Resistance projection welding method for an aeroengine support

Abstract

The application discloses a resistance projection welding method for an aero-engine support. The aero-engine support assembly is clamped by a limiting clamp, so that the position deviation of the support and the convex seat in the electrode welding or pressure process is prevented, and the upper electrode and the lower electrode are kept in the center of the convex seat. The blind hole design of the convex seat and the lower electrode is combined, the extrudate of the plastic deformation of the contact bump melting is accommodated, and the precision control property of the welding area is improved. The secondary resistance projection welding process is also adopted. Smaller current is used to ensure that the contact end surface of the convex seat and the support is uniformly welded along the circumferential gap, larger current is used to eliminate the residual gap between the convex seat and the support, the radial deformation amount of the convex seat is accurately controlled, the appearance quality and the internal quality of the part after the resistance projection welding are ensured, and the problems of the position deviation, the splash welding defect, the internal porosity after welding and the poor fusion quality of the existing aero-engine support in the projection welding process are solved.

Description

Technical Field

[0001] This invention relates to the field of aircraft engine bracket welding technology, and more specifically, to a resistance projection welding method for aircraft engine brackets. Background Technology

[0002] The aircraft engine bracket needs to be welded to the boss. After welding, a threaded hole needs to be drilled in the center of the boss. It is necessary to ensure that there is fusion in the circumference range of 2.5mm from the outer circle of the boss to the center. Therefore, it is necessary to precisely control the welding area while maintaining the welding strength between the bracket and the boss.

[0003] While spot welding can limit the current and heating area by relying on the contact area at the electrode tip, the weld nucleus preferentially forms at the center of the boss and cannot extend from the center outwards to the entire outer circle of the boss. After welding, drilling a threaded hole at the center of the boss will remove the spot weld nucleus, causing the support to detach from the boss. Resistance projection welding, on the other hand, involves pre-machining raised points—the protrusions—on one of the workpieces. During welding, pressure is applied through electrodes and current flows through the protrusions. These protrusions act as natural current concentrators; upon energization, they are rapidly heated, softened, melted, and eventually crushed. Under electrode pressure, the molten metal is confined within the contact area, and after cooling and solidification, one or more robust weld nuggets are formed, connecting two or more workpieces together. Therefore, resistance projection welding can control the molten metal within a specific area, forming multiple weld points simultaneously in a single welding stroke. All weld points can be completed with a single pressure application and energization, resulting in significantly higher production efficiency than point-by-point spot welding. Furthermore, the weld point position in resistance projection welding is determined by the protrusion position, preventing misalignment due to electrode displacement and resulting in high-quality welds. For example, CN119525671A discloses a bimetallic welding method and apparatus, which involves forming multiple annular protrusions on the surface of a steel substrate; placing the steel substrate on a lower electrode and placing a copper plate on the annular protrusions on the surface of the steel substrate; placing an upper electrode on the copper plate and applying a set pressure to the upper electrode; after reaching the set pressure, energizing the upper electrode, and heating the annular protrusions on the surface of the steel substrate to a melting or plastic state based on the generated resistance heat, so that they can bond with the copper plate to complete the welding. This method achieves copper-steel bimetallic welding by setting annular protrusions on the surface of the steel substrate, with virtually no weld marks on the welded surface, good surface quality, small deformation, no need for grinding, reduced processing steps, and improved production efficiency. However, due to the relative slippage between the resistance spot welding bracket and the protrusion in the free state, the relative positional dimensions of the two individual parts cannot be guaranteed. Meanwhile, during resistance projection welding, the contact points on both sides of the part melt or undergo plastic deformation under certain pressure and heat. If there is excess material or the excess material cannot be removed in time, it can easily lead to a series of serious defects such as spatter, internal porosity, insufficient weld nugget size, and lack of fusion, which greatly weakens the strength and reliability of the weld. Summary of the Invention

[0004] The main technical problem to be solved by the present invention is to address the shortcomings of the prior art in the use of resistance projection welding of aero-engine brackets, such as positional displacement, spatter welding defects, internal porosity and poor fusion quality after welding, and to provide a resistance projection welding method for aero-engine brackets.

