A method for improving the dimensional accuracy of batch welding of split diffusion welded parts

Abstract

The present invention relates to a method for improving the dimensional accuracy of batch welding of split diffusion welding parts, comprising step one: preparation of parts to be welded; step two: preparation of process pads; the material of the process pads has the same or stronger anti-deformation ability as the TC4 alloy parts to be welded, while the anti-deformation ability of the process pads is weaker than that of the diffusion welding fixture; step three: pretreatment of parts to be welded; step four: solder stop coating; step five: assembly and stacking; step six: diffusion welding; step seven: post-weld measurement; step eight: calibration of the process pads; and step nine: batch evaluation. The present invention introduces a process pad for height difference compensation in multi-layer stacking diffusion welding to achieve effective compensation for the accumulated height difference of the multi-layer stacking fixture, thereby improving the dimensional accuracy of the blank during single-furnace multi-layer stacking diffusion welding.

Description

Technical Field

[0001] The invention belongs to the technical field of manufacturing aero-engine blades, and in particular relates to a method for improving the batch welding dimensional accuracy of split diffusion welding parts. Background Art

[0002] With the continuous development of aerospace manufacturing technology, the demand for high-thrust and low-energy aircraft has become more and more obvious. Aircraft design has gradually evolved towards equal strength and light weight, integrated multifunctionality, and a new design form has developed, namely, cavity structures. In particular, with the continuous improvement of computer design and virtual simulation technology in recent years, structural topology optimization design technology has been increasingly used in aircraft design. Combining structural topology optimization design with aircraft mechanics and aerodynamics design, a variety of cavity structures have been derived, such as pure cavities based on variable wall thickness design, cavities with single-direction ribs, and cavity structures with complex rib forms such as topological structural features or bionic structural features. Through various innovative structural designs, cavity structures can not only achieve equal strength and weight reduction, but also achieve functions such as noise reduction, vibration reduction, heat insulation, transmission of cooling air or heating gas, and transmission of fuel. They are increasingly widely used not only in the field of aerospace manufacturing, but also in multiple manufacturing fields such as chemical industry, shipbuilding, and satellites.

[0003] By consulting domestic and foreign literature and patent information, it is known that the current manufacturing methods of cavity structural parts mainly include: mechanical connection such as riveting and bolting, melting welding such as electron beam welding and argon arc welding, solid phase connection such as stir friction welding and split diffusion welding, superplastic forming / diffusion bonding (SPF / DB) composite process, and brazing, etc. Among them, split diffusion welding has the characteristics of solid phase connection process on the one hand, no local melting occurs during the welding process, and the strength of the joint is as strong as or close to that of the parent material. On the other hand, it has the advantages of strong ability to realize cavity design structure, simple process route, high controllability of process and no reliance on high-end complex welding equipment (such as positive pressure diffusion bonding equipment, hot isostatic pressing equipment and other complex and high-value equipment), etc., and has become the preferred process method for manufacturing cavity structural parts.

[0004] The titanium alloy hollow rectifier support plate (also called air intake support plate, fixed support plate) and adjustable blades of aircraft engines manufactured by split diffusion welding process have become alternative products of SPF / DB process parts and have entered the engineering application stage. With the continuous increase in the output of components, the contradictions and conflicts between production efficiency, manufacturing cost and product quality have become more and more prominent. Combining the actual production of multiple part numbers, the current status and existing problems are as follows:

[0005] Hollow rectifier support plates and adjustable blades are high-performance parts with strict requirements on wall thickness, manufacturing compliance and consistency of internal and external profiles. Therefore, the diffusion welding blanks must have high dimensional consistency to facilitate subsequent shape processing, so as to deliver products that meet the use requirements. Figure 1 As shown in the figure, when multi-layer stacking diffusion welding is used, the cumulative manufacturing deviation of the fixture leads to poor consistency in the size of the diffusion welding blanks produced in continuous batches. According to existing data statistics, the multi-layer stacking method is used for continuous production of a TC4 alloy intake support plate. The height deviation of the diffusion welding blank reaches 0.25mm, which is 3 times the height deviation of the blank after single-layer diffusion welding of 0.08mm. The size deviation of the diffusion welding blank has seriously affected the subsequent process shape processing. In order to compensate for the size deviation of the diffusion welding blank, the subsequent process shape processing has to adopt the processing method of alternating offline measurement and on-machine processing, that is, customized processing plan, which greatly increases the cost of manpower and material resources and prolongs the product manufacturing cycle.

