Reliability and accuracy of rotating machinery is very essential for obtaining accurate components. The vibration level of the spindle and balancing of the rotating member in rotating machinery is very important to achieve this. This study involves vibration analysis and dynamic balancing in reducing the spindle vibrations to a minimum possible level. As the rotational speed of the machine increases, centrifugal forces due to unbalanced forces increase dramatically, which in turn increases the vibration leading to equipment reliability and product quality problems. This paper illustrates the balancing of CNC turning center with the help of vibration signatures. Three levels of balancing have been considered. The signal is acquired with the help of powerful dual channel vibration analyzer, ADASH V4300 along with the accelerometer and taco sensor. Graphs are presented before and after balancing.

Unbalanced rotating machinery causes more maintenance cost due to prematurely damaged components which, in turn, results in loss of production and excessive energy consumption. The method employed for dynamic balancing is the use of vibration signatures at the bearing housing. Vibration amplitude of rotor is proportional to the unbalanced mass. The coefficients of proportionality may conveniently be called influence coefficients as they give the vibration magnitude, measured at a specific location, per unit mass unbalanced placed in some known position in the rotor. They are complex in function of the dynamic characteristic of the system and depend strongly on the speed of the rotor. As they are not known in advance they must be determined from tests as an integral part of the balancing procedure. Once the coefficients have been obtained, the proper correction weights can be established either graphically or numerically as described by Timoshenko (1955), Den (1956) and Goodman (1964). The method described in Goodman (1964), and Lund and Tonnesen (1972) is generalized, but in practice, only one or two planes are used, the vibration is measured at one or two locations (typically at bearings) and measurements are taken at one speed and as such no minimization is involved.

The main purpose of this study is to provide a working background in the basic consideration of balancing and the criteria to be used in its application. The amount will manifest itself by producing a vibration response. Machinery vibration is the single contributor to equipment breakdown. As such, it is a needless cost on both equipment spares and production losses. Manufacturers as well as the ultimate users have recognized the relationship between vibration and equipment performance. To build quality into their product, manufacturers have taken the first step of balancing. It then becomes the responsibility of the user to maintain the same in order to achieve the optimum performance goals to be cost effective. When the centrifugal force of rotors exists due to unbalanced mass, the resulting vibratory force is imparted to its bearing housing (Dennis, 1994). The vibration of a machine may be caused, not only by the rotor unbalance, but also by a number of different forces appearing with certain defects as well (Barkov et al., 1994a and b). Keeping of vibrations within the limits and proper balancing of the spindle of CNC machinery, help achieve the faster cutting speeds, longer tool life, better surface finishing, longer life of the spindle and bearings of the spindle, noise reduction, breakages prevention and longer machine life with better performance.

Mechanical Engineering Journal, CNC Machine Spindle, Vibration Signatures, CNC Machinery, Vibration Analysis, FFT Spectrum, Dynamic Balancing Procedure, Correction Mass, Frequency Spectrum, Multi-Condition Machines, Integrated Condition Monitoring Technologies.