<4D6963726F736F667420576F7264202D20D3E3EDD120E6E3E5E4CF20E6C7E1CDE3D2C920DDC7D1E6DE312D203131>


 

 

Experimental Study the Effect of Tool Design on the Mechanical 

Properties of Bobbin Friction Stir Welded 6061-T6 Aluminum Alloy 
 

Samir Ali Amin*               Mohannad Yousif Hanna**                                

Alhamza Farooq Mohamed*** 
*,**,*** Department of Mechanical Engineering/ University of Technology 

*Email:alrabiee2002@yahoo.com 

** Email: mohannad_hanna@yahoo.com 

***Email: alhamza88f@yahoo.com  

 
(Received 27 September 2017; accepted 30 January 2018) 

https://doi.org/10.22153/kej.2018.01.003 

 

 

Abstract 

 
Bobbin friction stir welding (BFSW) is a variant of the conventional friction stir welding (CFSW); it can weld the 

upper and lower surface of the work-piece in the same pass. This technique involves the bonding of materials without 

melting. In this work, the influence of tool design on the mechanical properties of welding joints of 6061-T6 aluminum 

alloy with 6.25 mm thickness produced by FSW bobbin tools was investigated and the best bobbin tool design was 

determined. Five different probe shapes (threaded straight cylindrical, straight cylindrical with 3 flat surfaces, straight 

cylindrical with 4 flat surfaces, threaded straight cylindrical with 3 flat surface and threaded straight cylindrical with 4 

flat surfaces) with various dimensions of the tool (shoulders and pin) were used to create the welding joints. The direction 

of the welding process was perpendicular to the rolling direction for aluminum plates. Tensile and bending tests were 

performed to select the right design of the bobbin tools, which gave superior mechanical properties of the welded zone.  

The tool of straight cylindrical with four flats, 8 mm probe and 24 mm shoulders diameter gave better tensile strength 

(193 MPa), elongation (6.1%), bending force (5.7 KN), and welding efficiency (65.4%) according to tensile strength.       

 

 Keywords: Bobbin FSW, Bobbin tool design, AA6061-T6, Mechanical properties. 
 

 

1. Introduction 
 

Friction stir welding (FSW) is a solid-state 

bonding process feigned in 1991, at The Welding 

Institute. FSW is a substitutional welding 

technique to conventional fusion welding. The 

joint is produced via a non-consumed refractory 

cylindrical rotating tool, mechanically passed 

through the material of the work-piece. The friction 

between wear-resistant tool and the substrate 

generates heat. Because the frictional heat is 

generated, the stirred material is softened and 

mixed [1]. Under the shoulder of the tool, the 

material flows are like the forging operation, 

whereas the flows of material surrounding the tool 

probe are similar to the extrusion operation [2]. 

This technique is used for joining aluminum alloys, 

although other materials are possible inclusive 

dissimilar materials. The welding technology, 

patented via Thomas et al.  [3], has been used to 

automotive, shipbuilding, and aerospace industries 

[4].  

The usage of a bobbin friction stir welding 

(BFSW) tool, see figure (1), presented the 

capability to outdo of the limitations faced in the 

CFSW [5]. This technique uses a tool consisting of 

a probe and double shoulders. The tool shoulders 

contact with both the lower and upper substrate 

surface. It can be referred to that the aluminum 

alloy plates with higher thickness could be joined 

   

Al-Khwarizmi 

Engineering   
Journal  

Al-Khwarizmi Engineering Journal, Vol. 14, No.3, September, (2018)

P.P. 1- 11 

 



Samir Ali Amin                                   Al-Khwarizmi Engineering Journal, Vol. 14, No. 3, P.P. 1- 11 (2018) 

 

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by friction stir welding process; nevertheless, the 

next information show why it’s eligible to also use 

the BFSW-tool for this intent. Using double 

shoulders able to balance the down forces created 

via the tool with individual shoulders and so 

revokes the resulted axial down force. As well, the 

peril of root defect is basically removed with this 

type of tool design. Due to the uniform heat input 

distribution, the bobbin FSW process exhibits good 

welded joints with lest distortions compared to the 

CFSW process. In addition, the bobbin friction stir 

welding technique could superfast the transverse 

speed and raise the efficiency of the welding 

process in substrate with thicker section [6].  

