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Research Papers

Glues Make Gummy Metals Easy To Cut

[+] Author and Article Information
Anirudh Udupa

Center for Materials Processing and Tribology,
School of Industrial Engineering,
Purdue University,
West Lafayette, IN 47907
e-mail: audupa@purdue.edu

Tatsuya Sugihara

Associate Professor
Department of Mechanical Engineering,
Osaka University,
Suita, Osaka 565-0871, Japan
e-mail: t-sugihara@mech.eng.osaka-u.ac.jp

James B. Mann

Assistant Professor
Department of Mechanical Engineering,
University of West Florida,
Pensacola, FL 32514
e-mail: jbmann@uwf.edu

1Corresponding author.

Manuscript received May 7, 2019; final manuscript received June 26, 2019; published online July 26, 2019. Editor: Y. Lawrence Yao.

J. Manuf. Sci. Eng 141(9), 091011 (Jul 26, 2019) (5 pages) Paper No: MANU-19-1272; doi: 10.1115/1.4044158 History: Received May 07, 2019; Accepted June 27, 2019

Metals such as Cu, Al, Ni, Ta, and stainless steels, despite their softness and ductility, are considered difficult to machine. This is due to large cutting forces and corresponding formation of a very thick chip during cutting, and hence, these metals are referred to as “gummy.” Their poor machinability of these materials arises because of an unsteady and highly redundant mode of plastic deformation referred to as sinuous flow. The prevailing plastic deformation mode during machining can be overcome by the application of certain coatings and chemical media on the undeformed free surface of the workpiece ahead of the cutting process. Using in situ imaging and concurrent force measurements, we present two different mechanochemical routes through which these media can improve machinability. The first route, which requires chemicals that adhere to the metal surface, such as glues and inks, improves cutting by inducing a change in the local plastic deformation mode—from sinuous flow to one characterized by periodic fracture or segmented flow. The second route, which requires chemicals that can react with the workpiece to form a low-friction layer, changes the sinuous flow mode to a smooth, laminar one. Both routes decrease cutting forces by more than 50% with order of magnitude improvement in surface texture as characterized by measured roughness and defect density. The results suggest a broad range of opportunities for improving the performance of machining processes for many difficult-to-cut gummy metals.

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References

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Figures

Grahic Jump Location
Fig. 1

Schematic of the experimental setup used for cutting experiments. The SA medium is applied to part of the workpiece surface. In situ observation of the deformation flow field via a high-speed camera gives high-resolution flow field information. The width of the workpiece into the plane (b) is equal to the chip width.

Grahic Jump Location
Fig. 2

Large drop in the forces is the characteristic feature of the mechanochemical effect. (a) Cutting and thrust components of the force when cutting annealed Cu with a α = 0 deg tool. The latter half of the workpiece surface is coated with ink 1 (see inset). (b) Cutting force for annealed Al with a α = 30 deg tool. The workpiece surface is coated at regular intervals along the length with spots of ink 1 (see inset). The force now oscillates at a frequency corresponding to the spatial frequency of the ink spots. h0 = 50 μm, V0 = 2 mm/s.

Grahic Jump Location
Fig. 3

Strain fields in cutting of annealed Cu (α = 0 deg) obtained from the high-speed in situ imaging (a) without application of the SA medium. The flow (sinuous) is characterized by large-amplitude folding (wavy streaklines) and large nonhomogeneous strains (von Mises strain field) and (b) after applying glue 1 to the workpiece surface. The chip now consists of a series of cracks that nucleate from the free surface and is significantly thinner than that with sinuous flow. This flow mode represents segmented flow. α = 0 deg, h0 = 50 μm, V0 = 2 mm/s.

Grahic Jump Location
Fig. 4

Force in shear deformation under dry condition and in an IPA bath. (a) Cutting force (Fc) and (b) thrust force (Ft). Fc and Ft in IPA cutting are smaller by an order of magnitude compared to dry cutting.

Grahic Jump Location
Fig. 5

Streaklines in cutting of annealed Al (α = 0 deg) obtained from the high-speed in situ imaging (a) under dry conditions. The flow is sinuous, characterized by wavy streaklines and (b) in a bath of IPA. The flow is now smooth and laminar, and the chip is significantly thinner than that with sinuous flow. α = 10 deg, h0 = 50 μm, V0 = 5 mm/s.

Grahic Jump Location
Fig. 6

Cutting force in annealed Cu for dry and IPA cutting (α = 0 deg, h0 = 50 μm, V0 = 5 mm/s). In contrast to the Al cutting, IPA has no effect on cutting force in the Cu.

Grahic Jump Location
Fig. 7

3D surface profiles of machined annealed Cu surface obtained by optical profilometry. (a) With sinuous flow, large pit-like surface defects are observed. (b) With the SA medium (glue 1) applied, an order of magnitude improvement in the cut surface quality is observed, as quantified by average pit size, pit density, and surface roughness (Ra). α = 0 deg, h0 = 50 μm, V0 = 2 mm/s.

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