A stress relief method for additive manufacturing thin-walled, weakly rigid parts

Abstract

This invention relates to a stress-relief method for manufacturing thin-walled, weakly rigid parts, belonging to the field of thermal spraying technology. It solves the technical problem of deformation occurring during the thermal spraying coating process in additively manufactured thin-walled, weakly rigid parts with significant residual stress, affecting assembly. The stress-relief method for additively manufactured thin-walled, weakly rigid parts includes steps S1: initial residual stress detection and data processing of the part; step S2: assembling the part on a tooling fixture, applying preload, and then stress-relief annealing; step S3: vibration aging stress relief of the part assembled on the tooling fixture; step S4: after vibration aging stress relief, a second residual stress detection and data processing are performed, and the residual stress change rate is calculated; if the residual stress change rate does not meet the requirements, the process returns to step S3. This invention, through residual stress detection of the part, formulates a practical and scientific technical solution for stress-relief annealing and vibration aging stress relief based on the detection results.

Description

Technical Field

[0001] This invention belongs to the field of thermal spraying technology, and specifically relates to a stress relief method for additive manufacturing thin-walled, weakly rigid parts. Background Technology

[0002] Additive manufacturing boasts unique advantages such as low cost and short cycle time. With the gradual advancement of lightweighting goals, it has become an indispensable emerging technology in the aerospace field. However, additively manufactured products often exhibit unavoidable residual stress. In recent years, the demand for thermal spraying of additive products has been continuously increasing. Due to the inherently large residual stress in additive products, the release of residual stress after thermal spraying leads to part deformation and dimensional deviations, which is particularly severe in thin-walled, weakly rigid parts. The large residual stress causes deformation of thin-walled, weakly rigid parts during the thermal spraying coating process, affecting assembly and thus hindering the application of additive products.

[0003] However, the current shape control measures for easily deformable parts after thermal spraying mainly adopt the tooling design of shaft rollers, which can solve the bending phenomenon of long shaft parts after thermal spraying. However, there is no effective method for controlling the shape of thin-walled parts, such as parts with skin thickness ≤1mm.

[0004] Therefore, controlling the deformation of thin-walled, weakly rigid additive manufacturing parts during thermal spraying has become a technical problem to be solved. Summary of the Invention

[0005] Based on the above analysis, this invention proposes a stress relief method for additive manufacturing thin-walled weakly rigid parts, in order to solve the technical problem that deformation of additively manufactured thin-walled weakly rigid parts with large residual stress occurs during the thermal spray coating process, affecting assembly.

[0006] The objective of this invention is mainly achieved through the following technical solutions:

[0007] This invention provides a stress relief method for additive manufacturing thin-walled, weakly rigid parts, comprising the following steps:

[0008] Step S1: Perform initial residual stress detection on the part and process the data;

[0009] Step S2: Assemble the parts on the tooling, apply preload, and then perform stress-relief annealing;

[0010] Step S3: After stress-relief annealing, the parts assembled on the tooling are subjected to vibration aging to relieve stress.

[0011] Step S4: After vibration aging to relieve stress, the part undergoes a second residual stress test and data processing, and then the residual stress change rate is calculated; if the residual stress change rate does not meet the requirements, return to step S3.

[0012] Furthermore, in steps S1 and S4, residual stress is detected using an X-ray stress analyzer, with stress measured on the part surface at intervals of 400–500 mm. 2 / Set residual stress detection points at each detection point, and detect the normal stress in three directions: 0°, 45°, and 90° at each detection point. The direction along the right side of the part length is defined as the 0° direction, and the direction along the top of the part width is defined as the 90° direction.

[0013] Furthermore, in step S1, data processing includes the following steps:

[0014] Step S1.1: Calculate the principal stresses at each test point based on the normal stresses in the three directions at each test point;

[0015] Step S1.2: Calculate the equivalent stress at each test point based on the principal stress at each test point;

[0016] Step S1.3: Subtract the maximum and minimum equivalent stresses at the detection points to obtain the initial residual stress range Δσ. m The equivalent stress at each detection point is taken, and the magnitude and direction of the average equivalent stress on the entire surface of the part in the initial state are obtained according to the arithmetic mean calculation method.

[0017] Furthermore, in step S2, stress-relief annealing involves placing the part and tooling together in a box furnace at 0.3T. m Stress-relief annealing is performed after holding at the temperature for 2–4 hours. m The melting point of the part material is used for heat preservation, and the part is allowed to cool naturally to room temperature after the heat preservation is completed.

