Robust Design & Reliability
I delivered a webinar recently to describe the differences and similarities between robust design (RD) activities and reliability engineering (RE) activities in hardware product development . A survey we took from several hundred attendees indicated a diversity of opinions. About half the participants indicated they did not differentiate at all between the two methodologies. Approximately 20 % indicated they did differentiate between the two methodologies, and about 30% indicated that they did not know.
I was quite surprised at the result, especially since participants came from working quality engineers, reliability engineers, engineering directors, system engineers, etc. Somewhere along the way, the differences and similarities between the two seem to have become muddled. Below I have collected just twelve of the many ways in which the activities are different:
RD 1 Focus on design transfer functions, and ideal function development
RE 1 Focus on design dysfunction, failure modes, failure times, mechanisms of failure
RD 2 Engineering focus, empirical models, generic models , statistics.
RE 2 Mechanistic understanding, physical models, science oriented approach.
RD3 Optimization of input-output functions with verification testing requirement
RE3 Characterization of natural phenomena with root cause analysis and countermeasure decisions
RD4 Orthogonal array testing, design of experiments planning
RE4 Life tests , accelerated life tests, highly accelerated tests, accelerated degradation tests, survival methods
RD5 Multitude of control, noise, and signal factor combinations for reducing sensitivity to noise and amplifying sensitivity to signal
RE5 Single factor testing, some multifactor testing , fixed design with noise factors, acceleration factors
RD6 Actively change design parameters to improve insensitivity to noise factors, and sensitivity to signal factors
RE6 Design-Build-Test-Fix cycles for reliability growth
RD7 Failure inspection only with verification testing of improved functions
RE7 Design out failure mechanisms, reduce variation in product strength. Reduce the effect of usage/environment
RD8 Synergy with axiomatic design methodology including ideal design, and simpler design
RE8 Simplify design complexity for reliability improvement. Reuse reliable hardware .
RD9 Hierarchy of quantitative design limits including functional limits, spec limits, control limits, adjustment limits
RE9 Identify & Increase design margins, HALT & HASS testing to flesh out design weaknesses. Temperature & vibration stressors predominate
RD10 Measurement system and response selection paramount
RE10 Time-to-failure quantitative measurements supported by analytic methods
RD11 Ideal function development for energy relate measures
RE11 Fitting distributions to stochastic failure time data. Time compression by stress application
RD12 Compound noise factors largest stress. Reduce variability to noise factors by interaction between noise and control factors, signal and noise factor.
RE12 HALT & HASS highly accelerated testing to reveal design vulnerabilities and expand margins. Root cause exploration and mitigation
There are many other differences of course, but this list should start the conversation . I would invite bloggers to submit their own opinions and lists of differences (and similarities) .
Sr. Reliability Consultant
Ops a la Carte