Method for repairing surface plane defects of stainless steel structural component

Abstract

The invention discloses a method for repairing surface plane defects of a stainless steel structural member, which comprises the following steps: S1, defect positioning: observing a to-be-repaired end face of the structural member subjected to turn-milling, positioning all shrinkage cavity defect positions needing to be repaired, and marking; s2, cleaning the structural part: wiping the marked defect position and the periphery of the defect position, removing residual cutting fluid, greasy dirt and dust in processing, and then blowing a cleaning area of the structural part to remove impurities; s3, defect pre-shaping is conducted, specifically, the shrinkage cavity defect position of the repaired end face of the structural part is knocked, so that the shrinkage cavity defect is expanded to be close to a circular or conical pit; s4, welding wire pretreatment; s5, argon-laser power coordinated regulation and control repair is carried out; and S6, finishing the workpiece. According to the method, three core process steps of pre-shaping, welding wire flattening treatment and argon-laser power coordinated regulation are combined and coordinated, and cleaning and finishing procedures are supplemented, so that the deformation control problem in surface defect repair of the stainless steel structural part is solved.

Description

Technical Field

[0001] This invention belongs to the field of laser remanufacturing and special processing technology, specifically relating to a method for repairing shrinkage and porosity defects on the high-precision surface of stainless steel structural parts for aero-engines using laser melting technology. Background Technology

[0002] In the manufacturing process of high-end castings for aero-engines, large, complex, thin-walled components, such as stainless steel structural parts, are generally precision cast from high-temperature alloys. However, due to the inherent solidification shrinkage characteristics of metals, microscopic defects such as shrinkage porosity and shrinkage cavities inevitably occur inside the castings. These defects are exposed on the workpiece surface during subsequent high-precision end-face machining processes such as turning and milling, forming macroscopically visible surface defects such as pits and holes. Such defects not only severely damage the appearance integrity of the workpiece, but more importantly, they constitute potential stress concentration sources, significantly reducing the fatigue strength, mechanical properties, and wear and corrosion resistance of the material. Under the extremely harsh cyclic loads and vibration conditions of the engine, microcracks can easily initiate and propagate from these defects, leading to premature fatigue failure of components and posing a serious threat to the overall reliability and flight safety of the aircraft.

[0003] Given the crucial role of stainless steel structural components in engine load-bearing systems, their assembly surfaces have extremely stringent requirements for flatness (typically below 0.01 mm). Traditional repair processes such as arc welding, due to their large heat input and wide affected area, can trigger severe localized thermal expansion and contraction when repairing these micro-defects. This generates uncontrollable residual stress, leading to plastic deformation of the repaired area and surrounding materials, manifesting as localized surface bulges or collapses. Practice shows that the flatness after repair using traditional methods typically deteriorates to over 0.05 mm, severely exceeding the acceptable limit, ultimately rendering valuable workpieces unusable and causing significant economic losses.

[0004] Currently, most domestic manufacturers lack the capability to repair defects on such high-precision surfaces, typically requiring failed workpieces to be sent to facilities with advanced repair technologies. This not only incurs high repair costs but also involves lengthy transportation and production waiting periods, severely hindering production progress, increasing total lifecycle costs, and becoming a key bottleneck restricting production efficiency and cost control. Summary of the Invention

[0005] The purpose of this invention is to provide a method for repairing surface defects of stainless steel structural components, addressing the technical problems described in the background art.

[0006] The technical solution of this invention: A method for repairing surface defects in stainless steel structural components includes the following steps: S1: Defect location: Observe the end face of the structural part to be repaired after turning and milling, locate all shrinkage defects that need to be repaired, and mark them; S2: Structural component cleaning: Wipe the marked defect locations and their surroundings to remove residual cutting fluid, oil, and dust. Then, blow the cleaning area of ​​the structural component to remove impurities. S3: Defect pre-shaping: The location of shrinkage defects on the repair end face of the structural component is tapped to expand the shrinkage defects to a near-circular or conical pit. S4: Welding wire pretreatment: Select welding wire that matches the composition of the base material of the structural component, and tap the welding wire to make it into a flat strip. S5: Argon-Laser Power Coordinated Control Repair: The pre-shaped structural component is clamped on the laser processing worktable, and the surface to be repaired is adjusted to be horizontal. The positions of the laser head and the wire feeding mechanism are adjusted so that the laser focus, the wire feeding nozzle outlet, and the defect point are aligned. Then, the argon gas flow rate parameters and laser power parameters are set. Finally, the end of the pre-treated welding wire is sent directly above the defect to contact the substrate of the structural component, and then laser cladding is performed. S6: Workpiece finishing: After completing step S5, the repair area of ​​the structural component is repaired by fitter to make the surface accuracy <0.01mm.

