Research Papers

Investigation and Correction of Surface Distortion in Dies With Typical Depression Features

[+] Author and Article Information
Hui-Ping Wang

 Staff Researcher GM Research and Development Center, Mail Code 480-106-224, 30500 Mound Road, Warren, MI 48090hui-ping.wang@gm.com

Kunmin Zhao, Ping Hu, Zhengchun Fu

Jing-Ru Bao

 Dalian University of Technology, No. 2 Linggong Road, Dalian, 116024 Chinajingrubao@gmail.com

J. Manuf. Sci. Eng 133(4), 041004 (Jul 20, 2011) (10 pages) doi:10.1115/1.4004405 History: Received December 06, 2009; Revised June 08, 2011; Published July 20, 2011; Online July 20, 2011

Surface distortions are frequently introduced into Class “A” surfaces during various sheet metal forming operations such as drawing, trimming, and flanging. The origins of these surface distortions have not been well understood. The scope of this research is to investigate the distortion that occurs in the draw operation and to find effective and practical corrective methods. Five geometric parameters are first identified to represent typical depression features in automobile outer panels. Experimental dies are then designed to reflect various combinations of these five geometric parameters with the assistance of numerical simulations to ensure that the dies can make parts free of major defects such as splits and wrinkles. Surface distortions are observed in our stamping experiments and various techniques are used to measure and record the distortions for further mathematical analysis. Historical data of strains and deflections in distortion areas are collected through real-time measurement. The effects of three geometric parameters on distortion are analyzed using a full factorial DOE model. A geometry morphing program based on UG-NX platform is developed. The program is used to morph the die face in the distortion areas. Finally, three approaches that aim to correct distortions are tried out and the die morphing proves to be a practical and effective method.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Typical surface distortion in automotive skin panels

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Figure 2

Illustration of geometric variables and die setup

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Figure 3

Plan view of four basic depression shapes

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Figure 4

Cross-sectional view of the die design with depression shape in center

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Figure 5

Three-dimensional wireframe view of the solid die design

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Figure 6

(a) Upper die assembly. (b) Lower die assembly. (c) 16 pairs of interchangeable die inserts.

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Figure 7

Illustration of displacement sensors installed in low die

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Figure 8

Representative stamped specimens

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Figure 9

(a) Stoned specimen with αP  = 60 deg, RP  = 20 mm, and H = 5 mm. (b) Stoned specimen with αP  = 90 deg, RP  = 20 mm, and H = 5 mm. (c) Stoned specimen with αP  = 120 deg, RP  = 20 mm, and H = 5 mm.

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Figure 10

Distortion characteristics of specimen with αP  = 60 deg, RP  = 20 mm, and H = 5 mm

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Figure 11

Main effect of depression depth, plan view radius, and plan view angle on distortion magnitude

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Figure 12

A surface contour from the laser scanning

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Figure 13

Draw-in comparison between experimental measurement and numerical simulation (unit: mm)

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Figure 14

(a) Surface contour from the numerical simulation. (b) Zebra lines of the predicted numerical surface

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Figure 15

Strain histories from measurement and simulation

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Figure 16

Displacement history from measurement

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Figure 17

Revised upper die for good bearing

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Figure 18

Laser scan of the part with proper die bearing

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Figure 19

Stamped part for a blank with stress-relieving holes

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Figure 20

Surface distortion of a part when stress-relieving holes are designed in its blank

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Figure 21

Geometry morphing algorithms: (a) original B-spline surface; (b) morphed surface based on Gaussian function; (c) morphed surface based on parabolic function; (d) morphed surface based on quadratic spline function

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Figure 22

Surface morphing program based on UG-NX platform

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Figure 23

Morphed low die (four corners)

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Figure 24

Surface contour of the specimen stamped with the morphed die




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