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Chapter 8. Design for Six Sigma. Design for Six Sigma.
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Chapter 8 Design for Six Sigma
Design for Six Sigma • Design for Six Sigma (DFSS) represents a set of tools and methodologies used in product development for ensuring that goods and services will meet customer needs and achieve performance objectives and that the processes used to make and deliver them achieve six sigma capability. 2
DFSS Methodology: DMADV • Define – establish goals • Measure– identify voice of the customer and define CTQ measures • Analyze – propose and evaluate high-level design concepts • Design – design the details of the product and processes used to produce it • Verify – ensure that the product performs as expected and meets customer requirements
Features of DFSS • A high-level architectural view of the design • Use of CTQs with well-defined technical requirements • Application of statistical modeling and simulation approaches • Predicting defects, avoiding defects, and performance prediction using analysis methods • Examining the full range of product performance using variation analysis of subsystems and components
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.
Innovation • Innovationinvolves the adoption of an idea, process, technology, product, or business model that is either new or new to its proposed application. • The outcome of innovation is a discontinuous or breakthrough change that results in new and unique goods and services that delight customers and create competitive advantage.
Types of Innovation 1. An entirely new category of product (for example, Twitter) 2. First of its type on the market in a product category already in existence (for example, the DVD player) 3. A significant improvement in existing technology (for example, the Blu-ray disc technology) 4. A modest improvement to an existing product (for example, the latest iPad)
Creativity • Creativity is seeing things in new or novel ways. • Creativity tools, such as brainstorming and “brainwriting,” are designed to help change the context in which one views a problem or opportunity, thereby leading to fresh perspectives.
Understanding the Voice of the Customer • What is the product (good or service) intended to do? • Technical requirements, sometimes called design characteristics, translate the voice of the customer into technical language, specifically into measures of product performance.
Design Development • Design development - the process of applying scientific, engineering, and business knowledge to produce a basic functional design that meets all CTQs – both customer needs and manufacturing or service delivery requirements. • Designdevelopment usually starts with a high-level design and then moves toward more detail design of components or subsystems.
Axiomatic Design • Axiomatic design(developed by Dr. Nam Suh at MIT)is based on the premise that good design is governed by laws similar to those in natural science. 1. Independence Axiom: good design occurs when the functional requirements of the design are independent of one another. 2. Information Axiom: good design corresponds to minimum complexity.
Quality Function Deployment (QFD) • QFD is a planning process to guide the design, manufacturing, and marketing of goods by integrating the voice of the customer throughout the organization. • Through QFD, every design, manufacturing, and control decision is made to meet the expressed needs of customers.
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.
Example: Designing a Fitness Center Identify customer requirements
Example Identify technical requirements
Example Relate customer requirements to technical requirements
Example Conduct competitive evaluation
Example Develop deployment targets
Detailed Design and Analysis • Manufacturing specifications consist of nominal dimensions and tolerances. • Nominalrefers to the ideal dimension or the target value that manufacturing seeks to meet. • Toleranceis the permissible variation, recognizing the difficulty of meeting a target consistently.
Tolerance Design • Tolerance design involves determining the permissible variation in a dimension. • Narrow tolerances tend to raise manufacturing costs but they also increase the interchangeability of parts within the plant and in the field, product performance, durability, and appearance. • Wide tolerances increase material utilization, machine throughput, and labor productivity, but have a negative impact on product characteristics
The Taguchi Loss Function • Taguchi measured quality as the variation from the target value of a design specification, and then translated that variation into an economic “loss function” that expresses the cost of variation in monetary terms. • Taguchi assumes that losses can be approximated by a quadratic function so that larger deviations from target correspond to increasingly larger losses.
Expected Loss • A measure of variation that is independent of specification limits, showing the average loss over the distribution of output Expected loss = k(2 + D2) where 2 is the process variation and D is the deviation from the target.
