A method for determining tolerances of various machining steps for aircraft engine compressor blades

Abstract

The invention discloses a method for determining tolerances of various machining processes of an aero-engine compressor blade, comprising: step 1: establishing a calculation model for the tolerance of a semi-finishing process; step 2: solving the calculation model for the tolerance of the semi-finishing process to obtain a tolerance range of the semi-finishing process; step 3: establishing a calculation model for the tolerance of a rough machining process; step 4: solving the calculation model for the tolerance of the rough machining process to obtain a tolerance range of the rough machining process; the invention ensures that the error of each machining process is less than the maximum machining tolerance of the corresponding process in the design and production stages, effectively absorbs and corrects the error generated in the previous process, and meets the design accuracy requirements of the compressor blade.

Description

Technical Field

[0001] The invention belongs to the field of blade processing, and in particular relates to a method for determining tolerances of various processing steps of an aircraft engine compressor blade. Background Art

[0002] Compressor blades are widely used in aviation, energy, automobiles and other fields. The design of compressor blades can effectively improve the aerodynamic performance of the engine. Due to their unique geometry and streamlined design, compressor blades can reduce resistance and increase lift when air flows through. This allows the engine to more efficiently convert fuel energy into thrust when working, thereby improving the overall thrust-to-weight ratio and enhancing the flight performance of the aircraft. During engine operation, these blades are usually in extreme working environments, facing multiple tests such as high temperature, airflow and mechanical stress. If the processing accuracy is not effectively guaranteed, the geometric shape and specific size deviations of the blades will directly lead to a decrease in aerodynamic performance, which in turn affects the thrust and fuel efficiency of the entire machine. Therefore, it is particularly important to control the processing accuracy of compressor blades.

[0003] The geometry of compressor blades is very complex and their rigidity is weak. They are prone to elastic deformation under the action of cutting force. The cutting force and cutting heat generated during the cutting process will cause cutting residual stress on the surface of the blade, which will cause the blade to bend and twist. Therefore, in single-process processing, compressor blades are very prone to processing errors. The processing of compressor blades usually requires multiple processes. In the case of multi-process processing, the processing errors will gradually accumulate. After the first process is completed, the processing error will cause the geometric shape of the blade surface to be inconsistent with the theoretical shape, thereby changing the actual cutting depth of the next stage, causing the processing error of the next stage to increase. In this case, as each process proceeds, the errors generated by the processing will continue to accumulate, and ultimately the product will fail to meet the design requirements. Therefore, in multi-process processing, it is necessary to design the processing tolerance of each process to minimize the impact of error transmission and accumulation, and ensure that the quality and performance of the final product meet the design standards.

[0004] At present, the design of tolerances for machining process of aircraft engine compressor blades has the following deficiencies: (1) only the tolerances of the final machining process of the blade are specified, and the design of tolerances for the intermediate machining process is lacking, thus making it impossible to guarantee the final machining accuracy of the parts; (2) the tolerances of the intermediate machining process are specified based on design experience, but due to the lack of theoretical support and the failure to consider the transmission effect of machining errors between various processes in actual production, the design of machining tolerances for each process is unreasonable, making it impossible to effectively control the machining accuracy of the compressor blades. Summary of the invention

[0005] The purpose of the present invention is to provide a method for determining the tolerances of each processing step of an aircraft engine compressor blade, so as to solve the problem that the compressor blade lacks the design of the tolerances of the intermediate processing steps during the multi-process processing, thereby failing to ensure the final processing accuracy of the parts.

[0006] The present invention adopts the following technical solution: a method for determining tolerances of various processing steps of an aircraft engine compressor blade, comprising:

[0007] Step 1: Taking the machining error of the semi-finishing process of the compressor blade as the objective function, and taking the design tolerance range of the profile, the design tolerance range of the position, and the design tolerance range of the torsion angle of the finishing process of the compressor blade as constraints, a calculation model for the tolerance of the semi-finishing process is established;

[0008] Step 2: Using the heuristic algorithm and the upper and lower bounds of the actual machining error of the semi-finishing process, the calculation model of the semi-finishing process tolerance is solved to obtain the minimum machining error and the maximum machining error of the semi-finishing process, and then the tolerance range of the semi-finishing process is obtained according to the minimum machining error and the maximum machining error of the semi-finishing process;

[0009] Step 3: Taking the machining error of the rough machining process of the compressor blade as the objective function and the tolerance range of the semi-finishing process as the constraint, a calculation model for the tolerance of the rough machining process is established;

[0010] Step 4: Use the heuristic algorithm and the lower and upper bounds of the actual machining error of the rough machining process to solve the calculation model of the rough machining process tolerance to obtain the minimum machining error and maximum machining error of the rough machining process, and then obtain the tolerance range of the rough machining process based on the minimum machining error and maximum machining error of the rough machining process.