[0018] Furthermore, the residual stress after annealing satisfies:

[0019]

[0020] In the formula, σ 退火后残余应力 σ represents the residual stress of the part after annealing, in MPa. 退火前残余应力 The residual stress of the part after sandblasting and before annealing is expressed in MPa. The residual stress before annealing is σ. 退火后残余应力 The values ​​are: e is the average equivalent stress on the entire surface of the part under the initial state; e is the natural constant, dimensionless; ΔE is the energy difference between the energy during annealing and the energy before annealing, in joules; k is the Boltzmann constant, in joules per kainu; T a The annealing holding temperature is expressed in Kelvin (K); σ 压 The average compressive stress on the part derived from the preload is expressed in MPa.

[0021] Furthermore, in step S3, the vibration aging satisfies: σ动 +σ 退火后残余应力 <σ 零件 , where σ 动 The stress applied during the vibration process, expressed in MPa; σ 退火后残余应力 The residual stress of the part after annealing and before vibration is expressed in MPa; σ 零件 This represents the yield strength of the part material, expressed in MPa.

[0022] Furthermore, in step S3, the process parameters for vibration aging are within the range of: vibration acceleration 20–80 mm / s². 2 Frequency coverage: 2500–5000 r / min; test vibration parameters: frequency interval: 150–200 r / min; maximum acceleration at the dominant frequency: 50–80 mm / s². 2 The vibration time at the excitation point is 40 to 60 minutes.

[0023] Furthermore, in step S4, data processing includes the following steps:

[0024] Step S4.1: Calculate the principal stresses at each test point based on the normal stresses in the three directions at each test point;

[0025] Step S4.2: Calculate the equivalent stress at each test point based on the principal stress at each test point;

[0026] Step S4.3: Subtract the maximum and minimum equivalent stresses at the test points to obtain the residual stress range Δσ after stress relief. m去应力后 The equivalent stress at each test point is taken, and the average equivalent stress σ on the entire surface of the part after stress relief is obtained according to the arithmetic mean calculation method. avg去应力后 Size and orientation;

[0027] Step S4.4: Calculate the residual stress change rate and determine whether the residual stress change rate meets the requirements; if the residual stress change rate does not meet the requirements, return to step S3.

[0028] Furthermore, in step S4.4, the residual stress change rate includes the residual stress reduction rate and the comparison of the residual stress range;

[0029] The formula for calculating the residual stress reduction rate is: η=(σ avg -σ avg去应力后 ) / σ avg In the formula, η is the residual stress reduction rate, in percentage (%); σ avg σ represents the average equivalent stress on the entire surface of the part in the initial state, expressed in MPa. avg去应力后 This represents the average equivalent stress on the entire surface of the part after stress relief, expressed in MPa.

[0030] Furthermore, in step S4.4, the residual stress change rate meets the requirement that the residual stress reduction rate η > 40%, and the residual stress range Δσ after stress relief is within acceptable limits. m去应力后 Less than the initial residual stress range Δσ m .

[0031] Compared with the prior art, the present invention can achieve at least one of the following technical effects:

[0032] (1) This invention conducts residual stress testing on additively manufactured parts, and then formulates a practical and scientific technical solution for stress relief annealing and vibration aging stress relief based on the test results.

[0033] (2) By adjusting the annealing temperature and preload within a suitable range, the tooling preload and annealing temperature work together to achieve stress relief in the parts.

[0034] (3) By setting residual stress indexes for parts before spraying, this invention greatly reduces the probability of deformation of thin-walled and weakly rigid parts during the thermal spraying coating process, improves the surface accuracy of parts after plasma spraying, and avoids assembly step differences.

[0035] (4) The maximum deformation of the spraying scheme of the present invention is ±0.27mm, and the area with deformation greater than ±0.3mm is 0, which is far superior to the technical indicators of the traditional spraying scheme, where the maximum deformation is ±1.6mm and the area with deformation greater than ±0.3mm accounts for 27-38% of the total area.

[0036] Other features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0037] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0038] Figure 1 This is a schematic diagram of residual stress detection for a part.

[0039] Figure 2 This is a schematic diagram of the assembly of parts and tooling;

[0040] In the diagram, 1-part; 10-inspection point; 11-screw hole; 2-tooling; 20-tooling nut; 3-screw. Detailed Implementation

[0041] The following detailed description of a stress relief method for additive manufacturing thin-walled, weakly rigid parts, with reference to specific embodiments, is provided. These embodiments are for comparative and illustrative purposes only, and the present invention is not limited to these embodiments.

