ULSAB Executive Summary 

An UltraLight Steel Auto Body (ULSAB) structure has been assembled, weighed and tested 

validating results from the concept phase of a global steel industry study and satisfying the 

project goals. ULSAB has proven to be lightweight, structurally sound, safe, executable and 

affordable. 

The ULSAB structure weighs merely 203 kg, 25 percent less than the average benchmarked 

in the concept phase of the study. Physical tests of the structure reveal similar remarkable 

results: torsion and bending tests showed improvements over benchmark of 80 percent and 52 

percent, respectively, and 1st body structure mode indicates a 58 percent improvement. 

Analyses also show ULSAB satisfies mandated crash requirements, even at speeds exceeding 

the requirements. In addition to reduced weight and superior performance, ULSAB costs no 

more to build than typical auto body structures in its class and can even yield potential cost 

savings, according to economic analysis. 

The ULSAB structure consists of 94 major parts necessary for its structural integrity, plus 

brackets and additional reinforcements normally included in this type of auto body structure. 

It does not include doors, hood or decklids, which are the subject of a separate, independent 

study. 

Creation and testing of ULSAB body structures culminated this aggressive $22 million 

project to demonstrate a lightweight steel auto body structure that meets a wide range of 

safety and performance criteria. The ULSAB project was sponsored by a consortium of 35 

steel companies representing 18 countries around the world. 

The goal of the consortium was to meet the challenges issued by their automotive industry 

customers: reduce the weight of steel auto body structures at no additional cost, while 

maintaining or improving performance. The most prominent sheet steel producers from 

around the world joined together to design and validate an UltraLight Steel Auto Body. 

The ULSAB consortium contracted Porsche Engineering Services, Inc. (PES) to provide 

engineering and manufacturing management for the ULSAB project and also worked with 

them to define the project goals. They took a two-stage approach, encompassing a concept 

phase and a validation phase. 

The consortium is releasing patentable features of this project along with other project results 

freely to its customers and to the public. 
ULSAB summary 2

Design 

Benchmarking 

At the beginning of the design process, PES benchmarked mid-sized four door sedans to 

determine current performance standards against which to measure ULSAB. PES also 

established package constraints through this benchmarking process. To determine an 

“average base model,” 32 different cars representing varying worldwide customer 

requirements were selected for package benchmarking. 

For structural benchmarking (static torsion, static bending, 1st body structure mode), PES used 

a cross section of nine cars that represented current performance standards. Results of that 

benchmarking study produced the following performance specifications: 

Benchmark performance 

static torsional rigidity 11,531 Nm/deg 

static bending rigidity 11,902 N/mm 

1st body structure mode 38 Hz 

mass 271 kg 

This information was then used to predict a future reference structure with which ULSAB 

must ultimately compare. Recognizing continuing improvements in body design and 

engineering, the future reference structure represents improved performance in all areas. 

Assumptions for that future reference structure are as follows: 

Future reference structure performance 

Static torsional rigidity 13,000 Nm/deg 

Static bending rigidity 12,200 N/mm 

1st body structure mode 40 Hz 

mass 250 kg 

Philosophy 

Design considerations for ULSAB were, in large part, governed by mass reduction and 

improved performance. ULSAB’s design team started with a “clean sheet of paper” and used 

an iterative holistic approach to design, whereby the body structure is treated as an integrated 

system rather than as an assembly of individual components. The holistic approach 

emphasizes total structure analysis. Sophisticated computer models enable design engineers to 

view the body structure as an integrated whole. This perspective enables them to evaluate 
ULSAB summary 3

how changes in one area affect other areas and where future optimization opportunities exist. 

Through each iterative step, re-analysis confirms the effectiveness of the latest optimizations. 

This approach promotes weight savings and improved structural integrity by enabling 

engineers to reduce weight in certain areas while strengthening strategic locations. The net 

effect is the creation of a more efficient structure. 

Computer models were also used to analyze all structural aspects and to simulate specific 

crash events, demonstrating acceptable performance. Sophisticated architecture and refined 

joint designs ensure continuous load flow, which improves stiffness and strength in the body 

structure. 

Package 

ULSAB did not save mass through downsizing. Its package design includes a 3-liter V6 

engine, transverse front wheel drive, rack and pinion steering, McPherson front suspension, 

twist beam rear suspension, generous occupant space, exhaust system routing and a 65 liter 

fuel tank. Its wheelbase is 2700 mm; vehicle width is 1819 mm; and vehicle length is 4714 

mm. 

Styling 

Exterior styling of the ULSAB was necessary to create surfaces for design. Styling also 

provided the major feature lines for the doors, decklid, hood, fender and front and rear 

bumpers, which were used in development of mating structural parts. Styling also gave 

ULSAB a look that is easily recognized while preserving the opportunity to conduct further 

design studies – for doors or other closures – in the future. 

Materials selection and processes 

Advanced materials and technologies were employed to meet the project goals. The design 

relies on high strength steels, steel sandwich materials, tailored blanking, hydroforming and 

assembly laser welding for reduced weight and structural efficiency. 

Materials and Processes 

The materials for the body structure were chosen to meet mass, performance and safety goals. 

They include some grades and thicknesses of steel currently available but not commonly used 

in auto bodies. Steel is the most recycled material in the world, and all steel chosen for the 

ULSAB structure is recyclable. 

ULSAB uses high strength steel and ultra high strength steel for more than 90 percent of the 

body structure to improve structural performance and save mass. And nearly half of 

ULSAB’s mass consists of tailored blanked parts, which enable the design engineer to locate 

various steels within the part precisely where their attributes are most needed, thereby 

removing mass that does not contribute to performance. 

ULSAB also features a hydroformed side roof rail, which provides an essential load path for 

structural performance and crash energy management. In addition to tubular hydroforming, 

ULSAB uses sheet hydroforming for the roof panel. The work hardening effect produces 

improved dent resistance in the formed part, especially in the center of the panel. 
ULSAB summary 4

Steel sandwich material was chosen for mass reduction in the spare tire tub and dash panel. 

Additionally, laser welding was used in ULSAB assembly for high static and dynamic 

strength of joints, for areas where access was available on only one side and for good aesthetic 

appearance at joint areas. 

These advanced materials and processes enabled the design engineers to consolidate functions 

in fewer parts, resulting in mass savings and improved performance. 

Manufacturing 

Early involvement 

Manufacturability of parts was crucial to the project’s success and was contemplated 

throughout the design phase. Early in the design process the design engineers worked with 

component fabricators and steel manufacturers to optimize the design. The steel 

manufacturers were called upon to provide high strength and ultra high strength grades of 

steel for use in tailored blanks, hydroformed tubing and steel sandwich material. The project 

partners also used forming simulations early in the project to predict manufacturability. 

Tooling 

To prove manufacturing feasibility of ULSAB the consortium specified production intent 

standards for ULSAB parts, requiring that all parts be manufactured from tools with no 

manual forming. All stamping tools in this program are “soft” tools made of material such as 

kirksite. Due to pressure requirements, hydroforming was accomplished using hard tools. In 

all cases, part fabrication tolerances and quality standards were maintained the same as 

intended for full volume production. 

Analysis 

To help ensure that the part designs were feasible, the project partners performed forming 

simulation analysis on the most complex parts. Forming simulation was performed using 

finite element methods to show locations of strains and material thinning. The project 

partners then used this information to recommend product design and tooling adjustments 

accordingly. 

Part validation 

Upon completion of tooling, the component fabricators manufactured the parts and evaluated 

them using circle grid strain analysis to confirm that they were formed to full volume 

manufacturing standards. Confirmation was also established through measurement of key 

part dimensions and the use of check fixtures. Complete information to support 

manufacturing feasibility was documented and includes material characteristics, tooling 

parameters and press conditions. 

Assembly 

ULSAB assembly sequence is quite conventional, deviating from convention only in its twostage body side framing. The assembly sequence includes floor complete assembly, front end 

assembly, body side inner assembly, underbody complete assembly, framing and final 

assembly. The assembly sequence, processes and tolerances were established by PES. All 
ULSAB summary 5

tooling holes and locators that would be used for production were used during the build. 

Porsche in Germany assembled the demonstration hardware using a flexible, modular 

assembly fixture system. 