[0006] Solving the problem of manufacturing deviation accumulation of multi-layer stacked diffusion welding fixtures is not only beneficial to improving the dimensional consistency of batch diffusion welding blanks, but also can reduce the cost of mold repair and equipment maintenance to a certain extent. However, according to current literature and patents, there is no relevant information on the dimensional accuracy consistency control of multi-layer stacked diffusion welding, and no related literature has been found in related fields such as plastic forming and forging. Therefore, a method for improving the dimensional accuracy of batch welding of split diffusion welding parts is urgently needed. Summary of the invention

[0007] In view of the shortcomings of the prior art, based on a systematic study of the high-temperature performance and high-temperature deformation characteristics of TC4 titanium alloy and an analysis of the heating, loading process and compression deformation laws of diffusion welding of TC4 titanium alloy hollow rectifier support plates and adjustable blades, the present invention provides a method for improving the dimensional accuracy of batch welding of split diffusion welding parts. By introducing a process pad for height difference compensation in multi-layer stacked diffusion welding, the difference in internal stress and high-temperature deformation resistance between the process pad and the weldment is utilized to effectively compensate for the accumulated height difference of the multi-layer stacked fixture, thereby solving the problem of large deviation in dimensional accuracy of diffusion welding blanks in multi-layer stacked furnace diffusion welding, improving the dimensional accuracy of blanks in single-furnace multi-layer stacked diffusion welding, reducing the difficulty of process shape processing, and providing guarantee for batch production.

[0008] A method for improving the dimensional accuracy of batch welding of split diffusion welded parts comprises the following steps:

[0009] Step 1: Preparation of parts to be welded;

[0010] Step 2: Preparation of process pad;

[0011] The process pad material has the same or stronger anti-deformation capability as the TC4 alloy to be welded, while the process pad material has weaker anti-deformation capability than the diffusion welding fixture;

[0012] Step 3: Pretreatment of welded parts;

[0013] Step 4: Solder stop coating;

[0014] Step 5: Assemble and stack;

[0015] Step 6: Diffusion welding;

[0016] Step 7: Post-welding measurement;

[0017] Step 8: Calibration of process pad;

[0018] Step 9: Batch evaluation.

[0019] In the step 1, 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 ≤0.03 mm, and the parallelism between the two planes is ≤0.05 mm; if there is a contour of the curved surface to be welded, the contour of the curved surface to be welded is ≤0.03 mm.

[0020] The thickness of the process pad in step 2 is greater than or equal to 10 mm.

[0021] The method for pre-treating the workpiece to be welded in step three is to pre-treat the surface to be welded by a conventional pickling method to remove residual oxides and foreign particles attached to the surface; ultrasonically clean the workpiece to be welded with deionized water; after cleaning, check the surface to be welded to ensure that there are no water stains, scratches or marks.

[0022] The solder stop coating method in step 4 specifically comprises spraying boron nitride solder stop on the contact surface between the diffusion welding fixture and the parts and the upper and lower surfaces of the process pad, and placing the solder stop on the surface to dry.

[0023] The method of assembling and stacking in the step five is to assemble the diffusion welding fixture and the workpiece to be welded to form a module, wherein the diffusion welding fixture includes a fixture lower plate, a limit plate, and a fixture upper plate, the fixture lower plate and the fixture upper plate are L-shaped and placed opposite to each other, the workpiece to be welded is fixed between the fixture lower plate and the fixture upper plate, the limit plate is fixed between the fixture upper plate and the fixture lower plate, and is located on both sides of the workpiece to be welded; there is a gap between the fixture upper plate and the limit plate; the assembled multiple groups of modules are evenly placed on the equipment platform of the axially pressurized vacuum diffusion welding furnace, a process pad is placed on the top of each stack, and the equipment pressure plate of the axially pressurized vacuum diffusion welding furnace is in contact with the top of the process pad.

