A method for reducing cooling deformation of cavity parts during diffusion welding

Abstract

The present invention relates to a method for reducing cooling deformation of cavity parts by split diffusion welding, including preparation of parts to be welded; pretreatment of parts to be welded; solder stop coating; module assembly: aligning and fitting two parts to be welded up and down and positioning them to complete assembly, the total height of the assembled parts to be welded is H2, placing the assembled parts to be welded in the center of the lower template, and limiting blocks are placed on both sides of the parts to be welded, and the limiting blocks are placed between the upper and lower templates; the height of the limiting blocks is H1, 0.4mm≤H2-H1≤1.0mm; aligning the upper template with the lower template, the surface sprayed with solder stop facing the parts to be welded, placing it on the parts to be welded, completing the assembly of a group of modules; diffusion welding; when the diffusion welding insulation is finished, maintaining a vacuum state, and adjusting the axial pressurization pressure to 0.5MPa-2.0MPa until cooling is finished; post-weld measurement. The present invention provides an available reference plane for post-weld shape processing, realizes one-time clamping and alignment direct processing, and creates favorable conditions for improving efficiency and reducing costs in batch production of cavity structural parts.

Description

Technical Field

[0001] The invention belongs to the technical field of manufacturing aero-engine blades, and in particular relates to a method for reducing cooling deformation of split diffusion welding of cavity parts. Background Art

[0002] As the demand for high-performance engines in aerospace becomes more and more urgent, weight reduction and efficiency improvement have become one of the core goals of aircraft design, and cavity structural parts are undoubtedly a good choice. Cavity structural parts are generally composed of solid frames, cavity outer walls, and vertical ribs. Compared with solid structural parts, cavity structural parts have the advantages of weight reduction, reduced fuel consumption, and improved efficiency while ensuring structural stiffness and strength; combined with cavity structure topology optimization design technology, cavity structural parts can also have vibration reduction, noise reduction and integrated multi-functions, such as heat insulation, transmission of cooling air or heating gas, transmission of fuel oil, etc. Diffusion welding has become the preferred method for manufacturing cavity structural parts due to its advantages such as the non-melting of the parent material during the welding process and the joint strength being as strong as or close to the parent material.

[0003] At present, the diffusion welding manufacturing processes for cavity structural parts mainly include split diffusion welding and multi-layer plate superplastic forming / diffusion bonding (SPF / DB). Compared with the SPF / DB process, the split diffusion welding process has obvious application advantages and has become the preferred process for cavity structural parts. Typical applications include titanium alloy aircraft engine split air intake support plates (also called rectifier support plates, split branch plates, rectifier blades) and hollow adjustable blades, rudder surfaces, wall panels, etc.

[0004] The process route for diffusion welding of cavity structural parts is generally as follows: preparation of a single piece of workpiece with cavity and ribs - pretreatment of workpiece - solder stop coating - assembly of workpiece and mold - diffusion welding - post-weld measurement - post-weld shape processing.

[0005] In the diffusion welding production of titanium alloy split air intake support plates and hollow adjustable blades, in order to control the deformation of parts diffusion welding, the diffusion welding process adopts the method of reducing the heating rate, increasing the temperature equalization section and extending the temperature holding time of the temperature equalization section, and adopts the furnace cooling (that is, vacuum cooling) method during cooling. However, the parts still have uneven height, flexural deformation, and local bulging deformation after diffusion welding, such as Figure 1-Figure 3 As shown, the height deviation can reach ≥0.1mm, the flatness and parallelism deviations are both ≥0.20mm, and the local bulge is even more random.

[0006] At the same time, the limit blocks during diffusion welding of parts are made of graphite material. The linear expansion coefficient of graphite is much lower than that of titanium alloy, and it changes less with temperature. During diffusion welding, when the upper template of the mold and the limit blocks form a mold and enter the cooling stage after diffusion welding, as the temperature in the furnace decreases, the cooling shrinkage of the graphite material is much smaller than that of the parts, which causes the parts to be demolded from the upper template of the mold. The parts cool freely in an unconstrained state, resulting in uneven cooling deformation, resulting in uneven height, flexural deformation, and local bulging deformation after diffusion welding.

