Hole wall machining residual stress conversion loading method

Abstract

The invention discloses a hole wall machining residual stress conversion loading method, and belongs to the field of machining. The implementation method comprises the following steps of: converting the hole wall machining residual stress from the axial direction, the radial direction and the tangential direction of a hole system local coordinate system to x, y and z directions of a part global coordinate system, so that the stress is adaptive to the global coordinate system; equivalent plastic strain corresponding to the residual stress is loaded in the part deformation simulation process, and it is guaranteed that the residual stress cannot be released due to the geometric coordination process of elastic deformation of the part; through a method of only loading the machining residual stress with the maximum equivalent plastic strain on the outermost layer and neglecting the machining residual stress of other layer depths, the rebounding stress under the small plastic strain condition in the layer depth direction is neglected, and cross-scale loading under the condition that the micron-level machining residual stress does not correspond to the grid order of magnitude of an m-level part model is achieved. And a high-precision machining residual stress induced deformation simulation prediction result is obtained. And optimizing machining process parameters according to a simulation prediction result, and realizing active control on the deformation of the part.

Description

Technical Field

[0001] The invention relates to a hole wall processing residual stress conversion loading method, belonging to the field of mechanical processing. Background Art

[0002] In recent years, in the field of heavy-duty vehicles, various parts have gradually developed in the direction of lightweight and integration. The materials of various box parts have gradually transitioned from high-strength steel to lightweight alloys such as aluminum alloy and magnesium alloy to reduce engine weight and increase vehicle effective power. In the process of manufacturing with lightweight materials, the parts will undergo uncontrollable deformation during machining due to the decrease in material strength. Taking the aluminum alloy camshaft support body parts as an example, during the machining process of the parts, due to the presence of large-interval coaxial holes in the part structure, the lower joint surface of the part will undergo secondary deformation after the hole system is processed due to the residual stress induced by the hole system processing, resulting in the destruction of the original plane processing accuracy, and then causing the parts to be scrapped.

[0003] In order to solve the problem of residual stress-induced deformation of parts, the finite element simulation method is currently mainly used to solve the secondary deformation of parts under the action of machining residual stress, and then screen out the key positions of the parts and regulate the machining residual stress on this basis or use clamping constraints to limit the deformation of the parts. However, most of the current research (technology) is aimed at flat parts with simple structures and single features. For heavy-duty vehicle parts with large-interval coaxial holes and large joint surfaces, the existing residual stress conversion and loading methods will cause mismatch in stress results after loading the residual stress of the hole wall, which will eventually lead to distortion of the simulation results.

[0004] In summary, there is currently a problem of residual stress-induced deformation in the field of heavy-duty vehicles due to the lightweight and weak rigidity of part materials. However, the existing residual stress-induced deformation analysis technology is difficult to apply due to the complex characteristics and structure of automotive engine parts. In addition, there is a coordinate conversion problem in the calculation of stress for hole system residual stress. Therefore, it is necessary to develop a new finite element stress conversion loading method for part deformation induced by residual stress in hole wall processing, so as to solve the influence of residual stress in coaxial hole system processing on the overall deformation of parts and the processing accuracy of part joint surfaces. Summary of the invention

[0005] In view of the existing problems: (1) coordinate system conversion is required when loading residual stress of hole wall machining; (2) the existing technologies are mostly for flat plate parts with simple structure and single feature, and there is still a lack of hole wall machining residual stress conversion loading method for complex structure parts. The purpose of the present invention is to provide a hole wall machining residual stress conversion loading method, which 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, z directions of the part global coordinate system based on the stress state equation of any point in the object in three-dimensional elastic-plastic mechanics. The stress is adapted to the global coordinate system to obtain more accurate simulation results. During the deformation simulation of the part, the equivalent plastic strain corresponding to the residual stress is loaded to ensure that the residual stress will not be released due to the geometric coordination process of the elastic deformation of the part. By only loading the machining residual stress with the maximum equivalent plastic strain in the outermost layer and ignoring the machining residual stress in other layers, the reboundable stress under the condition of small plastic strain in the layer depth direction is ignored, so as to realize cross-scale loading when the μm-level machining residual stress and the m-level part model grid order do not correspond, and obtain high-precision machining residual stress-induced deformation simulation prediction results.

[0006] The objectives of the present invention are achieved through the following technical solutions.

