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Research Papers

Investigation on the Effects of Process Parameters on Defect Formation in Friction Stir Welded Samples Via Predictive Numerical Modeling and Experiments

[+] Author and Article Information
Abhishek Ajri

School of Mechanical Engineering,
Purdue University,
West Lafayette, IN 47907

Yung C. Shin

Fellow ASME
School of Mechanical Engineering,
Purdue University,
West Lafayette, IN 47907
e-mail: shin@purdue.edu

1Corresponding author.

Manuscript received June 12, 2017; final manuscript received June 22, 2017; published online September 13, 2017. Assoc. Editor: Wayne Cai.

J. Manuf. Sci. Eng 139(11), 111009 (Sep 13, 2017) (10 pages) Paper No: MANU-17-1370; doi: 10.1115/1.4037240 History: Received June 12, 2017; Revised June 22, 2017

Setting optimum process parameters is very critical in achieving a sound friction stir weld joint. Understanding the formation of defects and developing techniques to minimize them can help in improving the overall weld strength. The most common defects in friction stir welding (FSW) are tunnel defects, cavities, and excess flash formation, which are caused due to incorrect tool rotational or advancing speed. In this paper, the formation of these defects is explained with the help of an experimentally verified 3D finite element (FE) model. It was observed that the asymmetricity in temperature distribution varies for different types of defects formed during FSW. The location of the defect also changes based on the shoulder induced flow and pin induced flow during FSW. Besides formation of defects like excess flash, cavity defects, tunnel/wormhole defects, two types of groove like defects are also discussed in this paper. By studying the different types of defects formed, a methodology is proposed to recognize these defects and counter them by modifying the process parameters to achieve a sound joint for a displacement-based FSW process.

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Figures

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Fig. 1

Effect of process parameters on defect formation (adapted from Podržaj et al. [2])

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Fig. 2

Experimental setup for FSW of Al 7075 T6 butt welds

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Fig. 3

Temperature cycle recorded by thermocouple and pyrometer at emissivity of 0.16

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Fig. 5

Boundary conditions used in the CEL model

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Fig. 6

Spot chosen in front of tool to record the temperature cycle in the FE model

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Fig. 7

(a) Equivalent plastic strain distribution and (b) etched friction stir weld cross section (AS—advancing side; RS—retreating side)

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Fig. 8

Cross section a-a measuring peak temperature distribution during the formation of the weld cross section and cross section b-b showing fully formed weld microstructure

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Fig. 9

Effect of process parameters on defect formation in FSW

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Fig. 10

Temperature distribution during tunnel defect formation

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Fig. 11

Tunnel defect observed in the bottom half of the advancing side of the weld (as viewed from cross section B-B). (narrow long arrow—shoulder induced flow; wide short arrow—pin induced flow).

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Fig. 12

(a) Experimental and simulation results of tunnel defect formation and (b) top view of weld and material velocity distribution in friction stir weld

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Fig. 13

Groove-like defect (type B) observed in the top half of the advancing side of the weld (as viewed from cross section B-B). (top arrow—shoulder induced flow; bottom arrow—pin induced flow).

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Fig. 14

(a) Experimental and simulation results of groove-like type b defect formation and (b) top view of weld and material velocity distribution in friction stir weld. (AS—advancing side, RS—retreating side, LE—leading edge, TE—trailing edge).

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Fig. 15

Groove-like defect (type A) observed in the top half of the advancing side of the weld (as viewed from cross section B-B). (top arrow—shoulder induced flow; bottom arrow—pin induced flow).

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Fig. 16

Temperature distribution during groove defect type B formation

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Fig. 17

Cavity defect observed in the bottom half of the advancing side of the weld (as viewed from cross section B-B). (top long arrow—shoulder induced flow; bottom short arrow—pin induced flow).

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Fig. 18

(a) Experimental results and (b) simulation results of tunnel defect formation

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Fig. 19

Temperature distribution during cavity defect formation

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Fig. 20

Material velocity distribution during formation of cavity

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Fig. 21

Excess flash formation defect due to excessive heat input: (a) simulation and (b) experimental results

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Fig. 22

Temperature distribution during excess flash defect formation

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Fig. 23

Temperature distribution during sound weld formation

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Fig. 24

Material velocity distribution during sound weld joint formation

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