An engine line brazing process

Abstract

The application discloses an aero-engine pipeline brazing welding process and relates to the technical field of aero-engine manufacturing, aiming to solve the problems of many welding defects and difficult repair of small-diameter, thin-wall semi-ring pipeline welding. The process comprises four steps of welding preparation, welding material selection, flame brazing operation and post-welding detection. The welding position is ensured to be free of impurities through ultrasonic cleaning and acetone / alcohol secondary cleaning before welding; the brazing filler metal HLCuNi30-2-0.2 with stronger adaptability is selected, and the special brazing flux with boric acid 80%±1%, borax 14.5%±1% and calcium fluoride 5.5%±1% is matched; all the welds are synchronously heated during welding, the heating rate is controlled to avoid local overheating, and the brazing filler metal is uniformly filled in the gap; and the defects such as insufficient X-ray detection weld curve, incomplete fusion and porosity are detected after welding. The process is designed for the 0Cr18Ni9 stainless steel pipeline with a diameter of 6-8 mm and a wall thickness of 1 mm, has high standardization degree and good repeatability, and effectively improves the weld quality and production efficiency.

Description

Technical Field

[0001] This invention relates to the field of aero-engine manufacturing technology, specifically to a brazing process for engine pipelines. Background Technology

[0002] As a key component of the fuel system of an aero-engine, the fuel manifold is the main pipeline that supplies fuel to the fuel nozzles in the combustion chamber. It is formed by welding various parts into a ring pipeline. The quality of the weld directly determines the strength and service life of the parts, and thus affects the normal operation of the engine. In existing technologies, engine fuel mains are mostly welded using flame brazing. The main material is a 0Cr18Ni9 stainless steel conduit with a diameter of 6 / 8 mm and a wall thickness of 1 mm. It is assembled from the main pipe and multiple joints through more than ten weld seams, with all weld seams completed in a single process. However, the welding process for such small-diameter, thin-walled semi-ring-shaped parts presents numerous technical challenges: the large number of weld seams, high assembly requirements, and significant control difficulties; compared to other welding methods, flame brazing offers fewer means for controlling weld quality; and the small pipe diameter makes fine-tuning during welding difficult, leading to numerous uncertainties. In actual production, fuel mains processed using traditional flame brazing technology (using BAg50CuZnCd brazing filler metal and QJ103 or 1802PF flux) frequently exhibit defects such as insufficient weld seam curves during X-ray inspection, and these defects are irregularly distributed at the weld seams of various joints. After rework, the gaps between parts increase, and the difficulty of achieving satisfactory rework increases significantly with the number of reworks. The second-time rework pass rate is extremely low, seriously affecting production efficiency and product quality.

[0003] Therefore, we propose a brazing process for engine pipes. Summary of the Invention

[0004] The purpose of this invention is to provide a brazing process for engine pipelines, which solves the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a brazing process for engine pipelines, comprising the following process steps: Step 1: Pre-welding preparation: First, use ultrasonic cleaning to remove surface oil, oxide scale and other impurities from the main pipeline and joints. Then, use acetone or alcohol to clean the area to be welded a second time to ensure that there are no contaminants left in the welding area. Finally, assemble the cleaned joints with the main pipeline to ensure that the assembly gap is uniform and meets the basic assembly requirements of flame brazing. Step 2, Selection of Welding Materials: HLCuNi30-2-0.2 brazing filler metal is selected, and the matching flux consists of boric acid, borax, and calcium fluoride, with the following mass fractions: boric acid 80%±1%, borax 14.5%±1%, and calcium fluoride 5.5%±1%. Step 3, Flame Brazing Operation: Adjust the parameters of the flame brazing equipment, ignite the flame and evenly direct it to all areas to be welded for synchronous heating. Control the heating rate to avoid local overheating. When the area to be welded reaches the brazing temperature, fill the weld with the brazing filler metal and the flux to ensure that the brazing filler metal fully wets the surface to be welded and evenly fills the weld gap. After welding, allow it to cool naturally to room temperature. Step 4: Post-weld inspection: Use X-ray inspection to check for defects in the weld and ensure that the weld quality meets the standard requirements.

