EFFECT OF END PROFILE ON DISSIMILAR METAL FRICTION WELDS OF PURE ALUMINIUM AND PURE COPPER

International Journal of Mechanical and Production Engineering Research and Development (IJMPERD) ISSN (P): 2249–6890; ISSN (E): 2249–8001 Vol. 10, Issue 3, Jun 2020, 921-932 © TJPRC Pvt. Ltd.

EFFECT OF END PROFILE ON DISSIMILAR METAL FRICTION WELDS OF PURE ALUMINIUM AND PURE COPPER PRATYUSHA. M1, VENKATA RAMANA. P2 & PRASANTHI. G3 1

Research Scholar, Department of Mechanical Engineering, JNTUA College of Engineering, Anantapuramu, Andhra Pradesh, India

2

Professor, Department of Mechanical Engineering, Mahatma Gandhi Institute of Technology, Hyderabad, Telangana, India 3

Professor, Department of Mechanical Engineering, JNTUA College of Engineering, Anantapuramu, Andhra Pradesh, India

ABSTRACT Some of the applications in the fields of automobile, power transmission, aerospace etc. require materials with good corrosion resistance, high electrical conductivity, machinability and weldability. In such cases, aluminium (Al) and copper (Cu) are candidate materials. In most of the cases, the applications demand sound dissimilar metal welds of Al and Cu. Joining of dissimilar metals is always a challenging process because of notable difference in the chemical compounds which are brittle and hard at the boundary between base metals. Joining Al and Cu employing conventional fusion welding process is difficult due to metallurgical incompatibility, difference in melting point, thermal mismatch etc.

Inter-metallic compound phases formed during welding at the weld interface are brittle in nature and greatly affect the mechanical properties of Al-Cu joints. In order to overcome this problem, these metals are welded using solid-state welding process viz. friction welding. It is observed that significant joint strength is not obtained as Al is only deforming

Original Article

properties, mechanical properties and thermal properties of the materials and also the formation of intermetallic

and there is no deformation of Cu during friction welding. In order to achieve good joint strength an attempt is made by varying the end profile of the Cu and welded to Al by friction welding. Different profiles on Cu rod, such as conical, conical with threads and face knurled were taken and welded to plane Al rod. It is observed that the change in profile did not show significant improvement in the joint properties.

KEYWORDS: End Profile, Friction Welding, Joint Strength, Optimization, Pure Aluminium, Pure Copper & Process Parameters

Received: Apr 26, 2020; Accepted: May 16, 2020; Published: Jun 04, 2020; Paper Id.: IJMPERDJUN202082

1. INTRODUCTION Industrial applications demand sound joints of dissimilar metals especially, dissimilar combination of Al-Cu, because of numerous advantages. These joints are lighter in weight and have equivalent conductivity of copper and are economical [1]. The Al-Cu joints have unique characteristics like corrosion resistance, high electric conductivity, and thermal conductivity. But a strong dissimilar joint of these metals is always challenging especially by using conventional fusion welding processes. The problems of welding these metals using fusion welding process arise because of difference in their mechanical properties, thermal properties, chemical properties and also formation of inter-metallic compounds at the joint interface which are hard and brittle in nature. In order to overcome these problems, this dissimilar combination of metal welds is performed using solid-state welding

