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Finite element numerical simulation analysis of tool strength

1 introduction

metal cutting process is the process of tool workpiece interaction. In the machining system composed of machine tool, fixture, cutter and workpiece, it is very important to select cutters reasonably. The overall structure, cutting edge material and geometry of the tool will directly affect the service life of the tool, the machining quality of the workpiece and the cutting efficiency. Therefore, in the cutting process, the tool should have high strength, good toughness, long service life and good processability. The theoretical analysis of the tool strength and the understanding of the internal stress-strain state of the tool are not only conducive to the rational selection of the tool in the machining process, but also provide a theoretical basis for further improving the internal stress state of the tool and improving the service life of the tool

2 introduction to finite element numerical analysis software ANSYS

finite element numerical analysis software (ANSYS) combines the basic theories of modern mathematics and mechanics with finite element analysis technology, computer graphics and optimization technology. It has a rich and perfect element library, material model library and solver, and can effectively solve various structural dynamic, static, linear and nonlinear problems by using numerical simulation technology. As a finite element analysis software, ANSYS has become an effective tool for CAE and engineering numerical simulation. It is one of the mainstream products in cadfcaefcam software

when ANSYS is used for mechanical analysis of finite element structure, the stress-strain concentration area is analyzed through numerical simulation of the applied load, so as to achieve the purpose of strength analysis and optimization design. The three main steps of ANSYS solution are: create finite element model (pre-processing) → apply load and solve (solution) → view the analysis results (post-processing)

3 establishment of tool mechanics model

in the process of metal cutting, when the tool cuts into the workpiece, the force required to deform the machined material and form chips is called cutting force. The size of cutting force directly affects the design and use of cutting tools, machine tools and fixtures. The cutting force includes overcoming the elastic and plastic deformation resistance caused by the deformation of the material to be machined, overcoming the friction of the cutting chip on the rake face of the tool and the friction between the machined surface and the machined surface of the back face of the tool

in order to facilitate the analysis, calculation and measurement of the force on the tool, a spatial rectangular coordinate system xyyyz can be established according to the cutting main movement speed direction, cutting depth direction and feed direction, and the cutting force fr can be decomposed into three components in this coordinate system, namely, the main cutting force FZ - the cutting speed direction component (tangential force), the cutting depth resistance FY - the cutting depth direction component (radial force) and the feed resistance FX - the feed direction component (axial force) (see Figure 1)

Figure 1 Schematic diagram of tool stress analysis

the main cutting force FZ is the largest component, and it is also the main basis for designing and using tools. At the same time, it can also be used to check the strength, stiffness and motor power of machine tools and fixtures. The cutting depth resistance FY does not consume power and mainly affects the deformation of the process system and the processing quality of the parts. However, when the process system composed of machine tool fixture tool workpiece is not rigid enough, FY is the main factor causing the deformation and processing vibration of the parts. The feed resistance FX mainly acts on the machine tool feed system and is an important basis for checking the strength and rigidity of the main parts of the machine tool feed system

4 example of finite element analysis of tool strength

turning tool is one of the most widely used metal cutting tools, which is mainly used for turning various rotating surfaces and end faces of rotating bodies. Taking a typical cylindrical turning tool as an example, the finite element numerical simulation analysis of tool strength is carried out by using ANSYS

test parameters

carry out turning test on C630 horizontal lathe with cemented carbide turning tool. The workpiece material is carbon steel with s=90kgf/mm2 (0.883gpa). Select the geometric parameters of the tool: tool bar material: 45 steel; Geometric dimension of tool bar: B × H=20mm × 25mm，L=150mm。 Blade material: YT15; The turning tool is mainly used to improve the current manufacturing situation in California: front angle g=15 °, rear angle ao=ao'=5 °, main deflection angle kr=75 °, kr=10 °, and blade inclination ls=-5 °. Mechanical properties of tool materials: strength limit: 600MPa; Yield limit: 355MPa; Elastic modulus e=206gpa; Poisson's ratio =0.27. Cutting parameters: cutting speed) vc=100m/min, feed rate (or feed rate) f=0.5mm/r, back feed ap=5mm

divide cells

according to the geometric dimensions of the tool, create the finite element solid model of the tool in the ANSYS interactive mode

use the self-adaptive lattice division method of ANSYS to divide the cells and customize the cell length. The eight node hexahedral solid45 element type (which is convenient for loading and has high calculation accuracy) is adopted to divide the turning tool into 1569 nodes and 6934 elements (see Fig. 2. The dense element division is to more clearly show the stress concentration area), and the following assumptions are made:

the finite element grid diagram in Fig. 2

takes the tool bar and blade materials as one, which is convenient for simulated loading analysis and calculation

in the calculation, it is assumed that the material is linear elastic, i.e. no yield occurs

the tool will be subject to certain impact and vibration during the cutting process. Considering the finite nature of this impact and vibration, in order to simplify the calculation, the tool is regarded as a static stress distribution at a certain time during the cutting process

in the cutting process, the tool will produce high temperature due to severe friction, but for the convenience of calculation, the influence of temperature field is not considered temporarily

simulated loading solution

because there are many influencing factors of cutting force, the calculation is more complex, and the theoretical calculation formula of cutting force used at present is derived under the condition of ignoring temperature, normal stress, deformation and friction in the third deformation zone, which is quite different from the actual cutting state, so it can only be used for qualitative analysis of cutting force, not for actual calculation. Therefore, according to the original test data of this example, using an experimental formula in the literature, the empirical values of the three cutting components are calculated as fz=4407n, fy1410n, fx=1830n

according to the above analysis, simulate the loading according to the worst limit conditions of cutting conditions (i.e. FZ, FY, FX focus on a point at the tool tip), and impose all constraints on the tool end (this does not affect the analysis results)

result analysis

through the static load calculation of ANSYS, the internal stress distribution diagram of the tool shown in Figure 3, the partial strain distribution diagram of the tool tip shown in Figure 4 and the Usum distribution diagram of all degrees of freedom solutions shown in Figure 5 (displacement contour map) can be obtained

Fig. 3 stress distribution diagram of turning tool Fig. 4 strain distribution diagram of tool tip Fig. 5 displacement isoline diagram

it can be seen from Fig. 3 that the maximum stress point of turning tool is located at the tool tip (the 21st node), the maximum stress value is 676mpa, and the coordinates of the maximum stress point are (-0.025, -0.008, 0.002). Using the similar method, the maximum strain at the tool tip can be calculated as 0.00426m. According to figure 5, the maximum resultant displacement dmx=0.609, and the calculation results are consistent with the actual situation

because the upper system can automatically calibrate the indication accuracy; Some of these items have become local benchmark projects. The analysis results are obtained under the limit conditions (the cutting force is concentrated on a point at the tool tip), and the ANSYS linear analysis is adopted. Therefore, the maximum stress value slightly greater than the strength limit value should still be within the allowable range. If ANSYS nonlinear analysis is conducted, the maximum stress value shall be within the allowable stress range, and the analysis results will be more accurate

since the tool tip is the maximum stress point, it can be seen that the main forms of tool damage are tool tip and blade damage. Therefore, it is very necessary to select high-strength blade materials to increase tool strength. Due to the high temperature generated during the cutting process and the large pressure between the tool and the workpiece material, when the temperature and stress reach a certain level, the tool edge pitting and plastic deformation of the tool material may occur at the maximum stress, which makes it difficult to ensure the machining accuracy. Therefore, it is necessary to adjust the cutting parameters to reduce the stress to ensure that the tool works in a stable cutting state. In addition, due to the maximum stress and serious wear at the tool tip, the machining quality will be directly affected. Therefore, it is necessary to timely check the tool condition and make tool compensation

taking the above analysis as the theoretical basis, we can correctly select and use cutting tools in cutting and reasonably adjust cutting parameters

in order to more clearly explain the stress distribution at the stress concentration, ANSYS can also be used to make slices along the surface nodes of the longitudinal section at the maximum stress to display the section stress change curve. Since the structure of the turning tool analyzed in this paper is relatively simple, it is omitted

5 conclusion

by using the large-scale finite element numerical analysis software ANSYS to carry out numerical simulation analysis on the tool strength, we can accurately grasp the stress condition of each point on the tool, understand the distribution law of the internal stress and strain of the tool, obtain the stress-strain distribution diagram and easily find out the dangerous points. Putting the standard force measuring ring on the experimental machine, this method can provide a theoretical basis for improving the force condition of the tool, reasonably designing the tool structure and analyzing the failure of the tool. It also provides a new method for analyzing and calculating the strength and life of the tool

the numerical simulation analysis of the tool strength of the cylindrical turning tool in this paper is typical. This method can also be applied to the strength and failure analysis of other types of tools, spindles and other components. For the analysis objects with complex stress conditions, the nonlinear dynamic analysis method can be used to make the analysis results more accurate. The analysis results of this paper show that the ANSYS finite element numerical analysis software can complete the strength simulation analysis and calculation which is difficult to be completed (or the effect is poor) by the traditional calculation method, so it has important practical value

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