[0024] In step six, conventional diffusion welding process is used for diffusion welding.

[0025] In the step seven, after diffusion welding, a micrometer is used to measure the height of each part in the entire furnace to obtain the height deviation of the part after welding.

[0026] In the step eight, the process pad is calibrated after each furnace is used. Specifically, the process pad is surface ground or milled to ensure that the flatness of the process pad and the parallelism of the upper and lower surfaces are both ≤0.05mm, and the height difference between the process pads is ≤0.05mm.

[0027] In the step 10, the height dimension of the workpiece to be welded produced by continuous diffusion welding after welding is measured and evaluated to obtain the height dimension deviation between each furnace.

[0028] The beneficial effects of the present invention are as follows: the present invention effectively compensates for the accumulated height difference of the multi-layer stacking fixture by introducing a process pad for height difference compensation in the multi-layer stacking diffusion welding, thereby improving the blank size accuracy during the single-furnace multi-layer stacking diffusion welding. The method is used for continuous batch production of multi-layer stacking diffusion welding, and the height size deviation of the blank after diffusion welding is reduced from 0.25 mm to 0.11 mm, which is reduced by more than 50%.

[0029] The present invention effectively realizes the control of the dimensional accuracy of batch diffusion welding of split diffusion welding parts, provides blanks with high dimensional consistency for subsequent process shape processing, reduces repeated measurement and clamping work, reduces the difficulty of process shape processing, and provides guarantee for batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of multi-layer stacking diffusion welding in the prior art;

[0031] Figure 2 It is a schematic diagram of assembling the process pad provided in the present invention;

[0032] Figure 3 It is a schematic diagram of the compressive stress principle of the process pad provided in the present invention;

[0033] Figure 4 middle Figure 4 (a)- Figure 4 (c) is a schematic diagram of the time series of the height compensation principle in the method provided by the present invention;

[0034] in,

[0035] 1- Equipment platform, 2- Equipment pressure plate, 3- Fixture lower plate, 4- Fixture upper plate, 5- Limit plate, 6- Parts to be welded, 7- Process pad. DETAILED DESCRIPTION

[0036] 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.

[0037] Example 1

[0038] In this embodiment, the workpiece 6 to be welded is a TC4 alloy split structure air intake support plate as an example, and a method for improving the dimensional accuracy of batch welding of split diffusion welding parts specifically includes the following steps:

[0039] Step 1: Preparation of the welded part 6

[0040] Prepare the workpiece 6 to be welded, ensuring that 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.

[0041] Step 2: Preparation of process pad 7

[0042] In this embodiment, the material of the process pad 7 is a TC4 alloy thick plate, and the size of the process pad 7 is greater than or equal to the size of the upper plate 4 of the diffusion welding fixture. In this embodiment, the size of the process pad 7 is 200mm×400mm; the upper and lower surfaces of the process pad 7 are processed by grinding to make the thickness 30±0.03mm, and the flatness and parallelism of the upper and lower surfaces are both ≤0.05mm.

[0043] The material selection of the process pad 7 is extensive. Compared with the TC4 alloy workpiece 6, the process pad 7 has the same or stronger deformation resistance, while compared with the diffusion welding fixture, the deformation resistance of the process pad 7 is weaker than that of the diffusion welding fixture, thus playing the role of compensating the stacking height difference.

[0044] Step 3: Pretreatment of weldment 6

[0045] The surface to be welded is pre-treated by conventional pickling method to remove residual oxides and foreign particles attached to the surface; the welded part is ultrasonically cleaned with deionized water 6; after cleaning, the surface to be welded is checked to ensure that there are no water stains, scratches or marks.

[0046] Step 4: Solder paste application

[0047] Boron nitride solder stop is sprayed on the contact surface between the diffusion welding fixture and the parts, and the upper and lower surfaces of the process pad 7, and then left to dry.