[0006] In a preferred embodiment of the present invention, the ultrasonic cleaning time during the pre-welding preparation is 15-20 minutes. During the secondary cleaning, the area to be welded is repeatedly wiped with a cloth soaked in acetone or alcohol to ensure that there are no residual impurities.

[0007] In a preferred embodiment of the present invention, the control range of the assembly gap is consistent with the assembly gap of the same type of flame-brazed small-diameter pipe parts previously processed by the center, ensuring that the joint fits evenly with the main pipeline.

[0008] As a preferred embodiment of the present invention, the flux HLCuNi30-2-0.2 is more suitable for welding small-diameter pipes with a diameter of 6-8mm than the traditional flux BAg50CuZnCd, thus preventing the flux from flowing out of the welding area before solidification.

[0009] In a preferred embodiment of the present invention, during the flame brazing operation, when the areas to be welded are heated synchronously, all weld seams are within the flame heating coverage area, and the flame is kept focused on a single weld seam area for a long time during the heating process to avoid local overheating and deformation.

[0010] In a preferred embodiment of the present invention, the defect detection range of the post-weld inspection includes insufficient weld curve band, lack of fusion, and porosity.

[0011] In a preferred embodiment of the present invention, the engine pipeline includes a main pipeline and a connector. The main pipeline is made of 0Cr18Ni9 stainless steel, with a diameter of 6-8mm and a wall thickness of 1mm. The radius of the main semi-circle is R238mm.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention optimizes the selection of brazing filler metal and flux, using HLCuNi30-2-0.2 brazing filler metal with better fluidity for welding small-diameter pipes, and a specific ratio of flux, effectively solving the defect of insufficient weld curve in traditional processes; The process is specifically designed for small-diameter, thin-walled semi-ring type engine pipelines with a diameter of 6-8mm and a wall thickness of 1mm. It fully considers the structural characteristics and welding difficulties of such parts. During the welding process, the filler metal has uniform flow and good filling effect, which can meet the welding requirements of complex pipeline structures. By clarifying the pre-welding cleaning process, welding material ratio, and key points of welding operation, a standardized welding process has been formed, reducing uncertainties in the welding process and ensuring good process repeatability. Attached Figure Description

[0013] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a process flow diagram of the present invention; Figure 2 This is a schematic diagram of the fuel main pipe of the present invention; Figure 3 This is a schematic diagram of the pipe joint assembly of the present invention. Detailed Implementation

[0014] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0015] like Figure 1-3 As shown, a brazing process for engine pipelines is described. This process is for brazing 0Cr18Ni9 stainless steel engine pipelines (including the main pipeline and multiple joints) with a diameter of 6-8mm, a wall thickness of 1mm, and a main body semi-circular radius of R238mm. The aim is to ensure stable and reliable weld quality through standardized and refined operations, meeting the usage requirements of key components such as the fuel main pipe of aero engines. The specific implementation steps are as follows: Pre-welding preparation Parts Cleaning Procedure: First, place the main pipe and all joints to be welded into the ultrasonic cleaning equipment. Set the cleaning temperature to 40-50℃ and strictly control the cleaning time to 18 minutes (within the standard range of 15-20 minutes). Through the high-frequency vibration of the ultrasonic waves, thoroughly remove oil, oxide scale, and processing debris adhering to the surface of the parts. After cleaning, remove the parts and allow them to air dry naturally. Then, perform a second cleaning using acetone with a purity ≥99.5%. Cut a clean cloth into 5cm×5cm pieces, soak it in an appropriate amount of acetone, and repeatedly wipe the areas to be welded in one direction. Wipe each area at least three times to avoid secondary adhesion of impurities. For areas inside the joints that are difficult to clean, use cotton wool soaked in acetone wrapped around a thin wire to clean the inside, ensuring that no contaminants remain at the welded area.

