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The need for improved productivity without sacrificing quality, which is in line the prime target of many manufacturing industries. The aim of this study is to investigate the causes of production variation: a case study of the rail manufacturing industry, South Africa. In this study, the six-sigma Define, Measure, Analyse, Improve and Control (DMAIC) phases were applied to enhance the process capability (long term) in the production of bolster compression springs in the main line of bogie secondary suspension system. In every phase of DMAIC method, a combination of both qualitative and quantitative techniques was utilized. First, process capability index Cpk of the current process was computed which was found less than 1. The results obtained indicated that the process capability index values were found to be 1 after the improvement phase. Hence, significant improvement was achieved in the area of reduction in process variation and product quality after taking corrective actions. From outcomes of the study, it can be concluded that process performance of a train manufacturing plant can be improved significantly by implementing six-sigma DMAIC methodology. The novelty of this study lies in the fact that the implementation of the six-sigma DMAIC phases to enhance the process capability (long term) and minimise variations in the production of bolster compression springs has not be sufficiently highlighted by the existing literature. [ABSTRACT FROM AUTHOR]

The increasing need to develop renewable sources of energy to complement the energy generated via fossil fuel necessitates this study. This study demonstrates the process control and automation of a biodiesel processing plant. The developed biodiesel processing plant has a total output capacity of 200 litres per day with nine compartments divided into three major sections. The first section (pre-processing section) has the oil storage, pre-treatment, methanol and mixing tanks. The second section (main processing section) comprises of the reactor. The last section (post-processing section) comprises of the water, wash and separating tanks as well as the glycerol and biodiesel storages. The control and automation was achieved with the following components; three 3 kW variable speed electric motor, four 2.5 kW pumps, three 300 kW electric heater that are thermostatically controlled. Other materials used for the control and automation include: real time clock, Atmega328 microcontroller, LM6009 and LM 2596 modules, Liquid Crystal Display (LCD), switches, relay, LED, three temperature probes, 220 V AC alarm, four flow switches, 220 V timer relay, 220 V and 60 A contactor. Sensors are incorporated to measure the temperature, pressure, and flow level in the main reactor and the measured variables compared with the threshold values pre-set on the micro controller for control actions. The results obtained indicated that the performance of the plant was enhanced with the capacity to independently execute control actions during the biodiesel production. Thus, this study adds to the practical knowledge of system's control and automation for biodiesel production. [ABSTRACT FROM AUTHOR]