Abstract
Abstract : A number of foundries in South Africa (SA) are jobbing foundries, meaning that they produce a large number of different castings based on received orders. Due to this nature of business, the success and sustainability of local foundries depend on their ability to provide defect free castings at minimum cost. This means that SA foundries need to adopt quality systems and strategies that are cost-effective and would allow production of high integrity castings since the currently employed traditional quality control e.g. (Sand testing) imposes limitations in terms of the efficacy to avoid casting defects. This study focused on the application of Six Sigma technique to minimise defect due to the sand moulding process in the foundry. Six Sigma technique is a data driven method to process improvement that aims to eliminate variation in business processes using statistical control methods. Six Sigma technique focuses on business performance improvement through quality initiative using the basic tools of quality. The objectives of Six Sigma technique are to eliminate features that affect productivity, profit and meeting customers’ demands. The principle applied in Six Sigma Technique is Define-Measure-Analyse-Improve and Control (DMAIC). The Define-Measure and analyse phases of Six Sigma technique was implemented in a local automotive foundry that produces Sg and Grey cast iron castings and the following results were obtained. Using the Six Sigma technique tools, the results showed that the foundry produced 20266 sand inclusions, 9616 of broken mould, 5009 of shrinkage, 2716 of short cast and 1207 of porosity defects. These defects were classified as major defects that were affecting the performance of the sand moulding process in the foundry. It was also found that these defects were due to the sand moulding process parameters not meeting the specification due to constant machine breakdown in the foundry. The process capability of the sand moulding process was found to be 0.5; this process capability meant that the foundry process was not able to meet process specification. The foundry was found to be operating at 2 Sigma level. The Pareto chart results pointed out that the foundry needed to focus on the above-mentioned defects in order to improve the productivity and competitiveness of the foundry. Based on the fish bone results used in the analyse step, the foundry needed to improve the machine and the process. The possible solutions were listed during the improve phase. Statistical process control and total productive maintenance was proposed as control measures for both the process and the machine in the foundry. The study demonstrated that Six Sigma technique is an effective tool for the understanding and prevention of casting defects in the foundry industry.
M.Tech. (Metallurgical Engineering)