# ULSAB Executive Summary

An UltraLight Steel Auto Body (ULSAB) struct ure 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 lightwe ight, 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 test s of the structure reveal similar remarkable results: torsion and bending tests showed improvements over benchmark of 80 percent and 52 percent, respectively, and 1 st body structure mode indicates a 58 percent improvement. Analyses also show ULSAB satisfies mandated cr ash requirements, even at speeds exceeding the requirements. In addition to reduced wei ght 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 in cluded in this type of auto body structure. It does not include doors, hood or decklids, whic h 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 au to 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 Engi neering Services, Inc. (PES) to provide engineering and manufacturing management for the ULSAB project and also worked with them to define the project goals. They t ook 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 agai nst which to measure ULSAB. PES also established package constraints through this benchmarking process. To determine an “average base model,” 32 different cars re presenting varying worldwide customer requirements were selected for package benchmarking. For structural benchmarking (static torsion, static bending, 1 st body structure mode), PES used a cross section of nine cars that represented cu rrent 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
1 st

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 re presents 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
1 st

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 star ted 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 evaluateULSAB summary 3 how changes in one area affect other areas and where future optimization opportunities exist. Through each iterative step, re-analysis confirms th e effectiveness of the latest optimizations. This approach promotes weight savings a nd improved structural integrity by enabling engineers to reduce weight in certain areas wh ile strengthening strategic locations. The net effect is the creation of a more efficient structure. Computer models were also used to analyze a ll structural aspects and to simulate specific crash events, demonstrating acceptable performan ce. Sophisticated architecture and refined joint designs ensure continuous load flow, wh ich 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; vehicl e 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 door s, 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 empl oyed 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 mate rial in the world, and all steel chosen for the ULSAB structure is recyclable. ULSAB uses high strength steel and ultra high st rength steel for more than 90 percent of the body structure to improve structural performa nce 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 wher e their attributes are most needed, thereby removing mass that does not contribute to performance. ULSAB also features a hydroformed side roof ra il, which provides an essential load path for structural performance and crash energy mana gement. In addition to tubular hydroforming, ULSAB uses sheet hydroforming for the roof pa nel. 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 UL SAB 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 th e project’s success and was contemplated throughout the design phase. Early in the desi gn process the design engineers worked with component fabricators and steel manufactu rers 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 t ubing 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 a ll 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, hydrof orming was accomplished using hard tools. In all cases, part fabrication tolerances and qua lity standards were maintained the same as intended for full volume production. Analysis To help ensure that the part designs were f easible, the project partners performed forming simulation analysis on the most complex part s. 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 fabr icators manufactured the parts and evaluated them using circle grid strain analysis to confirm that they were formed to full volume manufacturing standards. Confirmation was al so established through measurement of key part dimensions and the use of check fi xtures. 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 a nd tolerances were established by PES. AllULSAB summary 5 tooling holes and locators that would be used for production were used during the build. Porsche in Germany assembled the demonstr ation hardware using a flexible, modular assembly fixture system. ULSAB employs about one-third fewer spot weld s 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)
1 st

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 i ndicate excellent crash behavior of the ULSAB structure in the following crash events: 35 m ph 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 barri er simulations were run at speeds that exceed mandated safety requirements by 17 pe rcent, and the AMS frontal is widely considered one of the most severe offset crashes performed today. 