 

 
 

Fig. 1. Schematic diagram of BFSW [4]. 

 

 

The design of a single shoulder tool (CFSW) 

has been focused by numerous researches, while 

the bobbin tool has had so less studies solicitude. 

T. Neuman et al. [7] have reported that the tool with 

threaded cylindrical probe and the tool with 

threaded cylindrical probe having 3 flats enable to 

create satisfying welding outcomes, since there is 

no formed internal defect. The above tools were 

utilized to weld AA2024-T351 with 4 mm 

thickness. M. K. Sued et al. [8] investigated the 

influence of probe geometry on the mechanical 

properties and microstructure development of 

6082-T6 aluminum alloy joining by BFSW and 

developed a model relating the basic physics to the 

manufacturing process in FSW bobbin-tool. W. M. 

Thomas et al. [9] notified complete permeation 

BFS welded joints, free of penetration shortage, 

and root flaws. For bobbin tool, two shoulders 

supply appropriate heat generation from both the 

surfaces of the substrate, and the inclusion of 

reactive forces within the tool itself denotes that 

compressive distortion (Squashing) of the pin does 

not take place. To promote the swept soft material 

volume via a tapered probe; investigators exhorted 

3 flat surfaces feature to be used on the probe. This 

tool geometry was applied to weld 12% chromium 

alloy steel 8 mm thick, and produced a successful 

good weld [10]. A tapered probe with three flats 

allows to reduce the diameter of the bottom 

shoulder that participates in lowering the bending 

moment and torque. A lot of other researchers 

studied the understanding of the influence of 

welding process parameters on the material flow 

characteristics, microstructure evolution and 

mechanical properties of the joint line welded by 

BFSW [11-15]. 

The aim of this paper is first to design and 

manufacture a new fixed type bobbin tool, to show 

the effect of changing the diameters of the pin and 

shoulders of this tool, and then select the best 

design of this bobbin tool depending on the 

mechanical properties (elongation, tensile strength 

and maximum bending force) and weld joint 

quality for aluminum alloy (6061-T6) welded by 

bobbin FSW.   

 

 

2. Experimental Work 
2.1 Selection of Material and Specimens 

Preparation  

 
In this work the base metal was aluminum alloy 

AA6061-T6, which is (Al-Mg-Si) grade alloy of 

6xxx series. The plate of AA6061-T6 was cut into 

the desired size (200 mm x 100 mm x 6.25 mm) via 

a power saw cutting machine, and the edge of the 

piece was ground to secure that there is no chasm 

exists between the two substrates that make the 

desired butt joint design. The chemical 

composition of the work-piece plate was obtained 

via a spectra device available in Special Institute 

for Engineering Industries (SIEI), as presented in 

table (1). The mechanical properties were 

performed for this plate in strength laboratory in 

Mechanical Engineering Department, University 

of Technology and are given in table (2). 

 
Table 1, 

Standard and actual chemical compositions of aluminum alloy 6061-T6 

 

 Wt.% 

 

Si 

 

Fe 

 

Cu 

 

Mn 

 

Mg 

 

Cr 

 

Zn 

 

Ti 

 

Ni 

 

Al 

Standard[16] 0.4-0.8 < 0.7 0.15-0.4 < 0.15 0.8-1.2 0.04-0.35 < 0.0.25 < 0.7 < 0.05 Bal. 

Actual 0.6 0.57 0.26 0.10 0.89 0.18 0.037 0.054 0.003 Bal. 

 

Element 



Samir Ali Amin                                   Al-Khwarizmi Engineering Journal, Vol. 14, No. 3, P.P. 1- 11 (2018) 

 

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Table 2, 

Standard and actual mechanical properties of aluminum alloy 6061-T6 

 Yield stress(MPa) Ultimate tensile stress(MPa) Elongation (%) 

Standard Value [16] ≥ 240 ≥ 290 ≥ 10 
Actual Value 244.5 295 11.5 

 
2.2 Design and Manufacturing of Bobbin 

Tools 

 
There are two significant domains of bobbin 

friction stir welding tool design: selection of tool 

material and geometry (features and dimensions). 