[0007] In order to ensure the consistency of the final shape and wall thickness of the parts, the post-welding shape processing has to adopt the processing method of alternating ultrasonic thickness measurement and shape processing, that is, after ultrasonic wall thickness measurement, the parts are re-clamped and the processing program is adjusted according to the measurement results. The wall thickness is measured again at a certain stage of processing. It often takes three to seven repeated operations to ensure that the wall thickness and shape meet the design requirements. Repeated clamping, measurement and program adjustment work not only increases labor costs and reduces production efficiency, but also cannot be applied to mass production or automated production.

[0008] There are many patents and documents about split diffusion welding. A Chinese patent (publication number: CN102825427A, publication date: December 19, 2012) provides a split diffusion welding method for aircraft rudder components, a Chinese patent (publication number: CN106041293A, publication date: October 26, 2016) provides a vacuum diffusion welding device and method for titanium alloy rudder wing parts, a Chinese patent (publication number: CN109955042A, publication date: July 2, 2019) provides a method for preparing a titanium alloy hollow structure, and a Chinese patent (publication number: CN110508891A, publication date: November 29, 2019) provides a method for forming a titanium alloy closed ribbed hollow structure. However, none of the above patents provide a method for controlling cooling deformation of diffusion welding. Summary of the invention

[0009] In view of the shortcomings of the prior art, the present invention provides a method for reducing the cooling deformation of the split diffusion welding of cavity parts. Through the selection and design of limit block materials and the optimization of the pressure in the diffusion welding cooling process, the conformal cooling and deformation constraint of the split diffusion welding of the cavity structural parts after the diffusion welding are achieved, the uneven height, flexural deformation and local bulging deformation after welding are reduced, the flatness and parallelism accuracy of the part's outer surface are improved, and a high-precision reference plane is provided for the outer shape processing after welding, thereby improving the outer shape processing efficiency, reducing costs and shortening the processing cycle.

[0010] A method for reducing cooling deformation of cavity parts during diffusion welding comprises the following steps:

[0011] Step 1: Preparation of parts to be welded:

[0012] Prepare a single piece with prefabricated inner cavity and vertical ribs, check that the vertical rib structure is intact, and the edge of the surface to be welded is sharp and has no missing parts;

[0013] Step 2: Pretreatment of welded parts;

[0014] Step 3: Solder paste application:

[0015] Spray boron nitride solder stop on the surfaces of the upper and lower templates that contact the workpieces to be welded, and leave them to dry;

[0016] Step 4: Module assembly:

[0017] Align the two parts to be welded up and down and position them to complete the assembly. The total height of the assembled parts to be welded is H2. Place the assembled parts to be welded in the center of the lower template, and place limit blocks on both sides of the parts to be welded. The limit blocks are placed between the upper and lower templates; the height of the limit blocks is H1, 0.4mm≤H2-H1≤1.0mm; align the upper template with the lower template, with the surface sprayed with solder stop facing the parts to be welded, and place them on the parts to be welded to complete the assembly of a set of modules;

[0018] Step 5: Diffusion welding:

[0019] Place the assembled modules in an axially pressurized vacuum diffusion welding furnace and perform diffusion welding using an existing conventional diffusion welding process; when the diffusion welding insulation is completed, maintain the vacuum state and adjust the axial pressurization pressure to 0.5MPa-2.0MPa until the cooling is completed;

[0020] Step 6: Post-welding measurement:

[0021] After diffusion welding, the height of the parts is measured with a micrometer, and the flatness and parallelism of the parts are tested with a three-coordinate machine.

