الفهرس 
Six Sigma Quality PhilosophyOnly 14 pages are availabe for public view
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Abstract
The purpose of this thesis is to provide a case study for improving quality of thermoforming process using a combination of statistical tools which are integrated in a quality improvement program. The case study is represented by the thermoforming processes used for refrigerator inner liner manufacturing in an Egyptian company of home appliances manufacturing. Six Sigma with its famous phases: Define, Measure, Analyze, Improve and Control (DMAIC), is considered as a statistically based quality improvement program that is because many of statistical tools and methods can be easily implemented in the phases of six sigma methodology. The objective of the present work was set in Define phase to decrease the defective percent of thermoformed inner liners from 12.3% by 50% to be about 6% at most after 8 months. This period was considered the time frame for implementing the five phases of six sigma for the case study. The baseline data were collected in the Measure phase and showed that the major defects category was the one due to extruded sheets defects, and the vital two defects in that category were hard particles imbedded in sheet layers and non homogeneity in sheet thickness. The base line of hard particles defect percent was 4.1%, and the process capability indicators (Cp, Cpk) for sheet thickness measurements were (0.56, 0.30) respectively. Results of Analyze phase revealed that the root causes of vital two defects were using two types of sheet material in the extruder of sheet extrusion machine, main units and dies of sheet extrusion machine not cleaned, and uncontrolled adjustment of some extrusion machine parameters such as screen filter changing period and screen filter size. In Improve phase, maintenance activities have been performed to the main units and dies of sheet extrusion machine. One type of sheet material was fixed to be iii extruded by the sheet extrusion machine. Designed experiments were carried out to determine the optimum settings for screen changing period, screen filter size and temperature of feeding dies of extrusion machine. The experiments revealed that the significant parameter was the screen filter changing period. The optimum settings for the investigated parameters were 8 hours filter changing period, filter size (#80), and temperature of feeding dies at 230ºC. The implementation of the improvement actions mentioned in this phase results in a breakthrough in reject percent reduction to be 5.5 %, with great improvement in the vital defect data to be 1.9% for hard particles defect and process capability indicators (Cp , Cpk) for sheet thickness measurements to be (1.46 , 0.76) respectively. In final Control phase, all the implemented changes were institutionalized with proper training, documentation, process monitoring, and response plan.
The results from the thesis have provided an insight on actual successful deployment of Six Sigma methodology DMAIC with application of its various statistical tools and techniques, and as the systematic problem solving framework for solving actual industrial issues.