## Economic Analysis Although lightweighting without sacrificing perf ormance was ULSAB’s priority, affordability was also important. Early in ULSAB’s c oncept 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 revi sited more thoroughly. A Porsche-led team of analysts developed a detailed cost model that in cludes all aspects of fabrication and assembly. The cost model can be used to analyze ULSA B costs in comparison with other options and also to generate costs associated with alternative designs. This model comprehends United States manufact uring costs, including investments for both plant and tooling, piece fabrica tion costs and assembly costs, through to the end of the body shop. The analysts used these details to genera te a part-specific cost model for ULSAB. They also created assumptions about a future t ypical four-door sedan (Year 2000) reference structure with which to compare ULSAB. Ba sic economic assumptions were identical for both ULSAB and the reference structure; howev er, 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 indi vidual 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 th e 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 a nd processes that were unique and deemed patentable by international attorneys. The cons ortium chose to make all patentable features along with other project results freely availabl e 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) be nchmarked 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 vary ing worldwide customer requirements were selected for package benchmarking. Benchm arking considered curb weight; wheelbase; overall length and width; leg, head and s houlder 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, 1 st body structure mode), PES used a cross section of nine cars that represented cu rrent performance standards. These vehicles include the



### • Acura Legend



### • BMW 5-seriesULSAB 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 am ong the above nine vehicles, PES adjusted the structural performance linearly to the ULSA B 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 sti ffness of reference vehicle These vehicles were also normalized for ma ss 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 th at the usable volume in the front (V 1 ) and the usable passenger compartment volume (V 2 ) and the usable luggage volume (V 3 ) add up to the entire usable volume (V total ) of the vehicle:
V 1 + V 2 + V 3 = 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
1 st

body structure mode 38 Hz mass 271 kgULSAB design 3 This information was then used to predic t a future reference vehicle with improved performance with which ULSAB must ultimatel y 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
1 st

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, emphasi zing 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 devel op the optimum ULSAB body structure. Some of these included full frame, space frame, uni body and hybrid solutions. Criteria for the structures under consideration were significa nt 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 al so doubted that the full frame would meet ULSAB’s structural performance criteria and we re concerned about high investment costs for assembly. Although a spaceframe was considere d, it was ultimately eliminated because it is not considered as mass efficient as other appr oaches. 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 th e vehicle concept type, exterior and interior dimensions and main components. With thes e package definitions, package drawings wereULSAB design 4 created and structural hard points defined. UL SAB 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 m 2 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 e ssential parts of the structure interior. Criteria for interior design included visibilit y, obscuration by the pillars, head clearance and seat belt anchors. In the engine compartmen t, 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 i ssues. 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-edgeULSAB 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 surf acing 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 base d on considerations of mass, performance, and crash requirements. In its effort to optimize th e best attributes of st eel in this project, PES engineers specified unusually large percentages of high and ultra high strength steels, tailored blanks and steel sandwich material. The materi als for the body were chosen to meet mass and performance targets and include some grades a nd thicknesses of steel currently available but not commonly used in auto bodies. ULSAB uses high strength steel and ultra high st rength 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 ta ilored blanked parts, which enable the design engineer to locate various steels within the pa rt precisely where their attributes are most needed, thereby removing mass that does not contribute to performance. ULSAB also features a hydroformed side roof ra il, which provides an essential load path for structural performance and crash energy manage ment 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 hi ghlights 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 2.00ULSAB 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 1.00ULSAB 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 Sho ck 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. Earl y 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 t ubing 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 a ll 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 qua lity standards were maintained the same as intended for full volume production. Tool deve lopment 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 f easible, the project partners performed forming simulation analysis on the most complex part s. 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 fabr icators manufactured the parts and evaluated them using circle grid strain analysis to confirm that they were formed to full volume manufacturing standards. Confirmation was al so established through measurement of key part dimensions and the use of check fixtur es. Complete information to support part manufacturing feasibility was documented and includes material characteristics, press conditions, forming limit diagrams, process sh eets and tolerance measurements. These reports comprehend all parts listed under section “T ooling” 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 attach ment of inner pieces and improves structural integrity by eliminating unnecessary weld access holes. ULSAB employs about one-third fewer spot weld s 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 in cludes 18,286 mm of laser welding, 2,206 spotwelds and 1,500 mm of MIG welding, the majority of wh ich 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 completeULSAB 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 inne r 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 b ack of the floor complete; the body side outer assembly is brought onto the side of th e 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 mate rial is a two-component, non-conductive, high modulus, high viscous, chemically curing polyuretha ne 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-a ided design system. All tooling holes and locators that would be used for production were used during the build. The final assembled body structures were check ed 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) desi gn 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 processe s. Steel is the most recycled material in the world, and all steel chosen for the ULSAB stru cture 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 st rength steel for more than 90 percent of the body structure. ULSAB define s high strength steel as yield strength 210 through 550 MPa and ultra high strength steel as yield strengt h 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 part s, 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. Hi gh 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 tailo red 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 pe rformance, 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 cost s 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 part s 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 pa rt 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 . 8

