A method for converting residual stress of hole wall machining

Abstract

The application discloses a hole wall machining residual stress conversion loading method and belongs to the field of machining.The application is characterized in that: the hole wall machining residual stress is converted from the axial direction, the radial direction and the tangential direction of the local coordinate system of the hole system to the x, y and z directions of the global coordinate system of the part, so that the stress is adapted to the global coordinate system; the equivalent plastic strain corresponding to the residual stress is loaded in the part deformation simulation process, so that the residual stress is ensured not to be released due to the geometric coordination process of the elastic deformation of the part; the stress that can rebound under the condition of small plastic strain in the layer depth direction is ignored by loading only the machining residual stress of the surface layer with the maximum equivalent plastic strain and ignoring the machining residual stress of other layers, so that the cross-scale loading under the condition that the machining residual stress of the mu (μ) level does not correspond to the grid number of the part model of the meter (m) level is realized, and the high-precision machining residual stress induced deformation simulation prediction result is obtained.The machining process parameters are optimized according to the simulation prediction result, and the active control on the deformation amount of the part is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to a hole wall machining residual stress conversion loading method, belonging to the field of machining. BACKGROUND

[0002] In recent years, in the field of heavy-duty vehicles, various parts gradually develop towards lightweight and integration, and the materials of various box parts gradually transition from high-strength steel to lightweight alloys such as aluminum alloy and magnesium alloy to reduce the weight of the engine and improve the effective power of the vehicle. In the process of manufacturing with lightweight materials, the uncontrolled deformation of the part may occur in the machining process due to the decrease in material strength. Taking the aluminum alloy camshaft support part as an example, after the machining of the hole series, the secondary deformation of the lower joint surface of the part may occur due to the residual stress induced by the machining of the hole series, which may destroy the original plane machining precision and further cause the part to be scrapped.

[0003] In view of the problem of residual stress-induced deformation of the part, at present, the possible secondary deformation of the part under the action of machining residual stress is mainly solved by finite element simulation, and then the key position of the part is screened and the machining residual stress is regulated or the deformation of the part is limited by clamping and restraining. Most of the current researches are mainly aimed at simple flat parts with single features. For heavy-duty vehicle parts with large-interval coaxial hole series and large joint surface, the existing residual stress conversion and loading method may cause the problem of mismatching of stress results after loading the residual stress of the hole wall, which may finally lead to distortion of the simulation results.

[0004] In summary, in the field of heavy-duty vehicles, there is a problem of residual stress-induced deformation of vehicle parts due to lightweight and weak stiffness of the material of the part. However, due to the complex features and structure of the engine parts for vehicles, the existing residual stress-induced deformation analysis technology is difficult to apply, and for the residual stress of the hole series, there is a problem of coordinate transformation in the calculation of stress, so it is necessary to develop a new finite element stress conversion loading method for residual stress-induced deformation of the part to solve the influence of the machining residual stress of the coaxial hole series on the overall deformation of the part and the machining precision of the joint surface of the part. SUMMARY

[0005] Aiming at the existing problems: (1) the coordinate system conversion is needed when loading the residual stress of hole wall machining; (2) most of the existing technologies are for simple structure and single feature flat plate parts, and there is still lack of hole wall machining residual stress conversion loading method for complex structure parts, the purpose of the present application is to provide a hole wall machining residual stress conversion loading method, based on the stress state equation of any point in the object in three-dimensional elastoplasticity, the hole wall machining residual stress is converted from the axial, radial and tangential directions of the local coordinate system of the hole system to the x, y and z directions of the global coordinate system of the part, so that the stress is adapted to the global coordinate system to obtain more accurate simulation results; the equivalent plastic strain corresponding to the residual stress is loaded in the part deformation simulation process, so as to ensure that the residual stress will not be released due to the geometric coordination process of the elastic deformation of the part; by loading only the machining residual stress of the surface layer with the maximum equivalent plastic strain and ignoring the machining residual stress of other layers, the stress that can rebound under the condition of small plastic strain in the layer depth direction is ignored, the cross-scale loading under the condition that the machining residual stress of μm level does not correspond to the grid number of the part model of m level is realized, and the high-precision machining residual stress induced deformation simulation prediction result is obtained.