There are significant influences to the tool 

pending welding: high temperature, abrasive wear 

and dynamic influences. Therefore, the good 

materials of the tool have the following 

characteristics: good wear resistance, high 

temperature strength, temper resistance and good 

toughness. In the FSW of aluminum alloys, the 

wear of the welding tool is not so much. Tool 

materials like tool steel can be utilized for FSW [2]. 

Hot-work tool steel (H13) is the most ordinarily 

utilized material, easy availability and 

machinability, wear resistance, thermal fatigue 

resistance, essentially for copper and aluminum 

[17]. The tools in this work were fabricated from a 

hot-work tool steel (H13).  

In order to select a best design, five various 

tools with probe profiles (threaded straight 

cylindrical pin, straight cylindrical with three flat 

surfaces, straight cylindrical with four flat surfaces, 

threaded straight cylindrical with three flat surfaces 

and threaded straight cylindrical with four flat 

surfaces) and flat shoulders with different 

diameters in all cases were utilized, see figure (2). 

The bobbin friction stir welding tools were 

fabricated by conventional lathe and milling 

machines. The tool heat treatment comprises 

heating the tool alloy to 1070°C about 30 min and 

then air cooling to room temperature, followed by 

two tempering steps at 550°C and 500°C, 

respectively. Then, the tool was air cooled to room 

temperature in each step, resulting in a hardness 

about 49 HRC [18, 19]. All details of designed and 

fabricated bobbin tools are given in table (3), 

including pin diameter, flat side width, pitch of the 

thread, shoulder diameter, feature of shoulder 

surface and shoulders gap.   

 

 

2.3 Welding Procedure 

 
 The substrate has to be clamped rigidly at a 

predetermined location onto a fixing framework, 

see figure (3). Bobbin welding is started by driving 

onto the edge of the work-piece and then the work-

piece is moved against the pin. The experiments 

were completed using a one pass normal to the 

plate rolling direction (longitudinal). At first, slow 

travel speed till plastic deformation occurs, 

followed by acceleration of the welding speed to 

the required speed, and then the tool moves over 

the joint line at a constant travel speed. The 

material in front of the rotating tool probe is 

plastically distorted and stirred back to the trail 

edge of the tool pin in the welding [20]. The used 

welding parameters were selected according to the 

information from the previous research in this field 

and the practical expertise. These parameters are 

given in table (4). Classic milling machine model 

(FU 251) was used to complete the welding 

process. 

 

     

  

  
 

Fig. 2. a) Threaded straight cylindrical with 4 flat surfaces, b) Straight cylindrical with 4 flat surfaces, c) Threaded 

straight cylindrical with 3 flat surfaces, d) Straight cylindrical with 3 flat surfaces, e) Threaded straight cylindrical 

pin. 

c d  

e 

a b 



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Table 3, 

BFSW tools (dimensions and features) 

Description  

of the probe 

BFSW  

Tool No. 

pin 

diameter  

(d) (mm) 

Flat side 

width(mm) 

 

Pitch of 

thread 

(mm) 

Shoulder  

Diameter 

(D)(mm) 

Feature 

of 

shoulder  

Gap of 

shoulders 

(mm) 

Straight threaded 

cylindrical  

BT-1 10 _____ 1.5 20 

(2d) 

Flat 6.25 

Straight threaded  

cylindrical 

BT-2 10 _____ 1 20 

(2d) 

Flat 6.25 

Straight cylindrical + 

3 flats 

BT-3 10 0.67 _____ 20 

(2d) 

Flat 6.25 

Straight cylindrical + 

4 flats 

BT-4 10 0.67 _____ 20 

(2d) 

Flat 6.25 

Straight threaded 

cylindrical+ 3 flats 

BT-5 10 0.67 1 20 

(2d) 

