The simulation of the impact process was carried out to study the time history of various impact loads and impact time on the root dynamic stress, and compared with the root stress state under static load.
1 Establishment of finite element model of small modulus gears 1.1 Related parameters of gears With the impact of electric drills and small modulus gears as the research object, the finite element analysis model of small modulus gears is established. The relevant parameters of small modulus gears are based on the principle of gear meshing. When the teeth are bent, the external load acts in a plane parallel to the end faces, and the direction is in the direction of the pressure angle. Under normal circumstances, the single tooth and the double tooth alternately mesh during the gear meshing process, and the maximum stress of the gear occurs at the highest point of the single tooth meshing.
In addition, when the gear is under load, only the part of the wheel body that is close to the gear teeth is deformed. Therefore, only the part of the gear is taken as the solution domain, without affecting the calculation accuracy, and considering the rounding off part of the wheel. The influence of the tooth on the calculation result, the finite element model of the tooth is established, and in the mesh division, because the gradient of the tooth stress at the root of the tooth changes greatly, a dense mesh is adopted at the root of the tooth. Divided into 2,523 nodes.
1.2 Boundary and Constraint The choice of boundary range and constraints is a fundamental problem of the finite element algorithm. In general, the larger the boundary range, the more accurate the calculation results. Considering the deformation of the portion connected to the teeth, it is generally considered that the distance from the root to the root of 1.5 m2 m (m is a modulus) is substantially unaffected, and therefore, the displacement at this point can be approximately considered to be zero. In addition, since the displacement on both sides of the gear teeth is also small, it is generally considered that the maximum displacement of the load acting point is not exceeded 3.5, which is negligible. Therefore, the displacement of the side surface is also considered to be zero. This determines the solution range and boundary constraints for calculating the dynamic stress of the gear using the finite element method.
1.3 Determination of impact load For the calculation of gear impact speed and impact load, according to the algorithm of reference [1], 2 is the moment of inertia of the large and small gears respectively; qs is the comprehensive flexibility of the meshing gear at the meshing point.
When the output speed of the impact drill is 2000r/min and 2500r/min respectively, the maximum impact loads are 300N and 500N respectively. It is assumed that the impact time of the impact drill is 40s and 80s respectively, so that the impact drill can be established during the stall. The time curve of the dynamic load.
Time curve of impact load In order to facilitate the analysis of the impact of different impact loads and impact time on the root stress, the impact process is divided into three kinds of working conditions. The impact drill often causes blockage due to the change of resistance during work (blocking is the working head) In the case of high-speed rotation, a phenomenon that suddenly hits the resistance and stops running, the stalling will impact the gear, and the phenomenon of gear damage will occur from time to time. At present, there are few researches on the motion characteristics and dynamic characteristics of the small-modulus gear shifting mechanism of electric tools. This paper uses the finite element analysis method to prove the rationality of the arc gear profile of the harmonic gear transmission. To establish a theoretical basis for further research on the application of arc profile in harmonic gear transmission. Xin Hongbing calculated the theoretical tooth profile of the rigid wheel with the circular tooth profile and the conjugate of the rigid wheel. By using the meshing arc to approximate it, the variation law of the meshing error is obtained. Zeng Shiqiang and Yang Jiajun analyzed the motion characteristics of the double arc toothed harmonic gear transmission, and calculated the meshing arc length and backlash of the double arc harmonic gear transmission. Theoretically, the double arc tooth shape was well worked. performance.
4 Conclusion Arc gear has developed into a gear transmission technology system with Chinese characteristics. In order to further improve the bearing capacity of the circular gear, especially to improve the bending strength of the root, the medium hard tooth surface and the hard tooth surface technology are one of the development trends of the circular gear.
Compared with the involute gear transmission, the arc gear transmission meshing process is close to pure rolling and has good running performance. At the same time, the arc gear also has some disadvantages such as sensitivity to the center distance and low bending strength of the root. Therefore, how to combine the center-distance separability of the involute gear transmission with the characteristics of the arc gear, and develop a new type of transmission that combines the advantages of ordinary arc gears and involute gears, which is an important development direction. .
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