A Case Study Of The Application Of Six Sigma In The Improvement Of Elevator Shutters

The purpose of this thesis is to study how to improve the yield rate of elevator shutters.From the perspectives of cost and quality, this thesis uses empirical approach, which includestheoretical analysis followed by practice, to study the yield rate of shutters. By Pareto chart, thisthesis finds out that the main factors hindering the yield rate of2011is welding deformation. Inthe light of the fact that GR Company has passed ISO9000and has implemented overall qualitymanagement mode with product quality at Three Sigma level, the thesis makes a comparisonbetween DMADV and DMAIC, the two primary Six Sigma methodologies, and finallysuggests implementing DMAIC to solve the yield rate problem. Given the five improvementsteps of DMAIC, this thesis analyzes the problem of welding deformation and finds solutions inboth qualitative and quantitative manner.1. Define the processes that need improvement by using SIPOC and set up Six Sigmaimprovement team.2. Analyze the measurement system to ensure the reliability of collected data.3. Find out12potential factors that may cause welding deformation by brain storm andcause-and-effect diagram, and later statistically analyze and define6key factors out of the12by using hypothesis testing.4. Figure out the best solution to solve3factors by teamwork and then further to find outsolutions for the remaining3factors by experimental design.5. Improvement solutions for the6factors1) Adopt air-operated clamping fixture when welding instead of fixing manually.2) Reserve1.5mm instead of no predeformation.3) Fix shell cover and stiffener by welding instead of using adhesive.4) Define optimum welding parameters:1.5s welding time, less than10%current changes,1.0mm welding wire diameter.6. Maintain improvement results by publishing standardization documents and operationinstructions.By the above-mentioned ways, the yield rate of shutters is raised and expected target ismet.Lastly, this thesis uses quality cost theory and quality cost model of Joseph M. Juran toanalyze and verify the rationality of the input, fully proving that the input-outcome ratio is reasonable without redundancy. Moreover, the thesis put forward “prevention first” qualitymanagement solution, which is a unique feature of this thesis when comparing with other thesesof this kind.