1 In recent years, domestic and foreign research on the precision gear forging process of spur gear has achieved certain results, but it can not be widely used in the actual production process. There are two main problems: tooth filling difficulty and forming load. Due to the development of computer hardware and software technology and the maturity of metal plastic forming theory, numerical simulation technology represented by finite element has been rapidly developed. Using three-dimensional finite element numerical simulation technology to study the precision forging forming process of spur gears, many information that can not be obtained or is difficult to obtain through experiments can be obtained, such as: plastic deformation behavior, flow law, temperature change, internal stress, strain distribution, Mold load, etc., to optimize process parameters and mold structure design.
Therefore, this paper uses the three-dimensional finite element analysis software DE-FORM-3D to numerically simulate the spur gear squeezing-squeezing process under the form of floating die, and analyze the influence of various process parameters on the forming process. The implementation of the forming and practical process provides theoretical support.
2 The process plan ensures that the working pressure is reduced under the condition that the tooth cavity is completely filled, which is the key to solving the problem of gear precision forging. In this paper, the mold structure shown in 1 is used, and the floating concave mold is used instead of the conventional fixed concave mold. By using the positive friction action of the floating die, not only the filling of the corner portion of the tooth cavity can be ensured, but also the forming force can be appropriately reduced. The specific process is as follows: after the end of the pressing process, the shoulder die 1 is pushed to move the movable die insert 2 downward, and the direction of the frictional force on the contact surface of the die is consistent with the metal flow direction in the upper cavity. Under the dual action of the inertial effect and the active friction of the lower chamber, the filling at both ends of the workpiece is easier.
3 The finite element simulation conditions were simulated by a factory tractor reduction pinion (2) with a modulus of 2.5 and a number of teeth of 18. According to the design principle and the volume constant condition of the outer diameter of the blank equal to the root diameter of the gear, it is determined that the solid cylinder of the blank mail 38mm×20.5mm is used, and the material is industrial pure aluminum. Because the gear has symmetry and is characteristic of the rotation period structure, 1/18 of the whole solid model is selected as the simulation object, and the four-node solid element is used for mesh division. The number of body units is 30000, when the mesh is deformed. When the distortion is large, the system automatically re-mesh. 3 is the workpiece model after meshing. 4 is the mold and workpiece model during simulation. Since the simulation is a single tooth forming process, the setting of the boundary conditions is the key to the correctness of the simulation, and the symmetry plane can be used to apply the symmetry constraint.
The mold is defined as a rigid body that does not deform during extrusion. During the simulation, the initial temperature is 20 ° C at room temperature, and the heat transfer between the blank and the mold and the environment is considered, that is, the heat transfer condition is set by the heat conduction-deformation coupling module in DEFORM-3D.
The friction between the blank and the mold is the shear friction model. The friction factor is defined as 0.25. The extrusion equipment is a hydraulic machine with a tool speed of 5 mm/s. When the punch completes the extrusion process, the floating die will be pushed down together. The die movement speed is also 5mm/s.
4 Simulation results analysis After the numerical simulation model of spur gear squeezing-squeeze forming was established, the three-dimensional finite element simulation software DEFORM-3D was used to analyze and calculate the post-processing, and the forming effect diagram, force-stroke curve and field quantity distribution were obtained. The specific analysis is as follows.
4.1 Simulation results of spur gear forming Figure 5 shows the forming effect of the spur gear extrusion. It can be seen that the gear profile of the gear member is clear and the upper and lower angular gap filling effect is good.
4.2 Forming force analysis The force received by the blank during the gear forming process is a very important parameter. It is the main reference factor for determining the size and shape of the mold, selecting the tonnage of the hydraulic machine, and also one of the main basis for checking the strength and stiffness. Figure 6 shows the force-stroke curve formed under the fixed die and the floating die. It can be seen from 6 that the forming force is increasing, and the whole process is clearly divided into three stages.
Stage I: The rushing stage, from the beginning of the punch to the billet until the shoulder contacts the billet. When the punch begins to move downward, the metal near the punch has significant plastic deformation, and the deformation is small at a distance from the punch. At this stage, since the deformation area is small, the amount of metal flowing into the tooth cavity is small, and therefore, the increase in the forming force is relatively slow.