[0016] Assembly Operation: Based on the center's previous assembly standards for processing similar small-diameter flame-brazed parts, the assembly gap between the main pipeline and the connector is controlled between 0.08-0.15mm. During assembly, a dedicated positioning fixture is used to precisely align the connector to the preset welding position on the main pipeline. The elastic clamping mechanism of the fixture ensures uniform fixation, preventing gap deviations caused by uneven force during assembly. After assembly, a feeler gauge is used to check each assembly gap individually, with check points spaced no more than 3mm apart, ensuring uniform and tight fit without looseness or excessively large gaps in any area, meeting the basic assembly requirements for flame brazing.

[0017] Welding material preparation Brazing filler metal selection and pretreatment: HLCuNi30-2-0.2 brazing filler metal is selected. Compared with the traditional brazing filler metal BAg50CuZnCd, this filler metal has better fluidity and is more suitable for welding small-diameter pipes. Before use, the filler metal is visually inspected to ensure that its surface is free of defects such as oxidation, cracks, and inclusions. Then, the filler metal is cut into small segments with a length of 5-8mm, each segment weighing 0.3-0.5g. These segments are pre-packaged according to the number of welds to facilitate quick access during welding and avoid waste or insufficient filler metal usage.

[0018] Flux Preparation and Storage: Accurately weigh the raw materials according to the mass fraction ratio, which is 80% boric acid, 14.5% borax, and 5.5% calcium fluoride. The purity of all raw materials must meet the industrial grade 1 standard. Place the weighed boric acid, borax, and calcium fluoride into a high-speed mixer and mix at 300 rpm for 20 minutes at room temperature to ensure uniform dispersion of each component. Store the prepared flux in a sealed container in a dry, cool environment to prevent moisture absorption from affecting its performance. Before use, check the flux condition; if lumps appear, crush and sieve it.

[0019] Flame brazing operation Equipment commissioning: An oxy-acetylene flame brazing device was selected. The oxygen pressure was adjusted to 0.3 MPa and the acetylene pressure to 0.05 MPa. After ignition, the flame properties were adjusted to a neutral flame to ensure stable combustion without flame deviation or flame detachment. The distance between the flame nozzle and the area to be welded was adjusted using the device's moving mechanism, maintaining it between 15-20 mm to ensure comprehensive heating coverage.

[0020] Simultaneous heating: Fix the assembled piping assembly onto the rotary table, start the table to rotate slowly at 5 r / min, and simultaneously turn on the flame heating. During the heating process, the operator visually observes and monitors in real time with a temperature gauge, controlling the heating rate to 5-8℃ / s to ensure that all weld seams are within the flame heating coverage area, avoiding prolonged flame focus on a single weld area. When the temperature gauge shows that the temperature of the area to be welded has reached the brazing critical temperature, maintain the heating state for 30 seconds to allow the temperature to diffuse evenly across the entire welding interface.

[0021] Filling with brazing filler metal and flux: While maintaining heating, use a specialized feeding tool to evenly place the pre-made brazing filler metal segments at each weld joint, while simultaneously sprinkling an appropriate amount of prepared flux. The ratio of flux to brazing filler metal is controlled at 1:3 to ensure that the flux can fully remove the oxide film at the weld interface and promote brazing filler metal wetting. During the filling process, the brazing filler metal is guided to flow evenly along the weld joint gap by rotating the rotary table and slightly adjusting the flame, ensuring that the brazing filler metal fully wets the surface to be welded and fills the entire weld joint gap without any omissions or unfilled areas.

[0022] Cooling process: After filling is completed, turn off the flame heating and let the piping assembly cool naturally to room temperature on the original workbench. Avoid touching or moving the assembly during the cooling process to prevent weld deformation or incomplete solidification of the brazing filler metal.

[0023] Post-weld inspection Visual inspection: After cooling, first conduct a visual inspection to observe whether the weld surface is flat and smooth, without obvious defects such as porosity, cracks, lack of fusion, or excessive brazing filler metal flow. The weld formation should be uniform and consistent, with the width controlled between 2-3 mm.

