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Research Papers

Influence of Single Point Incremental Forming on Mechanical Properties and Chain Orientation in Thermoplastic Polymers

[+] Author and Article Information
Mohammad Ali Davarpanah

Department of Mechanical Engineering,
Oregon State University,
Corvallis, OR 97331
e-mail: davarpam@oregonstate.edu

Shalu Bansal

Department of Mechanical Engineering,
Oregon State University,
Corvallis, OR 97331
e-mail: bansals@oregonstate.edu

Rajiv Malhotra

Department of Mechanical Engineering,
Oregon State University,
Corvallis, OR 97331
e-mail: malhotra@oregonstate.edu

1Corresponding author.

Manuscript received December 10, 2015; final manuscript received June 16, 2016; published online September 21, 2016. Assoc. Editor: Yannis Korkolis.

J. Manuf. Sci. Eng 139(2), 021012 (Sep 21, 2016) (9 pages) Paper No: MANU-15-1650; doi: 10.1115/1.4034036 History: Received December 10, 2015; Revised June 16, 2016

Incremental forming of thermoplastic surfaces has recently received significant interest due to the potential for simultaneous reduction in thermal energy consumption and in part-shape specific tooling. This paper examines the mechanical properties and the chain orientation of the formed material in single point incremental forming (SPIF) of amorphous polyvinyl chloride (PVC) and semicrystalline polyamide sheets. Tensile and stress relaxation properties of the formed polymers are compared to those of the unformed polymer. The effect of incremental depth and tool rotation speed on the above properties, and on the temperature rise of the sheet during SPIF, is quantified. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) are used to compare the chain orientation and crystallinity of the formed and the unformed polymers. It is observed that the formed material has greater toughness and ductility, but lower yield stress and reduced Young's modulus, as compared to the unformed material. We also observe deformation-induced chain reorientation in the formed polymer, with minimal change in the degree of crystallinity. The link between the SPIF process parameters, temperature rise of the polymer during SPIF, change in chain orientation, and change in mechanical properties of the polymer is discussed.

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Figures

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Fig. 1

Schematic of the SPIF process

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Fig. 2

(a) Experimental SPIF setup, (b) schematic of part, specimen, tool, toolpath, and incremental depth in SPIF, and (c) unformed and formed tensile test samples of polyamide and PVC, and the inset shows thickness distribution along gauge length at five different points

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Fig. 3

Tensile stress–strain curves for (a) unformed PVC and formed PVC with (b) Δz = 1.4 mm, (c) Δz = 1.8 mm, and (d) Δz = 2.0 mm at different ω

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Fig. 4

(a) Yield stress, (b) UTS, (c) true strain at failure, and (d) elastic modulus for formed and unformed PVC

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Fig. 5

Tensile stress–strain curves for (a) unformed polyamide and formed polyamide with (b) Δz = 1.4 mm, (c) Δz = 1.8 mm, and (d) Δz = 2.0 mm at different ω

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Fig. 6

(a) Yield stress, (b) UTS, (c) true strain at failure, and (d) elastic modulus for formed and unformed polyamide

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Fig. 7

(a) Relaxation test curves and (b) percentage stress reduction for the formed and unformed PVC

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Fig. 8

(a) Relaxation test curves and (b) percentage stress reduction for the formed and unformed polyamide

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Fig. 9

Thermal image of PVC during SPIF at (a) Δz = 1.4 mm, ω = 0 rpm, (b) Δz = 2.0 mm, ω = 1000 rpm, and (c) PVC temperatures at different Δz and ω

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Fig. 10

Thermal image of polyamide during SPIF at (a) Δz = 1.4 mm, ω = 0 rpm, (b) Δz = 2.0 mm, ω = 5000 rpm, and (c) polyamide temperatures at different Δz and ω

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Fig. 11

Integrated intensity versus 2θ curves of unformed PVC and formed PVC for (a) ω = 0 rpm, (b) ω = 500 rpm, and (c) ω = 1000 rpm at different Δz

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Fig. 12

Integrated intensity versus 2θ curves for the unformed polyamide and the formed polyamide for (a) ω = 0 rpm, (b) ω = 1000 rpm, and (c) ω = 5000 rpm at different Δz

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Fig. 13

(a) Representative thermograms of PVC for the unformed material and for the material formed at Δz = 2.0 mm and ω = 1000 rpm, (b) thermograms of polyamide with different Δz and ω, and (c) degree of crystallinity of formed and unformed polyamide

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