7/21/2019 Application of Taguchi method to optimize friction stir welding parameters for polypropylene composite lap joints.pdf http://slidepdf.com/reader/full/application-of-taguchi-method-to-optimize-friction-stir-welding-parameters 1/17 See discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/235412319 Application of Taguchi method to optimize friction stir welding parameters for polypropylene composite lap joints ARTICLEinARCHIVES DES SCIENCES JOURNAL · JULY 2012 Impact Factor: 0.3 READS 264 3 AUTHORS, INCLUDING: Hedi Ahmadi Shahid Rajaee University 3PUBLICATIONS 7CITATIONSSEE PROFILE Faramarz Ashenai Ghasemi Shahid Rajaee University 27PUBLICATIONS 129CITATIONSSEE PROFILE Available from: Hedi Ahmadi Retrieved on: 04 December 2015
17
Embed
Application of Taguchi method to optimize friction stir welding parameters for polypropylene composite lap joints.pdf
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
7/21/2019 Application of Taguchi method to optimize friction stir welding parameters for polypropylene composite lap joints.pdf
In this article, friction stir welding has been used for lap joining polypropylene composite plates having 20
wt% glass fiber. The effects of important process parameters such as tool rotational speed, welding speed,
tilt angle and tool pin geometry on tensile shear strength were investigated using the Minitab software and
the Taguchi method of design of experiments. A L16 orthogonal array with four factors at four levels was
employed to evaluate effects of rotational speed ( 630, 800, 1000 and 1250 rev/min), welding speed (12, 16,
20 and 25 mm/min), tilt angle (0, 1, 1.5 and 2 degree) and tool pin geometry (threaded cylindrical tool,
threaded cylindrical-conical tool, simple cylindrical-conical tool and threaded conical tool) on tensile shearstrength of the lap joints. The results indicated that the tensile shear strength was maximum when rotational
speed, welding speed, tilt angle and tool pin geometry were 1000 rev/min, 20 mm/min and 1 degree
respectively with threaded cylindrical-conical tool. Analysis of variance was performed to calculate the
percentage of contribution of each factor on tensile shear strength. It was found that, the rotational speed,
welding speed, tool pin geometry and tilt angle were significant factors respectively.
Friction Stir Welding (FSW) is a non-fusion welding process which is a derivative of conventional friction
welding giving good quality butt and lap joints [1]. The FSW process has proved to be ideal for creatinghigh quality welds in a number of materials including those which are extremely difficult to weld by
material flow, microstructure formation and mechanical properties of FSW joints for metals and metal
matrix composites [4, 8-10]. De filippis et al. [11] studied the effects of different shoulder geometries on
the mechanical and microstructural properties of friction stir welded 6082 T2 aluminium alloy in the
thickness of 1.5 mm. The three studied tools differed from shoulders with scroll and fillet, cavity and fillet,
and only fillet. The results showed that, for thin sheets, the best joint has been produced by a shoulder with
cavity and fillet. Kumar et al. [12] studied the effect of tool geometry on microstructural development andmechanical properties of friction stir welded precipitation hardenable Al-Zn-Mg alloy in the thickness of
4.4 mm and concluded that joints welded with frustum-shaped rounded-end pin profile had better
mechanical properties compared to cylindrical flat-end pin profile. Zhao et al. [13] studied the effect of pin
geometry on the weldability and mechanical properties of friction stir welded 2014 aluminium plates and
found out that the shape of the pin had a significant effect on the joint structure and the mechanical
properties. Buffa et al. [14] reported that in FSW of lap joints, tool geometry had significant effect on
mechanical properties. They used three tools with different pin geometry to weld aluminum alloy
AA2198-T4 and came to the conclusion that cylindrical-conical tool in comparison to conical tool and
cylindrical tool results in joints with better quality. Watanabe et al. [15] studied the weldability of FSW
AZ31 magnesium alloy/SS400 steel, and reported that the rotation speed and the position of the pin axis
had a significant effect on the strength and the microstructure of the joint. Cao and Jahazi [16] studied the
effect of welding speed on microstructures and mechanical properties of friction stir welded AZ31B-H24magnesium alloy and concluded that as the welding speed increased, the grain size in the stir zone
decreased while the yield strength increased. Higher welding speeds produced slightly higher hardness in
the stir zone and the tensile strength increased first with increasing welding speed but remained constant
later.
