A method for controlling thermal spraying deformation of thin-walled, weakly rigid parts manufactured by additive manufacturing

Abstract

This invention relates to a method for controlling the deformation of thin-walled, weakly rigid parts manufactured by additive manufacturing during thermal spraying. Belonging to the field of thermal spraying technology, it solves the technical problem of deformation occurring during the thermal spraying coating preparation process of thin-walled, weakly rigid parts with large residual stress, affecting assembly. The method for controlling the deformation of thin-walled, weakly rigid parts manufactured by additive manufacturing during thermal spraying includes the following steps: S1, detecting and processing the residual stress of the part; S2, designing and processing a thermal spraying shaping fixture; S3, assembling the fixture and part and then sandblasting; S4, performing stress-relief annealing on the part; S5, performing vibration aging stress relief on the part; S6, conducting a second residual stress detection and data processing on the part, and then calculating the residual stress change rate; S7, assembling the fixture and part and then performing plasma spraying; and S8, post-treatment after plasma spraying. This invention improves the surface accuracy of the part after plasma spraying and avoids assembly step differences.

Description

Technical Field

[0001] This invention belongs to the field of thermal spraying technology, and specifically relates to a method for controlling the deformation of thin-walled, weakly rigid parts produced by additive manufacturing during thermal spraying. 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 method for controlling the deformation of additively manufactured thin-walled weakly rigid parts during thermal spraying, 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 spraying coating preparation process, affecting assembly.

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

[0007] This invention provides a method for controlling the deformation of thermally sprayed thin-walled, weakly rigid parts manufactured by additive manufacturing, characterized by comprising the following steps:

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

[0009] Step S2: Based on the properties of the part material, the shape of the part and the residual stress state, as well as the properties of the thermal spray coating to be prepared, design and process the thermal spraying shape tooling.

[0010] Step S3: Develop a sandblasting plan and assemble the tooling and parts before sandblasting;

[0011] Step S4: After sandblasting, apply preload to the parts assembled on the tooling, and then perform stress-relief annealing.

[0012] Step S5: After stress-relief annealing, the parts assembled on the tooling are subjected to vibration aging to relieve stress.

[0013] Step S6: 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 meets the requirements, proceed to the next step S7; if the residual stress change rate does not meet the requirements, return to step S5.

[0014] Step S7: After assembling the tooling and parts, perform plasma spraying;

[0015] Step S8: Post-plasma spraying treatment.

[0016] Furthermore, in step S1, 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.

[0017] Furthermore, in step S1, data processing includes the following steps:

[0018] Step S1.1: Calculate the principal stresses at each test point based on the normal stresses in the three directions at each test point;

[0019] Step S1.2: Calculate the equivalent stress at each test point based on the principal stress at each test point;

[0020] Step S1.3: Subtract the maximum and minimum equivalent stresses at the test points to obtain the residual stress range. σ 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 are obtained according to the arithmetic mean calculation method.

[0021] Furthermore, in step S2, the selection of tooling materials satisfies: σ 涂层 ×τ 涂层 <σ 工装 ×rwt, where 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 rwt represents the yield strength of the tooling material, in MPa; rwt represents the relative wall thickness of the part, in mm.

[0022] The shape and dimensions of the tooling should meet the following requirements:

[0023] ,

[0024] In the formula, σ 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.

[0025] Furthermore, in step S3, the blowing pressure P of the sandblasting... 吹砂 and sand blowing distance λ 吹砂 satisfy:

[0026] In the formula, 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 and the direction of the average equivalent stress are chosen to form an obtuse or straight angle, and the sandblasting angle θ and this angle are supplementary angles; avg The average equivalent stress across the entire part surface is expressed in MPa; rwt is the relative wall thickness of the part, expressed in mm; A 吹砂 The area to be blown is in mm. 2 .

[0027] Furthermore, in step S4, the residual stress after annealing satisfies:

[0028] 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 Take the magnitude of the average equivalent stress on the entire surface of the part, σ. avg , i.e. σ 退火前残余应力 =σ avg 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.

