New Technique for Shear Zone Thickness Determination in Orthogonal Metal Cutting

The extent of the transition zone separating the uncut metal and fully formed chip in orthogonal cutting is examined. Earlier work in this field consisted of studying the magnified grain arrangement in the uncut metal and the chip, the width of the transition zone being measured at selected points.

The new method attempts a more positive assessment of the extent of the transition zone by the use of micro-hardness explorations along a series of generators running parallel to the sides of the chip, and passing through the shear zone into the workpiece. The transition zone and adjacent metal are thus covered with a network of indentations pitched a few thousandths of an inch apart.

As the variation in the size of the indentations is a measure of the work-hardening of the metal, it follows that, once the average hardness values of the uncut metal and the fully formed chip have been established, the transition zone is, in principle, defined by the location of those hardness values which lie between the average hardness values accepted for (1) the uncut metal and (2) the fully formed chip.

In order to find the width of the zone through which a definite increase in hardness occurs, four different methods have been investigated and the results are included. One of the methods gave satisfactory results on all the samples tested.