[0042] First, it should be noted that the thin-walled weakly rigid part manufactured by additive manufacturing in this invention refers to an additively manufactured metal part with a relative wall thickness rwt < 1 mm, where rwt = V / S, V is the volume of the part, S is the surface area, and the base material of the part is metal, such as a high-temperature alloy.

[0043] After 3D printing, surface treatment, and machining, residual stress gradually accumulates in the internal parts of additively manufactured thin-walled parts, resulting in uneven distribution of residual stress in some areas. To reduce the residual stress in the parts before thermal spraying, this invention provides a stress relief method for additively manufactured thin-walled weakly rigid parts, comprising the following steps:

[0044] Step S1: Perform initial residual stress detection on the part and process the data;

[0045] Step S2: Assemble the parts on the tooling, apply preload, and then perform stress-relief annealing;

[0046] Step S3: After stress-relief annealing, the parts assembled on the tooling are subjected to vibration aging to relieve stress.

[0047] Step S4: After vibration aging stress relief, the part undergoes a second residual stress test and data processing, and then the residual stress change rate is calculated; if the residual stress change rate does not meet the requirements, return to step S3.

[0048] Specifically, in step S1, an X-ray stress detector is used to detect the residual stress distribution of the thin-walled part in its initial state, and stress is measured on the part surface at intervals of 400-500 mm. 2 Each detection point is set as a residual stress detection point. At each detection point, the normal stress in three directions, namely 0°, 45° and 90°, is detected. The direction along the right side of the part length is defined as the 0° direction, and the direction along the top of the part width is defined as the 90° direction. Figure 1 This is a schematic diagram of residual stress detection for a part.

[0049] Before testing, electrolytic polishing and etching were performed to a depth of approximately 15μm. After testing, data processing was performed, and the data processing steps are as follows:

[0050] Step S1.1: Calculate the principal stresses at each test point based on the normal stresses in the three directions at each test point;

[0051] Step S1.2: Calculate the equivalent stress at each test point based on the principal stress at each test point;

[0052] Step S1.3: Subtract the maximum and minimum equivalent stresses at the detection points to obtain the initial residual stress range Δσ. m Take the equivalent stress at each detection point, and obtain the magnitude and direction of the average equivalent stress on the entire surface of the part in the initial state according to the arithmetic mean calculation method;

[0053] It should be noted that the calculation methods for the principal stress in step S1.1 and the equivalent stress in steps S1.2 adopt conventional calculation methods in mechanics of materials.

[0054] It should be noted that in step S2, the formwork accompanies the part throughout all processes, including stress-relief annealing, vibration aging stress relief, and thermal spraying. Therefore, the selection of the tooling material, as well as the shape and size of the tooling, plays a crucial role in eliminating residual stress. Tooling materials with high yield strength can better alleviate deformation caused by residual stress. In addition, the design of the tooling shape and size affects the uniformity of stress distribution and reduces the accumulation of residual stress. Figure 2 This is a schematic diagram of the assembly of parts and tooling.

[0055] Specifically, in step S2, the parts assembled on the tooling are preloaded using n fastening screws on the tooling. The preload of each screw is calculated based on existing technology, such as F. i =M / (cd), where M is the tightening torque, c is the torque coefficient, and d is the nominal diameter of the thread; the total preload of n screws is F = F1 + F2 + ... + F n Then, divide the total preload F by the surface area S of the part to obtain the average compressive stress σ on the part. 压 It should be noted that applying preload through the fastening screws induces a certain average strain ε on the surface of the part. The product of the average strain ε and the elastic modulus E of the part material is also equal to the average compressive stress σ experienced by the part. 压 , i.e. σ 压 =Eε.

[0056] Then, the parts and tooling are placed together in a box furnace at 0.3T. m Stress-relief annealing is performed after holding at the temperature for 2–4 hours. m The melting point of the part material is used for heat preservation, and the part is allowed to cool naturally to room temperature after the heat preservation is completed.

[0057] Residual stress state σ after annealing 退火后残余应力 The expression for the superposition of the secondary stress applied by the annealing temperature and the tooling is as follows:

[0058]

[0059] In equation (1), σ 退火后残余应力 σ represents the residual stress of the part after annealing, in MPa.退火前残余应力 This refers to the residual stress of a part after sandblasting and before annealing, expressed in MPa. Generally, the residual stress before annealing is taken as the average equivalent stress on the entire surface of the part in its initial state, i.e., σ. 退火前残余应力 =σ avg e is the natural constant, dimensionless; ΔE is the energy difference between the energy during the annealing and holding process and the energy before annealing, in joules; k is the Boltzmann constant, in joules per kaine; T a The annealing holding temperature is expressed in Kelvin (K); σ 压 The average compressive stress on the part resulting from the preload is expressed in MPa.