[0007] The invention discloses a hole wall machining residual stress conversion loading method, which constructs a finite element simulation model of the hole wall machining process and performs simulation calculation; extracts the simulation calculation results of the isotropic machining residual stress and equivalent plastic strain distribution with layer depth of the unit close to the middle position; obtains the isotropic machining residual stress and equivalent plastic strain of the most superficial unit; converts the hole wall machining residual stress results based on the stress state equation of any point in the object in three-dimensional elastic-plastic mechanics according to the position of the global coordinate system of the part; loads the hole wall most superficial machining residual stress and the most superficial equivalent plastic strain as predefined values ​​into the simulation model, and solves the residual stress induced deformation of the part.

[0008] The present invention discloses a hole wall machining residual stress conversion loading method, comprising the following steps:

[0009] Step 1: construct a finite element simulation model of the hole wall processing process and perform calculations to obtain the hole wall processing simulation results.

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

[0011] As a preferred method, the finite element simulation model of the hole wall processing process should use the overall hole when modeling the cut workpiece. To reduce the amount of finite element simulation calculations and speed up the calculations.

[0012] Preferably, the finite element simulation model of the hole wall machining process should set the normal contact to "hard contact" when defining the contact between the tool and the cut workpiece to reduce the amount of finite element simulation calculations 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 settings to speed up the calculation.

[0014] Step 2: Based on the hole wall processing simulation results, the simulation calculation results of the distribution of the isotropic processing residual stress and equivalent plastic strain with layer depth of the unit close to the middle position are extracted.

[0015] Step 3: Based on the simulation calculation results of the layer depth distribution in step 2, the isotropic machining residual stress and equivalent plastic strain of the surface unit are obtained, which are denoted as s 11 ,s 22 ,s 33 ,s 12 ,s 23 ,s 13 With ε p .

[0016] Step 4: According to the position of the global coordinate system of the part, the machining residual stress result obtained in step 3 is converted based on the stress state equation of any point in the object in three-dimensional elastic-plastic mechanics 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 commutation angle based on the loading point position in step 4.1. The commutation angle is shown in formula (1):

[0020]

[0021] Step 4.3: Based on the commutation angle α in step 4.2, the cosine value of the angle between the normal of the space plane and the coordinate axis of the local coordinate system of the loading point is calculated as shown in equations (2) and (3):

[0022]

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

[0024] Step 4.4: According to the cosine value of the angle between the normal direction of the space plane and the coordinate axis of the local coordinate system of the loading point obtained in step 4.3, the stress value is converted based on the three-dimensional elastic-plastic mechanical stress state equation shown in equations (4) to (7):

[0025]

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

[0027] 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 z-axis normal stress and shear stress in the global coordinate system and the axial stress in the local coordinate system of the hole are equal, satisfying the relationship described in formula (8):

[0028]

[0029] The subscript 3 represents the z-axis of the converted global coordinate system.

[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 equations (4) to (8).

[0031] Step 5: Repeat step 4 until the stress and strain distribution calculations of all loading points are completed, and the calculated stress and strain distribution values ​​s of all loading points are obtained. 1 ,s 2 ,s 3 ,t 1 ,t 2 ,t 3 ,ε p , due to the equivalent plastic strain ε p is a directionless scalar, so it is the same as ε in step 3. p is the same value.

[0032] Step 6: Calculate the stress distribution value s based on the conversion obtained in step 5 1 ,s 2 ,s 3 ,t 1 ,t 2 ,t 3 and the equivalent plastic strain ε of the most superficial element p , define the boundary conditions of the part deformation simulation model.

[0033] Preferably, based on ABAQUS finite element software, the converted stress distribution calculation value and the equivalent plastic strain of the outermost unit are embedded into the sigini and hardini subroutines to realize the boundary condition definition of the simulation model, that is, to obtain a simulation model with a 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 that ignores the machining residual stress of other layer depths in step 6, finite element calculation is performed, that is, 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, z directions of the global coordinate system of the part, to achieve cross-scale loading when the μm-level machining residual stress and the m-level part model grid order do not correspond, and then achieve high-precision machining residual stress induced deformation simulation prediction, and obtain the hole wall part deformation simulation result.

[0035] The method further includes step 8, optimizing the processing parameters according to the high-precision hole wall part deformation simulation result obtained in step 7, so as to realize active control of the part deformation amount.

[0036] Beneficial effects:

[0037] 1. The present invention discloses a hole wall machining residual stress conversion loading method, which constructs a three-dimensional elastic-plastic mechanical stress state equation, and uses the mutual relationship between the z-axis normal stress and shear stress in the global coordinate system and the axial stress in the local coordinate system of the hole system to calculate the machining residual stress distribution that conforms to the global coordinate system of the part, so that the hole wall machining residual stress conversion calculation result is more accurate.

