Preliminary study on finite element simulation of

2022-08-21
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Preliminary study on finite element simulation of metal cutting deformation process

metal cutting is one of the widely used machining methods. It is a process that uses a tool harder than the workpiece to cut metal on the surface of the workpiece to obtain the required shape, size and surface roughness. The essence of cutting is the process that the workpiece material is torn after elastic deformation and plastic deformation under the shear and extrusion of the tool, and the excess metal layer on the surface to be machined is separated from the workpiece body to produce chips and form the machined surface on the workpiece. The process of metal cutting deformation is very complex, and there are many influencing factors. The research on metal cutting mechanism has always been the focus and difficulty of scholars at home and abroad, but it is limited to technical reasons. The past research is mainly based on various experiments, and the key is to promote the use. Due to reasons such as cost and technical means, the popularization and improvement of the research on cutting deformation process are limited, but the emergence of new materials is endless, How to understand the cutting performance of new materials in time and deeply is an urgent need for attention

in recent years, the research of finite element technology in cutting deformation has begun to be applied. The use of finite element technology has the characteristics of low test cost and complete and diverse data, which has attracted the attention of people in the industry

discussion on the traditional analysis methods of cutting deformation process

the traditional methods of studying metal cutting deformation are mainly based on various test methods. The common methods are: side deformation observation method, high-speed photography method, rapid tool drop method, transient stereophotography method, scanning electron microscope microscopic observation method, photoelastic and photoelastic test methods, etc. In addition, there are various methods to measure cutting force and cutting temperature

because the working conditions of metal cutting are very bad, it is very difficult to track and observe the physical process, and the observation equipment is expensive, the test cycle is long, the human and material resources consumption is large, and the comprehensive cost is high, so the analysis results of various test methods are often not comprehensive. For example, the side deformation observation method infers the deformation of metal by observing the small lattice deformation manually drawn on the side of the material. Although the high-speed photography method can observe the deformation of the deformation area under the actual cutting speed of the knife, the cost is high. The speed of rapid tool drop method has a certain impact on the accuracy of cutting deformation area information, and the samples in the cutting area should be made into metallographic samples for observation. Both transient stereophotography and scanning electron microscopy have the disadvantage that the test equipment is very expensive

the above test methods often fail to measure the stress, strain, positive pressure on the tool surface, temperature and its distribution law in the deformation area. Although photoelastic and photoplastic test methods can describe the stress and strain in the cutting area, they cannot reflect the law of material flow

the method discussed above mainly focuses on the cutting deformation, that is, the material flow law and its physical quantitative description in the cutting process. In fact, the process of cutting deformation is also closely related to cutting force and cutting temperature. It is not advisable to study cutting deformation separately from cutting force and cutting heat, and it should be studied as a whole

the traditional research results of cutting force are basically empirical formulas obtained through experimental methods, and then used in practice. For some actual situations, if the test conditions are deviated, there may be errors, or even impossible to calculate. The measurement of cutting force mainly includes resistance strain gauge dynamometer and piezoelectric dynamometer. These measuring devices are generally expensive. Natural thermocouple and artificial thermocouple are mainly used to measure the cutting temperature. The former only measures the average temperature of the cutting area, but can not accurately reflect the distribution law of the temperature. The artificial thermocouple is used to measure the temperature of a certain point in the cutting area, but it is still very difficult to obtain the temperature field of the whole cutting area. In addition, measurement methods such as radiation thermometer method and thermal pigment method have limited their application due to the high cost of equipment

it can be seen from the above that the traditional research method based on experiment has more difficulties, and the finite element method can overcome some of the above shortcomings to some extent, so it gradually attracts the attention of researchers

finite element simulation analysis of cutting deformation process

finite element computer aided simulation technology the research on cutting process mainly focuses on two aspects: the first is the development of relevant simulation software, and the second is the physical simulation of cutting process based on special software

the former is generally studied by professionals. The existing relevant software includes "advanced edge" of third wavesystems, DEFORM software of scientific forming technologies, and some general-purpose software, such as ABAQUS, ANSYS, etc. The latter focuses on the research of practical application. This paper mainly discusses the research results of the latter. The following is an example

Figure 1 shows a model of right angle cutting, with cutting speed v=250m/min, cutting layer thickness ac=0.4mm, workpiece width w=2mm, and tool rake angle γ 0=5°, α 0=5 °, the blunt radius of the cutting edge rn=0.1mm, the friction coefficient between the tool and the workpiece is 0.6, the thermal conductivity is 40, and the tool surface is coated with 10% from the outside to the inside μ M thick tin and Al2O3 coating, tool body material WC Cemented Carbide, workpiece material AISI-1045 (equivalent to 45# steel), and the ambient temperature is taken as 20 ℃