[0007] In step S2, the wiping is performed using non-woven fabric or medical absorbent cotton soaked in acetone.

[0008] In step S3, a wooden or rubber mallet is used to strike the pit 1-2 times, increasing the opening diameter of the circular or conical pit to 0.4-0.5 mm.

[0009] In step S4, the diameter of the welding wire is 1.2 mm, and the thickness of the flat strip is between 1 / 2 and 1 / 3 of the diameter of the welding wire.

[0010] In step S5, the argon purity is ≥99.999%, the argon flow rate is 8-10 L / min, and the laser power is between 50-60%.

[0011] In step S5, the laser cladding adopts a short-time, multiple-intermittent control operation mode, and the single laser irradiation time is controlled within the range of 0.5-0.7s.

[0012] The intermittent control operation method includes the following steps: a1. After a single irradiation of the structural component, immediately remove the laser spot and stop feeding the welding wire; a2. Wait for the structural components to cool naturally to room temperature in the air before proceeding with the next laser cladding operation; a3. Repeat steps a1 and a2 2 to 4 times until the cladding metal is 0.05-0.1 mm above the substrate plane.

[0013] In step S2, the purging is performed using dry, clean compressed nitrogen or air gun at a pressure of 0.3-0.5 MPa.

[0014] The beneficial effects of this invention are: This invention solves the deformation control problem in the repair of surface defects in stainless steel structural components by combining and synergizing three core process steps: "pre-shaping," "welding wire flattening," and "argon-laser power coordinated control," supplemented by cleaning and finishing processes. This method offers controllable heat input, a small heat-affected zone, and a repair area free of defects such as porosity and incomplete fusion. The mechanical properties match the substrate, and the final precision meets stringent assembly specifications, breaking the dependence on foreign technologies for such advanced repair techniques. Detailed Implementation

[0015] This invention provides a method for repairing surface defects in stainless steel structural components, comprising the following steps: S1: Defect location: Observe the end face of the structural part to be repaired after turning and milling, locate all shrinkage defects that need to be repaired, and mark them; In this step, the specific operations are as follows: First, the end face of the stainless steel structural component to be repaired after milling and turning is observed macroscopically and microscopically to accurately locate all shrinkage defects that need to be repaired, and make tiny marks using a marker pen. The workpiece is then fixed on a clean work platform to ensure that there is no vibration or displacement during the operation.

[0016] In this application, the structural component being addressed is a stainless steel structural component.

[0017] S2: Structural component cleaning: Wipe the marked defect locations and their surroundings to remove residual cutting fluid, oil, and dust. Then, blow the cleaning area of ​​the structural component to remove impurities. Wiping is done using non-woven fabric or medical absorbent cotton soaked in acetone.

[0018] The purging process uses dry, clean compressed nitrogen or air guns at a pressure of 0.3-0.5 MPa.

[0019] The specific procedure for this step is as follows: Using tweezers, hold a non-woven fabric or medical absorbent cotton ball, dip it in analytical grade acetone, and repeatedly and carefully wipe the marked defect location and its surrounding area of ​​at least 10 mm to thoroughly remove residual cutting fluid, oil, and dust. Then, immediately use dry, clean compressed nitrogen or an air gun (pressure controlled at 0.3-0.5 MPa) to blow the cleaned area at an angle approximately perpendicular to the surface, ensuring that acetone and all loose impurities inside and on the surface of the defect are completely removed. The area should ultimately appear metallic and free of any visible contaminants.

[0020] S3: Defect pre-shaping: The location of shrinkage defects on the repair end face of the structural component is tapped to expand the shrinkage defects to a near-circular or conical pit. Use a wooden or rubber mallet to strike the pit 1-2 times, increasing the opening diameter of the circular or conical indentation to 0.4-0.5 mm.

[0021] The specific procedure for this step is as follows: Select a punch with a tip angle of approximately 90° and align its tip with the center of the cleaned shrinkage cavity defect. Use a small wooden or rubber mallet to gently and precisely tap the tail of the punch 1-2 times. Control the force applied during this process, aiming to expand the irregular original defect into a regularly shaped, slightly larger, approximately circular or conical pit, with an opening diameter of approximately 0.4-0.5 mm. This operation should be performed under a stereomicroscope to avoid excessive tapping that could cause plastic deformation of the substrate or create new cracks.

