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Effect of welding parameters on mechanical properties of aluminium thin sheet joints produced by ultrasonic welding.

INTRODUCTION

The welding is a process that joins the materials, usually metals or thermoplastics by causing the coalescence. In some welding processes a filler material is added to facilitate coalescence. The assemblage of parts that are joined by welding is called a weldment. Many different energy sources can be used for welding including the gas flame, electric arc, laser beam, electron beam, frictional heat and ultrasound [1]. Many welding processes are accomplished by heat alone, with no pressure applied; others by a combination of heat and pressure; and still others by pressure alone, with no external heat supplied.

There are some 50 different types of welding operations have been catalogued by the American Welding Society and they use various types or combinations of energy to provide the required power. We can divide the welding processes into two major groups as fusion welding and solid-state welding. Solid-state welding refers to joining processes in which coalescence results from application of pressure alone or a combination of heat and pressure [2].

Nowadays the automotive industry mostly prefers the innovative solid state welding technologies that would enable to welding of lightweight and high performance materials. Ultrasonic welding is a solid state welding process and it would be a interesting method for joining dissimilar alloys that can potentially avoid many of the issues associated with fusion welding processes including rapid inter metallic formation [3]. Ultrasonic welding joins the metal parts by applying the high frequency vibratory energy and moderate clamping pressure onto the interface area between the parts to be welded. Since 1950s, it has been used in the manufacture of electronics, food packaging, electrical appliances, high-quality component sealants. Whereas in USMW the high frequency vibrations are introduced horizontally to increase the temperature and to plastify the material. The moderate clamping pressure applied vertically to disperse the oxides and contaminants and to bring in an increasing area of pure metal contact. The progressive shearing forces and plastic deformation of asperities result in the bonding of the faying surfaces [4].

In the present investigation a typical pure aluminium sheets have been ultrasonically welded in similar manner through a 2-KW lateral drive ultrasonic welding machine. The objective of this work is to obtain the optimized welding parameters through the full factorial design of experiments methodology and also the interactions of each welding variables on the weld strength has been studied.

MATERIALS AND METHODS

Specimens were prepared as per the standard of ASTM D1002 [3]. They were cut into the dimensions of 0.5 mm x 15 mm x 55 mm with overlap distance of 15mm. The joint configuration of aluminium specimens are shown in Figure 1. The welding was carried out using a conventional ultrasonic metal welding machine as shown in Figure 2.

Full factorial design (FFD) of experiment is an experiment whose design consists of two or more factors, each with discrete possible values or levels. In this experimental units take on all possible combinations of these levels across all such factors and may also be called as a fully crossed design. Full factorial design of experiment allows the investigator to study the effect of each factor on the response variable. In this study, the weld strength as response variable was maximized by using FFD with the optimal level of the process parameters which has been obtained with the combination of individual parameters. Moreover the parameters as selected as the pressure, weld time and amplitude as the factors which having the response to weld strength. The experimental design for aluminium joint which having the 3 factors and 3 levels type of design as shown in table 1. Through this design there are 27 number of combination of parameters has been obtained to maximize the weld strength.

The parameters range has been obtained through trial and error method which will help to decide the weldability limits for aluminium samples through ultrasonic welding technique.

The aluminium to aluminium joints have been tested using tensometer to obtain the tensile shear strength on each combination of parameters. The microstructural and microhardness analysis has been carried out for joint with maximum strength.

RESULTS AND DISCUSSION

The tensile shear strength values of the ultrasonic welded aluminium joints are shown in Table 2 along with its welding parameters. Figure 3 shows the aluminium welds after the tensile shear test. The samples were fractured mostly on weld metal section. The maximum strength of 61.3 MPa was observed for the parameter combination of welding pressure 7 bar, amplitude 60 [micro]m and welding time 2.8 s.

The minitab software has been used to investigate the interaction of each welding parameters on weld strength. has been investigated as following. The main effects plot for tensile shear strength has been shown in Figure 4. The weld strength was decreased with increase in pressure and weld time. The weld strength was increased initially then dropped with increasing amplitude.

Figure 5 depicts the interaction of welding variables on weld strength. From this graph at 6 bar of pressure the weld strength was dropped by amplitude and dropped then increased after 3.2 seconds of weld time. At 6.5 bar of pressure strength was raised initially then dropped with amplitude and weld time. When pressure in 7 bar of pressure the maximum weld strength was obtained in both cases of amplitude and weld time but strength was dropped with increased in amplitude and weld time. Due to amplitude of 28 [micro]m the strength was raised with weld time and dropped when amplitude of 30 [micro]m and 32 [micro]m with increased in weld time.