Flat 6.25 

Straight threaded 

cylindrical+ 4 flats 

BT-6 10 0.67 1 20 

(2d) 

Flat  6.25 

Straight threaded 

cylindrical  

BT-7 8 _____ 1 16  

(2d) 

Flat 6.25 

Straight cylindrical + 

3 flats 

BT-8 8 0.5 _____ 16 

(2d) 

Flat 6.25 

Straight cylindrical + 

4 flats 

BT-9 8 0.5 _____ 16  

(2d) 

Flat 6.25 

Straight threaded 

cylindrical+ 3 flats 

BT-10 8 0.5 1 16 

(2d) 

Flat 6.25 

Straight threaded 

cylindrical+ 4 flats 

BT-11 8 0.5 1 16  

(2d) 

Flat 6.25 

Straight threaded 

cylindrical  

BT-12 12 _____ 1.5 24 

(2d) 

Flat 6.25 

Straight cylindrical + 

3 flats 

BT-13 12 0.8 _____ 24 

(2d) 

Flat 6.25 

Straight cylindrical + 

4 flats 

BT-14 12 0.8 

 

_____ 24 

(2d) 

Flat 6.25 

Straight threaded 

cylindrical+ 3 flats 

BT-15 12 0.8 1.5 24 

(2d) 

Flat 6.25 

Straight threaded 

cylindrical+ 4 flats 

BT-16 12 0.8 1.5 24 

(2d) 

Flat 6.25 

Straight cylindrical + 

4 flats 

BT-17 8 0.5 _____ 20 

(2.5d) 

Flat 6.25 

Straight cylindrical + 

4 flats 

BT-18 10 0.67 _____ 25 

(2.5d) 

Flat 6.25 

Straight cylindrical + 

4 flats 

BT-19 12 0.8  

_____ 

30 

(2.5d) 

Flat 6.25 

Straight cylindrical + 

4 flats 

BT-20 8 0.5 _____ 24 

(3d) 

Flat 6.25 

Straight cylindrical + 

4 flats 

BT-21 8 0.5 _____ 24 

(3d) 

Flat  6.4 

Straight cylindrical + 

4 flats 

BT-22 8 0.5 _____ 24 

(3d) 

Flat 6.1 

Straight threaded 

cylindrical+ 3 flats 

BT-23 8 0.5 1 24 

(3d) 

Flat  6.25 



Samir Ali Amin                                   Al-Khwarizmi Engineering Journal, Vol. 14, No. 3, P.P. 1- 11 (2018) 

 

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Fig. 3. Fixing framework. 

 

 

Table 4, 

Used Bobbin friction stir welding process 

parameters 

Tool rotational speed (spindle speed) 

(rpm) 

 

560 

Welding speed (travel speed) 

(mm/min) 

 

80 

Dwell speed  

(mm/min) 

 

manual 

Dwell time 

(s) 

 

40 

 

2.4 Mechanical Tests  

 
Tensile test was done on specimens possessed 

in direction normal to the joint line to define the 

tensile properties of the joints for all welding 

experiments. The form and dimensions of the 

longitudinal tensile specimens according to the 

standard (ASTM-E8) are presented in figure (4.a). 

Tensile experiments were done at 1 mm/min 

loading rate at room temperature using a 

computerized universal testing machine (Hydraulic 

Tunis Olsen). Then, the average value of three 

tested samples was taken for determining the 

elongation and ultimate tensile strength of each 

joint. Three point bending test was done to obtain 

the maximum bending force of the joints. The form 

and dimensions of the longitudinal bending sample 

according to the standard (ASTM-E190) are 

presented in figure (4.b). The bending test was 

done at constant loading rate (5 mm/min) at room 

temperature by a universal testing machine 

(Hydraulic LARYEE testing machine).    

 

  
 

 
 

Fig. 4. a) Tensile test specimen (all dimensions in 

mm) (ASTM-E8), b) Bending test specimen (all 

dimensions in mm) (ASTM-E190M) . 

