Bruce Mayer, PE Licensed Electrical & Mechanical Engineer BMayer@ChabotCollege

1. Engineering 11 Design for X Bruce Mayer, PE Licensed Electrical & Mechanical EngineerBMayer@ChabotCollege.edu

2. Customer Needs (CN) Functional Requirements (FR) Design Parameters (DP) Process Variables (PV) OutLine  Design for X • Trade-offs in Satisfaction • Robust design • Failure Modes & Effects Analysis • Tolerance design

3. Basic Design Engineering Goals • Design Engineering Goals for Product: • “performs as expected” • “works all the time” & “lasts long” • “is easy to maintain” • and THAT • no damage occurs to product • no damage or harm to environment • no harm or injury to operator or user

4. Design for X (DfX) • During design, we often focus on the final product, and not its manufacture. • The Design For X (DfX) philosophy suggests that a design be continually reviewed from the start to the end to find ways to improve production and other non-functional aspects • Advantages of DfX techniques include • shorter production times • fewer production steps • smaller parts inventory • more standardized parts • simpler designs that are more likely to be robust • they can help when expertise is not available, or as a way to re-examine traditional designs • proven to be very successful over decades of application

5. The “X” in DfX

6. Design for Robustness • Methods to reduce the sensitivity of product performance to variations such as: • manufacturing (materials & processes) • wear • operating environment • Currently used methods • Taguchi Method • Probabilistic optimal design (Monte Carlo) • Both Taguchi and Monte Carlo methods use statistics and probability theory

7. Failure Modes & Effects Analysis • The FMEA Method seeks to systematically identify and correct potential product or process deficiencies before they occur • The Process • Identify EVERY Way in Which Product Can FAIL; i.e., determine the Failure MODES • Analyze the CONSEQUENCES of Every Failure; i.e., determine the EFFECTS

8. Failure Modes & Effects Analysis • After Completion of the FMEA Work to REDUCE • The NUMBER of Failure MODES • The SEVERITY of the EFFECTS • Prioritize Risk Reduction using“Risk Priority No.”

9. FMEA Example  Log Splitter • FMEA considers Both DESIGN and MANUFACTURING Deficiencies • Example  Hydraulic Log Splitter • Hydraulic hose, on a home-use log splitter, begins to leak. • The leak reduces the pressure to the piston/ram resulting in poor splitting. • The leak drips oil on ground, creating a mess, costly too! • Upon examination, a weak spot is found on hose due to poor manufacturing!

10. FMEA Main Concepts • Failure Mode: the “way” a part fails to perform • e.g. failure mode: hose leaks • Effect: adverse consequence of failure mode • e.g. hose leak results in oil spills, refill costs • Effects can be severe or hardly noticeable. • Cause: why it fails (or may fail) • e.g. poor hose manufacturing, improper pressure • Causes occur with some likelihood or probability • Dectectability: the ability to discover the cause before the part is shipped from the factory. • e.g. conduct a pressure test to detect leaks?

11. FMEA Risk Metric  RPN • Determine a rating for each mode of failure …. using a “risk priority number” (RPN) RPN = [Severity rating] x [Occurrence rating] x [Detection rating] RPN = (S)•(O)•(D) • RPN will range from 1 to 1000 • Large RPN  “bad” • Small RPN  “good”

12. RPN Calculation • Step 1: determine the failure modes • From: • Engineering design specifications • Function decomposition diagrams • functions ---- matter, energy, signal • HoQ • free body diagrams • force flow diagrams • process flow diagrams • configuration sketches / drawings

13. RPN Calculation • Step 2: determine potential effects of each failure mode • Step 3: determine a severity (S) rating for each effect from the Severity rating table. • Step 4: determine an occurrence (O) rating for each cause from the Occurrence rating table. • Step 5: determine a detection (D) rating for each cause from the Detection rating table

