nwc 2015 - critical - path simulation
TRANSCRIPT
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
CRITICAL-PATH SIMULATION: CASE STUDIES IN THE IDENTIFICATION AND EXECUTION OF FINITE-ELEMENT ANALYSES EARLY IN
THE DESIGN PROCESS TO ASSURE FEASIBILITY AND INCREASE ROI
Bradford RangeAcorn Product Development
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
About Acorn Product DevelopmentAcorn was Founded in 1993 in Silicon Valley by product development
veterans Ken Haven, CEO (MSME Cornell) and Tim Lau, CTO (MSME
UC Berkeley).
Today Acorn is a global team of over 30 product development engineers
– BSME and MSME
ACORN’s Goal: Incorporate mechanical engineering analysis and
manufacturing considerations from the earliest stage of development
in order to accelerate the path to market and improve outcomes.
Offices in the Silicon Valley, Boston, Texas and China
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Who We Serve
Consumer Industrial Communication
s
Medical
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Example Projects
Robotex AvatarTeradyne Hard Drive Tester FLiP Video
AccuCheck Tester / Insulin PumpPowerMac G4 Tower
Siemens Medical Ultrasound
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Product Development Process
Traditional Product Design Process
Acorn DFM Oriented Process
Costing Metrics, DFM Reviews
Supply ChainAcorn Database
DFM ToolsExperience Advantages:
Faster TTM
Fewer prototypes/spins
Achieve cost/performance
targets
Design
Analysis -Simulation -Thermal -Tolerance -Etc.
Prototype
90%
Refine
Concept
Concept
Concept
Production Ready
Concept
Refine for production?
Concept
Concept
Design Design Fixes
Prototype #1Prototype #2
Production
Redesign for cost?
Engineering Manufacturing/Operations
40% 70%
Phase 1Phase 2 Phase 3 Phase 4
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Where is the Design Vetted?
TestingTesting
• Our classical value-add is vetting the design prior to prototype• Always a trade-off between technical risk and development effort • The question becomes: would it be beneficial to move this even earlier?
?
Traditional Product Design Process
Acorn DFM-Oriented Process
…
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Critical-Path Analysis
Differences: Selected early-stage analysis drives concept brainstorming
Advantages: In certain cases, can identify optimal or eliminate impossible technical directions to limit scope of brainstorming exercise & reduce development time
…
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Identifying Potential Benefits• Questions
– Is there a single subsystem that drives most of the functional requirements?– Are the target performance specs out on the “ragged edge” of what is possible
with the proposed technology?– Are there significant cost savings that could be realized by an unconventional
material choice or system architecture?
• Early-stage, critical-path analysis is a tradeoff between marginally higher technical risk and lower development effort
• Goal is to set a validated technical direction earlier in the development cycle, and focus concept brainstorming around this
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Case StudiesCase 1: Rifle ScopeCritical Requirements: Structural, Thermal, CostCritical Analysis Goals: Material Selection
Case 2: RF Telecom CabinetCritical Requirements: ThermalCritical Analysis Goals: Thermal Architecture
Case 3: Rack-Mounted Test SystemCritical Requirements: Structural, Tolerances, CostCritical Analysis Goals: Rack Sheetmetal Construction
Focusing on Case 3, see paper for others
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Case Study 3: Rack-Mounted Test System
Project Overview:- Re-design & cost reduction- Target production quantity: 1000’s- Tolerance requirements:
- Robot vision- Robotic equipment mate
- Structural requirements:- 800 lbs- Resist robot impact- Overall stiffness (modal)
Potential rack construction architectures(Clockwise: Baseline, A, C, B)
Overview
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Brainstorming
Design Refine
Analysis -Simulation -Thermal -Tolerance -Etc.
Prototype
90%
Concept
Concept
Production Ready
Requirements Definition
Identify Critical Design Feature
Critical-Path
Analysis
?
