Forming method for improving cementing property of titanium alloy blade wrapping piece

Abstract

The invention belongs to a plastic processing technology, and relates to a forming method for improving the cementing property of a titanium alloy paddle wrapping piece. The method is suitable for forming the non-uniform-section inverted-V-shaped narrow-cavity integrated titanium alloy wrapping piece with the torsion angle, and solves the problems that in the prior art, the requirement for the bonding condition of the titanium alloy blade wrapping piece is high, the roughness uniformity and deformation are difficult to guarantee through sand blasting after the narrow-cavity characteristic is formed, and the like; on the premise of meeting the material deformation amount required by hot forming, control over the roughness of material stretching in the hot forming process, material corrosion in the acid pickling process and the like is guaranteed, the roughness uniformity of the bonding face of the blade wrapping piece is improved, and the bonding success rate and bonding uniformity of the blade wrapping piece are improved.

Description

Technical Field

[0001] This invention belongs to the field of plastic processing technology and relates to a forming method for improving the adhesive bonding properties of titanium alloy propeller blade cladding. Background Technology

[0002] The rotor blade is the most distinctive core component of a helicopter, providing almost all lift, forward propulsion, and control force. Its performance directly determines the helicopter's payload capacity, maximum speed, maneuverability, handling qualities, and flight efficiency in all flight phases. It is also a major source of helicopter vibration and noise. The blade cladding is a core component of the blade, effectively reducing blade turbulence and drag to ensure lift efficiency, improving maintainability, lowering maintenance costs, preventing the propagation of internal cracks in composite materials caused by leading-edge damage, extending the overall lifespan of the blade, and ensuring helicopter flight safety. Currently, helicopter blade claddings are mostly of uniform cross-section or constant torsion angle configuration, and are often manufactured and installed using a segmented overlapping structure. However, the weak adhesive gaps in the segmented overlapping areas are a major failure risk point; the adhesive layer in these areas is prone to fatigue cracking under long-term alternating loads. Compared to segmented overlapping structures, integrated claddings have significant design advantages. The continuous structure can more evenly transmit impact energy, with less localized stress concentration, and the raw materials are gradually shifting from stainless steel to titanium alloys, which have higher specific strength and lower density.

[0003] With the increasing demands for high maneuverability and long endurance in future helicopters, the aerodynamic shape of the rotor blades has also changed. They now employ a titanium alloy variable chord length, double parabolic swept-back design, characterized by variable twist angle, variable cross-section narrow cavity, and a corresponding change in the blade envelope shape. Furthermore, the use of titanium alloy materials and the resulting component structures are as follows... Figure 6 Illustration. For example, patent CN 107570626A uses a stretch forming process, combined with a punch and die to complete the forming of a uniform cross-section sheath. This method cannot meet the processing requirements of sheaths with variable cross-section configurations and torsional angles, nor can it process titanium alloy materials. For example, patent CN 112916709B uses a thermoforming process to meet the problem of high springback forming of titanium alloys, but its processing method involves air expansion forming of titanium alloy tubes, which cannot treat the inner surface. For example, patent CN116176854A proposes a method to improve the bonding strength of the formed sheath before bonding, but it does not involve surface treatment during the sheath processing. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for improving the adhesive bonding performance of titanium alloy blade cladding. By controlling the surface roughness during the processing of the variable cross-section titanium alloy cladding with a torsion angle, the deformation of the part is ensured to meet the requirements, thereby improving the bonding performance during subsequent bonding, reducing the surface treatment work before bonding, and lowering the requirements for the strength of the adhesive.

[0005] The technical solution of the present invention: In order to achieve the above-mentioned objective, a method for improving the adhesive bonding of titanium alloy blade cladding is proposed and applied to the forming process of titanium alloy blade cladding, wherein the titanium alloy blade cladding has a non-uniform cross section and an inverted V-shaped narrow cavity configuration.

