High-precision processing technology for helicopter damper joint

Abstract

The application relates to the technical field of helicopter machining, and discloses a high-precision processing technology for a helicopter damper joint, which comprises the following steps: performing flaw detection and stress relief annealing treatment on raw material rods, then performing outer contour cutting and reserving machining allowance by using a five-axis machining center and a hard alloy end mill, performing vacuum heat treatment on the workpiece, reserving fine machining allowance by using a coated hard alloy cutter through multiple passes, then performing trace cutting by using a superfine grain hard alloy cutter with a coating to remove the fine machining allowance, spraying a nano composite powder containing aluminum oxide and titanium dioxide on the non-threaded matching surface of the joint by using a plasma device, and performing surface treatment through grinding and polishing, and finally detecting the tolerance by using a three-coordinate measuring instrument. The application combines stage material removal and heat treatment to control residual stress and micro deformation, and is matched with local surface strengthening to meet the engineering requirements of the joint on assembly size stability and local wear resistance.

Description

Technical Field

[0001] This invention relates to the field of aerospace machining technology, specifically a high-precision machining process for helicopter damper joints. Background Technology

[0002] In helicopter power transmission and vibration control systems, damper joints serve as structural connections and force transmission components. The machining quality of damper joints directly affects the dynamic characteristics of the entire aircraft. Currently, the machining of such joints generally follows a process of rough machining followed by finish machining. When processing aerospace metal materials such as titanium alloys or high-strength stainless steel, the continuous cutting process often generates significant residual tensile stress within the material. Due to the lack of corresponding stress release mechanisms, the workpiece will undergo microscopic deformation of its physical dimensions when placed naturally or subjected to stress during subsequent service, causing the tolerances of the hole diameter or mating surface to deviate from the design standards, resulting in a certain proportion of parts being scrapped.

[0003] In addition, conventional carbide cutting tools wear out quickly when cutting high-strength materials, making it difficult to maintain the flatness of the machined surface for a long time. This can leave deep cutting marks or induce microcracks on the surface of the parts. These surface defects can weaken the overall fatigue resistance of the joint to a certain extent. Conventional machining processes also lack targeted local surface strengthening treatments. Simple passivation operations are difficult to provide long-term protection in sand and dust friction or salt spray environments. As a result, the mating surfaces of the joints face the problem of faster wear and corrosion in actual use. The poor internal stress control and surface quality defects in the above-mentioned machining processes not only shorten the actual service life of the helicopter damper joint, but also cause large fluctuations in dimensional deviations between workpieces in the same batch, affecting the overall production yield and manufacturing efficiency. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high-precision machining process for helicopter damper joints, which solves the problems of workpiece dimensional deformation caused by residual stress accumulation in traditional cutting processes, and the difficulty of meeting the local high wear resistance requirements of mating surfaces in conventional machining methods.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a high-precision machining process for helicopter damper joints, comprising the following steps: After ultrasonic testing of the selected raw material bars and finding no defects, stress-relieving annealing was carried out. A five-axis machining center and a carbide end mill are used to cut the outer contour and leave machining allowance; The workpiece after cutting and leaving machining allowance is heat-treated in a vacuum heat treatment furnace. The heat treatment is vacuum solution treatment and aging treatment or vacuum quenching and tempering treatment. After multiple passes of the heat-treated workpiece using coated carbide tools, a finishing allowance is reserved. The aforementioned finishing allowance is removed by multiple passes using a coated ultrafine-grained cemented carbide tool. The surface treatment is completed by spraying nanopowder containing alumina and titanium dioxide onto the non-threaded mating surface using plasma spraying equipment, followed by grinding and polishing. A coordinate measuring machine was used to perform final inspection of the dimensional and geometric tolerances of the key mating surfaces. The step of using a five-axis machining center and a carbide end mill to cut the outer contour and leave a machining allowance includes: using an emulsion with a concentration of 6% to 7% for cooling, and leaving a machining allowance of 1.2 to 1.5 mm; The step of reserving a finishing allowance after multiple passes of a heat-treated workpiece using a coated carbide tool includes reserving a finishing allowance of 0.12 to 0.16 mm. The step of removing the aforementioned finishing allowance by selecting a coated ultra-fine grain cemented carbide tool through multiple passes includes: setting the cutting parameters to a rotational speed of 8500 to 9000 r / min and a feed rate of 0.012 to 0.018 mm / r; The steps of using plasma spraying equipment to spray nanopowder containing alumina and titanium dioxide onto non-threaded mating surfaces, followed by grinding and polishing to complete the surface treatment include: the final coating thickness is controlled within the range of 60 to 70 μm.

