TABLE OF CONTENTS Systematic measurements of grinding forces and specific energies in the early 1950s [12, 13] showed that the specific energies for grinding were much larger than for other metal-cutting operations. Furthermore, larger specific energies were found when the process parameters were adjusted so as to reduce the undeformed chip thickness, i.e., decrease v w or a in Figure 5-2.
At the time of these studies, the classic model of chip formation formulated in 1945 [14] was beginning to be extensively applied to various metal-cutting processes. According to this model, chip formation occurs by an intense shearing process in an extremely thin zone followed by friction as the chip slides over the tool rake face. Typically, shearing accounts for about 75% of the total chip formation energy, and chip-tool friction the remaining 25%. Although many other secondary effects have been observed over the years, this same model is still considered to present a reasonably accurate description of chip formation.
As with other metal-cutting processes, an attempt was made to interpret the grinding forces in terms of this chip-formation model [13]. By invoking plausible assumptions for the typical cutting-point geometry, estimates of the shear stress for plastic deformation during chip formation were obtained. However, these calculated shear stresses greatly exceeded the known flow stress of the metal being ground. Moreover, larger shear stresses were generally obtained with finer grinding conditions, i.e., those giving smaller undeformed chip thicknesses corresponding to the...