[0006] Includes the following steps:

[0007] Step 1: Fabricate a preforming mold; the preforming mold includes a preforming upper mold and a preforming lower mold that are combined and fitted together; the preforming upper mold is used to form a semi-finished blade wrapper with a wide spacing and shallow cavity. Compared with the theoretical size of the blade wrapper, the spacing at the beginning and end of the wrapper is increased by 0.6-1mm, and the spacing in the middle section of the wrapper gradually decreases following the change in the spacing at the beginning and end, controlled to be 0.2mm greater than the theoretical size. The cavity becomes shallower overall by 0.4-1mm as the spacing changes, avoiding the formation of a closed angle; the preforming lower mold is used in conjunction with the upper mold;

[0008] The final forming mold includes a final forming upper mold and a final forming lower mold that are combined and fitted together. The final forming upper mold is used to form the final shape of the blade envelope. To avoid the formation of a closed angle, the overall size of the lower mold is smaller than the theoretical size of the blade envelope, with the distance controlled to be no more than 0.2 mm and the cavity size controlled to be no more than 0.1 mm. The final forming lower mold has the same size as the final blade envelope, and the gap between the molds is used for material flow and stress release during the forming process.

[0009] Step 2: Perform single-sided surface sandblasting on the titanium alloy sheet before forming to control the amount of product deformation;

[0010] Step 3: Implement protective and lubrication measures to control the surface roughness of the sandblasted surface;

[0011] Step 4: Fix the upper and lower molds of the preformed mold on the upper and lower platforms of the thermoforming equipment respectively, keep the upper and lower molds safely separated, place the titanium alloy sheet on the lower mold of the preformed mold, and perform mold closing thermoforming under an inert gas protective atmosphere to obtain the preformed titanium alloy blade cladding.

[0012] Step 5: Remove the pre-formed titanium alloy blade sheath;

[0013] Step 6: The upper and lower molds of the final forming mold are fixed on the upper and lower platforms of the vacuum forming equipment, keeping the upper and lower molds safely separated. The pre-formed titanium alloy blade pack is placed on the lower mold of the final forming mold. The furnace door is closed. After the furnace reaches a vacuum state, the final forming is carried out to obtain the final formed titanium alloy blade pack.

[0014] Step 7: The final titanium alloy propeller blade is pickled and polished with surface protection.

[0015] Because the propeller blade envelope has a variable twist angle, non-uniform cross section, and inverted V-shaped narrow cavity configuration, in addition to considering the requirements of the thermoforming environment, the mold design must focus on whether there is a closed angle during the forming process. If there is a closed angle during the forming process of the upper and lower mold structures, it is difficult to complete the mold closing, and the feature processing is incomplete. The propeller blade envelope part has a typical closed angle feature caused by its configuration, which requires two-step forming to ensure the forming of the part features while avoiding the closed angle caused by the tooling.

[0016] Furthermore, based on the configuration, size, and required mold volume of different packaging pieces, the preforming mold structure is designed in reverse, and the shape of the preformed product is adjusted.

[0017] To avoid closed-angle formation in the mold, a transition blade envelope part with a wide spacing and shallow cavity is formed using a pre-forming mold. The spacing is increased at both ends of the mold to ensure no closed-angle caused by torsional features, and the depth of the pre-forming cavity is appropriately reduced to allow for material stretching during final forming, ensuring the blade envelope is formed along with the mold. To prevent closed-angle formation, the lower mold of the final forming mold has a smaller spacing than the theoretical dimensions of the blade envelope within a reasonable range, while ensuring the cavity dimensions after forming conform to the final blade envelope shape. The upper mold of the final forming mold maintains the same shape as the product, and the gap between the upper and lower molds is used for material flow and stress release.

[0018] Furthermore, step 2 specifically includes the following steps:

[0019] The first sandblasting process involves 80-mesh corundum particles, an air pressure of 0.4-0.5 MPa, and a sandblasting time of 5-10 minutes. The second sandblasting process involves 160-mesh corundum particles, an air pressure of 0.4-0.5 MPa, and a sandblasting time of 10-15 minutes. Sandblasting is performed in reverse. After sandblasting, the profile and roughness of the sheet are inspected to ensure that the part is in a single-curved arch shape, with a profile ≤5mm and a roughness of 1.2-2.5µm.