• Chicken-or-the-egg argument• Especially in cost reduction programs, there will be some pre-conceived notions• In this case, structural “skeleton” was identified as critical sub-system• In some cases, critical-path analysis looks like its own mini-development program
Other systems eventually fleshed out around structural skeleton:
Equipment interfaces
Thermal
Robot interfaces
Power & data handling
Case Study 3: Rack-Mounted Test System Semantic Considerations
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Case Study 3: Rack-Mounted Test System Tolerance Analysis
Tolerances are a critical aspect of vetting the design, to assure selected structural concept will meet robot interface requirementsThere are several approaches here, each with their own advantages:
Worst-Case Analysis:
“RSS”, Root Sum Squared
Direct Linearization
Method
Monte-Carlo
Setup Time(fast)
(slow)(high)
Accuracy
(low)In everyone’s toolbox. Not realistic, doesn’t hold up for multi-part solutions. Can’t plan for the worst!
Good approximation, weights all variables the same. Difficult to get a predicative value.
Good balance of speed, accuracy. Combines actual process capability into a predictive approach.
“Holy Grail”. Iterative, simulation to predict results. This is only as good as your input data. Not recommended unless you have measured manufacturing data on your parts.
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Case Study 3: Rack-Mounted Test System Tolerance Analysis
Direct Linearization Method:Element 1: Plastic Feature
Element 2: Shaft Dimension
Element 3: Bolt fit in clearance hole
Sum generates a composite Gaussian curve
Adding up our
elements, based on
a sketched loop
New Predicted Gaussian
3 sigma = 99.9%, or 1350 DPPM 4 sigma =
99.997%, or 32 DPPM
Element n: Hole clearance, biased by gravity
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Case Study 3: Rack-Mounted Test System Tolerance Analysis
Representative tolerance loop
Concept tolerance summaryResults:- Ran loops in X, Y, Theta for each concept- Some concepts much better than others at
accommodating robot requirements - Concept C appears best - feeds into tradeoffs- Identified potential issues in existing design to
be fixed
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Case Study 3: Rack-Mounted Test System Structural Analysis
- Combination static load from installed equipment and worst-case load from robot impact
- Constraints, analysis package, etc. secondary- Analysis with +/- 20% global accuracy is useful to
compare concepts at this stage
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Case Study 3: Rack-Mounted Test System Structural Analysis
- Similar to previous slide, modal analysis is useful for quick comparison between concepts
- Few ties to “real” world, but gives feeling of relative stiffness between concepts
- Concept C appears best – feeds into tradeoffs
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Case Study 3: Rack-Mounted Test System Cost & Weight Analysis
Sheetmetal Cost Model
System-Level Roll-Up
- Proprietary heuristic tools estimate cost for each component
- Analytical tools estimate time & cost for assembly (Boothroyd-Dewhurst)
- CAD models estimate weight deltas- Concept C is best cost-savings, at
increased weight and sub-optimal part count – feeds into tradeoffs
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Case Study 3: Rack-Mounted Test System Results
Based on client preferences, concept C was selected- Lowest overall cost- Best structural response (comparable to baseline)- Achievable tolerances (with continued design effort)- Increased weight & part count
What do we gain?- Selected structural design path- Allows for simpler tradeoff space later- Taken as baseline for other sub-system design- Faster overall development time- Reduced sub-system cost- Confidence that the design meets critical requirements
NAFEMS World Congress 2015 | 21-24 June | San Diego | California | USA
Summary
Case Technical Result Program Result
Rifle Scope Optimal materials selected for each subassembly, structural and thermal expansion requirements met
Saved ~50% cost on casing parts and ~20% on internal parts, reduced development time and cost
Telecom Cabinet
Successfully dissipated 8.5 kW with redundant fan failures
Reduced development time and cost, assured component layout viability. Schedule: 5 months kickoff to show unit
Rack Structure
Selected optimal construction geometry for primary structural element
Reduced system cost by ~$35K, decreased part count, assured tolerance and structural viability
Reference paper for other case studies (thermal, vibe, etc.)In all cases, critical-path analyses assured critical requirements were met, reduced development time and cost, and reduced component and assembly cost