[0022] In the step 1, when the surface to be welded of the workpiece to be welded is a plane, the roughness of the surface to be welded Ra≤0.8μm, the flatness of the outer surface and the surface to be welded are both ≤0.03mm, and the parallelism between the two planes is ≤0.05mm; when the surface to be welded of the workpiece to be welded is a curved surface, the roughness of the surface to be welded Ra≤0.8μm, the flatness of the outer surface ≤0.03mm, and the contour of the curved surface to be welded ≤0.03mm.

[0023] The pretreatment method in step 2 is to pretreat the surface to be welded by pickling or polishing to remove residual oxides and foreign particles attached to the surface; use deionized water, anhydrous ethanol or acetone as a cleaning medium to ultrasonically clean the welded parts; after cleaning, check that there are no water stains, scratches or marks on the surface of the welded surface.

[0024] The material of the limit block in step 4 is steel or high-temperature alloy.

[0025] The beneficial effects of the present invention are as follows: the present invention proposes a method for reducing the cooling deformation of the split diffusion welding of cavity parts, realizes the conformal cooling and deformation constraint of the split diffusion welding of the cavity parts, so that the uneven height, flexural deformation and local bulging deformation of the parts after welding are reduced, and the deviation of the shape flatness and parallelism is reduced to below 0.05mm, which provides an available reference plane for the post-welding shape processing, realizes direct processing with one-time clamping and alignment, and creates favorable conditions for improving efficiency and reducing costs in mass production of cavity structural parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the longitudinal deflection deformation of a hollow part after diffusion welding in the prior art;

[0027] Figure 2 It is a schematic diagram of the bulging of the local transverse cross section of a hollow part after diffusion welding in the prior art;

[0028] Figure 3 It is a schematic diagram of the lateral deflection deformation of a hollow part after diffusion welding in the prior art;

[0029] Figure 4 A schematic diagram of clamping when performing diffusion welding of parts using the method provided by the present invention;

[0030] in,

[0031] 1-upper template, 2-lower template, 3-limiting block, 4-parts to be welded. DETAILED DESCRIPTION

[0032] In order to better explain the present invention and facilitate understanding, the technical solutions and effects of the present invention are described in detail below through specific implementation modes in conjunction with the accompanying drawings.

[0033] A method for reducing cooling deformation of cavity parts during diffusion welding comprises the following steps:

[0034] Example 1

[0035] Step 1: Preparation of welded parts 4

[0036] In this embodiment, diffusion welding is performed on a titanium alloy split structure air intake support plate, and the welded parts 4 are two titanium alloy split structure air intake support plate half blanks. Prepare a single piece with a prefabricated inner cavity and vertical ribs, check that the vertical rib structure is complete, the edge of the welded surface is sharp and has no missing edges, the roughness of the welded surface Ra ≤ 0.8 μm, the flatness of the outer surface and the welded surface are both ≤ 0.03 mm, and the parallelism between the two planes is ≤ 0.05 mm.

[0037] Step 2: Pretreatment of weldment 4

[0038] The surface to be welded is pre-treated by pickling to remove residual oxides and foreign particles attached to the surface; the welded part is cleaned ultrasonically using deionized water as a cleaning medium 4; after cleaning, check that there are no water stains, scratches or marks on the surface of the welded surface.

[0039] Step 3: Solder paste application

[0040] Boron nitride solder stopper is sprayed on the contact surfaces of the upper template 1 and the lower template 2 with the workpiece 4 to be welded, and then left to dry.

[0041] Step 4: Module assembly

[0042] Align the two parts to be welded 4 up and down and position them to complete the assembly. In this embodiment, the total height of the assembled parts to be welded 4 is H2=16±0.02mm. Place the assembled parts to be welded 4 in the center of the lower template 2, place K3 alloy limit blocks 3 on both sides of the parts to be welded 4, and place the limit blocks 3 between the upper template 1 and the lower template 2; the height of the limit blocks 3 is H1, and in this embodiment, H2-H1=0.60mm. Align the upper template 1 with the lower template 2, with the surface sprayed with solder stop facing the parts to be welded 4, and place them on the parts to be welded 4 to complete the assembly of a set of modules, such as Figure 4 shown.