ULSAB employs about one-third fewer spot welds and significantly more laser welding than 

a conventional body structure, resulting in improved structural integrity, as well as some cost 

savings. 

Structural performance 

Physical tests show ULSAB to exceed all concept phase averages. 

Performance results comparison 

ULSAB 

structure

Benchmark 

structure 

average 

Future 

reference 

structure

Performance

Torsion (Nm/deg) 

bending (N/mm) 

1st body structure mode 

(Hz) 

20,800

18,100

60

11,531 

11,902 

38 

13,000

12,200

40

Mass (in kg) 203* 271 250

* natural range of variation ±1 percent 

Crash simulations to help predict safety indicate excellent crash behavior of the ULSAB 

structure in the following crash events: 35 mph frontal NCAP; 55 km/h 50 percent offset 

AMS frontal impact; 35 mph rear moving barrier; European side impact and roof crush. The 

35 mph frontal NCAP and 35 mph rear moving barrier simulations were run at speeds that 

exceed mandated safety requirements by 17 percent, and the AMS frontal is widely 

considered one of the most severe offset crashes performed today. 

Economic Analysis 

Although lightweighting without sacrificing performance was ULSAB’s priority, affordability 

was also important. Early in ULSAB’s concept phase the consortium commissioned an 

economic analysis to establish a reference by which to compare ULSAB. IBIS Associates 

estimated the cost to manufacture a current, typical body structure in the same class as 

ULSAB at $1116 each. 
ULSAB summary 6

In the validation phase, the cost issue was revisited more thoroughly. A Porsche-led team of 

analysts developed a detailed cost model that includes all aspects of fabrication and assembly. 

The cost model can be used to analyze ULSAB costs in comparison with other options and 

also to generate costs associated with alternative designs. 

This model comprehends United States manufacturing costs, including investments for both 

plant and tooling, piece fabrication costs and assembly costs, through to the end of the body 

shop. The analysts used these details to generate a part-specific cost model for ULSAB. They 

also created assumptions about a future typical four-door sedan (Year 2000) reference 

structure with which to compare ULSAB. Basic economic assumptions were identical for 

both ULSAB and the reference structure; however, inputs about specific parts and assembly 

steps are not directly comparable because the Year 2000 structure represents an average of 

typical vehicle structures in the same class as ULSAB. For the Year 2000 structure, the study 

identified part groupings – instead of individual parts as with ULSAB – and assumed 

significantly improved fabrication and assembly techniques as compared to the concept stage 

benchmark. 

The cost model with these inputs showed the ULSAB body structure to cost $947 each to 

manufacture and the Year 2000 structure to cost $979 each, demonstrating that sophisticated 

design of a steel body structure can achieve lightweight at no cost penalty and with potential 

cost savings. 

Sharing knowledge 

The ULSAB project employed many techniques and processes that were unique and deemed 

patentable by international attorneys. The consortium chose to make all patentable features 

along with other project results freely available to its customers and to the public. All 

intellectual property generated by ULSAB has been placed in the public domain. 

Conclusion 

The steel industry has demonstrated the viability of a lightweight, structurally superior steel 

auto body structure that is also affordable. ULSAB weighs less and performs better than 

benchmarked averages, while also providing potential cost savings. 
ULSAB Design 

The first objective of the UltraLight Steel Auto Body (ULSAB) consortium was to design a 

lightweight steel body structure that would meet increased functional and structural 

performance targets while remaining affordable. The consortium also specified that, while the 

design should be leading edge, it must also be feasible using near-reach manufacturing 

processes. 

Benchmarking 

Porsche Engineering Services, Inc. (PES) benchmarked mid-sized four door sedans to 

determine current performance against which to measure ULSAB. PES also established 

package constraints through this benchmarking process. To determine an “average base 

model,” 32 different cars that represent varying worldwide customer requirements were 

selected for package benchmarking. Benchmarking considered curb weight; wheelbase; 

overall length and width; leg, head and shoulder room; passenger compartment; and cargo 

volume. Benchmarking established the following package specifications: 

Package benchmark specifications 

body type 4-door sedan headroom 

front/rear 

960/940 mm 

wheelbase 2700 mm leg room front/rear 1060/890 mm 

overall length 4800 mm shoulder room f/r 1420/1400 mm 

overall width 1800 mm cargo volume 425 liters 

curb weight 1350 kg engine type V6 

passenger 5 drive front 

For structural benchmarking (static torsion, static bending, 1st body structure mode), PES used 

a cross section of nine cars that represented current performance standards. These vehicles 

include the 

• Acura Legend 

• BMW 5-series 
ULSAB design 2

• Chevrolet Lumina 

• Ford Taurus 

• Honda Accord 

• Lexus LS 400 

• Mazda 929 

• Mercedes 190 E 

• Toyota Cressida 

To make a direct correlation in performance among the above nine vehicles, PES adjusted the 

structural performance linearly to the ULSAB target wheelbase of 2700 mm. PES employed 

the following formula for this adjustment: 

C adjusted = C actual Wheelbase reference vehicle

 Wheelbase ULSAB 

where C adjusted = adjusted stiffness of reference vehicle 

and C actual = actual stiffness of reference vehicle 

These vehicles were also normalized for mass by comparing the interior body volumes with 

the projected area (length multiplied by width). Volume of these vehicles was determined 

using SAE Standard 1100a, which states that the usable volume in the front (V1) and the 

usable passenger compartment volume (V2) and the usable luggage volume (V3) add up to the 

entire usable volume (Vtotal) of the vehicle: 

V1 + V2 + V3 = V total

This benchmarking exercise generated the following performance averages: 

Benchmark performance 

static torsional rigidity 11,531 Nm/deg 

static bending rigidity 11,902 N/mm 

1st body structure mode 38 Hz 

mass 271 kg 
ULSAB design 3

This information was then used to predict a future reference vehicle with improved 

performance with which ULSAB must ultimately compare. Assumptions for that future 

reference vehicle were as follows: 

Future reference structure performance 

static torsional rigidity 13,000 Nm/deg 

static bending rigidity 12,200 N/mm 

1st body structure mode 40 Hz 

mass 250 kg 

Design philosophy and architecture 

PES determined to employ an holistic philosophy toward design early in the design process. 

This holistic approach treats the body structure as an integrated system rather than an 

assembly of individual components, emphasizing total body analysis. Through each iterative 

step, sophisticated computer re-analysis confirms the effectiveness of the latest optimizations. 

The holistic approach also allows evaluation of how other areas are affected by these changes 

and where future optimization opportunities exist. This approach promotes weight savings 

and improved structural integrity by enabling engineers to reduce weight in certain areas 

while strengthening strategic locations. The net effect is the creation of a more efficient 

structure. 

PES investigated various concepts to develop the optimum ULSAB body structure. Some of 

these included full frame, space frame, unibody and hybrid solutions. Criteria for the 

structures under consideration were significant weight savings potential, opportunity to 

achieve performance targets and assembly possibilities in future full volume production body 

shops. 

Early in the project PES engineers eliminated the full frame concept because it offered no 

significant mass saving opportunities. They also doubted that the full frame would meet 

ULSAB’s structural performance criteria and were concerned about high investment costs for 

assembly. Although a spaceframe was considered, it was ultimately eliminated because it is 

not considered as mass efficient as other approaches. The PES team ultimately narrowed its 

investigation to two structures—a unibody and a hydroform-intensive body structure— 

finally settling on creating a unibody or monocoque vehicle with key hydroformed parts. 

Packaging 

The first step in packaging was to define the vehicle concept type, exterior and interior 

dimensions and main components. With these package definitions, package drawings were 
ULSAB design 4

created and structural hard points defined. ULSAB did not save mass through downsizing: its 

wheelbase is 2700 mm; vehicle width is 1819 mm; and vehicle length is 4714 mm. 

Package specifications for ULSAB are: 

ULSAB package 

body type 4-door sedan headroom 

front/rear 

994/932 mm 

wheelbase 2700 mm leg room front/rear 1043/894 mm 

overall length 4714 mm shoulder room f/r 1512/1522 mm 

overall width 1819 mm cargo volume 490 liters 

curb weight 1350 kg engine type 3 liter V6 

passenger 5 drive front 

radiator size 0.252 m2 exhaust system single routing 

battery (in mm) 280 X 170 X 170 suspension front McPherson 

suspension rear twist beam tire size (f & r) 195/60R15 

spare tire space saver fuel tank volume 65 liters 

steering rack & pinion 

The ULSAB package drawings comprehend all essential parts of the structure interior. 