[0006] The purpose of the present application is realized by the following technical solutions.

[0007] The hole wall machining residual stress conversion loading method disclosed by the present application constructs a finite element simulation model of the hole wall machining process and performs simulation calculation; extracts the anisotropic machining residual stress and equivalent plastic strain of the element near the middle position and the simulation calculation results of the distribution with layer depth; obtains the anisotropic machining residual stress and equivalent plastic strain of the surface layer element; based on the stress state equation of any point in the object in three-dimensional elastoplasticity, the hole wall machining residual stress result is converted according to the position of the global coordinate system of the part; the anisotropic machining residual stress of the surface layer of the hole wall and the equivalent plastic strain of the surface layer are loaded into the simulation model as predefined values, and the residual stress induced deformation of the part is solved.

[0008] The hole wall machining residual stress conversion loading method disclosed by the present application comprises the following steps:

[0009] Step 1, constructing a finite element simulation model of the hole wall machining process and performing calculation to obtain the hole wall machining simulation result.

[0010] As a preferred, the finite element simulation model of the hole wall machining process should set the tool as a rigid body model in the modeling process, so as to reduce the finite element simulation calculation amount and speed up the calculation speed;

[0011] As a preferred, when modeling the machined workpiece in the finite element simulation model of the hole wall machining process, the overall hole should be taken so as to reduce the finite element simulation calculation amount and speed up the calculation speed.

[0012] As a preference, the finite element simulation model of the hole wall machining process should set the normal contact as "hard contact" when defining the contact between the tool and the machined workpiece to reduce the finite element simulation calculation amount and speed up the calculation speed.

[0013] As a preference, the finite element simulation model of the hole wall machining process should set "mass scaling" in the analysis step to speed up the calculation speed.

[0014] Step 2, based on the hole wall machining simulation results, extract the layer depth distribution simulation calculation results of the residual stress and equivalent plastic strain of the elements near the middle position.

[0015] Step 3, based on the layer depth distribution simulation calculation results in step 2, obtain the residual stress and equivalent plastic strain of the surface layer elements, respectively denoted as s 11 ,s 22 ,s 33 ,s 12 ,s 23 ,s 13 and ε p .

[0016] Step 4, according to the position of the part global coordinate system, based on the stress state equation of any point in the object in three-dimensional elastoplastic mechanics, the machining residual stress results obtained in step 3 are converted to obtain the converted hole wall machining residual stress distribution.

[0017] The specific implementation method of step 4 is:

[0018] Step 4.1, obtain the position (x, y) of the loading point in the global coordinate system.

[0019] Step 4.2, calculate the reversing angle based on the loading point position in step 4.1, and the reversing angle is shown in formula (1):

[0020]

[0021] Step 4.3, calculate the angle cosine value between the spatial plane normal and the coordinate axis of the loading point local coordinate system based on the reversing angle α in step 4.2, as shown in formula (2) (3):

[0022]

[0023] Wherein, formula (2) is used for transformation of the global coordinate system x axis, formula (3) is used for transformation of the global coordinate system y axis, and subscripts 1, 2 represent the global coordinate system x, y axes.

[0024] Step 4.4, based on the cosine value of the angle between the normal of the spatial plane and the coordinate axis of the loading point local coordinate system, the stress value is converted according to the stress state equation of three-dimensional elastic-plastic mechanics as shown in formula (4)~(7):

[0025]

[0026] Among them, formula (4), (5) are used to calculate the normal stress and shear stress in the x-axis direction of the global coordinate system, formula (6), (7) are used to calculate the normal stress and shear stress in the y-axis direction of the global coordinate system, wherein s, t represent the normal stress and shear stress in the direction respectively.

[0027] In the hole feature of the part, because the axis direction of the hole is parallel to the z-axis direction of the global coordinate system, the z-axis normal stress and shear stress in the global coordinate system are equal to the axial stress in the hole system local coordinate system, and satisfy the relationship as shown in formula (8):

[0028]

[0029] Among them, subscript 3 represents the converted global coordinate system z-axis.

[0030] According to the position of the global coordinate system of the part, the converted hole wall machining residual stress distribution is obtained based on formula (4)~(8).