[0020] Because the blade sheath is relatively thin, a sandblasting process is implemented to ensure surface roughness without affecting the forming process. The first sandblasting uses relatively high-mesh corundum to create a larger concave area on the surface. At this stage, air pressure and time must be carefully controlled to ensure the flatness and internal stress of the plate after sandblasting. Insufficient air pressure or time will not meet the roughness requirements, while excessive air pressure or time will lead to excessive internal stress, poor flatness, and defects such as inaccurate positioning, wrinkles, and out-of-tolerance shapes during forming. The second sandblasting process improves the uniformity of surface roughness. Using a smaller mesh will result in excessive material stress, while using a larger mesh will fail to meet the roughness requirements and will have the opposite effect to the first sandblasting, making the internal stress of the plate more uniform. The air pressure and time for the second sandblasting follow the same principles as the first sandblasting, but because the second sandblasting uses a larger mesh, the sandblasting time needs to be appropriately increased.

[0021] Furthermore, the preforming process of the titanium alloy sheet includes:

[0022] The sandblasted titanium alloy sheet is installed on the forming mold. Before installation, antioxidants and lubricants are applied thoroughly to completely cover the base color of the titanium alloy sheet. The sheet is heated to 700-800℃ at a heating rate of 50-150℃ / h. Inert protective gases such as argon are introduced into the cavity of the titanium alloy sheet through the ventilation pipe at a pressurization rate of 0.1MPa-0.5MPa / min, controlling the pressure to not exceed 2MPa. The pressure is held for 5-10 minutes. After the temperature inside the furnace drops to below 500℃, the sheet is placed in a heat preservation box for cooling.

[0023] During the preforming stage, it is crucial to ensure sufficient oxidation of the sheet material to guarantee its surface roughness. Firstly, applying antioxidants and lubricants ensures smooth material flow and oxidation resistance during the forming process. During forming, an argon atmosphere must be maintained; too low an atmosphere introduces oxygen, accelerating oxidation, while too high an atmosphere increases furnace pressure, affecting material flow. Forming parameters must be carefully controlled at appropriate stages of heating; excessively high temperatures or slow heating rates accelerate oxidation, while excessively low temperatures or rapid heating rates impair material flow and temperature transfer efficiency between the mold and the product. After forming, the parts must be removed and air-cooled while ensuring operational safety.

[0024] Furthermore, the final forming process of the titanium alloy sheet includes:

[0025] The pre-formed semi-finished package is taken out of the heat preservation box and placed into the vacuum forming equipment. Before placing it in, antioxidant and lubricant are reapplied. It is heated to 600-750℃ and held under pressure for 40-70 minutes. Then it is cooled with the furnace. The mold is opened and the part is taken out at 200-350℃ and placed into the heat preservation box to cool down.

[0026] Due to the unique configuration of the blade sheath, it requires a two-stage forming process. Each additional step increases the degree of material oxidation. To control the oxidation level and ensure surface roughness, vacuum equipment must be used during the final forming. The forming temperature is crucial for the final forming of the blade sheath. Excessive temperature significantly increases cooling time, affecting forming efficiency; insufficient temperature results in poor material flowability and potential shape defects after forming. Insufficient holding time leads to incomplete forming, while excessive holding time increases the continued reaction of existing oxides. The blade sheath must be removed under appropriate temperature and with guaranteed processing efficiency.

[0027] Furthermore, after the sheet has cooled to below 100°C and undergone pickling, a weakly tacky protective tape is applied to the sandblasted surface until the part is fully machined.

[0028] By applying protective coatings, the uniformity of the roughness of the sandblasted surface is ensured, effectively preventing damage to the sandblasted surface from excess material generated during turnover, cutting, and other processes.

[0029] Furthermore, the method also includes completing the final edge trimming and surface roughness measurement, with a roughness greater than 1.0 μm; if this condition is met, the product is qualified; if not, the product is unqualified.

