Research Papers

Optimization of Preform Design in Tadeusz Rut Forging of Heavy Crankshafts

[+] Author and Article Information
Min Churl Song

Forging Engineering Team,
Hyundai Steel, Co. Ltd,
Suncheon 58034, South Korea
e-mail: kalsong@hyundai-steel.com

Chester J. VanTyne

Department of Metallurgical
and Materials Engineering,
Colorado School of Mines,
Golden, CO 80401
e-mail: cvantyne@mines.edu

Jin Rae Cho

Department of Naval Architecture
and Ocean Engineering,
Hongik University,
Sejong 339-701, South Korea
e-mail: jrcho@hongik.ac.kr

Young Hoon Moon

School of Mechanical Engineering,
Pusan National University,
30 Jangjeon-dong, Geumjeong-gu,
Busan 609-735, Korea
e-mail: yhmoon@pusan.ac.kr

1Corresponding author.

Manuscript received January 14, 2017; final manuscript received June 3, 2017; published online July 20, 2017. Assoc. Editor: Gracious Ngaile.

J. Manuf. Sci. Eng 139(9), 091014 (Jul 20, 2017) (13 pages) Paper No: MANU-17-1025; doi: 10.1115/1.4037039 History: Received January 14, 2017; Revised June 03, 2017

Tadeusz Rut (TR) forging is a widely used forging method to create heavy, solid crankshafts for marine or power-generating engines. The preform of a TR forging is forged into a crank throw by simultaneously applying both a vertical and a horizontal deformation. It is necessary to optimize the preform design, since a conventional analytical design for the preform gives various choices for the geometric variables. The purpose of the current study is to optimize the preform design in TR forging for heavy crankshafts in order to improve the dimensional accuracy of a forged shape using a limited material volume. A finite element (FE) model for TR forging was developed and validated by comparing with experimental results. Parametric FE analyses were used to evaluate the effects of the geometric variables of the preform on the final dimensions of the forged product. The geometric variables of the preform were optimized by a response-surface method (RSM) to obtain the results of parametric FE analyses. The volume allocation between the pin and the web of the preform is the dominant factor that affects the desirability of the final forged shape. A multi-objective optimization is employed to consider the mutually exclusive changes of local machining allowances of the final forged product. Optimization using a response-surface method is a useful tool to reach the large and uniform machining allowances that are required for the preform necessary for a TR forging.

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Fig. 1

Heavy crankshaft for marine or power-generating engine: (a) after forging, (b) after machining, and (c) sequential forging process for a single crank throw in a TR forging

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Fig. 2

Schematic drawing of a TR forging for a single crank throw: (a) initial state and (b) final state

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Fig. 3

Kinematic characteristics of a TR device: (a) conversion of vertical press deformation into horizontal and (b) correlation between vertical and horizontal stroke

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Fig. 4

Assumption of volume allocation for the preform design of a TR forging in the conventional analytic design

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Fig. 5

Forging test for the prototype: (a) TR forging device attached to the press, (b) the position of preform in the dies, (c) shape immediately after forging, and (d) forged crank throw

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Fig. 6

Measurement of local machining allowance: (a) 3D coordinate measurement and (b) evaluation of local machining allowance by comparing measured coordinates on the forged product with the machined model

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Fig. 7

Finite element model for TR forging

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Fig. 8

Mesh and dimensions of preform for the prototype forging test

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Fig. 9

Measured flow stress of AISI 4140 steel: (a) strain rate 0.5/s and (b) strain rate 0.05/s

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Fig. 10

Change of forged shape during progress of the TR forging

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Fig. 11

Results of forging analysis at the final state: (a) temperature and (b) effective strain

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Fig. 12

Forging load from finite element analysis for the prototype forging test

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Fig. 13

Machining allowance distribution of the forged shape from FE analysis for the prototype forging test

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Fig. 14

Decrease of machining allowance due to the underfill: (a) CW and (b) PF

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Fig. 15

Flow chart for optimization of the preform design

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Fig. 16

Options of volume allocation in the preform design

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Fig. 17

Main effects plots of design variables on the preform geometry: (a) web diameter (Dpw), (b) web length (Lpw), and (c) pin length (Lpp)

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Fig. 18

Response surface of the design variables for the machining allowances: (a) CW, (b) PF, and (c) PT

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Fig. 19

Optimum zone of the design variables for trial no. 3

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Fig. 20

Comparison of maximum and minimum machining allowance between the parametric FE results and the optimum of trial no. 3

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Fig. 21

Optimization result: (a) comparison of preform between the test forging and optimum and (b) machining allowance distribution from FE analysis for the optimum preform




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