[0029] Furthermore, in step S5, 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 The yield strength of the part material is expressed in MPa.

[0030] The process parameters for vibration aging are: 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 The vibration time at the excitation point is 40-60 minutes.

[0031] Furthermore, in step S6, the residual stress change rate includes the residual stress reduction rate and the comparison of the residual stress range.

[0032] 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 across the entire surface of the part, 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.

[0033] The rate of change of residual stress 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 .

[0034] Furthermore, step S7 includes the following sub-steps:

[0035] Step S7.1: 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 as a whole.

[0036] Step S7.2: 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.

[0037] Furthermore, in step S8, the post-processing involves placing the parts and tooling together in a box furnace at 0.3T. m Keep warm for 2-3 hours, including T m The melting point of the part material is used as the reference point. After heat preservation, the part is allowed to cool naturally to room temperature before the tooling is removed.

[0038] Compared with the prior art, the present invention can achieve at least one of the following technical effects:

[0039] (1) This invention conducts residual stress testing on additively manufactured parts, and then formulates practical and scientific technical solutions for sandblasting, stress-relieving annealing, vibration aging stress relief, plasma spraying, and thermal spraying post-treatment based on the test results.

[0040] (2) Based on the limitation of the residual stress change after spraying, the present invention designs tooling from the yield strength of tooling material and the contact area between tooling and parts. By comprehensively considering the influence of tooling and various factors on the residual stress of parts, a more suitable tooling is formulated.

[0041] (3) The present invention formulates a sandblasting scheme based on the average equivalent stress of the entire part surface, so that the residual stress on the surface after sandblasting is released to a certain extent, and the deformation caused by sandblasting is prevented.

[0042] (4) By adjusting the annealing temperature and preload within a suitable range, the tooling preload and annealing temperature work together to achieve stress relief of the parts.

[0043] (5) 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 process of thermal spraying coating preparation, improves the surface accuracy of parts after plasma spraying, and avoids assembly step differences.

[0044] (6) 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.

[0045] 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

[0046] 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.

[0047] Figure 1 This is a schematic diagram of residual stress detection for a part.

[0048] Figure 2 This is a schematic diagram of the assembly of parts and tooling;

[0049] In the diagram, 1-part; 10-inspection point; 11-screw hole; 2-tooling; 20-tooling nut; 3-screw. Detailed Implementation

[0050] The following describes in further detail a method for controlling the deformation of thermal spraying of thin-walled, weakly rigid parts manufactured by additive manufacturing, with reference to specific embodiments. These embodiments are for comparative and illustrative purposes only, and the present invention is not limited to these embodiments.

[0051] First, it should be noted that the additively manufactured thin-walled weakly rigid parts of the present invention refer to additively manufactured metal parts 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 high-temperature alloys.

[0052] This invention designs processes for sandblasting, stress-relief annealing, vibration aging stress relief, plasma spraying, and post-thermal spraying treatment of additively manufactured parts, thereby providing a method for controlling thermal spraying deformation of thin-walled, weakly rigid additively manufactured parts, comprising the following steps:

[0053] Step S1: Perform residual stress detection on the parts and process the data;

[0054] Step S2: Based on the properties of the part material, the shape of the part and the residual stress state, as well as the properties of the thermal spray coating to be prepared, design and process the thermal spraying shape tooling.

[0055] Step S3: Develop a sandblasting plan and assemble the tooling and parts before sandblasting;

[0056] Step S4: After sandblasting, apply preload to the parts assembled on the tooling, and then perform stress-relief annealing.

[0057] Step S5: After stress-relief annealing, the parts assembled on the tooling are subjected to vibration aging to relieve stress.

[0058] Step S6: 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 meets the requirements, proceed to the next step S7; if the residual stress change rate does not meet the requirements, return to step S5.

[0059] Step S7: After assembling the tooling and parts, perform plasma spraying;

[0060] Step S8: Post-plasma spraying treatment.

