A study of the chip -tool contact conditions in machining
Abstract
The contact conditions along the chip-tool interface in machining have been studied using a combination of transparent sapphire tools, in-situ high-speed direct observations of this interface, and force measurements. Results have shown that the contact along this interface consists of four distinct regions: a region of stagnation at the cutting edge, a region of retardation adjoining the stagnation region, a region of sliding beyond the retardation region, followed by a region of sticking that is located furthest away from the cutting edge. While material in the stagnation region is stationary with respect to the tool, this region is confined to a very small fraction of the chip-tool interface. In the region of retardation, motion of the chip material has been observed at the chip-tool interface, but the velocity of this motion is less than that of the bulk chip velocity. The region of sliding is characterized by interfacial sliding at a velocity equal to the bulk chip velocity. The last region of contact, termed the sticking region, exhibits material transfer from the chip to the tool. This region of sticking has been found to be highly dependent on the cutting velocity. This work, for the first time, has provided direct experimental evidence for the theoretical model of the contact conditions proposed by Oxley. Force measurements have shown that the region of sticking carries little load, and is thus subjected to the lowest stresses, while the regions of contact subjected to the highest stresses, namely, the stagnation, retardation and sliding regions, show no material transfer from the chip to the tool. Further evidence for the development of the regions of stagnation and retardation has been provided by combining measurements of the force evolution with direct observations of the contact evolution. The condition of the cutting edge, at or below the micron level, has been shown to have a controlling influence on the chip-tool interface and the overall mechanics of machining. The condition of the cutting edge is believed to play a controlling factor in the development of the stagnation and retardation zones. Experiments with non-oxide tools such as aluminum and steel have provided evidence that our model of the contact conditions is equally applicable with other tool materials.
Degree
Ph.D.
Advisors
Chandrasekar, Purdue University.
Subject Area
Industrial engineering|Mechanical engineering
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.