[0006] This process gradually distributes the material removal amount between roughing, heat treatment, semi-finishing and finishing, isolating the material's deformation and internal residual stress release in stages. Combined with local plasma spraying treatment, it can, to a certain extent, meet the engineering requirements of component dimensional accuracy and surface strength.

[0007] Meanwhile, the use of an emulsion with a concentration of 6% to 7% has a relatively moderate specific heat capacity and permeability, which helps to suppress the formation of built-up edge at the cutting edge. The 1.2 to 1.5 mm machining allowance can provide room for correction of matrix distortion caused by phase transformation and residual stress release during the vacuum heat treatment stage. The 0.12 to 0.16 mm finishing allowance enables the final cutting action to peel off the modified layer and reduces the possibility of high-frequency tool chatter during machining. The finishing process uses a cutting mechanism consisting of high speed and extremely small feed rate, which causes the chips to be sheared and broken instantly, taking away most of the heat. This limits the temperature rise conducted to the damper joint body and reduces the residual tensile stress on the machined surface. The final coating thickness is controlled within the range of 60 to 70 μm to prevent excessive stress accumulation inside the coating from causing interface peeling.

[0008] Furthermore, the step of performing stress-relief annealing after selecting raw material bars for ultrasonic flaw detection and finding no defects includes: the "no defects found" refers to no defects larger than 0.1 mm.

[0009] Limiting the upper limit of the size of physical defects inside the raw materials is mainly to detect potential microcracks and inclusions in the early stage, so as to reduce the probability of stress concentration or even fatigue fracture in specific areas during subsequent cutting and actual service.

[0010] Furthermore, the step of using a five-axis machining center and a carbide end mill to cut the outer contour and leave machining allowance includes: setting the cutting parameters to a rotational speed of 3200 to 3500 r / min, a feed rate of 0.15 to 0.18 mm / r, and a depth of cut of 2.5 to 2.8 mm.

[0011] The above parameter combination settings can control cutting resistance while maintaining normal metal removal efficiency, prevent excessive temperature rise, slow down the conduction of heat to the inside of the workpiece, and thus avoid deep plastic deformation or thermal damage to the material surface.

[0012] Furthermore, the step of reserving a finishing allowance after multiple passes of the heat-treated workpiece using coated carbide tools includes: setting the cutting parameters to a rotational speed of 5500 to 5800 r / min, a feed rate of 0.06 to 0.07 mm / r, and a depth of cut of 0.4 to 0.5 mm.

[0013] As the depth of cut decreases and the spindle speed increases accordingly, the cutting force in the semi-finishing stage will decrease significantly. This not only helps to correct the contour deformation left by the previous heat treatment, but also provides a more reliable positioning surface for subsequent machining processes.

[0014] Furthermore, the step of removing the aforementioned finishing allowance by selecting a coated ultrafine grain cemented carbide tool through multiple passes includes: using oil mist lubrication throughout the finishing process, and adjusting the tool compensation amount by no more than 0.002 mm.

[0015] Using oil mist lubrication helps maintain local heat balance in the cutting area and prevents damage to the cutting edge caused by rapid cooling and heating, which is common with traditional liquid cooling. The tool compensation adjustment of no more than 0.002mm is mainly used to compensate for the gradual wear of the tool's flank face, which helps to alleviate large dimensional drift between parts in the same batch.

[0016] Furthermore, the step of using a coordinate measuring machine to perform final inspection of the dimensional tolerances and geometric tolerances of the key mating surfaces includes: controlling the dimensional tolerances of the key mating surfaces within the range of -0.005mm to +0.005mm, ensuring that the parallelism, perpendicularity, and coaxiality are all no greater than 0.01mm, and that the surface roughness Ra is no greater than 0.4μm.

