Decision Making and Concept Selection

Evaluation Methods - Absolute Criteria

Feasibility (feasible, always work, conditional?) Assessment of technology readiness (manufacturable, critical parameters, operating latitude, failure modes and effects?) PDS Comparison (evaluation based on customer requirements)

The design process is seen as a mapping of _____ to the _____.

Functional requirements Design parameters

Design objectives are defined in terms of ... (axiomatic design)

Functional requirements (FR's)

Axiomatic Design

Theoretical basis for design evaluation which attempts to answer key questions Both functional and physical domain requirements must be achieved

Problem with Pugh Concept Selection

All criteria is weighted the same

AHP

Analytic Hierarchy Process

Archibald Method

1) Brainstorm evaluation criteria 2) Pairwise compare the evaluation criteria (winner gets a 1, loser gets a 0) 3) Total and normalize criteria Criteria goes both in columns and rows so diagonal x's at intersection of each same Normalize = total row number / total for each row 4) New matrix, criteria on rows, Options on columns 5) Rank each design by criteria (3 highest, 1 lowest) 6) Multiple normalized value by each design ranking (each cell) 7) Total results (columns) for each design, highest number is winner

Pugh Concept Selection Process

1) Choose the criteria by which the concepts will be evaluated 2) Formulate the decision matrix 3) Clarify the design concepts 4) Choose the datum concept 5) Compare the alternatives to the datum 6) Evaluate the ratings 7) Establish a new datum and rerun matrix 8) Examine the selected concept for improvement opportunities

Sequence of Steps in Decision Making

1) Establish the objectives of the decision 2) Classify the importance of the objective (needs and wants) 3) Develop alternative options 4) Evaluate alternatives vs the objectives 5) Tentative decision - alternative most likely to achieve all objectives 6) Consider the adverse consequences of implementing the tentative decision 7) Final design and efforts to control possible adverse consequences

Pugh Concept Selection Matrix

Columns are criteria, top row is each concept with datum at last right column Each concept is evaluated for each criteria as "Better -> +, Worse -> -, Same -> S" Total +, - and S at bottom of each concept column

Axiomatic Design - Design Rules

Decouple a coupled design Minimize functional requirements Integrate of physical parts (only if functional requirements can be independently satisfied) Use of standardization Use of symmetry Largest tolerance possible Uncouple design with less information

Weighted Decision Making Processes

Each criteria has its own importance to decision so own weight 1) Construct a hierarchical objective tree 2) Weights of the individual categories at each level of the tree must add up to 1.0 3) Weights of the lower level factors - multiple the weights as you go up the chain Rating of each design is equal to the weight factor times the score (higher number is better)

Axioms (Axiomatic Design)

Information axiom Independence Axiom

Independence Axiom

Maintain the independence of functional requirements

AHP Explained

Method of mathematically ranking selection criteria and using that to rate design choices Similar to Archibald method Useful when evaluation is based on both quantitative and qualitative data.

Information Axiom

Minimize information content

Decision Making is influenced by...

Personality Circumstances

In order to satisfy functional requirements a _____ must be created in terms of design parameters

Physical embodiment

Dr. U's Evaluation Criteria

Quality (function, reliability, serviceability, safety) Delivery (Materials, processes, tolerances. risk) Cost (total to business, value, processes, tooling)