Finite element simulation analysis of warm forging of spur gear

Taking 18CrNiMo7-6 spur gear as the research object, the finite element models of three schemes are established, and the warm forging process of spur gear is simulated respectively. The distribution of forming load, equal effect force field distribution and tooth cavity filling in the forming process are analyzed, the metal flow law in the forming process is studied, and a reasonable scheme is selected according to the simulation results, It provides a theoretical reference for the practical application of precision forging process of spur gear.

1. Establishment of geometric model

According to the process scheme, the three-dimensional geometric models of blank, upper and lower punch and die are established in the Three-dimensional Modeling Software Solidworks, as shown in Figure, and output in STL format. In order to improve the efficiency of finite element calculation, a tooth is selected as the research object, and symmetrical boundary conditions are set in the preprocessing.

(a) Option I (b) Option II (c) Option III

2. Establishment of material model

The accurate establishment of the material model of the deformed body is the basis of finite element analysis. The material of the spur gear is 18CrNiMo7-6. The material data can not be found in the DEFORM-3D material library. It is understood that the material parameters in DEFORM-3D can be customized by users, that is, the stress-strain curve, elastic modulus, Poisson’s ratio, coefficient of thermal expansion and coefficient of thermal conductivity of the material can be input into the material library in the form of curve, table or function.

JMatPro is widely used in performance calculation of metal materials and can provide material performance parameters for many material forming CAE software (DEFORM-3D, ANSYS, abques, etc.). All physical models are verified by experiments to ensure the accuracy of material models [41]. It is mainly used in material processing process design (such as casting, forging, extrusion, rolling, etc.), heat treatment and welding process design.

It is known that the gearbox factory of Zhengzhou Machinery Research Institute has tested the chemical composition of the material. Input the detected chemical composition data into jmtpro software to generate the key file of 18CrNiMo7-6 material model. This file contains all the data required for 18CrNiMo7-6 material. This file can be directly called by finite element software DEFORM-3D.

Input the customized material model data of 18CrNiMo7-6 into the software, and select the appropriate constitutive model. During warm forging of spur gear, its deformation resistance is related to forming temperature, speed and deformation degree. The metal flow model, i.e. constitutive model, is as follows:

Where: σ — Flow stress; ε — Plastic strain; ε .— Strain rate; T – temperature

3. Selection of warm forging temperature of spur gear

Temperature is an important parameter for the warm forging of spur gear, which is different from hot forging and cold forging. The temperature range of warm forging is usually 750 ℃ ~ 850 ℃. The best warm forging temperature of different materials is different, so it is necessary to find the best temperature of materials. The research on the temperature deformation of 18CrNiMo7-6 material is still blank and needs further research.

Before forming, the mold needs to be preheated. The preheating temperature of the mold is generally 150 ℃ ~ 300 ℃. The purpose of preheating is: (1) to prevent mold cracking. (2) Make the billet temperature drop slow down and reduce the deformation resistance. (3) Reduce the temperature difference between the inside and outside of the blank and the die to avoid large temperature stress in the blank and the die.

4. Setting of other simulation parameters

(1) The blank of spur gear is set as a plastic body. The initial temperature of the workpiece is 850 ℃, and H13 in the material library is selected as the die material, which is a rigid body with a hardness of HRC62. The preheating temperature of the die is 250 ℃, and the ambient temperature is 20 ℃;

(2) The thermal conductivity between the contact surfaces is 11kw / (M2 ·℃), and the thermal radiation coefficient is 0.7;

(3) The shear friction model is selected, and the friction coefficient is 0.25;

(4) The motion speed is 20 mm / s and the simulation step is 0.2 mm;

(5) Set the die wear model and select the Archard model.

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