Introduction The elastic deformation (bending, torsion, shear deformation) occurs when the gear teeth are under load; the gears at high speed will be deformed due to the centrifugal force; the unevenness of the gear material will cause the deformation of the gear after heating to be unstable, and the toothing error will occur. At high speed and heavy load, each gear is heated unevenly, which will cause thermal deformation of the gear teeth; these deformations will cause uneven distribution of load along the tooth width of the gear teeth, resulting in local early pitting or gluing, and even causing rounds. The teeth are broken. In order to reduce gear biting and impact, improve load distribution unevenness, reduce vibration and noise, it is necessary to modify the helical gear tooth direction.
1 Tooth direction modification The determination of the tooth orientation usually only repairs the pinion, including drum shape modification and tooth end modification. The tooth end modification can effectively reduce the impact load when the helical gear is engaged and engaged; however, since the tooth end modification only performs local modification near the end surface, many influencing factors in the gear transmission result in the generation of the teeth. Such deformation, so when the tooth width of the meshing gear is large, it is easy to cause more serious load concentration, and the tooth end modification cannot achieve a good shape modification effect. The drum shape modification is a modification of the full tooth width direction, which can compensate for the gear manufacturing error and various elastic deformations when the gear is used for the load. Therefore, this paper focuses on the drum shape modification.
The traditional drum shape modification refers to the central drum shape modification, which can better shape the spur gear meshing; however, since the length of the mesh line is constantly changing when the helical gear meshes, only the center is used. The drum shape modification does not fully meet the requirements of the helical gear modification. This paper will expand the way of drum shape modification, propose a variety of drum shape modification schemes, use Pro/E to model, and then use AnsysWorkbench for finite element analysis verification, so as to obtain the optimal tooth direction modification scheme of helical gears. .
The design of the tooth profile modification curve. When determining the trimming curve, various factors of the meshing tooth error should be comprehensively considered, including the influence of manufacturing and mounting errors, as well as the deformation of the gear itself and the deformation of the gear shaft.
It is a tooth direction modification curve for compensating the bending and torsion combination deformation of the axle, curve 3 is a comprehensive deformation curve, and curve 4 is a tooth direction modification curve. When designing the curve, you should consider the combination of various deformations that may occur, and then determine the curve by the comprehensive deformation curve.
After the parametric modeling of the modified helical gear determines the tooth profile modification curve, we will use Pro/Engineer Wildfire 3.0 to parametrically model the modified gear to prepare for the finite element analysis in Ansys.
2.1 Standard helical gear modeling step 1) Determine the basic parameters of the helical gear. Including the number of teeth, modulus, pressure angle, helix angle and so on. These parameters can be called directly in the design to achieve parametric design goals.
2) Draw a reference circle. Use the default reference coordinate system to sketch the top circle, root circle, index circle, and base circle reference curve.
3) Generate a tooth profile involute. An involute and a mirror involute are generated by the equation, and the angle between the two involutes is 360°/(2Z).
4) Sketch the end face profile curve and scan trajectory. Using the addendum circle, the addendum arc and the two involutes, a root rounding arc tangent to the root circle is obtained to obtain a closed profile curve; then an origin trajectory line and a spiral trajectory line are created.
5) Using the method of scanning and mixing, one tooth of the helical gear is generated; after the feature array is used, other gear teeth are created; the keyway and the chamfer are opened, and the helical gear model is finally generated.
2.2 Shaped gear modeling The modified helical gear should be modified along the tooth direction. After the fourth step of modeling, the tooth profile curve should be copied, and multiple tooth profile curves can be obtained by “translation/rotation†(the number of copies is corrected by the curve). determine). The total translation distance is the tooth width, the total rotation angle is the helix angle, and the translation and rotation amount of each step is calculated from the number of copies.
Then use the tooth profile curve generated by the copy, according to the shape modification curve, and finally use the scan mixing command to stretch the gear teeth. The final gear model is shown in Figure 4.
3 Contact stress analysis of the modified gear After the three-dimensional modeling of the modified helical gear is completed by ProP/EWildfire3.0, the model can be directly transferred to ANSYSWorkbench through the data interface of ANSYSworkbench and Pro/E. Contact finite element analysis to verify tooth contact strength and bending strength.
3.1 Meshing The gear material of this paper is 45 steel, surface quenching, material properties are as follows: elastic modulus is 2.0×1011Pa, Poisson's ratio is 0.3, density is 7.85×105kg/m3. Manually adding two pairs of contacts, defining contact The size of the unit on the surface is manually mesh-encrypted to the teeth of the contact area, and the overall mesh is divided and the unit is generated.
3.2 Defining boundary conditions and loads In actual work, the drive wheel and the passive wheel are connected by a key to the drive. In the analysis, the force state should be simplified, a fixed constraint should be applied on the surface of the inner hole of the passive wheel; the degree of freedom of rotation can be added to the surface of the inner hole of the driving wheel, and the applied torque is 100 Nm, and other degrees of freedom are automatically applied by the system.
3.3 Solution and Post-Processing Define the physical quantity to be calculated. Using the powerful solution function of the AnsysWorkbench solver, the stress and strain of each node can be solved and reflected on the solid model by different colors. The stress distribution in the tooth direction can be seen by the stress contour map. The positions of the maximum and minimum stresses are represented by MX, MN, respectively. As long as the two gears are in different engagement positions in the Pro/E assembly (such as from the moment of engagement to the exit), the finite element analysis of the gears in different states can be introduced into ANSYS, so that the rationality of the modified gear can be verified. And get the best shape gear.
4 Conclusion In this paper, the shaping curve of the toothed modified helical gear is designed, and the parametric model of the modified helical gear is established by Pro/E software. The software's data exchange interface enables seamless connection of models between different CAD systems, providing an accurate model for ANSYS. The optimal shape modification curve of the helical gear is obtained by finite element analysis, which provides another way for the optimal design, reliability design and CAE of the gear.
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