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EML4550 - Engineering Design Methods. Concept development and Specifications From needs to requirements to specifications, Product Specification vs. Specs, Refining Specifications Hyman: Chapter 2 Dym and Little: Chapter 5 Ulrich and Eppinger: Chapter 4. Phases of the design process.

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EML4550 - Engineering Design Methods


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    1. EML4550 - Engineering Design Methods Concept development and Specifications From needs to requirements to specifications, Product Specification vs. Specs, Refining Specifications Hyman: Chapter 2 Dym and Little: Chapter 5 Ulrich and Eppinger: Chapter 4

    2. Phases of the design process • Concept development • Identify customer needs, gather information on competition or possible alternatives, generate and evaluate alternate concepts, select concept, define form and function of the artifact. [feasibility study] • System-level design • Determine system architecture (configuration) as well as all sub-systems and respective interfaces, produce system layout and specifications for the system and each sub-system • Detailed design • Complete and final specification of the system, including geometry, materials, tolerances, etc. (drawings), complete and final manufacturing process specification. • Testing and refinement • Review design, build prototype (if appropriate), alpha and beta prototype. • Production ramp-up and delivery • Production line checked and refined, product ‘launch’

    3. Generate Product Concepts Select Product Concept Plan Design/ Development Project Perform Economic Analysis Analyze Competitive Products Concept Development Diagram Establish Target Specs Identify Customer Needs Refine Specs Mission Statement Action Plan

    4. Customer Needs vs. Product Specifications • Subtle but important differences between customer needs and product specifications • Customer views a product without any technology bias • Customer uses product without knowledge of design process or internal sub-systems • It is important to always distinguish when a specific need is driving a feature, or when a designer is introducing an assumption in order to arrive at a specification • The specification is not “customer-driven” necessarily, it is “design-centric”, it is how the design engineer sees the product as a “black box” PRIOR to a full design definition. It is usually a QUANTIFICATION of functionality and perfromance

    5. From Customer Needs to Specifications • Turn subjective customer needs into precise engineering terms to guide the design effort • Force agreement among corporate stakeholders (management, marketing, engineering) on what will be designed • Serve as focal point for design trade-offs • Develop confidence that the product will have a successful market introduction

    6. What is a Specification? • Product specification is a precise description of what the product has to do • “Product Specifications” vs. “Specification” • Specification (“spec”): • Metric • Value (or range of values) • Product Specification as a collection of “specs” (requirements) plus other relevant information (including modes of use, design preferences: design criteria, etc.)

    7. Specifications • When: • Ideally specifications should be set early in the project. • However, specifications can only be done as an iterative process • Many specifications need to be changed after a concept is selected, or as a result of engineering-economic trade-offs • Establish target specs: • Step 1: Prepare List of Metrics • Step 2: Collect Competitive Benchmarking Information • Step 3: Set Ideal and Marginally Acceptable Targets for Each Metric • Step 4: Reflect on the Results of the Process

    8. Step 2: Collect Information on Competition (Example) • Prepare a subjective list of perceived attributes that fulfill the needs

    9. Generate Product Concepts Select Product Concept Plan Design/ Development Project Perform Economic Analysis Analyze Competitive Products Concept Development Diagram Establish Target Specs Identify Customer Needs Refine Specs Mission Statement Action Plan

    10. Refine Specification • Final specifications cannot be written in the absence of a design concept • Many trade-offs need to be considered before finalizing the specification document • Not all information for these trade-offs is available at the time the specification is needed • Finalizing a specification document is an iterative, often painful, process

    11. Refine Specification • Step 1: Develop technical model of product • Analytical models, computer models, technical calculations, parametric studies, etc. • Step 2: Develop economic model of product • Cost model, materials and manufacturing costs, part counts, etc. • Step 3: Finalize specification, perform trade-offs • Estimate cost associated with each spec, place product in a ‘competitive’ map • Step 4: Reflect on the results of the process • Will the product win? Level of uncertainty? Did we select the right concept? Do we need better modeling tools?

    12. Final Specification • Tabulate all quantifiable attributes that need to be on the specification • Add any other information that is needed to fully ‘spec’ the product (e.g., graphs, plots for input or desired output, etc.) • Include a narrative to the tabulation or plots to make the document ‘readable’ • The “Product Specification” is a ‘stand-alone’ document - it needs to be arranged and prepared as such. Treat it as a CONTRACT!

    13. Some useful techniques From needs to requirements to specification to design QFD and the House of Quality

    14. Quality Function Deployment (QFD) • How to identify customer requirements and turn them into design/performance parameters (specifications) • Construct a chart the explicitly depicts the relationship between 1) customer requirements, 2) engineering (product) requirements, and 3) competing products (or concepts) • The QFD table has five elements (regions): • Customer requirements • Engineering requirements • Matrix of requirements relations • Competitive benchmarks • Engineering targets

    15. QFD chart

    16. QFD chart • Customer requirements • Unfiltered needs (requirements) using customer’s own words • Exhaustive list compiled through customer interviews • Engineering requirements • Quantifiable aspects of the system that contribute to fulfillment of customer needs • Include as many as you can think of (mixture of design and performance parameters) • Some items may be a repetition of a customer requirement (sophisticated and technical customer)

    17. QFD chart (cont’d) • Matrix of requirements relations • At the center of the QFD “matrix” we correlate on a one-to-one basis the customer and the engineering requirements • Ask: Are these two requirements (customer vs. engineering) related? If so, mark it with an “x” • Competitive benchmarks • Indicate how competitors (external or internal/concept) match the customer needs • Engineering targets • Quantitative target for each of the engineering requirements • This is a first draft of the “specification” • Some may be “TBD” in the early stages.

    18. QFD chart - Example (Car Bumper)

    19. Variations on QFD: The House of Quality • Add triangular region • Keep track of relationships between engineering requirements (specs.) • Indicate positive correlation with a “+”, and negative correlations with a “-” • This is useful to visualize the design trade-offs