[0005] Another technical problem solved by this invention is the application of this device.

[0006] The objective of this invention is achieved through the following technical solution: A resistance projection welding method for an aircraft engine bracket, the aircraft engine bracket including a bracket and a boss disposed on the bracket, one end of the boss is provided with a contact protrusion, and a countersunk blind hole is provided at the center of the end of the boss where the contact protrusion is provided, and the bracket is provided with a chip removal through hole connected to the countersunk blind hole of the boss. The aircraft engine bracket is clamped by a limiting fixture, which includes a positioning block and a pressure block. The positioning block is provided with a through hole, which includes a concentric power limit positioning through hole and a boss limiting through hole. The peripheral wall of the power limit positioning through hole is provided with an electrode insulating sleeve, and the peripheral wall of the boss limiting through hole is provided with an insulating bushing. The positioning block and the pressure plate limit and press the bracket respectively. The steps of the resistance projection welding method include: S1. Install the upper and lower electrodes on the spot welding machine, and adjust the electrodes to ensure that the upper and lower electrodes are on the same center line, and that the upper electrode is pressed down and is in horizontal contact with the end face of the lower electrode. S2. Place the boss of the aircraft engine bracket in the boss limiting through hole of the limiting fixture, then fit the contact protrusion of the bracket and the boss together, and use the pressure plate to press the bracket and the positioning block together, and clamp the limiting fixture onto the spot welding machine. S3. Set the spot welding parameters as follows: preload time 380~420ms, pressurization time 180~220ms, welding pressure 0.22~0.24Mpa, welding current 6~10KA, welding time 250~270ms, holding time 200~400ms, and perform one projection weld. S3. Adjust the spot welding parameters: preload time to 380~420ms, pressurization time to 180~220ms, welding pressure to 0.22~0.24Mpa, welding current to 11~15KA, welding time to 250~270ms, and holding time to 400~600ms. Perform secondary projection welding to obtain the aircraft engine bracket.

[0007] This invention designs a projection welding structure, using pre-set projection points to offset the resistance spot welding nucleus from the center of the boss to the outer circumference, ensuring a firm connection after drilling the boss. A projection welding limiting fixture is used to ensure that the upper and lower electrodes are centered on the boss during resistance projection welding, guaranteeing stable placement of the boss and preventing relative slippage between the support and the boss. During resistance projection welding, the contact points of the boss are heated and melted, causing uniform plastic deformation of the entire outer circumference, allowing for controllable welding onto the support under electrode pressure.

[0008] Furthermore, the lower electrode has a countersunk blind hole II at its end. The countersunk blind hole II of the lower electrode is connected to the countersunk blind hole I of the boss through a chip removal through hole. This can accommodate the extruded material that undergoes plastic deformation when the contact point melts during resistance projection welding, ensuring that the contact end face of the part is flat.

[0009] Furthermore, the chip removal through-hole on the bracket has a diameter of 1~3mm.

[0010] Furthermore, the diameter of the second countersunk blind hole of the lower electrode is 2~4mm.

[0011] Furthermore, the electrode insulating sleeve and insulating bushing are made of white ceramic, which can prevent the part from being directly in contact with the metal fixture and causing damage to the surface of the part, and can also avoid the electrode directly contacting the limiting fixture during resistance projection welding, which would cause current shunting and make it impossible to guarantee the core width requirement.

[0012] Furthermore, the centers of the upper electrode, the lower electrode, and the protrusion are on the same axis.

[0013] Furthermore, the spot welding parameters for the single projection weld are: pre-pressing time of 400ms, pressurization time of 200ms, welding pressure of 0.22MPa, welding current of 8KA, welding time of 260ms, and holding time of 300ms.

[0014] Furthermore, the spot welding parameters for the secondary projection welding are: pre-pressing time of 400ms, pressurization time of 200ms, welding pressure of 0.22MPa, welding current of 13.8KA, welding time of 260ms, and holding time of 500ms.

[0015] Furthermore, the positioning block of the limiting fixture is also provided with a bracket limiting device.