Criteria for interior design included visibility, obscuration by the pillars, head clearance and 

seat belt anchors. In the engine compartment, the engine, gearbox, exhaust system, radiator 

and battery were used to define space for the structural members of the front body structure. 

Styling 

The ULSAB project also comprehended styling issues. Exterior styling of ULSAB was used 

to create surfaces for design. Styling also gave it a look that is easily recognized and afforded 

the opportunity to conduct closure design studies, the results of which will be made available 

in the future. 

Demonstrating exterior styling posed certain challenges. The styling had to follow precisely 

the engineering design of ULSAB. And, while not attempting to provide leading-edge 
ULSAB design 5

styling, the results had to illustrate the highest quality surfaces typical of steel-skinned 

vehicles, which global audiences have come to expect. 

ULSAB styling was entirely computer-aided using ALIAS Studio Paint Software for the 

creation of two-dimensional sketches and Pro-Designer for renderings and three-dimensional 

modeling. CATIA was used for the final surfacing on the ‘A’ class surfaces. In the studio, 

the CATIA package data was imported into a three-dimensional concept modeling software 

called CDRS, and a side view outline drawing was developed for sketching purposes. 

Material selection 

The selection of appropriate materials was based on considerations of mass, performance, and 

crash requirements. In its effort to optimize the best attributes of steel in this project, PES 

engineers specified unusually large percentages of high and ultra high strength steels, tailored 

blanks and steel sandwich material. The materials for the body were chosen to meet mass and 

performance targets and include some grades and thicknesses of steel currently available but 

not commonly used in auto bodies. 

ULSAB uses high strength steel and ultra high strength steel for more than 90 percent of the 

body structure to improve structural performance and save mass. 

Nearly half of ULSAB’s mass consists of tailored blanked parts, which enable the design 

engineer to locate various steels within the part precisely where their attributes are most 

needed, thereby removing mass that does not contribute to performance. 

ULSAB also features a hydroformed side roof rail, which provides an essential load path for 

structural performance and crash energy management from the top of the ‘A’ pillar along the 

roof, into the ‘B’ and ‘C’ pillars and into the rear of the structure. In addition to tubular 

hydroforming, ULSAB uses sheet hydroforming for the roof panel. The work hardening 

effect produces improved dent resistance in the formed part, especially in the center of the 

panel. 

Steel sandwich material was chose for mass reduction in the spare tire tub and dash panel. 

These advanced materials and processes enabled the design engineers to consolidate functions 

in fewer parts, reducing ULSAB’s part count to 94 major parts and 158 total parts, as 

compared with more than 200 total parts for an existing typical body structure in the same 

class. Reduced part count leads to reduced tooling and assembly costs. This function 

consolidation also leads to mass savings and improved structural performance. 
ULSAB design 6

ULSAB in detail 

Below is an exploded view of the ULSAB structure with numbers and corresponding parts 

list: 

Part drawings, typical sections and design highlights are included in the ULSAB Electronic 

Report, available through consortium members. 

ULSAB parts list 

Material Material 

Part Grade Thickness 

No Part Name (MPa) (mm) 

001 Assy Reinf Radiator Support Upper (Bolted on) 350 1.00 

002 Reinf Front Rail Extension RH 350 1.00 

003 Reinf Front Rail Extension LH 350 1.00 

008 A Assy Rail Front Outer RH 350 1.50 

B (Tailor Blank) 350 1.60 

C 350 2.00 

009 A Assy Rail Front Outer LH 350 1.50 

B (Tailor Blank) 350 1.60 

C 350 2.00 
ULSAB design 7

Material Material 

Part Grade Thickness 

No Part Name (MPa) (mm) 

010 A Assy Rail Front Inner RH 350 1.50 

B (Tailor Blank) 350 1.60 

C 350 1.80 

011 A Assy Rail Front Inner LH 350 1.50 

B (Tailor Blank) 350 1.60 

C 350 1.80 

012 Rail Front Extension RH 350 1.40 

013 Rail Front Extension LH 350 1.40 

014 Bracket Roof Rail Mount Lower RH 350 1.20 

015 Bracket Roof Rail Mount Lower LH 350 1.20 

021 Panel Dash 210 0.70 

022 Panel Dash Insert (Bolted on) Sandwich 0.95 

026 Member Dash Front 600 1.20 

028 Panel Cowl Lower 210 0.70 

032 Panel Cowl Upper 210 0.70 

034 Assy Member Front Floor Support (2-Req'd) 800 0.70 

038 Assy Reinf Floor Front Seat Rear Outer (2-Req'd) 280 0.80 

040 Pan Front Floor 210 0.70 

042 A Panel Rocker Inner RH 350 1.30 

B (Tailor Blank) 350 1.70 

043 A Panel Rocker Inner LH 350 1.30 

B (Tailor Blank) 350 1.70 

045 Member Rear Suspension 280 0.70 

046 A Assy Rail Rear Inner RH 350 1.00 

B (Tailor Blank) 350 1.30 

C 350 1.60 

047 A Assy Rail Rear Inner LH 350 1.00 

B (Tailor Blank) 350 1.30 

C 350 1.60 

048 A Assy Rail Rear Outer RH 350 1.00 

B (Tailor Blank) 350 1.30 

C 350 1.60 

049 A Assy Rail Rear Outer LH 350 1.00 

B (Tailor Blank) 350 1.30 

C 350 1.60 

050 Panel Spare Tire Tub (Bonded 

on) 

Sandwich 0.96 

055 Member Panel Back 210 0.65 

057 Panel Back 140 0.65 

060 A Panel Body Side Outer RH 210 0.70 

B (Tailor Blank) 280 0.90 

C 280 1.30 

D 350 1.50 

E 350 1.70 

061 A Panel Body Side Outer LH 210 0.70 

B (Tailor Blank) 280 0.90 

C 280 1.30 

D 350 1.50 

E 350 1.70 

062 Panel A-Pillar Inner Lower RH 350 1.00 

063 Panel A-Pillar Inner Lower LH 350 1.00 

064 Panel B-Pillar Inner RH 350 1.50 

065 Panel B-Pillar Inner LH 350 1.50 

066 Reinf B-Pillar Lower (2-Req'd) 350 0.90 

068 Panel Wheelhouse Inner RH 210 0.65 

069 Panel Wheelhouse Inner LH 210 0.65 

070 A Panel Wheelhouse Outer RH 140 0.65 

B (Tailor Blank) 210 0.80 

071 A Panel Wheelhouse Outer LH 140 0.65 

B (Tailor Blank) 210 0.80 

072 Rail Side Roof RH 280 1.00 
ULSAB design 8

Material Material 

Part Grade Thickness 

No Part Name (MPa) (mm) 

