Experimental Study of Sand Mold Process Parameters on Al-Alloy Sand Castings Using DoE

Abstract

Aluminum alloy castings are extensively used in general engineering, automobile, aerospace industries due to their excellent castability, machineability, corrosion resistance and high strength-to-weight ratio. Keeping in view the increase in demand for the use of aluminum in manufacturing of various components, aluminum foundries have to focus on producing quality castings. Sand mould casting process involves parameters like sand grain size, clay content, moisture content, permeability, green compression strength, mold hardness, number of ramming, shatter index, type of mold, etc., just to mention a few. Based on literature survey, brainstorming and experimental constraints; Grain size, Clay content, Moisture content and Number of ramming has been selected as process parameters keeping other parameters constant. Experiments were conducted as per Taguchi's L9 orthogonal array. Castings are made under the constraint of process parameters at three different levels. Results were evaluated to optimize the process parameters. The optimum levels are found to be: Grain size-55, Clay content-12%, Moisture content-13%, Number of ramming's-2. Confirmation test is conducted based on the optimum level of process parameters and result is found to be in confidence level. Keywords - Aluminium alloys, Design of Experiment (DoE), Sand casting process parameters, Taguchi method. I. INTRODUCTION Sand molding is a very ancient technique of manufacturing the product and is used to manufacture complex shape castings of various sizes depending upon the requirements. But still despite of science getting to new level every passing minute, there are defects, flaws or imperfections which still remain and are very difficult to eliminate from castings. In the present competitive environment, it is of paramount importance to maintain the quality of the castings and to aim at products with 'zero-defect' and 'right the first time'. The key element for achieving high quality and low cost product is parameter design. Through parameter design optimal levels of process parameters (or control factors) are selected (1). These parameters should be controlled to improve the quality of both casting process and the product. Numbers of problems of various types are associated with the casting process. These problems may be related to casting yield, defects, dimensional variations, solidification, surface texture, poor mechanical properties, porosities and so on (2). If the casting process is not being managed properly, the problems may aggravate further resulting in defects which render the product weak and of low quality, thus making them unfit for use (3). Therefore to overcome the problems in the casting, optimization of the process parameters should be done. Optimization is required right from the stage of selecting the sand to the removal of casting from the sand mold. Quality improvement in foundry industry have been carried over by researchers and foundry engineers for robust product at the customers end by applying various optimization methods to the sand casting process parameters: the Gradient search method, the Finite element method (FEM) and the Taguchi method (4). Taguchi has introduced several statistical tools and concepts of quality improvement that depend heavily on the statistical theory of experimental design. Some applications of Taguchi's method in the foundry industry have shown that the variation in casting quality caused by uncontrollable process variables can be minimized. The concept of robust design for the process and the product introduced by G. Taguchi (5, 6) seeks to make both the process and the product insensitive to disturbing factors that occasionally or systematically affect the variability of the process that may lead to imperfections in the products (7). In the present study, aluminium alloy test castings of same shape and size produced by sand mould casting process at selected sand grain size (or GFN - Grain Fineness Number), clay content, moisture content and number of ramming are studied and presented. The produced castings were examined for mechanical properties. The aim is to determine the optimum levels at which these parameters produce good quality castings. Many casting defects occur because the optimum conditions were not used during the casting process. By this