First, the abstract: This article will focus on machine Tools or plastic injection molding machine abnormalities - morning move and noise, for the diagnosis of anomalies, coupled with the CNC laboratory Spectrum Analyzer (Spectrum Analyzer), with accelerometer and decibel meter As an inductor, in addition to identifying a number of issues and successfully reducing the radial vibration of the motor support from 38 mg to 6.7 mg at one revolution of the motor, the sound pressure level measured by the noise meter (Sound Pressure Level) dropped from the original 91.8db 82.5db. 5.2 times in vibration, noise reduction 9.3db. (Note: Double improvement for 6db reduction) This article will present the entire vibration and noise diagnosis process and will suggest several improvement options. These improvements will be done in the future machine test bench, in order to achieve better sound quality and machine performance. Second, the source of vibration and noise Vibration and noise generated by the machine for many reasons, with the different scope of the machine and application, it is difficult to analyze and summarize a set of complete rules, need to assess the experience of multi-party. Usually mechanical vibration and noise caused by the following reasons: 1. Mechanical components poor assembly: the rotation axis connection misalignment or misalignment problems, the belt assembly loose, gear contact deflection, will produce vibration and unnecessary Noise 2. Mechanical components unbalanced or damaged gear, wheel blades, the uneven distribution of the quality of the main shaft, will carry uneven output in the radial vibration. Bearings in the ball damage, or inner and outer ring track dent, foreign body and other circumstances, will produce vibration and noise. 3. Thermal deformation caused by the loss of accuracy: The screw machine tool machine, if the pre-pull value is not enough, when the continuous operation, the temperature warmer deformation will make the ball screw bending, leaving the friction increases, will also cause vibration. 4. External force caused by strong vibration: Due to external excitation force 迼 into objects forced vibration, you can find the excitation source to exclude. Third, the vibration characteristics of the motor and hydraulic pump: 1. Motor: Figure 1 motor and hydraulic pump configuration Plastic molding machine motor and hydraulic pump configuration shown in Figure 1, the motor shaft and hydraulic pump bearings Coupling (Couping) to connect. The speed of the motor is about 1170 rpm, which corresponds to 1170/60 = 19.5 Hz. Therefore, the vibration characteristic of a normal motor is a vibration speed number generated in the radial direction at a single rotation speed and a harmonic wave is generated at a double frequency (1 × rotation speed, 2 × rotation speed, ... n × rotation speed). 2. Hydraulic Pump: At present, the hydraulic pump used in the injection machine is a Vane hydraulic pump, and its characteristics are shown in Fig. 2. As shown in Fig.2, AB is eccentric, A is rotated and B is fixed. A map leaf, can move freely in the slot. Wheels will also contact with the outer wall due to the centrifugal force, resulting in impact (Impact), and vibration. Therefore, when the number of blades for the hydraulic pump is n pieces, when the motor rotates one revolution, it completes n cycles. Therefore, the vibration of the pump occurs at n times the rotation speed. Therefore, the current injection molding machine used hydraulic pump, for the 12 of the leaves, so the vibration occurred at 12 times the speed, and 12 times the frequency multiplier (24 times, 36 times, 48 ​​times ...) Harmonic. Fourth, plastic injection molding machine vibration and noise measurements: Figure 3 experimental measurement frame for the machine for measurement, and online to find a good sound quality for comparison. Measure with spectrum analyzer (Hp3566A), place the Accelermeter in the radial and axial positions of the motor support, and add the decibel meter to measure the main noise frequency. The measurement position is shown in Fig.3 . Due to the factory environment noise is too large during the day and can not truly measure the vibration noise of the hydraulic pump, so the choice of measurement time for the plant after the shutdown, about 8:00 to 10:00 around the night. Fig.4 shows the experimental measurement of the original amount of vibration and noise. It can be seen from the figure that no matter what the vibration and noise value of any machine are, the 1170rpm occurs at the 12 times speed (───── × 12 = 235.5Hz) and 12 times harmonic (24f, 36f, 48f ...... 