073 Rail Side Roof LH 280 1.00 

074 Panel A-Pillar Inner Upper RH 350 1.50 

075 Panel A-Pillar Inner Upper LH 350 1.50 

080 Panel Package Tray Upper 210 0.65 

081 Panel Package Tray Lower 210 0.65 

082 Support Package Tray RH 280 0.80 

083 Support Package Tray LH 280 0.80 

085 Panel Roof 210 0.70 

086 Panel Front Header 280 0.70 

087 Panel Rear Header 140 0.70 

090 Member Pass Through (2-Req'd) 140 0.65 

091 Member Kick Up 800 0.70 

094 Reinf Radiator Rail Closeout RH (Bolted on) 350 1.00 

095 Reinf Radiator Rail Closeout LH (Bolted on) 350 1.00 

096 A Panel Skirt RH 140 2.00 

B (Tailor Blank) 140 1.60 

097 A Panel Skirt LH 140 2.00 

B (Tailor Blank) 140 1.60 

098 Panel Gutter Decklid RH 140 0.65 

099 Panel Gutter Decklid LH 140 0.65 

102 Support Panel Rear Header RH 140 0.70 

103 Support Panel Rear Header LH 140 0.70 

104 Rail Fender Support Inner RH 420 1.20 

105 Rail Fender Support Inner LH 420 1.20 

106 Rail Fender Support Outer RH 350 0.90 

107 Rail Fender Support Outer LH 350 0.90 

108 Reinf Front Rail RH 350 1.00 

109 Reinf Front Rail LH 350 1.00 

110 Plate Rear Spring Upper (2-Req'd) 350 2.00 

115 Reinf Panel Dash Brake Booster (Bolted on) 350 1.00 

116 Assy Bracket Rear Shock Absorber Mount RH 350 2.00 

117 Assy Bracket Rear Shock Absorber Mount LH 350 2.00 

120 Reinf Floor Front Seat Rear Center 350 1.20 

122 Assy Reinf Rear Seat Inner Belt Mount (2-Req'd) 350 2.00 

128 Bracket Member Pass Through Lower (2-Req'd) 350 1.00 

130 Bracket Member Pass Through Upper Front 350 1.00 

136 Reinf Panel Dash Upper 350 1.00 

140 Pan Rear Floor 210 0.70 

142 Assy Reinf Hinge Decklid (2-Req'd) 350 1.50 

144 Reinf A-Pillar RH 350 1.50 

145 Reinf A-Pillar LH 350 1.50 

152 Bracket Member Pass Through Upper Rear 350 1.00 

164 Assy Closeout Fender Support Rail RH 350 1.00 

165 Assy Closeout Fender Support Rail LH 350 1.00 

170 Reinf Rail Dash RH 350 1.30 

171 Reinf Rail Dash LH 350 1.30 

172 Assy Reinf Cowl Lower 350 1.00 

176 Hinge Base RH (4-Req'd) 280 - 

177 Hinge Base LH (4-Req'd) 280 - 

178 Hinge Stem 119 (4-Req'd) 280 2.00 

179 Hinge Stem 141 (4-Req'd) 280 2.00 

180 Bracket Trailing Arm Mount RH 350 2.00 

181 Bracket Trailing Arm Mount LH 350 2.00 

188 Brace Radiator (2-Req'd) (Bolted on) 350 0.80 

190 Assy Reinf Seat Belt Retractor Rear (2-Req'd) 350 1.20 
ULSAB Manufacturing 

Early involvement 

Manufacturability of parts was crucial to the ULSAB’s success and was contemplated 

throughout the design phase of the project. Early in the design process the design engineers 

worked with component fabricators and steel manufacturers to optimize the design. The steel 

manufacturers were called upon to provide high strength and ultra high strength grades of 

steel for use in tailored blanks, hydroformed tubing and steel sandwich material. The project 

partners also used forming simulations early in the project to predict manufacturability. 

Tooling 

To prove manufacturing feasibility of ULSAB, the Consortium specified production intent 

standards for ULSAB parts, requiring that all parts be manufactured from tools with no 

manual forming. All stamping tools in this program are “soft” tools made of material such as 

kirksite. Due to pressure requirements, hydroforming, was accomplished using hard tools. In 

all cases, part fabrication tolerances and quality standards were maintained the same as 

intended for full volume production. Tool development logs and coordinate measuring 

machine (CMM) reports were compiled for the most critical and complex parts, listed below. 

These documents are available for inspection. 

♦ Floor pan 

♦ Rocker inner 

♦ B pillar inner 

♦ Rear rail inner 

♦ Rear rail outer 

♦ Wheelhouse outer 

♦ Body side outer 

♦ Dash member front 

♦ Skirt and shock tower 

♦ Rail front inner 

♦ Rail front extension 

♦ Panel dash 

♦ Member kick up 

♦ Spare tire tub 

♦ Side roof rail 

♦ Panel roof 

Analysis 

To help ensure that the part designs were feasible, the project partners performed forming 

simulation analysis on the most complex parts. Forming simulation was performed using 

finite element methods to predict locations of strains and material thinning. The project 

partners then used this information to recommend product design and tooling adjustments 

accordingly. Simulation reports on the parts listed below are available for inspection upon 

request. 
ULSAB manufacturing 2

♦ Floor pan 

♦ Rocker inner 

♦ B pillar inner 

♦ Rear rail inner 

♦ Rear rail outer 

♦ Body side outer 

♦ Side roof rail 

♦ Panel roof 

Part validation 

Upon completion of tooling, the component fabricators manufactured the parts and evaluated 

them using circle grid strain analysis to confirm that they were formed to full volume 

manufacturing standards. Confirmation was also established through measurement of key 

part dimensions and the use of check fixtures. Complete information to support part 

manufacturing feasibility was documented and includes material characteristics, press 

conditions, forming limit diagrams, process sheets and tolerance measurements. These 

reports comprehend all parts listed under section “Tooling” in this report and are available for 

inspection upon request. 

Assembly 

Sequence 

ULSAB assembly sequence uses two-stage body side framing in which all inner parts of the 

body side are assembled to the body structure and the body side outer is subsequently 

attached. This approach enables better attachment of inner pieces and improves structural 

integrity by eliminating unnecessary weld access holes. 

ULSAB employs about one-third fewer spot welds and significantly more laser welding than 

a conventional body structure, resulting in improved structural integrity, as well as some cost 

savings. Assembly of the structure includes 18,286 mm of laser welding, 2,206 spotwelds 

and 1,500 mm of MIG welding, the majority of which is used to attach through pillar door 

hinges. 

Assembly requires joining the following subassemblies, as described: 

Floor complete assembly: the rear rail outer, right and left are attached to the 

assembly floor inner 

Front end assembly: the assembly dash is attached to the assembly front ladder 

complete 

Body side inner assembly: the side roof rail is attached to the assembly rocker inner; 

the ‘B’ pillar inner and assembly wheelhouse are then attached to that structure 

Underbody complete assembly: the assembly cowl lower is attached to the assembly 

front end and brought to the assembly floor complete 
ULSAB manufacturing 3

aFraming: to the underbody assembly complete is attached the assembly front rails 

outer right and left and the cowl panel upper. Then attached are the assembly member 

pass through and the assembly body side inner right and left. From the back the 

assembly package tray lower is inserted and then the front and rear headers are 

dropped on. 

Final assembly: the assembly package tray upper drops onto the package tray lower; 

the assembly panel back attaches to the back of the floor complete; the body side outer 

assembly is brought onto the side of the body; the fender rails support outer are 

attached; and, finally, the roof panel is dropped on. 

After the body structure leaves the body shop, the assembly radiator support upper is attached 

to the front end; the assembly dash insert is attached to the dash panel; and the spare tire tub 

(spare tire in place) is dropped into the rear trunk area. 

Adhesive bonding 

Steel sandwich material cannot be welded, so the ULSAB parts made of steel sandwich 

material employed adhesive bonding as the joining technology. Adhesive bonding provides 

structure as well as a seal. The bonding material is a two-component, non-conductive, high 

modulus, high viscous, chemically curing polyurethane adhesive / sealant that cures virtually 

independent of temperature and moisture. 

The parts to be joined must be held securely in place while the adhesive bonding cures. The 

steel sandwich dash panel insert was secured with adhesive bonding and then bolted in place. 

Adhesive bonding technical data 

Basis polyurethane prepolymer 

Processing temperature 10° to 35° C 

Working time about 10 minutes at 23° C / 50 % relative humidity 

Ultimate tensile strength >5.5Mpa 

Percentage elongation >200% 

G-modulus >2.5 MPa 

The assembly sequence, processes and tolerances were established by PES. Porsche in 

Germany assembled the body structures using a flexible, modular assembly fixture system 

that was developed in CATIA, a computer-aided design system. All tooling holes and 

locators that would be used for production were used during the build. 

The final assembled body structures were checked by coordinate measuring machines (CMM) 

to guarantee their dimensional integrity, and this data is available for inspection upon request. 
ULSAB Materials and 

Processes 

The UltraLight Steel Auto Body (ULSAB) design called for the application of some steel 

thicknesses and grades currently available but not commonly used in automotive bodies, as 

well as the use of advanced manufacturing processes. Steel is the most recycled material in 

the world, and all steel chosen for the ULSAB structure is recyclable. Steel specifications for 

the body were chosen to meet mass, performance and safety goals. 

In their effort to optimize the best attributes of steel in this project, PES engineers specified 

unusually large percentages of high and ultra high strength steels and steel sandwich material. 

They also called for the use of hydroforming and tailored blanking. 