[0043] Step 5: Diffusion welding

[0044] The assembled modules are placed in an axially pressurized vacuum diffusion welding furnace. In this embodiment, 3 modules are placed on one layer, and 3 layers are placed in total. The conventional diffusion welding process is used for diffusion welding. When the diffusion welding insulation is completed, the vacuum state is maintained, and the axial pressurization pressure is adjusted to 0.5MPa until the cooling is completed.

[0045] Step 6: Post-weld measurement

[0046] After diffusion welding, the height of the parts is measured with a micrometer, and the flatness and parallelism of the parts are tested with a three-dimensional coordinate machine. In this embodiment, the height deviation of the parts after welding is ≤0.03mm, and the flatness and parallelism are both ≤0.04mm.

[0047] Example 2

[0048] Step 1: Preparation of welded parts 4

[0049] In this embodiment, diffusion welding is performed on a titanium alloy split hollow adjustable blade, and the welded part 4 is a single piece of a titanium alloy split hollow adjustable blade. A single piece with a prefabricated inner cavity and vertical ribs is prepared, and the vertical rib structure is checked to be intact, the edge of the welded surface is sharp and has no missing edges, the roughness of the welded surface Ra ≤ 0.8 μm, the flatness of the outer surface ≤ 0.03 mm, and the contour of the welded curved surface ≤ 0.03 mm.

[0050] Step 2: Pretreatment of weldment 4

[0051] Polishing is used to pre-treat the surface to be welded to remove residual oxides and foreign particles attached to the surface; anhydrous ethanol is used as a cleaning medium to rinse the welded part 4; after cleaning, check that there are no water stains, scratches or scratches on the surface of the welded surface.

[0052] Step 3: Solder paste application

[0053] Boron nitride solder stopper is sprayed on the contact surfaces of the upper template 1 and the lower template 2 with the workpiece 4 to be welded, and then left to dry.

[0054] Step 4: Module assembly

[0055] Align the two parts to be welded 4 up and down and position them to complete the assembly. In this embodiment, the total height of the assembled parts to be welded 4 is H2 = 35 ± 0.02 mm. Place the assembled parts to be welded 4 in the center of the lower template 2, place 304 stainless steel limit blocks 3 on both sides of the parts to be welded 4, and place the limit blocks 3 between the upper template 1 and the lower template 2; the height of the limit blocks 3 is H1, and in this embodiment, H2-H1 = 0.90 mm. Align the upper template 1 with the lower template 2, with the surface sprayed with solder stop facing the parts to be welded 4, and place them on the parts to be welded 4 to complete the assembly of a set of modules.

[0056] Step 5: Diffusion welding

[0057] The assembled modules are placed in an axially pressurized vacuum diffusion welding furnace. In this embodiment, three modules are placed on one layer, and two layers are placed in total. The conventional diffusion welding process is used for diffusion welding. When the diffusion welding insulation is completed, the vacuum state is maintained, and the axial pressurization pressure is adjusted to 2.0 MPa until the cooling is completed.

[0058] Step 6: Post-weld measurement

[0059] After diffusion welding, the height of the parts is measured with a micrometer, and the flatness and parallelism of the parts are tested with a three-dimensional coordinate machine. In this embodiment, the height deviation of the parts after welding is ≤0.03mm, and the flatness and parallelism are both ≤0.03mm.

[0060] Example 3

[0061] Step 1: Preparation of welded parts 4

[0062] In this embodiment, diffusion welding is performed on a titanium alloy split structure air intake support plate, and the welded part 4 is a single piece of a titanium alloy split structure air intake support plate. Prepare a single piece with a prefabricated inner cavity and vertical ribs, check that the vertical rib structure is complete, the edge of the surface to be welded is sharp and has no missing edges, the roughness of the surface to be welded Ra ≤ 0.8 μm, the flatness of the outer surface and the surface to be welded are both ≤ 0.03 mm, and the parallelism between the two planes is ≤ 0.05 mm.