72f, f 60 motor speed). This phenomenon is very "obvious" and "law" to prove that the source of noise from the hydraulic pump blades flapping hydraulic sound. In addition, we can see the signal in the decibel meter shown in Fig. 4, and we can see a clear peak value around the frequency of 1-3, which is proved to be the high frequency noise generated by the motor cutting magnetic flux lines Has been changed to improve the motor. Fig.4 also shows a tendency that the vibration value of the corresponding frequency is also larger when the decibel meter is measured to a larger decibel value. If we can improve the vibration, then we can reduce the noise. That is, in this case, vibration → (correlation) ↠noise. (b) Axial signal (c) Decibel meter 1. Frequency response of motor and hydraulic pump \ fs24 (FRF) Fig. 5 Schematic of FRF experiment Plastic injection machine used Based on the above analysis, the motor will have a greater vibration frequency at multiples of 12 and 12 times, so we will knock the whole system of Freguency Response Function (FRF) To confirm whether it will cause a large amount of vibration due to "resonance". In seeking FRF modal test, the experimental equipment shown in Figure 5, is mainly required to obtain the vibration response of the hydraulic pump. 1.FRF results: Fig. 6 hydraulic pump frequency response curve shows that there is a significant peak in the 23HZ, the peak value of 23HZ and the motor speed frequency 20HZ very close to the vibration behavior will occur so-called " Resonance resonance "phenomenon, resulting in the shaft of the hydraulic pump in the radial there will be a great amount of vibration, which makes the hydraulic pump at 12 times the speed of the blade flapping the sound will increase. If we can move the peak of 23HZ to a higher frequency, that is, move it to the right to keep it away from the speed of rotation, the noise level will be improved. Fifth, to improve the program: According to the aforementioned analysis, SQP21 hydraulic pump hanging on the motor, causing the motor speed (20HZ), close to the resonant frequency (23HZ), based on this characteristic, in the process of improvement, that is, focusing on improving The rigidity of the hydraulic pump is such that the resonance frequency can be kept away from the speed of rotation. In general, the transmission path of noise problems can be divided into two categories. One is Air Born (via air) and the other is Structure Born (via structure). The relationship between the high and low frequency is as follows: In this hydraulic pump sound is too large, the 12-speed speed of 12 × 19.5HZ = 235HZ, are below 400HZ, and from Figure 4 observation point of view, the noise and vibration are relative The relationship, it is intended to start from the structural improvement. In order to determine the "effectiveness" of improving the structure against vibration and noise, we can start with the mass method and the rigid method. (A) The mass method changes the resonant frequency of the structure Decreases the amplitude. Try different mass sizes and positions (B) Rigid method to correct the position to correct the need to have a preliminary understanding of the modal characteristics required with the percussion test Stittness rigidity As the motor and pump placed in the machine Rack, in which there is the distribution of hydraulic pipelines, more difficult to use quality method to confirm the use of rigid method to confirm. Improved Results: Figure 7 Support Improvement Schematic Add a pump support with a support pin and a rubber dampener, as shown in Fig. Before and after the improvement of radial, axial vibration and decibel measured value of the noise as shown in Fig.8. (Dosing agent moter + SQ P21 PUMP). In terms of the amount of vibration in the radial direction, the amount of vibration was reduced from 38 mg to 6.7 mg at one rotation speed, while that of the blade at 12 times rotation speed was improved from 50 mg to 6.0 mg. In the same amount of axial vibration, the doubling speed has been improved from 10.1 mg to 9 mg, and the vibration at 12 times the speed has been reduced from 37 mg to 21.5 mg. In addition, Fig. 9 shows that the sound pressure level measured by a decibel meter before and after improvement has dropped from 91.8db to 82.5db after improvement, and the sound quality has been obtained Very clear improvement. It is enough to prove that this time from the vibration point of view to solve the noise problem, can be effectively improved. Sixth, the conclusion (A) the best position for the hydraulic pump support position selection: In the rigid method mentioned by adding a rigid object to change the system characteristics, which can effectively improve the sound quality. However, the location of the support pin placement, just related to the support bolt on the pump vibration effect. We have built a simple finite element model on the computer to test the impact of the support pin on the system rigidity. As shown in Fig. 7, when the distance d gradually increases, the rigidity of the whole system becomes stronger and the natural frequency also increases. Therefore, the experimental relationship between the position of the support pin and the noise should be tested experimentally! (B) the damping layer (damper) coating: the use of damping effect (damping) can reduce the vibration amplitude. As the vane hydraulic pump, a centrifugal and eccentric rotary vane, the vibration should be directly on the outer wall of the hydraulic pump, and the maximum vibration in the local area. Sold in the market, "Vibration Isolation paint" can be applied to the outer wall of the hydraulic pump to control the amount of vibration. It uses the thickness of the coating to control the damping value, but must take into account its heat transfer problems. (C) The design of the support pin of the hydraulic pump can be properly modified, for example by increasing the size of the support pin
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