal, and enables the first layer of the weld to be reshaped again; (7) The channel also moves with the transfer of liquid metal. Although the time of the energy channel at a fixed position is shortened, as long as the channel is open when the electron beam current passes through, it will not affect the energy input during the welding of the second layer of the weld, that is, the dynamic stability of the channel is realized. The molten pool in the channel also moves with the movement of the electron beam current, and the metal continuously flows and fills, better closing the first layer of the weld. The welding speed of the titanium alloy sheet is determined according to the thickness and the specific weldability of the material, but should be above 1000 mm / min. (8) The battery electromagnetic scanning oscillation of low frequency circular wave is supplemented, and the scanning amplitude is equal to half of the diameter of the channel; the molten pool metal is stirred by the low frequency rotating vortex under the action of electromagnetic force, so that the liquid metal does not gather to the center of the energy channel when the electron beam does not move, so that the energy channel is further stabilized, and when the electron beam moves, the electromagnetic rotating vortex also moves, the addition of electromagnetic stirring also increases the metal filling power, so that the liquid metal fills the previous channel better, and the first layer of weld is improved in forming; (9) By the convergence of the electromagnetic coil, the selection of the far lower focal point controls that the electron beam stream will not produce a large amount of divergence after penetrating the first layer of weld, while the acceleration voltage, welding current and welding speed are controlled to increase the sufficient energy density greater than 10 7 W / cm 2 , so that the remaining energy after penetrating the energy channel of the first layer of weld provides sufficient energy for the second layer of weld to conduct heat and fuse when the remaining energy reaches the second layer of weld, and the welding of the second layer of weld can be completed; that is, the first layer of weld is over deep penetration welding, and the second layer is converted into approximate heat conduction welding; (10) The focus position is located in the middle of the two layers of welds, the first layer of weld is welded by using the lower focus point, and the second layer of weld is welded by using the upper focus point; through the optimization of the focused current and the linear energy, the second layer of weld is equivalent to defocusing forming, so that the upper and lower surfaces are formed; (11) Due to the extremely fast propagation speed of the electron beam in the vacuum chamber, due to the existence of the energy channel, the second layer of weld is first welded and formed, at the same time, the first layer of weld immediately restores the shape with the movement of the electron beam, and the electron beam weld is narrow in shape and relatively small in stress; (12) The first layer of weld will have the existence of undercut defects on the surface due to the opening of the "spoon hole" channel and a small amount of metal spatter, and after the welding is completed, a small energy defocusing modification welding is used for repair.

2. The method of claim 1, wherein the titanium alloy component is a single-sided entry double-layer weld one-shot electron beam welding method, characterized by, In the step (8), the electromagnetic scanning amplitude formula is: where: d1 is the diameter of the energy channel of the electron beam in the first layer of weld x and V y are the electromagnetic scanning amplitudes in the x and y directions, respectively.

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