[0016] Compared with existing technologies, the beneficial effects are: This invention utilizes a limiting clamp to fix the boss and bracket of an aero-engine support, ensuring that the upper and lower electrodes are centered on the boss. This prevents displacement during electrode welding or pressure application. The contact point melts upon heating, causing uniform plastic deformation of the entire outer circumference, thus forming a uniform annular fusion weld point. Furthermore, this invention incorporates countersunk blind holes on the boss and lower electrode to accommodate the extrusions from the plastic deformation of the contact point, ensuring a flat contact surface between the boss and bracket.

[0017] This invention also incorporates a secondary resistance projection welding process. The primary welding uses a smaller current to ensure uniform circumferential gap between the boss and the support after welding, preventing weld point detachment and maintaining weld point positioning. The secondary welding uses a larger current to eliminate any remaining gap between the boss and the support, preventing excessive upsetting radial deformation of the boss and avoiding thermal deformation contact marks caused by rigid compression with the fixture's limiting holes, which are then used for projection welding. This invention, through a two-stage projection welding process, allows for precise control of the boss's radial deformation, ensuring the appearance and internal quality of the parts after resistance projection welding. It avoids the need for larger welding currents and pressures required for primary projection welding, thus solving the problem of excessive upsetting radial deformation of the boss from the center outwards due to high current and pressure. Such excessive radial deformation can exceed the assembly gap between the boss and the limiting fixture, potentially even crushing the boss and penetrating the sidewalls, reducing product quality. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the resistance projection welding structure of the present invention; Figure 2 This is a schematic diagram of the aircraft engine support structure of the present invention; Figure 3 This is a schematic diagram of the limiting clamp structure of the present invention; Figure 4 This is a schematic diagram of the lower electrode structure of the present invention.

[0019] Among them, 1 is the upper electrode, 2 is the aircraft engine bracket, 3 is the limiting clamp, 4 is the lower electrode, 5 is the boss, 6 is the bracket, 7 is the countersunk blind hole one, 8 is the contact protrusion, 9 is the chip removal through hole, 10 is the positioning block, 11 is the pressure block, 12 is the upper limit through hole, 13 is the boss limiting through hole, 14 is the electrode insulating sleeve, 15 is the insulating bushing, and 16 is the countersunk blind hole two. Detailed Implementation

[0020] The following examples further explain and clarify the invention, but the specific examples do not limit the invention in any way.

[0021] Example 1 This embodiment provides a resistance projection welding method for an aircraft engine bracket. The aircraft engine bracket 2 includes a bracket 6 and a boss 5 disposed on the bracket 6. Both the bracket 6 and the boss 5 are made of 1Cr18Ni9Ti. One end of the boss 5 is provided with a contact protrusion 8 and is chamfered, so that the center of the projection welding nucleus is offset from the center of the part to both sides. A countersunk blind hole 7 is provided at the center of the end of the boss 5 where the contact protrusion 8 is provided, which is used to accommodate the extrusion that undergoes plastic deformation due to melting of the contact protrusion 8 during resistance projection welding. The bracket 6 is provided with a chip removal through hole 9 with ΦA=2mm. The chip removal through hole 9 communicates with the countersunk blind hole 7 of the boss, so that the extrusion that has undergone plastic deformation due to high temperature melting can be discharged from the chip removal through hole 9.

[0022] The aircraft engine bracket 2 is clamped by a limiting fixture 3 during resistance projection welding. The limiting fixture 3 includes a positioning block 10 and a pressure block 11. The positioning block 10 has a through hole, which includes a concentric upper limit positioning through hole 12 and a boss limiting through hole 13. An electrode insulating sleeve 14 is provided on the peripheral wall of the upper limit positioning through hole 12. The electrode insulating sleeve 14 is made of white ceramic. The upper limit positioning through hole 12 can limit the upper electrode 1 to ensure that the upper electrode is located at the center of the boss 5. This can prevent the boss from tilting after positioning due to the deviation of the projection welding pressure, and also prevent the electrode from directly contacting the positioning block 10 of the structural steel material during resistance projection welding, thus avoiding current shunting. An insulating bushing 15 is provided on the peripheral wall of the boss limiting through hole 13. The insulating bushing 15 is made of white ceramic. The boss limiting through hole 13 can limit the boss 5 to prevent the boss 5 from directly contacting the positioning block 10 of the limiting fixture 3 during resistance projection welding, thus preventing damage to the surface of the part.