[0011] Furthermore, the calculation model of the semi-finishing process tolerance in step 1 is:

[0012] ,

[0013] ,

[0014] In the formula, is the machining error of the semi-finishing process of the compressor blade, is the profile error of the compressor blade finishing process, is the blade position error of the compressor blade finishing process, is the blade profile torsion error of the compressor blade finishing process, The design tolerance range of the profile of the compressor blade finishing process is: is the design tolerance range of the position of the compressor blade finishing process, This is the design tolerance range for the torsion angle of the compressor blade finishing process.

[0015] Furthermore, the calculation model of the rough machining process tolerance in step 3 is:

[0016] ,

[0017] ,

[0018] In the formula, d c is the machining error of the rough machining process of the compressor blade, d s-min is the minimum machining error of the compressor blade semi-finishing process, d s-max It is the maximum machining error of the semi-finishing process of compressor blades.

[0019] The beneficial effects of the present invention are:

[0020] The present invention ensures that the processing error of each process is within the tolerance range of the corresponding process by rationally planning and optimizing the tolerance of each process in the design and production stages, effectively absorbing and correcting the error generated in the previous process, so as to meet the design accuracy requirements of the compressor blades;

[0021] The present invention utilizes the tolerance range of each processing step obtained by calculation to constrain the processing error of the process, thereby improving the stability and consistency of the processing;

[0022] The present invention uses the design tolerance of the compressor blade finishing process as a constraint, and reasonably distributes the tolerance of each processing process in the reverse process direction, which helps to improve the processing accuracy of the final product and meet the design tolerance requirements; it can effectively reduce the scrap rate caused by error accumulation, reduce production costs, and improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of error transmission between multiple processes in the present invention;

[0024] Figure 2 It is a schematic diagram of the multi-step processing of the compressor blades in the present invention. DETAILED DESCRIPTION

[0025] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] The present invention discloses a method for determining tolerances of various processing steps of an aero-engine compressor blade, comprising:

[0027] Step 1: Taking the machining error of the semi-finishing process of the compressor blade as the objective function, and the design tolerance range of the contour, the design tolerance range of the position, and the design tolerance range of the torsion angle of the finishing process of the compressor blade as constraints, a calculation model for the tolerance of the semi-finishing process is established.

[0028] Assume that the blade has undergone a total of n Processing steps, such as Figure 1 As shown, Input dimensions for each machining operation With output size The relationship between them is expressed as:

[0029] ,

[0030] in, Indicates the output size in the processing step The law of change on is a random error and satisfies the normal distribution.

[0031] Assume The theoretical size of the blade after the processing steps are completed is , No. The theoretical size of the blade after the processing steps are completed is ,Will exist Performing Taylor expansion at , we can get:

[0032] ,

[0033] In the formula, For the The dimensional deviation between the input dimension and the theoretical dimension in a processing step.

[0034] In the actual processing of blades, the processing error will be controlled within a reasonable range, that is, , we can get:

[0035]

[0036] definition ,definition Assumptions , we can get:

[0037] ,

[0038] In the formula, is the error transfer coefficient, For transmission error.

[0039] Since each processing stage is usually aimed at reducing the processing error, it can be obtained ,and is very small and can be ignored, then:

[0040] .

[0041] Considering that the input error of the next process is the output error of the previous process, that is, , we can get

[0042] .

[0043] The machining errors of the rough machining process and the semi-finishing process of the compressor blade are the contour errors calculated by the coincidence of the detection coordinate system and the theoretical model coordinate system. Therefore, the relationship between the machining error of the semi-finishing process and the machining error of the rough machining process of the compressor blade is:

[0044] ,

[0045] in, d c is the machining error of the rough machining process of the compressor blade, d s is the machining error of the semi-finishing process of the compressor blade, is the error transfer coefficient of the semi-finishing process.

[0046] The machining error of the compressor blade finishing process is the contour error, blade position error, and blade torsion error obtained after the detection coordinate system and the theoretical model coordinate system are overlapped and each blade section is aligned by the ICP algorithm. Therefore, the machining error of the compressor blade finishing process is:

[0047] .

[0048] in, is the profile error of the compressor blade finishing process, is the blade position error of the compressor blade finishing process, is the blade profile torsion error of the compressor blade finishing process, is the profile error transfer coefficient of the finishing process, is the blade position error transmission coefficient of the finishing process, is the blade profile torsional error transmission coefficient of the finishing process.

