Dressing speed ratio, qd, gives the ratio between dressing roller speed and wheel speed (Eq. 6.28). In up-dressing, the speed vectors are counter-directional in the contact point and the speed ratio is denoted with a negative value; in down-dressing everything is inverted.
vR dressing roller speed vs wheel speed
Dressing speed defines the engagement curves of dressing diamonds into the grinding wheel [SCHU96]. The rotations of dressing roller and grinding wheel superpose, so that the dressing diamonds move along cycloidic paths viewed from the grinding wheel [SCHE73]. Dressing diamond paths for down-dressing have steeper flanks for the same value of the speed ratio in up-dressing, /qd / [SCHM68]. Therefore, rougher grinding wheel topography results. Contact length between dressing diamond and grinding wheel decreases with increasing value of the speed ratio, /qd /, and the engagement angle gets steeper [STUF96]. This affects the wear mechanisms of the abrasive grits. Grits dressed in down-dressing mode splinter and break more, whereas grits dressed in up-dressing are rather flattened [STUF96]. At the dressing speed ratio of qd = +1 grinding and dressing tool move with the same speed and high normal forces occur. The grinding layer is shattered by high normal forces and the dressing principle is called “Crushing” [HESS03]. Special brittle bond systems work best for crushing, for example brittle bronze bonding.
Experiments have shown that not only the dressing speed ratio, but also the relative speed between dressing roller and grinding wheel are important.