Abstract: In this modern manufacturing era, the production has become unimaginably sophisticated. The world class manufacturing is possible with CNC machines, robots and even unmanned factory will become real. But the productivity is improved not only by automated operations but there should not be any wastage (losses) by any means. Total Productive Maintenance (TPM) is an innovative Japanese concept to minimize the manufacturing losses and it has been proven as a successful technique used for corrective, preventive and predictive maintenance policies in many manufacturing industries. Overall Equipment Effectiveness (OEE) is the metric for TPM implementation. OEE attempts in identifying the production losses, expressed in terms of three factors, namely availability, performance and quality. Due to different applications and other varying circumstances like the type of industry, production system, process and machine type, some inconsistencies in the calculation of OEE have been encountered. Its definition also differed with respect to the applications and authors. In this study, it is proposed to introduce a new term `yield` in the OEE calculation. The proposed model has been analyzed with a case study in a casting industry. For any industry the main objective is to improve the performance of its processes, equipments etc. To achieve it, the parameters of the processes or equipment should be optimized. In this case analysis, Evolutionary Programming is used for optimizing the parameters to improve OEE.