Laser welding method for controlling engine heat shield weld defects

Abstract

This invention provides a laser welding method for controlling weld defects in engine heat shields, comprising the following steps: creating mounting holes in the heat shield substrate and machining studs that fit the mounting holes; selecting a laser beam with a triangular pulse waveform as the welding laser source and establishing a welding forming process database; assembling the studs into the mounting holes; selecting appropriate welding parameters to weld the normal weld area based on the welding forming process database; keeping other welding parameters constant while maintaining the welding parameters for the normal weld area; and gradually reducing parameters such as laser power and energy application time at proportional amplitudes to weld the weld defects in the weld area; ending the weld defect when the laser beam power is reduced to a level that only allows the base material to achieve a thermally conductive weld state. This invention gradually attenuates the welding energy in the weld defect area during the welding process, thereby significantly suppressing the probability of defects such as arc craters in the weld defect area and greatly improving the welding quality.

Description

Technical Field

[0001] This invention relates to the field of laser welding technology, and more specifically, to a laser welding method for controlling weld defects in engine heat shields. Background Technology

[0002] The heat shield is installed on the inner wall of the exhaust nozzle of an aircraft engine, and typically consists of a heat shield base 1 and studs 2 distributed on it (see typical structure for details). Figure 1 The heat shield substrate 1 is often curved, with multiple heat shields connected end-to-end to form a ring. The inner wall of the heat shield (the side without studs) has a smooth exhaust function, so the surface accuracy of the inner wall is very high. Several studs (spaced approximately 30mm-80mm apart) are spaced on the outer surface of the heat shield for mounting and fixing other structures. The stud specifications are approximately M6mm-M15mm. A certain pressure of cooling airflow passes through a densely designed array of cooling holes on the heat shield substrate (the array of cooling holes does not overlap with the weld seam, or the weld seam position avoids the cooling holes), forming a heat-insulating air film. This effectively isolates the heat transfer from the high-temperature jet to the surrounding titanium alloy and other metal load-bearing frame support structure, thereby effectively ensuring the service reliability and safety of the engine and its surrounding structures, and further enhancing the engine's lifespan.

[0003] The most common method for connecting the heat insulation shield substrate and studs is stud welding. This involves contacting one end of the stud with the substrate surface, applying an electric arc, and then applying pressure to the stud to complete the weld after the contact surface melts. The heat insulation shield (including the studs) is typically made of high-temperature alloys. During stud welding, the interface between the stud end and the base material completely melts, and a certain pressure is applied to the base material. To prevent significant deformation of the base material, it is necessary to provide support from the back of the base material to reduce the force applied to it. Furthermore, the thickness of the base material must exceed a certain threshold, which is closely related to the properties or performance of the base material itself. Therefore, the thickness δ of the base material should not be less than 0.5 mm, and the optimal thickness δ for thin-walled substrates suitable for stud welding is above 2 mm.

[0004] Aero-engine structures have stringent weight reduction requirements. Heat shields often employ thin-walled curved substrates with a wall thickness ranging from 0.5mm to 1.0mm, uniformly connected with numerous stud assemblies of diameters from M6 to M15. When these stud assemblies are connected to the substrate via stud welding, the large heat input during welding, coupled with the effect of the heat dissipation hole array on the heat shield substrate, results in very large deformation of the inner wall of the substrate after welding, often exceeding ±3mm. This deformation is difficult to correct through subsequent heat treatment. Therefore, the welded structure cannot meet the technical requirement of controlling surface deformation within ±2mm, severely impacting the engine's performance.