 

 

3. Experimental Results and Discussion    
3.1 Visual Inspections   

 
The visual inspection consequences are 

presented in Fig. 5. These exhibit the bottom and 

top of each joint. Some of the welded joint had a 

good appearance, while other welds appeared 

various flaws, involving open tunnel/void, 

excessive flash, cutting effects and incomplete 

joining.   

1) Open tunnel and excessive flash (figures 5a and 
5b): This phenomenon has not been discussed and 

identified its causes in the previous literature in 

large active area, but it can be explicated as 

follows. The distribution of vertical material flow 

was asymmetry that was evident in threaded 

cylindrical probe. This distribution had 

overflowing material on the upper substrate 

surface, and weld bead thinning on the lower 

surface. The probe threads might result much 

material motion toward the single surface. The 

potential of threaded profile potential resulting 

extravagant flux of vertical material has previously 

been specified [21]. The clockwise rotation of the 

tool, which is the state of present research, also the 

stationary vertical location of the bobbin tool 

prohibited the down movement of the tool. In this 

state, the threads existence on the probe draws up 

the work-piece. Thus, the swept material from the 

retreating side faces the soft material of the 

advancing side, and a complicated blending type 

a 



Samir Ali Amin                                   Al-Khwarizmi Engineering Journal, Vol. 14, No. 3, P.P. 1- 11 (2018) 

 

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engenders, see figure (6). The retreating side 

shown in figure (7A) is pushed vertically up toward 

the advancing side. Therefore, the top site of the 

advancing side (figure 7B) is firstly filled. The 

smaller threads pitch will possess minimal helix 

angle, thus minimizing the transportation of 

vertical material and the flash defect, see figure (7). 

2) Cutting effect (figure 5c): In this state, the plates 
were softened and cut via the bobbin tool and no 

welding took place. This was occurred when the 

diameter of the pin was 12 mm (about twice 

thickness of substrate) BT (12-16). The reason of 

this case is that the amount of heat input was not 

enough. The amount of heat generated is not 

significant to produce a good mixing for soft 

material flow and occur a dynamic recrystallization 

compared to the volume of the material was stirred. 

For (BT-19) design, the welding was successful, 

because the diameter of the shoulders was bigger; 

this means the heat input was significant to produce 

free defect welding.   

3) Incomplete joints/voids/flash defect (figures 5d 
to 5g): With gap's variation, there are changes in 

the semblance of welding line. When the bobbin 

tool (BT-21) has a gap of 6.4 mm, which is higher 

than the upper allowable limit of plate thickness 

(6.25 mm) due to the difficulty in filling and 

coalescing the stir zone. Another case was the tool 

(BT-22) having a gap of 6.1 mm. At the top surface, 

there was only a slight of flash, while at the bottom 

surface there was an excessive flash/ scraping and 

consequent decrease in thickness.  

Several welding joints were unacceptable, 

because there were flash and voids in the joint line 

and the other joints were incomplete. These defects 

are not dependent only on the pin geometry (shape 

and dimension). Other variables can cause these 

defects, e.g. bad tool fabrication, substrate 

condition (flatness variation), and support/clamp 

setting, see figure (8).  

Also, the failed outcomes possess partnership to 

how explicate the acceptable welding joints. It is 

submitted that the sundry influences participate to 

acceptable welds. The stirred material needs to 

have horizontal and vertical flow; the flow 

movement produces by the tool features. Thus, 

threads create vertical flow motion [21, 22] and 

flats produce horizontal movement [23]. Hence, the 

tools (threaded cylindrical with 3/4 flats), which 

comprise these profiles, achieved properly. Tools 

that own flats only, such as (straight cylindrical 

with 3/4 flats), are also capable to create sound 

welds. Since the used plate here was not thick, it is 

suggested that the fit gap between the shoulders of 

the tool and substrate thickness equips with a 

vertical motion flow element of soft material. Thus, 

whereas flat faces might not produce the movement 

of vertical flow, these features do not counter it [8]. 

  

 

          
 

 
 

        
  

        
 

Fig. 5.  a) Open tunnel defect/ lower surface (BT-1), b) Excessive flash defect/ upper surface (TB-1), c) Cutting 

effect (BT14), d) Void defect/ upper surface (BT-21), e) Incomplete welding/ lower surface (BT-21), f)  Excessive 

flash defect/ lower surface (TB-22),   Few flash/ upper surface (TB-22)  . 