[0048] Step 5: Assemble and stack

[0049] Assemble the diffusion welding fixture and the 6TC4 alloy split structure air intake support plate of the workpiece to be welded to form a module, wherein the diffusion welding fixture includes a fixture lower plate 3, a limit plate 5, and a fixture upper plate 4. The fixture lower plate 3 and the fixture upper plate 4 are L-shaped and placed opposite to each other. The workpiece 6 to be welded is fixed between the fixture lower plate 3 and the fixture upper plate 4. The limit plate 5 is fixed between the fixture upper plate 4 and the fixture lower plate 3, and is located on both sides of the workpiece 6 to be welded. There is a gap between the fixture upper plate 4 and the limit plate 5. The diffusion welding fixture material should be well matched with the diffusion welding process, have good deformation resistance during the diffusion welding pressure holding period, and must have deformation resistance that meets the requirements of the diffusion welding process. Figure 1 As shown, the assembled multiple groups of modules are evenly placed on the equipment platform 1 of the axial pressure vacuum diffusion welding furnace, with 3 pieces placed on one layer to form three stacks, and each stack has 3 layers; a process pad 7 is placed on the top of each stack, as shown in FIG. Figure 2 As shown, the equipment pressing plate 2 of the axially pressurized vacuum diffusion welding furnace is in contact with the top of the process pad 7.

[0050] Step 6: Diffusion welding

[0051] Conventional diffusion welding process is used for diffusion welding. During the diffusion welding process, Figure 3 As shown, the axial pressure head applies pressure P to the equipment platen 2, which is transmitted downward layer by layer through the stacking module to the equipment platform 1, and the equipment platform 1 forms a supporting force F to achieve an external force balance state, that is, P = F. When the diffusion welding insulation is completed, the vacuum state is maintained until the cooling is completed.

[0052] Under the action of the axial pressure of the equipment, the welded part 6 will produce compressive plastic deformation in the axial pressure direction, so that the height of the entire stack is continuously reduced. If the diffusion welding fixture has zero manufacturing deviation, when the diffusion welding is finished, the welded part will be pressed to the same height as the limit plate 5 under the action of the axial pressure, and the upper plate 4 of the fixture will contact and close the mold with the limit plate 5, and the height of the welded part blank after diffusion welding will also maintain good consistency. However, the manufacturing deviation of the diffusion welding fixture is always inevitable, that is to say, according to the traditional multi-layer stacking diffusion welding scheme, there is always a situation where the upper part of the fixture and the limit plate 5 cannot be contacted and closed, and the height of the welded part in the module that cannot be contacted and closed will be slightly larger than other closed mold modules. It can be foreseen that with the increase of the number of stacking layers, the inconsistency of the height size of the welded part will become more serious, which is why the height size deviation of the welded part becomes larger after multi-layer stacking diffusion welding.

[0053] The present invention places a process pad 7 with an area greater than or equal to the upper plate 4 of the diffusion welding fixture on each stack. Obviously, the process pad 7 and the weldment are subjected to the same axial pressure. The process pad 7 is a solid body, and the axial pressure is nearly evenly transmitted in the process pad 7, generating an axial compressive stress of σ1; the weldment is a structural member with a cavity, and its axial pressure is transmitted through the welding surface area. The cavity area does not bear the role of axial pressure transmission, thereby generating an axial compressive stress σ2 in the weldment, and it is obvious that σ1<σ2. According to the weldment diffusion welding process plan and the processing allowance design characteristics, the welding surface area is approximately 30% to 60% of the area of ​​the process pad 7. In other words, the axial compressive stress level in the process pad 7 is much lower than the axial compressive stress level in the weldment. Figure 3 shown.