[0031] Step 5, repeat step 4 until the stress and strain distribution calculation of all loading points is completed, and the stress and strain distribution calculation values s1, s2, s3, t1, t2, t3, ε p , since the equivalent plastic strain ε p is a scalar without direction, it is the same value as ε p in step 3.

[0032] Step 6, based on the converted stress distribution calculation values s1, s2, s3, t1, t2, t3 and the equivalent plastic strain ε p of the outermost layer element obtained in step 5, the boundary conditions of the part deformation simulation model are defined.

[0033] As preferred, based on the ABAQUS finite element software, the converted stress distribution calculation values and the equivalent plastic strain of the outermost layer element are embedded into the sigini and hardini subprograms to realize the boundary condition definition of the simulation model, that is, to obtain the simulation model with predefined field.

[0034] Step 7, based on the hole wall machining residual stress conversion result in step 5 and the part deformation simulation model with a predefined field in step 6 ignoring the machining residual stress of other layer depths, finite element calculation is carried out, that is, the hole wall machining residual stress is converted from the axial, radial and tangential directions of the hole system local coordinate system to the x, y and z directions of the part global coordinate system, the cross-scale loading under the condition that the machining residual stress of the order of μm does not correspond to the grid number of the part model of the order of m is realized, and then the high-precision machining residual stress induced deformation simulation prediction is realized, and the hole wall part deformation simulation result is obtained.

[0035] Further comprising step 8, optimizing the machining process parameters according to the high-precision hole wall part deformation simulation result obtained in step 7, and realizing the active control of the part deformation.

[0036] Advantages:

[0037] 1. The hole wall machining residual stress conversion loading method disclosed in the application constructs a three-dimensional elastic-plastic mechanics stress state equation, and utilizes the relationship that the z-axis normal stress and shear stress in the global coordinate system are equal to the axial stress in the hole system local coordinate system, to calculate the machining residual stress distribution conforming to the part global coordinate system, so that the hole wall machining residual stress conversion calculation result is more accurate.

[0038] 2. The hole wall machining residual stress conversion loading method disclosed in the application loads the equivalent plastic strain corresponding to the residual stress in the part deformation simulation process, to ensure that the residual stress will not be released due to the geometric coordination process of the part elastic deformation; the application completely simulates the real state of the actual work-hardening layer by simultaneously loading the stress field and the equivalent plastic strain, so that the residual stress field distribution is closer to the actual state.

[0039] 3. The hole wall machining residual stress conversion loading method disclosed in the application ignores the stress that can rebound under the condition of small plastic strain in the layer depth direction by loading only the machining residual stress of the most surface layer with the maximum equivalent plastic strain and ignoring the machining residual stress of other layer depths, solves the problem that the part model size does not match the machining simulation model size, realizes the cross-scale loading under the condition that the machining residual stress of the order of μm does not correspond to the grid number of the part model of the order of m, and further optimizes and speeds up the establishment process of the simulation model.

[0040] 4. The hole wall machining residual stress conversion loading method disclosed in the application converts the hole wall machining residual stress from the axial, radial and tangential directions of the hole system local coordinate system to the x, y and z directions of the part global coordinate system based on the stress state equation of any point in the three-dimensional elastic-plastic mechanics, so that the stress is adapted to the global coordinate system to obtain more accurate simulation results. BRIEF DESCRIPTION OF DRAWINGS

[0041] Figure 1 A method flow chart of a hole wall machining residual stress conversion loading method disclosed by the present application;

[0042] Figure 2 A schematic diagram of an aluminum alloy camshaft support body part;

[0043] Figure 3 A boring machining hole system multi-tool cutting finite element simulation model constructed based on ABAQUS finite element simulation software;

[0044] Figure 4 The distribution of residual stress and equivalent plastic strain in the depth direction;

[0045] Figure 5 The simulation calculation results of the deformation of the camshaft support body part induced by the hole wall machining residual stress by ABAQUS finite element simulation software. DETAILED DESCRIPTION

[0046] In order to better illustrate the purpose and advantages of the present application, the content of the application will be further described below in combination with the drawings and examples.

[0047] Example 1:

[0048] The deformation of the part induced by the residual stress of the coaxial hole system of the aluminum alloy camshaft support body part f18 is simulated and analyzed by the method of the present application.

