Executive Summary: Lightweight Suspension (ASP-340)/media/Files/Autosteel/NAIAS/01 - Front Lower... · Executive Summary: Lightweight Suspension (ASP-340) ... No part of this report

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-FC26-02OR22910.

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

Lightweight Suspension FLCA (ASP-340) – Executive Summary

2

Executive Summary

The objective of this project was to develop lightweight sheet and forged steel proof-of-concept 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.


3

Purpose

The objective of this project was to develop lightweight sheet and forged steel front lower control arm (FLCA) proof-of-concept designs1 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

Baseline FLCA assembly

Figure 1: Baseline OEM FLCA Forged Aluminum Assembly

1.65

2.01

3.07

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

FLCA structure

FLCA Assy lessbushings

Complete FLCA Assy

Mass [kg]

FLCA structure

Complete FLCA Assy

3.07 kg

Steel washerRide

bushing bolt

1.65

2.01

3.07

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

FLCA structure


Complete FLCA Assy

Mass [kg]

FLCA structure

Complete FLCA Assy

3.07 kg

Steel washerRide

bushing bolt

Figure 2: Baseline FLCA Assembly Mass Summary

1Designs are subjected to “typical” OEM requirements; specific OEM production requirements may require further development and validation.


4

Design Targets

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.

Structural PerformanceEqual to, or exceed the baseline and OEM requirements

MassLess than, or equal to the baselineCost

Reduced vs. the baseline (target 30%)

PackageMeet available packaging constraints

CorrosionMeet OEM corrosion requirements

Structural PerformanceEqual to, or exceed the baseline and OEM requirements

MassLess than, or equal to the baselineCost

Reduced vs. the baseline (target 30%)

PackageMeet available packaging constraints

CorrosionMeet OEM corrosion requirements

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.


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. .


6

1.65

2.01

3.07

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

FLCA structure


Complete FLCA Assy

Mass [kg]

FLCA structure

Complete FLCA Assy

3.07 kg

Steel washerRide

bushing bolt

1.65

2.01

3.07

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

FLCA structure


Complete FLCA Assy

Mass [kg]

FLCA structure

Complete FLCA Assy

3.07 kg

Steel washerRide

bushing bolt

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


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.

(b) Evolution of optimum volume

forged stamped

(c) Final optimized volume

forged stamped

(a) Application of stiffness constraints and loading conditions

(b) Evolution of optimum volume

forged stamped

(c) Final optimized volume

forged stamped



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.


8

T-pinBushing sleeve

Rivets

Ball joint housing

Upper & lower

stampings

Section A-A

All components MIG welded (~1.20m weld length)

MIG Weld

A

A

T-pinBushing sleeve

Rivets

Ball joint housing

Upper & lower

stampings

Section A-A


MIG Weld

A

A

A

A

A

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.


9

T-pin

Bushing sleeve

Rivets

Ball joint housing

Forward Flange

Inboard flange

Web Tube


MIG Weld

Section A-A

A

A

T-pin

Bushing sleeve

Rivets

Ball joint housing

Forward Flange

Inboard flange

Web Tube


MIG Weld

Section A-A

Section A-A

A

A

A

A

A

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.


10

AA

B

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•5o draft

Section A-A

Section B-B

Machined bushing sleeve and BJ housing

AA

B

B

AA

B

B

AA AA

B

B

B

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•5o draft

Section A-A

Section B-B

Machined bushing sleeve and BJ housing

Figure 9: Forged Design Concept


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.


12

Table 1: Steel Sheet Material Properties

0

400

800

1200

0% 5% 10% 15% 20% 25%

Engineering Strain

En

gin

eeri

ng

Str

ess

[MP

a]

DP980(y=715MPa, u=1,008 MPa)

HSLA550(y=550MPa, u=620 MPa)

DP780(y=567MPa, u=846 MPa)

T-Pin forging(y=760MPa, u=1,124 MPa)

BJ forging(y=420MPa, u=490 MPa)

DOM1020(y=414MPa, u=483 MPa)

6082-T6 forged aluminum(y=310MPa, u=340 MPa)

AISI 15V24 forging(y=646MPa, u=878 MPa)

0

400

800

1200

0% 5% 10% 15% 20% 25%

Engineering Strain

En

gin

eeri

ng

Str

ess

[MP

a]

DP980(y=715MPa, u=1,008 MPa)

HSLA550(y=550MPa, u=620 MPa)

DP780(y=567MPa, u=846 MPa)

T-Pin forging(y=760MPa, u=1,124 MPa)

BJ forging(y=420MPa, u=490 MPa)

DOM1020(y=414MPa, u=483 MPa)

6082-T6 forged aluminum(y=310MPa, u=340 MPa)

AISI 15V24 forging(y=646MPa, u=878 MPa)

Figure 10: Engineering Stress-Strain Curve Comparison


13

Material Selection

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.