14. Severity Rating Criteria

15. Occurrence Rating Criteria

16. Detection Rating Criteria

17. RPN Calculation & Reduction • Step 6: calculate the risk priority number for each effect • Step 7: prioritize or rank the failure modes for action • Step 8: take action to eliminate the failure mode or reduce its severity • Step 9: recalculate the risk priority number as failure modes are reduced or eliminated

18. RPN Calculation Summary • RPN Calculations are Usually Tabulated or put in a SpreadSheet

19. RPN Example  Hose Failure • Log-Splitter RPN & Remediation

20. Design for Safety Issues • Injury • Hazards • Conditional Circumstances • Legal Responsibilities • Guidelines for Safe Products/Systems • Safety Hierarchy • Safe Design Principles

21. Define Safe Product/System • No injury to user, (products liability) • No injury to consumer/society • No injury to production worker • No damage to personal property • No damage to real property or the environment

22. Hazards • Hazard≡ a source of danger which has the potential to injure people or damage property or the environment • Partial Hazard List • Entrapment – pinch, crush • Contact – heat, sharp edges, electric • Impact – hammer, robot arm • Ejection – grinder sparks, saw dust • Entanglement – hair, clothing • Noise & Vibration – hearing loss, HAVS

23. Conditional Circumstances • hazard is inherent during normal use • hazard originates from a component failure • hazard caused by user misuse • hazard exists during normal maintenance • hazard created by improper maintenance • hazard stems from lack of maintenance

24. Product Legal-Liability • Plaintiff’s attorney will try to prove that the company or its employees failed to: • perform “appropriate analyses.” • comply with published standards. • make use of state-of-the-art technology, due to ignorance. • include reasonable safety features or devices. • take into account how the user might misuse the product. • consider hidden dangers that might surprise the user. • consider variations in materials, mfg processes, or effects of wear. • carry out appropriate testing, or interpret results correctly.

25. Guidelines for Safe Products • Perform appropriate analyses • Comply with published standards • Use state-of-the-art technology • Include reasonable safety features or devices • Take into account how the user might misuse the product • Consider hidden dangers that might surprise the user

26. Guidelines for Safe Products • Consider variations in materials or manufacturing processes, or effects of wear • Carry out appropriate testing and interpret results correctly • Provide adequate warnings • Implement superior quality control • Document everything

27. Safety Hierarchy Method • Eliminate the hazard - ProActive approach, “design-out” the hazard (eliminate any moving parts, hot or sharp surfaces) • Protect against the hazard with passive approach, (machine guards, seat belts) • Warn against the hazard - weak remedy (warning labels, alarms) • Provide Training - Provide and require operating training. • Provide Personal Protection - LEAST effective, (safety glasses, gloves, shoes)

28. Safe-Design Principles • Safe-Life  Good • entire predicted useful life without malfunction. • designers to identify all operating conditions, misuses and abuses • design appropriate maintenance and repair schedules. • Fail-Safe  Better • upon failure of a component, product/system SHUTS DOWN safely, • critical functions are sometimes still performed • e.g. boiler feed-water valve failing in the open position • Redundant design  Best (but EXPENSIVE) • additional product components or systems are designed to take over the principle function of the failed component or system. • e.g., multi-engine airplanes, emergency brakes, BackUp pumps in nuclear PowerPlants

29. All Done for Today EnvironmentalToleranceZone • The ETZ is the Limits of SURVIVAL • Well Beyond the Comfort Zone

30. Engineering 11 Appendix Bruce Mayer, PE Registered Electrical & Mechanical EngineerBMayer@ChabotCollege.edu

31. Method 6-3-5 (Brain-Writing) • The traditional brainstorming relies on verbal communications. • Idea generation may be dominated by a small number of aggressive members. • Guidelines for 6-3-5 method • Team members are arranged around a circular table to provide continuity. Six (6) members are ideal. • Each member sketches three (3) ideas for the product configuration or functions. Sketches should be the focus of this activity. The top five product functionswith respect to the customer needs are considered.