Research Papers

The Origin of Flank Wear in Turning Ti-6Al-4V

[+] Author and Article Information
Trung Nguyen

Department of Mechanical Engineering,
Hanoi University of Science and Technology,
Room C112,
C5 building, No. 1,
Dai Co Viet Road,
Hanoi, Vietnam
e-mail: rockhomedo@gmail.com

Patrick Kwon

Department of Mechanical Engineering,
Michigan State University,
East Lansing, MI 48824
e-mail: pkwon@egr.msu.edu

Di Kang

Department of Chemical Engineering and
Materials Science,
Michigan State University,
East Lansing, MI 48824
e-mail: Kangdi@egr.msu.edu

Thomas R. Bieler

Department of Chemical Engineering and
Materials Science,
Michigan State University,
East Lansing, MI 48824
e-mail: bieler@egr.msu.edu

1Corresponding author.

Manuscript received August 10, 2015; final manuscript received June 9, 2016; published online September 29, 2016. Assoc. Editor: Radu Pavel.

J. Manuf. Sci. Eng 138(12), 121013 (Sep 29, 2016) (12 pages) Paper No: MANU-15-1401; doi: 10.1115/1.4034008 History: Received August 10, 2015; Revised June 09, 2016

Unlike ferrous materials, where the cementite (Fe3C) phase acts as an abrasive that contributes to flank wear on the cutting tool, most titanium (Ti) alloys possesses no significant hard phase. Thus, the origin of flank wear is unclear in machining Ti alloys. To address this question, a Ti-6Al-4V bar was turned under various conditions with uncoated carbide and polycrystalline diamond (PCD) inserts, most commonly used tool materials for machining Ti alloys. These inserts were retrieved sporadically while tuning to examine the wear patterns using a confocal microscope. To correlate the patterns with the microstructure of the original bar, the microstructure was carefully characterized using Orientation Image Microscopy (OIM) with electron-backscattered diffraction (EBSD). From the wear patterns, two distinct types of damage were identified: (a) microscopic and macroscopic fractures on the cutting edges and (b) scoring marks on flank faces. This paper demonstrates that both types of damage were caused primarily by the heterogeneity in hardness in the α-crystals, where the plane perpendicular to the c-axis in an α-crystal is substantially harder than any other direction in the α-crystal as well as the isotropic β-crystal. In addition to such heterogeneities, adhesion layer, ubiquitous to machining Ti alloys, detaches small fragments of the tool, which resulted in microscopic and macroscopic fractures observed on flank wear.

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Fig. 1

Scoring marks on the flank face of inserts in machining of Ti alloys

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Fig. 2

Tool wear observed in machining Ti alloys

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Fig. 3

The geometric transformation on the tool nose: (a) 2D view, (b) 3D natural view, and (c) 3D transformed view

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Fig. 4

Sectioned Bulk-Ti for EBSD and scan areas

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Fig. 5

The configuration of the turning experiment and chip flow direction

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Fig. 6

Microstructure of Bulk-Ti (α: dark, β: white)

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Fig. 7

Hardness of a single α-grain as a function of the declination angle [after 36]

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Fig. 8

The cutting plane in the workmaterial (denoted as B) with the hard α-crystal respected to flank face of tool

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Fig. 9

The arrangement of the hard α-crystals (darker color) in 3 samples at two distinct rotation angles: (a) at rotation angle of 0 deg and (b) at rotation angle of 90 deg

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Fig. 10

Flank wear evolution of carbide inserts in three cutting speeds

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Fig. 11

The flank wear evolution of PCD inserts in three cutting speeds

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Fig. 12

Comparison of flank wear land on carbides and PCD inserts in all cutting speeds

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Fig. 13

The size of hard α-cluster in Bulk-Ti and interaction of the hard α-cluster and the tools: (a) size estimation of the hard α-clusters on Sample A and (b) interaction of hard α-cluster and tool in straight turning

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Fig. 14

The scoring marks on the carbides and PCD inserts

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Fig. 15

Adhesion layer on the rake face of YD101 and PCD inserts

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Fig. 16

Width (μm) of ten scoring marks on YD101 insert

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Fig. 17

Range and distribution of width of scoring marks on flank face respect to “hard” α-cluster size: (a) Vc = 200 sfm, DOC = 0.635 mm, (b) Vc = 300 sfm, DOC = 0.635 mm, and (c) Vc = 400 sfm, DOC = 0.635 mm

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Fig. 18

Classifying of scoring marks on YD101 (Left: confocal image, Right: SEM image)

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Fig. 19

Classifying of scoring marks on PCD1200 (Left: confocal image, Right: SEM image

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Fig. 20

Cutting Ti64 with two planes respected to different microstructures: (a) straight turning (cutting microstructure in XY plane) and (b) face turning (cutting microstructure in YZ or XZ plane)

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Fig. 21

Scoring marks on flank face with YD101 at cutting speed 91 m/min, DOC = 1.2 mm: (a) inserts in face turning and (b) inserts in straight turning

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Fig. 22

Width of scoring marks on flank face of YD101 inserts in straight turning and face turning




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