In order to reduce the vibration and noise of the hydraulic system of CNC machine tools and avoid the expansion of noise, prevention and improvement should be done in the following aspects:
（1） Improvement of Hydraulic System Structure
In the process of controlling the hydraulic system of CNC machine tools, attention should be paid to the use of low-noise hydraulic components. Through research, it is found that the old hydraulic pumps are mainly plunger pumps or gear pumps, and their noise vibration and noise are much higher than those of vane pumps, and their rated pressure is also very high. Therefore, many CNC machine tool hydraulic systems still use plunger pumps or gear pumps. In view of this situation, it is necessary to improve the rated pressure of vane pumps, The rated pressure shall be at least 20 MPa to reduce vibration and noise. Secondly, control the number of hydraulic pumps. It is found through research that when the number of hydraulic pumps decreases, the vibration and noise will also decrease. Therefore, it is necessary to control the number of hydraulic pumps. In the traditional hydraulic system, multiple hydraulic pumps are needed to adjust the flow and pressure. To ensure the flow and pressure of hydraulic pumps, the pressure and flow can be adjusted in proportion to reduce the number of hydraulic pumps.
Moreover, when the accumulator is used, it is easy to generate noise under the effect of pressure pulsation. To eliminate noise, the accumulator can be used. Although the accumulator has small capacity, its inertia is relatively small and its response is very sensitive. During the use of the accumulator, the frequency of the accumulator should be controlled at about tens of hertz to reduce the pressure pulsation. Finally, set up vibration eliminator and filter. Generally speaking, there are many types of vibration eliminator, including high-frequency pressure vibration eliminator and micro perforated liquid vibration eliminator. The common filters in practical use are hydraulic filters. The application of these devices can minimize vibration and noise.
（2） Improvement of installation mode of hydraulic device
In order to control vibration and noise, it is necessary to further improve the installation method of hydraulic devices, which can be started from the following two aspects: first, install a suitable hydraulic pump. During the installation of hydraulic pump and motor, it shall be ensured that the axial error between them does not exceed 0.02mm, and the flexible coupling shall be used. In the process of installing the hydraulic pump, if the pump and motor are installed on the oil tank cover, then it is necessary to install anti vibration materials and noise elimination materials on the oil tank cover. At the same time, equipment with good oil absorption height and density can also be used in combination with the actual situation. Only in this way can the design be reasonable. Second, pipe installation. It is also a very important work to do a good job in pipeline installation. In order to do a good job in vibration prevention and noise elimination, hose can be used for connection, and the length of the pipeline can be appropriately shortened to improve the rigidity of the pipeline and avoid resonance between the pipelines. At the same time, in the process of sealing, vertical sealing shall prevail. For valve parts, attention shall be paid to the application of springs in actual use, and the use of densified gaskets shall be paid to prevent vibration and noise caused by air inclusion in the oil pipe. In addition, the curvature of the pipe shall be controlled to a maximum of 30 degrees, and the curvature radius of the elbow shall be more than five times of the pipe diameter.
（3） Select the proper oil
In the process of vibration and noise prevention of hydraulic system, attention should be paid to the selection of oil and avoid oil pollution. In the process of selecting oil, it is necessary to avoid selecting oil with high viscosity. If such oil is used, it will bring a certain amount of large suction resistance to the hydraulic pump, thus generating noise. Therefore, it is necessary to control the viscosity of the oil to ensure that the oil has good defoaming ability. Although this practice requires a lot of capital investment, it has a good effect in the later period, which can not only extend the operating life of the equipment, It can also reduce the damage to hydraulic pump and components. Through the research, it is found that the anti-wear hydraulic oil has a high solidifying point and a good overall effect. Therefore, the anti-wear hydraulic oil is the best choice. At the same time, even the best oil can not play its due role after being polluted. Once the oil is polluted, the filter screen in the oil tank will be blocked, which will also lead to the failure of the oil pump to absorb oil smoothly, which will further affect the oil return, and cause noise and vibration. In this case, the relevant personnel need to clean the oil tank frequently, and the filter or filter screen can be used in the oil filling process, In this way, the oil can be filtered again to improve the quality of the oil. A partition is also set at the bottom of the oil. Under the action of the partition, the oil in the oil return area will leave impurities in the oil return area under the action of sedimentation, effectively preventing the oil from flowing back to the oil suction area.
（4） Avoid hydraulic shock
In the process of preventing hydraulic shock, we can start from the following two aspects: first, the hydraulic shock when the valve port is suddenly closed. In the process of solving such problems, the closing speed of the reversing valve should be appropriately reduced. As the closing speed of the reversing valve decreases, the reversing time will increase. After the braking reversing time is higher than 0.2s, the impact pressure will decrease. Therefore, the adjustable reversing valve can be applied to the hydraulic system. Since the flow rate is also a factor that causes vibration and noise, the flow rate should also be controlled in the process of preventing hydraulic shock. It is better to control the flow rate of the pipeline below 4.5m per second. At the same time, control the length of the pipe, try not to choose the pipe with curvature, and use the hose as the main pipe. In order to minimize the hydraulic impact, it is better to properly control the liquid flow rate before the slide valve is closed, which is also an effective way to effectively reduce the hydraulic impact.
Second, when the moving parts brake and decelerate, it will bring hydraulic shock. To prevent such impact, first of all, safety valves with sensitive response and good flexibility can be set at the inlet and outlet of the hydraulic cylinder. It is better to focus on the direct acting safety valve and control its pressure. Only in this way can the impact caused by excessive pressure be avoided. Secondly, the deceleration valve is the key point of application to avoid unnecessary impact caused by slow oil circuit closing. At the same time, the speed of moving parts should be controlled well, and its speed should be controlled below 10m per minute. Moreover, in order to avoid excessive hydraulic impact, it is better to set a certain buffer device on the upper part of the hydraulic cylinder, which can not only prevent the oil discharge speed in the hydraulic cylinder from being too fast, but also control the operating speed of the hydraulic cylinder to avoid excessive impact. In addition, the hydraulic cylinder should be installed with a balance valve and a back pressure valve, which can not only minimize the hydraulic flow speed, but also effectively avoid forward impact, This is also an effective way to increase the back pressure. Finally, it is necessary to apply the directional valve with damping function, mainly large damping, and close the one-way throttle valve, and control the lubricating pressure to avoid excessive lubricating pressure. In the process of reducing hydraulic impact, it is also necessary to control the clearance of the hydraulic cylinder body to prevent excessive clearance or unreasonable sealing from affecting the normal operation of the hydraulic system. In order to prevent such events, it is better to use new pistons and set appropriate seals, so as to avoid adverse events to the greatest extent.