Design for Manufacturability (DFM) • Design for manufacturability (DFM) is the process of designing a product for efficient production at the highest level of quality. • DFM is intended to prevent • product designs that simplify assembly operations but require more complex and expensive components, • designs that simplify component manufacture while complicating the assembly process, and • designs that are simple and inexpensive to produce but difficult or expensive to service or support
Design Reviews • Design review – a structured review of design progress intended to stimulate discussion, raise questions, and generate new ideas and solutions to help designers anticipate problems before they occur
DFMEA • Design failure mode and effects analysis (DFMEA)– identification of all the ways in which a failure can occur, to estimate the effect and seriousness of the failure, and to recommend corrective design actions.
DFMEA Elements • Failure modes • Effect of failures on customers • Severity, likelihood of occurrence, and detection rating (risk priority) • Potential causes of failure • Corrective actions or controls
Reliability Prediction • Reliability - the ability of a product to perform as expected over time • Formally defined as the probabilitythat a product, piece of equipment, or system performsits intended function for a stated period of timeunder specified operating conditions
Types of Failures • Functional failure – failure that occurs at the start of product life due to manufacturing or material detects • Reliability failure – failure after some period of use
Types of Reliability • Inherent reliability – determined by product design • Achieved reliability – observed during use
Mathematics of Reliability • Reliability is determined by the number of failures per unit time during the duration under consideration (called the failure rate,λ). • For items that must be replaced when a failure occurs, the reciprocal of the failure rate (having dimensions of time units per failure) is called the mean time to failure (MTTF). • For repairable items, the mean time between failures (MTBF) is used.
Product Life Characteristics Curve • Many electronic components commonly exhibit a high, but decreasing, failure rate early in their lives, followed by a period of a relatively constant failure rate, and ending with an increasing failure rate.
Reliability Function • The reliability function, R(T), characterizes the probability of survival to time T. • Properties: 1. R(0) = 1 2. As T becomes larger, R(T) is non-increasing 3. R(T) = 1 - F(T), where F(T) is the cumulative probability distribution of failures
Exponential Reliability • Exponential probability density function of failures f(t) = le-lt for t ≥ 0 • Probability of failure from (0, T) F(t) = 1 – e-lT • Probability of failure during the interval (t1 , t2) F(t2) - F(t1) = e-λ(t2 –t1) • Reliability function (probability of survival) R(T) = 1 – F(T) = e-lT
Hazard Function • The hazard function is the probability that an item that has not failed up to time t will fail immediately after time t . • For the exponential distribution, the hazard function is
System Reliability • Series system: all components must function or the system will fail. • the reliability of the system is the product of the individual reliabilities
System Reliability • Parallel system: uses redundancy. The system will successfully operate as long as one component functions. • The reliability is calculated as • If all components have identical reliabilities R, then
Series-Parallel Systems • To compute the reliability of systems with both series and parallel components, decompose the system into smaller series and/or parallel subsets of component, compute the reliabilities of these subsets, and continue until you are left with a simple series or parallel system.
Design Optimization • Robust design refers to designing goods and services that are insensitive to variation in manufacturing processes and when consumers use them. • Robust design is facilitated by design of experiments and alternative Taguchi methods
Design for Reliability • Reliability requirements are determined during the product design phase. • Techniques used to improve designs and optimize reliability include: • Standardization • Redundancy • Physics of failure
Design Verification • Design verification is necessary to ensure that designs meet customer requirements and can be produced to specifications. • The purpose of verification is to validate product and process designs and to prepare procedures and documentation for full-scale production rollout.
Reliability Evaluation • Life testing– running devices until they fail, is designed to measure the distribution of failures to better understand and eliminate their causes. • Accelerated life testing involves overstressing components to reduce the time to failure and find weaknesses. • Environmental testing involves testing products for temperature, shock-resistance, and other environmental conditions. • Burn-in, (component stress testing), involves exposing integrated circuits to elevated temperatures in order to force latent defects to occur.
Simulation • Simulation is an approach to building a logical model of a real business system and experimenting with it to obtain insight about the behavior of the system or to evaluate the impact of changes in assumptions or potential improvements to it. • Process simulation models the dynamics and behavior over time of interacting elements in a system such as a manufacturing facility or a call center. • Monte-Carlo simulation is based on repeated sampling from probability distributions of model inputs to characterize the distributions of model outputs, usually in a spreadsheet environment.