[0022] In this invention, the center punch, also known as a centering punch, dotting punch, or foreign punch, is a commonly used positioning tool in metal processing fields such as machining, fitter work, and mold making. Its main function is to pre-hammer a small indentation (center point) on the material surface, providing precise positioning and guidance for subsequent processing steps.

[0023] S4: Welding wire pretreatment: Select welding wire that matches the composition of the base material of the structural component, and tap the welding wire to make it into a flat strip. The diameter of the welding wire is 1.2 mm, and the thickness of the flat strip is between 1 / 2 and 1 / 3 of the diameter of the welding wire.

[0024] The specific steps are as follows: Select a nickel-based high-temperature alloy welding wire with a nominal diameter of 1.2mm that matches the composition of the structural component's base material. Cut a suitable length of welding wire and place it on a flat, smooth steel platform. Use a flat-headed hammer to evenly strike it, deforming it into a flat strip of uniform thickness. Measure with a micrometer to ensure that the final thickness is controlled between 1 / 2 and 1 / 3 of the original diameter, i.e., within the range of 0.4mm to 0.6mm. During the striking process, care should be taken to avoid introducing obvious transverse creases or burrs.

[0025] S5: Argon-Laser Power Coordinated Control Repair: The pre-shaped structural component is clamped on the laser processing worktable, and the surface to be repaired is adjusted to be horizontal. The positions of the laser head and the wire feeding mechanism are adjusted so that the laser focus, the wire feeding nozzle outlet, and the defect point are aligned. Then, the argon gas flow rate parameters and laser power parameters are set. Finally, the end of the pre-treated welding wire is sent directly above the defect to contact the substrate of the structural component, and then laser cladding is performed. Argon purity ≥ 99.999%, argon flow rate 8-10 L / min, laser power between 50-60%.

[0026] In this invention, the wire feeding mechanism, commonly referred to as a wire feeder or wire feeding system, is a key actuator in automated welding equipment (such as MIG / MAG welding, flux-cored wire welding, and some TIG welding). Its core function is to stably, continuously, and at adjustable speed "push" or "pull" the welding wire from the wire spool to the welding arc area. It is a type of welding equipment.

[0027] The specific steps for this process are as follows: Clamp the pre-treated workpiece onto the laser processing table, ensuring that the surface to be repaired is in a horizontal position. Adjust the position of the laser head (preferably a fiber laser or a disk laser) and the wire feeding mechanism to ensure that the laser focus, the wire feeding nozzle exit, and the defect point are precisely aligned.

[0028] Parameter settings: Turn on the high-purity argon gas (purity ≥99.999%) gas path, and set and stabilize the protective gas flow rate at 9 L / min (within the preferred range of 8-10 L / min). Set the laser power to 55% of its rated output power (within the preferred range of 50%-60%).

[0029] Repair procedure: The flattened welding wire tip is fed directly above the defect, making slight contact with the substrate. Pulsed laser cladding is then performed. The duration of each laser irradiation is strictly controlled within the range of 0.5-0.7 seconds. At the moment of laser irradiation, the tip of the welding wire and the micro-area at the edge of the substrate defect melt simultaneously, forming a tiny molten pool. The molten metal then flows into the defect through capillary action.

[0030] Laser cladding employs a short-duration, multiple-intermittent control operation mode, with the duration of a single laser irradiation controlled within the range of 0.5-0.7 seconds.

[0031] The intermittent control operation method includes the following steps: a1. After a single irradiation of the structural component, immediately remove the laser spot and stop feeding the welding wire; a2. Wait for the structural components to cool naturally to room temperature in the air before proceeding with the next laser cladding operation; a3. Repeat steps a1 and a2 2 to 4 times until the cladding metal is 0.05-0.1 mm above the substrate plane.

[0032] The specific operation of this step is as follows: immediately remove the laser spot after a single irradiation and stop wire feeding. Wait for the workpiece to cool naturally to room temperature in the air (usually requiring an interval of 1-2 minutes). Only after confirming cooling by using an infrared thermometer or by touch can the next laser cladding operation be performed. Depending on the defect depth, this "irradiation-cooling" process usually needs to be repeated 2 to 4 times until the cladding metal is slightly higher than the surrounding substrate plane by about 0.05-0.1 mm.

[0033] S6: Workpiece finishing: After completing step S5, the repair area of ​​the structural component is repaired by fitter to make the surface accuracy <0.01mm.