[0054] Obviously, by utilizing the internal pressure stress difference between the process pad 7 and the weldment and selecting a suitable material for the process pad 7, the following effects can be achieved: during the diffusion welding process, when the axial pressure P is applied, compressive stress is generated in the process pad 7 and the weldment, and both the process pad 7 and the weldment will produce plastic deformation under the action of the compressive stress. Since the material of the process pad 7 has the same or stronger deformation resistance than the TC4 alloy weldment 6, and the process pad 7 has a weaker deformation resistance than the diffusion welding fixture, the compression plastic deformation speed and deformation amount of the process pad 7 can be much smaller than that of the TC4 alloy, thereby forcing the TC4 weldment to preferentially reach the compression deformation limit preset in the diffusion welding process, and the upper plate 4 of the fixture is molded with the limit plate 5. Continuing to maintain the axial pressure of the vacuum diffusion welding furnace will not increase the compression plastic deformation in the height direction of the weldment. Assuming that the total height of a stack is the largest, the mold will be closed layer by layer during the diffusion welding pressurization process, so that the diffusion welding fixture upper plate 4, the fixture lower plate 3, the limit plate 5 and the welded part 6 form a group of relatively rigid bodies; if the pressurization continues, the process pad 7 will continue to produce compression deformation due to the rigid constraint of the fixture upper plate 4 below it, and the height of the entire stack will continue to decrease. At this time, for stacks with a lower total height of the diffusion welding fixture, since the deformation rate of the aforementioned process pad 7 is lower than that of the TC4 weldment, the TC4 weldment in the unclosed module will continue to deform until each layer of the module is closed to form a group of rigid bodies, and so on, the stacks with lower fixture heights will also repeat the above process, such as Figure 4 As shown, in this embodiment, the heights of the three stacks are different before welding, such as Figure 4 As shown in (a), the height of the leftmost stack is higher than the two stacks on the right, and the height of the middle stack is the lowest. As welding proceeds, Figure 4 As shown in (b), the process pad 7 is deformed, and the three stacked fixture upper plates 4 and the limit blocks are molded in sequence; Figure 4As shown in (c), after welding, the heights of the three stacks are consistent, and the gap between the fixture upper plate 4 and the limit block in each stack disappears, achieving mold closing. The heights of the process pads 7 of the three stacks are different. Among them, the process pad 7 in the stack with the highest height before welding on the leftmost side has the smallest thickness, and the process pad 7 in the stack with the lowest height before welding in the middle has the lowest thickness. Due to thermal deformation, the process pad 7 compensates for the height of the clamp upper plate 4 and the limit block for mold closing, so that the clamp upper plate 4 will contact the limit plate 5 for mold closing, and the heights of different stacks are completely consistent.

[0055] Step 7: Post-welding measurement

[0056] After diffusion welding, the height of each part in the entire furnace was measured with a micrometer, and the result was that the height deviation of the parts after welding was ≤0.07mm.

[0057] Step 8: Calibration of process pad 7

[0058] Since the principle of compensating the stacking height difference of the process pad 7 during the diffusion welding process is plastic deformation compensation, different degrees of plastic deformation will occur after each use, that is, after the end of each furnace of diffusion welding. In order not to affect the compensation effect, the process pad 7 is calibrated after each furnace is used. Specifically: the process pad 7 is surface ground so that the flatness of the process pad 7 and the parallelism of the upper and lower surfaces are ≤0.05mm, and the height difference between the process pads 7 is ≤0.05mm.

[0059] Step 9: Batch Evaluation

[0060] The height dimensions of the TC4 alloy split structure air intake support plates produced by continuous diffusion welding were measured and evaluated after welding. The result showed that the height dimension deviation between each furnace was ≤0.11mm.

[0061] Example 2

[0062] In this embodiment, the welded part 6 is a TC4 alloy split hollow adjustable blade as an example, and a method for improving the dimensional accuracy of split diffusion welding parts in batch welding specifically includes the following steps:

[0063] Step 1: Preparation of the welded part 6

[0064] Prepare the workpiece 6 to be welded, ensuring that the roughness of the surface to be welded Ra ≤ 0.8 μm, the flatness of the outer surface ≤ 0.03 mm, and the contour of the curved surface to be welded ≤ 0.03 mm.

[0065] Step 2: Preparation of process pad 7

[0066] In this embodiment, the material of the process pad 7 is GH4169 alloy forging blank, and the size of the process pad 7 is greater than or equal to the size of the upper plate 4 of the diffusion welding fixture. In this embodiment, the size of the process pad 7 is 180mm×360mm; the upper and lower surfaces of the process pad 7 are processed by grinding to make its thickness 10±0.03mm, and the flatness and parallelism of the upper and lower surfaces are both ≤0.05mm.

[0067] The material selection of the process pad 7 is extensive. Compared with the TC4 alloy workpiece 6, the process pad 7 has the same or stronger deformation resistance, while compared with the diffusion welding fixture, the deformation resistance of the process pad 7 is weaker than that of the diffusion welding fixture, thus playing the role of compensating the stacking height difference.

