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EML4550 - Engineering Design Methods

EML4550 - Engineering Design Methods. Concept Selection Settling on one or more promising ideas to pursue to final design Hyman: Chapter 9, Sec. 9.1 & 9.2 Ulrich and Eppinger: Chapters 5 and 6 Dym and Little: Sections 6.1 – 6.3. Plan Design/ Development Project. Perform Economic

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EML4550 - Engineering Design Methods

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  1. EML4550 - Engineering Design Methods Concept Selection Settling on one or more promising ideas to pursue to final design Hyman: Chapter 9, Sec. 9.1 & 9.2 Ulrich and Eppinger: Chapters 5 and 6 Dym and Little: Sections 6.1 – 6.3

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

  3. Concept Selection • The ‘Concept Generation’ phase spawned many ideas (good and bad) and potential solutions to the problem at hand • How do we select from all these competing concepts? • A ‘method’ is needed to systematically weed out poor concepts and select the best one to proceed with to Final Design

  4. Concept Selection Methods • External decision (customers, consultants, etc.) • Product “Champion” (strong personal decision) • Intuition (no rational method) • Pros and Cons (systematic but subjective) • Prototype and test (hardware, expensive and time-consuming) • Decision matrices (match characteristics vs. pre-specified and weighted criteria)

  5. Concept Selection Methods (Cont.) • Although all methods are used in practice, most of the ‘subjective’ methods are very case-specific • Decision matrices represent the most ‘rational’ approach to concept selection • We will focus this section on the Decision Matrix method

  6. Concept Selection: Why a Structured Approach? • A customer-focused product (use the needs as guidelines) • A competitive design (do not overlook competing designs) • Better product-process coordination (forces manufacturing issues into the trade-off) • Reduced time to market (accelerated ‘downselect’) • Effective group decision-making (minimize ‘arbitrary’ decisions and maximize team exposure) • Documentation of decision process (not lost in someone’s ‘memory’)

  7. Concept Selection: Why a Structured Approach? (Cont.) • Need to balance: • Desire to have an expedient ‘downselect’ • Expediency: proceed to design sooner • Faster time-to market • Less cost of ‘carrying’ many concepts forward • Desire ‘to know more’ before deciding • Risk of making a mistake (pick a loser) • Risk of avoiding a concept because it is new (potential big winner) • Engineers tend to be conservative

  8. Decision Matrix Method • Stage 1: Concept Screening • Apply an initial ‘filter’ to ‘weed out’ bad concepts and determine likely ‘winners’. Apply some elements of ‘scoring’ for the purposes of ranking only • Stage 2: Concept Scoring • Apply weighted criteria to the concepts and proceed with a quantitative ‘scoring’ system to pick a winner (or winners)

  9. Decision Matrix Method (Cont.) • Each Stage has 6 steps: • Prepare the selection matrix • Rate the concepts • Rank the concepts • Combine and improve the concepts • Select one or more concepts • Reflect on the results of the process

  10. Concept Screening

  11. Screening: Step 1 - Prepare Selection Matrix • Develop a set of criteria • Customer needs (condensed into criteria) • Corporate needs (cost, manufacturing, liability, image, etc.) • Give equal weight to all criteria

  12. Screening: Step 2 - Rate the Concepts • Give +, -, or neutral rating to each concept based on criteria • Use general notions (no need to get ‘specific’) • Use team consensus (or majority vote) • Refine or split criteria if team consensus is hard to reach

  13. Screening: Step 3 - Rank Concepts • Add scores and build a ranking • Identify a “benchmark” concept (from ranking or from external products - competition) • Group the concepts into three categories: “possible winners”, “neutral”, and “losers”

  14. Screening: Step 4 - Combine and Improve Concepts • Are we throwing away as ‘loser’ a ‘good’ concept because it has one or two negatives? Can they be neutralized? • Can two concepts be combined to preserve ‘better than’ qualities while neutralizing ‘worse than’ items? Can we derive a concept that takes the ‘best of both worlds’?

  15. Screening: Step 5 - Select one or more concepts • If there is a ‘clear’ winner, then select it and proceed with it • MISSION ACCOMPLISHED • However, usually more than one concept will survive the screening • Number of concepts to carry forward will depend on resources and time available

  16. Screening: Step 6 - Reflect on the Process • Did we achieve consensus? • Were all the team members treated equally? No trampling? • Did we avoid personal agendas? Department politics? It is very disruptive to team spirit to ‘drop’ a concept that someone was championing. Grudges linger for a long time within a team

  17. Concept Screening An example

  18. From Screening to Scoring (quantitative)

  19. Scoring: Step 1 - Prepare Selection Matrix • Using the same selection criteria used in screening give relative weight to each (must add to 100%) • It is possible to slightly modify the criteria in light of the surviving concepts • Weights to each criterion are given by team consensus or related to customer needs An example

  20. Scoring: Step 2 - Rate the Concepts • As with screening, give a ‘score’ to each concept based on a ‘quantitative’ (yet still subjective) numbering scale as follows: Relative Performance 1 - Much worse than reference concept 2 - Worse than reference concept 3 - Same as reference concept 4 - Better than reference concept 5 - Much better than reference concept

  21. Scoring: Step 3 - Rank the Concepts • Compute score for each concept

  22. From Screening to Scoring

  23. Scoring: Step 4 - Combine and Improve Concepts • As before, can concepts be combined to arrive at a better solution? • Looking at the concepts in the new light of ‘scoring’ can encourage the team to improve on the initial ideas

  24. Scoring: Step 5 - Select One or More Concepts • The final selection is never easy • Do ‘parametric’ studies by assigning different weight distributions and see which concepts come on top on each try

  25. Scoring: Step 6 - Reflect on the Process • Are we ready to proceed with the ‘winning’ concept? • Did the method facilitate the selection? • Can the method be improved?

  26. Concept Selection: Caveats! • Decomposition of product quality • Failure to capture relationship among criteria • Subjective criteria • Methodical, but still high content of subjectivity • Where to include cost • Derived from customer needs, but how about ‘manufacturing’ the product, not all parameters known • Selecting elements of complex systems • Can a complex concept be reduced to a set of simpler concepts? How about interactions between sub-concepts? • Applying concept selection throughout the development process • The same approach can apply to the selection of concepts within a design effort when developing sub-systems of a larger system

  27. Concept Selection: Implications to Project • If many concepts are considered, perform a screening • Record results of screening (and criteria used) • Decision matrix for the selection and scores for each concept • Presentation of the ‘winning’ concept

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