TABLE OF CONTENTS For grinding of metals, it has been generally assumed that material removal occurs by a shearing process of chip formation, similar to that found with other machining methods such as turning or milling [1]. This idea was first suggested more than 90 years ago [2], and optical microscopy of grinding debris (swarf) more than 50 years ago revealed chip-like shapes [3 5].
With the advent of the electron microscope, the similarity between grinding chips and larger-scale metal-cutting chips became much more apparent [6 8]. A scanning electron micrograph of the swarf recovered after grinding a plain carbon steel is shown in Figure 5-1 (a). Mostly curled chips are found, very much like those produced by turning or milling, although somewhat irregular in size and shape owing to the variability in cutting-point shape and penetration depth. These chips have a fine lamella structure, similar to what is generally found with other machining chips. Lamella formation during chip formation has been attributed to a thermal instability, whereby the shear resistance of the material decreases due to localized heating caused by intense plastic deformation [9]. At higher magnification in Figure 5-1(b), the lamella spacing can be estimated to be about 0.5 ?m, which is somewhat finer than on chips produced by turning. The difference may be attributed to the typical rake angle being much more negative in grinding, as will be discussed later in this chapter. Another factor may be the much higher velocities and strain rates in grinding, which...
