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Chapter 12 - Design for six sigma. This chapter presents the following content: DFSS activities four principal activities, tools for concept development, house of quality, quality function deployment, building the house of quality, tolerance design,...
Chapter 12 Design for Six Sigma DFSS Activities Four Principal Activities Concept development, determining product functionality based upon customer requirements, technological capabilities, and economic realities Design development, focusing on product and process performance issues necessary to fulfill the product and service requirements in manufacturing or delivery Design optimization, seeking to minimize the impact of variation in production and use, creating a “robust” design Design verification, ensuring that the capability of the production system meets the appropriate sigma level Key Idea Like Six Sigma itself, most tools for DFSS have been around for some time; its uniqueness lies in the manner in which they are integrated into a formal methodology, driven by the Six Sigma philosophy, with clear business objectives in mind Tools for Concept Development Concept development – the process of applying scientific, engineering, and business knowledge to produce a basic functional design that meets both customer needs and manufacturing or service delivery requirements. – Quality function deployment (QFD) – Concept engineering Key Idea Concept Development Developing a basic functional design involves translating customer requirements into measurable technical requirements and, subsequently, into detailed design specifications Key Idea QFD QFD benefits companies through improved communication and teamwork between all constituencies in the value chain, such as between marketing and design, between design and manufacturing, and between purchasing and suppliers House of Quality Interrelationships Technical requirements Voice of the customer Customer requirement priorities Relationship matrix Technical requirement priorities Competitive evaluation Quality Function Deployment technical requirements component characteristics process operations quality plan Building the House of Quality Identify customer requirements Identify technical requirements Relate the customer requirements to the technical requirements Conduct an evaluation of competing products or services Evaluate technical requirements and develop targets Determine which technical requirements to deploy in the remainder of the production/delivery process Reliability testing Life testing Accelerated life testing Environmental testing Vibration and shock testing Burnin (component stress testing) Measurement System Evaluation Whenever variation is observed in measurements, some portion is due to measurement system error. Some errors are systematic (called bias); others are random. The size of the errors relative to the measurement value can significantly affect the quality of the data and resulting decisions Metrology Science of Measurement Accuracy closeness of agreement between an observed value and a standard – can lead to systematic bias Precision closeness of agreement between randomly selected individual measurements – can lead to random variation Accuracy vs. Precision Repeatability and Reproducibility Repeatability (equipment variation) – variation in multiple measurements by an individual using the same instrument. Reproducibility (operator variation) variation in the same measuring instrument used by different individuals Key Idea Calibration One of the most important functions of metrology is calibration—the comparison of a measurement device or system having a known relationship to national standards against another device or system whose relationship to national standards is unknown Process Capability The range over which the natural variation of a process occurs as determined by the system of common causes Measured by the proportion of output that can be produced within design specifications 44 Process Capability Study Typical Questions Asked Where is the process centered? How much variability exists in the process? Is the performance relative to specs acceptable? What proportion of output will be expected to meet the specs? What factors contribute to variability? Types of Capability Studies Peak performance study how a process performs under ideal conditions Process characterization study how a process performs under actual operating conditions Component variability study relative contribution of different sources of variation (e.g., process factors, measurement system) Process Capability (a) specification natural variation (c) specification natural variation (b) specification natural variation (d) specification natural variation 47 Process Capability Nominal value Process distribution Upper specification Lower specification 20 25 Process is capable 30 Minutes Process Capability Nominal value Process distribution Upper specification Lower specification 20 25 30 Process is not capable Minutes Effects of Reducing Variability on Process Capability Nominal value Six sigma Four sigma Two sigma Lower specification Upper specification Mean Key Idea Process Capability The process capability index, Cp (sometimes called the process potential index), is defined as the ratio of the specification width to the natural tolerance of the process. Cp relates the natural variation of the process with the design specifications in a single, quantitative measure Process Capability Index Cp = UTL - LTL Cpu = UTL - LTL Cpl = Cpk = min{ Cpl, Cpu } 52 ... are systematic (called bias); others are random.? ?The? ?size? ?of? ?the? ?errors relative to the? ?measurement value can significantly affect? ?the? ?quality? ?of? ?the? ?data? ?and? ?resulting decisions Metrology Science? ?of? ? Measurement... (sometimes called? ?the? ?process potential index), is defined as? ?the? ?ratio? ?of? ?the? ? specification width to? ?the? ?natural tolerance? ?of? ?the? ?process. Cp relates? ?the? ? natural variation? ?of? ?the? ?process with? ?the? ? design? ?specifications in a single, ... between marketing? ?and? ?design, between design? ?and? ?manufacturing,? ?and? ?between purchasing? ?and? ?suppliers House? ?of? ?Quality Interrelationships Technical requirements Voice of the customer Customer