Polypropylene (PP) and PP composites have already been joined by some of the welding or bonding
techniques [17-19]. Arici et al. [20] studied the effects of two parameters of tool penetration depth and
dwell time on the tensile shear strength of lap joints of friction stir spot welds for PP sheets and found out
that both parameters affected the joint strength of the welds. Scialpy et al. [21] used titanium tool for FSW
of PP extruded sheets and compared it with that of common welding methods such as hot gas welding and
extrusion. They concluded that mechanical properties of the welds and the welding speed of FSW is higher
than the other two methods. Bilici [22] studied the effects of friction stir spot welding parameters (dwell
time, tool plunge depth and tool rotational speed) on PP sheet weld strength with the help of the Taguchimethod. It was found that, all the parameter were effective on joint strength of PP friction stir spot welds
with the dwell time being the dominant parameter and the tool rotational speed the least important one.
Arab et al. [23] investigated the effects of FSW process parameters (tool pin geometry, tool rotational speed,
work linear speed and tool tilt angle) on weld appearance and tensile strength of butt joints in PP
composites with 30% glass fiber (GF) and concluded that the tool pin geometry had a significant influence
on weld appearance and the effects of rotational speed and tilt angle on weld appearance and tensile
strength were more than that of work linear speed.
The survey of the previous works shows that FSW has been mostly used for welding of metals and plastics.
Therefore, it deserves to investigate the ability of this process for welding of PP composites reinforced with
GF. Although research on friction stir butt welding of PP composites has been carried out [23], but lap
welding of this composite by FSW has not been reported yet. This study is therefore intended to explain the
effects of FSW parameters on lap shear strength of PP composite welds with 20 wt% GF.Basically, classical experimental design methods are too complex and not easy to use, especially when the
number of experiments increases. To solve this problem, the Taguchi method uses a special design of
orthogonal arrays to study the entire parameter space with only a small number of experiments [24, 25].
The Taguchi design method has been found to be a simple and robust technique for optimizing the welding
parameters [26]. Considering the above facts, the Minitab software [27] and Taguchi L16 orthogonal arrays
(OAs) method are employed to analyze the effect of each FSW process parameter (i.e. rotational speed,
welding speed, tilt angle and tool pin geometry) on tensile shear strength of lap joints in PP composites
with 20 wt% GF.
7/21/2019 Application of Taguchi method to optimize friction stir welding parameters for polypropylene composite lap joints.pdf
The means and S/N ratio of the various process parameters when they changed from the lower to higher
levels are also given in Table 4. It is clear that a larger S/N ratio corresponds to better quality characteristics.
Therefore, the optimal level of process parameter is the level of highest S/N ratio [31]. The mean effect and
S/N ratio for tensile shear strength calculated by Minitab statistical software indicate that the tensile shear
strength was maximum when rotational speed, welding speed and tilt angle were 1000 rev/min, 20 mm/min
and 1 degree respectively with tool number 2. From the results of Table 4, diagrams were drawn to display
the welding parameters effects on weld strength. These diagrams are shown in Figures 6 to 9.
Figure 6 shows the effect of tool rotational speed on means (tensile shear strength) and S/N ratio of the joint.When the rotational speeds were 630 and 800 rev/min, the heat generated by the friction between the tool
shoulder and the base material may be low. Under this condition, the material transportation from the
advancing side of the tool to the retreating side of the tool may not occur sufficiently which end in
formation of joints with lower strength (Figure 7 a and 7 b). When the rotational speed was 1250 rev/min,
the generated frictional heat is too high which may cause turbulence of the plasticized material under the
tool shoulder which in turn may lead to reduction of joint strength (Figure 7 c) [32]. However with the
rotational speed of 1000 rev/min, the generated heat and turbulence are enough to produce a weld of
highest strength, i.e. 4.21 MPa (Figure 7 d). Better weld surface may be an indication of a better weld.