[0068] Step 3: Pretreatment of weldment 6

[0069] The surface to be welded is pre-treated by conventional pickling method to remove residual oxides and foreign particles attached to the surface; the welded part is ultrasonically cleaned with deionized water 6; after cleaning, the surface to be welded is checked to ensure that there are no water stains, scratches or marks.

[0070] Step 4: Solder paste application

[0071] Boron nitride solder stop is sprayed on the contact surface between the diffusion welding fixture and the parts, and the upper and lower surfaces of the process pad 7, and then left to dry.

[0072] Step 5: Assemble and stack

[0073] Assemble the diffusion welding fixture and the 6TC4 alloy split structure air intake support plate of the workpiece to be welded to form a module, wherein the diffusion welding fixture includes a fixture lower plate 3, a limit plate 5, and a fixture upper plate 4. The fixture lower plate 3 and the fixture upper plate 4 are L-shaped and placed opposite to each other. The workpiece 6 to be welded is fixed between the fixture lower plate 3 and the fixture upper plate 4. The limit plate 5 is fixed between the fixture upper plate 4 and the fixture lower plate 3, and is located on both sides of the workpiece 6 to be welded. There is a gap between the fixture upper plate 4 and the limit plate 5. The diffusion welding fixture material should be well matched with the diffusion welding process, have good deformation resistance during the diffusion welding pressure holding period, and must have deformation resistance that meets the requirements of the diffusion welding process. Figure 1 As shown, the assembled multiple groups of modules are evenly placed on the equipment platform 1 of the axial pressure vacuum diffusion welding furnace, with 3 pieces placed on one layer to form three stacks, and each stack has 3 layers; a process pad 7 is placed on the top of each stack, as shown in FIG. Figure 2 As shown, the equipment pressing plate 2 of the axially pressurized vacuum diffusion welding furnace is in contact with the top of the process pad 7.

[0074] Step 6: Diffusion welding

[0075] Conventional diffusion welding process is used for diffusion welding. During the diffusion welding process, Figure 3As shown, the axial pressure head applies pressure P to the equipment platen 2, which is transmitted downward layer by layer through the stacking module to the equipment platform 1, and the equipment platform 1 forms a supporting force F to achieve an external force balance state, that is, P = F. When the diffusion welding insulation is completed, the vacuum state is maintained until the cooling is completed.

[0076] Under the action of the axial pressure of the equipment, the welded part 6 will produce compressive plastic deformation in the axial pressure direction, so that the height of the entire stack is continuously reduced. If the diffusion welding fixture has zero manufacturing deviation, when the diffusion welding is finished, the welded part will be pressed to the same height as the limit plate 5 under the action of the axial pressure, and the upper plate 4 of the fixture will contact and close the mold with the limit plate 5, and the height of the welded part blank after diffusion welding will also maintain good consistency. However, the manufacturing deviation of the diffusion welding fixture is always inevitable, that is to say, according to the traditional multi-layer stacking diffusion welding scheme, there is always a situation where the upper part of the fixture and the limit plate 5 cannot be contacted and closed, and the height of the welded part in the module that cannot be contacted and closed will be slightly larger than other closed mold modules. It can be foreseen that with the increase of the number of stacking layers, the inconsistency of the height size of the welded part will become more serious, which is why the height size deviation of the welded part becomes larger after multi-layer stacking diffusion welding.

[0077] The present invention places a process pad 7 with an area greater than or equal to the upper plate 4 of the diffusion welding fixture on each stack. Obviously, the process pad 7 and the weldment are subjected to the same axial pressure. The process pad 7 is a solid body, and the axial pressure is nearly evenly transmitted in the process pad 7, generating an axial compressive stress of σ1; the weldment is a structural member with a cavity, and its axial pressure is transmitted through the welding surface area. The cavity area does not bear the role of axial pressure transmission, thereby generating an axial compressive stress σ2 in the weldment, and it is obvious that σ1<σ2. According to the weldment diffusion welding process plan and the processing allowance design characteristics, the welding surface area is approximately 30% to 60% of the area of ​​the process pad 7. In other words, the axial compressive stress level in the process pad 7 is much lower than the axial compressive stress level in the weldment. Figure 3 shown.