[0005] To address the stud welding problem in high-temperature alloy heat shields with wall thicknesses ranging from 0.5mm to 1.0mm, and to minimize the impact of the heat dissipation hole array on the heat shield substrate on welding deformation, a laser welding method with very low heat input is proposed as an alternative to stud welding. Patent application number 202011375525.5 proposes optimizing the stud overlap into a corner joint and employing laser-interval spot welding and circumferentially distributed circumferential welding to achieve the stud connection. However, the joint strength obtained by this method is not high and cannot meet the long-life, high-strength service requirements of engine-related structures. Furthermore, during circumferential welding, the arc crater at the weld termination is prone to defects such as cracks and depressions. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] The technical problem to be solved by the present invention is that the welded joints of existing engine heat shields have low strength and are prone to defects such as cracks and dents at the weld termination.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] This invention provides a laser welding method for controlling weld defects in engine heat shields, used to weld the heat shield substrate and studs, comprising the following steps:

[0011] Step S1: Open assembly holes on the heat insulation screen substrate and machine studs that are compatible with the assembly holes;

[0012] Step S2: Select a laser beam with a triangular pulse waveform as the welding laser source. The pulse width of the laser beam is B = 2t1 + t2, where 2t1 is the width of the triangular pulse waveform and t2 is the delay width when the laser is in a state of no energy.

[0013] Step S3: Conduct multiple sets of welding tests with t1 as a single variable and multiple sets of welding tests with t2 as a single variable to obtain the weld width and weld joint state under different t1 and different t2 values, and statistically analyze the test results to establish a welding forming process database.

[0014] Step S4: Assemble the stud into the assembly hole, and plan the weld area between the stud and the connecting heat insulation screen substrate. The weld area includes a normal weld area that can achieve a sealed connection between the stud and the connecting heat insulation screen substrate, and a weld bead area connected to the normal weld area.

[0015] Step S5: Based on the welding forming process database, keep other welding parameters unchanged, select appropriate t1 and t2 values ​​to weld the normal weld area. During the welding process: when the laser beam runs to N·B+t1, the power of the laser beam rises to the peak power P0, where N is an integer and N≥0.

[0016] Step S6: Keep other welding parameters unchanged, reduce the laser power P0, t1 and t2 by a proportional amplitude η, and weld the weld bead area. When the power of the laser beam is reduced to the point where it can only make the base material form a heat-conducting weld state, the weld beading ends.

[0017] Preferably, the laser welding method further includes:

[0018] Step S7: Perform non-destructive testing on the weld area.

[0019] Preferably, the weld area is subjected to non-destructive testing using penetrant testing or X-ray testing. When X-ray testing is used, the weld area is irradiated 2-3 times in a circumferentially even manner with X-rays tilted at a preset angle α, wherein the preset angle α is adjustable within the range of 30° to 60°.

[0020] Preferably, the value of t1 is in the range of 20ms to 60ms, the value of t2 is in the range of 20ms to 40ms, and the value of η is in the range of 70% to 90%.

[0021] Preferably, in step S1: the stud has a flange end and a threaded end that are disposed opposite to each other, the heat insulation screen base has an assembly hole that matches the diameter of the flange end, and the thickness of the flange end is equal to the thickness of the heat insulation screen base.

[0022] Preferably, when the flange end is assembled into the assembly hole, the outer surface of the flange end away from the threaded end is flush with the outer surface of the heat insulation screen substrate, and the misalignment between the two is not greater than 0.1mm, and the assembly gap between the flange end and the assembly hole is not greater than 0.1mm.

[0023] Preferably, the other welding parameters include welding speed, laser power, defocusing amount, inert shielding gas flow rate, scanning trajectory, scanning amplitude, and scanning frequency; wherein the scanning trajectory is circular, the scanning amplitude is no greater than 1.2 mm, and the scanning frequency is adjustable within the range of 50 Hz to 100 Hz.

[0024] Preferably, before welding the normal weld area, the heat insulation screen substrate and studs are cleaned by laser cleaning or chemical cleaning.

[0025] Preferably, when welding the normal weld bead area and the weld bead finishing area, an inert gas is used to protect the weld pool and high-temperature zone.

[0026] Preferably, the stud and the connecting heat insulation screen substrate have a closed annular weld, and the length of the normal weld area is 1 to 1.2 times the length of the annular weld.