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processes such as Friction Welding and Friction Stir Welding. Friction Welding is a solid state welding process in which one of the work pieces is rotated at high speed and the other is stationary. Initially, one of the components is rotated and other is brought into contact after which rotating component is stopped and axial force is increased so that joint occurs at the interface, as shown in Figure 1. Here, heat is generated at the interface of work pieces because of the transformation of mechanical energy due to the friction between the surfaces to be joined [2]. Figure 2 presents the basic steps involved in friction welding. In the first step, one work piece is rotated while the other is kept stationary (Fig. 2a). The work pieces are brought together and axial force is applied as and when the appropriate rotational speed is reached (Fig. 2b). Rubbing at the interface of both the work pieces heat them locally which initiates upsetting (Fig. 2c). Finally, rotation of one of the work pieces is stopped which completes the upsetting (Fig. 2d). The friction weld produced is characterised by a narrow Heat Affected Zone (HAZ), the presence of plastically deformed material around the weld (flash) and the absence of a fusion zone. Initially, this process was used for welding of steels and later on applied in the process of welding light metals. This method of joining the work pieces is applicable for both ferrous and nonferrous metals [3]. Both similar and dissimilar welds can be made economically and also in a high productive manner by using friction welding [4]. This process is mostly used for the metals which are difficult to join using fusion welding process [5]. Friction time, upsetting time, rotation speed, friction pressure, upsetting pressure are some of the important process parameters in continuous drive friction welding process [6]. Such process parameters will influence the microstructure and mechanical properties of the joint to a great extent. Friction welding process gains some of the advantages over fusion welding process like no filler material is required, joint can be made with in less time, clean joint at the interface, no shielding atmosphere is required, applicable for welding both similar and dissimilar metals, no fumes or harmful gases are emitted during the process, no scope of porosity, and many more.

Keeping in view all the advantages of the friction welding process, this process was selected for joining pure Al and pure Cu. An attempt was made to optimize the process parameters for plane specimens and also to join pure Al to pure Cu with different end profiles of Cu specimen.

Figure 1: Phases of Friction Welding Process.

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Figure 2: Basic steps in Friction Welding Process [7].

2. EXPERIMENTAL PROCEDURE 2.1 Material Pure Al and Pure Cu were the materials used in the present work with analyzed purity of 99%.

2.2 Welding process Pure Al and pure Cu rods of 10 mm diameter and 60 mm length were welded using friction welding process. A continuous drive friction welding machine (Figure 3) was used in carrying out the welds. Initially, rods with flat or plane ends are welded and later joints using different profiles of Cu are welded to know the variation in the strength of dissimilar combination of pure Al and pure Cu. In order to carry out the experiments, various parameters of friction welding process were considered. These include Spindle Speed (rpm), Friction Force (kN), Upset Force (kN) and Burn-Off (mm). These process parameters were used in order to analyze the tensile and shear strengths of the joints. These parameters will be indicated as Spindle Speed- X1, Friction Force – X2, Upset Force –X3 and Burn-Off – X4. The following are the major steps in experimentation

Figure 3: Continuous Drive Friction Welding Machine. www.tjprc.org

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2.3 Selection of Welding Process Parameters and their Levels and Orthogonal Array Since the output characteristics of the joint would mostly dependent on the process parameters, the selection of process parameters and their levels is very important in obtaining a sound dissimilar joint. In this experimentation, the above said four process parameters with 3 levels were chosen in order to access the accurate values of responses. Table 1 shows the selected process parameters and their levels. The three levels of process parameters will be indicated as L1, L2, and L3 respectively.

Table 1: Process Parameters and their Levels Process Parameters X1(rpm) X2(kN) X3(kN) X4(mm)

L1 1000 6 12 4

L2 1050 8 14 6

L3 1100 9 16 8

2.4 Selection of Appropriate Orthogonal Array and Assignment of Process Parameters to the Columns Using Taguchi Array selector, for these specified four process parameters and three levels, L9 Orthogonal array was selected as shown in Table 2 and accordingly nine experiments are conducted after assigning the parameters to the columns, as shown in Table3. Each set of these 9 experiments were repeated thrice and the average value of the required responses was calculated to meet the accuracy. Initially, experiments were carried out for rods with plane ends.

Table 2: L9 Orthogonal Array Experiment 1 2 3 1 1 1 1 2 1 2 2 3 1 3 3 4 2 1 2 5 2 2 3 6 2 3 1 7 3 1 3 8 3 2 1 9 3 3 2

4 1 2 3 3 1 2 2 3 1

Table 3: L9 Orthogonal Array of Selected Process Parameters Experiment Number 1 2 3 4 5 6 7 8 9

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X1 (rpm) 1000 1000 1000 1050 1050 1050 1100 1100 1100

X2 (kN) 6 8 9 6 8 9 6 8 9

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X3 (kN) 12 14 16 14 16 12 16 12 14

X4 (mm) 4 6 8 8 4 6 6 8 4

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3. RESULTS AND DISCUSSIONS 3.1 Plane Joints Using Taguchi Array selector, for the specified four process parameters and three levels, L9 Orthogonal array was selected.