[0078] Obviously, by utilizing the internal pressure stress difference between the process pad 7 and the weldment and selecting a suitable material for the process pad 7, the following effects can be achieved: during the diffusion welding process, when the axial pressure P is applied, compressive stress is generated in the process pad 7 and the weldment, and both the process pad 7 and the weldment will produce plastic deformation under the action of the compressive stress. Since the material of the process pad 7 has the same or stronger deformation resistance than the TC4 alloy weldment 6, and the process pad 7 has a weaker deformation resistance than the diffusion welding fixture, the compression plastic deformation speed and deformation amount of the process pad 7 can be much smaller than that of the TC4 alloy, thereby forcing the TC4 weldment to preferentially reach the compression deformation limit preset in the diffusion welding process, and the upper plate 4 of the fixture is molded with the limit plate 5. Continuing to maintain the axial pressure of the vacuum diffusion welding furnace will not increase the compression plastic deformation in the height direction of the weldment. Assuming that the total height of a stack is the largest, the mold will be closed layer by layer during the diffusion welding pressurization process, so that the diffusion welding fixture upper plate 4, the fixture lower plate 3, the limit plate 5 and the welded part 6 form a group of relatively rigid bodies; if the pressurization continues, the process pad 7 will continue to produce compression deformation due to the rigid constraint of the fixture upper plate 4 below it, and the height of the entire stack will continue to decrease. At this time, for stacks with a lower total height of the diffusion welding fixture, since the deformation rate of the aforementioned process pad 7 is lower than that of the TC4 weldment, the TC4 weldment in the unclosed module will continue to deform until each layer of the module is closed to form a group of rigid bodies, and so on, the stacks with lower fixture heights will also repeat the above process, such as Figure 4 shown.

[0079] Step 7: Post-welding measurement

[0080] After diffusion welding, the height of each part in the entire furnace was measured using a micrometer, and the result was that the height deviation of the parts after welding was ≤0.05mm.

[0081] Step 8: Calibration of process pad 7

[0082] Since the principle of compensating the stacking height difference during the diffusion welding process of the process pad 7 is plastic deformation compensation, different degrees of plastic deformation will occur after each use, that is, after the end of each furnace of diffusion welding. In order not to affect the compensation effect, the process pad 7 is calibrated after each furnace is used. Specifically: the process pad 7 is plane milled to make the flatness of the process pad 7 and the parallelism of the upper and lower surfaces ≤0.05mm, and the height difference between the process pads 7 ≤0.05mm.

[0083] Step 9: Batch Evaluation

[0084] The height dimensions of the TC4 alloy split-structure hollow adjustable blades produced by continuous diffusion welding were measured and evaluated after welding. The result showed that the height dimension deviation between each furnace was ≤0.10mm.

[0085] This method is used for continuous batch production of multi-layer stacked diffusion welding. The height dimensional deviation of the blank after diffusion welding is no more than 0.11mm, which effectively realizes the control of the dimensional accuracy of batch diffusion welding of split diffusion welding parts, and provides blanks with high height dimensional consistency for subsequent process shape processing; reduces repeated measurement and clamping work, reduces the difficulty of process shape processing, and provides guarantee for batch production.

