Executive Summary: Lightweight Suspension (ASP-340)

Transcription

1 Executive Summary: Lightweight Suspension (ASP-340) Published and Distributed by Multimatic Engineering Prepared by Hannes Fuchs, Ph.D. Acknowledgement This material is based upon work supported by the Department of Energy National Energy Technology Laboratory under Award Number: DE-FC26-02OR Printed in the United States of America All rights reserved. No part of this report may be reproduced in any form or by any means, electronic, mechanical, photocopy, recording or otherwise, without written permission of USAMP. Full Report Released May 7, 2010 Executive Summary Version Released January 16, 2013

2 Executive Summary The objective of this project was to develop lightweight sheet and forged steel proof-ofconcept front lower control arm (FLCA) designs that achieve equivalent structural performance and function at a reduced cost relative to the baseline forged aluminum FLCA assembly. A current production OEM FLCA assembly was used to establish the baseline for package, performance, mass, and cost. CAE structural optimization methods were used to determine the initial candidate sheet steel and forged designs. Two (2) sheet steel FLCA designs and one (1) forged steel FLCA design were selected and developed to meet all typical performance criteria. An iterative optimization strategy was used to minimize the mass of each design while meeting the specified stiffness, durability, extreme load, and longitudinal buckling strength requirements. In order to achieve sufficient mass reduction with the forged design, an aggressive 3 mm minimum gage manufacturing target was assumed. The manufacturing cost was estimated for the sheet steel designs relative to the baseline design for three production volumes. The costs of the forged design could not be assessed due to insufficient data. The results of the study indicate that a Clamshell Design based on DP780 steel sheet achieves equal mass to the baseline assembly, and up to a 34% reduction in manufacturing cost. The I-beam Design based on DP780 and DP980 sheet, DP780 tube, and HSLA550 was predicted to have a 2% (0.05 kg) mass increase relative to the baseline assembly, and up to a 21% reduction in manufacturing cost. The Forged Design based on AISI 15V24 grade material and the 3 mm minimum gage target was predicted to have a 4% (0.13 kg) mass increase relative to the baseline assembly. All sheet steel designs were deemed manufacturable based on forming simulations, and relevant production application examples. Manufacturing studies are recommended to assess the ability to meet the assumed aggressive minimum forging gage target and to provide a basis for developing the associated manufacturing costs. 2

3 Purpose Lightweight Suspension FLCA (ASP-340) Executive Summary The objective of this project was to develop lightweight sheet and forged steel front lower control arm (FLCA) proof-of-concept designs 1 that achieve equivalent structural performance and function at a reduced cost relative to the baseline forged aluminum FLCA assembly. A current production OEM FLCA assembly (Figure 1) with baseline weight (Figure 2) was used to establish the baseline for package, performance, mass, and cost. Baseline FLCA assembly Figure 1: Baseline OEM FLCA Forged Aluminum Assembly Complete FLCA Assy 3.07 Complete FLCA Assy 3.07 kg FLCA Assy less bushings 2.01 Steel washer Ride bushing bolt FLCA structure Mass [kg] FLCA structure Figure 2: Baseline FLCA Assembly Mass Summary 1 Designs are subjected to typical OEM requirements; specific OEM production requirements may require further development and validation. 3

4 Design Targets Lightweight Suspension FLCA (ASP-340) Executive Summary The overall project design targets are illustrated in the schematic shown in Error! Reference source not found.. The objective is to develop minimum mass designs within the packaging constraints that meet the structural performance targets. Corrosion requirements are addressed by appropriate selection of material coatings, which typically do not add significant mass, but can increase cost. Mass and cost are the primary outputs of the study. Cost Reduced vs. the baseline (target 30%) Structural Performance Equal to, or exceed the baseline and OEM requirements Mass Less than, or equal to the baseline Corrosion Meet OEM corrosion requirements Package Meet available packaging constraints Figure 2: FLCA Design Targets Design Optimization Methodology An iterative optimization strategy was used to minimize the mass of each design while meeting the specified structural requirements. A schematic of the overall development strategy is shown in Figure 4. The key elements of the strategy are discussed in the following sections. 4

