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Research Papers

Study of the Shear Strain and Shear Strain Rate Progression During Titanium Machining

[+] Author and Article Information
Brian Davis, David Dabrow, Peter Ifju

Department of Mechanical and
Aerospace Engineering,
University of Florida,
Gainesville, FL 32611

Guoxian Xiao

General Motors Global R&D,
Warren, MI 48090

Steven Y. Liang

George W. Woodruff School of Mechanical
Engineering,
Georgia Institute of Technology,
Atlanta, GA 30332

Yong Huang

Department of Mechanical and
Aerospace Engineering,
University of Florida,
Gainesville, FL 32611
e-mail: yongh@ufl.edu

1Corresponding author.

Manuscript received June 25, 2017; final manuscript received December 1, 2017; published online March 6, 2018. Assoc. Editor: Radu Pavel.

J. Manuf. Sci. Eng 140(5), 051007 (Mar 06, 2018) (13 pages) Paper No: MANU-17-1394; doi: 10.1115/1.4038891 History: Received June 25, 2017; Revised December 01, 2017

Machining is among the most versatile material removal processes in the manufacturing industry. To better optimize the machining process, the knowledge of shear strains and shear strain rates within the primary shear zone (PSZ) during chip formation has been of great interest. The objective of this study is to study the strain and strain rate progression within the PSZ both in the chip flow direction and along the thickness direction during machining equal channel angular extrusion (ECAE) processed titanium (Ti). ECAE-processed ultrafine-grained Ti has been machined at cutting speeds of 0.1 and 0.5 m/s, and the shear strain and the shear strain rate have been determined using high speed imaging and digital image correlation (DIC). It is found that the chip morphology is saw-tooth at 0.1 m/s while continuous at 0.5 m/s. The cumulative shear strain and the incremental shear strain rate of the saw-tooth chip morphology can reach approximately 3.9 and 2.4 × 103 s−1, respectively, and those of the continuous chip morphology may be approximately 1.3 and 5.0 × 103 s−1, respectively. There is a distinct peak shift in the shear strain rate distribution during saw-tooth chip formation while there is a stable peak position of the strain rate distribution during continuous chip formation. The PSZ thickness during saw-tooth chip formation is more localized and smaller than that during continuous chip formation (28 versus 35 μm).

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Figures

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Fig. 1

(a) Schematic representation of the experimental imaging setup together with an inset showing a typical image of chip formation process and (b) top view of the actual imaging setup implemented on the Whacheon machine lathe

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Fig. 2

Schematic of the deformation measurement directions for (a) cumulative shear strain along the chip flow direction (ABC) and (b) incremental shear strain rate along the chip flow (ABC) and transverse (DEF) directions (S1, S2, and S3 represent the bulk saw-tooth segments, SB1 and SB2 represent shear bands, FS represents the free surface, and W represents the workpiece)

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Fig. 3

(a) Surface texture of machined surface (200 × 200 pixels) and (b) associated normalized autocorrelation functions based on the experiments herein and others [27]

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Fig. 4

High speed camera images for the progression of (a)–(e) saw-tooth chip morphology and (f)–(j) continuous chip morphology

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Fig. 5

Shear strain distribution along the chip flow direction during the progression of three saw-tooth segments at cutting speed of V = 0.1 m/s

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Fig. 6

Shear strain distribution along the chip flow direction for the chip formation progression of a continuous chip at a cutting speed, V = 0.5 m/s

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Fig. 7

Shear strain rate distribution during the development of a single saw-tooth segment along the chip flow direction, machined at a cutting speed of 0.1 m/s. (a) Stage 1: wedge compression/beginning of upsetting, (b) stage 2: upsetting stage, (c) stage 3: instability, (d) stage 4: initial sliding, (e) stage 5: complete sliding, and (f) shift of shear strain rate curves (inset: FWHM thickness of the PSZ).

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Fig. 8

Shear strain rate distribution during the development of a single saw-tooth segment through the chip thickness (parallel to the PSZ), machined at a cutting speed of 0.1 m/s. (a) Stage 1: wedge compression/beginning of upsetting, (b) stage 2: upsetting, (c) stage 3: instability, (d) stage 4: initial sliding, (e) stage 5: complete sliding, and (f) slope of the flattening region along the chip thickness direction.

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Fig. 9

(a) Representative shear strain rate distribution along the chip flow direction (perpendicular) and (b) shift of shear strain rate curves (inset: related FWHM measurements of the PSZ), and (c) representative shear strain rate distribution through the thickness direction and (d) related slope of the shear strain rate of the flattening region at 0.5 m/s

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Fig. 10

Comparison of (a) shear strains and (b) shear strain rates at cutting speeds of 0.1 and 0.5 m/s

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