Design for Quality and Product Excellence Chapter 7 Design for Quality and Product Excellence MANAGING FOR QUALITY AND PERFORMANCE EXCELLENCE, 10E, © 2017 Cengage Publishing,

Importance of Design Better designs reduce costs and improve quality. For example, simpler designs have fewer components, which mean fewer points of failure and less chance of assembly error. Many product failures and service upsets result form poor design or inadequate design processes.

Quality Profile: Lockheed Martin Missles and Fire Control (MFC) MFC designs, develops, manufactures, and supports advanced combat, missile, rocket, and sensor systems for the U.S. and foreign military. MFC’s nine-step Strategic Planning and Execution System (SPES) process allows for performance optimization and agility while promoting long-term sustainability and accountability. MFC uses design reviews for hardware and software, Lean Six Sigma methods, including mistake proofing, failure trend analysis, statistical process controls, and quality system reliability analyses.

Quality Profile: Poudre Valley Health System PVHS designs new services using the Voice-of-the-Customer (VOC) approach. PVHS was among the first health systems in the nation to use a robotic-assisted surgery system in four medical specialty areas and among the first 24 health systems in the world to integrate medical imaging systems across service lines. From design of new services to bedside care, PVHS uses interdisciplinary teams to meet patient needs.

Product Development 1. Idea Generation: Develop concept incorporating customer needs and expectations. 2. Preliminary Concept Development: Study new ideas for feasibility. 3. Product/Process Development: Evaluate design alternatives and determining engineering specifications; test prototypes; develop, test, and standardize processes. 4. Full-Scale Production: Release the product to manufacturing or service delivery teams. 5. Market Introduction: Distribute to customers. 6. Market Evaluation: Market evaluation and customer feedback to initiate continuous improvements.

Concurrent Engineering Concurrent engineering is a process in which all major functions involved with bringing a product to market are continuously involved with product development from conception through sales. Multifunctional teams, usually consisting of 4 to 20 members and including every specialty in the company. The functions of such teams are to perform and coordinate the activities in the product development process simultaneously, rather than sequentially.

Design for Six Sigma Design for Six Sigma (DFSS) represents a structured approach to product development and a set of tools and methodologies 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 high levels of quality. Concept development Detailed design Design optimization Design verification These activities are often incorporated into a process, known as DMADV, which stands for define, measure, analyze, design, and verify.

Concept Development and Innovation Concept development is 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 involves the adoption of an idea, process, technology, product, or business model that is either new or new to its proposed application. Innovation is built upon strong research and development (R&D) processes.

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. TRIZ, a Russian acronym for the Theory of Inventive Problem Solving Developed by a Russian patent clerk who studied thousands of submissions, and observed patterns of innovation common to the evolution of scientific and technical advances. He recognized that these concepts could be taught, and he developed some 200 exercises to foster creative problem solving.

Detailed Design Detailed design focuses on establishing technical requirements and specifications, which represent the transition from a designer’s concept to a producible design, while also ensuring that it can be produced economically, efficiently, and with high quality. Axiomatic design 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) … 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. 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 manufacturing and quality control.

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 Identify customer requirements

Example Identify technical requirements

Example Relate customer requirements to technical requirements

Example Conduct competitive evaluation

Example Develop deployment targets

Target and Tolerance Design Manufacturing specifications consist of nominal dimensions and tolerances. Nominal refers to the ideal dimension or the target value that manufacturing seeks to meet. Tolerance is 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

Traditional Economic View of Conformance to Specifications

Modern Perspective A Japanese engineer, Genichi Taguchi maintained that this “ goal-post” definition of quality is inherently flawed. No strict cut-off point divides good quality from poor quality, but that losses occur whenever there is a deviation from the nominal specification.

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. The loss function is a quadratic function so that larger deviations from target correspond to increasingly larger losses.

Expected Loss If the distribution of the variation about the target value is known, the average loss per unit can be computed by finding the expected value of the loss using routine expected value calculations.