[0061] It should be noted that in step S1, after the additively manufactured thin-walled part undergoes 3D printing, surface treatment, and machining, residual stress gradually accumulates inside, and the local residual stress distribution is uneven.

[0062] Specifically, in step S1, an X-ray stress detector is used to detect the residual stress distribution of the thin-walled part, 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.

[0063] 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:

[0064] Step S1.1: Calculate the principal stresses at each test point based on the normal stresses in the three directions at each test point;

[0065] Step S1.2: Calculate the equivalent stress at each test point based on the principal stress at each test point;

[0066] Step S1.3: Subtract the maximum and minimum equivalent stresses at the test points to obtain the residual stress range. σ m Take the equivalent stress at each detection point, and calculate the magnitude and direction of the average equivalent stress on the entire surface of the part according to the arithmetic mean method.

[0067] 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.

[0068] It should be noted that in step S2, the shaped tooling accompanies the part throughout all processes, including sandblasting, stress-relief annealing, vibration aging stress relief, plasma spraying, and post-thermal spraying treatment. Therefore, the selection of 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's shape and size affects the uniformity of stress distribution and reduces the accumulation of residual stress.

[0069] Specifically, in step S2, based on the wall thickness of the part and the performance of the thermal spray coating to be prepared, appropriate tooling materials are selected, which should meet the following requirements:

[0070] σ 涂层 ×τ 涂层 <σ 工装 In equation (1), σ = ×rwt(1) 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.

[0071] Furthermore, the shape and dimensions of the coating and tooling during the plasma spraying process are used to determine the variation of residual stress in the part using the following formula. σ 残余 Impact:

[0072] (2)

[0073] In equation (2), σ 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.

[0074] 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 residual stress after spraying, tooling with high yield strength and large size should be used to meet the requirements. σ 残余 / σ 涂层 <400%. Figure 2 This is a schematic diagram of the assembly of parts and tooling.

[0075] It should be noted that in step S3, sandblasting, as a pretreatment process for thermal spraying, will further cause local residual stress concentration in the parts, leading to deformation exceeding the tolerance. 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 of the entire part surface, 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.

[0076] Specifically, in step S3, the sand blowing pressure P 吹砂 and sand blowing distance λ 吹砂 It should be within the following range:

[0077] (3)

[0078] In equation (3), 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 and the direction of the average equivalent stress are chosen to form an obtuse or straight angle, and the sandblasting angle θ and this angle are supplementary angles; avg The average equivalent stress across the entire part surface is expressed in MPa; rwt is the relative wall thickness of the part, expressed in mm; A 吹砂 The area to be blown is in mm. 2 .

[0079] Specifically, in step S4, after sandblasting, the part is fastened to the fixture without being removed, and a preload is applied through n fastening screws on the fixture. 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.

[0080] Then, the parts and tooling are placed 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 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.

[0081] 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:

[0082] (4)

[0083] In equation (4), 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 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 resulting from the preload is expressed in MPa.

[0084] 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.

[0085] Specifically, in step S5, 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.

[0086] 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.

[0087] Specifically, the process parameters for vibration aging are: 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 The vibration time at the excitation point is 40-60 minutes.

[0088] Specifically, in step S6, 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 400~500mm. 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.

[0089] 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:

[0090] Step S6.1: Calculate the principal stresses at each test point based on the normal stresses in the three directions at each test point;

[0091] Step S6.2: Calculate the equivalent stress at each test point based on the principal stress at each test point;

[0092] Step S6.3: Subtract the maximum and minimum equivalent stresses at the test points to obtain the residual stress range. σ m去应力后 The equivalent stress at each detection point is taken, and the average equivalent stress σ on the entire surface of the part is obtained according to the arithmetic mean calculation method. avg去应力后 Size and orientation;

[0093] Step S6.4: Calculate the residual stress change rate and determine whether the residual stress change rate meets the requirements; if the residual stress change rate meets the requirements, proceed to the next step S7; if the residual stress change rate does not meet the requirements, return to step S5.

