Optimization of process parameters of High Pressure Die Casting process for ADC12 Aluminium alloy using Taguchi method

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1 Volume 120 No , ISSN: (on-line version) url: Optimization of process parameters of High Pressure Die Casting process for ADC12 Aluminium alloy using Taguchi method Veeresh G Balikai 1, I G Siddlingeshwar 1, Mahesh Gorwar 1, 1 Associate Professor, Dept of Mechanical Engineering, BVBCET, Hubli , Karnataka, India, veeresh gb@bvb.edu June 11, 2018 Abstract A study has been carried out to optimize the die casting process parameters in order to achieve the improved quality of high pressure die casting (HPDC) products, which is the challenge for the small and large scale manufacturers of HPDC products. In this study the approach used is the experimental study to optimize the die casting process parameters for the ADC12 aluminum alloys. The ADC12 aluminum alloy components were chosen for the study and objective was to reduce the porosity in these components which help to obtain the good quality castings. The porosity is the most common defect frequently encountered in aluminium high pressure die castings, which increases the rejection rate and scrap rate and reduces the productivity. Porosity formation is closely related to die casting process 1 959

2 parameters. Hence in order to minimize the porosity, this paper investigated the effect of process parameters on porosity formation in HPDC of ADC12 alloys and optimization of process parameters carried out using Taguchis parameter design approach. Experiments were conducted by varying selected process parameters with different levels as per Taguchi method. ANOVA was performed to find the significance of parameters on porosity formation in die castings. Results indicated that selected process parameters have significant effect on porosity formation. The optimum process parameters were obtained for minimum porosity in HPDC of ADC12 alloy. Key Words:Optimisation, DOE, Taguchi Method, HPDC, Process parameters, Porosity 1 Introduction High pressure die casting (HPDC) process is an efficient manufacturing process to produce complex, thin and thick wall components economically with high productivity and high dimensional accuracy for automotive, aerospace, defence and other industries [9,13]. In aluminium high pressure die casting process, molten aluminium alloy is injected into a metal mould at high speed and allowed to solidify under high holding pressure [10]. ADC12 based alloys have been widely used in the field of HPDC process to produce lightweight components with low cost, good mechanical properties and high corrosion resistance for electric, electronic and automobile and other applications [5]. In high pressure die casting of ADC12 aluminium alloys, Porosity is the most common defect caused due to entrapment of air/gas and oxides due to the turbulent flow of metal during the cavity filling [8]. This defect is classified as gas porosity (caused due to air trapped air in sleeve), shrinkage porosity (due to solidification of the metal in the gate before solidification in other areas of the casting) and flow porosity (caused due to insufficient pressure towards the end of cavity filling). The mechanical properties and pressure tightness are affected due to presence of porosity in castings. Porosity in a high pressure die casting varies both with part geometry of component and casting parameters of the process [9]

3 Porosity formation is determined by several independent process parameters. The focus of this research is to investigate the effects of selected process parameters on casting porosity and reduction of porosity formation in die castings of ADC12 aluminium alloy can be achieved by using Taguchis parameter design approach for the Design of experiments (DOE). The porosity formation is minimized by selecting the optimum process parameters for HPDC process. 2 Taguchi Technique for the Design of experiments (DOE) Taguchis parameter design approach is an experimental technique that helps to investigate the best combinations of process parameter and levels in order to obtain statically reliable results. The Taguchi optimization procedure begins with the selection of the orthogonal array with distinct number of levels defined for each of the parameter selected and finds the optimum levels of selected parameters [3]. The steps to achieve optimum porosity in casting are summarised below: Select the significant process parameters that cause the porosity formation in pressure die casting of ADC12 aluminium alloy and the aim of the die casting process is minimum porosity in castings. Perform the high pressure die casting process under the experimental conditions as per chosen orthogonal array (OA) and parameter levels. Collect and analyse the data on casting porosity. An Analysis Of Variance (ANOVA) is to be performed to find the significance of the selected parameters. Response graphs are plotted to find optimum levels for each parameter. Based on results select the optimum process parameters for the minimum casting porosity in die castings. A. Selection of process parameters affecting the casting porosity On reviewing of literature, optimum casing porosity in pressure die casting is the result of a great number of process parameters. Cause and effect diagram (also called Ishikawa diagram, as shown in Fig.1) was constructed to identify the significant process parameters that may affect the porosity in the high pressure die castings of 3 961