[0060] It should be noted that to achieve stress relief through the combined effect of tooling preload and annealing temperature, both the annealing temperature and preload must be adjusted to a suitable range. If the annealing temperature is too high, recrystallization will occur, affecting the solid solution treatment of the part. Therefore, annealing is generally performed below the recrystallization temperature of the part material, which is approximately the melting point T of the part material. m The annealing temperature is selected at 0.3T, which is 0.3 to 0.45 times that of the standard temperature range. m Below this; the higher the preload applied by the tooling, the lower the final residual stress. However, excessive preload can cause the part to yield and deform. When the average compressive stress σ 压 When the yield strength of a part is exceeded, the part undergoes plastic deformation, affecting its profile.

[0061] Specifically, in step S3, a vibration motor and a vibration pickup are installed, and the workpiece is clamped together with the tooling. Then, the position of the vibration pickup on the platform is adjusted, and a test vibration is performed to find the frequency. A certain frequency of vibration is applied to the workpiece through the vibration table. The vibration generates alternating external stress, thereby making the residual stress distribution on the surface and inside of the workpiece more uniform, avoiding local stress concentration, and effectively reducing local deformation of the workpiece during the spraying process.

[0062] During vibration testing, one or two vibration points should be selected based on the vibration energy transfer. For thin-walled parts, supplementary vibration should be applied to the weakest points in their vibration response. The following condition should be met: σ 动 +σ 退火后残余应力 <σ 零件 , where σ 动 The stress applied during the vibration process, σ 退火后残余应力 The residual stress is the stress after annealing and before vibration. The sum of the two stresses must be less than the yield strength of the part material to prevent plastic deformation of the part during vibration.

[0063] Specifically, the process parameters for vibration aging are: vibration acceleration 20–80 mm / s². 2Frequency coverage: 2500–5000 r / min; test vibration parameters: frequency interval: 150–200 r / min; maximum acceleration at the dominant frequency: 50–80 mm / s². 2 The vibration time at the excitation point is 40 to 60 minutes.

[0064] Specifically, in step S4, an X-ray stress detector is used to detect the residual stress distribution of the part after stress relief, and the stress is measured on the part surface at intervals of 400-500 mm. 2 Each detection point is set as a residual stress detection point. At each detection point, the normal stress in three directions, namely 0°, 45° and 90°, is detected. The direction along the right side of the part length is defined as the 0° direction, and the direction along the top of the part width is defined as the 90° direction.

[0065] Before testing, electrolytic polishing and etching were performed to a depth of approximately 15μm. After testing, data processing was performed, and the data processing steps are as follows:

[0066] Step S4.1: Calculate the principal stresses at each test point based on the normal stresses in the three directions at each test point;

[0067] Step S4.2: Calculate the equivalent stress at each test point based on the principal stress at each test point;

[0068] Step S4.3: Subtract the maximum and minimum equivalent stresses at the test points to obtain the residual stress range Δσ after stress relief. m去应力后 The equivalent stress at each test point is taken, and the average equivalent stress σ on the entire surface of the part after stress relief is obtained according to the arithmetic mean calculation method. avg去应力后 Size and orientation;

[0069] Step S4.4: Calculate the residual stress change rate and determine whether the residual stress change rate meets the requirements; if the residual stress change rate does not meet the requirements, return to step S3.

[0070] It should be noted that the calculation methods for the principal stress in step S4.1 and the equivalent stress in steps S4.2 adopt conventional calculation methods in mechanics of materials.

[0071] Specifically, the residual stress change rate in step S4.4 includes the residual stress reduction rate and the comparison of the residual stress range. The formula for calculating the residual stress reduction rate is: η=(σ avg -σ avg去应力后 ) / σ avg In the formula, η is the residual stress reduction rate, in percentage (%); σ avg σ represents the average equivalent stress on the entire surface of the part in the initial state, expressed in MPa. avg去应力后This represents the average equivalent stress on the entire surface of the part after stress relief, expressed in MPa. The comparison of residual stress ranges compares the residual stress range Δσ in the initial state. m and the range of residual stress after stress relief Δσ m去应力后 The magnitude of the residual stress. When the residual stress reduction rate η ≤ 40%, or the residual stress range Δσ after stress relief. m去应力后 Not less than the initial residual stress range Δσ m That is, Δσ m去应力后 ≥Δσ m When the residual stress reduction rate η > 40%, and the residual stress range Δσ after stress relief is found to be non-compliant; m去应力后 Less than the initial residual stress range Δσ m That is, Δσ m去应力后 <Δσ m At that time, it was determined to meet the requirements. The effects of stress-relieving annealing and vibration aging on stress relief were evaluated through a second residual stress test.