7/21/2019 Application of Taguchi method to optimize friction stir welding parameters for polypropylene composite lap joints.pdf
amount of heat generated and material flow during welding [34-36]. After contacting the work piece the
shoulder creates friction and causes heat generation which consequently results in weld width. The more
the heat created by the shoulder, the material flow will occur more and easier, however, this heat should not
exceed a certain limit because in that case, partial melting occurs and the material sticking to the tool
surface results in low weld quality. If the length of the pin is short for the thickness of the two plates, the
second piece which is under the first one will not be welded well, therefore, lack of penetration defect willoccur. Although the shoulder has the main role of creating heat, the pin to a lesser degree also plays a role
in creating heat [34-36]. Therefore, shortness of the pin because of decrease in contact surface with the
lower piece results in decrease of the created heat in the lower piece. Compensating the shortness of the pin
through pushing the tool more in the work piece causes pressure increase which forces the materials out of
the molten pool, therefore, flash defect shown Figure 12 shows occurs. As a result, the pin length should be
chosen accurately. To do so, it is better to choose the pin length 0.2 mm to 0.3 mm shorter than the sum of
thickness of the two pieces [37].
Figure 12. Formation of flash defect while welding.
As seen in Figure 13, the resulted tensile shear strength (means) and S/N ratio with tool number 2 is higher
than all other tools. Tool number 2 results in higher tensile shear strength, because its contact surface with
the work piece is more and greater friction created results in more heat [38]. On the other hand, the threadaround the tool pin causes great amount of turbulence on the weld seam and molten material mixes better
and as a result a higher tensile shear strength is produced. The tensile shear strength from tool number 3 is
lower than other tools, because it is the only tool whose pin is simple and this does not cause the materials
to mix well when the tool pin enters the molten material and creates lesser turbulence compared to other
tools. When material turbulence in the weld pool drops, tensile shear strength of the weld decreases. In
addition, it can be observed that tools number 2 and 3 are alike except for their pins. The presence of thread
on tool pin is significantly important, therefore tool number 2 is the best and tool number 3 is the worst one.
Tool number 1 has a lesser contact surface with the work piece in comparison to tool number 2 and this
contact surface decrease results in friction and heat drop and ultimately decreases tensile shear strength of
the weld. Tool number 4 whose pin is threaded conical, creates lesser contact surface with the work piece
compared with tool number 1, which causes tensile shear strength in tool number 4 to decrease in
comparison to that of tool number 1 because lesser friction and heat are generated at the contact area.
7/21/2019 Application of Taguchi method to optimize friction stir welding parameters for polypropylene composite lap joints.pdf
predicted and the actual weld lap shear strength using the optimum welding parameters. Good agreement
between the predicted and the actual weld lap shear strength is observed.
Table 7. Results of the confirmation test for weld lap shear strength.
Optimal welding parameters
Prediction Experiment
Parameter levels N3, S3, θ2, T2 N3, S3, θ2, T2
Tensile shear strength (MPa) 5.29 4.83
S/N ratio 14.46 13.67
4. Conclusion
In this paper, the effect of friction stir welding process parameters on lap shear strength of PP composite
plates with 20 wt% GF were evaluated with the help of the Taguchi method. The results indicated that:
1.
Tool 2 (threaded cylindrical-conical tool) was the best tool compared to other tools for producing
higher strength welds.
2.
For maximum weld strength, the optimum values of rotational speed, welding speed and tilt angle
were determined to be 1000 rev/min, 20 mm/min and 1° respectively when using tool 2.
3.
The weld strength was maximum when rotational speed and welding speed were at the
intermediate level of 3 whereas the tilt angle level was 2.
