Research Papers

Indirect Strain Control in Aluminum Stamp Formed Pans

[+] Author and Article Information
William J. Emblom

Department of Mechanical Engineering,
University of Louisiana at Lafayette,
P.O. Box 44170,
Lafayette, LA 70504
e-mail: wjemblom@louisiana.edu

Manuscript received July 8, 2016; final manuscript received April 1, 2017; published online May 11, 2017. Assoc. Editor: Gracious Ngaile.

J. Manuf. Sci. Eng 139(8), 081013 (May 11, 2017) (10 pages) Paper No: MANU-16-1373; doi: 10.1115/1.4036489 History: Received July 08, 2016; Revised April 01, 2017

A stamp forming die whose flexible blank holder (BH) was designed using finite element (FE) analysis was built. The tooling also included active draw beads, local wrinkling sensors, and local force transducers. Wrinkling was controlled using a proportional–integral–derivative (PID) feedback loop and blank holder force (BHF). Local forces in the tooling were also controlled using blank holder forces in a PID feedback loop. A third closed-loop control system that could be used to control local punch forces (LPF) near draw beads featured an advanced PID controller with a Smith Predictor and Kalman Filter. A Bang–bang controller was also incorporated into that control system in order to prevent control saturation. Fuzzy logic was used to transition from one controller to the other. Once closed-loop control was implemented, tests were performed in order to evaluate the strains in the pans for various forming conditions. These results were compared to open-loop tests and it was found that the strains' paths for closed-loop control tests resulted in convergence and were further from the forming limit than strains from open-loop control tests. Furthermore, it was seen that the strains in critical regions had more uniform strain fields once closed-loop control of local punch forces was implemented. Hence, it was concluded that controlling local punch forces resulted in the indirect control of strains in critical regions.

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Fig. 1

Typical sheet metal stamping operation [9]

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Fig. 2

Process/Press optimization system

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Fig. 3

Aluminum test panel [4]

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Fig. 4

Location of the oval stamp forming research die instrumentation [4]

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Fig. 5

Schematic of forming and photo of lower die with sensors and draw beads [4]

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Fig. 6

Closed-loop control based upon BHP [4]: (a) LPF control and (b) wrinkle control

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Fig. 7

Control of LPF based upon draw beads

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Fig. 8

Demonstration of closed-loop control of LPF [4]: (a) control of LPF using BHF and (b) control of LPF using draw beads

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Fig. 9

Quarter model of the oval pan showing strain paths [4]

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Fig. 10

Strains along path A for various DB positions: BHF = 110 kN and draw depth = 51 mm

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Fig. 11

Strains along path A for various BHF: DB = 3 mm and draw depth = 51 mm

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Fig. 12

Strains along path B for various BHF: BD = 3 mm and draw depth = 51 mm

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Fig. 13

Strains along path B for various DB: BHF = 83 kN and draw depth = 51 mm

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Fig. 14

Strains along path D and Pt B1 for BHF = 83 kN. Inside pan. Open-loop tests. Draw depth = 51 mm.

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Fig. 15

Path D and PT B1 for DB = 3 mm. Inside pan. Open-loop tests. Draw depth = 51 mm.

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Fig. 16

Strains at Pt B1. Inside pan. Draw depth = 51 mm: (a) BHF = 83 kN, DB varies and (b) DB = 1 mm, BHF varies.

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Fig. 17

Forming limit diagram: DB = 8 and BHF = 83 kN (failed at 42 mm draw depth)

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Fig. 18

FLD of path B for various O–L forming conditions: BHF = 83 kN and draw depth = 51 mm

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Fig. 19

FLD of path B for various O–L forming conditions: DB = 3 MM and draw depth = 51 mm

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Fig. 20

Closed-loop control. Strain path A. BHF = 83 kN and draw depth = 51 mm.

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Fig. 21

Strains in straight portion of pan. Draw depth = 51 mm: (a) major strains and (b) minor strains.

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Fig. 22

Strain path B forming limit diagram for closed-loop control of LPF 13 using draw beads: BHF = 83 KN and draw depth = 51 mm

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Fig. 23

Strains for path D and Pt B1 for closed-loop tests, variable corner BHF used to control LPF 15, variable middle BHF controlling wrinkles. DB = 2 mm unless stated. Draw depth = 51 mm.

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Fig. 24

FLD for closed-loop control at die ends. Draw depth = 51 mm.




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