[0072] It should be noted that the stress relief method for additive manufacturing of thin-walled, weakly rigid parts in this invention ultimately serves the thermal spraying process, so combining stress relief and thermal spraying is to be expected.

[0073] Specifically, firstly, the design of stress-relieving tooling and thermal spraying tooling should be combined. For example, based on the wall thickness of the part and the performance of the thermal spray coating to be prepared, appropriate tooling materials should be selected, which should meet the following requirements:

[0074] σ 涂层 ×τ 涂层 <σ 工装 ×rwt (2)

[0075] In equation (2), σ 涂层 τ represents the bonding strength between the coating and the part, expressed in MPa. 涂层 σ represents the coating thickness, in mm. 工装 σ represents the yield strength of the tooling material, in MPa; rwt represents the relative wall thickness of the part, in mm. It should be noted that if the yield strength σ of the tooling material... 工装 If equation (1) cannot be satisfied, the coating and the parts will bend and deform, leading to coating failure.

[0076] Furthermore, the shape and dimensions of the coating and tooling during the plasma spraying process are used to determine the variation value Δσ of the residual stress in the part using the following formula. 残余 Impact:

[0077]

[0078] In equation (3), Δσ 残余τ represents the change in residual stress on the part caused by the coating and tooling during the spraying process, expressed in MPa. 涂层 The coating thickness is expressed in mm; α 零件 A is the coefficient of thermal expansion of the part, expressed in 1 / ℃; 涂层 The coating area is in mm. 2 rwt is the relative wall thickness of the part, in mm; α 涂层 A is the coefficient of thermal expansion of the coating, expressed in 1 / ℃; 工装-零件 The assembly contact area between the tooling and the parts, in mm. 2 ;σ 涂层 The bonding strength between the coating and the part is expressed in MPa.

[0079] Therefore, the design of tooling should start from the yield strength of the material and the contact area between the tooling and the parts. To reduce the residual stress after spraying, tooling with high yield strength and large size should be used to meet Δσ. 残余 / σ 涂层 <400%.

[0080] Secondly, after step S1 and before step S2, step S1′ is added.

[0081] Step S1′: Develop a sandblasting plan and assemble the tooling and parts before sandblasting;

[0082] It should be noted that sandblasting, as a pretreatment process for thermal spraying, can further cause localized residual stress concentration in the parts, leading to deformation exceeding tolerances. Therefore, before sandblasting, it is necessary to formulate a sandblasting plan based on the residual stress distribution of the parts in their initial state and the average equivalent stress on the entire surface of the parts, so that the residual stress on the surface after sandblasting can be released to a certain extent and deformation caused by sandblasting can be prevented.

[0083] Specifically, in step S1′, the sand blowing pressure P 吹砂 and sand blowing distance λ 吹砂 It should be within the following range:

[0084]

[0085] In equation (4), P 吹砂 λ represents the sandblasting pressure, measured in MPa. 吹砂 σ represents the sand blowing distance in mm. 零件 σ represents the yield strength of the part material, in MPa; θ represents the sandblasting angle, in degrees. The sandblasting direction is chosen to form an obtuse or straight angle with the direction of the average equivalent stress on the entire surface of the part in its initial state. The sandblasting angle θ and this angle are complementary. avg Rwt represents the average equivalent stress on the entire surface of the part in the initial state, in MPa; rwt represents the relative wall thickness of the part, in mm; A吹砂 The area to be blown is in mm. 2 .

[0086] Finally, after step S4, there are steps S5 and S6.

[0087] Step S5: After assembling the tooling and parts, perform plasma spraying.

[0088] Step S6: Post-plasma spraying treatment.

[0089] Specifically, step S5 includes the following sub-steps:

[0090] Step S5.1: After assembling the tooling and parts, place them in a high-temperature oven and preheat at 150-250℃ for 1-2 hours to ensure uniform temperature of the parts and tooling.