[0049] The error transfer coefficient is related to the process parameters and the size of the processing error of the previous process. Therefore, under the same processing parameters, the processing error of this process can be completely determined by the processing error of the previous process. The mapping relationship between the processing error of this process and the processing error of the previous process can be obtained by polynomial fitting using experimental data.

[0050] During the processing of compressor blades, if the processing error of the previous process is too large, the processing error of the next process will increase, thus exceeding the design tolerance range. The smaller the tolerance, the easier it is to meet the accuracy requirements, but the corresponding processing cost is higher. Therefore, when designing the processing tolerance of each process of compressor blades, it is necessary not only to consider how to reduce the processing cost, but also to ensure that the processing accuracy requirements are met. This means that the design problem of the processing tolerance of each process of compressor blades can be transformed into the problem of solving the minimum and maximum processing errors of the previous process while ensuring the processing accuracy of the current process.

[0051] Assumptions The design tolerance range of the profile of the compressor blade finishing process is: is the design tolerance range of the position of the compressor blade finishing process, The design tolerance range of the torsion angle of the compressor blade finishing process is taken as the design tolerance range, the machining error of the compressor blade semi-finishing process is taken as the objective function, and the design tolerance range of the contour, the design tolerance range of the position, and the design tolerance range of the torsion angle of the compressor blade finishing process are taken as constraints. The calculation model of the tolerance of the semi-finishing process is established:

[0052] ,

[0053] .

[0054] Step 2: Use the heuristic algorithm and the upper and lower bounds of the actual machining error of the semi-finishing process to solve the calculation model of the semi-finishing process tolerance to obtain the minimum machining error and maximum machining error of the semi-finishing process, and then obtain the tolerance range of the semi-finishing process based on the minimum machining error and maximum machining error of the semi-finishing process.

[0055] When solving the above equation, we first need to determine the lower bound of the actual machining error of the semi-finishing process of the compressor blade. l b,s and upper bound u b,s Next, a suitable heuristic algorithm is selected to solve the minimum machining error of the semi-finishing process of the compressor blade. d s-min and maximum machining error d s-max, and then determine the tolerance range T of the semi-finishing process of the compressor blade s =[ d s-min , d s-max ].

[0056] Step 3: Taking the machining error of the rough machining process of the compressor blade as the objective function and the tolerance range of the semi-finishing process as the constraint, a calculation model for the tolerance of the rough machining process is established:

[0057] ,

[0058] .

[0059] Step 4: Use the heuristic algorithm and the lower and upper bounds of the actual machining error of the rough machining process to solve the calculation model of the rough machining process tolerance to obtain the minimum machining error and maximum machining error of the rough machining process, and then obtain the tolerance range of the rough machining process based on the minimum machining error and maximum machining error of the rough machining process.

[0060] When solving the above equation, we first need to determine the lower bound of the actual machining error of the compressor blade rough machining process. l b,c and upper bound u b,c Next, a suitable heuristic algorithm is selected to solve the minimum machining error of the rough machining process of the compressor blade. d c-min and maximum machining error d c-max , and then determine the tolerance range T of the rough machining process of the compressor blade c =[ d c-min , d c-max ].

[0061] Example 1: The schematic diagram of the processing process of the compressor blade selected in this example is as follows Figure 2As shown: First, the rough machining process is carried out, including the insertion milling channel and milling the blade profile to a uniform allowance, then the semi-finishing process is carried out, and finally the finishing process is carried out. The finishing process includes two cutting layers, and the two cutting layers are milled synchronously. 10 blanks are selected for rough machining and the machining error is detected by a three-coordinate detection machine. Then, 10 groups of experiments are carried out in the semi-finishing process, and the machining error is detected by a three-coordinate detection machine. 10 groups of experiments are carried out in the finishing process, and the machining error is detected by a three-coordinate detection machine. The maximum machining error of each blade is counted, and it is found that the measuring point position coordinates of the maximum machining error of the compressor blade are u=0.1, v=0.9. Therefore, the machining error with the measuring point position u=0.1, v=0.9 is counted. Among them, the actual machining error of the semi-finishing process is shown in Table 1, and the actual machining error of the finishing process is shown in Table 2.

[0062] Table 1 Actual machining error of the semi-finishing process of compressor blades

[0063]

[0064] The relationship between the profile error of the rough machining process and the profile error of the semi-finishing process is obtained by fitting the polynomial:

[0065] .

[0066] The relationship between the profile error of the semi-finishing process and the profile error of the finishing process is obtained by polynomial fitting:

[0067] .

[0068] The relationship between the profile error of the semi-finishing process and the blade position error of the finishing process is obtained by polynomial fitting:

[0069] .

[0070] The relationship between the profile error of the semi-finishing process and the blade twist angle error of the finishing process is obtained by polynomial fitting:

[0071] .

