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The cross-rolling gear rolling is formed by heating the gear blank to a good plastic state, and rolling the blank out of the gear by combining the wedge-cross rolling blank and the fan-forming principle. Specifically, the free indexing method is adopted, and a pair of oppositely moving wedge-shaped rack molds are used to gradually apply pressure to the blank during the rolling process, the tooth blank is freely rotated, and the wedge-shaped rack mold is contacted with the tooth blank to roll out the groove. After the groove reaches a certain depth, the teeth of the wedge-shaped rack mold are gradually rolled in along the groove, and finally the teeth are extruded in the outer circumference of the blank as shown.
Since the free-index rolling method does not have precise indexing conditions, if the groove that is initially rolled does not conform to the specified number of teeth (sliding between the tooth blank and the rack mold during rolling), it often causes disordered teeth. In order to roll out the gear with the specified number of teeth, it is necessary to accurately divide the outer circle of the tooth blank, and correctly calculate the relationship between the size of the blank and the size of the rack mold to ensure the accuracy of the indexing number.
The rack mold shown is indexed by the chord length AB. If the rack modulus is m, the length of AB on the rack mold is AB=m(1)AB=d1sin1(2) Let the number of teeth of the rolling gear be z1, in order to make the tooth top of the rack mold be outside the tooth blank The specified number of teeth is accurately indexed, and 1 must be the 12 center angle of each rolling section of the rolling gear. That is, 1=z1(3)d1=msin(z1)(4) gives the basic parameters of the rack mold, and the diameter of the blank can be calculated. The gears produced by this process have a continuous streamline distribution along the shape of the product, so the bending strength, fatigue strength and wear resistance are significantly improved compared with the conventional process.
Gear rolling forming thermo-mechanical coupling model deformation field elastoplastic constitutive equation wedge rolling gear rolling is a large deformation problem, its elastoplastic constitutive relation is nonlinear, and its strain process and loading path are related, so its constitutive model also Has transient properties. Based on the deformation properties of the cross-roll rolling gear rolling, the constitutive relation is described by the Euler parameter using the plastic flow increment theory. The Euler stress tensor and the Almansi strain tensor are used to express the stress and strain relationship [2] ].
For elastoplastic media, the yield function is expressed in Euler stress in the spatial description: f(ij,k) = 0 (5) where the variable k is the material integral of the equivalent strain rate. In the large deformation, if the elastic deformation portion is relatively small, the total deformation increment can be decomposed into the elastic portion and the plastic portion. It is assumed that the plastic deformation rate is related to the yield surface by the orthogonal law, and the Hooke's law is satisfied between the elastic strain rate and the focal point derivative of the stress. The large deformation constitutive equation is derived as Vij=DepijklVkl(6) where Vkl is the deformation rate. For the isotropically strengthened Mises material, there is Depijkl=E1 carrying history: defining the rolling process as a quasi-static analysis loading history, given the number of incremental steps, and solving the adaptive detection step.
During the gear forming process, the temperature distribution of the rolling stock is uneven during the temperature field distribution deformation process. Due to the short deformation time, the main factors affecting the temperature are the heat conduction caused by the contact between the rolling stock and the mold and the temperature rise caused by the plastic deformation of the metal. The combined effect of the two basically determines the variation of the temperature field in the rolling stock.
After the rolling stock contacts the mold, the temperature at the contact first decreases, and the temperature at the center of the rolled product changes little. As the deformation continues, the surface temperature gradually decreases to a minimum value, and the center temperature generates heat due to plastic deformation, which causes a temperature gradient to form, and a significant temperature gradient is formed across the entire section of the rolled piece.
It is the temperature distribution on the section of the rolled section in the initial rolling stage. The temperature gradient is mainly concentrated on the contact surface, and the temperature does not change much in most of the central portion of the rolled product. The region with the largest temperature rise is near the surface in the middle of the rolled product; the deformation here is large, and the influence of contact heat conduction is also large, and the deformation is severe. The area of ​​influence of the contact heat conduction is located at a thickness of 510 mm from the outer surface of the tooth blank.
In the rolling stage and finishing rolling stage, the temperature distribution is less affected by the heat transfer of the mold and is affected by the heat conduction of the mold. As shown, the temperature gradient of the metal surface in contact with the mold is very obvious. With the deepening of the rolling stage, the temperature distribution of the whole rolling stock shows a regular annular distribution; from increment 200 to increment 746, especially in the final stage of rolling, the display center temperature is the highest and the surface temperature is the lowest, and The distribution is reduced, which is due to the contact between the surface of the rolled piece and the mold and the heat exchange caused by the room temperature, resulting in low surface temperature, high core temperature, and the temperature of the core is transmitted to the surface. The temperature of the core is maintained at 9894. The closer to the surface, the more pronounced the temperature decrease.
The rolling stage and the finishing step are compared with the change of the core part and the surface temperature of the rolling piece, which basically has a downward trend with a certain slope, and the surface temperature is always lower than the core temperature. However, due to the fluctuation of the unevenness of the deformation of the rolling stock, when the temperature drops to 897, large fluctuations begin to occur, and at the same time there is a large increase in amplitude, which is due to the increase of the contact surface between the rolling stock and the mold, plastic deformation and The friction produces more heat than the external radiation; in the finishing section, the small slope begins to decrease due to the small deformation.
Rolling force energy parameter variation law During the gear forming process, it is very important to determine the rolling force and rolling moment between the die and the rolling stock. According to the force of the mold, the mold can be reasonably designed and the environmental parameters can be changed to optimize the gear forming. It can be seen from the tangential force of the die during the gear rolling process that the tangential force of the die is in a certain alternating state, and the peak value increases with the increase of the rolling amount. When setting the feed amount, the first step is the largest, then each step is equal, and the last step is the smallest. As can be seen from the figure, the first step has the largest tangential force peak and the last step is the smallest, in line with the principle of metal deformation. The alternating state of the tangential force is mainly due to the change of the force state caused by the change of the contact point between the mold and the rolling stock during the rolling process. The change of the radial force of the rolling is different from the tangential direction. The main force is that the force in the Y direction is basically positive. Although there is fluctuation, the deformation direction of the plastic deformation is caused by the mold. The vector direction is opposite to the coordinate axis. So it is positive. The trend of change is the same as the tangential force, that is, the first and last steps are maximum and minimum respectively, and the middle is average, but showing a decreasing trend, as shown. The rolling moment increases with a certain slope. During the gear forming process, the tangential reaction force of the die becomes smaller, as shown by 0. This is because the die begins to roll in as the rolling process progresses. In the rolling stock, the contact area between the rolling stock and the mold increases, and the force required to overcome the plastic deformation and friction increases, so the rolling moment increases with a certain inclination; after entering the finishing section, the deformation amount is small, so rolling The torque is slowly reduced.
Conclusion Combining the advantages of wedge-cross rolling blank and the principle of gear vane machining, a mold suitable for cross-rolling gear blanking is designed. The thermal coupling constitutive equation and finite element model of gear rolling forming are established. The model considers rolling. The coupling between the deformation field and the temperature field in the process, the numerical simulation of the forming process was carried out with SuperForm as the simulation platform, and the results were analyzed in detail. The radial reversal of the rolling process during the rolling process of the wedge rolling gear was summarized. The variation law of force energy parameters, temperature field and deformation field in the process of force g has important reference value for correctly understanding the law of gear rolling forming and guiding actual production.
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