[0091] Step S5.2: After the parts are preheated, place the parts and tooling directly on the spraying table. Before the parts and tooling have completely cooled down, perform plasma spraying. During the spraying process, use an infrared thermometer to monitor the surface temperature of the parts in real time. The maximum temperature shall not exceed 250°C.

[0092] The specific process parameters for plasma spraying are related to the spraying powder, as shown in Table 1:

[0093] Table 1. Plasma Spraying Process Parameters

[0094]

[0095]

[0096] Specifically, in step S6, after plasma spraying is completed, the part is kept fixed on the fixture and allowed to cool to room temperature. Then, the part and fixture are placed together in a box furnace at 0.3T. m Keep warm for 2-3 hours, including T m The material's melting point was used as the reference value. After heat preservation, the parts were allowed to cool naturally to room temperature. Finally, the tooling was removed, and the deformation of the parts was detected and compared using a laser surface scanner. The results showed that the maximum deformation of the thin-walled parts after spraying was ±0.27 mm, and the area with deformation within ±0.3 mm accounted for 100% of the total area. The deformation comparison results between the new spraying scheme and the traditional spraying scheme are shown in Table 2 below:

[0097] Table 2 Comparison of Deformation Variables

[0098]

[0099] As can be seen from Table 2, the maximum deformation of the traditional spraying scheme is ±1.6mm, and the area with deformation greater than ±0.3mm accounts for 27-38% of the total area. The maximum deformation of the spraying scheme of the present invention is ±0.27mm, and the area with deformation greater than ±0.3mm is 0.

[0100] Example

[0101] A thin-walled part of GH3536 high-temperature alloy manufactured by additive manufacturing, with an elastic modulus of 206 GPa and a melting point of T. m Its temperature is 1395℃, its specific heat capacity is C = 372.6 J / kg·℃, and its coefficient of thermal expansion is α. 零件 =12.1×10 -6 The part has an arc shape, a central angle of 75°, a wall thickness of rwt of 0.6 mm, and unfolds to a length of 90 mm × a width of 25 mm. The part area S is 2250 mm². 2 The mass m of the part is 0.0118 kg.

[0102] A stress relief method for additive manufacturing thin-walled, weakly rigid parts:

[0103] Step S1: Perform initial residual stress detection on the part and process the data;

[0104] An Xstress 3000 X-ray stress analyzer was used with Mn as the target material, at a voltage of 30kV and a current of 6.6mA to detect the residual stress distribution in thin-walled parts. The stress distribution was determined based on a 450mm diameter. 2 Five test points are evenly selected along the centerline of the curved surface of the part. At each test point, the normal stress is measured in three directions: 0°, 45°, and 90°. The direction along the right side of the part's length is defined as the 0° direction, and the direction along the top of the part's width is defined as the 90° direction. Before testing, electrolytic polishing is used to etch approximately 15 μm. The test results and subsequent data processing are shown in Table 3.

[0105] Step S2: Assemble the parts on the tooling, apply preload, and then perform stress-relief annealing;

[0106] The parts assembled on the tooling are preloaded using 18 fastening screws on the tooling. The preload force of each screw is F = M / (cd), the tightening torque is M = 2370 N / mm, the torque coefficient is c = 0.15, and the nominal thread diameter is d = 4 mm. The total preload force of the 18 screws is nF = 71100 N. Then, the total preload force nF is divided by the surface area of ​​the part, S = 2250 mm². 2 The average compressive stress σ on the part is obtained. 压 =31.6MPa.

[0107] The parts and tooling were placed together in a box furnace and held at 350℃ for 3 hours for stress-relieving annealing. After holding, they were allowed to cool naturally to room temperature. a =623K.

[0108] Residual stress state σ after annealing 退火后残余应力 The residual stress σ before annealing is a superposition of the secondary stresses applied by the annealing temperature and the tooling. 退火前残余应力 =σ avg =111.36MPa, the energy difference between the part before annealing and the energy during annealing holding ΔE = m(T) a -293K)C = 1450.9 Joules, according to the formula:

[0109] Calculate the residual stress σ after annealing. 退火后残余应力 =79.76MPa.

[0110] Step S3: After stress-relief annealing, the parts assembled on the tooling are subjected to vibration aging to relieve stress.

[0111] Process parameters for vibration aging: vibration acceleration 40 mm / s² 2 Frequency coverage 3500 r / min, test vibration parameters frequency interval 180 r / min, maximum acceleration at the dominant frequency 60 mm / s² 2 Vibration time at the excitation point: 50 min.