[0030] Beneficial technical effects of the present invention:

[0031] The improved titanium alloy blade cladding bonding forming method provided by this invention is applicable to the forming of integrated titanium alloy cladding with non-uniform cross-section and inverted V-shaped narrow cavity configuration with torsion angle. It solves the problems in the prior art such as high requirements for the bonding conditions of titanium alloy blade cladding, difficulty in ensuring the roughness uniformity and deformation of narrow cavity features after sandblasting, and for cladding with complex features, it ensures the control of roughness by material stretching during hot forming and material corrosion during pickling, while meeting the material deformation required for hot forming. This improves the roughness uniformity of the blade cladding bonding surface, and increases the success rate and uniformity of blade cladding bonding. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a flowchart of the method of the present invention.

[0034] Figure 2 This is a schematic diagram of a preforming mold according to an embodiment of the present invention;

[0035] In the diagram: 100 - Pre-forming mold; 101 - Upper pre-forming mold; 102 - Lower pre-forming mold

[0036] Figure 3 This is a schematic diagram of the cross-section of the preforming mold;

[0037] Figure 4 This is a schematic diagram of the final forming mold according to an embodiment of the present invention;

[0038] In the diagram: 200 - Final forming mold; 201 - Upper final forming mold; 202 - Lower final forming mold

[0039] Figure 5 This is a schematic diagram of the final forming mold cross-section;

[0040] Figure 6 This is a schematic diagram of the structure of the sheet component according to an embodiment of the present invention. Detailed Implementation

[0041] To make the results, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail, clearly, and completely below with reference to the accompanying drawings. Based on the description in this invention, all other practical examples obtained by those skilled in the art without inventive effort are within the scope of protection of this invention.

[0042] This invention provides a method for improving the bonding properties of titanium alloy propeller blade cladding during forming, such as... Figure 1 As shown, the patch forming method includes:

[0043] Step 1: Fabrication of the preforming mold. The preforming mold includes a preforming upper mold and a preforming lower mold that are combined and fitted together. The preforming upper mold is used to form a semi-finished blade sheath with a wide pitch and shallow cavity. Compared with the final blade sheath size, the pitch at the beginning and end of the sheath is increased by 0.6-1mm, and the pitch in the middle section of the sheath gradually decreases following the change in the pitch at the beginning and end, controlled to be about 0.2mm greater than the theoretical size. The overall cavity is shallower by 0.4-1mm to avoid forming a closed angle. The preforming lower mold is used in conjunction with the upper mold.

[0044] The final forming mold includes a final forming upper mold and a final forming lower mold that are combined and fitted together. The final forming upper mold is used to form the final blade envelope. To avoid closed angles, the overall trend of the upper mold is consistent with that of the pre-forming upper mold. Compared with the final blade envelope size, the distance is controlled to be no more than 0.2 mm, and the cavity size is controlled to be no more than 0.1 mm. The final forming lower mold has the same size as the final blade envelope. The gap between the molds is used for material flow and stress release during the forming process.

[0045] Step 2: Perform single-sided surface sandblasting on the titanium alloy sheet before forming to control the amount of product deformation;

[0046] Step 3: Implement protective and lubrication measures to control the surface roughness of the sandblasted surface;

[0047] Step 4: Fix the upper and lower molds of the preformed mold on the upper and lower platforms of the thermoforming equipment respectively, keep the upper and lower molds safely separated, place the titanium alloy sheet on the lower mold of the preformed mold, and perform mold closing thermoforming under an inert gas protective atmosphere to obtain the preformed titanium alloy blade cladding.

[0048] Step 5: Remove the pre-formed titanium alloy blade sheath;

[0049] Step 6: The upper and lower molds of the final forming mold are fixed on the upper and lower platforms of the vacuum forming equipment, keeping the upper and lower molds safely separated. The pre-formed titanium alloy blade pack is placed on the lower mold of the final forming mold. The furnace door is closed. After the furnace reaches a vacuum state, the final forming is carried out to obtain the final formed titanium alloy blade pack.

[0050] Step 7: The final titanium alloy propeller blade is pickled and polished with surface protection.

