Research Papers

Influence of Preheating on Chip Segmentation and Microstructure in Orthogonal Machining of Ti6Al4V

[+] Author and Article Information
Suhas Joshi

e-mail: ssjoshi@iitb.ac.in

Department of Mechanical Engineering,
Indian Institute of Technology Bombay,
Powai, Mumbai 400076, India

1Corresponding author.

Manuscript received May 1, 2013; final manuscript received October 13, 2013; published online November 18, 2013. Assoc. Editor: Yung Shin.

J. Manuf. Sci. Eng 135(6), 061017 (Nov 18, 2013) (11 pages) Paper No: MANU-13-1198; doi: 10.1115/1.4025741 History: Received May 01, 2013; Revised October 13, 2013

Chip segmentation due to shear localization during machining of titanium alloys affects cutting forces and their machinability. Despite several studies on modeling and understanding influence of chip segmentation, little is known about the effect of preheating on it. This work therefore, involves orthogonal machining of Ti6Al4V alloy under preheating between 100 °C and 350 °C to investigate chip segmentation, shear band configuration, and microstructure of machined surfaces, through optical and scanning electron microscopy of chips and chip roots. Conceptual models of chip segment formation have been evolved. Shear band formation appears to be the dominant mechanism of chip segmentation up to 260 °C preheating, however at 350 °C, extent of fracture along the shear plane increases. The preheating increases spacing between shear bands in chips, reduces shear band thickness from 21 μm at 100 °C to 8 μm at 350 °C, and ultimately reduces cutting forces fluctuation, and compressive residual stresses in the machined surfaces.

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Fig. 1

Theme of experiment

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Fig. 2

Experimental set up: (a) microstructure of Ti6Al4V in radial direction, (b) quick-stop chip freezing device, and (c) thermal image showing preheating

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Fig. 3

SEM images of chip and segment at different preheating temperatures at a cutting speed of 23.4 m/min and feed rate of 0.11 mm/rev: (a) and (b) at room temperature, (c) and (d) at 100 °C, (e) and (f) at 260 °C, and (g) and (h) at 350 °C

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Fig. 4

Influence of preheating temperatures on ratio of fracture length to shear plane length

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Fig. 5

Analysis of chip morphology: (a) evaluation of segment ratios and (b) variation in segment ratios with the preheating temperature

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Fig. 6

Measurement of (a) shear angle, (b) shear plane length, (c) shear band thickness, and (d) temperature reached during machining

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Fig. 7

Shear energy versus preheating temperature

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Fig. 8

Conceptual model showing influence of preheating temperatures on (a) chip segments and (b) included angle of chip segments at various preheating temperatures

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Fig. 9

Influence of preheating temperature on (a) segment area and (b) strain hardening coefficient

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Fig. 10

(a) and (b) Number of segment formed per mm of chip length at 23.4 m/min

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Fig. 11

(a) and (b) Microstructure of the machined chips obtained at room temperature and at cutting speed of 23.4 m/min and feed rate of 0.11 mm/rev

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Fig. 12

Chip microstructure at a cutting speed of 23.4 m/min and at a preheating temperature of (a) and (b) 100 °C, (c) and (d) 260 °C, and (e) and (f) 350 °C

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Fig. 13

Influence of preheating on (a) spacing between shear band and chip segmentation frequency and (b) shear band thickness

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Fig. 14

Machining affected zone at various preheating temperatures: (a) at room temperature, (b) at 100 °C, (c) at 260 °C, and (d) at 350 °C

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Fig. 15

Analysis of machining affected zone: (a) evaluation of strain beneath the machining affected zone and (b) its variation at various preheating temperatures

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Fig. 16

Influence of preheating temperature on residual stresses at machined surface




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