Improvement of quality of sand-casting products of cast iron using Taguchi methods

Abstract

Sand casting is a widely used method for manufacturing metal parts due to its low cost and versatility. In Uganda, foundries are few and the available ones do not produce adequate products both in quantity and quality, hence most castings are imported. The few operating foundries produce as much as 60% rejects, and castings that need rework due to many casting defects. This increases the cost of operation thus affecting the bottom line of the company. A study to optimize the quality of sand-casting process was therefore undertaken. The study was conducted in a foundry operated by John Lugendo and Company Ltd located in Ndeeba, Kampala City. Scrap of cast iron was used in this study to make rail wheels by sand casting and the defects analysed. Cast iron was used because it is the most used material in manufacturing. It also has low melting point and is susceptible to defects that can be addressed through the optimization of process parameters. Rail wheels were preferred because they have a simple shape and design, and are produced in large quantities, which makes them a cost-effective choice for conducting experiments. Moulding sand for this study was sourced from Luzira, Buwaya and Kapeeka. The aim of this study was to improve the quality of sand-casting using Taguchi method, which is a statistical approach for optimizing the manufacturing process. This method was used due to its ability to analyse a combination of process parameters at once. The Ishikawa diagram was used to determine parameters that influence formation of defects in sand castings. The identified four process parameters were sand grain size, pouring temperature, sand moisture content and pouring time. The effect of these parameters on the quality of sand castings was investigated. An L18 orthogonal array was used to design the experiments, and signal-to-noise (S/N) ratios were used to evaluate the quality of the castings. The results showed that the sand moisture content had the most significant effect on the quality of the castings, followed by sand grain size, pouring time and pouring temperature in that order. The optimal process parameters for achieving the best quality of castings were found to be a sand moisture content of 2.6% and a sand grain fineness number of 44.11. The effect of pouring temperature and pouring time was not found significant. The use of these parameters in confirmation tests resulted in an average of three casting defects, compared to the eight defects observed in the rail wheel castings prior to this study. The results of this study can be used as a guideline for selecting the appropriate process parameters to achieve high-quality sand castings in the manufacturing industry.