[0063] Step 2: Pretreatment of weldment 4

[0064] The surface to be welded is pre-treated by pickling to remove residual oxides and foreign particles attached to the surface; acetone is used as a cleaning medium to wipe the welded part 4; after cleaning, check that there are no water stains, scratches or marks on the surface of the welded surface.

[0065] Step 3: Solder paste application

[0066] Boron nitride solder stopper is sprayed on the contact surfaces of the upper template 1 and the lower template 2 with the workpiece 4 to be welded, and then left to dry.

[0067] Step 4: Module assembly

[0068] Align the two parts to be welded 4 up and down and position them to complete the assembly. In this embodiment, the total height of the assembled parts to be welded 4 is H2=16±0.02mm. Place the assembled parts to be welded 4 in the center of the lower template 2, place K3 alloy limit blocks 3 on both sides of the parts to be welded 4, and place the limit blocks 3 between the upper template 1 and the lower template 2; the height of the limit blocks 3 is H1, and in this embodiment, H2-H1=0.40mm. Align the upper template 1 with the lower template 2, with the surface sprayed with solder stop facing the parts to be welded 4, and place them on the parts to be welded 4 to complete the assembly of a set of modules, such as Figure 4 shown.

[0069] Step 5: Diffusion welding

[0070] The assembled modules are placed in an axially pressurized vacuum diffusion welding furnace. In this embodiment, 3 modules are placed on one layer, and 3 layers are placed in total. The conventional diffusion welding process is used for diffusion welding. When the diffusion welding insulation is completed, the vacuum state is maintained, and the axial pressurization pressure is adjusted to 1.0 MPa until the cooling is completed.

[0071] Step 6: Post-weld measurement

[0072] After diffusion welding, the height of the parts is measured with a micrometer, and the flatness and parallelism of the parts are tested with a three-dimensional coordinate machine. In this embodiment, the height deviation of the parts after welding is ≤0.03mm, and the flatness and parallelism are both ≤0.03mm.

[0073] In order to highlight the effect of the present invention, a comparative example is provided below:

[0074] Comparative Example 1

[0075] Step 1: Preparation of welded parts 4

[0076] In this embodiment, diffusion welding is performed on a titanium alloy split structure air intake support plate, and the welded part 4 is a single piece of a titanium alloy split structure air intake support plate. Prepare a single piece with a prefabricated inner cavity and vertical ribs, check that the vertical rib structure is complete, the edge of the surface to be welded is sharp and has no missing edges, the roughness of the surface to be welded Ra ≤ 0.8 μm, the flatness of the outer surface and the surface to be welded are both ≤ 0.03 mm, and the parallelism between the two planes is ≤ 0.05 mm.

[0077] Step 2: Pretreatment of weldment 4

[0078] The surface to be welded is pre-treated by pickling to remove residual oxides and foreign particles attached to the surface; the welded part is ultrasonically cleaned with deionized water 4; after cleaning, check that there are no water stains, scratches or marks on the surface of the welded surface.

[0079] Step 3: Solder paste application

[0080] Boron nitride solder stopper is sprayed on the contact surfaces of the upper template 1 and the lower template 2 with the workpiece 4 to be welded, and then left to dry.

[0081] Step 4: Module assembly

[0082] The two parts to be welded 4 are aligned and positioned up and down to complete the assembly. In this embodiment, the total height of the assembled parts to be welded 4 is H2 = 16 ± 0.02 mm. The assembled parts to be welded 4 are placed in the center of the lower template 2, and graphite limit blocks 3 are placed on both sides of the parts to be welded 4. The limit blocks 3 are placed between the upper template 1 and the lower template 2; the height of the limit blocks 3 is H1, and in this embodiment, H2-H1 = 0.35 mm. The upper template 1 is aligned with the lower template 2, and the surface sprayed with the solder stop faces the part to be welded 4, and is placed on the part to be welded 4 to complete the assembly of a module.

