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Research Papers

Effect of Profile Corners on the Nitriding Treatment of AISI H13 Hot Extrusion Dies

[+] Author and Article Information
Syed Sohail Akhtar

Mechanical Engineering Department,
King Fahd University of Petroleum & Minerals,
Dhahran 31261, Saudi Arabia
e-mail: ssakhtar@kfupm.edu.sa

Abul Fazal M. Arif

Mechanical Engineering Department,
King Fahd University of Petroleum & Minerals,
Dhahran 31261, Saudi Arabia
e-mail: afmarif@kfupm.edu.sa

1Corresponding author.

Manuscript received January 10, 2013; final manuscript received October 9, 2013; published online January 16, 2014. Assoc. Editor: Donggang Yao.

J. Manuf. Sci. Eng 136(2), 021010 (Jan 16, 2014) (9 pages) Paper No: MANU-13-1010; doi: 10.1115/1.4025911 History: Received January 10, 2013; Revised October 09, 2013

One of the utmost challenges of hot aluminum extrusion is to design the die cavities with sharp corners (used to extrude thin-walled profiles) by considering the effective nitriding surface treatment of the die bearing surface in terms of nitride layer uniformity. In the present study, various AISI H13 steel samples (having commonly used profile geometric features) are manufactured using wire electro-discharge machining (EDM) and subsequently nitrided using two-stage controlled nitriding treatment. As a special case, corner features are investigated in terms of compound and nitride layers formation using optical and scanning electron microscopes. Finite element (FE) code abaqus is used to simulate the nitriding process using mass diffusion analysis in line with experimental set up. Both experimental and numerical results are found in close agreement in terms of nitrogen concentration and corresponding microhardness profiles. Some design modifications are implemented in FE code for corner profile features for uniform nitride layer development. In view of the current results, some design guidelines are suggested for effective and uniform nitride layer formation in order to secure high quality extruded product and extended die life.

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Figures

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Fig. 5

(a) Finite element geometric model and mesh layout and (b) the studied profiles are shown in close-up

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Fig. 4

Selected die profiles and geometric features. (a) external and internal corner features selected in path brush and (b) external and internal corner features in tip.

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Fig. 3

In-process variations of temperature (a) and nitriding potential, Kn (b) during two-stage nitriding of AISI H13 samples having different geometric profiles [8].

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Fig. 2

(a) Sample after EDM wire cutting and (b) dimensional drawings of the studied profiles (all dimensions are in millimeter)

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Fig. 1

Representative extruded profile drawings used in the study. (a) Profile depicting extruded path brush and (b) profile depicting tip

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Fig. 7

Optical micrograph (a) and scanning electron micrograph (b) of nitrided cross section observed at internal corner (IC-2)

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Fig. 8

Hardness-depth profiles for path- brush and tip features

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Fig. 9

(a) Numerically predicted nitrided layer for features EC-1 and IC-1 and (b) Numerically predicted nitrided layer for features EC-2 and IC-2 at the end of nitriding cycle. The nitrogen concentration is in atoms/mm3.

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Fig. 10

Nitrogen concentration profiles for features EC-1, EC-2, IC-1, and IC-2 at the end of nitriding cycle

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Fig. 6

Optical micrograph (a) and scanning electron micrograph (b) of nitrided cross section observed at external corner (EC-1)

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Fig. 11

Nitrogen concentration contours for the path-brush modified features. (a) Original features, (b) when fillet radius of 0.2 mm is used, and (c) when fillet radius of 0.5 mm is used

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