Research on Noise Sources of Machine Tools

Noise is a critical quality indicator for machine tool products, directly impacting the physical and mental health of operators and the global competitiveness of the machines. Machine noise typically originates from multiple sound sources, making it challenging to assess the overall noise level without advanced analytical equipment. This has long been a concern for engineers and craftsmen. Based on this, an addition and subtraction method for decibel values of sound pressure levels was developed, and it has shown significant effectiveness in practical applications. The study concluded that improving the maximum noise source is key to reducing machine tool noise. **1. The Relationship Between Sound Pressure Level and Logarithmic Function of Sound Pressure** Sound intensity (I) can be expressed as power per unit area: I = P × V, where P is the effective sound pressure, and V is the effective particle velocity. From this, the relationship between sound intensity and sound pressure can be written as: I = P² / 400, where 400 J represents the acoustic impedance of air. The sound pressure level (SPL) is defined as: SPL = 10 log(I/I₀) = 10 log(I) + 120 dB, where I₀ = 10⁻¹² W/m² is the reference sound intensity. Substituting I into the equation gives: SPL = 20 log(P / 2×10⁻⁵), where 2×10⁻⁵ N/m² is the reference sound pressure. This logarithmic relationship shows how small changes in sound pressure lead to significant changes in perceived loudness. Table 1 illustrates the variation in SPL based on different sound pressure values, showing that a tenfold increase in sound intensity results in a 10 dB rise in SPL. **2. The Relationship Between Synthetic Sound Pressure Level and Individual Sound Pressure Levels** In real-world scenarios, when multiple noise sources are present, the synthetic sound pressure level (SSPL) is used to evaluate the total noise. Using the formula: SSPL = 10 log(P² / 400) + 120 dB, we can calculate the combined effect of two sound sources. If one source has a higher decibel level than the other, the SSPL will approach the higher value. For example, if SPLa = 65 dB and SPLb = 60 dB, the combined level is approximately 66.2 dB. As the difference in decibel levels increases, the SSPL tends to align with the highest individual source. This implies that reducing the loudest noise source is the most effective way to lower overall machine noise. **3. Comparison of Application Results with Experimental Data** For a CW6163A lathe, the measured sound pressure levels at various points were found to be within acceptable limits. According to calculations, the total noise level should be around 83.4 dB, while the experimental data showed a maximum of 83.2 dB, which is only 0.2 dB off. This confirms the accuracy of the proposed method. The experiments were conducted under controlled conditions, using a precision sound level meter at different spindle speeds. Multiple measurement points were tested, and the results aligned well with the theoretical predictions. **4. Conclusion** By analyzing the decibel values of individual noise sources, it is possible to determine whether the overall machine noise falls within acceptable limits. The synthetic sound pressure level always approaches the highest single source, emphasizing the importance of targeting the primary noise contributor. Reducing the decibel level of the main noise source is therefore essential for achieving quieter and more efficient machine tools. This method not only simplifies noise assessment but also provides a clear path for improvement in design and manufacturing processes.

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