[0017] Controlling the relevant physical dimensions and roughness within the above-mentioned parameters can indirectly reflect that the joint end face and hole position have a relatively ideal assembly clearance, so that the components can maintain a certain force transmission stability when facing the high-frequency and small vibration conditions of the helicopter body.

[0018] Furthermore, the step of using plasma spraying equipment to spray nanopowder containing alumina and titanium dioxide onto a non-threaded mating surface, followed by grinding and polishing to complete the surface treatment includes: the coating formed by spraying exhibits a composite layered state, the composite layered state including a transition layer attached to one side of the metal substrate, and a working layer located above the transition layer; the working layer exhibits a mixed crystalline morphology in which columnar crystals and equiaxed crystals intertwine.

[0019] Setting a transition layer helps alleviate the interfacial thermal stress caused by the difference in thermal expansion coefficients between the underlying metal and the surface ceramic, reducing the risk of interfacial delamination caused by temperature changes. In the mixed crystalline morphology of columnar and equiaxed crystals intertwined inside the working layer, the vertically grown columnar crystal structure is responsible for providing high surface hardness and normal bearing capacity, while the blocky equiaxed crystals dispersed around the grain boundaries can change the linear propagation path of microcracks under medium and high frequency vibration stress, thereby giving the local coating good impact toughness.

[0020] This invention provides a high-precision machining process for helicopter damper joints. It offers the following advantages: 1. This invention introduces vacuum heat treatment and semi-finishing processes between roughing and finishing, physically isolating the large-scale material removal and internal residual stress release processes. This phased, decreasing machining strategy, combined with dynamic compensation of tool parameters with slight amplitude, alleviates the problem of thermal deformation accumulation caused by traditional single continuous cutting. This allows the final dimensional tolerance of the key mating surfaces of the joint to be stably controlled between -0.005mm and +0.005mm, meeting the physical dimensional stability requirements of helicopter damper components in complex assembly environments.

[0021] 2. This invention utilizes a material removal mechanism with a high rotational speed and a small feed rate designed for the finishing process. This allows the metal chips to carry away most of the heat the moment they leave the workpiece, significantly suppressing the temperature rise conducted to the damper joint body. Combined with continuous oil mist lubrication, this reduces the risk of rapid cooling and heating damage between the cutting edge and the machined surface. As a result, a surface roughness of no more than 0.4 micrometers and no obvious deep thermal damage layer are obtained, which helps to delay the initiation of fatigue cracks in stressed components under alternating loads.

[0022] 3. This invention applies a composite coating containing alumina and titanium dioxide nanoparticles to the non-threaded mating surface using plasma spraying technology. The nanoparticles are small in size, which facilitates full heating, melting, and uniform spreading of the particles during the plasma spraying process. This refines the coating structure, improves the uniformity and density of the coating, and helps to leverage the synergistic effect of alumina's wear resistance and titanium dioxide's toughness improvement. After grinding and polishing, the final overall thickness of the composite coating is controlled within the range of 60 to 70 μm. The specific ratio of ceramic powder components balances the wear resistance hardness and a certain degree of toughness of the contact surface, while the limited thickness range prevents the coating from peeling off due to excessive accumulation of internal tensile stress. This provides the necessary local anti-wear working layer for the joint surface under long-term fretting friction conditions, while avoiding the risk of damaging the assembly thread profile by spraying ceramics into the threaded area. Attached Figure Description

[0023] Figure 1 This is a three-dimensional schematic diagram of the damper joint in Embodiment 2 of the present invention; Figure 2 This is a schematic diagram of the ceramic coating structure in Embodiment 1 of the present invention, wherein, Figure 2 (a) is a schematic diagram of the composite layered structure. Figure 2 (b) is a schematic diagram of the microstructure of the working layer.

[0024] Among them, 1. transition layer; 2. working layer; 3. columnar crystals; 4. equiaxed crystals. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Please see the appendix Figure 1 and attached Figure 2 . Example 1

[0027] The object to be processed is a fork-shaped structure with a diameter of φ80mm×120mm and a high-precision connection hole in the center.

[0028] Final processed product parameters: flatness of key mating surfaces ≤ 0.01mm, final size of connecting holes φ29.995mm to 30.005mm, surface roughness Ra≤ 0.4μm, service life ≥ 8000 flight hours.