These materials and advanced processes enabled the design engineers to consolidate functions 

in fewer parts, resulting in mass savings and improved performance. 

Materials 

High strength steel 

ULSAB uses high strength steel and ultra high strength steel for more than 90 percent of the 

body structure. ULSAB defines high strength steel as yield strength 210 through 550 MPa 

and ultra high strength steel as yield strength above 550 MPa. Material thicknesses range 

from 0.65 mm to 2.0 mm. 

High and ultra high strength steels were used where the design required certain crash and 

strength characteristics. For high and ultra high strength steel parts, ULSAB uses phosphoralloyed steels, bake-hardened steels, isotropic steels, high-strength IF steels, transformation 

induced plasticity steels and dual phase steels. Ultra high strength steel was used for most of 

the lower crossmembers. 

One challenge posed by these steels is that they form differently from the mild steel to which 

many component fabricators are accustomed. High strength steel has greater springback and 

requires different draw angles so each different grade must be treated by the design engineer 

and manufacturing engineer as a unique material. 
ULSAB material and process 2

Thickness usage in ULSAB is illustrated in the chart below. 

Tailored blanks 

Nearly half of ULSAB’s mass consists of tailored blanked parts, which promote smooth load 

flow, reducing structural discontinuities and allowing for the combination of thicker and 

higher strength materials within the same part. Tailored blanking enables the design engineer 

to accurately situate the steel within the part precisely where its attributes are most needed. 

While this benefit results in improved crash performance, it also leads to weight reduction 

because it allows the design engineer to remove mass that does not contribute to performance. 

Tailored blanks also reduce the total number of parts, which leads to the reduction of dies 

needed for part stamping and the reduction of costs associated with those dies. Likewise, they 

reduce the number of spot welds and promote improved dimensional accuracy due to 

reduction in assembly steps. 

ULSAB’s body side outer is one of several parts that employs a fully laser welded tailored 

blank with different thicknesses and grades of steels. The body side outer panel uses a laser 

welded tailor blank and employs a one-piece design which includes the complete body side 

ring as well as the rear quarter. This part was designed for weight savings — through 

elimination of reinforcements in the body side assembly — and structural performance. It 

provides exact door fit and also leads to cost savings. 

7.6%

25.1%

0.8%

3.0%

10.8%

4.2%

10.9%

2.1%

9.1% 8.4% 7.6%

3.0%

4.4%

1.5% 1.5%

0.65

0.70

0.80

0.90

1.00

1.20

1.30

1.40

1.50

1.60

1.70

1.80

2.00

Sandwich

Misc

Percent Distribution of Material
ULSAB material and process 3

Careful placement of the seams in the tailored blank was critical for minimizing weight and 

facilitating forming. This consideration was especially important in the body side outer 

because of its complexity, its size, its use of high strength steels and the inclusion of a class A 

surface quarter panel. Nearly half of the ULSAB mass consists of tailored blank parts. 

Tailored blank usage 

Part Material grade 

(yield strength) 

in MPa 

Material 

thickness 

(mm) 

rail front outer (r&l) 350 1.5 - 2.0 

rail front inner (r&l) 350 1.5 - 1.8 

panel rocker inner (r&l) 350 1.3, 1.7 

rear rail inner and outer (r&l) 350 1.0 - 1.6 

panel body side outer (r&l) 210 - 350 .7 - 1.7 

panel wheelhouse outer (r&l) 140, 210 .65, .8 

panel skirt 140 1.6, 2.0 

Steel sandwich 

Steel sandwich material consists of a thermoplastic (polypropylene) core sandwiched between 

two thin steel skins. This material can be up to 50 percent lighter than a comparable sheet of 

homogeneous steel without compromising performance. It is favored where bending stiffness 

is the design criterion. The thermoplastic core acts as a spacer between the two outer sheets, 

separating the outer surfaces from the neutral axis when a bending load is applied. It shares 

many of the same processing possibilities — deep drawing, shear cutting, laser cutting, 

drilling, adhesive bonding and riveting — with sheet steel but cannot be welded. 

Steel sandwich material was chosen for mass reduction and was used for the spare tire tub and 

the dash panel. The steel yield strength for the spare tire tub is 240 MPa with a width of 1050 

mm and a thickness of .14 mm. Its core has a thickness of .65 mm. For the dash panel, the 

steel yield strength is 140 MPa with thickness of .12. Its core is .65 mm. 

Processes 

Hydroforming 

Tubular hydroforming and its cold working effect produces high dimensional stability and 

increases effective yield strength in any component. The part making process incorporates 

four steps: 1) making the tube; 2) bending the tube; 3) pre-forming the pre-bent tube; and 4) 

hydroforming the pre-formed tube into the final component shape. 

ULSAB’s hydroformed side roof rail provides an essential load path for structural 

performance and crash energy management from the top of the ‘A’ pillar along the roof, into 

the ‘B’ and ‘C’ pillars and into the rear of the structure. The hydroformed side roof rail 
ULSAB material and process 4

reduces the total number of parts and maximizes section size, allowing for both mass and cost 

savings. 

The raw material for the side roof rail is a welded, high strength steel tube of thickness 1 mm 

and outside diameter of 96 mm. The yield strength is 280 MPa. 

Sheet hydroforming was chosen for the roof panel for weight reduction. This process 

provided the opportunity to manufacture the roof panel at a thinner gauge and still achieve a 

work-hardening effect, especially in the center area where the degree of stretch is normally 

minimal. Typically, additional thickness is needed to meet dent resistance requirements there. 

With sheet hydroforming, the work-hardening effect is achieved by using fluid pressure to 

stretch the blanks in the opposite direction towards the punch. This plastic elongation causes 

a work-hardening effect in the center area of the blank. In the second step, the punch forms 

the panel towards controlled fluid pressure achieving excellent part quality because there is no 

metal-to-metal contact on the outer part surface. The roof panel is manufactured in 0.7 mm 

high strength isotropic steel with a yield strength of 210 Mpa. 

Assembly laser welding 

Laser welding was used in ULSAB to improve static and dynamic strength of joints, for areas 

where access was available on only one side and for good aesthetic appearance at joint areas. 

Laser welding also has the benefit of small a heat-affected zone, which reduces dimensional 

distortion and material property changes. Total length of laser welding in ULSAB is 18,286 

mm. 

The laser welding and laser cutting cabin was equipped with a KUKA KR 125 robot to which 

the laser heads were attached. The maximum load was 125 kg with a working range of 2410 

mm. The laser source was a Rofin Sinar CW 025 Nd:YAG Laser. The maximum output of 

2500 watts was transferred through a switching device with two outlets via two 15 m glass 

fiber cables of 0.6 mm diameter to the laser optic. In addition to the laser cutting head, two 

types of laser welding heads were used: Laser picker and single roller. Welding requires 

contact between the surfaces that are being joined, and each of these laser heads employs a 

different method by which they help ensure zero gap prior to welding. 
ULSAB Structural Performance 

Satisfactory performance of any body structure is critical to its success. Performance includes 

measures of static torsional rigidity, static bending rigidity, body structure modes and safety. 

Static torsional and bending rigidity refer to body stiffness, and the body structure modes refer 

to the shapes the body assumes at its natural frequencies, which are related to noise, vibration 

and harshness (NVH). These factors affect the ride and handling and structural feel of an 

automobile and have a direct impact on ride satisfaction. Safety refers to the body structure’s 

ability to withstand impacts and meet specific crash criteria. 

A stiff auto body is preferred to a pliant one because it handles better and resists excitement 

(vibration) produced by road inputs, which are created when the tires strike bumps or 

potholes. When excited by outside forces such as a bump in the road, an auto body vibrates at 

a particular frequency, called its natural frequency, and in a particular manner, called its mode 

shape. Components attached to the car body — such as the suspension and the powertrain — 

also vibrate at individual natural frequencies. 

It is important to design structural systems with vibration frequencies that do not excite each 

other, or “couple.” Coupling creates dissonance and unpleasant vibration and is caused when 

two major systems resonate at similar natural frequencies. 