[0094] It should be noted that the calculation methods for the principal stress in step S6.1 and the equivalent stress in steps S6.2 adopt conventional calculation methods in mechanics of materials.

[0095] Specifically, the residual stress change rate in step S6.4 includes the residual stress reduction rate and the comparison of the residual stress range. The formula for calculating the residual stress reduction rate is as follows: =(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 magnitude of the average equivalent stress across 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 ranges in the initial state. σ m and the range of residual stress after stress relief σ m去应力后 The magnitude of the residual stress reduction rate. ≤40%, or the residual stress range after stress relief is extremely small. σ m去应力后 Not less than the initial residual stress range σ m ,Right now σ m去应力后 ≥ σ m When the residual stress reduction rate is [not specified], it is judged as not meeting the requirements; when the residual stress reduction rate is [not specified], it is judged as not meeting the requirements. >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 ,Right now σ m去应力后 < σ m At that time, it was determined to meet the requirements. The effect of stress-relieving annealing and vibration aging on stress relief was evaluated through a second residual stress test.

[0096] Specifically, step S7 includes the following sub-steps:

[0097] Step S7.1: 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 as a whole.

[0098] Step S7.2: 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.

[0099] The specific process parameters for plasma spraying are related to the spraying powder, as shown in Table 1:

[0100] Table 1. Plasma Spraying Process Parameters

[0101]

[0102] Specifically, in step S8, 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:

[0103] Table 2 Comparison of Deformation Variables

[0104]

[0105] 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.

[0106] Example

[0107] 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℃, specific heat capacity C = 372.6 J / kg·℃, and coefficient of thermal expansion 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.

[0108] A method for controlling thermal spraying deformation of thin-walled, weakly rigid parts manufactured by additive manufacturing:

[0109] Step S1: Perform residual stress detection on the parts and process the data;

[0110] 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.

[0111] Step S2: Based on the properties of the part material, the shape of the part and the residual stress state, as well as the properties of the thermal spray coating to be prepared, design and process the thermal spraying shape tooling.

[0112] 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 =30~35 MPa, select 30CrMnSi as the tooling material, 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.

[0113] The coefficient of thermal expansion of the part α 零件 =12.1×10 -6 / ℃, coating area A 涂层 =2250 mm 2 The coefficient of thermal expansion of the coating α 涂层 = 9.6 × 10 -6 / ℃, in order to meet σ 残余 / σ 涂层 In the case of <400%, according to the formula The assembly contact area A between the tooling and the part is calculated. 工装-零件 >590.8 mm 2 Take 700 mm 2 .

[0114] Step S3: Develop a sandblasting plan and assemble the tooling and parts before sandblasting;

[0115] Yield strength σ of the part material 零件 =310MPa, sand blowing area A 吹砂 =2250mm 2Based 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 =111.36 MPa, the direction of the average equivalent stress is outward at an angle of 22.4° to the plane normal, the sand blowing direction is at an angle of 177.6° to the direction of the average equivalent stress, so the sand blowing angle θ=70°.

[0116] Furthermore, according to the formula:

[0117]

[0118] The sand-blowing pressure P that satisfies this formula is calculated. 吹砂 =0.21 MPa, sand blowing distance λ 吹砂 =80 mm.

[0119] Step S4: After sandblasting, the parts assembled on the tooling are subjected to stress-relief annealing.

[0120] After sandblasting, the part is fastened to the fixture without removal. Preload is applied through 18 fastening screws on the fixture. 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.

[0121] 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.

[0122] 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 =111.36 MPa, the difference between the energy of the part before annealing and the energy during annealing and holding. E=m(T) a -293K) C = 1450.9 Joules, according to the formula:

[0123] Calculate the residual stress σ after annealing. 退火后残余应力 = 79.76MPa.

[0124] Step S5: After stress-relief annealing, the parts assembled on the tooling are subjected to vibration aging to relieve stress.

[0125] 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.

[0126] Step S6: 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.