[0051] Step 8: Complete the final edge trimming and surface roughness measurement; the roughness is greater than 1.0 μm.

[0052] The improved bonding forming method for titanium alloy blade cladding provided by this invention is applicable to the forming process of integrated titanium alloy cladding with variable cross-section and torsion angle. It solves the problems of ensuring the control of roughness such as material stretching during hot forming and material corrosion during pickling while meeting the material deformation required for hot forming, thereby improving the blade bonding success rate and bonding uniformity.

[0053] The titanium alloy sheet is a thin-walled sheet from the GJB2505 series. The unfolded material and tooling dimensions are selected according to the actual product. The aforementioned titanium alloy pre-forming + final forming process is used for cases with torsion angles or closed angles during forming. A schematic diagram of the tooling structure is shown below. Figures 2-5 .

[0054] First, the titanium alloy sheet undergoes sandblasting. It's important to note that the sheet needs to be sandblasted twice using different materials to ensure sufficient deformation after sandblasting, meeting the material contour requirements of the subsequent hot forming mold. Specific parameters are as follows:

[0055] The single-sided surface sandblasting treatment of the titanium alloy sheet before forming includes: first sandblasting with corundum particle size of 80 mesh, air pressure of 0.4-0.5 MPa, nozzle tilt angle of 70-90° to the surface to be sprayed, and path in a diagonal direction to facilitate surface uniformity, sandblasting time of 5-10 min; second sandblasting with corundum particle size of 160 mesh, air pressure of 0.4-0.5 MPa, nozzle tilt angle of 70-90° to the surface to be sprayed, path in the opposite direction to the first sandblasting, sandblasting time of 10-15 min; after sandblasting, the sheet profile and roughness are inspected to ensure that the part is in a single-curved arch shape, with a profile ≤5 mm and a roughness of 1.2-2.5 μm; the sandblasted sheet is stored separately in a polyethylene anti-rust bag, and wrapped with kraft paper and cotton cloth during handling to prevent wear.

[0056] The preforming process for the titanium alloy sheet includes: first, clamping the tooling onto the equipment and heating the tooling to 600-750℃. It should be noted that before each clamping, the mold surfaces must be cleaned with 1000-1500 grit sandpaper to ensure cleanliness, followed by cleaning the surfaces with an organic solvent and evenly applying a layer of lubricant. Then, the preforming process is performed. The preforming process includes: installing the titanium alloy sheet onto the mold, which has stop pins on both sides to accurately position the sheet. Before installation, a thorough application of antioxidant and lubricant is made to completely cover the base color of the titanium alloy sheet. Before closing the mold, the material needs to be preheated for 2-5 minutes, then the mold is slowly closed while continuously introducing inert protective gas such as argon at a pressurization rate of 0.1MPa-0.5MPa / min, controlling the pressure to not exceed 2MPa. After the mold is closed, pressure is applied to 20-80T and held for 5-10 minutes. Then, the furnace temperature is lowered to below 500℃. The mold is then opened, and the parts are simultaneously clamped from both ends. It is important to note that during clamping, actions that could cause excessive deformation of the sheet metal, such as prying, are prohibited. The parts are then placed in an insulated box to cool, and after cooling, they are individually stored in polyethylene rust-proof bags. It is worth mentioning that the pre-forming time needs to be strictly controlled. Inert gas shielding cannot completely prevent oxidation of the part surface; the entire process should minimize factors that cause oxidation of the sandblasted surface.

[0057] The final forming process for the packaged parts includes: removing the pre-formed semi-finished packaged parts from the heat preservation box and placing them into a vacuum forming equipment. The tooling and pre-forming treatment of the parts are the same as in the pre-forming process. Before placing the parts in, antioxidants and lubricants are reapplied. Before closing the mold, the material needs to be preheated for 2-5 minutes. The forming process requires heating to 600-750℃, holding pressure for 40-70 minutes, and then cooling in the furnace. The mold is opened and the parts are removed at 200-350℃, with the removal requirements being the same as those for pre-forming. The final parts are then placed in a heat preservation box for cooling. It should be noted that the final forming is a secondary thermoforming process, which affects the surface quality and performance of the material. Therefore, a vacuum thermoforming equipment must be used, and the parts must be cooled in the furnace. By combining the pre-forming and final forming methods, the delivery schedule of the parts can be reasonably guaranteed while ensuring the surface roughness of the parts.