Validation 

Two methods have been used to validate ULSAB’s performance: Computer-aided 

engineering (CAE) and physical testing. Both analyses yield information on static bending, 

static torsion, normal modes and mass. CAE analysis is predictive of physical test results and 

is performed through computer simulation. Physical testing is used to validate CAE analysis 

and is performed by loading the physical structure after it has been built. For ULSAB, no 

physical crash tests were performed because they are destructive and they require crashing a 

full running vehicle (not merely the body structure). Only CAE was used to predict ULSAB 

crash results. 

CAE analysis 

ULSAB analysis employed a fully surfaced body structure that includes all exterior styling 

surfaces. All surfaces were generated from CAE CATIA design software. That design data 

was used to create finite element analysis static and crash models. The models were 

comprehensive, the largest requiring approximately 178,000 elements (1 million degrees of 

freedom) and the use of a supercomputer to analyze. 
ULSAB structural performance 2

Static and modal analysis 

Static analysis included static torsion and static bending and free-free normal mode (as if the 

structure were floating in space). Static models were run and optimized using NASTRAN, a 

linear static analysis code. Half-models symmetric about the centerline were used and 

constrained accordingly at all nodes on the centerline. All spot welds were represented using a 

rigid element placed in the middle of the weld flange with an average spacing of 50 mm. A 

free node exists between welds. Urethane glass adhesive was simulated for the windshield and 

backlite using spring elements with stiffness in three directions, x, y and z. The mesh was 

created accordingly. 

Crash analysis 

ULSAB was subjected to crash simulations using LS Dyna-3D, an explicit finite element 

analysis code, and exhibited acceptable crash behavior. The models were created using 

industry accepted methods. For realistic crash behavior in the simulation, all spot welds and 

laser welded areas were considered in the model, and the following relevant components were 

added to the model: 

· Wheels with tire model 

· Engine and gearbox 

· Steering system 

· Chassis system with subframe 

· Fuel tank 

· Bumper system including crushbox 

· Radiator with fan 

· Battery 

· Spare tire 

· Brake booster, ABS box and cylinder 

All simulations were run to their completion. Test and full vehicle mass was assumed to be 

1612 kg, which included luggage at 113 kg and occupants at 149 kg. 
ULSAB structural performance 3

Analysis was performed with models of the following size: 

Model definition

 Static 

half 

model 

front 

impact 

and 

offset 

side 

impact 

rear 

impact 

half 

model 

roof 

crush 

Number of elements 54,521 178,386 181,963 90,105 119,226 

Nodes 53,460 174,532 179,918 88,769 117,053 

ULSAB was designed to meet five crash requirements: 

35 MPH NCAP 0 DEGREE FRONTAL (FMVSS 208) 

The conditions for the front crash analysis are based on several requirements. In the ULSAB 

project, the focus was on progressive crush of the upper and lower load path; sequential stack 

up of the bumper, radiator and powertrain; integrity between individual components; ‘A’ 

pillar displacement; definition of the door opening; uniform distribution of the load; toe pan 

intrusion; and passenger compartment residual space. These requirements contribute to 

occupant safety and reflect the United States Federal Motor Vehicle Safety Standard, FMVSS 

208. 

Analysis was set up as shown. The maximum deformation image shows the deformed 

structure at event completion, which occurred at 67 msec. The crash pulse can be seen in the 

graph below. The table below lists the major events that occur during the simulation. 

Maximum footwell intrusion was 94 mm. Peak deceleration was approximately 31 gs. 

Maximum dynamic crush was approximately 620 mm. 

35 mph NCAP simulation behavior 

TIME (MS) EVENTS

12 initial folding of longitudinal 

16 initial folding of subframe 

21 1st buckling of rails upper in front of shock tower 

35 engine contacts barrier 

37 buckling rear of subframe at fixture on extension longitudinals 

50 rear end of longitudinals start to buckle behind reinforcements 

51 wheels contact barrier 

67 maximum dynamic deformation 
ULSAB structural performance 4

This analysis illustrates good progressive crush of the upper and lower structure and 

subframe. It shows peak deceleration of 31 gs, which is satisfactory considering that this 

structure is designed with stiffer body sides to meet 50 % AMS offset crash requirements. 

The pulse graph is sympathetic to current occupant restraint systems. It shows a consistent 

rise to the peak of 31 gs then a smooth ride down to zero, indicating that the occupant would 

experience controlled restraint. The initial, early peak should trigger airbag systems. Low 

intrusion at the footwell indicates that leg damage is unlikely. 

55 KM/H 50% AMS FRONTAL OFFSET 

The aim of the AMS offset crash is to secure the passenger compartment residual space. For 

this requirement, a stiff passenger compartment and good energy absorption in the front 

structure is needed. 

The offset barrier is a block with a 15 degree rotated contact area, including two anti-slide 

devices mounted on the contact surface. The left side of the car hits the barrier with an 

overlap of 50 percent. 

Analysis was set up as shown below. The maximum deformation image shows the deformed 

structure at event completion, which occurred at 88 msec. The crash pulse can be seen in the 

graph below. The table below lists the major events that occur during the simulation. 

Maximum footwell intrusion was 146 mm. Peak deceleration was approximately 35 gs. 

Maximum dynamic crush was approximately 740 mm. 

AMS offset simulation behavior 

TIME (MS) EVENTS

12 Initial folding of longitudinal left hand side 

16 Initial folding of subframe 

18 1st buckling of upper rails in front of shock tower 

36 Wheels left hand side contact barrier 

40 Engine contacts barrier; start of vehicle rotation around Z axis 

44 Subframe front totally deformed; left hand longitudinal rail moves rearward, 

causing deformation in front floor; buckling of longitudinal rail in area of 

shock tower 

48 2nd buckling of upper rails left hand side behind shock tower 

52 Buckling of rear end of subframe at fixture on extension longitudinals 

60 buckling of brace cowl to shock tower left hand side; engine hits steering 

gear 

68 gearbox mounting contacts brake booster 

70 wheel left hand side contacts hinge pillar 

88 maximum dynamic deformation 
ULSAB structural performance 5

This analysis shows good progressive crush on the barrier side (left), as well as crush on the 

right, indicating transfer of load to the right side of the structure. This transfer means that the 

barrier side is not relied upon solely to manage the crash event. 

This transfer also contributes to the preservation of the occupant compartment. The intrusion 

of 146 mm into the footwell is minimal given the severity of this event. 

The initial, early peak shown in the pulse graph should trigger airbag systems. 

Peak deceleration of approximately 35 gs, a good result considering the severity of this event. 

35 MPH REAR MOVING BARRIER (FMVSS 301) 

The conditions for rear impact analysis are based on United States Rear Moving Barrier test 

FMVSS 301. The test specifically addresses fuel system integrity during rear impact. 

Automotive companies also specify goals for structural integrity and passenger compartment 

volume. 

The impacting barrier is designed to represent a rigid body with a mass of 1830 kg that 

contacts the vehicle at zero degrees relative to the vehicle longitudinal axis. FMVSS 301 

specifies the velocity of the rear moving barrier to be 30 mph at the time of impact. ULSAB 

ran its analysis at a velocity of 35 mph, which represents 36 percent more kinetic energy. 

Analysis was set up as shown below. The maximum deformation image shows the deformed 

structure at event completion, which occurred at 86 msec. The crash pulse can be seen in the 

graph below. The table below lists the major events that occur during the simulation. 

Maximum intrusion into rear passenger compartment was 120 mm. Peak acceleration of the 

vehicle was approximately 14 gs. Maximum dynamic crush was approximately 650 mm. 

Rear moving barrier simulation behavior 

TIME (MS) EVENTS

4 Initial folding of longitudinals rear 

20 Spare tire contacts barrier 

35 First buckling of crossmember rear suspension 

40 Spare tire contacts crossmember rear suspension 

48 Buckling of rear end rocker at connection to longitudinal rear 

44 Buckling of crossemember rear suspension 

52 Collapse of crossmember rear suspension 

56 Buckling of front end of longitudinal rear 

86 Maximum dynamic deformation 
ULSAB structural performance 6

This analysis shows that the structural integrity of fuel tank and fuel filler was maintained 

during the event, so no fuel leakage is expected. The spare tire tub rides up during impact, 

avoiding contact with the tank. 

Rear passenger compartment intrusion was restricted to rear most portion of the passenger 

compartment, largely in the area behind right rear seat. This result is due to good progressive 

crush exhibited by the rear rail. 

