Study of effect of process parameter setting on porosity levels of aluminium pressure die casting process using Taguchi Methodology

Abstract

This paper discusses the study and examined effect of die casting process parameters on porosity in aluminium alloy SAE 308 by using Taguchi method. In any die casting industry porosity is a very serious problem faced by production department and also being an invisible defect it is not identified visually in running production. It is shown in this work that die casting parameters which are related with machine such as first phase speed, second phase speed, first phase length and injection pressure all have significant influence on porosity level. The quality assessment of the die casting part was based on porosity measurement. The experiment have been performed as per the combination of levels of different process parameters suggested by L9 orthogonal array and conformation experiments have been performed to validate the optimum levels of Pressure Die Casting Process (PDC) is a complex industrial system. In a typical die casting machine the molten metal is poured in the shot sleeve through a ladle after the die is closed. A movement of plunger (piston) forces the metal through the die resulting in that the moveable part coincides with the fixed part. Some die casting machines allow for this plunger movement to be completed in four stages. However, typically it is done in two stages only. The plunger starts initially with a low velocity, then the velocity increases during the piston's motion at a change over position, the length of travel of the piston in the low velocity up to the change over point is known as first phase length and the injection pressure is decreases at the end when nearly all the liquid metal is injected into the die and solidifies.. During this process taking place inside the shot sleeve the flow of the metal inside the shot sleeve before plunger should be in laminar if these speeds, first phase length, and injection pressure are not set properly the flow of metal will disturbed and convert into turbulence and there will be possibility of formation of porosity during process (7). Though die casting process has a large number of parameters that may affect the quality of the casting some of these are controllable while others are noise factors. Therefore, a die casting company can be an ideal place to apply Taguchi's test method for continuous and rapid quality improvement. In this experiment more importance is given for the parameter design stage. The basic steps to investigate the role process parameters in porosity formation and to improve casting quality are summarized below. 1. Determine the casting porosity as a quality characteristic 2. Select the most significant die casting parameters that cause variation in porosity. 3. Operate the die casting process under the experimental conditions dictated by the chosen L9 orthogonal array (OA) and parameter levels. Collect data. 4. Analyses the data. An analysis of variance (ANOVA) table can be generated to determine the statistical significance of the parameters. Response graphs are plotted to determine preferred levels of each parameter. 5. Make decisions regarding optimum setting of control parameters. 6. Predict the treatment casting porosity conditions that derive from the new optimum level of each parameter