4 ADC12 aluminium alloy [10]. Among these, pouring temperature, injection pressure, plunger velocity at 1st phase and plunger velocity at 2nd phase were selected as the most significant process parameters to minimize the porosity in the experimental design. The selected casting process parameters and their ranges along with 5 levels are given in Table 1. Fig.1. Cause and effect diagram (Ishikawa diagram) for casting porosity Most of the available literature on aluminium high pressure die castings focuses on the influence of process parameters on the porosity formation in die castings. G.O. Verran et al (2008) investigated optimization of of three injection parameters (slow shot, fast shot and upset pressure) for minimum porosity in the die casting SAE 305 alloys using Taguchi method. The best results in terms of the density of the die casting part were obtained when low slow and fast shots and high up set pressure were used. The porosity in metal casting products was reduced and hence improving the quality of the product by selected process parameters of die casting [3]. V. D. Tsoukalas (2003) investigated the effect of die casting machine related parameters on porosity formation in complex aluminium diecasting using Taguchi s technique. Among the machine parameters considered, multiplied pressure in the 3rd phase, Plunger velocity in the 2nd phase, die cavity filling time have the more significant effect on porosity formation in aluminium die castings and optimum machine parameters were determined for minimum porosity in aluminium die-casting [6]. Lars Arnberg et al (2015) reviewed the effect of injection parameters on the porosity and tensile properties of Al-Si alloy high 4 962

5 pressure die castings. Tensile properties were increased and porosity was reduced at Higher values of intensification pressure and gate velocity. Hence sound and reliable castings had been achieved by controlling the injection parameters such as the intensification pressure and gate velocity and by selecting the best runner-gate system to minimize defects [8]. G.P.Syrcos (2003) carried out work on Optimization of the aluminium alloy die casting process based on the Taguchi method. The experiments have been performed by varying process parameters such as metal temperature, filling time, piston velocity and hydraulic pressure using as suggested by L27 orthogonal array of Taguchi method. ANOVA was performed in order to study the significance of selected parameters. The results indicated that the selected parameters affect the casting density of the aluminium alloy castings effectively and optimum process parameters were obtained for optimum porosity in castings [4]. B. Selection of orthogonal array (OA) The parts are produced at room temperature as per experimental design. Taguchi design of experiment methods are used to optimize the experimental design based on the number of control parameters and the number of their levels. An experimental design is conducted using an orthogonal array (OA). OA is selected based on degree of freedom (DOF) of process. In this study, total DOF for 4 parameters and 5 levels is 25; hence choose L25 OA which is used as the experimental design [14-15]. The total number of experiments is equal to the number of rows in OA and should be equal to or greater than degrees of freedom. Table 1: Process parameters and their ranges along with 5 levels Experiment and Discussions The experiments, as well as the manufacturing process of this part, were conducted in the high pressure die casting machine 400T HMT model by varying operating parameters as given in the Table 1. The molten metal of ADC12 is poured manually into the 5 963

6 shot sleeve. The casting extraction and the application of lubricant spray have been done manually and automatically. The experiments are conducted for 25 different combinations as per L25 OA as shown in Table 3 and each combination of experiments will be repeated three times to acquire a more accurate result in this process. The chemical composition of the ADC12 aluminium alloy used in the experimental procedure is given in Table 2. The casting density being directly related to its porosity was considered and measured in each trial conditions using Archimedess principle. The quality assessment of the die casting parts was carried out by a quantitative analysis of the porosity. Density of 3 castings for each combination was calculated using formula, M castinginair ρ apparent = [ ρ water ] (1) M castinginair M castinginwater Where ρ apparent Apparentdensityofthecasting(measured)(gm/cm 3 ), M castinginair Massofthecastinginair(gm); M castinginwater Massofthecastinginwater(gm). Average density of 3 sample castings for each combination was calculated. The porosity for each combination was calculated using formula, porosity(%) = [ ρ apparent ρ th ρ th ] 100 (2) Where ρ th th Theoretical density of a fully dense casting of ADC12 alloy having no porosity (2.67 gm/cm3). The density of 3 samples for each combination, average values of casting density is calculated and casting porosities obtained in the experiments are shown in Table 3. Porosity values of 25 combinations was taken as response for the analysis and used in Minitab 16 software to carry out Taguchi optimization. The results of die casting porosity for each process parameter at 5 levels are given in Table 3 and are plotted in Fig