[0029] The implementation steps are as follows: φ80mm titanium alloy TC4 bar stock, i.e. Ti-6Al-4V, with chemical composition conforming to GB / T3620.1-2016 standard, was selected. A CTS-9006 ultrasonic flaw detector was used for testing, with a frequency of 5MHz and a probe diameter of 14mm. No defects larger than 0.1mm were found. After stress-relief annealing at 650℃ for 2 hours, the hardness was measured to be HRC28. After rough grinding of the outer diameter, the roundness reached 0.08mm. The surface was cleaned with alcohol and then transferred to the rough machining stage.

[0030] The VMC-850 vertical machining center, equipped with a dual-axis rotary table to achieve five-axis machining capability, is used. It is equipped with a φ20mm WC-Co carbide end mill. The cutting parameters are set as follows: spindle speed 3500r / min, feed rate 0.15mm / r, depth of cut 2.5mm. The cooling method is 6% emulsion cooling. The machining path adopts a combination of helical cutting and contour cutting to cut the outer contour and leave a 1.2mm machining allowance. At the same time, a process pilot hole with a diameter of φ25mm is pre-drilled at the center of the connecting hole. After machining, the outer dimensions are φ79.9mm to 80.1mm, and the end face runout is 0.04mm, which meets the rough machining quality requirements.

[0031] A ZRC-60 vacuum heat treatment furnace was used, with the vacuum level controlled at 3×10⁻⁶. -3 The process parameters were set as follows: solution treatment at 930℃ for 1 hour, followed by furnace cooling to 550℃ and holding for 4 hours, and finally air cooling to room temperature. The hardness after heat treatment was HRC38, and the residual stress was 35MPa with X-ray stress meter. The stress relief rate was 92%, and the surface was free of oxidation color, which met the requirements for subsequent processing.

[0032] Using the end face as the reference surface, two φ8mm positioning holes were machined, with the hole spacing error controlled within -0.01mm to +0.01mm. TiAlN coated carbide tools were used, and the planar milling parameters were set as follows: rotation speed 5500r / min, feed rate 0.06mm / r, and depth of cut 0.4mm. After multiple passes, a finishing allowance of 0.12mm was reserved on the end face. The hole system machining parameters were as follows: drilling rotation speed 3000r / min, feed rate 0.1mm / r, and reaming rotation speed 1500r / min, feed rate 0.05mm / r. At the same time, the central process bottom hole was semi-finished and enlarged to a diameter of φ29.84mm, thus reserving a diameter tolerance finishing allowance of 0.16mm for the final connecting hole. After semi-finishing, the surface roughness Ra=2.0μm and flatness 0.02mm were measured, which met the semi-finishing accuracy standard.

[0033] A DMG MORI DMC 80 U five-axis machining center was selected, equipped with TiAlN-coated ultra-fine grain carbide tools, including a φ12mm end mill and a φ30mm boring bar. The boring parameters for the connecting holes were set to a spindle speed of 9000 r / min, a feed rate of 0.015 mm / r, and a depth of cut of 0.08 mm. The single-sided depth of cut of 0.08 mm precisely removed 0.16 mm of diameter allowance. The end face finish milling parameters were a spindle speed of 8500 r / min, a feed rate of 0.018 mm / r, and a depth of cut of 0.06 mm. The end face allowance was removed in two passes. Oil mist lubrication was used throughout the finish machining process. Online inspection was performed after every 3 parts were machined. The tool compensation adjustment range was ≤0.002 mm to ensure dimensional stability.

[0034] Plasma spraying equipment was used, and 150nm nano powder containing 97% alumina and 3% titanium dioxide was selected. The pretreatment was carried out by sanding with 800# sandpaper, ultrasonic cleaning with acetone and sandblasting. The spraying parameters were set as follows: power 45kW, Ar to H2 ratio 95:5 and spraying distance 120mm.