[0027] (III) Beneficial Effects

[0028] The above-described technical solution of the present invention has at least the following advantages:

[0029] 1. A laser beam with a triangular pulse waveform is selected as the welding laser source, and there is an extended width between two adjacent pulse waveforms of the laser beam. During welding, the base material is exposed to the thermal radiation of the high-energy-density laser beam for a very short time. Accompanied by rapid energy rise and fall and time delay of the energy-free state, the heat input of laser welding is kept at a very low level, which is beneficial to control the surface deformation of the engine heat shield stud laser welding within a very small range.

[0030] 2. Based on the welding parameters in the normal weld area, while keeping other parameters such as welding speed constant, the laser power and energy application time are gradually reduced by proportionally decreasing the laser power and energy application time. This causes the energy in the weld bead area to gradually decay, and the laser welding mode is correspondingly changed from deep penetration welding mode to heat conduction welding mode. This effectively weakens the arc crater phenomenon, greatly suppresses the probability of arc crater defects (including arc crater cracks), significantly reduces the probability of repair welding, and greatly improves welding quality and welding operation efficiency.

[0031] 3. The joint design between the heat insulation screen substrate and the stud has been optimized. By opening assembly holes on the heat insulation screen substrate and machining studs that match the assembly holes, the outer diameter of the flange end of the stud is made larger than that of the threaded end. At the same time, it is ensured that the preset weld position avoids the heat dissipation holes on the heat insulation screen substrate. This optimizes the connection method between the stud and the heat insulation screen substrate from a corner joint to a butt joint, reducing welding difficulty, reducing stress concentration, and further improving the service reliability of the welded joint. It also helps to reduce the surface deformation of the stud and the heat insulation screen substrate during laser welding, and is more conducive to obtaining welded joints with excellent welding quality. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic flowchart of a laser welding method for controlling weld defects in engine heat shields, provided in an embodiment of the present invention.

[0034] Figure 2 This is a schematic diagram of the heat insulation screen.

[0035] Figure 3 This is a schematic diagram of the connection between the heat insulation screen substrate and the studs provided in an embodiment of the present invention.

[0036] Figure 4 This is a waveform diagram of the laser beam during welding of the normal weld area provided in an embodiment of the present invention.

[0037] Figure 5 This is a waveform diagram of the laser beam during the welding of the weld bead area provided in an embodiment of the present invention.

[0038] Figure 6 This is a schematic diagram illustrating the principle of using X-ray inspection to perform non-destructive testing on the weld area, as provided in an embodiment of the present invention.

[0039] Figure 7 The results are the correlation test results between t1 and weld formation provided in the embodiments of the present invention.

[0040] The labels for the attached figures are as follows:

[0041] 1. Heat insulation shield substrate; 2. Stud; 3. Laser beam; 4. X-ray; 5. Weld area; 21. Flange end; 22. Threaded end. Detailed Implementation

[0042] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0043] It should be noted that when a component is referred to as "fixed to" or "set on" another component, it can be located directly on or indirectly on the other component. When a component is referred to as "connected to" another component, it can be directly or indirectly connected to the other component.

[0044] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate that the device or element must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0045] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating relative importance or the number of technical features. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified. The specific implementation of this invention will be described in more detail below with reference to specific embodiments:

[0046] like Figure 1 , Figure 2 , Figure 3 , Figure 4 as well as Figure 5 As shown in the figure, this invention provides a laser welding method for controlling weld defects in engine heat shields, used to weld and connect the heat shield substrate 1 and the stud 2, including the following steps:

[0047] Step S1: Open assembly holes on the heat insulation screen substrate 1 and machine studs 2 that are compatible with the assembly holes;

[0048] Step S2: Select a laser beam 3 with a triangular pulse waveform as the welding laser source. The pulse laser width B of the laser beam 3 is B = 2t1 + t2, where 2t1 is the width of the triangular pulse waveform and t2 is the delay width when the laser is in a state of no energy.