[0023] The positioning block 10 and the pressure plate 11 limit and press the bracket 6 respectively.

[0024] In this embodiment, the upper electrode 1 and the lower electrode 4 are provided with a ΦB=3mm chip removal countersunk blind hole 16, which is used to accommodate the extruded material that undergoes plastic deformation when the contact point 8 melts during resistance projection welding, so as to ensure that the contact end face of the part is flat.

[0025] The steps of the resistance projection welding method include: S1. Make contact between the upper electrode 1 and the lower electrode 4 and the handle of the spot welding machine, ensuring that the contact area is more than 65%. Install them directly on the spot welding machine and adjust the electrodes to ensure that the upper electrode 1 and the lower electrode 4 are on the same center line. Visually check that the upper electrode 1 is pressed down and is in horizontal contact with the end face of the lower electrode 4.

[0026] S2. Place the boss 5 of the aircraft engine bracket 2 into the boss limiting through hole 13 of the limiting fixture 3, then fit the bracket 6 with the contact protrusion 8 of the boss, and use the pressure block 11 to press the bracket and the positioning block 10 together, and clamp the limiting fixture 3 onto the spot welding machine.

[0027] S3. Set the spot welding parameters as follows: preload time 400ms, pressurization time 200ms, welding pressure 0.22Mpa, welding current 8KA, welding time 260ms, and holding time 300ms. Fix the aircraft engine bracket 2 and the limit clamp 3 to ensure they are level. First, use the auxiliary stroke on the spot welding machine to preload the parts, then turn on the switch. The upper electrode 1 and lower electrode 4 press the parts together and perform a resistance projection weld. After the positioning projection weld, ensure that the boss and the bracket are firmly welded. At the same time, confirm that there is no skewing when welding the two parts and keep the gap uniform.

[0028] S4. After the tack welding and projection welding are completed, the parts are cooled to room temperature. The tack welding parameters are adjusted as follows: preload time is 400ms, pressurization time is 200ms, welding pressure is 0.22Mpa, welding current is 13.8KA, welding time is 260ms, and holding time is 500ms. Secondary resistance projection welding is then performed to ensure good fusion within 2.5mm on both sides of the contact surface between the boss 5 and the bracket 6. Once it is confirmed that there are no defects such as burns or penetrations on the surface of the aero-engine bracket 2, the aero-engine bracket 2 is obtained.

[0029] Example 2 The process in this embodiment is the same as that in Embodiment 1, except that the process parameters for the first resistance projection welding in this embodiment are: pre-pressure time of 400ms, pressure application time of 200ms, welding pressure of 0.12MPa, welding current of 5KA, welding time of 260ms, and holding time of 300ms; and the process parameters for the second resistance projection welding are: pre-pressure time of 400ms, pressure application time of 200ms, welding pressure of 0.14MPa, welding current of 10KA, welding time of 260ms, and holding time of 500ms.

[0030] In this embodiment, due to the insufficient resistance projection welding current and welding pressure, the gap between the contact points of the boss cannot be eliminated, and the fusion width cannot meet the requirement of good fusion within 2.5mm on both sides of the contact surface between the boss and the bracket.

[0031] Example 3 The process in this embodiment is the same as that in Embodiment 1, except that the process parameters for the first projection welding are: pre-pressure time of 400ms, pressure application time of 200ms, welding pressure of 0.30MPa, welding current of 10KA, welding time of 260ms, and holding time of 300ms; and the process parameters for the second projection welding are: pre-pressure time of 400ms, pressure application time of 200ms, welding pressure of 0.30MPa, welding current of 16KA, welding time of 260ms, and holding time of 500ms.

