Forced vibrations can be eliminated in three ways. First is to eliminate the energy at its source. Wheels, motors, belts, and workpieces should all be balanced as should the three-phase power supply. Ultra-precision bearings and ball screws should be used and properly maintained in work and wheel spindles and slides. Second, the grinder should be insulated from sources of vibration such as hydraulic and coolant pumps, and vibrations carried through the foundations. Third, where resonances cannot be eliminated the machine dynamics must be modified. Where a particularly prominent frequency exists in, for example, a motor or cantilevered member, tuned mass dampers consisting of a weight with a damped spring can be fitted at the point where the vibration needs to be reduced. This may often consist of a weight attached to the member via a rubber sheet sandwiched between. The sizes of the mass, spring, and damper are selected so that the mass oscillates out of phase with the driving frequency and, hence, dissipates energy. A relatively small — tuned mass can have a large effect in reducing vibration amplitude.
4.7.2.1 Self-Excited Vibration
Self-excited chatter occurs only during grinding and the amplitude of vibration climbs with time. A small perturbation due to instability in the system causes a regular variation in grinding forces that in turn creates an uneven level of wear around the wheel. The process is thus regenerative. There are several methods available for suppressing this form of chatter.
First, the system stiffness and damping can be increased. Second, the grinding conditions can be continuously varied by changing the work speed, wheel speed, work support compliance, or by periodically disengaging the wheel from the workpiece. For example, Gallemaers, Yegenoglu, and Vatovez [1986] reported that by periodically varying the work speed to prevent lobe buildup on the wheel, they could increase the grind (G) ratio by up to 40% and productivity (by extending the time between dresses) by up to 300%. Third, the stiffness of the contact area can be reduced to shift the state of the system more toward a stable grinding configuration [Snoeys 1968]. Fourth is the use of various filter effects to reduce the wavelength to less than the contact width. The work speed can be slowed to the point the chatter lines merge. Alternatively, and more interesting, the frequency of the chatter can be increased to the point that the grinding process itself acts as a filter to absorb the vibration energy. For this reason, the natural frequency of wheels is targeted at >500 Hz or ideally >1,000 Hz.