the metal cutting process shows that the metal deformation is large. For the finite element simulation of this cutting model, after the finite element lattice distortion reaches a certain degree, the system must be able to automatically re divide the lattice. Figure 2 shows the lattice before cutting and the lattice of cutting tool steps respectively. Figure 2 (a) shows the grid condition before processing. It can be seen that the processing area is dense. Figure (b) shows the automatic division of the lattice when cutting to 500 steps. In fact, in the process of simulation, the system will automatically re divide the lattice according to the lattice distortion

the finite element simulation of the cutting process has rich results, including stress, strain, strain rate, metal flow and flow velocity, normal pressure on the tool surface, temperature field distribution in the cutting area, cutting force chart, tool wear, and can simulate the metal flow law like the traditional side deformation observation method. In addition, by using these results, the relevant parameters describing cutting deformation, such as shear angle, can be measured φ And cutting thickness deformation coefficient ξ A, etc., the analysis results can be expressed in the form of cloud map, contour map and animation, and Dr. Feng Xiaohai said that polyglutamic acid and polylysine belong to poly amino acids, which can be reproduced at any time, and the animation process can be demonstrated in one step or continuously. All these visual results and the description of cutting deformation process have been greatly improved compared with the traditional test method. The following are some analysis results of 500 steps of simulation for reference

Figure 3 is the deformation strain diagram of the cutting process. In the figure, you can not only see the strain of the three deformation areas in the cutting deformation process, but also see the residual strain on the surface after cutting. In the figure, the strain caused by the second deformation zone is the largest, followed by the strain produced by the first deformation zone, and the strain produced by the third deformation zone is the smallest

Figure 4 shows the cutting stress diagram. It can be seen that the deformation stress in the first deformation area is the largest, and the deformation stress mainly occurs near the tool tip and the first deformation area

Figure 5 (a) shows the strain rate diagram of cutting deformation. The strain rate shows that the shear strain rate along the first deformation zone is the largest. Using this result, the shear angle can be analyzed φ , Specifically, the cutting angle can be measured by copying the drawing into AutoCAD and drawing horizontal lines and cutting lines, as shown in Figure 5 (b), the cutting angle measured in this example φ 35 °

of course, using the simulation results of cutting deformation, the thickness deformation coefficient can be calculated by measuring the chip thickness a ch and the cutting thickness a C on the workpiece (known above) ξ a=a ch/ac =0.64/0.4=1.6。 The measurement results are shown in Figure 5 (c)

Fig. 6 (a) is a partial enlarged view of the material flow speed in the cutting process. This figure can not only see the direction of the material flow, but also observe the movement speed of the material flow everywhere by visual means such as cloud diagram (Fig. 6 (b)) or contour map (Fig. 6 (c))

Figure 7 (a) shows the cutting temperature diagram in the form of cloud diagram, which is essentially a temperature field diagram. It can also be represented by contour map, as shown in Figure 7 (b). If the cutting area is locally enlarged, it can be seen more clearly, as shown in Figure 7 (c). It can be seen from the figure that the maximum temperature deviates from the tool tip, and the temperature on the chip is higher than the temperature of the tool rake face. The reason why the highest temperature is this situation is that the increase of temperature is not only related to cutting deformation, but also related to the friction between chips and the rake face

figure 8 is an enlarged view of the positive pressure contour on the tool surface. It can be seen that the stability of the product is enhanced from the tool tip to the front and rear tool surfaces, and there are many positive pressure areas on the front tool surface. The maximum positive pressure is about 0.8MPa or more

Figure 9 shows the cutting lattice flow simulation diagram (310 steps), and the simulation results are very similar to the results obtained by the traditional side deformation observation method

Figure 10 shows the change diagram of main cutting force and cutting time in the cutting process. It can be seen that the cutting force increases rapidly at the initial stage when the tool cuts into the workpiece material, and then gradually tends to stabilize. Here, the cutting force can also be directly displayed. It can be seen that the cutting force is basically maintained at about 750~850n after stable cutting

the above only lists several analysis results of interest in the research of cutting deformation. It can be seen that the results of post-processing of finite element simulation are relatively rich and complete, which is of great help to a deep understanding of cutting deformation

conclusion

cutting is a complex process of cutting deformation, and the working conditions are very poor. The traditional research methods are mainly based on experimental research. It is difficult to track and observe the physical process, and the test cost is very high. If you want to obtain more test data, you need to use more test methods and do more tests, so that people can have a deeper understanding of the cutting performance of various materials. However, with the help of finite element analysis and computer technology, the cutting process can be revealed at a low cost, and a relatively rich variety of data can be obtained in a relatively short time, which is of great help to the actual production

of course, because the practice of finite element technology in machining is not long, there are still many technical problems worth discussing. In addition, there are some differences between the results of finite element simulation and the actual situation. Analyzing the reasons, the author believes that there are two points: first, the mathematical model of software programming ignores some secondary factors; Second, the setting of relevant parameters during simulation is related to the knowledge level and practical experience of the users of the software. If the setting parameters deviate more, there will inevitably be some differences in the simulation results. Therefore, at present, it is a practical research method to combine finite experiments with more finite element simulation. (end)

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