tolerance analysis – an engineering simulation of ...key takeaways 1. engineering simulations...
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Tolerance Analysis –An Engineering Simulation of Production and Performance Quality
Stephen Werst, Senior Product Strategist, Sigmetrix, LLC.
The Motivation for Simulation
The Real Motivation• Reduce number of prototypes• More thorough and accurate understanding of product capabilities and limitations in less time
• More efficient transition to production• Predictable results• “Learning opportunities” are virtual
• Ensure product will perform as expected by customers when it’s in their hands
• Greater profitability
Achieving Product Targets
Pequin, Reid and Prouty, Kevin - Aberdeen Group. The Value of Virtual Simulation Versus Traditional Methods. 2014.
Impact on New Product Development & Introduction
Pequin, Reid and Prouty, Kevin - Aberdeen Group. The Value of Virtual Simulation Versus Traditional Methods. 2014.
Example – Flight Simulator
Questions Answered by Engineering Simulations• Will it break during operation?• Will it overheat during operation?• Will it last as long as expected by the customer?• Could there be resonance?• …
StructuralStructural ThermalThermal FatigueFatigue
Tolerance Analysis ‐A Simulation of Dimensional Variation
• Will the parts fit together?• Will the assembly work as expected?• Will manufacturing be able to assess new vendors, processes, etc. based on the design package?
• Is manufacturing monitoring the right things to ensure a quality product to the customer?
• Will the product be profitable?
Pitfalls of 1D Analysis AssumptionsName: Hub with Cap
Description: Axial clearance between hub and cap
Part Dimension Description NominalHub large DIA face to shim mount 1.100 ± 0.010Shim thickness 0.050 ± 0.002Cap shim mount to top 1.150 ± 0.007Cap top to bottom ‐2.200 ± 0.010
0.1 ± 0.029Nominal
Tolerance
Worst‐CaseTotal Variation
What to Consider? (Sources of Dimensional Variation)
• Process variation during part creation (setup, positioning errors, tool deflection, casting and molding errors from mold or shrinkage, etc.)
• Supplementary processing (plating, painting, etc.)• Assembly process (sequence, fixture, joining methods, clearances between parts, etc.)
• Operational Environment (thermal expansion, deflection under load, vibration, etc.)
Case Study ‐ Vestas
Case Study – Cover Redesign• Spinner Cover Redesigned in OCT 2014• The two components typically assembled for the first time in the field on the top of a 100m pole
Spinner Cover on HUB
Nacelle
Case Study – Problem with Prototype• Prototype to check fit of Hub and Nacelle
Case Study – Initial Analysis with Spreadsheet
Case Study – First Update with Clearance
Case Study – Assembly Method• The spinner cover is assembled to the hub with both in the vertical position as shown.
• Gravity pulls the cover downward during assembly.
• This bias is in the direction of the Nacelle when assembled thus minimizing the gap.
Spinner Cover
Hub(machined casting)
Assembly brackets
Case Study – Analysis Reflecting Reality
Closing the Loop with Manufacturing• Like all simulations validating the assumptions is critical• If Engineering and Manufacturing aren’t aligned the actual results may be significantly different from what was predicted
• Garbage In, Garbage Out
Example – One‐way Clutch
Hub = 69.25% of variation
Example – Analysis Updated with MFG Data
! By machining to maximum material to permit rework manufacturing is changing assembly defect rate from predicted 2.1% to actual 97.5%
Ring ID:
Hub axis to flat:
Example – After MFG Changes TargetsRing ID:
Hub axis to flat:
! Changing setup target to tolerance midpoint results in new predicted defect rate of .0182%.
Key Takeaways1. Engineering simulations offer quantifiable business benefits vs.
hand calculations and prototyping.2. Tolerance analysis, like other engineering simulations, is intended to
predict many characteristics of the design.3. Traditional approaches with simple tools like spreadsheets can
often lead to predicting less variation than what will actually occur.4. The best predictions of real‐world performance require considering
many aspects beyond tolerances on part drawings.
Questions?