impact of a gap on defect formation in friction …

© 2019 JETIR March 2019, Volume 6, Issue 3 www.jetir.org (ISSN-2349-5162)

JETIR1903E55 Journal of Emerging Technologies and Innovative Research (JETIR) www.jetir.org 373

IMPACT OF A GAP ON DEFECT FORMATION

IN FRICTION STIR WELDING OF ALUMINIUM

ALLOY USING THREADED TOOL PIN

PROFILE TOOL

1Avtar Singh, 2Dr. Vinod Kumar, 3Dr. Neel Kanth Grover 1Assistant Professor, 2 Professor, 3Associate Professor

1Yadavindra College of Engineering, Talwandi Sabo, Bathinda (Punjab) – 151302 (India)

Abstract: In this experimental study an attempt has been made to study the effect of a gap on defect formation on friction stir

welding of aluminium alloy. However, for FSW butt joints, two plates should be clamped without any mismatch between

abutting plates. The lack of straightness, Distortion etc. can cause gap between abutting plates. Gap between abutting plates

reduces the availability of material in the FSW stir zone which significantly affect the mechanical Properties of welded joint

[1]. In this study friction stir welding carried out using cylindrical threaded tool pin profile (RHT) with and without a gap

formation in abutting plates. The welded joints were sectioned and visual inspection reported tunnel defects in all the welding

joints.

Keywords: FSW (Friction Stir welding), RHT (Right handed threads), Gap, Tunnel Defect

1. Introduction

Friction stir welding process is a novel approach which is successfully used for joining of soft materials.

FSW is a solid state welding process in which materials to be welded are not melted fully but plasticize

with the help of frictional heat generated between non consumable tool and work piece. The principle of

FSW process is shown in fig. 1.

Fig 1 Principle of FSW process [2]

FSW tool consist of shoulder and pin profile which significantly affects the mechanical properties of the

welded joints. The heat input mainly depends on it shape and size of tool attributes. Pin profiles generate

the heat and mix the plasticizing material into the nugget zone. Whereas shoulder generated the

additional heat and apply pressure for the consolidation of plasticizing material. The different types of

pin profile are available for friction stir welding as shown in the fig. 2.

Fig. 2 Tool pin profiles [3]

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The various investigations have been conducted recently to study the effect of tool pin profile on joint

integrity of friction stir welded joints. Elangoven & Balasubramanian [3] studied the effect of different

tool pin profiles and shoulder diameter in the friction stir welding of aluminium alloy. It was noticed that

welded joints fabricated using smaller shoulder diameter tool produced tunnel defects in the nugget zone.

Smaller shoulder diameter produced low frictional heat which unable to plasticize the material properly.

Kumar & Raju [4] investigated the influence of various types of tool pin profiles on the friction stir

welding of cooper. From the results it was found that sound welded joint were produced at the rotational

speed of 900 rpm and 40 mm/min welding speed. In a similar study, Hussain et al. [5] found that

cylindrical taper pin profile tool produced higher tensile strength joint of AA 6063 and triangular pin

profile tool produced tunnel defect. Bayazid et al. [6] studied the effect of various tool pin profile on the

defect formation in the nugget zone of FSW at rotational speed 1600 rpm and welding speed 63 mm/min.

It was observed from the results that different types of defect were formed such as kissing bond, cracks,

etc. with triangular and cylindrical tool pin profiles. It is revealed from the above investigations that tool

pin profile geometry significantly affect the joint integrity by heat input and the consolidation of

material. The presence of tunnel defect in the joint reduced the mechanical properties by of 25-82% [7].

The heat and plastic flow is also principally affected by the process parameters. The primary process

parameters of friction stir welding are rotational and welding speed, tool tilt angle and axial force. The

effects of each parameter of friction stir welding as shown in table-1.

Table 1 - Effect of parameters of FSW [8]

Parameter Effect

Rotational speed Frictional heat generation, stirring and mixing of plasticizing

material, breaking of oxide layer

Welding speed Heat input control and appearance of welded joint

Tilt angle Appearance and thinning of joint

Axial force Frictional heat generation, maintain correct plunge depth

A gap between abutting plates severely influenced the mechanical properties of the joint. A gap may

form due to distortion, mismatch, and misalignment in the abutting plates. As per the TWI maximum

tolerance in between the abutting plates should be less than 10% of the plate thickness. The increase in

gap resulting in significantly decrease in joint integrity due to formation of defect in nugget zone [9, 10].

Inada et al. [1] conducted an investigation on gap formation of aluminium alloy 1050. The joint were

prepared by maintaining the gap between abutting plates. Friction stir welding joints using threaded

cylindrical tool were produced by maintaining gap of 1, 2 & 3 mm in the abutting plates. From results, it

was found that defective welded joints were produced, when the gap between abutting plates increased

from 1 mm. Tunneling defects were produced in the nugget zone of friction stir welding joints. It was

happened due to a gap which subsequently reduces the material availability at the interface of abutting

plate.

2. Experimental procedure

In this experimental study, aluminium alloy AA6082 was cut into required size of 150x70x6 mm for

friction stir welding. The composition of aluminium alloy used for welding is given in table-2. Friction

stir welding performed with maintaining a gap of 1 & 2 mm between the abutting plates shown in fig. 3.

A conventional milling machine having maximum rotational speed 4600 rpm (CW) and automatic

variable welding speed 500 mm/min was used to carry out this experiment. Threaded (RH) cylindrical

tool was used as shown in fig. 4. The FSW joints were fabricated at different rotational and welding

speed while plunge depth and tilt angle 0.2 mm & 2° were constant. Friction stir welding process

parameters are given in table-3.After welding the joints were sectioned and visually inspected.

