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Research Papers

Brittle Removal Mechanism of Ductile Materials With Ultrahigh-Speed Machining

[+] Author and Article Information
Bing Wang

Key Laboratory of High Efficiency and
Clean Mechanical Manufacture,
School of Mechanical Engineering,
Shandong University,
Jinan 250061, Shandong, China
e-mail: sduwangbing@gmail.com

Zhanqiang Liu

Key Laboratory of High Efficiency and
Clean Mechanical Manufacture,
School of Mechanical Engineering,
Shandong University,
Jinan 250061, Shandong, China
e-mail: melius@sdu.edu.cn

Guosheng Su

School of Mechanical and Automotive Engineering,
Qilu University of Technology,
Jinan 250353, Shandong, China
e-mail: guoshengsu@126.com

Xing Ai

Key Laboratory of High Efficiency and
Clean Mechanical Manufacture,
School of Mechanical Engineering,
Shandong University,
Jinan 250061, Shandong, China
e-mail: aixing@sdu.edu.cn

1Corresponding author.

Manuscript received May 10, 2014; final manuscript received June 5, 2015; published online September 9, 2015. Assoc. Editor: Patrick Kwon.

J. Manuf. Sci. Eng 137(6), 061002 (Sep 09, 2015) (9 pages) Paper No: MANU-14-1276; doi: 10.1115/1.4030826 History: Received May 10, 2014

Material removal mechanism depends on the material property and machining parameters during machining process. This paper investigates the brittle removal mechanism of ductile materials with ultrahigh-speed machining. Based on the theory of stress wave propagation, the prediction model of critical cutting speed for ultrahigh-speed machining is proposed. The predicted critical cutting speed values are then validated with ultrahigh-speed machining experiments of Inconel 718 and 7050-T7451 aluminum alloy at the cutting speeds range from 50 m/min to 8000 m/min. The experimental results show that fragmented chips are produced above the critical cutting speed of 7000 m/min for Inconel 718 and 5000 m/min for 7050-T7451 aluminum alloy. The scanning electron microscopy (SEM) micrographs of fragmented chip fracture surface and finished workpiece surface are analyzed. Large amounts of cleavage steps and brittle cracks are observed on the fragmented chip surface. With the brittle cracks remains, the finished surface quality of ultrahigh-speed machining is worse than that of high-speed machining. The results show that the material property undergoes ductile-to-brittle transition so the brittle regime machining of ductile materials can be implemented with ultrahigh-speed machining. Taking both the machining efficiency and machining quality into account, the ultrahigh-speed machining is recommended to apply in rough machining or semifinishing, while high-speed machining is recommended to apply in finishing process. In the end, the definition and essence of ultrahigh-speed machining are concluded. This paper is enticing from both the engineering and the analytical perspectives aimed at revealing the mechanism of ultrahigh-speed machining and optimizing the machining parameters.

Copyright © 2015 by ASME
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Figures

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Fig. 1

Effects of loading rate on material strength

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Fig. 2

Strain rate range reached in different metalworking processes and corresponding response of material behavior

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Fig. 3

Outline of this study

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Fig. 4

Brittle removal of materials under impact loading (a) cutting process and (b) impact process

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Fig. 5

Stress distribution of an element body in the removed layer of cutting process

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Fig. 6

Static stress–strain curves of Inconel 718 and 7050-T7451 aluminum alloy [23,24]

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Fig. 7

Experimental setup of ultrahigh-speed machining

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Fig. 8

SEM micrographs of slide surface on serrated segments (a) workpiece: Inconel 718, cutting speed: 800 m/min, and uncut chip thickness: 0.10 mm and (b) workpiece: 7050-T7451 aluminum alloy, cutting speed: 2500 m/min, and uncut chip thickness: 0.10 mm

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Fig. 9

SEM micrographs of fracture surface on fragmented chips (workpiece: Inconel 718, cutting speed: 7000 m/min, and uncut chip thickness: 0.10 mm)

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Fig. 10

SEM micrographs of fracture surface on fragmented chips (workpiece: 7050-T7451 aluminum alloy, cutting speed: 5000 m/min, and uncut chip thickness: 0.10 mm)

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Fig. 11

Micrographs of fracture surface on fragmented chips (a) optical micrograph and (b) SEM micrograph of fracture surface (workpiece: 7050-T7451 aluminum alloy, cutting speed: 7000 m/min, and uncut chip thickness: 0.10 mm)

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Fig. 12

Experimental setup for capture of chip roots with orthogonal cutting (a) arrangement of the experimental setup, (b) workpiece for chip root experiments, and (c) schematic diagram of chip root experiments

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Fig. 13

SEM micrographs of fracture surface on the chip roots (a) and (b) cutting speed: 2500 m/min; (c) and (d) cutting speed: 7000 m/min (workpiece: 7050-T7451 aluminum alloy and uncut chip thickness: 0.10 mm)

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Fig. 14

SEM micrographs of finished surface under different cutting speeds (workpiece: Inconel 718 and uncut chip thickness: 0.10 mm) (a) cutting speed: 800 m/min and (b) cutting speed: 7000 m/min

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Fig. 15

Division of different machining phases based on chip morphology and deformation mechanism

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