[0032] In this embodiment, the resistance projection welding current and welding pressure are too high. The boss 5 is heated and melts, resulting in plastic deformation. When eliminating the gap of the contact point along the axial direction, the boss 5 also undergoes excessive upsetting radial deformation from the center to the periphery. The radial deformation of the boss 5 is greater than the assembly gap between the boss 5 and the limiting fixture 3. This causes the boss 5 and the limiting hole of the limiting fixture 3 to be rigidly squeezed, forming thermal deformation contact marks, bulging of the side wall, or even crushing the boss 5 and penetrating the side wall, affecting the appearance and internal quality of the part after projection welding.

[0033] Example 4 The process in this embodiment is the same as in embodiment 1, except that this embodiment does not use the limiting fixture 3 to limit the boss, the bracket, and the upper electrode respectively. During resistance projection welding, the pressure and heating cause relative slippage between the boss 5 and the bracket 6, making it impossible to guarantee the dimensional requirements of the distance from the center of the drilled hole of the boss to the side of the bracket after welding. In addition, the lack of limiting fixture 3 for the upper electrode will cause the projection welding pressure to be biased to one side of the boss 5, resulting in the boss being skewed after projection welding positioning. Furthermore, it cannot be guaranteed that the countersunk blind hole 16 of the lower electrode 4 is located at the exact center of the chip removal through hole 9 of the bracket. The extruded material from the resistance projection welding causes uneven contact between the end face of the bracket 6 and the electrode, affecting the transmission of the resistance projection welding current and thus affecting the quality of the resistance projection welding nucleation.

[0034] Example 5 The process in this embodiment is the same as in embodiment 1, except that the limiting fixture 3 in this embodiment does not use the material with insulating bushing 15. When the limiting holes of the limiting fixture 3, the boss 5, and the upper electrode 4 are all made of metal, the boss softens and deforms due to heat during resistance projection welding, and the pressure applied during resistance projection welding causes the boss 5 to slip laterally. This results in rigid contact with the limiting holes of the metal fixture, causing current shunting and forming a discharge effect, which damages the outer circumference of the boss 5. During the solidification process of the side molten area, shrinkage defects are formed inside. In addition, the upper electrode 1 will also rigidly contact with the limiting holes of the metal fixture, causing current shunting. This results in uncontrollable heat input at the resistance projection welding nucleation site between the boss 5 and the support 6, and the inability to form good fusion within 2.5mm on both sides of the contact surface, resulting in problems such as incomplete welding or insufficient weld nucleus.

[0035] Example 6 The process in this embodiment is the same as in Embodiment 1, except that the boss 5 and the support 6 in this embodiment do not have countersunk blind holes 1-7 and chip removal holes 9, and the lower electrode 4 does not have countersunk blind holes 2-16. Because the boss 5 does not have countersunk blind holes 1-7, the nucleus formed after resistance projection welding is located at the center of the boss 5, and a weld nucleus cannot be formed within a 2.5mm range from the outer circle of the boss 5 to the center and the contact surface with the support 6. After welding, when a hole is drilled and tapped at the center of the boss 5, the boss 5 and the support 6 cannot connect and will detach. The lack of chip removal holes 9 on the support 6 causes the resistance projection welding extrudate to not be discharged in time, resulting in lateral breakdown defects caused by extrusion from the side of the boss 5. The lack of countersunk blind holes 2-16 on the lower electrode 4 causes the extrudate discharged from the chip removal holes 9 on the support to accumulate on the end face of the support 6 in contact with the electrode, resulting in uneven contact between the support and the electrode, affecting the transmission of resistance projection welding current and the quality of the resistance projection welding nucleus.

