An experimental method for determining the service life and reliability of the CNC lathe main spindle bearing assembly

The main spindle bearing assembly (MSBA) plays an important role in the quality and service life of CNC machine tools and industrial equipment. The MSBA is usually evaluated based on the allowable wear or the stiffness independently combined with the vibration characteristics. Therefore, it is very important to determine the service life of MSBA when the wear reaches the allowable value, and the stiffness is reduced to the allowable value. This paper studies the simultaneous relationship of wear, stiffness, and vibration characteristics of MSBA in a CNC lathe. The results show that the service life of MSBA is different when evaluated based on each criterion (wear or stiffness). The stiffness of the MSBA is reduced to the allowable limit [J] = 200 N/μm with a Root Mean Square (RMS) value of about 5.75 mm/s2. The wear of the MSBA reaches the allowable limit [δa] = 5 μm with an RMS value of about 4.5 mm/s2. The life of MSBA calculated according to the stiffness criterion is about 1.18 times higher than that calculated based on the wear criterion. The average life of MSBA with standard lubrication according to the wear criterion reaches ∼15,799 h and RMS reaches ∼2.4508 mm/s2.