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TECHNICAL PAPERS

Process Maps for Predicting Residual Stress and Melt Pool Size in the Laser-Based Fabrication of Thin-Walled Structures

[+] Author and Article Information
Aditad Vasinonta

Department of Mechanical Engineering,  Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213

Jack L. Beuth

Department of Mechanical Engineering,  Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213beuth@andrew.cmu.edu

Michelle Griffith

Mechanical Process Engineering,  Sandia National Laboratories, P. O. Box 5800, MS 0958, Albuquerque, NM 87185

J. Manuf. Sci. Eng 129(1), 101-109 (Mar 31, 2006) (9 pages) doi:10.1115/1.2335852 History: Received August 19, 2004; Revised March 31, 2006

Thermomechanical models are presented for the building of thin-walled structures by laser-based solid freeform fabrication (SFF) processes. Thermal simulations are used to develop quasi-non-dimensional plots (termed process maps) that quantify the effects of changes in wall height, laser power, deposition speed, and part preheating on thermal gradients, with the goal of limiting residual stresses in manufactured components. Mechanical simulations are used to demonstrate the link between thermal gradients and maximum final residual stresses. The approach taken is analogous to that taken in previous research by the authors in developing process maps for melt pool length, for maintaining an optimal melt pool size during component fabrication. Process maps are tailored for application to the laser engineered net shaping process; however, the general approach, insights, and conclusions are applicable to most SFF processes involving a moving heat source, and to other laser-based fusion processes. Results from the residual stress simulations identify two mechanisms for reducing residual stresses and quantify maximum stress reductions achievable through manipulation of all process variables. Results from thermal gradient and melt pool length process maps are used to identify a manufacturing strategy for obtaining a consistent melt pool size while limiting residual stress in a thin-walled part.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Thin-walled geometry considered in this study

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Figure 2

Two-dimensional thermomechanical model and boundary conditions

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Figure 3

Process map for melt pool length

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Figure 4

Plot of z¯0 versus T for typical process variables

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Figure 5

Comparison of temperature gradient results from temperature-dependent simulations for three normalizing temperatures with the Rosenthal solution (15)(Tbase=303K)

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Figure 6

Comparison of temperature gradient results from temperature-dependent simulations with a preheated substrate and V=7.62mm∕s with the Rosenthal solution (15)

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Figure 7

Process map for temperature gradient

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Figure 8

Predicted and measured surface temperature profiles behind the laser source

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Figure 9

Relation of maximum final stresses to temperature gradient

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Figure 10

Effect of temperature on the yield stress of SS304

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