Expected Loss Formula A measure of variation that is independent of specification limits, showing the average loss over the distribution of output Expected loss (EL) = k(2 + D2) (7.2) where 2 is the process variation and D is the deviation from the target.

Using the Taguchi Loss Function for Tolerance Design

Design for Reliability Reliability is defined as the probability that a product, piece of equipment, or system performs its intended function for a stated period of time under specified operating conditions. Key elements: Probability Time Performance 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

Reliability Concepts Inherent reliability is the predicted reliability determined by the design of the product or process. Achieved reliability is the actual reliability observed during use. Achieved reliability can be less than the inherent reliability due to the effects of the manufacturing process and the conditions of 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.

Computing the Failure Rate

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 (7.6) Probability of failure from (0, T) F(t) = 1 – e-lT (7.7) Probability of failure during the interval (t1 , t2) F(t2) - F(t1) = e-λ(t2 –t1) (7.8) Reliability function (probability of survival) R(T) = 1 – F(T) = e-lT (7.9)

Hazard Function Reliability engineers characterize the instantaneous failure rate over time by what is called the hazard function. The hazard function may be interpreted as the probability that an item that has not failed up to time t will fail immediately after time t. Exponential hazard function:

Using the MTTF For nonrepairable items, θ = 1/λ is defined as the mean time to failure (MTTF). For exponential assumptions:

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

Series Systems with Exponential Reliability

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

Excel Template: System Reliability.xlsx

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 for Reliability Reliability requirements are determined during the product design phase. The designer may use these techniques to determine the effects of adding redundancy, substituting different components, or reconfiguring the design.

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 to identify optimal levels for nominal dimensions and other tools to minimize failures, reduce defects during the manufacturing process, facilitate assembly and disassembly (for both the manufacturer and the customer), and improve reliability.

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.

Elements of DFMEA Failure modes Effect of the failure on the customer Severity, likelihood of occurrence, and detection rating The severity rating is based on how serious the impact would be if the potential failure were to occur. The occurrence rating is based on the probability of the potential failure occurring. The detection rating is based on how easily the potential failure could be detected prior to occurrence Based on these assessments, a risk priority number (RPN) is calculated. Potential causes of failure Corrective actions or controls

Fault Tree Analysis Fault Tree Analysis (FTA), sometimes called cause and effect tree analysis, is a method to describe combinations of conditions or events that can lead to a failure. A cause and effect tree is composed of conditions or events connected by “and” gates and “or” gates. An effect with an “and” gate occurs only if all of the causes below it occur; an effect with an “or” gate occurs whenever any of the causes occur.

Design for Manufacturability DFM - the process of designing a product for efficient production at the highest level of quality. Example guidelines (see Table 7.1) Minimize number of parts Design for robustness Eliminate adjustments Make assembly easy and foolproof Use repeatable, well-understood processes Choose parts that can survive process operations Design for efficient and adequate testing Lay out parts for reliable process completion Eliminate engineering changes

Design and Environmental Responsibility Design for Environment (DFE) - the explicit consideration of environmental concerns during the design of products and processes, and includes such practices as designing for recyclability and disassembly.

Design for Excellence DFX - an emerging concept that includes many design-related initiatives such as concurrent engineering, design for manufacturability, design for assembly, design for environment, and other “design for” approaches Principles Constantly thinking in terms of how one can design or manufacture products better Focusing on “things done right” rather than “things gone wrong” Defining customer expectations and going beyond them Optimizing desirable features or results Minimizing the overall cost without compromising quality

Design Verification Design Reviews Reliability Testing The purpose of a design review is to stimulate discussion, raise questions, and generate new ideas and solutions to help designers anticipate problems before they occur. Reliability Testing Life testing – run devices until failure occurs Accelerated life testing – overstress devices to reduce time to failure Highly accelerated life testing - focused on discovering latent defects that would not otherwise be found through conventional methods. For example, it might expose products to rapid, extreme temperature changes in temperature chambers that can move products between hot and cold zones to test thermal shock, or also extreme vibrations.