5 Figure 4: Design Optimization Process Diagram Mass A high-level breakdown of the baseline FLCA assembly mass is shown in Figure 3. The mass is shown for three levels of content. The complete assembly mass of 3.07 kg is used as the overall basis for comparison of all designs. The 1.65 kg mass of the FLCA structure will be used as the basis for cost estimation.. 5

6 Complete FLCA Assy 3.07 Complete FLCA Assy 3.07 kg FLCA Assy less bushings 2.01 Steel washer Ride bushing bolt FLCA structure Mass [kg] FLCA structure Figure 3: Baseline FLCA Assembly Mass Summary Corrosion To meet OEM corrosion requirements, corrosion protection must be applied to components based on material gage. The sheet steel material gage limit is OEM specific, and is assumed to be 2.0 mm for the purpose of this study. For the forged aluminum baseline FLCA, no corrosion coating is required. For the steel components, the following is assumed: Gage > 2.0 mm: E-coat finish required. Gage < 2.0 mm: Hot dipped galvanized coating + E-coat finish required. The specific type of galvanized coating is also OEM specific. Examples of coating specifications include Hot Dip G60/G60 (GI) or Hot Dip Galvanneal A-40 (GA). Cost The project cost reduction target is a 30% reduction relative to the baseline. To assess cost reduction, the manufacturing cost is estimated for each design proposal and compared to the baseline design cost. The project costing assumptions are: Manufacturing cost for the FLCA structure only Production volumes of 30,000, 100,000, and 250,000 vehicles per year 6 year program life 6

7 1. Concept development Initial design concepts were developed based on size and shape optimization of the available design space. Stiffness-based topology optimization methods were used to identify promising concepts using the Optistruct solver [Error! Reference source not found.]. An example of using various constraints to identify potential forged and stamped designs concepts is shown in Figure 6. (a) Application of stiffness constraints and loading conditions forged stamped forged stamped (b) Evolution of optimum volume (c) Final optimized volume Figure 6: Volume Topology Optimization Using Various Draw Constraints Design Proposals The final clamshell, I-beam, and forged design proposals are shown in Figure 4, Figure, and Figure, respectively. Clamshell Design The clamshell design features an upper and lower stamping, a bushing sleeve, a forged T-pin, and a riveted forged ball joint housing. All components are assumed to be MIG welded, and the stampings are butt-welded to maximize the component cross-section. 7

8 MIG Weld Section A-A Bushing sleeve T-pin Upper & lower stampings A Rivets All components MIG welded (~1.20m weld length) Ball joint housing A Figure 4: Clamshell Design Concept I-Beam Design The I-beam design features a web, inboard and forward flanges, a bushing sleeve, a bent tube, a forged T-pin, and a riveted forged ball joint housing. Note that the ball joint housing is supported in double shear via an additional reinforcement. All components are assumed to be MIG welded on one side. 8

9 MIG Weld Section A-A Inboard flange T-pin Bushing sleeve Web Tube Forward Flange A Rivets All components MIG welded (~1.35m weld length) Ball joint housing A Figure 8: I-Beam Design Concept Forged Design It was determined early in the concept development phase that an aggressive minimum gage manufacturing target of < 4.5 mm would be required to be mass-competitive with the baseline design (see Error! Reference source not found.). For the purpose of this study, a minimum gage of 3 mm was assumed to gain insight into the potential mass and performance of a forged steel design. 9

10 B Design Assumptions: Min web thickness 2.8 mm Flange thickness 3.0 to 7.8mm Flange height 10.0 to 30.0mm Flange to web rads 3.0 mm 5 o draft B Section B-B A A Machined bushing sleeve and BJ housing Section A-A Figure 9: Forged Design Concept 10