 

 

 

c 

d e 

f g 

a b 



Samir Ali Amin                                   Al-Khwarizmi Engineering Journal, Vol. 14, No. 3, P.P. 1- 11 (2018) 

 

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Fig. 6. Material motion around threaded probe. 

 

 
 

Fig. 7. Minimizing the flash defect (BT-2) . 

 

 
 

Fig. 8. Variation of flatness plate (BT-20) . 

 

 
 

 
 

Fig. 9. a) Upper surface, b) Lower surface  . 
 

 

3.2 Destructive Inspections  

 
After implementing the welding experiments, 

the joints were visually tested and the welds with 

perfect surface appearance were selected and 

machined according to the standard test samples 

for the mechanical testing. Mechanical tests were 

conducted to define the mechanical behavior of the 

weld zone and select the best probe design by the 

maximum welding efficiency in terms of tensile 

strength. Tensile and bending tests were done, and 

the results have been classed according to the tool 

probe shape. The results are listed in table (5). 

From these results, the best bobbin tool design for 

the investigation condition (substrate type, 

thickness, and process settings) is (BT-20), which 

provides superior mechanical properties, see figure 

(9). Since the spindle and welding speeds used in 

this work cannot be considered as optimum 

parameters, so the obtained results of the 

mechanical properties are not the maximum for this 

bobbin tool (BT-20) design.  

 

3.3 Effects of Used Bobbin Tool Design 

Features and Dimensions on Weld Quality  

 
The outcomes characterize specifically the  

functional effects, for example, the thread on tool 

probe. The following duty is to establish a 

systematic explication for the causality by tool 

shape and other parameters that cause weld quality 

influences. These are established on the 

interpretations (above) of the empirical clues 

compiled in this work, and informed via the 

conclusions of other research in this field.   

a) Threads feature (BT1, BT6 and BT11) produces 
high heat input and vertical flow movement 

following the thread orientation. The result is 

harmonious with pervious studies [21, 22, and 24]. 

However, the point of distinction in this research is 

the threads on the pin cause open tunnel defect in 

the advanced side on the bottom surface of the 

substrate and lead to excessive flash. This effect 

can be termed a drill effect as discussed above. 

 
 
 
 
 
 
 
 
 

 

 

 

 

 

 

 

 

 

a 

b 



Samir Ali Amin                                   Al-Khwarizmi Engineering Journal, Vol. 14, No. 3, P.P. 1- 11 (2018) 

 

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Table 5, 

Results of mechanical properties tests 

Notes B. F 

(KN) 

W. Eff. 

% 

U.T.S 

(MPa) 

Elongation 

(%) 

Tool 

type 

Exp. No. 

d = 10 mm, D = 20 mm 

  (D = 2d) 

Open tunnel defect ------ --------- ------- -------- BT-1 Test 1 

Open tunnel defect ------ --------- ------- -------- BT-2 Test 2 

Acceptable appearance 3.88 28.6 84.5 3.3 BT-3 Test 3 

Acceptable appearance 4.9 35.6 105 4.1 BT-4 Test 4 

Acceptable appearance 4.1 29.7 87.5 3.52 BT-5 Test 5 

Acceptable appearance 2.3 25.4 75 2.7 BT-6 Test 6 

d = 8 mm, D =16 mm 

(D = 2d) 

Open tunnel defect ------ ------- ------- -------- BT-7 Test 7 

Acceptable appearance 5.5 40.8 95.5 5.15 BT-8 Test 8 

Acceptable appearance 4.8 34.6 120 3.97 BT-9 Test 9 

Acceptable appearance 2.5 30.2 102 3.4 BT-10 Test 10 

Acceptable appearance 4.5 32.4 89 3.8 BT-11 Test 11 

d = 12 mm, D = 24 mm 

(D = 2d) 