T-pin(forging)

Bushing sleeve(2.5 mm SAE1020

DOM)

Rivets

Common ball joint housing

(forging)

Upper stamping

(1.9 mm DP780)

Lower stamping

(1.9 mm DP780)

Note: Steel bolt & washer not required w/ press-on bushing

T-pin(forging)


DOM)

Rivets


(forging)

Upper stamping

(1.9 mm DP780)

Lower stamping

(1.9 mm DP780)


Figure 5: Clamshell Design Material Selection and Gage


14

Rivets

Tube(2.2 mm DP780)

Forward Flange

(2.7 mm DP780)

Ball joint reinforcement

(1.5 mm HSLA550)

Inboard flange – thick(5.0 mm HSLA550)

Web(2.3 mm

DP980 web)

Inboard flange – thin(2.2 mm DP980) T-pin

(forging)


(forging)


DOM)


16mm

28mm

Rivets

Tube(2.2 mm DP780)

Forward Flange

(2.7 mm DP780)

Ball joint reinforcement

(1.5 mm HSLA550)

Inboard flange – thick(5.0 mm HSLA550)

Web(2.3 mm

DP980 web)

Inboard flange – thin(2.2 mm DP980) T-pin

(forging)


(forging)


DOM)


16mm

28mm

16mm

28mm

Figure 12: I-Beam Design Material Selection and Gage

Figure 6: Forged Design Material Selection and Gage


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.


16

Table 2: Performance Summary

DesignBaseline AL

ForgingStamped

ClamshellI-Beam w/

tubular flangeForged Steel

Image - Assembly

Trial Base Tr344 Tr485 Tr108

Material type A6082-T6 DP780SAE 550X, DP 980,

DP 780 tube AISI 15V24

Stiffness (rigid bushings)

DirectionStiffness

Target (kN/mm)

Stiffness / Target

Stiffness / Target

Stiffness / Target

Stiffness / Target

Longitudinal 2.9 1.00 1.10 1.24 1.24

Lateral 125.2 1.00 1.00 1.19 1.51Strength / Buckling Load Cases (nonlinear bushings, nonlinear material & geomertry)

DirectionMin Load

(kN)Strength /

TargetStrength /

TargetStrength /

TargetStrength /

Target

Longitudinal Buckling 25 1.12 1.17 1.23 1.08Extreme Load / permanent set (nonlinear bushings, nonlinear material & geomertry)

Load Case NameMax Target

(mm)Set / Target Set / Target Set / Target Set / Target

Static Pothole – LHS Max Vertical 1.0 0.00 0.00 0.01 0.00Static Pothole – LHS Max Fore/Aft 1.0 0.03 0.12 0.87 0.19Froward braking # 3 1.0 0.00 0.01 0.02 0.01Durability Analysis (distributed coupling)

Load eventTarget (1 life)

Life / Target Life / Target Life / Target Life / Target

Forward Braking 1.0 1.1 1.1 1.0 1.2Braking Left/Right Turn 1.0 4.0 1.5 1.3 3.2Forward Impact 1.0 3.1 4.1 3.6 18.1

Primary

Design Drivers

Secondary

*Note: Highly localized issues not considered a design limitation

* *

DesignBaseline AL

ForgingStamped

ClamshellI-Beam w/


Image - Assembly



DP 780 tube AISI 15V24

Stiffness (rigid bushings)

DirectionStiffness

Target (kN/mm)

Stiffness / Target

Stiffness / Target

Stiffness / Target

Stiffness / Target

Longitudinal 2.9 1.00 1.10 1.24 1.24

Lateral 125.2 1.00 1.00 1.19 1.51Strength / Buckling Load Cases (nonlinear bushings, nonlinear material & geomertry)