[0035] During the specific spraying process, the plasma spray gun is reciprocated along the area to be strengthened on the non-threaded mating surface. First, a transition layer 1 is deposited. Under the conditions of 45kW power, Ar:H2 ratio of 95:5 and spraying distance of 120mm, alumina and titanium dioxide nanoparticles are fed into the plasma jet. After the powder particles are heated to form a molten or semi-molten state, they impact the surface of the sandblasted metal substrate and spread, fill and solidify in the micro-uneven areas of the metal substrate surface. The molten or semi-molten particles are directly deposited on the surface of the metal substrate and fill the micro-recesses formed by sandblasting. Through continuous reciprocating spraying, the deposition thickness reaches about 10μm, thereby forming a transition layer 1 that adheres to the surface of the metal substrate.

[0036] After the transition layer 1 is formed, while keeping the spraying power at 45kW, the Ar to H2 ratio at 95:5 and the spraying distance at 120mm constant, the plasma spray gun continues to spray repeatedly along the same non-threaded mating surface, so that the molten or semi-molten alumina and titanium dioxide particles are continuously deposited on the surface of the transition layer 1. The adjacent spray lines overlap and are stacked layer by layer until a working layer 2 with an initial thickness of 60 to 80μm is formed.

[0037] The transition layer 1 is in direct contact with the metal substrate and is used to improve the interfacial bonding state between the ceramic coating and the metal substrate, and to buffer the interfacial stress caused by the difference in thermophysical properties between the metal substrate and the ceramic coating. The working layer 2 is located outside the transition layer 1 and serves as the main wear-resistant area that directly bears the friction load. The composite layered structure is formed by the transition layer 1, which is directly attached to the metal substrate, and the working layer 2, which is located outside the transition layer 1, along the coating thickness direction.

[0038] Combination Figure 2 (a) It can be seen that the surface strengthening layer attached to the non-threaded mating surface by plasma spraying presents a composite layered state. A transition layer 1 with a thickness of about 10 μm is distributed on the side that is in contact with the metal substrate. The transition layer 1 helps to alleviate the interfacial thermal stress caused by the difference in thermal expansion coefficient between the bottom metal and the surface ceramic, and reduces the risk of interfacial delamination caused by temperature changes. Above the transition layer 1 is the working layer 2 that mainly bears external friction. The initial thickness of the working layer 2 after spraying is between 60 and 80 μm. Subsequently, the loose structure of the surface of the composite coating is removed by grinding and polishing, and the composite coating after grinding and polishing is controlled to the predetermined final thickness.

[0039] Further observation Figure 2 (b) The microstructure of the working layer 2 shows a mixed crystal morphology in which columnar crystals 3 and equiaxed crystals 4 are intertwined. The vertically growing columnar crystals 3 are responsible for providing high surface hardness and normal bearing capacity, while the blocky equiaxed crystals 4 dispersed around the grain boundaries can change the straight propagation path of microcracks when subjected to medium and high frequency vibration, thereby giving the local coating a certain impact toughness.

[0040] During the continuous deposition process, the nanopowder is rapidly heated after being subjected to plasma jets, and then spreads and solidifies rapidly after impacting the deposited surface. The continuous overlap between adjacent spray lines makes the working layer 2 form a relatively continuous and dense composite structure. The small particle size of the nanopowder also helps to improve the uniformity of the deposited structure and reduce the possibility of local loose defects caused by coarse unmelted particles.

[0041] After the composite coating, which includes transition layer 1 and working layer 2, undergoes subsequent grinding and fine polishing processes to remove the loose surface structure, the final overall coating thickness is controlled at 60μm. After grinding and polishing, the surface roughness Ra=0.32μm and the coating hardness reaches HV960.

[0042] Using a Leitz PMM-C coordinate measuring machine, the hole diameter was found to be φ30.002mm, meeting the tolerance requirements of -0.005mm to +0.005mm, with parallelism of 0.008mm, perpendicularity of 0.009mm, and coaxiality of 0.007mm. Atomic force microscopy confirmed the absence of microcracks on the surface. Fatigue testing was conducted for 10... 7 No breakage was observed in the second cycle; no rust was observed after 72 hours of salt spray testing, and the indicators met the design requirements. Example 2

[0043] The object to be machined is a stepped shaft structure with a diameter of φ100mm×150mm, one end of which has an external thread section to be machined.