Open tunnel defect ------ -------- ------- -------- BT-12 Test 12 

Cutting defect ------ -------- ------- -------- BT-13 Test 13 

Cutting defect ------ -------- ------- -------- BT-14 Test 14 

Cutting defect ------ -------- ------- -------- BT-15 Test 15 

Cutting defect ------ -------- ------- -------- BT-16 Test 16 

d = 8, 10 and 12 mm (respectively) 

(D = 2.5 d) 

Acceptable appearance 5.75 47.5 140 5.57 BT-17 Test 17 

Acceptable appearance 4.7 36 106 4.3 BT-18 Test 18 

Acceptable appearance 5.1 33.9 100 3.88 BT-19 Test 19 

d = 8 mm, D = 24 mm 

(D = 3d) 

Acceptable appearance 5.7 65.4 193 6.1 BT-20 Test 20 

Incomplete ------ --------- ------- -------- BT-21 Test 21 

Flash (scraping) ------ --------- ------- -------- BT-22 Test 22 

Acceptable appearance 5.1 45.1 133 5.45 BT-23 Test 23 

 

 

b) The visual analysis denotes that the gap of the 
bobbin tool effects on the welded appearance. 

When the gap was bigger than the thickness of the 

substrate, there were incomplete joints and voids 

because of lack of strength in forging (thrust load). 

When the gap was lower than thickness, the edge 

of the shoulder scraped very thin layer of the 

surface of the substrate that leaded to produce an 

excessive flash and reduce the thickness of the 

plate. Consequently, the gap between shoulders 

must be equal to the thickness of the work-piece 

because it is the one with superior properties, 

which is harmonious with other study [4, 25].  

c) In general, the bobbin tool (TB-10) created a 
good weld joint compared to that was produced by 

(TB-5). The reason of this is the tool (TB-10) had 

smaller dimensions than (TB-10). The reduction of 

strength is supposed to be on account of the amount 

of area (volume of material sweeping) that was 

influenced via the bobbin tool during welding 

process [26]. This interpretation applies to others 

tools. 

d) The design of shoulders influences the 
generation of heat [26]. For the thickness of plate 

as used in this investigation, the needed heat 

generation could readily be taken out by the two 

sides of the bobbin tool features. Shoulder diameter 

has significant effect to improve the welding zone 

properties. The swell in the diameter of the 

shoulder means the growing of the friction area and 

thus increases the heat generated.  Large amount of 

heat input is desired to break the grain boundary in 

transverse the welding through the work-piece [8]. 

The tunnel flaw at sample (TB-10) is elucidated 

that the reduced zone of  provided heat via the 

smaller shoulder diamete probably resulted in 

premature solidification of the welding zone. The 

premature solidification and the tool dimension and 



Samir Ali Amin                                   Al-Khwarizmi Engineering Journal, Vol. 14, No. 3, P.P. 1- 11 (2018) 

 

9 

 

its influence on the flow stress stated in [27, 28, and 

29]. The above reason explains the results of 

welding obtained from (TB-10) and (TB-23), see 

figure (10).    

 

 
 

 
 

Fig. 10. a) Internal void (BT-10), b) Perfect cross-

section welded zone (BT-23). 

 

4. Conclusions  
 

The overall aim of this investigation was to 

better comprehend the influence of tool geometry 

(features and dimensions) on the weld joint quality 

and select the best tool design for bobbin kind 

friction stir welding. So, from the present wok, the 

followings can be concluded:  

1- Straight cylindrical probe with four flats created 
a free defect weld joint for the used thin substrate 

aluminum alloy 6061-T6 with superior mechanical 

properties (elongation, ultimate tensile strength 

and maximum bending force), resulting in a 

preferable bobbin tool design in the present 

investigation.  

2- The dimensions of the bobbin tool (shoulders 
and pin) have a significant effect on the welding 

quality.  

3- For the best bobbin tool design, the internal 
diameter of the pin is nearly similar to the substrate 

thickness, and the shoulder diameter should be 

three times the pin diameter.  

4- The gap between the tool shoulders must be 
equal to substrate thickness.  

5- The distance between tool shoulders can be 
adjusted to insert a useful compression influence, 

hence vertical flow movement.  

