Concept Selection and DFMEA Heidi Ploeg Associate Professor Mechanical Engineering and Biomedical Engineering

Design Process Flowchart 6/18/2016Page 2 1. Develop problem statement and design specifications 2. Devise potential solutions and select most promising alternatives 3. Develop selected alternatives and evaluate potential 4. Refine and prepare final design 5. Validate final design 6. Communicate design in detail

Outline Models in evaluation Design concept selection –Absolute Criteria –Decision matrix –Pugh’s Concept Controlled Convergence DFMEA 6/18/2016Page 3

Models in Evaluation Analog: rep. unfamiliar with familiar concepts e.g. circuits and thermo Symbolic: e.g. mathematical, FBD, FEA Prototypes: –Proof-of-concept –Form Study –User Experience –Visual –Functional 6/18/2016 Page 4

Outline Models in evaluation Design concept selection –Absolute Criteria –Decision matrix –Pugh’s Concept Controlled Convergence DFMEA 6/18/2016Page 5

Morphological Chart: Beverage Container 6/18/2016Page 6 Function/ Attribute 1234 Contain Beverage CanBottleBagBox Provide Access to Beverage Pull TabStrawScrew CapUnzip MaterialAluminumPlasticGlassCardboard 4x4x4 = 64 solutions?

Power Wheelchair Safety System 6/18/2016 Page 7

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Begin Selection with Absolute Criteria Judgment of functional feasibility Assessment of technology readiness Elimination of designs that don’t meet constraints or technical specifications 6/18/2016 Page 9

Assess remaining concepts with measurement scales Nominal Scale: yes or no –Are categories the same or not? Ordinal Scale: ranking Interval Scale: ranking with value Ratio Scale: cardinal numbers, e.g. technical metrics like weight, strength,… 6/18/2016 Page 10

Nominal Scale Concept Reseal- able? Recycl- able? Break- able? AYYY BNYN CNNN 6/18/2016 Page 11 Glass Aluminum Plastic

Ordinal Scale, Ranking ConceptABCTotal A-011 B1-12 C00-0 Total number of comparisons, N=n(n-1)/2=3 6/18/2016 Page 12 Glass Aluminum Plastic

Interval Scale CAB 6/18/2016 Page 13

Decision Matrix Weight Factor ABC WF x A WF x B WF x C aesthetics low cost low weight durable resealable recyclable Sum Ranking321 6/18/2016 Page 14

Decision Matrix Weight Factor ABC WF x A WF x B WF x C aesthetics low cost low weight durable resealable recyclable Sum Ranking213 6/18/2016 Page 15

Pugh’s Concept Controlled Convergence Develop conceptual designs, create small sketches Create a matrix with column for each design concept and row for each key criterion from technical and customer requirements Choose one concept as datum to compare others against with +,-,= Total scores, discuss, iterate 6/18/2016 Page 16

Pugh’s Concept Controlled Convergence Chart Datum ACE aesthetics=-- low cost-++ low weight=++ durable=+- resealable+=+ recyclable== /18/2016 Page 17

Pugh’s Concept Controlled Convergence Chart Datum ABCDEF aesthetics=----- low cost low weight=+++++ durable=++--- resealable++==+= recyclable=== /18/2016 Page 18

Design Failure Mode and Effect Analysis (DFMEA) Preventative, systematic approach to design development –Cause = reason for failure –Failure Mode = how it fails –Effect = adverse consequence on customer Ranking of risks associated with product failure modes Prioritizing and addressing highest risks 6/18/2016 Page 19

Benefits of DFMEA Systematic process that focuses design on failure modes Provides –a record of preventative action –a record for failure investigations –a list of critical characteristics –criterion based prioritization –new ideas for improvements 6/18/2016 Page 20

Basic Concepts Failure Model: Risk Concept: –Severity: of consequences for customer –Occurrence: probability of failure mode –Detection: risk that failure mode is not detected 6/18/2016 Page 21 Root Cause Effect on Customer Failure Mode

Basic Concepts Pareto’s 80/20 Rule: 80% of Effects are due to 20% of the Causes Therefore, prioritize and reduce risks! Continuous Improvement, “Kaizen” Loop 6/18/2016 Page 22

Basic Tools Bill of Materials, BOM –Detailed list of all components, quantities, and functions Brainstorming –for potential Failure Modes Root Cause Analysis Why? Apparent Cause Why? Root Cause Late for class Slept in Alarm didn’t work Batteries dead Forgot to charge Didn’t plug phone in

Process Outline – Part 1 Create a component list  BOM –Identify functions –Identify Failure Modes  Brainstorming Describe the Effects –Assign a Severity Ranking, SR Identify Root Cause  Root Cause Analysis –Assign a Occurrence Ranking, OR Identify current control –Assign a Detection Ranking, DR

Process Outline – Part 2 For each Failure Mode calculate Risk Priority Number (RPN) –RPN = SR x OR x DR Sort RPN’s from high to low Take action on high risk items  80/20 rule Recalculate RPN’s and repeat until remaining risk is acceptable  Kaisen Loop 6/18/2016 Page 25

Types of Corrective Action Severity Improvement –Change the mode of failure –Performance monitoring –Redundancy 6/18/2016 Page 26

Types of Corrective Action Occurrence Improvement –Change the design to fix the problem –Choose an alternative/better design –Add more (e.g. material) –Add more reliable components 6/18/2016 Page 27

Types of Corrective Action Detection Improvement –Increased Testability, K.I.S.S. –Quality at Source Everyone is responsible for quality control –Stronger Quality Control 6/18/2016 Page 28

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