Finite element analysis of meshing performance of

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Finite element analysis of meshing performance of plastic worm gear drive

plastic worm gear and steel worm drive is a worm drive mechanism that uses plastic as the worm gear material instead of traditional metal. Plastic gears are widely used in light power transmission such as car seats and household appliances because of their advantages of good processing economy, stable transmission, vibration absorption and noise reduction, light weight, wear resistance and self lubrication. In the transmission process, because the elastic modulus of plastic is lower than that of carbon steel, the worm gear is in local area contact after being loaded. The whole transmission wear is almost on the plastic worm gear, and the friction heat in the meshing area will also rise rapidly, which directly affects the service life of the plastic worm gear. And the plastic worm gear has the disadvantages of low strength, easy deformation, poor thermal conductivity and heat resistance, and the heat generated is not easy to be eliminated, so the failure temperature of the plastic worm gear is dominant. Therefore, it is very important to study the influence of the temperature in the meshing area of plastic worm gear on the meshing performance. In this paper, through the transmission model established by SolidWorks, using msc Patran/nastran finite element software analyzes the deformation stress of the tooth profile of plastic worm gear after the meshing temperature reaches equilibrium in the transmission. It is compared with the working condition that the meshing temperature is normal temperature

1 establish the transmission model and finite element preprocessing

according to the basic parameters and structural dimensions of the worm gear (see Table 1), use SolidWorks to generate the worm gear transmission model. Lead msc Patran/nastran, as shown in Figure 1

in order to fully reflect the gear meshing condition of the gear in the periodic movement process, it is necessary to establish the position models in the worm gear transmission process. As the worm rotates, the position of the contact area on the gear teeth changes periodically. Its cycle is 9 °. For every 9 ° rotation of the plastic worm gear, the worm needs to rotate for one cycle. The worm gear engagement positions are divided into 6 positions (see Table 2)

set the material properties of worm gear to POM and alloy steel 16MnCr5 respectively. In order to improve the accuracy of the contact surface, the meshing part of the gear teeth is refined. The total number of nodes is 160023, the total number of units is 141168, and the total number of node degrees of freedom is 852152. Physical performance parameters and thermodynamic coefficients of worm and gear materials (see Table 3 and table 4)

set boundary conditions. After the worm gear and worm are loaded, the temperature in the meshing area reaches equilibrium, and the meshing temperature is 100 ℃. The temperature field of the worm gear body is established (as shown in Figure 2), which provides the boundary condition of the temperature field for the finite element structure analysis of the worm gear. From Figure 2, it can be seen that the temperature in the meshing area is 100 ℃; Set the worm gear to fixed; Bearing supports are set at both ends of the worm, and only the worm shaft is allowed to move and rotate, which has attracted the attention of aerospace, ordnance industry, new energy vehicles and other enterprises; Set the external load force acting on the worm, and set the thrust in the axial direction on the left end face of the worm; Contact type sets the worm gear and worm contact tooth pairs as contact groups, and defines the worm gear contact type as gap. And set the maximum load of worm gear to 30 n · M

2 calculation results and analysis

2.1 calculation results and treatment

numerical calculation can obtain the stress nephogram of meshing temperature at 100 ℃ and any load. Figure 3 shows the deformation stress nephogram under the meshing temperature of 100 ℃ and 50% load

the plastic worm gear and the steel worm are in six meshing positions, and the external load force gradually increases from 10% load to 100%. Note that the five teeth participating in the meshing of the plastic worm gear are from left to right, from tooth 1 to tooth 5 respectively. The curve is formed by the numerical interpolation analysis method, as shown in Figure 4

the deformation and stress comparison curves of plastic worm gear and steel worm drive at 100 ℃ meshing temperature and at room temperature are obtained from the calculated data (as shown in Figure 5), which respectively simulate the influence of temperature on the gears when there is oxidant in such water at 10%, 50%, and 100%

according to table 2, we can know the angular relationship of worm gear and worm at different meshing positions. As the load increases from 10% to 100%, the stress and deformation of the plastic worm gear can be determined during the whole load change process. Similarly, the numerical interpolation analysis method can be used to approximately determine the stress value and deformation of the plastic worm gear at any meshing position and within any load range (see Figure)

Figure 6 stress and deformation curve of plastic worm gear teeth under 10% load and different meshing angles

Figure 6 stress and deformation curve of plastic worm gear teeth under 50% load and different meshing angles

Figure 6 stress and deformation curve of plastic worm gear teeth under 100% load and different meshing angles

2.2 result analysis

1) plastic worm gear and steel worm at 100 ℃ meshing temperature, It is obvious from the deformation nephogram 3 that the contact area of the tooth profile under load is an elliptical area, which is the same as that under normal temperature. It shows that under the temperature field of the gear body, the plastic worm gear and steel worm drive also follow the Hertz contact theory, which means that when two smooth surfaces contact, they can be approximately treated as two parabolic surfaces near the contact point. After the load is applied, a contact ellipse area is formed at the contact point

2) under 10% to 40% load, due to the elastic properties of plastic materials, the top of plastic worm gear is prone to contact failure, which exceeds the limit stress value of 103 MPa. And the load is mainly concentrated in plastic gear 2, gear 3 and gear 4, and has good heat resistance, electrical insulation, weather resistance and chemistry. With the different meshing positions of worm gears, the load distribution proportion of gear teeth also changes; When the load is greater than 12 N · m (greater than 40% load), tooth 5 or tooth 1 will also enter the meshing state. It can be seen from tooth 3 in Figure 5 that after the contact failure of the plastic worm gear contact tooth profile, that is, the contact stress is greater than the ultimate stress of the material, the maximum stress at the contact will decrease with the further increase of the load

3) comparing the finite element structure analysis results of the worm gear at 100 ℃ meshing temperature and normal temperature, the maximum stress of the plastic worm gear changes very little, and the maximum deformation of the meshing tooth surface of the plastic worm gear increases by 5%

4) from Figure 6 to figure 8, due to the low elastic modulus of plastic worm gear material, contact damage is easy to occur in the worm gear meshing process, resulting in plastic deformation on the tooth profile. With the increase of load, the teeth change from point meshing to multiple pairs of teeth meshing, and the increase of coincidence and contact area makes the deformation of the tooth profile and bearing capacity tend to balance

3 conclusion

through the numerical simulation of the meshing of plastic worm gear and steel worm gear, the advantages and disadvantages of the mechanical properties of the meshing of plastic gear under two temperature fields are obtained. It provides a valuable reference for the design and manufacture of this kind of transmission. (end)

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