A method for measuring plastic strain components of a thin-walled rotary body

Abstract

The present invention discloses a method for measuring plastic strain components of a thin-walled rotary part, belonging to the field of machining; it includes the creation of a micro-grid, the use of a high-speed camera and digital image correlation technology (DIC), and the calculation of plastic strain components; among which, the calculation of plastic strain components adopts a more accurate non-linear calculation; first, after selecting the blank part, its surface is precisely ground to high quality, and then a micro-grid is created on the outer surface, and laser marking technology can be used; then the workpiece is clamped and the facilities are arranged, and at the same time, a high-speed camera is used to record the cutting process; after the cutting is completed, the Ncorr1 software is used to obtain the grid pattern, and the coordinates of each grid point are obtained by using DIC technology; finally, the plastic strain components are obtained through calculation; the present invention indirectly obtains the plastic strain components of the thin-walled rotary part by analyzing and calculating the deformed grid, which has practical application value.

Description

Technical Field

[0001] The present invention belongs to the field of machining, and particularly relates to a method for measuring plastic strain components of a thin-walled rotary part. Background Art

[0002] With the rapid development of aviation technology, higher requirements are put forward for the safety, reliability, stability and light weight of aero-engines. Therefore, a large number of thin-walled and integral parts are used in aero-engines. Such parts have the characteristics of complex shape structure, large machining allowance, low rigidity, high precision requirements and poor machining processability. Deformation problems occur during their manufacturing and use, which have seriously hindered the development of aero-engines.

[0003] Directly measuring plastic strain and strain rate during metal cutting is still a challenge. To solve this problem, measuring grid deformation and digital image correlation technology (DIC) have been mentioned in some studies.

[0004] Grids can be generated by different methods, such as electron laser imaging technology, photoresist method, mechanical method or laser printing. The use of grids is not new and they are widely accepted for measuring strain in mechanical processes. Since the grids are engraved on the workpiece, they will undergo the same deformation as the workpiece material. However, this technique is usually not applicable under very aggressive conditions. During machining, Thimm et al. used digital image correlation technology to perform inverse simulation at high cutting speeds (up to 160 m / min). Zhang et al. conducted similar analyses but at lower cutting speeds. Under these cutting conditions, it is assumed that temperature and strain rate effects can be ignored to optimize Johnson-Cook material parameters. Moreover, the tested cutting conditions usually differ significantly from the actual conditions achieved in machining. Sela et al. conducted measurement experiments on plastic strain and plastic strain rate during orthogonal cutting of Ti-6Al-4V, but only did planar studies. M.R. Vaziri Sereshk et al. proposed a calculation of non-linear grid distortion based on linear calculations, but only applied it to face milling and did not attempt to apply it to surface turning. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention designs a method for measuring plastic strain components of a thin-walled rotary part.

[0006] A method for measuring plastic strain components of a thin-walled rotary part specifically includes the following steps:

[0007] Step 1: Use a grinding wheel to finely grind the outer surface of the thin-walled part to be machined;

[0008] Step 2: Use laser printing technology to generate a microgrid on the outer surface of the thin-walled part obtained in Step 1, which consists of several square grids, and each grid is obtained by the orthogonality of two sets of parallel lines;

[0009] Step 3: In order to fix the thin-walled part obtained in Step 2, use a three-jaw chuck to clamp the thin-walled part, and the tool acts on the inner surface of the workpiece;

[0010] Step 4: Use a high-speed camera to record the deformation process of the microgrid on the outer surface of the thin-walled part during turning processing, and the recorded time nodes are synchronized with the turning time nodes;

[0011] Step 5: Set the machining parameters on the lathe, complete the turning process, and obtain the deformed grid pattern after turning;

[0012] Step 6: Use Ncorr1 software to perform DIC measurement on the deformed grid pattern after turning to obtain the coordinates of 8 grid points, and these 8 grid points are the 4 corners and 4 midpoints of the sides of the square grid; expressed as: A(α1, β1), B(α2, β2), ……, H(α8, β8);

[0013] Step 7: Use the non-linear calculation method to represent the plastic strain components of the thin-walled body of the revolving body;

[0014] The non-linear term is implemented in the polynomial function used to interpolate the node values; assuming that the midpoint of the boundary of the square grid element remains in the middle, the displacement field after the deformation of this grid is:

[0015] U(x,y) = α1 + α2x + α3y + α4xy + α5x 2 + α6y 2 + α7x 2 y + α8xy 2 (1)

[0016] V(x,y) = β1 + β2x + β3y + β4xy + β5x 2 + β6y 2 + β7x 2 y + β8xy 2 (2)

[0017] where α and β are the coordinate values of each grid point;

[0018] Then the plastic strain components of the thin-walled body of the revolving body are:

[0019]

[0020]

[0021]

[0022] Among them, exy, exx, and eyy represent shear strains, normal strains parallel and perpendicular to the relative tool-workpiece movement direction, respectively.

[0023] Advantageous technical effects of the present invention:

[0024] The method for measuring the strain and strain rate of a thin-walled rotary part provided by the present invention solves the problem that it is difficult to measure the surface strain and strain rate. It has great universality for workpiece materials. This method allows the use of a unique image to measure plastic strain and strain rate, avoiding the typical decorrelation problem in the DIC-based method, and has practical application value. Description of the drawings

[0025] Figure 1 Flowchart of the invention of a method for measuring plastic strain components of a thin-walled rotary part in an embodiment of the present invention;

[0026] Figure 2 Schematic diagram of 8 nodes of a square grid after deformation in an embodiment of the present invention;

[0027] Figure 3 Schematic diagram of a turning scheme in an embodiment of the present invention;

[0028] Figure 4 Schematic diagram of a microgrid grid in an embodiment of the present invention. Detailed implementation manners

[0029] Next, the present invention will be described in detail in conjunction with the embodiments of the present invention.