According to L9 array, set of nine experiments were performed and one set of obtained joints are shown in Figure 4.

Figure 4: Dissimilar Joints of Al and Cu. 3.2 Mechanical Tests Tests were conducted to evaluate the responses, namely tensile strength and shear strength. Instron 1185 UTM at a cross head speed of 0.5 mm/min was used to carry out plane tensile tests for all the welds. Shear strength testing machine was used to carry out shear strength for all the welds.

3.3 Design of Experiments and ANOVA Process parameters were optimized to get accurate values of responses. Design of experiments was conducted so that the influence of selected process parameters on the responses to be assessed.

Nominal-the-better, Larger the better, Smaller the better are the performance characteristic classification in order to evaluate the S/N ratio. To maximize the responses, larger S/N ratio was chosen. Response tables for S/N ratio and means were obtained for both tensile and shear strengths respectively. In the response table for S/N ratio, the value of delta is the difference between the highest value and the smallest value of a particular process parameter. The value of delta is the criteria for ranking the process parameters for a response. Table 4 and Table 5 show the value of delta and the rank of each process parameter for both the responses namely tensile strength and shear strength respectively. Response table for means of tensile and shear strengths are tabulated in Table 6 and Table 7 respectively.

Table 4: Response Table for signal to Noise Ratio of Tensile Strength Process Parameter Delta Rank X1 (rpm) 0.39 3 X2 (kN) 0.56 2 X3 (kN) 0.6 1 X4 (mm) 0.3 4

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Table 5: Response Table for Signal to Noise Ratio of Shear Strength Process Parameter Delta Rank X1 (rpm) 1.56 1 X2 (kN) 0.75 3 X3 (kN) 1.4 2 X4 (mm) 0.58 4

Table 6: Response Table for Means of Tensile Strength Level 1 2 3 Delta Rank

X1(rpm) 165.2 159.1 166.2 7.1 3

X2 (kN) 168.1 158 164.4 10.1 2

X3 (kN) 169.8 162.1 158.7 11.1 1

X4 (rpm) 166.8 160.6 163.2 6.2 4

Table 7: Response Table for Means of Shear Strength Level

X1(rpm)

X2 (kN)

X3 (kN)

X4 (rpm)

1 2 3 Delta Rank

94.67 112.56 103.56 17.89 1

98.33 106.67 105.78 8.33 3

96.22 102.22 112.33 16.11 2

101.56 102.22 107 5.44 4

Main effects plot for tensile and shear strengths are shown in Figure 5. Since, Design of experiments could not judge the percentage contribution of individual process parameter on response, ANOVA analysis was performed so that percentage contribution of each parameter can be determined as it indicates the relative power of a factor to reduce variation [8].

From ANOVA analysis, it was found that the most significant factor influencing the tensile strength is X3 with pvalue 0.002 followed by X2, X1 and X4 whose p-values are 0.004, 0.031, and 0.088 respectively as shown in Table 8. The most significant factor influencing the shear strength is X1, X3 and X2 with p-Values 0.000 followed by X4 whose pValue is 0.003, as tabulated in Table 8.

Figure 5: Main Effects Plot for Means of Tensile Strength and Shear Strength.

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Table 8: ANOVA Analysis of Tensile Strength and Shear Strength P-Value Process Parameter Tensile Strength Shear Strength X1 (rpm) 0.031 0.000 X2 (kN) 0.004 0.000 X3 (kN) 0.002 0.000 X4 (mm) 0.088 0.003 In either case, the results are correlated with S/N ratios and are satisfactory. Regression Analysis was performed in order to correlate the independent variables and dependent variables known as process parameters and responses respectively. To validate the obtained regression model for the observed mechanical properties of friction welded dissimilar joints of pure Al and pure Cu, welding was performed with optimized process parameters, as shown in Table 9 and also experiments were conducted using these parameters for plane joints again and responses are verified with calculated values using regression equations and found to be in good agreement with each other.