[0049] As Figure 1 shown, the hole wall machining residual stress conversion loading method disclosed in the present embodiment has the following specific implementation steps:

[0050] Step 1, construct a finite element simulation model of the hole wall machining process and perform calculation to obtain the hole wall machining simulation results.

[0051] The boring machining hole system multi-tool cutting finite element simulation model constructed based on ABAQUS finite element simulation software is shown in Figure 3 .

[0052] Step 2, based on the hole wall machining simulation results, extract the element residual stress and equivalent plastic strain distribution simulation calculation results of the elements near the middle position.

[0053] Based on the element residual stress and equivalent plastic strain distribution results extracted from the simulation model and simulation results in Figure 3 , shown in Figure 4 .

[0054] Step 3, based on the layer depth distribution simulation calculation results in step 2, obtain the element residual stress and equivalent plastic strain of the surface layer elements, respectively denoted as s 11 , s 22,s 33 ,s 12 ,s 23 ,s 13 With ε p .

[0055] based on Figure 4 From the results, we can see that:

[0056] s 11 =-4.32,s 22 =-77.99,s 33 =-93.44,s 12 = -0.018,s 23 =28.45,s 13 =-14.77,ε p =1.14

[0057] Step 4: Based on the position of the part in the global coordinate system, the residual stress results obtained in Step 3 are converted according to the stress state equation of any point in the object in three-dimensional elastoplastic mechanics to obtain the converted residual stress distribution of the hole wall.

[0058] Step 5: Repeat step 4 until the stress and strain distribution calculations for all loading points are completed, obtaining the calculated stress and strain distribution values ​​s1, s2, s3, t1, t2, t3, ε for all loading points. p Due to the equivalent plastic strain ε p Since it is a scalar without direction, it is related to ε in step 3. p They are the same value.

[0059] After completing step 5, based on the characteristics of the ABAQUS finite element software, the stress and strain distribution of all model loading points are calculated and loaded into the finite element model through the sigini and hardini subroutines.

[0060] Step 6: Based on the converted stress distribution values ​​s1, s2, s3, t1, t2, t3 obtained in Step 5 and the equivalent plastic strain ε of the outermost element. p Define the boundary conditions for the part deformation simulation model.

[0061] Step 7: Based on the conversion results of residual stress in hole wall machining in Step 5 and the part deformation simulation model with predefined field that ignores residual stress in other layer depths in Step 6, perform finite element calculation. That is, convert the residual stress in hole wall machining from the axial, radial and tangential directions of the local coordinate system of the hole system to the x, y and z directions of the global coordinate system of the part. This realizes cross-scale loading under the condition that the residual stress at the μm level does not correspond to the mesh size of the m-level part model, thereby realizing high-precision simulation prediction of deformation induced by residual stress in machining, and obtaining the simulation results of hole wall part deformation.

[0062] The final camshaft support body part hole wall processing residual stress induced part deformation result is shown in Figure 5

[0063] Step 8, according to the high-precision hole wall part deformation simulation result obtained in step 7, optimize the machining process parameters, and realize the active control of the part deformation.

[0064] The above specific description further describes the purpose, technical scheme and beneficial effects of the application. It should be understood that the above description is only a specific embodiment of the application and does not limit the protection scope of the application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the application shall be included in the protection scope of the application.​