[0112] Step S4: After vibration aging stress relief, the part undergoes a second residual stress test using an Xstress 3000 X-ray stress analyzer with Mn as the target material, a voltage of 30kV, and a current of 6.6mA to detect the residual stress distribution of the thin-walled part. (Based on a 450mm...) 2 Five test points are evenly selected along the centerline of the curved surface of the part. At each test point, the normal stress is measured in three directions: 0°, 45°, and 90°. The direction along the right side of the part's length is defined as the 0° direction, and the direction along the top of the part's width is defined as the 90° direction. Before testing, electrolytic polishing is used to etch approximately 15 μm. The test results and subsequent data processing are shown in Table 3.

[0113] Then calculate the rate of change of residual stress. The rate of decrease in residual stress is: η=(σ avg -σ avg去应力后 ) / σ avg =(111.36-63.68) / 111.36=42.8%>40%, residual stress range comparison Δσ m去应力后 =169.1MPa<Δσ m =292.3MPa, the residual stress change rate meets the requirements.

[0114] By combining stress relief and thermal spraying processes, and based on the properties of the part material, the shape of the part, the residual stress state, and the performance of the thermal spray coating to be prepared, thermal spraying shape tooling is designed and processed.

[0115] The parts need to be coated with ZrO2 powder, and the coating thickness τ is designed. 涂层 =0.5mm, the bonding strength σ between the coating and the part 涂层 =30~35MPa, the tooling material is selected as 30CrMnSi, the yield strength σ of the tooling material is... 工装 =800MPa, satisfying the formula σ 涂层 ×τ 涂层 <σ 工装 The requirements of ×rwt.

[0116] The coefficient of thermal expansion of the part α 零件 =12.1×10 -6 / ℃, coating area A 涂层 =2250mm 2 The coefficient of thermal expansion of the coating α 涂层 =9.6×10 -6 / ℃, while satisfying Δσ 残余 / σ 涂层 In cases where the percentage is less than 400%, according to the formula... The assembly contact area A between the tooling and the part is calculated. 工装-零件 >590.8mm 2 Take 700mm 2 .

[0117] After step S1 and before step S2, step S1′ is added, which involves formulating a sandblasting plan and assembling the tooling and parts before sandblasting.

[0118] Yield strength σ of the part material 零件 =310MPa, sand blowing area A 吹砂 =2250mm 2 Based on the residual stress detection results of step S1, the magnitude of the average equivalent stress σ on the entire surface of the part is... avg =111.36MPa, the direction of the average equivalent stress is outward at an angle of 22.4° with the plane normal, the sand blowing direction is at an angle of 177.6° with the direction of the average equivalent stress, so the sand blowing angle θ = 70°.

[0119] Furthermore, according to the formula:

[0120]

[0121] The sand-blowing pressure P that satisfies this formula is calculated. 吹砂 =0.21MPa, sand blowing distance λ 吹砂 =80mm.

[0122] Step S4 is followed by steps S5 and S6.

[0123] Step S5: After assembling the tooling and parts, perform plasma spraying.

[0124] Step S5.1: After assembling the tooling and parts, place them in a high-temperature oven and preheat at 200℃ for 2 hours to ensure uniform temperature of the parts and tooling.

[0125] Step S5.2: After the part is preheated, place the part and tooling directly on the spraying table. Before the part and tooling have completely cooled down, perform plasma spraying of ZrO2 powder. During the spraying process, use an infrared thermometer to monitor the surface temperature of the part in real time. The maximum temperature shall not exceed 250°C.

[0126] The specific process parameters for plasma spraying are: current 600A, main gas flow rate 35NLPM, powder feeding speed 50g / min, spraying distance 100mm, spray gun speed 500mm / s, auxiliary gas flow rate 12NLPM, and carrier gas flow rate 2.2NLPM.

[0127] Step S6: Post-treatment after plasma spraying;

[0128] After plasma spraying, the parts were kept fixed on the fixture and allowed to cool to room temperature. Then, the parts and fixture were placed in a box furnace and held at 350℃ for 3 hours. After this period, they were allowed to cool naturally to room temperature. Finally, the fixture was removed, and the deformation of the parts was measured and compared using a laser surface scanner. The results showed that the maximum deformation of the thin-walled parts after spraying was ±0.27 mm, and the area with deformation within ±0.3 mm accounted for 100% of the total area.

