Research Papers

Microtexturing Into AISI-SUS420 Molds for Injection Molding Via Plasma Nitriding

[+] Author and Article Information
T. Aizawa

Department of Materials
Science and Engineering,
Shibaura Institute of Technology,
3-9-14 Shibaura, Minato-City,
Tokyo 108-8548, Japan
e-mail: taizawa@sic.shibaura-it.ac.jp

H. Suga

Department of Engineering and Design,
Shibaura Institute of Technology,
3-9-14 Shibaura, Minato-City,
Tokyo 108-8548, Japan
e-mail: i032544@shibaura-it.ac.jp

T. Nagata

Graduate School of Engineering,
Shibaura Institute of Technology,
3-9-14 Shibaura, Minato-City,
Tokyo 108-8548, Japan
e-mail: mb15040@shibaura-it.ac.jp

T. Yamaguchi

Division of Research and Development,
Sanko-Light Industry, Co., Ltd.,
Ue-kotanaka 6-22-10, Nakahara-City,
Kawasaki 211-0053, Japan
e-mail: yamaguchi@slkco.jp

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received September 20, 2015; final manuscript received January 30, 2017; published online March 23, 2017. Editor: Jian Cao.

J. Micro Nano-Manuf 5(2), 021004 (Mar 23, 2017) (8 pages) Paper No: JMNM-15-1070; doi: 10.1115/1.4035953 History: Received September 20, 2015; Revised January 30, 2017

The initial microdot and microline patterns were first ink-jet printed onto the surface of polished AISI420 stainless steel mold. This masked mold substrate was nitrided at 693 K for 7.2 ks at 70 Pa by using the high-density plasma nitriding system. The unmasked parts were selectively nitrided to have higher hardness than 1200 HV. This hardness-profiled substrate was mechanically sand-blasted to fabricate the microtextured mold. Microdisk patterned plastic cover-case for cellular phones were injection-molded by using this method for practical demonstration. Both the selective hardening and anisotropic inner nitriding processes were experimentally discussed as a key step in the present processing.

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Fig. 1

An experimental procedure of the plasma printing: 1. ink-jet printing, 2. plasma nitriding, 3. sand–blasting, and 4. microtextured mold

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Fig. 2

Ink-jet printing process: (a) setup of nozzle head for directly printing onto the surface of mold substrate and (b) test-patterns for the ink-jet printing to investigate the special resolution in practice

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Fig. 3

High-density plasma nitriding system: (1) vacuum chamber, (2) RF/DC generators, (3) controlling panel, (4) RF/DC power supply, (5) evacuation units, and (6) carrier supply and control

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Fig. 4

Sand-blasting system: (a) chamber with rubber hand-gloves and (b) nozzle and air-pressurizing unit in the chamber

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Fig. 5

SUS420-HRC40 specimen with the printed microdots and lines

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Fig. 6

SUS420-HRC40 specimen after plasma nitriding

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Fig. 7

Hardness profile across the two lines on the surface of plasma-nitrided SUS420-HRC40 specimen

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Fig. 8

SUS420-HRC40 specimen after sand-blasting

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Fig. 9

Microtextures on the blasted SUS420-HRC40 specimen: (a) optical microscopic image and (b) surface profile of microtextures on the blasted SUS420-HRC40

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Fig. 10

Microtextured SUS420-HRC40 mold: (a) a microtextured SUS420-HRC40 mold for injection molding the 65 × 120 mm2 plastic cover case and (b) SEM image and surface profile of microdimple pattern formed in this mold

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Fig. 11

Injection-molded plastic cover case of cellular phone: (a) optical microscopic image of microdisks duplicated on the surface of plastic case and (b) surface profile of microdisk pattern

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Fig. 12

Selectively hardened SUS420-HRC30 specimen: (a) two-line masked SUS420-HRC30 specimen after plasma nitriding at 693 K for 7.2 ks and (b) hardness profile measured along the white line in (a) across the two masked lines

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Fig. 13

Nitrogen mapping by EDX in the cross section of nitrided SUS420-HRC30 specimen

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Fig. 14

Evaluation on the injection mold surface and microtextured plastic cover-case after continuous injection molding operation for 10.8 ks or 3 h: (a) the microtextured mold after continuous molding operation and (b) optical microscope image of microdisk alignment on the plastic cover case



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