[0058] The pickling and surface protection polishing process includes: before and after pickling, and during the polishing and trimming process, a weakly adhesive protective tape needs to be pasted on the sandblasting surface to ensure the roughness and uniformity of the sandblasting surface and prevent metal debris from scratching the surface.

[0059] The improved bonding forming method for titanium alloy blade cladding provided by this invention is applicable to the forming of integrated titanium alloy cladding with non-uniform cross-sections and inverted V-shaped narrow cavity configurations with twist angles. It solves the problems of difficulty in ensuring roughness uniformity and deformation after sandblasting of blade cladding with narrow cavity features. For cladding with complex features, it ensures the control of roughness by material stretching during hot forming and material corrosion during pickling, while meeting the material deformation required for hot forming. This improves the roughness uniformity of the bonding surface of the blade cladding, and increases the bonding success rate and bonding uniformity of the blade cladding.

[0060] Example 1

[0061] The process involves forming a 0.5mm thick, 2500mm long cladding sheet with a torsion angle from TC4 material. The part structure is as follows: Figure 4 The material is made from 2700mm x 550mm sheet metal, using a pre-forming + final vacuum forming process. Two surface sandblasting treatments are performed, with sandblasting times of 7 minutes and 12 minutes respectively. Multiple measurements are taken after sandblasting, with an average surface roughness of 2.0µm and a roughness range of 1.5-2.5µm. The sheet metal exhibits good contour after sandblasting, without issues such as hyperbola or torsion. After cleaning the mold and applying antioxidants and lubricants to the sheet metal, pre-forming is performed at a forming temperature of 710℃, holding pressure for 8 minutes, forming tonnage of 40T. The part is then removed after the furnace temperature is cooled to 500℃ for final forming at a final forming temperature of 680℃, holding pressure for 50 minutes, and then cooled to 300℃ before removal. After surface protection, pickling, grinding, and cutting, the final part is formed, with an internal surface roughness of 1.2-1.8µm.

[0062] Example 2

[0063] The process involves forming a 0.5mm thick, 2500mm long cladding sheet with a torsion angle from TC4 material. The part structure is as follows: Figure 4 The blade was processed using a 2700mm x 550mm sheet metal, employing a pre-forming + final vacuum forming method. Two surface sandblasting treatments were performed, each lasting 17 minutes, which deviates from the above requirements. Multiple measurements were taken after sandblasting, with an average surface roughness of 2.5µm and a roughness range of 1.8-2.9µm. The profile of the sheet metal after sandblasting was relatively poor, reaching a maximum of 7mm. The remaining forming methods were the same as in Example 1, and the final surface roughness was 1.5-2.2µm, meeting the requirements. However, the blade envelope shape exceeded tolerances in multiple places, with the largest deviation from the theoretical value by 0.7mm, exceeding the allowable value by 0.2mm, thus classifying it as a non-conforming product.

[0064] Example 3

[0065] The process involves forming a 0.5mm thick, 2500mm long cladding sheet with a torsion angle from TC4 material. The part structure is as follows: Figure 4 The material was processed using 2700mm x 550mm sheet metal, employing a pre-forming + final vacuum forming method. Two surface sandblasting treatments were performed, with sandblasting times of 8 minutes and 13 minutes respectively. Multiple measurements were taken after sandblasting, resulting in an average surface roughness of 2.3µm, ranging from 1.6-2.6µm. The sheet metal exhibited good contour after sandblasting. After cleaning the mold and applying antioxidant and lubricant to the sheet metal, pre-forming was performed at 730℃ for 15 minutes, deviating from the above requirements. The forming tonnage was 40T. The part was removed after the furnace temperature cooled to 500℃ for final forming at 680℃ for 50 minutes. After cooling to 300℃ in the furnace, the part was removed, surface protected, acid-washed, ground, and cut to form the final part. The internal surface roughness of the part was 0.7-1.3µm, failing to meet the requirement of a roughness of not less than 1µm, thus constituting a substandard product.

