Process Capability and Six Sigma Methodology Including Fuzzy and Lean Approaches

Abstract

Process capability ProcessProcess is defined as a combination of materials, methods, equipments and people engaged in producing a measurable output.As a matter of fact, all processes have inherent statistical variability, which can be identified, evaluated and reduced by statistical methods.The source and amount of variability should always be considered by organizations.In order to satisfy customer requirements, organizations must improve the quality by reducing variance in production processes.The less variation the system has, the better quality it provides.Thereby, the variability of critical-to-quality characteristics (CTQs) is a measure of the uniformity of outputs.When the variation is large, the numbers of products that are nonconforming are large.Nonconforming (NC) is the failure of meeting specification limits whereas specifications are the desired measurements for a quality characteristic. Process capabilityIn particular, process capability deals with the uniformity of the process.Variability of CTQs in the process is a measure of the uniformity of outputs.Here, variability can be thought in two ways: one is inherent variability in a CTQ at a specified time, and the other is variability in a CTQ over time.It should be considered that process capability study frequently measures functional parameters or CTQs on the product.It does not measure the process itself (Montgomery, 2009).Process capability compares inherent variability in a process with the specifications that are determined according to the customer requirements.In other words, process capability is the proportion of actual process spread to the allowable process spread, which is measured by six process standard deviation units.Process capability compares the output of a process that is an in-control state to the specification limits by using PCIs.To sum up, a capable process is the one where almost all the measurements fall inside the specification limits and process capability study can be conducted to indicate the extent to which the process can meet these specifications.In a true process capability study, when there is direct observation of the process, inferences can be made about the stability of the process over time by directly controlling or monitoring data collection activity and understanding the time sequence of the data.However, when there is no direct observation of the process, only sample units of product are known, in this case, the study is called product characterization.In a product characterization study, distribution of the product quality characteristic or the fraction that conforms to specifications, which is referred to as process yield, can only be estimated, notably information about stability or dynamic behavior of the process cannot be given (Montgomery, 2009). Process Capability Analysis (PCA)PCA involves statistical techniques, which are useful throughout the product cycle.Generally, PCA is used in development activities prior to manufacturing process, in quantification of process variability, in analysis of this variability relative to specifications and in elimination or reduction of the process variability (Montgomery, 2009).As a fundamental technique in any production, quality and process improvement efforts, PCA is used to improve processes, products or services to achieve higher levels of customer satisfaction.PCA has become widely adopted as the measure of performance to evaluate the ability of a process to satisfy customer requirements in terms of specification limits (English How to referenceIn order to correctly reference this scholarly work, feel free to copy and paste the following: Ozlem Senvar and Hakan Tozan (2010).Process Capability and Six Sigma Methodology Including Fuzzy and Lean Approaches, Products and Services; from R&D to Final Solutions, Igor Fuerstner (Ed.), ISBN: 978-953-307-211-1, InTech, Available from: http://www.intechopen.com/books/products-and-services--from-r-d-to

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