11 Materials For the sheet steel FLCA designs, the material grade selection was primarily influenced by the extreme and longitudinal strength load cases. Additional material selection criteria included formability and welding, and availability and cost. A table summarizing the A/SP Team recommended sheet materials is provided in Table 1. For forged FLCA applications, material selection was primarily driven by manufacturing considerations with some minimum strength requirements to meet the longitudinal strength load case. Engineering stress-strain curves for the sheet and forged materials utilized in this study are compared in Figure 10. The yield and ultimate tensile strengths are indicated for each material. 11

12 Table 1: Steel Sheet Material Properties 1200 DP980 ( y =715MPa, u =1,008 MPa) T-Pin forging ( y =760MPa, u =1,124 MPa) DP780 ( y =567MPa, u =846 MPa) AISI 15V24 forging ( y =646MPa, u =878 MPa) Engineering Stress [MPa] DOM1020 HSLA550 ( y =414MPa, u =483 MPa) ( y =550MPa, u =620 MPa) BJ forging ( y =420MPa, u =490 MPa) 6082-T6 forged aluminum ( y =310MPa, u =340 MPa) 0 0% 5% 10% 15% 20% 25% Engineering Strain Figure 10: Engineering Stress-Strain Curve Comparison 12

13 Material Selection Lightweight Suspension FLCA (ASP-340) Executive Summary The materials were selected for each design based on meeting all of the strength and durability requirements, formability considerations, and A/SP Team recommendations. The resulting material selections and gage are illustrated Figure 5 through Figure 6. The forged aluminum material for the baseline design is called out in Error! Reference source not found.. Based on the results and the corrosion requirements, hot dipped galvanized sheet steel products are recommended for the 1.9 mm thick DP780 stampings in the clamshell design (see Figure 11), and the 1.5 mm thick HSLA550 ball joint reinforcement in the I- beam design (see Figure ). An appropriate E-coat finish is also recommended. Upper stamping (1.9 mm DP780) Note: Steel bolt & washer not required w/ presson bushing Bushing sleeve (2.5 mm SAE1020 DOM) T-pin (forging) Rivets Lower stamping (1.9 mm DP780) Common ball joint housing (forging) Figure 5: Clamshell Design Material Selection and Gage 13

14 Inboard flange thin (2.2 mm DP980) T-pin Inboard flange thick (forging) (5.0 mm HSLA550) Note: Steel bolt & washer not required w/ press-on bushing Bushing sleeve (2.5 mm SAE1020 DOM) Web (2.3 mm DP980 web) Tube (2.2 mm DP780) 16mm 28mm Forward Flange (2.7 mm DP780) Ball joint reinforcement (1.5 mm HSLA550) Rivets Common ball joint housing (forging) Figure 12: I-Beam Design Material Selection and Gage Figure 6: Forged Design Material Selection and Gage 14

15 Performance Summary The relative structural performance of each design is summarized in Table 2, where the relative performance is defined as the actual performance normalized by the indicated target value. To meet the required level of stiffness, strength, and durability performance, the relative value must be 1.0, while the relative value for permanent set due to extreme loads must be 1.0. The primary and secondary design drivers for each design are identified in the table. The results indicate that the baseline forged aluminum design is primarily stiffness limited, while the forged steel design is mainly buckling limited. The limiting factors for the stamped clamshell design are lateral stiffness and durability. The limiting factor for the I-beam design is primarily durability, followed by permanent set. 15

16 Table 2: Performance Summary Design Design Drivers Baseline AL Forging Stamped Clamshell I-Beam w/ tubular flange Forged Steel Image - Assembly Primary Trial Base Tr344 Tr485 Tr108 Secondary Material type A6082-T6 DP780 SAE 550X, DP 980, DP 780 tube AISI 15V24 Stiffness (rigid bushings) Direction Stiffness Stiffness / Stiffness / Stiffness / Stiffness / Target Target Target Target Target (kn/mm) Longitudinal Lateral Strength / Buckling Load Cases (nonlinear bushings, nonlinear material & geomertry) Direction Min Load Strength / Strength / Strength / Strength / (kn) Target Target Target Target Longitudinal Buckling Extreme Load / permanent set (nonlinear bushings, nonlinear material & geomertry) Load Case Name Max Target (mm) Set / Target Set / Target Set / Target Set / Target Static Pothole LHS Max Vertical Static Pothole LHS Max Fore/Aft Froward braking # Durability Analysis (distributed coupling) Load event Target (1 life) Life / Target Life / Target Life / Target Life / Target Forward Braking * * Braking Left/Right Turn Forward Impact *Note: Highly localized issues not considered a design limitation 16

