MINIMIZATION OF CRACKS IN ALUMINUM ALLOY CASTING Shashidhar Channappa Honnihalli* 1, Dr. Vinayak N. Gaitonde 2

Size: px
Start display at page:

Download "MINIMIZATION OF CRACKS IN ALUMINUM ALLOY CASTING Shashidhar Channappa Honnihalli* 1, Dr. Vinayak N. Gaitonde 2"

Transcription

1 ISSN IJESR/October 2014/ Vol-4/Issue-10/ Shashidhar Channappa Honnihalli et al./ International Journal of Engineering & Science Research MINIMIZATION OF CRACKS IN ALUMINUM ALLOY CASTING Shashidhar Channappa Honnihalli* 1, Dr. Vinayak N. Gaitonde 2 1 M. Tech. Student, Dept. of Industrial and Production Engineering, B. V. Bhoomaraddi College of Engineering and Technology, Hubli, Karnataka, India. 2 Prof, Dept. of Industrial and Production Engineering, B. V. Bhoomaraddi College of Engineering and ABSTRACT Technology, Hubli, Karnataka, India. The present work discusses the effect of process parameters on minimization of cracks in aluminium alloy castings of engine casing production. The high pressure die casting (HPDC) is generally applied to casting of aluminum alloys to get good surface finish with required tolerances and dimensional accuracy. The cracks can be minimized by selecting the optimal process parameters such as holding furnace temperature, erature and injection pressure. The experiments were planned as per L 9 orthogonal array (OA). The analysis of means (ANOM) has been performed for the selection of best combination parameters and analysis of variance (ANOVA) has been carried out for determining the relative significance of process parameters. Keywords: Aluminum alloys, Cracks, High pressure die casting, Orthogonal array and Taguchi technique. INTRODUCTION The high pressure die casting (HPDC) is a mechanized process in which the molten metal is injected with a die casting machine under force using substantial pressure into a steel mold or die to form components [1]. As a result of exceptional dimensional precision and smooth surfaces, most of the high pressure die castings do not require machining except the removal of flash around the edge and probable drilling and tapping of holes. The high pressure die casting production is fast and inexpensive when compared to other casting processes. Even though, in HPDC process, high velocity permits for the manufacture of thin - walled castings, the related turbulent conditions remain the key source of interior and surface casting defects, which may have harmful effects on the mechanical properties [2]. In this paper, in order to minimize the cracks in aluminium alloy castings of engine casing produced through HPDC, the techniques like cause-effect diagram and Taguchi methods were applied to know the factors affecting the process and the selection of the optimal process parameters respectively. The process flow of HPDC of our present investigation is shown in Fig.1. Raw Material Melting Furnace Robot Control Holding Furnace HPDC Machine CNC Machine 1 Rare half finishing CNC Machine 2 Front half finishing CNC Machine 3Finishing Fig 1: Process flow of High Pressure Die Casting (HPDC) *Corresponding Author 598

2 METHODOLOGY In the proposed investigation on crack minimization of aluminium alloy casting of HPDC process, Taguchi method is used for the optimization of process parameters. Cracks in casting product MATERIAL ALLUMINIUM ALLOY LM24 GRADE Si11% Cu2% CASTING MATERIAL AND IMPURITIES TEMPERATURE IS MAINTAINED AT ABOVE C MELTING FURNASE HOLDING FURNASE TEMPERATURE IS MAINTAINED CONST. AT C TO C DIE TEMPERATURE (160 0 C TO C) INTENSIFICATION PRESSURE (650 TO 700 bar) HPDC MACHINE Fig. 2: Cause and effect diagram Initially, cause and effect diagram was drawn to identify the factors affecting the process (Fig.2). After careful analysis through cause and effect diagram, major factors affecting the cracks formation in casting products were identified, namely, holding furnace temperature, erature and injection pressure. For each of these three parameters, three levels were selected based on our preliminary investigations. L 9 orthogonal array (OA) was selected to conduct the experiments [3]. 2.1 Taguchi Method Taguchi method is an influential optimization tool for the design of a high quality system. It offers an efficient and a methodical approach to optimize the performance/quality of a process. Taguchi parameter design optimizes the performance through the settings of design parameters and reduces the sensitivity of system performance to source of variation [4]. Copyright 2013 Published by IJESR. All rights reserved 599

3 STEPS INVOLVED IN THE CURRENT RESEARCH Conducting the experiments on HPDC machine using L 9 orthogonal array (OA) Selection of optimal parameters using analysis of means (ANOM) Performing analysis of analysis variance (ANOVA) for determining relative importance of each parameter Validation. DATA COLLECTION The present study was undertaken at the leading industry of aluminium alloy casings production involving HPDC process. The relevant data was collected from the daily reports. The data was collected for 25 working days in a month for every 10 outputs. After conducting a matrix experiment as per L 9 orthogonal array (OA), the data from all the experiments in the set taken together were analyzed to determine the effects of various parameters. In the existing process, it was noticed that the cracks generated in the casting products (Engine Casing) was higher and also not up to the desired level and hence lead to rejection of castings. Therefore, it has been decided to select the optimal HPDC parameters to minimize the cracks in HPDC process. The HPDC line process parameters evaluated through cause and effect diagram are Holding furnace temperature ( 0 C). Die temperature in ( 0 C). Injection pressure (bar). Table 1 gives the control factors and their identified levels. Table 2 illustrates the experimental plan for HPDC process along with the % of cracks produced in aluminium alloy casting. Table 1: Factors and their level S. No. Factors Levels Level 1 Level 2 Level 3 1. Holding Furnace Temperature in 0 C Die Temperature in 0 C Injection Pressure in bar Table 2: Experimental plan and % of cracks for aluminum alloy casting of HPDC process Trial No. Level of factor A B C Cracks (% ) In the current research, the main objective is to minimize the cracks generated in the die casting products. Hence, the objective function as smaller the better type category was selected. For smaller the better type, the objective function is given by: Copyright 2013 Published by IJESR. All rights reserved 600