The 22nd parameter combination i.e., welding pressure 7 bar, amplitude 60 [micro]m and weld time 2.8 s shows the maximum weld strength of 61.3 MPa. The microstructure of the weld joint with maximum strength has been shown in Figure 6. The microhardness values of the ultrasonic welded aluminium joint with maximum strength has been shown in Figure 7.

The base metal shows higher hardness than the interface region in the ultrasonic welded aluminium joints. The parent sheet in the upper side during the welding show high hardness than the sheet placed in the bottom side during welding. This may be due high strain hardening in the upper sheets due severe ultrasonic vibrations.

Conclusion:

* The aluminium sheets have been successfully joined through ultrasonic welding.

* The welding parameters have been optimized using full factorial design.

* The maximum tensile shear strength observed for ultrasonic welded aluminium joint is 61.3 MPa.

* The optimum parameters for achieving higher strength is welding pressure of 7 bar, amplitude of 60 [micro]m and welding time of 2.8 s.

REFERENCES

[1.] Black, J.T. and R.A. Kohser, 2008. DeGarmo's Materials and Processes in Manufacturing, 10th Ed, John Wiley & Sons, Inc, USA

[2.] Groover, M.P., 2010. Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, 4th Ed, John Wiley & Sons, Inc, USA.

[3.] Elangovan, S., P.J. Shenton and K. Prakasan, 2010. Experimental studies on optimization of process parameters and finite element analysis of temperature and stress distribution on joining of Al-Al and Al-Al2O3 using ultrasonic welding, The International Journal of Advanced Manufacturing Technology, 55(5): 631-640.

[4.] Patel, V.K., S.D. Bhole and D.L. Chen, 2011. Influence of ultrasonic spot welding on microstructure in a magnesium alloy, Scripta Materialia, 65(10): 911-914.

P. Kumar, P.G. Venkatakrishnan, V. Karthik

Department of Metallurgical Engineering, Government College of Engineering,

Salem-636011, Tamilnadu, India.

Received 28 February 2017; Accepted 22 May 2017; Available online 6 June 2017

Address For Correspondence: Dr. V. Karthik, Department of Metallurgical Engineering, Government College of Engineering, Salem-636011, Tamilnadu, India. E-mail: karthik@gcesalem.edu.in

Caption: Fig. 1: Joint configuration of USMW

Caption: Fig. 2: Ultrasonic metal welding machine

Caption: Fig. 3: Ultrasonic welded aluminium joints after tensile shear test

Caption: Fig. 4: Main effects plot for tensile shear strength on ultrasonic welding aluminium joint

Caption: Fig. 5: Interaction plot for tensile shear strength

Caption: Fig. 6: Microstructure of ultrasonic welded Al-Al joint at 100X magnification

Caption: Fig. 7: Microhardness values at joint interface and parent metal
Table 1: Full factorial design for aluminium joint.

PARAMETERS                   PARAMETER LEVEL

                             1     2     3

Weld pressure                6     6.5   7
  (bar)
Amplitude                    56    60    64
  ([micro]m)
Time (sec)      Weld time    2.8   3.2   3.6
                Hold time    1.5   1.5   1.5
                Delay time   1     1     1

Table 3: Tensile shear strength of ultrasonic welded aluminium
joints

S.No.   WELD       AMPLITUDE    WELD    TENSILE
        PRESSURE   ([micro]m)   TIME    STRENGTH
        (bar)                   (sec)   (MPa)

1       6          56           2.8     54
2       6          56           3.2     45
3       6          56           3.6     60
4       6          60           2.8     55
5       6          60           3.2     45
6       6          60           3.6     61
7       6          64           2.8     59.6
8       6          64           3.2     57
9       6          64           3.6     38.3
10      6.5        56           2.8     38.3
11      6.5        56           3.2     58.6
12      6.5        56           3.6     57.6
13      6.5        60           2.8     59.6
14      6.5        60           3.2     58.6
15      6.5        60           3.6     54
16      6.5        64           2.8     44
17      6.5        64           3.2     44.3
18      6.5        64           3.6     37.6
19      7          56           2.8     54
20      7          56           3.2     61
21      7          56           3.6     56.6
22      7          60           2.8     61.3
23      7          60           3.2     57
24      7          60           3.6     46.6
25      7          64           2.8     53.6
26      7          64           3.2     27.6
27      7          64           3.6     28.6
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Author:Kumar, P.; Venkatakrishnan, P.G.; Karthik, V.
Publication:Advances in Natural and Applied Sciences
Geographic Code:1USA
Date:Jun 1, 2017
Words:1607
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