Marius Pop-Calimanu, Traian Fleser. Politehnica University of Timisora, Faculty of Mechanics, Bv. Mihai Viteazu no. 1,

Transcription

1 THE INCREASING OF WELD STRENGTH BY PARAMETERS OPTIMIZATION OF ULTRASONIC WELDING FOR COMPOSITE MATERIAL BASED ON ALUMINIUM USING DESIGN OF EXPERIMENTS. Abstract Marius Pop-Calimanu, Traian Fleser Politehnica University of Timisora, Faculty of Mechanics, Bv. Mihai Viteazu no. 1, Ultrasonic welding is a solid-state welding process in which similar or dissimilar work pieces are jointed by the application of high frequency vibratory energy, where the work pieces are held together under pressure without melting. The problem faced by researchers and industry which have deals with ultrasonic welding process is poor strength of the weld, due to improper selection of welding parameters. Therefore, we are usually interested to determine which variables process affects the response. A stage is to optimize, this means that we can determine the region in the important factors that lead to the best possible response. In this paper, welding parameters, like welding time, welding pressure and amplitude of the vibration are taken into account during the realization of ultrasonic welded joints of Al/20%SiC composite material under disks form, whose thickness are 1 mm. This work focuses on the development of an effective methodology to determine the optimum conditions for welding, that maximize the strength of joints produced by ultrasonic welding. Here we have investigated the effect of process variables and energy input on joints formation between Al/20%SiC composite material disks, and a report on the optimum welding conditions. A suitable experimental design, based on 2 k factorial design was designed and executed for conducting trials. These designs have a greatly simplified analysis. Keywords: composite material, ultrasonic welding, design of experiments, welding strength 1. INTRODUCTION Metal matrix composite MMC s are extremely versatile materials which allow the designer to put together various properties of metals and non-metals in one piece.[1] Because these types of new materials start to be exploited more and more in automotive industry, in aeronautics industry etc., due to its advantages such as: high corrosion resistance, good stiffness, low density, improving of properties at high temperatures etc. [2]. Generally, these composite materials are difficult to weld compared with conventional materials, due to large differences between melting temperature of reinforcing elements and matrix, as well as thermal conductivity and different specific heat of the components, which lead to differences between thermal fields and crystallization conditions [3]. Ultrasonic welding of metals is an industrial technique, where similar or non-similar materials are joining together by applying a high frequency ultrasonic vibration, parallel on the surface which follows to be jointed, under the pressure of forces to create a solid state welding. Therefore, the temperature developed between parts that must be joined, are under the melting temperature of the respective material [4]. Ultrasonic welding can be done in few seconds without being modified the properties of material Fig.1. Because this process has been used successfully in the joining of the conventional materials, we don t see any impediment to use it, in the joining of metal matrix composites. In this process of welding there are many variables and also exist a large enough domain for study the ultrasonic welding of Al/20%SiC metal matrix composite. In the ultrasonic welding process, industries obtain a poor quality of the welds [5]. The selection of parameters which have a significant influence in the weld strength is very important. From the literature review, it was clearly observed that welding pressure, welding time and amplitude are critical parameters in deciding the weld strength and quality of the welds [6]. It seems that the

2 optimization method used, and certain the full factorial experiment method in ultrasonic welding of the Al/20%SiC metal matrix composite, has not been reported. Fig.1 Basic principle of ultrasonic metal welding Therefore, in this paper is achieved a systematic study regarding the ultrasonic welding of Al/20%SiC composite material and an optimization of process parameters, using the full factorial experiment method. Also, the objective of this study is to conduct the experiments using the full factorial experiments method, to find out the optimum levels of the parameters and their interactions, which will produce a high strength of the joint in case of the ultrasonic welding of Al/20%SiC composite material. 2. EXPERIMENTAL SECTION 2.1 Full factorial experiments method Although the full factorial experiments method is known very well, we present some important steps. For this category of programs we will use influence factors, with two levels of variation high level (+1) and low level (-1). Having three influence factors, with two levels of variation, we will have to do eight runs. From the geometric point of view, the design is a cube as shown in Fig. 2a, with eight runs which are forming the corners of the cube. In Fig. 2b it is the matrix program. This type of design allows the estimation of three main effects (A, B and C), the estimation of the effects of three interactions having two influence factors (AB, AC, and BC) and the estimation of the effect of one interaction having three influence factors (ABC) [7]. 2.2 Experimental setup Fig. 2 The 2 3 factorial design The jointing was performed using a conventional ultrasonic metal welding machine (2000 W, 20 khz), for different ranges of the joint parameters which is shown in Fig. 3. The sonotrode used for this experiment is made of steel. The anvil is also made of steel provided with serrations at the top surface. The area of

