The source of machine tool noise
machine tool noise mainly includes structural noise, fluid noise and electromagnetic noise. As far as ordinary lathes are concerned, the noise of machine tools mainly reflects the structural noise
frequency analysis is widely used to identify structural noise sources. This method is to use a sound level meter to measure the running noise of the machine tool in the running state, calculate the white spectrum of the mountain noise (also known as the white power spectrum), and then compare the working frequency of each moving part of the machine tool (such as the meshing frequency of the transmission gear, the operating frequency of the rolling bearing) with the spectral peak frequency in the spectrum. When the working frequency of a moving part is equal to a spectral peak frequency, it is considered that the moving part is a noise source
spectrum analysis method is simple and easy, and has been widely used in the identification of machine tool structural noise sources. Especially for general-purpose machine tools, the spindle speed range is wide, the transmission chain is long, and there are many moving parts. The frequency analysis method can easily identify the main sound source of the mountain structure noise, so as to carry out targeted noise control
6. After the completion of the number of experiments, the structural noise includes the noise generated by the vibration of the running parts in the machine tool, such as gear shafts, bearings, cams, etc., and the noise generated by the vibration of the static parts such as the box and housing, which are excited by the moving parts. Therefore, all factors affecting the structural vibration also affect the structural noise
1.1 determine the noise source of the whole machine
the noise of jh32 lathe is mainly generated by the headstock and the recycling of resources, feed box, slide box, change gear system and main motor. Use a sound level meter to measure the noise of the whole machine, headstock and main motor respectively, The results show that the noise of the headstock measured alone (the rotation of the 160 mm chuck in the spindle belt) is only about 2 dB (∞) lower than that of the whole machine with the tool feeding system, and the noise of the main motor measured alone is generally 70 ~ 72 dB (∞). This is secondary to the noise of the whole machine, so it is determined that the headstock is the main noise source of the machine tool.
1.2 determine the main noise source of the headstock
there are many factors affecting the headstock noise, of which one or more must be the main factors. Therefore, we believe that when analyzing the noise situation of multiple headstock, we can determine the main noise source by looking for mountains and analyzing the causes of the same points. Due to restrictions, we only need to The sound level meter is used to measure the noise level when the main shaft of each gear of multiple headstock stops and reverses, and the measurement results are expressed in the form of "noise diagram"
1.3 determine the main causes of the noise affecting the headstock
through the analysis of the noise diagram, it is found that there are the following similarities:
(1) the maximum noise value occurs when the spindle is reversed at the highest speed, that is, when it is reversed at 2200 R/min:
(2) the noise increases with the increase of the number of spindle revolutions:
(3) the rotation noise of each gear spindle is greater than its corresponding stall noise, The noise value changes between 1 ~ 3 dB (∞):
(4) the noise value of the first gear of reversing 342 R/min is significantly higher than that of its adjacent gears
based on this, the demand for biodegradable materials in developed countries such as Europe and the United States has maintained a rapid growth in recent years. We focused on the situation of the maximum reversal of the spindle and the reversal at 342 R/min. From the main transmission route map and speed distribution map of the headstock (Fig. 3 and Fig. 4), it is not difficult for us to find that the manufacturing accuracy of the headstock gear can be improved by realizing
2.1 in the headstock
considering that the above four gears are the main noise sources of the headstock gear, and the gear accuracy has a direct relationship with the noise. We have improved the manufacturing accuracy of two high-speed gears (i.e. the number of teeth is 55 and 39) from the original level 7 to the current level 5 accuracy, and the manufacturing accuracy of two gears (the number of teeth is 17 and 77 respectively) with a reverse rotation of 342 R/min from the original level 7 to level 6, Mainly considering the high linear speed when it works (up to 9 m/s and 3 M/curve respectively. According to the gear accuracy standard, the gear shape tolerance grade is determined according to its noise intensity and rounding speed.
the four gears were originally selected as grade 7 accuracy, so the actual machining process adopts the hobbing, shaving and honing process, so the gear shape tolerance is difficult to control. Several gears were measured, which are between o.015 ~ o.024 itlin, and the shape is concave ", while the concave gear has two impacts during meshing, Therefore, the noise is also the largest
now we will improve the manufacturing accuracy of these four gears to level 5 and 6 respectively, and also improve the manufacturing accuracy of the remaining four transmission gears to level 7. Its processing technology is also changed from the original hobbing, shaving and honing to the requirements of hobbing, shaving and grinding. For gears with 6-7 precision, the dished wheel gear grinding machine is used for processing; for gears with 5 precision, the high-precision worm wheel gear grinding machine is used for processing, which better ensures the radial runout tolerance of the gear ring. The tooth profile tolerance and tooth direction tolerance meet the requirements of corresponding standards
after the rectification test, only the gear manufacturing accuracy is improved, The noise of the headstock is 1.5 ~ 2 dB lower than the original (∞).
2.2 improve the processing requirements and assembly accuracy of boxes, shafts, bearings, etc.
considering that the noise of machine tools is mainly generated by headstock, feed box, chute box and other parts, it is necessary to strictly control the dimensional tolerance and geometric tolerance of headstock and other shells. In addition to strict requirements for corresponding parts, special boring dies, boring rods and other tooling are also designed, and it is clearly stipulated that the box processing is on coordinate boring or boring machines with digital display devices Use special tooling for processing to ensure the processing accuracy requirements of shell hole system
for the bearings used in the headstock, P4 grade bearings are strictly used. The radial runout of the main shaft bearings is slightly higher than the requirements of the national standard when selecting. P4 grade and P5 grade bearings are selected for the feed box, and other precision grade bearings are not used as much as possible
install the bearing journal on the transmission shaft. The radial runout of the opposite gear journal is not greater than 0.01 itiittl, and the radial runout of the gear ring relative to the bearing journal is less than 0.02 itiittl. The main shaft system is carefully dynamically balanced after assembly
2.3 strictly screen the purchased electrical appliances, hydraulic materials, and improve the design of the motion system
the main demands for the use of the purchased electrical appliances, especially the lining materials of the main electrical case (leather bag, leather case, jewelry box) are: high tensile resilience, material plasticity and leather and cloth fit, and the noise indicators of the machine, cooling pump motor and lubrication pump motor are slightly higher than the requirements of the standard. When each motor enters the factory, Strict inspection shall be carried out to ensure that the electromagnetic noise does not meet the specified requirements
improve the design of the motion system and strive to shorten the transmission chain at high speed. In addition, ningzhuan gear should ensure that the umbrella is disengaged
considering that the box wall and shell generally have large and accumulated thin walls, under the influence of other exciting forces, the vibration and noise of thin walls will often be caused. In the design, more stiffened plates should be added appropriately, so as to change their natural frequencies and reduce the noise
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