[0072] Table 2 Actual machining error of the finishing process of compressor blades

[0073]

[0074] The design tolerance range of the contour degree of the finishing process of this type of compressor blade is [0, +0.04mm], the design tolerance range of the position degree of the finishing process is [0, +0.15mm], and the design tolerance range of the torsion angle of the finishing process is [0, +0.33°]. Therefore, the calculation model of the semi-finishing process tolerance of the compressor blade is:

[0075] ,

[0076] .

[0077] The gray wolf algorithm is used to solve the problem. The population size is set to 50, the number of iterations is 500, the dimension is 1, and the lower bound of the actual machining error of the semi-finishing process is l b,s is 0, the upper limit of the actual machining error of the semi-finishing process u b,s is 0.0773, we can calculate d s-min is 0, d s-max is 0.0688. Therefore, the tolerance range T of the semi-finishing process of the compressor blade can be obtained. s =[0,+0.0688mm].

[0078] Then the tolerance range T of the semi-finishing process is s To constrain, a calculation model for the tolerance of the rough machining process is established:

[0079] ,

[0080] .

[0081] The gray wolf algorithm is used to solve the problem. The population size is set to 50, the number of iterations is 500, the dimension is 1, and the lower bound of the actual machining error of the rough machining process is l b,c is 0, the upper limit of the actual machining error of the rough machining process u b,c is 0.1667, so we can calculate d c-min is 0, d c-max is 0.1468. Therefore, the tolerance range T of the rough machining process of the compressor blade can be obtained. c =[0,+0.1468mm].

[0082] In the prior art, engineers design the rough machining process to have a tolerance range of [0, +0.25mm] and the semi-finishing process to have a tolerance range of [0, +0.10mm] based on experience and the national standard tolerance value GB / T1800. The chord length of the compressor blade of this model is between 30mm and 50mm.

[0083] Table 3 Machining error of compressor blades in this embodiment

[0084]

[0085] In order to verify the rationality of the tolerance design of this embodiment, three groups of milling experiments were carried out. The experimental results are shown in Table 3. It can be seen that the two compressor blades with errors of 0.1862mm and 0.1627mm in the rough machining process meet the tolerance of the rough machining process designed based on experience, that is, within [0, +0.25mm]; but both exceed the tolerance of the rough machining process designed in this embodiment, that is, both are not within [0, +0.1468mm]; then after the fine machining process, the two compressor blades do not meet the design tolerance, that is, the final machining accuracy requirements of the parts are not met.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining tolerances of various processing steps of an aircraft engine compressor blade, characterized in that: include: Step 1: Taking the machining error of the semi-finishing process of the compressor blade as the objective function, and taking the design tolerance range of the profile, the design tolerance range of the position, and the design tolerance range of the torsion angle of the finishing process of the compressor blade as constraints, a calculation model for the tolerance of the semi-finishing process is established; Step 2: using a heuristic algorithm and the upper and lower bounds of the actual machining error of the semi-finishing process to solve the calculation model of the semi-finishing process tolerance to obtain the minimum machining error and the maximum machining error of the semi-finishing process, and then obtaining the tolerance range of the semi-finishing process according to the minimum machining error and the maximum machining error of the semi-finishing process; Step 3: Taking the machining error of the rough machining process of the compressor blade as the objective function and the tolerance range of the semi-finishing process as the constraint, a calculation model of the tolerance of the rough machining process is established; Step 4: Use the heuristic algorithm and the lower and upper bounds of the actual machining error of the rough machining process to solve the calculation model of the rough machining process tolerance to obtain the minimum machining error and the maximum machining error of the rough machining process, and then obtain the tolerance range of the rough machining process based on the minimum machining error and the maximum machining error of the rough machining process.

2. The method for determining tolerances of each processing step of an aircraft engine compressor blade according to claim 1, characterized in that: The calculation model of the semi-finishing process tolerance in step 1 is: ， ， In the formula, is the machining error of the semi-finishing process of the compressor blade, is the profile error of the compressor blade finishing process, is the blade position error of the compressor blade finishing process, is the blade profile torsion error of the compressor blade finishing process, The design tolerance range of the profile of the compressor blade finishing process is: is the design tolerance range of the position of the compressor blade finishing process, This is the design tolerance range for the torsion angle of the compressor blade finishing process.

3. The method for determining tolerances of each processing step of an aircraft engine compressor blade according to claim 2, characterized in that: The calculation model of the rough machining process tolerance in step 3 is: ， ， In the formula, δ c is the machining error of the rough machining process of the compressor blade, δ s-min is the minimum machining error of the compressor blade semi-finishing process, δ s-max It is the maximum machining error of the semi-finishing process of compressor blades.

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