Claims

1. A method for converting residual stress during hole wall machining, characterized in that: Includes the following steps, Step 1: Construct a finite element simulation model of the hole wall machining process and perform calculations to obtain the simulation results of the hole wall machining. Step 2: Extract the simulation results of the distribution of residual stress and equivalent plastic strain in all directions of the unit near the middle position as a function of layer depth based on the simulation results of hole wall processing; Step 3: Based on the simulation results of the layer depth distribution in Step 2, obtain the anisotropic processing residual stress and equivalent plastic strain of the outermost element, denoted as s. 11 ,s 22 ,s 33 ,s 12 ,s 23 ,s 13 With ε p ; Step 4: Based on the position of the part in the global coordinate system, the residual stress result obtained in Step 3 is converted according to the stress state equation of any point in the object in three-dimensional elastoplastic mechanics to obtain the converted residual stress distribution of the hole wall. Step 5: Repeat step 4 until the stress and strain distribution calculations for all loading points are completed, obtaining the calculated stress and strain distribution values ​​s1, s2, s3, t1, t2, t3, ε for all loading points. p Due to the equivalent plastic strain ε p Since it is a scalar without direction, it is related to ε in step 3. p They are the same value; Step 6: Based on the converted stress distribution values ​​s1, s2, s3, t1, t2, t3 obtained in Step 5 and the equivalent plastic strain ε of the outermost element. p Define the boundary conditions for the part deformation simulation model; Step 7: Based on the conversion results of residual stress in hole wall machining in Step 5 and the part deformation simulation model with predefined field that ignores residual stress in other layer depths in Step 6, perform finite element calculation. That is, convert the residual stress in hole wall machining from the axial, radial and tangential directions of the local coordinate system of the hole system to the x, y and z directions of the global coordinate system of the part. This realizes cross-scale loading under the condition that the residual stress at the μm level does not correspond to the mesh size of the m-level part model, thereby realizing high-precision simulation prediction of deformation induced by residual stress in machining, and obtaining the simulation results of hole wall part deformation.

2. The method for converting residual stress during hole wall machining as described in claim 1, characterized in that: It also includes step 8, which optimizes the processing parameters based on the high-precision hole wall deformation simulation results obtained in step 7, so as to achieve active control of the deformation of the part.

3. The method for converting residual stress during hole wall machining as described in claim 1 or 2, characterized in that: The specific implementation method of step 4 is as follows: Step 4.1: Obtain the position (x, y) of the loading point in the global coordinate system; Step 4.2: Calculate the reversal angle based on the loading point position in Step 4.

1. The reversal angle is shown in Equation (1): Step 4.3: Based on the reversal angle α in Step 4.2, calculate the cosine value of the angle between the spatial plane normal and the coordinate axes of the local coordinate system of the loading point, as shown in equations (2) and (3): Equation (2) is used for the transformation of the x-axis of the global coordinate system, and equation (3) is used for the transformation of the y-axis of the global coordinate system. Subscripts 1 and 2 represent the x and y axes of the global coordinate system being transformed. Step 4.4: Based on the cosine value of the angle between the spatial plane normal and the coordinate axis of the local coordinate system of the loading point obtained in Step 4.3, the stress value is converted according to the three-dimensional elastoplastic stress state equations shown in equations (4) to (7): Formulas (4) and (5) are used to calculate the normal stress and shear stress in the x-axis direction under the global coordinate system, and formulas (6) and (7) are used to calculate the normal stress and shear stress in the y-axis direction under the global coordinate system. In the formulas, s and t represent the normal stress and shear stress in the direction respectively. In the hole feature of the part, since the axial direction of the hole is parallel to the z-axis direction of the global coordinate system, the normal stress and shear stress of the z-axis in the global coordinate system are equal to the axial stress in the local coordinate system of the hole system, satisfying the relationship described in equation (8): Wherein, the subscript 3 represents the z-axis of the converted global coordinate system; Based on the position of the part in the global coordinate system, the distribution of residual stress after hole wall machining after conversion is obtained based on equations (4) to (8).

4. The method for converting residual stress during hole wall machining as described in claim 3, characterized in that: In the finite element simulation model of the hole wall machining process, the tool should be set as a rigid body model during the modeling process.

5. The method for converting residual stress during hole wall machining as described in claim 3, characterized in that: When modeling the workpiece, the finite element simulation model of the hole wall machining process should use a monolithic hole.

6. The method for converting residual stress during hole wall machining as described in claim 3, characterized in that: When defining the contact between the tool and the workpiece in the finite element simulation model of the hole wall machining process, the normal contact should be set to "hard contact".

7. The method for converting residual stress during hole wall machining as described in claim 3, characterized in that: In the analysis step settings, the finite element simulation model of the hole wall machining process should have "mass scaling" set.

8. The method for converting residual stress during hole wall machining as described in claim 3, characterized in that: Based on the ABAQUS finite element software, the calculated stress distribution and the equivalent plastic strain of the outermost element are embedded into the sigini and hardini subroutines to define the boundary conditions of the simulation model, thus obtaining a simulation model with predefined fields.

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