0 0 . 90 1 . 0

0 1 . 2

0 1 . 3

0 1 . 4

0 1 . 5 0 1 . 6

0 1 . 7 0 1.80 2.00 Sand wich Mi sc 

# Percent Distribution of MaterialULSAB 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 si ze, 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 therm oplastic (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 performan ce. 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 re duction 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 th ickness 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 com ponent. The part making process incorporates four steps: 1) making the tube; 2) bending the t ube; 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 railULSAB 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 cente r 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 to wards 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 achie ving excellent part quality because there is no metal-to-metal contact on the outer part surfac e. 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. To tal 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 de vice 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: Lase r picker and single roller. Welding requires contact between the surfaces that are being join ed, 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 ri de and handling and structural feel of an automobile and have a direct impact on ride sa tisfaction. 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 ar e 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 frequenc y, 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 w ith vibration frequencies that do not excite each other, or “couple.” Coupling creates dissonanc e 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 analys is is predictive of physical test results and is performed through computer simulation. Physi cal testing is used to validate CAE analysis and is performed by loading the physical struct ure 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 structur e). Only CAE was used to predict ULSAB crash results. 

## CAE analysis ULSAB analysis employed a fully surfaced body st ructure that includes all exterior styling surfaces. All surfaces were generated from CA E 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 st atic bending and free-free normal mode (as if the structure were floating in space). Static m odels were run and optimized using NASTRAN, a linear static analysis code. Half-models sy mmetric about the centerline were used and constrained accordingly at all nodes on the centerlin e. 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 be havior 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 majo r 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 T IME ( MS ) E VENTS 12 initial folding of longitudinal 16 initial folding of subframe 21 1 st 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 deformationULSAB structural performance 4 This analysis illustrates good progressive cr ush 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 occupa nt restraint systems. It shows a consistent rise to the peak of 31 gs then a smooth ride down to zero, indicating th at the occupant would experience controlled restraint. The initial, ear ly 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 degr ee 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 majo r 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 T IME ( MS ) E VENTS 12 Initial folding of longitudinal left hand side 16 Initial folding of subframe 18 1 st 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 deformationULSAB 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 preservati on 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 ba sed on United States Rear Moving Barrier test FMVSS 301. The test specifically addresses fu el system integrity during rear impact. Automotive companies also specify goals for st ructural integrity and passenger compartment volume. The impacting barrier is designed to repr esent 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 majo r events that occur during the simulation. Maximum intrusion into rear passenger compar tment was 120 mm. Peak acceleration of the vehicle was approximately 14 gs. Maximum dynamic crush was approximately 650 mm.
Rear moving barrier simulation behavior T IME ( MS ) E VENTS 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 deformationULSAB structural performance 6 This analysis shows that the structural integr ity of fuel tank and fuel filler was maintained during the event, so no fuel leakage is expe cted. The spare tire tub rides up during impact, avoiding contact with the tank. Rear passenger compartment intrusion was restri cted 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 st ructural integrity and passenger compartment volume. The impacting barrier has a mass of 950 kg and cont acts 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. Th e 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 T IME ( MS ) E VENTS 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 vehi cle reach the same velocity, in this case 64 msec.ULSAB structural performance 7 ROOF CRUSH (FMVSS 216) The conditions for the roof crush analysis ar e based on United States Federal Motor Vehicle Standard, FMVSS 216. This requirement is designe d to protect the occupants in the event of a rollover. The surface and angle of impact repr esent 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 we ight 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 lo ad was approximately 36 kN at 75 mm of crush versus the requirement of 22.25 kN. Analysis showed that 22.25 kN was reached with in 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 to rsion, static bending and normal modes. Normal mode testing was performed by suspending th e body structure on a test rack with rubber straps while exciting it at all four corners usi ng electrodynamic shakers. To validate mass, the ULSAB structure was weighed.