[0034] The specific steps for this process are as follows: After laser repair, the workpiece is sent to a precision fitter's workbench. A senior fitter carefully scrapes and grinds the raised cladding metal in the repair area using tools such as a fine oilstone and diamond file. The flatness of the repair area and its surroundings needs to be frequently checked using a knife-edge straightedge (or a flat surface and feeler gauge), ultimately finishing to the assembly requirement that the flatness error of the entire end face is no greater than 0.01mm (one thread). After finishing, fine-grit sandpaper can be used for polishing to make the surface finish consistent with the substrate.

[0035] The end face of the structural component repaired using the above-described process showed no new defects such as cracks or porosity detected by penetrant testing (PT). Metallographic examination revealed a dense metallurgical bond between the repaired area and the substrate, with an extremely narrow heat-affected zone (<100μm). After installation and testing, the repaired component operated stably and met all performance indicators. This invention successfully achieved the repair goals of high precision, low deformation, and high performance.

[0036] This invention solves the deformation control problem in the repair of surface defects in structural components by combining and synergizing three core process steps: "pre-shaping," "welding wire flattening," and "argon-laser power coordinated control," supplemented by cleaning and finishing processes. This method offers controllable heat input, a small heat-affected zone, and a repair area free of defects such as porosity and incomplete fusion. The mechanical properties match the substrate, and the final precision meets stringent assembly specifications, breaking the dependence on foreign technologies for such advanced repair techniques.

Claims

1. A method for repairing surface defects in stainless steel structural components, characterized in that... Includes the following steps: S1: Defect location: Observe the end face of the structural part to be repaired after turning and milling, locate all shrinkage defects that need to be repaired, and mark them; S2: Structural component cleaning: Wipe the marked defect locations and their surroundings to remove residual cutting fluid, oil, and dust. Then blow the cleaning area of ​​the structural component to remove impurities. S3: Defect pre-shaping: The location of shrinkage defects on the repair end face of the structural component is tapped to expand the shrinkage defects to a near-circular or conical pit. S4: Welding wire pretreatment: Select welding wire that matches the composition of the base material of the structural component, and hammer the welding wire to make it into a flat strip. S5: Argon-Laser Power Coordinated Control Repair: The pre-shaped structural component is clamped on the laser processing worktable, and the surface to be repaired is adjusted to be horizontal. The positions of the laser head and the wire feeding mechanism are adjusted so that the laser focus, the wire feeding nozzle outlet, and the defect point are aligned. Then, the argon gas flow rate parameters and laser power parameters are set. Finally, the end of the pre-treated welding wire is sent directly above the defect to contact the substrate of the structural component, and then laser cladding is performed. S6: Workpiece finishing: After completing step S5, the repair area of ​​the structural component is repaired by fitter to make the surface accuracy <0.01mm.

2. The method for repairing surface defects of stainless steel structural components according to claim 1, characterized in that: In step S2, the wiping is performed using non-woven fabric or medical absorbent cotton soaked in acetone.

3. The method for repairing surface defects of stainless steel structural components according to claim 1, characterized in that: In step S3, a wooden or rubber mallet is used to strike the pit 1-2 times, increasing the opening diameter of the circular or conical pit to 0.4-0.5 mm.

4. The method for repairing surface defects of stainless steel structural components according to claim 1, characterized in that: In step S4, the diameter of the welding wire is 1.2 mm, and the thickness of the flat strip is between 1 / 2 and 1 / 3 of the diameter of the welding wire.

5. The method for repairing surface defects of stainless steel structural components according to claim 1, characterized in that: In step S5, the argon purity is ≥99.999%, the argon flow rate is 8-10 L / min, and the laser power is between 50-60%.

6. The method for repairing surface defects of stainless steel structural components according to claim 1, characterized in that: In step S5, the laser cladding adopts a short-time, multiple-intermittent control operation mode, and the single laser irradiation time is controlled within the range of 0.5-0.7s.

7. The method for repairing surface defects of stainless steel structural components according to claim 6, characterized in that: The intermittent control operation method includes the following steps: a1. After a single irradiation of the structural component, immediately remove the laser spot and stop feeding the welding wire; a2. Wait for the structural components to cool naturally to room temperature in the air before proceeding with the next laser cladding operation; a3. Repeat steps a1 and a2 2 to 4 times until the cladding metal is 0.05-0.1 mm above the substrate plane.

8. The method for repairing surface defects of stainless steel structural components according to claim 1, characterized in that: In step S2, the purging is performed using dry, clean compressed nitrogen or air gun at a pressure of 0.3-0.5 MPa.