3 sonotrode which come into contact with the work piece is also provided with serrations, similar to the top surface of the anvil, for preventing the sliding of the work pieces which follow to be jointed. The samples used in the experiment, are formed from Al/20%SiC composite material, under disks form with size 15x1 mm, this means that we have 20% silicon carbide in the form of very fine particles. Fig. 3 Ultrasonic welding equipment Tab. 1 Mechanical and thermal properties of Al/20%SiC [8] Mechanical and thermal properties of this material (Al/20%SiC) are shown in Tab. 1. Before joining process, the samples were cleaned mechanically and chemically to remove the oxide layer from the surface because we don t want to affect the weld strength. 2.3 Indentifying the influence factors Material Properties Value Young s Modulus of 1 Elastic[GPa] Poisson s Ratio 0.29 Initial Yield Stress [MPa] 125 Ultimate Tensile Strength 3 [MPa] Thermal Conductivity [W/mK] 160 Coefficient of Thermal Expansion [ C ] 3 Density [kg/ m ] 2800 In the full factorial experiments method, there are two types of influence factors for indentify the settings of the optimal process and this are controllable and uncontrollable influence factors. The controllable influence factors are those factors which can be controlled during the technological process (time, power, pressure, etc.), and, uncontrollable influence factors are those factors which can t be controlled during the technological process (noise factors). In this paper, the noise factors are neglected, and the chosen controllable factors are the welding time, welding pressure and amplitude of sonotrode, each of the factors with two levels of variation, as shown in Tab. 2. Because the pieces which need to be jointed are very small, and we can not clamp in the pull test machine to determine the strength of the joint, so the pursued objective functions is net area of the joint and the energy input on joints formation of this kind of material. The obtained results were done with specialized software for statistical designing and analysis MINITAB [9]. Tab. 2 The settings of factors and levels No. Factor Description Level 1 Level 2 1 Weld pressure(bar) A Weld time (sec) B (%) C 6 Are taken into account the interactions between those three controllable factors, which is the interaction between welding pressure and welding time, the interaction between welding time and the amplitude of sonotrode and the interaction between welding pressure and the amplitude of the sonotrode. In this work welding time is expressed in seconds, welding pressure which in its turn determine the welding force expressed in bar, and the amplitude expressed in percentage from the maximum value, A max = 100µm. For measuring surface of the joint, we have used a caliper with a precision of 0.1 mm, and the energy input on the joints formation was read from the ultrasonic generator interface.

4 Term , Brno, Czech Republic, EU 3. RESULTS AND DISCUSSION The design of experiments by using the full factorial experiments method was adopted systematically to optimize the jointing process parameters of Al/20%SiC composite material samples with thickness of 1 mm. The obtained results for evaluate the objective function (net area of the joint S and the energy input on joint formation) are presented in Tab. 3 and Fig. 4. In the Pareto charts, influence factors are note: A welding pressure, B welding time and C amplitude of the sonotrode. From Pareto chart for net area of the joint S, Fig. 5a, can be observed that interaction between welding time and amplitude of the sontrode (BC), welding pressure and welding time (AB), welding pressure and Fig. 4 The welded samples (Al/20%SiC) amplitude of the sonotrode (AC), prove to have the most significant effect on response (weld strength), but neither the influence of welding time factor (B) and the interaction between welding pressure, welding time and amplitude of the sonotrode not be neglected. Tab. 3 Experimental results No. [bar] [sec] [%] Net area of joint S [mm 2 ] Energy [J] The fact that the influence of welding time factor is the most significant in relation with welding pressure and amplitude of the sonotrode factors, can be seen also in the graphic representation of main effects Fig. 6a. From Pareto chart of energy input on joint formation, Pareto Chart of the Effects Fig. 5b, we can see that welding pressure factor has (response is Net area "S", Alpha = 0,05) the greatest effect on response which is also 13,80 Factor Name confirmed in the Fig. 6b, but in this case, the other BC A factors and their interactions have a quite significant AB B effect on the response. From Tab. 3 is concluded that AC C welding pressure at level 1 (1.4 bar) and welding time B at level 1 (1.2 sec), the measured values of net area ABC A of joint and energy input on the joint formation are C greater than the welding pressure from level 2 (1.7 bar) and welding time from level 2 (2 sec). It is Effect someway normal, because increasing the welding Lenth's PSE = 3,6675 pressure and welding time the sonotrode automatically a) maintains more the work pieces, without significant