[0036] Example 7 This embodiment does not employ secondary projection welding. Under the premise of spot welding parameters of 400ms pre-pressing time, 300ms pressurization time, 0.32MPa welding pressure, 16.5KA welding current, 320ms welding time, and 500ms holding time, direct one-time resistance projection welding is performed. In order to eliminate the gap formed by the contact points between the boss 5 and the bracket 6 in one welding, a larger welding current and welding pressure are set compared to secondary resistance projection welding. Under the action of high current and high pressure, the boss 5 is heated and melts, resulting in plastic deformation. While eliminating the gap along the axial contact points, excessive upsetting radial deformation also occurs from the center to the periphery. The radial deformation of the boss 5 is greater than the assembly gap between the boss 5 and the limiting fixture 3, causing rigid extrusion between the boss 5 and the limiting hole of the limiting fixture 3, forming heat deformation contact marks, bulging of the sidewall, and even crushing of the boss 5 and penetration of the sidewall, affecting the appearance and internal quality of the part after projection welding.

[0037] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A resistance projection welding method for an aircraft engine bracket, characterized in that, The aircraft engine support includes a support and a boss mounted on the support. One end of the boss is provided with a contact protrusion, and a countersunk blind hole is provided at the center of the end of the boss where the contact protrusion is provided. The support is provided with a chip removal through hole that connects to the countersunk blind hole of the boss. The aircraft engine bracket is clamped by a limiting fixture, which includes a positioning block and a pressure block. The positioning block is provided with a through hole, which includes a concentric power limit positioning through hole and a boss limiting through hole. The peripheral wall of the power limit positioning through hole is provided with an electrode insulating sleeve, and the peripheral wall of the boss limiting through hole is provided with an insulating bushing. The positioning block and the pressure plate limit and press the bracket respectively. The steps of the resistance projection welding method include: S1. Install the upper and lower electrodes on the spot welding machine, and adjust the electrodes to ensure that the upper and lower electrodes are on the same center line, and that the upper electrode is pressed down and is in horizontal contact with the end face of the lower electrode. S2. Place the boss of the aircraft engine bracket in the boss limiting through hole of the limiting fixture, then fit the contact protrusion of the bracket and the boss together, and use the pressure plate to press the bracket and the positioning block together before clamping it onto the spot welding machine. S3. Set the spot welding parameters as follows: preload time 380~420ms, pressurization time 180~220ms, welding pressure 0.22~0.24Mpa, welding current 6~10KA, welding time 250~270ms, holding time 200~400ms, and perform one projection weld. S4. Adjust the spot welding parameters: preload time to 380~420ms, pressurization time to 180~220ms, welding pressure to 0.22~0.24Mpa, welding current to 11~15KA, welding time to 250~270ms, and holding time to 400~600ms. Perform secondary projection welding to obtain the aircraft engine bracket.

2. The resistance projection welding method for the aircraft engine bracket according to claim 1, characterized in that, The lower electrode has a countersunk blind hole at its end.

3. The resistance projection welding method for the aircraft engine bracket according to claim 1, characterized in that, The second countersunk blind hole of the lower electrode is connected to the first countersunk blind hole of the boss through the chip removal through hole.

4. The resistance projection welding method according to claim 1, characterized in that, The chip removal holes on the bracket have a diameter of 1~3mm.

5. The resistance projection welding method according to claim 1, characterized in that, The diameter of the second countersunk blind hole of the lower electrode is 2~4mm.

6. The resistance projection welding method according to claim 1, characterized in that, The electrode insulating sleeve and insulating bushing are made of white ceramic.

7. The resistance projection welding method for the aircraft engine bracket according to claim 1, characterized in that, The centers of the upper electrode, lower electrode, and protrusion are on a single axis.

8. The resistance projection welding method for the aircraft engine bracket according to claim 1, characterized in that, The spot welding parameters for the first projection weld are: pre-pressurization time of 400ms, pressurization time of 200ms, welding pressure of 0.22MPa, welding current of 8KA, welding time of 260ms, and holding time of 300ms.

9. The resistance projection welding method for the aircraft engine bracket according to claim 1, characterized in that, The spot welding parameters for the secondary projection welding are: pre-pressing time of 400ms, pressurization time of 200ms, welding pressure of 0.22MPa, welding current of 13.8KA, welding time of 260ms, and holding time of 500ms.

10. The resistance projection welding method for the aircraft engine bracket according to claim 1, characterized in that, The positioning block of the limiting clamp is also equipped with a bracket limiting device.

Images