DirectionMin Load

(kN)Strength /

TargetStrength /

TargetStrength /

TargetStrength /

Target

Longitudinal Buckling 25 1.12 1.17 1.23 1.08Extreme Load / permanent set (nonlinear bushings, nonlinear material & geomertry)

Load Case NameMax Target

(mm)Set / Target Set / Target Set / Target Set / Target

Static Pothole – LHS Max Vertical 1.0 0.00 0.00 0.01 0.00Static Pothole – LHS Max Fore/Aft 1.0 0.03 0.12 0.87 0.19Froward braking # 3 1.0 0.00 0.01 0.02 0.01Durability Analysis (distributed coupling)

Load eventTarget (1 life)

Life / Target Life / Target Life / Target Life / Target

Forward Braking 1.0 1.1 1.1 1.0 1.2Braking Left/Right Turn 1.0 4.0 1.5 1.3 3.2Forward Impact 1.0 3.1 4.1 3.6 18.1

Primary

Design Drivers

Secondary

Primary

Design Drivers

Secondary

*Note: Highly localized issues not considered a design limitation

* *


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.

1.65 1.79 1.83 1.91

1.42 1.30 1.30 1.30

0.0

1.0

2.0

3.0

4.0

Baseline ALForging

StampedClamshell

I-Beam w/tubular flange

Forged Steel

Mas

s [k

g]

FLCA structure Bushings & BJ internals

3.07 3.08 3.12 3.20+4%+2%

1.65 1.79 1.83 1.91

1.42 1.30 1.30 1.30

0.0

1.0

2.0

3.0

4.0

Baseline ALForging

StampedClamshell

I-Beam w/tubular flange

Forged Steel

Mas

s [k

g]

FLCA structure Bushings & BJ internals

3.07 3.08 3.12 3.20+4%+2%

Figure 14: Assembly Mass Comparison


18

Table 3: Detail Mass Summary

DesignBaseline AL

ForgingStamped

ClamshellI-Beam w/


Image - Assembly



DP 780 tubeAISI 15V24

Mass DetailControl arm only 1.48 1.69 1.71 1.91Washer 0.10 0.00 0.00 0.00Ride bush bolt 0.07 0.00 0.00 0.00Rivets 0.00 0.06 0.06 0.00Weld 0.00 0.04 0.06 0.00

FLCA w/ BJ housing & bolt 1.65 1.79 1.83 1.91Ball joint internals* 0.36 0.24 0.24 0.24FLCA w/ integrated BJ 2.01 2.03 2.06 2.14Handling bush (A) 0.22 0.22 0.22 0.22Ride bush (B) 0.84 0.84 0.84 0.84Complete FLCA Assy 3.07 3.08 3.12 3.20

(kg)

*Note: Steel designs incorporate a weight optimized ball joint (-0.12kg); re-design of the baseline FLCA ball joint out of the scope of this project

DesignBaseline AL

ForgingStamped

ClamshellI-Beam w/


Image - Assembly



DP 780 tubeAISI 15V24

Mass DetailControl arm only 1.48 1.69 1.71 1.91Washer 0.10 0.00 0.00 0.00Ride bush bolt 0.07 0.00 0.00 0.00Rivets 0.00 0.06 0.06 0.00Weld 0.00 0.04 0.06 0.00

FLCA w/ BJ housing & bolt 1.65 1.79 1.83 1.91Ball joint internals* 0.36 0.24 0.24 0.24FLCA w/ integrated BJ 2.01 2.03 2.06 2.14Handling bush (A) 0.22 0.22 0.22 0.22Ride bush (B) 0.84 0.84 0.84 0.84Complete FLCA Assy 3.07 3.08 3.12 3.20

(kg)

*Note: Steel designs incorporate a weight optimized ball joint (-0.12kg); re-design of the baseline FLCA ball joint out of the scope of this project


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/P-provided 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 2010. 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*

No Coating GI / GA Coating$US/kg $US/kg

Aluminum $3.36 n/aHSLA 550 $0.95 $1.12DP 780 $1.31 $1.47DP 980 $1.42 $1.58

Material Type

* CRU Index for steel costs, December 11, 2009 through January 13, 2010


20

Conclusions

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.

Documents

Executive Summary: Lightweight Suspension (ASP-340)/media/Files/Autosteel/NAIAS/01 - Front Lower... · Executive Summary: Lightweight Suspension (ASP-340) ... No part of this report