Stage II: the stage of squeezing and squeezing, that is, filling the stage of the tooth. When the billet continues to deform, the billet is filled more and more into the concave mold cavity, the free surface is also reduced, and the metal flow resistance is correspondingly increased, so that the extrusion forming is difficult and the forming force is larger.
Stage III: Forging stage, that is, full of upper and lower corners. This phase lasts for a short period of time. Since most of the materials are already in place, in order to complete the formation of the local fill angle, even if a large amount of material is moved, it must overcome the hydrostatic pressure generated by most of the metal filled in a static state, and thus only in great Under the action of pressure, the metal at the corner gap can be deformed and flowed. This is the main reason why the forming force increases sharply and the curve rises almost linearly. Due to the excessive forming force, a longitudinal burr is formed in the lower portion of the forming gear tooth profile.
Comparing the force-stroke curves of two different mold structures, it can be seen that in the first and second stages, the force changes with the downward movement of the punch with the shoulders; in the third stage, due to the floating The positive friction of the die makes it easier to flow the metal at the corner gap relative to the fixed die, thus reducing the forming force.
4.3 Equivalent stress distribution 0-100 steps are the extrusion phase, and 100-158 steps are the extrusion and squeezing composite stages. This paper selects the different steps of the 100th step, the 129th step and the 158th step for analysis.
7 is an equivalent stress distribution diagram in the process of forming the spur gear teeth. Under the action of external load, the process of punching down the punch is a partial loading process. As the punch moves downward, the metal deformation mainly concentrates on the area near the loading point, while the deformation at the far side is very small, and there is basically no plastic deformation in the far distance, which is also due to the gradually expanding the force area along the loading direction. The reason why the equivalent stress is gradually reduced. Due to the direct action with the mold, the maximum equivalent stress mainly occurs in the area where the punch is rounded. At the same time, it can be seen from b and c that the equivalent stress is approximately evenly distributed in the radial direction, and the external stress is gradually reduced from the inside of the blank. When the blank is filled into the concave tooth profile, the stress at the contact between the blank and the mold is the largest.
4.4 Equivalent strain distribution 8 is the equivalent strain distribution 7 equivalent stress distribution layout of the spur gear teeth forming process. The equivalent strain value reflects the degree of deformation of the metal. Therefore, the deformation flow trend and filling law of the blank during the whole deformation process can be seen from the figure. During the extrusion process, the maximum degree of deformation is concentrated near the rounded corners of the punch, and the other parts are deformed little or even without deformation; in the subsequent deformation process, the metal begins to fill the tooth cavity; in the later stage of filling, the involute of the gear The strain value at the transitional fillet with the root circle is large, indicating that the metal flow in these areas is relatively severe and the amount of deformation is also large.
4.5 Temperature Field Distribution 9 is a temperature field distribution diagram during the formation of spur gear teeth. During the forming process, most of the plastic deformation work consumed inside the billet is converted into heat energy, which causes the temperature rise of the billet. This temperature rise is closely related to the deformation distribution inside the billet. It can be seen from the figure that the temperature gradient of the billet is mainly concentrated in the vicinity of the contact area between the mold and the billet, and the temperature gradient of the contact point is the largest, and the further the temperature gradient is smaller from the contact point. At the same time, it can be seen from the temperature change of b that when the metal starts to fill the tooth cavity, the filling of the lower end tooth shape is faster than the upper end, that is, the force of the lower end tooth shape filling is relatively large, and the temperature of this part is relatively high. As the filling process progresses, the upper end tooth shape gradually fills up, and the temperature at the corner gap reaches the highest.
5 Conclusions (1) In this paper, Deform-3D is used to simulate the spur gear squeezing-squeezing process in the form of floating die, and the relationship between forming force and stroke is obtained. The whole process can be divided into three stages: The squeezing stage, the squeezing and squeezing compounding stage and the forging stage.
(2) The floating die is used to replace the traditional fixed die. The positive friction of the floating die not only makes the upper and lower corners of the tooth cavity can be filled, but also greatly reduces the deformation force of the metal at the end of the forming process.
(3) After the simulation, the paper analyzes the variation of σ, ε, and T in the deformation body at different deformation stages. It can be seen that the spur gear squeezing stage is a partial loading process, and as the load is gradually increased, the plastic deformation will first occur in the upper part of the direct force receiving area, and then gradually spread evenly. The squeezing and squeezing compounding phase is an integral loading process with higher stress, strain and temperature in areas where filling is difficult.
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