[0049] Step S3: Conduct multiple sets of welding tests with t1 as a single variable and multiple sets of welding tests with t2 as a single variable to obtain the weld width and weld joint overlap state corresponding to different t1 and different t2 values, and statistically analyze the test results to establish a welding forming process database; specifically, fix welding speed, decoking amount and other process parameters, obtain the weld width and weld joint overlap state corresponding to different t1 and t2 through process tests, and then form a weld forming process database by detecting geometric quantities such as weld width and weld overlap rate.

[0050] Step S4: Assemble the stud 2 into the assembly hole, and plan the weld area 5 between the stud 2 and the heat insulation screen base 1. The weld area 5 includes a normal weld area that can achieve a sealed connection between the stud 2 and the heat insulation screen base 1, and a weld bead area connected to the normal weld area.

[0051] Step S5: Based on the welding forming process database, keep other welding parameters unchanged, select appropriate t1 and t2 values ​​to weld the normal weld area. During the welding process: when the laser beam runs to N·B+t1, the power of the laser beam rises to the peak power P0, where N is an integer and N≥0; under the action of the peak power P0, the heat insulation screen substrate 1 and the stud 2 can achieve stable "small hole" deep penetration welding.

[0052] Step S6: Keep other welding parameters unchanged, reduce the laser power P0, t1 and t2 by the same proportional amplitude η, and weld the weld bead area. When the power of the laser beam 3 is reduced to the point that it can only make the base material form a heat-conducting weld state, the welding ends.

[0053] Step S7: Perform non-destructive testing on weld area 5.

[0054] like Figure 6 As shown, in one embodiment, the weld area 5 is subjected to non-destructive testing using either penetrant testing or X-ray testing. When X-ray testing is used, X-rays 4 are tilted at a preset angle α and irradiated circumferentially in the weld area 2-3 times, wherein the preset angle α is adjustable from 30° to 60°.

[0055] In one embodiment, the value of t1 ranges from 20ms to 60ms, the value of t2 ranges from 20ms to 40ms, and the value of η ranges from 70% to 90%.

[0056] In one embodiment, in step S1: the stud has a flange end 21 and a threaded end 22 disposed opposite to each other; the heat insulation screen base 1 has an assembly hole matching the diameter of the flange end 21; the thickness of the flange end 21 is equal to the thickness δ of the heat insulation screen base 1. The wall thickness δ of the heat insulation screen base 1 ranges from 0.5mm to 1.0mm, the diameter M of the threaded end 22 ranges from 6mm to 15mm, and the outer diameter of the flange end 21... and The difference between M and M is in the range of 3mm-5mm.

[0057] In one embodiment, when the flange end is assembled into the assembly hole, the outer surface of the flange end 21 away from the threaded end 22 is flush with the outer surface of the heat insulation screen base 1, and the misalignment between the two is not greater than 0.1mm, and the assembly gap between the flange end 21 and the assembly hole is not greater than 0.1mm.

[0058] In one embodiment, other welding parameters include welding speed, laser power, defocusing amount, inert gas flow rate, scanning trajectory, scanning amplitude, and scanning frequency; wherein the scanning trajectory is circular, the scanning amplitude is no greater than 1.2 mm, and the scanning frequency is adjustable in the range of 50 Hz to 100 Hz.

[0059] In one embodiment, before welding the normal weld area, the heat insulation shield substrate and studs are cleaned using laser cleaning or chemical cleaning methods. Laser cleaning or chemical cleaning thoroughly removes oil and oxide film from the surfaces of the heat insulation shield substrate and studs to avoid affecting the welding quality.

[0060] In one embodiment, an inert gas is used to protect the weld pool and high-temperature zone during the welding of the normal weld bead area and the weld bead finishing area. The inert gas includes, but is not limited to, argon and helium.

[0061] In one embodiment, the stud and the connecting heat insulation screen substrate have a closed annular weld, and the length of the normal weld area is 1 to 1.2 times the length of the annular weld. This ensures that the weld formed by welding the normal weld area can be completely closed (when the length is greater than 1, the excess weld length will form an overlap area to ensure the complete closure of the weld), thus guaranteeing welding quality.

