It is interesting to note that most scientific studies on “damped” wheel designs are based on suppressing self-excited chatter. Furthermore, they all use hub materials that not only have good damping characteristics, but are also considerably more compliant and lightweight than “standard” hub materials such as steel. As the following examples illustrate, it is not only damping that is important for reducing vibrations. Reducing stiffness at the wheel contact has a similar effect. The analysis of chatter with added compliance at the wheel contact is given in the chapter on centerless grinding. Sexton, Howes, and Stone [1982] reported excellent results in reducing chatter when grinding steel with resin CBN wheels by the use of a “Retimet” nickel foam hub material with a radial stiffness of 0.5 N/pm. mm. This was compared with values of 4 to 10 N/pm. mm for standard phenolic (Bakelite) or aluminum-filled phenolic hubs. McFarland, Bailey, and Howes [1999] used polypropylene with a radial stiffness of 1.56 N/pm. mm and natural frequency of 1,169 Hz. This was compared to a radial stiffness for an aluminum hub of 24 N/pm. mm. Warnecke and Barth [1999] compared the performance of a resin-bonded diamond wheel on a flexible phenolic aluminum composite hub with a similar bond on an aluminum hub grinding SiN and demonstrated an improvement in life of over 70%. FEA analysis of the contact zone revealed over twice the radial deflection with the flexible hub. It would appear that compliance in the hub can be transferred through a resin superabrasive layer and can significantly increase contact width. See also Zitt and Warnecke [1996].
In 1989, Frost carried out an internal study for Unicorn (Saint-Gobain Abrasives) to evaluate the impact of the higher stiffness of vitrified CBN bonds on the centerless grinding process. The following radial contact stiffness values were obtained for conventional and CBN vitrified specifications:
47A100 L6YMRAA 0.06 N/pm. mm
5B46 P50 VSS 0.78 N/pm. mm
5B76 P50 VSS 0.31 N/pm. mm
The compliance of the CBN bonds were an order of magnitude greater than the conventional bond and approached or exceeded that of the hub materials described above. It would, therefore, be expected that as with the example earlier of resin-bonded diamond wheels, flexible hubs with radial stiffness values of the order of 0.5 N/pm. mm could increase the contact width in the grind zone for wheels with a thin vitrified CBN layer. Further analysis of the effect of wheel compliance on chatter in centerless grinding is given in Chapter 19.