NWC 2015 - Critical - Path Simulation

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


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


Who We Serve

Consumer Industrial Communication

s

Medical


Example Projects

Robotex AvatarTeradyne Hard Drive Tester FLiP Video

AccuCheck Tester / Insulin PumpPowerMac G4 Tower

Siemens Medical Ultrasound


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


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

…


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

…


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


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


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


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


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.



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



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


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


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


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


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


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

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