Static torsion test The static torsion test yielded a stiffne ss of 20,800 Nm/deg. The displacement along the length of the body structure can be seen in th e 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 dyna mic 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 

# ModalULSAB structural performance 9 

## Results and prediction CAE was employed in the design and manufactur e process to predict physical confirmation and ensure that the concept would meet estab lished 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 cas es, predictive of the physical tests, as shown below.
Static analysis torsional rigidity (Nm/deg) bending rigidity (N/mm) 1 st 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 correlati on would exist between CAE and physical crash results. The disparity in the mass numbers ex ists because the CAE model assumed constant thickness within each part; however, actual stam ped 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 ULSA B 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)
1 st

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 manufactu red) — such as the battery tray and the spare tire mounting. The exploded view of th e body structure shown below represents the parts that were included in the measured body.

# ULSAB Economic Analysis

Although lightweighting without sacrificing perf ormance 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 cu rrent, typical body structures for vehicles in the same class as ULSAB. The North American manu facturing 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 revi sited more thoroughly. The ULSAB Consortium’s primary objective was to provide a cost model th at 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 a ssumptions 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 deta iled cost model that includes all aspects of fabrication and assembly. This model comprehend s United States manufacturing costs, including investments for both plant and tooling, piece fabric ation costs and assembly costs, through to the end of the body shop. The analysts used these d etails 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 th e 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 – in stead 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 inpu ts 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 requi rement 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 invest ments, 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 tec hnical processes used in the manufacture and assembly of the body structure. Data for stampi ng include blanking, welding of tailored blanks and stamping for all parts; data for hydrofor ming 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 cost s, which include fabrication and assembly of the body structure. Indirect manufacturing cost s – executive salaries, marketing and sales, shipping and purchasing, research and deve lopment, 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 co st 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 stam ped 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
P

ARTS FABRICATION 584 62
material 351 37
labor 36 4 energy 6 1
fixed costs 191 20
H YDROFORMING 41 4
P URCHASED COMPONENTS 41 4ULSAB economic analysis 4 A

SSEMBLY 281 30
Variable 55 6
fixed 226 24
TOTAL COST 947 100

Fabrication breakdown Total fabrication costs can be broken down fu rther. 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
T OTAL VARIABLE 393 equipment 89 tooling 51
overhead labor 27 building 8
maintenance 15 working capital 1
T OTAL FIXED 191
TOTAL COST 584ULSAB 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
T OTAL VARIABLE 55 equipment 50 tooling 23
overhead labor 125 building 18
maintenance 9 working capital 1
T OTAL 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 investment s 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 3.2ULSAB 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 determi ne 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 blanki ng, hydroforming and laser welding increases, so should efficiency, resulting in further cost reductions. The sensitivity analysis, shown in the graph belo w, 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 ca lculated the cost of manufacturing a future reference (Year 2000) structure in addition to ULSA B. This reference is a hypothetical construct intended to represent an averaging of typical mi d-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 ar e 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 / m 2 -20% 3 years 5 years 8 years

+10% $352 -10%

Equipment Life Building Unit Cost Production Life Material Costs Stamping Parts Unit Energy Cost 

# OverallULSAB 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 le ss expensive than structures that do not have its benefits. ULSAB demonstrates that reduced weight and superior performance are achievable and affordable.