7 The Taguchi technique stresses the importance of studying the variation of the response using the signal to noise (S/N) ratio [11-12]. The reason for this is to minimize the porosity variation due to uncontrollable process parameters. In this, the porosity is a Lower the better type of quality characteristic. So the S/N ratio was used for that type of response, and is given by S N ratio = 10 log[ 1 n n ( 1 )] (3) y 2 i=1 i Where Yi is the response value for a trial condition repeated n times. The S/N ratios were computed for 25 trial conditions. The results of S/N ratios of die casting porosity for considered parameters at five levels are given in table 3. Taguchi method suggested the S/N ratio as the objective function for matrix experiments to measure response (porosity %) and also the significant process parameters through analysis of variance (ANOVA). The 6thtrial is matched with results and this is worst component which contains more porosity. And 21sttrial is matched with results and this is the best component which has minimum porosity. Both the trials are highlighted in bold fonts in the table 3. Table 3 Orthogonal Array, porosity and S/N ratios for porosity at different levels for ADC 12 aluminium HPDC alloy 7 965

8 ANOVA (analysis of variance) was performed to find the significance of selected process parameters on porosity formation in aluminium high pressure die castings and ANOVA for S/N ratios of die casting porosity is given in Table 4. From this Table, it is concluded that plunger velocity (1st phase), plunger velocity (2nd phase) and pouring temperature significantly affects the die casting porosity, representing a contribution of %, % and %. Also intensification pressure contributes 2.134% to die casting porosity. Table 4: ANOVA for S/N ratios of die casting porosities 3 CONCLUSION: The Experimental results shows that variations in die casting process parameters have significantly effects on the porosity formation of aluminium alloy die casting. Pouring temperature, intensification pressure, plunger velocity (1st phase), plunger velocity (2nd phase) are the influential process parameters which are affecting the formation of porosity in ADC12 aluminium alloy castings. The percentage contribution of each parameter and optimum process parameters with their levels for the optimum casting porosity in high pressure die castings of ADC12 aluminium alloy was as follows: The Taguchi Method parameter design approach for the optimisation of the process parameters in HPDC for ADC12 alloy has given the satisfactory results by reducing the porosity and improving the quality of the castings. The parts have been validated through the microscopic studies

9 References [1] S. W. Choi, Y. C. Kim, J. I. Cho & C. S. Kang (2008), Influence of die casting process parameters on castability and properties of thin walled aluminium housings, International Journal of Cast Metals Research, 21:1-4, pp [2] Murray, M.T. (2011) High pressure die casting of aluminium and its alloys, M Murray & Associates Pty Ltd, Australia. [3] G.O. Verran, R.P.K. Mendes, L.V.O. Dalla Valentina (2008), DOE applied to optimization of aluminium alloy die castings journal of materials processing technology, 200 pp [4] G.P.Syrcos (2003), Die casting process optimization using Taguchi method, journal of materials processing technology, 135, pp [5] M.A. Irfan, D. Schwam, A. Karve, R. Ryder (2012), Porosity reduction and mechanical properties improvement in die cast engine blocks, Materials Science and Engineering A 535, pp [6] V. D. Tsoukalas (2003), The effect of die casting machine parameters on porosity of aluminium die castings, International Journal of Cast Metals Research, 15:6, pp [7] Guilherme Ourique Verran, Rui Patrick Konrad Mendes, Marco Aurelio Rossi, Influence of injection parameters on defects formation in die casting Al12Si1.3Cu alloy: Experimental results and numeric simulation, Journal of Materials Processing Technology, 179 (2006) pp [8] Anilchandra R. Adamane, Lars Arnberg, Elena Fiorese, Giulio Timelli, Franco Bonollo, (2015), Influence of Injection parameters on the porosity and tensile properties of High pressure die cast Al-Si Alloys: A Review, International Journal of Metalcasting, Volume 9, Issue 1. [9] Laihua Wang, Peter Turnley, Gary Savage (2011), Gas content in high pressure die castings, Journal of Materials Processing Technology 211, pp

10 [10] V.D. Tsoukalas (2008), Optimization of porosity formation in AlSi9Cu3 pressure die castings using genetic algorithm analysis, Materials and Design 29, pp [11] Roy, R. K. Design of Experiments Using the Taguchi Approach: 16 Steps to Product and Process Improvement, 2001 (J. Wiley, New York). [12] Taguchi, G. and Konishi, S. Orthogonal Arrays and Linear Graphs, 1987 (American Supplier Institute, Dearborn, Michigan). [13] Quang-Cherng Hsu and Anh Tuan Do (2013), Minimum Porosity Formation in Pressure Die Casting by Taguchi Method, Mathematical Problems in Engineering. [14] Taguchi G. Introduction to quality engineering. 1st ed. New York: Asian Productivity Organization, UNIPUB; [15] Logothetis N. Total quality control. 2nd ed. UK: Prentice-Hall International Limited; [16] K.Ch.Apparao and Anil Kumar Birru, Optimization of Die casting process based on Taguchi approach, Materials Today: Proceedings 4 (2017) pp

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