50 KM/H EUROPEAN SIDE IMPACT (96/27 EG, WITH DEFORMABLE BARRIER) 

The conditions of the side impact analysis are based on a European Side Moving Barrier test 

that addresses injury criterion gathered from EUROSID side impact crash dummies. 

Automotive companies also specify goals for structural integrity and passenger compartment 

volume. 

The impacting barrier has a mass of 950 kg and contacts the vehicle at ninety degrees relative 

to the vehicle longitudinal axis. The velocity of the barrier is 50 km/hr at the time of impact. 

Analysis was set up as shown below. The maximum deformation image shows the deformed 

structure at event completion, which occurred at 64 msec. Side impact velocity versus 

intrusion can be seen in the graph below. The table below lists the major events that occur 

during the simulation. Maximum dynamic inboard displacement was 248 mm at the rear of 

the front door. Maximum velocity of the intruding structure was 8 m/sec. 

Side impact simulation behavior 

TIME (MS) EVENTS

16 Buckling of rocker in front of B pillar 

28 Buckling of floor 

35 Buckling of roof 

40 Buckling of roof frame at b-pillar 

44 Buckling of member kick up 

48 Buckling of brace tunnel 

64 Maximum dynamic deformation 

The body side ring and doors maintained their integrity with only 248 mm of intrusion. The 

velocity of the intruding structure was tracked to determine the degree of injury an occupant 

may sustain. The maximum velocity was only 8 meters per second. The event is considered 

complete when the deformable barrier and vehicle reach the same velocity, in this case 64 

msec. 
ULSAB structural performance 7

ROOF CRUSH (FMVSS 216) 

The conditions for the roof crush analysis are based on United States Federal Motor Vehicle 

Standard, FMVSS 216. This requirement is designed to protect the occupants in the event of 

a rollover. The surface and angle of impact represent impact on the front corner of the roof. 

The federal standard requires roof deformation to be limited to 127 mm of crush. The roof 

structure must support 1.5 times the vehicle weight or 5,000 pounds, whichever is less. For 

testing, the complete body structure is assembled and clamped at the lower edge of the rocker. 

The roof crush uses a quasi-static force versus displacement arrangement. 

Analysis was set up as shown below. The maximum deformation image shows the deformed 

structure at event completion, which is 127 mm of crush. The force versus displacement 

curve can be seen in graph below. Peak load was approximately 36 kN at 75 mm of crush 

versus the requirement of 22.25 kN. 

Analysis showed that 22.25 kN was reached within 30 mm of crush. The structure resisted 

the applied load all the way up its peak of 36 kN and continued to maintained it quite well 

even after peak, when it dropped to about 28 kN at 127 mm. The load was well distributed 

through the ‘A,’ ‘B’ and ‘C’ pillars and down into the rear rail. 

Physical testing 

Physical tests were used to validate static torsion, static bending and normal modes. Normal 

mode testing was performed by suspending the body structure on a test rack with rubber 

straps while exciting it at all four corners using electrodynamic shakers. To validate mass, the 

ULSAB structure was weighed. 

Static torsion test 

The static torsion test yielded a stiffness of 20,800 Nm/deg. The displacement along the 

length of the body structure can be seen in the graph below. The plot shows excellent 

structural continuity with a local increase in stiffness between x=3800 and 4200 due to the 

member pass through. 

Static bending test 

The bending test yielded a stiffness of 18,100 N/mm. The displacement along the length of 

the body structure can be seen in the graph below. The plot shows excellent continuity with a 

local increase in stiffness between x=3500 and 4200. This result indicates a stiff joint 

between rocker and rear rails. 
ULSAB structural performance 8

Modal test 

The first three major body structure modes with and without glass are shown in the graph 

below. The ULSAB body structure shows good dynamic rigidity, as indicated previously by 

the static test. The following graph shows the natural frequencies of the body structure. 

 60.1

63.9 64.9

40

50

60

70

Torsion Bending Front End Lateral

with glass

Fir

st 

Mo

de 

(H

Modal 
ULSAB structural performance 9

Results and prediction 

CAE was employed in the design and manufacture process to predict physical confirmation 

and ensure that the concept would meet established performance targets. Physical testing 

following development was used to validate results generated earlier in the process by CAE. 

In ULSAB’s case, CAE results were, in most cases, predictive of the physical tests, as shown 

below. 

Static analysis

 torsional rigidity 

(Nm/deg)

bending rigidity 

(N/mm) 

1st body 

structure mode 

(Hz) 

Mass (kg) 

CAE 20,347 20,543 60.3 212 

Physical 20,800 18,100 60.1 203* 

* natural range of variation ±1 percent 

The reliable correlation demonstrated (above) between CAE and physical results for static 

analysis indicates that a similar correlation would exist between CAE and physical crash 

results. The disparity in the mass numbers exists because the CAE model assumed constant 

thickness within each part; however, actual stamped parts — thinned in the stamping process 

— exhibit varying degrees of thickness throughout. Constant material thickness assumed in 

the CAE model yielded mass numbers that are higher than actual. 

Structural performance 

Physical tests and CAE results show ULSAB to exceed all concept phase benchmarked 

averages. 
ULSAB structural performance 10

Structural performance comparison 

 ULSAB structure benchmark 

structure average 

Future reference 

structure 

Performance 

torsion (Nm/deg) 

bending (N/mm) 

1st body structure 

mode (Hz) 

20,800 

18,100 

60 

11,531 

11,902 

38 

13,000 

12,200 

40 

Mass (in kg) 203* 271 250 

* natural range of variation ±1 percent 

Body structure 

The body structure consists of 94 major parts plus 31 reinforcements (not manufactured) — 

such as the hood hinge, steering rack assembly mounting, deck lid latch support and gearshift 

mounting — as well as 22 brackets (not manufactured) — such as the battery tray and the 

spare tire mounting. The exploded view of the body structure shown below represents the 

parts that were included in the measured body. 
ULSAB Economic Analysis 

Although lightweighting without sacrificing performance was ULSAB’s priority, affordability was 

also important. Early in ULSAB’s concept phase the Consortium commissioned an economic 

analysis to establish a reference by which to compare ULSAB. At that time, IBIS Associates 

estimated a cost of $1116 each to manufacture current, typical body structures for vehicles in the 

same class as ULSAB. The North American manufacturing costs calculated during the concept 

phase of the project represent the estimated cost to manufacture a typical body structure in the 

same class as ULSAB at the time of the project’s inception in 1994. 

In the validation phase, the cost issue was revisited more thoroughly. The ULSAB Consortium’s 

primary objective was to provide a cost model that automotive customers could use to analyze 

ULSAB costs in comparison with other options and could also be used to generate costs 

associated with alternative designs. The cost model should allow auto companies to use their 

own manufacturing and business environment assumptions to compare with the assumptions 

used for ULSAB. This cost estimation tool should permit the user to easily adapt various input 

parameters, allowing cost investigations for any design on a consistent basis. 

A Porsche-led team of analysts developed the detailed cost model that includes all aspects of 

fabrication and assembly. This model comprehends United States manufacturing costs, including 

investments for both plant and tooling, piece fabrication costs and assembly costs, through to the 

end of the body shop. The analysts used these details to generate a part-specific cost model for 

ULSAB. This particular analysis showed part manufacturing and assembly costs for the ULSAB 

body structure to be $947 each. 

Using the same cost model, the team also created assumptions about a future typical four-door 

sedan (Year 2000) reference body structure with which to compare ULSAB. Basic economic 

assumptions were identical for both ULSAB and the Year 2000 structure; however, inputs about 

specific parts and assembly steps are not directly comparable because the Year 2000 structure 

represents an average of typical vehicle structures in the same class as ULSAB. For the Year 2000 

structure, the study identified part groupings – instead of individual parts as with ULSAB – and 

assumed significantly improved fabrication and assembly techniques as compared to the concept 

stage reference. The cost model with these inputs showed part manufacturing and assembly costs 

for the Year 2000 structure to be $979 each. 

The team began analysis by establishing general inputs or assumptions for the cost model. 