[0066] Example 4

[0067] The process involves forming a 0.5mm thick, 2500mm long cladding sheet with a torsion angle from TC4 material. The part structure is as follows: Figure 4 The material was processed using 2700mm x 550mm sheet metal, employing a pre-forming + final vacuum forming method. Two surface sandblasting treatments were performed, with sandblasting times of 7 minutes and 13 minutes respectively. After sandblasting, multiple measurements were taken, resulting in an average surface roughness of 2.2µm, ranging from 1.4-2.5µm. The sheet metal exhibited good contour after sandblasting. After cleaning the mold and applying antioxidant and lubricant to the sheet metal, pre-forming was performed at 780℃, with a holding pressure of 9 minutes and a forming tonnage of 40T. The part was then removed after cooling to 500℃ in the furnace. Final forming was then performed at 800℃, with a holding pressure of 30 minutes. This deviated from the above requirements, so the furnace was cooled to 300℃ before the part was removed. After surface protection, pickling, grinding, and cutting, the final part was formed. The internal surface roughness of the part was 1.2-1.6µm, meeting the requirements. However, the part's shape deviated from the theoretical shape, with the largest deviation exceeding the theoretical value by 0.8mm and the allowable value by 0.2mm, thus classifying it as a non-conforming product.

[0068] Comparative Example

[0069] The process involves forming a 0.5mm thick, 2500mm long cladding sheet with a torsion angle from TC4 material. The part structure is as follows: Figure 4The material was processed using 2700mm x 550mm sheet metal, employing a pre-forming + final vacuum forming method. Two surface sandblasting treatments were performed, each lasting 4 minutes. Multiple measurements were taken after sandblasting, resulting in an average surface roughness of 0.9µm, ranging from 0.6-1.4µm, which is relatively low. The sheet metal exhibited good contour after sandblasting. After cleaning the mold and applying antioxidants and lubricants to the sheet metal, pre-forming was performed at 780℃ for 15 minutes, with a forming tonnage of 40T. The part was then removed after cooling to 500℃. Final forming was then performed at 600℃ for 30 minutes, deviating from the above requirements. The part was then removed after cooling to 300℃, followed by surface protection, pickling, grinding, and cutting to form the final part. The internal surface roughness of the part was 0.4-1µm, failing to meet the requirements. The part's shape deviated from the theoretical shape in one location, exceeding the theoretical value by 0.6mm and the allowable value by 0.1mm. The part's thickness was uneven and severely thinned, classifying it as a substandard product.

Claims

1. A method for improving the adhesive bonding properties of titanium alloy propeller blade cladding, characterized in that, It is applied to the forming process of titanium alloy blade cladding, wherein the titanium alloy blade cladding has a non-uniform cross section and an inverted V-shaped narrow cavity configuration; Includes the following steps: Step 1: Make the pre-forming mold and the final forming mold; Step 2: Perform single-sided surface sandblasting on the titanium alloy sheet before forming to control the amount of product deformation; Step 3: Implement protective and lubrication measures to control the surface roughness of the sandblasted surface; Step 4: Fix the upper and lower molds of the preformed mold on the upper and lower platforms of the thermoforming equipment respectively, keep the upper and lower molds safely separated, place the titanium alloy sheet on the lower mold of the preformed mold, and perform mold closing thermoforming under an inert gas protective atmosphere to obtain the preformed titanium alloy blade cladding. Step 5: Remove the pre-formed titanium alloy blade sheath; Step 6: The upper and lower molds of the final forming mold are fixed on the upper and lower platforms of the vacuum forming equipment, keeping the upper and lower molds safely separated. The pre-formed titanium alloy blade pack is placed on the lower mold of the final forming mold. The furnace door is closed. After the furnace reaches a vacuum state, the final forming is carried out to obtain the final formed titanium alloy blade pack. Step 7: The final titanium alloy propeller blade is pickled and polished with surface protection.

