CO2 laser welding of front and rear air-conditioni

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Research on CO2 laser welding of front and rear cooling ducts of new aero-engine <1 PCT patent application/p>

aero gas turbine engine has high thrust to weight ratio and high combustion chamber temperature. The high-temperature air flow generated in the flame tube is ejected into the guide vane. The front and rear cold air ducts installed in the guide vane are used to cool and adjust the temperature field in the vane cavity. The air flow in the cold air duct has two flow paths, one is flowing out along the axial direction of the duct, and the other is flowing to the inner cavity of the blade through the small hole on the pipe wall. Obviously, the cold air duct is subject to tension and temperature stress

the cold air duct is made of nickel base deformed high-temperature alloy incol 625, which is a thin wall part of Jinan new era Gold Testing Instrument Co., Ltd. welcome users to visit. The thickness is only 0.2mm. The product requires weld joint, no overlap, no filler, uniform weld appearance and no cracks. After welding, it must meet the mold cavity matching with the inner cavity of the guide blade, so it requires small deformation

for this part, the manufacturer once listed it as a key problem to be tackled. A variety of welding methods were used for testing, but they could not meet the technical requirements. Finally, the manufacturer and the calibration decided to combine and use laser welding to tackle the problem

1 design of test scheme

1.1 preparation of workpiece

because the workpiece is too thin, it puts forward higher requirements for the preparation of workpiece without filler: 1) the forming size of parts should be accurate; 2) When WEDM is performed after forming, ensure that the electrode wire cuts in the direction consistent with the normal of the surface to be cut of the cold air duct

1.2 making of cores

process red copper cores on the CNC milling machine, with a group of front and rear air-conditioning duct cores respectively

1.3 cleaning before welding

(1) pickling: add 130g hydrofluoric acid and 300g ferric sulfate to 1L water at 60 ~ 70 ℃, and soak the weldment in the solution for 15 ~ 20min

(2) neutralization: add 8 ~ 10g NaOH and 30 ~ 50g Na 2 CO 3 into 1L water at 60 ℃ and soak the weldment for 1 ~ 2min

(3) ultrasonic cleaning: after washing the parts, use ultrasonic cleaning for 1H

(4) clean the parts to be welded with degreasing cotton ball dipped in acetone

(5) do not touch the parts to be welded by hand during assembly

1.4 tooling and assembly requirements

(1) the misalignment of both sides of the weld shall not be greater than 0.08mm; (2) On the whole weld, the pre welding assembly clearance shall not be greater than 0.05mm; (3) Apply clamping force in the direction perpendicular to the longitudinal direction of the weld; (4) Apply pressing force on the core and the place to be welded; (5) The position to be welded shall closely fit with the core, and the gap shall not be greater than 0.05mm; (6) The distance between the pressure blocks on both sides of the place to be welded and the weld center is 3 ~ 5mm; (7) A 10mm long allowance is reserved for the weld size

1.5 inspection, grinding and cleaning of the core at any time during the welding process

when welding an air-conditioning duct, carefully knock the core with a wooden board, and carefully check whether there is ablation at the corresponding position with the weld after taking it out. If there is any ablation, grind it in time. Carefully clean with acetone before installing the new conduit

1.6 selection of focal length of focus lens

the focus lens with longer focal length should be used to improve the focal depth. The expression of focal depth L is

, where l - focal depth, K - beam quality coefficient, F - focal length of focusing lens, the actual structural yield of the company in 2016 and 2017 increased by 2.02% and 1.76% respectively, and D - laser beam diameter before focusing. According to formula (1), the focal depth is proportional to the square of the focal length of the focusing lens. The increase of focal depth will reduce the sensitivity of welding quality to weld misalignment, which is particularly important for thin plate welding. In this study, a rotating paraboloid reflector is used for focusing, with a focal length of f=200mm

1.7 defocusing amount

positive defocusing and defocusing amount were used in this study Δ f=+5 mm。

1.8 laser power

the experiment was carried out on the rs850 5 kW CO 2 laser imported from Germany, and the output power can reach 5.5 kW. The laser has three operation modes: constant current control, constant power control and program automatic control

the final selected laser power of this part is 1050W, and the constant power operation mode is adopted. Under normal conditions, the power fluctuation shall not be greater than 3%

1.9 selection of other process parameters

according to the comprehensive performance of the numerical control workbench, the welding speed is selected as 2.2m/min, he gas protection is adopted, and the flow is 5l/min

2 test results and analysis

results show that the weld appearance is flat, the width is uniform, the deformation is minimal, there is no crack through fluorescent inspection, and the product qualification rate reaches more than 90%. The tensile strength of the weld can reach more than 95% of the base metal

the metallographic analysis of the weld shows that the heat affected zone of the weld is very small, almost zero, and the grain growth in the fusion zone is not obvious, which is caused by the concentrated heating, less heat input and fast welding speed of laser welding. There are obvious junctions in the weld fusion zone, and the results obtained from different tensile test speeds are also different. The needle like structure deep into the liquid phase is formed on the crystal surface, and there are short secondary crystals in the transverse direction of the needle like structure. There are dispersed, granular and black carbide precipitates at austenite grains and grain boundaries, which can hinder the dislocation movement and improve the strength of the material

the structure in the center of the weld is equiaxed austenite dendrite, which is due to the relatively slow heat conduction in the center of the weld, the small temperature gradient relative to the fusion zone, the fast crystallization speed, and the large degree of supercooling in the liquid phase, which can nucleate in the liquid phase far away from the interface to form equiaxed dendrite

fracture analysis shows that the fracture belongs to microporous polymeric fracture, and a large number of dimples can be seen from the fracture morphology. The short and curved white part in the figure is the tearing edge of the early fracture, the protruding part of the tearing edge is small, and the dimples are shallow and discontinuous; The large white bending part in the figure is the late fracture part. Due to large plastic deformation, the tearing edge is large and continuous. The reason is that some carbide precipitates with small plasticity are distributed at the bottom of the dimple. When the weld is stressed, the plastic deformation first occurs at the boundary of the grain containing carbide. When the plastic deformation reaches a certain degree, dislocation accumulation occurs at some parts, resulting in the formation of microcracks. When the load continues, the microcracks expand and connect until the final fracture

3 service condition

after repeated research and test, six sets of front and rear air-conditioning ducts have been successfully welded. Two of them have been tested on the ground, and the front and rear air-conditioning ducts are in good condition

the success of CO2 laser welding of front and rear air-conditioning ducts is the first time in the welding of similar parts of domestic aero-engine, which accelerates the development progress of aero-engine

4 conclusion

(1) the design requirements for front and rear cold air duct laser welding equipment are reasonable, and the selected process parameters are appropriate

(2) the front and rear cold air ducts with thickness of 0.2mm and material of Inconel 625 are welded by continuous CO 2 laser, and the tensile strength of the weld can reach more than 95% of the base metal

(3) the ground test of aeroengine shows that CO 2 laser welding is successful in the welding of front and rear cold air ducts. (end)

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