Then they established production costs, which include part fabrication and assembly. And 

finally they created the model scope, which comprehends direct manufacturing costs. The cost 

model examines the 158-part, 203 kg ULSAB structure and a 200-part, 250kg Year 2000 

structure. 
ULSAB economic analysis 2

General inputs 

The first step in economic analysis began with the formulation of general inputs that may vary for 

different locations. Inputs used for this project are as follows: 

General inputs 

 Input 

Production volume 60 jobs per hour 

(225,000 vehicles 

per year) 

Working days per year 240 (2 shifts) 

Production location mid-west USA 

Wage including benefits $44.00 per hour 

Interest rate 12% 

Production life 5 years 

Equipment life 20 years 

Building life 25 years 

Production costs 

Production costs comprise fabrication and assembly of ULSAB’s 158 parts, which include 

brackets and reinforcements. 

Fabrication 

To calculate costs for part fabrication, the team established a press line time requirement based on 

the machine clean running rate, line downtimes, part reject rates and total annual production 

volume. They then used that press line time requirement to calculate the total number of each 

press line type needed to produce ULSAB. This calculation specified 15 press lines and five 

blanking lines to produce all necessary parts and blanks. 

Assembly 

Assembly costs include equipment and tooling investments, assembly plant area and labor force. 

Additional assembly inputs consider material, energy, overhead labor and maintenance. The 

assembly line was designed for a net line rate of 60 jobs per hour, as well as a specific number of 

spot and length of laser welds. Any change in practice of these two operations necessitates a 

change in the investment inputs for accurate estimates at other production volumes. Also, 

because the line was designed for one line speed, the model cannot adjust the investment based 

on different rates. 
ULSAB economic analysis 3

Model scope 

This cost model accounts for economic and technical processes used in the manufacture and 

assembly of the body structure. Data for stamping include blanking, welding of tailored blanks 

and stamping for all parts; data for hydroforming include bending, pre-forming and final 

hydroforming; and data for assembly include spot welding, MIG welding, laser welding and 

adhesive bonding. 

This model is limited to direct manufacturing costs, which include fabrication and assembly of 

the body structure. Indirect manufacturing costs – executive salaries, marketing and sales, 

shipping and purchasing, research and development, profits – are not considered. 

Cost is assigned to each unit operation from a process flow diagram and then those operations 

are separated into individual elements. Fixed cost elements include equipment, tooling, building 

maintenance, overhead labor and cost of capital; variable cost elements include materials, labor 

and energy. 

ULSAB results 

Manufacturing costs for the ULSAB structure are $666 for parts fabrication and $281 for 

assembly. Of the 158 total parts, 94 major stamped parts represent the largest cost element at 

$584. Total fixed costs account for 43 percent of the total. 

ULSAB results 

 ULSAB cost in $US % of Total

PARTS FABRICATION 584 62 

material 351 37 

labor 36 4 

energy 6 1 

fixed costs 191 20 

HYDROFORMING 41 4 

PURCHASED 

COMPONENTS

41 4 
ULSAB economic analysis 4

ASSEMBLY 281 30 

Variable 55 6 

fixed 226 24 

TOTAL COST 947 100 

Fabrication breakdown 

Total fabrication costs can be broken down further. Major stamped components account for 

$584; the hydroformed side roof rail accounts for $41. 

Fabrication breakdown 

Breakdown for stamped parts Cost per structure in $US 

material 351 

labor 36 

energy 6 

TOTAL VARIABLE 393 

equipment 89 

tooling 51 

overhead labor 27 

building 8 

maintenance 15 

working capital 1 

TOTAL FIXED 191 

TOTAL COST 584 
ULSAB economic analysis 5

Assembly breakdown 

Assembly accounts for less than one-third of the overall cost. Largest single items are labor and 

assembly line equipment. 

Assembly breakdown 

Breakdown for assembly cost per vehicle in $US 

material 0 

labor 45 

energy 10 

TOTAL VARIABLE 55 

equipment 50 

tooling 23 

overhead labor 125 

building 18 

maintenance 9 

working capital 1 

TOTAL FIXED 226 

TOTAL COST 281 

Investments 

Investments for the assembly line and related tooling and building expenses account for 

approximately one-third of the total investment. Press lines represent nearly half of the total 

investment. Weld line investments for tailored blanks are also significant, despite the fact that 

there are only 16 tailor welded blank parts in the vehicle. Investments are comprehended in the 

ULSAB results and are represented in the table below. 

Investments 

Investments ULSAB ($US M) % of total

Blanking tooling 4.4 1.4 

Blanking lines 10.1 3.2 
ULSAB economic analysis 6

Blanking build 1.2 0.4 

Welding line 37.2 11.9 

Welding building 5.9 1.9 

Stamping tooling 37.1 11.8 

Stamping lines 102.9 32.8 

Stamping building 6.1 1.9 

Hydroforming tooling 1.3 0.4 

Hydroform lines 16.3 5.2 

Hydroform building 0.5 0.2 

Assembly tooling 19.0 6.0 

Assembly equipment 40.4 12.9 

Assembly building 31.4 10.0 

TOTAL 

INVESTMENTS 

313.8 100 

Sensitivity analysis 

A key element of economic analysis is to determine potential cost movements as a result of 

sensitivity analysis and other scenarios that could impact cost. It includes investigation of labor 

wage, unit energy costs, equipment life, building unit cost, production life and material costs. As 

the use of new technologies such as tailored blanking, hydroforming and laser welding increases, 

so should efficiency, resulting in further cost reductions. 

The sensitivity analysis, shown in the graph below, illustrates that the factors that most affect 

body structure cost are labor wage, production life and material costs. Factors of least influence 

on total cost are unit energy cost, equipment life and building unit cost. 
ULSAB economic analysis 7

Sensitivity Analysis 

Comparison 

For comparison purposes, this economic analysis calculated the cost of manufacturing a future 

reference (Year 2000) structure in addition to ULSAB. This reference is a hypothetical construct 

intended to represent an averaging of typical mid-sized four-door sedans in the same class as 

ULSAB. The model inputs assume significantly improved fabrication and assembly techniques in 

year 2000 body structure manufacturing in the United States, including a lower part count, double 

attachments, and completely automated assembly. 

Because no design details were assigned to the Year 2000 structure, the study identified part 

groupings instead of individual parts, as with ULSAB. The groupings are based on part size and 

complexity as well as assembly operations grouped by levels of automation and size. 

The comparison below represents a single run of the cost model based on United States inputs. 

 

 

Labor 

Wage

+20% 

$ 44 / hour 

-20%

+20% 

$0.10 / kwh 

-20%

15 years 

20 years 

25 years

+20% 

$1500 / m2

-20%

3 years 

5 years 

8 years

+10% 

$352 

-10%

Equipment 

Life

Building 

Unit Cost

Production 

Life

Material Costs 

Stamping Parts

Unit 

Energy Cost

Overall 
ULSAB economic analysis 8

Comparison of ULSAB with Year 2000 structure 

 ULSAB Year 

2000 

Body Structure Mass: 

 Net weight (kg) 203 250

 Stampings 184 230

 Hydroformings 10 0

 Purchased parts 9 20

 Material utilization 49 55

Parts Fabrication: 

 Direct labor 59 79

 Indirect labor 47 36

 Parts count: 158 200

 Large stampings 11 6

 Medium stampings 39 79

 Small stampings 44 50

 Hydroformings 2 0

 Purchased parts 62 65

 Die sets: 61 109

 Transfer 14 20

 Tandem 27 59

 Progressive 18 30

 Hydroform 2 0

 Hits per die set: 

 Transfer 4.1 3.8

 Tandem 3.6 3.2

 Hits per part: 

 Transfer/tandem combined 2.5 2.5

Assembly: 

 Direct labor 64 80

 Indirect labor 178 210

 Number of spot welds 2206 3250

 Length (mm) laser weld 18286 0

 Number of robots 136 200

 Number of laser 

welders 

 13 0

 Number of assbly 

stations 

 114 130

 Assembly bldg. area 

(m2) 

 20925 30000

Cost: (in $US) 

 Stamped parts 584 609

 Hydroformed rail 41 0

 Purchased parts 41 41

 Assembly 281 329 

 TOTAL COST $947 $979 

Conclusion 

Achieving lightweight and superior performance in a steel body structure can be done at no cost 

penalty. In fact, it can be less expensive than structures that do not have its benefits. ULSAB 

demonstrates that reduced weight and superior performance are achievable and affordable.