EMU Spring Fretting-grinding Mechanical Analysis And Selection Of Grinding Parameters

With the rapid development of rail transportation industry in our country, the quality of train components and parts become more and more important. As an important part of train vibration damping system, spring plays an important role in the train, such as absorbing and isolating vibration, ensuring the comfort and safety of passengers, improving the stability of the vehicle at high speed, and prolonging the service life of the train components and tracks etc. It is obvious that the quality of the spring influences the performance and safety of the train directly. Therefore, the high precision design criterion of the spring is of great importance.The EMU springs often cause damage in practice, most occur in the first or second coil. Bulges, pits, wrinkles and other defects often appear between spring supporting section and working section in the process, which may lead to point contact. The point contact can easily cause stress concentration and fatigue crack, and become position to extend fatigue crack fast. The point contact reduces mechanical performance of the EMU spring easily, which seriously affect the service life of the spring.In coiling process of the EMU spring, underhand polish is adopted in solving the point contact between the spring supporting section and working section mostly. There exist drawbacks in underhand polish. For example, production efficiency is extremely low; it is difficult to achieve large-scale and efficient manufacturing; grinding strength is not uniform, which influence the quality of spring; and that, it is difficult to maintain continuity contact of spring.In this paper, a novel vibration grinding machine is designed for realizing fretting grinding between the supporting section and working section of spring and eliminating the point contact between the EMU springs. Moreover, in order to find the main grinding parameters affecting the fretting grinding effect of the grinding machine, and establish the relationship between the fretting-grinding mechanical quantities and the main grinding parameters without damaging the spring mechanical performance. It is necessary to make the mechanical analysis of spring in the grinding process.The main work accomplished and achievements are as follows:(1) The value and significance of the EMU vibration grinding machine is expounded, its fretting-grinding principle is analyzed, and the main grinding parameters of the grinding machine is determined, including force applied to the spring of the grinder, grinding speed and the displacement of the grinder, and finally the relationship between the main grinding parameters and the fretting-grinding mechanical quantities is established.(2) Taking an EMU spring for instance, by means of combining Solidworks and ANSYS(Workbench) the finite element model of spring is built up. Stiffness and strength of the spring is analyzed, the results show that the error of stiffness value is about 2.3 %, and the error of strength value is about 6.0%. Based on t he results, the model is verified. And the finite element results of stiffness are obtained, namely, the axial stiffness of spring is 241.0624N/mm, and the lateral stiffness is 65.20677N/mm.(3) In order to obtain the pressure of the grinder and the contact stress between spring support section and working sections, the contact analysis of EMU spring should be carried out. The contact analysis spring without bulges is carried out first with ABAQUS, the curves of the contact stress and compression displacement are obtained, which show that the contact stress reaches to maximum value when the compression displacement is 45 mm. Then the contact analysis of spring models with bulges of different position and different size is carried out. The results show that the maximum contact stresses between the support and working section of these kinds of spring model are less than 45 mm. So, 45 mm is selected as the maximum compression displacement, and the corresponding reaction force, about 10845 N, is selected as the grinding force of the spring, the weight of the grinder when grinding a single spring is calculated, its value is about 1106.6kg.(4) In the grinding process of EMU springs, in addition to the static quantity, it also relates to a large amount of dynamic quantity. To avoid spring resonance occurring during operation process, the modal analysis and prestressed modal analysis of spring are carried out firstly, the natural frequencies and corresponding mode shapes of the spring is gained. On the basis of modal analysis, the harmonic response analysis is carried out, the results obtained show that resonant frequency is 8Hz, 118 Hz and 140 Hz. In the actual process of grinding, should try to avoid external excitation frequency on the frequencies near. In order to gaining grinding velocity and displacement, the transient analysis is carried out. The relationships among the load amplitude, the exciting frequency and the fretting displacement, the fretting velocity response of the spring ring are obtained. The results show that: the best fretting grinding effect is achieved when grinding displacement is 17.638 mm,and the motor speed is 900rad/min.In a word, when the weight of the grinder calculated is about 1106.6kg, grinding speed is about 526 mm/s, the displacement of grinder is 17.638 mm, motor speed is about 900 rad/min, or the exciting frequency is 15 Hz, the fretting-grinding effect reaches the best.