[0044] Final processed product parameters: key mating surface dimensional tolerance is -0.004mm to +0.004mm, coaxiality ≤0.007mm, surface roughness Ra≤0.4μm, and wear in a sandy environment ≤0.01mm / thousand hours.

[0045] The implementation steps are as follows: φ100mm 30CrMnSiA alloy structural steel bar material is selected, with carbon 0.30%, chromium 0.95%, and manganese 0.90%, which conforms to GB / T 3077-2015 standard. After ultrasonic testing at a frequency of 5MHz, no defects exceeding the standard are detected. After stress relief annealing at 550℃ for 3 hours, the hardness is HRC26. After rough grinding of the outer circle, the roundness is 0.09mm. After cleaning, it is transferred to rough machining.

[0046] The VMC-850 five-axis machining center was used, equipped with a φ20mm carbide end mill. The cutting parameters were set as follows: spindle speed 3200r / min, feed rate 0.18mm / r, and depth of cut 2.8mm. A 7% concentration emulsion was used for cooling. Rough milling was performed on the stepped surfaces of the outer diameter, and rough machining was also performed on the outer diameter of the threaded section at the tail. A machining allowance of 1.5mm was uniformly reserved. After machining, the main dimensions of the outer diameter were φ99.9mm to 100.1mm, and the end face runout was 0.05mm, which met the requirements of rough machining.

[0047] The ZRC-60 vacuum heat treatment furnace was used. The process parameters were: quenching at 880℃ for 1 hour, oil cooling at a cooling rate of 60℃ / s, and air cooling tempering at 520℃ for 3 hours. After heat treatment, the hardness was HRC36, the residual stress was 42MPa, the surface quality was good, and there was no deformation or cracking.

[0048] The machine employs a two-pin positioning method and is equipped with a TiAlN coated tool. The milling parameters for the plane are set as follows: spindle speed 5800 r / min, feed rate 0.07 mm / r, and depth of cut 0.5 mm. After multiple passes, a finishing allowance of 0.12 mm is reserved on the key mating surfaces. The machining parameters for the contour and the outer diameter of the thread are set as follows: spindle speed 5500 r / min, feed rate 0.06 mm / r, and depth of cut 0.4 mm. After semi-finishing passes, a finishing allowance of 0.12 mm is also uniformly reserved on each outer diameter surface and the bottom diameter of the thread. After semi-finishing, the surface roughness Ra is 2.2 μm and the roundness of the positioning hole is 0.01 mm.

[0049] A DMG MORI DMC 80 U machining center was selected, equipped with TiCN-coated ultra-fine grain carbide tools. The finishing parameters for the key mating surfaces and the outer diameter of the thread were set as follows: spindle speed 8500 r / min, feed rate 0.012 mm / r, and depth of cut 0.06 mm. The semi-finishing allowance of 0.12 mm was precisely removed in two passes. The final milling of the external thread section was performed using a thread end mill with the following parameters: spindle speed 300 r / min and feed rate 0.5 mm / r. The tool compensation was monitored online and dynamically adjusted throughout the finishing process, with the adjustment range controlled within 0.0015 mm.

[0050] The non-threaded mating surfaces were coated using the same plasma spraying equipment and powder ratio as in Example 1. The phased spraying method of Example 1 was adopted, in which a transition layer 1 was first deposited and then a working layer 2 was continuously deposited on the surface of the transition layer 1. The spraying power was 45kW, the ratio of Ar to H2 was 95:5, and the spraying distance was 120mm. The transition layer 1 formed first was directly attached to the metal substrate, and the working layer 2 formed subsequently covered the outside of the transition layer 1, thus forming a composite layered structure with the transition layer 1 and the working layer 2.

[0051] After grinding and polishing, the final coating thickness of the composite coating, which includes transition layer 1 and working layer 2, is controlled at 70 μm. The surface roughness Ra after grinding and polishing is 0.35 μm. The bonding strength test specimen is prepared using the same spraying process as the composite coating above and tested according to ASTM C633 standard. The coating bonding strength is measured to be 21 MPa.