[0024] X-ray inspection: All welds were comprehensively inspected using industrial X-ray flaw detection equipment. The inspection parameters were set as follows: tube voltage 100kV, tube current 5mA, and exposure time 30s. During inspection, each weld was scanned sequentially according to its distribution, with a focus on checking the sufficiency of the weld curve band and the presence of defects such as incomplete fusion and porosity. For any defects found, their location, size, and type were recorded. If a defect exceeded standard requirements, targeted rework was required; if the defect was small and within acceptable limits, a proper inspection record was kept and archived.

[0025] In summary, this invention effectively solves the defect of insufficient weld curve band in traditional processes by optimizing the selection of brazing filler metal and flux, using HLCuNi30-2-0.2 brazing filler metal with better fluidity suitable for welding small-diameter pipes, and matching it with a specific ratio of flux. The process is specifically designed for small-diameter, thin-walled semi-annular engine pipes with a diameter of 6-8mm and a wall thickness of 1mm, fully considering the structural characteristics and welding difficulties of such parts. During the welding process, the brazing filler metal has uniform fluidity and good filling effect, which can meet the welding requirements of complex pipe structures. By clarifying the pre-welding cleaning process, welding material ratio, and key points of welding operation, a standardized welding process is formed, reducing the uncertainty in the welding process and ensuring good process repeatability.

[0026] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or basic characteristics. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0027] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A brazing process for engine pipes, characterized in that: The process includes the following steps: Step 1: Pre-welding preparation: First, use ultrasonic cleaning to remove surface oil, oxide scale and other impurities from the main pipeline and joints. Then, use acetone or alcohol to clean the area to be welded a second time to ensure that there are no contaminants left in the welding area. Finally, assemble the cleaned joints with the main pipeline to ensure that the assembly gap is uniform and meets the basic assembly requirements of flame brazing. Step 2, Selection of Welding Materials: HLCuNi30-2-0.2 brazing filler metal is selected, and the matching flux consists of boric acid, borax, and calcium fluoride, with the following mass fractions: boric acid 80%±1%, borax 14.5%±1%, and calcium fluoride 5.5%±1%. Step 3, Flame Brazing Operation: Adjust the parameters of the flame brazing equipment, ignite the flame and evenly direct it to all areas to be welded for synchronous heating. Control the heating rate to avoid local overheating. When the area to be welded reaches the brazing temperature, fill the weld with the brazing filler metal and the flux to ensure that the brazing filler metal fully wets the surface to be welded and evenly fills the weld gap. After welding, allow it to cool naturally to room temperature. Step 4: Post-weld inspection: Use X-ray inspection to check for defects in the weld and ensure that the weld quality meets the standard requirements.

2. The brazing process for engine pipelines according to claim 1, characterized in that: During the pre-welding preparation, the ultrasonic cleaning time is 15-20 minutes. During the secondary cleaning, the area to be welded is repeatedly wiped with a cloth soaked in acetone or alcohol to ensure that there are no residual impurities.

3. The brazing process for engine pipelines according to claim 1, characterized in that: The control range of the assembly gap is consistent with the assembly gap of the same type of flame-brazed small-diameter parts previously processed by the center, ensuring that the joint fits evenly with the main pipeline.

4. The brazing process for engine pipelines according to claim 1, characterized in that: The flux of the HLCuNi30-2-0.2 brazing filler metal is more suitable for welding small-diameter pipes with a diameter of 6-8mm than that of the traditional brazing filler metal BAg50CuZnCd, thus preventing the filler metal from flowing away from the welding area before solidification.

5. The brazing process for engine pipelines according to claim 1, characterized in that: In the flame brazing operation, when the areas to be welded are heated synchronously, all weld seams are within the flame heating coverage area, and the flame is kept focused on a single weld seam area for a long time during the heating process to avoid local overheating and deformation.

6. The brazing process for engine pipelines according to claim 1, characterized in that: The defect detection range of the post-weld inspection includes insufficient weld curve band, lack of fusion, and porosity.

7. The brazing process for engine pipelines according to claim 1, characterized in that: The engine piping includes a main pipe and a connector. The main pipe is made of 0Cr18Ni9 stainless steel, with a diameter of 6-8mm and a wall thickness of 1mm. The radius of the main semi-circle is R238mm.

Images