[0083] Step 5: Diffusion welding

[0084] The assembled modules are placed in an axially pressurized vacuum diffusion welding furnace. In this embodiment, 3 modules are placed on one layer, and 3 layers are placed in total. The conventional diffusion welding process is used for diffusion welding. When the diffusion welding insulation is completed, the vacuum state is maintained, and the axial pressurization pressure is adjusted to 0 MPa until the cooling is completed.

[0085] Step 6: Post-weld measurement

[0086] After diffusion welding, the height of the parts is measured with a micrometer, and the flatness and parallelism of the parts are tested with a three-dimensional coordinate machine. In this embodiment, the height deviation of the parts after welding is ≥0.1mm, and the flatness and parallelism are both ≥0.20mm.

[0087] When assembling the module of the present invention, the limit block 3 is placed between the upper template 1 and the lower template 2. During diffusion welding, the welding pressure passes through the upper template 1 to compress and deform the welded part 4. Finally, the upper template 1 contacts the limit block 3 to form a closed mold.

[0088] The material of the stop block 3 in the present invention is steel or high-temperature alloy. Compared with titanium alloy, the linear expansion coefficient of steel and high-temperature alloy at the same temperature is larger. During diffusion welding, the upper template 1 is continuously moved downward under the pressure of diffusion welding, forcing the welded part 4 to be compressed and deformed. Finally, the upper template 1 and the stop block 3 form a mold. When the diffusion welding insulation ends and enters the cooling stage, as the temperature in the furnace continues to decrease, the stop block 3 and the part are continuously cooled and shrunk, and the stop block 3 has a greater shrinkage rate, and its height is always lower than the part height. In this way, the upper template 1 will always keep in contact with the part, thereby realizing the shape-following movement and shape-following constraint of the upper template 1 relative to the part's outer surface, thereby achieving the purpose of reducing the flexural deformation and local bulging of the part.

[0089] By using the known linear expansion coefficient of steel or high-temperature alloy materials and the calculation method of metal high-temperature expansion deformation, and taking the existing conventional diffusion welding process and diffusion welding compression deformation as input, the height of the steel or high-temperature alloy limit block 3 at the diffusion welding temperature can be calculated, and appropriate corrections can be made in combination with the diffusion welding test verification, thereby ensuring that the newly introduced steel or high-temperature alloy limit block 3 is well integrated with the original diffusion welding process of the part, thereby reducing a large amount of diffusion welding process development and verification costs.

[0090] At the same time, considering that the weight of the diffusion welding mold and the upper parts is the only factor that limits the deformation of the cooling of the parts, in order to further restrict the deformation of the parts, after the insulation is completed, the axial pressure of the equipment is adjusted to 0.5MPa-2.0MPa and maintained until the end of cooling. During the cooling process, the height of the parts and the diffusion welding molds decreases with the decrease of the temperature in the furnace. That is to say, relative to the axial pressure head, the parts and the diffusion welding molds are always in a state of being about to be separated. This requires the axial pressure to be adjusted in real time to ensure that the pressure head is always in contact with the parts and the diffusion welding mold. If a smaller axial pressure is used, the axial pressure system of the vacuum diffusion welding furnace cannot be adjusted in time, which will lead to untimely pressure application. Once the pressure head is separated, it may even be impossible to pressurize again. Since the parts and the diffusion welding molds are always in a state of being about to be separated from the pressure head, a slightly larger axial pressure will not further increase the compression deformation of the parts; further tests show that when the axial pressure of 0.5MPa-2.0MPa is used, the pressure is applied smoothly during the entire cooling process, and the parts do not produce additional compression deformation.

