A Study of Plunge (or Form) Machining of Low-Carbon Resulfurized Steel on a Multispindle Automatic Screw Machine: Part 2—Influence of Speed, Feed, and Duration of Cutting on Worn Tool Geometry

Abstract

During the plunge-machining experiments described in Part 1, the crater and wearland profiles were obtained on plunge-cutting tools at five intervals in each of the fifty 4600-piece runs. The objective was to understand how worn tool profiles change during prolonged plunge machining of low-carbon resulfurized steels and how these changes in a worn profile affect surface finish and dimensional tolerance. First, mathematical models were developed to convert the measurements taken from worn tool profiles into tool wear parameters such as crater length, crater depth, crater curvature, BUE height, wearland, effective rake angle, and the deepest point in the crater. Second, the effect of changes in speed, feed, and of cutting duration on the tool wear parameters was studied. Finally, an effort was made to establish empirical relationships between wear parameters and machining performance. Some of the results of this investigation are: (a) For each combination of speed and feed there exists a worn tool geometry (steady state) which sets in after the initial transient wear and which lasts during the remainder of the run except at the end when rapid deterioration takes place. (b) The steady-state geometry can be described by the effective rake angle, crater curvature, wearland, BUE height and projection, and the distance to the deepest point in the crater from the highest point on BUE. (c) The surface finish in plunge machining depends on BUE height. BUE nonuniformity, and the grooves on the worn tool. (d) The wear parameters describing the worn tool geometries were more sensitive to changes in feed than to changes in speed. With feed, an optimum was observed around 0.0015 ipr where wearland, crater depth, and effective rake angle were minimum and crater radius was maximum. The results presented in Parts 1 and 2 show that plunge machining is markedly different from single-point turning in its response to changes in speed, feed, depth of cut, coolant, and workpiece materials.