17 Mass The final FLCA assembly mass results are compared in Figure 14. The results indicate that the mass of clamshell design is equivalent to the 3.07 kg baseline assembly mass, while the I-beam and forged steel designs are 2% (0.05 kg) and 4% (0.13 kg) heavier, respectively. Note that the steel designs benefit from the elimination of the ride bushing bolt and washer, and also a weight-optimized ball joint which was provided to the project by the OEM component supplier. The detail component masses are summarized in Table 3. FLCA structure Bushings & BJ internals % % Mass [kg] Baseline AL Forging Stamped Clamshell I-Beam w/ tubular flange Forged Steel Figure 14: Assembly Mass Comparison 17

18 Table 3: Detail Mass Summary Design Baseline AL Forging Stamped Clamshell I-Beam w/ tubular flange Forged Steel Image - Assembly Trial Base Tr344 Tr485 Tr108 Material type A6082-T6 DP780 SAE 550X, DP 980, DP 780 tube AISI 15V24 Mass Detail Control arm only (kg) Washer Ride bush bolt Rivets Weld FLCA w/ BJ housing & bolt Ball joint internals* FLCA w/ integrated BJ Handling bush (A) Ride bush (B) Complete FLCA Assy *Note: Steel designs incorporate a weight optimized ball joint (-0.12kg); redesign of the baseline FLCA ball joint out of the scope of this project 18

19 Manufacturing Each design was assessed to ensure manufacturing feasibility. Assessment included a combination of engineering and manufacturing experience, stamping feasibility evaluations, and industry benchmarking. Additional design development was conducted in some cases to meet manufacturing feasibility requirements. Cost Estimates Production costs were estimated for the FLCA arm structure based on the AS/Pprovided project assumptions. All costs are reported relative to a functionally equivalent baseline aluminum forging for comparison purposes. Costing was completed using Multimatic s proprietary production cost estimation methodology. Assumptions The following assumptions were used to estimate the cost of the FLCA arm structure for the baseline aluminum, the clamshell design, and the I-beam design. It was not possible to estimate the costs for the forged steel design due to insufficient data related to the manufacturing feasibility. Material Costs Sheet steel material costs were based on published data for the period of December 2009 through January Aluminum material costs were taken as a representative average. The assumed costs for both un-coated and galvanized materials are summarized in Table 4. Table 4: Assumed Material Costs * Material Type No Coating GI / GA Coating $US/kg $US/kg Aluminum $3.36 n/a HSLA 550 $0.95 $1.12 DP 780 $1.31 $1.47 DP 980 $1.42 $1.58 * CRU Index for steel costs, December 11, 2009 through January 13,

20 Conclusions Lightweight Suspension FLCA (ASP-340) Executive Summary The results of the study support the following conclusions: The Clamshell Design is predicted to have equivalent mass to the baseline assembly with up to a 34% cost reduction potential at a production volume of 250,000 vehicles per year. The design is deemed production feasible based on forming simulations and industry welding examples. The I-beam Design is predicted to have the highest buckling resistance and high stiffness with a 2% (0.05 kg) higher mass than the baseline assembly, with up to a 21% cost reduction potential at a production volume of 250,000 vehicles per year. The design is deemed production feasible based on typical welding process development and industry tube bending examples. The Forged Design is predicted to have the highest stiffness and durability performance (no welds) of all designs with a 4% (0.13 kg) higher mass than the baseline assembly, assuming an aggressive 3 mm minimum gage manufacturing target. It is recommended that the forging industry evaluate the manufacturing feasibility of the current assumptions, propose further design optimization opportunities, and determine the associated manufacturing costs. 20