[0127] Then calculate the rate of change of residual stress; the rate of decrease in residual stress is: =(σ avg -σ avg去应力后 ) / σ avg =(111.36-63.68) / 111.36=42.8%>40%, comparison of residual stress range σ m去应力后 =169.1MPa< σ m =292.3 MPa, the residual stress change rate meets the requirements, proceed to the next step;

[0128] Step S7: After assembling the tooling and parts, perform plasma spraying;

[0129] Step S7.1: After assembling the tooling and parts, place them in a high-temperature oven and preheat at 200°C for 2 hours to ensure uniform temperature of the parts and tooling.

[0130] Step S7.2: 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.

[0131] 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.

[0132] Step S8: Post-plasma spraying treatment;

[0133] 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 holding period, the parts 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.

[0134] Table 3. Residual stress test results of parts in the example (unit: MPa)

[0135]

[0136] 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 method for controlling the deformation of thermally sprayed thin-walled, weakly rigid parts manufactured by additive manufacturing, characterized in that, The method includes the following steps: Step S1: Perform residual stress detection on the parts and process the data; Step S2: Based on the properties of the part material, the shape of the part and the residual stress state, as well as the properties of the thermal spray coating to be prepared, design and process the thermal spraying shape tooling. Step S3: Develop a sandblasting plan and assemble the tooling and parts before sandblasting; Step S4: After sandblasting, apply preload to the parts assembled on the tooling, and then perform stress-relief annealing. Step S5: After stress-relief annealing, the parts assembled on the tooling are subjected to vibration aging to relieve stress. Step S6: 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 meets the requirements, proceed to the next step S7; if the residual stress change rate does not meet the requirements, return to step S5. Step S7: After assembling the tooling and parts, perform plasma spraying; Step S8: Post-plasma spraying treatment; In step S2, the selection of tooling material satisfies: σ 涂层 ×τ 涂层 <σ 工装 ×rwt, where 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 rwt represents the yield strength of the tooling material, in MPa; rwt represents the relative wall thickness of the part, in mm. The shape and dimensions of the tooling should meet the following requirements: ， In the formula, σ 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.

2. The method according to claim 1, characterized in that, In step S1, the residual stress detection is performed using an X-ray stress detector, with stress measured on the surface of the part 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.

3. The method according to claim 1, characterized in that, 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 test points to obtain the residual stress range. σ 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 are obtained according to the arithmetic mean calculation method.

4. The method according to claim 1, characterized in that, In step S3, the sand blowing pressure P 吹砂 and sand blowing distance λ 吹砂 satisfy: In the formula, 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 and the direction of the average equivalent stress are chosen to form an obtuse or straight angle, and the sandblasting angle θ and this angle are supplementary angles; avg The average equivalent stress across the entire part surface is expressed in MPa; rwt is the relative wall thickness of the part, expressed in mm; A 吹砂 The area to be blown is in mm. 2 .

5. The method according to claim 1, characterized in that, In step S4, 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 Take the magnitude of the average equivalent stress on the entire surface of the part, σ. avg , i.e. σ 退火前残余应力 =σ avg 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.

6. The method according to claim 1, characterized in that, In step S5, 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 The yield strength of the part material is expressed in MPa. 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 The vibration time at the excitation point is 40-60 minutes.

7. The method according to claim 1, characterized in that, In step S6, the residual stress change rate includes the residual stress reduction rate and the residual stress range comparison; 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 across the entire surface of the part, 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 residual stress change rate meets the requirement of being the 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 .

8. The method according to claim 1, characterized in that, Step S7 includes the following sub-steps: Step S7.1: 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 as a whole. Step S7.2: 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.

9. The method according to claim 1, characterized in that, In step S8, the post-processing involves placing the parts and tooling together in a box furnace at a temperature of 0.3T. m Keep warm for 2-3 hours, including T m The melting point of the part material is used as the reference point. After heat preservation, the part is allowed to cool naturally to room temperature before the tooling is removed.

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