Evaluation of Assembly Joining Concepts, With Limited Information, Using Technical Cost Modeling in a Multi-Material Body in White Theresa M. Lee General Motors Company
Overview Ø Description and Purpose Ø Baseline Assumptions and Scope Ø Process Based Cost Modeling Ø Results
Project Description and Purpose
Project Description and Purpose Purpose: Compare lightweight joining processes (Steel and Aluminum) for a representative automotive body in white Cost Complexity Procedure Technical Cost Modeling (cost implications) Vehicle assumption RWD based body in white (lux class 3) OEM (USCAR) available model which was modified for study assumptions Camanoe Associates (Roth, Gregory et al.) - USCAR is not responsible for the analysis, assumptions or conclusions.
Baseline Design Assumptions and Scope
Baseline Vehicle (No Closures) Process Quan,ty of Components Stamping (Steel) 315 Roll Forming 6 Other 12 Total 333 Underbody Complete Motor Compartment Underbody Front Inner framing Header and Greenhouse subs Underbody Rear Outer Framing Framing Subs Body side Inner RH and LH Body Side Outer Rh&LH
Assumptions for Variants Ø Baseline representative steel design RWD Lux 3 vehicle using Resistance Spot Welding (RSW) Ø Representative aluminum design with primary joining technique of RSW (adjusted for aluminum), 5% more parts assumed and 10% more attaching points 20% more MIG welds, 10% less sealing and 5X more structural adhesive. Ø Multi-material Concept with Self piercing rivets (SPR) and Flow Drill Screws (FDS) are added accordingly to the aluminum RWS design in 25% increments until we reached 100% of the inserted technology replacing Resistance Spot Welding (RSW).
Discrete Joining Assumptions per Variant Discrete A6aching Points Process Steel Full Al RSW Full Al SPR Full Al FDS RSW 3906 4296 Rivets (or SPR) 13 13 4309 13 FDS 0 4296 Structural Adhesive 28 140 140 140 Sealing 35 32 32 32 MIG 145 174 174 174 # of Components 333 350 350 350 Total Discrete A6achment Points 4127 4309 4309 4309
Key Process Assumptions Ø RWS for Al and Steel have the same cycle time Ø SPR Same cycle time as RSW Ø SPR fastener cost assumed to be $0.035 and the FDS fastener cost assumed to be $0.075 Ø FDS 80% increased cycle time over RWS and SPR. Ø Energy Usage and Cycle time for SPR and RSW based on Briskham et al (SAE 2006-01-0774) Ø Adhesive (crash toughened) Ø Vision inspection systems (assumed), buffers and hot back up added as required.
Process Based Cost Modeling
Process Based Cost Modeling Inputs: Outputs: Forming Technology Part Mass Material Assembly Order Joining Method Forming Speed, Joining Speed, Volume expectations Process Model OperaQons Model Financial Model Fixed Costs- Equipment, Tooling, Facility, Maintenance, Fixed Overhead Variable Costs Materials, Energy, Labor Allocated Equipment Cost = (Time required to make parts/time available) Equipment Purchase Cost (13 years)
General Cost Model Assumptions Ø Equipment and Labor is non-dedicated Ø Equipment/tooling costs are annualized over the equipment/tooling life Ø Greenfield Ø US economic framework Cost modeling results are most accurately used as comparators to a baseline Ø Representative Example (not a specific business case)
General Modeling Assumptions Assumption Production Volume Production Days Production Shifts *Representative Industry-based Assembly Wage (with benefits) Energy 100,000 units per year 235 per year 2 shifts per day $35/hour Cost of Capital 10% Assembly Equipment Life Building Cost Tooling life $0.10/kwhr 13 years $1500/sqm 5 years
Results
Aluminum RSW Design Compared to Steel RSW Design (BASELINE) Assumes the increased # of components and adhesive usage from a representative Al design
Comparison of Steel vs. Al RSW Modeled Assembly Cost 100,000 Annual Production Volume Aluminum Intensive RSW Design Steel Intensive RSW Design Assumes the increased # of components and adhesive usage from a Representative Al design
Cost Delta Between Steel and Aluminum RSW for Representative Designs 100,000 Annual Production Volume Assumes the increased # of components and adhesive usage from a Representative Al design Assembly Cost Delta to Baseline Steel Design ($)
Self Piercing Rivet Study
SPR Production Volume Sensitivity Representative Assembly Cost Only
SPR Representative Study
Flow Drill Screw Study
FDS Production Volume Sensitivity Representative Assembly Cost Only
FDS Representative Study
Cost Delta to Steel RSW at 25,000 Annual Production Volume
Cost Delta to Steel RSW at 100,000 Annual Production Volume
Production Volume Comparison for Assembly Modeled Cost Delta 25,000 ANNUAL PRODUCTION VOLUME MODELED 100,000 ANNUAL PRODUCTION VOLUME MODELED
Cost Sensitivity Study to Fastener Price at 100,000 Annual Production Volume
Cost Sensitivity to FDS Cycle Time Delta to Baseline Steel at 100,000 Annual Production Volume
Conclusions Ø RSW is the lowest cost assembly process for this modeled representative design and assumptions. Ø SPR (Self Piercing Rivets) are good a option primarily due similar cycle times to RSW and reduced energy usage for this representative design. Ø FDR (Flow Drilled Screws) are a higher cost assembly method option primarily due to increased material cost, slower cycle time and highest downtime. Ø As more processes are added into the assembly process overall assembly cost increases when number of attaching points is held the same until a breakpoint is reached and variable cost dominates. Ø Minimizing the joining complexity in a process (number of various methods) will decrease overall assembly cost for any process but careful consideration needs to be considered as the lowest cost option can be based on design specific considerations.
Acknowledgments Thank you Elaine Garcia, Jeremy Gregory, Paul Krajewski, Scott Miller, Richard Roth, Peter Vossler, and Cindy Willman
DOE Disclaimer This material is based on work supported by the U.S. Department of Energy (DOE). Such support does not consqtute an endorsement by the DOE of the views expressed herein. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily consqtute or imply its endorsement, recommendaqon, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.