Table 9: Optimized Process Parameters Responses X1 (rpm) X2 (kN) X3 (kN) Tensile Strength 1100 6 12 Shear Strength 1050 8 16

X4 (mm) 4 8

The experimental values of tensile strength and shear strength at optimized Process parameters were found to be 198 MPa and 122 MPa respectively.

3.4 Joints with Different End Profiles The macro structural evaluation of joints carried out by taking plane ended Al and Cu revealed that there is no deformation on Cu side and the deformation has occurred only on the side of Al, as shown in Figure 6. This may be the reason for not having reasonable strength of the joints. Friction welding process of dissimilar metals will get eased, if it is ensured that the deformation of both the metals is similar and enhances the bonding of the materials [9]. Attempts were made in dissimilar metal friction welding by reducing the diameter of Cu and also by using interlayers [10,11]. Therefore, an attempt has been made by changing the end profile of copper rods so that there will be some deformation on Cu side which may enhance the strength of the dissimilar Al and Cu joint. The profiles selected in this experimentation were taper, taper with threads and knurling on the face of the copper specimens, as shown in Figure 7 and the dimensions of Cu specimens are shown in Figure 8. The friction welding of the joints was carried out using optimized process parameters of plane joints. The friction welded joints of plane Al and Cu with various end profiles were subjected to tensile test and shear test. The attempt of welding Al to Cu various profiles was made assuming that the mechanical locking of materials will be there in addition to the friction bonding of the materials. But the joint strengths revealed that there is no improvement in the strength and significant mechanical locking is not observed.

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Figure 6: Macrostructure at Interface Showing Deformation of Al and Cu.

Figure 7: Cu specimens with Various Profiles.

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Figure 8: Dimensions of Cu Specimens with Various Profiles.

4. CONCLUSIONS Friction welding of pure Aluminium and pure Copper rods of specified dimensions was carried out using Taguchi L9 Orthogonal array with 4 process parameters and 3 levels. The responses measured were tensile strength and shear strength.

Following are the conclusions: 

Optimization of process parameters was done.



The most significant factor influencing the tensile strength is Upset Force followed by Friction Force, Spindle Speed and Burn-Off.



The most significant factor influencing the shear strength is Spindle Speed, Upset Force and Friction Force followed by Burn-Off.



Tensile strength is found to be maximum when the Spindle Speed is 1100 rpm, Friction Force is 6 kN, Upset Force is 12 kN and Burn-Off 4 mm.



Shear strength is found to be maximum when Spindle Speed is 1050 rpm, Friction Force is 8 kN, Upset Force is 16 kN and Burn-Off 8 mm.



ANOVA analysis is performed, and the results are co related with S/N ratios of tensile strength and shear strength.



The joints obtained with plane end Al and Cu with various end profiles did not show any improvement of joint strength compared to that of the joints obtained with Al and Cu rods with plane end profiles.

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ACKNOWLEDGEMENT The authors wish to thank the management of MGIT and JNTUA for their support in carrying out this work. The authors express sincere thanks to Dr. G. Madhusudhan Reddy, Outstanding Scientist and Director, DMRL, Hyderabad for the guidance and help in carrying out the work at DMRL. The authors also thank Mr. B. Chandra Sekhar, Scientist, DMRL for the help provided.

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AUTHOR’S PROFILE

Ms. M. PRATYUSHA received her M.Tech. from JNTU Hyderabad and pursuing her Ph.D. at JNTUA, Ananthapuramu.

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She is currently working as Asst.Professor in the Department of Mechnical Engineering at Mahatma Gandhi Institute of Technology, Hyderabad.

Dr. P.VENKATA RAMANA is currently a Professor in the in the Department of Mechnical Engineering at Mahatma Gandhi Institute of Technology, Hyderabad. He has published 40 papers in variuos National and International Journals/Conferences.

Dr. G. PRASANTHI is currently a Professor in the in the Department of Mechnical Engineering at College of Engineering, Jawaharlal Nehru Technological University Anantapuramu. She has published more than 100 papers in various National and International Journals/Conferences.

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