[0062] The following is a specific embodiment of the present invention: In this embodiment, the wall thickness δ of the heat insulation screen substrate 1 is 1.0 mm, and the stud specification is M8mm×1mm. Laser welding is performed according to the following steps in this embodiment:

[0063] First, mounting holes are made on the heat insulation screen substrate 1. The mounting hole specifications are as follows: A stud 2 is machined to fit the assembly hole; one end of the stud 2 is a flange end 21, and the other end is a threaded end 22 (M8mm×1mm). The flange end 21 is of the same thickness as the heat insulation screen base 1. The diameter of the flange end 21 and the assembly hole are... Compatible, meaning the outer dimensions of flange end 21 are as follows: Therefore, when flange end 21 is assembled with the assembly hole, the local gap between the two should be within the range of 0-0.1mm.

[0064] Then, a laser beam 3 with a triangular pulse waveform is selected as the welding laser source. The pulse width of the laser beam 3 is B = 2t1 + t2, where 2t1 is the width of the triangular pulse waveform and t2 is the delay width when the laser is in an energy-free state; t1 ranges from 20ms to 60ms, and t2 ranges from 20ms to 40ms. With welding speed, defocusing amount, and other process parameters fixed, process experiments are conducted to obtain the weld width and weld overlap state corresponding to different t1 and t2 states. Then, a weld formation process database is formed by detecting geometric quantities such as weld width and weld overlap rate. For example, fixing t2, P0, welding speed, and defocusing amount, and changing t1 yields weld formations such as... Figure 7 As shown. From Figure 7 It can be seen that the smaller t1 is, the denser the weld points are, but the worse the weld formation on the back side is; the larger t1 is, the wider the weld points are, which leads to a corresponding increase in welding deformation. At the same time, the larger t2 is, the more unstable the transition between weld points becomes, resulting not only in a worse weld formation, but also an increased tendency for porosity to form inside the weld.

[0065] Next, the stud 2 is assembled into the mounting hole. Using a special welding fixture, the flange end 21 of the stud 2 is assembled with the corresponding mounting hole on the heat insulation screen base 1. The outer surface of the flange end 21 away from the threaded end 22 is flush with the outer surface of the heat insulation screen base 1, and the misalignment should not exceed 0.1mm.

[0066] Next, laser welding is performed on the heat insulation screen substrate and studs. Before welding, laser cleaning is required to thoroughly remove oil and oxide film from the base material surface to avoid affecting the welding quality. During welding, inert gases such as Ar are used to provide comprehensive protection for the weld pool and high-temperature zone. The normal weld bead area is 1.1 times the length of the entire circumferential weld. Based on the welding forming process database, t1 = 30ms, t2 = 20ms, P0 = 1400W, welding speed 9mm / s, and defocusing amount 0mm are selected as the welding parameters for the normal weld bead area. Welding is then performed on the normal weld bead area. Based on the welding parameters for the normal weld bead area, while keeping the welding speed, defocusing amount, and other parameters unchanged, the laser power P0, t1, and t2 are gradually reduced by an amplitude of η = 80% as the welding process parameters for the finishing weld bead area. Welding is then performed on the finishing weld bead area. When the laser power is reduced to below 700W, the finishing weld is terminated because the laser energy can only bring the base material into a thermally conductive state.

[0067] Finally, X-ray non-destructive testing was performed on the weld area. To avoid the influence of stud 2 on the weld inspection, the X-ray beam was tilted at a preset angle α = 60°, and the circumferential weld was irradiated twice evenly along the circumference to achieve 100% non-destructive testing of the weld.

[0068] After welding using the above method, the welded joint (including the weld bead section) meets the quality requirements of a Class I joint, effectively eliminating arc crater defects. The deformation of the inner wall of the heat shield substrate 1 after welding can be controlled within ±2mm, strongly ensuring the heat insulation function of the heat shield in the engine structure. It also significantly reduces the need for re-welding in the weld bead area, significantly improving welding efficiency. This is also the first time that a laser welding method for butt joints has been proposed for stud welding of engine heat shields, greatly improving and enhancing the welding quality and surface deformation control of the heat shield.