[0091] Therefore, it can be seen from the above embodiments that the height deviation, flatness and parallelism of the parts after diffusion welding in the embodiments of the present invention are better than the data of the comparative example, indicating that the method proposed by the present invention of using steel or high-temperature alloy material to make the limit block 3 and applying conformal axial pressure during the cooling process realizes conformal cooling and deformation constraint of the cavity parts after diffusion welding, so that the deviation of the flatness and parallelism of the parts after welding is reduced to below 0.05mm, providing a usable reference plane for post-weld shape processing, and the post-weld shape processing realizes direct processing with one-time clamping and alignment, creating favorable conditions for improving efficiency and reducing costs in mass production of cavity structural parts.

Claims

1. A method for reducing cooling deformation of cavity parts during diffusion welding, characterized in that: The specific steps include: Step 1: Preparation of parts to be welded: Prepare a single piece with prefabricated inner cavity and vertical ribs, check that the vertical rib structure is intact, and the edge of the surface to be welded is sharp and has no missing parts; Step 2: Pretreatment of welded parts; Step 3: Solder paste application: Spray boron nitride solder stop on the surfaces of the upper and lower templates that contact the workpieces to be welded, and leave them to dry; Step 4: Module assembly: Align the two parts to be welded up and down, fit them and position them to complete the assembly. The total height of the assembled parts to be welded is H2. Place the assembled parts to be welded in the center of the lower template, place limit blocks on both sides of the parts to be welded, and place the limit blocks between the upper template and the lower template. Compared with the parts to be welded, the limit blocks have a larger linear expansion coefficient. The parts to be welded are made of titanium alloy, the limit blocks are made of steel or high-temperature alloy, the height of the limit blocks is H1, and 0.4mm≤H2-H1≤1.0mm. Align the upper template with the lower template, with the surface sprayed with solder stop facing the parts to be welded, and place them on the parts to be welded to complete the assembly of a set of modules. Step 5: Diffusion welding: The assembled multiple groups of modules are placed in an axially pressurized vacuum diffusion welding furnace, and diffusion welding is performed using an existing conventional diffusion welding process; during diffusion welding, the upper template is continuously moved downward under the action of the diffusion welding pressure, forcing the welded parts to be compressed and deformed, and finally the upper template and the limit block form a mold; when the diffusion welding insulation ends and enters the cooling stage, the vacuum state is maintained, and as the temperature in the furnace continues to decrease, the limit block and the parts are continuously cooled and contracted, and the limit block has a greater contraction rate, and the axial pressurization pressure is adjusted to 0.5MPa-2.0MPa, so that the height of the limit block is always lower than the height of the part, so that the upper template will always keep in contact with the part, thereby realizing the shape-following movement and shape-following constraint of the upper template relative to the part's outer surface, thereby achieving the purpose of reducing the flexural deformation and local bulging of the part until the cooling is completed; Step 6: Post-welding measurement: After diffusion welding, the height of the parts is measured with a micrometer, and the flatness and parallelism of the parts are tested with a three-coordinate machine.

2. A method for reducing cooling deformation of cavity parts during diffusion welding according to claim 1, characterized in that: In the step 1, when the surface to be welded of the workpiece to be welded is a plane, the roughness of the surface to be welded Ra≤0.8μm, the flatness of the outer surface and the surface to be welded are both ≤0.03mm, and the parallelism between the two planes is ≤0.05mm; when the surface to be welded of the workpiece to be welded is a curved surface, the roughness of the surface to be welded Ra≤0.8μm, the flatness of the outer surface ≤0.03mm, and the contour of the curved surface to be welded ≤0.03mm.

3. The method for reducing cooling deformation of cavity parts during diffusion welding according to claim 1, characterized in that: The pretreatment method in step 2 is to pretreat the surface to be welded by pickling or polishing to remove residual oxides and foreign particles attached to the surface; use deionized water, anhydrous ethanol or acetone as a cleaning medium to ultrasonically clean the welded parts; after cleaning, check that there are no water stains, scratches or marks on the surface of the welded surface.

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