[0038] 2. The present invention discloses a method for converting and loading residual stress in hole wall processing, which loads equivalent plastic strain corresponding to residual stress during part deformation simulation to ensure that residual stress will not be released due to the geometric coordination process of part elastic deformation. The present invention completely simulates the actual state of the actual processing hardened layer by simultaneously loading stress field and equivalent plastic strain, so that the residual stress field distribution is closer to reality.

[0039] 3. The present invention discloses a hole wall machining residual stress conversion loading method, which ignores the reboundable stress under the condition of small plastic strain in the layer depth direction by only loading the machining residual stress with the maximum equivalent plastic strain in the outermost layer and ignoring the machining residual stress in other layers, thereby solving the problem of mismatch between the part model size and the machining simulation model scale, and realizing cross-scale loading when the μm-level machining residual stress and the m-level part model grid order of magnitude do not correspond, thereby optimizing and accelerating the simulation model establishment process.

[0040] 4. The present invention discloses a method for converting and loading residual stress of hole wall processing, which converts the residual stress of hole wall processing based on the stress state equation of any point in an object in three-dimensional elastic-plastic mechanics, and converts the residual stress of hole wall processing 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 adapts to the global coordinate system to obtain more accurate simulation results. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0042] Figure 2 It is a schematic diagram of the aluminum alloy camshaft support body parts;

[0043] Figure 3 It is a multi-tool cutting finite element simulation model for boring hole system built based on ABAQUS finite element simulation software;

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

[0045] Figure 5 This is the simulation calculation result of the camshaft support body deformation induced by residual stress in hole wall processing using ABAQUS finite element simulation software. DETAILED DESCRIPTION

[0046] In order to better illustrate the purpose and advantages of the present invention, the invention is further described below with reference to the accompanying drawings and examples.

[0047] Embodiment 1:

[0048] The method of the present invention is used to simulate and analyze the deformation of aluminum alloy camshaft support body parts f18 coaxial hole system induced by residual stress during machining.

[0049] like Figure 1 As shown, the present embodiment discloses a method for converting and loading residual stress in hole wall processing, and the specific implementation steps are as follows:

[0050] Step 1: construct a finite element simulation model of the hole wall processing process and perform calculations to obtain the hole wall processing simulation results.

[0051] The finite element simulation model of multi-tool cutting for boring hole system built based on ABAQUS finite element simulation software is as follows: Figure 3 shown.

[0052] Step 2: Based on the hole wall processing simulation results, the simulation calculation results of the distribution of the isotropic processing residual stress and equivalent plastic strain with layer depth of the unit close to the middle position are extracted.

[0053] based on Figure 3 The simulation model and simulation results in the unit are extracted to obtain the distribution results of the isotropic residual stress and equivalent plastic strain with layer depth. Figure 4 shown.

[0054] Step 3: Based on the simulation calculation results of the layer depth distribution in step 2, the isotropic machining residual stress and equivalent plastic strain of the surface unit are obtained, which are denoted as s 11 ,s 22 ,s 33 ,s 12 ,s 23 ,s 13 With ε p .

[0055] based on Figure 4 As a result, 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: According to the position of the global coordinate system of the part, the machining residual stress result obtained in step 3 is converted based on the stress state equation of any point in the object in three-dimensional elastic-plastic mechanics to obtain the converted hole wall machining residual stress distribution.

[0058] Step 5: Repeat step 4 until the stress and strain distribution calculations of all loading points are completed, and the calculated stress and strain distribution values ​​s of all loading points are obtained. 1 ,s 2 ,s 3 ,t 1 ,t 2 ,t 3 ,ε p , due to the equivalent plastic strain ε p is a directionless scalar, so it is the same as ε in step 3. p is the same value.

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

[0060] Step 6: Calculate the stress distribution value s based on the conversion obtained in step 5 1 ,s 2 ,s3 ,t 1 ,t 2 ,t 3 and the equivalent plastic strain ε of the most superficial element p , define the boundary conditions of the part deformation simulation model.

[0061] 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 that ignores the machining residual stress of other layer depths in step 6, finite element calculation is performed, that is, 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, z directions of the global coordinate system of the part, to achieve cross-scale loading when the μm-level machining residual stress and the m-level part model grid order do not correspond, and then achieve high-precision machining residual stress induced deformation simulation prediction, and obtain the hole wall part deformation simulation result.

[0062] The final calculated results of the camshaft support body part hole wall machining residual stress induced part deformation are as follows Figure 5 shown.

[0063] Step 8: Optimize the processing parameters according to the high-precision hole wall part deformation simulation results obtained in step 7 to achieve active control of the part deformation.