[0069] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A laser welding method for controlling a welding defect of an engine heat shield, for welding a heat shield base and a stud, characterized by, The method comprises the following steps: Step S1, drilling an assembly hole on the heat shield base body and processing a threaded stud matched with the assembly hole; Step S2, selecting a laser beam with a triangular pulse waveform as a welding laser source, the pulse laser width B of the laser beam is 2t1+t2, wherein 2t1 is the width of the triangular pulse waveform, and t2 is the delay width of the laser in the non-energy state; Step S3, performing a plurality of welding tests with t1 as a single variable and a plurality of welding tests with t2 as a single variable, obtaining the corresponding weld width and weld joint state under different t1 and t2, and establishing a welding forming process database by counting the test results; Step S4, assembling the threaded stud into the assembly hole, planning a weld area between the threaded stud and the connecting heat shield base body, and the weld area comprises a normal welding bead area capable of achieving airtight connection between the threaded stud and the connecting heat shield base body and a closing welding bead area connected with the normal welding bead area; Step S5, according to the welding forming process database, controlling other welding parameters to be unchanged, selecting appropriate t1 and t2 values to weld the normal welding bead area, and during the welding process: when the laser beam runs to N·B+t1, the power of the laser beam rises to the peak power P0, wherein N is an integer and N≥0; Step S6, controlling other welding parameters to be unchanged, reducing the laser power P0, t1 and t2 by an equal proportion amplitude η, and welding the closing welding bead area, and when the power of the laser beam is reduced to only form a heat conduction welding state of the base material, the closing welding is ended.

2. The laser welding method for controlling the welding defects of the engine heat shield according to claim 1, wherein The laser welding method further comprises: Step S7, performing non-destructive testing on the weld area.

3. The laser welding method for controlling the lack of fusion of an engine heat shield according to Claim 2, wherein The non-destructive testing on the weld area is performed by using a penetration detection method or an X-ray detection method; when the X-ray detection method is used for non-destructive testing, the X-ray is inclined at a preset angle α and irradiates the weld area circumferentially for 2-3 times, wherein the adjustment range of the preset angle α is 30°-60°.

4. The laser welding method for controlling the lack of fusion of an engine heat shield according to Claim 1, wherein The value range of t1 is 20ms-60ms, the value range of t2 is 20ms-40ms, and the value range of η is 70%-90%.

5. The laser welding method for controlling the lack of fusion of an engine heat shield according to Claim 1, wherein In the step S1, the threaded stud has oppositely arranged flange ends and threaded ends, the assembly hole matched with the diameter of the flange end is drilled on the heat shield base body, and the thickness of the flange end is equal to the thickness of the heat shield base body.

6. The laser welding method for controlling the lack of fusion of an engine heat shield according to Claim 5, wherein When the flange end is assembled into the assembly hole, the outer surface of the flange end away from the threaded end is flush with the outer surface of the heat shield base body, and the gap between them is not greater than 0.1mm, and the assembly gap between the flange end and the assembly hole is not greater than 0.1mm.

7. The laser welding method for controlling the lack of fusion of an engine heat shield according to Claim 1, wherein The other welding parameters include welding speed, laser power, defocusing amount, inert protective gas flow, scanning track, scanning amplitude and scanning frequency; wherein the scanning track is circular, the scanning amplitude is not greater than 1.2mm, and the adjustment range of the scanning frequency is 50Hz-100Hz.

8. The laser welding method for controlling the lack of fusion of an engine heat shield according to Claim 1, wherein Before welding the normal welding bead area, the heat shield base body and the threaded stud are cleaned by using laser cleaning or chemical cleaning.

9. The laser welding method for controlling the lack of fusion of an engine heat shield according to Claim 1, wherein During welding of the normal bead area and the collecting bead area, an inert gas is used to protect the welding pool and high temperature area.

10. The laser welding method for controlling the lack of fusion of an engine heat shield according to Claim 1, wherein The length of the normal bead area is 1-1.2 times the length of the closed annular weld between the stud and the connecting heat shield base.

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