[0052] The dimensional tolerances of the key mating surfaces were checked using a coordinate measuring machine, and the results were within the range of -0.004 mm to +0.004 mm, with a coaxiality of 0.007 mm and a parallelism of 0.009 mm. In the wear test under a load of 500 N and a rotation speed of 200 r / min, the wear amount was 0.008 mm / thousand-hour. In the high-temperature test at 150 °C for 2 h, the dimensional change rate was 0.0008%, and the indicators met the design requirements.

[0053] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-precision machining process for a helicopter damper joint, characterized in that, The process includes the following steps: After ultrasonic testing of the selected raw material bars and finding no defects, stress-relieving annealing was carried out. A five-axis machining center and a carbide end mill are used to cut the outer contour and leave machining allowance; The workpiece after cutting and leaving machining allowance is heat-treated in a vacuum heat treatment furnace. The heat treatment is vacuum solution treatment and aging treatment or vacuum quenching and tempering treatment. After multiple passes of the heat-treated workpiece using coated carbide tools, a finishing allowance is reserved. The aforementioned finishing allowance is removed by multiple passes using a coated ultrafine-grained cemented carbide tool. The surface treatment is completed by spraying nanopowder containing alumina and titanium dioxide onto the non-threaded mating surface using plasma spraying equipment, followed by grinding and polishing. A coordinate measuring machine was used to perform final inspection of the dimensional and geometric tolerances of the key mating surfaces. The step of using a five-axis machining center and a carbide end mill to cut the outer contour and leave a machining allowance includes: using an emulsion with a concentration of 6% to 7% for cooling, and leaving a machining allowance of 1.2 to 1.5 mm; The step of reserving a finishing allowance after multiple passes of a heat-treated workpiece using a coated carbide tool includes reserving a finishing allowance of 0.12 to 0.16 mm. The step of removing the aforementioned finishing allowance by selecting a coated ultra-fine grain cemented carbide tool through multiple passes includes: setting the cutting parameters to a rotational speed of 8500 to 9000 r / min and a feed rate of 0.012 to 0.018 mm / r; The step of using plasma spraying equipment to spray nanopowder containing alumina and titanium dioxide onto non-threaded mating surfaces, followed by grinding and polishing to complete the surface treatment includes: the final coating thickness is controlled within the range of 60 to 70 μm; The coating formed by spraying exhibits a composite layered state, which includes a transition layer (1) attached to one side of the metal substrate and a working layer (2) located above the transition layer (1); the working layer (2) exhibits a mixed crystal morphology in which columnar crystals (3) and equiaxed crystals (4) are interwoven.

2. The high-precision machining process for the helicopter damper joint according to claim 1, characterized in that, The step of performing ultrasonic flaw detection on the selected raw material bar and then performing stress-relief annealing after no defects are found includes: the no defects found are defined as no defects larger than 0.1 mm.

3. The high-precision machining process for the helicopter damper joint according to claim 1, characterized in that, The steps of using a five-axis machining center and a carbide end mill to cut the outer contour and leave machining allowance include: setting the cutting parameters to a speed of 3200 to 3500 r / min, a feed rate of 0.15 to 0.18 mm / r, and a depth of cut of 2.5 to 2.8 mm.

4. The high-precision machining process for the helicopter damper joint according to claim 1, characterized in that, The step of reserving a finishing allowance after multiple passes of a heat-treated workpiece using a coated carbide tool includes: setting the cutting parameters to a rotational speed of 5500 to 5800 r / min, a feed rate of 0.06 to 0.07 mm / r, and a depth of cut of 0.4 to 0.5 mm.

5. The high-precision machining process for the helicopter damper joint according to claim 1, characterized in that, The step of removing the aforementioned finishing allowance by selecting a coated ultra-fine grain cemented carbide tool through multiple passes includes: using oil mist lubrication throughout the finishing process, and adjusting the tool compensation amount by no more than 0.002 mm.

6. The high-precision machining process for the helicopter damper joint according to claim 1, characterized in that, The steps for final inspection of the dimensional tolerances and geometric tolerances of the key mating surfaces using a coordinate measuring machine include: controlling the dimensional tolerances of the key mating surfaces within the range of -0.005mm to +0.005mm, ensuring that the parallelism, perpendicularity, and coaxiality are all no greater than 0.01mm, and that the surface roughness Ra is no greater than 0.4μm.

Images