[0064] The specific description above further illustrates the purpose, technical solutions and beneficial effects of the invention in detail. It should be understood that the above is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for converting and loading residual stress in hole wall machining, characterized in that: The following steps are included: Step 1, construct a finite element simulation model of the hole wall processing process and perform calculations to obtain the hole wall processing simulation results; Step 2, based on the hole wall processing simulation results, extract the simulation calculation results of the distribution of the isotropic processing residual stress and equivalent plastic strain with layer depth of the unit close to the middle position; Step 3: Based on the simulation calculation results of the layer depth distribution in step 2, the isotropic machining residual stress and equivalent plastic strain of the surface unit are obtained, which are denoted as s 11 ,s 22 ,s 33 ,s 12 ,s 23 ,s 13 With ε p ; Step 4: According to the position of the global coordinate system of the part, the machining residual stress result obtained in step 3 is converted based on the stress state equation of any point in the object in three-dimensional elastic-plastic mechanics to obtain the converted hole wall machining residual stress distribution; Step 5: Repeat step 4 until the stress and strain distribution calculations of all loading points are completed, and the stress and strain distribution calculation values ​​s1, s2, s3, t1, t2, t3, ε of all loading points are obtained. p , due to the equivalent plastic strain ε p is a directionless scalar, so it is the same as ε in step 3. p are the same value; Step 6: Based on the converted stress distribution calculated values ​​s1, s2, s3, t1, t2, t3 and the equivalent plastic strain ε of the most superficial unit obtained in step 5 p , define the boundary conditions of the part deformation simulation model; 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 that ignores the machining residual stress of other layer depths in step 6, finite element calculation is performed, that is, 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, z directions of the global coordinate system of the part, to achieve cross-scale loading when the μm-level machining residual stress and the m-level part model grid order do not correspond, and then achieve high-precision machining residual stress induced deformation simulation prediction, and obtain the hole wall part deformation simulation result.

2. A hole wall machining residual stress conversion loading method as claimed in claim 1, characterized in that: The method further includes step 8, optimizing the processing parameters according to the high-precision hole wall part deformation simulation result obtained in step 7, so as to realize active control of the part deformation amount.

3. A hole wall machining residual stress conversion loading method as claimed in claim 1 or 2, characterized in that: The specific implementation method of step 4 is: Step 4.1, obtain the position (x, y) of the loading point in the global coordinate system; Step 4.2: Calculate the commutation angle based on the loading point position in step 4.

1. The commutation angle is shown in formula (1): Step 4.3: Based on the commutation angle α in step 4.2, the cosine value of the angle between the normal of the space plane and the coordinate axis of the local coordinate system of the loading point is calculated as shown in equations (2) and (3): Wherein, formula (2) is used for the transformation of the x-axis of the global coordinate system, and formula (3) is used for the transformation of the y-axis of the global coordinate system. The subscripts 1 and 2 represent the converted x and y axes of the global coordinate system. Step 4.4: According to the cosine value of the angle between the normal direction of the space plane and the coordinate axis of the local coordinate system of the loading point obtained in step 4.3, the stress value is converted based on the three-dimensional elastic-plastic mechanical stress state equation shown in equations (4) to (7): Among them, formulas (4) and (5) are used to calculate the normal stress and shear stress in the x-axis direction in the global coordinate system, and formulas (6) and (7) are used to calculate the normal stress and shear stress in the y-axis direction in the global coordinate system, where s and t represent the normal stress and shear stress in this 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 z-axis normal stress and shear stress in the global coordinate system and the axial stress in the local coordinate system of the hole are equal, satisfying the relationship described in formula (8): Among them, the subscript 3 represents the z-axis of the converted global coordinate system; According to the position of the global coordinate system of the part, the converted hole wall machining residual stress distribution is obtained based on equations (4) to (8).

4. A hole wall machining residual stress conversion loading method as claimed in claim 3, characterized in that: The finite element simulation model of the hole wall machining process should set the tool as a rigid body model during the modeling process.

5. A hole wall machining residual stress conversion loading method as claimed in claim 3, characterized in that: The finite element simulation model of the hole wall processing process should use the overall hole when modeling the cut workpiece.

6. A hole wall machining residual stress conversion loading method as claimed in claim 3, characterized in that: When defining the contact between the tool and the workpiece, the finite element simulation model of the hole wall machining process should set the normal contact to "hard contact".

7. A hole wall machining residual stress conversion loading method as claimed in claim 3, characterized in that: The finite element simulation model of the hole wall machining process should set "mass scaling" in the analysis step settings.

8. A hole wall machining residual stress conversion loading method as claimed in claim 3, characterized in that: Based on ABAQUS finite element software, the converted stress distribution calculation value and the equivalent plastic strain of the outermost unit are embedded into the sigini and hardini subroutines to realize the boundary condition definition of the simulation model, that is, to obtain a simulation model with a predefined field.

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