2. The method for improving the adhesive bonding properties of titanium alloy propeller blade cladding according to claim 1, characterized in that, In step 1, the preforming mold includes a preforming upper mold and a preforming lower mold that are combined and fitted together. The preforming upper mold is used to form a semi-finished blade wrapper with a wide spacing and shallow cavity. Compared with the theoretical size of the blade wrapper, the spacing at the beginning and end of the wrapper is increased by 0.6-1mm, and the spacing in the middle section of the wrapper gradually decreases following the change in the spacing at the beginning and end, controlled to be 0.2mm greater than the theoretical size. The cavity becomes shallower overall by 0.4-1mm as the spacing changes. The preforming lower mold is used in conjunction with the upper mold. The final forming mold includes a final forming upper mold and a final forming lower mold that are combined and fitted together. The final forming upper mold is used to form the final shape of the blade envelope. To avoid the formation of a closed angle, the overall size of the lower mold is smaller than the theoretical size of the blade envelope. The distance is controlled to be no more than 0.2 mm and the cavity size is controlled to be no more than 0.1 mm. The final forming lower mold has the same size as the final blade envelope. The gap between the molds is used for material flow and stress release during the forming process.

3. The method for improving the adhesive bonding properties of titanium alloy propeller blade cladding according to claim 1, characterized in that, In step 1, the preforming mold structure is designed in reverse according to the configuration, size and volume of different packaging pieces and the required mold volume, and the shape of the preformed product is adjusted.

4. The method for improving the adhesive bonding properties of titanium alloy propeller blade cladding according to claim 1, characterized in that, Step 2 specifically includes the following steps: The first sandblasting process involves 80-mesh corundum particles, an air pressure of 0.4-0.5 MPa, and a sandblasting time of 5-10 minutes. The second sandblasting process involves 160-mesh corundum particles, an air pressure of 0.4-0.5 MPa, and a sandblasting time of 10-15 minutes. Sandblasting is performed in reverse. After sandblasting, the profile and roughness of the sheet are inspected to ensure that the part is in a single-curved arch shape, with a profile ≤5mm and a roughness of 1.2-2.5µm.

5. The method for improving the adhesive bonding properties of titanium alloy propeller blade cladding according to claim 1, characterized in that, The preforming process of the titanium alloy sheet includes: Install the titanium alloy sheet after sandblasting on the forming die. Before installation, fully apply an antioxidant and a lubricant until the base color of the titanium alloy sheet is completely covered. Heat it to 700 - 800 °C at a heating rate of 50 - 150 °C / h. Pass an inert protective gas such as argon into the cavity of the titanium alloy sheet through a ventilation pipeline. The pressurization speed is 0.1 Mpa - 0.5 MPa / min, control the pressure not to exceed 2 MPa, hold the pressure for 5 - 10 min, and then after the furnace temperature drops below 500 °C, put it into an incubator to cool down.

6. The method for improving the adhesive bonding properties of titanium alloy propeller blade cladding according to claim 1, characterized in that, The final forming process of the titanium alloy sheet includes: Take out the preformed semi-finished product wrap from the incubator and put it into a vacuum forming device. Before putting it in, reapply the antioxidant and the lubricant, heat it to 600 - 750 °C, hold the pressure for 40 - 70 min, and then cool it with the furnace. Open the mold to take out the part at a temperature of 200 - 350 °C and put it into an incubator to cool down.

7. The method for improving the adhesive bonding properties of titanium alloy propeller blade cladding according to claim 1, characterized in that, After the wrap cools below 100 °C and is pickled, paste a weakly adhesive protective tape on the sandblasted surface until the part is completely processed.

8. The method for improving the adhesive bonding properties of titanium alloy propeller blade cladding according to claim 1, characterized in that, The method also includes completing the final trimming and surface roughness measurement, with the roughness greater than 1.0um; If it meets the requirements, it means the product is qualified; if it does not meet the requirements, the product is unqualified.

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