Claims

1. A method for improving the dimensional accuracy of batch welding of split diffusion welded parts, characterized in that: The following steps are involved: Step 1: Preparation of TC4 alloy welded parts: The TC4 alloy welded parts are structural parts with cavities; Step 2: Preparation of process pad: The process pad is a solid part. The material of the process pad has the same or stronger anti-deformation ability as the TC4 alloy to be welded, while the anti-deformation ability of the process pad is weaker than that of the diffusion welding fixture. Step 3: Pretreatment of the TC4 alloy to be welded; Step 4: Solder stop coating; Step 5: Assembling and stacking: assembling the diffusion welding fixture and the TC4 alloy workpiece to be welded to form a module, wherein the diffusion welding fixture comprises a fixture lower plate, a limiting plate, and a fixture upper plate, wherein the fixture lower plate and the fixture upper plate are L-shaped and placed opposite to each other, the TC4 alloy workpiece to be welded is fixed between the fixture lower plate and the fixture upper plate, and the limiting plate is fixed between the fixture upper plate and the fixture lower plate, and is located on both sides of the TC4 alloy workpiece to be welded; there is a gap between the fixture upper plate and the limiting plate; the assembled multiple groups of modules are evenly placed on the equipment platform of the axially pressurized vacuum diffusion welding furnace, the process pad is placed on the top of each stack, and the equipment pressure plate of the axially pressurized vacuum diffusion welding furnace is in contact with the top of the process pad; wherein the area of ​​the process pad is greater than or equal to the size of the fixture upper plate; Step 6: Diffusion welding: Diffusion welding is performed using a conventional diffusion welding process; during the diffusion welding process, the process pad and the TC4 alloy to be welded are subjected to the same axial pressure, and the axial pressure is nearly evenly distributed in the process pad, generating an axial compressive stress of σ1; the axial pressure of the TC4 alloy to be welded is transmitted through the welding surface area, and its cavity area does not bear the role of axial pressure transmission, thereby generating an axial compressive stress of σ2 in the TC4 alloy to be welded, and σ1<σ2, and utilizing the compressive stress difference between the process pad and the TC4 alloy to be welded, the process pad and the TC4 alloy to be welded produce plastic deformation under the action of the compressive stress, and ... Compared with the TC4 alloy to be welded, the material of the process pad has the same or stronger anti-deformation ability, while compared with the diffusion welding fixture, the anti-deformation ability of the process pad is weaker than that of the diffusion welding fixture. The compression plastic deformation speed and deformation amount generated by the process pad are much smaller than those of the TC4 alloy to be welded, thereby forcing the TC4 alloy to be welded to reach the compression deformation limit preset in the diffusion welding process first, so that the upper plate of the fixture is molded with the limiting plate; the axial pressure of the axial pressure vacuum diffusion welding furnace is continuously maintained, and the compression plastic deformation of the TC4 alloy to be welded in the height direction will not be increased, thereby achieving completely consistent heights of different stacks; Step 7: Post-welding measurement; Step 8: Calibration of process pad; Step 9: Batch evaluation.

2. A method for improving the dimensional accuracy of batch welding of split diffusion welded parts according to claim 1, characterized in that: The roughness of the surface to be welded of the TC4 alloy weldment to be welded in the step 1 is 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; if there is a curved surface contour to be welded, the contour of the curved surface to be welded is ≤0.03mm.

3. A method for improving the dimensional accuracy of batch welding of split diffusion welded parts according to claim 1, characterized in that: The thickness of the process pad in step 2 is greater than or equal to 10 mm.

4. A method for improving the dimensional accuracy of batch welding of split diffusion welded parts according to claim 1, characterized in that: The method for pretreating the TC4 alloy weldment in step three is: pretreating the weld surface by a conventional pickling method to remove residual oxides and foreign particles attached to the surface; ultrasonically cleaning the TC4 alloy weldment with deionized water; after cleaning, inspecting the weld surface to ensure that there are no water stains, scratches or marks.

5. The method for improving the dimensional accuracy of batch welding of split diffusion welded parts according to claim 1, characterized in that: The method for coating the solder stop in step 4 is specifically as follows: spraying boron nitride solder stop on the contact surface between the diffusion welding fixture and the parts and the upper and lower surfaces of the process pad, and leaving them to dry.

6. The method for improving the dimensional accuracy of batch welding of split diffusion welded parts according to claim 1, characterized in that: In the step seven, after diffusion welding, a micrometer is used to measure the height of each part in the entire furnace to obtain the height deviation of the part after welding.

7. The method for improving the dimensional accuracy of batch welding of split diffusion welded parts according to claim 1, characterized in that: In the step eight, the process pad is calibrated after each furnace is used. Specifically, the process pad is surface ground or milled so that the flatness of the process pad and the parallelism of the upper and lower surfaces are both ≤0.05mm, and the height difference between the process pads is ≤0.05mm.

8. The method for improving the dimensional accuracy of batch welding of split diffusion welded parts according to claim 1, characterized in that: In the step nine, the post-weld height dimensions of the TC4 alloy welded parts produced by continuous diffusion welding are measured and evaluated to obtain the height dimension deviation between each furnace.

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