4 Where, n = Number of trials; y i = Cracks RESULTS AND DISCUSSION Analysis of experimental results based on signal to noise (S/N ratio was performed using Minitab software [5] and analysis of means (ANOM) plots obtained are given in Table 3 and Fig. 3 respectively. Table 3: ANOM results based on S/N ratio Factor Level 1 Level 2 Level 3 Optimum level A * 3 B * 3 C * Main Effects Plot for SN ratios Data Means Furnace temp Mean of SN ratios injection press Signal-to-noise: Smaller is better 700 Fig 3: Main effects plot of crack based on S/N ratio ANOM plot (Fig. 3) indicates that % rejection due to cracks is minimal at higher level (3) of holding furnace temperature, higher level (3) of erature and medium level (2) of injection pressure. The relative magnitude of the factor effects could be judged from the ANOM table (Table 3), which gives the average S/N ratio for each factor level. A better feel for the relative effect of different factors can be determined by the decomposition of variance, commonly called analysis of variance (ANOVA). It is also used to estimate the error variance for the effects and variance of the prediction error. Table 4: Summary of ANOVA results based on S/N ratio Factor Degree of freedom ( ) Sum of squares (SS) Mean square (MS) % contribution A B C Error Total From the results of ANOVA as presented in Table 4, it is observed that holding furnace temperature has major contributions in minimizing the cracks. On the other hand, injection pressure has moderate effect and the die temperature has least effect on minimizing the cracks in aluminium casting of HPDC process. Since, the ANOVA has resulted in % error contribution; we can suspect the possibility of inclusion of interaction effects of identified process parameters in minimizing the cracks in aluminium casting of HPDC process. Hence, interaction plots were generated using Minitab [5] and are given in Fig. 4. The nonparallel lines on the interaction plots clearly indicate synergistic interaction between the process parameters identified. Copyright 2013 Published by IJESR. All rights reserved 601

5 Interaction Plot for defects in % Data Means Furnace temp Furnace temp injection press Fig 4: Interaction effects plot of crack based on S/N ratio After selecting the optimal levels of process parameters, the final step is to predict and verify the adequacy of the model. The experiments were conducted with optimal levels of factors obtained by Taguchi optimization. The measured values of cracks under the optimal process conditions were used to determine the observed values of signal to noise ratio. In order to judge the closeness of observed value of S/N ratio with that of the predicted value, the variance of prediction error is determined and the corresponding two-standard deviation confidence limits for the prediction error of the S/N ratio is calculated. The results of conformity tests are analyzed that the prediction error is less than or equal to the standard deviation limit and it is summarized in Table 5 and found that the additive model of cracks is adequate. Table 5: Confirmatory Test Results CONCLUSION Levels (A, B, C) 3, 3, 2 Signal to noise ratio observed (η obs ), db Predicted Signal to noise ratio (η pred ), db Prediction error, db 4.35 Confidence limit ( 2σ), db ±18.47 The following conclusions are drawn from the present investigation: 1. Minimization of cracks in aluminum alloy casting produced through HPDC process is achieved with optimal level settings of process parameters such as holding furnace temperature (640 0 C), erature (170 0 C) and injection pressure (650bar). 2. Holding furnace temperature has main contribution in minimizing the cracks followed by injection pressure and erature for minimizing the cracks in aluminium casting of HPDC process. 3. ANOVA has resulted in 37.38% error contribution, clearly indicating the presence of interactions between the two process parameters; which is clearly evidenced in the interaction plots.. 4. Robust design can be used as an effective tool for optimization of HPDC process for aluminium alloy casting with less experimentation using Taguchi L 9 orthogonal array (OA). REFERENCES [1] Gariboldi E, Bonollo F, Rosso M. Proposal of a Classification of Defects of High-pressure die cast Products 2007; [2] Lee SG, Patel GR, Gokhale M, Horstemeyer MF. Quantitative fractographic analysis of variability in the tensile ductility of high-pressure die-cast AE44 Mg-alloy. Materials Science and Engineering 2006; 427: 1-2, [3] Phadke MS. Quality Engineering Using Robust Design. Prentice Hall, International, New Jersey, [4] Ross PJ. Taguchi Techniques for Quality Engineering, McGraw Hill Inc., USA, [5] Minitab Inc. Minitab User Manual Version 16, Quality Plaza, Copyright 2013 Published by IJESR. All rights reserved 602