6-  The effects of stirring consisting of horizontal 
and vertical flow movements are significant to 

generate good weld quality.  

 

 

5. References  
 

[1] Kumbhar N. T., and Bhanumurthy K., “Friction 
stir welding of Al 6061 alloy”, Asian J. Exp. 

Sci., Vol. 22, 2008 pp. 63-74. 

[2] Mishra R. S., Ma Z. Y., “Friction stir welding 
and processing”, Materials Science and 

Engineering R 50 (2005) pp. 1–78. 

[3] W. M. Thomas, E. D. Nicholas, M.G. Needham, 
and D. J. Templesmith, “Friction Stir Butt 

Welding”, International Patent Application 

PCT/GB92/02203, GB Patent Application 

9125978.8, US Patent 5.460.317, 1991.  

[4] Mohammad K. Sued and Dirk J. Pons, 
“Dynamic Interaction between Machine, Tool, 

and Substrate in Bobbin Friction Stir Welding”, 

International Journal of Manufacturing 

Engineering Vol. 2016, Article ID 8697453, 14 

pages.  

[5] R. S. Mishra P. S. De and N. Kumar, “Friction 
Stir Welding and Processing Science and   

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 )2018( 1-11، صفحة 3د، العد14دجلة الخوارزمي الهندسية المجلم                                                           سمير علي امين      
 

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على الخواص الميكانيكية  (Bobbin)دراسة تأثير تصميم عدة اللحام بالخلط االحتكاكي نوع 
  (T6-6061)لسبيكة المنيوم 
  

  الحمزة فاروق محمد***      مهند يوسف حنا**         سمير علي أمين*  
  التكنولوجيةقسم الهندسة الميكانيكية/ الجامعة *،**، ***  

alrabiee2002@yahoo.com :البريد االلكتروني * 
mohannad_hanna@yahoo.com: البريد االلكتروني ** 

alhamza88f@yahoo.com :البريد اإللكتروني *** 
 

 

 

  الخالصة
  

، حيث يتم لحام قطعة العمل من الوجهين نفسها لطريقةل) يكون مختلف عن اللحام المتعارف علية bobbinاللحام بالخلط االحتكاكي بأداة تشبه البكرة (
. يتضمن هذا األسلوب لحام اللوحين من دون االنصهار. في هذا العمل، تم التحقق من تأثير تصميم األداة على الخواص نفسها  لشوطلاالعلى و االسفل في 

كذلك  ،و(bobbin)الملحومة بطريقة اللحام الخلطي االحتكاكي نوع وملم)  ٦٬٢٥و بسمك ( (T6-6061)الميكانيكية لوصالت اللحام لسبيكة االلمنيوم نوع 
أوجه، أسطواني مستقيم  ٣. خمسة أشكال مختلفة  لوتد أداة اللحام (أسطواني مستقيم مسنن، أسطواني مستقيم ذو (bobbin)تحديد أفضل تصميم ألداة اللحام نوع 

أوجه) وبأبعاد  مختلفة لألداة ( الدبوس و األكتاف ) استخدمت ألجراء عملية   ٤ستقيم مسنن ذو أوجه و أسطواني م ٣أوجه، أسطواني مستقيم مسنن ذو  ٤ذو 
ها ألختيار التصميم األفضل ألداة اللحام نوع ؤاللحام. أتجاه عملية اللحام  كان عموديا على أتجاه الدرفلة أللواح األلمنيوم. اختبارات الشد واالنحناء تم اجرا

)bobbin٨أوجه، بقطر  للوتد ( ٤ي افضل الخواص الميكانيكية لمنطقة اللحام. األداة ذات االسطواني المستقيم ذو ) والتي تعط mm) ٢٤) واالكتاف mm (
) نسبة الى مقاومة %٦٥٫٤كيلو نيوتن) وأفضل كفاءة لحام ( ٥٫٧) مع أقصى قوة انحناء (%٦٫١ميكا باسكال) وأستطالة ( ١٩٣أعطت افضل مقاومة شد (

  الشد.