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Research Papers

Finite Element Thermal/Mechanical Analysis of Transmission Laser Microjoining of Titanium and Polyimide

[+] Author and Article Information
Ankitkumar P. Dhorajiya, Mohammed S. Mayeed

Department of Mechanical Engineering, Wayne State University, Detroit, MI

Gregory W. Auner

Department of Electrical and Computer Engineering, Wayne State University, Detroit, MI

Ronald J. Baird

Institute for Manufacturing Research, Wayne State University, Detroit, MI 48202

Golam M. Newaz

Department of Mechanical Engineering, Institute for Manufacturing Research, and Department of Biomedical Engineering, Wayne State University, Detroit, MI

Rahul Patwa, Hans Herfurth

Fraunhofer Center for Laser Technology, Plymouth, MI 48170

J. Eng. Mater. Technol 132(1), 011004 (Nov 03, 2009) (10 pages) doi:10.1115/1.3184031 History: Received August 29, 2008; Revised April 19, 2009; Published November 03, 2009; Online November 03, 2009

Abstract

Detailed analysis of a residual stress profile due to laser microjoining of two dissimilar biocompatible materials, polyimide (PI) and titanium (Ti), is vital for the long-term application of bio-implants. In this work, a comprehensive three-dimensional (3D) transient model for sequentially coupled thermal/mechanical analysis of transmission laser (laser beam with wavelength of 1100 nm and diameter of 0.2 mm) microjoining of two dissimilar materials has been developed by using the finite element code ABAQUS , along with a moving Gaussian laser heat source. First the model has been used to optimize the laser parameters like laser traveling speed and power to obtain good bonding (burnout temperature of $PI>maximum$ temperature of PI achieved during $heating>melting$ temperature of PI) and a good combination has been found to be 100 mm/min and 3.14 W for a joint-length of 6.5 mm as supported by the experiment. The developed computational model has been observed to generate a bonding zone that is similar in width (0.33 mm) to the bond width of the Ti/PI joint observed experimentally by an optical microscope. The maximum temperatures measured at three locations by thermocouples have also been found to be similar to those observed computationally. After these verifications, the residual stress profile of the laser microjoint (100 mm/min and 3.14 W) has been calculated using the developed model with the system cooling down to room temperature. The residual stress profiles on the PI surface have shown low value near the centerline of the laser travel, increased to higher values at about $165 μm$ from the centerline symmetrically at both sides, and to the contrary, have shown higher values near the centerline on the Ti surface. Maximum residual stresses on both the Ti and PI surfaces are obtained at the end of laser travel, and are in the orders of the yield stresses of the respective materials. It has been explained that the patterned accumulation of residual stresses is due to the thermal expansion and contraction mismatches between the dissimilar materials at the opposite sides of the bond along with the melting and softening of PI during the joining process.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

Figure 1

Schematic (a) of the transmission laser joining of two dissimilar materials (titanium and polyimide), and (b) of the 3D geometry of the model

Figure 2

Flowchart for the sequentially coupled thermal/mechanical analysis

Figure 3

Meshing for the finite element model of the laser microjoining

Figure 4

Boundary conditions during cooling

Figure 5

Temperature profiles across the traveling line of the laser beam at a traveling velocity of 100 mm/min and various laser powers

Figure 6

Process diagram for the Ti/PI system using fiber laser

Figure 7

Temperature profiles along the centerline of the traveling laser beam on (a) PI and (b) Ti surfaces

Figure 8

Microscopic picture of the polyimide surface in the bond region (3.14 W and 100 mm/min)

Figure 9

Comparison of the maximum temperatures at three locations: (a) locations of three thermocouples; (b) experimental results versus finite element analysis results

Figure 10

Residual stress contours on the PI and Ti surfaces after cooling the system down to room temperature: (a) von Mises stress on PI; (b) von Mises stress on Ti; (c) σxx on PI; (d) σxx on Ti; (e) σyy on PI; and (f) σyy on Ti

Figure 11

Profiles of σxx plotted transverse to the direction of the laser travel at the middle of the bond length on the (a) PI and (b) Ti surfaces

Figure 12

Temperature and residual stress (von Mises stress) profiles on the PI surface across the centerline of the traveling laser beam: ((a) and (b)) at the start of the laser travel; ((c) and (d)) in the middle of the laser travel; and ((e) and (f)) at the end of the laser travel

Figure 13

Residual stress (von Mises stress) profiles along the centerline of the traveling laser beam on (a) PI and (b) Ti surfaces

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