Table – 2: Composition of AA6082 as welded material

Major Element Si Mg Fe Al

%age 1.215 1.175 0.259 Rest




Table – 3: Process parameters used for FSW

S. No. Rotational Speed (rpm) Welding speed (mm/min)

1 1200 30

2. 1540 50

3. Results and discussion

The results revealed the tunnel defect present in all friction stir welding joints as shown in Fig. 4 & 5 at

the rotational speed 1200 & 1540 rpm and welding speed 30 & 50 mm/min respectively. The size of

tunnel defect goes on increasing with the increase of gap between the abutting plates. The effect of gap

and tool pin profile discussed in the next section.

3.1 Effect of gap

The contact area between the tool pin and workpiece affects the heat input in the nugget zone of friction

stir welding. Similarly a gap between the abutting plates reduced the availability of material to stir by

tool which resulting in improper heat generation and consolidation of material [1]. The reduction in

material at the interface generates low frictional heat which is significantly influence the plastic flow in

the nugget zone. The material evacuated by the tool from advancing side unable to fill the cavity behind

the tool pin due to lack of material & stirring action. Consequently, tunnel defect formed into the nugget

zone as shown in Fig 4 & 5. The increase in rotational speed is also failed to diminish the effect of gap

between the abutting plates. So it is inferred that a gap between abutting plates significantly affect the

joint integrity.

Fig. 3. Schematic view of Friction stir welding process

6mm

Gap

AA6082–T6

Fig. 4 Friction stir welding tool used

18mm

Shank

5.7mm 6 mm




3.2 Effect of tool pin profile

Threaded (RH) cylindrical tool pin profile was used in this experimental study. The clockwise rotation of

FSW machine spindle with right handed threaded pin profile caused the upward flow of plasticizing

material. Hence the more material deposition in upper portion on contrary low material deposition at the

bottom of nugget zone resulting in the formation of tunnel in the bottom side of FSW nugget zone. The

increase in rotational speed increase the size of cavity formation as shown in fig. 5

4. Conclusion

From this experimental study the following conclusion drawn

Gap between the abutting plates considerably affect the friction stir welding joint integrity due to

reduction in material availability at the interface of abutting plates.

The tool pin profile should be selected carefully so that appropriate heat and consolidation of

material should be prevailed in the nugget zone of the friction stir welded joints.

References 1. Inada K, Fujii H, Ji YS, et al (2010) Effect of gap on FSW joint formation and development of friction powder

processing. Sci Technol Weld Join 15:131–136. https://doi.org/10.1179/136217109X12568132624244

2. Çam G, Mistikoglu S (2014) Recent developments in friction stir welding of al-Alloys. J Mater Eng Perform 23:1936–

1953. https://doi.org/10.1007/s11665-014-0968-x

3. Elangovan K, Balasubramanian V (2008) Influences of tool pin profile and tool shoulder diameter on the formation of

friction stir processing zone in AA6061 aluminium alloy. Mater Des 29:362–373. https://doi.org/10.1007/s00170-007-

1100-2

4. Kumar A, Raju LS (2012) Influence of tool pin profiles on friction stir welding of copper. Mater Manuf Process 27:1414–

1418. https://doi.org/10.1080/10426914.2012.689455

5. Azmal Hussain M, Zaman Khan N, Noor Siddiquee A, Akhtar Khan Z (2018) Effect of Different Tool Pin Profiles on the

Joint Quality of Friction Stir Welded AA 6063. Mater Today Proc 5:4175–4182.

https://doi.org/10.1016/j.matpr.2017.11.680

6. Bayazid SM, Farhangi H, Ghahramani A (2015) Effect of Pin Profile on Defects of Friction Stir Welded 7075 Aluminum

Alloy. Procedia Mater Sci 11:12–16. https://doi.org/10.1016/j.mspro.2015.11.013

7. Khan NZ, Siddiquee AN, Khan ZA, Shihab SK (2015) Investigations on tunneling and kissing bond defects in FSW joints

for dissimilar aluminum alloys. J Alloys Compd 648:360–367. https://doi.org/10.1016/j.jallcom.2015.06.246

8. Shah S, Tosunoglu S (2012) Friction Stir Welding : Current State of the Art and Future Prospects. Mater Sci Technol 1–6

9. Khan NZ, Khan ZA, Siddiquee AN, et al (2017) Analysis of defects in clean fabrication process of friction stir welding.

Trans Nonferrous Met Soc China (English Ed 27:1507–1516. https://doi.org/10.1016/S1003-6326(17)60171-7

10. Oyedemi K, McGrath P, Lombard H, Varbai B (2017) A comparative study of tool-pin profile on process response of

friction stir welding of AA6082-T6 aluminium alloy. Period Polytech Mech Eng 61:296–302.

https://doi.org/10.3311/PPme.11149

2 mm

1 mm

Fig. 4 Cross sectional view of welded joints at rotational

speed 1200 rpm & welding speed 30 mm/min [(a,b)

without gap (c,d) with 1mm gap & (e,f) with 2 mm gap in

abutting plates]

b

c

d

e

f

a

1 mm

2 mm

Fig. 5 Cross sectional view of welded joints at rotational

speed 1540 rpm & welding speed 40 mm/min, [(a,b) without

gap (c,d) with 1mm gap& (e,f) with 2 mm gap in abutting

plates]

a

b

c

d

e

a

f


impact of a gap on defect formation in friction …

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