Adiabatic Shearing in Metal Machining
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Adiabatic Shearing in Metal Machining Tom Childs Faculty of Engineering, University of Leeds, Leeds, UK
Synonyms See sections Definition”
“Definition”
and
“Extended
condition in which enough heating occurs. The term catastrophic thermal shear covers this. It focuses more on the observed behavior, less so on its cause. Catastrophic thermal shear leads to chips with a segmented or serrated or sawtooth form when viewed from a direction normal to the cutting tool’s cutting edge (see section “Applications” for examples). It is theory and applications of shear localization, leading to segmented, serrated, or sawtooth chip formation which is the subject of this entry.
Theory and Application Definition Adiabatic shearing in metal machining is plastic straining to form a chip so quickly that the heat generated has no time to flow away. If the heating causes the metal to soften (overcoming the strain hardening), further straining may concentrate in the soft part so that it becomes even hotter and softer. Shearing becomes localized in a narrow band of increasingly hot metal. Extended Definition Strain softening, shear localization, and shear banding are all associated with adiabatic shearing, but they are not synonyms as they can also occur, for other reasons, in isothermal conditions. Shear localization or banding due to thermal softening does not require truly adiabatic (i.e., no heat flow) conditions. All that is required is a
The kinematic and geometrical conditions of serrated chip formation are more complex than those of deformation in simple shear, torsion, compression, and punching tests that are commonly used to study adiabatic shearing fundamentals. Fig. 1 shows a cycle of flow during serrated chip formation from (a) localized shear in a shear band to (b) mixed localized flow and upsetting (upsetting is needed to accommodate the displacement of the cutting edge into the work material as the shear band moves up the rake face), to (c) homogeneous flow as the shear band moves out of the chip formation region (the shear band is deformation rather than load driven), and to (d) localized flow again (h is the uncut chip thickness, vc the cutting speed). The role of theory is to determine the conditions of h, vc, tool geometry (rake angle), and work material thermo-physical-mechanical
# CIRP 2016 The International Academy for Production Engineering et al. (eds.), CIRP Encyclopedia of Production Engineering, DOI 10.1007/978-3-642-35950-7_6392-4
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Adiabatic Shearing in Metal Machining
Adiabatic Shearing in Metal Machining, Fig. 1 Numerical simulation of serrated chip formation at relative displacement intervals (a–d) of the work toward
the tool of 0.5 h, from the author’s work. The particular strain-rate values are associated with h = 0.1 mm and vc = 50 m/min
properties that give rise to serrated rather than continuous or other classifications of chips and, in the conditions of serrated chip formation, to predict such measurable features of the serration as the maximum and minimum chip thickness h1 and h2, the angle y at
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