[0030] The purpose of the present invention is to provide a method for measuring plastic strain components of a thin-walled rotary part; first, improve the quality of the surface to be machined; then create a microgrid on it, clamp the workpiece, set turning parameters, and at the same time use a high-speed camera to record the turning process, and its recording time is consistent with the turning time; after completing the turning process, obtain the captured grid image, use DIC technology to measure the coordinates of each grid point, so as to obtain grid deformation data; indirectly calculate the strain components of the thin-walled rotary part, and the calculation adopts non-linear calculation, which more conforms to the actual machining requirements and has practical application value.

[0031] A method for measuring plastic strain components of a thin-walled rotary part, as shown in the attached Figure 1 figure, specifically includes the following steps:

[0032] Step 1: Obtain a thin-walled blank part, and use a grinding wheel to finely grind the outer surface of the thin-walled part to be machined; finely grind until the surface roughness Ra measured by a roughness meter reaches 1.4 μm.

[0033] Step 2: Use laser printing technology to generate a microgrid on the outer surface of the thin-walled part obtained in Step 1. The microgrid consists of a number of 30×30 μm square grids. Each grid is obtained by the orthogonal intersection of two sets of parallel lines, and a grid is created every 60 μm, as Figure 4 shown;

[0034] Step 3: To fix the thin-walled part obtained in Step 2, use a three-jaw chuck to clamp the thin-walled part, and the cutting tool acts on the inner surface of the workpiece, as Figure 3 shown;

[0035] Step 4: Use a high-speed camera Photron Fastcam APX RS 250K to record the deformation process of the microgrid on the outer surface of the thin-walled part during turning processing. The recorded time nodes are synchronized with the turning time nodes;

[0036] Step 5: Set the machining parameters of the feed rate of 0.2 m / min, the cutting speed of 60 m / min, and the cutting depth of 0.2 mm on the lathe, complete the turning process, and obtain the deformed grid diagram after turning recorded by the high-speed camera;

[0037] Step 6: Use Ncorr1 software to perform DIC measurement on the deformed grid diagram after turning to obtain the coordinates of 8 grid points. These 8 grid points are the 4 corners and the midpoints of the 4 side lines of the square grid; denoted as: A(α1, β1), B(α2, β2), ……, H(α8, β8); The schematic diagram of the 8 nodes of the deformed square grid is shown in the appendix Figure 2 shown;

[0038] Step 7: Use the non-linear calculation method to represent the plastic strain components of the thin-walled rotary body;

[0039] The non-linear term is implemented in the polynomial function used to interpolate the node values; assuming that the midpoint of the boundary of the square grid cell remains in the middle, the displacement field after the deformation of the grid is:

[0040] U(x,y) = α1 + α2x + α3y + α4xy + α5x 2 + α6y 2 + α7x 2 y + α8xy 2 (1)

[0041] V(x,y) = β1 + β2x + β3y + β4xy + β5x 2 + β6y 2 + β7x 2 y + β8xy 2 (2)

[0042] where α and β are the coordinate values of each grid point;

[0043] The plastic strain components of the thin-walled rotary body are as follows:

[0044]

[0045]

[0046]

[0047] Among them, exy, exx, and eyy represent the shear strain, the normal strain parallel and perpendicular to the relative tool-workpiece movement direction, respectively.

Claims

1. A method for measuring the plastic strain components of a thin-walled rotary body, characterized in that, Specifically, it includes the following steps: Step 1: Use a grinding wheel to finely grind the outer surface of the thin-walled part to be machined; Step 2: Use laser printing technology to generate a microgrid on the outer surface of the thin-walled part obtained in Step 1, which consists of several square grids, and each grid is obtained by the orthogonal intersection of two sets of parallel lines; Step 3: In order to fix the thin-walled part obtained in Step 2, use a three-jaw chuck to clamp the thin-walled part, and the tool acts on the inner surface of the workpiece; Step 4: Use a high-speed camera to record the deformation process of the microgrid on the outer surface of the thin-walled part during turning processing, and the recorded time nodes are synchronized with the turning time nodes; Step 5: Set the machining parameters on the lathe, complete the turning process, and obtain the deformed grid pattern after turning; Step 6: Use Ncorr1 software to perform DIC measurement on the deformed grid pattern after turning to obtain the coordinates of 8 grid points, and these 8 grid points are the 4 corners and the midpoints of the 4 sides of the square grid; expressed as: A(α1, β1), B(α2, β2), ……, H(α8, β8); Step 7: Use the non-linear calculation method to represent the plastic strain components of the thin-walled part of the revolving body; The specific content of Step 7 is as follows: The non-linear term is implemented in the polynomial function used to interpolate the node values; assuming that the midpoints of the boundaries of the square grid cells remain in the middle, the displacement field after the deformation of this grid is: U(x,y) = α1 + α2x + α3y + α4xy + α5x 2 + α6y 2 + α7x 2 y + α8xy 2 (1) V(x,y) = β1 + β2x + β3y + β4xy + β5x 2 + β6y 2 + β7x 2 y + β8xy 2 (2) where α, β are the coordinate values of each grid point; Then the plastic strain components of the thin-walled part of the revolving body are: where exy, exx and eyy represent the shear strain, the normal strain parallel and perpendicular to the relative tool-workpiece movement direction respectively.

Images