[0129] Table 3. Residual stress test results of parts in the examples (unit: MPa)

[0130]

[0131] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A stress-relieving method for additive manufacturing thin-walled, weakly rigid high-temperature alloy parts, characterized in that, The relative wall thickness rwt of the part is less than 1 mm, where rwt = V / S, V is the volume of the part, and S is the surface area; the method includes the following steps: Step S1: Perform initial residual stress detection on the part and process the data; Step S2: Assemble the parts on the tooling, apply preload, and then perform stress-relief annealing; Step S3: After stress-relief annealing, the parts assembled on the tooling are subjected to vibration aging to relieve stress. Step S4: After vibration aging stress relief, the part undergoes a second residual stress test and data processing, and then the residual stress change rate is calculated; if the residual stress change rate does not meet the requirements, return to step S3. In steps S1 and S4, the surface of the part is sized at 400~500mm. 2 / Set residual stress detection points at each detection point, and detect the normal stress in three directions: 0°, 45°, and 90° at each detection point. The direction along the right side of the part length is defined as the 0° direction, and the direction along the top of the part width is defined as the 90° direction. In step S1, the data processing includes the following steps: Step S1.1: Calculate the principal stresses at each test point based on the normal stresses in the three directions at each test point; Step S1.2: Calculate the equivalent stress at each test point based on the principal stress at each test point; Step S1.3: Subtract the maximum and minimum equivalent stresses at the detection points to obtain the initial residual stress range. σ m Take the equivalent stress at each detection point, and obtain the magnitude and direction of the average equivalent stress on the entire surface of the part in the initial state according to the arithmetic mean calculation method; In step S2, the stress-relief annealing involves placing the part and tooling together in a box furnace at 0.3T. m The following conditions require 2-4 hours of heat treatment followed by stress-relief annealing: T m The part material has a melting point of 1, and after heat treatment, it is allowed to cool naturally to room temperature; the residual stress after annealing satisfies: In the formula, σ 退火后残余应力 σ represents the residual stress of the part after annealing, in MPa. 退火前残余应力 The residual stress of the part after sandblasting and before annealing is expressed in MPa. The residual stress before annealing is σ. 退火前残余应力 The value is the average equivalent stress on the entire surface of the part under the initial state; e is a natural constant, dimensionless. E is the energy difference between the energy during the annealing and holding process and the energy before annealing, expressed in joules; k is the Boltzmann constant, expressed in joules per kainu; T a The annealing holding temperature is expressed in Kelvin; σ 压 The average compressive stress on the part derived from the preload is expressed in MPa. In step S3, the process parameters for vibration aging are in the range of vibration acceleration 20~80 mm / s². 2 Frequency coverage: 2500~5000 r / min; test vibration parameters: frequency interval: 150~200 r / min; maximum acceleration at the main frequency: 50~80 mm / s² 2 Vibration time at the excitation point: 40-60 minutes; In step S4, the data processing includes the following steps: Step S4.1: Calculate the principal stresses at each test point based on the normal stresses in the three directions at each test point; Step S4.2: Calculate the equivalent stress at each test point based on the principal stress at each test point; Step S4.3: Subtract the maximum and minimum equivalent stresses at the test points to obtain the residual stress range after stress relief. σ m去应力后 Take the equivalent stress at each test point, and calculate the magnitude and direction of the average equivalent stress on the entire surface of the part after stress relief according to the arithmetic mean calculation method. Step S4.4: Calculate the residual stress change rate and determine whether the residual stress change rate meets the requirements; if the residual stress change rate does not meet the requirements, return to step S3. The residual stress change rate includes the residual stress reduction rate and the comparison of the residual stress range; The formula for calculating the residual stress reduction rate is: =(σ avg -σ avg去应力后 ) / σ avg In the formula, The residual stress reduction rate is expressed in %; σ avg σ represents the average equivalent stress on the entire surface of the part in the initial state, expressed in MPa. avg去应力后 The residual stress is the average equivalent stress on the entire surface of the part after stress relief, expressed in MPa; the residual stress change rate meets the requirement of residual stress reduction rate. >40%, and the residual stress after stress relief is extremely poor. σ m去应力后 Less than the initial state residual stress range σ m .

2. The method according to claim 1, characterized in that, In steps S1 and S4, the residual stress is detected using an X-ray stress detector.

3. The method according to claim 1, characterized in that, In step S3, the vibration aging satisfies: σ 动 +σ 退火后残余应力 <σ 零件 , where σ 动 The stress applied during the vibration process, expressed in MPa; σ 退火后残余应力 The residual stress of the part after annealing and before vibration is expressed in MPa; σ 零件 This represents the yield strength of the part material, expressed in MPa.

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