Concept Evaluation/Selection

1. AE 207 Introduction to Engineering Design Concept Evaluation/Selection Dept. of Aerospace Engineering IIT Bombay

2. Journey So Far • Need/Mission statement/Design Brief • Stakeholder Identification – Active, Passive • Requirements capture, grouping & prioritization – Stakeholder needs • Functional Decomposition • Concept Generation – Number of alternate solution concepts attempting to satisfy the need

3. Next Step • Decide which conceptual solutions are good potential candidates for further investigation/ product development • ALL ? • Some ? • One ? • Concept Evaluation • Evaluation criteria • Compare generated concepts: strengths & weaknesses wrt criteria • Concept Selection • Decision making: Eliminate, Retain, Combine, Modify • One Shot / Stages/ Iterative (?) • Final Selection Resources, Time, Risk, Policy, Culture

4. Difficulties/Issues • Limited knowledge/data • Conceptual solutions - Rough/abstract ideas • Concensus among team members • Other ??

5. Some methods • External Decision – company chairman?, customer • Product Champion – personal preference • Voting – team concensus (subjective) • Intuition – feel good factor • Prototype & test – Expensive & time consuming • Decision Matrices – relatively more objective

6. Process overview • Initial filtering – qualitative, absolute comparison • Quantitative screening based on decision matrix – Pugh Matrix • Prepare matrix • Rate concepts • Rank concepts • Combine/improve/retain promising concepts • Select one or more concepts • Concept Scoring – similar steps, weighted scores, more refinement and advancement over Pugh matrix

7. Evaluation Criteria • Extracted from stakeholder requirements • Identify a few key requirements through prioritization • Primary, secondary, tertiary • Level of abstraction/refinement of requirements must be consistent with concept abstraction/ refinement There is No Sense in Being Exact About Something if You Don’t Even Know What You are Talking About (John von Neuman, 1950)

8. Initial Filtering (absolute)(In case of large number of concepts) • “Gut feel” feasibility judgment • Comparison made with prior experience (“design knowledge”) • Concept will not work • Too radical • Not original • Conditional feasibility – something else required • Feasible - Worth considering • Go - No go screening • Customer requirements • Technology readiness/maturity/availability

9. Pugh Matrix • Select one concept as a reference or datum • Familiar, straightforward concept • Existing similar benchmark product in market • Existing product in case of re-design/ modification problem • Arbitrarily picked from the generated concepts • Pair-wise relative rating of each concept vs datum for each criteria • Better than datum: + • Same as datum: 0 • Worse than datum: - • Count number of pluses and minuses for each concept. Overall rating is difference between no. of pluses and no. of minuses. • Rank the concepts based on overall rating

10. Pugh Matrix Structure

11. Concept Scoring Matrix • Select one concept as a reference or datum • Best in Pugh Matrix • Select weights for each criteria • Importance rating of each criterion: scale of 1 to 5 or %age with total = 100% etc. • Relative rating of each concept vs datum for each criteria. Datum maybe different for each criterion • Much better than datum: 5 • Better than datum: 4 • Same as datum: 3 • Worse than datum: 2 • Much worse than datum: 1 • Finer scales (1 to 9) etc. may also be used. • Weighted score for each concept – criterion pair • Rank the concepts based on total score (sum of weighted scores) • Combine/ Improve/ Retain concepts • Select one or more concepts

12. Concept Scoring Matrix Structure

13. Selection process Generation Screening Scoring Selected

14. Additional Reading • Product Design & Development, Ullrich & Eppinger – Chapter 7 • The Mechanical Design Process, Ullman – Chapter 8