4.
It was found that the rotational speed, welding speed, tool pin geometry and tilt angle had 47.21%,
17.35%, 13.96% and 5.65% contribution on weld strength respectively. Hence, rotational speed is
the most significant parameter whereas tilt angle is the least important one.
References
[1] Liu G, Murr LE, Niou C-S, McClure JC, Vega FR. (1997). Microstructural issues of friction stirwelding of 6061-T6 aluminum. Scripta Mater; 37:355 – 61.
[2] Thomas WM, Nicholas ED. (1997). Friction stir welding for the transportation industries. Mater
Design; 18:269 – 73.
[3] RS Mishra, ZY Ma. (2005). Friction stir welding and processing. Mat Sci Eng R; 50:1 – 78.
[4] Amirizad M, Kokabi AH, Abbasi Gharacheh M, Sarrafi R, Shalchi B, Azizieh M. (2006).
Evaluation of microstructure and mechanical properties in friction stir welded A356+15% SiCp
cast composite. Mater Lett; 40:565 – 568.
[5] Sato YS, Park SHC, Matsunaga A, Honda A, Kokawa H. (2005). Novel production for highly
formable Mg alloy plate. J Mater Sci; 40:637 – 642.
[6] Barcellona A, Buffa G, Fratini L, Palmeri D. (2006). On microstructural phenomena occurring in
friction stir welding of aluminum alloys. J Mater Process Tech. 2006; 177:340-343.
[7] Dickerson TL, Pryzdatek J. (December 2003). Fatigue of friction stir welds in aluminium alloys
that contain root flaws. Int J Fatigue; 25:1399-1409.
[8] Saeid T, Abdollah-zadeh A, Assadi H, MalekGhaini F. (2008). Effect of friction stir welding
speed on the microstructure and mechanical properties of a duplex stainless steel. Mat Sci Eng.;
496:262 – 268.
[9] Cavaliere P, Campanile G, Panella F, Squillace A. (2006). Effect of welding parameters on
mechanical and microstructural properties of AA6056 joints produced by friction stir welding, J
7/21/2019 Application of Taguchi method to optimize friction stir welding parameters for polypropylene composite lap joints.pdf
[10] Abbasi Gharacheh M, Kokabi AH, Daneshi GH, Shalchi B, Sarrafi R. (2006). The influence of
the ratio of ‘‘rotational speed/traverse speed’’ (o/v) on mechanical properties of AZ31 friction stir
welds. Int J Mach Tool Manu; 46:1983 – 1987.
[11] Scialpi A, De Filippis LAC, Cavaliere P. (2007). Influence of shoulder geometry onmicrostructure and mechanical properties of friction stir welded 6082 aluminium alloy. Mater
Design; 28:1124 – 1129.
[12] Kumar K, Kailas Satish V, Srivatsan TS. (2008). Influence of tool geometry in friction stir
welding. Mater Manu Process; 23(2):188 -194.
[13] Zhao Y-h, Lin S-b, Wu L, Qu F-x. (2005). The influence of pin geometry on bonding and
mechanical properties in friction stir weld 2014 Al alloy. Mater Lett; 59:2948 – 2952.
[14] Buffa G, Campanile G, Fratini L, Prisco A. (2008). Friction stir welding of lap joints: Influence of
process parameters on the metallurgical and mechanical properties. Mat Sci Eng A; 519:19-26.
[15] Watanabe T, Kagiya K, Yanagisawa A, Tanabe H. (2006). Solid state welding of steel and
magnesium alloy using a rotating pin-solid state welding of dissimilar metals using a rotating pin.
Quart J Jpn Weld Soc; 24:108 – 15. [16] Cao X, Jahazi M. (2009). Effect of welding speed on the quality of friction stir welded butt joints
of a magnesium alloy. Mater Design; 30:2033 – 2042.
[17] Rudolf R, Mitschang P, Neitzel M and Rueckert C. (1999). Welding of high-performance