5 Mean Mean Term , Brno, Czech Republic, EU A ABC AB B C BC AC 0 Lenth's PSE = Pareto Chart of the Effects (response is Energy, Alpha = 0,05) 200 Effect 0 429,1 Factor A B C Name friction, but exist also the possibility that the material in question is a heterogeneous material, thing which make difficult the achievement a high that the material in question is a heterogeneous material, strength of joint. So between of these two levels of variation, level 1 is the best. In the Fig. 6ab the main effects are plotted for net area of the joint and for energy input on the joints formation, obtained using a special statistical analysis software, representations that are based on the conclusions from table 3. So in this paper combination of factors that maximizes the joint strength of Al/20%SiC composite material is welding pressure (A) 1.4 bar b) welding time (B) -1.2 sec and amplitude of the sonotrode Fig. 5 Pareto chart for: a) net area of joint S (C) -% and the combination of factors that minimizes energy input on the joint formation the joint strength is welding pressure (A) 1.4 bar, welding time (B) 2 sec and amplitude of the sonotrode (C) % (Tab. 3). Main Effects Plot for Net area "S" Data Means Main Effects Plot for Energy Data Means a) b) Fig.6 Plot of main effects at various levels of factors for: a) - net area of joint S ; b) - energy input on the joint formation Graphical representation of interactions of welding parameters for net area of the joint and for energy input on the joint formation it is shown in Fig. 7ab. It can be seen that significant interactions of factors are only in the first chart, Fig. 7a, between B and C factors, between A and B factors and between A and C factors, this can be seen by crossing the levels of variation, and in the second chart, Fig. 7b, levels of variation are almost parallel to each other, this means that there are not interactions between influence factors. Interactions Plot for Net area "S" Interactions Plot for Energy T ime A mplitude 25 Fig. 7 Graphical representation of interactions of influence factor for net area of joint and energy input on the joint formation at different levels of factor

6 4. CONCLUSIONS 1) Have been studied those variabiles which affect the Al/20%SiC composite material by ultrasonic welding process. 2) Have been identified the optimal parameters for maximize and minimize the strength of joint. 3) The optimal parameters settings to achieve the maximum strength of the joint is: - welding pressure of 1.4 bar; - welding time of 1.2 sec.; - and, amplitude of the sonotrode of %. 4) The optimal parameters settings for minimize the strength of the joint is: - welding pressure of 1.4 bar; - welding time of 2 sec; - and, amplitude of the sonotrode of %. 5) It was observed that welding pressure and welding time has a significant effect on the response (joint strength). 6) It was observed that the interactions of influence factors are more significant on the net area of the joint, than on the energy input on joint formation. ACKNOWLEDGEMENTS: This work was partially supported by the strategic grant POSDRU 107/1.5/S/77265, inside POSDRU Romania co-financed by the European Social Fund- Investing in People. LITERATURE [1] KAINER, K.U. Basics of Metal Matrix Composites, Metal Matrix Composites, Wiley-vch Verlang GmbH&Co, Weinheim, 2006, page [2] MATSOUKA, S.I. Ultrsonic Welding of Ceramics/Metals Using Inserts, Journal of Material Processing Technology, 1998, Vol. 75, No. 1-3, page [3] YANG,Y., RAM, J., STUCKER, B. An experimental Determination of Optimum Processing Parameters for Al/SiC Metal Matrix Composites Made Using Ultrasonic Consolidation, Journal of Materials Precessing Technology-Transactions of ASME, 2007, Vol. 129, No. 4, page [4] VRIES, E. Mechanics and Mechanism of Ultrasonic Metal Welding, Ph.D. thesis, Ohio state University Columbus, 2004, page 40-. [5] ELANGOVAN, S., PRAKASAN, K., JAIGANESH, V. Optimization of Ultrasonic Welding Parameters for Copper to Copper Joints Using Design of Experiments, Int J Adv Manuf Technol, 2010, No. 51, page 163 [6] ELANGOVAN, S., SHENTON, P., PRAKASAN, K. Experimental Studies on Optimization of Process Parameters and Finite Element Analysis of Temperature and Stress Distrbution on Joining of Al-Al and Al- Al 2O 3 Using Ultrasonic Welding, Int J Adv Manuf Technol, 2011, No. 55, page 631. [7] MONTGOMERY, D. Introduction to Statical Quality Control. Sixth Edition, John Wiley & Sons, 2009, page , ISBN [8] Available from: Accessed: [9] Available from: Minitab Inc., Analysis-User s Tutorials, Accessed: